Author name code: braun ADS astronomy entries on 2022-09-14 author:"Braun, Douglas C." ------------------------------------------------------------------------ Title: Performance of the X-Calibur hard X-ray polarimetry mission during its 2018/19 long-duration balloon flight Authors: Abarr, Q.; Beheshtipour, B.; Beilicke, M.; Bose, R.; Braun, D.; de Geronimo, G.; Dowkontt, P.; Errando, M.; Gadson, T.; Guarino, V.; Heatwole, S.; Hossen, M.; Iyer, N.; Kislat, F.; Kiss, M.; Kitaguchi, T.; Krawczynski, H.; Lanzi, J.; Li, S.; Lisalda, L.; Okajima, T.; Pearce, M.; Peterson, Z.; Press, L.; Rauch, B.; Simburger, G.; Stuchlik, D.; Takahashi, H.; Tang, J.; Uchida, N.; West, A. Bibcode: 2022APh...14302749A Altcode: 2022arXiv220409761A X-Calibur is a balloon-borne telescope that measures the polarization of high-energy X-rays in the 15-50 keV energy range. The instrument makes use of the fact that X-rays scatter preferentially perpendicular to the polarization direction. A beryllium scattering element surrounded by pixellated CZT detectors is located at the focal point of the InFOCμS hard X-ray mirror. The instrument was launched for a long-duration balloon (LDB) flight from McMurdo (Antarctica) on December 29, 2018, and obtained the first constraints of the hard X-ray polarization of an accretion-powered pulsar. Here, we describe the characterization and calibration of the instrument on the ground and its performance during the flight, as well as simulations of particle backgrounds and a comparison to measured rates. The pointing system and polarimeter achieved the excellent projected performance. The energy detection threshold for the anticoincidence system was found to be higher than expected and it exhibited unanticipated dead time. Both issues will be remedied for future flights. Overall, the mission performance was nominal, and results will inform the design of the follow-up mission XL-Calibur, which is scheduled to be launched in summer 2022. Title: SuperTIGER Abundances of Galactic Cosmic Rays for the Atomic Number (Z) Interval 30 to 56 Authors: Walsh, N. E.; Akaike, Y.; Binns, W. R.; Bose, R. G.; Brandt, T. J.; Braun, D.; Cannady, N.; Dowkontt, P. F.; Hams, T.; Israel, M. H.; Krizmanic, J. F.; Labrador, A. W.; Link, J. T.; Mewaldt, R. A.; Mitchell, J. W.; Murphy, R. P.; Rauch, B. F.; Sakai, K.; Sasaki, M.; Simburger, G.; Stone, E. C.; Tatoli, T.; Ward, J. E.; Wiedenbeck, M. E.; Zober, W. V.; deNolfo, G. A. Bibcode: 2022icrc.confE.118W Altcode: 2022PoS...395E.118W No abstract at ADS Title: Erratum: "Probing the Solar Meridional Circulation Using Fourier Legendre Decomposition" (2021, ApJ, 911, 54) Authors: Braun, D. C.; Birch, A. C.; Fan, Y. Bibcode: 2022ApJ...924..140B Altcode: No abstract at ADS Title: Global solar flows and their impact on magnetic activity Authors: Dikpati, Mausumi; Braun, Douglas; Featherstone, Nicholas; Hindman, Bradley; Komm, Rudolf; Liu, Yang; Scherrer, Philip; Upton, Lisa; Wang, Haimin Bibcode: 2021AGUFMSH55D1872D Altcode: This poster presents the second year progress report of the LWS focused-science team-4 of 2019. The main science objective is to jointly develop the most comprehensive, dynamically consistent picture of solar flows at the surface, in the convection zone and tachocline, and determine the MHD effects induced by these motions. Our major team-achievements in the second year include: (i) consensus about active regions' flow and their contributions in modifying the global flow; (ii) long-term global flow map from various magnetograms, and their specific properties as function of cycle phase, (iii) impacts of the flows in polar field evolutions, (iv) simulations of global flows with various solar-like interior conditions, (v) roles of simulated flows in driving the nonlinear dynamics of spot-producing magnetic fields and producing their spatio-temporal patterns, which are compared with that manifested as active regions patterns in surface magnetograms. We will describe in detail how these observationally constrained local and global flows are leading us to improved simulations of model-outputs of magnetic activity and flows. In turn, these outputs can reliably be used as inputs to heliospheric models, for example, for simulating properties of reconnection of active regions' magnetic fields, high-speed streams, sector passages, all of which have profound influence on various aspects of space weather and impact on terrestrial atmosphere. Title: Probing the Solar Meridional Circulation Using Fourier Legendre Decomposition Authors: Braun, D. C.; Birch, A. C.; Fan, Y. Bibcode: 2021ApJ...911...54B Altcode: 2021arXiv210302499B We apply the helioseismic methodology of Fourier Legendre decomposition to 88 months of Dopplergrams obtained by the Helioseismic and Magnetic Imager (HMI) as the basis of inferring the depth variation of the mean meridional flow, as averaged between 20° and 60° latitude and in time, in both the northern and southern hemispheres. We develop and apply control procedures designed to assess and remove center-to-limb artifacts using measurements obtained by performing the analysis with respect to artificial poles at the east and west limbs. Forward modeling is carried out using sensitivity functions proportional to the mode kinetic energy density to evaluate the consistency of the corrected frequency shifts with models of the depth variation of the meridional circulation in the top half of the convection zone. The results, taken at face value, imply substantial differences between the meridional circulation in the northern and southern hemispheres. The inferred presence of a return (equatorward propagating) flow at a depth of approximately 40 Mm below the photosphere in the northern hemisphere is surprising and appears to be inconsistent with many other helioseismic analyses. This discrepancy may be the result of the inadequacy of our methodology to remove systematic errors in HMI data. Our results appear to be at least qualitatively similar to those by Gizon et al., which point to an anomaly in HMI data that is not present in MDI or GONG data. Title: Global Solar Flows and Magnetic Fields: Observing, Simulating and Predicting Their Impact on the Heliosphere and Terrestrial Atmosphere Authors: Dikpati, M.; Braun, D. C.; Featherstone, N. A.; Komm, R.; Liu, Y.; Scherrer, P. H.; Upton, L.; Wang, H. Bibcode: 2020AGUFMSH0020008D Altcode: Understanding origins and evolution of solar magnetic activity occurring on a wide range of time-scales, and the space weather effects caused by the particles and electromagnetic outputs that reach the Earth, requires knowledge of the physical origins of this activity below photosphere. Despite much progress, our knowledge of processes responsible for driving the magnetohydrodynamics of flows and fields below photosphere and their relation to observed flows and magnetic activity is far from complete. For example, there is no consensus as to the number of meridional circulation-cells that exist in the Sun and the depth at which the poleward-flow switches direction to equatorward. Main objective of our LWS focused-science team is to jointly develop the most comprehensive, dynamically consistent picture of solar flows at the surface, in the convection zone and tachocline, and determine the MHD effects induced by these motions. We will present how we are developing consensus sets of observational constraints and simulating model-outputs of magnetic activity and flows, which can reliably be used as inputs to heliospheric and terrestrial- atmospheric models. The ultimate success will be in our ability to predict the features of solar cycle 25, including the active-latitudes and -longitudes, global- and localized-flows several months to years ahead. Title: Submerged Sources of Transient Acoustic Emission from Solar Flares Authors: Lindsey, Charles; Buitrago-Casas, J. C.; Martínez Oliveros, Juan Carlos; Braun, Douglas; Martínez, Angel D.; Quintero Ortega, Valeria; Calvo-Mozo, Benjamín; Donea, Alina-Catalina Bibcode: 2020ApJ...901L...9L Altcode: We report the discovery of ultra-impulsive acoustic emission from a solar flare, emission with a seismic signature that indicates submersion of its source approximately a Mm beneath the photosphere of the active region that hosted the flare. Just over two decades ago V. V. Zharkova and A. G. Kosovichev discovered the first acoustic transient released into the Sun's interior by a solar flare. These acoustic waves, refracted back upward to the solar surface after their release, make conspicuous Doppler ripples spreading outward from the flaring region that tell us a lot about their sources. The mechanism by which these transients are driven has stubbornly eluded our understanding. Some of the source regions, for example, are devoid of secondary Doppler, magnetic, or thermal disturbances in the outer atmosphere of the source regions that would signify the driving agent of an intense seismic transient in the outer atmosphere. In this study, we have applied helioseismic holography, a diagnostic based upon standard wave optics, to reconstruct a 3D image of the sources of acoustic waves emanating from the M9.3-class flare of 2011 July 30. These images contain a source component that is submerged a full Mm beneath the active-region photosphere. The signature of acoustic sources this deep in the solar interior opens new considerations into the physics that must be involved in transient acoustic emission from flares—and possibly of flare physics at large. We develop analogies to seismicity remotely triggered by tremors from distant earthquakes, and consider prospects of new insight into the architecture of magnetic flux beneath flaring active regions. Title: Average motion of emerging solar active region polarities. II. Joy's law Authors: Schunker, H.; Baumgartner, C.; Birch, A. C.; Cameron, R. H.; Braun, D. C.; Gizon, L. Bibcode: 2020A&A...640A.116S Altcode: 2020arXiv200605565S Context. The tilt of solar active regions described by Joy's law is essential for converting a toroidal field to a poloidal field in Babcock-Leighton dynamo models. In thin flux tube models the Coriolis force causes what we observe as Joy's law, acting on east-west flows as they rise towards the surface.
