Author name code: gary-dale ADS astronomy entries on 2022-09-14 author:"Gary, Dale E." ------------------------------------------------------------------------ Title: Hard X-ray solar flare observed by Solar Orbiter/STIX associated with escaping electron beams Authors: Battaglia, Andrea Francesco; Warmuth, Alexander; Krucker, Samuel; Gary, Dale; Veronig, Astrid; Purkhart, Stefan; Saqri, Jonas; Collier, Hannah; Wang, Wen Bibcode: 2022cosp...44.1542B Altcode: Dramatic changes of the magnetic field configuration in the solar corona may reduce the magnetic energy in favor of the kinetic energy of high-energy particles. Such a phenomenon, known as magnetic reconnection, can lead to solar eruptions in the form of flares and coronal mass ejections. On the one hand, the accelerated particles heat the ambient plasma to temperatures of the order of tens of MK, while, on the other hand, particles can escape along open magnetic field lines into the heliosphere. Combining remote sensing and in-situ observations closer to the Sun, Solar Orbiter is able to study the acceleration region, the escape and the transport of solar energetic particles into the heliosphere. We analyze images obtained with remote-sensing hard X-ray observations by Solar Orbiter/STIX (Spectrometer/Telescope for Imaging X-rays) to investigate the acceleration region and escape of electron beams detected with in-situ measurements in the heliosphere. The prompt electron events show temporal correlation with the hard X-ray nonthermal emissions observed by STIX, favoring the idea of eruptive solar flares at the origin of the beams under investigation. For the SOL2021-08-26 event, the presence of accelerated electrons is further confirmed by the synchrotron emission measured by the EOVSA (Expanded Owens Valley Solar Array), which originate from electrons being accelerated along magnetic field lines. Title: Erratum: "A Study of Sunspot 3 Minute Oscillations Using ALMA and GST" (2022, ApJ, 924, 100) Authors: Chai, Yi; Gary, Dale E.; Reardon, Kevin P.; Yurchyshyn, Vasyl Bibcode: 2022ApJ...933..247C Altcode: No abstract at ADS Title: The relativistic solar particle event on 28 October 2021: Evidence of particle acceleration within and escape from the solar corona Authors: Klein, Karl-Ludwig; Musset, Sophie; Vilmer, Nicole; Briand, Carine; Krucker, Säm; Francesco Battaglia, Andrea; Dresing, Nina; Palmroos, Christian; Gary, Dale E. Bibcode: 2022A&A...663A.173K Altcode:
Aims: We analyse particle, radio, and X-ray observations during the first relativistic proton event of solar cycle 25 detected on Earth. The aim is to gain insight into the relationship between relativistic solar particles detected in space and the processes of acceleration and propagation in solar eruptive events.
Methods: To this end, we used ground-based neutron monitor measurements of relativistic nucleons and space-borne measurements of electrons with similar speed to determine the arrival times of the first particles at 1 AU and to infer their solar release times. We compared the release times with the time histories of non-thermal electrons in the solar atmosphere and their escape to interplanetary space, as traced by radio spectra and X-ray light curves and images.
Results: Non-thermal electrons in the corona are found to be accelerated in different regions. Some are confined in closed magnetic structures expanding during the course of the event. Three episodes of electron escape to the interplanetary space are revealed by groups of decametric-to-kilometric type III bursts. The first group appears on the low-frequency side of a type II burst produced by a coronal shock wave. The two latter groups are accompanied at higher frequencies by bursts with rapid drifts to both lower and higher frequencies (forward- or reverse-drifting bursts). They are produced by electron beams that propagate both sunward and anti-sunward. The first relativistic electrons and nucleons observed near Earth are released with the third group of type III bursts, more than ten minutes after the first signatures of non-thermal electrons and of the formation of the shock wave in the corona. Although the eruptive active region is near the central meridian, several tens of degrees east of the footpoint of the nominal Parker spiral to the Earth, the kilometric spectrum of the type III bursts and the in situ detection of Langmuir waves demonstrate a direct magnetic connection between the L1 Lagrange point and the field lines onto which the electron beams are released at the Sun.
Conclusions: We interpret the forward- and reverse-drifting radio bursts as evidence of reconnection between the closed expanding magnetic structures of an erupting flux rope and ambient open magnetic field lines. We discuss the origin of relativistic particles near the Earth across two scenarios: (1) acceleration at the CME-driven shock as it intercepts interplanetary magnetic field lines rooted in the western solar hemisphere and (2) an alternative where the relativistic particles are initially confined in the erupting magnetic fields and get access to the open field lines to the Earth through these reconnection events.

Movie is available at https://www.aanda.org Title: Solar flare accelerates nearly all electrons in a large coronal volume Authors: Fleishman, Gregory D.; Nita, Gelu M.; Chen, Bin; Yu, Sijie; Gary, Dale E. Bibcode: 2022Natur.606..674F Altcode: Solar flares, driven by prompt release of free magnetic energy in the solar corona1,2, are known to accelerate a substantial portion (ten per cent or more)3,4 of available electrons to high energies. Hard X-rays, produced by high-energy electrons accelerated in the flare5, require a high ambient density for their detection. This restricts the observed volume to denser regions that do not necessarily sample the entire volume of accelerated electrons6. Here we report evolving spatially resolved distributions of thermal and non-thermal electrons in a solar flare derived from microwave observations that show the true extent of the acceleration region. These distributions show a volume filled with only (or almost only) non-thermal electrons while being depleted of the thermal plasma, implying that all electrons have experienced a prominent acceleration there. This volume is isolated from a surrounding, more typical flare plasma of mainly thermal particles with a smaller proportion of non-thermal electrons. This highly efficient acceleration happens in the same volume in which the free magnetic energy is being released2. Title: Revisiting the Solar Research Cyberinfrastructure Needs: A White Paper of Findings and Recommendations Authors: Nita, Gelu; Ahmadzadeh, Azim; Criscuoli, Serena; Davey, Alisdair; Gary, Dale; Georgoulis, Manolis; Hurlburt, Neal; Kitiashvili, Irina; Kempton, Dustin; Kosovichev, Alexander; Martens, Piet; McGranaghan, Ryan; Oria, Vincent; Reardon, Kevin; Sadykov, Viacheslav; Timmons, Ryan; Wang, Haimin; Wang, Jason T. L. Bibcode: 2022arXiv220309544N Altcode: Solar and Heliosphere physics are areas of remarkable data-driven discoveries. Recent advances in high-cadence, high-resolution multiwavelength observations, growing amounts of data from realistic modeling, and operational needs for uninterrupted science-quality data coverage generate the demand for a solar metadata standardization and overall healthy data infrastructure. This white paper is prepared as an effort of the working group "Uniform Semantics and Syntax of Solar Observations and Events" created within the "Towards Integration of Heliophysics Data, Modeling, and Analysis Tools" EarthCube Research Coordination Network (@HDMIEC RCN), with primary objectives to discuss current advances and identify future needs for the solar research cyberinfrastructure. The white paper summarizes presentations and discussions held during the special working group session at the EarthCube Annual Meeting on June 19th, 2020, as well as community contribution gathered during a series of preceding workshops and subsequent RCN working group sessions. The authors provide examples of the current standing of the solar research cyberinfrastructure, and describe the problems related to current data handling approaches. The list of the top-level recommendations agreed by the authors of the current white paper is presented at the beginning of the paper. Title: A solar flare driven by thermal conduction observed in mid-infrared Authors: López, Fernando M.; Giménez de Castro, Carlos Guillermo; Mandrini, Cristina H.; Simões, Paulo J. A.; Cristiani, Germán D.; Gary, Dale E.; Francile, Carlos; Démoulin, Pascal Bibcode: 2022A&A...657A..51L Altcode: 2021arXiv211015751L Context. The mid-infrared (mid-IR) range has been mostly unexplored for the investigation of solar flares. It is only recently that new mid-IR flare observations have begun opening a new window into the response and evolution of the solar chromosphere. These new observations have been mostly performed by the AR30T and BR30T telescopes that are operating in Argentina and Brazil, respectively.
Aims: We present the analysis of SOL2019-05-15T19:24, a GOES class C2.0 solar flare observed at 30 THz (10 μm) by the ground-based telescope AR30T. Our aim is to characterize the evolution of the flaring atmosphere and the energy transport mechanism in the context of mid-IR emission.
Methods: We performed a multi-wavelength analysis of the event by complementing the mid-IR data with diverse ground- and space-based data from the Solar Dynamics Observatory (SDO), the H-α Solar Telescope for Argentina, and the Expanded Owens Valley Solar Array (EOVSA). Our study includes the analysis of the magnetic field evolution of the flaring region and of the development of the flare.
Results: The mid-IR images from AR30T show two bright and compact flare sources that are spatially associated with the flare kernels observed in ultraviolet (UV) by SDO. We confirm that the temporal association between mid-IR and UV fluxes previously reported for strong flares is also observed for this small flare. The EOVSA microwave data revealed flare spectra consistent with thermal free-free emission, which lead us to dismiss the existence of a significant number of non-thermal electrons. We thus consider thermal conduction as the primary mechanism responsible for energy transport. Our estimates for the thermal conduction energy and total radiated energy fall within the same order of magnitude, reinforcing our conclusions.

Movies associated to Figs. 1, 2 and 4 are available at https://www.aanda.org Title: A Study of Sunspot 3 Minute Oscillations Using ALMA and GST Authors: Chai, Yi; Gary, Dale E.; Reardon, Kevin P.; Yurchyshyn, Vasyl Bibcode: 2022ApJ...924..100C Altcode: 2021arXiv211105812C Waves and oscillations are important solar phenomena, not only because they can propagate and dissipate energy in the chromosphere, but also because they carry information about the structure of the atmosphere in which they propagate. The nature of the 3 minute oscillations observed in the umbral region of sunspots is considered to be an effect of propagation of magnetohydrodynamic waves upward from below the photosphere. We present a study of sunspot oscillations and wave propagation in NOAA Active Region 12470 using an approximately 1 hr long data set acquired on 2015 December 17 by the Atacama Large Millimeter/submillimeter Array (ALMA), the Goode Solar Telescope (GST) operating at the Big Bear Solar Observatory, the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, and the Interface Region Imaging Spectrograph. The ALMA data are unique in providing a time series of direct temperature measurements in the sunspot chromosphere. The 2 s cadence of ALMA images allows us to well resolve the 3 minute periods typical of sunspot oscillations in the chromosphere. Fourier analysis is applied to ALMA Band 3 (~100 GHz, ~3 mm) and GST Hα data sets to obtain power spectra as well as oscillation phase information. We analyzed properties of the wave propagation by combining multiple wavelengths that probe physical parameters of solar atmosphere at different heights. We find that the ALMA temperature fluctuations are consistent with that expected for a propagating acoustic wave, with a slight asymmetry indicating nonlinear steepening. Title: Large Microwave Flare Sources observed by EOVSA Imaging Spectroscopy Authors: Shaik, Shaheda Begum; Gary, Dale Bibcode: 2021AGUFMSH24B..08S Altcode: We present the imaging spectroscopy of gyrosynchrotron emission from C-class flare SOL2017-04-04 observed by the Expanded Owens Valley Solar Array (EOVSA) in 3.44 to 18 GHz. At the low microwave frequencies, we observe large sources that are almost ten times as large as the associated high frequency and hard X-ray flare emission. The source area seems to decrease steeply by more than an order of magnitude as we move from low to high frequencies. Unlike a single and straightforward loop standard solar model type flare, this event in the microwave emission shows the contribution of the multiple flux loops in different sizes with the three-dimensional loop-loop interaction scenario, resulting in the flare eruption. The emission at other wavelengths barely shows any sign of particle transport at the secondary sites where we see the low-frequency extended sources. These high-resolution microwave observations indicate that, after the main reconnection process, the accelerated particles have access to a much larger volume of the flaring region through the overlying loops. Title: An In Situ Type III Radio Burst Event Observed Jointly by the Expanded Owens Valley Solar Array and the Parker Solar Probe Authors: Wang, Meiqi; Chen, Bin; Yu, Sijie; Gary, Dale; Lee, Jeongwoo Bibcode: 2021AGUFMSH15C2046W Altcode: Solar type III radio bursts are generated by beams of energetic electrons that travel outward along open magnetic field lines through the corona and the interplanetary space. Here we report a type III burst event observed jointly by the Expanded Owens Valley Solar Array (EOVSA) and the Parker Solar Probe (PSP) shortly after its second perihelion in April 2019. This type III burst event is associated with a solar jet near the western boundary of a solar active region, which manifests in EOVSA 118 GHz dynamic spectrum as a group of impulsive microwave bursts. The type III burst event continues to the interplanetary space in the decameterkilometer wavelength range (300 kHz30 MHz) observed by multiple spacecraft including PSP/FIELDS, Wind/WAVEs, and STEREO/WAVES, and appears to reach the local plasma frequency at the PSP spacecraft. The multi-point spacecraft measurements allow us to constrain the source location of the bursts and their directivity in the interplanetary space. In addition, the type III burst event coincides with an enhanced suprathermal electron population with an anti-sunward beam-like component as measured by PSP/SWEAP. We argue that the type-III-burst-emitting energetic electrons observed in situ may be associated with an electron beam produced during the jet event that propagating upwards along open field lines reaching the PSP spacecraft. Title: Study of Type III Radio bursts in the Closed Corona and the Solar Wind from Small-scale Reconnection: Observations Authors: Chhabra, Sherry; Klimchuk, James; Gary, Dale Bibcode: 2021AGUFMSH24B..06C Altcode: It is widely agreed that the ubiquitous presence of reconnection events and the associated impulsive heating (nanoflares) are a strong candidate for heating the magnetically closed corona. Whether nanoflares accelerate energetic particles like fullsized flares is unknown. The lack of strong emission in hard Xrays suggests that the quantity of highly energetic particles is small. There could, however, be large numbers of mildly energetic particles (~ 10 keV). Similarly, in the context of the solar wind, these energetic particles can originate from interchange reconnection, streamer tip reconnection, or turbulence reconnection in the solar wind itself, in which case they stream away from the Sun along the open field lines. To understand whether these processes are efficient at accelerating particles, we search for the type III radio bursts that they may produce. The timelag technique that was developed to study subtle delays in light curves from different EUV channels [Viall & Klimchuk 2012] can also be used to detect subtle delays at different radio frequencies. We have modeled the expected radio emission from mildly energetic particles propagating in the closed corona and open corona/solar wind. The models were used to test and calibrate the technique. We are currently applying the technique to radio observations from VLA (Very Large Array), LOFAR (LowFrequency Array), LWA, NM (Long Wavelength Array, New Mexico), and the FIELDS experiment (encounters 1-6) to search for such signatures of type IIIs. We also plan to investigate the relationship between the bursts and activity on the Sun, such as the presence/absence of active regions, relationship with their age etc. We will report the results from our analysis. Title: Goldstone Apple Valley Radio Telescope (GAVRT) Solar Patrol as a New Citizen Scientist Program in the Era of the Parker Solar Probe (PSP) and a Gateway to NASA Heliophysics Missions Authors: Lamb, Lisa; Thangasamy, Velusamy; Levin, Steven; Gary, Dale; Dorcey, Ryan; Kuiper, Thomas; Lazio, Joseph; Chen, Bin; Yu, Sijie; Desai, Mihir Bibcode: 2021AGUFMED55D0317L Altcode: Goldstone Apple Valley Radio Telescope (GAVRT) Program operates a decommissioned NASA Deep Space Network 34-m antenna for science education under a unique partnership between the Jet Propulsion Laboratory, California Institute of Technology (JPL), and Lewis Center for Educational Research (LCER). GAVRT strives to inspire and enrich student learning through active contribution to professional science. For over 20 years, GAVRT has provided opportunities for K-12 students and teachers to operate the telescope remotely and take science data. In 2021, using ROSES 2020 Citizen Science seed funding, GAVRT has developed Solar Patrol as a new opportunity to engage citizen scientists outside of K-12 schools. GAVRT Solar Patrol conducts raster scans to generate radio images of the Sun to provide information about the structure of the solar atmosphere including the corona, transition region, and upper chromosphere. These images help us understand how magnetic fields on the Sun can interact and generate intense explosions, which in turn produce strong radio emission, particularly in regions associated with sunspots. GAVRT Solar Patrol conducts daily observations of the Sun at four frequencies (wavelengths or colors) chosen to enable the tracking of radio-emitting material as it rises or falls above the Sun following magnetic field interactions. Citizen scientists, including but not limited to K-12 students, can engage in GAVRT Solar Patrol by taking data, constructing images, & analysis to be used as a gateway to integration with NASAs Heliophysics missions. In addition to being scientifically valuable in their own right, the Solar Patrol data can be combined with measurements from other telescopes, especially with EOVSA interferometer data at GAVRT frequencies, and they complement measurements by the Parker Solar Probe. In particular, data from the GAVRT Solar Patrol and Parker Solar Probe help illustrate how a combination of ground-based and spacecraft measurements can be combined to enhance understanding of the Sun. Title: Understanding the Initiation of the M2.4 Flare on 2017 July 14 Authors: Jing, Ju; Inoue, Satoshi; Lee, Jeongwoo; Li, Qin; Nita, Gelu M.; Xu, Yan; Liu, Chang; Gary, Dale E.; Wang, Haimin Bibcode: 2021ApJ...922..108J Altcode: We present both the observation and the magnetohydrodynamics (MHD) simulation of the M2.4 flare (SOL2017-07-14T02:09) of NOAA active region (AR) 12665 with a goal to identify its initiation mechanism. The observation by the Atmospheric Image Assembly (AIA) on board the Solar Dynamics Observatory (SDO) shows that the major topology of the AR is a sigmoidal configuration associated with a filament/flux rope. A persistent emerging magnetic flux and the rotation of the sunspot in the core region were observed with Magnetic Imager (HMI) on board the SDO on the timescale of hours before and during the flare, which may provide free magnetic energy needed for the flare/coronal mass ejection (CME). A high-lying coronal loop is seen moving outward in AIA EUV passbands, which is immediately followed by the impulsive phase of the flare. We perform an MHD simulation using the potential magnetic field extrapolated from the measured pre-flare photospheric magnetic field as initial conditions and adopting the observed sunspot rotation and flux emergence as the driving boundary conditions. In our simulation, a sigmoidal magnetic structure and an overlying magnetic flux rope (MFR) form as a response to the imposed sunspot rotation, and the MFR rises to erupt like a CME. These simulation results in good agreement with the observation suggest that the formation of the MFR due to the sunspot rotation and the resulting torus and kink instabilities were essential to the initiation of this flare and the associated coronal mass ejection. Title: A Solar-Dedicated Observing System for the OVRO Long Wavelength Array Authors: Gary, Dale; Chhabra, Sherry; O'Donnell, Brian; Chen, Bin Bibcode: 2021AGUFMSH52A..03G Altcode: A new, solar-dedicated imaging and spectroscopy pipeline capability is being added to the Owens Valley Long Wavelength Array (OVRO-LWA), an all-sky radio imaging array operating in the metric frequency range from 20-88 MHz. The first capability to go online is a solar-dedicated beam that tracks the Sun and provides a continuous high frequency and time resolution (< 100 kHz and 1 ms, respectively) dynamic spectrum of solar activity simultaneously over this entire frequency range. The sensitivity to weak, extended emission from the core of the array will provide new insights into some of the weak activity missed by many other instruments. Shortly thereafter (early 2022), an imaging pipeline will begin operating that will produce images at up to 700 frequencies and 0.1 s time resolution, with spatial resolution down to 5 arcmin at 88 GHz, so that the sources can be spatially located with respect to disturbances imaged in other wavelengths. This will allow mapping of trajectories of electron beams (type III bursts) and the outward-propagating source regions of shock-related coherent emission (type II bursts), as well as tracking of weak incoherent emission from within the body of CMEs. This is illustrated by a recently published study (Chhabra et al. 2021, ApJ 906, 132) for a CME observed in 2015 with an earlier version of OVRO-LWA, but the capabilities of the new instrument will be vastly superior. In addition to providing near-real-time coverage of events with Space Weather impacts, the imaging pipeline with its unprecidented sensitivity is sure to lead to new science discoveries about high-energy particle acceleration and transport over the 1.3-2.5 Rsun range of heights where the closed corona interfaces with the open solar wind. Title: Signatures of Type III Solar Radio Bursts from Nanoflares: Modeling Authors: Chhabra, Sherry; Klimchuk, James A.; Gary, Dale E. Bibcode: 2021ApJ...922..128C Altcode: 2021arXiv210903355C There is a wide consensus that the ubiquitous presence of magnetic reconnection events and the associated impulsive heating (nanoflares) are strong candidates for solving the solar coronal heating problem. Whether nanoflares accelerate particles to high energies like full-sized flares is unknown. We investigate this question by studying the type III radio bursts that the nanoflares may produce on closed loops. The characteristic frequency drifts that type III bursts exhibit can be detected using a novel application of the time-lag technique developed by Viall & Klimchuk (2012) even when there are multiple overlapping events. We present a simple numerical model that simulates the expected radio emission from nanoflares in an active region, which we use to test and calibrate the technique. We find that in the case of closed loops the frequency spectrum of type III bursts is expected to be extremely steep such that significant emission is produced at a given frequency only for a rather narrow range of loop lengths. We also find that the signature of bursts in the time-lag signal diminishes as: (1) the variety of participating loops within that range increases; (2) the occurrence rate of bursts increases; (3) the duration of bursts increases; and (4) the brightness of bursts decreases relative to noise. In addition, our model suggests a possible origin of type I bursts as a natural consequence of type III emission in a closed-loop geometry. Title: Long-Lasting Intense Radio Bursts from a Sunspot Authors: Yu, Sijie; Chen, Bin; Sharma, Rohit; Battaglia, Marina; Luo, Yingjie; Gary, Dale Bibcode: 2021AGUFMSH52A..04Y Altcode: We present the detection of a new type of long-lasting (>4 hours), highly circularly polarized, intense radio bursts from a sunspot at decimetric wavelengths. The temporal and spectral characteristics of the radio bursts resemble certain planetary coherent radio emissions in the solar system generated by the electron cyclotron maser (ECM) instability. We track the morphology and dynamic evolution of the radio source using high-cadence radio imaging spectroscopy provided by Karl G. Jansky Very Large Array. We show that the radio emission is located within the large-scale, converging magnetic field rooted at the sunspot. The spatial-spectral distribution of the radio source location agrees with that expected from the ECM emission by using a non-linear force-free magnetic field extrapolation model. Our observations suggest that the radio emission is powered by the injection of energetic electrons accelerated in a series of flare activities into the converging magnetic field above the sunspot, which drives ECM instability in the source region. Title: Coronal Magnetic Field Measurements along a Partially Erupting Filament in a Solar Flare Authors: Wei, Yuqian; Chen, Bin; Yu, Sijie; Wang, Haimin; Jing, Ju; Gary, Dale E. Bibcode: 2021ApJ...923..213W Altcode: 2021arXiv211006414W Magnetic flux ropes are the centerpiece of solar eruptions. Direct measurements for the magnetic field of flux ropes are crucial for understanding the triggering and energy release processes, yet they remain heretofore elusive. Here we report microwave imaging spectroscopy observations of an M1.4-class solar flare that occurred on 2017 September 6, using data obtained by the Expanded Owens Valley Solar Array. This flare event is associated with a partial eruption of a twisted filament observed in Hα by the Goode Solar Telescope at the Big Bear Solar Observatory. The extreme ultraviolet (EUV) and X-ray signatures of the event are generally consistent with the standard scenario of eruptive flares, with the presence of double flare ribbons connected by a bright flare arcade. Intriguingly, this partial eruption event features a microwave counterpart, whose spatial and temporal evolution closely follow the filament seen in Hα and EUV. The spectral properties of the microwave source are consistent with nonthermal gyrosynchrotron radiation. Using spatially resolved microwave spectral analysis, we derive the magnetic field strength along the filament spine, which ranges from 600 to 1400 Gauss from its apex to the legs. The results agree well with the nonlinear force-free magnetic model extrapolated from the preflare photospheric magnetogram. We conclude that the microwave counterpart of the erupting filament is likely due to flare-accelerated electrons injected into the filament-hosting magnetic flux rope cavity following the newly reconnected magnetic field lines. Title: High-frequency Wave Power Observed in the Solar Chromosphere with IBIS and ALMA Authors: Molnar, Momchil E.; Reardon, Kevin P.; Cranmer, Steven R.; Kowalski, Adam F.; Chai, Yi; Gary, Dale Bibcode: 2021ApJ...920..125M Altcode: 2021arXiv210708952M We present observational constraints on the chromospheric heating contribution from acoustic waves with frequencies between 5 and 50 mHz. We use observations from the Dunn Solar Telescope in New Mexico, complemented with observations from the Atacama Large Millimeter Array collected on 2017 April 23. The properties of the power spectra of the various quantities are derived from the spectral lines of Ca II 854.2 nm, H I 656.3 nm, and the millimeter continuum at 1.25 and 3 mm. At the observed frequencies, the diagnostics almost all show a power-law behavior, whose particulars (slope, peak, and white-noise floors) are correlated with the type of solar feature (internetwork, network, and plage). In order to disentangle the vertical versus transverse Alfvénic plasma motions, we examine two different fields of view: one near disk center, and the other close to the limb. To infer the acoustic flux in the middle chromosphere, we compare our observations with synthetic observables from the time-dependent radiative hydrodynamic RADYN code. Our findings show that acoustic waves carry up to about 1 kW m-2 of energy flux in the middle chromosphere, which is not enough to maintain the quiet chromosphere. This is in contrast to previous publications. Title: Implications of Flat Optically Thick Microwave Spectra in Solar Flares for Source Size and Morphology Authors: Shaik, Shaheda Begum; Gary, Dale E. Bibcode: 2021ApJ...919...44S Altcode: 2021arXiv210700192B; 2021arXiv210700192S The study aims to examine the spectral dynamics of the low-frequency, optically thick gyrosynchrotron microwave emission in solar flares to determine the characteristics of the emitting source. We present the high-resolution spectra of a set of microwave bursts observed by the Expanded Owens Valley Solar Array (EOVSA) during its commissioning phase in the 2.5-18 GHz frequency range with 1 second time resolution. Out of the 12 events analyzed in this study, nine bursts exhibit a direct decrease with time in the optically thick spectral index αl, an indicator of source morphology. Particularly, five bursts display a "flat" spectrum (αl ≤ 1.0) compared to that expected for a homogeneous/uniform source (αl ≍ 2.9). These flat spectra at low frequencies (<10 GHz) can be defined as the emission from a spatially inhomogeneous source with a large area and/or with multiple emission components. In a subset of six events with partial cross-correlation data, both the events with flat spectra show a source size of ~120″ at 2.6-3 GHz. Modeling based on inhomogeneity supports the conclusion that multiple discrete sources can only reproduce a flat spectrum. We report that these flat spectra appear predominantly in the decay phase and typically grow flatter over the duration in most of the bursts, which indicates an increasing inhomogeneity and complexity of the emitting volume as the flare progresses. This large volume of flare emission filled with the trapped energetic particles is often invisible in other wavelengths, like hard X-rays, presumably due to the collisionless conditions in these regions of low ambient density and magnetic field strength. Title: Multiple Sources of Solar High-energy Protons Authors: Kocharov, Leon; Omodei, Nicola; Mishev, Alexander; Pesce-Rollins, Melissa; Longo, Francesco; Yu, Sijie; Gary, Dale E.; Vainio, Rami; Usoskin, Ilya Bibcode: 2021ApJ...915...12K Altcode: During the 24th solar cycle, the Fermi Large Area Telescope (LAT) has observed a total of 27 solar flares possessing delayed γ-ray emission, including the exceptionally well-observed flare and coronal mass ejection (CME) on 2017 September 10. Based on the Fermi/LAT data, we plot, for the first time, maps of possible sources of the delayed >100 MeV γ-ray emission of the 2017 September 10 event. The long-lasting γ-ray emission is localized under the CME core. The γ-ray spectrum exhibits intermittent changes in time, implying that more than one source of high-energy protons was formed during the flare-CME eruption. We find a good statistical correlation between the γ-ray fluences of the Fermi/LAT-observed delayed events and the products of corresponding CME speed and the square root of the soft X-ray flare magnitude. Data support the idea that both flares and CMEs jointly contribute to the production of subrelativistic and relativistic protons near the Sun. Title: Signatures of Type III Radio Bursts from Small-scale Reconnection Events in the Solar Wind Authors: Chhabra, S.; Klimchuk, J.; Gary, D.; Psp/Fields Team Bibcode: 2021AAS...23812307C Altcode: We look for evidence of energetic particles in the solar wind, that could be produced by reconnection in the solar wind itself or reconnection in the lower corona, where particles escape on open field lines, from e.g. interchange reconnection.We expect reconnection to be common at the current sheets that separate the thin magnetic strands that make up the corona and solar wind, but whether it is efficient at accelerating particles is an open question. Type III radio bursts have been very frequently observed in the solar wind over the past few decades. Energetic electron beams propagating along magnetic field lines cause a bump-on-tail instability generating Langmuir waves. Produced by their interaction with other particles and waves, type III bursts exhibit a characteristic drift in frequency as they propagate through the density gradient in the field. An interesting question is whether there is a ubiquitous presence of type IIIs in the radio 'background' observed. The radio background outside of clearly identified bursts may actually be comprised of multiple overlapping events. The time-lag technique that was developed to study subtle delays in light curves from different EUV channels [Viall & Klimchuk 2012] can also be used to detect subtle delays at different frequencies in the radio background even when there is no hint in the individual light curves. The FIELDS instrument onboard the Parker Solar Probe (PSP) is utilized to investigate the solar wind for these signatures. We perform a systematic study of the observed type III storms in Encounters 1-5, to understand the signatures that can identify their presence and the different features observed using the technique. Our findings are then employed to study the times where no activity is visibly detected by the instrument. We are currently analyzing multiple periods of no visible activity and will report our findings. Title: Magnetic Field Measurements Of A Twisted Flux Rope In A Failed Solar Eruption Authors: Wei, Y.; Chen, B.; Yu, S.; Wang, H.; Jing, J.; Gary, D. Bibcode: 2021AAS...23821311W Altcode: Magnetic flux ropes are the centerpiece of solar eruptions. Direct measurements for the magnetic field of flux ropes are crucial for understanding the triggering and energy release processes, yet they remain heretofore elusive. Here we report microwave imaging spectroscopy observations of an M1.4-class solar flare that occurred on 2017 September 6, using data obtained by the Expanded Owens Valley Solar Array. This flare event is associated with a failed eruption of a twisted filament observed in Hɑ by the Goode Solar Telescope at the Big Bear Solar Observatory. The filament, initially located along the magnetic polarity inversion line prior to the event, undergoes a failed eruption during the course of the flare. The upper portion of the erupting filament has a counterpart in microwaves, whose spectral properties indicate gyrosynchrotron radiation from flare-accelerated nonthermal electrons. Using spatially resolved microwave spectral analysis, we derive the magnetic field strength along the filament spine, which ranges from 600-1400 Gauss from its apex to the legs. The results agree well with the non-linear force-free magnetic model extrapolated from the pre-flare photospheric magnetogram. The multi-wavelength signatures of the event are consistent with the standard scenario of eruptive flares, except that the eruption failed to fully develop and escape as a coronal mass ejection. We conclude that the failed eruption is likely due to the strong strapping coronal magnetic field above the filament. Title: Characterizing a "Solar FRB" Authors: Hudson, H.; Briggs, M.; Chitta, L.; Fletcher, L.; Gary, D.; Monstein, C.; Nimmo, K.; Saint-Hilaire, P.; White, S. Bibcode: 2021AAS...23812716H Altcode: A remarkable solar microwave (1.4 GHz) burst, SOL2019-05-06T17:47:35.385, has been reported by the STARE2 fast cosmic transient survey (Bochenek et al., 2020). Its behavior resembles that of the Fast Radio Burst (FRB) extragalactic events in having a relatively broad spectral bandwidth and brief (19-msec) duration. It also had no measureable dispersion. The associated flare, GOES class C1, had a relatively hard X-ray spectrum as observed by Fermi/GBM, but no temporal association at the msec time scale suggested by the microwaves. Although msec variability in the microwave domain has been known to solar radio astronomy since the 1970s, the brightness and isolation of this event (both spatial and temporal) suggests novelty. Accordingly we survey the available correlative data from many sources and discuss possible interpretations in terms of type III-like behavior, electron cyclotron masering, and gyrosynchrotron emission. We note that the radio data (e-Callisto and EOVSA) revealed abundant type III activity in the vicinity, and the related flares as observed by GOES had exceptionally short time scales, suggesting burst origins in the lower solar atmosphere. Title: Diagnostics of Magnetic Field and Electron Densities in a Solar Flare using Microwave Imaging Spectroscopy Authors: O'Donnell, B.; Gary, D.; Chen, B.; Nita, G.; Yu, S. Bibcode: 2021AAS...23812704O Altcode: Here we report on the multi-frequency observations made of the C2.9 class solar flare (21:04 UT on 2017 August 18) by the Expanded Owen's Valley Solar Array. The resolution in space and frequency allows for multiparameter fitting to probe the magnetic field strength, the thermal and non-thermal electron densities, and electron spectral index delta in the microwave source throughout the flare. Evidence for two interacting loops is seen in microwaves, allowing for analysis of those parameters in the separate individual loops, including some along overlapping lines of sight. Title: Understanding The Initiation Of The M2.4 Flare On 2017 July 14 Authors: Jing, J.; Inoue, S.; Lee, J.; Li, Q.; Nita, G.; Xu, Y.; Liu, C.; Gary, D.; Wang, H. Bibcode: 2021AAS...23812706J Altcode: We present both the observation and the magnetohydrodynamics (MHD) simulation of the M2.4 flare (SOL2017-07-14T02:09) of NOAA active region (AR) 12665 to understand the initiation mechanism of this eruptive flare, which is associated with a coronal mass ejection (CME) and produces a storm of Solar Energetic Particles (SEPs). The observation by the Atmospheric Image Assembly (AIA) on the Solar Dynamics Observatory (SDO) shows that the major topology of the AR is a sigmoidal configuration associated with a filament/flux rope, which could be well reconstructed in the nonlinear force-free (NLFF) field model. Persistent emerging magnetic flux and the rotation of the sunspot are observed with Magnetic Imager (HMI) on the SDO in the core region, in the timescale of hours before and during the flare, providing sufficient free magnetic energy accounting for the flare/CME. A high-lying coronal loop is seen moving outward in AIA EUV passbands, which is immediately followed by the impulsive phase of the flare. We perform the MHD simulation that uses the potential magnetic field extrapolated from the measured pre-flare photospheric magnetic field as initial conditions and adopts the sunspot rotation as the driving force. In our simulation, a sigmoidal magnetic structure and an overlying magnetic flux rope (MFR) form as a response to the imposed sunspot rotation. The MFR rises up and erupts like a CME. These simulation results are in good agreement with observation, and suggests that the the loss of MHD stability might be the main cause for this eruption. Title: A Type III Radio Burst Event Observed Jointly by the Expanded Owens Valley Solar Array and the Parker Solar Probe Authors: Wang, M.; Chen, B.; Yu, S.; Gary, D.; Lee, J. Bibcode: 2021AAS...23832811W Altcode: Solar type III radio bursts are generated by beams of energetic electrons that travel outward along open magnetic field lines through the corona and the interplanetary space. Here we report a type III burst event observed jointly by the Expanded Owens Valley Solar Array (EOVSA) and the Parker Solar Probe (PSP) near its second perihelion in April 2019. This type III burst event is associated with a solar jet near the boundary of a solar active region, which manifests in EOVSA 1-18 GHz dynamic spectrum as a group of impulsive microwave bursts. The type III burst event continues to the interplanetary space in the decameter-kilometer wavelength range (300kHz-30MHz) observed by multiple spacecraft including PSP/FIELDS, and appears to reach the local plasma frequency at the spacecraft. In addition, the type III burst event coincides with an enhanced suprathermal electron population with an anti-sunward beam-like component as measured by PSP/SWEAP. We discuss the source region of the type-III-burst-emitting energetic electrons and their transport from near the solar surface to the interplanetary space. Title: Acceleration without significant heating in the late impulsive phase of large solar flares Authors: Alaoui, M.; Gary, D.; Hayes, L.; Dennis, B.; Allred, J.; Tolbert, K.; Holman, G. Bibcode: 2021AAS...23812715A Altcode: We investigate characteristics of electron acceleration during the late impulsive phase of large flares. Specifically, whether characteristic parameters of the acceleration process change during the late phase acceleration during the same event. We present X-ray (HXR) and microwave (MW) observations of the late impulsive phase from seven M- and X-class flares with insignificant heating. All these peaks are consistent with the absence of Neupert effect where the derivative of the thermal emission is flat, similarly to the flare reported by Warmuth et al. 2009. The X-ray spectral fits from RHESSI are consistent with a higher-than-usual low-energy cutoff value (> 70 keV). This is inferred from RHESSI spatially integrated spectra and spectroscopic imaging using an extended collisional thick target model (ECTTM), where electron propagation mechanisms such as the co-spatial return current, warm target and magnetic mirroring are also considered. Radio/MW emission from these peaks reveals an additional sub-group where 4/7 flares are associated with an increase and 3/7 with a decrease in magnetic field strengths compared to the main impulsive phase. The gradual (impulsive) peaks have a higher (lower) emission and are associated with increased (decreased) magnetic field strengths compared to earlier HXR peaks, except one flare which exhibits characteristics of gradual and impulsive events. Magnetograms further show that the HXR footpoints move into a region of increased magnetic field for gradual events. No such evidence is observed for the impulsive peaks. The main result is that these late peaks are consistent with a higher-than-usual injected low-energy cutoff and a total injected flux density insufficient to significantly heat the solar atmosphere compared to the initial HXR impulsive phase. Title: Solar Radio Burst Effects on Radio- and Radar-Based Systems Authors: Gary, Dale E.; Bastian, Timothy S. Bibcode: 2021GMS...262..141G Altcode: Radio emission from solar flares can attain such high flux density that the Sun becomes the dominant source of broadband radio noise in the terrestrial environment. The effects of this radio noise on wireless communication and navigation systems can take many forms, depending on the design and operation of the affected system. These effects can be of special concern for regional or global systems, since the effects can occur simultaneously over the entire sunlit hemisphere of Earth. This chapter reviews the origin of solar radio bursts, the threat they pose based on statistics of the flux-density distribution of such events vs. frequency, and some of the effects that have been documented in the literature. The chapter concludes with a discussion of the potential impacts on current and future technology and how these impacts can be mitigated (1) through improved radio monitoring of the Sun in both circular polarizations to supply meaningful real-time warnings, (2) through improved scientific understanding of the solar phenomena underlying the radio bursts, and (3) through improved system design that takes account of solar radio noise. Title: Imaging Spectroscopy of CME-associated Solar Radio Bursts using OVRO-LWA Authors: Chhabra, Sherry; Gary, Dale E.; Hallinan, Gregg; Anderson, Marin M.; Chen, Bin; Greenhill, Lincoln J.; Price, Danny C. Bibcode: 2021ApJ...906..132C Altcode: 2020arXiv201106073C We present the first results of a solar radio event observed with the Owens Valley Radio Observatory Long Wavelength Array at metric wavelengths. We examine a complex event consisting of multiple radio sources/bursts associated with a fast coronal mass ejection (CME) and an M2.1 GOES soft X-ray flare from 2015 September 20. Images of 9 s cadence are used to analyze the event over a 120 minute period, and solar emission is observed out to a distance of ≍3.5 R⊙, with an instantaneous bandwidth covering 22 MHz within the frequency range of 40-70 MHz. We present our results from the investigation of the radio event, focusing particularly on one burst source that exhibits outward motion, which we classify as a moving type IV burst. We image the event at multiple frequencies and use the source centroids to obtain the velocity for the outward motion. Spatial and temporal comparison with observations of the CME in white light from the C2 coronagraph of the Large Angle and Spectrometric COronagraph, indicates an association of the outward motion with the core of the CME. By performing graduated-cylindrical-shell reconstruction of the CME, we constrain the density in the volume. The electron plasma frequency obtained from the density estimates do not allow us to completely dismiss plasma emission as the underlying mechanism. However, based on source height and smoothness of the emission in frequency and time, we argue that gyrosynchrotron is the more plausible mechanism. We use gyrosynchrotron spectral-fitting techniques to estimate the evolving physical conditions during the outward motion of this burst source. Title: Radio Measurements of the Magnetic field in the Solar Chromosphere and the Corona Authors: Alissandrakis, Costas E.; Gary, Dale E. Bibcode: 2021FrASS...7...77A Altcode: The structure of the upper solar atmosphere, on all observable scales, is intimately governed by the magnetic field. The same holds for a variety of solar phenomena that constitute solar activity, from tiny transient brightening to huge Coronal Mass Ejections. Due to inherent difficulties in measuring magnetic field effects on atoms (Zeeman and Hanle effects) in the corona, radio methods sensitive to electrons are of primary importance in obtaining quantitative information about its magnetic field. In this review we explore these methods and point out their advantages and limitations. After a brief presentation of the magneto-ionic theory of wave propagation in cold, collisionless plasmas, we discuss how the magnetic field affects the radio emission produced by incoherent emission mechanisms (free-free, gyroresonance and gyrosynchrotron processes) and give examples of measurements of magnetic filed parameters in the quiet sun, active regions and radio CMEs. We proceed by discussing how the inversion of the sense of circular polarization can be used to measure the field above active regions. Subsequently we pass to coherent emission mechanisms and present results of measurements from fiber bursts, zebra patterns and type II burst emission. We close this review with a discussion of the variation of the magnetic field, deduced by radio measurement, from the low corona up to 10 solar radii and with some thoughts about future work. Title: EOVSA Full-Disk Imaging of the Sun at Microwave Frequencies: Techniques and Updates Authors: Wang, M.; Chen, B.; Yu, S.; Gary, D. E. Bibcode: 2020AGUFMSH0480001W Altcode: The Expanded Owens Valley Solar Array (EOVSA), which consists of thirteen 2.1-meter antennas, is a recently commissioned radio interferometer dedicated to solar observing. It provides daily observations of the full solar disk in the microwave range 1-18 GHz, with up to 451 frequency channels at 1-s time cadence. Despite the small number of antennas, spectral imaging of the full solar disk can be achieved by taking advantage of the Earth-rotation synthesis technique to integrate the visibilities over an entire day (typically 8 hours) to improve the uv coverage. Here we discuss techniques and recent updates to our full-disk imaging pipeline, with a particular focus on the self-calibration techniques we developed to improve the image quality and fidelity. We present examples of the updated full-disk imaging results for both the cases when the disk is spotless and when it has sunspots/active regions present. These images reveal a rich variety of features of the quiescent Sun at different microwave frequencies, including active regions, filaments, coronal holes, and network structures, providing a unique dataset to the solar community. Title: Next-Generation Solar Radio Imaging Spectroscopy Authors: Gary, D. E.; Bastian, T.; Chen, B.; Saint-Hilaire, P.; White, S. M. Bibcode: 2020AGUFMSH056..07G Altcode: Recent progress using instruments such as the Expanded Owens Valley Solar Array (EOVSA) and the Jansky Very Large Array (JVLA) have amply demonstrated the power of radio imaging spectroscopy at centimeter and decimeter wavelengths for quantitative diagnostics of both flaring and non-flaring solar plasma. For example, the unique sensitivity of radio emission to the flaring coronal magnetic field has been dramatically shown in a series of recent EOVSA papers, along with accelerated electron diagnostics in the same volume. JVLA observations have been used to probe particle acceleration in a termination shock during a flare. In addition, multi-frequency full-disk imaging of the non-flaring Sun with EOVSA is showing promise for quantitative diagnostics of electron-based emission measure and active region magnetic field and temperature structure. But EOVSA and the JVLA are mere demonstrators for a far more advanced solar radio instrument, the Frequency Agile Solar Radiotelescope (FASR), that is designed to address a much more comprehensive science program with much greater precision than is possible with EOVSA or non-solar-dedicated instruments like the JVLA. This includes direct imaging of Coronal Mass Ejections (CMEs) and their associated energetic particles both on and off the solar disk, routine coronal magnetic field measurements at high cadence, and continuous sampling of the full-Sun coronal temperature and emission measure. Here we use examples from EOVSA and the JVLA to envision what FASR's advanced design will be capable of. When paired with highly complementary new X-ray-based diagnostics from space, the remote sensing of high-energy particles through radio imaging spectroscopy from the ground provides a far more complete picture of the broad range of energetic phenomena that occur on the Sun than either alone. Scientists interested in high-energy solar phenomena have ample incentive to coordinate their efforts to ensure that space- and ground-based capabilities advance together. Title: Signatures of Type III Solar Radio Bursts from Nanoflares: Final Results Authors: Chhabra, S.; Klimchuk, J. A.; Gary, D. E.; Viall, N. M. Bibcode: 2020AGUFMSH0430016C Altcode: The heating mechanisms responsible for the million degree solar corona remain one of the most intriguing problems in space science. It is widely agreed, that the ubiquitous presence o f reconnection events and the associated impulsive heating (nanoflares) are a strong candidate in solving this problem [Klimchuk J.A., 2015 and references therein].

Whether nanoflares accelerate energetic particles like full sized flares is unknown. The lack of strong emission in hard X rays suggests that the quantity of highly energetic particles is small. There could, however, be large numbers of mildly energetic particles (~ 10 keV). We investigate such particles by searching for the type III radio bursts that they may produce. If energetic electron beams propagating along magnetic field lines generate a bump on tail instability, they will produce Langmuir waves, which can then interact with other particles and waves to give rise to emission at the local plasma frequency and its first harmonic. Type III radio bursts bursts are characteristically known to exhibit high frequency drifts as the beam propagates through a density gradient. The time lag technique that was developed to study subtle delays in light curves from different EUV channels [Viall & Klimchuk 2012] can also be used to detect subtle delays at different radio frequencies. We have modeled the expected radio emission from nanoflares, which we used to test and calibrate the technique. We will present the final results of our modeling efforts along with results from application of the technique to actual radio observations from VLA (Very Large Array), MWA (Murchison Widefield Array) and seeking data from LOFAR (Low Frequency Array) as well.We are also using data from the PSP (Parker Solar Probe) to look for similar reconnection signatures in the Solar Wind. Our goal is to determine whether nanoflares accelerate energetic particles and to determine their properties. The results will have important implications for both the particle acceleration and reconnection physics. Title: Untangling the global coronal magnetic field with multiwavelength observations Authors: Gibson, S. E.; Malanushenko, A.; de Toma, G.; Tomczyk, S.; Reeves, K.; Tian, H.; Yang, Z.; Chen, B.; Fleishman, G.; Gary, D.; Nita, G.; Pillet, V. M.; White, S.; Bąk-Stęślicka, U.; Dalmasse, K.; Kucera, T.; Rachmeler, L. A.; Raouafi, N. E.; Zhao, J. Bibcode: 2020arXiv201209992G Altcode: Magnetism defines the complex and dynamic solar corona. Coronal mass ejections (CMEs) are thought to be caused by stresses, twists, and tangles in coronal magnetic fields that build up energy and ultimately erupt, hurling plasma into interplanetary space. Even the ever-present solar wind possesses a three-dimensional morphology shaped by the global coronal magnetic field, forming geoeffective corotating interaction regions. CME evolution and the structure of the solar wind depend intimately on the coronal magnetic field, so comprehensive observations of the global magnetothermal atmosphere are crucial both for scientific progress and space weather predictions. Although some advances have been made in measuring coronal magnetic fields locally, synoptic measurements of the global coronal magnetic field are not yet available. We conclude that a key goal for 2050 should be comprehensive, ongoing 3D synoptic maps of the global coronal magnetic field. This will require the construction of new telescopes, ground and space-based, to obtain complementary, multiwavelength observations sensitive to the coronal magnetic field. It will also require development of inversion frameworks capable of incorporating multi-wavelength data, and forward analysis tools and simulation testbeds to prioritize and establish observational requirements on the proposed telescopes. Title: Magnetic Reconnection during the Post-impulsive Phase of a Long-duration Solar Flare: Bidirectional Outflows as a Cause of Microwave and X-Ray Bursts Authors: Yu, Sijie; Chen, Bin; Reeves, Katharine K.; Gary, Dale E.; Musset, Sophie; Fleishman, Gregory D.; Nita, Gelu M.; Glesener, Lindsay Bibcode: 2020ApJ...900...17Y Altcode: 2020arXiv200710443Y Magnetic reconnection plays a crucial role in powering solar flares, production of energetic particles, and plasma heating. However, where the magnetic reconnections occur, how and where the released magnetic energy is transported, and how it is converted to other forms remain unclear. Here we report recurring bidirectional plasma outflows located within a large-scale plasma sheet observed in extreme-ultraviolet emission and scattered white light during the post-impulsive gradual phase of the X8.2 solar flare on 2017 September 10. Each of the bidirectional outflows originates in the plasma sheet from a discrete site, identified as a magnetic reconnection site. These reconnection sites reside at very low altitudes (<180 Mm, or 0.26 R⊙) above the top of the flare arcade, a distance only <3% of the total length of a plasma sheet that extends to at least 10 R⊙. Each arrival of sunward outflows at the loop-top region appears to coincide with an impulsive microwave and X-ray burst dominated by a hot source (10-20 MK) at the loop top and a nonthermal microwave burst located in the loop-leg region. We propose that the reconnection outflows transport the magnetic energy released at localized magnetic reconnection sites outward in the form of kinetic energy flux and/or electromagnetic Poynting flux. The sunward-directed energy flux induces particle acceleration and plasma heating in the post-flare arcades, observed as the hot and nonthermal flare emissions. Title: Imaging Spectroscopy of CME-Associated Solar Radio Bursts using OVRO-LWA Authors: Chhabra, S.; Gary, D. E.; Hallinan, G. Bibcode: 2020SPD....5121009C Altcode: Radio emission from the solar corona provides a unique perspective on the physical properties of energetic phenomena, such as solar flares and coronal mass ejections (CMEs). We present first results of a solar radio event observed with the new state-of-the-art Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA) at metric wavelengths. We examine a complex event consisting of multiple radio sources/bursts associated with a fast coronal mass ejection and an M2.1 GOES soft X-ray flare from 2015 September 20, as well as quiet Sun images before and after the bursts. Images of 9-s cadence are used to analyze the event over a 120-minute period, and solar emission is observed out to a distance of ≈3.5R, over the frequency range of 40-70MHz available at that time. We present our results from the investigation of the radio event, focusing particularly on one burst source that exhibits outward motion, which we classify as a moving type IV burst. We image the event at multiple frequencies and use the source centroids to obtain the velocity for the outward motion. A coalignment with the LASCO(C2) coronagraph allows a spatial and temporal comparison with observations of the CME in white light, indicating an association of the outward motion with the core of the CME. By performing graduated-cylindrical-shell (GCS) reconstruction of the CME, we constrain the density in the volume. We find that the estimated density values yield an electron plasma frequency lower than, but close to the observed emission frequency, rendering it difficult to completely dismiss the possibility of plasma emission as the underlying mechanism. However, based on source height and smoothness of the emission in frequency and time, we argue that gyrosynchrotron is the more plausible mechanism. We use gyrosynchrotron spectral fitting techniques to estimate the evolving physical conditions during the outward motion of this CME-associated radio burst source. Title: Magnetic Reconnection in a Solar Flare: Bi-Directional Outflows vs. Microwave and X-ray Bursts Authors: Yu, S.; Chen, B.; Reeves, K.; Gary, D.; Fleishman, G. Bibcode: 2020SPD....5121103Y Altcode: Magnetic reconnection is fundamental for the astrophysical and laboratory plasma. Its role is crucial in powering solar flares, production of energetic particles, and plasma heating. However, where the magnetic reconnections occur, how and where the released magnetic energy is transported, and how it is converted to other forms remain unclear. Here we report recurring bi-directional plasma outflows located within a large-scale plasma sheet observed in extreme ultraviolet and white light during the post-impulsive gradual phase of the X8.2 solar flare on 2017 September 10. Each pair of the bi-directional outflows originates in the plasma sheet from a discrete site, identified as the magnetic reconnection site. These reconnection sites reside at very low altitudes (< 180 Mm, or 0.26 solar radii) above the top of the flare arcade, which is only 4% of the total length of the plasma sheet that extends to at least 10 solar radii. Each arrival of sunward outflows at the looptop region appears to coincide with an impulsive microwave and X-ray burst dominated by a superhot source (10-20 MK) at the looptop, which is immediately followed by a nonthermal microwave burst located in the loop-leg region. We propose that the reconnection outflows transport the magnetic energy released at localized magnetic reconnection sites outward in the form of kinetic energy flux and/or electromagnetic Poynting flux. The sunward-directing energy flux induces particle acceleration and plasma heating in the post-flare arcades observed as the superhot and nonthermal flare emissions. Title: Magnetic Reconnection During the Post-Impulsive Phase of a Long-Duration Solar Flare: Bi-Directional Outflows vs. Microwave and X-ray Bursts Authors: Yu, S.; Chen, B.; Reeves, K.; Gary, D.; Musset, S.; Fleishman, G.; Nita, G.; Glesener, L. Bibcode: 2020AAS...23611203Y Altcode: Magnetic reconnection is fundamental for the astrophysical and laboratory plasma. Its role is crucial in powering solar flares, production of energetic particles, and plasma heating. However, where the magnetic reconnections occur, how and where the released magnetic energy is transported, and how it is converted to other forms remain unclear. Here we report recurring bi-directional plasma outflows located within a large-scale plasma sheet observed in extreme ultraviolet and white light during the post-impulsive gradual phase of the X8.2 solar flare on 2017 September 10. Each pair of the bi-directional outflows originates in the plasma sheet from a discrete site, identified as the magnetic reconnection site. These reconnection sites reside at very low altitudes (< 180 Mm, or 0.26 Rsun) above the top of the flare arcade, which is only 4% of the total length of the plasma sheet that extends to at least 10 Rsun. Each arrival of sunward outflows at the looptop region appears to coincide with an impulsive microwave and X-ray burst dominated by a superhot source (10-20 MK) at the looptop, which is immediately followed by a nonthermal microwave burst located in the loop-leg region. We propose that the reconnection outflows transport the magnetic energy released at localized magnetic reconnection sites outward in the form of kinetic energy flux and/or electromagnetic Poynting flux. The sunward-directing energy flux induces particle acceleration and plasma heating in the post-flare arcades observed as the superhot and nonthermal flare emissions. Title: Microwave Spectral Imaging of an Erupting Magnetic Flux Rope: Implications for the Standard Solar Flare Model in Three Dimensions Authors: Chen, Bin; Yu, Sijie; Reeves, Katharine K.; Gary, Dale E. Bibcode: 2020ApJ...895L..50C Altcode: 2020arXiv200501900C We report microwave spectral imaging observations of an erupting magnetic flux rope during the early impulsive phase of the X8.2-class limb flare on 2017 September 10, obtained by the Expanded Owens Valley Solar Array. A few days prior to the eruption, when viewed against the disk, the flux rope appeared as a reverse S-shaped dark filament along the magnetic polarity inversion line. During the eruption, the rope exhibited a "hot channel" structure in extreme ultraviolet and soft X-ray passbands sensitive to ∼10 MK plasma. The central portion of the flux rope was nearly aligned with the line of sight, which quickly developed into a teardrop-shaped dark cavity during the early phase of the eruption. A long and thin plasma sheet formed below the cavity, interpreted as the reconnection current sheet viewed edge on. A nonthermal microwave source was present at the location of the central current sheet, which extended upward encompassing the dark cavity. A pair of nonthermal microwave sources were observed for several minutes on both sides of the main flaring region. They shared a similar temporal behavior and spectral property to the central microwave source below the cavity, interpreted as the conjugate footpoints of the erupting flux rope. These observations are broadly consistent with the magnetic topology and the associated energy release scenario suggested in the three-dimensional standard model for eruptive solar flares. In particular, our detection of nonthermal emission at conjugate flux rope footpoints provides solid evidence of particle transport along an erupting magnetic flux rope. Title: Observation and modeling of the umbra of sunspot AR 12470 using ALMA and BBSO data Authors: Chai, Y.; Gary, D. Bibcode: 2020AAS...23633005C Altcode: Waves and oscillations are an enduring topic in the study of the solar atmosphere since they have been considered an important candidate for solving the coronal heating problem. For decades, numerous efforts in observation and modeling have been put forth, yet the complexity of the solar atmosphere has left many questions unanswered . Now that the Atacama Large Millimeter/submillimeter Array (ALMA) has become available, we have entered a new era when it is possible to directly probe the chromospheric temperature variation on very short (1-2 s) timescales. Combined with some solar dedicated instruments, such as Goode Solar Telescope (GST) at the Big Bear Solar Observatory (BBSO), we are able to carry out high spatial and temporal observations that target the sunspot umbra, so that they can provide additional guidance to sunspot modeling. We present a study of umbral waves and oscillations in the sunspot AR12470 using the data from both ALMA and BBSO that were taken on December 17, 2015. With the help of fourier analysis, we found the locations of the maximum power of the 3-min oscillation signal in the sunspot umbra at ALMA band 3 (3 mm) wavelength. We found a stable phase relation between ALMA band 3 temperature variations and Hα intensities at various wavelengths in the line, taken with the GST. With the help of these data, we model the waves as a perturbation of the existing 1D solar models by Fontenla et al. and the numerical radiative transfer RH (Rybicki & Hummer) code. The detailed information and discussion are in the poster. Title: Measurement of magnetic field and relativistic electrons along a solar flare current sheet Authors: Chen, B.; Shen, C.; Gary, D.; Reeves, K.; Fleishman, G.; Yu, S.; Guo, F.; Krucker, S.; Lin, J.; Nita, G.; Kong, X. Bibcode: 2020AAS...23611202C Altcode: In the standard model of solar flares, a large-scale reconnection current sheet is postulated as the central engine for powering the flare energy release and accelerating particles. However, where and how the energy release and particle acceleration occur remain unclear due to the lack of measurements for the magnetic properties of the current sheet. Here we report the first measurement of spatially-resolved magnetic field and flare-accelerated relativistic electrons along a current-sheet feature in a solar flare. The measured magnetic field profile shows a local maximum where the reconnecting field lines of opposite polarities closely approach each other, known as the reconnection X point. The measurements also reveal a local minimum near the bottom of the current sheet above the flare loop-top, referred to as a "magnetic bottle". This spatial structure agrees with theoretical predictions and numerical modeling results. A strong reconnection electric field of ~4000 V/m is inferred near the X point. This location, however, shows a local depletion of microwave-emitting relativistic electrons. In contrast, these electrons concentrate at or near the magnetic bottle structure, where more than 99% of them reside at each instant. Our observations suggest crucial new input to the current picture of high energy electron acceleration. Title: Machine Learning in Heliophysics and Space Weather Forecasting: A White Paper of Findings and Recommendations Authors: Nita, Gelu; Georgoulis, Manolis; Kitiashvili, Irina; Sadykov, Viacheslav; Camporeale, Enrico; Kosovichev, Alexander; Wang, Haimin; Oria, Vincent; Wang, Jason; Angryk, Rafal; Aydin, Berkay; Ahmadzadeh, Azim; Bai, Xiaoli; Bastian, Timothy; Filali Boubrahimi, Soukaina; Chen, Bin; Davey, Alisdair; Fereira, Sheldon; Fleishman, Gregory; Gary, Dale; Gerrard, Andrew; Hellbourg, Gregory; Herbert, Katherine; Ireland, Jack; Illarionov, Egor; Kuroda, Natsuha; Li, Qin; Liu, Chang; Liu, Yuexin; Kim, Hyomin; Kempton, Dustin; Ma, Ruizhe; Martens, Petrus; McGranaghan, Ryan; Semones, Edward; Stefan, John; Stejko, Andrey; Collado-Vega, Yaireska; Wang, Meiqi; Xu, Yan; Yu, Sijie Bibcode: 2020arXiv200612224N Altcode: The authors of this white paper met on 16-17 January 2020 at the New Jersey Institute of Technology, Newark, NJ, for a 2-day workshop that brought together a group of heliophysicists, data providers, expert modelers, and computer/data scientists. Their objective was to discuss critical developments and prospects of the application of machine and/or deep learning techniques for data analysis, modeling and forecasting in Heliophysics, and to shape a strategy for further developments in the field. The workshop combined a set of plenary sessions featuring invited introductory talks interleaved with a set of open discussion sessions. The outcome of the discussion is encapsulated in this white paper that also features a top-level list of recommendations agreed by participants. Title: Characterization of turbulent magnetic reconnection in solar flares with microwave imaging spectroscopy Authors: Fleishman, Gregory; Gary, Dale; Chen, Bin; Yu, Sijie; Kuroda, Natsuha; Nita, Gelu Bibcode: 2020EGUGA..22.2099F Altcode: Magnetic reconnection plays a central role in highly magnetized plasma, for example, in solar corona. Release of magnetic energy due to reconnection is believed to drive such transient phenomena as solar flares, eruptions, and jets. This energy release should be associated with a decrease of the coronal magnetic field. Quantitative measurements of the evolving magnetic field strength in the corona are required to find out where exactly and with what rate this decrease takes place. The only available methodology capable of providing such measurements employs microwave imaging spectroscopy of gyrosynchrotron emission from nonthermal electrons accelerated in flares. Here, we report microwave observations of a solar flare, showing spatial and temporal changes in the coronal magnetic field at the cusp region; well below the nominal reconnection X point. The field decays at a rate of ~5 Gauss per second for 2 minutes. This fast rate of decay implies a highly enhanced, turbulent magnetic diffusivity and sufficiently strong electric field to account for the particle acceleration that produces the microwave emission. Moreover, spatially resolved maps of the nonthermal and thermal electron densities derived from the same microwave spectroscopy data set allow us to detect the very acceleration site located within the cusp region. The nonthermal number density is extremely high, while the thermal one is undetectably low in this region indicative of a bulk acceleration process exactly where the magnetic field displays the fast decay. The decrease in stored magnetic energy is sufficient to power the solar flare, including the associated eruption, particle acceleration, and plasma heating. We discuss implications of these findings for understanding particle acceleration in solar flares and in a broader space plasma context. Title: Evolution of Flare-accelerated Electrons Quantified by Spatially Resolved Analysis Authors: Kuroda, Natsuha; Fleishman, Gregory D.; Gary, Dale E.; Nita, Gelu M.; Chen, Bin; Yu, Sijie Bibcode: 2020FrASS...7...22K Altcode: 2020arXiv200413155K Nonthermal electrons accelerated in solar flares produce electromagnetic emission in two distinct, highly complementary domains---hard X-rays (HXRs) and microwaves (MWs). This paper reports MW imaging spectroscopy observations from the Expanded Owens Valley Solar Array of an M1.2 flare that occurred on 2017 September 9, from which we deduce evolving coronal parameter maps. We analyze these data jointly with the complementary Reuven Ramaty High-Energy Solar Spectroscopic Imager HXR data to reveal the spatially-resolved evolution of the nonthermal electrons in the flaring volume. We find that the high-energy portion of the nonthermal electron distribution, responsible for the MW emission, displays a much more prominent evolution (in the form of strong spectral hardening) than the low-energy portion, responsible for the HXR emission. We show that the revealed trends are consistent with a single electron population evolving according to a simplified trap-plus-precipitation model with sustained injection/acceleration of nonthermal electrons, which produces a double-powerlaw with steadily increasing break energy. Title: Evolution of Flare-accelerated Electrons in the Solar Corona and Chromosphere Revealed by Spatially Resolved Microwave and Hard X-Ray Analysis Authors: Kuroda, Natsuha; Fleishman, Gregory; Gary, Dale; Nita, Gelu; Chen, Bin; Yu, Sijie Bibcode: 2020EGUGA..22.3145K Altcode: Hard X-ray (HXR) and microwave (MW) observations are highly complementary for studying electron acceleration and transport processes in solar flares. In recent years, a new effort has been made in the MW domain using new high-resolution, multifrequency data from The Expanded Owens Valley Solar Array (EOVSA) and a breakthrough numerical modeling infrastructure that enables us to study properties of high-energy electrons in unprecedented cadence and quantitative detail. This study introduces the observation of an M1.2 flare that occurred on 2017 September 9 and analyzes the evolution of the nonthermal electrons in the corona based on EOVSA MW spectral imaging data. We find a significant spectral hardening of the MWemitting nonthermal electron population in the corona, using EOVSA lower-frequency (<7 GHz) observations over a selected 4-minute window of the flare's impulsive phase. We compare this spectral evolution with the evolution of the spectral index of nonthermal electrons emitting in the chromosphere, derived from HXR observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager. We discuss the general picture of the evolution of the nonthermal electron population in this flare by incorporating observations at the two complementary wavelengths. We also make an estimate of the total energy of the nonthermal electrons contained in the observed coronal low-frequency MW source and discuss its temporal evolution. Title: Drifting Pulsation Structure at the Very Beginning of the 2017 September 10 Limb Flare Authors: Karlický, Marian; Chen, Bin; Gary, Dale E.; Kašparová, Jana; Rybák, Jan Bibcode: 2020ApJ...889...72K Altcode: 2019arXiv191212518K Drifting pulsation structures (DPSs) are important radio fine structures usually observed at the beginning of eruptive solar flares. It has been suggested that DPSs carry important information on the energy release processes in solar flares. We study DPS observed in an X8.2-class flare on 2017 September 10 in the context of spatial and spectral diagnostics provided by microwave, EUV, and X-ray observations. We describe DPS and its substructures that were observed for the first time. We use a new wavelet technique to reveal characteristic periods in DPS and their frequency bands. Comparing the periods of pulsations found in this DPS with those in previous DPSs, we found new very short periods in the 0.09-0.15 s range. We present Expanded Owens Valley Solar Array images and spectra of microwave sources observed during the DPS. This DPS at its very beginning has pulsations in two frequency bands (1000-1300 MHz and 1600-1800 MHz), which are interconnected by fast drifting bursts. We show that these double-band pulsations started just at the moment when the ejected filament splits apart in a tearing motion at the location where a signature of the flare current sheet later appeared. Using the standard flare model and previous observations of DPSs, we interpret these double-band pulsations as a radio signature of superthermal electrons trapped in the rising magnetic rope and flare arcade at the moment when the flare magnetic reconnection starts. The results are discussed in a scenario with the plasmoid in the rising magnetic rope. Title: A new view of the solar atmosphere: daily full-disk multifrequency radio images from EOVSA Authors: Gary, D.; Yu, S.; Chen, B.; LaVilla, V. Bibcode: 2020AAS...23538501G Altcode: A new pipeline processing system is producing unprecedented daily full-disk images of the Sun from the Expanded Owens Valley Solar Array (EOVSA) in 6 frequency bands from 1-14 GHz. The images are produced by fitting a disk model to the measured visibilities and using the disk for self-calibration of the radio imaging data, resulting in images that faithfully show even the weakest of features in the solar atmosphere, including clear limb brightening, coronal holes, weak plage regions, filaments, and prominences. The multi-frequency data can be used to investigate the physical properties of these features of the solar corona, transition region, and upper chromosphere, but the data are so new that the interpretation is still in progress. We highlight some initial results on the frequency dependence of equatorial limb brightening and polar coronal hole darkening. Title: Decay of the coronal magnetic field can release sufficient energy to power a solar flare Authors: Fleishman, Gregory D.; Gary, Dale E.; Chen, Bin; Kuroda, Natsuha; Yu, Sijie; Nita, Gelu M. Bibcode: 2020Sci...367..278F Altcode: Solar flares are powered by a rapid release of energy in the solar corona, thought to be produced by the decay of the coronal magnetic field strength. Direct quantitative measurements of the evolving magnetic field strength are required to test this. We report microwave observations of a solar flare, showing spatial and temporal changes in the coronal magnetic field. The field decays at a rate of ~5 Gauss per second for 2 minutes, as measured within a flare subvolume of ~1028 cubic centimeters. This fast rate of decay implies a sufficiently strong electric field to account for the particle acceleration that produces the microwave emission. The decrease in stored magnetic energy is enough to power the solar flare, including the associated eruption, particle acceleration, and plasma heating. Title: Measurement of magnetic field and relativistic electrons along a solar flare current sheet Authors: Chen, Bin; Shen, Chengcai; Gary, Dale E.; Reeves, Katharine K.; Fleishman, Gregory D.; Yu, Sijie; Guo, Fan; Krucker, Säm; Lin, Jun; Nita, Gelu M.; Kong, Xiangliang Bibcode: 2020NatAs...4.1140C Altcode: 2020arXiv200512757C; 2020NatAs.tmp..150C In the standard model of solar flares, a large-scale reconnection current sheet is postulated to be the central engine for powering the flare energy release1-3 and accelerating particles4-6. However, where and how the energy release and particle acceleration occur remain unclear owing to the lack of measurements of the magnetic properties of the current sheet. Here we report the measurement of the spatially resolved magnetic field and flare-accelerated relativistic electrons along a current-sheet feature in a solar flare. The measured magnetic field profile shows a local maximum where the reconnecting field lines of opposite polarities closely approach each other, known as the reconnection X point. The measurements also reveal a local minimum near the bottom of the current sheet above the flare loop-top, referred to as a `magnetic bottle'. This spatial structure agrees with theoretical predictions1,7 and numerical modelling results. A strong reconnection electric field of about 4,000 V m-1 is inferred near the X point. This location, however, shows a local depletion of microwave-emitting relativistic electrons. These electrons instead concentrate at or near the magnetic bottle structure, where more than 99% of them reside at each instant. Our observations suggest that the loop-top magnetic bottle is probably the primary site for accelerating and confining the relativistic electrons. Title: Imaging-Spectroscopy of CME-Associated Solar Radio Emission using OVRO-LWA Authors: Chhabra, S.; Gary, D. E.; Hallinan, G.; Anderson, M.; Chen, B. Bibcode: 2019AGUFMSH21B..03C Altcode: Radio emission from the solar corona provides a unique perspective on the physical properties of energetic phenomena, such as solar flares and coronal mass ejections (CMEs). We use the new state-of-the-art Owens Valley Radio Observatory - Long Wavelength Array (OVRO-LWA) for the purpose. We examine a complex event consisting multiple radio sources/bursts associated with a fast CME and a M2.1 GOES SXR flare from 2015 Sep 20, as well as quiet Sun images before and after the bursts. Images of 9-s cadence are used to analyze the event over a 90-minute period, out to a distance of ~3 Rsun, over the frequency range of 40-70 MHz available at that time.