Aims: Our goal is to measure the evolution of the average tilt angle of hundreds of active regions as they emerge, so that we can constrain the origins of Joy's law.
Methods: We measured the tilt angle of the primary bipoles in 153 emerging active regions (EARs) in the Solar Dynamics Observatory Helioseismic Emerging Active Region survey. We used line-of-sight magnetic field measurements averaged over 6 h to define the polarities and measure the tilt angle up to four days after emergence.
Results: We find that at the time of emergence the polarities are on average aligned east-west, and that neither the separation nor the tilt depends on latitude. We do find, however, that EARs at higher latitudes have a faster north-south separation speed than those closer to the equator at the emergence time. After emergence, the tilt angle increases and Joy's law is evident about two days later. The scatter in the tilt angle is independent of flux until about one day after emergence, when we find that higher-flux regions have a smaller scatter in tilt angle than lower-flux regions.
Conclusions: Our finding that active regions emerge with an east-west alignment is consistent with earlier observations, but is still surprising since thin flux tube models predict that tilt angles of rising flux tubes are generated below the surface. Previously reported tilt angle relaxation of deeply anchored flux tubes can be largely explained by the change in east-west separation. We conclude that Joy's law is caused by an inherent north-south separation speed present when the flux first reaches the surface, and that the scatter in the tilt angle is consistent with buffeting of the polarities by supergranulation. Title: Majorana representation for mixed states Authors: Serrano-Ensástiga, E.; Braun, D. Bibcode: 2020PhRvA.101b2332S Altcode: 2019arXiv190907740S We generalize the Majorana stellar representation of spin-s pure states to mixed states, and in general to any Hermitian operator, defining a bijective correspondence between three spaces: the spin-density matrices, a projective space of homogeneous polynomials of four variables, and a set of equivalence classes of points (constellations) on spheres of different radii. The representation behaves well under rotations by construction, and also under partial traces where the reduced density matrices inherit their constellation classes from the original state ρ . We express several concepts and operations related to density matrices in terms of the corresponding polynomials, such as the anticoherence criterion and the tensor representation of spin-s states described in Giraud et al. [Phys. Rev. Lett. 114, 080401 (2015)]., 10.1103/PhysRevLett.114.080401 Title: Probing the Variation with Depth of the Solar Meridional Circulation Using Legendre Function Decomposition Authors: Braun, D. C.; Birch, A.; Fan, Y. Bibcode: 2020ASSP...57..125B Altcode: We apply the helioseismic methodology of Legendre Function Decomposition to 7.5 years of Dopplergrams obtained by the Helioseismic and Magnetic Imager (HMI) as the basis of inferring the depth variation of the meridional flow between 20∘ and 60∘ latitude in both hemispheres. We assess and remove center-to-limb artifacts using measurements obtained by applying the procedure to pseudo poles at the east and west limbs. Forward modeling is carried out to evaluate the consistency of the corrected frequency shifts with models of the depth variation of the meridional circulation in the top half of the convection zone. The observations are consistent with a return flow in the northern hemisphere below about 40 Mm depth, but no obvious return flow in the south. Title: Average surface flows before the formation of solar active regions and their relationship to the supergranulation pattern Authors: Birch, A. C.; Schunker, H.; Braun, D. C.; Gizon, L. Bibcode: 2019A&A...628A..37B Altcode: Context. The emergence of solar active regions is an important but poorly understood aspect of the solar dynamo.
Aims: Knowledge of the flows associated with the rise of active-region-forming magnetic concentrations through the near-surface layers will help determine the mechanisms of active region formation.
Methods: We used helioseismic holography and granulation tracking to measure the horizontal flows at the surface that precede the emergence of active regions. We then averaged these flows over about sixty emerging active regions to reduce the noise, selecting active regions that emerge into relatively quiet Sun. To help interpret the results, we constructed a simple model flow field by generating synthetic "emergence locations" that are probabilistically related to the locations of supergranulation-scale convergence regions in the quiet Sun.
Results: The flow maps obtained from helioseismology and granulation tracking are very similar (correlation coefficients for single maps around 0.96). We find that active region emergence is, on average, preceded by converging horizontal flows of amplitude about 40 m s-1. The convergence region extends over about 40 Mm in the east-west direction and about 20 Mm in the north-south direction and is centered in the retrograde direction relative to the emergence location. This flow pattern is largely reproduced by a model in which active region emergence occurs preferentially in the prograde direction relative to supergranulation inflows.
Conclusions: Averaging over many active regions reveals a statistically significant pattern of near-surface flows prior to emergence. The qualitative success of our simple model suggests that rising flux concentrations and supergranule-scale flows interact during the emergence process. Title: Probing the Variation with Depth of the Solar Meridional Circulation using Legendre Function Decomposition Authors: Braun, Douglas; Birch, Aaron C.; Fan, Yuhong Bibcode: 2019AAS...23431802B Altcode: The solar meridional circulation is a crucial component of magnetic flux transport and dynamo models. Despite decades of helioseismic study, no consensus exists regarding the variation of its properties with depth. It has become apparent that the main challenges consist of 1) overcoming realization noise with multi-year long datasets, and 2) the identification and robust removal of systematic center-to-limb effects. Here we apply the helioseismic methodology of Legendre Function Decomposition (LFD) to 7.5 years of Dopplergrams obtained by the Helioseismic and Magnetic Imager (HMI) as the basis of inferring the depth variation of the meridional flow between 20 and 60 degrees latitude in both hemispheres. The LFD method, first developed by Braun and Fan in 1998, probes subsurface flows through the Doppler-effect induced distortion of power spectra. The procedure is optimized for the detection of meridional flows and uses Legendre functions (of the first and second kind) to characterize poleward and equatorward wave propagation in spherical coordinates. For this study we have developed control procedures which assess and remove center-to-limb artifacts, using measurements obtained by applying the procedure to pseudo poles at the east and west limbs. Forward modeling is carried out to evaluate the consistency of the corrected LFD frequency shifts with various assumed models of the depth variation of the meridional circulation.

DB is supported by the NASA Heliophysics Division (awards 80NSSC18K0066 and 80NSSC18K0068) and by the Solar Terrestrial program of the National Science Foundation (award AGS-1623844). Title: Active Region Flows and their Contribution to Varying Global Dynamics Authors: Braun, Douglas Bibcode: 2019AAS...23430210B Altcode: We explore the general properties of the near-surface dynamics of solar active regions (ARs) and show how AR flows may contribute to longitudinally averaged measurements of global properties such as meridional circulation and torsional oscillations. Helioseismic holography is applied to HMI Dopplergrams yielding about 5000 flow measurements of 336 ARs observed by SDO between 2010 and 2014. Ensemble averages of the AR flows are presented, binned into subsets based on total magnetic flux. These averages show converging flows, with speeds about 10 m/s and spanning 10 degrees from the active region centers, which are apparent for most ARs above the flux limit of our survey at 1021 Mx. Retrograde flows are also detected, with amplitudes around 10 m/s, which predominantly, but not exclusively, flank the polar side of the ARs. The high signal-to-noise levels of these averages makes possible the assessment of individual AR contributions to time-varying global flows. We demonstrate this for several solar rotations, showing that individual active regions contribute substantially to these global flows.

This work is supported by the Solar Terrestrial program of the National Science Foundation (award AGS-1623844) and by the NASA Heliophysics Division (awards 80NSSC18K0066 and 80NSSC18K0068). Title: Average motion of emerging solar active region polarities. I. Two phases of emergence Authors: Schunker, H.; Birch, A. C.; Cameron, R. H.; Braun, D. C.; Gizon, L.; Burston, R. B. Bibcode: 2019A&A...625A..53S Altcode: 2019arXiv190311839S
Aims: Our goal is to constrain models of active region formation by tracking the average motion of active region polarity pairs as they emerge onto the surface.
Methods: We measured the motion of the two main opposite polarities in 153 emerging active regions using line-of-sight magnetic field observations from the Solar Dynamics Observatory Helioseismic Emerging Active Region (SDO/HEAR) survey. We first measured the position of each of the polarities eight hours after emergence, when they could be clearly identified, using a feature recognition method. We then tracked their location forwards and backwards in time.
Results: We find that, on average, the polarities emerge with an east-west orientation and the separation speed between the polarities increases. At about 0.1 days after emergence, the average separation speed reaches a peak value of 229 ± 11 ms-1, and then starts to decrease. About 2.5 days after emergence the polarities stop separating. We also find that the separation and the separation speed in the east-west direction are systematically larger for active regions that have higher flux. The scatter in the location of the polarities increases from about 5 Mm at the time of emergence to about 15 Mm at two days after emergence.
Conclusions: Our results reveal two phases of the emergence process defined by the rate of change of the separation speed as the polarities move apart. Phase 1 begins when the opposite polarity pairs first appear at the surface, with an east-west alignment and an increasing separation speed. We define Phase 2 to begin when the separation speed starts to decrease, and ends when the polarities have stopped separating. This is consistent with a previous study: the peak of a flux tube breaks through the surface during Phase 1. During Phase 2 the magnetic field lines are straightened by magnetic tension, so that the polarities continue to move apart, until they eventually lie directly above their anchored subsurface footpoints. The scatter in the location of the polarities is consistent with the length and timescales of supergranulation, supporting the idea that convection buffets the polarities as they separate. Title: Flows around Averaged Solar Active Regions Authors: Braun, D. C. Bibcode: 2019ApJ...873...94B Altcode: 2019arXiv190202298B We explore the general properties of near-surface flows around solar active regions. Helioseismic holography is applied to HMI Dopplergrams yielding nearly 5000 flow measurements of 336 unique active regions observed by the Solar Dynamics Observatory between 2010 and 2014. Ensemble averages of the flows, over subsets of regions sorted on the basis of magnetic flux, are performed. These averages show that converging flows, with speeds of about 10 m s-1 and extending up to 10° from the active-region centers, are prevalent and have similar properties for all regions with magnetic flux above 1021 Mx. Retrograde flows are also detected, with amplitudes around 10 m s-1, which predominantly, but not exclusively, flank the polar side of the active regions. We estimate the expected contribution of these active-region flows to longitudinal averages of zonal and meridional flows and demonstrate the plausibility that they are responsible for at least some component of the time-varying global-scale flows. The reliability of our flow determination is tested using publicly available MHD simulations of both quiet-Sun convection and of a sunspot. While validating the overall methodology in general, the sunspot simulation demonstrates the presence of artifacts that may compromise quantitative flow inferences from some helioseismic measurements. Title: Validating Forward Modeling and Inversions of Helioseismic Holography Measurements Authors: DeGrave, K.; Braun, D. C.; Birch, A. C.; Crouch, A. D.; Javornik, B. Bibcode: 2018ApJ...863...34D Altcode: 2018arXiv180703841D Here, we use synthetic data to explore the performance of forward models and inverse methods for helioseismic holography. Specifically, this work presents the first comprehensive test of inverse modeling for flows using lateral-vantage (deep-focus) holography. We derive sensitivity functions in the Born approximation. We then use these sensitivity functions in a series of forward models and inversions of flows from a publicly available magnetohydrodynamic quiet-Sun simulation. The forward travel times computed using the kernels generally compare favorably with measurements obtained by applying holography, in a lateral-vantage configuration, on a 15 hr time series of artificial Dopplergrams extracted from the simulation. Inversions for the horizontal flow components are able to reproduce the flows in the upper 3 Mm of the domain, but are compromised by noise at greater depths. Title: Helioseismic Holography of Flows Around the Averaged Active Region Authors: Braun, Douglas C. Bibcode: 2018tess.conf10628B Altcode: We apply helioseismic holography to HMI observations of several hundred of the largest active regions and assess the inferred flows averaged after spatially aligning active regions selected in several ranges of magnetic flux. This ensemble averaging helps greatly reduce the dominating effect of the supergranulation signal. We also report progress on inferring the depth variation of these flows from modeling the variation of the helioseismic signatures as a function of focus depth. Some general features of the active-region flows among all flux groups include 1) compact outflows centered on both magnetic polarities, and 2) surrounding inflows with greater amplitudes in the trailing polarities.

This work is supported by the NSF Solar Terrestrial Program through grant AGS-1623844. Title: Helioseismic Constraints on the Subsurface Flows of the Averaged Supergranule Authors: Braun, Douglas C.; Duvall, Thomas L., Jr.; Felipe, Tobias; DeGrave, Kyle Bibcode: 2018tess.conf11506B Altcode: We report progress on constraining the subsurface flow properties of supergranulation from helioseismic holography applied to HMI/SDO observations of over 63,000 individual supergranules. First, using surface-focused measurements, we confirm the advantages of broader phase-speed filters in reducing diffraction effects, noted by Duvall and collaborators in prior time-distance analyses. Second, we expand the type of measurements to include deep-focusing geometries. Third, we compare all measurements with predictions made using numerical wave-propagation simulations performed with the 3D MANCHA code using a number of prescribed flow patterns. These model flows include those inferred from prior time-distance analyses as well as a model based on results of recent fully-convective MURaM-based computations. While the model predictions are in general qualitative agreement with the ensemble averaged measurements, no single model is fully consistent with the complete set of measurements. This suggests there is room for improvement in constraining the subsurface flows.

This work is supported by NASA grant 80NSSC18K0068 awarded to NWRA, as well as by the NASA High-End Computing program at Ames Research Center. Title: EMIC wave events during the four QARBM challenge intervals Authors: Engebretson, M. J.; Posch, J. L.; Braun, D.; Li, W.; Angelopoulos, V.; Kellerman, A. C.; Kletzing, C.; Lessard, M.; Mann, I. R.; Tero, R.; Shiokawa, K.; Wygant, J. R. Bibcode: 2017AGUFMSM51B2433E Altcode: We present observations of EMIC waves from multiple data sources during the four GEM challenge events in 2013 selected by the GEM focus group on Quantitative Assessment of Radiation Belt Modeling: March 17-18 (Stormtime Enhancement), May 31-June 2 (Stormtime Dropout), September 19-20 (Non-storm Enhancement), and September 23-25 (Non-storm Dropout). Observations include EMIC wave data from the Van Allen Probes and THEMIS spacecraft in the inner magnetosphere and from several arrays of ground-based search coil magnetometers worldwide, as well as localized ring current proton precipitation data from the low-altitude POES spacecraft. Each of these data sets provides only limited spatial coverage, but their combination reveals consistent occurrence patterns, which are then used to evaluate the effectiveness of EMIC waves in causing dropouts of radiation belt electrons during these GEM events. Title: Nightside High Latitude Magnetic Impulse Events Authors: Engebretson, M. J.; Connors, M. G.; Braun, D.; Posch, J. L.; Kaur, M.; Guillon, S.; Hartinger, M.; Kim, H.; Behlke, R.; Reiter, K.; Jackel, B. J.; Russell, C. T. Bibcode: 2017AGUFMSM31B2629E Altcode: High latitude Magnetic Impulse Events (MIEs), isolated pulses with periods 5-10 min, were first noted in ground-based magnetometer data near local noon, and are now understood to be signatures of transient pressure increases in the solar wind (sudden impulses - SIs) and/or in the ion foreshock (traveling convection vortex events - TCVs). However, solitary pulses with considerably larger amplitude (ΔB up to 1500 nT) have often been observed in the night sector at these same latitudes. These events are not directly associated with transient external pressure increases, and are often large enough to produce significant ground induced currents. Although many night sector MIEs occur in association with substorm signatures, others appear to be very isolated. We present here a survey of intense MIE events identified in magnetometer data from the AUTUMNX and MACCS arrays in eastern Arctic Canada at all local times between July 1, 2014 and June 30, 2017. We also show maps of horizontal and vertical perturbations and maximum dB/dt values, as well as sample magnetograms, for several example events using data from these and other arrays in Arctic Canada, as well as in West Greenland and Antarctica, the latter to show the conjugate nature of these events. A basic relation to GIC data in the Hydro-Québec electrical transmission network in eastern Canada has been determined and will be discussed. Title: Helioseismic holography of simulated sunspots: dependence of the travel time on magnetic field strength and Wilson depression Authors: Felipe, T.; Braun, D. C.; Birch, A. C. Bibcode: 2017A&A...604A.126F Altcode: 2017arXiv170509135F Improving methods for determining the subsurface structure of sunspots from their seismic signature requires a better understanding of the interaction of waves with magnetic field concentrations. We aim to quantify the impact of changes in the internal structure of sunspots on local helioseismic signals. We have numerically simulated the propagation of a stochastic wave field through sunspot models with different properties, accounting for changes in the Wilson depression between 250 and 550 km and in the photospheric umbral magnetic field between 1500 and 3500 G. The results show that travel-time shifts at frequencies above approximately 3.50 mHz (depending on the phase-speed filter) are insensitive to the magnetic field strength. The travel time of these waves is determined exclusively by the Wilson depression and sound-speed perturbation. The travel time of waves with lower frequencies is affected by the direct effect of the magnetic field, although photospheric field strengths below 1500 G do not leave a significant trace on the travel-time measurements. These results could potentially be used to develop simplified travel-time inversion methods. Title: VizieR Online Data Catalog: Statistical analysis of solar active regions (Barnes+, 2014) Authors: Barnes, G.; Birch, A. C.; Leka, K. D.; Braun, D. C. Bibcode: 2017yCat..17860019B Altcode: In brief, samples from two populations are considered: "pre-emergence" targets (PE) that track a 32°x32° patch of the Sun prior to the emergence of a NOAA-numbered AR and "non-emergence" targets (NE) selected for lack of emergence and lack of strong fields in the central portions of the tracked patch. The PE sample size comprises 107 targets obtained between 2001 and 2007, matched to 107 NE targets drawn from an initially larger sample and selected further to match the PE distributions in time and observing location on the disk.