We present our results from the investigation of the radio sources, focusing particularly on one burst source that exhibits outward motion. In order to understand better the evolution of the burst, we image the event at hundreds of frequencies and use the source centroids to obtain the velocity for the outward motion. A coalignment with LASCO(C2) allows a spatial and temporal comparison with observations of the CME in white light indicating an association of the outward motion with the core of the CME. We perform graduating-cylindrical-shell reconstruction of the CME to constrain the density in the volume to verify that the emission from the moving source is not consistent with plasma emission, and therefore is likely due to gyrosynchrotron emission. This then allows the use gyrosynchrotron spectral fitting techniques to estimate the evolving physical conditions. The results suggest that both accelerated electron density and magnetic field strength decline as the source expands outward, while the powerlaw index of the electrons hardens. Title: Towards Next Generation Radio Imaging Spectroscopy: a Path Forward to FASR Authors: Bastian, T.; Chen, B.; Gary, D. E. Bibcode: 2019AGUFMSH31C3327B Altcode: A long term goal of the solar physics community, one that has been endorsed by several NRC decadal surveys, is the Frequency Agile Solar Radiotelescope (FASR). FASR is designed to address a broad program of fundamental solar physics, including coronal magnetic fields, magnetic energy release, particle acceleration and transport, coronal and chromospheric heating, and drivers of space weather such as coronal mass ejections. Fundamental to the FASR concept is observing the chromosphere and corona as a system using innovative measurements — ultra-broadband imaging spectropolarimetry — that will yield unique science data products that are complementary to those produced in, e.g., the O/IR and EUV/X-ray wavelength regimes. The potential of the instrument is already being demonstrated by pathfinder observations made by the Expanded Owens Valley Solar Array (EOVSA) and by the Jansky Very Large Array (JVLA). This talk discusses a step-by-step Implementation of FASR to spread out the cost (the full FASR concept would be in excess of $75M) and achieve some of the most compelling science in time for the upcoming solar maximum. This "stepping stone" approach would first build out the high frequency subsystem at Owens Valley (~1-20 GHz) and rely on other initiatives such as the OVRO Long Wavelength Array to cover the metric wavelength range, deferring the mid-frequency subsystem (~0.2-2 GHz) for the following decade. Such an approach allows a timely deployment of critical science infrastructure that can meet the demands of the wider community while training students and researchers to exploit this new asset. The talk will emphasize the great gain in image quality and science capability of the larger array relative to EOVSA and JVLA. Title: Measuring Coronal Magnetic Fields with the Jansky Very Large Array and RATAN Telescopes Authors: Bastian, T.; Gary, D. E.; Fleishman, G. D.; Nita, G. M.; Chen, B.; Kaltman, T.; Bogod, V. Bibcode: 2019AGUFMSH41B..05B Altcode: Quantitative knowledge of coronal magnetic fields is fundamental to understanding essentially all solar phenomena above the photosphere, including the structure and evolution of solar active regions, magnetic energy release, charged particle acceleration, flares, coronal mass ejections (CMEs), coronal heating, the solar wind and, ultimately, space weather and its impact on Earth. Characterized as the solar and space physics community's "dark energy" problem, useful quantitative measurements of the coronal magnetic field have been largely unavailable until recently. Although understood in principle for many years, suitable instrumentation at radio wavelengths - requiring the ability to perform wideband imaging spectropolarimetry - has not been available in practice for making quantitative maps of coronal magnetic fields. This has changed in recent years, with the advent of the Jansky Very Large Array (JVLA) and the Expanded Owens Valley Solar Array (EOVSA) which are being exploited to demonstrate the utility of radio observations for measuring coronal magnetic fields.

We report radio observations of a large solar active region by the Jansky Very Large Array (JVLA). The active region, AR 12209, was mapped on four days: 18, 20, 22, and 24 November 2014 in 56 spectral windows spanning 1-8 GHz. At the lowest frequencies the emission is dominated by thermal free-free emission but at frequencies >1.5 GHz thermal gyroresonance (GR) emission at the second or third harmonic of the electron gyrofrequency dominates. GR emission enables nested coronal isogauss surfaces ranging from approximately 180 G to as high as 1400 G to be mapped. At the time these observations were obtained, the JVLA was not yet fully commissioned for solar observing. In particular, the switched-power flux calibration system was not yet implemented. We therefore cross-calibrated the JVLA observations against well-calibrated one-dimensional observations obtained by the RATAN 600 telescope in Zelenchukskaya, Russia. We present coronal magnetograms obtained by the JVLA and compare them to model calculations. Title: Study of Type III Solar Radio Bursts in Nanoflares Authors: Chhabra, S.; Klimchuk, J. A.; Gary, D. E.; Viall, N. M. Bibcode: 2019AGUFMSH23C3337C Altcode: The heating mechanisms responsible for the million-degree solar corona remain one of the most intriguing problems in space science. It is widely agreed, that the ubiquitous presence of reconnection events and the associated impulsive heating (nanoflares) are a strong candidate in solving this problem [Klimchuk J.A., 2015 and references therein].

Whether nanoflares accelerate energetic particles like full-sized flares is unknown. The lack of strong emission in hard X-rays suggests that the quantity of highly energetic particles is small. There could, however, be large numbers of mildly energetic particles (~ 10 keV). We investigate such particles by searching for the type III radio bursts that they may produce. If energetic electron beams propagating along magnetic field lines generate a bump-on-tail instability, they will produce Langmuir waves, which can then interact with other particles and waves to give rise to emission at the local plasma frequency and its first harmonic. Type III bursts are characteristically known to exhibit high frequency drifts as the beam propagates through a density gradient. The time-lag technique that was developed to study subtle delays in light curves from different EUV channels [Viall & Klimchuk 2012] can also be used to detect subtle delays at different radio frequencies. We have modeled the expected radio emission from nanoflares, which we used to test and calibrate the technique. We are applying the technique to actual radio observations from VLA (Very Large Array), MWA (Murchison Widefield Array) and seeking data from LOFAR (Low-Frequency Array) as well. We also plan to use data from the PSP (Parker Solar Probe) to look for similar reconnection signatures in the Solar Wind. Our goal is to determine whether nanoflares accelerate energetic particles and to determine their properties. The results will have important implications for both the particle acceleration and reconnection physics. Title: Probing the thermal structure of the solar chromosphere with ALMA and optical/NIR observations Authors: Gary, Dale Bibcode: 2019asrc.confE..13G Altcode: ALMA is a powerful new instrument that allows an unambiguous determination of the solar chromospheric temperature, and its rapid evolution. When combined with multiwavelength observations in other diagnostics, most notably strong optical/NIR spectral lines, this allows us to probe the highly structured atmosphere throughout much of its height and with high spatial and temporal resolution. We will discuss several unique datasets that combine solar ALMA observations in Bands 3 and 6 with simultaneous imaging spectroscopy from the Interferometric Bidimensional Spectrometer (IBIS) operating at the Dunn Solar Telescope/NSO. We find that parameters of ""classical"" chromospheric spectral lines of H-alpha and Ca II are in some cases closely correlated with the ALMA brightness temperatures, posing strong constraints to interpretation of the observed spectral intensities in terms of dynamical properties. We will also present information on the temporal evolution of dynamic events as seen by ALMA, comparing those with the shocks and small-scale impulsive events seen in the co-temporal ground-based optical data. Finally, we will describe the opportunities and advantages of joint observations between ALMA and the soon-to-be-operational, four-meter DKI Solar Telescope (DKIST). Title: Imaging Spectroscopic Observations of Type I Noise Storms with Ultrahigh Temporal and Spectral Resolution Authors: Yu, S.; Chen, B.; Bastian, T.; Gary, D. E. Bibcode: 2019AGUFMSH23C3336Y Altcode: Type I noise storms are the most common, but perhaps the least understood type of solar radio bursts in the decimeter-meter wavelength range. Noise storms are non-flare-related radio phenomena. Their existence indicates that energy release and particle energization can continue in the corona without notable solar activities such as flares or coronal mass ejections. Noise storms manifest themselves as intermittent short-lived narrow-band bursts superposed on a broad-band, long-lasting continuum (sometimes referred to as the noise storm continuum). However, previous studies were either based on total-power dynamic spectroscopy (without spatial resolution), or on imaging observations at one or few frequency channels. During the recent Karl G. Jansky Very Large Array (VLA) solar observing campaign, we performed dynamic imaging spectroscopic observations with unprecedentedly high temporal resolution,10 milliseconds, along with fine spectral resolution (250 kHz) in the 290-450 MHz P band. We recorded several noise storm events associated with quiescent, non-flaring solar active regions. For the first time, we are able to image these type I bursts and fully resolve them in the frequency-time domain, which are used to better elucidate the origin of these bursts. We discuss the implications of our results for understanding energy release and particle energization in the seemly quiescent solar corona. Title: Frequency Agile Solar Radiotelescope Authors: Bastian, Tim; Bain, H.; Bradley, R.; Chen, B.; Dahlin, J.; DeLuca, E.; Drake, J.; Fleishman, G.; Gary, D.; Glesener, L.; Guo, Fan; Hallinan, G.; Hurford, G.; Kasper, J.; Ji, Hantao; Klimchuk, J.; Kobelski, A.; Krucker, S.; Kuroda, N.; Loncope, D.; Lonsdale, C.; McTiernan, J.; Nita, G.; Qiu, J.; Reeves, K.; Saint-Hilaire, P.; Schonfeld, S.; Shen, Chengcai; Tun, S.; Wertheimer, D.; White, S. Bibcode: 2019astro2020U..56B Altcode: We describe the science objectives and technical requirements for a re-scoped Frequency Agile Solar Radiotelescope (FASR). FASR fulfills a long term community need for a ground-based, solar-dedicated, radio telescope - a next-generation radioheliograph - designed to perform ultra-broadband imaging spectropolarimetry. Title: Solar Chromospheric Temperature Diagnostics: A Joint ALMA-Hα Analysis Authors: Molnar, Momchil E.; Reardon, Kevin P.; Chai, Yi; Gary, Dale; Uitenbroek, Han; Cauzzi, Gianna; Cranmer, Steven R. Bibcode: 2019ApJ...881...99M Altcode: 2019arXiv190608896M We present the first high-resolution, simultaneous observations of the solar chromosphere in the optical and millimeter wavelength ranges, obtained with the Atacama Large Millimeter Array (ALMA) and the Interferometric Bidimensional Spectrometer at the Dunn Solar Telescope. In this paper we concentrate on the comparison between the brightness temperature observed in ALMA Band 3 (3 mm; 100 GHz) and the core width of the Hα 6563 Å line, previously identified as a possible diagnostic of the chromospheric temperature. We find that in the area of plage, network and fibrils covered by our field of view, the two diagnostics are well correlated, with similar spatial structures observed in both. The strength of the correlation is remarkable, given that the source function of the millimeter radiation obeys local thermodynamic equilibrium, while the Hα line has a source function that deviates significantly from the local Planck function. The observed range of ALMA brightness temperatures is sensibly smaller than the temperature range that was previously invoked to explain the observed width variations in Hα. We employ analysis from forward modeling with the Rybicki-Hummer (RH) code to argue that the strong correlation between Hα width and ALMA brightness temperature is caused by their shared dependence on the population number n 2 of the first excited level of hydrogen. This population number drives millimeter opacity through hydrogen ionization via the Balmer continuum, and Hα width through a curve-of-growth-like opacity effect. Ultimately, the n 2 population is regulated by the enhancement or lack of downward Lyα flux, which coherently shifts the formation height of both diagnostics to regions with different temperature, respectively. Title: Modeling the 2017 September 10 Long Duration Gamma Ray Flare Authors: Ryan, J.; De Nolfo, G. A.; Gary, D. Bibcode: 2019ICRC...36.1144R Altcode: 2019PoS...358.1144R No abstract at ADS Title: Magnetic Energy Release in Solar Flares seen through Microwave Eyes Authors: Fleishman, Gregory D.; Gary, Dale E.; Chen, Bin; Yu, Sijie; Nita, Gelu M.; Kuroda, Natsuha Bibcode: 2019AAS...23421602F Altcode: Solar Coronal Magnetism includes emergence of the magnetic flux from the sub-photospheric volume, evolution of the coronal magnetic field, generation and accumulation of a free non-potential magnetic energy, gradual and explosive release of this energy, generation and dissipation of turbulence. This set of phenomena drives solar flares and other forms of eruptive activity such as jets or coronal mass ejections. An emerging new remote sensing window - Microwave Imaging Spectroscopy - offers a science-transforming, entirely new look at the coronal magnetism. The foundation of this new capability is the sensitivity of the microwave emission to the magnetic field. A break-through, however, comes only when this emission is measured at many frequencies with a reasonably high spatial and temporal resolution, which is the case of a new imaging instrument - the Expanded Owens Valley Solar Array (EOVSA). In this talk we briefly present the key methodology needed to obtain the target physical parameters, show a few examples of solar flares observed with EOVSA, and discuss main physical findings made with these new data and methodology, in particular - about rapid decay of the magnetic field at the site of the primary energy release in solar flares, associated electric field and accelerated particles, plasma heating, and turbulent magnetic diffusivity. We discuss these new findings in the context of the standard model of solar flare and the contemporary ideas about the magnetic energy release, magnetic reconnection, turbulence generation, and particle acceleration. Title: The Focusing Optics X-ray Solar Imager (FOXSI) Authors: Christe, Steven; Shih, Albert Y.; Krucker, Sam; Glesener, Lindsay; Saint-Hilaire, Pascal; Caspi, Amir; Gburek, Szymon; Steslicki, Marek; Allred, Joel C.; Battaglia, Marina; Baumgartner, Wayne H.; Drake, James; Goetz, Keith; Grefenstette, Brian; Hannah, Iain; Holman, Gordon D.; Inglis, Andrew; Ireland, Jack; Klimchuk, James A.; Ishikawa, Shin-Nosuke; Kontar, Eduard; Massone, Anna-maria; Piana, Michele; Ramsey, Brian; Schwartz, Richard A.; Woods, Thomas N.; Chen, Bin; Gary, Dale E.; Hudson, Hugh S.; Kowalski, Adam; Warmuth, Alexander; White, Stephen M.; Veronig, Astrid; Vilmer, Nicole Bibcode: 2019AAS...23422501C Altcode: The Focusing Optics X-ray Solar Imager (FOXSI), a SMEX mission concept in Phase A, is the first-ever solar-dedicated, direct-imaging, hard X-ray telescope. FOXSI provides a revolutionary new approach to viewing explosive magnetic-energy release on the Sun by detecting signatures of accelerated electrons and hot plasma directly in and near the energy-release sites of solar eruptive events (e.g., solar flares). FOXSI's primary science objective is to understand the mystery of how impulsive energy release leads to solar eruptions, the primary drivers of space weather at Earth, and how those eruptions are energized and evolve. FOXSI addresses three important science questions: (1) How are particles accelerated at the Sun? (2) How do solar plasmas get heated to high temperatures? (3) How does magnetic energy released on the Sun lead to flares and eruptions? These fundamental physics questions are key to our understanding of phenomena throughout the Universe from planetary magnetospheres to black hole accretion disks. FOXSI measures the energy distributions and spatial structure of accelerated electrons throughout solar eruptive events for the first time by directly focusing hard X-rays from the Sun. This naturally enables high imaging dynamic range, while previous instruments have typically been blinded by bright emission. FOXSI provides 20-100 times more sensitivity as well as 20 times faster imaging spectroscopy than previously available, probing physically relevant timescales (<1 second) never before accessible. FOXSI's launch in July 2022 is aligned with the peak of the 11-year solar cycle, enabling FOXSI to observe the many large solar eruptions that are expected to take place throughout its two-year mission. Title: Fast plasma outflows associated with impulsive microwave and hard X-ray bursts during the gradual phase of the 2017 September 10 X8.2 flare Authors: Chen, Bin; Yu, Sijie; Musset, Sophie; Gary, Dale E.; Fleishman, Gregory D.; Glesener, Lindsay; Reeves, Kathy; Nita, Gelu M. Bibcode: 2019AAS...23421601C Altcode: The 2017 September 10 X8.2 flare is a spectacular long duration event associated with a fast coronal mass ejection (CME). It features an extended gradual phase associated with hard X-ray (HXR) and microwave (MW) bursts that last for at least two hours after the flare peak (at 1600 UT). We examine the gradual phase using multi-wavelength data recorded by the Expanded Owens Valley Solar Array (EOVSA), RHESSI, Fermi/GBM, SDO/AIA, and MLSO/K-Cor. During the extended gradual phase ( 17-18 UT) when the CME already propagates to >10 solar radii, an extremely long and thin plasma sheet is visible in white light (WL) images that extends to at least 1.5 solar radii above the solar surface. We find evidence of multitudes of fast bi-directional plasma outflows ( 300-700 km/s) within the plasma sheet emanating from localized sites at very low coronal heights (0.1-0.2 solar radii above the surface), interpreted as magnetic reconnection occurring in the low corona. The occurrence of the fast plasma outflows correlates very well in time with the intermittent broadband MW emission and HXR enhancements. MW spectroscopic imaging reveals a MW source located at the looptop that coincides with a HXR looptop source. Another MW source is present in the northern leg of the flare arcade, whose temporal evolution seems to correlate with the looptop MW source but shows a time lag characteristic of the Alfvén transit time. We examine the temporal and spatial correlations among the plasma outflows, looptop MW/HXR source, and loopleg MW source, and discuss implications for magnetic energy release, plasma heating, and electron acceleration during the extended gradual phase of the flare. Title: New Insights into the 10 September 2017 Mega-Eruption Authors: Karpen, Judith T.; Kumar, Pankaj; Antiochos, Spiro K.; Gary, Dale E.; Dahlin, Joel Bibcode: 2019AAS...23431702K Altcode: The X8.2 flare on 10 September 2017 was part of a well-observed, extremely energetic solar eruption that has been intensely studied. Much attention has been devoted to the striking appearance and persistence of a current sheet behind the explosively accelerating CME. We focus here on the unusual appearance of prominent emission features on either side of the flare arcade, which were detected in microwave emissions by NJIT's EOVSA before the peak impulsive phase. Our analysis combines the results of 3D numerical simulations with observations by SDO, EOVSA, and IRIS to decipher the underlying magnetic structure of the erupting region and the initiation mechanism. The event originated in a complex active region with a large-scale quadrupolar magnetic field punctuated by many intrusions of minority polarity. We interpret the observed microwave features as evidence of electron acceleration due to breakout reconnection, and present compelling evidence for this conclusion. Title: Statistical analysis of evolving flare parameters inferred from spatially-resolved microwave spectra observed with the Expanded Owens Valley Solar Array Authors: Nita, Gelu M.; Fleishman, Gregory D.; Gary, Dale E.; Chen, Bin; Yu, Sijie; Kuroda, Natsuha Bibcode: 2019AAS...23420602N Altcode: The newly completed Expanded Owens Valley Solar Array (EOVSA) performed microwave (MW) imaging spectroscopy observations during several flares that occurred during the first half of September 2017. The unprecedented high frequency and spatial resolution of these observations allowed us for the first time to infer, with 2-arcsecond spatial resolution and 1-second temporal cadence, the spatial distribution and evolution of the coronal magnetic field strength, the number density of the accelerated electrons, the power-law index of their energy distribution, as well as other associated flare parameters. Our methodology, which consists of independently fitting the MW spectra corresponding to each individual pixel of the evolving mult-frequency maps with uniform gyrosynchrotron source models, generated a statistically significant collection of evolving flare parameters whose generally smooth spatial and time variation demonstrates a collective behavior of the neighboring volume elements, and thus validates our approach. Here we report on the statistical properties of these physical flare parameters, their spatial distributions, and their temporal trends for significant portions of the duration of each flare, and we interpret our results in the context of the standard solar flare model involving magnetic energy release, magnetic reconnection, and particle acceleration. Title: Probing the plasma sheet of the 2017 September 10 limb event using microwave spectroscopy Authors: Gary, Dale E.; Chen, Bin; Fleishman, Gregory D.; Nita, Gelu M.; Yu, Sijie Bibcode: 2019AAS...23431001G Altcode: In its later phases, the 2017 Sep 10 X8.2 limb flare produced a dramatic, nearly radial plasma sheet that was the site of both bi-directional radial flows (inward and outward) and 100 km/s turbulent motions measured in highly ionized Fe lines (Warren et al. 2018). Below the plasma sheet is a dense set of post-reconnection flare loops whose upper loops emit strongly in thermal hard X-rays and hot EUV lines (T 20 MK), while the lower loops emit in much cooler lines such as Ca II (Kuridze et al. 2019). Observations of gyrosynchrotron emission from the Expanded Owens Valley Solar Array (EOVSA) show the presence of high-energy (> 300 keV) electrons at still higher heights above the EUV and hard X-ray loops. At microwave frequencies above about 14 GHz, EOVSA shows that the source shape is a nearly complete loop while at frequencies below about 10 GHz, the source is split into two lobes on either side of the plasma sheet. Using the spatially resolved EOVSA brightness temperature spectra, we investigate the cause of this bifurcated spatial structure. There are two competing possibilities for the "missing" emission at lower frequencies: (a) the emission may be absorbed by intervening high-density, relatively cool material in the plasma sheet or (b) the emission may be suppressed by the Razin effect due to a combination of hot high density material and low magnetic field strength. We use diagnostics from microwave imaging spectroscopy and AIA DEM analysis to determine the likely plasma parameters and other characteristics of the plasma sheet, and the relative placement of the microwave-emitting electrons and the plasma sheet along the line of sight. Title: Multi-wavelength Multi-height Study of Super Strong Surface and Coronal Magnetic Fields in Active Region 12673 Authors: Wang, Haimin; Chen, Bin; Jing, Ju; Yu, Sijie; Liu, Chang; Yurchyshyn, Vasyl B.; Ahn, Kwangsu; Okamoto, Takenori; Toriumi, Shin; Cao, Wenda; Gary, Dale E. Bibcode: 2019AAS...23440205W Altcode: Using the joint observations of Goode Solar telescope (GST), Expanded Owens Valley Solar Array (EOVSA), Solar Dynamics Observatory (SDO) and Hinode, we study the Solar Active Region (AR) 12673 in September 2017, which is the most flare productive AR in the solar cycle 24. GST observations show the strong photospheric magnetic fields (nearly 6000 G) in polarity inversion line (PIL) and apparent photospheric twist. Consistent upward flows are also observed in Dopplergrams of Hinode, HMI and GST at the center part of that section of PIL, while the down flows are observed in two ends, indicating that the structure was rising from subsurface. Combining Non-Linear Force Free Extrapolation and EOVSA microwave imaging spectroscopy, we also look into the coronal structure of magnetic fields in this unusual AR, including the evolution before and after the X9.3 flare on September 6, 2017. Coronal fields between 1000 and 2000 gauss are found above the flaring PIL at the height range between 8 and 4Mm, outlining the structure of a fluxrope or sheared arcade. Title: Study of Type III Radio Bursts in Nanoflares Authors: Chhabra, Sherry; Klimchuk, James A.; Viall, Nicholeen M.; Gary, Dale E. Bibcode: 2019shin.confE..12C Altcode: The heating mechanisms responsible for the million-degree solar corona remain one of the most intriguing problems in space science. It is widely agreed, that the ubiquitous presence of reconnection events and the associated impulsive heating (nanoflares) are a strong candidate in solving this problem [Klimchuk J.A., 2015 and references therein].