(2 data files). Title: Driving Early Biochemical Reactions by the Thermal Accumulation of ATP over ADP/AMP? Authors: Kühnlein, A.; Mast, C. B.; Benk, A.; Spatz, J. P.; Braun, D. Bibcode: 2017LPICo1967.4142K Altcode: We propose a system which uses the prebiotically realistic thermal trap to locally shift the equilibrium of ADP and ATP towards an ATP bias and thereby allows biochemical reactions to take off. Title: Hosting Early Evolution in Heated Pores of Rock Authors: Mast, C. B.; Möller, F.; Lanzmich, S.; Keil, L.; Braun, D. Bibcode: 2017LPICo1967.4037M Altcode: Recent experiments with non-equilibrium micro­systems suggest that porous rock conditions drive early molecular evolution in many ways, including accumulation, polymerization, replication, length selection and gelation. Title: Thermally Driven Accumulation and Dry-Wet Cycles of Nucleotides Authors: Morasch, M.; Liu, J.; Braun, D. Bibcode: 2017LPICo1967.4153M Altcode: We show how a nonequilibrium system in form of a temperature gradient across porous rock creates high local concentrations and dry-wet cycles of nucleotides and other molecules. Title: Elucidating Signatures of the Genetic Code with Binding Assays Authors: Edeleva, E. V.; Schwintek, P. J.; Braun, D. Bibcode: 2017LPICo1967.4036E Altcode: What defined specific assignment of amino acids to their cognate codons during the emergence of the genetic code? In this project, we develop experimental strategies to test the stereochemical theory of the genetic code origin. Title: A Fixed-point Scheme for the Numerical Construction of Magnetohydrostatic Atmospheres in Three Dimensions Authors: Gilchrist, S. A.; Braun, D. C.; Barnes, G. Bibcode: 2016SoPh..291.3583G Altcode: 2016arXiv160900733G; 2016SoPh..tmp..182G Magnetohydrostatic models of the solar atmosphere are often based on idealized analytic solutions because the underlying equations are too difficult to solve in full generality. Numerical approaches, too, are often limited in scope and have tended to focus on the two-dimensional problem. In this article we develop a numerical method for solving the nonlinear magnetohydrostatic equations in three dimensions. Our method is a fixed-point iteration scheme that extends the method of Grad and Rubin (Proc. 2nd Int. Conf. on Peaceful Uses of Atomic Energy31, 190, 1958) to include a finite gravity force. We apply the method to a test case to demonstrate the method in general and our implementation in code in particular. Title: SDO/HMI survey of emerging active regions for helioseismology Authors: Schunker, H.; Braun, D. C.; Birch, A. C.; Burston, R. B.; Gizon, L. Bibcode: 2016A&A...595A.107S Altcode: 2016arXiv160808005S Context. Observations from the Solar Dynamics Observatory (SDO) have the potential for allowing the helioseismic study of the formation of hundreds of active regions, which would enable us to perform statistical analyses.
Aims: Our goal is to collate a uniform data set of emerging active regions observed by the SDO/HMI instrument suitable for helioseismic analysis, where each active region is centred on a 60° × 60° area and can be observed up to seven days before emergence.
Methods: We restricted the sample to active regions that were visible in the continuum and emerged into quiet Sun largely avoiding pre-existing magnetic regions. As a reference data set we paired a control region (CR), with the same latitude and distance from central meridian, with each emerging active region (EAR). The control regions do not have any strong emerging flux within 10° of the centre of the map. Each region was tracked at the Carrington rotation rate as it crossed the solar disk, within approximately 65° from the central meridian and up to seven days before, and seven days after, emergence. The mapped and tracked data, consisting of line-of-sight velocity, line-of-sight magnetic field, and intensity as observed by SDO/HMI, are stored in datacubes that are 410 min in duration and spaced 320 min apart. We call this data set, which is currently comprised of 105 emerging active regions observed between May 2010 and November 2012, the SDO Helioseismic Emerging Active Region (SDO/HEAR) survey.
Results: To demonstrate the utility of a data set of a large number of emerging active regions, we measure the relative east-west velocity of the leading and trailing polarities from the line-of-sight magnetogram maps during the first day after emergence. The latitudinally averaged line-of-sight magnetic field of all the EARs shows that, on average, the leading (trailing) polarity moves in a prograde (retrograde) direction with a speed of 121 ± 22 m s-1 (-70 ± 13 m s-1) relative to the Carrington rotation rate in the first day. However, relative to the differential rotation of the surface plasma, the east-west velocity is symmetric, with a mean of 95 ± 13 m s-1.
Conclusions: The SDO/HEAR data set will not only be useful for helioseismic studies, but will also be useful to study other features such as the surface magnetic field evolution of a large sample of EARs. We intend to extend this survey forwards in time to include more EARs observed by SDO/HMI. Title: Helioseismic Holography of Simulated Sunspots: Magnetic and Thermal Contributions to Travel Times Authors: Felipe, T.; Braun, D. C.; Crouch, A. D.; Birch, A. C. Bibcode: 2016ApJ...829...67F Altcode: 2016arXiv160804893F Wave propagation through sunspots involves conversion between waves of acoustic and magnetic character. In addition, the thermal structure of sunspots is very different than that of the quiet Sun. As a consequence, the interpretation of local helioseismic measurements of sunspots has long been a challenge. With the aim of understanding these measurements, we carry out numerical simulations of wave propagation through sunspots. Helioseismic holography measurements made from the resulting simulated wavefields show qualitative agreement with observations of real sunspots. We use additional numerical experiments to determine, separately, the influence of the thermal structure of the sunspot and the direct effect of the sunspot magnetic field. We use the ray approximation to show that the travel-time shifts in the thermal (non-magnetic) sunspot model are primarily produced by changes in the wave path due to the Wilson depression rather than variations in the wave speed. This shows that inversions for the subsurface structure of sunspots must account for local changes in the density. In some ranges of horizontal phase speed and frequency there is agreement (within the noise level in the simulations) between the travel times measured in the full magnetic sunspot model and the thermal model. If this conclusion proves to be robust for a wide range of models, it would suggest a path toward inversions for sunspot structure. Title: Constraining the common properties of active region formation using the SDO/HEAR dataset Authors: Schunker, H.; Braun, D. C.; Birch, A. C. Bibcode: 2016usc..confE...2S Altcode: Observations from the Solar Dynamics Observatory (SDO) have the potential for allowing the helioseismic study of the formation of hundreds of active regions, which enable us to perform statistical analyses. We collated a uniform data set of emerging active regions (EARs) observed by the SDO/HMI instrument suitable for helioseismic analysis, where each active region can be observed up to 7 days before emergence. We call this dataset the SDO Helioseismic Emerging Active Region (SDO/HEAR) survey. We have used this dataset to to understand the nature of active region emergence. The latitudinally averaged line-of-sight magnetic field of all the EARs shows that the leading (trailing) polarity moves in a prograde (retrograde) direction with a speed of 110 ± 15 m/s (-60 ± 10 m/s) relative to the Carrington rotation rate in the first day after emergence. However, relative to the differential rotation of the surface plasma the East-West velocity is symmetric, with a mean of 90 ± 10 m/s. We have also compared the surface flows associated with the EARs at the time of emergence with surface flows from numerical simulations of flux emergence with different rise speeds. We found that the surface flows in simulations of emerging flux with a low rise speed of 70 m/s best match the observations. Title: A low upper limit on the subsurface rise speed of solar active regions Authors: Birch, A. C.; Schunker, H.; Braun, D. C.; Cameron, R.; Gizon, L.; Lo ptien, B.; Rempel, M. Bibcode: 2016SciA....2E0557B Altcode: 2016arXiv160705250B Magnetic field emerges at the surface of the Sun as sunspots and active regions. This process generates a poloidal magnetic field from a rising toroidal flux tube, it is a crucial but poorly understood aspect of the solar dynamo. The emergence of magnetic field is also important because it is a key driver of solar activity. We show that measurements of horizontal flows at the solar surface around emerging active regions, in combination with numerical simulations of solar magnetoconvection, can constrain the subsurface rise speed of emerging magnetic flux. The observed flows imply that the rise speed of the magnetic field is no larger than 150 m/s at a depth of 20 Mm, that is, well below the prediction of the (standard) thin flux tube model but in the range expected for convective velocities at this depth. We conclude that convective flows control the dynamics of rising flux tubes in the upper layers of the Sun and cannot be neglected in models of flux emergence. Title: Helioseismic Survey of the Near-surface Flows Around the Largest Active Regions with SDO-HMI Observations Authors: Braun, Douglas; DeGrave, Kyle Bibcode: 2016SPD....47.0702B Altcode: We report on the properties of the near-surface flows, determined from helioseismic holography applied to HMI Dopplergrams, of approximately 250 of the largest active regions observed during the first five years of SDO observations. A recent study which examined the potential association of flows with the production of solar flares in this survey has recently been published (Braun 2016, ApJ 819, 106). We discuss here additional findings on general flow properties of the regions in our survey derived from ensemble averages of the flows. This averaging eliminates the dominating effect of the supergranulation signal, and shows outflows from sunspots surrounded by compact inflows. The properties of these flows are described. The potential use of these measurements for determining the contribution of active-region related flows to global dynamics (including differential rotation and meridional circulation) and flux-transport models is discussed. This work is supported by the NSF Solar Terrestrial Program through grant AGS-1127327 and by the NASA Heliophysics Division through NNH12CF68C and NNX16AG88G. Title: Forward and Inverse Modeling of Helioseismic Holography Measurements of MHD Simulations of Convection and Sunspot Flows Authors: DeGrave, Kyle; Braun, Douglas; Birch, Aaron; Crouch, Ashley D.; Javornik, Brenda; Rempel, Matthias D. Bibcode: 2016SPD....4720303D Altcode: We test and validate newly-developed, empirically-derived sensitivity kernels for use in helioseismic analysis. These kernels are based on the Born approximation and derived from applying direct measurements to artificial realizations of incoming and scattered wavefields. These kernels are employed in a series of forward and inverse modeling of flows from the near-surface layers of two publicly available magnetohydrodynamic (MURaM-based) solar simulations - a quiet-Sun simulation, and one containing a sunspot. Forward travel times computed using the kernels generally compare favorably in non-magnetic regions. One finding of note is the presence of flow-like artifacts in the sunspot measurements which appear when the spot umbra or penumbra falls within the measurement pupils. Inversions for the horizontal flow components are able to reproduce the large-scale supergranule-sized flows in the upper 3Mm of both domains, but are compromised by noise at greater depths. In spite of the magnetic artifact, the moat flow surrounding the spot is at least qualitatively recovered. This work is supported by the NASA Heliophysics Division through NNH12CF68C, NNH12CF23C, and NNX16AG88G, and by the NSF Solar-Terrestrial Program through grant AGS-1127327. Title: Numerical construction of magneto-hydrostatic atmospheres in three dimensions Authors: Gilchrist, Stuart; Braun, Douglas; Barnes, Graham Bibcode: 2016SPD....47.0706G Altcode: There is a general interest in constructing magneto-hydrostatic models of the solar atmosphere. These models describe large-scale, long-lived magnetic structures like sunspots, prominences, coronal loops, and the corona itself on global scales. The nonlinearity of the magneto-hydrostatic equations prohibits direct analytic solution except when idealized approximations like self-similarity are made. Numerical approaches, too, are limited in scope, and primarily focus on the two-dimensional problem --- the general three-dimensional magneto-hydrostatic problem is not treated. In this presentation we present a new numerical scheme for solving the magneto-hydrostatic equations in three dimensions. We are presently using this method to construct sunspot models for helioseismic MHD wave-propagation simulations with the goal of comparing the simulations to local-helioseismic measurements. We will present the details of the method and its application to test cases.This work is supported by NASA Heliophysics Division through grant NNX14AD42G and by the NSF Solar-Terrestrial program through grant AGS-1127327. Title: Magnetic and Thermal Contributions to Helioseismic Travel times in Simulated Sunspots Authors: Braun, Douglas; Felipe, Tobias; Birch, Aaron; Crouch, Ashley D. Bibcode: 2016SPD....47.0701B Altcode: The interpretation of local helioseismic measurements of sunspots has long been a challenge, since waves propagating through sunspots are potentially affected by both mode conversion and changes in the thermal structure of the spots. We carry out numerical simulations of wave propagation through a variety of models which alternately isolate either the thermal or magnetic structure of the sunspot or include both of these. We find that helioseismic holography measurements made from the resulting simulated wavefields show qualitative agreement with observations of real sunspots. Using insight from ray theory, we find that travel-time shifts in the thermal (non-magnetic) sunspot model are primarily produced by changes in the wave path due to the Wilson depression rather than variations in the wave speed. This shows that inversions for the subsurface structure of sunspots must account for local changes in the density. In some ranges of horizontal phase speed and frequency there is agreement (within the noise level of the measurements) between the travel times measured in the full magnetic sunspot model and the thermal model. If this conclusion proves to be robust for a wide range of models, it suggests a path towards inversions for sunspot structure. This research has been funded by the Spanish MINECO through grant AYA2014-55078-P, by the NASA Heliophysics Division through NNX14AD42G and NNH12CF23C, and the NSF Solar Terrestrial program through AGS-1127327. Title: A Helioseismic Survey of Near-surface Flows Around Active Regions and their Association with Flares Authors: Braun, D. C. Bibcode: 2016ApJ...819..106B Altcode: 2016arXiv160200038B We use helioseismic holography to study the association of shallow flows with solar flare activity in about 250 large sunspot groups observed between 2010 and 2014 with the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory. Four basic flow parameters: horizontal speed, horizontal component of divergence, vertical component of vorticity, and a vertical kinetic helicity proxy, are mapped for each active region (AR) during its passage across the solar disk. Flow indices are derived representing the mean and standard deviation of these parameters over magnetic masks and compared with contemporary measures of flare X-ray flux. A correlation exists for several of the flow indices, especially those based on the speed and the standard deviation of all flow parameters. However, their correlation with X-ray flux is similar to that observed with the mean unsigned magnetic flux density over the same masks. The temporal variation of the flow indices are studied, and a superposed epoch analysis with respect to the occurrence to 70 M and X-class flares is made. While flows evolve with the passage of the ARs across the disk, no discernible precursors or other temporal changes specifically associated with flares are detected. Title: Measurements with local helioseismology Authors: Braun, D. C. Bibcode: 2015exse.book...77B Altcode: No abstract at ADS Title: Influence of Magnetic and Thermal Effects on Helioseismic Travel-time Shifts in Sunspot Models Authors: Felipe, Tobias; Braun, Douglas; Crouch, Ashley D.; Birch, Aaron Bibcode: 2014AAS...22420206F Altcode: Sunspots are one of the most prominent manifestations of solar magnetic activity and have been studied using local helioseismology for decades. Recent modeling and observational studies indicate that the interpretation of travel-time shifts is still subject to uncertainties regarding the physical causes of the wave perturbations. Numerical wave propagation has proved useful in addressing this problem. In this work, we have analyzed travel-time shifts obtained from three dimensional numerical simulations of wave propagation in a magnetohydrostatic sunspot-like atmosphere. In particular, we isolate the individual effects of the magnetic field and thermal perturbations on the measurements by means of simulations where only one kind of perturbation (magnetic or thermal) is included. The resulting travel-time shift maps, obtained by applying helioseismic holography to the photospheric Doppler signals in the simulated domain, will be compared and discussed. We plan to make the artificial data available to the community for the development and validation of other helioseismic methods. This work is supported by the NASA SDO Science Center program (through contract NNH09CE41C) and by the NASA Living With a Star Program (through grant NNX14AD42G). Title: A Helioseismic Survey of Emerging Active Regions Using HMI-SDO Data Authors: Braun, Douglas; Schunker, Hannah; Birch, Aaron Bibcode: 2014AAS...22420201B Altcode: A survey of the subsurface properties of approximately 100 emerging active regions, determined from the application of helioseismic holography to Dopplergrams obtained with the HMI instrument onboard the Solar Dynamics Observatory, is being carried out. The goal of this research is to use helioseismology and numerical simulations to identify and understand possible signatures, in the form of acoustic travel time shifts, due to rising magnetic flux concentrations prior to their emergence at the solar photosphere. The status of the project and current results will be discussed. We make use of ensemble averages of travel-time shift measurements as proxies for near-surface depth-integrated wave-speed changes and flows. The latter include horizontal components of the flows as well as their horizontal divergence and the vertical component of the flow vorticity. A control sample of a similar number of quiet-Sun regions is used for comparison and for identifying potential systematic effects. Preliminary results confirm previous suggestions (obtained from a prior survey using GONG data) that emergence sites are associated with converging photospheric flows, such as the boundaries of supergranulation.This work is supported by the NASA Heliophysics Supporting Research program through contract NNH12CF23C. Title: A Helioseismic Survey to Investigate Relationships between Subsurface Flows beneath Large Active Regions and Solar Flares Authors: Braun, Douglas; Leka, K D.; Barnes, Graham Bibcode: 2014AAS...22421815B Altcode: A survey of the subsurface flow properties of about 120 of the largest active regions, determined from the application of helioseismic holography to Dopplergrams obtained with the HMI instrument onboard the Solar Dynamics Observatory, is being carried out. The overriding goal is to characterize differences in the subsurface flows between active regions associated with eruptive flares and the flows observed in relatively quiescent regions. Applications to flare forecasting comprise only one part of this investigation, since the potential response of the subsurface environment to eruptive events during and after their occurrence is also of scientific interest. Other priorities include understanding the limitations of the helioseismic methods, identifying and correcting systematic effects, and validating the reliability of the measurements using artificial data. While inversions to determine the variation with depth of subsurface flows are planned, preliminary results will be discussed which make use of proxies for near-surface depth-integrated properties, including the horizontal component of the flow divergence and the vertical component of the flow vorticity.This work is supported by the Solar Terrestrial Program of the National Science Foundation, through grant AGS-1127327, and by the National Oceanic and Atmospheric Administration SBIR program. Title: Studies on Forecasting Solar Flares Authors: Leka, K. D.; Barnes, G.; Braun, D. C.; Wagner, E. L. Bibcode: 2014shin.confE.171L Altcode: Forecasting solar flares is a challenge from various scientific perspectives; major solar flares are inherently rare events, and all observations available with which to evaluate the flare-readiness of the Sun are remote, with inferences about the physical state rather than direct measurements. We report on efforts to improve forecasts, using data from the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory using magnetic field and helioseismic parametrization, magnetic charge topology and Discriminant Analysis. We report on preliminary results of the performance, including the temporal variations of the parametrizations.