Whether nanoflares accelerate energetic particles like full-sized flares is unknown. The lack of strong emission in hard X-rays suggests that the quantity of highly energetic particles is small. There could, however, be large numbers of mildly energetic particles ( 10 keV). We investigate such particles by searching for the type III radio bursts that they may produce. If energetic electron beams propagating along magnetic field lines generate a bump-on-tail instability, they will produce Langmuir waves, which can then interact with other particles and waves to give rise to emission at the local plasma frequency and its first harmonic. Type III bursts are characteristically known to exhibit high frequency drifts as the beam propagates through a density gradient. The time-lag technique that was developed to study subtle delays in light curves from different EUV channels [Viall & Klimchuk 2012] can also be used to detect subtle delays at different radio frequencies. We have modeled the expected radio emission from nanoflares, which we used to test and calibrate the technique. We have begun applying the technique to actual radio observations from VLA (Very Large Array) and seeking data from MWA (Murchison Widefield Array) as well. We also plan to use data from the PSP(Parker Solar Probe) to look for similar reconnection signatures in the Solar Wind. Our goal is to determine whether nanoflares accelerate energetic particles and to determine their properties. The results will have important implications for both the particle acceleration and reconnection physics." Title: Particle Acceleration and Transport, New Perspectives from Radio, X-ray, and Gamma-Ray Observations Authors: Gary, Dale; Bastian, Timothy S.; Chen, Bin; Drake, James F.; Fleishman, Gregory; Glesener, Lindsay; Saint-Hilaire, Pascal; White, Stephen M. Bibcode: 2019BAAS...51c.371G Altcode: 2019astro2020T.371G Particle acceleration and particle transport are ubiquitous in astrophysics. The Sun offers an astrophysical laboratory to study these in minute detail, using radio dynamic imaging spectroscopy to measure coronal magnetic fields, time and space evolution of the electron distribution function. Title: Diagnostics of Space Weather Drivers Enabled by Radio Observations Authors: Bastian, Tim; Bain, Hazel; Chen, Bin; Gary, Dale E.; Fleishman, Gregory D.; Glesener, Lindsay; Saint-Hilaire, Pascal; Lonsdale, Colin; White, Stephen M. Bibcode: 2019BAAS...51c.323B Altcode: 2019astro2020T.323B; 2019arXiv190405817B The Sun is an active star that can impact the Earth, its magnetosphere, and the technological infrastructure on which modern society depends. Radio emission from space weather drivers offers unique diagnostics that complement those available at other wavelengths. We discuss the requirements for an instrument to enable such diagnostics. Title: Radio, Millimeter, Submillimeter Observations of the Quiet Sun Authors: Bastian, Tim; Chen, Bin; Gary, Dale E.; Fleishman, Gregory D.; Glesener, Lindsay; Lonsdale, Colin; Saint-Hilaire, Pascal; White, Stephen M. Bibcode: 2019BAAS...51c.493B Altcode: 2019arXiv190405826B; 2019astro2020T.493B We point out the lack of suitable radio observations of the quiet Sun chromosphere and corona and outline requirements for next generation instrumentation to address the gap. Title: Probing Magnetic Reconnection in Solar Flares: New Perspectives from Radio Dynamic Imaging Spectroscopy Authors: Chen, Bin; Bastian, Tim; Dahlin, Joel; Drake, James F.; Fleishman, Gregory; Gary, Dale; Glesener, Lindsay; Guo, Fan; Ji, Hantao; Saint-Hilaire, Pascal; Shen, Chengcai; White, Stephen M. Bibcode: 2019BAAS...51c.507C Altcode: 2019astro2020T.507C; 2019arXiv190311192C Magnetic reconnection is a fundamental physical process in many laboratory, space, and astrophysical plasma contexts. In this white paper we emphasize the unique power of remote-sensing observations of solar flares at radio wavelengths in probing fundamental physical processes in magnetic reconnection. Title: Modeling the 2017 September 10 LDGRF Authors: Ryan, James Michael; de Nolfo, Georgia A.; Gary, Dale Bibcode: 2019shin.confE.104R Altcode: The series of large flares from 2017 September 4 to 10 were significant microwave events with revealing multi-wavelength images of the flare environment. The event on September 10 was a large long-duration, gamma-ray flare (LDGRF). The event also produced a Ground Level Enhancement (GLE). Using the microwave imaging data from the Expanded Owens Valley Solar Array (EVOSA) we interpret and model the behavior of the energetic-flare protons of September 10 as measured with the Large Area Telescope (LAT) on the Fermi mission. We do this in the context of stochastic acceleration in a large coronal bipolar structure to produce the high-energy long-duration gamma-ray emission. Our preliminary analysis suggests that the acceleration of the GeV protons takes place in a large structure about 1.4 solar radii in length. The requirements for the magnetic field and turbulence in this structure will be presented. Title: Solar Coronal Magnetic Fields: Quantitative Measurements at Radio Wavelengths Authors: Fleishman, Gregory; Bastian, Timothy S.; Chen, Bin; Gary, Dale E.; Glesener, Lindsay; Nita, Gelu; Saint-Hilaire, Pascal; White, Stephen M. Bibcode: 2019BAAS...51c.426F Altcode: 2019astro2020T.426F Quantitative measurements of coronal and chromospheric magnetic field is currently in its infancy. We describe a foundation of such observations, which is a key input for MHD numerical models of the solar atmosphere and eruptive processes, and a key link between lower layers of the solar atmosphere and the heliosphere. Title: Cause and Extent of the Extreme Radio Flux Density Reached by the Solar Flare of 2006 December 06 Authors: Gary, Dale E. Bibcode: 2019arXiv190109262G Altcode: The solar burst of 2006 December 06 reached a radio flux density of more than 1 million solar flux units (1 sfu = $10^{-22}$ W/m$^2$/Hz), as much as 10 times the previous record, and caused widespread loss of satellite tracking by GPS receivers. The event was well observed by NJITs Owens Valley Solar Array (OVSA). This work concentrates on an accurate determination of the flux density (made difficult due to the receiver systems being driving into non-linearity), and discuss the physical conditions on the Sun that gave rise to this unusual event. At least two other radio outbursts occurred in the same region (on 2006 December 13 and 14) that had significant, but smaller effects on GPS. We discuss the differences among these three events, and consider the implications of these events for the upcoming solar cycle. Title: ngVLA Observations of Coronal Magnetic Fields Authors: Fleishman, G. D.; Nita, G. M.; White, S. M.; Gary, D. E.; Bastian, T. S. Bibcode: 2018ASPC..517..125F Altcode: Energy stored in the magnetic field in the solar atmosphere above active regions is a key driver of all solar activity (e.g., solar flares and coronal mass ejections), some of which can affect life on Earth. Radio observations provide a unique diagnostic of the coronal magnetic fields that make them a critical tool for the study of these phenomena, using the technique of broadband radio imaging spectropolarimetry. Observations with the ngVLA will provide unique observations of coronal magnetic fields and their evolution, key inputs and constraints for MHD numerical models of the solar atmosphere and eruptive processes, and a key link between lower layers of the solar atmosphere and the heliosphere. In doing so they will also provide practical "research to operations" guidance for space weather forecasting. Title: Radio Observations of Solar Flares Authors: Gary, D. E.; Bastian, T. S.; Chen, B.; Fleishman, G. D.; Glesener, L. Bibcode: 2018ASPC..517...99G Altcode: Solar flares are due to the catastrophic release of magnetic energy in the Sun's corona, resulting in plasma heating, mass motions, particle acceleration, and radiation emitted from radio to γ-ray wavelengths. They are associated with global coronal eruptions of plasma into the interplanetary medium—coronal mass ejections—that can result in a variety of “space weather” phenomena. Flares release energy over a vast range of energies, from ∼1023 ergs (nanoflares) to more than 1032 ergs. Solar flares are a phenomenon of general astrophysical interest, allowing detailed study of magnetic energy release, eruptive processes, shock formation and propagation, particle acceleration and transport, and radiative processes. Observations at radio wavelengths offer unique diagnostics of the physics of flares. To fully exploit these diagnostics requires the means of performing time-resolved imaging spectropolarimetry. Recent observations with the Jansky Very Large Array (JVLA) and the Expanded Owens Valley Solar Array (EOVSA), supported by extensive development in forward modeling, have demonstrated the power of the approach. The ngVLA has the potential to bring our understanding of flare processes to a new level through its combination of high spatial resolution, broad frequency range, and imaging dynamic range—especially when used in concert with multi-wavelength observations and data at hard X-ray energies. Title: The Coronal Volume of Energetic Particles in Solar Flares as Revealed by Microwave Imaging Authors: Fleishman, Gregory D.; Loukitcheva, Maria A.; Kopnina, Varvara Yu.; Nita, Gelu M.; Gary, Dale E. Bibcode: 2018ApJ...867...81F Altcode: 2018arXiv180904753F The spectrum of gyrosynchrotron emission from solar flares generally peaks in the microwave range. Its optically thin, high-frequency component, above the spectral peak, is often used for diagnostics of the nonthermal electrons and the magnetic field in the radio source. Under favorable conditions, its low-frequency counterpart brings additional, complementary information about these parameters as well as thermal plasma diagnostics, either through gyrosynchrotron self-absorption, free-free absorption by the thermal plasma, or the suppression of emission through the so-called Razin effect. However, their effect on the low-frequency spectrum is often masked by spatial nonuniformity. To disentangle the various contributions to low-frequency gyrosynchrotron emission, a combination of spectral and imaging data is needed. To this end, we have investigated Owens Valley Solar Array (OVSA) multi-frequency images for 26 solar bursts observed jointly with RHESSI during the first half of 2002. For each, we examined dynamic spectra, time- and frequency-synthesis maps, RHESSI images with overlaid OVSA contours, and a few representative single-frequency snapshot OVSA images. We focus on the frequency dependence of microwave source sizes derived from the OVSA images and their effect on the low-frequency microwave spectral slope. We succeed in categorizing 18 analyzed events into several groups. Four events demonstrate clear evidence of being dominated by gyrosynchrotron self-absorption, with an inferred brightness temperature of ≥108 K. The low-frequency spectra in the remaining events are affected to varying degrees by Razin suppression. We find that many radio sources are rather large at low frequencies, which can have important implications for solar energetic particle production and escape. Title: Science with an ngVLA: Radio Observations of Solar Flares Authors: Gary, Dale E.; Bastian, Timothy S.; Chen, Bin; Fleishman, Gregory D.; Glesener, Lindsay Bibcode: 2018arXiv181006336G Altcode: Solar flares are due to the catastrophic release of magnetic energy in the Sun's corona, resulting in plasma heating, mass motions, particle acceleration, and radiation emitted from radio to $\gamma$-ray wavelengths. They are associated with global coronal eruptions of plasma into the interplanetary medium---coronal mass ejections---that can result in a variety of "space weather" phenomena. Flares release energy over a vast range of energies, from $\sim\!10^{23}$ ergs (nanoflares) to more than $10^{32}$ ergs. Solar flares are a phenomenon of general astrophysical interest, allowing detailed study of magnetic energy release, eruptive processes, shock formation and propagation, particle acceleration and transport, and radiative processes. Observations at radio wavelengths offer unique diagnostics of the physics of flares. To fully exploit these diagnostics requires the means of performing time-resolved imaging spectropolarimetry. Recent observations with the Jansky Very Large Array (JVLA) and the Expanded Owens Valley Solar Array (EOVSA), supported by extensive development in forward modeling, have demonstrated the power of the approach. The ngVLA has the potential to bring our understanding of flare processes to a new level through its combination of high spatial resolution, broad frequency range, and imaging dynamic range---especially when used in concert with multi-wavelength observations and data at hard X-ray energies. Title: Roadmap for Reliable Ensemble Forecasting of the Sun-Earth System Authors: Nita, Gelu; Angryk, Rafal; Aydin, Berkay; Banda, Juan; Bastian, Tim; Berger, Tom; Bindi, Veronica; Boucheron, Laura; Cao, Wenda; Christian, Eric; de Nolfo, Georgia; DeLuca, Edward; DeRosa, Marc; Downs, Cooper; Fleishman, Gregory; Fuentes, Olac; Gary, Dale; Hill, Frank; Hoeksema, Todd; Hu, Qiang; Ilie, Raluca; Ireland, Jack; Kamalabadi, Farzad; Korreck, Kelly; Kosovichev, Alexander; Lin, Jessica; Lugaz, Noe; Mannucci, Anthony; Mansour, Nagi; Martens, Petrus; Mays, Leila; McAteer, James; McIntosh, Scott W.; Oria, Vincent; Pan, David; Panesi, Marco; Pesnell, W. Dean; Pevtsov, Alexei; Pillet, Valentin; Rachmeler, Laurel; Ridley, Aaron; Scherliess, Ludger; Toth, Gabor; Velli, Marco; White, Stephen; Zhang, Jie; Zou, Shasha Bibcode: 2018arXiv181008728N Altcode: The authors of this report met on 28-30 March 2018 at the New Jersey Institute of Technology, Newark, New Jersey, for a 3-day workshop that brought together a group of data providers, expert modelers, and computer and data scientists, in the solar discipline. Their objective was to identify challenges in the path towards building an effective framework to achieve transformative advances in the understanding and forecasting of the Sun-Earth system from the upper convection zone of the Sun to the Earth's magnetosphere. The workshop aimed to develop a research roadmap that targets the scientific challenge of coupling observations and modeling with emerging data-science research to extract knowledge from the large volumes of data (observed and simulated) while stimulating computer science with new research applications. The desire among the attendees was to promote future trans-disciplinary collaborations and identify areas of convergence across disciplines. The workshop combined a set of plenary sessions featuring invited introductory talks and workshop progress reports, interleaved with a set of breakout sessions focused on specific topics of interest. Each breakout group generated short documents, listing the challenges identified during their discussions in addition to possible ways of attacking them collectively. These documents were combined into this report-wherein a list of prioritized activities have been collated, shared and endorsed. Title: Science with an ngVLA: ngVLA Observations of Coronal Magnetic Fields Authors: Fleishman, Gregory D.; Nita, Gelu M.; White, Stephen M.; Gary, Dale E.; Bastian, Tim S. Bibcode: 2018arXiv181006622F Altcode: Energy stored in the magnetic field in the solar atmosphere above active regions is a key driver of all solar activity (e.g., solar flares and coronal mass ejections), some of which can affect life on Earth. Radio observations provide a unique diagnostic of the coronal magnetic fields that make them a critical tool for the study of these phenomena, using the technique of broadband radio imaging spectropolarimetry. Observations with the ngVLA will provide unique observations of coronal magnetic fields and their evolution, key inputs and constraints for MHD numerical models of the solar atmosphere and eruptive processes, and a key link between lower layers of the solar atmosphere and the heliosphere. In doing so they will also provide practical "research to operations" guidance for space weather forecasting. Title: Microwave and Hard X-Ray Observations of the 2017 September 10 Solar Limb Flare Authors: Gary, Dale E.; Chen, Bin; Dennis, Brian R.; Fleishman, Gregory D.; Hurford, Gordon J.; Krucker, Säm; McTiernan, James M.; Nita, Gelu M.; Shih, Albert Y.; White, Stephen M.; Yu, Sijie Bibcode: 2018ApJ...863...83G Altcode: 2018arXiv180702498G We report the first science results from the newly completed Expanded Owens Valley Solar Array (EOVSA), which obtained excellent microwave (MW) imaging spectroscopy observations of SOL2017-09-10, a classic partially occulted solar limb flare associated with an erupting flux rope. This event is also well-covered by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) in hard X-rays (HXRs). We present an overview of this event focusing on MW and HXR data, both associated with high-energy nonthermal electrons, and we discuss them within the context of the flare geometry and evolution revealed by extreme ultraviolet observations from the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory. The EOVSA and RHESSI data reveal the evolving spatial and energy distribution of high-energy electrons throughout the entire flaring region. The results suggest that the MW and HXR sources largely arise from a common nonthermal electron population, although the MW imaging spectroscopy provides information over a much larger volume of the corona. Title: Microwave Spectroscopic Imaging of the Decay Phase of the X8.2 flare on 2017 Sep 10 Authors: Yu, Sijie; Chen, Bin; Musset, Sophie; Reeves, Kathy; Glesener, Lindsay; Gary, Dale Bibcode: 2018shin.confE.213Y Altcode: We present microwave imaging spectroscopic observation of the decay phase of the X8.2 flare on 2017 September 10 recorded by the Expanded Owens Valley Solar Array (EOVSA) at 2.5-18 GHz. The time period ( 17-18 UT) under this study is preceded by two major microwave peaks - one at 16:00 UT (which corresponds to the main hard X-ray peak) and another at 16:40 UT - showing multiple short-duration, broadband microwave bursts that reappear at an interval of 3-5 minutes. During this period the flare, as imaged by SDO/AIA and Hinode/XRT in EUV and soft X-ray, develops a thin plasma sheet extending from the top of the post-flare arcades to 200" above the loop-top. EOVSA spectroscopic imaging shows a nonthermal microwave source that appears to follow the outer rim of the EUV post-flare arcades, which is consistent with the classic picture of nonthermal electrons gyrating in newly reconnected, closed arcades. In particular, the upper portion of the microwave source coincides with a looptop RHESSI X-ray source located at bottom of the current-sheet-like feature and the multitudes of fast plasma downflows. We investigate the physical properties of the source by combining the concurrent microwave, EUV, and X-ray data, and discuss implications for particle acceleration during the flare decay phase. Title: Microwave Spectral Imaging of Bi-Directional Magnetic Reconnection Outflow Region of the 2017 Sep 10 X8.2 Flare Authors: Chen, Bin; Gary, Dale E.; Fleishman, Gregory D.; Krucker, Sam; Nita, Gelu M.; Dennis, Brian R.; Yu, Sijie; Kuroda, Natsuha; Reeves, Katharine K.; Polito, Vanessa; Shih, Albert Bibcode: 2018shin.confE.211C Altcode: The newly commissioned Expanded Owens Valley Solar Array (EOVSA) obtained microwave spectral imaging of the spectacular eruptive solar flare on 2017 September 10 in 2.5-18 GHz. During the early impulsive phase of the flare ( 15:54 UT), An elongated microwave source appears to connect the top of the flare arcade to the bottom of the erupting magnetic flux rope. Multi-frequency images reveal that the source bifurcates into two parts: One is located at and above the hard X-ray looptop source, and another located behind the flux rope. They appear to follow closely with the bi-directional reconnection downflow and upflow region as inferred from the SDO/AIA EUV images. The spatially resolved spectra of this microwave source show characteristics of gyrosynchrotron radiation, suggesting the presence of high-energy (100s of keV to MeV) electrons throughout the bi-directional reconnection outflow region. We derive physical parameters of the source region, and discuss their implications in magnetic energy release and electron acceleration. Title: Microwave Imaging Spectroscopy of the 2017 Sep 10 X8.2 Flare with EOVSA Authors: Gary, Dale; Fleishman, Gregory; Nita, Gelu; Chen, Bin; Kuroda, Natsuha Bibcode: 2018shin.confE.210G Altcode: The Expanded Owens Valley Solar Array (EOVSA) became fully operational just in time to record breakthrough multi-frequency microwave images, on a 1-s cadence, of several of the events of 2017 September. The X8.2 flare on September 10 was particularly well observed, and offers an opportunity to use imaging spectroscopy to create diagnostic parameter maps of magnetic field, plasma, and energetic electron parameters as a function of position and time. The EOVSA multi-frequency images and movies show a dramatic change from the initial flux-rope eruption, where microwave emission extends all along the plasma sheet below the flux rope, to the later post-flare loop phase, where an extremely bright microwave-emitting source located well above the EUV loops rises slowly at the same rate as the growing EUV loops. We fit the spatially-resolved microwave spectrum at each point in the emitting source using a multi-parameter homogeneous gyrosynchrotron emission model, and show the resulting parameter maps at several key times. We discuss the findings, as well as the limitations of the results, in terms of the expectations from the standard solar flare model. The parameter maps are the starting point for further 3D forward-fit modeling which we plan to undertake next. Title: Microwave Spectroscopic Imaging of the Magnetic Reconnection Region in the 2017 September 10 Eruptive Solar Flare Authors: Chen, Bin; Gary, Dale E.; Fleishman, Gregory D.; Krucker, Sam; Nita, Gelu M.; Dennis, Brian R.; Yu, Sijie; Kuroda, Natsuha; Reeves, Katharine; Polito, Vanessa; Shih, Albert Y. Bibcode: 2018tess.conf30603C Altcode: The newly commissioned Expanded Owens Valley Solar Array (EOVSA) obtained excellent high-cadence (1 s), microwave spectroscopic imaging of the spectacular eruptive solar flare on 2017 September 10 in 2.5-18 GHz. During the early impulsive phase of the flare (~15:53-15:55 UT), EOVSA images reveal an elongated microwave source that connects the top of the cusp-shaped flare arcade to the bottom of the erupting magnetic flux rope. The spatially resolved spectra of this microwave source show characteristics of gyrosynchrotron radiation, suggesting the presence of high-energy nonthermal electrons throughout the source region that presumably encloses the magnetic reconnection site(s) and bi-directional reconnection outflows. In addition, the lower and upper portions of the source seem to have different spatial and spectral properties. We derive physical parameters of the source region, and discuss their implications in magnetic energy release and electron acceleration. Title: The Focusing Optics X-ray Solar Imager (FOXSI) Authors: Christe, Steven; Shih, Albert Y.; Krucker, Sam; Glesener, Lindsay; Saint-Hilaire, Pascal; Caspi, Amir; Allred, Joel C.; Chen, Bin; Battaglia, Marina; Drake, James Frederick; Gary, Dale E.; Goetz, Keith; Gburek, Szymon; Grefenstette, Brian; Hannah, Iain G.; Holman, Gordon; Hudson, Hugh S.; Inglis, Andrew R.; Ireland, Jack; Ishikawa, Shin-nosuke; Klimchuk, James A.; Kontar, Eduard; Kowalski, Adam F.; Massone, Anna Maria; Piana, Michele; Ramsey, Brian; Schwartz, Richard; Steslicki, Marek; Ryan, Daniel; Warmuth, Alexander; Veronig, Astrid; Vilmer, Nicole; White, Stephen M.; Woods, Thomas N. Bibcode: 2018tess.conf40444C Altcode: We present FOXSI (Focusing Optics X-ray Solar Imager), a Small Explorer (SMEX) Heliophysics mission that is currently undergoing a Phase A concept study. FOXSI will provide a revolutionary new perspective on energy release and particle acceleration on the Sun. FOXSI's primary instrument, the Direct Spectroscopic Imager (DSI), is a direct imaging X-ray spectrometer with higher dynamic range and better than 10x the sensitivity of previous instruments. Flown on a 3-axis-stabilized spacecraft in low-Earth orbit, DSI uses high-angular-resolution grazing-incidence focusing optics combined with state-of-the-art pixelated solid-state detectors to provide direct imaging of solar hard X-rays for the first time. DSI is composed of a pair of X-ray telescopes with a 14-meter focal length enabled by a deployable boom. DSI has a field of view of 9 arcminutes and an angular resolution of better than 8 arcsec FWHM; it will cover the energy range from 3 up to 50-70 keV with a spectral resolution of better than 1 keV. DSI will measure each photon individually and will be able to create useful images at a sub-second temporal resolution. FOXSI will also measure soft x-ray emission down to 0.8 keV with a 0.25 keV resolution with its secondary instrument, the Spectrometer for Temperature and Composition (STC) provided by the Polish Academy of Sciences. Making use of an attenuator-wheel and high-rate-capable detectors, FOXSI will be able to observe the largest flares without saturation while still maintaining the sensitivity to detect X-ray emission from weak flares, escaping electrons, and hot active regions. This presentation will cover the data products and software that can be expected from FOXSI and how they could be used by the community. Title: Microwave Imaging of Flares and Active Regions with the Expanded Owens Valley Solar Array Authors: Gary, Dale E.; Chen, Bin; Fleishman, Gregory D.; Kuroda, Natsuha; Nita, Gelu M.; White, Stephen M.; Yu, Sijie Bibcode: 2018tess.conf21058G Altcode: The Expanded Owens Valley Solar Array (EOVSA), operating in the microwave range (2.5-18 GHz), is the first solar-dedicated radio instrument to achieve true multi-frequency imaging of the Sun. As of the time of this Triennial Earth-Sun Summit meeting, EOVSA will have completed its first year of full operation. We present some highlights of both active region and flare observations that demonstrate the exciting new capabilities of the instrument, including excellent coverage of several large flares that occurred in the 2017 September period. We also provide information for public access to the data, and for getting started with analysis. We are developing tools to simplify working with the data, as well as modeling tools for interpreting the results in the context of complementary multi-wavelength data from space- and ground-based instruments. The progress and current status of these efforts is given in this and a number of companion presentations at the meeting. Title: Highlights of EOVSA Microwave Imaging Spectroscopy of the Flares of September 2017. Authors: Gary, Dale E. Bibcode: 2018tess.conf31501G Altcode: The Expanded Owens Valley Solar Array (EOVSA) began full operations only in April of 2017, just in time to cover the late surge of solar activity in Cycle 24. The solar flare events of September 4 and 10 were especially well observed, and the 2.5-18 GHz images provide outstanding and never-before-obtained spatially-resolved microwave spectra produced by high-energy electron of energy ~0.5 to a few MeV. The combination of timing, position, and spectrum of the emission, compared with multi-wavelength observations from other instruments, provides a new view of the high-energy component of these important events, both of which were associated with solar energetic particle (SEP) events. The highlights of results from these spectacular events are presented. Title: Absorption Spectroscopy of Mercury's Exosphere During the 2016 Solar Transit Authors: Schmidt, C. A.; Leblanc, F.; Reardon, K.; Killen, R. M.; Gary, D. E.; Ahn, K. Bibcode: 2018LPICo2047.6022S Altcode: Solar transits of Mercury provide a rare opportunity to study the exosphere in absorption and a valuable analog to transiting exoplanet studies. This presentation will characterize the sodium exosphere during the 2016 transit. Title: Exploring the Sun with ALMA Authors: Bastian, T. S.; Bárta, M.; Brajša, R.; Chen, B.; Pontieu, B. D.; Gary, D. E.; Fleishman, G. D.; Hales, A. S.; Iwai, K.; Hudson, H.; Kim, S.; Kobelski, A.; Loukitcheva, M.; Shimojo, M.; Skokić, I.; Wedemeyer, S.; White, S. M.; Yan, Y. Bibcode: 2018Msngr.171...25B Altcode: The Atacama Large Millimeter/submillimeter Array (ALMA) Observatory opens a new window onto the Universe. The ability to perform continuum imaging and spectroscopy of astrophysical phenomena at millimetre and submillimetre wavelengths with unprecedented sensitivity opens up new avenues for the study of cosmology and the evolution of galaxies, the formation of stars and planets, and astrochemistry. ALMA also allows fundamentally new observations to be made of objects much closer to home, including the Sun. The Sun has long served as a touchstone for our understanding of astrophysical processes, from the nature of stellar interiors, to magnetic dynamos, non-radiative heating, stellar mass loss, and energetic phenomena such as solar flares. ALMA offers new insights into all of these processes. Title: Dressing the Coronal Magnetic Extrapolations of Active Regions with a Parameterized Thermal Structure Authors: Nita, Gelu M.; Viall, Nicholeen M.; Klimchuk, James A.; Loukitcheva, Maria A.; Gary, Dale E.; Kuznetsov, Alexey A.; Fleishman, Gregory D. Bibcode: 2018ApJ...853...66N Altcode: The study of time-dependent solar active region (AR) morphology and its relation to eruptive events requires analysis of imaging data obtained in multiple wavelength domains with differing spatial and time resolution, ideally in combination with 3D physical models. To facilitate this goal, we have undertaken a major enhancement of our IDL-based simulation tool, GX_Simulator, previously developed for modeling microwave and X-ray emission from flaring loops, to allow it to simulate quiescent emission from solar ARs. The framework includes new tools for building the atmospheric model and enhanced routines for calculating emission that include new wavelengths. In this paper, we use our upgraded tool to model and analyze an AR and compare the synthetic emission maps with observations. We conclude that the modeled magneto-thermal structure is a reasonably good approximation of the real one. Title: Transient rotation of photospheric vector magnetic fields associated with a solar flare Authors: Xu, Yan; Cao, Wenda; Ahn, Kwangsu; Jing, Ju; Liu, Chang; Chae, Jongchul; Huang, Nengyi; Deng, Na; Gary, Dale E.; Wang, Haimin Bibcode: 2018NatCo...9...46X Altcode: 2018arXiv180103171X As one of the most violent eruptions on the Sun, flares are believed to be powered by magnetic reconnection. The fundamental physics involving the release, transfer, and deposition of energy have been studied extensively. Taking advantage of the unprecedented resolution provided by the 1.6 m Goode Solar Telescope, here, we show a sudden rotation of vector magnetic fields, about 12-20° counterclockwise, associated with a flare. Unlike the permanent changes reported previously, the azimuth-angle change is transient and cospatial/temporal with Hα emission. The measured azimuth angle becomes closer to that in potential fields suggesting untwist of flare loops. The magnetograms were obtained in the near infrared at 1.56 μm, which is minimally affected by flare emission and no intensity profile change was detected. We believe that these transient changes are real and discuss the possible explanations in which the high-energy electron beams or Alfve'n waves play a crucial role. Title: Three-dimensional Forward-fit Modeling of the Hard X-Ray and Microwave Emissions of the 2015 June 22 M6.5 Flare Authors: Kuroda, Natsuha; Gary, Dale E.; Wang, Haimin; Fleishman, Gregory D.; Nita, Gelu M.; Jing, Ju Bibcode: 2018ApJ...852...32K Altcode: 2017arXiv171207253K The well-established notion of a “common population” of the accelerated electrons simultaneously producing the hard X-ray (HXR) and microwave (MW) emission during the flare impulsive phase has been challenged by some studies reporting the discrepancies between the HXR-inferred and MW-inferred electron energy spectra. The traditional methods of spectral inversion have some problems that can be mainly attributed to the unrealistic and oversimplified treatment of the flare emission. To properly address this problem, we use a nonlinear force-free field (NLFFF) model extrapolated from an observed photospheric magnetogram as input to the three-dimensional, multiwavelength modeling platform GX Simulator and create a unified electron population model that can simultaneously reproduce the observed HXR and MW observations. We model the end of the impulsive phase of the 2015 June 22 M6.5 flare and constrain the modeled electron spatial and energy parameters using observations made by the highest-resolving instruments currently available in two wavelengths, the Reuven Ramaty High Energy Solar Spectroscopic Imager for HXR and the Expanded Owens Valley Solar Array for MW. Our results suggest that the HXR-emitting electron population model fits the standard flare model with a broken power-law spectrum ({E}{break}∼ 200 keV) that simultaneously produces the HXR footpoint emission and the MW high-frequency emission. The model also includes an “HXR-invisible” population of nonthermal electrons that are trapped in a large volume of magnetic field above the HXR-emitting loops, which is observable by its gyrosynchrotron radiation emitting mainly in the MW low-frequency range. Title: The Focusing Optics X-ray Solar Imager (FOXSI) SMEX Mission Authors: Christe, S.; Shih, A. Y.; Krucker, S.; Glesener, L.; Saint-Hilaire, P.; Caspi, A.; Allred, J. C.; Battaglia, M.; Chen, B.; Drake, J. F.; Gary, D. E.; Goetz, K.; Gburek, S.; Grefenstette, B.; Hannah, I. G.; Holman, G.; Hudson, H. S.; Inglis, A. R.; Ireland, J.; Ishikawa, S. N.; Klimchuk, J. A.; Kontar, E.; Kowalski, A. F.; Massone, A. M.; Piana, M.; Ramsey, B.; Schwartz, R.; Steslicki, M.; Turin, P.; Ryan, D.; Warmuth, A.; Veronig, A.; Vilmer, N.; White, S. M.; Woods, T. N. Bibcode: 2017AGUFMSH44A..07C Altcode: We present FOXSI (Focusing Optics X-ray Solar Imager), a Small Explorer (SMEX) Heliophysics mission that is currently undergoing a Phase A concept study. FOXSI will provide a revolutionary new perspective on energy release and particle acceleration on the Sun. FOXSI is a direct imaging X-ray spectrometer with higher dynamic range and better than 10x the sensitivity of previous instruments. Flown on a 3-axis-stabilized spacecraft in low-Earth orbit, FOXSI uses high-angular-resolution grazing-incidence focusing optics combined with state-of-the-art pixelated solid-state detectors to provide direct imaging of solar hard X-rays for the first time. FOXSI is composed of a pair of x-ray telescopes with a 14-meter focal length enabled by a deployable boom. Making use of a filter-wheel and high-rate-capable solid-state detectors, FOXSI will be able to observe the largest flares without saturation while still maintaining the sensitivity to detect x-ray emission from weak flares, escaping electrons, and hot active regions. This mission concept is made possible by past experience with similar instruments on two FOXSI sounding rocket flights, in 2012 and 2014, and on the HEROES balloon flight in 2013. FOXSI's hard X-ray imager has a field of view of 9 arcminutes and an angular resolution of better than 8 arcsec; it will cover the energy range from 3 up to 50-70 keV with a spectral resolution of better than 1 keV; and it will have sub-second temporal resolution. Title: Three-Dimensional Forward-Fit Modeling of The Hard X-ray and The Microwave Emissions of The 2015-06-22 M6.5 Flare Authors: Kuroda, N.; Gary, D. E.; Wang, H.; Fleishman, G. D.; Nita, G. M.; Jing, J. Bibcode: 2017AGUFMSH41A2753K Altcode: The well-established notion of a "common population" of the accelerated electrons simultaneously producing the hard X-ray (HXR) and the microwave (MW) emission during the flare impulsive phase has been challenged by some studies reporting the discrepancies between the HXR-inferred and the MW-inferred electron energy spectra. The traditional methods of their spectral inversion have some problems that can be mainly attributed to the unrealistic and the oversimplified treatment of the flare emission. To properly address this problem, we use a Non-linear Force Free Field (NLFFF) model extrapolated from an observed photospheric magnetogram as input to the threedimensional, multi-wavelength modeling platform GX Simulator, and create a unified electron population model that can simultaneously reproduce the observed HXR and MW observations. We model the end of the impulsive phase of the 2015-06-22 M6.5 flare, and constrain the modeled electron spatial and energy parameters using observations made by the highest-resolving instruments currently available in two wavelengths, the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) for HXR and the Expanded Owens Valley Solar Array (EOVSA) for MW. Our results suggest that the HXR-emitting electron population model fits the standard flare model with a broken power-law spectrum that simultaneously produces the HXR footpoint emission and the MW high frequency emission. The model also includes an "HXR invisible" population of nonthermal electrons that are trapped in a large volume of magnetic field above the HXR-emitting loops, which is observable by its gyrosynchrotron (GS) radiation emitting mainly in MW low frequency range. Title: Anticipated Results from the FOXSI SMEX Mission Authors: Shih, A. Y.; Christe, S.; Krucker, S.; Glesener, L.; Saint-Hilaire, P.; Caspi, A.; Allred, J. C.; Battaglia, M.; Chen, B.; Drake, J. F.; Gary, D. E.; Gburek, S.; Goetz, K.; Grefenstette, B.; Gubarev, M.; Hannah, I. G.; Holman, G.; Hudson, H. S.; Inglis, A. R.; Ireland, J.; Ishikawa, S. N.; Klimchuk, J. A.; Kontar, E.; Kowalski, A. F.; Massone, A. M.; Piana, M.; Ramsey, B.; Ryan, D.; Schwartz, R.; Steslicki, M.; Turin, P.; Veronig, A.; Vilmer, N.; Warmuth, A.; White, S. M.; Woods, T. N. Bibcode: 2017AGUFMSH43C..03S Altcode: While there have been significant advances in our understanding of impulsive energy release at the Sun since the advent of RHESSI observations, there is a clear need for new X-ray observations that can capture the full range of emission in flares (e.g., faint coronal sources near bright chromospheric sources), follow the intricate evolution of energy release and changes in morphology, and search for the signatures of impulsive energy release in even the quiescent Sun. The FOXSI Small Explorer (SMEX) mission, currently undergoing a Phase A concept study, combines state-of-the-art grazing-incidence focusing optics with pixelated solid-state detectors to provide direct imaging of hard X-rays for the first time on a solar observatory. FOXSI's X-ray observations will provide quantitative information on (1) the non-thermal populations of accelerated electrons and (2) the thermal plasma distributions at the high temperatures inaccessible through other wavelengths. FOXSI's major science questions include: Where are electrons accelerated and on what time scales? Where do escaping flare-accelerated electrons originate? What is the energy input of accelerated electrons into the chromosphere and corona? How much do flare-like processes heat the corona above active regions? Here we present examples with simulated observations to show how FOXSI's capabilities will address and resolve these and other questions. Title: Solar Flare Dynamic Microwave Imaging with EOVSA Authors: Gary, D. E.; Chen, B.; Nita, G. M.; Fleishman, G. D.; Yu, S.; White, S. M.; Hurford, G. J.; McTiernan, J. M. Bibcode: 2017AGUFMSH41A2755G Altcode: The Expanded Owens Valley Solar Array (EOVSA) is both an expansion of our existing solar array and serves as a prototype for a much larger future project, the Frequency Agile Solar Radiotelescope (FASR). EOVSA is now complete, and is producing daily imaging of the full solar disk, including active regions and solar radio bursts at hundreds of frequencies in the range 2.8-18 GHz. We present highlights of the 1-s-cadence dynamic imaging spectroscropy of radio bursts we have obtained to date, along with deeper analysis of multi-wavelength observations and modeling of a well-observed burst. These observations are revealing the full life-cycle of the trapped population of high-energy electrons, from their initial acceleration and subsequent energy-evolution to their eventual decay through escape and thermalization. All of our data are being made available for download in both quick-look image form and in the form of the community-standard CASA measurement sets for subsequent imaging and analysis. Title: Dynamic Spectral Imaging of Decimetric Fiber Bursts in an Eruptive Solar Flare Authors: Wang, Zhitao; Chen, Bin; Gary, Dale E. Bibcode: 2017ApJ...848...77W Altcode: 2017arXiv170908137W Fiber bursts are a type of fine structure that is often superposed on type IV radio continuum emission during solar flares. Although studied for many decades, its physical exciter, emission mechanism, and association with the flare energy release remain unclear, partly due to the lack of simultaneous imaging observations. We report the first dynamic spectroscopic imaging observations of decimetric fiber bursts, which occurred during the rise phase of a long-duration eruptive flare on 2012 March 3, as obtained by the Karl G. Jansky Very Large Array in 1-2 GHz. Our results show that the fiber sources are located near and above one footpoint of the flare loops. The fiber source and the background continuum source are found to be co-spatial and share the same morphology. It is likely that they are associated with nonthermal electrons trapped in the converging magnetic fields near the footpoint, as supported by a persistent coronal hard X-ray source present during the flare rise phase. We analyze three groups of fiber bursts in detail with dynamic imaging spectroscopy and obtain their mean frequency-dependent centroid trajectories in projection. By using a barometric density model and magnetic field based on a potential field extrapolation, we further reconstruct the 3D source trajectories of fiber bursts, for comparison with expectations from the whistler wave model and two MHD-based models. We conclude that the observed fiber burst properties are consistent with an exciter moving at the propagation velocity expected for whistler waves, or models that posit similar exciter velocities. Title: Imaging Spectroscopy of CME-Associated Solar Radio Bursts using OVRO-LWA Authors: Chhabra, Sherry; Gary, Dale; Chen, Bin; Hallinan, Gregg; Anderson, Marin Bibcode: 2017SPD....4820605C Altcode: Energetic phenomenon on the Sun, such as solar flares and CMEs are a dynamic laboratory to study radio emission. We use Owens Valley Long Wavelength Array (OVRO-LWA) for the study. The new array with its 251 crossed broadband dipoles spread over a 200 m diameter core and 37 long baseline antennas extending to 1600 m baselines allows spatially resolving the Sun in the frequency range 24-82 MHz, with high spectral resolution.We examine coherent Type III and Type IV burst emission associated with a CME from 2015 Sep 20, as well as quiet Sun images before and after the bursts. Images of 9 s cadence are used to study the event over a 100 minute period, out to a distance of about 2 solar radii, over the frequency range of 40-70 MHz available at that time. In order to understand better the behaviour and structural evolution of the bursts, we image the event at hundreds of frequencies and use the source centroids to obtain the velocity of outward motion. A coalignment with LASCO(C2) and SWAP data allows spatial and temporal comparison with observations of the CME in white light and EUV. We also place the bursts in context of AIA-EUV, Fermi hard X-ray and EOVSA Microwave emission associated with the event. Title: Science with the Expanded Owens Valley Solar Array Authors: Nita, Gelu M.; Gary, Dale E.; Fleishman, Gregory D.; Chen, Bin; White, Stephen M.; Hurford, Gordon J.; McTiernan, James; Hickish, Jack; Yu, Sijie; Nelin, Kjell B. Bibcode: 2017SPD....4811009N Altcode: The Expanded Owens Valley Solar Array (EOVSA) is a solar-dedicated radio array that makes images and spectra of the full Sun on a daily basis. Our main science goals are to understand the basic physics of solar activity, such as how the Sun releases stored magnetic energy on timescales of seconds, and how that solar activity, in the form of solar flares and coronal mass ejections, influences the Earth and near-Earth space environment, through disruptions of communication and navigation systems, and effects on satellites and systems on the ground. The array, which is composed out of thirteen 2.1 m dishes and two 27 m dishes (used only for calibration), has a footprint of 1.1 km EW x 1.2 km NS and it is capable of producing, every second, microwave images at two polarizations and 500 science channels spanning the 1-18 GHz frequency range. Such ability to make multi-frequency images of the Sun in this broad range of frequencies, with a frequency dependent resolution ranging from ∼53” at 1 GHz to ∼3”at 18 GHz, is unique in the world. Here we present an overview of the EOVSA instrument and a first set of science-quality active region and solar flare images produced from data taken during April 2017.This research is supported by NSF grant AST-1615807 and NASA grant NNX14AK66G to New Jersey Institute of Technology. Title: Magnetic vector rotation in response to the energetic electron beam during a flare Authors: Xu, Yan; Cao, Wenda; Kwangsu, Ahn; Jing, Ju; Liu, Chang; Chae, Jongchul; Huang, Nengyi; Deng, Na; Gary, Dale E.; Wang, Haimin Bibcode: 2017SPD....4810001X Altcode: As one of the most violent forms of eruption on the Sun, flares are believed to be powered by magnetic reconnection, by which stored magnetic energy is released. The fundamental physical processes involving the release, transfer and deposition of energy in multiple layers of the solar atmosphere have been studied extensively with significant progress. Taking advantage of recent developments in observing facilities, new phenomena are continually revealed, bringing new understanding of solar flares. Here we report the discovery of a transient rotation of vector magnetic fields associated with a flare observed by the 1.6-m New Solar Telescope at Big Bear Solar Observatory. After ruling out the possibility that the rotation is caused by line profile changes due to flare heating, our observation shows that the transverse field rotateded by about 12-20 degrees counterclockwise, and returned quickly to previous values after the flare ribbons swept through. More importantly, as a consequence of the rotation, the flare loops untwisted and became more potential. The vector magnetograms were obtained in the near infrared at 1560 nm, which is minimally affected by flare emission and no intensity profile change was detected. Therefore, we believe that these transient changes are real, and conclude the high energy electron beams play an crucial role in the field changes. A straightforward and instructive explanation is that the induced magnetic field of the electron beam superimposed on the pre-flare field leads to a transient rotation of the overall field. Title: A Large-scale Plume in an X-class Solar Flare Authors: Fleishman, Gregory D.; Nita, Gelu M.; Gary, Dale E. Bibcode: 2017ApJ...845..135F Altcode: 2017arXiv170706636F Ever-increasing multi-frequency imaging of solar observations suggests that solar flares often involve more than one magnetic fluxtube. Some of the fluxtubes are closed, while others can contain open fields. The relative proportion of nonthermal electrons among those distinct loops is highly important for understanding energy release, particle acceleration, and transport. The access of nonthermal electrons to the open field is also important because the open field facilitates the solar energetic particle (SEP) escape from the flaring site, and thus controls the SEP fluxes in the solar system, both directly and as seed particles for further acceleration. The large-scale fluxtubes are often filled with a tenuous plasma, which is difficult to detect in either EUV or X-ray wavelengths; however, they can dominate at low radio frequencies, where a modest component of nonthermal electrons can render the source optically thick and, thus, bright enough to be observed. Here we report the detection of a large-scale “plume” at the impulsive phase of an X-class solar flare, SOL2001-08-25T16:23, using multi-frequency radio data from Owens Valley Solar Array. To quantify the flare’s spatial structure, we employ 3D modeling utilizing force-free-field extrapolations from the line of sight SOHO/MDI magnetograms with our modeling tool GX_Simulator. We found that a significant fraction of the nonthermal electrons that accelerated at the flare site low in the corona escapes to the plume, which contains both closed and open fields. We propose that the proportion between the closed and open fields at the plume is what determines the SEP population escaping into interplanetary space. Title: The analysis and the three-dimensional, forward-fit modeling of the X-ray and the microwave emissions of major solar flares Authors: Kuroda, Natsuha; Wang, Haimin; Gary, Dale E. Bibcode: 2017SPD....4840003K Altcode: It is well known that the time profiles of the hard X-ray (HXR) emission and the microwave (MW) emission during the impulsive phase of the solar flare are well correlated, and that their analysis can lead to the understandings of the flare-accelerated electrons. In this work, we first studied the source locations of seven distinct temporal peaks observed in HXR and MW lightcurves of the 2011-02-15 X2.2 flare using the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and Nobeyama Radioheliograph. We found that the seven emission peaks did not come from seven spatially distinct sites in HXR and MW, but rather in HXR we observed a sudden change in location only between the second and the third peak, with the same pattern occurring, but evolving more slowly in MW, which is consistent with the tether-cutting model of solar flares. Next, we closely examine the widely-used notion of a "common population" of the accelerated electrons producing the HXR and the MW, which has been challenged by some studies suggesting the differences in the inferred energy spectral index and emitting energies of the HXR- and MW- producing electrons. We use the Non-linear Force Free Field model extrapolated from the observed photospheric magnetogram in the three-dimensional, multi-wavelength modeling platform GX Simulator, and attempt to create a unified electron population model that can simultaneously reproduce the observed X-ray and MW observations of the 2015-06-22 M6.5 flare. We constrain the model parameters by the observations made by the highest-resolving instruments currently available in two wavelengths, the RHESSI for X-ray and the Expanded Owens Valley Solar Array for MW. The results suggest that the X-ray emitting electron population model fits to the standard flare model with the broken, hardening power-law spectrum at ~300 keV that simultaneously produces the HXR footpoint emission and the MW high frequency emission, and also reveals that there could be a “X-ray invisible” population of nonthermal electrons that are trapped in a large magnetic field volume above the X-ray emitting loops, that emits gyrosynchrotron radiation mainly in MW low frequency range. Title: Observing the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA): High-Resolution Interferometric Imaging Authors: Shimojo, M.; Bastian, T. S.; Hales, A. S.; White, S. M.; Iwai, K.; Hills, R. E.; Hirota, A.; Phillips, N. M.; Sawada, T.; Yagoubov, P.; Siringo, G.; Asayama, S.; Sugimoto, M.; Brajša, R.; Skokić, I.; Bárta, M.; Kim, S.; de Gregorio-Monsalvo, I.; Corder, S. A.; Hudson, H. S.; Wedemeyer, S.; Gary, D. E.; De Pontieu, B.; Loukitcheva, M.; Fleishman, G. D.; Chen, B.; Kobelski, A.; Yan, Y. Bibcode: 2017SoPh..292...87S Altcode: 2017arXiv170403236S Observations of the Sun at millimeter and submillimeter wavelengths offer a unique probe into the structure, dynamics, and heating of the chromosphere; the structure of sunspots; the formation and eruption of prominences and filaments; and energetic phenomena such as jets and flares. High-resolution observations of the Sun at millimeter and submillimeter wavelengths are challenging due to the intense, extended, low-contrast, and dynamic nature of emission from the quiet Sun, and the extremely intense and variable nature of emissions associated with energetic phenomena. The Atacama Large Millimeter/submillimeter Array (ALMA) was designed with solar observations in mind. The requirements for solar observations are significantly different from observations of sidereal sources and special measures are necessary to successfully carry out this type of observations. We describe the commissioning efforts that enable the use of two frequency bands, the 3-mm band (Band 3) and the 1.25-mm band (Band 6), for continuum interferometric-imaging observations of the Sun with ALMA. Examples of high-resolution synthesized images obtained using the newly commissioned modes during the solar-commissioning campaign held in December 2015 are presented. Although only 30 of the eventual 66 ALMA antennas were used for the campaign, the solar images synthesized from the ALMA commissioning data reveal new features of the solar atmosphere that demonstrate the potential power of ALMA solar observations. The ongoing expansion of ALMA and solar-commissioning efforts will continue to enable new and unique solar observing capabilities. Title: Observing the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA): Fast-Scan Single-Dish Mapping Authors: White, S. M.; Iwai, K.; Phillips, N. M.; Hills, R. E.; Hirota, A.; Yagoubov, P.; Siringo, G.; Shimojo, M.; Bastian, T. S.; Hales, A. S.; Sawada, T.; Asayama, S.; Sugimoto, M.; Marson, R. G.; Kawasaki, W.; Muller, E.; Nakazato, T.; Sugimoto, K.; Brajša, R.; Skokić, I.; Bárta, M.; Kim, S.; Remijan, A. J.; de Gregorio, I.; Corder, S. A.; Hudson, H. S.; Loukitcheva, M.; Chen, B.; De Pontieu, B.; Fleishmann, G. D.; Gary, D. E.; Kobelski, A.; Wedemeyer, S.; Yan, Y. Bibcode: 2017SoPh..292...88W Altcode: 2017arXiv170504766W The Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope has commenced science observations of the Sun starting in late 2016. Since the Sun is much larger than the field of view of individual ALMA dishes, the ALMA interferometer is unable to measure the background level of solar emission when observing the solar disk. The absolute temperature scale is a critical measurement for much of ALMA solar science, including the understanding of energy transfer through the solar atmosphere, the properties of prominences, and the study of shock heating in the chromosphere. In order to provide an absolute temperature scale, ALMA solar observing will take advantage of the remarkable fast-scanning capabilities of the ALMA 12 m dishes to make single-dish maps of the full Sun. This article reports on the results of an extensive commissioning effort to optimize the mapping procedure, and it describes the nature of the resulting data. Amplitude calibration is discussed in detail: a path that uses the two loads in the ALMA calibration system as well as sky measurements is described and applied to commissioning data. Inspection of a large number of single-dish datasets shows significant variation in the resulting temperatures, and based on the temperature distributions, we derive quiet-Sun values at disk center of 7300 K at λ =3 mm and 5900 K at λ =1.3 mm. These values have statistical uncertainties of about 100 K, but systematic uncertainties in the temperature scale that may be significantly larger. Example images are presented from two periods with very different levels of solar activity. At a resolution of about 25″, the 1.3 mm wavelength images show temperatures on the disk that vary over about a 2000 K range. Active regions and plages are among the hotter features, while a large sunspot umbra shows up as a depression, and filament channels are relatively cool. Prominences above the solar limb are a common feature of the single-dish images. Title: The 2012 November 20 impulsive SEP event: likely sources and their properties Authors: Ireland, Jack; de Nolfo, Georgia; Fleishman, Gregory; Ryan, James; Gary, Dale Bibcode: 2017shin.confE..84I Altcode: Helium-3 (3He) enriched impulsive events are one of the most common phenomena associated with eruptive events on the Sun. In most cases, impulsive ions are associated with increases in electron intensity, though not always. We examine an unusual event in which 3He ions were abundant but there was no detectable accompanying electron signature. We derive injections times from 3He ions observed with ACE/ULEIS and LEMPT/WIND that are consistent with jets emanating from either of two active regions on the Sun. Both active regions exhibit jetting features but only one has type III radio emission associated with it. We evaluate the potential for ion and electron acceleration and escape} within these two regions using the Nonlinear Force-Free Field (NLFFF) extrapolation of the underlying magnetic field and discuss scenarios of ion acceleration with suppressed electron acceleration. Title: Investigating the Origins of Two Extreme Solar Particle Events: Proton Source Profile and Associated Electromagnetic Emissions Authors: Kocharov, Leon; Pohjolainen, Silja; Mishev, Alexander; Reiner, Mike J.; Lee, Jeongwoo; Laitinen, Timo; Didkovsky, Leonid V.; Pizzo, Victor J.; Kim, Roksoon; Klassen, Andreas; Karlicky, Marian; Cho, Kyung-Suk; Gary, Dale E.; Usoskin, Ilya; Valtonen, Eino; Vainio, Rami Bibcode: 2017ApJ...839...79K Altcode: We analyze the high-energy particle emission from the Sun in two extreme solar particle events in which protons are accelerated to relativistic energies and can cause a significant signal even in the ground-based particle detectors. Analysis of a relativistic proton event is based on modeling of the particle transport and interaction, from a near-Sun source through the solar wind and the Earth’s magnetosphere and atmosphere to a detector on the ground. This allows us to deduce the time profile of the proton source at the Sun and compare it with observed electromagnetic emissions. The 1998 May 2 event is associated with a flare and a coronal mass ejection (CME), which were well observed by the Nançay Radioheliograph, thus the images of the radio sources are available. For the 2003 November 2 event, the low corona images of the CME liftoff obtained at the Mauna Loa Solar Observatory are available. Those complementary data sets are analyzed jointly with the broadband dynamic radio spectra, EUV images, and other data available for both events. We find a common scenario for both eruptions, including the flare’s dual impulsive phase, the CME-launch-associated decimetric-continuum burst, and the late, low-frequency type III radio bursts at the time of the relativistic proton injection into the interplanetary medium. The analysis supports the idea that the two considered events start with emission of relativistic protons previously accelerated during the flare and CME launch, then trapped in large-scale magnetic loops and later released by the expanding CME. Title: High-resolution observations of flare precursors in the low solar atmosphere Authors: Wang, Haimin; Liu, Chang; Ahn, Kwangsu; Xu, Yan; Jing, Ju; Deng, Na; Huang, Nengyi; Liu, Rui; Kusano, Kanya; Fleishman, Gregory D.; Gary, Dale E.; Cao, Wenda Bibcode: 2017NatAs...1E..85W Altcode: 2017arXiv170309866W Solar flares are generally believed to be powered by free magnetic energy stored in the corona1, but the build up of coronal energy alone may be insufficient to trigger the flare to occur2. The flare onset mechanism is a critical but poorly understood problem, insights into which could be gained from small-scale energy releases known as precursors. These precursors are observed as small pre-flare brightenings in various wavelengths3-13 and also from certain small-scale magnetic configurations such as opposite-polarity fluxes14-16, where the magnetic orientation of small bipoles is opposite to that of the ambient main polarities. However, high-resolution observations of flare precursors together with the associated photospheric magnetic field dynamics are lacking. Here we study precursors of a flare using the unprecedented spatiotemporal resolution of the 1.6-m New Solar Telescope, complemented by new microwave data. Two episodes of precursor brightenings are initiated at a small-scale magnetic channel17-20 (a form of opposite-polarity flux) with multiple polarity inversions and enhanced magnetic fluxes and currents, lying near the footpoints of sheared magnetic loops. Microwave spectra corroborate that these precursor emissions originate in the atmosphere. These results provide evidence of low-atmospheric small-scale energy release, possibly linked to the onset of the main flare. Title: HeRO: A space-based low frequency interferometric observatory for heliophysics enabled by novel vector sensor technology Authors: Knapp, M.; Gary, D. E.; Hecht, M. H.; Lonsdale, C.; Lind, F. D.; Robey, F. C.; Fuhrman, L.; Chen, B.; Fenn, A. J.; HeRO Team Bibcode: 2017pre8.conf..411K Altcode: HeRO (Heliophysics Radio Observer) is a hybrid ground and space mission concept for radio interferometry of solar radio bursts. The space segment (HeRO-S) covers low frequencies, 100 kHz-20 MHz, and is composed of 6 free-flying CubeSats equipped with vector sensors. The ground segment (HeRO-G), covers higher frequencies, 15 MHz-300 MHz. HeRO will explore conditions and disturbances in a key region of the heliosphere, from two to tens of solar radii, using interferometric observations of solar radio bursts over three decades in frequency. Spot mapping across the full frequency range will provide precise positions and basic structural information about type II and III radio bursts. The morphology of CME shock fronts will be traced via type II burst emissions, and heliospheric magnetic field geometries will be probed by measuring precise trajectories of type III bursts. Refraction in the heliospheric plasma on large and intermediate scales will be investigated throughout large volumes via the frequency dependence of accurate interferometric positional data on bursts. The HeRO data will be information rich with high resolution in time, frequency and spatial position, and high SNR, creating fertile ground for discovery of new phenomena. Title: Exploring impulsive solar magnetic energy release and particle acceleration with focused hard X-ray imaging spectroscopy Authors: Christe, Steven; Krucker, Samuel; Glesener, Lindsay; Shih, Albert; Saint-Hilaire, Pascal; Caspi, Amir; Allred, Joel; Battaglia, Marina; Chen, Bin; Drake, James; Dennis, Brian; Gary, Dale; Gburek, Szymon; Goetz, Keith; Grefenstette, Brian; Gubarev, Mikhail; Hannah, Iain; Holman, Gordon; Hudson, Hugh; Inglis, Andrew; Ireland, Jack; Ishikawa, Shinosuke; Klimchuk, James; Kontar, Eduard; Kowalski, Adam; Longcope, Dana; Massone, Anna-Maria; Musset, Sophie; Piana, Michele; Ramsey, Brian; Ryan, Daniel; Schwartz, Richard; Stęślicki, Marek; Turin, Paul; Warmuth, Alexander; Wilson-Hodge, Colleen; White, Stephen; Veronig, Astrid; Vilmer, Nicole; Woods, Tom Bibcode: 2017arXiv170100792C Altcode: How impulsive magnetic energy release leads to solar eruptions and how those eruptions are energized and evolve are vital unsolved problems in Heliophysics. The standard model for solar eruptions summarizes our current understanding of these events. Magnetic energy in the corona is released through drastic restructuring of the magnetic field via reconnection. Electrons and ions are then accelerated by poorly understood processes. Theories include contracting loops, merging magnetic islands, stochastic acceleration, and turbulence at shocks, among others. Although this basic model is well established, the fundamental physics is poorly understood. HXR observations using grazing-incidence focusing optics can now probe all of the key regions of the standard model. These include two above-the-looptop (ALT) sources which bookend the reconnection region and are likely the sites of particle acceleration and direct heating. The science achievable by a direct HXR imaging instrument can be summarized by the following science questions and objectives which are some of the most outstanding issues in solar physics (1) How are particles accelerated at the Sun? (1a) Where are electrons accelerated and on what time scales? (1b) What fraction of electrons is accelerated out of the ambient medium? (2) How does magnetic energy release on the Sun lead to flares and eruptions? A Focusing Optics X-ray Solar Imager (FOXSI) instrument, which can be built now using proven technology and at modest cost, would enable revolutionary advancements in our understanding of impulsive magnetic energy release and particle acceleration, a process which is known to occur at the Sun but also throughout the Universe. Title: Absorption by Mercury's Exosphere During the May 9th, 2016 Solar Transit. Authors: Schmidt, C.; Reardon, K.; Killen, R. M.; Gary, D. E.; Ahn, K.; Leblanc, F.; Baumgardner, J. L.; Mendillo, M.; Beck, C.; Mangano, V. Bibcode: 2016AGUFM.P53B2198S Altcode: Observations of Mercury during a solar transit have the unique property that line absorption may be used to retrieve the exosphere's column density at all points above the terminator simultaneously. We report on measurements during the 9 May 2016 transit with the Dunn Solar Telescope (Interferometric BIdimensional Spectropolarimeter: IBIS & Horizontal Spectrograph: HSG) and the Big Bear Solar Observatory (Fast Imaging Solar Spectrograph: FISS). The sodium exosphere was observed via Fabry-Perot imaging with IBIS in 9 mA increments, and with FISS at a dispersion of 17 mA/pixel by scanning the spectrograph slit over the planet's disk. A search for potassium D line absorption was performed using slit spectroscopy with HSG at a resolution of R 270,000. In each instrument, exposures of 20-40 ms and adaptive optics enable spatial structure to be resolved on sub-arcsecond scales. The line profiles at every spatial bin are divided by a shifted and scaled reference spectrum in order to isolate the exosphere's absorption from line absorption in the solar atmosphere and structures inherent to granulation. Analysis of these data sets is ongoing, but preliminary findings clearly show the densest column of sodium near the poles and the content at dawn enhanced several times with respect to dusk. Such is consistent with 2003 transit results taken at the same Mercury season (Schleicher et al., 2004), however the data volumes herein permit a more in-depth study in which time-dependence of the exosphere may be considered. Title: Focusing Solar Hard X-rays: Expected Results from a FOXSI Spacecraft Authors: Glesener, L.; Christe, S.; Shih, A. Y.; Dennis, B. R.; Krucker, S.; Saint-Hilaire, P.; Hudson, H. S.; Ryan, D.; Inglis, A. R.; Hannah, I. G.; Caspi, A.; Klimchuk, J. A.; Drake, J. F.; Kontar, E.; Holman, G.; White, S. M.; Alaoui, M.; Battaglia, M.; Vilmer, N.; Allred, J. C.; Longcope, D. W.; Gary, D. E.; Jeffrey, N. L. S.; Musset, S.; Swisdak, M. Bibcode: 2016AGUFMSH13A2282G Altcode: Over the course of two solar cycles, RHESSI has examined high-energy processes in flares via high-resolution spectroscopy and imaging of soft and hard X-rays (HXRs). The detected X-rays are the thermal and nonthermal bremsstrahlung from heated coronal plasma and from accelerated electrons, respectively, making them uniquely suited to explore the highest-energy processes that occur in the corona. RHESSI produces images using an indirect, Fourier-based method and has made giant strides in our understanding of these processes, but it has also uncovered intriguing new mysteries regarding energy release location, acceleration mechanisms, and energy propagation in flares. Focusing optics are now available for the HXR regime and stand poised to perform another revolution in the field of high-energy solar physics. With two successful sounding rocket flights completed, the Focusing Optics X-ray Solar Imager (FOXSI) program has demonstrated the feasibility and power of direct solar HXR imaging with its vastly superior sensitivity and dynamic range. Placing this mature technology aboard a spacecraft will offer a systematic way to explore high-energy aspects of the solar corona and to address scientific questions left unanswered by RHESSI. Here we present examples of such questions and show simulations of expected results from a FOXSI spaceborne instrument to demonstrate how these questions can be addressed with the focusing of hard X-rays. Title: EOVSA Implementation of a Spectral Kurtosis Correlator for Transient Detection and Classification Authors: Nita, Gelu M.; Hickish, Jack; MacMahon, David; Gary, Dale E. Bibcode: 2016JAI.....541009N Altcode: 2017arXiv170205391N We describe in general terms the practical use in astronomy of a higher-order statistical quantity called spectral kurtosis (SK), and describe the first implementation of SK-enabled firmware in the Fourier transform-engine (F-engine) of a digital FX correlator for the Expanded Owens Valley Solar Array (EOVSA). The development of the theory for SK is summarized, leading to an expression for generalized SK that is applicable to both SK spectrometers and those not specifically designed for SK. We also give the means for computing both the SK̂ estimator and thresholds for its application as a discriminator of RFI contamination. Tests of the performance of EOVSA as an SK spectrometer are shown to agree precisely with theoretical expectations, and the methods for configuring the correlator for correct SK operation are described. Title: The Focusing Optics X-ray Solar Imager (FOXSI) SMEX Mission Authors: Christe, S.; Shih, A. Y.; Krucker, S.; Glesener, L.; Saint-Hilaire, P.; Caspi, A.; Allred, J. C.; Battaglia, M.; Chen, B.; Drake, J. F.; Gary, D. E.; Goetz, K.; Grefenstette, B.; Hannah, I. G.; Holman, G.; Hudson, H. S.; Inglis, A. R.; Ireland, J.; Ishikawa, S. N.; Klimchuk, J. A.; Kontar, E.; Kowalski, A. F.; Massone, A. M.; Piana, M.; Ramsey, B.; Gubarev, M.; Schwartz, R. A.; Steslicki, M.; Ryan, D.; Turin, P.; Warmuth, A.; White, S. M.; Veronig, A.; Vilmer, N.; Dennis, B. R. Bibcode: 2016AGUFMSH13A2281C Altcode: We present FOXSI (Focusing Optics X-ray Solar Imager), a recently proposed Small Explorer (SMEX) mission that will provide a revolutionary new perspective on energy release and particle acceleration on the Sun. FOXSI is a direct imaging X-ray spectrometer with higher dynamic range and better than 10x the sensitivity of previous instruments. Flown on a 3-axis stabilized spacecraft in low-Earth orbit, FOXSI uses high-angular-resolution grazing-incidence focusing optics combined with state-of-the-art pixelated solid-state detectors to provide direct imaging of solar hard X-rays for the first time. FOXSI is composed of two individual x-ray telescopes with a 14-meter focal length enabled by a deployable boom. Making use of a filter-wheel and high-rate-capable solid-state detectors, FOXSI will be able to observe the largest flares without saturation while still maintaining the sensitivity to detect x-ray emission from weak flares, escaping electrons, and hot active regions. This SMEX mission is made possible by past experience with similar instruments on two sounding rocket flights, in 2012 and 2014, and on the HEROES balloon flight in 2013. FOXSI will image the Sun with a field of view of 9 arcminutes and an angular resolution of better than 8 arcsec; it will cover the energy range from 3 to 100 keV with a spectral resolution of better than 1 keV; and it will have sub-second temporal resolution. Title: Imaging Spectroscopy of CME-Associated Solar Radio Bursts With OVRO-LWA Authors: Chhabra, S.; Gary, D. E.; Chen, B.; Hallinan, G.; Anderson, M. Bibcode: 2016AGUFMSH33A..05C Altcode: Energetic phenomenon on the Sun, such as solar flares and CMEs are a dynamic laboratory to study radio emission. We use Owens Valley Long Wavelength Array (OVRO-LWA) for the study. The new array with its 251 crossed broadband dipoles spread over a 200 m diameter core and 37 long baseline antennas extending to 1600 m baselines allows spatially resolving the Sun in the frequency range 24-82 MHz, with high spectral resolution. We examine coherent Type III and Type IV burst emission associated with a CME from 2015 Sep 20, as well as quiet Sun images before and after the bursts. Images of 9 s cadence are used to study the event over a 100 minute period, out to a distance of about 2 solar radii, over the frequency range of 40-70 MHz available at that time. In order to understand better the behaviour and structural evolution of the bursts, we image the event at hundreds of frequencies and use the source centroids to obtain the velocity of outward motion. A co-alignment with LASCO (C2) and SWAP data allows spatial and temporal comparison with observations of the CME in white light and EUV. We also place the bursts in context of AIA EUV, Fermi hard X-ray, and EOVSA microwave emission associated with the event. Title: The 2016 Transit of Mercury Observed from Major Solar Telescopes and Satellites Authors: Pasachoff, Jay M.; Schneider, Glenn; Gary, Dale; Chen, Bin; Sterling, Alphonse C.; Reardon, Kevin P.; Dantowitz, Ronald; Kopp, Greg A. Bibcode: 2016DPS....4811705P Altcode: We report observations from the ground and space of the 9 May 2016 transit of Mercury. We build on our explanation of the black-drop effect in transits of Venus based on spacecraft observations of the 1999 transit of Mercury (Schneider, Pasachoff, and Golub, Icarus 168, 249, 2004). In 2016, we used the 1.6-m New Solar Telescope at the Big Bear Solar Observatory with active optics to observe Mercury's transit at high spatial resolution. We again saw a small black-drop effect as 3rd contact neared, confirming the data that led to our earlier explanation as a confluence of the point-spread function and the extreme solar limb darkening (Pasachoff, Schneider, and Golub, in IAU Colloq. 196, 2004). We again used IBIS on the Dunn Solar Telescope of the Sacramento Peak Observatory, as A. Potter continued his observations, previously made at the 2006 transit of Mercury, at both telescopes of the sodium exosphere of Mercury (Potter, Killen, Reardon, and Bida, Icarus 226, 172, 2013). We imaged the transit with IBIS as well as with two RED Epic IMAX-quality cameras alongside it, one with a narrow passband. We show animations of our high-resolution ground-based observations along with observations from XRT on JAXA's Hinode and from NASA's Solar Dynamics Observatory. Further, we report on the limit of the transit change in the Total Solar Irradiance, continuing our interest from the transit of Venus TSI (Schneider, Pasachoff, and Willson, ApJ 641, 565, 2006; Pasachoff, Schneider, and Willson, AAS 2005), using NASA's SORCE/TIM and the Air Force's TCTE/TIM. See http://transitofvenus.info and http://nicmosis.as.arizona.edu.Acknowledgments: We were glad for the collaboration at Big Bear of Claude Plymate and his colleagues of the staff of the Big Bear Solar Observatory. We also appreciate the collaboration on the transit studies of Robert Lucas (Sydney, Australia) and Evan Zucker (San Diego, California). JMP appreciates the sabbatical hospitality of the Division of Geosciences and Planetary Sciences of the California Institute of Technology, and of Prof. Andrew Ingersoll there. The solar observations lead into the 2017 eclipse studies, for which JMP is supported by grants from the NSF AGS and National Geographic CRE. Title: Flare differentially rotates sunspot on Sun's surface Authors: Liu, Chang; Xu, Yan; Cao, Wenda; Deng, Na; Lee, Jeongwoo; Hudson, Hugh S.; Gary, Dale E.; Wang, Jiasheng; Jing, Ju; Wang, Haimin Bibcode: 2016NatCo...713104L Altcode: 2016arXiv161002969L Sunspots are concentrations of magnetic field visible on the solar surface (photosphere). It was considered implausible that solar flares, as resulted from magnetic reconnection in the tenuous corona, would cause a direct perturbation of the dense photosphere involving bulk motion. Here we report the sudden flare-induced rotation of a sunspot using the unprecedented spatiotemporal resolution of the 1.6 m New Solar Telescope, supplemented by magnetic data from the Solar Dynamics Observatory. It is clearly observed that the rotation is non-uniform over the sunspot: as the flare ribbon sweeps across, its different portions accelerate (up to ~50° h-1) at different times corresponding to peaks of flare hard X-ray emission. The rotation may be driven by the surface Lorentz-force change due to the back reaction of coronal magnetic restructuring and is accompanied by a downward Poynting flux. These results have direct consequences for our understanding of energy and momentum transportation in the flare-related phenomena. Title: Measurement of duration and signal-to-noise ratio of astronomical transients using a Spectral Kurtosis spectrometer Authors: Nita, Gelu M.; Gary, Dale E. Bibcode: 2016JGRA..121.7353N Altcode: Following our prior theoretical and instrumental work addressing the problem of automatic real-time radio frequency interference (RFI) detection and excision from astronomical signals, the wideband Spectral Kurtosis (SK) spectrometer design we proposed is currently being considered as an alternative to the traditional spectrometers when building the new generation of radio instruments. The unique characteristic of an SK spectrometer is that it accumulates both power and power-squared, which are then used to compute an SK statistical estimator proven to be very effective in detecting and excising certain types of RFI signals. In this paper we introduce a novel measurement technique that exploits the power and power square statistics of an SK spectrometer to determine durations and signal-to-noise ratios of transient signals, whether they are RFI or natural signals, even when they are below the time resolution of the instrument. We demonstrate this novel experimental technique by analyzing a segment of data recorded by the Expanded Owens Valley Solar Array Subsystem Testbed (EST) during a solar radio burst in which microwave spike bursts occurred with durations shorter than the 20 ms time resolution of the instrument. The duration of one well-observed spike is quantitatively shown to be within a few percent of 8 ms despite the 20 ms resolution of the data. Title: Narrowband Gyrosynchrotron Bursts: Probing Electron Acceleration in Solar Flares Authors: Fleishman, Gregory D.; Nita, Gelu M.; Kontar, Eduard P.; Gary, Dale E. Bibcode: 2016ApJ...826...38F Altcode: 2016arXiv160500948F Recently, in a few case studies we demonstrated that gyrosynchrotron microwave emission can be detected directly from the acceleration region when the trapped electron component is insignificant. For the statistical study reported here, we have identified events with steep (narrowband) microwave spectra that do not show a significant trapped component and, at the same time, show evidence of source uniformity, which simplifies the data analysis greatly. Initially, we identified a subset of more than 20 radio bursts with such narrow spectra, having low- and high-frequency spectral indices larger than three in absolute value. A steep low-frequency spectrum implies that the emission is nonthermal (for optically thick thermal emission, the spectral index cannot be steeper than two), and the source is reasonably dense and uniform. A steep high-frequency spectrum implies that no significant electron trapping occurs, otherwise a progressive spectral flattening would be observed. Roughly half of these radio bursts have RHESSI data, which allow for detailed, joint diagnostics of the source parameters and evolution. Based on an analysis of radio-to-X-ray spatial relationships, timing, and spectral fits, we conclude that the microwave emission in these narrowband bursts originates directly from the acceleration regions, which have a relatively strong magnetic field, high density, and low temperature. In contrast, the thermal X-ray emission comes from a distinct loop with a smaller magnetic field, lower density, but higher temperature. Therefore, these flares likely occurred due to interaction between two (or more) magnetic loops. Title: Ultra-Narrow Negative Flare Front Observed in Helium-10830 Å Using the1.6m New Solar Telescope Authors: Xu, Yan; Cao, Wenda; Ding, Mingde; Kleint, Lucia; Su, Jiangtao; Liu, Chang; Ji, Haisheng; Chae, Jongchul; Jing, Ju; Cho, Kyuhyoun; Cho, Kyung-Suk; Gary, Dale E.; Wang, Haimin Bibcode: 2016SPD....47.0633X Altcode: Solar flares are sudden flashes of brightness on the Sun and are often associated with coronal mass ejections and solar energetic particles that have adverse effects on the near-Earth environment. By definition, flares are usually referred to as bright features resulting from excess emission. Using the newly commissioned 1.6-m New Solar Telescope at Big Bear Solar Observatory, we show a striking “negative” flare with a narrow but unambiguous “dark” moving front observed in He I 10830 Å, which is as narrow as 340 km and is associated with distinct spectral characteristics in Hα and Mg II lines. Theoretically, such negative contrast in He I 10830 Å can be produced under special circumstances by nonthermal electron collisions or photoionization followed by recombination. Our discovery, made possible due to unprecedented spatial resolution, confirms the presence of the required plasma conditions and provides unique information in understanding the energy release and radiative transfer in solar flares. Title: Radio Spectroscopic Imaging of Bi-directional Electron Beam Pairs in a Solar Flare Authors: Chen, Bin; Wang, Zhitao; Gary, Dale E. Bibcode: 2016SPD....4730201C Altcode: In solar flares, energetic electrons are believed to be accelerated at or near the magnetic reconnection site. They propagate outward along newly reconnected field lines usually in the form of electron beams. These beams can emit radio waves commonly known as type III radio bursts. An important feature of these bursts is that they are emitted near the local plasma frequency or its harmonic, which is only a function of the ambient plasma density. In particular, an electron beam propagating upward in the corona encounters plasma with lower and lower density, producing a radio burst with a “normal” frequency slope (whose frequency decreases in time). Similarly, a downward propagating beam produces a reverse-slope burst. Sometimes both the normal- and reverse-slope type III bursts are observed simultaneously. These type III burst with opposite slopes have been considered to be the signature of a pair of bi-directional electron beams emerging from a common acceleration site. However, previous studies had no imaging capability to locate these bursts and put them in the flare context. Here we report observations of decimetric type III burst pairs by the Karl G. Jansky Very Large Array (VLA) during the impulsive phase of a C5.6 flare. Using VLA’s unprecedented ultra-high-cadence spectroscopic imaging capability, we demonstrate that the type III burst pairs indeed correspond to high speed (~0.1c), bi-directional electron beams emerging from a common site in the corona where post-flare loops appeared later on. Implications of our results on magnetic reconnection and particle acceleration will be briefly discussed. Title: Early Observations with the Expanded Owens Valley Solar Array Authors: Gary, Dale E. Bibcode: 2016SPD....4730101G Altcode: The Expanded Owens Valley Solar Array (EOVSA) is a newly expanded and upgraded, solar-dedicated radio array consisting of 13 antennas of 2.1 m diameter equipped with receivers designed to cover the 1-18 GHz frequency range. Two large (27-m diameter) dishes are being outfitted with He-cooled receivers for use in calibration of the small dishes. During 2015, the array obtained observations from dozens of flares in total power mode on 8 antennas. Since February 2016, it has begun taking solar data on all 13 small antennas with full interferometric correlations, as well as calibration observations with the first of the two large antennas equipped with its He-cooled receiver. The second He-cooled receiver is nearly complete, and will be available around the time of the meeting. We briefly review the commissioning activities leading up to full operations, including polarization and gain measurements and calibration methods, and resulting measures of array performance. We then present some early imaging observations with the array, emphasizing the remarkable temporal and spectral resolution of the instrument, together with joint RHESSI hard X-ray and SDO EUV observations. Title: BBSO/NST Observations of the Sudden Differential Rotation of a Sunspot Caused by a Major Flare Authors: Liu, Chang; Xu, Yan; Deng, Na; Cao, Wenda; Lee, Jeongwoo; Hudson, Hugh S.; Gary, Dale E.; Wang, Jiasheng; Jing, Ju; Wang, Haimin Bibcode: 2016SPD....47.0615L Altcode: Sunspots are concentrations of magnetic field visible on the solar surface (photosphere), from which the field extends high into the corona. Complex plasma motions that drag field in the photosphere can build up free energy in the corona that powers solar eruptions. It is known that solar flares and the often associated coronal ejections (CMEs) can produce various radiations in the low atmosphere. However, it was considered implausible that disturbances created in the tenuous corona would cause a direct perturbation of the dense photosphere involving bulk motion. Here we report the sudden rotational motion of a sunspot clearly induced by a major solar flare (SOL2015-06-22T18:23 M6.6), using the unprecedented spatiotemporal resolution of the 1.6 m New Solar Telescope (NST) at Big Bear Solar Observatory (BBSO). It is particularly striking that the rotation is not uniform over the sunspot: as the flare ribbon sweeps across, its different portions accelerate (up to ~50 degree per hour) at different times corresponding to peaks of flare hard X-ray emission. The intensity and magnetic field of the sunspot also change significantly associated with the flare. Our results reveal an intrinsic relationship between the photospheric plasma bulk motions and coronal energy release, with direct consequences for our understanding of energy and momentum balance in the flare/CME phenomenon. This work is mainly supported by NASA grants NNX13AF76G and NNX13AG13G (LWS), and NNX16AF72G, and NSF grants AGS 1250818 and 1408703. Title: Hard X-ray and Microwave Simulation of 2015-06-22 M6.6 flare Authors: Kuroda, Natsuha; Wang, Haimin; Gary, Dale E.; Fleishman, Gregory D.; Nita, Gelu M.; Chen, Bin; Xu, Yan; Jing, Ju Bibcode: 2016SPD....47.0614K Altcode: It is well known that the time profiles of the hard X-ray (HXR) emission and the microwave (MW) emission during the impulsive phase of the solar flare are well correlated, and this has led to the expectation that these emissions come from a common population of flare-accelerated electrons. However, the energy ranges of the electrons producing two emissions are believed to be different (below and above several hundred keV for HXR-producing and MW-producing electrons, respectively), and some studies have shown that the indices of their energy spectra may differ as well. To better understand the energy distributions of the electrons producing these emissions, we present realistic forward-fit simulations of the HXR and the MW emissions of 2015 June 22, M6.6 flare using the newly developed, IDL-based platform GX simulator. We use the 3D magnetic field model extrapolated from magnetogram data from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO), the images and the electron energy distribution parameters deduced from the photon spectrum from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), and the spatially integrated MW spectrum and the cross-correlated amplitude data from the Expanded Owens Valley Solar Array (EOVSA) to guide the modeling. We have observed a possible above the-loop-top HXR source in 20-25 keV image, well separated from the source seen in 6-12 keV that is typically interpreted as a thermal loop-top source. Therefore, we simulate the HXR emissions by combining two flux tubes at different heights: the lower loop dominated by thermal electrons and the higher loop dominated by nonthermal electrons. The MW and HXR emissions produced from the forward-fit model are compared with observations to investigate possible differences in the energy spectra of the HXR-producing and the MW-producing electrons and what they can tell us about particle acceleration. Title: Science Objectives of the FOXSI Small Explorer Mission Concept Authors: Shih, Albert Y.; Christe, Steven; Alaoui, Meriem; Allred, Joel C.; Antiochos, Spiro K.; Battaglia, Marina; Buitrago-Casas, Juan Camilo; Caspi, Amir; Dennis, Brian R.; Drake, James; Fleishman, Gregory D.; Gary, Dale E.; Glesener, Lindsay; Grefenstette, Brian; Hannah, Iain; Holman, Gordon D.; Hudson, Hugh S.; Inglis, Andrew R.; Ireland, Jack; Ishikawa, Shin-Nosuke; Jeffrey, Natasha; Klimchuk, James A.; Kontar, Eduard; Krucker, Sam; Longcope, Dana; Musset, Sophie; Nita, Gelu M.; Ramsey, Brian; Ryan, Daniel; Saint-Hilaire, Pascal; Schwartz, Richard A.; Vilmer, Nicole; White, Stephen M.; Wilson-Hodge, Colleen Bibcode: 2016SPD....47.0814S Altcode: Impulsive particle acceleration and plasma heating at the Sun, from the largest solar eruptive events to the smallest flares, are related to fundamental processes throughout the Universe. While there have been significant advances in our understanding of impulsive energy release since the advent of RHESSI observations, there is a clear need for new X-ray observations that can capture the full range of emission in flares (e.g., faint coronal sources near bright chromospheric sources), follow the intricate evolution of energy release and changes in morphology, and search for the signatures of impulsive energy release in even the quiescent Sun. The FOXSI Small Explorer (SMEX) mission concept combines state-of-the-art grazing-incidence focusing optics with pixelated solid-state detectors to provide direct imaging of hard X-rays for the first time on a solar observatory. We present the science objectives of FOXSI and how its capabilities will address and resolve open questions regarding impulsive energy release at the Sun. These questions include: What are the time scales of the processes that accelerate electrons? How do flare-accelerated electrons escape into the heliosphere? What is the energy input of accelerated electrons into the chromosphere, and how is super-heated coronal plasma produced? Title: High-Resolution Observations of Flare Precursors and Their Relationship with Magnetic Channels Authors: Wang, Haimin; Xu, Yan; Ahn, Kwangsu; Jing, Ju; Liu, Chang; Deng, Na; Huang, Nengyi; Gary, Dale E.; Cao, Wenda Bibcode: 2016SPD....4720501W Altcode: The study of precursors of flares is important for understanding the basic magnetic instability leading to solar flares, which can aid the forecasting of eruptions potentially related to severe space weather effects. Although literatures reported many important clues, high-resolution observations of pre-flare activities before a well-observed solar flare have been rare. Even rarely, the associated magnetic structures in fine scale (below 1") were also observed. In this study we take advantage of multiwavelength high-resolution observations completely covering the 2015 June 22 M6.6 flare, which were obtained under excellent seeing condition with the 1.6 m New Solar Telescope (NST) at Big Bear Solar Observatory. The NST data includes observations of the H-alpha line in five spectral positions at a spatial resolution of 0.1" and magnetograms at a resolution of 0.25". These are complemented by IRIS UV observations with a resolution of 0.25". We find that there are two episodes of pre-flare brightenings (precursors), which are spatially associated with magnetic channels, i.e., elongated structures comprising alternating magnetic polarity inversion lines (Zirin & Wang, 1993, Nature, 363, 426). The pre-flare chromospheric and coronal features reflect an extremely sheared magnetic topology, while the initiation of main flare brightenings correspond to a much less sheared configuration. RHESSI HXR observations reveal that the precursors have both thermal and nonthermal components, and the latter is further evidenced by the microwave observations of the newly expanded Solar Radio Array at Owens Valley.We further investigate the electric current system above the magnetic channels using NLFFF extrapolations, which show strong current sheets above the channel structure. This is consistent with the MHD modeling of Kusano et al (2012, Ap.J., 760, 31), who noted the importance of localized small-scale magnetic structure in triggering the eruption of the whole active region. We suggest that small-scale magnetic reconnection along the channels destabilizes the magnetic structure of the active region and subsequently triggers the main M6.6 flare and the associated halo CME. Title: Source dynamics of the microwave emission during a solar flare Authors: Shaik, Shaheda Begum; Gary, Dale E.; Nita, Gelu M. Bibcode: 2016SPD....4730702S Altcode: 2016SPD....4730702B Determining the microwave burst source characteristics is important to understand the parameters of the flare process which produce the microwave emission. Previous studies show that the microwave solar bursts do typically exhibit a single source of emission but also often show inhomogeneous sources as a function of frequency at some periods during the burst. This study focuses on the spectral and spatial dynamics of the microwave gyrosynchrotron source through the microwave spectral and imaging analysis. We report the source characteristics of few impulsive flare events observed by the newly upgraded Expanded Owens Valley Solar Array (EOVSA) in the frequency range of 2.5 to 18 GHz and from the complimentary data of (Nobeyama Radioheliograph / Nobeyama Radio Polarimeters) NoRH / NoRP. The low frequency optically thick part of the microwave spectrum is an indicator of spatial inhomogeneity and complexity of the sources. We concentrate in the dynamics of the low frequency spectrum (intensity and spectral index) measured by EOVSA, and compare it to the corresponding spatial propoerties of the NoRH sources observed at 17 GHz and to the loop structures seen in the EUV (Extreme Ultraviolet) images with SDO (Solar Dynamics Observatory). Title: Unprecedented Fine Structure of a Solar Flare Revealed by the 1.6~m New Solar Telescope Authors: Jing, Ju; Xu, Yan; Cao, Wenda; Liu, Chang; Gary, Dale E.; Wang, Haimin Bibcode: 2016SPD....47.0601J Altcode: Solar flares signify the sudden release of magnetic energy and are sources of so called space weather. The fine structures (below 500 km) of flares are rarely observed and are accessible to only a few instruments world-wide. Here we present observation of a solar flare using exceptionally high resolution images from the 1.6~m New Solar Telescope (NST) equipped with high order adaptive optics at Big Bear Solar Observatory (BBSO). The observation reveals the process of the flare in unprecedented detail, including the flare ribbon propagating across the sunspots, coronal rain (made of condensing plasma) streaming down along the post-flare loops, and the chromosphere's response to the impact of coronal rain, showing fine-scale brightenings at the footpoints of the falling plasma. Taking advantage of the resolving power of the NST, we measure the cross-sectional widths of flare ribbons, post-flare loops and footpoint brighenings, which generally lie in the range of 80-200 km, well below the resolution of most current instruments used for flare studies. Confining the scale of such fine structure provides an essential piece of information in modeling the energy transport mechanism of flares, which is an important issue in solar and plasma physics. Title: Solar Observations with the Atacama Large Millimeter/submillimeter Array (ALMA) Authors: Kobelski, A.; Bastian, T. S.; Bárta, M.; Brajša, R.; Chen, B.; De Pontieu, B.; Fleishman, G.; Gary, D.; Hales, A.; Hills, R.; Hudson, H.; Hurford, G.; Loukitcheva, M.; Iwai, K.; Krucker, S.; Shimojo, M.; Skokić, I.; Wedemeyer, S.; White, S.; Yan, Y.; ALMA Solar Development Team Bibcode: 2016ASPC..504..327K Altcode: The Atacama Large Millimeter/Submillimeter Array (ALMA) is a joint North American, European, and East Asian project that opens the mm-sub mm wavelength part of the electromagnetic spectrum for general astrophysical exploration, providing high-resolution imaging in frequency bands currently ranging from 84 GHz to 950 GHz (300 microns to 3 mm). It is located in the Atacama desert in northern Chile at an elevation of 5000 m. Despite being a general purpose instrument, provisions have been made to enable solar observations with ALMA. Radiation emitted at ALMA wavelengths originates mostly from the chromosphere, which plays an important role in the transport of matter and energy, and the in heating the outer layers of the solar atmosphere. Despite decades of research, the solar chromosphere remains a significant challenge: both to observe, owing to the complicated formation mechanisms of currently available diagnostics; and to understand, as a result of the complex nature of the structure and dynamics of the chromosphere. ALMA has the potential to change the scene substantially as it serves as a nearly linear thermometer at high spatial and temporal resolution, enabling us to study the complex interaction of magnetic fields and shock waves and yet-to-be-discovered dynamical processes. Moreover, ALMA will play an important role in the study of energetic emissions associated with solar flares at sub-THz frequencies. Title: Solar Science with the Atacama Large Millimeter/Submillimeter Array—A New View of Our Sun Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Hudson, H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E. P.; De Pontieu, B.; Yagoubov, P.; Tiwari, S. K.; Soler, R.; Black, J. H.; Antolin, P.; Scullion, E.; Gunár, S.; Labrosse, N.; Ludwig, H. -G.; Benz, A. O.; White, S. M.; Hauschildt, P.; Doyle, J. G.; Nakariakov, V. M.; Ayres, T.; Heinzel, P.; Karlicky, M.; Van Doorsselaere, T.; Gary, D.; Alissandrakis, C. E.; Nindos, A.; Solanki, S. K.; Rouppe van der Voort, L.; Shimojo, M.; Kato, Y.; Zaqarashvili, T.; Perez, E.; Selhorst, C. L.; Barta, M. Bibcode: 2016SSRv..200....1W Altcode: 2015SSRv..tmp..118W; 2015arXiv150406887W The Atacama Large Millimeter/submillimeter Array (ALMA) is a new powerful tool for observing the Sun at high spatial, temporal, and spectral resolution. These capabilities can address a broad range of fundamental scientific questions in solar physics. The radiation observed by ALMA originates mostly from the chromosphere—a complex and dynamic region between the photosphere and corona, which plays a crucial role in the transport of energy and matter and, ultimately, the heating of the outer layers of the solar atmosphere. Based on first solar test observations, strategies for regular solar campaigns are currently being developed. State-of-the-art numerical simulations of the solar atmosphere and modeling of instrumental effects can help constrain and optimize future observing modes for ALMA. Here we present a short technical description of ALMA and an overview of past efforts and future possibilities for solar observations at submillimeter and millimeter wavelengths. In addition, selected numerical simulations and observations at other wavelengths demonstrate ALMA's scientific potential for studying the Sun for a large range of science cases. Title: Unprecedented Fine Structure of a Solar Flare Revealed by the 1.6 m New Solar Telescope Authors: Jing, Ju; Xu, Yan; Cao, Wenda; Liu, Chang; Gary, Dale; Wang, Haimin Bibcode: 2016NatSR...624319J Altcode: 2016arXiv160408562J Solar flares signify the sudden release of magnetic energy and are sources of so called space weather. The fine structures (below 500 km) of flares are rarely observed and are accessible to only a few instruments world-wide. Here we present observation of a solar flare using exceptionally high resolution images from the 1.6 m New Solar Telescope (NST) equipped with high order adaptive optics at Big Bear Solar Observatory (BBSO). The observation reveals the process of the flare in unprecedented detail, including the flare ribbon propagating across the sunspots, coronal rain (made of condensing plasma) streaming down along the post-flare loops, and the chromosphere’s response to the impact of coronal rain, showing fine-scale brightenings at the footpoints of the falling plasma. Taking advantage of the resolving power of the NST, we measure the cross-sectional widths of flare ribbons, post-flare loops and footpoint brighenings, which generally lie in the range of 80-200 km, well below the resolution of most current instruments used for flare studies. Confining the scale of such fine structure provides an essential piece of information in modeling the energy transport mechanism of flares, which is an important issue in solar and plasma physics. Title: Ultra-narrow Negative Flare Front Observed in Helium-10830 Å Using the 1.6 m New Solar Telescope Authors: Xu, Yan; Cao, Wenda; Ding, Mingde; Kleint, Lucia; Su, Jiangtao; Liu, Chang; Ji, Haisheng; Chae, Jongchul; Jing, Ju; Cho, Kyuhyoun; Cho, Kyungsuk; Gary, Dale; Wang, Haimin Bibcode: 2016ApJ...819...89X Altcode: 2016arXiv160104729X Solar flares are sudden flashes of brightness on the Sun and are often associated with coronal mass ejections and solar energetic particles that have adverse effects on the near-Earth environment. By definition, flares are usually referred to as bright features resulting from excess emission. Using the newly commissioned 1.6 m New Solar Telescope at Big Bear Solar Observatory, we show a striking “negative” flare with a narrow but unambiguous “dark” moving front observed in He I 10830 Å, which is as narrow as 340 km and is associated with distinct spectral characteristics in Hα and Mg II lines. Theoretically, such negative contrast in He I 10830 Å can be produced under special circumstances by nonthermal electron collisions or photoionization followed by recombination. Our discovery, made possible due to unprecedented spatial resolution, confirms the presence of the required plasma conditions and provides unique information in understanding the energy release and radiative transfer in astronomical objects. Title: Validation of the Coronal Thick Target Source Model Authors: Fleishman, Gregory D.; Xu, Yan; Nita, Gelu N.; Gary, Dale E. Bibcode: 2016ApJ...816...62F Altcode: 2015arXiv151106947F We present detailed 3D modeling of a dense, coronal thick-target X-ray flare using the GX Simulator tool, photospheric magnetic measurements, and microwave imaging and spectroscopy data. The developed model offers a remarkable agreement between the synthesized and observed spectra and images in both X-ray and microwave domains, which validates the entire model. The flaring loop parameters are chosen to reproduce the emission measure, temperature, and the nonthermal electron distribution at low energies derived from the X-ray spectral fit, while the remaining parameters, unconstrained by the X-ray data, are selected such as to match the microwave images and total power spectra. The modeling suggests that the accelerated electrons are trapped in the coronal part of the flaring loop, but away from where the magnetic field is minimal, and, thus, demonstrates that the data are clearly inconsistent with electron magnetic trapping in the weak diffusion regime mediated by the Coulomb collisions. Thus, the modeling supports the interpretation of the coronal thick-target sources as sites of electron acceleration in flares and supplies us with a realistic 3D model with physical parameters of the acceleration region and flaring loop. Title: Particle acceleration by a solar flare termination shock Authors: Chen, Bin; Bastian, Timothy S.; Shen, Chengcai; Gary, Dale E.; Krucker, Säm; Glesener, Lindsay Bibcode: 2015Sci...350.1238C Altcode: 2015arXiv151202237C Solar flares—the most powerful explosions in the solar system—are also efficient particle accelerators, capable of energizing a large number of charged particles to relativistic speeds. A termination shock is often invoked in the standard model of solar flares as a possible driver for particle acceleration, yet its existence and role have remained controversial. We present observations of a solar flare termination shock and trace its morphology and dynamics using high-cadence radio imaging spectroscopy. We show that a disruption of the shock coincides with an abrupt reduction of the energetic electron population. The observed properties of the shock are well reproduced by simulations. These results strongly suggest that a termination shock is responsible, at least in part, for accelerating energetic electrons in solar flares. Title: Observations and Simulations of a Termination Shock in an Eruptive Solar Flare as a Possible Particle Accelerator Authors: Chen, B.; Bastian, T.; Shen, C.; Gary, D. E.; Krucker, S.; Glesener, L. Bibcode: 2015AGUFMSH11F..05C Altcode: A termination shock has been often invoked in the standard model for eruptive solar flares as a possible driver for particle acceleration. It is hypothesized as a standing shock wave generated by super-magnetosonic reconnection outflows impinging upon dense, newly-reconnected magnetic loops during the flare energy release process. However, such shock wave has largely remained a theoretical concept inferred from model predictions due to the lack of observational evidence. Here we present observations of a termination shock in a solar flare and trace its morphology and dynamics using high-cadence radio imaging spectroscopy enabled by the upgraded Karl G. Jansky Very Large Array. The observed properties of the shock, including its location, morphology, and dynamics, are well-reproduced by magnetohydrodynamics simulations in a standard Kopp-Pneuman-type reconnection geometry for two-ribbon flares. We further show that a disruption of the shock coincides with an abrupt reduction of the energetic electron population. These results strongly suggest that a termination shock is responsible, at least in part, for accelerating energetic electrons in solar flares. Title: On Using Solar Radio Emission to Probe Interiors of Asteroids and Comets Authors: Winebrenner, D. P.; Gary, D. E.; Sahr, J. D.; Asphaug, E. I. Bibcode: 2015AGUFM.P51C2083W Altcode: Asteroids, comets and other primitive solar system bodies are key sources of information on the early solar system, on volatiles and organics delivered to the terrestrial planets, and on processes of planetary formation now observed in operation around other stars. Whether asteroids (in various size classes) are rubble piles or monolithic, and whether any porosity or internal voids contain volatiles, are first-order questions for understanding the delivery of volatiles to the early Earth, and for assessing impact hazards. Information on bulk composition aids discrimination between types and origins of primitive bodies, .e.g., the degree of aqueous alteration and bound-water content of carbonaceous chondrite bodies, and the volatile mass fraction of comets. Radar and radio methods can provide direct information on bulk composition, micro- and macro-porosity, body-scale internal structure, and on whether voids in rocky materials are volatile- or vacuum-filled. Such methods therefore figure prominently in current missions to primitive bodies (e.g., CONSERT) and in a variety of proposed missions. Radio transmitters necessary for conventional methods, however, add considerably to spacecraft mass and power requirements. Moreover, at many wavelengths most useful for radio sounding, powerful radio emission from the Sun strongly interferes with conventional signals. Here we present initial results from an investigation of how solar radio emission could serve as a natural resource for probing interiors of primitive bodies, rather than as interference. We briefly review methods for using stochastic radio illumination (aka noise radar methods), and illustrate the characteristics of solar radio emission relevant to mission design (e.g., observed intervals between emission events of specified intensity for different points in the solar cycle). We then discuss methods for selecting and interpreting observations in terms of interior properties, for bodies is different size classes (relative to the radio wavelength). Our preliminary results indicate considerable promise, certainly for bodies near 1 AU, and possibly also for bodies farther from the Sun. Title: The Atacama Large Millimeter/Submillimeter Array: a New Asset for Solar and Heliospheric Physics Authors: Bastian, Timothy S.; Barta, Miroslav; Brajsa, Roman; Chen, Bin; De Pontieu, Bart; Fleishman, Gregory; Gary, Dale; Hales, Antonio; Hills, Richard; Hudson, Hugh; Iwai, Kazamasu; Shimojo, Masumi; White, Stephen; Wedemeyer, Sven; Yan, Yihua Bibcode: 2015IAUGA..2257295B Altcode: The Atacama Large Millimeter/Submillimeter Array (ALMA) is a joint North American, European, and East Asian interferometric array that opens the mm-submm wavelength part of the electromagnetic spectrum for general astrophysical exploration, providing high-resolution imaging in frequency bands ranging from 86 to 950 GHz. Despite being a general purpose instrument, provisions have been made to enable solar observations with ALMA. Radiation emitted at ALMA wavelengths originates mostly from the chromosphere, which plays an important role in the transport of energy and matter and the heating of the outer layers of the solar atmosphere. In this paper we describe recent efforts to ensure that ALMA can be usefully exploited by the scientific community to address outstanding questions in solar physics. We summarize activities under North American and European ALMA development studies, including instrument testing, calibration and imaging strategies, a science simulations. With the support of solar observations, ALMA joins next-generation groundbased instruments that can be used alone or in combination with other ground-based and space-based instruments to address outstanding questions in solar and heliospheric physics. Opportunities for the wider community to contribute to these efforts will be highlighted. Title: Observation of the 2011-02-15 X2.2 Flare in the Hard X-Ray and Microwave Authors: Kuroda, Natsuha; Wang, Haimin; Gary, Dale E. Bibcode: 2015ApJ...807..124K Altcode: 2015arXiv150601424K Previous studies have shown that the energy release mechanism of some solar flares follow the Standard magnetic-reconnection model, but the detailed properties of high-energy electrons produced in the flare are still not well understood. We conducted a unique, multi-wavelength study that discloses the spatial, temporal and energy distributions of the accelerated electrons in the X2.2 solar flare on 2011 February 15. We studied the source locations of seven distinct temporal peaks observed in hard X-ray (HXR) and microwave (MW) light curves using the RHESSI in 50-75 keV channels and Nobeyama Radioheliograph in 34 GHz, respectively. We found that the seven emission peaks did not come from seven spatially distinct sites in HXR and MW, but rather in HXR we observed a sudden change in location only between the second and the third peak, with the same pattern occurring, but evolving more slowly in MW. Comparison between the HXR light curve and the temporal variations in intensity in the two MW source kernels also confirmed that the seven peaks came predominantly from two sources, each with multiple temporal peaks. In addition, we studied the polarization properties of MW sources, and time delay between HXR and MW. We discuss our results in the context of the tether-cutting model. Title: Coronal Magnetography of a Simulated Solar Active Region from Microwave Imaging Spectropolarimetry Authors: Wang, Zhitao; Gary, Dale E.; Fleishman, Gregory D.; White, Stephen M. Bibcode: 2015ApJ...805...93W Altcode: 2015arXiv150305239W We have simulated the Expanded Owens Valley Solar Array (EOVSA) radio images generated at multiple frequencies from a model solar active region, embedded in a realistic solar disk model, and explored the resulting data cube for different spectral analysis schemes to evaluate the potential for realizing one of EOVSA’s most important scientific goals—coronal magnetography. In this paper, we focus on modeling the gyroresonance and free-free emission from an on-disk solar active region model with realistic complexities in electron density, temperature and magnetic field distribution. We compare the magnetic field parameters extrapolated from the image data cube along each line of sight after folding through the EOVSA instrumental profile with the original (unfolded) parameters used in the model. We find that even the most easily automated, image-based analysis approach (Level-0) provides reasonable quantitative results, although they are affected by systematic effects due to finite sampling in the Fourier (UV) plane. Finally, we note the potential for errors due to misidentified harmonics of the gyrofrequency, and discuss the prospects for applying a more sophisticated spectrally based analysis scheme (Level-1) to resolve the issue in cases where improved UV coverage and spatial resolution are available. Title: Radio Coronal Magnetography of a Large Active Region Authors: Bastian, Timothy S.; Gary, Dale E.; White, Stephen; Fleishman, Gregory; Chen, Bin Bibcode: 2015TESS....111301B Altcode: Quantitative knowledge of coronal magnetic fields is fundamental to understanding energetic phenomena such as solar flares. Flares occur in solar active regions where strong, non-potential magnetic fields provide free energy. While constraints on the coronal magnetic field topology are readily available through high resolution SXR and EUV imaging of solar active regions, useful quantitative measurements of coronal magnetic fields have thus far been elusive. Recent progress has been made at infrared (IR) wavelengths in exploiting both the Zeeman and Hanle effects to infer the line-of-sight magnetic field strength or the orientation of the magnetic field vector in the plane of the sky above the solar limb. However, no measurements of coronal magnetic fields against the solar disk are possible using IR observations. Radio observations of gyroresonance emission from active regions offer the means of measuring coronal magnetic fields above the limb and on the solar disk. In particular, for plasma plasma conditions in the solar corona, active regions typically become optically thick to emission over a range of radio frequencies through gyroresonance absorption at a low harmonic of the electron gyrofrequency. The specific range of resonant frequencies depends on the range of coronal magnetic field strengths present in the active region.The Karl G. Jansky Very Large Array was used in November 2014 to image NOAA/USAF active region AR12209 over a continuous frequency range of 1-8 GHz, corresponding to a wavelength range of 3.75-30 cm. This frequency range is sensitive to coronal magnetic field strengths ranging from ~120-1400G. The active region was observed on four different dates - November 18, 20, 22, and 24 - during which the active region longitude ranged from -15 to +70 degrees, providing a wide range of aspect angles. In this paper we provide a preliminary description of the coronal magnetic field measurements derived from the radio observations. Title: Energy Partitions and Evolution in a Purely Thermal Solar Flare Authors: Fleishman, Gregory D.; Nita, Gelu M.; Gary, Dale E. Bibcode: 2015ApJ...802..122F Altcode: 2015arXiv150200315F This paper presents a solely thermal flare, which we detected in the microwave range from the thermal gyro- and free-free emission it produced. An advantage of analyzing thermal gyro emission is its unique ability to precisely yield the magnetic field in the radiating volume. When combined with observationally deduced plasma density and temperature, these magnetic field measurements offer a straightforward way of tracking evolution of the magnetic and thermal energies in the flare. For the event described here, the magnetic energy density in the radio-emitting volume declines over the flare rise phase, then stays roughly constant during the extended peak phase, but recovers to the original level over the decay phase. At the stage where the magnetic energy density decreases, the thermal energy density increases; however, this increase is insufficient, by roughly an order of magnitude, to compensate for the magnetic energy decrease. When the magnetic energy release is over, the source parameters come back to nearly their original values. We discuss possible scenarios to explain this behavior. Title: Tracing Solar Fiber Bursts Spatially and Spectrally with Microwave Imaging Spectroscopy Authors: Wang, Zhitao; Chen, Bin; Gary, Dale E. Bibcode: 2015TESS....120321W Altcode: We report observations of fiber fine structures during type IV decimetric radio bursts on March 3, 2012 using the recently upgraded Karl G. Jansky Very Large Array (VLA). For the first time, the technique of microwave imaging spectroscopy with high temporal and spectral resolution allowed us to image the fiber bursts over a continuous frequency range from 1-2 GHz, and precisely measure the centroid trajectories in the heliocentric coordinate. We found that the burst source originates at lower height near the footpoint, and streams upward through the corona along some field lines, whose trend is similar to some coronal loops seen in extreme ultra violet (EUV) wavelengths. In the dynamic spectrum, we also studied the average drift rates of different groups. Using an automatic fiber-tracing algorithm, we obtained the normalized drift rates between -0.1 and -0.025 s-1 from over 2000 fiber samples. Together with an appropriate coronal density model, we determined a subset of 3D field lines in the extrapolated coronal magnetic field, provided by the potential field source surface model (PFSS). As a result, we obtained the 3D source velocity of the fiber bursts at more than 2000 km/s above 1.1 GHz. The derived velocity can be used to discriminate between the two competing theories, the whistler wave model and Alfvén wave model. Title: Observation and Modeling of a Termination Shock in a Solar Eruption as a Possible Particle Accelerator Authors: Gary, Dale E.; Chen, Bin; Bastian, Timothy S.; Shen, Chengcai; Krucker, Sam Bibcode: 2015TESS....130402G Altcode: Solar eruptions and their associated solar flares are the most energetic particle accelerators in our solar system. Yet the acceleration mechanism remains uncertain. A possible candidate often invoked in the standard picture of solar eruptions is a termination shock, produced by fast reconnection outflows impinging upon dense, closed loops in a helmet-type geometry. However, the importance of termination shocks in solar particle acceleration remains controversial, mainly because there has been no direct detection of such shocks. Here we report direct imaging of the location and evolution of a termination shock during the rise phase of a solar eruption. The shock appears at radio wavelengths as a narrow surface sandwiched between multitudes of downward-moving plasma blobs and the underlying, newly-reconnected flaring loops, and evolves coherently with a loop-top hard X-ray source in the shock downstream region. The shock produces many short-lived, point-like radio sources, each interpreted as emission from a turbulence cell interacting with fast (nonthermal) electrons. These point-like radio sources clearly outline the termination shock front and their positions change in reaction to the arrival of the fast plasma blobs, which are well-reproduced by our numerical simulations based on a resistive magnetohydrodynamics reconnection model in a standard two-ribbon flare geometry. We further show that a temporary disruption of the shock coincides with a reduction of radio and hard X-ray emission associated with the energetic electron population. Our observations strongly favor a scenario in which the termination shock is responsible for accelerating electrons to high energies. Title: Energy partitions and evolution in a purely thermal solar flare Authors: Fleishman, Gregory; Nita, Gelu M.; Gary, Dale E. Bibcode: 2015TESS....130703F Altcode: A conventional way of producing a hot plasma in the flaring loops is via the impact of the nonthermal particles accelerated in flares due to release of the excessive magnetic energy, which has come to be known as the Neupert effect. We know, however, that in many events the heating starts clearly before the particle acceleration, which implies that no accelerated particles may be required for this heating. To this end, we present here a flare whose microwave emission is consistent with a purely thermal distribution of electrons, based on the gyro- and free-free emission it produced. An advantage of analyzing thermal gyro emission is its unique ability to precisely yield the magnetic field in the radiating volume. When combined with observationally-deduced plasma density and temperature, these magnetic field measurements offer a straightforward way of tracking evolution of the magnetic and thermal energies in the flare. For the event described here, the magnetic energy density in the radio-emitting volume declines over the flare rise phase, then stays roughly constant during the extended peak phase, but recovers to the original level over the decay phase. At the stage where the magnetic energy density decreases, the thermal energy density increases; however, this increase is insufficient, by roughly an order of magnitude, to compensate for the magnetic energy decrease. We conclude that the apparent decrease of the magnetic field in the radio source over the rise phase of the flare requires an upward propagating magnetic reconnection/plasma heating process, such as in the standard flare scenario, but with one remarkable difference: the absence of any significant nonthermal electron generation. We expect that the study of these rare thermal flares will better clarify the origin of such purely thermal events, characterized by significant energy release observed through the plasma heating, but without any measurable acceleration of the charged particles.This work was partially supported by NSF grants AGS-1250374 and AGS-1262772, and NASA grant NNX14AC87G. Title: Initial Observations of Solar Bursts with the Expanded Owens Valley Solar Array Authors: Gary, Dale E.; Kuroda, Natsuha; Fleishman, Gregory; Nita, Gelu M.; White, Stephen; Hurford, Gordon; McTiernan, James Bibcode: 2015TESS....130706G Altcode: The Expanded Owens Valley Solar Array (EOVSA) is a newly expanded and upgraded, solar-dedicated radio array consisting of 13 antennas equipped with receivers designed to cover the 1-18 GHz frequency range. Beginning in the fall of 2014, it began taking data on four antennas in total power mode, and observed a number of solar flares ranging from the X3.1 flare of 2014 Oct 24 to small events of low C-class, with 1-s time resolution at more than 300 frequencies in the range 2.5-18 GHz. The array is now (Feb. 2015) operating with 8 antennas in both total power and interferometry mode, and is rapidly being commissioned for full operation with all 13 antennas. Here we present some initial observations with the array, emphasizing the remarkable temporal and spectral resolution of the instrument, together with joint RHESSI hard X-ray and SDO EUV observations. Title: Synthetic 3D modeling of active regions and simulation of their multi-wavelength emission Authors: Nita, Gelu M.; Fleishman, Gregory; Kuznetsov, Alexey A.; Loukitcheva, Maria A.; Viall, Nicholeen M.; Klimchuk, James A.; Gary, Dale E. Bibcode: 2015TESS....131204N Altcode: To facilitate the study of solar active regions, we have created a synthetic modeling framework that combines 3D magnetic structures obtained from magnetic extrapolations with simplified 1D thermal models of the chromosphere, transition region, and corona. To handle, visualize, and use such synthetic data cubes to compute multi-wavelength emission maps and compare them with observations, we have undertaken a major enhancement of our simulation tools, GX_Simulator (ftp://sohoftp.nascom.nasa.gov/solarsoft/packages/gx_simulator/), developed earlier for modeling emission from flaring loops. The greatly enhanced, object-based architecture, which now runs on Windows, Mac, and UNIX platform, offers important new capabilities that include the ability to either import 3D density and temperature distribution models, or to assign to each individual voxel numerically defined coronal or chromospheric temperature and densities, or coronal Differential Emission Measure distributions. Due to these new capabilities, the GX_Simulator can now apply parametric heating models involving average properties of the magnetic field lines crossing a given voxel volume, as well as compute and investigate the spatial and spectral properties of radio (to be compared with VLA or EOVSA data), (sub-)millimeter (ALMA), EUV (AIA/SDO), and X-ray (RHESSI) emission calculated from the model. The application integrates shared-object libraries containing fast free-free, gyrosynchrotron, and gyroresonance emission codes developed in FORTRAN and C++, and soft and hard X-ray and EUV codes developed in IDL. We use this tool to model and analyze an active region and compare the synthetic emission maps obtained in different wavelengths with observations.This work was partially supported by NSF grants AGS-1250374, AGS-1262772, NASA grant NNX14AC87G, the Marie Curie International Research Staff Exchange Scheme "Radiosun" (PEOPLE-2011-IRSES-295272), RFBR grants 14-02-91157, 15-02-01089, 15-02-03717, 15-02-03835, 15-02-08028. Title: Three-dimensional Radio and X-Ray Modeling and Data Analysis Software: Revealing Flare Complexity Authors: Nita, Gelu M.; Fleishman, Gregory D.; Kuznetsov, Alexey A.; Kontar, Eduard P.; Gary, Dale E. Bibcode: 2015ApJ...799..236N Altcode: 2014arXiv1409.0896N Many problems in solar physics require analysis of imaging data obtained in multiple wavelength domains with differing spatial resolution in a framework supplied by advanced three-dimensional (3D) physical models. To facilitate this goal, we have undertaken a major enhancement of our IDL-based simulation tools developed earlier for modeling microwave and X-ray emission. The enhanced software architecture allows the user to (1) import photospheric magnetic field maps and perform magnetic field extrapolations to generate 3D magnetic field models; (2) investigate the magnetic topology by interactively creating field lines and associated flux tubes; (3) populate the flux tubes with user-defined nonuniform thermal plasma and anisotropic, nonuniform, nonthermal electron distributions; (4) investigate the spatial and spectral properties of radio and X-ray emission calculated from the model; and (5) compare the model-derived images and spectra with observational data. The package integrates shared-object libraries containing fast gyrosynchrotron emission codes, IDL-based soft and hard X-ray codes, and potential and linear force-free field extrapolation routines. The package accepts user-defined radiation and magnetic field extrapolation plug-ins. We use this tool to analyze a relatively simple single-loop flare and use the model to constrain the magnetic 3D structure and spatial distribution of the fast electrons inside this loop. We iteratively compute multi-frequency microwave and multi-energy X-ray images from realistic magnetic flux tubes obtained from pre-flare extrapolations, and compare them with imaging data obtained by SDO, NoRH, and RHESSI. We use this event to illustrate the tool's use for the general interpretation of solar flares to address disparate problems in solar physics. Title: Reduced Coronal Emission Above Large Isolated Sunspots Authors: Ryabov, B. I.; Gary, D. E.; Peterova, N. G.; Shibasaki, K.; Topchilo, N. A. Bibcode: 2015SoPh..290...21R Altcode: 2014SoPh..tmp..192R We analysed specific regions of reduced soft X-ray and microwave emission in five large isolated sunspots. The Nobeyama Radioheliograph 17 GHz observations reveal a local depression of microwave brightness in the peripheral area of the sunspots. The depression regions appear light (weak absorption) in the He 10830 Å line in areas with extended (open) field lines, as indicated by potential field source surface model (PFSS) extrapolations up to 1.5 R⊙. The observed depressions of 3 - 8 % in ordinary mode at 17 GHz are interpreted as resulting from free-free emission when the plasma density is lower by 5 - 10 %. Our model estimates show that the decrease in density in both the coronal and the lower layers above the depression region accounts for the depression. These depression regions lend themselves well to marking the location of outward plasma motions. Title: Constraining Solar Coronal Magnetic Fields with New Radio Observing Techniques Authors: Chen, B.; Gary, D. E.; Bastian, T. Bibcode: 2014AGUFMSH23C..07C Altcode: Solar radio emission, produced by energetic electrons in the low-beta solar corona, is highly dependent on coronal magnetic field strength and direction, hence offering a rich potential for constraining coronal magnetic fields. However, the observed radio intensity is contributed by several different emission mechanisms and moreover, is known to be sensitive to parameters other than the magnetic field, such as the electron distribution function. Collectively, they introduce ambiguities that are difficult to resolve in the absence of high-quality, broadband radio dynamic imaging spectroscopic observations with sufficiently high spatial, spectral, and temporal resolution. Such observations have not been possible until very recently, thanks to the newly developed radio instruments such as the Karl G. Jansky Very Large Array (VLA) and the Expanded Owens Valley Solar Array (EOVSA). In this talk, we will present first results obtained from the Jansky VLA demonstrating their ability of constraining the coronal magnetic fields in active regions. We will also introduce a forward-modeling tool currently under development, which can be used to reconstruct the 3D coronal magnetic fields based on the newly available radio observations. Title: VLA Observations of Solar Decimetric Spike Bursts: Direct Signature of Accelerated Electrons in Reconnection Outflow Region Authors: Chen, B.; Bastian, T.; Gary, D. E. Bibcode: 2014AGUFMSH23A4149C Altcode: Solar decimetric spike bursts, which appear in a radio dynamic spectrum as a cluster of short-lived and narrowband brightenings, have been suggested as a possible signature of many, "elementary" particle accelerations at or near a magnetic reconnection site. Their dynamic spectral feature can be potentially used to diagnose important parameters of the reconnection site such as plasma density and spatial size of the fragmentation. Yet direct observational evidence supporting this scenario has been elusive mainly due to the lack of imaging observations. The upgraded Karl G. Jansky Very Large Array (VLA) provides the first opportunity of performing simultaneous radio imaging and dynamic spectroscopy, which allows radio sources to be imaged at every spatio-temporal pixel in the dynamic spectrum. Here we report Jansky VLA observations of decimetric spike bursts recorded during an eruptive solar limb flare. Combined with EUV and X-ray data from SDO and RHESSI, we show that the spike bursts coincide spatially with a loop-top hard X-ray source, which are located in a region where supra-arcade downflows meet the underlying hot, EUV/X-ray loops. We interpret the observed spike bursts as a direct signature of non-thermal electrons accelerated by turbulences and/or shocks in the reconnection outflow region. Title: The South Pole, Antarctica, Solar Radio Telescope (SPASRT) System Authors: Gerrard, A. J.; Weatherwax, A. T.; Gary, D. E.; Kujawski, J. T.; Nita, G. M.; Melville, R.; Stillinger, A.; Jeffer, G. Bibcode: 2014AGUFMSA13B3990G Altcode: The study of the sun in the radio portion of the electromagnetic spectrum furthers our understanding of fundamental solar processes observed in the X-ray, UV, and visible regions of the spectrum. For example, the study of solar radio bursts, which have been shown to cause serious disruptions of technologies at Earth, are essential for advancing our knowledge and understanding of solar flares and their relationship to coronal mass ejections and solar energetic particles, as well as the underlying particle acceleration mechanisms associated with these processes. In addition, radio coverage of the solar atmosphere could yield completely new insights into the variations of output solar energy, including Alfven wave propagation through the solar atmosphere and into the solar wind, which can potentially modulate and disturb the solar wind and Earth's geospace environment. In this presentation we discuss the development, construction, and testing of the South Pole, Antarctica, Solar Radio Telescope that is planned for installation at South Pole. The system will allow for 24-hour continuous, long-term observations of the sun across the 1-18 GHz frequency band and allow for truly continuous solar observations. We show that this system will enable unique scientific investigations of the solar atmosphere. Title: Observation of 2011-02-15 X2.2 Flare in Hard X-Ray and Microwave Authors: Kuroda, N.; Wang, H.; Gary, D. E. Bibcode: 2014AGUFMSH41C4153K Altcode: Previous studies have shown that the energy release mechanism of some solar flares follow the Standard magnetic-reconnection model, but the detailed properties of high-energy electrons produced in the flare are still not well understood. We conducted a unique, multi-wavelength study that discloses the spatial, temporal and energy distributions of the accelerated electrons in the X2.2 solar flare on Feb. 15, 2011. We studied the source locations of the observed seven temporal peaks in hard X-ray (HXR) and microwave (MW) lightcurves using the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) in 50-75 keV channels and Nobeyama Radioheliograph (NoRH) in 34 GHz, respectively. We found that peak emissions were coming from two spatially distinct sites in HXR and MW, and in HXR we observed a sudden change between these sites over the second and the third peak. Comparison between the HXR lightcurve and the temporal variations in MW source kernel intensity also confirmed that seven peak emissions were actually coming from two sources, each with their own multiple peaks. Title: Direct Evidence of an Eruptive, Filament-hosting Magnetic Flux Rope Leading to a Fast Solar Coronal Mass Ejection Authors: Chen, Bin; Bastian, T. S.; Gary, D. E. Bibcode: 2014ApJ...794..149C Altcode: 2014arXiv1408.6473C Magnetic flux ropes (MFRs) are believed to be at the heart of solar coronal mass ejections (CMEs). A well-known example is the prominence cavity in the low corona that sometimes makes up a three-part white-light (WL) CME upon its eruption. Such a system, which is usually observed in quiet-Sun regions, has long been suggested to be the manifestation of an MFR with relatively cool filament material collecting near its bottom. However, observational evidence of eruptive, filament-hosting MFR systems has been elusive for those originating in active regions. By utilizing multi-passband extreme-ultraviolet (EUV) observations from Solar Dynamics Observatory/Atmospheric Imaging Assembly, we present direct evidence of an eruptive MFR in the low corona that exhibits a hot envelope and a cooler core; the latter is likely the upper part of a filament that undergoes a partial eruption, which is later observed in the upper corona as the coiled kernel of a fast, WL CME. This MFR-like structure exists more than 1 hr prior to its eruption, and displays successive stages of dynamical evolution, in which both ideal and non-ideal physical processes may be involved. The timing of the MFR kinematics is found to be well correlated with the energy release of the associated long-duration C1.9 flare. We suggest that the long-duration flare is the result of prolonged energy release associated with the vertical current sheet induced by the erupting MFR. Title: Fitting FFT-derived Spectra: Theory, Tool, and Application to Solar Radio Spike Decomposition Authors: Nita, Gelu M.; Fleishman, Gregory D.; Gary, Dale E.; Marin, William; Boone, Kristine Bibcode: 2014ApJ...789..152N Altcode: 2014arXiv1406.2280N Spectra derived from fast Fourier transform (FFT) analysis of time-domain data intrinsically contain statistical fluctuations whose distribution depends on the number of accumulated spectra contributing to a measurement. The tail of this distribution, which is essential for separating the true signal from the statistical fluctuations, deviates noticeably from the normal distribution for a finite number of accumulations. In this paper, we develop a theory to properly account for the statistical fluctuations when fitting a model to a given accumulated spectrum. The method is implemented in software for the purpose of automatically fitting a large body of such FFT-derived spectra. We apply this tool to analyze a portion of a dense cluster of spikes recorded by our FASR Subsystem Testbed instrument during a record-breaking event that occurred on 2006 December 6. The outcome of this analysis is briefly discussed. Title: WIMAGR: An Interactive SSW IDL Tool for Mapping OVSA Legacy Microwave Interferometry Data Authors: Nita, Gelu M.; Fleishman, Gregory D.; Gary, Dale E. Bibcode: 2014AAS...22421845N Altcode: The Owens Valley Solar Array (OVSA), which is currently the subject of a major upgrade leading to the new Expanded Owens Valley Solar Array (EOVSA), has operated between the years 2000-2007 as a 5-7 antenna solar-dedicated radio interferometer, with daily observations at typically 40 frequencies in the microwave frequency range, 1-18 GHz. Given the importance of these unique data for complementary studies with data taken during the same period by Yohkoh, RHESSI, SoHO, TRACE, Hinode and other NASA spacecraft, we have undertaken an effort to maximize their usefulness, ease of use, and longevity by creating a uniform, calibrated OVSA legacy database and community-friendly, SSW-based software, compatible with the RHESSI and EOVSA software packages. With these efforts, we can anticipate that the data will continue serving the community well into the future. In this presentation, we will introduce one of the recent upgrades of the OVSA SSW software package, WIMAGR, whose interface allows the user to generate OVSA radio maps in intensity and polarization at many available frequencies with a spatial resolution about 3” at 18 GHz, which is comparable with the spatial resolution of other imaging instruments. To illustrate the main capabilities of this software tool and its potential for promoting scientific discovery, we will present a real-time computation of a sequence of multi-frequency OVSA microwave maps and compare them with images obtained by other instruments. This work was supported in part by NSF grants AGS-1250374, and NASA grants NNX11AB49G and NNX14AC87G to New Jersey Institute of Technology Title: Coronal Magnetography of a Simulated Solar Active Region from Microwave Imaging Spectropolarimetry Authors: Wang, Zhitao; Gary, Dale E.; White, Stephen M. Bibcode: 2014AAS...22432345W Altcode: We have simulated the Expanded Owens Valley Solar Array (EOVSA) radio images generated at multiple frequencies from a model solar active region, embedded in a realistic solar disk model, and evaluated the resulting datacube for different spectral analysis schemes to evaluate the potential for realizing one of EOVSA's most important scientific goals — coronal magnetography. In this paper, we focus on modeling the gyroresonance and free-free emission from an on-disk solar active region model with realistic complexities in electron density, temperature and magnetic field distribution. We compare the magnetic field parameters extrapolated from the image datacube along each line of sight after folding through the EOVSA instrumental profile with the original (unfolded) parameters used in the model. We find that even the most easily automated, image-based analysis approach (Level 0) provides reasonable quantitative results, although they are affected by systematic effects due to finite sampling in the Fourier (uv) plane. Title: Observation of 2011-02-15 X2.2 solar flare in Hard X-ray and microwave Authors: Kuroda, Natsuha; Wang, Haimin; Gary, Dale E. Bibcode: 2014AAS...22412332K Altcode: Previous studies have shown that the energy release mechanism of some solar flares follow the Standard magnetic-reconnection model, but the detailed properties of high-energy electrons produced in the flare are still not well understood. We conducted a unique, multi-wavelength study that discloses the spatial, temporal and energy distributions of the accelerated electrons in the X2.2 solar flare on Feb. 15, 2011. We studied the source locations of the observed seven temporal peaks in hard X-ray (HXR) and microwave (MW) lightcurves using the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) in 50-75 keV channels and Nobeyama Radioheliograph (NoRH) in 34 GHz, respectively. We confirmed that peak emissions were coming from two spatially distinct sites in HXR and MW, and in HXR we observed a sudden change between these sites over the second and the third peak. Comparison between the HXR lightcurve and the temporal variations in MW source kernel intensity also confirmed that seven peak emissions were actually coming from two sources, each with their own multiple peaks. Title: The Expanded Owens Valley Solar Array (EOVSA) Authors: Gary, Dale E.; Hurford, Gordon J.; Nita, Gelu M.; White, Stephen M.; McTiernan, James; Fleishman, Gregory D. Bibcode: 2014AAS...22412360G Altcode: The Expanded Owens Valley Solar Array (EOVSA) near Big Pine, CA is undergoing commissioning as a solar-dedicated microwave imaging array operating in the frequency range 2.5-18 GHz. The solar science to be addressed focuses on the 3D structure of the solar corona (magnetic field, temperature and density), and on the particle acceleration, transport and heating in solar flares. The project will support the scientific community by providing open data access and software tools for analysis and modeling of the data, to exploit synergies with on-going solar research in other wavelengths. The array consists of a total of 15 antennas, including the two 27-m antennas with He-cooled receivers for sensitive calibration, and thirteen 2.1-m antennas that each view the entire disk of the Sun. The system includes a completely new control system, broadband signal transmission, and high-speed digital signal processing, using new technology developed for the Frequency Agile Solar Radiotelescope (FASR). We present an overview of the instrument, the current status of commissioning activities, and some initial observations to assess performance.This research is supported by NSF grants AST-1312802, and NASA grants NNX11AB49G and NNX10AF27G to New Jersey Institute of Technology. Title: Acceleration Regions Jointly Observed with Microwave and X-Ray Imaging Spectroscopy in a Number of Solar Flares Authors: Fleishman, Gregory D.; Kontar, Eduard; Nita, Gelu M.; Gary, Dale E. Bibcode: 2014AAS...22412312F Altcode: Detection of acceleration regions in solar flares has proved challenging for many reasons, in particular, because the X-ray emission is weighted by denser regions of the flare volume, although the acceleration can take place in a tenuous region, while the microwave emission, which can be significant even from the tenuous regions, is often dominated by a (looptop) trapped population, rather than the acceleration region itself. For these reasons we undertook a systematic database search to identify events that do not show a significant trapped component and at the same time show evidence of the source uniformity, which simplifies the data analysis greatly. Initially, we identified a subset of more than 20 radio bursts with a relatively narrow spectrum, having the low- and high- frequency spectral indices larger than 3 by the absolute value. That steep low-frequency spectrum implies that the emission is nonthermal (for the thermal emission the spectral index is supposed to be 2 or flatter), and the source is reasonably dense and uniform. The steep high-frequency spectrum implies that no significant electron trapping occurs; otherwise a progressive spectral flattening would be observed. Roughly half of these radio bursts have RHESSI data, which allows for a detail joint diagnostics of the source parameters and evolution. Based on the studied radio-to-X-ray spatial relationships, timing, and spectral fits we do conclude that we deal here with emission from directly the acceleration regions. We discuss the implications of these observations for the acceleration mechanism involved. We also discuss further strategy of how to detect the acceleration region with the currently available observational means. This work was supported in part by NSF grants AGS-1250374, and NASA grants NNX11AB49G and NNX14AC87G to New Jersey Institute of Technology. Title: Solar Activity and Motions in the Solar Chromosphere and Corona at the 2012 and 2013 Total and Annular Eclipses in the U.S., Australia, and Africa Authors: Pasachoff, Jay M.; Babcock, B. A.; Davis, A. B.; Demianski, M.; Lucas, R.; Lu, M.; Dantowitz, R.; Rusin, V.; Saniga, M.; Seaton, D. B.; Gaintatzis, P.; Voulgaris, A.; Seiradakis, J. H.; Gary, D. E.; Shaik, S. B. Bibcode: 2014AAS...22311801P Altcode: Our studies of the solar chromosphere and corona at the 2012 and 2013 eclipses shortly after cycle maximum 24 (2011/2012) of solar activity (see: http://www.swpc.noaa.gov/SolarCycle/) involved radio observations of the 2012 annular eclipse with the Jansky Very Large Array, optical observations of the 2012 total eclipse from Australia, optical observations of the 2013 annular eclipse from Tennant Creek, Australia, and the 3 November 2013 total solar eclipse from Gabon. Our observations are coordinated with those from solar spacecraft: Solar Dynamics Observatory AIA and HMI, Hinode XRT and SOT, SOHO LASCO and EIT, PROBA2 SWAP, and STEREO SECCHI. Our 2012 totality observations include a CME whose motion was observed with a 37-minute interval. We include first results from the expedition to Gabon for the 3 November 2013 eclipse, a summary of eclipse results from along the path of totality across Africa, and a summary of the concomitant spacecraft observations. The Williams College 2012 expeditions were supported in part by NSF grant AGS-1047726 from Solar Terrestrial Research/NSF AGS, and by the Rob Spring Fund and Science Center funds at Williams. The JVLA is supported by the NSF. The Williams College 2013 total-eclipse expedition was supported in part by grant 9327-13 from the Committee for Research and Exploration of the National Geographic Society. ML was also supported in part by a Grant-In-Aid of Research from the National Academy of Sciences, administered by Sigma Xi, The Scientific Research Society (Grant ID: G20120315159311). VR and MS acknowledge support for 2012 from projects VEGA 2/0003/13 and NGS-3139-12 of the National Geographic Society. We are grateful to K. Shiota (Japan) for kindly providing us with some of his 2012 eclipse coronal images. We thank Alec Engell (Montana State U) for assistance on site, and Terry Cuttle (Queensland Amateur Astronomers) for help with site arrangements. We thank Aram Friedman (Ansible Technologies), Michael Kentrianakis, and Nicholas Weber (Dexter Southfield School) for collaboration on imaging at the Australian total eclipse. Title: Probing Magnetic Energy Release in a Solar Flare with Radio Dynamic Imaging Spectroscopy Authors: Chen, Bin; Bastian, T. S.; Gary, D. E.; White, S. M. Bibcode: 2014AAS...22311804C Altcode: Solar flares involve sudden release of magnetic energy that is previously stored in the Sun's corona. Yet details of the flare energy release processes are still poorly understood. Solar radio bursts are intense and short-lived radio emissions that occur in solar flares. They are believed to be intimately related to flare energy release processes. However, their potential in diagnosing flare energy release has been greatly limited by the lack of simultaneous spatial information. The upgraded Karl G. Jansky Very Large Array (VLA) provides the first opportunity of radio synthesis imaging along with high spectral and temporal resolution, making the new technique of radio dynamic imaging spectroscopy possible. We report VLA observations of a solar flare event using this new technique, during which a rich variety of radio bursts are recorded. With the help of concurrent data in extreme ultra-violet and X-ray wavelengths, these observations allow us to establish the relation between the bursts and flare energy release, and use them to probe physical properties of the energy release site. Title: Advanced approaches to modeling and analysis of radio imaging data Authors: Fleishman, Gregory; Nita, Gelu; Gary, Dale Bibcode: 2014cosp...40E.878F Altcode: High-resolution imaging radio observations have an amazingly strong, but yet largely unexploited, potential for probing solar corona and chromosphere. The rich variety of radio emission processes offers multiple ways of detecting and tracking electron beams, studying chromospheric and coronal thermal structure, plasma processes, particle acceleration and transport, and measuring magnetic fields. Currently existing, real radio instruments have various kinds of imperfections that severely limit their diagnostics ability. Examples of the imperfections include a small number of spectral channels (low frequency resolution) or low (and frequency-dependent) spatial resolution. These and other issues call the practicality of the precise imaging diagnostics into question. To clarify this question the performance of a given radio instrument for quantitative diagnostics has to be properly evaluated, which can be done via realistic 3D modeling. This report presents advanced modeling and forward fitting tools, which are based on realistic (extrapolated) 3D magnetic structure and powerful, recently developed fast gyrosynchrotron and gyroresonant computing codes. We are going to demonstrate creation of a 3D model in real time and compute different emissions from this model—radio, EUV, and X-ray. Then, we show how this ‘ideal’ imaging data will look when folded with a point spread function of a given radio interferometer (Expanded Owens Valley Solar Array, EOVSA, to give a specific example), and finally apply pixel-by-pixel forward fitting to give a quantitative assessment of the EOVSA ability to derive the magnetic field, fast electron, and thermal plasma data from the imaging spectropolarimetry measurements. To conclude, we also present the diagnostics derived from the use of real OVSA/EOVSA imaging spectroscopy data and discuss the microwave diagnostics perspectives in a broader context of modern solar physics. Title: Mapping the 3D Coronal Magnetic Field and Temperature Structure Using Radio Techniques Authors: Gary, Dale; Fleishman, Gregory; Nita, Gelu; Wang, Zhitao Bibcode: 2014cosp...40E.945G Altcode: Solar radio emission is highly dependent on the magnetic field strength and direction in the corona, and at the same time provides a direct measure of electron temperature/energy. A variety of radiation mechanisms contribute to the emission, each with their own dependences, and which mechanism dominates in a particular circumstance is determined by electron energetics, magnetic field strength and direction, and density. The key to accessing the inherent diagnostic power of radio emission is to have multi-frequency radio images of sufficient quality, resolution, and polarization purity, with which to confidently identify and separate the different emission mechanisms, to remove the ambiguities that have limited many past radio studies. The technical challenge of obtaining high-quality, multi-frequency images is being addressed for the first time by a number of new radio instruments such as EOVSA, JVLA, CSRH, USSRT, and FASR, each of which are designed specifically for this purpose. This report emphasizes one of the more important applications—determining the three-dimensional coronal magnetic field and temperature structure of solar active regions. We illustrate the talk with new and accurate 3D modeling of radio emission and radiative transfer, based on the nonlinear force-free field extrapolation of vector magnetic field measurements, and describe the potent combination of new observations with forward fitting tools in development. Title: Future Trends in Solar Radio Astronomy and Coronal Magnetic-Field Measurements Authors: Fleishman, Gregory; Nita, Gelu; Gary, Dale Bibcode: 2014cosp...40E.877F Altcode: Solar radio astronomy has an amazingly rich, but yet largely unexploited, potential for probing the solar corona and chromosphere. Radio emission offers multiple ways of detecting and tracking electron beams, studying chromospheric and coronal thermal structure, plasma processes, particle acceleration, and measuring magnetic fields. To turn the mentioned potential into real routine diagnostics, two major components are needed: (1) well-calibrated observations with high spatial, spectral, and temporal resolutions and (2) accurate and reliable theoretical models and fast numerical tools capable of recovering the emission source parameters from the radio data. This report gives a brief overview of the new, expanded, and planned radio facilities, such as Expanded Owens Valley Solar Array (EOVSA), Jansky Very Large Array (JVLA), Chinese Solar Radio Heliograph (CSRH), Upgraded Siberian Solar Radio Telescope (USSRT), and Frequency Agile Solar Radiotelescope (FASR) with the emphasis on their ability to measure the coronal magnetic fields in active regions and flares. In particular, we emphasize the new tools for 3D modeling of the radio emission and forward fitting tools in development needed to derive the magnetic field data from the radio measurements. Title: Magnetography of Solar Flaring Loops with Microwave Imaging Spectropolarimetry Authors: Gary, D. E.; Fleishman, G. D.; Nita, G. M. Bibcode: 2013SoPh..288..549G Altcode: 2013arXiv1303.1573G We have developed a general framework for modeling gyrosynchrotron and free-free emission from solar flaring loops and used it to test the premise that 2D maps of source parameters, particularly the magnetic field, can be deduced from spatially resolved microwave spectropolarimetry data. We show quantitative results for a flaring loop with a realistic magnetic geometry, derived from a magnetic-field extrapolation, and containing an electron distribution with typical thermal and nonthermal parameters, after folding through the instrumental profile of a realistic interferometric array. We compare the parameters generated from forward-fitting a homogeneous source model to each line of sight through the folded image data cube both with the original parameters used in the model and with parameters generated from forward-fitting a homogeneous source model to the original (unfolded) image data cube. We find excellent agreement in general, but with systematic effects that can be understood as due to the finite resolution in the folded images and the variation of parameters along the line of sight, which are ignored in the homogeneous source model. We discuss the use of such 2D parameter maps within a larger framework of 3D modeling, and the prospects for applying these methods to data from a new generation of multifrequency radio arrays now or soon to be available. Title: Probing Dynamics of Electron Acceleration with Radio and X-Ray Spectroscopy, Imaging, and Timing in the 2002 April 11 Solar Flare Authors: Fleishman, Gregory D.; Kontar, Eduard P.; Nita, Gelu M.; Gary, Dale E. Bibcode: 2013ApJ...768..190F Altcode: 2013arXiv1303.4098F Based on detailed analysis of radio and X-ray observations of a flare on 2002 April 11 augmented by realistic three-dimensional modeling, we have identified a radio emission component produced directly at the flare acceleration region. This acceleration region radio component has distinctly different (1) spectrum, (2) light curves, (3) spatial location, and, thus, (4) physical parameters from those of the separately identified trapped or precipitating electron components. To derive evolution of physical parameters of the radio sources we apply forward fitting of the radio spectrum time sequence with the gyrosynchrotron source function with five to six free parameters. At the stage when the contribution from the acceleration region dominates the radio spectrum, the X-ray- and radio-derived electron energy spectral indices agree well with each other. During this time the maximum energy of the accelerated electron spectrum displays a monotonic increase with time from ~300 keV to ~2 MeV over roughly one minute duration indicative of an acceleration process in the form of growth of the power-law tail; the fast electron residence time in the acceleration region is about 2-4 s, which is much longer than the time of flight and so requires a strong diffusion mode there to inhibit free-streaming propagation. The acceleration region has a relatively strong magnetic field, B ~ 120 G, and a low thermal density, ne <~ 2 × 109 cm-3. These acceleration region properties are consistent with a stochastic acceleration mechanism. Title: Time delays between radio and HXR observed during the 2011-02-15 X2.2 solar flare Authors: Kuroda, Natsuha; Wang, Haimin; Gary, Dale Bibcode: 2013enss.confE..86K Altcode: We report the second-scale delays observed between radio and HXR during the X2.2 solar flare on February 15, 2011. The delays between different energy channels from various instruments were previously reported by Dolla et al. in 2012; they reported that the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) channels in the 25-100 keV range lead all the other channels including the Nobeyama RadioPolarimeters at 9 and 17 GHz and the Extreme Ultra-Violet (EUV) channels of the Euv SpectroPhotometer (ESP) onboard the Solar Dynamic Observatory (SDO). We looked at RHESSI channels in 25-250 keV and Nobeyama channels in 1-35 GHz and found that, in four data pairs that showed more than 80 % correlation, the same several RHESSI peaks lead Nobeyama peaks by few seconds. We discuss the possible physical meaning of this delay. Title: Tracing Electron Beams in the Sun's Corona with Radio Dynamic Imaging Spectroscopy Authors: Chen, Bin; Bastian, T. S.; White, S. M.; Gary, D. E.; Perley, R.; Rupen, M.; Carlson, B. Bibcode: 2013ApJ...763L..21C Altcode: 2012arXiv1211.3058C We report observations of type III radio bursts at decimeter wavelengths (type IIIdm bursts)—signatures of suprathermal electron beams propagating in the low corona—using the new technique of radio dynamic imaging spectroscopy provided by the recently upgraded Karl G. Jansky Very Large Array. For the first time, type IIIdm bursts were imaged with high time and frequency resolution over a broad frequency band, allowing electron beam trajectories in the corona to be deduced. Together with simultaneous hard X-ray and extreme ultraviolet observations, we show that these beams emanate from an energy release site located in the low corona at a height below ~15 Mm, and propagate along a bundle of discrete magnetic loops upward into the corona. Our observations enable direct measurements of the plasma density along the magnetic loops, and allow us to constrain the diameter of these loops to be less than 100 km. These overdense and ultra-thin loops reveal the fundamentally fibrous structure of the Sun's corona. The impulsive nature of the electron beams, their accessibility to different magnetic field lines, and the detailed structure of the magnetic release site revealed by the radio observations indicate that the localized energy release is highly fragmentary in time and space, supporting a bursty reconnection model that involves secondary magnetic structures for magnetic energy release and particle acceleration. Title: Observing the Sun at Radio Wavelengths: Current Status and Future Prospects Authors: Bastian, T.; Gary, D. Bibcode: 2012IAUSS...6E.215B Altcode: Radio emission from the Sun offers the means of probing thermal and non-thermal processes in the chromosphere and corona using diagnostics that are largely complementary to those available at optical wavelengths. This talk briefly reviews radio diagnostics and observing techniques and several of the science objectives motivating new and planned instrumentation, including coronal magnetography, magnetic energy release and particle acceleration, drivers of space weather, and the quiet solar atmosphere. New instrumentation includes ALMA, opening a new spectral window at millimeter and submillimeter wavelengths; and the Jansky Very Large Array (JVLA), a powerful new instrument operating at centimeter and decimeter wavelengths. A solar-dedicated instrument under construction is the Expanded Owens Valley Solar Array (EOVSA); and a planned, new, solar-dedicated facility is the Frequency Agile Solar Radiotelescope (FASR). EOVSA will soon pioneer dynamic imaging spectroscopy techniques. FASR will fully exploit these techniques as a general purpose radioheliograph designed to perform ultra-wideband dynamic imaging spectroscopy. Title: Integrated Idl Tool For 3d Modeling And Imaging Data Analysis Authors: Nita, Gelu M.; Fleishman, G. D.; Gary, D. E.; Kuznetsov, A. A.; Kontar, E. P. Bibcode: 2012AAS...22020451N Altcode: Addressing many key problems in solar physics requires detailed analysis of non-simultaneous imaging data obtained in various wavelength domains with different spatial resolution and their comparison with each other supplied by advanced 3D physical models. To facilitate achieving this goal, we have undertaken a major enhancement and improvements of IDL-based simulation tools developed earlier for modeling microwave and X-ray emission. The greatly enhanced object-based architecture provides interactive graphic user interface that allows the user i) to import photospheric magnetic field maps and perform magnetic field extrapolations to almost instantly generate 3D magnetic field models, ii) to investigate the magnetic topology of these models by interactively creating magnetic field lines and associated magnetic field tubes, iii) to populate them with user-defined nonuniform thermal plasma and anisotropic nonuniform nonthermal electron distributions; and iv) to calculate the spatial and spectral properties of radio and X-ray emission. The application integrates DLL and Shared Libraries containing fast gyrosynchrotron emission codes developed in FORTRAN and C++, soft and hard X-ray codes developed in IDL, and a potential field extrapolation DLL produced based on original FORTRAN code developed by V. Abramenko and V. Yurchishin. The interactive interface allows users to add any user-defined IDL or external callable radiation code, as well as user-defined magnetic field extrapolation routines. To illustrate the tool capabilities, we present a step-by-step live computation of microwave and X-ray images from realistic magnetic structures obtained from a magnetic field extrapolation preceding a real event, and compare them with the actual imaging data produced by NORH and RHESSI instruments.