This work is supported by NASA contract NNH12CG10C and NOAA Contract WC-133R-13-CN-0079 Title: Using Synthetic Data From Convection Simulations To Test Helioseismic Holography Inversions For Three-Dimensional Vector Flows Authors: Crouch, Ashley D.; Birch, Aaron; Braun, Douglas; Javornik, Brenda; Rempel, Matthias D. Bibcode: 2014AAS...22421807C Altcode: We investigate the efficacy of helioseismic holography for inferring the three-dimensional vector flows in the near-surface layers of the solar interior. Synthetic helioseismic data are taken from compressible convection simulations. Travel times are measured from the synthetic data using helioseismic holography. Kernels for the sensitivity of travel times to subsurface flows are calculated using the Born approximation. Inversions for subsurface flows are then performed using subtractive optimally localized averaging. This provides an opportunity to evaluate the accuracy of the inversion technique. We compare the actual flows present in the convection simulations to the flows retrieved by the inversion. We discuss the influence of the regularization used by the inversion, and the effects of noise and spatial resolution. This work is supported by the NASA SDO Science Center program (NNH09CE41C), the NASA Heliophysics Guest Investigator program (NNH12CF68C), and the NASA LWS TR&T tools and methods program (NNH09CF68C). The National Center for Atmospheric Research is sponsored by the National Science Foundation. Title: Helioseismology of Pre-emerging Active Regions. III. Statistical Analysis Authors: Barnes, G.; Birch, A. C.; Leka, K. D.; Braun, D. C. Bibcode: 2014ApJ...786...19B Altcode: 2013arXiv1307.1938B The subsurface properties of active regions (ARs) prior to their appearance at the solar surface may shed light on the process of AR formation. Helioseismic holography has been applied to samples taken from two populations of regions on the Sun (pre-emergence and without emergence), each sample having over 100 members, that were selected to minimize systematic bias, as described in Paper I. Paper II showed that there are statistically significant signatures in the average helioseismic properties that precede the formation of an AR. This paper describes a more detailed analysis of the samples of pre-emergence regions and regions without emergence based on discriminant analysis. The property that is best able to distinguish the populations is found to be the surface magnetic field, even a day before the emergence time. However, after accounting for the correlations between the surface field and the quantities derived from helioseismology, there is still evidence of a helioseismic precursor to AR emergence that is present for at least a day prior to emergence, although the analysis presented cannot definitively determine the subsurface properties prior to emergence due to the small sample sizes. Title: Helioseismic Holography of an Artificial Submerged Sound Speed Perturbation and Implications for the Detection of Pre-emergence Signatures of Active Regions Authors: Braun, D. C. Bibcode: 2014SoPh..289..459B Altcode: 2012SoPh..tmp..306B; 2012arXiv1210.7504B We use a publicly available numerical wave-propagation simulation of Hartlep et al. (Solar Phys.268, 321, 2011) to test the ability of helioseismic holography to detect signatures of a compact, fully submerged, 5 % sound-speed perturbation placed at a depth of 50 Mm within a solar model. We find that helioseismic holography employed in a nominal "lateral-vantage" or "deep-focus" geometry employing quadrants of an annular pupil can detect and characterize the perturbation. A number of tests of the methodology, including the use of a plane-parallel approximation, the definition of travel-time shifts, the use of different phase-speed filters, and changes to the pupils, are also performed. It is found that travel-time shifts made using Gabor-wavelet fitting are essentially identical to those derived from the phase of the Fourier transform of the cross-covariance functions. The errors in travel-time shifts caused by the plane-parallel approximation can be minimized to less than a second for the depths and fields of view considered here. Based on the measured strength of the mean travel-time signal of the perturbation, no substantial improvement in sensitivity is produced by varying the analysis procedure from the nominal methodology in conformance with expectations. The measured travel-time shifts are essentially unchanged by varying the profile of the phase-speed filter or omitting the filter entirely. The method remains maximally sensitive when applied with pupils that are wide quadrants, as opposed to narrower quadrants or with pupils composed of smaller arcs. We discuss the significance of these results for the recent controversy regarding suspected pre-emergence signatures of active regions. Title: A Full-Sun Magnetic Index from Helioseismology Inferences Authors: González Hernández, I.; Díaz Alfaro, M.; Jain, K.; Tobiska, W. K.; Braun, D. C.; Hill, F.; Pérez Hernández, F. Bibcode: 2014SoPh..289..503G Altcode: Solar magnetic indices are used to model the solar irradiance and ultimately to forecast it. However, the observation of such indices is generally limited to the Earth-facing hemisphere of the Sun. Seismic maps of the far side of the Sun have proven their capability to locate and track medium-large active regions at the non-visible hemisphere. We present here the possibility of using the average signal from these seismic far-side maps, combined with similarly calculated near-side maps, as a proxy to the full-Sun magnetic activity. Title: The Relativistic Electron-Proton Telescope (REPT) Instrument on Board the Radiation Belt Storm Probes (RBSP) Spacecraft: Characterization of Earth's Radiation Belt High-Energy Particle Populations Authors: Baker, D. N.; Kanekal, S. G.; Hoxie, V. C.; Batiste, S.; Bolton, M.; Li, X.; Elkington, S. R.; Monk, S.; Reukauf, R.; Steg, S.; Westfall, J.; Belting, C.; Bolton, B.; Braun, D.; Cervelli, B.; Hubbell, K.; Kien, M.; Knappmiller, S.; Wade, S.; Lamprecht, B.; Stevens, K.; Wallace, J.; Yehle, A.; Spence, H. E.; Friedel, R. Bibcode: 2013SSRv..179..337B Altcode: 2012SSRv..tmp..101B Particle acceleration and loss in the million electron Volt (MeV) energy range (and above) is the least understood aspect of radiation belt science. In order to measure cleanly and separately both the energetic electron and energetic proton components, there is a need for a carefully designed detector system. The Relativistic Electron-Proton Telescope (REPT) on board the Radiation Belt Storm Probe (RBSP) pair of spacecraft consists of a stack of high-performance silicon solid-state detectors in a telescope configuration, a collimation aperture, and a thick case surrounding the detector stack to shield the sensors from penetrating radiation and bremsstrahlung. The instrument points perpendicular to the spin axis of the spacecraft and measures high-energy electrons (up to ∼20 MeV) with excellent sensitivity and also measures magnetospheric and solar protons to energies well above E=100 MeV. The instrument has a large geometric factor ( g=0.2 cm2 sr) to get reasonable count rates (above background) at the higher energies and yet will not saturate at the lower energy ranges. There must be fast enough electronics to avert undue dead-time limitations and chance coincidence effects. The key goal for the REPT design is to measure the directional electron intensities (in the range 10-2-106 particles/cm2 s sr MeV) and energy spectra (Δ E/ E∼25 %) throughout the slot and outer radiation belt region. Present simulations and detailed laboratory calibrations show that an excellent design has been attained for the RBSP needs. We describe the engineering design, operational approaches, science objectives, and planned data products for REPT. Title: A Search for Pre-Emergence Helioseismic Signatures of Active Regions: Study Design and some Average Results Authors: Leka, K. D.; Birch, A.; Barnes, G.; Braun, D.; Javornik, B.; Gonzalez-Hernandez, I.; Dunn, T. Bibcode: 2013SPD....44...91L Altcode: Helioseismology can be an important tool for understanding the formation of active regions. This poster describes the design of a recently completed study, testing whether pre-appearance signatures of solar magnetic active regions were detectable using various tools of local helioseismology. We provide details of the data selection and preparation of samples, each containing over 100 members, of two populations: regions on the Sun which produced a numbered NOAA active region, and a "control" sample of areas which did not. The seismology is performed on data from the GONG network; accompanying magnetic data from the Michelson Doppler Imager aboard SoHO are used for co-temporal analysis of the surface magnetic field. Samples are drawn from 2001--2007, and each target is analyzed for 27.7hr prior to an objectively determined time of emergence. We describe known sources of bias and the approaches used to mitigate them. Examining the average ensemble differences between the two populations, we describe significant and surprising differences between our samples in both quantities determined from helioseismology and from surface magnetic fields. This work was supported by NASA contract NNH07CD25C. Title: Far-side helioseismic maps: the next generation Authors: González Hernández, Irene; Lindsey, Charles; Braun, Douglas C.; Bogart, Richard S.; Scherrer, Philip H.; Hill, Frank Bibcode: 2013JPhCS.440a2029G Altcode: For more than a decade, far-side seismic maps of medium-to-large active regions have proven their capability as a space weather forecasting tool. In the last few years, these maps have started to serve another purpose: complementing the front side observations that are input to different solar models. Photospheric flux transport as well as solar spectral irradiance models have been shown to produce improved results when incorporating the far-side seismic maps as well as providing better forecasting. The challenge for the future is twofold: Far-side seismic monitoring needs to be more sensitive, and it needs to offer more information. We present here initial steps towards fulfilling these goals using higher resolution input images, adding extra skips to the analysis and changing the presentation of the maps. Title: The Helioseismic