This work was supported in part by NSF grants AGS-0961867, AST-0908344, AGS-0969761, and NASA grants NNX10AF27G and NNX11AB49G to New Jersey Institute of Technology, by a UK STFC rolling grant, the Leverhulme Trust, UK, and by the European Commission through the Radiosun and HESPE Networks. Title: Expanded Owens Valley Solar Array (EOVSA) Testbed and Prototype Authors: Gary, Dale E.; Nita, G. M.; Sane, N. Bibcode: 2012AAS...22020430G Altcode: NJIT is engaged in constructing a new solar-dedicated radio array, the Expanded Owens Valley Solar Array (EOVSA), which is slated for completion in late 2013. An initial 3-antenna array, the EOVSA Subsystem Testbed (EST), is now in operation from 1-9 GHz based on three of the old OVSA antennas, to test certain design elements of the new array. We describe this instrument and show some results from recent solar flares observed with it. We also describe plans for an upcoming prototype of EOVSA, which will use three antennas of the new design over the full 1-18 GHz signal chain of the entirely new system. The EOVSA prototype will be in operation by late 2012. Highlights of the new design are ability to cover the entire 1-18 GHz in less than 1 s, simultaneous dual polarization, and improved sensitivity and stability. We discuss what can be expected from the prototype, and how it will compare with the full 13-antenna EOVSA. This work was supported by NSF grants AGS-0961867 and AST-0908344, and NASA grant NNX11AB49G to New Jersey Institute of Technology. Title: Novel 3D Approach to Flare Modeling via Interactive IDL Widget Tools Authors: Nita, G. M.; Fleishman, G. D.; Gary, D. E.; Kuznetsov, A.; Kontar, E. P. Bibcode: 2011AGUFMSH44A..07N Altcode: Currently, and soon-to-be, available sophisticated 3D models of particle acceleration and transport in solar flares require a new level of user-friendly visualization and analysis tools allowing quick and easy adjustment of the model parameters and computation of realistic radiation patterns (images, spectra, polarization, etc). We report the current state of the art of these tools in development, already proved to be highly efficient for the direct flare modeling. We present an interactive IDL widget application intended to provide a flexible tool that allows the user to generate spatially resolved radio and X-ray spectra. The object-based architecture of this application provides full interaction with imported 3D magnetic field models (e.g., from an extrapolation) that may be embedded in a global coronal model. Various tools provided allow users to explore the magnetic connectivity of the model by generating magnetic field lines originating in user-specified volume positions. Such lines may serve as reference lines for creating magnetic flux tubes, which are further populated with user-defined analytical thermal/non thermal particle distribution models. By default, the application integrates IDL callable DLL and Shared libraries containing fast GS emission codes developed in FORTRAN and C++ and soft and hard X-ray codes developed in IDL. However, the interactive interface allows interchanging these default libraries with any user-defined IDL or external callable codes designed to solve the radiation transfer equation in the same or other wavelength ranges of interest. To illustrate the tool capacity and generality, we present a step-by-step real-time computation of microwave and X-ray images from realistic magnetic structures obtained from a magnetic field extrapolation preceding a real event, and compare them with the actual imaging data obtained by NORH and RHESSI instruments. We discuss further anticipated developments of the tools needed to accommodate temporal evolution of the magnetic field structure and/or fast electron population implied by the electron acceleration and transport. This work was supported in part by NSF grants AGS-0961867, AST-0908344, and NASA grants NNX10AF27G and NNX11AB49G to New Jersey Institute of Technology, by a UK STFC rolling grant, STFC/PPARC Advanced Fellowship, and the Leverhulme Trust, UK. Financial support by the European Commission through the SOLAIRE and HESPE Networks is gratefully acknowledged. Title: Three-dimensional Structure of Microwave Sources from Solar Rotation Stereoscopy Versus Magnetic Extrapolations Authors: Nita, Gelu M.; Fleishman, Gregory D.; Jing, Ju; Lesovoi, Sergey V.; Bogod, Vladimir M.; Yasnov, Leonid V.; Wang, Haimin; Gary, Dale E. Bibcode: 2011ApJ...737...82N Altcode: 2011arXiv1106.0262N We use rotation stereoscopy to estimate the height of a steady-state solar feature relative to the photosphere, based on its apparent motion in the image plane recorded over several days of observation. The stereoscopy algorithm is adapted to work with either one- or two-dimensional data (i.e., from images or from observations that record the projected position of the source along an arbitrary axis). The accuracy of the algorithm is tested on simulated data, and then the algorithm is used to estimate the coronal radio source heights associated with the active region NOAA 10956, based on multifrequency imaging data over seven days from the Siberian Solar Radio Telescope near 5.7 GHz, the Nobeyama Radio Heliograph at 17 GHz, as well as one-dimensional scans at multiple frequencies spanning the 5.98-15.95 GHz frequency range from the RATAN-600 instrument. The gyroresonance emission mechanism, which is sensitive to the coronal magnetic field strength, is applied to convert the estimated radio source heights at various frequencies, h(f), to information about magnetic field versus height B(h), and the results are compared to a magnetic field extrapolation derived from photospheric magnetic field observations obtained by Hinode and Michelson Doppler Imager. We found that the gyroresonant emission comes from heights exceeding the location of the third gyrolayer irrespective of the magnetic extrapolation method; implications of this finding for coronal magnetography and coronal plasma physics are discussed. Title: Spatially and Spectrally Resolved Observations of a Zebra Pattern in a Solar Decimetric Radio Burst Authors: Chen, Bin; Bastian, T. S.; Gary, D. E.; Jing, Ju Bibcode: 2011ApJ...736...64C Altcode: 2011arXiv1105.0715C We present the first interferometric observation of a zebra-pattern radio burst with simultaneous high spectral (≈1 MHz) and high time (20 ms) resolution. The Frequency-Agile Solar Radiotelescope Subsystem Testbed (FST) and the Owens Valley Solar Array (OVSA) were used in parallel to observe the X1.5 flare on 2006 December 14. By using OVSA to calibrate the FST, the source position of the zebra pattern can be located on the solar disk. With the help of multi-wavelength observations and a nonlinear force-free field extrapolation, the zebra source is explored in relation to the magnetic field configuration. New constraints are placed on the source size and position as a function of frequency and time. We conclude that the zebra burst is consistent with a double-plasma resonance model in which the radio emission occurs in resonance layers where the upper-hybrid frequency is harmonically related to the electron cyclotron frequency in a coronal magnetic loop. Title: New interactive solar flare modeling and advanced radio diagnostics tools Authors: Fleishman, Gregory D.; Nita, Gelu M.; Gary, Dale E. Bibcode: 2011IAUS..274..280F Altcode: 2010arXiv1011.0237F The coming years will see routine use of solar data of unprecedented spatial and spectral resolution, time cadence, and completeness in the wavelength domain. To capitalize on the soon to be available radio facilities such as the expanded OVSA, SSRT and FASR, and the challenges they present in the visualization and synthesis of the multi-frequency datasets, we propose that realistic, sophisticated 3D active region and flare modeling is timely now and will be a forefront of coronal studies over the coming years. Here we summarize our 3D modeling efforts, aimed at forward fitting of imaging spectroscopy data, and describe currently available 3D modeling tools. We also discuss plans for future generalization of our modeling tools. Title: Detection of the Acceleration Site in a Solar Flare Authors: Fleishman, Gregory D.; Kontar, E. P.; Nita, G. M.; Gary, D. E. Bibcode: 2011SPD....42.1203F Altcode: 2011BAAS..43S.1203F We report the observation of an unusual cold, tenuous solar flare (ApJL, v. 731, p. L19, 2011), which reveals itself via numerous and prominent non-thermal manifestations, while lacking any noticeable thermal emission signature. RHESSI hard X-rays and 0.1-18 GHz radio data from OVSA and Phoenix-2 show copious electron acceleration (1035 electrons per second above 10 keV) typical for GOES M-class flares with electrons energies up to 100 keV, but GOES temperatures not exceeding 6.1 MK. The HXR footpoints and coronal radio sources belong, supposedly, to a single magnetic loop, which departs strongly from the corresponding potential loop (obtained from a photospheric extrapolation) in agreement with the apparent need of a non-potential magnetic field structure to produce a flare. The imaging, temporal, and spectral characteristics of the flare have led us to a firm conclusion that the bulk of the microwave continuum emission from this flare was produced directly in the acceleration region. We found that the electron acceleration efficiency is very high in the flare, so almost all available thermal electrons are eventually accelerated. However, given a relatively small flaring volume and rather low thermal density at the flaring loop, the total energy release turned out to be insufficient for a significant heating of the coronal plasma or for a prominent chromospheric response giving rise to chromospheric evaporation. Some sort of stochastic acceleration process is needed to account for an approximately energy-independent lifetime of about 3 s for the electrons in the acceleration region.

This work was supported in part by NSF grants AGS-0961867, AST-0908344, and NASA grants NNX10AF27G and NNX11AB49G to New Jersey Institute of Technology. This work was supported by a UK STFC rolling grant, STFC/PPARC Advanced Fellowship, and the Leverhulme Trust, UK. Financial support by the European Commission through the SOLAIRE and HESPE Networks is gratefully acknowledged. Title: HXR and Microwave Spectroscopy of the X2.2 flare on February 15 2011 Authors: Xu, Yan; Park, S.; Gary, D. E.; Bong, S.; Jing, J.; Wang, H. Bibcode: 2011SPD....42.2203X Altcode: 2011BAAS..43S.2203X We present a spectroscopic study of an X-class flare observed on 2011 Feb. 15, which is confirmed as a white-light flare by HINODE/SOT continuum images. HXR observation of this flare was taken by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and radio observation was taken by the Korean Solar Radio Burst Locator (KSRBL).

During the 10 minute lifetime of this flare, four major temporal peaks have

been identified in both HXR and radio emissions. Spectra at each individual peak are obtained with a frequency range in microwave from 5 to 18 GHz and an energy range in HXR from 35 to 150 keV, respectively. The high cadence observations in HXR and microwave provide an unique tool to diagnose the properties of energetic electrons and their temporal evolution. In particular, we will present the result of electron power index as derived from these two wavelengths, and its peak-to-peak variation. Title: Three-dimensional Mapping of the Lower Corona and Transition Region Authors: Tun, Samuel D.; Gary, D. E. Bibcode: 2011SPD....42.0704T Altcode: 2011BAAS..43S.0704T Numerous studies have shown that temperature in the solar atmosphere rises abruptly from chromospheric to coronal values through a spatially thin transition region. Through the use of a novel method by which to obtain three-dimensional temperature and magnetic field strength maps of the lower corona and transition region from microwave observations [Tun, Gary & Georgoulis, 2011, ApJ 728, 1], a region of relatively cool material is found to extend to greater heights over the sunspot's umbra than in surrounding regions. While previous studies have occasionally pointed toward the existence of such material, this mapping represents a direct observation of this feature and of its three dimensional distribution above the sunspot. This distribution, in turn, has a direct application to the investigation of heat distribution in the higher corona, as evidence is presented that temperatures in different loop systems are correlated to the location of their footpoints in the sunspot. The mapping method itself also represents a test of the accuracy of magnetic field extrapolations.

This work was supported in part by NSF grants AGS-0961867, AST-0908344, and NASA grants NNX10AF27G and NNX11AB49G to New Jersey Institute of Technology. Title: Study of Magnetic Helicity Injection in the Active Region NOAA 11158 Associated with the X-class Flare of 2011 February 15 Authors: Park, Sung-Hong; Cho, K.; Kim, Y.; Bong, S.; Gary, D. E.; Park, Y. Bibcode: 2011SPD....42.2227P Altcode: 2011BAAS..43S.2227P The main objective of this study is to examine a long-term (a few days) precondition and a trigger mechanism for an X2.2 flare peaking at 01:56 UT on 2011 February 15 in GOES soft X-ray flux. For this, we investigated the variation of magnetic helicity injection through the photospheric surface of the flare-productive active region NOAA 11158 during (1) the long-term period of February 11 to 15 with a 1-hour cadence and (2) the short-term period of 01:26 to 02:10 UT on February 15 with a 45-second cadence. The helicity injection was determined using line-of-sight magnetograms with high spatial and temporal resolution taken by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). As a result, we found two characteristic phases of helicity injection related to the X2.2 flare. A large amount of positive helicity was first injected over 2 days with a phase of monotonically increasing helicity. And then the flare started simultaneously with a significant injection of the opposite (negative) sign of helicity around the flaring magnetic polarity inversion line. This observational finding clearly supports the previous studies that there is a continuous injection of helicity a few days before flares and a rapid injection of the helicity in the opposite sign into an existing helicity system triggers flares. Title: The Expanded Owens Valley Solar Array Authors: Gary, Dale E.; Hurford, G. J.; Nita, G. M.; White, S. M.; Tun, S. D.; Fleishman, G. D.; McTiernan, J. M. Bibcode: 2011SPD....42.0102G Altcode: 2011BAAS..43S.0102G The Expanded Owens Valley Solar Array (EOVSA) is now under construction near Big Pine, CA as a solar-dedicated microwave imaging array operating in the frequency range 1-18 GHz. The solar science to be addressed focuses on the 3D structure of the solar corona (magnetic field, temperature and density), on the sudden release of energy and subsequent particle acceleration, transport and heating, and on space weather phenomena. The project will support the scientific community by providing open data access and software tools for analysis of the data, to exploit synergies with on-going solar research in other wavelengths.

The New Jersey Institute of Technology (NJIT) is expanding OVSA from its previous complement of 7 antennas to a total of 15 by adding 8 new antennas, and will reinvest in the existing infrastructure by replacing the existing control systems, signal transmission, and signal processing with modern, far more capable and reliable systems based on new technology developed for the Frequency Agile Solar Radiotelescope (FASR). The project will be completed in time to provide solar-dedicated observations during the upcoming solar maximum in 2013 and beyond. We provide an update on current status and our preparations for exploiting the data through modeling and data analysis tools.

This research is supported by NSF grants AST-0908344, and AGS-0961867 and NASA grant NNX10AF27G to New Jersey Institute of Technology. Title: GX_Simulator: An Interactive Idl Widget Tool For Visualization And Simulation Of Imaging Spectroscopy Models And Data Authors: Nita, Gelu M.; Fleishman, G. D.; Gary, D. E.; Kuznetsov, A. A.; Kontar, E. P. Bibcode: 2011SPD....42.1811N Altcode: 2011BAAS..43S.1811N An interactive IDL widget application intended to provide a flexible tool that allows the user to generate spatially resolved radio and/or X-ray spectra is presented. The object-based architecture of this application provides full interaction with local 3D magnetic field models (e.g., from an extrapolation) that may be embedded in a global coronal model. Various tools provided allow users to explore the magnetic connectivity of the model by generating magnetic field lines originating in user-specified volume positions. Such lines may serve as reference lines for creating magnetic flux tubes, which are further populated with user-defined analytical thermal/non thermal particle distribution models. By default, the application integrates IDL callable DLL and Shared libraries containing fast GS emission codes developed in FORTRAN and C++ and soft and hard X-ray codes developed in IDL. However, the interactive interface allows interchanging these default libraries with any user-defined IDL or external callable codes designed to solve the radiation transfer equation in the same or other wavelength ranges of interest. We illustrate the tool capacity and generality by a real-time computation of microwave and X-ray images from realistic magnetic structures obtained from nonlinear force-free field extrapolations.

This work was supported in part by NSF grants AGS-0961867, AST-0908344, and NASA grants NNX10AF27G and NNX11AB49G to New Jersey Institute of Technology, by a UK STFC rolling grant, STFC/PPARC Advanced Fellowship, and the Leverhulme Trust, UK. Financial support by the European Commission through the SOLAIRE and HESPE Networks is gratefully acknowledged. Title: A Cold, Tenuous Solar Flare: Acceleration Without Heating Authors: Fleishman, Gregory D.; Kontar, Eduard P.; Nita, Gelu M.; Gary, Dale E. Bibcode: 2011ApJ...731L..19F Altcode: 2011arXiv1103.2705F We report the observation of an unusual cold, tenuous solar flare, which reveals itself via numerous and prominent non-thermal manifestations, while lacking any noticeable thermal emission signature. RHESSI hard X-rays and 0.1-18 GHz radio data from OVSA and Phoenix-2 show copious electron acceleration (1035 electrons s-1 above 10 keV) typical for GOES M-class flares with electrons energies up to 100 keV, but GOES temperatures not exceeding 6.1 MK. The imaging, temporal, and spectral characteristics of the flare have led us to a firm conclusion that the bulk of the microwave continuum emission from this flare was produced directly in the acceleration region. The implications of this finding for the flaring energy release and particle acceleration are discussed. Title: Three-dimensional Structure of a Solar Active Region from Spatially and Spectrally Resolved Microwave Observations Authors: Tun, Samuel D.; Gary, Dale E.; Georgoulis, Manolis K. Bibcode: 2011ApJ...728....1T Altcode: We report on the structure of the solar atmosphere above active region (AR) 10923, observed on 2006 November 10, as deduced from multi-wavelength studies including combined microwave observations from the Very Large Array (VLA) and the Owens Valley Solar Array (OVSA). The VLA observations provide excellent image quality at a few widely spaced frequencies, while the OVSA data provide information at many intermediate frequencies to fill in the spectral coverage. Images at 25 distinct frequencies are used to provide spatially resolved spectra along many lines of sight in the AR, from which microwave spectral diagnostics are obtained for deducing maps of temperature, magnetic field, and column density. The derived quantities are compared with multiwavelength observations from the Solar and Heliospheric Observatory and Hinode spacecraft, and with a current-free magnetic field extrapolation. We find that a two-component temperature model is required to fit the data, in which a hot (>2 MK) lower corona above the strong-field plage and sunspot regions (emitting via the gyroresonance process) is overlaid with somewhat cooler (~1 MK) coronal loops that partially absorb the gyroresonance emission through the free-free (Bremsstrahlung) process. We also find that the extrapolated potential magnetic fields can quantitatively account for the observed gyroresonance emission over most of the AR, but in a few areas a higher field strength is required. The results are used to explore the coronal configuration needed to explain the observations. These results show that the bulk of free-free emission in both radio and X-rays emanates from two loop systems, distinguished by the location of their loop footpoints. We discuss the implications of such comparisons for studies of AR structure when better microwave spectral imaging becomes available in the future. Title: Uncovering Mechanisms of Coronal Magnetism via Advanced 3D Modeling of Flares and Active Regions Authors: Fleishman, Gregory; Gary, Dale; Nita, Gelu; Alexander, David; Aschwanden, Markus; Bastian, Tim; Hudson, Hugh; Hurford, Gordon; Kontar, Eduard; Longcope, Dana; Mikic, Zoran; DeRosa, Marc; Ryan, James; White, Stephen Bibcode: 2010arXiv1011.2800F Altcode: The coming decade will see the routine use of solar data of unprecedented spatial and spectral resolution, time cadence, and completeness. To capitalize on the new (or soon to be available) facilities such as SDO, ATST and FASR, and the challenges they present in the visualization and synthesis of multi-wavelength datasets, we propose that realistic, sophisticated, 3D active region and flare modeling is timely and critical, and will be a forefront of coronal studies over the coming decade. To make such modeling a reality, a broad, concerted effort is needed to capture the wealth of information resulting from the data, develop a synergistic modeling effort, and generate the necessary visualization, interpretation and model-data comparison tools to accurately extract the key physics. Title: The generalized spectral kurtosis estimator Authors: Nita, G. M.; Gary, D. E. Bibcode: 2010MNRAS.406L..60N Altcode: 2010arXiv1005.4371N; 2010MNRAS.tmpL..83N Due to its conceptual simplicity and its proven effectiveness in real-time detection and removal of radio frequency interference (RFI) from radio astronomy data, the spectral kurtosis (SK) estimator is likely to become a standard tool of a new generation of radio telescopes. However, the SK estimator in its original form must be developed from instantaneous power spectral density estimates, and hence cannot be employed as an RFI excision tool downstream of the data pipeline in existing instruments where any time averaging is performed. In this Letter, we develop a generalized estimator with wider applicability for both instantaneous and averaged spectral data, which extends its practical use to a much larger pool of radio instruments. Title: Statistics of the Spectral Kurtosis Estimator Authors: Nita, G.; Gary, D. Bibcode: 2010rfim.workE..19N Altcode: 2010PoS...107E..19N No abstract at ADS Title: Statistics of the Spectral Kurtosis Estimator Authors: Nita, Gelu M.; Gary, Dale E. Bibcode: 2010PASP..122..595N Altcode: Spectral kurtosis (SK) is a statistical approach for detecting and removing radio-frequency interference (RFI) in radio astronomy data. In this article, the statistical properties of the SK estimator are investigated and all moments of its probability density function are analytically determined. These moments provide a means to determine the tail probabilities of the estimator that are essential to defining the thresholds for RFI discrimination. It is shown that, for a number of accumulated spectra M≥24, the first SK standard moments satisfy the conditions required by a Pearson type IV probability density function (pdf), which is shown to accurately reproduce the observed distributions. The cumulative function (CF) of the Pearson type IV is then found, in both analytical and numerical forms, suitable for accurate estimation of the tail probabilities of the SK estimator. This same framework is also shown to be applicable to the related time-domain kurtosis (TDK) estimator, whose pdf corresponds to Pearson type IV when the number of time-domain samples is M≥46. The pdf and CF also are determined for this case. Title: A Wideband Spectrometer with RFI Detection Authors: Gary, Dale E.; Liu, Zhiwei; Nita, Gelu M. Bibcode: 2010PASP..122..560G Altcode: We report on the design and construction of a wideband spectrometer of 500 MHz instantaneous bandwidth that includes automatic radio frequency interference (RFI) detection. The implementation is based on hardware developed at the Center for Astronomical Signal Processing and Electronics Research (CASPER). The unique aspect of the spectrometer is that it accumulates both power and power-squared, which are then used to develop a spectral kurtosis (SK) estimator. The SK estimator statistics are used for real-time detection and excision of certain types of RFI embedded in the received signal. We report on the use of this spectrometer in the Korean Solar Radio Burst Locator (KSRBL). This instrument utilizes four of these 500 MHz bandwidth SK spectrometers in parallel, to achieve a 2 GHz instantaneous bandwidth that is time multiplexed over the entire 0.24-18 GHz radio frequency range, to study solar bursts. The performance of the spectrometers for excising RFI over this range is presented. It is found that the algorithm is especially useful for excising highly intermittent RFI but is less successful for RFI due to digital signals. A method we call multiscale SK is presented that addresses the known blindness of Kurtosis-based estimators to 50% duty-cycle RFI. The SK algorithm can also be applied to spectral channels prior to correlation to remove unwanted RFI from interferometer data. Title: Erratum: A Wideband Spectrometer with RFI Detection by Dale E. Gary, Zhiwei Liu, and Gelu M. Nita (PASP, 122, 560, [2010]) Authors: Gary, Dale E.; Liu, Zhiwei; Nita, Gelu, M. Bibcode: 2010PASP..122..743G Altcode: 2010PASP..122..743. In the paper ``A Wideband Spectrometer with RFI Detection'' by Dale E. Gary, Zhiwei Liu, and Gelu M. Nita (PASP, 122, 560, [2010]), Figure 9 was omitted and Figure appeared twice as a result of an error in the production process. The correct figures and their legends appear below.

The Press sincerely regrets this error. Title: Hardware Implementation of an SK Spectrometer Authors: Gary, D.; Li, Z.; Nita, G. Bibcode: 2010rfim.workE..20G Altcode: 2010PoS...107E..20G No abstract at ADS Title: Expanded Owens Valley Solar Array Science and Data Products Authors: Gary, Dale E.; Hurford, G. J.; Nita, G. M.; Fleishman, G. D.; McTiernan, J. M. Bibcode: 2010AAS...21640520G Altcode: 2010BAAS...41..892G The Owens Valley Solar Array (OVSA) has been funded for major expansion, to create a university-based facility serving a broad scientific community, to keep the U.S. competitive in the field of solar radio physics. The project, funded by the National Science Foundation through the MRI-Recovery and Reinvestment program, will result in a world-class facility for scientific research at microwave radio frequencies (1-18 GHz) in solar and space weather physics. The project also includes an exciting program of targeted astronomical science. The solar science to be addressed focuses on the magnetic structure of the solar corona, on transient phenomena resulting from magnetic interactions, including the sudden release of energy and subsequent particle acceleration and heating, and on space weather phenomena. The project will support the scientific community by providing open data access and software tools for analysis of the data, to exploit synergies with on-going solar research in other wavelength bands.

The New Jersey Institute of Technology (NJIT) will upgrade OVSA from its current complement of 7 antennas to a total of 15 by adding 8 new antennas, and will reinvest in the existing infrastructure by replacing the existing control systems, signal transmission, and signal processing with modern, far more capable and reliable systems based on new technology developed for the Frequency Agile Solar Radiotelescope (FASR). The project will be completed in time to provide solar-dedicated observations during the upcoming solar maximum in 2013 and beyond. We will detail the new science addressed by the expanded array, and provide an overview of the expected data products. Title: Spatially and Spectrally Resolved Observations of a "Zebra” Solar Radio Burst Authors: Bastian, Timothy S.; Chen, B.; Gary, D. E. Bibcode: 2010AAS...21542201B Altcode: 2010BAAS...42..291B The FASR Subsystems Testbed (FST) is a frequency-agile three-element interferometer located at the Owens Valley Radio Observatory in California. A frequency band of 500 MHz can be dynamically selected within the 1-9 GHz frequency FST operating range. The signal from each antenna is sampled at 1 Gsps and written to disk. The full-resolution time-domain data are then correlated offline to produce amplitude and phase spectra on three interferometric baselines. The FST was used on 14 December 2006 to observe the GOES X1.5 soft X-ray flare in NOAA/USAF active region 10930 at S06W46. The FST observed the event between 1.0-1.5 GHz with a time resolution of 20 ms and a frequency resolution of approximately 1 MHz, time sharing between observations sensitive to right- and left-circularly polarized radiation. A variety of coherent radio bursts was observed, including a highly circularly polarized "Zebra” burst characterized by 7-10 regularly spaced bands of emission in the dynamic spectrum. With new constraints available on the source size and the relative source position as a function of frequency, the double-plasma resonance model is explored, wherein emission in a given band occurs at the upper hybrid frequency that is, in turn, harmonically related to the local electron cyclotron frequency. Title: Statistical Hypothesis Testing and Variance Analysis for Radio Frequency Interference Identification in Solar Data Authors: Wang, Xiaoli; Ge, Hongya; Gary, Dale E.; Nita, Gelu M. Bibcode: 2009PASP..121.1139W Altcode: This work presents an effective algorithm for radio frequency interference (RFI) identification using dynamic power spectrum statistics in the frequency domain. Statistical signal processing techniques such as hypothesis testing and variance analysis are utilized to derive a test statistic for effective and efficient RFI identification. Starting from the generalized likelihood ratio test (GLRT), we formulate the problem systematically and propose a practical test statistic T(x f), shown to be distributed, for RFI identification. A threshold approach working on this test statistic is developed to identify the presence of narrowband RFI in the power spectrum with additive Gaussian noise and/or solar flare background, corresponding to a desired constant false alarm rate (CFAR). Detailed analysis on detector performance and effect of RFI duty cycle are also provided. The proposed statistical test is applied to experimental solar data collected by our frequency-agile solar radio telescope (FASR) subsystem testbed (FST) to demonstrate the robustness and scalability of the algorithm, as well as its capability for real-time implementation. Title: Global Positioning System and solar radio burst forensics Authors: Kintner, P. M.; O'Hanlon, B.; Gary, D. E.; Kintner, P. M. S. Bibcode: 2009RaSc...44.0A08K Altcode: On 6 December 2006, a solar radio burst associated with a class X6 solar flare demonstrated that GPS receiver operation is vulnerable to solar radio burst noise at 1.2 GHz and 1.6 GHz. Within 8 days, two more solar radio bursts confirmed the initial results. These solar radio bursts occurred at solar minimum when they were least expected. Given that measurements of solar radio bursts extend back to at least 1960, why did 40 years pass before anyone realized that solar radio bursts could be so intense or pose a potential threat to the continuous availability of GPS operations? An investigation has been conducted to see if archived solar radio burst data or GPS data could be used to detect intense solar radio bursts. With the exception of the intense solar radio bursts of December 2006, we find that when both GPS data and Radio Solar Telescope Network (RSTN) data are available, they agree within the limits presented by differing reception frequencies and unknown polarization. However, inconsistencies and lapses within the RSTN data set were also discovered, making it unlikely that we will ever know the true number of intense (>150,000 solar flux unit) solar radio bursts that may have occurred during the last 40 years. Title: Dynamic Magnetography of Solar Flaring Loops Authors: Fleishman, Gregory D.; Nita, Gelu M.; Gary, Dale E. Bibcode: 2009ApJ...698L.183F Altcode: 2009arXiv0906.0192F We develop a practical forward fitting method based on the SIMPLEX algorithm with shaking, which allows the derivation of the magnetic field and other parameters along a solar flaring loop using microwave imaging spectroscopy of gyrosynchrotron emission. We illustrate the method using a model loop with spatially varying magnetic field, filled with uniform ambient density and an evenly distributed fast electron population with an isotropic, power-law energy distribution. Title: Dynamic Magnetography of Solar Flaring Loops Authors: Fleishman, Gregory D.; Nita, G. M.; Gary, D. E. Bibcode: 2009SPD....40.1522F Altcode: The coronal magnetic field is a key parameter controlling most solar flaring activity, particle acceleration and transport. However, unlike photospheric and chromospheric magnetography data, there is currently a clear lack of quantitative information on the coronal magnetic field in the dynamically flaring region, which complicates the detailed modeling of fundamental physical processes occurring in the corona. It has been understood, and often proposed, that the coronal magnetic field can in principle be evaluated from the microwave gyrosynchrotron radiation, which is indeed sensitive to the instantaneous magnetic field strength and orientation relative to the line of sight.

Anticipating a large breakthrough in the radio imaging spectroscopy observations, which will become possible soon due to the next generation of the radio instruments, we develop a practical forward fitting method based on the SIMPLEX algorithm with shaking that allows reliable derivation of the magnetic field and other parameters along a solar flaring loop using microwave imaging spectroscopy of gyrosynchrotron emission. We illustrate the method using a model loop (the subject of another presentation at this meeting, Nita et al., abstract # 09-A-57-SPD40) with spatially varying magnetic field, filled with uniform ambient density and an evenly distributed fast electron population with an isotropic, power-law energy distribution.

This work was supported in part by NSF grants AST-0607544 and ATM-0707319 and NASA grant NNG06GJ40G to New Jersey Institute of Technology Title: Electron Energy and Magnetic Field Derived from Solar Microwave Burst Spectra Authors: Lee, Jeongwoo; Nita, Gelu M.; Gary, Dale E. Bibcode: 2009ApJ...696..274L Altcode: Microwave bursts during solar flares are known to be sensitive to high-energy electrons and magnetic field, both of which are important ingredients of solar flare physics. This paper presents such information derived from the microwave bursts of the 412 flares that were measured with the Owens Valley Solar Array. We assumed that these bursts are predominantly due to gyrosynchrotron radiation by nonthermal electrons in a single power-law energy distribution to use the simplified formulae for gyrosynchrotron radiation in the data analysis. A second major assumption was that statistical properties of flare electrons derived from this microwave database should agree with an earlier result based on the hard X-ray burst spectrometer on Solar Maximum Mission. Magnetic field information was obtained in the form of a scaling law between the average magnetic field and the total source area, which turns out to be a narrow distribution around ~400 G. The derived nonthermal electron energy is related to the peak flux, peak frequency, and spectral index, through a multistep regression fit, which can be used for a quick estimate for the nonthermal electron energy from spatially integrated microwave spectral observations. Title: Spatial Locations of Solar Decimetric Bursts at Spectrographic Resolution Authors: Gary, Dale E.; Naqvi, M. Bibcode: 2009SPD....40.1927G Altcode: Several large (X-class) solar flares occurred in 2006 December that included strong decimetric components displaying several burst types, including zebra bursts, spike bursts, fiber bursts, pulsations, and others. The bursts were observed with the FASR Subsystem Testbed (FST---a prototype system for the Frequency Agile Solar Radiotelescope), which is operating at Owens Valley Radio Observatory. The FST, described in Liu et al. (2007), PASP 119, 303, is a three-element interferometer with spectrograph-like frequency and time resolution, and so is able to locate burst centroids with unprecedented temporal and spectral resolution. Using FST, with some assumptions, we are able to place different types of burst spatially in context with Hinode and TRACE data taken at the same time. The spatial placement of burst types within the magnetic structure extrapolated from Hinode SOT-SP vector field measurements for 2006 December 14 constrains the physical mechanisms responsible for them. We discuss the implications of these results in the context of the true spectral imaging that will be available with the full FASR. Title: Evaluating Mean Magnetic Field in Flare Loops Authors: Qiu, Jiong; Gary, D. E.; Fleishman, G. D. Bibcode: 2009SPD....40.1906Q Altcode: We apply a new method to measure the mean magnetic field in flare loops by analyzing multiple-wavelength observations of a two-ribbon flare. The flare exhibits apparent expansion motion of the ribbons in the lower-atmosphere and rising motion of the top of newly formed flare loops observed in X-rays. These apparent motion patterns are signatures of progressive magnetic reconnection proceeding in a macroscopically organized manner, which may be approximated by a 2D model. Therefore, the reconnection rate is expressed in terms of the reconnection electric field E. As the reconnection flux along the newly formed flare loop is conserved, the relation holds that, when averaged over time, E = VrBr = VtBt, where Vr and Br refer to the ribbon expansion speed and magnetic field swept by the ribbons, and Vt and Bt denote the apparent rising speed of the X-ray source and mean magnetic field at the loop top. By directly measuring Vr, Br, and Vt, we find Bt to be 120 and 60 G, respectively, during two emission peaks 5 min apart in the impulsive phase. An estimate of magnetic field in flare loops is also achieved by analyzing the microwave and hard X-ray spectral observations, yielding B = 250, 120 G at the two emission peaks, respectively. The measured B from the microwave spectrum is an appropriately weighted value of magnetic field from the loop top to the loop leg. Therefore, the two methods to evaluate magnetic field in flaring loops produce fully consistent results, which provides evidence that parameters of reconnection rate derived from ribbon motions are quantitatively valid.

This work is supported by NSF grant and by NSF grant ATM-0748428 and NASA grant NNX08AE44G to Montana State University and NSF grants AST-0607544 and ATM-0707319 and NASA grant NNG06GJ40G to New Jersey Institute of Technology. Title: A Kinetic Model for the Radio CME Authors: Lee, Jeongwoo; Gary, D. E. Bibcode: 2009SPD....40.2209L Altcode: Current studies on Coronal Mass Ejections (CMEs) are mostly concentrated on their macroscopic properties as measured on White-Light images. On the other hand, radio emissions from CMEs carry the information of high energy particles associated with them, but usually without spatial information. In this regard, the rare radio maps of the 1998 April 20 CME obtained with the Nancay radioheliograph between 164 and 432 MHz (called a radio CME by Bastian et al. in 2001) offer an exceptional opportunity to explore the spatial distribution of high energy electrons inside the CME loop. We present a detailed kinetic model for the radio CME employing the lower hybrid (LH) waves excited by the CME shock as the primary electron acceleration mechanism, and magnetic mirroring and Coulomb collisions as the propagation effects inside the expanding loop. The main constraint in this modeling comes from the fact that the LH waves accelerate electrons parallel to the magnetic field and the accelerated electrons should gain, during propagation, sufficient amount of the perpendicular momentum to emit the synchrotron radiation as observed. The relative magnetic field variation responsible for the magnetic mirroring is inferred from the geometrical shape of the CME on the images of the Large Angle and Spectrometric Coronagraph Experiment (LASCO), and the field strength and the amplitude of the LH waves are determined from the observed radio spectra. The modeling is focused on the spatial distribution of the LH waves most plausible to explain the radio maps, and the result is discussed in relation to the associated shock property. Title: GS-3D Simulator: An Interactive IDL Widget Tool for Simulating Spatially Resolved Gyrosynchrotron Spectra Emitted by Solar Radio Bursts Authors: Nita, Gelu M.; Fleishman, G. D.; Gary, D. E. Bibcode: 2009SPD....40.1524N Altcode: An interactive IDL widget application intended to provide a flexible tool that allows the user to generate spatially resolved gyrosynchrotron spectra is presented. The object-based architecture of this application provides full 3D interaction with a user-specified magnetic loop geometry. Alternatively, the user may define and pass to the same interface arbitrary analytical or numerical models, including those derived from magnetic field extrapolation, provided that they inherit the generic properties of the base class defined in this package. The default code generating the GS emission from the input geometrical model was developed in FORTRAN based on the Petrosian-Klein approximation, and compiled as a DLL callable by IDL. However, the interactive interface allows interchanging this default library with any user-defined callable code. To illustrate the concept, a simple dipole magnetic loop object is analytically defined, and GS radio maps at 100 frequencies in the 1-100 GHz frequency range are produced. Similar maps produced by this tool were used as input test data in a forward-fitting algorithm that makes the subject of another presentation at this meeting (Fleishman et al. 09-D-83-SPD40).

This work was supported by NSF grants AST-0607544 and ATM-0707319 and NASA grant NNG06GJ40G to New Jersey Institute of Technology. Title: The Korean Solar Radio Burst Locator (KSRBL) Authors: Dou, Yujiang; Gary, Dale E.; Liu, Zhiwei; Nita, Gelu M.; Bong, Su-Chan; Cho, Kyung-Suk; Park, Young-Deuk; Moon, Yong-Jae Bibcode: 2009PASP..121..512D Altcode: This paper describes the design and operation of the Korean Solar Radio Burst Locator (KSRBL). The KSRBL is a radio spectrometer designed to observe solar decimeter and microwave bursts over a wide band (0.245-18 GHz) as well as to detect the burst locations without interferometry or mechanical sweeping. As a prototype, it is temporarily observing at the Owens Valley Radio Observatory (OVRO), California, USA, and after commissioning will be operated at the Korea Astronomy and Space Science Institute (KASI), Daejeon, Republic of Korea. The control system can agilely choose four 500 MHz intermediate frequency (IF) bands (2 GHz instantaneous bandwidth) from the entire 0.245-18 GHz band, with a standard time resolution of 100 ms, although higher time resolution is possible subject to data-rate constraints. To cover the entire band requires 10 tunings, which are therefore completed in 1 s. Each 500 MHz band is sampled at a 1 GS s-1 (gigasample per second) rate, and 4096 time samples are Fast Fourier transformed (FFT) to 2048 subchannels for a frequency resolution of 0.24 MHz. To cover the entire range also requires two different feeds, a dual-frequency Yagi centered at 245 and 410 MHz, and a broadband spiral feed covering 0.5-18 GHz. The dynamic range is 35 dB over the 0.5-18 GHz band, and 55 dB in the 245 and 410 MHz bands, set by using switchable attenuators in steps of 5 dB. Each 500 MHz IF has a further 63 dB of settable analog attenuation. The characteristics of the spiral feed provide the ability to locate flaring sources on the Sun to typically 2‧. The KSRBL will provide a broadband view of solar bursts for the purposes of studying solar activity for basic research, and for monitoring solar activity as the source of Space Weather and solar-terrestrial effects. Title: Evaluating Mean Magnetic Field in Flare Loops Authors: Qiu, Jiong; Gary, Dale E.; Fleishman, Gregory D. Bibcode: 2009SoPh..255..107Q Altcode: We analyze multiple-wavelength observations of a two-ribbon flare exhibiting apparent expansion motion of the flare ribbons in the lower atmosphere and rising motion of X-ray emission at the top of newly-formed flare loops. We evaluate magnetic reconnection rate in terms of VrBr by measuring the ribbon-expansion velocity (Vr) and the chromospheric magnetic field (Br) swept by the ribbons. We also measure the velocity (Vt) of the apparent rising motion of the loop-top X-ray source, and estimate the mean magnetic field (Bt) at the top of newly-formed flare loops using the relation «VtBt»≈«VrBr», namely, conservation of reconnection flux along flare loops. For this flare, Bt is found to be 120 and 60 G, respectively, during two emission peaks five minutes apart in the impulsive phase. An estimate of the magnetic field in flare loops is also achieved by analyzing the microwave and hard X-ray spectral observations, yielding B=250 and 120 G at the two emission peaks, respectively. The measured B from the microwave spectrum is an appropriately-weighted value of magnetic field from the loop top to the loop leg. Therefore, the two methods to evaluate coronal magnetic field in flaring loops produce fully-consistent results in this event. Title: Digital Instrumentation for the Radio Astronomy Community Authors: Parsons, Aaron; Werthimer, Dan; Backer, Donald; Bastian, Tim; Bower, Geoffrey; Brisken, Walter; Chen, Henry; Deller, Adam; Filiba, Terry; Gary, Dale; Greenhill, Lincoln; Hawkins, David; Jones, Glenn; Langston, Glen; Lasio, Joseph; Van Leeuwen, Joeri; Mitchell, Daniel; Manley, Jason; Siemion, Andrew; So, Hayden Kwok-Hay; Whitney, Alan; Woody, Dave; Wright, Melvyn; Zarb-Adami, Kristian Bibcode: 2009astro2010T..21P Altcode: 2009arXiv0904.1181P Time-to-science is an important figure of merit for digital instrumentation serving the astronomical community. A digital signal processing (DSP) community is forming that uses shared hardware development, signal processing libraries, and instrument architectures to reduce development time of digital instrumentation and to improve time-to-science for a wide variety of projects. We suggest prioritizing technological development supporting the needs of this nascent DSP community. After outlining several instrument classes that are relying on digital instrumentation development to achieve new science objectives, we identify key areas where technologies pertaining to interoperability and processing flexibility will reduce the time, risk, and cost of developing the digital instrumentation for radio astronomy. These areas represent focus points where support of general-purpose, open-source development for a DSP community should be prioritized in the next decade. Contributors to such technological development may be centers of support for this DSP community, science groups that contribute general-purpose DSP solutions as part of their own instrumentation needs, or engineering groups engaging in research that may be applied to next-generation DSP instrumentation. Title: A Wideband Spectrometer with Automatic RFI Detection Authors: Gary, Dale E.; Liu, Zhiwei; Nita, Gelu M. Bibcode: 2009ursi.confE..30G Altcode: No abstract at ADS Title: Particle Acceleration and Transport on the Sun Authors: Bastian, T. S.; Emslie, G.; Fleishman, G.; Gary, D. E.; Holman, G.; Hudson, H.; Hurford, G.; Krucker, S.; Lee, J.; Miller, J.; White, S. Bibcode: 2009astro2010S..13B Altcode: No abstract at ADS Title: Erratum: Peak Frequency Dynamics in Solar Microwave Bursts Authors: Melnikov, V. F.; Gary, Dale E.; Nita, Gelu M. Bibcode: 2008SoPh..253...75M Altcode: 2008SoPh..tmp..187M No abstract at ADS Title: Peak Frequency Dynamics in Solar Microwave Bursts Authors: Melnikov, V. F.; Gary, Dale E.; Nita, Gelu M. Bibcode: 2008SoPh..253...43M Altcode: 2008SoPh..tmp..180M We analyze the dynamics of the broadband frequency spectrum of 338 microwave bursts observed in the years 2001 - 2002 with the Owens Valley Solar Array. A subset of 38 strong microwave bursts that show a single spectral maximum are studied in detail. Our main goal is to study changes in spectral peak frequency νpk with time. We show that, for a majority of these simple bursts, the peak frequency shows a high positive correlation with flux density - it increases on the rise phase in ≈83% of 24 bursts where it could be cleanly measured, and decreases immediately after the peak time in ≈62% of 34 bursts. This behavior is in qualitative agreement with theoretical expectations based on gyrosynchrotron self-absorption. However, for a significant number of events (≈30 - 36%) the peak frequency variation is much smaller than expected from self-absorption, or may be entirely absent. The observed temporal behavior of νpk is compared with a simple model of gyrosynchrotron radio emission. We show that the anomalous behavior is well accounted for by the effects of Razin suppression, and further show how an analysis of the temporal evolution of νpk can be used to uniquely determine the relative importance of self-absorption and Razin suppression in a given burst. The analysis technique provides a new, quantitative diagnostic for the gyrosynchrotron component of solar microwave bursts. Applying this analysis technique to our sample of bursts, we find that in most of the bursts (60%) the spectral dynamics of νpk around the time of peak flux density is caused by self-absorption. On the other hand, for a significant number of events (≈70%), the Razin effect may play the dominant role in defining the spectral peak and dynamics of νpk, especially on the early rise phase and late decay phase of the bursts. Title: Spike Decomposition Technique: Modeling and Performance Tests Authors: Nita, Gelu M.; Fleishman, Gregory D.; Gary, Dale E. Bibcode: 2008ApJ...689..545N Altcode: We develop an automated technique for fitting the spectral components of solar microwave spike bursts, which are characterized by narrowband spectral features. The algorithm is especially useful for periods when the spikes occur in densely packed clusters, where the algorithm is capable of decomposing overlapping spike structures into individual spectral components. To test the performance and applicability limits of this data reduction tool, we perform comprehensive modeling of spike clusters characterized by various typical bandwidths, spike densities, and amplitude distributions. We find that, for a wide range of favorable combinations of input parameters, the algorithm is able to recover the characteristic features of the modeled distributions within reasonable confidence intervals. Having model-tested the algorithm against spike overlap, broadband spectral background, noise contamination, and possible malfunction of some spectral channels, we apply the technique to a spike cluster recorded by the Chinese Purple Mountain Observatory (PMO) spectrometer, operating above 4.5 GHz. We study the variation of the spike distribution parameters, such as amplitude, bandwidth, and related derived physical parameters, as a function of time. The method can be further applied to observations from other instruments and to other types of fine structures. Title: Broadband Quasi-periodic Radio and X-Ray Pulsations in a Solar Flare Authors: Fleishman, Gregory D.; Bastian, T. S.; Gary, Dale E. Bibcode: 2008ApJ...684.1433F Altcode: 2008arXiv0804.4037F We describe microwave and hard X-ray observations of strong quasi-periodic pulsations from the GOES X1.3 solar flare on 2003 June 15. The radio observations were made jointly by the Owens Valley Solar Array (OVSA), the Nobeyama Polarimeter (NoRP), and the Nobeyama Radioheliograph (NoRH). Hard X-ray observations were made by RHESSI. Using Fourier analysis, we study the frequency- and energy-dependent oscillation periods, differential phase, and modulation amplitudes of the radio and X-ray pulsations. Focusing on the more complete radio observations, we also examine the modulation of the degree of circular polarization and of the radio spectral index. The observed properties of the oscillations are compared with those derived from two simple models for the radio emission. In particular, we explicitly fit the observed modulation amplitude data to the two competing models. The first model considers the effects of MHD oscillations on the radio emission. The second model considers the quasi-periodic injection of fast electrons. We demonstrate that quasi-periodic acceleration and injection of fast electrons is the more likely cause of the quasi-periodic oscillations observed in the radio and hard X-ray emission, which has important implications for particle acceleration and transport in the flaring sources. Title: Parallel Motions of Coronal Hard X-Ray Source and Hα Ribbons Authors: Lee, Jeongwoo; Gary, Dale E. Bibcode: 2008ApJ...685L..87L Altcode: During solar flares Hα ribbons form and often move away from the local magnetic polarity inversion line (PIL). While the motion perpendicular to the PIL has been taken as evidence for coronal magnetic reconnection in the so-called CSHKP standard model, the other velocity component parallel to the PIL is much less adopted as a property of the magnetic reconnection process. In this Letter we report an event in which the motion parallel to the PIL is found in both Hα ribbons and a thermal hard X-ray source. Such commonality would indicate a link between the coronal magnetic reconnection and footpoint emissions as in the standard solar flare model. However, its direction implies a reconnection region that is increasing in length, a feature missing from the standard two-dimensional model. We present a modified framework in which the variation along the third dimension is allowed, in order to assess the effect of such a proper motion on estimation of the magnetic reconnection rate. Data used are hard X-ray maps from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), Hα filtergrams of Big Bear Solar Observatory (BBSO), and the SOHO Michelson Doppler Imager (MDI) magnetogram obtained for the 2004 March 30 flare. Title: Positions of Fiber Bursts in the 2006 December 6 Flare Authors: White, S. M.; Liu, Z.; Gary, D. E. Bibcode: 2008AGUSMSP44A..07W Altcode: The large flare of 2006 December 6 produced one of the brightest radio bursts ever recorded. The burst was observed with very rapid sampling by the FASR Subsystem Testbed, operating on 3 antennas of the OVSA array at Owens Valley. The burst contained a range of emission types within the FST band (1.0-1.5 GHz), including continuum and "fiber" bursts. This is the first time that fiber bursts have been observed over a significant frequency range with an interferometer. Data are processed into visibilities using a software correlator with positional information retained. We present an analysis of the fiber bursts relative to the continuum, in order to investigate whether the projected position of the bursts varies with frequency. This information is used to test models for fiber bursts, in particular the model that they represent propagating whistler wave trains. Title: Detection of explosives by Terahertz synthetic aperture imaging—focusing and spectral classification Authors: Sinyukov, Alexander; Zorych, Ivan; Michalopoulou, Zoi-Heleni; Gary, Dale; Barat, Robert; Federici, John F. Bibcode: 2008CRPhy...9..248S Altcode: In the adaptation of Terahertz (THz) synthetic aperture imaging to stand-off screening of concealed weapons and explosives, the incoming THz wavefronts exhibit significant curvature that must be considered in the image reconstruction. Consequently, the imaging array must be focused at a specific distance to correct for the wavefront curvature. In addition to the focusing correction, detection of explosives requires spectral analysis of the reconstructed THz image. Kohonen self-organizing maps are shown to be promising tools for differentiating the spectral signature of C4 explosive from the reflection spectra of metal and semi-transparent barrier materials. To cite this article: A. Sinyukov et al., C. R. Physique 9 (2008). Title: The Spatial Distribution of the Hard X-Ray Spectral Index and the Local Magnetic Reconnection Rate Authors: Liu, Chang; Lee, Jeongwoo; Jing, Ju; Gary, Dale E.; Wang, Haimin Bibcode: 2008ApJ...672L..69L Altcode: 2007arXiv0711.1370L The rare phenomenon of ribbon-like hard X-ray (HXR) sources up to 100 keV found in the 2005 May 13 M8.0 flare observed with the Reuven Ramaty High Energy Solar Spectroscopic Imager provides detailed information on the spatial distribution of flare HXR emission. In this Letter, we further investigate the characteristics of HXR emission in this event using imaging spectroscopy, from which we obtain spatially resolved HXR spectral maps during the flare impulsive phase. As a result we found, along a flare ribbon, an anticorrelation relationship between the local HXR flux and the local HXR spectral index. We suggest that this can be regarded as a spatial analog of the well-known temporal soft-hard-soft spectral evolution pattern of the integrated HXR flux. We also found an anticorrelation between the HXR spectral index and the local electric field along the ribbon, which suggests electron acceleration by the electric field during flares. Title: Transition radiation in turbulent astrophysical medium. Application to solar radio bursts Authors: Fleishman, Gregory D.; Gary, Dale E.; Nita, Gelu M. Bibcode: 2007arXiv0710.0351F Altcode: Modern observations and models of various astrophysical objects suggest that many of their physical parameters fluctuate substantially at different spatial scales. The rich variety of the emission processes, including Transition Radiation but not limited to it, arising in such turbulent media constitutes the scope of Stochastic Theory of Radiation. We review general approaches applied in the stochastic theory of radiation and specific methods used to calculate the transition radiation produced by fast particles in the magnetized randomly inhomogeneous plasma. The importance of the theory of transition radiation for astrophysics is illustrated by one example of its detailed application to a solar radio burst, including specially designed algorithms of the spectral forward fitting. Title: Radio Spectral Evolution of an X-Ray-poor Impulsive Solar Flare: Implications for Plasma Heating and Electron Acceleration Authors: Bastian, T. S.; Fleishman, G. D.; Gary, D. E. Bibcode: 2007ApJ...666.1256B Altcode: 2007arXiv0704.2413B We present radio and X-ray observations of an impulsive solar flare that was moderately intense in microwaves, yet showed very meager EUV and X-ray emission. The flare occurred on 2001 October 24 and was well observed at radio wavelengths by the Nobeyama Radioheliograph (NoRH), the Nobeyama Radio Polarimeters (NoRP), and the Owens Valley Solar Array (OVSA). It was also observed in EUV and X-ray wavelength bands by the TRACE, GOES, and Yohkoh satellites. We find that the impulsive onset of the radio emission is progressively delayed with increasing frequency relative to the onset of hard X-ray emission. In contrast, the time of flux density maximum is progressively delayed with decreasing frequency. The decay phase is independent of radio frequency. The simple source morphology and the excellent spectral coverage at radio wavelengths allowed us to employ a nonlinear χ2-minimization scheme to fit the time series of radio spectra to a source model that accounts for the observed radio emission in terms of gyrosynchrotron radiation from MeV-energy electrons in a relatively dense thermal plasma. We discuss plasma heating and electron acceleration in view of the parametric trends implied by the model fitting. We suggest that stochastic acceleration likely plays a role in accelerating the radio-emitting electrons. Title: Hard X-Ray Intensity Distribution along Hα Ribbons Authors: Jing, Ju; Lee, Jeongwoo; Liu, Chang; Gary, Dale E.; Wang, Haimin Bibcode: 2007ApJ...664L.127J Altcode: Unusual ribbon-like hard X-ray sources were found with the RHESSI observation of a 2B/M8.0 flare on 2005 May 13. We use this unique observation to investigate the spatial distribution of the hard X-ray intensity along the ribbons and compare it with the local magnetic reconnection rate and energy release rate predicted by the standard magnetic reconnection model for two ribbon flares. In the early phase of the flare, the hard X-ray sources appear to be concentrated in strong field regions within the Hα ribbons, which is explicable by the model. At and after the flare maximum phase, the hard X-ray sources become spatially extended to resemble Hα ribbons in morphology, during which the spatial distribution of hard X-ray intensity lacks a correlation with that of the local magnetic reconnection rate and energy release rate predicted by the model. We argue that the magnetic reconnection during this event may involve the rearrangement of magnetic field along the magnetic arcade axis that is inevitably overlooked by the two-dimensional model and suggest that this type of three-dimensional reconnection will be best seen in so-called sigmoid-to-arcade transformations. Title: Magnetic Field Strength in the Solar Corona from Type II Band Splitting Authors: Cho, K. -S.; Lee, J.; Gary, D. E.; Moon, Y. -J.; Park, Y. D. Bibcode: 2007ApJ...665..799C Altcode: The phenomenon of band splitting in type II bursts can be a unique diagnostic for the magnetic field in the corona, which is, however, inevitably sensitive to the ambient density. We apply this diagnostic to the CME-flare event on 2004 August 18, for which we are able to locate the propagation of the type II burst and determine the ambient coronal electron density by other means. We measure the width of the band splitting on a dynamic spectrum of the bursts observed with the Green Bank Solar Radio Burst Spectrometer (GBSRBS), and convert it to the Alfvén Mach number under the Rankine-Hugoniot relation. We then determine the Alfvén speed and magnetic field strength using the coronal background density and shock speed measured with the MLSO/MK4 coronameter. In this way we find that the shock compression ratio is in the range of 1.5-1.6, the Alfvénic Mach number is 1.4-1.5, the Alfvén speed is 550-400 km s-1, and finally the magnetic field strength decreases from 1.3 to 0.4 G while the shock passes from 1.6 to 2.1 Rsolar. The magnetic field strength derived from the type II spectrum is finally compared with the potential field source surface (PFSS) model for further evaluation of this diagnostic. Title: Radio Frequency Interference Excision Using Spectral-Domain Statistics Authors: Nita, Gelu M.; Gary, Dale E.; Liu, Zhiwei; Hurford, Gordon J.; White, Stephen M. Bibcode: 2007PASP..119..805N Altcode: A radio frequency interference (RFI) excision algorithm based on spectral kurtosis, a spectral variant of time-domain kurtosis, is proposed and implemented in software. The algorithm works by providing a robust estimator for Gaussian noise that, when violated, indicates the presence of non-Gaussian RFI. A theoretical formalism is used that unifies the well-known time-domain kurtosis estimator with past work related to spectral kurtosis, and leads naturally to a single expression encompassing both. The algorithm accumulates the first two powers of M power spectral density (PSD) estimates, obtained via Fourier transform, to form a spectral kurtosis (SK) estimator whose expected statistical variance is used to define an RFI detection threshold. The performance of the algorithm is theoretically evaluated for different time-domain RFI characteristics and signal-to-noise ratios η. The theoretical performance of the algorithm for intermittent RFI (RFI present in R out of M PSD estimates) is evaluated and shown to depend greatly on the duty cycle, d=R/M. The algorithm is most effective for d=1/(4+η), but cannot distinguish RFI from Gaussian noise at any η when d=0.5. The expected efficiency and robustness of the algorithm are tested using data from the newly designed FASR Subsystem Testbed radio interferometer operating at the Owens Valley Solar Array. The ability of the algorithm to discriminate RFI against the temporally and spectrally complex radio emission produced during solar radio bursts is demonstrated. Title: Positional Properties of Solar Decimetric Fiber Bursts Authors: Liu, Zhiwei; Gary, D. E.; Nita, G. M.; White, S. M.; Hurford, G. J. Bibcode: 2007AAS...210.9328L Altcode: 2007BAAS...39..215L The large solar flare of 2006 December 6 was detected by the newly constructed FASR Subsystem Testbed (FST; Liu et al. 2007, PASP, 119), which is operating on three antennas of Owens Valley Solar Array. This record-setting burst produced an especially fine set of fibers bursts--so-called intermediate-drift bursts that drift from high to low frequencies over 6-10s. According to a leading theory, the fibers are generated by packets of whistler waves propagating along a magnetic loop, which coalesce with Langmuir waves to produce escaping electromagnetic radiation in the decimeter band. With this three element interferometer, for the first time fiber burst source locations can be determined. We use the radio information over a 500 MHz band (1.0-1.5 GHz) to determine the trajectories of the bursts. We attempt to define three-dimensional trajectories by combining the two-dimensional radio positions with height of the fiber source determined from a coronal density model. Title: Interferometric Observations of the Record-Breaking Decimetric Solar Radio Event of 2006 December 06 Authors: Gary, Dale E.; White, S. M.; Hurford, G. J.; Nita, G. M.; Liu, Z. Bibcode: 2007AAS...210.9329G Altcode: 2007BAAS...39..216G The radio burst associated with the 2006 Dec 06, X6.5 solar flare attained a record-breaking radio flux density of nearly 1 million solar flux units in the decimetric ( 1 GHz) frequency band, exceeding the previous record by nearly a factor of 10. The event was so strong in the range 1-2 GHz that it caused loss of lock of Global Positioning System (GPS) receivers everywhere in the sunlit hemisphere of Earth. The event was observed with a new instrument operating at the Owens Valley Solar Array (OVSA), the FASR Subsystem Testbed (FST), which features not only unprecedented time and frequency resolution ( 1 microsecond and < 1 MHz, respectively), but also interferomety on three baselines to provide corresponding spatial information on a 10 arcsecond scale. The event produced about 10 million individual decimetric spike bursts produced by the Electron Cyclotron Maser (ECM) mechanism over a period of nearly 1 hour. We discuss the spectral, temporal, and positional characteristics of individual spike bursts, their statistical properties and their relation to the flare observed at other wavelengths. This work is supported by NSF grant AST-0352915 to the New Jersey Institute of Technology. We acknowledge additional support for the Owens Valley Solar Array through NSF grant AST-0607544 and NASA grant NNG06GJ40G. Title: Fiber Bursts in Solar Flares at High Time and Frequency Resolution Authors: White, Stephen M.; Liu, Z.; Gary, D. E.; Nita, G. M.; Hurford, G. J. Bibcode: 2007AAS...210.6806W Altcode: 2007BAAS...39..176W The FASR Subsystem Testbed (FST), operating on three dishes of the Owens Valley Solar Array, detected radio fiber bursts in two large solar flares in 2006. The frequencies of observation correspond to densities of order 10 to the 10 per cc, so the bursts are being emitted low in the corona, presumably near the energy release region. The fiber bursts drift in frequency with time, and appear to be travelling outwards. In one model, fiber bursts can be used to infer the magnetic field in the corona in the emission site. The FST data provide radio spectra of the bursts with a time resolution of milliseconds: using this exceptional data, we present the properties of the bursts and discuss their physical interpretation. Title: Solar Burst Submillimeter Wave Emission Components Associated To Microwaves, Uv, X- And γ- Rays Continuum In Time And Space Authors: Kaufmann, Pierre; Trottet, G.; Giménez de Castro, C.; Raulin, J.; Gary, D.; Fernandez, G.; Godoy, R.; Levato, H.; Marun, A.; Pereyra, P. Bibcode: 2007AAS...210.9330K Altcode: 2007BAAS...39..216K The solar burst spectral component peaking somewhere in the terahertz (THz) range, along with, but distinct from, the well-known microwave component, bring new observational and theoretical possibilities to explore the flaring physical processes. The solar event of December 6, 2006, 18:30 UT, exhibited a particularly well-defined double spectral structure, with the THz spectral component detected at 212 and 405 GHz by SST and microwaves (1-18 GHz) by OVSA. The burst was observed by instruments in satellites at high energies, UV by TRACE, soft X-rays by GOES, X- to γ- rays by RHESSI. Although the event occupied an extended area at optical and UV wavelengths, showing various brightnings along several arcminutes, the hard X-ray emission region is restricted (within a region 30” x 50”) showing three sources at low energies (< 150 keV) and a single source above 300 keV. At submillimeter-waves, a precursor was observed, followed by a rapid impulsive event and a post-burst long-enduring component. This post-burst component was also accompanied by the largest flux-density decimeter burst ever reported, reaching 1 million solar flux units. The submillimeter impulsive burst centroid position at 212 GHz was clearly displaced from the precursor component by almost 1 arc-minute. The maximum limit sizes, estimated at 212 GHz, were of the order or smaller than the beam-sizes (4’). The microwave spectra for the precursor and long-enduring burst components peak at about 5-10 GHz. The submillimeter precursor spectrum might be optically thick emission of the cold chromospheric plasma. Despite the complexity in space, time and spectra of the superimposed impulsive and post-impulsive emission, it was remarkable that the THz impulsive component had its closer counterpart only in the higher energy X- and γ- rays ranges, suggesting that they are part of the same physical process, produced by a source of continuously accelerated high-energy particles. Title: The Ribbon-like Hard X-Ray Emission in a Sigmoidal Solar Active Region Authors: Liu, Chang; Lee, Jeongwoo; Gary, Dale E.; Wang, Haimin Bibcode: 2007ApJ...658L.127L Altcode: 2007astro.ph..2326L Solar flare emissions at Hα and EUV/UV wavelengths often appear in the form of two ribbons, and this has been regarded as evidence of a typical configuration of solar magnetic reconnection. However, such a ribbon structure has rarely been observed in hard X-rays (HXRs), although it is expected. We report a ribbon-like HXR source observed with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) at energies as high as 25-100 keV during the 2005 May 13 flare. For a qualitative understanding of this unusual HXR morphology, we also note that the source active region appeared in a conspicuous sigmoid shape before the eruption and changed to an arcade structure afterward as observed with the Transition Region and Coronal Explorer (TRACE) at 171 Å. We suggest that the ribbon-like HXR structure is associated with the sigmoid-to-arcade transformation during this type of reconnection. Title: Minor Planet Observations [H93 Berkeley Heights] Authors: Gary, D. Bibcode: 2007MPC..59317..16G Altcode: No abstract at ADS Title: Radio and White-Light Coronal Signatures Associated with the RHESSI Hard X-Ray Event of 2002 July 23 Authors: Reiner, M. J.; Krucker, S.; Gary, D. E.; Dougherty, B. L.; Kaiser, M. L.; Bougeret, J. -L. Bibcode: 2007ApJ...657.1107R Altcode: Simultaneous radio, white-light, and hard X-ray (HXR) observations for the 2002 July 23 γ-ray flare event are used to establish the relationship of a complex type III-like burst to the corresponding coronal mass ejection (CME) and the coronal electron acceleration signatures observed in the decimeter/microwave (dm-cm) emissions and X-rays. We find that the onset of the type III-like emissions for this event is coincident with the impulsive RHESSI HXR event, the dm-cm radio emissions and with the linearly extrapolated liftoff time of the CME. The overall intensity-time characteristics of the complex type III-like burst resembles that of both the dm-cm flux and the HXR light curve that correspond to an electron acceleration event deep in the corona. Furthermore, the complex radiation characteristics of the type III-like emissions are found to be directly related to the CME kinematics, which is directly related to the frequency drift of the associated low-frequency (kilometric) type II emissions. The frequency-drift characteristics of the high-frequency (metric) type II emissions observed for this event, on the other hand, are not clearly related to the kilometric type II emissions and therefore to the observed CME height-time characteristics, indicating that these emissions may correspond to an independent coronal shock wave. Title: A Subsystem Test Bed for the Frequency-Agile Solar Radiotelescope Authors: Liu, Zhiwei; Gary, Dale E.; Nita, Gelu M.; White, Stephen M.; Hurford, Gordon J. Bibcode: 2007PASP..119..303L Altcode: This paper describes the design and operation of the Frequency-Agile Solar Radiotelescope (FASR) Subsystem Testbed (FST) and the first observational results. Three antennas of the Owens Valley Solar Array have been modified so that each sends a 1-9 GHz band of radio frequency to a central location using a broadband analog optical fiber link. A dynamically selected 500 MHz subset of this frequency range is digitized at 1 Gsps (gigasample per second) and recorded to disk. The full-resolution time-domain data thus recorded are then correlated through offline software to provide interferometric phase and amplitude spectra on three baselines. An important feature of this approach is that the data can be reanalyzed multiple times with different digital signal-processing techniques (e.g., different bit-sampling, windowing, and radio frequency interference [RFI] excision methods) to test the effect of different designs. As a prototype of the FASR system, FST provides the opportunity to study the design, calibration, and interference-avoidance requirements of FASR. In addition, FST provides, for the first time, the ability to perform broadband spectroscopy of the Sun with spectrograph-like spectral and temporal resolution, while providing locating ability for simple sources. Initial observations of local RFI, geostationary satellite signals, global positioning system (GPS) satellite signals, and the Sun are presented to illustrate the system performance. Title: Ground-based solar facilities in the U.S.A. Authors: Denker, C.; Gary, D. E.; Rimmele, T. R. Bibcode: 2007msfa.conf...31D Altcode: In this review, we present the status of new ground-based facilities for optical and radio observations of the Sun in the United States. The 4-meter aperture Advanced Technology Solar Telescope (ATST) under the stewardship of the National Solar Observatory (NSO) has successfully completed its design phase and awaits funding approval. The 1.6-meter aperture New Solar Telescope (NST) at Big Bear Solar Observatory (BBSO) is currently under construction. Complementing these optical telescopes is the Frequency Agile Solar Radiotelescope (FASR) an instrument for dynamic broadband imaging spectroscopy covering a multitude of radio frequencies from 50 MHz to 20 GHz. Imaging spectroscopy and polarimetry are common features of these telescopes, which will provide new insight regarding the evolution and nature of solar magnetic fields. High-resolution observations of solar activity, bridging the solar atmosphere from the photosphere to the corona, will be obtained with a dedicated suite of instruments. Special emphasis of this review will be put on the interplay between instrumentation and scientific discovery. Title: Minor Planet Observations [H93 Berkeley Heights] Authors: Gary, D. Bibcode: 2006MPC..58116...9G Altcode: No abstract at ADS Title: FASR Flare Science: Lessons from the Nobeyama Radioheliograph Authors: Gary, D. E. Bibcode: 2006spnr.conf..121G Altcode: We compare and contrast the instrumental parameters of the Nobeyama Radioheliograph (NoRH) and the future Frequency Agile Solar Radiotelescope (FASR) with an emphasis on flare research. The primary results and discoveries of NoRH in the realm of flare science are presented and used to motivate many of the choices for design parameters and science goals for FASR. Key parameters of NoRH for flare science are its dual-frequency, dual-polarization, excellent image quality, solar-dedicated and solar-optimized design, and high time resolution. Its main limitations are spatial resolution, frequency coverage, and frequency resolution. FASR's design makes use of the strengths of NoRH, and adds these three missing elements: a factor of 10 improvement in spatial resolution, broad frequency coverage and high frequency resolution. We discuss the manner in which these improvements extend the legacy of NoRH for flare science. Title: Observed solar radio burst effects on GPS/Wide Area Augmentation System carrier-to-noise ratio Authors: Cerruti, Alessandro P.; Kintner, Paul M.; Gary, Dale E.; Lanzerotti, Louis J.; de Paula, Eurico R.; Vo, Hien B. Bibcode: 2006SpWea...410006C Altcode: The first direct observations of Global Positioning System (GPS) L1 (1.57542 GHz) carrier-to-noise ratio degradation due to a solar radio burst are presented for an event that occurred on 7 September 2005. Concurrent carrier-to-noise ratio data from GPS satellites are available from receivers at Arecibo Observatory, Puerto Rico; San Juan, Puerto Rico; and also from Anderson, South Carolina, United States. The right-hand circularly polarized (RHCP) signals from this solar radio burst caused a corresponding decrease in the carrier-to-noise ratio of about 2.3 dB across all visible satellites. The maximum solar radio burst power associated with this event was 8700 solar flux units (1 SFU = 10-22 W/m2/Hz) RHCP at 1600 MHz. Direct observations of GPS semicodeless L2 carrier-to-noise ratio degradation from receivers in Brazil are also presented for a solar radio burst that occurred on 28 October 2003. The maximum degradation at GPS L1 was about 3.0 dB, and a degradation of 10.0 dB was observed on the semicodeless L2 signal. Scaling to historic solar radio burst records suggests that GPS L1 receivers could fail to produce a navigation solution and that semicodeless L1/L2 receivers will fail. Title: The Frequency Agile Solar Radiotelescope (FASR) Authors: Gary, D. E. Bibcode: 2006IAUJD..12E..19G Altcode: The Frequency Agile Solar Radiotelescope (FASR) is a solar-optimized, solar-dedicated radio array that is expected to be the world's premier solar radio facility for two decades after completion in 2012. This talk describes the instrument and focuses on the broad science it is to address. The key science objectives are: 1) the nature and evolution of coronal magnetic fields; 2) the physics of flares; 3) drivers of space weather; and 4) physics of the quiet solar atmosphere. Science goals include coronal magnetography, electron energy and transport, initiation and acceleration of Coronal Mass Ejections, and coronal and chromospheric heating, among many others. The instrument, made up of hundreds of individual antenna elements, will provide solar images of the highest quality and spatial resolution ever obtained, at hundreds of frequencies ranging from 50 MHz - 20 GHz, with less optimized coverage to 30 GHz. The talk will also discuss the key instrumental design characteristics, and will give the current status of the project, as well as describing prototyping and study activities leading to the final proposal for construction. Title: Magnetic Energy Release during the 2002 September 9 Solar Flare Authors: Lee, Jeongwoo; Gary, Dale E.; Choe, G. S. Bibcode: 2006ApJ...647..638L Altcode: We study the magnetic energy release during the 2002 September 9 flare using the high-cadence (40 ms) Hα filtergram at Big Bear Solar Observatory (BBSO), along with hard X-ray and microwave data from the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) and the Owens Valley Solar Array (OVSA), respectively. We take the Poynting vector approach with the standard two-dimensional geometry of the reconnecting current sheet (RCS) but suggest a new technique to infer the area of the RCS, in order to complete the magnetic energy calculation entirely with observed quantities. We found five peaks of impulsive magnetic energy release, concentrated within 10-30 s periods, that are episodic with the peaks of the hard X-ray light curve. The maximum amount of energy released per peak reaches ~2.6×1030 ergs s-1, and the electron energy deposition rate derived from the RHESSI spectra falls into the range of 10%-80% of the magnetic energy release rate. We briefly discuss this result in comparison with other studies thus far made toward understanding of the magnetic reconnection in solar flares and suggest the pulsating current sheet model as the most plausible interpretation of our result. Title: Quasi-periodic Radio And X-ray Pulsations In A Solar Flare Authors: Bastian, Timothy S.; Fleishman, G.; Gary, D. E. Bibcode: 2006SPD....37.1309B Altcode: 2006BAAS...38..242B We describe microwave and hard X-ray observations of strong quasiperiodic pulsations from the GOES X1.3 solar flare on 15 June 2003. Using Fourier analysis, we study the frequency- and energy-dependent oscillation periods, phase differences, and modulation depths of the radio and X-ray pulsations. Focusing on the more complete radio observations, the observational properties of the oscillations are compared with those derived from models for the radio emission. Two simple models are considered: i) gyrosynchrotron emission modulated by the quasiperiodic injection of fast electrons; ii) gyrosynchrotron emission modulated by an MHD oscillation of the magnetic field. We demonstrate that quasiperiodic injection of fast electrons is the more likely cause of the observed quasiperiodic oscillations observed in the radio and hard X-ray emission. We discuss the implications of this finding for particle acceleration and transport in the flaring sources. Title: Sigmoid, Type II Precursor, and Coronal Mass Ejection Authors: Lee, Jeongwoo; Liu, C.; Cho, K.; Gary, D. E.; Yurchyshyn, V.; Deng, N.; Wang, H. Bibcode: 2006SPD....37.0907L Altcode: 2006BAAS...38..236L The 2005 May 13 flare occurred in the sigmoidal active region, NOAA 10759, and its time dependent change on the TRACE, EIT, and SXI images suggests an eruption process as envisioned by the runaway tether-cutting model. However, the onset of the eruption in the low corona and the final explosion of the magnetic field in the high corona are not directly observable at these wavelengths and we infer them indirectly from the radio data obtained with the Owens Valley Solar Array (OVSA), Green Bank Solar Radio Burst Spectrometer (GBSRBS), PHOENIX-spectrograph of ETH Zurich, and the Potsdam-Tremsdorf Spectrograph. The Potsdam spectrograph shows a so-called Type II Precursor in the early phase of loop expansion, indicating a coronal shock formed near the flare site. The GBSRBS spectra show a type III burst followed by type II bursts in the maximum phase, which implies opening of field lines and strong shock formation in the high corona. Finally, the radio pulsations are detected on the OVSA and PHOENIX spectrographs, which we interpret as due to the magnetic loop oscillation as a dynamic response to the mass ejection. These radio data along with the EUV and X-ray images are used to infer the runaway tether-cutting process during this event in all coronal heights.This work is supported by NSF/SHINE grant ATM-0548952 and NSF grant AST-0307670 to NJIT. Title: FASR Subsystem Testbed Authors: Liu, Zhiwei; Gary, D. E.; Nita, G. M.; White, S. M.; Hurford, G. J. Bibcode: 2006SPD....37.0602L Altcode: 2006BAAS...38..225L The construction of the Frequency Agile Solar Radiotelescope (FASR) Subsystem Testbed (FST) and first results are described. Three antennas of Owens Valley Solar Array (OVSA) are upgraded with the newly designed, state of art technology. The 1-9 GHz RF signal from the feed is transmitted through the fiber optical system to the control room. Then it is downconverted to a 500 MHz single-sideband signal that can be tuned across the 1-9 GHz RF band. The data are sampled with an 8-bit, 1 GHz sampling-rate digitizer, and further saved to the hard disk. The correlated (phase and amplitude) spectra are derived through offline software. As a prototype of the FASR system, FST provides the opportunity to study the design, calibration, and interference-avoidance requirements of FASR. FST provides, for the first time, the ability to perform broadband imaging spectroscopy with high spectral, temporal and moderate spatial resolution. With this three element interferometer, we have the ability to determine the location of simple source structures with very high time resolution (20 ms) and frequency resolution ( <1 MHz) as well as the dynamic spectrum. Initial examples of geostationary satellite, GPS satellite and solar observations are presented. Title: First Solar Results with the FASR Subsystem Testbed Authors: Gary, Dale E.; Hurford, G. J.; Liu, Z.; Nita, G. M.; White, S. M. Bibcode: 2006SPD....37.2502G Altcode: 2006BAAS...38..252G The Frequency Agile Solar Radiotelescope (FASR) Subsystem Testbed (FST) is a new, three-element interferometer, utilizing three antennas of the Owens Valley Solar Array. FST is the first radio instrument capable of measuring solar burst locations with spectrograph-like time and frequency resolution. Operating with 500 MHz instantaneous bandwidth, tunable anywhere in the 1-9 GHz range, FST can measure centroid locations of typical bursts on millisecond timescales and MHz frequency resolution. The system is designed as a prototype for FASR, for several purposes including the study of radio frequency interference (RFI) mitigation techniques, a testbed for the design of FASR's digitial signal processing, and investigating use of satellite signals for calibration. In addition, however, FST is unique in its ability to locate solar bursts on the extremely fine frequency and time scales on which their emission varies.A technical description of the instrument can be found in an accompanying poster (Liu et al.), along with first results on the several topics mentioned above. In this talk we focus on the solar applications of FST. We describe the operation of the system for solar observations, the science goals of the instrument, and some first results of observations of solar bursts. The first recorded burst, obtained on the first day of solar observations, was a group of type III bursts associated with a B5.1 X-ray burst, also observed with RHESSI. Individual type IIIs show downward propagation (reverse-frequency slope), with significant positional differences from one type III to another, while within a type III are seen smaller positional changes as a function of frequency. This suggests smooth trajectories for individual bursts, but widely diverging locations for separate bursts. We describe joint RHESSI/FST observations and findings for those bursts observed so far. This work is supported by NSF grant AST-0352915 to NJIT. Title: Analysis of a Flare Producing Active Region Using Data from the Upgraded OVSA Authors: Tun, Samuel D.; Gary, D. E.; Nita, G. M.; Lee, J. Bibcode: 2006SPD....37.0117T Altcode: 2006BAAS...38..218T The Owens Valley Solar Array (OVSA) provides spectral imaging data in the microwave radio range, 1-18 GHz. In August 2004, work was completed on adding two 2-m antennas to the existing array, for a total of seven elements. In addition, the five 2-m antennas were upgraded to record right and left circular polarization, a feature previously available only on the two 27-m dishes. The increased number of baselines improves the instrument's imaging capability and, thus, allows a more accurate analysis of solar features. We have embarked on a project to study active regions that were well observed by OVSA from August 2004 through the end of 2005. This poster concentrates on the period in September 2005 when NOAA active region AR 10808 crossed the disk (and produced several strong flares). The present work is an analysis of the AR 10808's structure during non-flaring times in order to determine coronal parameters such as temperature, magnetic field strength, and column emission measure by means of the radio brightness temperature spectra obtained from radio maps of the region. Polarization information is used to determine these parameters more precisely, using the magnetic-field-induced polarization as a constraint. The results are compared to those inferred from concurrent observations by BBSO and MDI. This is part of a work in progress to make similar analyses of the active region over several days in order to determine changes in the active region structure around flare times, as well as changes in the active region during its passage across the solar disk. Title: The Eruption from a Sigmoid Active Region on 2005 May 13 Authors: Liu, Chang; Lee, J.; Yurchyshyn, V.; Cho, K.; Deng, N.; Gary, D. E.; Wang, H. Bibcode: 2006SPD....37.0821L Altcode: 2006BAAS...38..234L A sigmoidal structure of active regions has been of interest as is believed to lead to magnetic eruption. We found from TRACE EUV images that NOAA AR 10759 exhibited a typical sigmoid shape just before the M8.0 flare and a fast halo CME on 2005 May 13, and reduced to a more confined arcade after the eruption. We have thus examined these time dependent changes during the flare by utilizing a multiwavelength data set: EUV (TRACE, EIT), soft X-rays (SXI), H-alpha (BBSO,ISOON), radio spectra (OVSA, Potsdam-Tremsdorf, GBSRBS, Phoenix, RSTN), and CME (LASCO). Several similarities of this event with the runaway tether-cutting scenario elaborated by Moore et al. (2001) has been found. Before the maximum phase, the flare brightening first occurred in the core of the active region, and then two elbows in the outer region gradually expanded, which we compare to the tether-cutting in the sigmoid center and the ejective eruption, respectively. At the flare maximum, the large-scale disturbances such as Moreton waves, type II, and III radio bursts were observed, which we suggest as evidence for the blow-out of the envelope field and particle acceleration. Finally the flare arcade formed along the neutral line as the opened legs of the envelop field reconnect with each other. This dataset therefore supports the idea that the eruption may start in the sheared core field and proceeds outward with the rising plasmoid via the runaway tether-cutting reconnection and finally becomes a CME.This work is supported by NSF/SHINE grant ATM-0548952, NSF grant ATM-0536921, and NASA grant NNG0-4GJ51G. Title: Direct Observations of GPS L1 Signal-to-Noise Degradation due to Solar Radio Bursts Authors: Cerruti, A. P.; Kintner, P. M.; Gary, D.; Lanzerotti, L. Bibcode: 2006AGUSMSH53A..07C Altcode: GPS signals, systems, and navigation accuracy are vulnerable to a variety of space weather effects mostly caused by the ionosphere. This paper considers a different class of space weather effects on GPS signals: solar radio bursts. We present the first direct observations of GPS L1 (1.6 GHz) carrier-to-noise degradation on two different models of GPS receivers due to the solar radio burst associated with the 7 September, 2005 solar flare. The solar radio burst consisted of two periods of 1.6 GHz activity at approximately 17:40 UT and again at 18:30 UT. All the receivers that were affected by the solar radio burst were in the sun-lit hemisphere: three identical receivers were collocated at the Arecibo Observatory, and four identical receivers of a different model were located in Brazil. For both models, all GPS satellites in view were affected similarly. In some cases the decrease in the GPS L1 signal-to-noise agreed perfectly with the solar radio burst amplitudes, while in other cases there was no association. Further analysis indicated that only the right hand circularly polarized (RHCP) emissions affected the GPS signals. Since GPS signals are RHCP and GPS antennas are also RHCP, the null effect of the LHCP power confirms our hypothesis that the solar radio bursts are causal. The maximum solar radio burst power associated with the 7 September 2005 flare had a peak intensity of about 8,700 solar flux units (SFU) RHCP at 1,600 MHz, which caused a corresponding decrease in the signal- to-noise of about 2.5 dB across all visible satellites. Furthermore, an event with a peak intensity of 5,000 SFU RHCP at 1,600 MHz caused a 2 dB fade for nearly 15 minutes. To further investigate the effect of solar radio bursts, we also examined the emissions associated with the 28 October 2003 flare. Although polarization data was not available for this even, a similar association was found between 1,400 MHz solar radio power and GPS signal-to-noise degradation. The maximum degradation at GPS L1 was about 3 dB, and a degradation of 10 dB was observed on the semi-codeless L2 signal. This is larger than previously estimated by (Klobuchar et al. 1999). Although the events shown are small, scaling to historical solar radio bursts of 80,000 SFU imply a 12-15 dB drop in the signal-to-noise ratio. Furthermore, solar radio bursts affect all satellites in view of a receiver and all receivers in the sun-lit hemisphere. The implications are clear that the largest solar radio bursts could cause loss-of-tracking for inadequately designed GPS receivers. Solar radio bursts will also affect the new Galileo navigation system and all space-based augmentation systems such as WAAS and EGNOS. Kobuchar, J.A., J.M. Kunches, and A.J. VanDierendonck (1999), Eye on the Ionosphere: Potential Solar Radio Burst Effects on GPS Signal to Noise, GPS Solutions, 3(2), 69-71 Title: The FASR Reference Instrument Authors: Bastian, T. S.; Gary, D. E.; Hurford, G. J.; Kawakubo, H.; Ruf, C.; White, S. M.; Zurbuchen, T. Bibcode: 2006AGUSMSH33A..08B Altcode: The Frequency Agile Solar Radiotelescope (FASR) is a unique, solar-dedicated radio facility slated for completion by 2012. The instrument will address an extremely broad range of solar and space weather science, including routine measurement of coronal magnetic fields, imaging coronal mass ejections near the solar surface, quantitative diagnostics of energy release and particle acceleration in flares, and the extension of the solar corona into the heliosphere. Although the precise details of the FASR design are still being developed, we present for the first time a complete high-level design referred to as the FASR Reference Instrument. The Reference Instrument meets the science requirements and will serve as the basis for cost estimates for construction and operation of the instrument. This paper gives an overview of the FASR Reference Instrument, describes the science goals and objectives, and gives the flowdown of science goals to engineering specifications. The innovative aspects of the FASR design are highlighted, and a complete, end-to-end description of the instrument is given. The instrument operations plan is also discussed. Title: Large-Scale Activities Associated with the 2003 October 29 X10 Flare Authors: Liu, Chang; Lee, Jeongwoo; Deng, Na; Gary, Dale E.; Wang, Haimin Bibcode: 2006ApJ...642.1205L Altcode: We present a multiwavelength study focusing on the large-scale activities associated with the 2003 October 29 X10 flare and a halo CME. This event was strong enough to clearly show several large-scale activities, such as remote brightenings, Moreton waves at Hα off-bands, and type II radio bursts, which offers an excellent opportunity to clarify the relationship among them. The remote brightenings were found near two coronal holes more than 2×105 km from the main flare in eastern and southern directions, respectively. Coronal dimmings were seen at the locus of the remote brightenings right after the flare at both EUV and soft X-ray wavelengths. The Moreton waves propagated both northeastward and southward, toward the aforementioned remote regions, at speeds of approximately 1100 and 1900 km s-1, respectively. Our analyses show that the Moreton waves, the type II radio bursts, and the CME started almost simultaneously, but were not cotemporal with the remote brightenings. The remote brightenings are rather consistent with the flare hard X-ray emissions within the active region, although they have much smaller scales. We therefore conclude that the two remote brightening regions were magnetically connected to the flaring active region, and that the remote brightenings, as well as all other activities, were due to the interaction of an erupting flux rope at the core of the flare with magnetic field overlying the region. In this scenario, the large overlying loops should open to allow the flare activity underneath them, which points to a picture similar to the magnetic break-out process in such a large scale. Title: Comet Observations [H93 Berkeley Heights] Authors: Gary, D. Bibcode: 2006MPC..56559...6G Altcode: No abstract at ADS Title: Observations of Comets Authors: Tichy, M.; Kadota, K.; Abe, H.; Wakuda, S.; Herald, D.; Sanchez, A.; Stevens, B. L.; Skiff, B. A.; Kowalski, R. A.; Beshore, E. C.; Christensen, E. J.; Garradd, G. J.; Grauer, A. D.; Hill, R. E.; Larson, S. M.; McNaught, R. H.; Bezpalko, M.; Manguso, L.; Torres, D.; Kracke, R.; Blythe, M.; Love, H.; Stuart, J.; Kommers, J.; Durig, D. T.; Castellano, J.; Ferrando, R.; Garcia, F.; Cortes, E.; Takbou, S.; Kocher, P.; Brinkmann, B.; Denzau, H.; Oksanen, A.; Yang, M.; Ye, Q.; Sugiyama, Y.; Nicholson, M.; Bell, C.; Levin, K.; Pelle, J. C.; Gary, D.; Mendicini, D.; Morales, R.; Doreste, J. L.; Arce, E.; Navarro Pina, J. Pablo; Pastor, S.; Reyes, J. A.; Birtwhistle, P.; Climent, T.; Marsden, B. G. Bibcode: 2006MPEC....F...16T Altcode: No abstract at ADS Title: Minor Planet Observations [H93 Berkeley Heights] Authors: Gary, D. Bibcode: 2006MPC..56167...9G Altcode: No abstract at ADS Title: Sunspot Gyroresonance Emission at 17 GHz: A Statistical Study Authors: Vourlidas, Angelos; Gary, Dale E.; Shibasaki, Kiyoto Bibcode: 2006PASJ...58...11V Altcode: We investigate the sunspot gyroresonance emission at 17 GHz using the synoptic database of the Nobeyama Radioheliograph. Our statistical study is based on full disk observations obtained during the maximum of Cycle 22 (1992-94). We study the center-to-limb variation of the brightness and polarization of the sunspot radio emission and present some cases of polarization reversal. We find that the radio emission is most likely 3rd-harmonic gyroresonance emission arising from 2000 G fields in transition region, or low corona temperatures. Title: Spatio-spectral Maximum Entropy Method. I. Formulation and Test Authors: Bong, Su-Chan; Lee, Jeongwoo; Gary, Dale E.; Yun, Hong Sik Bibcode: 2006ApJ...636.1159B Altcode: The spatio-spectral maximum entropy method (SSMEM) has been developed by Komm and coworkers in 1997 for use with solar multifrequency interferometric observation. In this paper we further improve the formulation of the SSMEM to establish it as a tool for astronomical imaging spectroscopy. We maintain their original idea that spectral smoothness at neighboring frequencies can be used as an additional a priori assumption in astrophysical problems and that this can be implemented by adding a spectral entropy term to the usual maximum entropy method (MEM) formulation. We, however, address major technical difficulties in introducing the spectral entropy into the imaging problem that are not encountered in the conventional MEM. These include calculation of the spectral entropy in a generally frequency-dependent map grid, simultaneous adjustment of the temperature variables and Lagrangian multipliers in the spatial and spectral domain, and matching the solutions to the observational constraints at a large number of frequencies. We test the performance of the SSMEM in comparison with the conventional MEM. Title: NoRH and RHESSI Observations of Quasiperiodic Radio and X-ray Oscillations in a Solar Flare Authors: Bastian, T.; Fleishman, G.; Gary, D. Bibcode: 2006cosp...36.3251B Altcode: 2006cosp.meet.3251B We describe microwave and hard X-ray observations of strong quasiperiodic pulsations from the GOES X1 3 solar flare of 15 June 2003 Using Fourier analysis we study the frequency- and energy-dependent oscillation periods phase differences and modulation depths of the radio and X-ray pulsations Focusing on the more complete radio observations the observational properties of the oscillations are compared with those derived from models for the radio emission Two simple models are considered i gyrosynchrotron emission modulated by the quasiperiodic injection of fast electrons ii gyrosynchrotron emission modulated by an MHD oscillation of the magnetic field We demonstrate that quasiperiodic injection of fast electrons is the more likely cause of the observed quasiperiodic oscillations observed in the radio and hard X-ray emission We discuss the implications of this finding for particle acceleration and transport in the flaring sources Title: An Evaluation of the Solar Radio Burst Locator (SRBL) at OVRO Authors: HwangBo, J. E.; Bong, Su-Chan; Cho, K. S.; Moon, Y. J.; Lee, D. Y.; Park, Y. D.; Gary, Dale E.; Dougherty, Brian L. Bibcode: 2005JKAS...38..437H Altcode: No abstract at ADS Title: Spatio-Spectral Maximum Entropy Method: II. Solar Microwave Imaging Spectroscopy Authors: Bong, Su-Chan; Lee, Jeong-Woo; Gary, Dale E.; Yun, Hong-Sik; Chae, Jong-Chul Bibcode: 2005JKAS...38..445B Altcode: No abstract at ADS Title: Low Frequency Solar Radiophysics and Next Generation Instrumentation Authors: Bastian, T. S.; Gary, D. E. Bibcode: 2005ASPC..345..142B Altcode: Radio astronomy and solar radio astronomy developed rapidly together in the years following the Second World War. Much of this development occurred at low frequencies. In more recent decades, the emphasis has been on centimeter and millimeter wavelengths. However, motivated by both computational advances and new science drivers, there is a strong desire on the part of both the solar and astronomical communities to build modern low frequency radio telescopes. Here, some of the early work in solar radio astronomy is briefly reviewed and recent developments in solar and heliospheric physics are noted. Two next-generation radio telescopes, the Frequency Agile Solar Radiotelescope and the Long Wavelength Array, are described. Possible synergies between the two projects are discussed. Title: Our Solar Connection: A themed Set of Activities for Grades 5-12 Authors: van der Veen, W. E.; Gary, D. E.; Gallagher, A. C.; Vinski, J. M. Bibcode: 2005AAS...207.6505V Altcode: 2005BAAS...37.1260V The project is a partnership between the Center for Solar-Terrestrial Research at New Jersey Institute of Technology (NJIT), and the New Jersey Astronomy Center for Education (NJACE) at Raritan Valley Community College. It was supported by a NASA Education/Public Outreach grant from the Office of Space Science.

The project involved the development of a set of seven activities connected by the theme of solar magnetism and designed to meet the New Jersey Science Process Standards and the Science Core Curriculum Content Standards in Physics and Astronomy. The products include a 70-page teacher guide and an integrated CD-ROM with video clips, internet links, image sets used in the activities, and worksheets. The activities were presented at a series of teacher workshops. The teachers performed the activities themselves, learned additional background information on the Sun, solar magnetism, and the Sun-Earth connection, and were trained to use several items of equipment, which were made available in two "resource centers," one at NJIT and one at NJACE.

In all, 81 teachers have been exposed to some or all of the activities. After the training, the teachers took the activities back to their classrooms, and 15 equipment to use with their students. Some teachers had access to, or had their schools purchase, Sunspotters and spectrometers rather than borrow the equipment. The success of the teacher training was assessed by questionnaires at the end of the workshops, by evaluation forms that the teachers filled out on returning the borrowed equipment. Title: An RFI Survey at the Site of the Long Wavelength Deomonstration Array (LWDA) Authors: Stewart, K. P.; Crane, P. C.; Paravastu, N.; Hicks, B. C.; Theodorou, A.; Price, R. M.; Pihlstrom, Y. M.; Bastian, T. S.; Gary, D. E. Bibcode: 2005AAS...20713604S Altcode: 2005BAAS...37.1389S An initial survey of the radio-frequency environment at the site of the Long Wavelength Demonstration Array (LWDA) has been performed using a measurement protocol developed for both the Long Wavelength Array (LWA) and the Frequency Agile Solar Radiotelescope (FASR). The measurements cover the frequency range from 25 MHz to 18 GHz to include the LWA (23-80 MHz) and FASR (30 MHz-30 GHz). Measurements were obtained nearly continuously for a week to characterize the day/night and weekday/weekend variations expected for many sources of RFI. The equipment, antennas, and protocols are suitable for measuring strong RFI that potentially threatens the linearity of radio-astronomical receivers and may therefore rule out possible sites or influence the design of the receivers. (Weak RFI which may obscure weak signals of interest is beyond the capabilities of these measurements.) The protocol seeks only to identify RFI originating from terrestrial sources; RFI from satellites and astrophysical sources is assumed to be site independent and not a factor in site selection. Therefore, the receiving antennas provide azimuthal coverage in the direction of the horizon. This first survey, conducted prior to the start of LWDA construction, establishes a baseline for the later identification of any self-generated interference from the LWDA and its mitigation to ensure no adverse effect on the operations of the VLA. Title: Minor Planet Observations [H93 Berkeley Heights] Authors: Gary, D. Bibcode: 2005MPC..54984...3G Altcode: No abstract at ADS Title: Spatial Evidence for Transition Radiation in a Solar Radio Burst Authors: Nita, Gelu M.; Gary, Dale E.; Fleishman, Gregory D. Bibcode: 2005ApJ...629L..65N Altcode: 2005astro.ph..7230N Microturbulence, i.e., enhanced fluctuations of plasma density and electric and magnetic fields, is of great interest in astrophysical plasmas, but occurs on spatial scales far too small to resolve by remote sensing, e.g., at ~1-100 cm in the solar corona. This Letter reports spatially resolved observations that offer strong support for the presence in solar flares of a suspected radio emission mechanism, resonant transition radiation, which is tightly coupled to the level of microturbulence and provides direct diagnostics of the existence and level of fluctuations on decimeter spatial scales. Although the level of the microturbulence derived from the radio data is not particularly high, <Δn2>/n2~10-5, it is large enough to affect the charged particle diffusion and give rise to effective stochastic acceleration. This finding has exceptionally broad astrophysical implications, since modern sophisticated numerical models predict generation of much stronger turbulence in relativistic objects, e.g., in gamma-ray burst sources. Title: Minor Planet Observations [H93 Berkeley Heights] Authors: Gary, D. Bibcode: 2005MPC..54362...7G Altcode: No abstract at ADS Title: Comet Observations [H93 Berkeley Heights] Authors: Gary, D. Bibcode: 2005MPC..54306..23G Altcode: No abstract at ADS Title: Comet P/2005 JY126 (catalina) Authors: Dawson, M.; Lopez, A.; Pacheco, R.; Galli, G.; Seki, T.; Herald, D.; Blythe, M.; Shelly, F.; Bezpalko, M.; Huber, R.; Manguso, L.; Torres, D.; Kracke, R.; McCleary, M.; Stange, H.; Milner, A.; Stuart, J.; Sayer, R.; Evans, J.; Kommers, J.; Emmerich, M.; Melchert, S.; Sherrod, P. C.; Gary, D.; Sanchez, J.; Marsden, B. G. Bibcode: 2005MPEC....L...56D Altcode: No abstract at ADS Title: Terahertz imaging using an interferometric array Authors: Federici, John F.; Gary, Dale; Barat, Robert; Zimdars, David Bibcode: 2005SPIE.5790...11F Altcode: It has been suggested that interferometric/ synthetic aperture imaging techniques, when applied to the THz regime, can provide sufficient imaging resolution and spectral content to detect concealed explosives and other weapons from a standoff distance. The interferometric imaging method is demonstrated using CW THz generation and detection. Using this hardware, the reconstruction of THz images from a point source is emphasized and compared to theoretical predictions. Title: The Spatial Association of OVSA and RHESSI Sources with H-alpha Ribbons Authors: Lee, J.; Gary, D. E. Bibcode: 2005AGUSMSP52A..03L Altcode: We present detailed comparisons of microwave and hard X-ray maps with H-alpha ribbons that are obtained with the Owens Valley Solar Array (OVSA), Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), and H-alpha filtergrams at Big Bear Solar Observatory (BBSO), respectively, for the 2002 September 9 flare. Since microwave emission can be sensitive to nonthermal electrons residing in any part of the flaring volume depending on local magnetic field and observing frequency, our investigation is motivated to see whether the OVSA's imaging spectroscopy will reveal a link between typically confined hard X-ray sources and rather extended H-alpha kernels. For this event, we observe single hard X-ray source, three kernels at H-alpha blue wing, and more than five kernels at H-alpha line center. The microwave morphology changes from a large arcade-like structure at low frequencies to single dominant footpoint source at high frequencies, and indeed indicates the overall connection between the hard X-ray source and H-alpha kernels. However, one H-alpha kernel lying in an outer weak-field region has neither hard X-ray nor microwave counterparts, and the energetic particle transport to this kernel is yet to be explained by other means. Another non-standard feature of this event is that the H-alpha kernels remained fixed in space rather than separating away from the magnetic neutral line while the flare energy release was going on. We still argue, based on the multifrequency lightcurves, that all these separate components are energetically related, and the wavelength dependent morphology is perhaps due to energy threshold associated with each radiation. Title: Antenna Configurations for the FASR B Array Authors: Tun, S. D.; Gary, D.; White, S. M. Bibcode: 2005AGUSMSP43A..09T Altcode: The proposed Frequency-Agile Solar Radiotelescope (FASR) is to produce high space, time, and frequency resolution full disk solar images. These will allow the reconstructions of the 3-D structure of the Sun's atmosphere from chromosphere to mid-corona. The high resolutions are required to carry out detailed diagnostics of fast-moving phenomena, such as flares and CMEs, as well as of quasi-static structures above active and quiet regions. The full disk images will capture all activity in the corona, even when there are many active regions at solar maximum. One of the tasks necessary to ensure optimal imaging for the array is to determine the best antenna configuration. The current poster presents work done towards this goal. We focus on the FASR-B array, which will cover the 200-3000 MHz range with 60 to 90 antennas of 6-m diameter. We have examined the imaging characteristics for a 3 arm, log-spiral configuration with radius of about 3 km. Multi-frequency observations are simulated for arrays varying in initial antenna spacing, number of antenna elements, and number of turns for each arm. The images reconstructed from the simulated snapshot observations are compared to the original model, convolved with the appropriate beam, to see which configuration yields the most faithful images. We discuss the implications of the findings for the planning of the FASR array configurations. Title: Imaging Type IIIdm Burst Trajectories Authors: Liu, Z.; Gary, D. E.; Nita, G. M.; White, S. M.; Hurford, G. J. Bibcode: 2005AGUSMSP21B..06L Altcode: Type IIIdm radio bursts are important diagnostics of the upward and downward directed beams of nonthermal electrons that originate in the energy release site. Because these bursts have a very high frequency drift rate ( |df/dt|=(0.09±0.03)× f1.35±0.10, Melendez et al., 1999), high time and frequency resolution is a necessary for their observation. Since existing interferometers do not have this combination of spectral and time resolution in the decimetric range, we still do not have detailed information about the location and trajectory of Type IIIdm bursts. We are developing the new FASR Subsystem Testbed (FST) with three existing antennas of Owens Valley Solar Array (OVSA) that will permit imaging with high time and spectral resolution over the 1-9 GHz band. To accomplish this, the received signal is downconverted to 500 MHz bandwidth, then digitized with 1 GHz sampling rate, with digital correlation performed offline. With this three element interferometer, we have the ability to determine the centroid of simple source structures with very high time resolution (10 ms) and frequency resolution (<1 MHz). Such centroids as a function of frequency may outline the trajectories of nonthermal electron beams and so may show the magnetic topology at the energy release site. The FST is expected to be operational in early 2006. This poster presents the FST system configuration and the results of simulations of such trajectories, using a loop model with a simple magnetic geometry, density and temperature profiles given by hydrostatic equilibrium, for different loop heating functions (Aschwanden 2004, Physics of The Solar Corona, Chapter 3). Title: Our Solar Connection: A Themed Set of Activities for Grades 5-12 Authors: Gary, D. E.; van der Veen, W.; Gallagher, A. Bibcode: 2005AGUSMSH11A..04G Altcode: We present a set of 7 interconnected activities on the theme of Sun-Earth connections that we have developed and presented at teacher workshops as part of a NASA-funded Education and Public Outreach project. Associated with the activities are two resource centers that are maintained locally at NJIT in Newark, NJ, and at Raritan Valley Community College (RVCC) in North Branch, NJ. We describe each of the activities and the resource equipment, and present some statistics of how successful the teachers have been in using the activities in their classrooms. A resource CD containing the text of a teacher's guide is available that explains each activity, lists the associated materials needed for each activity, gives estimates for the time required for each activity, and points out specific New Jersey Science Standards met by each activity. Additional resources including movies and photos are included on the CD, and links to this material are contained in the teacher's guide. Title: Quasiperiodic Electron Acceleration in the 15 June 2003 Solar Flare Authors: Fleishman, G. D.; Bastian, T. S.; Gary, D. E. Bibcode: 2005AGUSMSP41C..04F Altcode: We report a comprehensive analysis of strong quasiperiodic radio- and X-ray pulsations observed from the X1.3-class flare which occurred at S06E78 on 23:42-23:50 UT, 15 June 2003. Because of the favorable time of the flare, it was jointly observed by the Owens Valley Solar Array (OVSA) and the Nobeyama Solar Radio Observatory, which allowed us the advantage of combining high spectral, temporal, and spatial resolution radio observations. In addition, the part of this event displaying the strongest pulsations was also observed in hard X-rays with RHESSI. We study the frequency dependence of quantitative measures of the pulsations, including Fourier spectra, phase differences, modulation depth, as well as the degree of (radio) polarization. We compare these measures with the expectations of competing radio pulsation models, i.e., MHD loop oscillations and quasiperiodic electron injection. Although the Fourier spectra display a few significant peaks at each observing frequency, we found that none of them can be explained by the MHD-oscillations. In contrast, the model of quasiperiodic particle acceleration/injection is capable of explaining all quantitative measures observed for this event in a natural way. We discuss implications of these findings for electron acceleration and transport in solar flares. Title: Spatially Resolved Observations Confirm Transition Radiation in a Solar Radio Burst Authors: Nita, G. M.; Gary, D. E.; Fleishman, G. D. Bibcode: 2005AGUSMSP52A..01N Altcode: We report the first confirmed spatially resolved observation of the decimetric Resonant Transition Radiation (RTR) in a solar radio burst, which is an unavoidable by-product of microturbulences present in dense enough astrophysical plasmas. A number of recent publications, based mainly on studies of individual events, found some indication that RTR may be produced in solar radio bursts. Most recently, we have described the observational characteristics expected for RTR in the case of solar radio bursts (Fleishman, Nita, and Gary, 2005, ApJ, 620, 506), and found that the correlations and associations predicted for total power data are indeed present in the decimetric components of a statistical sample of two-component solar continuum radio bursts. However, interpretations based on non-imaging total power data remain indirect (and, thus, ambiguous) until they can be combined with direct imaging evidence from multi-wavelength spatially resolved observations, which so far have been missing in the previous studies. The spectral components of such RTR candidate bursts (one at centimeter wavelengths due to the usual gyrosynchrotron mechanism, and one at decimeter wavelengths suspected as RTR), must be co-spatial to allow an unambiguous RTR interpretation. This study presents comprehensive (radio, optical, and soft X-ray) spatially resolved observations for one of these bursts, which, together with the already demanding spectral and polarization correlations found previously, provide direct evidence for the presence of RTR. Title: Evidence for Resonant Transition Radiation in Decimetric Continuum Solar Bursts Authors: Fleishman, Gregory D.; Nita, Gelu M.; Gary, Dale E. Bibcode: 2005ApJ...620..506F Altcode: We investigate the properties of radio bursts observed in the 1-18 GHz frequency range that display two distinct spectral components peaking at decimetric (dm) and centimetric (cm) ranges. The dm emission is relatively smooth in both frequency and time, with timescales comparable to those of the cm component. The two spectral components display specific correlations in their temporal and spectral behavior. Through detailed analysis, we find the following: (1) A large ratio of plasma frequency to gyrofrequency is a characteristic of all of these events. (2) The dm component generally displays a high degree of o-mode polarization. (3) The dm component is produced by an incoherent emission mechanism. (4) The dm and cm components are generated by the same electron distribution. (5) The characteristic energy of the fast electrons producing the dm continuum is significantly lower than the energy of the electrons generating the microwave gyrosynchrotron component. (6) The spectral shape of the dm component is not well correlated with the fast electron distribution over energy. These findings cannot easily be explained with standard mechanisms for dm solar burst emission but agree well with the predictions of the theory of resonant transition radiation. We conclude that these two-component bursts represent a distinctive subclass of events, comprising about 10% of all bursts, with the dm continuum component generated most probably by resonant transition radiation produced by interaction of fast electrons with small-scale inhomogeneities of the background plasma. We discuss new possibilities for flaring plasma diagnostics using these two-component bursts. Title: Minor Planet Observations [H93 Berkeley Heights] Authors: Gary, D. Bibcode: 2005MPC..53647..13G Altcode: No abstract at ADS Title: Noise in wireless systems from solar radio bursts Authors: Lanzerotti, L. J.; Gary, D. E.; Nita, G. M.; Thomson, D. J.; Maclennan, C. G. Bibcode: 2005AdSpR..36.2253L Altcode: Solar radio bursts were first discovered as result of their interference in early defensive radar systems during the Second World War (1942). Such bursts can still affect radar systems, as well as new wireless technologies. We have investigated a forty-year record of solar radio burst data (1960-1999) as well as several individual radio events in the 23rd solar cycle. This paper reviews the results of a portion of this research. Statistically, for frequencies f ∼ 1 GHz (near current wireless bands), there can be a burst with amplitudes >103 solar flux units (SFU; 1 SFU = 10-22 W/m2) every few days during solar maximum conditions, and such burst levels can produce problems in contemporary wireless systems. Title: Solar system science with SKA Authors: Butler, B. J.; Campbell, D. B.; de Pater, I.; Gary, D. E. Bibcode: 2004NewAR..48.1511B Altcode: 2004astro.ph..9220B Radio wavelength observations of solar system bodies reveal unique information about them, as they probe to regions inaccessible by nearly all other remote sensing techniques and wavelengths. As such, the SKA will be an important telescope for planetary science studies. With its sensitivity, spatial resolution, and spectral flexibility and resolution, it will be used extensively in planetary studies. It will make significant advances possible in studies of the deep atmospheres, magnetospheres and rings of the giant planets, atmospheres, surfaces, and subsurfaces of the terrestrial planets, and properties of small bodies, including comets, asteroids, and KBOs. Further, it will allow unique studies of the Sun. Finally, it will allow for both indirect and direct observations of extrasolar giant planets. Title: Statistics of solar microwave radio burst spectra with implications for operations of microwave radio systems Authors: Nita, Gelu M.; Gary, Dale E.; Lanzerotti, Louis J. Bibcode: 2004SpWea...211005N Altcode: Analysis of 412 solar radio burst events in the microwave range [1.2-18] GHz that were measured at the New Jersey Institute of Technology Owens Valley Solar Array over 2 years (2001-2002) during the peak of the 23rd solar cycle is conducted in the context of the possible interference of such bursts with radio-receiving and radar systems that operate at these frequencies. It is found that there is a small probability for solar interference for systems operating at a frequency ν > 2.6 GHz and with a typical noise floor, but the probability increases significantly at lower frequencies. The probability is greater for more sensitive systems operating with higher gain, but the likelihood of interference can be partially ameliorated by an increase in the operating frequency. Finally, our statistics indicate that it could be beneficial for radio and radar systems operating below 2.6 GHz to employ an adaptable mode wherein, if the prediction of solar activity suggested the possible occurrence of a large radio burst, system operators could switch operations to a less susceptible frequency band above 2.6 GHz. Title: Terahertz near-field interferometric and synthetic aperture imaging Authors: Walsh, Kenneth P.; Schulkin, Brian; Gary, Dale; Federici, John F.; Barat, Robert; Zimdars, David Bibcode: 2004SPIE.5411....9W Altcode: The imaging properties of planar, spherical, and circular interferometric imaging arrays are examined in the near-field region limit. In this region, spherical and circular array architectures can compensate for near-field distortions and increase the field of view and depth of focus. The application of near-field interferometric imaging to the Terahertz frequency range for detection of concealed objects is emphasized. Title: Analysis of terahertz spectral images of explosives and bioagents using trained neural networks Authors: Oliveira, Filipe; Barat, Robert; Schulkin, Brian; Huang, Feng; Federici, John F.; Gary, Dale; Zimdars, David Bibcode: 2004SPIE.5411...45O Altcode: A non-invasive means to detect and characterize concealed agents of mass destruction in near real-time with a wide field-of-view is under development. The method employs spatial interferometric imaging of the characteristic transmission or reflection frequency spectrum in the Terahertz range. However, the successful (i.e. low false alarm rate) analysis of such images will depend on correct distinction of the true agent from non-lethal background signals. Neural networks are being trained to successfully distinguish images of explosives and bioagents from images of harmless items. Artificial neural networks are mathematical devices for modeling complex, non-linear relationships. Both multilayer perceptron and radial basis function neural network architectures are used to analyze these spectral images. Positive identifications are generally made, though, neural network performance does deteriorate with reduction in frequency information. Internal tolerances within the identification process can affect the outcome. Title: Radio Spectral Diagnostics Authors: Gary, Dale E.; Hurford, G. J. Bibcode: 2004ASSL..314...71G Altcode: We review solar radio emission from the perspective of imaging spectroscopy. Radio emission mechanisms differ in their spectral properties, which can be used to determine parameters of the emitting particles and the ambient solar atmosphere in the emitting volume. After generation, the propagation of radiation in the solar atmosphere leads to changes in the spectrum that can be exploited to gain further information about the atmospheric parameters along the line of sight. Title: Analysis of the impulsive phase of a solar flare at submillimeter wavelengths Authors: Raulin, Jean Pierre; Makhmutov, Vladimir S.; Kaufmann, Pierre; Pacini, Alessandra Abe; Lüthi, Thomas; Hudson, Hugh S.; Gary, Dale E. Bibcode: 2004SoPh..223..181R Altcode: We present a report on the strong X5.3 solar flare which occurred on 25 August 2001, producing high-level γ-ray activity, nuclear lines and a dramatic long-duration white-light continuum. The bulk of millimeter radio fluxes reached a peak of ∼100 000 solar flux units at 89.4 GHz, and a few thousands of solar flux units were detected in the submillimeter range during the impulsive phase. In this paper we focus on and discuss (i) the implications inferred from high frequency radio observations during the impulsive phase; (ii) the dynamics of the low corona active region during the impulsive phase. In particular we found that 4-5 × 1036 accelerated (>20 keV) electrons s−1 radiating in a 1000-1100 G region, are needed to explain the millimeter to submillimeter-wave emissions. We present evidence that the magnetic field in the active region was very dynamic, and that strong non-thermal processes were triggered by the appearance of new, compact, low-lying (few thousand kilometers) loop systems, suggesting the acceleration site(s) were also located in the low solar atmosphere. Title: Solar and Space Weather Radiophysics - Current Status and Future Developments Authors: Gary, D. E.; Keller, C. U. Bibcode: 2004ASSL..314.....G Altcode: 2004sswr.book.....G The book explores what can be learned about the Sun and interplanetary space using present-day and future radio observations and techniques. The emphasis is on interpretation of radio data with high spatial and spectral resolution, motivated by the planned construction of a new, powerful, solar-dedicated radio array called the Frequency Agile Solar Radiotelescope (FASR). The book is unique in exploring a broad frequency range, which corresponds to heights ranging from the low solar atmosphere out to the Earth. The book contains a thorough review of the entire field of solar and Space Weather radio research; gives background information suitable for advanced undergraduates, graduates, and researchers in solar and Space Weather research and related fields; and looks at what new results may be expected in the next two decades with FASR and other new instruments now under development. The individual chapters are written by international experts in each topic, and although each chapter may be read as a stand-alone article, the ordering of the chapters and the topical development makes the book readable from beginning to end, to provide an excellent understanding of the field as a whole. Title: Hard X-Ray and Microwave Observations of Microflares Authors: Qiu, Jiong; Liu, Chang; Gary, Dale E.; Nita, Gelu M.; Wang, Haimin Bibcode: 2004ApJ...612..530Q Altcode: In this paper, we study solar microflares using the coordinated hard X-ray and microwave observations obtained by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) during its open-shutter operation mode and the Owens Valley Solar Array (OVSA). The events in our study are selected in the energy range of 12-25 keV and are relatively large microflares with an average GOES soft X-ray incremental flux at the B2.0 level. A total of 760 microflares are identified from the RHESSI burst catalog. Of the 200 microflares that fall into the OVSA observing window, about 40% are detected in microwaves. Using these hundreds of events as samples, we study the event distribution with respect to the flux, the solar activity, and active regions, in comparison with flares of larger scales. Nonthermal properties of microflares are investigated through spectral analysis of X-rays and microwaves. (1) We find that the event frequency distribution with respect to the RHESSI peak count rates at 12-25 keV can be accurately described with a power-law function down to 8 counts s-1, the power-law index being 1.75+/-0.03, consistent with previous studies. (2) Similar to large flares, the occurrence rate of microflares is correlated with solar activity. The studied samples of microflares are mostly produced by active regions, as suggested by the large percentage of events detected by OVSA, which observes target active regions. However, all active regions do not have equal productivity, and certain active regions are a lot more productive than other regions. (3) While some large and complex active regions are predominantly productive in both very weak and strong events, we also find an active region that produces many microflares and C-class events but does not produce powerful events. (4) Analysis of energy-dependent time profiles suggests that there is a pronounced temporal correlation between the time derivative of soft X-rays and 14-20 keV hard X-rays, i.e., the Neupert effect, in about one-half the studied events. (5) Albeit small, many microflares exhibit hard X-ray emission at over 10 keV and microwave emission at around 10 GHz. Spectral analysis in these two wavelengths corroborates the nonthermal nature of these emissions. (6) In a limited number of samples, the RHESSI spectral fitting yields a photon spectral index of 4.5-7, and microwave spectral analysis on the same events shows that the power-law index of the electron spectrum is in the range of 2-5. The discrepancy in the electron spectrum index derived from hard X-rays and microwaves is substantially greater than previously reported in big flares, hinting at the existence of high-energy, microwave-emitting electrons that have a much hardened spectrum compared with electrons emitting hard X-rays. Title: FASR Simulation of Solar Flare Microwave Spectrum Authors: Lee, J.; Gary, D. E.; White, S. M. Bibcode: 2004AAS...204.5414L Altcode: 2004BAAS...36..760L We investigate microwave diagnostics on solar flare electrons at the quality of imaging spectroscopy expected from the proposed Frequency Agile Solar Radiotelescope (FASR). We mainly concern ourselves with influence of the spatial inhomogeneities upon microwave spectral features and realistic magnetic configurations of flare active regions. Solar flare microwave radiations are calculated by using nonthermal electrons distributed along a set of reconnected field lines, and by sampling the resulting gyrosynchrotron intensities at the resolution of the FASR. The simulated observations are then compared with reference spectra of homogeneous source models to find a strategy for inversion of the observed spectrum to the physical parameters of flare electrons.