Search for Emerging Flux Authors: Braun, D. C. Bibcode: 2013enss.confE..64B Altcode: Arguably considered the holy grail of local helioseismology is the detection of emerging flux before its appearance as a sunspot or magnetic region on the photosphere. After almost two decades of searching, this goal remains elusive and, at best, controversial. Helioseismic exploration is increasingly assisted by numerical simulations of rising flux which offer predictions of the magnitude and type of signatures, and also by computational wave propagation models which can validate and help improve the methods. We discuss some of these developments as well as results of a recent survey, carried out at NWRA, of approximately one hundred emerging active regions observed with the GONG network. A new survey, carried out in collaboration with colleagues at the Max Planck Institute for Solar System Research and made using the observations obtained by the HMI instrument on SDO is under way. This talk reviews work at NWRA which has been funded through the NASA Living with a Star program and currently though the NASA Solar and Heliospheric SR&T program (contract NNH12CF23C) and Heliophysics GI program (contract NNH12CF68C). Title: Testing Helioseismic-Holography Inversions for Supergranular Flows Using Synthetic Data Authors: Dombroski, D. E.; Birch, A. C.; Braun, D. C.; Hanasoge, S. M. Bibcode: 2013SoPh..282..361D Altcode: 2012arXiv1211.6886D Supergranulation is one of the most visible length scales of solar convection and has been studied extensively by local helioseismology. We use synthetic data computed with the Seismic Propagation through Active Regions and Convection (SPARC) code to test regularized-least squares (RLS) inversions of helioseismic-holography measurements for a supergranulation-like flow. The code simulates the acoustic wavefield by solving the linearized three-dimensional Euler equations in Cartesian geometry. We model a single supergranulation cell with a simple, axisymmetric, mass-conserving flow. Title: Helioseismology of Pre-emerging Active Regions. II. Average Emergence Properties Authors: Birch, A. C.; Braun, D. C.; Leka, K. D.; Barnes, G.; Javornik, B. Bibcode: 2013ApJ...762..131B Altcode: 2013arXiv1303.1391B We report on average subsurface properties of pre-emerging active regions as compared to areas where no active region emergence was detected. Helioseismic holography is applied to samples of the two populations (pre-emergence and without emergence), each sample having over 100 members, which were selected to minimize systematic bias, as described in Leka et al. We find that there are statistically significant signatures (i.e., difference in the means of more than a few standard errors) in the average subsurface flows and the apparent wave speed that precede the formation of an active region. The measurements here rule out spatially extended flows of more than about 15 m s-1 in the top 20 Mm below the photosphere over the course of the day preceding the start of visible emergence. These measurements place strong constraints on models of active region formation. Title: Helioseismology of Pre-emerging Active Regions. I. Overview, Data, and Target Selection Criteria Authors: Leka, K. D.; Barnes, G.; Birch, A. C.; Gonzalez-Hernandez, I.; Dunn, T.; Javornik, B.; Braun, D. C. Bibcode: 2013ApJ...762..130L Altcode: 2013arXiv1303.1433L This first paper in a series describes the design of a study testing whether pre-appearance signatures of solar magnetic active regions were detectable using various tools of local helioseismology. The ultimate goal is to understand flux-emergence mechanisms by setting observational constraints on pre-appearance subsurface changes, for comparison with results from simulation efforts. This first paper provides details of the data selection and preparation of the samples, each containing over 100 members, of two populations: regions on the Sun that produced a numbered NOAA active region, and a "control" sample of areas that did not. The seismology is performed on data from the GONG network; accompanying magnetic data from SOHO/MDI are used for co-temporal analysis of the surface magnetic field. Samples are drawn from 2001-2007, and each target is analyzed for 27.7 hr prior to an objectively determined time of emergence. The results of two analysis approaches are published separately: one based on averages of the seismology- and magnetic-derived signals over the samples, another based on Discriminant Analysis of these signals, for a statistical test of detectable differences between the two populations. We include here descriptions of a new potential-field calculation approach and the algorithm for matching sample distributions over multiple variables. We describe known sources of bias and the approaches used to mitigate them. We also describe unexpected bias sources uncovered during the course of the study and include a discussion of refinements that should be included in future work on this topic. Title: X-Spec: A Multi-Object Wideband Survey Spectrograph for CCAT Authors: Bradford, Charles; Hailey-Dunsheath, S.; Shirokoff, E.; Hollister, M.; Kovacs, A.; Zmuidzinas, J.; Padin, S.; Seiffert, M. D.; Braun, D.; Banales, G.; LeDuc, H.; Stacey, G. J.; Nikola, T.; Glenn, J.; Chapman, S. Bibcode: 2013AAS...22115009B Altcode: We are developing a multi-object dispersive survey spectrograph for CCAT. X-Spec is optimized for rest-frame far-IR / submm atomic and molecular transitions in high-z galaxies, and it will conduct multi-galaxy spectral survey up to 10x faster than ALMA. Detected lines will provide redshifts for and interstellar gas conditions in tens of thousands of galaxies ranging from the early universe (z > 6) to the present day. X-Spec will be particularly sensitive to the 158-micron ionized carbon fine-structure transition [CII], and the initial instrument will target the 650-um, 850-um, and 1-mm atmospheric windows, corresponding to 3.5 to 9 for [CII]. By following up high-z candidate objects, X-Spec surveys of [CII] will reveal the early evolution of galaxies' energy sources and interstellar gas conditions. CCAT/X-Spec can also probe below individually-detected sources by using fluctuation analyses; the spatial-spectral fluctuations mm and submm bands are dominated by [CII], and can be used to measure the growth of large-scale structure and the global properties of galaxies in the reionization epoch. X-Spec will have at least 15 independent spectrometer backend 'pixels', each covering 195-520 GHz instantaneously at R=400-700, in both polarizations with photon-background-limited sensitivity. It will use lithographically-patterned filterbank chips formed with superconducting transmission line. The detectors are titanium-nitride kinetic inductance detectors (KIDs), and each spectrometer chip will have ~500 KIDs integrated with the filterbank in a package a few square cm in size. Each chip has a bandwidth of ~ 1:1.6 and is single-polarization, so coverage of the full 195-520 GHz range in dual-pol requires 4 chips and ~2000 detectors. With the compact size and inexpensive mass production, much larger spectrometer formats (100-300 pixels) will be possible as detector readout technology progresses. To optimize on-source observation efficiency, a 2-axis rotary positioning system for each pixel will steer to an arbitrary position in a circular patch of sky; this system will steer to target galaxies, compensate for field rotation, and enable beam modulation (chopping) at ~1-2 Hz for sky subtraction. Title: Scattering of the f-mode by Small Magnetic Flux Elements from Observations and Numerical Simulations Authors: Felipe, T.; Braun, D.; Crouch, A.; Birch, A. Bibcode: 2012ApJ...757..148F Altcode: 2012arXiv1208.4024F The scattering of f-modes by magnetic tubes is analyzed using three-dimensional numerical simulations. An f-mode wave packet is propagated through a solar atmosphere embedded with three different flux tube models that differ in radius and total magnetic flux. A quiet-Sun simulation without a tube present is also performed as a reference. Waves are excited inside the flux tube and propagate along the field lines, and jacket modes are generated in the surroundings of the flux tube, carrying 40% as much energy as the tube modes. The resulting scattered wave is mainly an f-mode composed of a mixture of m = 0 and m = ±1 modes. The amplitude of the scattered wave approximately scales with the magnetic flux. A small amount of power is scattered into the p 1-mode. We have evaluated the absorption and phase shift from a Fourier-Hankel decomposition of the photospheric vertical velocities. They are compared with the results obtained from the ensemble average of 3400 small magnetic elements observed in high-resolution MDI Doppler datacubes. The comparison shows that the observed dependence of the phase shift with wavenumber can be matched reasonably well with the simulated flux tube model. The observed variation of the phase shifts with the azimuthal order m appears to depend on details of the ensemble averaging, including possible motions of the magnetic elements and asymmetrically shaped elements. Title: A Search for Pre-Emergence Helioseismic Signatures of Active Regions Authors: Barnes, Graham; Birch, A.; Leka, K.; Braun, D.; Dunn, T.; Javornik, B.; Gonzalez Hernandez, I. Bibcode: 2012AAS...22020510B Altcode: Helioseismology can be an important tool for understanding the formation of active regions. As a first step towards this goal, we have carried out a search for statistically significant helioseismic precursors of active region emergence. We used an automatic method to determine the time of emergence based on the NOAA/NGDC active region catalog and MDI/SOHO 96 minute magnetograms. Using GONG data, we applied helioseismic holography to 107 pre-emergence active regions and a control sample of 107 regions where no active region was present. We found some significant and surprising differences between our samples in both quantities determined from helioseismology and from surface magnetic fields. However, we do not see a clear signature of emergence when considering individual active regions. The results of this investigation may shed some light on the mechanism responsible for flux emergence, and certainly illustrate the care which must be taken in conducting such an investigation.