This work is supported by the NSF grant AST-0138317 and NASA grant NAG5-10891 to New Jersey Institute of Technology. Title: Decimetic Continuum Bursts Observed with the Owens Valley Solar Array Authors: Nita, G. M.; Fleishman, G. D.; Gary, D. E. Bibcode: 2004AAS...204.3805N Altcode: 2004BAAS...36..713N A recent statistical study of 412 microwave burst spectra observed with OVSA during 2001-2002 (Nita, Gary and Lee 2004) revealed that about 16% of these spectra display a decimetric (dm) spectral component accompanying the centimetric (cm) emission. Rather surprisingly, most of the dm components display smooth spectra, with time scales comparable with those of their cm counterparts. In all considered events, the dm and cm spectral components are correlated in different aspects, so related to each other. We find no indication for these events of an anisotropic pitch-angle distribution, neither loss-cone nor beam-like, so no condition for any kinetic instability producing coherent radio emission is found. The dm component is likely produced by an incoherent emission mechanism, since its flux is proportional to the number of emitting electrons. The dm component is O-polarized, the degree of polarization being very large in some cases. We also find that the characteristic energy of fast electrons producing the dm continuum is significantly lower than the energy of the electrons generating the microwave gyrosynchrotron component. It appears that the spectral shape of the dm component is fairly independent of the fast electron distribution over energy. These findings agree well with the theoretical predictions for resonant transition radiation arising as a result of interaction of fast electrons and small-scale inhomogeneities of the background plasma, while they can hardly be interpreted within other known mechanisms of incoherent emission (like gyrosynchrotron, bremsstrahlung or inverse Compton). We discuss new possibilities of flaring plasma diagnostics with the use of these two-component bursts. This work is supported by NSF grant AST-0307670 to New Jersey Institute of Technology. Title: A New Radio Diagnostic for Razin Suppression Authors: Gary, D. E.; Melnikov, V. F.; Nita, G. M. Bibcode: 2004AAS...204.8806G Altcode: 2004BAAS...36..820G We have investigated the dynamical behavior of the radio spectrum of more than 300 microwave bursts observed with the Owens Valley Solar Array in the range 1.2-18 GHz. For this talk, we concentrate on the evolution of the peak frequency of the spectrum as measured throughout the bursts. We find that in most bursts the evolution fits the expected behavior for gyrosynchrotron emission, moving to higher frequencies on the rise and falling back on the decay of the burst. However, for some 35% of bursts we find that this expected behavior is modified during part or all of the burst by the presence of Razin Suppression, which is expected in sources with higher than usual ambient density. Looking at other aspects of the spectral evolution, we deduce several measures that occur together to uniquely distinguish the presence of Razin Suppression. The presence of Razin Suppression has historically been associated only with the presence of a steeper than usual low frequency spectral slope, but this traditional diagnostic is valid only for homogeneous sources and can be completely masked in the typical case of inhomogeneous or multiple sources. Our new diagnostics of Razin Suppression reveal its presence even for inhomogeneous sources, and hence has a wider range of validity. The new diagnostics will be especially useful with the high resolution imaging microwave spectroscopy that will be provided by the proposed FASR array. This work is supported by NSF grant AST-0307670 to New Jersey Institute of Technology. Title: Simulation of Microwave Emissions from Helmet Streamer Authors: Tun, S. D.; Gary, D. E.; Lee, J. Bibcode: 2004AAS...204.7102T Altcode: 2004BAAS...36R.797T Helmet streamers are an important magnetic structure on the sun in relation to prominence formation and coronal mass ejections. We investigate some methods by which the magnetic field configuration in a streamer can be reconstructed from observations with the proposed Frequency Agile Solar Radio telescope (FASR). We begin with the global coronal magnetic field model for the forward problem proposed by Judge and Low in 2004. We add a realistic coronal temperature and density model that obeys hydrostatic equilibrium and allows gyroresonance emission to dominate the free-free emission at a selected observing frequency. Theoretical brightness temperature maps are created from the model at multi-frequencies and are then sampled using AIPS to simulate observations with the FASR. The magnetic field structure reconstructed from the simulated observations is compared with the original input configuration as a test of our diagnostics on the magnetic field.

This work is supported by the NSF grants AST-0138317 and ATM-0077273 to New Jersey Institute of Technology. Title: Magnetic Reconnection and Mass Acceleration in Flare-Coronal Mass Ejection Events Authors: Qiu, Jiong; Wang, Haimin; Cheng, C. Z.; Gary, Dale E. Bibcode: 2004ApJ...604..900Q Altcode: An observational relationship has been well established among magnetic reconnection, high-energy flare emissions and the rising motion of erupting flux ropes. In this paper, we verify that the rate of magnetic reconnection in the low corona is temporally correlated with the evolution of flare nonthermal emissions in hard X-rays and microwaves, all reaching their peak values during the rising phase of the soft X-ray emission. In addition, however, our new observations reveal a temporal correlation between the magnetic reconnection rate and the directly observed acceleration of the accompanying coronal mass ejection (CME) and filament in the low corona, thus establishing a correlation with the rising flux rope. These results are obtained by examining two well-observed two-ribbon flare events, for which we have good measurements of the rise motion of filament eruption and CMEs associated with the flares. By measuring the magnetic flux swept through by flare ribbons as they separate in the lower atmosphere, we infer the magnetic reconnection rate in terms of the reconnection electric field Erec inside the reconnecting current sheet (RCS) and the rate of magnetic flux convected into the diffusion region. For the X1.6 flare event, the inferred Erec is ~5.8 V cm-1 and the peak mass acceleration is ~3 km s-2, while for the M1.0 flare event Erec is ~0.5 V cm-1 and the peak mass acceleration is 0.2-0.4 km s-2. Title: Statistical Study of Two Years of Solar Flare Radio Spectra Obtained with the Owens Valley Solar Array Authors: Nita, Gelu M.; Gary, Dale E.; Lee, Jeongwoo Bibcode: 2004ApJ...605..528N Altcode: We present results of analysis of 412 flares during 2001-2002 as detected by the Owens Valley Solar Array (OVSA). This is an in-depth study to investigate some results suggested by a previous study of solar bursts (Nita et al. 2002), which was limited to the peak time of the bursts at a few frequency bands. The new study includes the temporal dependence, at 4 s time resolution, of parameters measured at 40 frequencies in the range 1-18 GHz. We investigate distributions of burst parameters such as maximum flux density in the spectra, peak frequency, spectral slopes below and above the peak frequency (optically thick and thin slopes, respectively), and burst durations. We classify the microwave bursts according to their spectral properties and provide tables of averaged spectral parameters for each spectral type and for different frequency and intensity ranges. Title: Impulsive and Gradual Nonthermal Emissions in an X-Class Flare Authors: Qiu, Jiong; Lee, Jeongwoo; Gary, Dale E. Bibcode: 2004ApJ...603..335Q Altcode: In this paper we present a comprehensive case study of an X-class flare observed on 2001 April 6. The flare consists of two episodes, the first characterized by impulsive spiky bursts and the second by gradual smooth emission at hard X-ray and microwave wavelengths. Emissions in the two episodes are regarded as the impulsive and gradual components, respectively. We compare the temporal, spatial, and spectral evolution of the two components in hard X-rays and microwaves. For this event, the most important finding is that both the impulsive and gradual hard X-rays at >=50 keV are thick-target emissions at conjugate footpoints. Evolution of hard X-rays and microwaves during the gradual phase exhibits a separation motion between two footpoint sources, which reflects progressive magnetic reconnection. Observations further reveal distinct spectral properties of the gradual component. It is most prominently observed in the high-energy (>20 keV) range, and the gradual hard X-rays have a harder and hardening spectrum compared with the impulsive component. The gradual component is also a microwave-rich event, with the microwaves lagging the hard X-rays by tens of seconds. A correlation analysis of the hard X-ray light curves shows energy-dependent time delays, with the 200 keV hard X-rays lagging the 40 keV emission by 20 s. The observations and analyses suggest that magnetic reconnection occurs during both the impulsive and gradual phases that generate nonthermal electrons, primarily precipitating at the footpoints. However, the temporal and spectral properties of the gradual component must be produced by an acceleration mechanism different from that of the impulsive phase. We propose that the ``collapsing-trap'' effect, as a product of progressive magnetic reconnection in bipolar magnetic fields, is a viable mechanism that continuously accelerates the gradual-phase electrons in a low-density trap before they precipitate into the footpoints. Title: Studies of Microflares in RHESSI Hard X-Ray, Big Bear Solar Observatory Hα, and Michelson Doppler Imager Magnetograms Authors: Liu, Chang; Qiu, Jiong; Gary, Dale E.; Krucker, Säm; Wang, Haimin Bibcode: 2004ApJ...604..442L Altcode: In this paper, we present a study of the morphology of 12 microflares jointly observed by RHESSI in the energy range from 3 to 15 keV and by Big Bear Solar Observatory (BBSO) at the Hα line. They are A2-B3 events in GOES classification. From their time profiles, we find that all of these microflares are seen in soft X-ray, hard X-ray, and Hα wavelengths, and their temporal evolution resembles that of large flares. Co-aligned hard X-ray, Hα, and magnetic field observations show that the events all occurred in active regions and were located near magnetic neutral lines. In almost all of the events, the hard X-ray sources are elongated structures connecting two Hα bright kernels in opposite magnetic fields. These results suggest that, similar to large flares, the X-ray sources of the microflares represent emission from small magnetic loops and that the Hα bright kernels indicate emission at footpoints of these flare loops in the lower atmosphere. Among the 12 microflares, we include five events that are clearly associated with type III radio bursts as observed by the radio spectrometer on board Wind. Spectral fitting results indicate the nonthermal origin of the X-ray emission at over ~10 keV during the impulsive phase of all the events, and the photon spectra of the microflares associated with type III bursts are generally harder than those without type III bursts. TRACE observations at EUV wavelengths are available for five events in our list, and in two of these, coincident EUV jets are clearly identified to be spatially associated with the microflares. Such findings suggest that some microflares are produced by magnetic reconnection, which results in closed compact loops and open field lines. Electrons accelerated during the flare escape along the open field lines to interplanetary space. Title: A New Solar Burst Spectral Component Emitting Only in the Terahertz Range Authors: Kaufmann, Pierre; Raulin, Jean-Pierre; de Castro, C. G. Giménez; Levato, Hugo; Gary, Dale E.; Costa, Joaquim E. R.; Marun, Adolfo; Pereyra, Pablo; Silva, Adriana V. R.; Correia, Emilia Bibcode: 2004ApJ...603L.121K Altcode: Solar flare energy manifestations were believed to be the result of the same kind of particle acceleration. It is generally accepted that a population of relativistic electrons accelerated during the impulsive phase of solar flares produces microwaves by synchrotron losses in the solar magnetic field and X-rays by collisions in denser regions of the solar atmosphere. We report the discovery of a new intense solar flare spectral radiation component, peaking somewhere in the shorter submillimeter to far-infrared range, identified during the 2003 November 4 large flare. The new solar submillimeter telescope, designed to extend the frequency range to above 100 GHz, detected this new component with increasing fluxes between 212 and 405 GHz. It appears along with, but is separated from, the well-known gyrosynchrotron emission component seen at microwave frequencies. The novel emission component had three major peaks with time, originated in a compact source whose position remained remarkably steady within 15". Intense subsecond pulses are superposed with excess fluxes also increasing with frequency and amplitude increasing with the pulse repetition rate. The origin of the terahertz emission component during the flare impulsive phase is not known. It might be representative of emission due to electrons with energies considerably larger than the energies assumed to explain emission at microwaves. This component can attain considerably larger intensities in the far-infrared, with a spectrum extending to the white-light emission observed for that flare. Title: Flare-related Magnetic Anomaly with a Sign Reversal Authors: Qiu, Jiong; Gary, Dale E. Bibcode: 2003ApJ...599..615Q Altcode: In this paper we report a significant magnetic anomaly, specifically an apparent sign reversal of magnetic polarities in small areas of Michelson Doppler Imager (MDI) magnetograms during the impulsive phase of an X5.6 flare on 2001 April 6. Three flare kernels were observed to emit >=50 keV hard X-rays, which are located in strong magnetic fields of order +/-1000-1500 G. We find that the apparent sign reversal began and persisted for a few minutes in all three kernels, in precise temporal and spatial correspondence with the hard X-ray sources. We search for a combination of instrumental and flare-induced line profile effects that can account for this behavior. Our studies provide a viable scenario that the observed transient sign reversal is likely to be produced by distorted measurements when the Ni I 6768 Å line comes into emission or strong central reversal as a result of nonthermal beam impact on the atmosphere in regions of strong magnetic fields. Title: Radio Coverage from Chromosphere to Earth: FASR-LOFAR-SIRA Synergy Authors: Gary, D. E.; Kassim, N.; Gopalswamy, N.; Aschwanden, M. J. Bibcode: 2003AGUFMSH42E..02G Altcode: Radio emission is uniquely sensitive to a number of key plasma parameters (magnetic field, temperature, density, high-energy electrons, and various plasma waves) over heights ranging without gaps from the chromosphere, throughout the corona and heliosphere, to the Earth. Two ground-based radio arrays, the Frequency Agile Solar Radiotelescope (FASR) and the Low Frequency Array (LOFAR), together with the space-based Solar Imaging Radio Array (SIRA) are planned that will for the first time provide direct imaging of disturbances over this vast height range through interferometric imaging over their equally impressive frequency range of 24 GHz to 30 kHz. We describe the science goals of these instruments, focusing especially on the science addressed jointly by all three instruments. Among the examples are (1) simultaneous imaging of CMEs, flaring loops, and shock-associated (type II) emission and (2) imaging the propagation of electrons on open field lines (type III), from their acceleration point through the corona and heliosphere to the point where they are measured in situ by near-Earth spacecraft. In addition to spatially relating the different phenomena, the spectral information is rich in quantitative diagnostics. We give some examples of the revolutionary results we can expect from the combined instruments. Title: Coronal Magnetic Diagnostics With FASR Authors: White, S. M.; Gary, D. E.; Lee, J.; Giordano, G. Bibcode: 2003AGUFMSH42D..04W Altcode: Coronal magnetography is one of the main scientific drivers for the proposed Frequency Agile Solar Radiotelescope (FASR). Radio emission is particularly valuable as a diagnostic of coronal magnetic fields because (a) the emission mechanisms all depend on magnetic field, and (b) typical values of the electron gyroresonance frequency f_B for coronal field strengths lie in the radio domain. The microwave emission from active regions is dominated by thermal gyroresonance emission at low harmonics of f_B and this provides a well-understood diagnostic. Since f_B is proportional to magnetic field strength, there is a simple mapping between frequency and magnetic field. A wide range of coronal magnetic field strengths can be sampled by observing across a wide range of radio frequencies simultaneously, and FASR is designed to do this quickly enough to follow changes in coronal fields. We demonstrate the ability to measure coronal fields with this technique by simulating a FASR observation of a realistic three-dimensional model of an active region and then determining the coronal magnetic field at the base of the corona from the simulated images. Comparison with radio images of gyroresonance emission from active regions is also a valuable tool for assessing extrapolations of surface magnetic field measurements into the corona, and we discuss several applications of this comparison. Gyrosynchrotron radio emission from nonthermal electrons accelerated by solar flares also can reveal the magnetic topology of the flare source and we discuss this briefly. Title: Probing Solar Energetic Particles with SIRA Authors: Aschwanden, M. J.; Nitta, N.; Lemaster, E.; Byler, E.; Gary, D.; Kassim, N.; Gopalswamy, N. Bibcode: 2003AGUFMSH42C0555A Altcode: The space-based SIRA (Solar Imaging Radio Array) will provide a powerful capability to track high energy particles from solar flare and CME sites through interplanetary/heliospheric space all the way to Earth. Together with two other overlapping planned radio interferometers, i.e., FASR (Frequency-Agile Solar Radiotelescope) and LOFAR (Low-Frequency Array) the entire plasma frequency range from 30 GHz all the way down to the plasma frequency cutoff of 30 kHz at 1 AU will be covered. These instruments will track the magnetic trajectory of high energy particles, beam-driven radio emission, and localize the acceleration sites in the corona or interplanetary shocks. We simulate some CME and type III events, as they will be mapped with these instruments, using realistic scattering functions of radio waves on coronal and heliospheric density inhomogeneities. Title: Cutoff of non-thermal electrons responsible for solar microwave and hard X-ray bursts Authors: Huang, G. L.; Zhang, J.; Gary, D. Bibcode: 2003ESASP.535..663H Altcode: 2003iscs.symp..663H The method to estimate the low cutoff energy of non-thermal electrons in solar microwave and hard X-ray bursts is discussed in this paper. At first, for a given radiation mechanism, the ratio between two frequency (or energy) channels is calculated with different value of the cutoff to fit the observational data. Secondly, the cross point of the spectral profiles at different time for a given burst may provide the information of the low or high cutoff energy of non-thermal electrons. Two events on June 3 and 10, 2000 are studied with data of OVSA and YOHKOH. Title: Detecção da fase impulsiva de uma explosão solar gigante até 405 GHz Authors: Raulin, J. -P.; Makhmutov, V.; Kaufmann, P.; Pacini, A. A.; Luethi, T.; Hudson, H. S.; Gary, D. E.; Yoshimori, M. Bibcode: 2003BASBr..23..179R Altcode: A explosão ocorrida no dia 25/08/2001 foi uma das mais intensas do presente ciclo solar em ondas de rádio de altas frequências. Foram medidas em ondas milimétricas e submilimétricas, aproximadamente, 105 e vários milhares de unidades de fluxo solar, respectivamente. Apresentamos um estudo deste evento em múltiplas frequências, desde microondas (1GHz), até ondas submilimétricas (405 GHz) detectadas pelo Telescópio Solar para ondas Submilimétricas (SST). Esta base de dados foi complementada utilizando-se o experimento Yohkoh, incluindo a emissão em raios-X duros e raios-g (até 100 MeV), e imagens em raios-X moles da região ativa envolvida. Enfocamos e discutimos principalmente os seguintes aspectos da fase impulsiva do evento: (i) as implicações deduzidas do espectro eletromagnético, obtido pela primeira vez até 405 GHz; (ii) a dinâmica da região ativa. Os resultados mostram que para explicar o espectro rádio observado, são necessários entre 3.5×1037 e 1.5×1039 elétrons acelerados acima de 20 keV em uma região de campo magnético entre 300 e 800 Gauss. A estimativa do fluxo de fótons que seria produzido por estes elétrons, mostra que grande parte deles não precipitou na baixa atmosfera. A evolução temporal da emissão em raios-X moles revela que a configuração magnética da região ativa foi muito dinâmica durante a fase impulsiva da explosão. Em particular, mostramos que a produção dos elétrons altamente energéticos foi iniciada junto com a aparição, na baixa coroa solar, de um novo sistema compacto de estruturas magnéticas. Este fato sugere que os locais de aceleração estão localizados na baixa atmosfera do Sol, como resultado da interação entre o novo sistema compacto e o campo magnético ambiente da região ativa. Title: Decimetric Spike Bursts versus Microwave Continuum Authors: Fleishman, Gregory D.; Gary, Dale E.; Nita, Gelu M. Bibcode: 2003ApJ...593..571F Altcode: We analyze properties of decimetric spike bursts occurring simultaneously with microwave gyrosynchrotron continuum bursts. We found that all of the accompanying microwave bursts were highly polarized in the optically thin range. The sense of polarization of the spike clusters is typically the same as that of the optically thin gyrosynchrotron emission, implying preferential extraordinary wave-mode spike polarization. Optically thick spectral indices of the continuum in spike-producing events were not observed to be larger than 2.5, suggesting low or absent Razin suppression. This implies that the plasma frequency-to-gyrofrequency ratio is systematically lower in the spike-producing bursts than in other bursts. The spike cluster flux density is found to be tightly correlated with the high-frequency spectral index of the microwave continuum for each event, while the flux-to-flux correlation may not be present. We discovered strong evidence that the trapped fast electrons producing the microwave gyrosynchrotron continuum have an anisotropic pitch-angle distribution of the loss cone type in the spike-producing bursts. The spike clusters are mainly generated when the trapped electrons have the hardest and the most anisotropic distributions. The new properties are discussed against the currently available ideas about emission processes and models for spike generation. We conclude that the findings strongly support the electron cyclotron maser mechanism of spike emission, with characteristics agreeing with expectations from the local-trap model. Title: The Frequency Agile Solar Radiotelescope Authors: GARY, DALE E. Bibcode: 2003JKAS...36S.135G Altcode: No abstract at ADS Title: Solar Active Region Study Using Microwave Maps Authors: Bong, Su-Cran; Lee, Jeongwoo; Gary, Dale E.; Yun, Hong Sik Bibcode: 2003JKAS...36S..29B Altcode: No abstract at ADS Title: Small Radio Interferometer Arrays in Solar Physics Authors: Gary, Dale E. Bibcode: 2003ASSL..288..309G Altcode: 2003ASSL..287..609G No abstract at ADS Title: Coronal Magnetography with the Frequency Agile Solar Radiotelescope Authors: Gary, D. E.; Lee, J. Bibcode: 2003SPD....34.2016G Altcode: 2003BAAS...35..847G We investigate the expected performance of the proposed Frequency Agile Solar Radiotelescope (FASR) for coronal magnetography. FASR is expected to produce high quality radio images at hundreds of radio frequencies in the appropriate frequency range (1-24 GHz) to measure active region coronal magnetic fields with exquisite precision. We start with a realistic coronal active region model provided by Y. Mok (UC-Irvine), and calculate the radio emission expected from the region due to both the gyroresonance and free-free mechanisms. We then sample the model images with a candidate FASR antenna configuration and add noise, to obtain a set of multifrequency images of the same spatial resolution and quality expected from the instrument.

The resulting data-cube of two spatial and one spectral dimensions yields microwave spectra at each point in the active region, which are then inverted to obtain the active region plasma parameters (temperature, emission measure, and magnetic field strength and direction). These are finally compared to the input model, to determine the quantitative precision of the inversion. We try several inversion techniques of varying sophistication, to simulate both automated quick-look coronal magnetograms and more time-consuming, research-quality magnetograms.

This work is supported by the National Science Foundation under grant AST-0138317 to New Jersey Institute of Technology. Title: Spectral Dynamics of Solar Broadband Microwave Bursts. Authors: Melnikov, V. F.; Gary, D. E.; Nita, G. Bibcode: 2003SPD....34.1505M Altcode: 2003BAAS...35..831M Microwave spectral observations provide important information on acceleration and transport of mildly relativistic electrons as well as on magnetoactive plasma in solar flaring loops. In this study we analyze dynamics of the frequency spectrum of a sample of broad band microwave bursts selected to have only a single spectral maximum and simple time profiles, using data obtained in 2001 with the OVSA solar-dedicated frequency-agile interferometer. In particular, we study the evolution during a burst of such parameters as the spectral peak frequency fp, the ratio of fluxes at f > fp and f < fp, the average spectral indices above and below fp, as well as the frequency distribution of local spectral indices.

The most common dynamic properties of the parameters are as follows. Peak frequency changes with time, increasing on the rising phase and decreasing on the decay phase of bursts. The ratio of fluxes at f > fp and f < fp in most of cases increases on the rise phase and decreases on the decay phase. Spectral indices above and below fp decrease their absolute value on the decay phase. However this general time behavior may change to opposite one in some events.

The spectral peculiarities found are then compared with relevant theoretical expectations derived from model simulations of radio emission that take into account some effects of energetic electron spectral and spatial evolution in flaring loops and also their pitch-angle anisotropy. We also consider the influence of self-absorption and dense plasma inside the loop (Razin effect) on the spectral characteristics of the gyrosynchrotron emission. Finally, results of the comparisons are used to get new information on the high energy electron kinematics and temporal evolution of plasma parameters inside flaring loops.

This work is supported by NASA grants NAG5-10212 and NAG5-10891. OVSA/NJIT is supported by NSF under grant AST-9987366. Title: Hα , EUV, and Microwave Observations of a Large Flare as Evidence for Spontaneous Magnetic Reconnection Authors: Lee, J.; Gallagher, P. T.; Gary, D. E.; Nita, G. M.; Choe, G. S. Bibcode: 2003SPD....34.1604L Altcode: 2003BAAS...35Q.833L The large solar flare with GOES class X1.1 occurred on 2000 March 22 is observed with the Owens Valley Solar Array (OVSA), Hα filtergram of Big Bear Solar observatory (bbso), the Transition region and Coronal Explorer (trace), and the Michelson Doppler Imager (mdi) onboard Solar and Heliospheric Observatory (SOHO). During the impulsive phase a set of EUV loops are visible in a small volume confined to the center of the large β γ δ -type active region. Radio emission at 5 GHz appears as a single source encompassing multiple Hα ribbons, and radio emissions at other frequencies also appear within the central core region. We interpret these observations under the idea of the confined flare in contrast with the more commonly cited, eruptive flare, using a schematic magnetic reconnection geometry based on the mdi magnetogram. It is suggested that the EUV loops represent a separatrix in part, and that the radio and Hα sources coincide with the whole part of the separatrix and its footpoints, respectively. In addition, a Coronal Mass Ejection (CME) as detected in the LASCO coronagraph after this flare is briefly discussed in relation to the above idea of magnetic reconnection.

This work has been supported by NASA grants NAG 5-10891 and NAG-11875. Title: Statistical study of flare radio spectra obtained with OVSA Authors: Nita, G. M.; Gary, D. E.; Lee, J. Bibcode: 2003SPD....34.1506N Altcode: 2003BAAS...35..831N We present results of analysis of 397 flares during 2001 as detected by the Owens Valley Solar Array (OVSA). This is a more in-depth study to investigate some results indicated by a previous study of solar bursts (Nita, Gary, Lanzerotti & Thomson 2002, ApJ, 570, 423.), which was limited at the peak time of the bursts at a few frequencies.

The new study involves temporal dependence of parameters and the more complete frequency coverage available with OVSA, which measures solar fluxes at 40 frequencies in 1-18 GHz range with 4 s time resolution.

We investigate distributions of the burst parameters such as maximum flux density in the spectra, peak frequency, spectral slopes below and above peak frequency, duration in both rise and decay phases and total energy at selected frequencies. We discuss correlations between these parameters, which help us to understand particle acceleration and flare energetics. Title: Studies of Microflares with RHESSI, Hard X-ray in BBSO Hα and MDI Magnetograms Authors: Liu, C.; Qiu, J.; Gary, D.; Krucker, S.; Wang, H. Bibcode: 2003SPD....34.2203L Altcode: 2003BAAS...35..850L Microflares are among the most interesting subjects because its accumulated energy may be a substantial part to heat the upper solar atmosphere. The unique high sensitivity in the energy range from ∼3 to 15 keV and excellent spectral and spatial resolution provided by the Ramaty High Energy Solar Spectroscopic Imager mission (RHESSI) allow for the first time the detailed study of the locations and the spectra property of solar microflares. We studied a number of microflares in the energy range from 3 to 15 keV which occurred in several active regions, in July 2002, and we found: (1) from the co-alignment results between RHESSI and MDI, we confirm that almost all the microflares are located in magnetic neutral lines; (2) from the co-alignment results between RHESSI and Hα images, we find that the hard X-ray source tends to connect two Hα footpoints and the RHESSI peaks always occur ∼1 minute earlier than the observable Hα brightening, which indicates the possible loop-top source before the Hα footpoint brightening; (3) We also notice that some microflares are associated with type III radio bursts as observed by the radio spectrometer on-board WIND. Title: Study of Microflares at Hard X-ray and Microwave Wavelengths Authors: Qiu, J.; Gary, D. E.; Liu, C.; Wang, H. Bibcode: 2003SPD....34.1504Q Altcode: 2003BAAS...35..831Q We present the preliminary results of studying microflares at hard X-ray and microwave wavelengths which are observed by Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and Owens Valley Solar Array (OVSA). Among over 700 microflare bursts that are observed by RHESSI during the open-shutter mode from May to September in 2002, more than 200 fall into the OVSA observing time window. In this study, we analyze the first set of about 130 events jointly observed by the two instruments. These events are predominantly detected by RHESSI in the energy range below 15 keV. They are mostly accompanied by a minor increase in GOES flux below B5 level, but the time profiles at >10keV peak earlier than GOES flux by tens of seconds. By examining the lightcurves and dynamic spectra at hard X-ray and radio wavelengths, we find that more than 40% of the RHESSI bursts are unambiguously identified as microwave bursts, with the peak flux ranging from a few to several tens of solar flux units and the peak frequency at greater than 5 GHz. These results are indications of non-thermal features of the microflare events. We also discuss the distribution of microflares in quiet-Sun and active regions, the temporal and spatial relationship between microflares and major flares, and the spectral properties of microflares in comparison with major flares.

This work is supported by the NASA grant NAG5-10212. Title: A Multi-wavelength Analysis of a Solar Limb Flare on 2002 April 15 Authors: Sui, L.; Holman, G. D.; Gary, D. E.; Shibasaki, K. Bibcode: 2003SPD....34.1807S Altcode: 2003BAAS...35..840S A detailed analysis of a limb flare on 2002 April 15 was carried out using RHESSI X-ray images and spectra, Nobeyama microwave images, Owens Valley Solar Array (OVSA) microwave spectra, and SOHO EIT & LASCO images. This M1.2 flare lasted about 40 minutes in GOES soft X-rays. RHESSI missed part of the decay phase of the flare. RHESSI images show a thermal flare loop at 6-25 keV and a bright thermal looptop source within the loop throughout the flare. At the peak of the flare, a coronal source 6 arcseconds above the flare loop and two clear-cut footpoints appear at 25-50 keV. Another coronal source above the loop at 10-25 keV ejected outward at about 600 km/s after the peak. By fitting the RHESSI spectra, we found that a low-energy cut-off at about 22 keV is required in order to get a consistent evolution of the thermal plasma parameters with time. After the hard X-ray peak, the flare loop moves outward in both the SOHO/EIT 195 Å band and the Nobeyama microwave images. It precedes an expanding coronal anomaly observed in SOHO/LASCO C2 images. We will show images and movies of our results, and a comparison of the microwave images and spectra with the RHESSI observations.

This project was supported in part by the RHESSI Project and the NASA Sun-Earth Connection Program. Title: The Frequency Agile Solar Radiotelescope (FASR) Authors: White, S. M.; Gary, D. E.; Bastian, T. S.; Hurford, G. J.; Lanzerotti, L. J. Bibcode: 2003EAEJA....11021W Altcode: The Frequency Agile Solar Radiotelescope (FASR) is a radio interferometer designed to make high spatial resolution images of the Sun across a broad range of radio wavelengths simultaneously, allowing the technique of imaging spectroscopy to be exploited on a routine basis. The telescope will cover the frequency range 0.1-30 GHz using several sets of receiving elements that provide full-disk imaging, with of order 100 antennas at highest frequency range. FASR will be optimized for solar radio phenomena and will be the most powerful and versatile radioheliograph ever built, providing an improvement of orders of magnitude in image quality over existing instruments. FASR recently received the top ranking amongst all small projects considered by the decadal survey of the National Academy of Science Committee on Solar and Space Physics. FASR will probe all phenomena in the solar atmosphere from the mid-chromosphere outwards. In particular, FASR will provide direct measurement of coronal magnetic field strengths, will image the nonthermal solar atmosphere and show directly the locations of electrons accelerated by solar flares, will provide images of coronal mass ejections travelling outwwards through the solar corona, and supply extensive data products for forecasting and synoptic studies. A major emphasis in the project is to make FASR data as widely and easily used as possible, i.e., providing the general user with processed, fully-calibrated high-quality images that do not need particular knowledge of radio astronomy for interpretation. This paper will describe the telescope and its science goals, and summarize its current status. Title: Hα, Extreme-Ultraviolet, and Microwave Observations of the 2000 March 22 Solar Flare and Spontaneous Magnetic Reconnection Authors: Lee, Jeongwoo; Gallagher, Peter T.; Gary, Dale E.; Nita, Gelu M.; Choe, G. S.; Bong, Su-Chan; Yun, Hong Sik Bibcode: 2003ApJ...585..524L Altcode: The evolution of a GOES class X1.1 solar flare, which occurred in NOAA Active Region 8910 on 2000 March 22, is discussed using observations from the Owens Valley Solar Array (OVSA), Big Bear Solar observatory (BBSO), Transition Region and Coronal Explorer (TRACE), and the Michelson Doppler Imager (MDI) on board Solar and Heliospheric Observatory (SOHO). During the impulsive phase, a set of coronal loops are visible in the TRACE 171 Å (~1×106 K) wavelength band, which is confined to a small volume in the center of the large βγδ-type active region. This is rapidly followed by the emergence of bright Hα ribbons that coincide with the EUV emission. Radio images show a single source encompassing the Hα ribbons at 5 GHz, but at higher frequencies a double source is seen within the area bounded by the compact Hα and EUV emissions. We interpret the observation under the idea of the confined flare in contrast with the more commonly cited, eruptive flare. We use a schematic magnetic reconnection geometry based on the MDI magnetogram to suggest that the EUV loops show some parts of a separatrix, and that the radio and Hα sources coincide with the whole part of the separatrix and its footpoints, respectively. First of all, it explains why this flare lacks the separating motion of Hα ribbons, a signature for eruptive flares. Second, the very short duration of microwave bursts in spite of the large amount of soft X-ray flux is explicable under this scenario, since energy release via spontaneous reconnection in a confined magnetic structure can be very rapid. Third, the confined magnetic geometry is also considered favorable for preserving chromospheric evaporation and plasma turbulence as inferred from the OVSA microwave spectrum. In addition, a coronal mass ejection as detected in the LASCO coronagraph after this flare is briefly discussed in relation to the above flare model. Title: Site testing issues for the frequency agile solar radiotelescope (FASR) Authors: Gary, Dale E.; Keller, Christoph U. Bibcode: 2003SPIE.4853..523G Altcode: The Frequency Agile Solar Radiotelescope (FASR) will be a broadband synthesis-imaging array with 3-km or larger baselines, operating over a broad frequency range of 0.1-30 GHz. The instrument demands a site with low levels of Radio Frequency Interference (RFI) over this entire band. The site also must be large enough to accommodate the expected size of the array configuration and ideally would provide room to grow with future upgrades. The site must have a benign environment in which at least 100 separate elements will operate with little degradation and weather-related downtime. Several sites in the U.S. are being considered. We discuss what criteria are being used to assess the sites, and give some initial results of testing some of the sites. Title: Solar Submillimeter and Gamma-Ray Burst Emission Authors: Kaufmann, P.; Raulin, J. -P.; Melo, A. M.; Correia, E.; Costa, J. E. R.; de Castro, C. G. Giménez; Silva, A. V. R.; Yoshimori, M.; Hudson, H. S.; Gan, W. Q.; Gary, D. E.; Gallagher, P. T.; Levato, H.; Marun, A.; Rovira, M. Bibcode: 2002ApJ...574.1059K Altcode: Solar flare emission was measured at 212 GHz in the submillimeter range by the Submillimeter Solar Telescope in the 1.2-18 GHz microwave range by the Owens Valley Solar Array and in the gamma-ray energy range (continuum) by experiments on board the Yohkoh (>1.2 MeV) and Shenzhou 2 (>0.2 MeV) satellites. At the burst onset, the submillimeter and microwave time profiles were well correlated with gamma rays to the limit of the temporal resolution (<=10 s). At 212 GHz, fast pulses (<1 s), defined as time structures in excess of the bulk emission, were identified as the flux increased. Their spatial positions were scattered by tens of arcseconds with respect to the main burst emission position. Correlation of submillimeter emission with gamma-ray fast time structures shorter than 500 ms is suggested at the gamma-ray maximum. The time variation of the rate of occurrence of the submillimeter rapid pulses was remarkably well correlated with gamma-ray intensities in the energy range (>1.2 MeV), attaining nearly 50 pulses per minute at the maximum. These results suggest that gamma rays might be the response to multiple rapid pulses at 212 GHz and might be produced at different sites within the flaring region. Title: Electron Transport during the 1999 August 20 Flare Inferred from Microwave and Hard X-Ray Observations Authors: Lee, Jeongwoo; Gary, Dale E.; Qiu, Jiong; Gallagher, Peter T. Bibcode: 2002ApJ...572..609L Altcode: We discuss injection and transport of high-energy electrons during a GOES X-ray class M9.8 flare observed in microwaves with the Owens Valley Solar Array (OVSA) and in hard X-rays (HXRs) with the hard X-ray telescope (HXT) on board Yohkoh. Observed at 1 s timescales or better in both wavelength regimes, the event shows (1) a large difference in scale between the microwave source and the HXR source; (2) an unusually hard HXR spectrum (maximum spectral index ~-1.6), followed by rapid spectral softening; and (3) a microwave light curve containing both impulsive peaks (3 s rise time) simultaneous with those of the HXRs and a long, extended tail with a uniform decay rate (2.3 minutes). We analyze the observations within the framework of the electron trap-and-precipitation model, allowing a time-dependent injection energy spectrum. Assuming thick-target bremsstrahlung for the HXRs, we infer the electron injection function in the form Q(E,t)~(E/E0)-δ(t), where the timescale for δ(t) to change by unity is ~7 s. This injection function can account for the characteristics of the impulsive part of the microwave burst by considering the bulk of the electrons to be directly precipitating without trapping. The same injection function also accounts for the gradual part of the microwave emission by convolving the injection function with a kernel representing the trapping process, which at late times gives N(E,t)~e-νt(E/E0)-b. We require b~1.4 and ν~6×10-3β s-1, where β is the electron speed divided by the speed of light. Therefore, the derived form of the precipitation rate ν itself indicates strong pitch-angle diffusion, but the slow decay of the microwave radiation requires a small loss cone (~4°) and a low ambient density in the coronal trap. Also, the numbers of electrons needed to account for the two components of the microwave emission differ by an order of magnitude. We estimate that the >=100 keV number of the directly precipitating electrons is ~1033, while the trapped population requires ~1032 electrons. This leads us to a model of two interacting loops, the larger of which serves as an efficient trap while the smaller provides the impulsive source. These characteristics are consistent with the spatially resolved observations. Title: The Peak Flux Distribution of Solar Radio Bursts Authors: Nita, Gelu M.; Gary, Dale E.; Lanzerotti, L. J.; Thomson, D. J. Bibcode: 2002ApJ...570..423N Altcode: We have investigated the peak flux distribution of 40 years of solar radio burst data as a function of frequency and time over a wide range of frequencies. The bursts were reported by observing stations around the world during 1960-1999, as compiled by the National Geophysical Data Center (NGDC) of the National Oceanic and Atmospheric Administration (NOAA). This period covers three full and two partial solar cycles. We have analyzed the data set to find correction factors for missed events, and find evidence that nearly half of the events were missed by the worldwide network. We obtain power-law fits to the differential (density) (dN/dS in events sfu-1) and cumulative [N(>S) in events] distributions as a function of frequency, time, and phase of the solar cycle. The typical power-law index, ~-1.8, is similar to that found in many hard X-ray studies. The average waiting time between bursts with flux density exceeding 1000 sfu was found to be 6 days at solar maximum, and 33 days at solar minimum. Taking account of missed events, the expected waiting time decreases to 3.5 and 18.5 days, respectively. Bursts of this flux level can cause problems with wireless communication systems. We present tables of fit parameters that can be used to find burst occurrence rates in a number of frequency ranges. We find no significant variation of power-law index from one solar cycle to the next, or with phase of the solar cycle, but we do find significant changes of power-law index with frequency. Title: Solar Radio Bursts and Their Effects on Wireless Systems Authors: Gary, D. E.; Lanzerotti, L. J.; Nita, G. M.; Thomson, D. J. Bibcode: 2002AAS...200.4911G Altcode: 2002BAAS...34..723G We review the state of current understanding of the potential for interference and interruption of service of wireless communications systems due to solar radio bursts. There have been several reported instances of an enhanced rate of dropped cell-phone calls during solar bursts, and the design of current base station systems make them vulnerable to problems near sunrise and sunset for antennas facing in the direction of the Sun during outbursts. It is likely that many cases of interference have gone unreported and perhaps unrecognized. We determine the level of radio noise that can cause potential problems, and then discuss how often bursts of the required magnitude might happen. We find that bursts that can cause potential problems occur on average once every 3.5 days at solar maximum, but also occur at a reduced rate of 18.5 days between events at solar minimum. We investigate the rate of occurrence as a function of frequency, which is relevant for future wireless systems that will operate at higher frequencies than the present systems. This work is supported by NSF grant ATM-0077273 to New Jersey Institute of Technology. Title: Impulsive and gradual energetic emissions in a flare Authors: Qiu, J.; Lee, J.; Gary, D. E. Bibcode: 2002AAS...200.2901Q Altcode: 2002BAAS...34..680Q We present a comprehensive case study of an X-class flare observed on April 6, 2001. The flare consists of two peaks, the first characterized by an impulsive spiky emission and the second by a gradual smooth emission in the same magnetic environment. We compare the temporal and spectral evolution of the two components in hard X-rays and microwaves. Images at both wavelengths are obtained to locate the emission source as it evolves during the flare. We find the following results: (1) The impulsive hard X-ray and microwave emissions are from complex loop structures, primarily in low-lying loops, while the gradual energetic emissions occur in a simple and over-lying loop. Both the impulsive and gradual hard X-rays at > 50keV are thick-target emission. We also find a microwave source that evolves from the loop top toward the foot-point during the gradual phase. (2) A time lag analysis reveals energy-dependent time delays in the impulsive hard X-rays, with the 200 keV hard X-rays lagging the 40keV emission by about 5s. (3) The gradual component is a microwave-rich event. Large delays are seen in the gradual hard X-ray emissions, and the gradual microwaves further lag the hard X-rays by tens of seconds. The correlation study suggests that the gradual microwaves are emitted by > 200keV hard X-ray electrons, possibly MeV electrons. The gradual hard X-rays exhibit a harder and hardening spectrum than the impulsive component, while the electron spectrum derived from the gradual microwaves is still harder. Based on the observations, we suggest that magnetic energy release primarily occurs during the impulsive phase in the complex loop system involving both low-lying and over-lying magnetic loops. Electrons injected into the low-lying loops rapidly escape the coronal trap and precipitate, giving rise to the impulsive energetic bursts at both wavelengths. Electrons that are injected into the over-lying loop are well trapped, which soon undergo a new acceleration, most probably in the form of a stochastic mechanism. It is likely that the secondary acceleration produces a pitch angle distribution in favor of electron trapping, and an evolving trapping condition may result in the moving microwave source along the magnetic loop. This work is supported by NASA grants NAG5-10212 and NAG5-10891. OVSA/NJIT is supported by NSF under grant AST-9987366. Title: First Results of Joint OVSA and HESSI Observations Authors: Gary, D. E.; Schmahl, E. J.; Nita, G. M. Bibcode: 2002AAS...200.6904G Altcode: 2002BAAS...34..757G We report on an initial study of several solar bursts observed with the Owens Valley Solar Array (OVSA) and the new RHESSI X-ray spacecraft. Six M-class soft X-ray bursts were observed jointly in the first month of RHESSI operations, with a wide range of radio and hard X-ray fluxes. Both the hard X-rays and microwaves are well known to arise from electrons of similar energies, so spatial and spectral comparisons of jointly observed events are fruitful for investigating the initial energy release and subsequent evolution of the thermal plasma. The new capabilities of RHESSI to image both high and low energy X-rays with high spectral resolution offer the possibility to learn about this process in unprecedented detail. We compare and contrast the radio and hard X-ray spectra for the 6 events, and show the results of an initial investigation of the spatial characteristics as observed in the two wavelength regimes. Title: Noise in wireless systems produced by solar radio bursts Authors: Bala, B.; Lanzerotti, L. J.; Gary, D. E.; Thomson, D. J. Bibcode: 2002RaSc...37.1018B Altcode: 2002RaSc...37b...2B We have carried out an investigation of 40 years of solar radio burst data in a wide range of frequencies that have been reported by observing stations around the world during 1960-1999. The data were compiled by the National Geophysical Data Center of the National Oceanic and Atmospheric Administration. This period covers three full and two partial solar cycles. We find that the number of bursts per day with amplitudes >103 solar flux units (SFU) falls as an approximate power law with increasing flux level for the frequency bands investigated(1-10 and 10-20 GHz). Also, the number of events with peak flux density >103 SFU varies, as expected, with the solar cycle in the bands investigated (1-2, 2-4, and 4-10 GHz). We discuss the rate of occurrence of events (>103 SFU) in the context of the noise levels in typical wireless communications systems. We find that statistically, depending upon wireless system parameters, several solar events per year are likely to occur that could cause severe interference in a given cell site during solar maximum periods. Title: Motion of Flare Footpoint Emission and Inferred Electric Field in Reconnecting Current Sheets Authors: Qiu, Jiong; Lee, Jeongwoo; Gary, Dale E.; Wang, Haimin Bibcode: 2002ApJ...565.1335Q Altcode: A systematic motion of Hα kernels during solar flares can be regarded as the chromospheric signature of progressive magnetic reconnection in the corona, in that the magnetic field lines swept through by the kernel motion are those connected to the diffusion region at the reconnection point. In this paper, we present high-cadence and high-resolution Hα-1.3 Å observations of an impulsive flare that exhibits a systematic kernel motion and relate them to the reconnecting current sheet (RCS) in the corona. Through analyses of X-ray and microwave observations, we further examine the role of the macroscopic electric field inside the RCS in accelerating electrons. We measure the velocity of the kernel motion to be 20-100 km s-1. This is used together with the longitudinal magnetic field to infer an electric field as high as 90 V cm-1 at the flare maximum. This event shows a special magnetic field configuration and motion pattern of Hα kernels, in that a light bridge divides a flare kernel into two parts that move in different manners: one moving into the stronger magnetic field and the other moving along the isogauss contour of the longitudinal magnetic field. The temporal variation of the electric field inferred from the former type of kernel motion is found to be correlated with 20-85 keV hard X-ray light curves during the rise of the major impulsive phase. This would support the scenario of magnetic energy release via current dissipation inside the RCS, along with the hypothesis of the DC electric field acceleration of X-ray-emitting electrons below 100 keV. However, there is no good temporal correlation between the hard X-ray emission and the inferred electric field from the other motion pattern. Furthermore, the microwave emission, which supposedly comes from higher energy electrons, shows a time profile and electron spectrum that differs from those of the X-ray bursts. We conclude that either the two-dimensional magnetic reconnection theory related to the Hα kernel motion is applicable to only some part of the flare region due to its special magnetic geometry, or the electron acceleration is dominated by other mechanisms depending on the electron energy. Title: Noise in wireless systems from solar radio bursts Authors: Lanzerotti, L.; Gary, D.; Nita, G.; Thomson, D.; Maclennan, C. Bibcode: 2002cosp...34E.501L Altcode: 2002cosp.meetE.501L Solar radio bursts were first discovered as a result of their interference in early defensive radar systems during the second World War (1942). Such bursts can still affect radar systems, as well as new wireless technologies. We have investigated a forty year record of solar radio burst data (1960 - 2000) as well as several individual radio events in the 23rd solar cycle. We show statistically that for f1 GHz there can be a burst > 103 solar flux units (SFU) every few days during solar maximum conditions, and that such burst levels can produce problems in contemporary wireless systems. We also discuss individual burst events and show that the event of April 2001 had signal levels > 103 SFU for more than three quarters of the event duration (order 30 minutes). Such long duration, high intensity, bursts can be especially disruptive to wireless systems. Title: First detection of the impulsive and extended phases of a solar radio burst above 200 GHz Authors: Trottet, G.; Raulin, J. -P.; Kaufmann, P.; Siarkowski, M.; Klein, K. -L.; Gary, D. E. Bibcode: 2002A&A...381..694T Altcode: We present a detailed analysis of radio observations obtained at 212 and 405 GHz during the 2000 March 22 Hα 2N flare that occured in AR8910 at ~ 1834 UT. These data are compared with microwave, soft X-ray and hard X-ray measurements of this flare. While the flare emission is not clearly detected at 405 GHz, the time profile of the 212 GHz emission exhibits an impulsive burst, associated in time with the 1-18 GHz impulsive microwave burst and a long-lasting thermal burst which finishes at about the same time as the soft X-ray emission but reaches its maximum later. The 212 GHz impulsive emission and the lack of detection at 405 GHz are consistent with synchrotron radiation from a population of ultrarelativistic electrons in an average magnetic field of 400-600 G. This radiating population of electrons has a hard energy spectrum (power law index ~2.7). The expected >1 MeV gamma-ray continuum emission from the radio emitting electrons is comparable to that detected for mid-size electron-dominated events and the hard X-ray flux they would produce at 100 keV is consistently lower than the upper limit inferred from the observations. It is shown that the 212 GHz thermal source has to be different from that radiating the soft X-ray and microwave thermal emission. The present observations of a solar burst provide the first evidence of the extension of the gyrosynchrotron spectrum of an impulsive radio burst in the synchrotron domain above 200 GHz. Title: First Detection of the Impulsive and Extended Phases of a Solar Radio Burst above 200 GHZ Authors: Raulin, J. P.; Kaufmann, P.; Trottet, G.; Klein, K. L.; Gary, D.; Siarkowski, M. Bibcode: 2002RMxAC..14..108R Altcode: No abstract at ADS Title: The frequency agile solar telescope (FASR) Authors: Bastian, T.; Gary, D.; White, S.; Hurford, G. Bibcode: 2002cosp...34E1870B Altcode: 2002cosp.meetE1870B The Frequency Agile Solar Radiotelescope (FASR) will be a large-N, solar- dedicated, Fourier synthesis array designed to perform broadband imaging spectroscopy across a frequency range of approximately 0.1-30 GHz with an angular resolution as high as 1" (>20 GHz). This paper reviews the FASR science drivers -- including coronal magnetic fields, energetic phenomena, and thermal physics -- and the associated instrument requirements and specifications. Applications for synoptic studies and space weather are also discussed. Ongoing activities are briefly described, including site surveys, configuration studies, science simulations, and system design. Title: 2800 MHz Solar Radio Bursts: A Statistical Analysis of 40 years of Data Authors: Balachandran, B.; Lanzerotti, L. J.; Gary, D. E. Bibcode: 2001AGUFMSH31A0692B Altcode: The daily values of solar flux and radio bursts at 2800 MHz (10.7 cm wavelength) are known to be closely related to various manifestations of solar activity. The flux values, which vary slowly with time, have long been used as indicators of solar activity. Also, the number of radio bursts shows a variation with the phase of the solar cycle. The close relationships between the 2800 MHz bursts, the associated flares and geophysical phenomena such as shortwave fadeouts have been studied extensively and were established as early as the 1960s. Therefore, a constant monitoring of the Sun at this frequency would enable us to forecast the terrestrial disturbances following the solar activity. Moreover, a detailed study based on past data would help understand solar activity phenomena as well as the origin of these burst events. In the present analysis, we are revisiting some of these points by carrying out an analysis of 40 year data of solar radio bursts with special emphasis on 2800 MHz bursts. A scatter plot of the intensity vs duration shows that the distribution is not completely random but is double--pronged. This result is consistent with earlier works (e.g., Covington, 1959). The two-pronged distribution suggests the existence of two distinct types of burst events: impulsive and gradual rise and fall. The mechanisms that cause the emission of the two types of bursts are also different: the former due to nonthermal processes and the latter due to thermal processes. Our present analysis shows that the intensity--duration plot has a significant variation with the phase of the solar cycle. In addition to this, we present the behaviour of risetime vs duration as well as the frequency distribution of peak flux of these events. The analysis has also been extended to high frequency (> 10 GHz) bursts and the behaviour is contrasted to that of 2800 MHz bursts. Title: Solar Microwave Imaging Software for the Owens Vally Solar Array Authors: Gary, D. E.; Lee, J.; Bong, S. Bibcode: 2001AGUSM..SH41B18G Altcode: A package of solar microwave imaging software has been developed mainly to support general users of microwave data obtained with the Owens Valley Solar Array (OVSA). While the Astronomical Image Processing System (AIPS) maintained by NRAO is widely used for radio interferometry data and can be used for the OVSA data as well, we consider it worthwhile to have new imaging software optimized for OVSA data, especially for accommodating the large number of frequencies in the OVSA data. Another motivation, in collaboration with the High Energy Solar Spectroscopic Imager (HESSI--which uses Fourier-Transform imaging at energies of hard X rays), is to make the OVSA imaging software conform to the HESSI software. The OVSA imaging software is written in IDL, and conforms to the Solarsoft software tree while maintaining radio standards. With typical input parameters set by the user, the imaging software carries out the standard Clean algorithm and then prompts for further processing options. These include Self-Calibration, Maximum Entropy, and Forward-Fitting algorithms. We describe the software and demonstrate the capabilities of each algorithm when applied to solar microwave imaging with OVSA. We also describe progress on an improved version of the Spatial/Spectral Maximum Entropy Method and test it against the above-mentioned, more conventional techniques. Title: Optical, EUV, and Microwave Observations of the March 22, 2000 X-class Flare. Authors: Gallagher, P. T.; Gary, D. E.; Lee, J. Bibcode: 2001AGUSM..SP42A08G Altcode: The evolution of an X-class flare which occured in NOAA 8910 on March 22, 2000 is discussed using observations from the Owens Valley Solar Array (ovsa), Big Bear Solar Observatory (bbso), the Transition Region and Coronal Explorer (trace), and the Michelson Doppler Imager (mdi). The main energy release occurs in a set of coronal loops visible in the trace 171 Å (1 x 106~K) wavelength band, which is rapidly followed by the emergence of two bright Hα ribbons. High-cadence radio images at around 5 GHz obtained using the ovsa appears in the middle of two Hα ribbons, which thus indicates presence of energetic electrons flowing across the two ribbons. During the impulsive phase, short-lived (τ <= 30 s), narrow-band (BW <= 500 MHz), and highly polarized microwave emission is observed in radio images in the 1-2 GHz frequency range, which is possibly due to plasma radiation. At optically-thin, high frequencies ovsa total power spectra also show a typical soft-hard-soft evolution indicative of highly efficient nonthermal electron acceleration during the impulsive phase. The microwave emission from this flare is surprisingly short considering that active region is large (> 200 arc sec in diameter) and the flare is energetic (GOES X class). We consider that the compact magnetic field geometry in the flaring region and subsequent strong chromospheric evaporation into it may have limited life of high energy electrons trapped in the loops to such a short duration. Title: Shifting Emission Source in an Impulsive Flare Authors: Qiu, J.; Gary, D. E.; Wang, H. Bibcode: 2001AGUSM..SP42A05Q Altcode: We study high resolution observations of a compact impulsive C9.0 flare. We include in the analysis high cadence Hα -1.3~Å filtergrams from the Big Bear Solar Observatory (BBSO), radio data from Owens Valley Solar Array (OVSA), soft and hard X-ray data from Yohkoh, and UV~1600~Å continuum images from Transition Region And Corona Explorer (TRACE). Observations show two emission kernels located at the feet of a general bipolar structure. The impulsive phase of the flare consisted of two major emission peaks in hard X-ray, radio and Hα emission, each lasting for about a minute, indicating the existence of two major episodes of flare energy release. We find that these different episodes in the flare temporal evolution were related to different spatial locations as shown by the Hα kernels. The high cadence time profiles at various wavelengths exhibit temporal structures on a shorter time scales from a few seconds to less than a second, while Hα - 1.3~Å and radio images show that the location of the footpoint emission was shifting. This may be an indication that emission in these two episodes was produced in different magnetic structures, which we explore through spectral analysis of hard X-ray and microwave emission. Title: Noise in Wireless Systems Produced by Solar Radio Bursts Authors: Balachandran, B.; Lanzerotti, L. J.; Gary, D. E.; Thomson, D. J. Bibcode: 2001AGUSM..SP52B07B Altcode: We have carried out an investigation of 40 years of solar radio burst data in a wide range of frequencies that have been reported by observing stations aroundthe world during 1960-1999. The data were compiled by the NGDC of NOAA. This period covers three full and two partial solar cycles. We find that the number of bursts per day with amplitudes >103 solar flux units (SFU) falls as an approximate power law with increasing burst flux level for the frequency bands investigated (1-10 and 10-20 GHz). We also find that the number of eventswith peak flux >103 SFU varies, as expecterd, with the solar cycle in the bands investigated (1-2, 2-4, and 4-10 GHz). We discuss the event (>103 SFU) occurrence rate in the context of the noise levels in typical wireless communications systems. We find that there are likely to be a few solar events per year that could cause severe interference in a given cell site during solar maximum conditions. We also discuss other aspects of possible solar radio influence on wireless systems, including the potential impacts of lower flux levels of solar radio bursts on system bit error rates. Title: Radio and X ray Observations of a Limb Flare during the Max Millennium Campaign Authors: Lee, J.; Gallagher, P. T.; Gary, D. E.; Harra, L. K. Bibcode: 2001AGUSM..SP51A03L Altcode: A powerful (GOES Class M9.8), limb flare was observed on 1999 August 20 above AR 8673 during the second Max Millennium campaign. Due to its location on the limb as well as its strength, the flare observation provides an ideal case of studying vertical structure of electron acceleration and its transport. The hard X ray images from Yohkoh/HXT along with EUV images from SoHO/EIT show an impulsive, compact double brightening in the lower atmosphere and a hypothesis of footpoint emission from a compact loop seems likely. In contrast, microwave visibilities obtained using the Owens Valley Solar Array (OVSA) suggest a region of high energy electrons high in the corona (2x 105 km), requiring large loops that can act as a good trap of electrons. The duration of radio emission is also much extended compared with the hard X ray emission. We present this set of observations as a good example of the trap-plus-precipitation hypothesis, and derive numbers of electrons emitting the microwaves and hard X rays, respectively, as a measure for the trap vs. precipitation. The derived time evolution of electron numbers in energy space is not compatible with a simple hypothesis of energy-independent acceleration solely under Coulomb collisions, but instead requires an acceleration or transport process that is highly energy-dependent. Title: 40 Years of Solar Microwave Burst Flux Measurements Authors: Nita, G. M.; Gary, D. E.; Lanzerotti, L. J.; Thomson, D. J. Bibcode: 2001AGUSM..SP41A03N Altcode: We report results from an investigation of 40 years of solar radio burst data, from 1960-1999, compiled by the National Geophysical Data Center at NOAA, Boulder, CO. This dataset consists of more than a half-million entries corresponding to several hundred thousand bursts measured at many frequencies from approximately 150 MHz to 35 GHz, and covering more than three 11-year solar activity cycles. We discuss the ways in which limitations and biases in the dataset are identified and, where possible, corrected. We present the corrected number distributions for bursts greater than 10 SFU (solar flux units, 1 SFU = 10-22 W/m2/Hz), and powerlaw fits to them, as a function of frequency, time, and phase of the solar cycle. We compare these distributions and their variation with similar measures in other wavelengths, and discuss the implications for coronal heating and other aspects of flare physics. Title: The Frequency-Agile Solar Radiotelescope (FASR) (invited) Authors: Gary, D. E.; Bastian, T. S.; White, S. M.; Hurford, G. J. Bibcode: 2001aprs.conf..236G Altcode: No abstract at ADS Title: Correlation of Microwave and Hard X-Ray Spectral Parameters Authors: Silva, Adriana V. R.; Wang, Haimin; Gary, Dale E. Bibcode: 2000ApJ...545.1116S Altcode: We present the analysis of 27 solar flares with multiple peaks that were observed at hard X-ray and microwave wavelengths. A total of 57 simultaneous peaks were observed by BATSE (hard X-rays) and Owens Valley Radio Observatory (microwaves). Throughout the duration of a flare, its spectra at both wavelengths are fitted independently at all times. The hard X-ray spectra were fitted by a single power law in most cases, whereas the microwave spectra were fitted as gyrosynchrotron emission. For each individual peak, the parameters at both wavelengths (peak flux, turnover frequency, spectral indices, and delays between hard X-ray and microwave peak emission) were then compared and correlated. We have also studied impulsive and nonimpulsive bursts individually. The main results obtained were as follows. (1) In 75% of the bursts, the inferred index of the electron energy distribution of the microwave-emitting electrons, δr, is harder than that of the lower energy hard X-ray-emitting electrons, δX, on average by 0.5-2.0. This implies that there is a breakup in the energy spectra of the electrons, as is sometimes observed in the hard X-ray spectra of giant flares. (2) A soft-hard-harder spectral index temporal evolution is more commonly seen in the microwave spectra (47%) than in the hard X-ray observations (32%) and in nonimpulsive flares than in impulsive ones. (3) Delays larger than 2 s were observed between the radio and hard X-ray peaks in 65% of the bursts, with the delays decreasing as the hard X-ray energy increased. (4) Nonimpulsive flares are more microwave rich, have higher delays between their radio emission and the hard X-ray peaks, and display harder spectral indices than impulsive bursts. Title: Solar Microwave Bursts and Injection Pitch-Angle Distribution of Flare Electrons Authors: Lee, J.; Gary, Dale E. Bibcode: 2000ApJ...543..457L Altcode: We calculate the time variation of the energy and pitch angle of high-energy electrons injected into a magnetic loop and subsequently trapped there because of magnetic mirroring. We use the evolving distribution in the calculation of gyrosynchrotron emission, as an aid to interpretation of a particular microwave burst observed using the Owens Valley Solar Array (OVSA) during a GOES class C2.8 flare on 1993 June 3. The electrons are assumed to have a Gaussian pitch-angle distribution, whose width and mean pitch angle are calculated as they evolve in time, taking into account the electron energy loss and a specific magnetic loop structure set as a model for the target active region. Various temporal behaviors of the microwave spectrum are found as a function of injection and trap conditions, which can be used to infer some of the injection properties directly from the observed microwave spectra. As a main result we found that initial pitch-angle distribution plays an important role in the microwave spectral evolution. This is largely due to the fact that pitch-angle diffusion of electrons under Coulomb collisions markedly differs at those electron energies to which the microwave spectrum is sensitive. This effect cannot be reproduced by adjusting the trap properties and therefore could be used to determine whether the initial pitch-angle distribution is isotropic or narrowly beamed. The microwave burst spectra observed during the 1993 June 3 flare are found to be most consistent with the hypothesis of an initially narrow beamed injection (<=30°) into a low-density (~4×109 cm-3) magnetic trap. This result explains the observed asymmetric microwave time curve consisting of a relatively short rise (~32 s) and a long decay (>=5 minutes) in terms of a transport effect rather than acceleration characteristics. The physical connection of the proposed microwave model to hard X-ray models in thin/thick targets is briefly discussed. Title: First results from the upgraded Owens Valley Solar Array. Authors: Gary, D. E.; Hurford, G. J.; Lee, J.; Gallagher, P. T. Bibcode: 2000BAAS...32..818G Altcode: No abstract at ADS Title: Magnetic Reconnection and Energetics of the 2000 March 22 Solar Flare Authors: Gallagher, P. T.; Gary, D. E.; Lee, J. Bibcode: 2000SPD....31.0260G Altcode: 2000BAAS...32..821G The evolution and properties of the 2000 March 22 X--class flare from the β δ active region NOAA 8910 are discussed using high resolution radio observations from the Owen's Valley Solar Array, TRACE UV and EUV filtergrams, GOES soft X-rays, and magnetograms from MDI on board SOHO. The episodic flare evolution is found to be extremely complicated at all observed wavelengths and releases a large amount of both thermal and non--thermal energy. From the UV and EUV observations, the flare is shown to be consistent with the model in which the release of energy is caused by several, successive loop interactions while the radio observations identify multiple non--thermal electron acceleration sites. The final stage of the flare is then characterised by the emergence of a set of post--flare loops parallel to the magnetic neutral line as the system relaxes. Title: Electron Acceleration During the 1999 August 20 Flare Authors: Lee, J.; Gary, D. E.; Gallagher, P. T. Bibcode: 2000SPD....31.0250L Altcode: 2000BAAS...32..820L A powerful flare (GOES SX class of M9.8) occurred on 1999 August 20 at 23:06 UT near the eastern limb during a Max Millennium campaign. The Owens Valley Solar Array (OVSA) at the time was operating in a high time resolution (1 s) mode to observe an impulsive microwave burst rising very rapidly (within 3 s) at all observing frequencies in the range of 1.4 to 18 GHz. As a main characteristic of the burst, the microwave spectrum decays in a remarkably well-defined exponential profile with a timescale varying in the range of ~ 30 s to ~ 4 min, in proportion to the wavelength. The accompanying hard X ray emission from the BATSE DISCLA data is confined to a short time interval ( ~ 30 s), and its light curve is very similar to that of the high-frequency (15--18 GHz) microwaves. Our analysis is therefore focused on whether these observartions are consistent with theoretical predictions for the microwave emission from trapped electrons in the corona and thick target X-ray emission from the electrons precipitating into the chromosphere. In addition, we infer the magnetic reconnection geometry from EUV images obtained from SoHO/EIT which is used as another constraint to study the property of the acceleration. The OVSA is supported by NSF grants ATM-9796213 and AST-9796238 and NASA grant NAG5-6381 to New Jersey Institute of Technology. Title: Observations and models of a flaring loop. Authors: Nindos, A.; White, S. M.; Kundu, M. R.; Gary, D. E. Bibcode: 2000BAAS...32..818N Altcode: No abstract at ADS Title: First Results from the Upgraded Owens Valley Solar Array Authors: Gary, D. E.; Hurford, G. J.; Lee, Jeongwoo; Gallagher, P. T. Bibcode: 2000SPD....31.0244G Altcode: The Owens Valley Solar Array (OVSA) has undergone extensive hardware and software upgrades in preparation for the current solar maximum and the launch of HESSI. We present an overview of the now completed upgrade from 5 to 6 antennas, and show first results from the newly expanded instrument. We show results from several recent flares, as well as multi-frequency maps of active region coronal structure, to demonstrate the improvements now possible with the instrument. The data and analysis software are freely available on the web, and we invite all who are interested in working with these data to contact the associated website. Title: Observations and Models of a Flaring Loop Authors: Nindos, A.; White, S. M.; Kundu, M. R.; Gary, D. E. Bibcode: 2000SPD....31.0243N Altcode: Simultaneous images of a flaring loop at two frequencies are used to model the magnetic structure of the loop and the energy distribution of the radiating electrons. The imaging data were obtained with the VLA at 5 and 15 GHz. Additional spectral data were provided by the OVRO Solar Array at several frequencies between 2 GHz and 15 GHz. At 15 GHz, the flare emission was optically thin and came from the footpoints of the flaring loop, while at 5 GHz the loop itself was outlined. Most of the 5 GHz emission was optically thick and its spatial maximum was close to the loop top. A striking feature of the observations is that the 5 GHz emission does not reach down to the 15 GHz footpoints. We compare the observations with calculations of gyrosynchrotron emission from an inhomogeneous magnetic loop in order to determine the conditions in the flaring loop. The best fit to the OVRO fluxes was reached with a model flaring loop with photospheric footpoint magnetic field strength of 870 G. The thickness of the model loop was small compared to its footpoint separation. The energy spectral index of the energetic electrons was 3.7 and their number density was 7.9 x 107 cm-3. The low and high energy cutoffs of the nonthermal electrons were 8 and 210 keV. The 5 GHz emission in this model is at low harmonics (3--7) and harmonic effects are responsible for the weak 5 GHz emission at the footpoints. The absence of electrons above 210 keV is necessary in this model to explain why no emission is observed from the loop top at 15 GHz. That model reproduced well the high frequency part of the OVRO flux spectrum as well as the VLA spatial structure. Thus comparisons between the spatially--resolved observations and models reveal the three-dimensional structure of the loop geometry. Title: Observations and Models of a Flaring Loop Authors: Nindos, A.; White, S. M.; Kundu, M. R.; Gary, D. E. Bibcode: 2000ApJ...533.1053N Altcode: Simultaneous images of a flaring loop at two frequencies are used to model the magnetic structure of the loop and the energy distribution of the radiating electrons. The imaging data were obtained with the VLA at 5 and 15 GHz. Additional spectral data were provided by the Owens Valley Radio Observatory (OVRO) solar array at several frequencies between 2 and 15 GHz. At 15 GHz, the flare emission was optically thin and came from the footpoints of the flaring loop, while at 5 GHz the loop itself was outlined. Most of the 5 GHz emission was optically thick, and its spatial maximum was close to the loop top. A striking feature of the observations is that the 5 GHz emission does not reach down to the 15 GHz footpoints. We compare the observations with calculations of gyrosynchrotron emission from an inhomogeneous magnetic loop in order to determine the conditions in the flaring loop. The best fit to the OVRO fluxes was reached with a model flaring loop with photospheric footpoint magnetic field strength of 870 G. The thickness of the model loop was small compared with its footpoint separation. The energy spectral index of the energetic electrons was 3.7, and their number density was 7.9×107 cm-3. The low- and high-energy cutoffs of the nonthermal electrons were 8 and 210 keV, respectively. The 5 GHz emission in this model is at low harmonics (3-7), and harmonic effects are responsible for the weak 5 GHz emission at the footpoints. The absence of electrons above 210 keV is necessary in this model to explain why no emission is observed from the loop top at 15 GHz. That model reproduced well the high-frequency part of the OVRO flux spectrum as well as the VLA spatial structure. Thus, comparisons between the spatially resolved observations and models reveal the three-dimensional structure of the loop geometry. Title: Magnetic Trapping and Electron Injection in Two Contrasting Solar Microwave Bursts Authors: Lee, J.; Gary, Dale E.; Shibasaki, K. Bibcode: 2000ApJ...531.1109L Altcode: We study two microwave bursts (which occurred about 12 minutes apart in the same active region) that show contrasting characteristics in morphology and spectral variation in microwave data from the Owens Valley Radio Observatory (OVRO) Solar Array and the Nobeyama Radioheliograph (NoRH). The first flare (X-ray class C2.8, 23:22 UT) shows radio morphology that changes from a single source at a low frequency (5 GHz) to a double source at high frequencies (10-17 GHz), and shows a total power spectrum that hardens in the decay phase. In contrast, the second flare (X-ray class M1.0, 23:35 UT) shows a simple, single-source morphology at 7-17 GHz. This source is located at one of the two footpoints of a small loop identified in Yohkoh/HXT maps, and its spectrum evolves in a typical soft-hard-soft pattern. We infer the trap properties of these two loops from the microwave spectral behaviors and a coronal field extrapolation from the vector magnetogram of the active region obtained from Mees Solar Observatory, along with X-ray maps obtained from Yohkoh/SXT. It is shown that the radio characteristics of the first event are consistent with the hypothesis in which Coulomb collisions dominate in a highly anisotropic loop with low ambient electron density ~5x109 cm-3. The second flare involves a small loop in which a more uniform field strength allows rapid loss of electrons by precipitation, resulting in a spectral variation mainly controlled by the energy dependence and time profile of the injection. In spite of the significantly differing decay times (~8 and ~1 minutes, respectively), very similar injection times of ~30 s are inferred from the analysis of time profiles under the above hypotheses. We therefore present a view that the largely different morphologies and the corresponding spectral variations are consequences of the differing trap properties rather than dissimilar injection properties. The low trap density inferred for the first event (~5x109 cm-3) as compared with the second event (~8x1010 cm-3) also explains why this event showed richer microwave output in spite of weaker GOES activity. Title: Microwave Bursts and Electron Pitch Angles Authors: Lee, J.; Gary, D. E. Bibcode: 2000ASPC..206..323L Altcode: 2000hesp.conf..323L No abstract at ADS Title: Solar Radio Burst Locator Authors: Dougherty, B. L.; Freely, W. B.; Zirin, H.; Gary, D. E.; Hurford, G. J. Bibcode: 2000ASPC..206..367D Altcode: 2000hesp.conf..367D No abstract at ADS Title: OVRO Solar Array Analysis Software in Support of HESSI Authors: Gallagher, P. T.; Gary, D. E.; Lee, J. Bibcode: 2000ASPC..206..363G Altcode: 2000hesp.conf..363G No abstract at ADS Title: Radio View of Particle Acceleration and Complementarity with HESSI Authors: Gary, Dale E. Bibcode: 2000ASPC..206..297G Altcode: 2000hesp.conf..297G No abstract at ADS Title: Observations and Models of a Flaring Loop Authors: Nindos, A.; White, S. M.; Kundu, M. R.; Gary, D. E. Bibcode: 2000ASPC..206..359N Altcode: 2000hesp.conf..359N No abstract at ADS Title: Microwave and Extreme Ultraviolet Observations of Solar Polar Regions Authors: Nindos, A.; Kundu, M. R.; White, S. M.; Gary, D. E.; Shibasaki, K.; Dere, K. P. Bibcode: 1999ApJ...527..415N Altcode: The poles of the Sun are brighter than the rest of the quiet Sun's emission in a limited range of radio frequencies from 17 GHz to 87 GHz. We have studied microwave images of the quiet Sun made with the Nobeyama radioheliograph at 17 GHz. They show that the so-called polar-cap brightening consists of two components: a diffuse component of 1500 K excess brightness and patchy compact sources with localized excess brightness of about 3500 K. We test the reality of the compact sources using the maximum entropy method deconvolution. The total flux and the number of compact polar sources as well as the north-south extent of the diffuse polar emission are larger in the pole that is closest to the Earth. We compared the microwave polar emission with nearly simultaneous SOHO EIT images taken in the lines of He II at 304 Å and Fe XII at 195 Å. No one-to-one correlation between the compact radio sources and the bright EUV features was found: most of the radio emission arises between the plumes visible to EIT. The boundaries of the polar-cap brightenings did not match exactly the boundaries of the coronal holes as seen in either the Fe XII 195 Å images or the He II 304 Å images. The temporal variations of the compact microwave sources did not correspond to any significant changes in EUV emission. On the other hand, most He II 304 Å changing features were associated with the diffuse polar microwave emission, which was practically constant. Our data suggest that the origin of the polar brightening is not coronal; it seems that the bulk of the patchy radio emission comes from heights below the 80,000 K layer. Title: Radio Counterparts to SXR Transients Authors: Gary, D. E. Bibcode: 1999spro.proc..129G Altcode: By now several studies have been done on small-scale brightenings seen at radio, UV, EUV, and soft X-ray wavelengths. These are to be reviewed by Kundu in these proceedings. In this talk we concentrate on the radio counterpart of a particular type of brightening---the soft X-ray transient brightenings of Shimizu. These brightenings are associated with active regions, and a study of radio counterparts by White et al. (1995) using Nobeyama data found an excellent correspondence between the 17 GHz and SXR brightenings, both spatially and temporally. However, this study found that both the SXR and microwave emissions could be satisfactorily explained as purely thermal emission, and a search of BATSE hard X-ray data showed no nonthermal counterpart. White et al. (1995) were forced to conclude that the events may be different from flares. A more sensitive search for nonthermal emission was needed, in particular using lower frequency microwaves where the influence of nonthermal electrons would be more easily detected. Gary, Hartl and Shimizu (1997) found 34 SXR transient brightenings over a 10-day period in May 1992, for which OVRO (1-18 GHz) total power data were available. A comparison of the data showed a number of clear nonthermal signatures. In addition, one of the events was seen in the lowest energy (6-9.3 keV) channel of the BATSE SPEC detector, suggesting a connection between the microflares discovered in hard X-rays by Lin et al. (1984). The evidence that SXR transient brightenings are microflares is reviewed in this talk. We also attempt to place other small-scale brightenings in context with regard to SXR transient brightenings and microflares. Title: Comparison of Microwave and HXR Spectra from Solar Flares Authors: Silva, A. V. R.; Wang, H.; Gary, D. E. Bibcode: 1999spro.proc..255S Altcode: We analyze simultaneous hard X-ray and microwave emission from 28 solar flares with multiple peaks. A total of 44 simultaneous peaks were observed at both wavelengths by BATSE (hard X-ray) and Owens Valley Radio Observatory (microwave). Spectra during each burst were fitted throughout the duration of the flare. The hard X-ray spectra were fitted by a single power-law in most cases, whereas the microwave spectra were fitted as gyrosynchrotron emission. The parameters at both wavelengths (peak flux, turnover frequency, duration, spectral indices, and delays between hard X-ray and microwave peak emission) are then compared and correlated for each individual peak. We find that for 74% of the bursts, the inferred index of the electron energy distribution of the microwave emitting electrons, δr, is harder than that of the lower energy hard X-ray emitting electrons, δx. This implies that there is a breakup in the energy spectra of the electrons, as is sometimes observed in the hard X-ray spectra of giant flares. Moreover, 65% of all bursts with δx > δr also showed delayed radio peak emission with respect to hard X-ray maximum. Implications on electron acceleration mechanisms are discussed. Title: OVRO Solar Array Upgrades in Preparation for MAX 2000 Authors: Gary, D. E.; Hurford, G. J. Bibcode: 1999spro.proc..429G Altcode: Several significant changes to the OVRO Solar Array are underway in preparation for the coming solar maximum in the year 2000. The array currently consists of 5 antennas with a maximum baseline of about 670 m. By mid-2000, two additional antennas will be operating, with a maximum baseline of about 1250 m, nearly doubling the spatial resolution (to 5'' at 10 GHz). The number of baselines recorded typically during the previous solar maximum was 7. A new data system, coupled with the additional antennas, will allow us to record 21 baselines for a factor of three improvement in imaging. The new data system, which is already in place, offers many additional advantages in ease of use of the data, as well as improved calibration. In concert with the HESSI (High Energy Solar Spectroscopic Imager) team, we plan to make the OVRO data and the IDL-based analysis software widely available via the World Wide Web. The current state of these improvements is discussed. Title: Microwave and Extreme Ultraviolet Observations of Solar Polar Regions Authors: Nindos, A.; Kundu, M. R.; White, S. M.; Gary, D. E.; Shibasaki, K.; Dere, K. P. Bibcode: 1999AAS...194.3207N Altcode: 1999BAAS...31..871N The radio emission of solar poles is brighter than the rest of the quiet Sun's emission in a limited range of frequencies from 17 GHz to 87 GHz. We have studied microwave images of the quiet Sun made with the Nobeyama Radioheliograph at 17 GHz. They show that the so-called polar-cap brightening consists of two components: a diffuse component of 1500 K excess brightness, and patchy compact sources with localized excess brightness of about 3500 K. The total flux and the number of compact polar sources as well as the North-South extent of the diffuse polar emission are larger in the pole which is closest to the Earth. We compared the microwave polar emission with nearly simultaneous SoHO EIT images taken in the lines of He ii at 304 Angstroms and Fe xii at 195 Angstroms. No one-to-one correlation between the compact radio sources and the bright EUV features was found: most of the radio emission arises between the plumes visible to EIT. The boundaries of the polar-cap brightenings did not match exactly the boundaries of the coronal holes as seen in the Fe xii 195 Angstroms images. The temporal variations of the compact microwave sources did not correspond to any significant changes in EUV emission. On the other hand, most He ii 304 Angstroms changing features were associated with the diffuse polar microwave emission which was practically constant. Our data suggest that the origin of the polar brightening is not coronal; it seems that the bulk of the patchy radio emission comes from heights below the 80000 K layer. Title: The OVRO Solar Array During Max Millenium Authors: Gary, D. E.; Hurford, G. J. Bibcode: 1999AAS...194.8007G Altcode: 1999BAAS...31..965G The Owens Valley Radio Observatory (OVRO) Solar Array is a solar-dedicated radio imaging instrument that obtains flare and active region data in the range 1-18 GHz. The array is currently undergoing extensive software and hardware upgrades, to be completed by mid-2000 -- in time for the launch of the HESSI spacecraft. The hardware improvements include adding two antennas to the 5 existing ones, bringing the number of antennas to 7 and the number of baselines to 21. This addition will improve the image quality and double the east-west spatial resolution, to 5" at 10 GHz. Along with the hardware improvements, the computer control and data systems are being completely revamped to modernize the data handling and make the data available and useful to outside users on a daily basis. Certain standard data products (e.g. calibrated total power spectra of flares), will be available by this summer, via web server, for open use by the solar community. Complete interferometry data will be available by the time of the HESSI launch, in self-contained data files that can be analyzed using freely-available, user-friendly IDL widget-driven software. It is planned to model the analysis software after the HESSI analysis software, so that those who have mastered the use of the HESSI software will be able to use the OVRO software without difficulty. This is possible since the HESSI and OVRO data are parallel in many ways. Both obtain spatial data in the form of time profiles of spatial fourier components, at many spectral points. Both pertain to emission from both high-energy and thermal electrons in the corona. The two data-sets are highly complementary, and it is expected that the OVRO data will be of great interest to many researchers working on HESSI data. Ultimately, the full OVRO data will be archived at the HESSI European Data Center (HEDC). The OVRO Solar Array is supported through NSF grants AST-9796238 and ATM-9796213, and NASA grant NAG5-6831 to New Jersey Institute of Technology. Title: FASR - A Frequency-Agile Solar Radiotelescope Authors: Hurford, G. J.; Gary, D. E.; Bastian, T. S.; White, S. M. Bibcode: 1999AAS...194.7603H Altcode: 1999BAAS...31..956H The Frequency-Agile Solar Radiotelescope (FASR) is a multi-frequency imaging array designed specifically for imaging spectroscopy of the Sun. Using < 100 antennas, it will combine high-quality/high spatial resolution imaging (1" resolution at 20 GHz) with spectroscopy (dnu /nu 0.01-0.03) and high time resolution (<1 s) across two decades in frequency from 0.3-30 GHz. In so doing, it will produce a continuous, dynamic, three-dimensional picture of the solar atmosphere from the chromosphere through the mid-corona. These capabilities represent a quantum leap beyond existing solar radio instruments, yet are well within reach of emerging technologies. The range of science that can be addressed by such an instrument is as broad as solar physics itself. Virtually every solar feature from within a few hundred km of the visible surface of the Sun to high in the solar corona can be studied in detail with the unique diagnostics available in the radio regime. Particular diagnostics include measuring the properties of both thermal and nonthermal electrons accelerated in solar flares from the largest events to the tiniest microflares/nanoflares, measuring coronal magnetic field strengths in active regions and elsewhere (coronal magnetography), and mapping kinetic electron temperatures throughout the chromosphere and corona. In addition, FASR's far-reaching exploration of the Sun in the radio regime gives the instrument tremendous potential for new discoveries beyond those that we can now anticipate. FASR is expected to be one of the major new ground-based solar instruments of the next decade, and can be operational by 2006, well before the decade is out. It will play a major role in supporting NASA space missions with the unique diagnostics and perspective provided by high-resolution radio imaging/spectroscopy. Title: Magnetic Trapping of Flare Electrons and Microwave Emission Authors: Lee, J.; Gary, D. E. Bibcode: 1999AAS...194.2204L Altcode: 1999BAAS...31..859L The topic of trapping of flare-produced electrons in magnetic loops and their evolution under Coulomb collision has received considerable attention in relation to interpreting hard X ray observations, since the first work by Melrose and Brown in 1976. However, application of the idea to the study of microwave radiation has been more limited. Petrosian in 1982 illustrated how the magnetic field affects the trapping and beaming of electrons to predict spatial morphology of microwave emission given magnetic structure and location of a flaring loop. Mel'nikov in 1994 used a model for trap and precipitation to study relative intensities and time delays between microwaves and hard X rays. We present a detailed modeling of microwave emission from electrons undergoing Coulomb interaction in magnetic traps, designed for quantitative analysis of spatially-resolved, multiwavelength microwave observations such as those of the Solar Arrays at Owens Valley Radio Observatory (OVRO). Our main concern is to properly relate the precipitation rate and pitch angle diffusion to magnetic quantities of the flaring loop and injection parameters. In this approach, we use coronal field extrapolation and overlays of soft X ray loops to provide the magnetic quantities so that the microwave spectrum can be used mainly as the electron diagnostic. We discuss the model capabilities and apply the results to a flare that occurred in AR 7515 on 1993 June 3. This flare showed spectral flattening in the decay phase along with morphological variation suggestive of a magnetic trap around the loop top, and the spectral flattening is interpreted as driven by Coulomb collision in the magnetic trap. The OVRO Solar Array is supported through NSF grants AST-9796238 and ATM-9796213, and NASA grant NAG5-6831 to New Jersey Institute of Technology. Title: IDL-based Database of Solar Active Regions Authors: Gary, D. E.; Grechnev, V. V.; Shabarova, L. V.; Vourlidas, A.; Nishio, M. Bibcode: 1999ASPC..172..391G Altcode: 1999adass...8..391G A database on solar active regions has been implemented in IDL (Interactive Data Language). The observational parameters of the regions are stored in a multi-level structure array that is distributed as a standard IDL save file. Convenient access to the data is provided by an application equipped with a graphical user interface (GUI). A variety of search modes are implemented. Full-disk 17 GHz radio maps produced by the Nobeyama Radioheliograph provide the basis for the database. Title: Broadband microwave imaging spectroscopy with a solar-dedicated array Authors: Bastian, Tim S.; Gary, D. E.; White, S. M.; Hurford, Gordon J. Bibcode: 1998SPIE.3357..609B Altcode: For many years, ground-based radio observations of the Sun have proceeded into two directions: (1) high resolution imaging at a few discrete wavelengths; (2) spectroscopy with limited or no spatial resolution at centimeter, decimeter, and meter wavelengths. Full exploitation of the radio spectrum to measure coronal magnetic fields in both quiescent active regions and flares, to probe the thermal structure of the solar atmosphere, and to study energy release and particle energization in transient events, requires a solar-dedicated, frequency-agile solar radiotelescope, capable of high-time, - spatial, and -spectral resolution imaging spectroscopy. In this paper we summarize the science program and instrument requirements for such a telescope, and present a strawman interferometric array composed of many (greater than 40), small (2 m) antenna elements, each equipped with a frequency- agile receiver operating over the range 1 - 26.5 GHz. Title: Radio Emission from Solar Flares Authors: Bastian, T. S.; Benz, A. O.; Gary, D. E. Bibcode: 1998ARA&A..36..131B Altcode: Radio emission from solar flares offers a number of unique diagnostic tools to address long-standing questions about energy release, plasma heating, particle acceleration, and particle transport in magnetized plasmas. At millimeter and centimeter wavelengths, incoherent gyrosynchrotron emission from electrons with energies of tens of kilo electron volts (keV) to several mega electron volts (MeV) plays a dominant role. These electrons carry a significant fraction of the energy released during the impulsive phase of flares. At decimeter and meter wavelengths, coherent plasma radiation can play a dominant role. Particularly important are type III and type III-like radio bursts, which are due to upward- and downward-directed beams of nonthermal electrons, presumed to originate in the energy release site. With the launch of Yohkoh and the Compton Gamma-Ray Observatory, the relationship between radio emission and energetic photon emissions has been clarified. In this review, recent progress on our understanding of radio emission from impulsive flares and its relation to X-ray emission is discussed, as well as energy release in flare-like phenomena (microflares, nanoflares) and their bearing on coronal heating. Title: Toward a Frequency-Agile Solar Radiotelescope Authors: Bastian, T. S.; Gary, D. E.; White, S. M.; Hurford, G. J. Bibcode: 1998ASPC..140..563B Altcode: 1998ssp..conf..563B No abstract at ADS Title: First Images of Impulsive Millimeter Emission and Spectral Analysis of the 1994 August 18 Solar Flare Authors: Silva, Adriana V. R.; Gary, Dale E.; White, Stephen M.; Lin, R. P.; de Pater, Imke Bibcode: 1997SoPh..175..157S Altcode: We present here the first images of impulsive millimeter emission of a flare. The flare on 1994 August 18 was simultaneously observed at millimeter (86 GHz), microwave (1-18 GHz), and soft and hard X-ray wavelengths. Images of millimeter, soft and hard X-ray emission show the same compact ( 8'') source. Both the impulsive and the gradual phases are studied in order to determine the emission mechanisms. During the impulsive phase, the radio spectrum was obtained by combining the millimeter with simultaneous microwave emission. Fitting the nonthermal radio spectra as gyrosynchrotron radiation from a homogeneous source model with constant magnetic field yields the physical properties of the flaring source, that is, total number of electrons, power-law index of the electron energy distribution, and the nonthermal source size. These results are compared to those obtained from the hard X-ray spectra. The energy distribution of the energetic electrons inferred from the hard X-ray and radio spectra is found to follow a double power-law with slope ∼6-8 below ∼50 keV and ∼3-4 above those energies. The temporal evolution of the electron energy spectrum and its implication for the acceleration mechanism are discussed. Comparison of millimeter and soft X-ray emissions during the gradual phase implies that the millimeter emission is free-free radiation from the same hot soft X-ray emitting plasma, and further suggests that the flare source contains multiple temperatures. Title: On the feasibility of imaging coronal mass ejections at radio wavelengths Authors: Bastian, T. S.; Gary, D. E. Bibcode: 1997JGR...10214031B Altcode: Coronal mass ejections (CMEs) can have a profound impact on the interplanetary medium and the near-Earth environment. We discuss the feasibility of detecting coronal mass ejections at radio wavelengths with a ground-based instrument. In particular, we explore the possibility that a radio telescope employing Fourier synthesis imaging techniques can detect thermal bremsstrahlung emission from CMEs. Using a simulated database from such a telescope, we explore three detection schemes: direct detection, an approximate differential detection scheme, and an ``exact'' differential detection scheme. We conclude that thermal bremsstrahlung emission from CMEs can be detected by such a telescope provided differential techniques are employed. While the approximate differential detection scheme may be sufficient for CMEs viewed near the solar limb, detection of CMEs against the solar disk may require the more sensitive exact differential scheme. The detection and imaging of nonthermal radio emissions from CMEs is also discussed. Title: Imaging the Chromospheric Evaporation of the 1994 June 30 Solar Flare Authors: Silva, Adriana V. R.; Wang, Haimin; Gary, Dale E.; Nitta, Nariaki; Zirin, Harold Bibcode: 1997ApJ...481..978S Altcode: We analyze simultaneous Hα images (from the Big Bear Solar Observatory), soft and hard X-ray images and spectra (from the soft X-ray telescope [SXT], the Bragg Crystal Spectrometer [BCS], and the hard X-ray telescope [HXT] on Yohkoh), and radio time profiles (from the Owens Valley Radio Observatory) during the first 3 minutes of the 1994 June 30 flare. The strong blueshifts observed in the Ca XIX soft X-ray line are interpreted as evidence of chromospheric evaporation, with maximum up-flow velocities occurring 2 minutes prior to the hard X-ray emission peak. In this study, we search for moving sources in Hα, soft and hard X-ray images that correspond to the blueshifted component. The chromospheric evaporation in this flare is divided into two phases: an early phase with up-flow velocities of 350-450 km s-1, and a later phase (during the hard X-ray peak) characterized by velocities of 100-200 km s-1. During the first chromospheric evaporation phase, the footpoints of a loop seen in HXT low-energy maps are seen to move toward the loop-top source. No source displacement is observed in SXT images at this time. Images of the later phase of chromospheric evaporation show a change in the source morphology. The early HXT loop is no longer visible, and HXT maps during this time display the two footpoints of a new loop visible in SXT images. Now the HXT sources are stationary, and a SXT footpoint source is seen to move toward the loop top. We interpret the observed displacement of footpoint sources in HXT (early phase) and SXT (later phase) maps to be the images of the evaporating front projected onto the solar disk, while the up-flow velocities (inferred from the blueshifts) are due to the movement of the same evaporating material along the line of sight. By combining the up-flow velocities with the proper motion of the footpoint sources seen in the maps, we constructed a three-dimensional view of the magnetic loop for each chromospheric evaporation phase. The early loop is almost semicircular, with a height of 1.7 × 109 cm, whereas the later magnetic loop is more elongated (a height of 3.2 × 109 cm), with its apex closer to the footpoint where most of the evaporation took place. The implications of these magnetic configurations and the distinct evaporation phases are discussed. Title: Nobeyama/SOHO/BBSO Comparison of Solar Polar Coronal Holes Authors: Gary, D. E.; Enome, S.; Shibasaki, K.; Gurman, J. B.; Shine, R. A. Bibcode: 1997SPD....28.0801G Altcode: 1997BAAS...29..912G Although it is not widely known outside the discipline of solar radiophysics, a long-standing puzzle exists: the poles of the Sun appear brighter than the rest of the quiet Sun in a restricted range of wavelengths roughly from 15 GHz to about 48 GHz (cf. Kosugi et al. 1986). At somewhat lower radio frequencies the poles appear darker than the quiet Sun due to a deficit of coronal material, while at mm-wavelengths the polar and non-polar quiet Sun appear quite uniform due to the similarity of the atmospheric structure at lower heights in the chromosphere. The excess brightness at the poles has also been reported in coronal holes on the disk, and so is apparently related to the phenomenon of coronal holes. The brightening likely corresponds to an elevated temperature in the upper chromosphere in coronal holes relative to normal quiet Sun. The phenomenon is especially well suited to study via radio emission due to the unique sensitivity of radio waves to this height range in the chromosphere. The possibility exists that the different chromospheric structure for coronal holes implied by the radio brightening may offer some clue to the origin of the fast solar wind, which is now well established to arise in coronal holes. Radio brightening of coronal holes is a difficult observational problem because an instrument is needed that can image large areas of the Sun at relatively high resolution. The Nobeyama Radioheliograph has the required capability and operates at 17 and 34 GHz, nicely within the frequency range where the brightening occurs. We compare Nobeyama radio synthesis images on several days in 1996 with images from the EIT, CDS, and MDI experiments on the Solar and Heliospheric Observatory (SOHO) spacecraft, and with high resolution images from the Big Bear Solar Observatory, with the aim of determining the spatial and temporal characteristics of the brightening. We compare the extent of the radio brightening with the boundaries of the coronal holes seen from the SOHO data, to establish the previously suggested identity of the polar brightening with coronal holes. We investigate whether the brightening is primarily associated with network features, faculae, or perhaps bipolar magnetic elements, or whether it is instead a diffuse brightening more-or-less uniformly covering the coronal hole area. We look for temporal variations, and their correlation with changing features seen from SOHO. We conclude with some ideas for how the chromospheric structure may be different in coronal holes than in normal quiet Sun, and speculate on the implications for acceleration of the fast solar wind. Title: Sunspot Gyroresonance Emission at 17 GHz: A Statistical Study Authors: Vourlidas, A.; Gary, D. E.; Shibasaki, K. Bibcode: 1997SPD....28.0134V Altcode: 1997BAAS...29..885V Our statistical study is based on a compilation of the daily Nobeyama Radioheliograph full-disk maps obtained at 17 GHz between July 1992 -- December 1994. It includes 533 active regions, 20% of which appear to have gyroresonance cores during some part of their disk crossing. At least one of the regions reaches coronal temperatures (T>10(6) K) while several others show a polarization reversal at the extreme limb. Our study indicates that the gyroresonance cores are polarized in the sense of the x-mode and are due to s=3 (B=2024 G) and/or s=4 (B=1518 G) gyroresonance absorption in the transition region and/or corona. We also investigate the dependence between various physical quantities such as brightness temperature, degree of polarization, spot area, photospheric magnetic field and heliographic longitude and comment on the polarization reversals at the limb. A more detailed study of individual active regions, that have been also observed with the Owens Valley Solar Array, will follow. Title: A spatial and spectral maximum entropy method as applied to OVRO solar data Authors: Komm, R. W.; Hurford, G. J.; Gary, D. E. Bibcode: 1997A&AS..122..181K Altcode: We present first results of applying a Maximum Entropy Method (MEM) algorithm that acts in both the spatial and spectral domains to data obtained with the frequency-agile solar interferometer at Owens Valley Radio Observatory (OVRO) taken at 45 frequencies in the range 1-18 GHz. The traditional MEM algorithm does not exploit the spatial information available at adjacent frequencies in the OVRO data, but rather applies separately to each frequency. We seek an algorithm that obtains a global solution to the visibilities in both the spatial and spectral domains. To simplify the development process, the algorithm is at present limited to the one-dimensional spatial case. We apply our 1-d algorithm to observations taken with the OVRO frequency-agile interferometer of active region AR 5417 near the solar limb on March 20, 1989 (vernal equinox). The interferometer's two 27 m antennas and 40 m antenna were arranged in a linear east-west array, which at the vernal equinox gives a good match to the 1-d algorithm. Our results show that including the spectral MEM term greatly improves the dynamic range of the reconstructed image compared with a reconstruction without using this information. The derived brightness temperature spectra show that for AR 5417 the dominant radio emission mechanism is thermal gyroresonance and we use this information to deduce the spatial variation of electron temperature and magnetic field strength in the corona above the active region. Title: Nonthermal Radio Emission from Solar Soft X-Ray Transient Brightenings Authors: Gary, Dale E.; Hartl, Michael D.; Shimizu, Toshifumi Bibcode: 1997ApJ...477..958G Altcode: We compare microwave total power spectral data from the Owens Valley Radio Observatory Solar Array with soft X-ray transient brightenings observed with the Yohkoh soft X-ray telescope. We find that the transient brightenings are clearly detected in microwaves in 12 of 34 events (35%), possibly detected in another 17 of 34 events (50%), and only five of 34 events (15%) had no apparent microwave counterpart. Comparing the radio and soft X-ray characteristics, we find that (1) the soft X-ray peak is delayed relative to the microwave peak in 16 of 20 events, (2) the microwave flux is correlated with the flux seen in soft X-rays, (3) when radio fluence is used instead of radio flux (24 events) the correlation increases substantially, (4) the microwave spectra in the range 1-18 GHz vary greatly from event to event, (5) the microwave spectra often peak in the range 5-10 GHz (13 of 16 events), and (6) the microwave spectra of some events show narrowband spectra with a steep low-frequency slope.

We conclude that the emission from at least some events is the result of a nonthermal population of electrons, and that transient brightenings as a whole can therefore be identified as microflares, the low-energy extension of the general flare energy distribution. Soft X-ray transient brightenings, and therefore microflares, cannot heat the corona. Title: Prospects for the Solar Radio Telescope Authors: Bastian, Timothy S.; Gary, Dale E. Bibcode: 1997LNP...483..218B Altcode: 1997cprs.conf..218B The Solar Radio Telescope (SRT) is an instrument concept for a powerful solar-dedicated radio telescope. As presently conceived. it would combine a high-resolution imaging capability (2″ at 20 GHz) with a broadband spectroscopic capability (0.3-26 GHz). In other words, the SRT would perform broadband imaging spectroscopy on a wide range of quiet- and active-Sun phenomena. On 17-20 April, 1995, a workshop was held in San Juan Capistrano, California. The purpose of the workshop, which was attended by more than 40 scientists from the US and around the world, was to discuss the science that could be done with a solar-dedicated radio synthesis telescope, and to discuss the design constraints imposed by the science envisioned. Special attention was also given to nighttime uses for the instrument. We summarize the "strawman" concept for the instrument here. Title: Comprehensive Multiwavelength Observations of the 1992 January 7 Solar Flare Authors: Silva, Adriana V. R.; White, Stephen M.; Lin, Robert P.; de Pater, Imke; Gary, Dale E.; McTiernan, James M.; Hudson, Hugh S.; Doyle, J. Gerry; Hagyard, Mona J.; Kundu, Mukul R. Bibcode: 1996ApJS..106..621S Altcode: Observations of a solar flare that occurred at 2022 UT on 1992 January 7, during the 1991 December/1992 January Max `91 campaign, are presented. This flare was observed simultaneously in Hα, radio (at microwave and millimeter wavelengths), and soft and hard X-rays (by the Yohkoh spacecraft) with high spatial and moderate spectral resolution. A comparison of magneto grams before and after the flare shows evidence of the emergence of new magnetic flux of opposite polarity at the flare site. Although this flare was only of moderate size (GOES classification C8.9 and Hα importance SF), it exhibited several distinct bursts and at least 10 spatially distinct hard/soft X-ray sources. Cospatial Hα brightenings suggest that most of the X-ray sources are located at footpoints of magnetic loops. Two of the hard X-ray sources have no Hα counterparts and are therefore believed to be located at loop tops. The flare consisted of three bursts of particle acceleration followed by a purely thermal phase. High spectral resolution Ca XIX line profiles indicate upflows shortly after the second acceleration phase. Analysis of the microwave/hard X-ray/soft X-ray emission from individual sources provides information on the radio emission mechanisms, the energetic electron population, the magnetic field strength, and the plasma density. These parameters were estimated for the two microwave sources observed during the third acceleration burst; these sources were simultaneously detected in soft X-rays, and one of the sources is also seen in hard X-ray maps. Although the microwave emission is consistent with the gyro synchrotron mechanism, the millimeter emission, which peaks during the thermal phase when all nonthermal activity has ceased, is likely due to thermal bremsstrahlung from the soft X-ray emitting hot plasma. The energy lost to collisions by the energetic (>15 keV) electrons and the energy contained in the thermal plasma are calculated for each source. The energy injected by the nonthermal electrons from all sources is estimated to be 1030 ergs. Only the soft X-ray sources with gradual time profiles seem to show the Neupert effect. Title: Flare energetics: analysis of a large flare on YZ Canis Minoris observed simultaneously in the ultraviolet, optical and radio. Authors: van den Oord, G. H. J.; Doyle, J. G.; Rodono, M.; Gary, D. E.; Henry, G. W.; Byrne, P. B.; Linsky, J. L.; Haisch, B. M.; Pagano, I.; Leto, G. Bibcode: 1996A&A...310..908V Altcode: The results of coordinated observations of the dMe star YZ CMi at optical, UV and radio wavelengths during 3-7 February 1983 are presented. YZ CMi showed repeated optical flaring with the largest flare having a magnitude of 3.8 in the U-band. This flare coincided with an IUE exposure which permits a comparison of the emission measure curves of YZ CMi in its flaring and quiescent state. During the flare a downward shift of the transition zone is observed while the radiative losses in the range 10^4^-10^7^K strongly increase. The optical flare is accompanied with a radio flare at 6cm, while at 20cm no emission is detected. The flare is interpreted in terms of optically thick synchrotron emission. We present a combined interpretation of the optical/radio flare and show that the flare can be interpreted within the context of solar two-ribbon/white-light flares. Special attention is paid to the bombardment of dMe atmospheres by particle beams. We show that the characteristic temperature of the heated atmosphere is almost independent of the beam flux and lies within the range of solar white-light flare temperatures. We also show that it is unlikely that stellar flares emit black-body spectra. The fraction of accelerated particles, as follows from our combined optical/radio interpretation is in good agreement with the fraction determined by two-ribbon flare reconnection models. Title: Microwave and Soft X-Ray Emission from a Flare-activated Coronal Loop Authors: Gary, D. E.; Wang, H.; Nitta, N.; Kosugi, T. Bibcode: 1996ApJ...464..965G Altcode: We study the microwave and soft X-ray emissions produced by a flare-activated coronal loop, using total power spectral data from the Owens Valley Radio Observatory Solar Array, as well as soft X-ray data from the Yohkoh Soft X-ray Telescope, and the GOES soft X-ray monitors. We show that both the microwave and soft X-ray emissions, late in the loop development, can be well understood as thermal bremsstrahlung (free-free emission) from a hot (∼8 MK) plasma. From an investigation of the microwave spectrum we suggest that an overlying or cospatial, cooler (∼4 MK) plasma may also be present.

We also study the time development of the loop, as observed with the three instruments. The loop appears to grow in size from a lower lying, initially invisible loop. New loops appear at greater heights, or else the initial loop rises at a top speed of more than 150 km s-1, but the growth of the loop or loops slows after about 3 minutes and becomes stable at its inflated size. We study the subsequent brightening of the loop, using the SXT, GOES, and microwave data to investigate the changing physical parameters of the loop as it evolves. Title: Imaging the Chromospheric Evaporation of the 1994 June 30 Solar Flare Authors: Silva, Adriana V. R.; Wang, H.; Gary, D. E.; Zirin, H.; Nitta, N. Bibcode: 1996AAS...188.3310S Altcode: 1996BAAS...28R.869S We analyze simultaneous H _alpha images (from Big Bear Solar Observatory), soft and hard X-ray images and spectra (from Yohkoh during the first three minutes of the 1994 June 30 flare. The strong blueshifts observed in the Ca XIX soft X-ray line are interpreted as evidence of chromospheric evaporation, with maximum up--flow velocities occurring two minutes prior to the hard X-ray emission peak. In this paper, we search for moving sources in H_alpha , soft and hard X-ray images that correspond to the blueshifted component. The chromospheric evaporation in this flare is divided into two phases: an early phase with up-flow velocities of 300-450 km s(-1) , and a later phase (during the hard X-ray peak) characterized by velocities of 100-200 km s(-1) . During the first chromospheric evaporation phase, the footpoints of a loop seen in HXT maps are seen to move towards the loop top source. No source displacement is observed in SXT images. The hard X-ray spectra of individual sources, obtained from HXT maps, display a very steep slope (gamma ~ 10-12). Thermal fitting of the spectra yield temperatures of 20-50 MK. Images of the later phase of chromospheric evaporation show the magnetic configuration to have changed. The early HXT loop is no longer visible and HXT maps during this time display the two footpoints of a new loop also visible in SXT images. Now the HXT sources are stationary and a SXT footpoint source is seen to move toward the loop top. We interpret the observed displacement of footpoint sources in HXT (early phase) and SXT (later phase) maps to be the images of the evaporating front projected onto the solar disk, while the up--flow velocities (inferred from the blueshifts) are due to the movement of the same evaporating material along the line of sight. By combining the up--flow velocities with the proper motion of the footpoint sources seen in the maps, we constructed a 3-D view of the magnetic loop for each chromospheric evaporation phase. The early loop is almost semi--circular with a height of 1.7x 10(9) cm, whereas the later magnetic loop is more elongated (height of 2.3x 10(9) cm) and asymmetric with its apex closer to the footpoint where most of the evaporation took place. The implications of these magnetic configurations and the distinct evaporation phases are discussed. Title: Large Scale Features of the Radio Sun Authors: White, S. M.; Gary, D. E.; Kundu, M. R. Bibcode: 1996AAS...188.7907W Altcode: 1996BAAS...28Q.956W We present full-disk images of the Sun at 5 GHz made by observing 26 different fields with the Very Large Array and combining them using mosaicking techniques. The resulting image combines sensitivity to large-scale structures with good resolution. Full-disk images at 0.33, 1.4 and 17 GHz, a high-resolution magnetogram and a soft X-ray image are compared with the 5 GHz image to investigate the physical properties of large-scale features. Title: Nonthermal Microwave Emission from Soft X-ray Transient Brightenings. Authors: Gary, D. E.; Hartl, M.; Shimizu, T. Bibcode: 1996AAS...188.2609G Altcode: 1996BAAS...28..858G Soft X-ray transient brightenings (TBs) are small enhancements, generally associated with active region loops, that last for 5-10 min. Shimizu et al. (1994) has shown that the rate of energy release in TBs has the same form as that for flares, and if they are interpreted as tiny flares they would extend the flare energy release rate to lower energy by two orders of magnitude. However, in initial investigation of radio counterparts of TBs near 15 GHz (Gopalswamy et al 1995; White et al. 1995) showed no conclusive evidence for nonthermal electrons, which brings into question whether TBs are flare-like energy releases. The presence of nonthermal electrons is most easily seen at somewhat lower radio frequencies, which led us to search for such emission in radio data from the OVRO Solar Array in the range 1-18 GHz. Using soft X-ray observations from Yohkoh, we identified 34 transient brightenings in solar active region AR7172 observed from 20-29 May 1992. A comparison with radio data from OVRO yielded the following new results: 1) enhanced radio emission can be positively associated with TBs in 12 events (35%), with another 17 (50%) showing a possible association; 2) a number of the positive associations show radio peaks that occur near the onset of the soft X-ray enhancement, with a Neupert-Effect-like relationship (mean delay of the soft X-ray peak relative to the microwave peak is 2.5 min); 3) the radio power spectra of those events intense enough to give good spectra indicate the presence of a nonthermal electron population; 4) the correlation between peak radio flux and peak soft X-ray flux is weak. For the 7 events with the clearest Neupert-Effect relationship, there is a much higher correlation between integrated radio flux and peak soft X-ray flux. Together these results suggest that TBs are the analog of solar flares extended below the subflare energy range. We may now state that the low-energy extension of flare events is not sufficient to heat the corona, but the study of TBs can shed light on flare processes that may be masked in larger flares. Title: Spatial/Spectral MEM Applied to OVRO Flare Data Authors: Komm, R. W.; Gary, D. E.; Hurford, G. J. Bibcode: 1996AAS...188.8502K Altcode: 1996BAAS...28..961K We present observations of a flare that occured on 1995 Oct 11, in AR 7912 obtained with the frequency-agile solar interferometer at Owens Valley Radio Observatory (OVRO) made with both high spatial and spectral resolution. We analyzed data at 32 frequencies in the range 1.2-12.4 GHz for both left-handed and right-handed circular polarizations applying the recently completed Spatial/Spectral Maximum Entropy Method (MEM). In contrast to the traditional MEM algorithm, which does not exploit the spatial information available at adjacent frequencies in the OVRO data, the new algorithm obtains a global solution to the visibilities in both the spatial and spectral domains and leads to spectra which are greatly improved in smoothness and dynamic range. A comparison with BBSO data shows that the optical flare is associated with the trailing sunspot of the active region, while the leading sunspot shows no flare related brightning. The reconstructed radio images show two sources; one of them, the primary source, is associated with the optical flare and has its peak emission at about 7.0 GHz, while the other one, the secondary source, is associated with the leading sunspot with a peak emission at about 2.8 GHz. The slopes of the brightness temperature spectra imply that in both cases non-thermal gyrosynchrotron emission is the process responsible for the microwave radiation. A preliminary model fit of the spectra shows that the emission of both sources comes from low-order harmonics and that the estimated magnetic field strength and the estimated density of nonthermal electrons of the primary source are much larger than the corresponding values of the secondary source. The results suggest that the two sources are connected by a large secondary loop and that the emission of the secondary source is caused by nonthermal electrons escaping from the primary source. The time evolution of the two sources within about +/- 3 min of the flux peak time can be described by an increase in the number of nonthermal electrons up to the peak time and by a subsequent decrease. Title: Ground-based Gamma-Ray Burst Follow-up Efforts: Results of the First Two Years of the BATSE/COMPTEL/NMSU Rapid Response Network Authors: McNamara, Bernard J.; Harrison, Thomas E.; Ryan, J.; Kippen, R. M.; McConnell, M.; Macri, J.; Kouveliotou, C.; Fishman, G. J.; Meegan, C. A.; Green, D. A.; Koranyi, D. M.; Warner, P. J.; Waldram, E. M.; Hanlon, L.; Bennett, K.; Spoelstra, T. A. Th.; Metlov, V. G.; Metlova, N. V.; Feigelson, E.; Beasley, A. J.; Palmer, D. M.; Barthelmy, S. D.; Gary, Dale E.; Olsen, E. T.; Levin, S.; Wannier, P. G.; Janssen, M. A.; MACHO Collaboration; Borovicka, J.; Pravec, P.; Hudec, R.; Coe, M. J. Bibcode: 1996ApJS..103..173M Altcode: In this paper we describe the capabilities of the BATSE/COMPTEL/NMSU Rapid Response Network and report on results obtained during its first 2 years of operation. This network is a worldwide association of 22 radio and optical observatories that perform follow-up searches of newly discovered gamma-ray burst error boxes by the Compton Gamma Ray Observatory. During the last 2 years, it has deeply imaged 10 gamma-ray error boxes over time frames from a few hours to a month after burst detection, and it finds no sources that can be associated unambiguously with a gamma-ray burst. We suggest that significant optical or radio emission is not produced by gamma-ray bursts more than a day after the burst. This result is consistent with recent theoretical models by Katz, Meszaros, Rees, & Papathanassiou, and Paczynski & Rhoads; however, our hours to days optical response time and radio sensitivity limits allow only a weak constraint to be placed on these models. Based upon this study and other published works, we surest that future work should concentrate on acquiring deep optical images (m >= 12) of small gamma-ray error boxes well within a day of the burst. Ideally, radio observations should begin as soon after the burst as possible, reach a sensitivity of <= 1 mJy, and be continued with occasional images being acquired for at least a month following burst detection. Title: Imaging Spectroscopy of the Non-Flaring Sun Authors: Gary, D. E. Bibcode: 1996ASPC...93..387G Altcode: 1996ress.conf..387G No abstract at ADS Title: Broadband Imaging Spectroscopy with the Solar Radio Telescope Authors: Bastian, T. S.; Gary, D. E.; Hurford, G. J.; Hudson, H. S.; Klimchuk, J. A.; Petrosian, V.; White, S. M. Bibcode: 1996ASPC...93..430B Altcode: 1996ress.conf..430B No abstract at ADS Title: OVRO, BBSO, BATSE, and YOHKOH Observations of a Twin Solar Flare Authors: Wang, H.; Gary, D. E.; Zirin, H.; Nitta, N.; Schwartz, R. A.; Kosugi, T. Bibcode: 1996ApJ...456..403W Altcode: We present the results of studies on two solar flares that occurred on 1993 February 11: an M1.1 flare at 18:07 UT and an M2.7 flare at 18:31 UT. Our study was based on comprehensive observations by the following observatories: Owens Valley Radio Observatory, which obtains 1-18 GHz microwave images; Big Bear Solar Observatory, which obtains magnetograms, Hα and He D3 filtergrams; BATSE on board Compton Gamma Ray Observatory, which obtains high-resolution hard X-ray spectra; and the Japanese satellite Yohkoh, which obtains high-resolution soft and hard X-ray images. We find the following: (1) While the optical and hard X-ray emissions are confined to a small loop near the leading spot of the active region for both flares, a large-scale soft X-ray loop connects from the leading to the following spot 160" away. In low-frequency micro-waves (<4 GHz), sources appear at each end of the big loop, and the source near the following spot (away from the Hα flare site) dominates at frequencies <2.8 GHz. For both flares, as frequency increases, the source near the leading spot becomes dominant, and the source near the following spot vanishes gradually. (2) As frequency increases, the centroid of the leading microwave source moves progressively downward until it reaches the footpoint at high frequencies. (3) For the M2.7 event, in the compact loop near the leading spot, two footpoints are seen in both soft and hard X-rays. The dominant hard X-ray source has a softer spectrum than the weaker one, suggesting that the weaker one may become dominant at the higher energies (>100 keV) responsible for the microwave emission. The high-frequency microwave emission is better associated with this latter footpoint. (4) The large soft X-ray loop in the M2.7 flare is the postflare loop of the M1.1 flare. This flare is associated with a different compact loop which is 40" away from the main flare. (5) For the M2.7 flare, the microwave brightness temperature spectra in the sources at the two ends of the big loop require very different source parameters. The primary source near the leading spot can be explained by nonthermal gyrosynchrotron emission from electrons with a power-law energy index (δ) of 5.3. The same group of electrons can explain the observed BATSE hard X-ray spectra. The low-frequency radio source near the following spot is due to either a thermal component, or a nonthermal component with a steep energy index (δ= 9.4). Based on the available information, we cannot distinguish these two possibilities. Title: Recent Results from the OVRO Solar Array Authors: Gary, D. E. Bibcode: 1996ASPC...93..409G Altcode: 1996ress.conf..409G No abstract at ADS Title: Coordinated OVRO, BATSE, Yohkoh, and BBSO Observations of the 1992 June 25 M1.4 Flare Authors: Wang, H.; Gary, D. E.; Zirin, H.; Schwartz, R. A.; Sakao, T.; Kosugi, T.; Shibata, K. Bibcode: 1995ApJ...453..505W Altcode: We compare 1-14 GHz microwave images observed at the Owens Valley Radio Observatory (OVRO), 16- and 256-channel hard X-ray spectra obtained by the Burst and Transient Source Experiment (BATSE) onboard the Compton Gamma Ray Observatory (CGRO), soft and and hard X-ray images obtained by Yohkoh, and Hα images and magnetograms observed at the Big Bear Solar Observatory (BBSO) for the 1992 June 25 M1.4 flare. We find the following unique properties for this flare: (1) Soft X-ray emissions connect two foot- points, the primary microwave source is located at one footpoint, and hard X-ray emissions are concentrated in the other footpoint The radio footpoint is associated with an umbra and may have stronger magnetic field. (2) During the period that 256-channel BATSE data are available, the hard X-ray photon spectrum consists of two components: a superhot component with a temperature of 8.4 × 107 K and emission measure of 2.5 × 1046 cm-3 and a power-law component with a photon index of 4.2. This is the first time that such a high temperature is reported for the hard X-ray thermal components. It is even more interesting that such a superhot component is identified before the peak of the flare. The microwave brightness temperature spectra during the same period also demonstrate two components: a thermal component near the loop top and a nonthermal component at the footpoint of the loop. The microwave thermal component has the similar temperature as that of the hard X-ray superhot component. These measurements are consistent with the theory that the microwaves and hard X-rays are due to the same group of electrons, despite the fact that they are separated by 35,000 km. (3) The soft X-ray emissions brighten the existing loops and co-align with Hα emissions throughout the entire duration of the flare. Title: Solar Rotation Stereoscopy in Microwaves Authors: Aschwanden, Markus J.; Lim, Jeremy; Gary, Dale E.; Klimchuk, James A. Bibcode: 1995ApJ...454..512A Altcode: We present here the first stereoscopic altitude measurements of active region sources observed at microwave frequencies (10-14 GHz The active region NOAA 7128 was observed with the Owens Valley Radio Observatory (OVRO) on 1992 April 13, 14, 15, and 16 as it passed through the central meridian. From white-light data of the underlying sunspot we determined the rotation rate of the active region, which was found to have a relative motion of dL/dt = +0°.240 day-1 with respect to the standard photospheric differential rotation rate. Based on this rotation rate we determine for the microwave sources stereoscopic altitudes of 3.3-11.0 Mm above the photosphere. The altitude spectrum h(v) of the right circular polarization (RCP) main source shows a discontinuity at 12 GHz and can be satisfactorily fitted with a dipole model with a transition from the second to the third harmonic level at 12 GHz. The dominance of the third harmonic for frequencies above 12 GHz occurs because the second harmonic level drops below the transition region, at a height of 2.6±0.6 Mm according to the microwave data. The altitude spectrum h(v) serves also to invert the temperature profile T(h) from the optically thick parts of the radio brightness temperature spectrum TB(ν[h]). The microwave emission in both circular polarizations can be modeled with gyroresonance emission, with x-mode for RCP and o-mode in LCP, with the same harmonics at each frequency, but different emission angles in both modes. The contributions from free-free emission are negligible in both polarizations, based on the peak emission measure of EM ≍ 6 × 1028 cm-5 observed in soft X-rays by Yohkoh/SXT.

This study demonstrates that the height dependence of the coronal magnetic field B(h) and the plasma temperature T(h) in an active region can be inverted from the stereoscopic altitude spectra h(v) and the observed brightness temperature spectra TB(ν). Title: A Comparison of Active Region Temperatures and Emission Measures Observed in Soft X-Rays and Microwaves and Implications for Coronal Heating Authors: Klimchuk, J. A.; Gary, D. E. Bibcode: 1995ApJ...448..925K Altcode: We have determined active region temperatures and emission measures using both broad-band soft X-ray images from the Yohkoh satellite and spatially and spectrally resolved microwave data from the Owens Valley Radio Observatory (OVRO). This work differs from previous work in that the microwave temperatures and emission measures are directly measured from the microwave spectrum, and are not model-dependent. The soft X-ray temperatures and emission measures are ≍2.5 times greater than the corresponding microwave values, on average. Detailed error analysis indicates that the temperature differences are real, but that the emission measure differences may not be.

We have simulated Yohkoh and OVRO observations of idealized plane-parallel and nested-loop coronal models. The plane-parallel model reproduces the observed temperature differences if the coronal temperature decreases exponentially with height from a maximum value of 4 × 106 K at the base to an asymptotic value of ≍106 K. The nested-loop model, which assumes quasi-static loop equilibrium, also reproduces the observed temperature differences and indicates that the volumetric coronal heating rate varies inversely with loop length to a power greater than 2. Both models predict microwave emission measures that are larger than observed. We suggest that a more complex model is required to explain the observed emission measures and that more than one coronal heating mechanism may be operative in solar active regions.

We present derivations of the temperature and emission measure uncertainties that result from random and systematic errors in the Yohkoh observations. The expression for the random error emission measure uncertainty is different from that used previously and is especially important for observations of nonflaring plasmas. Title: The Microwave and H alpha Sources of the 1992 January 13 Flare Authors: Wang, H.; Gary, D. E.; Zirin, H.; Kosugi, T.; Schwartz, R. A.; Linford, G. Bibcode: 1995ApJ...444L.115W Altcode: We compare X-ray, microwave and H-alpha observations for the 1992 January 13 limb flare. The soft and hard X-ray images of the flare have been studied thoroughly by Masuda et al. (1994) with Yohkoh SXT and HXT images. We find that during the hard X-ray emission peak there is no H-alpha brightening on the disk nor at the limb, so the main ribbons of this flare must be beyond the limb. The microwave source maintains a fixed distance about 10 arcsecs from the optical limb in the frequency range 2.8-14.0 GHz. We interpret this limit in source position as due to the presence of a microwave limb that extends higher than the white-light limb -- to a height of 7300 +/- 1500 km. We believe that the high-frequency microwave emissions are occulted by this extended limb, while the soft and hard X-ray emissions are able to pass through largely unaffected. We also believe, however, that the hard X-ray footpoints are also partially occulted by the photospheric limb, despite the appearance of 'footpoint sources' in HXT data shown by Masuda et al. The smooth X-ray and microwave time profiles, microwave-rich emission relative to hard X-rays, and progressive hard X-ray spectral hardening through the flare peak are all characteristics that we interpret as being a direct result of the occultation of footpoint emission. Title: Solar Microwave and Soft X-ray Observations of Thermal Bremsstrahlung from a Post-Flare Loop Authors: Gary, D. E.; Wang, H.; Nitta, N.; Kosugi, T. Bibcode: 1995SPD....26.1214G Altcode: 1995BAAS...27..986G No abstract at ADS Title: The Flare of 1992 July 16: Gyrosynchrotron Radiation and Razin Suppression Authors: Belkora, L.; Kiplinger, A.; Gary, D. E. Bibcode: 1995SPD....26..803B Altcode: 1995BAAS...27..972B No abstract at ADS Title: A Solar Radio Telescope for the Future: Science Summary from the SRT Workshop Authors: Gary, D. E.; Bastian, T. S.; Hudson, H. S.; Hurford, G. J.; Klimchuk, J. A.; Petrosian, V.; White, S. M. Bibcode: 1995SPD....26..801G Altcode: 1995BAAS...27..971G No abstract at ADS Title: The Microwave and Hα Sources of the 1992 January 13 Flare Authors: Wang, H.; Gary, D. E.; Zirin, H.; Kosugi, T.; Schwartz, R. A.; Linford, G. Bibcode: 1995SPD....26..805W Altcode: 1995BAAS...27..972W No abstract at ADS Title: The Application of Spatial and Spectral MEM to OVRO Solar Data Authors: Komm, R. W.; Hurford, G. J.; Gary, D. E. Bibcode: 1995SPD....26.1301K Altcode: 1995BAAS...27..986K No abstract at ADS Title: Initial Operation of the Solar Radio Burst Locator Authors: Hurford, G. J.; Freely, W. F.; Gary, D. E. Bibcode: 1995SPD....26.1311H Altcode: 1995BAAS...27..989H No abstract at ADS Title: A Solar Radio Telescope for the Future: Strawman Concept from the SRT Workshop Authors: Hurford, G. J.; Bastian, T. S.; Gary, D. E.; Hudson, H. S.; Klimchuk, J. A.; Petrosian, V.; White, S. M. Bibcode: 1995SPD....26..802H Altcode: 1995BAAS...27..971H No abstract at ADS Title: A Multisource Limb Flare Observed at Multiple Radio Wavelengths Authors: Kucera, T. A.; Dulk, G. A.; Gary, D. E.; Bastian, T. S. Bibcode: 1994ApJ...433..875K Altcode: A flare with several radio sources occurred on the solar limb at 2155 UT on 1989 June 20. It was observed by the Very Large Array (VLA) and the Owens Valley Radio Observatory (OVRO). The VLA data consisted of images at 1.4 GHz, while OVRO provided spectral and spatial information over the range 1-15 GHz. We develop a new gyrosynchrotron model to analyze the sources observed at flare peak. This model differs from many previous ones in that it contains spatial variations of both the magnetic field and accelerated particle density. It uses a new gyrosynchrotron approximation which is valid at very low harmonics of the gyrofrequency. For the first time we find that the cause of the change of microwave source size with frequency in the event studied was due primarily to the spatial variation of the accelerated electron density. This is contrary to the common assumption that the variation in size is due to a nonuniform magnetic field. We also investigate a polarized source which brightened later in the flare, finding that it could have been due to plasma radiation or gyrosynchrotron emission. Title: Microwave Spectral Imaging, H alpha , and Hard X-Ray Observations of a Solar Limb Flare Authors: Wang, H.; Gary, D. E.; Lim, J.; Schwartz, R. A. Bibcode: 1994ApJ...433..379W Altcode: We compare the microwave, H-alpha, and hard X-ray observations for a west limb C7.3 flare that occurred at 17:10 UT, 1992 June 26. H-alpha movies were obtained at Big Bear Solar Observatory. Before the onset of the flare, overexposed H-alpha images show the complicated flux loop structure above the limb. Material was observed to descend along the loops toward the site where the flare occurred hours later. Using the five-antenna solar array at Owens Valley Radio Observatory, we obtain two-dimensional maps of flare emission from 1.4 to 14 GHz. In all three temporal peaks of the microwave bursts, the maps show the same characteristics. The peak low-frequency emission comes from the top of one bundle of the H-alpha loops and gradually shifts to the foot-point of the loops (the location of H-alpha flare) as the frequency increases. The location of the emission peak shifts 88 sec between 1 and 14 GHz. Seventy percent of the shift occurs between 1 and 5 GHz. The locus of the shift of the emission peak follows the shape of an H-alpha surge that occurred after the flare. For each point along the locus, we create the microwave brightness temperature spectrum and compare the radio-derived electron distribution with that derived from the high-resolution hard X-ray spectra measured with Burst and Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory (CGRO). We find that the peak frequency changes from approximately 3 GHz at the loop top to approximately 7 GHz at the footprint, presumably due to the increase of the magnetic field from approximately 160 GHz at the loop top to approximately 300 G at the footpoint. The high-frequency slope of the microwave power-law spectrum decreases from approximately 10 at the loop top to approximately 5 at the footprint due to a change in the energy distribution of the dominant electrons. The microwave brightness temperature spectral index predicted by the BATSE power-law hard X-ray spectra agrees with the measured value only at the footpoint. At the loop top, the emission may be thermal gyrosynchrotron with a temperature of 3.5 x 107 K, which is likely to correspond to the superhot component seen in the hard X-ray emission. Title: Spectral evolution of microwaves and hard X-rays in the 1989 March 18 flare and its interpretation Authors: Lee, Jeongwoo W.; Gary, Dale E. Bibcode: 1994SoPh..153..347L Altcode: We analyze the time variation of microwave spectra and hard X-ray spectra of 1989 March 18, which are obtained from the Solar Array at the Owens Valley Radio Observatory (OVRO) and the Hard X-Ray Burst Spectrometer (HXRBS) on the Solar Maximum Mission (SMM), respectively. From this observation, it is noted that the hard X-ray spectra gradually soften over 50-200 keV on-and-after the maximum phase while the microwaves at 1-15 GHz show neither a change in spectral shape nor as rapid a decay as hard X-rays. This leads to decoupling of hard X-rays from the microwaves in the decay phase away from their good correlation seen in the initial rise phase. To interpret this observation, we adopt a view that microwave-emitting particles and hard X-ray particles are physically separated in an inhomogeneous magnetic loop, but linked via interactions with the Whistler waves generated during flares. From this viewpoint, it is argued that the observed decoupling of microwaves from hard X-rays may be due to the different ability of each source region to maintain high energy electrons in response to the Whistler waves passing through the entire loop. To demonstrate this possibility, we solve a Fokker-Planck equation that describes evolution of electrons interacting with the Whistler waves, taking into account the variation of Fokker-Planck coefficients with physical quantities of the background medium. The numerical Fokker-Planck solutions are then used to calculate microwave spectra and hard X-ray spectra for agreement with observations. Our model results are as follows: in a stronger field region, the energy loss by electron escape due to scattering by the waves is greatly enhanced resulting in steep particle distributions that reproduce the observed hard X-ray spectra. In a region with weaker fields and lower density, this loss term is reduced allowing high energy electrons to survive longer so that microwaves can be emitted there in excess of hard X-rays during the decay phase of the flare. Our results based on spectral fitting of a flare event are discussed in comparison with previous studies of microwaves and hard X-rays based on either temporal or spatial information. Title: Flat Microwave Spectra Seen at X-Class Flares Authors: Lee, Jeongwoo W.; Gary, Dale E.; Zirin, H. Bibcode: 1994SoPh..152..409L Altcode: We report peculiar spectral activity of four large microwave bursts as obtained from the Solar Arrays at the Owens Valley Radio Observatory during observations of X-class flares on 1990 May 24 and 1991 March 7, 8, and 22. Main observational points that we newly uncovered are: (1) flat flux spectra over 1-18 GHz in large amounts of flux ranging from 102 to 104 s.f.u. at the maximum phase, (2) a common evolutionary pattern in which the spectral region of dominant flux shifts from high frequencies at the initial rise to low frequencies at the decaying phase, and (3) unusual time profiles that are impulsive at high frequencies but more extended at lower frequencies. Title: OVRO and NRO Observations of the Solar Flare on 1993 June 3 Authors: Gary, D. E.; Enome, S.; Bruner, M. Bibcode: 1994kofu.symp..165G Altcode: A flare that began on 1993 June 3 was observed jointly by the Owens Valley Radio Observatory (OVRO) Solar Array and the Nobeyama Radio Observatory (NRO) Radioheliograph. We present preliminary results from these observations, along with soft X-ray data from the Yohkoh SXT and GOES. The burst had a gradual time profile in the 17GHz NRO data, except for a pair of unusual spikes in the decay phase. However, the OVRO data show that the burst was impulsive, comprising several peaks at progressively higher frequencies. We suggest that the gradual 17GHz emission is thermal, and discuss the relationship of the thermal emission to the impulsive emission. Title: Multiwavelength Observations of a Solar Flare Authors: White, S. M.; Silva, A.; de Pater, I.; Lin, R. P.; Gary, D. E.; Hudson, H. S.; Doyle, J. G.; Hagyard, M. J.; Kundu, M. R. Bibcode: 1994kofu.symp..203W Altcode: No abstract at ADS Title: Imaging Spectroscopy of Solar Microwave Radiation. I. Flaring Emission Authors: Lim, Jeremy; Gary, Dale E.; Hurford, Gordon J.; Lemen, James R. Bibcode: 1994ApJ...430..425L Altcode: We present observations of an impulsive microwave burst on the Sun with both high spatial and spectral resolution, made with the Solar Array at the Owens Valley Radio Observatory (OVRO). We used the measured brightness temperature spectrum to infer the emission process responsible for each microwave source, and to derive physical conditions in the source region. We confimed our predictions using soft X-ray measurements from Geostationary Operational Environmental Satellite (GOES), soft X-ray images from Yohkoh, and H-alpha flare images together with sunspots and magnetogram images from the Big Bear Solar Observatory. Title: Coronal Temperature, Density, and Magnetic Field Maps of a Solar Active Region Using the Owens Valley Solar Array Authors: Gary, Dale E.; Hurford, G. J. Bibcode: 1994ApJ...420..903G Altcode: We present the first results of solar active region observations with the recently completed five-element Owens Valley Solar Array. On 1991 October 24, maps of Active Region AR 6891 were obtained at 22 frequencies from 1.2-7.0 GHz to provide brightness temperature spectra at each point. This is the first time that both high spatial and frequency-resolution brightness temperature spectra have been available over such a broad radio-frequency range. We find that over most of the region the spectra fall into one of the two well-defined categories: thermal free-free or thermal gyroresonance. In these cases, we use the spectra to deduce the spatial variation of physical parameters-electron temperature, column emission measure (intergral n2e dl), and the coronal magnetic field strength-in and around the active region. Over a limited area of the region, the spectra resemble neither of the simple types, and alternative interpretations are required. The possibilties include the presence of fine structure that is unresolved at low frequencies; the presence of a small number of nonthermal electrons; or the presence of overlying, cooler 106 K material which at low frequencies absorbs the hot (3 x 106 K) thermal emission generated below. Title: Particle Acceleration and Flare Triggering in Large-Scale Magnetic Loops Joining Widely Spaced Active Regions Authors: Willson, Robert F.; Lang, Kenneth R.; Gary, Dale E. Bibcode: 1993ApJ...418..490W Altcode: We provide new observations that contradict the canonical model of solar flare emission in the coronal loops of a single active region, and indicate instead particle acceleration and flare triggering in otherwise invisible, large-scale magnetic loops joining widely separated active regions. Very Large Array (VLA) snapshot maps and NSO-Kitt Peak photospheric magnetograms indicate that bursts at 20 cm wavelength occurred in two widely separated active regions, and that 91 cm radiation originated in large-scale magnetic loops joining them. Images taken by the Yohkoh satellite showed no substantial enhanced soft X-ray emission from coronal loops joining these active regions either before or after the flare. Observations from the Owens Valley Solar Array (OVRO) confirm the VLA 20 cm results while also showing decimetric emission that is relatively narrow-band and superposed on a broader background. Comparisons of the time profiles of the radio radiation from the two active regions with simultaneous hard X-ray time profiles, observed with the Burst and Transient Source Spectrometer Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO), suggest that energetic electrons were first accelerated in one active region, and then injected into the largescale magnetic loops at velocities ≥ 0.4c to trigger 20 cm burst emission in the active region at the other footpoint of these loops, while also leading to 91 cm radiation from the entire loop system. These observations provide another example of the diversified mechanisms for particle acceleration and flare triggering on the Sun. Title: High spectral resolution, high sensitivity microwave and associated hard X-ray bursts Authors: Sawant, H. S.; Cecatto, J. R.; Dennis, B. R.; Gary, D. E.; Hurford, G. J. Bibcode: 1993AdSpR..13i.191S Altcode: 1993AdSpR..13..191S We have carried out mm-wavelength (18 - 23) GHz observations of solar bursts in June 1989, in Brazil. Nine of the bursts were observed simultaneously with the Hard X-ray Burst Spectrometer (HXRBS) on the Solar Maximum Mission (SMM). The Owens Valley Radio Observatory (OVRO) observed five of these events from 1 to 18 GHz. To date, we have analyzed six of these events and the preliminary results are: (i) The turnover frequency of all of these bursts were in the frequency range of 7 - 11 GHz and the radio spectral index ranged from -0.3 to -5.3 (ii) In three bursts, dominant features of high energy (>= 200 keV) X-rays coincided in time with mm-wavelength peaks, suggesting that the high energy electrons are responsible for the mm-wavelength emission. Title: The Magnetic Field in the Corona above Sunspots at the Eclipse of 1991 July 11 Authors: Gary, D. E.; Leblanc, Y.; Dulk, G. A.; Golub, L. Bibcode: 1993ApJ...412..421G Altcode: A partial solar eclipse and an X-ray image are used to study the magnetic field as a function of height in the corona above an active region during the solar eclipse of July 11, 1991. The dominant features of AR 6718 are two leading spots of positive polarity followed by two spots of negative polarity about 3 arcmin to the east. Bright radio emission coincides with the positions of the sunspots, attributable to a gyroresonance radiation from ambient electrons above the spots. A simplified model of the source as a function of frequency based on the interferometer fringe amplitudes is used to obtain brightness temperature spectra for the emission associated with the sunspots. It is deduced that the magnetic field strength at the base of the corona above the leading spots was 1200 G, and about 1100 G above the following spots. The soft X-ray brightness above the sunspots was very low, about 30 times lower than that of the adjacent plage-associated emission. Title: Imaging Spectroscopy of a Solar Microwave Flare Authors: Lim, J.; Gary, D. E.; Hurford, G. J.; Lemen, J. R. Bibcode: 1993BAAS...25.1198L Altcode: No abstract at ADS Title: Flare of July 16, 1992 Observed with OVRO and YOHKOH Authors: Belkora, L.; Gary, D. E. Bibcode: 1993BAAS...25.1186B Altcode: No abstract at ADS Title: Comparison of Coronal Temperatures and Emission Measures Determined from X-Ray and Microwave Observations Authors: Klimchuk, J. A.; Gary, D. E. Bibcode: 1993BAAS...25.1179K Altcode: No abstract at ADS Title: Microwave, Hα and Hard X-ray Observations of the 1992 June 26 C7.3 Solar Flare Authors: Wang, H.; Gary, D. E. Bibcode: 1993BAAS...25.1198W Altcode: No abstract at ADS Title: Millimeter, Microwave and X-Ray Morphology and Spectra of the 07Jan92 Flare Authors: Silva, A. V.; Lin, R. P.; de Pater, I.; White, S. M.; Kundu, M. R.; Gary, D. E.; Hudson, H. S. Bibcode: 1993BAAS...25Q1223S Altcode: No abstract at ADS Title: OVRO Microwave and Yohkoh HXT and SXT Observations of a Solar Flare Authors: Gary, D. E.; Hurford, G. J.; Sakao, T. Bibcode: 1993BAAS...25.1180G Altcode: No abstract at ADS Title: OVRO Microwave Observations During the Max'91/CoMStOC'92 Campaign Authors: Gary, D. E.; Hurford, G. J.; Bastian, T. Bibcode: 1993BAAS...25.1224G Altcode: No abstract at ADS Title: Model of Gyrosynchrotron Emission Sources Observed in the Microwaves Authors: Kucera, T. A.; Dulk, G. A.; Gary, D. E. Bibcode: 1993BAAS...25.1214K Altcode: No abstract at ADS Title: Microwave Emission from a Sunspot - Part Two Authors: Lee, Jeongwoo W.; Gary, Dale E.; Hurford, G. J. Bibcode: 1993SoPh..144..349L Altcode: A series of microwave observations of a sunspot in the active region NOAA 4741 was made with the Owens Valley Solar Array for the purpose of investigating the center-to-limb variation of both the spectral and spatial brightness distribution. In this investigation, several properties of the sunspot microwave radiation are found. First, sunspot microwave emission appears in two typical profiles depending on the heliocentric position of the spot: either the ring structure near disk center or single-peak structure near the limb. Second, the brightness temperature at high, optically thin frequencies (>6 GHz) increases slightly as the spot approaches the limb, which we interpret as being due to the increase of the gyroresonance opacity of the field lines near the spot center as they gain greater viewing angles. Third, the center-to-limb variation of the gyroresonance spectrum seems to be mostly characterized by a change of effective harmonic, which accompanies a discontinuous change of the degree of polarization. Fourth, a change of spectrum from gyroresonance to free-free emission is found in the passage of the spot over the solar limb, which gives a determination of the height of the gyroresonance layer to confirm its location low in the corona of the active region. Title: Microwave Emission from a Sunspot - Part One Authors: Lee, Jeongwoo W.; Hurford, G. J.; Gary, Dale E. Bibcode: 1993SoPh..144...45L Altcode: From the gyroresonance brightness temperature spectrum of a sunspot, one can determine the magnetic field strength by using the property that microwave brightness is limited above a frequency given by an integer-multiple of the gyrofrequency. In this paper, we use this idea to find the radial distribution of magnetic field at the coronal base of a sunspot in the active region, NOAA 4741. The gyroresonance brightness temperature spectra of this sunspot are obtained from multi-frequency interferometric observations made at the Owens Valley Radio Observatory at 24 frequencies in the range of 4.0-12.4 GHz with spatial resolution 2.2″-6.8″. The main results of present study are summarized as follows: first, by comparison of the coronal magnetic flux deduced from our microwave observation with the photospheric magnetic flux measured by KPNO magnetograms, we show that theo-mode emission must arise predominantly from the second harmonic of the gyrofrequency, while thex-mode arises from the third harmonic. Second, the radial distribution of magnetic fieldsB(r) at the coronal base of this spot (say, 2000-4000 km above the photosphere) can be adequately fitted by B(r) = 1420(1±0.008)exp[-(r/{11.05"(1±0.014)})2]G, where r is the radial distance from the spot center at coronal base. Third, it is found that coronal magnetic fields originate mostly from the photospheric umbral region. Fourth, although the derived vertical variation of magnetic fields can be approximated roughly by a dipole model with dipole moment 1.6 × 1030 erg G−1 buried at 11000 km below the photosphere, the radial field distribution at coronal heights is found to be more confined than predicted by the dipole model. Title: Microwave Emission From a Sunspot III. Implications for the Force Balance in a Static Sunspot Authors: Lee, J. W.; Gary, D. E.; Hurford, G. J.; Zirin, H. Bibcode: 1993ASPC...46..287L Altcode: 1993IAUCo.141..287L; 1993mvfs.conf..287L No abstract at ADS Title: Measurement of the Solar Limb Brightness Profile at 3 Millimeters during the Total Eclipse of 1991 July 11 Authors: Belkora, L.; Hurford, G. J.; Gary, Dale E.; Woody, D. P. Bibcode: 1992ApJ...400..692B Altcode: Observations of the solar limb at the point of first contact during the eclipse of 1991 July 11, with a spatial resolution of about 1.6 arcsec, are reported. The visibility amplitude and phase were modeled to yield the height of the 3-mm limb above the visible photosphere, and the data were differentiated to yield the brightness profile of the limb in strips about 1.6 arcsec wide. The 3-mm limb was found to extend 7.5 +/- 0.8 arcsec above the visible photosphere, with no evidence of a limb spike. The 3-mm limb, at a temperature of about 6500 K, extends to altitudes far beyond the expected location of the transition region in the model of Vernazza et al. (1981). A comparison of the 3-mm profile and an off-band H-alpha photograph of the limb reveals a close correspondence between the 3-mm limb and the height of H-alpha spicules. Title: The High-Frequency Characteristics of Solar Radio Bursts Authors: Lim, J.; White, S. M.; Kundu, M. R.; Gary, D. E. Bibcode: 1992SoPh..140..343L Altcode: We compare the millimeter, microwave, and soft X-ray emission from a number of solar flares in order to determine the properties of the high-frequency radio emission of flares. The millimeter observations use a sensitive interferometer at 86 GHz which offers much better sensitivity and spatial resolution than most previous high-frequency observations. We find a number of important results for these flares: (i) the 86 GHz emission onset appears often to be delayed with respect to the microwave onset; (ii) even in large flares the millimeter-wavelength emission can arise in sources of only a few arc sec dimension; (iii) the millimeter emission in the impulsive phase does not correlate with the soft X-ray emission, and thus is unlikely to contain any significant thermal bremsstrahlung component; and (iv) the electron energy distributions implied by the millimeter observations are much flatter (spectral indices of 2.5 to 3.6) than is usual for microwave or hard X-ray observations. Title: Radio observations of the M8.1 solar flare of 23 June, 1988: Evidence for energy transport by thermal processes Authors: Bastian, T. S.; Gary, D. E. Bibcode: 1992SoPh..139..357B Altcode: The Very Large Array (VLA) and the frequency agile interferometer at the Owens Valley Radio Observatory (OVRO) were used to observe the M8.1 flare of 23 June, 1988. The VLA obtained images prior to and during the flare at 333 MHz, and at 1.5 and 4.7 GHz. The frequency agile interferometer at Owens Valley obtained interferometer amplitude and total power spectra of the flare at 45 frequencies between 1 and 18 GHz. The observations were supplemented by radiometer measurements made by the USAF RSTN network site at Palehua, HI, by GOES soft X-ray observations, by USAF SOON Hα filtergrams, and by a KPNO photospheric magnetogram. Title: Measurement of the Solar Limb Brightness Profile at 3 MM During the Total Eclipse of 1991 July 11 Authors: Belkora, L.; Hurford, G. J.; Gary, D. E.; Woody, D. P. Bibcode: 1992AAS...180.4202B Altcode: 1992BAAS...24..796B We observed the solar limb at the point of first contact during the eclipse of 1991 July 11, with a spatial resolution ~ 1.6''. The observations were carried out at the Owens Valley Radio Observatory millimeter interferometer, operating at 3 millimeters. The visibility amplitude and phase were modeled to yield the height of the 3 mm limb above the visible photosphere, and the data were differentiated to yield the brightness profile of the limb in strips ~ 1.6'' wide. We found that the 3 mm limb extends 7.5+/-0.8'' or 5500 km above the visible photosphere, with no evidence of a limb spike. This result, and the overall shape of the limb profile, are similar to the interferometric results of Wannier, Hurford, & Seielstad (1983) obtained with the same intrument but without the benefit of an eclipse. The 3 mm limb, at a temperature of ~ 7200 K, extends to altitudes far beyond the expected location of the transition region in the model of Vernazza, Avrett, & Loeser (1981). A comparison of the 3 mm profile and an offband Hα photograph of the limb reveals a close correspondence between the 3 mm limb and the height of Hα spicules. Title: First Results from 5-Element Observations with the OVRO Solar Array Authors: Gary, Dale E.; Hurford, G. J. Bibcode: 1992AAS...180.4201G Altcode: 1992BAAS...24R.795G We report the first synthesis imaging results using the 5 antennas of the newly expanded solar array at Owens Valley Radio Observatory. The observations were made on 1991 Oct 24 and give the spatial and spectral structure of the complex active region NOAA 6891 as well as the spatial, spectral, and temporal structure of three flares that occurred during our observations. We show aperture synthesis maps of the active region from 1.2 to 7 GHz, with spatial resolution from 60'' to 9'' over the same range, and plot brightness temperature spectra for various points in the maps to show the region of dominance of free-free emission versus the region of dominance of gyroresonance emission. From the free-free dominated spectra we can deduce the coronal column density and temperature as a function of position over the active region. Where the source is dominated by gyroresonance emission, the spectra can be used to determine the magnetic field strength at the base of the corona (see the paper by Lee, Gary, and Hurford also being presented at this meeting). We also investigate the three flares that occurred during our observations, using frequency synthesis to map the spatial structure over relatively broad frequency ranges. We find several interesting results, including a radio emission source with no accompanying Hα emission and motion of the radio source along the spreading Hα ribbon. These results represent the first, but not necessarily the best-suited, observations of active regions and flares with the new OVRO Solar Array. They serve to show the tremendous capability of the instrument to resolve the ambiguities that for so long have plagued radio studies because simultaneous spatial and spectral observations were not available. Title: OVRO Solar Array Observations During HIREGS Campaign Authors: Gary, Dale E.; Hurford, G. J.; Belkora, L. Bibcode: 1992AAS...180.4509G Altcode: 1992BAAS...24..803G The newly expanded solar interferometer array at Owens Valley Radio Observatory (OVRO Solar Array) was in full operation with 5 antennas before and during the Max '91 Campaign that was associated with the HIREGS hard X-ray balloon experiment. For the two weeks prior to 1992 Jan 6, we obtained at least 21 flares within our UT time range of ~1600-2400 UT. During this pre-campaign period we were using an observing mode that measured 45 frequencies in both right- and left-hand circular polarization every 12 s. For the campaign period itself, from 1992 Jan 6-24, we obtained at least 10 large events along with many smaller ones. For the time that the HIREGS balloon was up, we were observing in a mode where we obtained only stokes I (total intensity), but at 20 frequencies with a 2 s cycle time to maximize our time resolution. In addition to the flare observations, OVRO is now capable of synthesis imaging of the active regions each day, which will be of interest for active region studies. We present early results from one or two of the best observed events by OVRO and other observatories participating in the campaign, including the event of 1941 UT on 1992 Jan 21. We emphasize multifrequency imaging of the flare as a function of time, a capability that is unique to the expanded OVRO Solar Array. Title: Center-to-Limb Variation of Sunspot Microwave Radiation Authors: Lee, Jeongwoo W.; Gary, Dale E.; Hurford, G. J. Bibcode: 1992AAS...180.4203L Altcode: 1992BAAS...24..796L A series of microwave observations of a sunspot in the active region NOAA 6761 was made with the Owens Valley Solar Array for the purpose of investigating the center-to-limb variation of both spectral and spatial brightness distribution. In this investigation, several properties of the sunspot microwave radiation are found. First, sunspot microwave emission appears in two typical profiles depending on the heliocentric position of the spot: either the ring structure near disk center or single-peak structure near the limb. Second, the brightness temperature at high, optically thin frequencies (>6 GHz) increases slightly as the spot approaches the limb, which we interpret as being due to the increase of the gyroresonance opacity of the field lines near the spot center as they gain greater viewing angles at the position. Third, the center-to-limb variation of the gyroresonance spectrum seems to be mostly characterized by a change of effective harmonic, which accompanies a discontinuous change of the degree of polarization. Fourth, a change of spectrum from gyroresonance to free-free emission feature is found in the passage of the spot over the solar limb, which gives a determination of the height of the gyroresonance layer to confirm its location low in the corona of the active region. Title: Hard X ray/microwave spectroscopy of solar flares Authors: Gary, Dale E. Bibcode: 1992cait.rept.....G Altcode: The joint study of hard x ray and microwave observations of solar flares is extremely important because the two complementary ways of viewing the accelerated electrons yield information that cannot be obtained using hard x rays or microwaves alone. The microwaves can provide spatial information lacking in the hard x rays, and the x ray data can give information on the energy distribution of electrons that remove ambiguities in the radio data. A prerequisite for combining the two data-sets, however, is to first understand which range of microwave frequencies correlate best with the hard x rays. This SMM Guest Investigator grant enabled us to combine multi-frequency OVRO data with calibrated hard x ray data to shed light on the relationship between the two emissions. In particular, the questions of which microwave frequencies correspond to which hard x ray energies, and what is the corresponding energy of the electrons that produce both types of emission are investigated. Title: Solar Radio Pulsation Event Observed by the VLA and OVRO Authors: Aschwanden, M. J.; Bastian, T. S.; Gary, D. E. Bibcode: 1992AAS...180.4505A Altcode: 1992BAAS...24..802A We investigate interpretational aspects of the radio pulsation event which has been observed by the Very Large Array (VLA) and the Owens Valley Radio Observatory (OVRO) on December 21, 1990, 1930 UT, during the second MAX'91 observing campaign. The VLA was observing with a time resolution of 0.4 s at 0.33, 1.4 and 4.9 GHz, while OVRO used a time resolution of 0.2 s at 1.2, 1.4, 1.6, 1.8 and 2.0 GHz. The radio pulsation event was triggered by a C3.3 class flare in soft X-rays in active region 6412 (NOAA). The time profile of the quasi-periodic radio emission exhibits a period of 8.8 s and shows indications of secondary periodicities with faster periods. We investigate whether these periodicities can be explained in terms of (i) MHD eigen-modes in cylindrical fluxtubes (MHD surface modes and harmonic modes), or (ii) relaxational oscillations of a nonlinear dissipative system. We test these two options by means of Fourier spectra and by reconstruction of the ``strange attractor dimension'' of nonlinear systems. We attempt a three-dimensional reconstruction of the pulsating source by means of magnetic field extrapolation from the photospheric magnetogram and by using the constraints of the radio maps at multiple frequencies. Preliminary analysis indicates that plasma emission as well as gyrosynchrotron emission is coherently modulated in spatially diverging magnetic structures. We investigate whether the pulsating radio emission originates from plasma confined in a pulsating loop structure or whether the radio emission is driven by electron beams which are produced in a pulsating acceleration mechanism. The latter possibility would support a model where the primary energy release itself is governed by a nonlinear dissipative system, e.g. by oscillatory magnetic reconnection. Title: Radio synthesis imaging during the GRO solar campaign. Authors: Gary, Dale E. Bibcode: 1992NASCP3137..514G Altcode: 1992como.work..514G The Owens Valley (OVRO) Solar Array was recently expanded to 5 antennas. Using frequency synthesis, the 5-element OVRO Solar Array has up to 450 effective baselines, which can be employed as necessary to make maps at frequencies in the range 1 to 18 GHz. Fortuitously, the last of the 5 antennas was completed and brought into operation on 7 Jun., just in time for the Gamma Ray Observatory (GRO)/Max 1991 observing campaign. Many events were observed jointly with OVRO and the BATSE experiment on GRO, including the six larger events that are presented in tabular form. Unfortunately, the X flares that occurred during the campaign all occurred outside the OVRO time range. The UV coverage of the newly expanded solar array, combined with frequency synthesis, should give a more complete view of solar flares in the microwave range by providing simultaneous spatial and spectral resolution. A promising application of MEM (maximum entropy) is also being pursued that will use smoothness criteria in both the spatial and spectral domains to give brightness temperature maps at each observed frequency (up to 45 frequencies every 10 s). Such maps can be compared directly with the theory of microwave emission to yield plasma parameters in the source - notably the number and energy distribution of electrons, for comparison with the x ray and gamma ray results from GRO. Title: Multifrequency Observations of a Remarkable Solar Radio Burst Authors: White, S. M.; Kundu, M. R.; Bastian, T. S.; Gary, D. E.; Hurford, G. J.; Kucera, T.; Bieging, J. H. Bibcode: 1992ApJ...384..656W Altcode: Observations of an impulsive solar-radio burst from three observatories are presented. The striking observational aspects of this flare are that the time profile was identical throughout at 8.6, 15, and 86 GHz, that the spectrum was apparently flat from 15 to 86 GHz, and that there was a sharp cutoff in the spectrum between 5.0 and 8.6 GHz. The simplest interpretation of the cutoff, namely as a plasma frequency effect, leads to the conclusion that there was exceptionally high-density material in the solar corona (of about 5 x 10 exp 11/cu cm). Very Large Array images at 15 GHz show a single-loop structure which brightened uniformly and showed little change in size during the whole impulsive phase. The flat spectrum is consistent with optically thin thermal bremsstrahlung emission, but the lack of observed soft X-ray emission and other properties of the flare cannot easily be accommodated by this mechanism. The possibility is explored that the emission is optically thick due to thermal absorption of nonthermal gyrosynchrotron emission, or optically thin gyrosynchrotron emission absorbed by high-density material intervening along the line of sight. Both of these explanations also face difficulties. Title: Rotationalmodulation and flares on RS Canum Venaticorum and BY Draconis stars. XVI. IUE spectroscopy and VLA observations of GL 182 (=V 1005 Orionis) in October 1983. Authors: Mathioudakis, M.; Doyle, J. G.; Rodono, M.; Gibson, D. M.; Byrne, P. B.; Avgoloupis, S.; Linsky, J. L.; Gary, D.; Mavridis, L. N.; Varvoglis, P. Bibcode: 1991A&A...244..155M Altcode: A large flare was detected simultaneously with IUE and VLA on Gl 182 on October 5, 1983, this event showing the largest C IV flare enhancement yet observed by IUE. A smaller flare was also detected on October 4, although only with the IUE satellite. Line ratio and emission measure techniques are used to derive various physical parameters of the flares. The radiative losses in the temperature region log T(e) = 4.3-5.4 in the two flares are 2.9 x 10 to the 33rd and 8.4 x 10 to the 32nd ergs, respectively. Total radiative losses over the whole temperature range log T(e) = 4.0-8.0 are estimated to be of the order of 6.4 x 10 to the 34th and 1.1 x 10 to the 34th ergs, respectively. In the October 5, flare, a very strong ultraviolet continuum is present with a total energy of 1.9 x 10 to the 33rd ergs over the wavelength range 1250-1950 A. Title: Observations of Two Large Off Limb Solar Flares in the Radio, X-Rays, and Hα Authors: Kucera, T. A.; Dulk, G. A.; Winglee, R. M.; Kiplinger, A. L.; Bastian, T. S.; Gary, D. E. Bibcode: 1991BAAS...23R1065K Altcode: No abstract at ADS Title: Joint Microwave/Hard X-ray Observations of Solar Bursts During March 1989 Authors: Gary, D. E.; Hurford, G. J. Bibcode: 1991BAAS...23.1066G Altcode: No abstract at ADS Title: First Interferometric Observations of Solar Microwave Millisecond Spike Bursts Authors: Gary, Dale E.; Hurford, G. J.; Flees, D. J. Bibcode: 1991ApJ...369..255G Altcode: Observations, with one-dimensional spatial resolution, of solar microwave millisecond spikes at 2.8 GHz are reported. The observations were made with the Owens Valley frequency-agile interferometer with 20 ms time resolution. It is found that the spikes occur at a position different from that of the underlying gyrosynchrotron radio burst source. All of the spikes during the rising part of the burst come from the same one-dimensional location to within + or - 1 arcsec, despite the fact that rapid evolution in the sense and degree of circular polarization was observed. The one-dimensional position of the spikes is consistent with a location over a large sunspot, suggesting that the emission occurs in a region of strong, converging magnetic field. The observations support the suggestion that the spikes are due to the electron-cyclotron maser mechanism. Title: Multifrequency Observations of a Remarkable Solar Radio Burst Authors: White, S. M.; Kundu, M. R.; Bastian, T. S.; Gary, D. E.; Hurford, G. J.; Kucera, T.; Bieging, J. H. Bibcode: 1991BAAS...23.1043W Altcode: No abstract at ADS Title: The Effects of Source Inhomogeneity on Solar Microwave Bursts Authors: Hurford, G. J.; Gary, D. E. Bibcode: 1991BAAS...23.1066H Altcode: No abstract at ADS Title: Temporally, Spectrally, and Spatially Resolved Observations of a Pulsating Solar Radio Burst Authors: Bastian, T. S.; Aschwanden, M. J.; Gary, D. E. Bibcode: 1991BAAS...23Q1072B Altcode: No abstract at ADS Title: Summary of Observations with the Owens Valley Solar Array During Max '91 Campaign 2 Authors: Gary, D. E.; Hurford, G. J. Bibcode: 1991BAAS...23.1072G Altcode: No abstract at ADS Title: Observations of Two Large Limb Flares on 20 June 1989 Authors: Kucera, T. A.; Winglee, R. M.; Dulk, G. A.; Bastian, T. S.; Gary, D. E. Bibcode: 1991max..conf..172K Altcode: No abstract at ADS Title: Multiwavelength Investigations of the 1989 June 30 Solar Flares Including Interferometric Observations of Their Microwave Emitting Sources Authors: Crannell, C. J.; Gary, D. E.; Hurford, G. J.; Starr, R.; Kucera, T. Bibcode: 1991max..conf..192C Altcode: No abstract at ADS Title: Radio Observations During Max'91 Campaign 1 Authors: Gary, D. E. Bibcode: 1991max..conf....1G Altcode: No abstract at ADS Title: Multifrequency Observations of a Solar Microwave Burst with Two-dimensional Spatial Resolution Authors: Gary, Dale E.; Hurford, G. J. Bibcode: 1990ApJ...361..290G Altcode: Frequency-agile interferometry observations using three baselines and the technique of frequency synthesis were used to obtain two-dimensional positions of multiple microwave sources at several frequency ranges in a solar flare. Source size and brightness temperature spectra were obtained near the peak of the burst. The size spectrum shows that the source size decreases rapidly with increasing frequency, but the brightness temperature spectrum can be well-fitted by gyrosynchrotron emission from a nonthermal distribution of electrons with power-law index of 4.8. The spatial structure of the burst showed several characteristics in common with primary/secondary bursts discussed by Nakajima et al. (1985). A source of coherent plasma emission at low frequencies is found near the secondary gyrosynchrotron source, associated with the leader spots of the active region. Title: Microwave and Hard X-Ray Diagnostics of Nonthermal Electrons in a Solar Burst Authors: Hurford, G. J.; Gary, D. E.; Bromley, J. W. Bibcode: 1990BAAS...22.1196H Altcode: No abstract at ADS Title: The Secondary Spectral Component of Solar Microwave Bursts Authors: Stahli, M.; Gary, D. E.; Hurford, G. J. Bibcode: 1990SoPh..125..343S Altcode: Microwave observations in the range 1 to 18 GHz with high spectral resolution (40 frequencies) have shown that many events display a complex microwave spectrum. From a set of 14 events with two or more spectral components, we find that two different classes of complex events can be distinguished. The first group (4 events) is characterized by a different temporal evolution of the spectral components, resulting in a change of the spectral shape. These events probably can be explained by gyrosynchrotron emission from two or more individual sources. The second class (10 events) has a constant spectral shape, so that the two spectral components vary together in intensity. For all ten events in this second class, the ratio of primary to secondary peak frequencies is remarkably similar, exhibiting an average value of 3.4, and both components show a common circular polarization. These properties suggest either a common source for the different spectral components or several sources which are closely coupled. An additional example of this class of burst was observed interferometrically to provide spatial resolution. This event suggests that the primary and secondary components have a similar location, but that the surface area of the secondary component is larger. Title: Microwave Structure of the Quiet Sun at 8.5 GHz Authors: Gary, Dale E.; Zirin, Harold; Wang, Haimin Bibcode: 1990ApJ...355..321G Altcode: Multifrequency VLA observations of the quiet sun near 8.5 GHz are presented. Two regions of the sun were observed, one dominated by an enhanced network corresponding to a decayed active region, and the other corresponding to an enhanced network with no active features. The full-day synthesis maps for both show nearly perfect correspondence to H-alpha images, and to longitudinal magnetograms. The coronal loops were observed to appear as regions of radio emission with no underlying longitudinal magnetic fields, being aligned with H-alpha fibrils in the photosphere, and connecting regions of opposite magnetic polarity. The emission can be modeled as optically thin free-free emission from a coronal loop with a peak axial density of approximately 2.4-2.8 x 10 to the 9th/cu cm, for an assumed coronal temperature of 1-2 x 10 to the 6th K. The quiet chromosphere sources are measured, and the significance of these measurements for existing chromospheric models is discussed. Title: Solar Microwave Spectroscopy with the Owens Valley Solar Array Authors: Hurford, G. J.; Gary, D. E. Bibcode: 1990BAAS...22..808H Altcode: No abstract at ADS Title: First Observations of Millisecond Microwave Spike Bursts with Spatial Resolution Authors: Gary, D. E.; Hurford, G. J.; Flees, D. J. Bibcode: 1990BAAS...22..823G Altcode: No abstract at ADS Title: High Resolution Microwave Spectras of Solar Bursts Authors: Stahli, M.; Gary, D. E.; Hurford, G. J. Bibcode: 1989SoPh..120..351S Altcode: Microwave observations with exceptionally high spectral resolution are described for a set of 49 solar flares observed between May and October 1981. Total power data were obtained at 40 frequencies between 1 and 18 GHz by the Owens Valley frequency-agile interferometer with 10 s time resolution. Statistical analysis of this sample of microwave bursts established the following significant characteristics of their microwave spectra: (i) Most (≈ 80%) of the microwave events displayed complex spectra consisting of more than one component during some or all of their lifetime. Single spectral component bursts are rare. It is shown that the presence of more than one component can lead to significant errors when data with low spectral resolution are used to determine the low-side spectral index. (ii) The high-resolution data show that many bursts have a low-side spectral index that is larger than the maximum value of about 3 that might be expected from theory. Possible explanations include the effect of the underlying active region on the perceived burst spectrum and/or the necessity for more accurate calculations for bursts with low effective temperatures, (iii) the peak frequencies of the bursts are remarkably constant during their lifetimes. This is contrary to expectations based on simple models in which the source size and ambient field remain constant during the evolution of a burst. Title: A Simple Solar Microwave Burst Observed with High Spectral Resolution Authors: Gary, Dale E.; Hurford, G. J. Bibcode: 1989ApJ...339.1115G Altcode: A small flare that occurred on February 3, 1986 which was dominated by a single homogeneous source is analyzed. The theory of microwave emission from homogeneous sources was used to trace the evolution of the burst. The spectral profile indicates a thermal origin. It was found that the source expanded with time during the burst. Title: The Secondary Spectral Component of Solar Microwave Bursts Authors: Hurford, G. J.; Stahli, M.; Gary, D. E. Bibcode: 1989BAAS...21..836H Altcode: No abstract at ADS Title: The Owens Valley Solar Array Authors: Hurford, G. J.; Gary, D. E. Bibcode: 1989BAAS...21..861H Altcode: No abstract at ADS Title: Solar radio burst spectral observations, particle acceleration, and wave-particle interactions. Authors: Gary, D. E.; Hurford, G. J. Bibcode: 1989GMS....54..237G Altcode: 1989sspp.conf..237G; 1989opss.conf..237G The authors consider solar radio bursts throughout the radio spectrum from 30 kHz to 30 GHz. The subject can be conceptualized by considering three characteristic frequencies of the plasma: the plasma frequency fp, the gyrofrequency fB, and the frequency f(τff = 1) at which the plasma becomes optically thick due to bremsstrahlung. The authors present an overview in terms of these characteristic frequencies to show why each dominates under various physical conditions in the Sun and solar wind. In the broad regime where plasma emission dominates, they discuss the progress that has been made in explaining the observed burst characteristics theoretically, concentrating on bursts of type II (shock wave related) and type III (excited by electron beams). Title: Coronal mass ejections and coronal structures. Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.; Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing, R. M. E.; Jackson, B. V.; Kahler, S. W.; Kopp, K.; Low, B. C.; Lantos, P.; Phillips, K. J. H.; Poletto, G.; Sheeley, N. R., Jr.; Stewart, R. T.; Svestka, Z.; Waggett, P. W.; Wu, S. T. Bibcode: 1989epos.conf..493H Altcode: The work of this team was concerned with modelling of post-flare arches, the reconnection theory of flares, the slow variation of coronal structure, and the coronal and interplanetary detection, evolution, and consequences of mass ejections. Title: The Owens Valley solar array Authors: Hurford, G. J.; Gary, D. E. Bibcode: 1989dots.work..328H Altcode: Solar microwave emission contains essential information for the study of the coronal magnetic structure of active regions and of thermal and nonthermal flare electrons. To exploit this potential requires BOTH imaging and spectroscopy with sufficient resolution to resolve spatial and spectral features. The VLA provides excellent solar imaging (when in the C and D configurations) but inadequate spectral coverage. The existing Owens Valley system has excellent spectral coverage but imaging that is adequate only for very simple sources. The Owens Valley system is currently undergoing an expansion, which when completed in October 1990 will provide a SOLAR-DEDICATED 5 antenna array (10 baselines). By using frequency-synthesis, this will provide a significant imaging capability in addition to its current spectral coverage. Title: Simultaneous multi-wavelength observations of an intense flare on AD Leonis. Authors: Rodono', M.; Houdebine, E. R.; Catalano, S.; Foing, B.; Butler, C. J.; Scaltriti, F.; Cutispoto, G.; Gary, D. E.; Gibson, D. M.; Haisch, B. M. Bibcode: 1989sasf.confP..53R Altcode: 1989IAUCo.104P..53R; 1988sasf.conf...53R The authors report on the first successful coordinated observations of stellar flares carried out on March 28, 1984 simultaneously over a wide range of wavelengths, from UV to microwaves, using the IUE satellite, three ESO telescopes at La Silla (Chile) and the VLA at Socorro (NM, USA). Title: A flare on AD Leo observed in optical, UV and microwaves. Authors: Byrne, P. B.; Gary, D. E. Bibcode: 1989sasf.confP..63B Altcode: 1988sasf.conf...63B; 1989IAUCo.104P..63B The authors report a simultaneous IUE, VLA and ground-based photometric observation of a flare on the dMe star, AD Leo, on 2nd February 1983. The optical flare was extremely impulsive, lasting in total only about 3 mins. A relatively longlived 6 cm flare was observed with the VLA which was initially 100% polarized. An IUE spectrum, taken ≍8 min after the onset of the optical U band flare, shows more than a factor of 2 increase in the He II λ1640 Å emission line. The other mid-transition region lines such as C IV λλ1548/52 Å show almost no response. Title: Planned improvements to the Owens Valley frequency-agile interferometer Authors: Hurford, Gordon J.; Gary, D. E. Bibcode: 1988fnsm.work...98H Altcode: Three small antennas will be added to the OVRO interferometer to form a five-element solar-dedicated array. This would provide up to 7 or 10 baselines (compared to the present 1 or 3). This would be sufficient to apply microwave diagnostics to most active region and burst sources. By using frequency-synthesis it would also provide an imaging capability comparable to that of an approximately 100 baseline interferometer. Expansion of the array is discussed. Title: Microwave Structure of the Quiet Sun Authors: Gary, Dale E.; Zirin, Harold Bibcode: 1988ApJ...329..991G Altcode: The authors present two-frequency VLA observations of the quiet Sun obtained on 1985 July 13, when the Sun was particularly quiet. The 4.9 GHz full-day synthesis maps correspond closely to images made in Hα, Ca II K, and magnetograms, while the correspondence is much reduced at 1.45 GHz. The 4.9 GHz maps have a meshlike appearance reminiscent of chromospheric network structure. Simultaneous magnetograms from Big Bear Solar Observatory are used to compare the structure of the magnetic field with the radio source structure at the two frequencies. Magnetograms of each pointing field were taken at least once every half-hour for monitoring the changing structure of the longitudinal component of the magnetic fields. The authors identify changes such as the appearance of an ephemeral region and the cancellation of opposite-polarity magnetic flux, and discuss corresponding changes in radio sources. Title: Planned Improvements to the Owens Valley Frequency-agile Interferometer for MAX 91 Authors: Hurford, G. J.; Gary, D. E. Bibcode: 1988BAAS...20..746H Altcode: No abstract at ADS Title: Spatially-Integrated, High Frequency Resolution, Solar Active Region Microwave Spectra Authors: Hurford, G. J.; Gary, D. E. Bibcode: 1988BAAS...20R.713H Altcode: No abstract at ADS Title: A Simple Solar Microwave Burst Observed with High Spectral Resolution Authors: Gary, D. E.; Hurford, G. J. Bibcode: 1988BAAS...20..713G Altcode: No abstract at ADS Title: Solar Microwave Spectroscopy Authors: Gary, D. E. Bibcode: 1988BAAS...20..723G Altcode: No abstract at ADS Title: The Microwave Spectrum of Solar Bursts Authors: Stähli, M.; Gary, D. E.; Hurford, G. J. Bibcode: 1988BAAS...20..713S Altcode: No abstract at ADS Title: Rotational modulation and flares on RS CVn and BY DRA stars. IV. The spatially resolved chromosphere of AR Lacertae. Authors: Walter, F. M.; Neff, J. E.; Gibson, D. M.; Linsky, J. L.; Rodono, M.; Gary, D. E.; Butler, C. J. Bibcode: 1987A&A...186..241W Altcode: The authors observed the RS CVn system AR Lacertae systematically over an orbital period with the International Ultraviolet Explorer in October 1983. Contemporaneous radio observations were obtained at the Very Large Array. The spectra of the Mg II k emission line were analyzed using a Doppler imaging technique. In this way, the authors identified three discrete regions of emission in the outer atmosphere of the K star - two "plages" and a chromospheric brightening that was related to a radio flare. The widths of the plage profiles indicate that the two plages together cover about 2% of the visible stellar hemisphere, and their v sin i values indicate that they lie close to the equator of the K star. The Mg II k surface flux in the plages is about five times the mean Mg II k surface flux of the K star. The authors then used the far-ultraviolet spectra obtained at the eclipse phases to separate the individual contributions of the two stars and the plage and flare regions in order to estimate their line surface fluxes. Title: Multifrequency Observations of a Solar Active Region during a Partial Eclipse Authors: Gary, Dale E.; Hurford, G. J. Bibcode: 1987ApJ...317..522G Altcode: Spatially-resolved microwave observations of a complex active region at 16 frequencies in the range 1.4-8 GHz are presented. One-dimensional profiles of the active region at each frequency were obtained with the Owens Valley frequency-agile interferometer, with 2.6-arcsec spatial resolution provided by the lunar limb during a partial eclipse. Simultaneous two-dimensional maps were obtained with the VLA at 1.45 and 4.9 GHz. The combination of spatial and spectral resolution allows the direct observation of the change in emission mechanism from predominantly free-free emission from dense active region loops at low frequencies to gyroresonance emission from regions of intense magnetic fields at high frequencies. The change occurs, for this active region, at about 3 GHz. The implications of the brightness temperature spectrum for the coronal structure of the active region are discussed. Title: Microwave spectroscopy as a diagnostic of solar flares: The effect of source inhomogeneity Authors: Hurford, G. J.; Gary, D. E. Bibcode: 1987SoPh..113..183H Altcode: 1982SoPh..113..183H No abstract at ADS Title: IUE/Optical/VLA Flares on AD Leo Authors: Gary, Dale E.; Byrne, P. B.; Butler, C. J. Bibcode: 1987LNP...291..106G Altcode: 1987LNP87.291..106G; 1987csss....5..106G We discuss joint observations of flares on the dMe star AD Leo made with IUE, the VLA, and the Tinsley photometer at the University of Hawaii's 24-inch reflector on Mauna Kea. We find that optical emission is correlated with C IV while radio emission is better correlated with He II. We reach some tentative conclusions concerning timescales and source characteristics. Title: Interplanetary Effects of Coronal Mass Ejections Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.; Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing, R. M. E.; Jackson, B. V.; Kahler, S. W.; Kopp, K.; Low, B. C.; Lantos, P.; Phillips, K. J. H.; Poletto, G.; Sheeley, N. R., Jr.; Steward, R. T.; Svestka, Z.; Waggett, P. W.; Wu, S. T. Bibcode: 1986epos.conf.6.52H Altcode: 1986epos.confF..52H No abstract at ADS Title: The microwave structure of quiescent solar filaments at high resolution. Authors: Gary, D. E. Bibcode: 1986NASCP2442..121G Altcode: The author presents high resolution VLA maps of a quiescent filament at three frequencies. At each frequency, the filament appears as a depression in the quiet Sun background. The depression is measurably wider and longer in extent than the corresponding Hα filament at 1.45 GHz and 4.9 GHz, indicating that the depression is due in large part to a deficit in coronal density associated with the filament channel. In contrast, the shape of the radio depression at 15 GHz closely matches that of the Hα filament. In addition, the 15 GHz map shows enhanced emission along both sides of the radio depression. A similar enhancement is seen in an observation of a second filament obtained 4 days later, which suggests that the enhancement is a general feature of filaments. Possible causes of the enhanced emission are explored. Title: Initiations of Coronal Mass Ejections Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.; Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing, R. M. E.; Jackson, B. V.; Kahler, S. W.; Kopp, K.; Low, B. C.; Lantos, P.; Phillips, K. J. H.; Poletto, G.; Sheeley, N. R., Jr.; Steward, R. T.; Svestka, Z.; Waggett, P. W.; Wu, S. T. Bibcode: 1986epos.conf.6.27H Altcode: 1986epos.confF..27H No abstract at ADS Title: Measurement of coronal fields using spatially resolved microwave spectroscopy. Authors: Hurford, G. J.; Gary, D. E. Bibcode: 1986NASCP2442..319H Altcode: 1986copp.nasa..319H The authors consider the potential implications of observations which combine both high spatial and high spectral resolution. In particular, they are interested in the ability to measure the magnetic field at the base of the corona on a point by point basis, as in a true magnetograph. They present model calculations of the microwave brightness temperature spectrum along specific lines of sight near a sunspot. They believe that spatially resolved microwave spectroscopy provides a promising new coronal diagnostic. At present, however, a key limitation in its application is the lack of sufficient number of antennas with which to map complex active regions. Title: The Slowly Varying Corona Near Solar Activity Maximum Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.; Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing, R. M. E.; Jackson, B. V.; Kahler, S. W.; Kopp, K.; Low, B. C.; Lantos, P.; Phillips, K. J. H.; Poletto, G.; Sheeley, N. R., Jr.; Steward, R. T.; Svestka, Z.; Waggett, P. W.; Wu, S. T. Bibcode: 1986epos.conf.6.57H Altcode: 1986epos.confF..57H No abstract at ADS Title: Modelling of Coronal Mass Ejections and POST Flare Arches Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.; Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing, R. M. E.; Jackson, B. V.; Kahler, S. W.; Kopp, K.; Low, B. C.; Lantos, P.; Phillips, K. J. H.; Poletto, G.; Sheeley, N. R., Jr.; Steward, R. T.; Svestka, Z.; Waggett, P. W.; Wu, S. T. Bibcode: 1986epos.conf6.366H Altcode: 1986epos.confF.366H No abstract at ADS Title: Coronal mass ejections and coronal structures Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.; Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing, R. M. E.; Jackson, B. V. Bibcode: 1986epos.conf..6.1H Altcode: 1986epos.confF...1H Research on coronal mass ejections (CMF) took a variety of forms, both observational and theoretical. On the observational side there were: case studies of individual events, in which it was attempted to provide the most complete descriptions possible, using correlative observations in diverse wavelengths; statistical studies of the properties CMEs and their associated activity; observations which may tell us about the initiation of mass ejections; interplanetary observations of associated shocks and energetic particles even observations of CMEs traversing interplanetary space; and the beautiful synoptic charts which show to what degree mass ejections affect the background corona and how rapidly (if at all) the corona recovers its pre-disturbance form. These efforts are described in capsule form with an emphasis on presenting pictures, graphs, and tables so that the reader can form a personal appreciation of the work and its results. Title: Spectral Structure of Solar Microwave Bursts Authors: Gary, D. E.; Hurford, G. J. Bibcode: 1986BAAS...18Q.900G Altcode: No abstract at ADS Title: Frequency-Synthesis Imaging of Solar Microwave Bursts Authors: Hurford, G. J.; Gary, D. E. Bibcode: 1986BAAS...18..899H Altcode: No abstract at ADS Title: Coordinated IUE and ground-based observations of stellar flares: YZ CMi, Proxima Cen and AD Leo. Authors: Foing, B. H.; Rodono, M.; Cutispoto, G.; Catalano, S.; Linsky, J. L.; Gibson, D. M.; Brown, A.; Haisch, B. M.; Butler, C. J.; Byrne, P. B.; Andrews, A. D.; Doyle, J. G.; Gary, D. E.; Henry, G. W.; Russo, G.; Vittone, A.; Scaltriti, F. Bibcode: 1986RMxAA..12..213F Altcode: Coordinated observations of stellar flares were obtained with lUE and several ground-based facilities in March 1984.The simultaneous observations allowed it to cover a wide range of wavelengths from ii5nm to 6cm.We intend to study the effect ofthe observed flares at different atmospheric heights in order to estimate the energy budget,the time scales and the cooling processes.Our observations includetime-resolved IUE spectroscopy at SWP(115-195nm) and LWP(190-320nm),optical spectroscopy at the ESO 3.6m+IDS (355-440nm),high resolution spectroscopy at the ESO 1.4m CAT+CES(653-659nm),narrow band H alpha and wide band optical photometry, infrared photometry at 2.2microns and microwave observations at 2,6 and 20 cm We present for some flare events,among the results,the first detection of infrared flux decrease -or "negative flare"-in coincidence with the flux increase at the other wavelengths:the broadening and changes of the Balmer H lines,He and high excitation lines;the appearance of higher members of the Balmer serie;the enhancements of Mg II doublet and Fe II blend (260nm);and the flare detection at 2cm and 6cm Title: Models of Quiescent Stellar Microwave Emission Authors: Gary, D. E. Bibcode: 1986LNP...254..235G Altcode: 1986csss....4..235G Models for gyrosynchrotron emission from thermal electrons in dMe stellar coronae are developed using the formula for electron emissivity given by Robinson and Melrose (1984). The most physically plausible model also closely fits VIA observations. A comparison of this model to the observations is presented. Title: Shock waves and coronal transients: The event of 1980 April 17 Authors: Gary, D. E.; Gergely, T. E.; Kundu, M. R. Bibcode: 1986AdSpR...6f.311G Altcode: 1986AdSpR...6..311G The coronal mass ejection (CME) event of 1980 April 17 was observed with the SMM coronagraph, and an accompanying Type II (shock wave related) burst was observed simultaneously with the Culgoora and Clark Lake radioheliographs. The method of analysis of the combined radio observations is presented. Although the radio positions were affected by severe ionospheric refraction, the combined radio observations allow a useful reduction in the range of possible positions of the 80 MHz source when the 43 MHz source is required to lie within the range of position angles of the CME. The positions of the 80 MHz radio sources under this assumption are compared with the positions of the CME loop. Title: Coronal mass ejections and coronal structures. Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.; Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing, R. M. E.; Jackson, B. V.; Kahler, S. W.; Kopp, K.; Low, B. C.; Lantos, P.; Phillips, K. J. H.; Poletto, G.; Sheeley, N. R., Jr.; Stewart, R. T.; Svestka, Z.; Waggett, P. W.; Wu, S. T. Bibcode: 1986NASCP2439....6H Altcode: Contents: 1. Introduction. 2. Observations. 3. Initiation of coronal mass ejections - observations. 4. Modelling of coronal mass ejections and post-flare arches. 5. Interplanetary effects of coronal mass ejections. 6. The slowly varying corona near solar activity maximum. 7. Summary. Title: Optical, UV and Radio Observations of RS Canum Venaticorum Authors: Catalano, S.; Rodono, M.; Linsky, J. F.; Carpenter, K.; Gibson, D.; Gary, D.; Butler, J. Bibcode: 1986LNP...254..253C Altcode: 1986csss....4..253C No abstract at ADS Title: The type IV burst of 1980 June 29, 0233 UT - Harmonic plasma emission? Authors: Gary, D. E.; Dulk, G. A.; House, L. L.; Illing, R.; Wagner, W. J.; Mclean, D. J. Bibcode: 1985A&A...152...42G Altcode: The coronal transient event of 1980 June 29, 0233 UT, was well observed by the HAO Coronagraph/Polarimeter aboard SMM and at meter radio wavelengths by the Culgoora Radioheliograph. The radio event consisted of a strong Type II (shock wave related) burst followed by weak Type IV (storm) continuum. The authors discuss the details of the Type IV portion of the event in terms of two possible emission mechanisms-plasma emission (at the second harmonic) and gyro-synchrotron emission. They find that gyro-synchrotron emission is a possible mechanism only if more stringent requirements are met, viz., that the density of electrons of energy greater than 10 keV is about 10% of the ambient density, that the average energy is about 40 keV, and that the magnetic field strength at 2.5 solar radii is about 2.8 gauss. The authors conclude that this Type IV event is likely due to plasma emission at the 2nd harmonic of the plasma frequency. Title: The numbers of fast electrons in solar flares as deduced from hard X-ray and microwave spectral data Authors: Gary, D. E. Bibcode: 1985ApJ...297..799G Altcode: The previously reported discrepancy between the number of fast solar flare electrons deduced from hard X-ray burst observations and microwave observations of the same events is reexamined. The thin and thick-target models for hard X-ray production and their consequences for gyrosynchrotron emission of microwaves are discussed. Previous work that led to the perceived discrepancy is reviewed, and it is suggested that the discrepancy can be reduced when thick-target hard X-ray emission is assumed. The number of electrons in microwaves and hard X-rays are calculated assuming a homogeneous source for a sample of flares given by Wiehl et al. (1983). The numbers are given separately under the two assumptions of thin and thick-target hard X-ray emission. It is found that when the latter emission is assumed, the number of electrons deduced from the microwaves is very similar to the number deduced from the hard X-rays. Title: The Cyg X3 Radio Outburst of 1985 Authors: Johnston, K. J.; Spencer, J. H.; Waltman, E. B.; Pooley, G. G.; Spencer, R. E.; Angerhofer, P. E.; Florkowski, D. R.; Josties, F. J.; McCarthy, D. D.; Matsakis, D. N.; Herford, G.; Gary, D.; Hjellming, R. M.; Schalinski, C.; Molnar, L.; Reid, M. Bibcode: 1985BAAS...17..855J Altcode: No abstract at ADS Title: A Technique for Removing Confusion Sources from VLA Data Authors: Gary, D. E. Bibcode: 1985ASSL..116..385G Altcode: 1985rst..conf..385G A procedure for removing confusing sources from VLA visibility data is described and illustrated using the field near the flare star AD Leo. A map containing the confusing sources is made using the entire time range of the observation to maximize signal to noise. The map is cleaned of all sources except the one of interest, and positions and fluxes of the cleaned sources are saved for use in the next step. The 'dirty' visibilities are then 'cleaned' by subtracting the contribution of each cleaned component obtained in the previous step. The resulting visibilities contain no contribution from the confusing sources, and maps made with the 'clean' databases contain only the source of interest. Title: Quiescent Stellar Microwave Emission (Invited Paper) Authors: Gary, D. E. Bibcode: 1985ASSL..116..185G Altcode: 1985rst..conf..185G The quiescent microwave flux expected from hot stellar coronae, as predicted from analogy with the Sun and from X-ray derived temperatures and densities, is about 10 times smaller than the observed fluxes for many dMe stars observed with the VLA. The implications of these high observed fluxes to the coronal parameters of magnetic field strength, temperature, and source size are discussed, and observations are suggested that potentially allow a choice among the several possibilities. Title: Deduction of Coronal Magnetic Fields Using Microwave Spectroscopy Authors: Hurford, G. J.; Gary, D. E.; Garrett, H. B. Bibcode: 1985ASSL..116..379H Altcode: 1985rst..conf..379H Gyroresonance opacity renders the solar corona optically thick at frequencies which are low integral multiples of the local gyrofrequency. This causes the microwave spectrum of sunspots to be sensitive to the strength of coronal magnetic fields. The concept is illustrated by high spectral resolution observations of a sunspot acquired with the Owens Valley frequency-agile interferometer. The observed spectrum is compared to the results of three-dimensional atmospheric model calculations in which the sunspot field is represented by the potential field of a dipole located beneath the photosphere. The comparison enables the depth, orientation and magnetic moment of the dipole that best fits the observations to be determined. Since such observations require that the microwave emission be resolved spectrally, not spatially, the technique may be applicable to the study of stellar coronal fields. Title: Coordinated Multiband Observations of Stellar Flares Authors: Rodono, M.; Foing, B. H.; Linsky, J. L.; Butler, J. C.; Haisch, B. M.; Gary, D. E.; Gibson, D. M. Bibcode: 1985Msngr..39....9R Altcode: The March 28, 1984 flare of AD Leo is characterized on the basis of observations obtained over the spectral range from 200 nm to 20 cm using the IUE, the VLA, and four ESO telescopes as part of a coordinated multiband international campaign. The data are presented graphically and discussed, with consideration of faint negative K-band events observed simultaneously with the optical flare; an H-alpha precursor with longer energy-release relaxation than in the U continuum; and remarkably enhanced UV continuum, Mg II doublet, and 260-nm Fe II blend during the last secondary optical peak. Title: An impulsive solar burst observed in H-alpha, microwaves, and hard X-rays Authors: Gary, D. E.; Tang, F. Bibcode: 1985ApJ...288..385G Altcode: The authors present Hα, 10.6 GHz microwave, and greater than 100 keV X-ray observations of a single impulsive spike flare that occurred on 1980 May 28, 1947 UT. The isolated high flux spike provides an excellent opportunity to infer the time behavior of the electron acceleration that is assumed to yield the microwave and hard X-ray flux profiles. It is found that, although the time profile consists of a simple, single peak, the spike is actually due to two acceleration episodes in separate sources. The authors adopt a source model for microwave and hard X-ray sources, in which the microwave source is due to electrons trapped at the top of a magnetic loop, and the hard X-ray source is due to thick-target emission at the footpoints. Title: High Resolution VLA Observations of an Active Region During a Partial Solar Eclipse Authors: Gary, D. E.; Hurford, G. J. Bibcode: 1984BAAS...16.1003G Altcode: No abstract at ADS Title: Coordinated IUE and ground-based observations of active stars: flare events on YZ CMi, V1005 Ori, AD Leo and AR Lac. Authors: Rodonò, M.; Cutispoto, G.; Catalano, S.; Linsky, J. L.; Gibson, D. M.; Brown, A.; Haisch, B. M.; Butler, C. J.; Byrne, P. B.; Andrews, A. D.; Doyle, J. G.; Gary, D. E.; Henry, G. W.; Russo, G.; Vittone, A.; Scaltriti, F.; Foing, B. Bibcode: 1984ESASP.218..247R Altcode: 1984iue..conf..247R Observations of stellar flares were obtained with IUE and ground-based facilities simultaneously over a wide range of wavelengths in order to study the effect of the flare radiation at different atmospheric levels. Observations include time-resolved IUE and optical spectroscopy, narrow and wide-band optical photometry, IR photometry, and microwave observations. Results include detection of IR flux decrease, or negative flare, in coincidence with flux increase at all other wavelengths. Title: Type II bursts, shock waves, and coronal transients - The event of 1980 June 29, 0233 UT Authors: Gary, D. E.; Dulk, G. A.; House, L.; Illing, R.; Sawyer, C.; Wagner, W. J.; McLean, D. J.; Hildner, E. Bibcode: 1984A&A...134..222G Altcode: The metric Type-II solar burst event of June 29, 1980, is characterized on the basis of spatially resolved radioheliograph observations obtained at Culgoora, Australia, and visible-light observations obtained with the coronograph/polarimeter of the SMM satellite. The data are presented in images, diagrams, and graphs and discussed in detail. The Type-II emission is found to arise in the dense moving material behind the transient loops, which have sky-plane width 0.5 solar radius and line-of-sight depth 0.1-0.4 solar radius. A faint arc observed moving ahead of the transient loops at about 900 km/sec and not associated with the Type-II burst is attributed to a shock front, and the compression ratio and Alfven Mach number of the enhanced-density region are estimated as n2/n1 = 1.3-3 and M(A) = 1.2-3. The ambient material at 3 solar radii is determined to have Alfven speed 250-625 km/sec and magnetic-field strength 50-120 mG. The total mass of the event is calculated as 700 Tg; the total magnetic energy of the loops is (1.5-15) x 10 to the 29th ergs. Title: The Numbers of Fast Electrons in Solar Flares as Deduced From Hard X-Ray and Microwave Spectral Data Authors: Gary, D. E. Bibcode: 1984BAAS...16..523G Altcode: No abstract at ADS Title: Microwave emission from the coronae of late-type dwarf stars. Authors: Linsky, J. L.; Gary, D. E. Bibcode: 1983ApJ...274..776L Altcode: VLA microwave observations of 14 late-type dwarf and subgiant stars and binary systems are examined. In this extensive set of observations, four sources at 6 cm (Chi-1 Ori, UV Cet, YY Gem, and Wolf 630AB) were detected and low upper limits for the remaining stars were found. The microwave luminosities of the nondetected F-K dwarfs are as small as 0.01 those of the dMe stars. The detected emission is slowly variable in all cases and is consistent with gyroresonant emission from thermal electrons spiraling in magnetic fields of about 300 gauss if the source sizes are as large as R/R(asterisk) = 3-4. This would correspond to magnetic fields that are probably in the range 0.001-0.0001 gauss at the photospheric level. An alternative mechanism is gyrosynchrotron emission from a relatively small number of electrons with effective temperature. Title: Gamma-ray, Radio, and Hα Observations of a Single Spike Solar Flare Authors: Gary, D. E.; Tang, F. Bibcode: 1983BAAS...15R.919G Altcode: No abstract at ADS Title: The sun at 1.4 GHz: intensity and polarization. Authors: Dulk, G. A.; Gary, D. E. Bibcode: 1983A&A...124..103D Altcode: The authors present 1.4 GHz radio pictures of the sun made on 1981 September 26 using the VLA with a resolution of 40arcsec. Features observed include active regions, limb brightening, coronal holes and filament channels; all correspond well with features seen in Hα or He λ10830 Å, and can be explained as relative enhancements or depressions of free-free bremsstrahlung from the corona and upper transition region. The degree of circular polarization of the radiation from active regions ranges up to 0.2 and the sense corresponds, with a few exceptions, with the polarity of the photospheric magnetograms. The polarization is in the sense of the x-mode and is highest near the edges of active regions, whereas the brightness is highest near the line of zero polarization. The polarization can be explained by the different effects of the magnetic field on the bremsstrahlung opacities of the two modes; the observed values imply field strengths between about 20 and 70 Gauss near the boundaries of the active region corona. Title: Coordinated Ultraviolet, Microwave, and Optical Observations of Flares on YZ CMi and AD Leo Authors: Linsky, J. L.; Bornmann, P.; Brown, A.; Gary, D. E.; Rodono, M.; Pazzani, V.; Andrews, A. D.; Butler, C. J.; Byrne, P. B. Bibcode: 1983BAAS...15..650L Altcode: No abstract at ADS Title: VLA observations of quiescent and flare microwave emission from late-type stars - A unique probe of coronal magnetic fields Authors: Gary, D. E.; Linsky, J. L.; Dulk, G. A. Bibcode: 1983IAUS..102..387G Altcode: No abstract at ADS Title: An unusual microwave flare with 56 second oscillations on the M dwarf L726-8 A. Authors: Gary, D. E.; Linsky, J. L.; Dulk, G. A. Bibcode: 1982ApJ...263L..79G Altcode: Using the VLA, an unusual flare event has been observed on L726-8 A (dM5.5e), the primary star in the M dwarf system containing the prototype flare star UV Cet. This flare had a peak flux of 8 mJy at 6 cm and a corresponding brightness temperature greater than 10 to the 10th K, was almost entirely right-hand circularly polarized, showed large flux variations on the 10 s time resolution of the VLA, and exhibited quasi-periodic oscillations with a period of about 56 + or - 5 s. While periodic flux variations have been detected during solar flares and RS CVn type stellar flares, this is apparently the first detection of periodicity in microwaves from M dwarf stars. It is proposed that the observed radiation was due to maser action, probably an electron maser, and that the energy release mechanism was modulated. Title: Radio Emission from Solar and Stellar Coronae. Authors: Gary, D. E. Bibcode: 1982PhDT.........5G Altcode: Several problems in radiophysics are explored utilizing new and unique observations. Polarization measurements of two types of solar bursts--Reverse Drift Pairs and Type V bursts--allowed identification of the radiation as due to fundamental plasma emission for RDPs and harmonic plasma emission for Type Vs. Two other types of solar radio burst--Type II (shock related) and Type IV--observed at Culgoora, Australia, are studied with the aid of Coronagraph/Polarimeter (C/P) observations. Together, the radio and C/P data indicate the presence of two separate shocks in the coronal transient event of 1980 June 29. One shock, without radio emission, led the transient and was driven by it. Estimates of the density enhancement caused by the shock give Mach number l.2 < M(,A) < 3 and, hence, magnetic field strength in the ambient corona 0.05 < B < 0.12 gauss. The second shock, which gave rise to the radio emission, was associated with the loops. The Type II sources appeared to lie behind the leading edge of the loops, and a measurement of the density from the C/P images showed that only behind the loops was the density high enough to account for the plasma emission. The second shock is interpreted as a blast-wave, initiated by the impulsive flare, which traversed the transient material and weakened when it encountered the faster moving, upper part of the transient. The Type IV burst observed at 80 MHz in the same event showed slight outward movement in association with a rising of the relevant plasma level as transient material entered the corona. The characteristics of the sources observed at 80 and 43 MHz suggest that plasma radiation at the second harmonic was the probable emission mechanism. The possibility of gyro-synchrotron emission is explored, and it is found that the sources could have been due to this mechanism only if the magnetic field strength at 2.5R(,0) was > 2.8 gauss. Finally, the discovery of quiescent microwave emission from solar-type stars is discussed. Two sources, (chi)('1) Ori and UV Cet, were detected. The emission is interpreted as gyroresonance emission from hot extended coronae; free-free emission is shown to be unlikely. Title: Radio emission from solar and stellar coronae Authors: Gary, Dale Everett Bibcode: 1982PhDT.......115G Altcode: No abstract at ADS Title: Evidence for a shock wave in visible light and radio observations of the 1980 June 29 event Authors: Gary, D. E.; Dulk, G. A.; House, L. L.; Wagner, W. J.; Illing, R. I.; Sawyer, C.; McLean, D. J. Bibcode: 1982AdSpR...2k.253G Altcode: 1982AdSpR...2..253G Shock waves, as evidenced by type II radio bursts, often accompany flares and coronal mass ejection transients. At present, the density enhancements observed by coronagraphs are believed by some to be ejected matter from the low corona, and by others to be the compressed material behind a shock front. If the former is correct, one would expect in some cases to see a density enhancement, associated with the compression region of the shock, some distance ahead of the transient ejecta. Such a density enhancement has not been previously reported.

The coronal transient of 1980 June 29 (0233 UT) was observed with the High Altitude Observatory's Coronagraph/Polarimeter aboard SMM. This flare-associated coronal transient event was well observed with the Culgoora Radioheliograph, including a well-developed type II burst. Visible on the coronagraph images is a faint circular arc moving out well ahead of the transient loops. This arc is moving at more than 900 km s-1 while the transient itself is moving at a speed of about 600 km s-1. Both the arc and transient appear to have originated either prior to the X-ray flare or at some height above the flare at the time of the flare. The type II burst observed at Culgoora is associated with the transient loops, and no type II emission is identified with the faint arc.

Due to its great speed, we interpret the faint arc as a manifestation of a shock wave, but also envision a separate shock wave associated with the transient loops as evidenced by the type II emission. Preliminary density measurements are consistent with this interpretation, and show the outer shock wave associated with the faint arc to have a Mach number MA <= 1.7. At present we have no convincing explanation for the lack of a type II burst in association with the arc.

This work was supported in part by NASA through grants NSG-7287 and NAGW-91 to the University of Colorado, Boulder, and S-55989 to the High Altitude Observatory, National Center for Atmospheric Research. The National Center for Atmospheric Research, NCAR, is sponsored by the National Science Foundation. Title: First detection of nonflare microwave emission from the coronae of single late-type dwarf stars. Authors: Gary, D. E.; Linsky, J. L. Bibcode: 1981ApJ...250..284G Altcode: Results are presented of a search for nonflare microwave radiation from the coronae of nearby late-type dwarf stars comparable to the sun: single stars without evidence for either a large wind or circumstellar envelope. The observing program consisted of flux measurements of six stars over a 24-h period with the VLA in the C configuration at a wavelength of 6 cm with 50 MHz bandwidth. Positive detections at 6 cm were made for Chi 1 Ori (0.6 mJy) and the flare star UV Cet (1.55 mJy), and upper limits were obtained for the stars Pi 1 UMa, Xi Boo A, 70 Oph A and Epsilon Eri. It is suggested that Chi 1 Ori, and possibly UV Cet, represent the first detected members of a new class of radio sources which are driven by gyroresonance emission, i.e. cyclotron emission from nonrelativistic Maxwellian electrons. Title: The Sun at 1.4 GHz as Observed with the VLA Authors: Dulk, G. A.; Gary, D. E. Bibcode: 1981BAAS...13..878D Altcode: No abstract at ADS Title: First Detection of Steady 6 cm Emission from Coronae of Single Dwarf Stars of Spectral Type G-M Authors: Gary, D.; Linsky, J. L. Bibcode: 1980BAAS...12..898G Altcode: No abstract at ADS Title: Visible Light and Radio Observations of the First Coronal Transient Event of 1980 June 29 Authors: Gary, D. E.; Dulk, G. A.; Wagner, W.; Sawyer, C.; House, L.; Stewart, R. T.; McLean, D. Bibcode: 1980BAAS...12..904G Altcode: No abstract at ADS Title: The position and polarization of Type V solar bursts Authors: Dulk, G. A.; Gary, D. E.; Suzuki, S. Bibcode: 1980A&A....88..218D Altcode: Observations of the position and polarization of Type V solar radio bursts and their preceding Type III bursts are presented. The polarization, frequency range, source position, source movement, source size and brightness temperature of the bursts were measured using a 24-220 MHz spectropolarimeter, an 8-8000 MHz spectrograph and a three-frequency radioheliograph. Type V radiation is frequently found to have the opposite sense of circular polarization from that of the preceding Type III burst, with a degree of polarization similar to that of harmonic Type III radiation. A reversal of polarization is not observed when the accompanying Type III burst has no fundamental-harmonic structure, or when the Type V radiation is poorly developed. Possible mechanisms for the reversal are examined, including opposite magnetic field directions in Type III and V bursts, changes in mode coupling and a change in the mode of emission from o-mode for Type III to x-mode for Type V, and conditions needed for the mode change which is considered the most likely mechanism, are determined. Title: The Polarization of Type-V Bursts Authors: Gary, D. E.; Suzuki, S.; Dulk, G. A. Bibcode: 1980IAUS...86..333G Altcode: No abstract at ADS Title: Corrected formula for the polarization of second harmonic plasma emission Authors: Melrose, D. B.; Dulk, G. A.; Gary, D. E. Bibcode: 1980PASA....4...50M Altcode: 1980PASAu...4...50M Corrections for the theory of polarization of second harmonic plasma emission are proposed. The nontransversality of the magnetoionic waves was not taken into account correctly and is here corrected. The corrected and uncorrected results are compared for two simple cases of parallel and isotropic distributions of Langmuir waves. It is found that whereas with the uncorrected formula plausible values of the coronal magnetic fields were obtained from the observed polarization of the second harmonic, the present results imply fields which are stronger by a factor of three to four. Title: Erratum: "Position and polarization of solar drift pair bursts" [Proc. Astron. Soc. Aust., Vol. 3, p. 379 - 383 (1979)]. Authors: Suzuki, S.; Gary, D. E. Bibcode: 1980PASA....4..129S Altcode: 1980PASAu...4..129S No abstract at ADS Title: Position and polarization of solar drift pair bursts Authors: Suzuki, S.; Gary, D. E. Bibcode: 1979PASA....3..379S Altcode: 1979PASAu...3..379S The paper presents an analysis of the observations of Type I bursts, Type III bursts, and an underlying continuum made with the Culgoora spectropolarimeter, spectrograph, and radioheliograph during a noise storm of February 17/18, 1979. Several hundred RDP bursts, and about fifty FDPs were observed. The results on the polarization of drift pair bursts confirm the results of Sastry (1972) that the two components of drift pairs are polarized in the same sense. However, the observed significant difference in degree of polarization between the two components of a pair has not been previously reported. Data on RDP positional and frequency characteristics are presented, and existing theories concerning RDPs are reviewed.