This work was supported by NASA contract NNH07CD25C. Title: Comparison of Numerical and Observational Scattering of the f-mode by Small Magnetic Elements Authors: Felipe, Tobias; Braun, D. C.; Crouch, A. D.; Birch, A. C. Bibcode: 2012AAS...22010906F Altcode: The observed scattering of the f-mode by small magnetic elements is studied through Fourier-Hankel analysis and compared with three-dimensional numerical simulations of the scattering produced by magnetic flux tube models. The numerical setup consists of an f-mode wave packet which is propagated through a realistic solar atmosphere embedded with a flux tube model. A quiet Sun simulation without a tube present is also performed as a reference. Sausage (m=0) and kink (m=±1) modes are excited in the flux tube and propagate along the field lines, and jacket modes are generated in the surroundings of the flux tube, carrying 40% as much energy as the tube modes. The resulting scattered wave is mainly an f-mode composed of a mixture of m=0 and m=±1 modes. We find the observed dependence of the phase shift with wavenumber for an ensemble average of about 3400 magnetic elements can be matched reasonably well with the simulated flux tube model. The observed variation with azimuthal order m of the phase-shifts appears to depend on details of the ensemble averaging, including possible motions of the magnetic elements and asymmetrically shaped elements.

This research has been funded by NASA through projects NNH09CE43C, NNH09CF68C, and NNH07CD25C. Title: Comment on “Detection of Emerging Sunspot Regions in the Solar Interior” Authors: Braun, Douglas C. Bibcode: 2012Sci...336..296B Altcode: Ilonidis et al. (Reports, 19 August 2011, p. 993) report acoustic travel-time decreases associated with emerging sunspot regions before their appearance on the solar surface. An independent analysis using helioseismic holography does not confirm these travel-time anomalies for the four regions illustrated by Ilonidis et al. This negative finding is consistent with expectations based on current emerging flux models. Title: Helioseismology of a Realistic Magnetoconvective Sunspot Simulation Authors: Braun, D. C.; Birch, A. C.; Rempel, M.; Duvall, T. L. Bibcode: 2012ApJ...744...77B Altcode: We compare helioseismic travel-time shifts measured from a realistic magnetoconvective sunspot simulation using both helioseismic holography and time-distance helioseismology, and measured from real sunspots observed with the Helioseismic and Magnetic Imager instrument on board the Solar Dynamics Observatory and the Michelson Doppler Imager instrument on board the Solar and Heliospheric Observatory. We find remarkable similarities in the travel-time shifts measured between the methodologies applied and between the simulated and real sunspots. Forward modeling of the travel-time shifts using either Born or ray approximation kernels and the sound-speed perturbations present in the simulation indicates major disagreements with the measured travel-time shifts. These findings do not substantially change with the application of a correction for the reduction of wave amplitudes in the simulated and real sunspots. Overall, our findings demonstrate the need for new methods for inferring the subsurface structure of sunspots through helioseismic inversions. Title: Numerical simulations of the subsurface structure of sunspots Authors: Rempel, M.; Cheung, M.; Birch, A. C.; Braun, D. C. Bibcode: 2011AGUFMSH52B..02R Altcode: Knowledge of the subsurface magnetic field and flow structure of sunspots is essential for understanding the processes involved in their formation, dynamic evolution and decay. Information on the subsurface structure can be obtained by either direct numerical modeling or helioseismic inversions. Numerical simulations have reached only in recent years the point at which entire sunspots or even active regions can be modeled including all relevant physical processes such as 3D radiative transfer and a realistic equation of state. We present in this talk results from a series of different models: from simulations of individual sunspots (with and without penumbrae) in differently sized computational domains to simulations of the active region formation process (flux emergence). It is found in all models that the subsurface magnetic field fragments on an intermediate scale (larger than the scale of sunspot fine structure such as umbral dots); most of these fragmentations become visible as light bridges or flux separation events in the photosphere. The subsurface field strength is found to be in the 5-10 kG range. The simulated sunspots are surrounded by large scale flows, the most dominant and robust flow component is a deep reaching outflow with an amplitude reaching about 50% of the convective RMS velocity at the respective depth. The simulated sunspots show helioseismic signatures (frequency dependent travel time shifts) similar to those in observed sunspots. On the other hand it is clear from the simulations that these signatures originate in the upper most 2-3 Mm of the convection zone, since only there substantial perturbations of the wave speed are present. The contributions from deeper layers are insignificant, in particular a direct comparison between an 8 Mm and 16 Mm deep simulation leads to indiscernible helioseismic differences. The National Center for Atmospheric Research is sponsored by the National Science Foundation. This work is in part supported through the NASA SDO Science Center. Title: Numerical simulations of scattering of f-modes by magnetic flux tubes Authors: Felipe, Tobias; Birch, Aaron C.; Crouch, Ashley D.; Braun, Douglas C. Bibcode: 2011sdmi.confE..80F Altcode: The scattering of the f-mode by a magnetic flux tube is analyzed using three-dimensional numerical simulations. An f-mode wave packet is propagated through a realistic solar atmosphere embedded with a flux tube of 200 km radius and 1600 G field strength. A quiet Sun simulation without the tube being present is also performed as a reference. Sausage (m=0) and kink (m=± 1) modes are excited in the magnetic tube and propagate downward along the field lines, while the resulting scattered wave is mainly an f-mode composed of a mixture of m=0 and m=± 1 modes. Low power is also scattered into high-order acoustic p-modes. We have evaluated the absorption and phase shift from a Fourier-Hankel decomposition of the vertical velocities. Title: "Hare and Hounds" Tests of Helioseismic Holography Authors: Birch, A. C.; Parchevsky, K. V.; Braun, D. C.; Kosovichev, A. G. Bibcode: 2011SoPh..272...11B Altcode: 2011SoPh..tmp..315B; 2011SoPh..tmp..290B; 2011SoPh..tmp..257B; 2011SoPh..tmp..188B We use the output of numerical wave-propagation simulations as synthetic data for "hare and hounds" tests of helioseismic holography. In the simple non-magnetic models examined here, we show that when the inversion method includes a consistent treatment of the filtering applied during the data analysis the inversions for the subsurface sound speed are qualitatively correct. Title: Towards physics-based helioseismic inversions of subsurface sunspot structure Authors: Braun, D. C.; Birch, A. C.; Crouch, A. D.; Rempel, M. Bibcode: 2011IAUS..273..379B Altcode: Numerical computations of wave propagation through sunspot-like magnetic field structures are critical to developing and testing methods to deduce the subsurface structure of sunspots and active regions. We show that helioseismic analysis applied to the MHD sunspot simulations of Rempel and collaborators, as well as to translation-invariant models of umbral-like fields, yield wave travel-time measurements in qualitative agreement with those obtained in real sunspots. However, standard inversion methods applied to these data fail to reproduce the true wave-speed structure beneath the surface of the model. Inversion methods which incorporate direct effects of the magnetic field, including mode conversion, may be required. Title: Helioseismic probing of the subsurface structure of sunspots Authors: Crouch, A. D.; Birch, A. C.; Braun, D. C.; Clack, C. T. M. Bibcode: 2011IAUS..273..384C Altcode: We discuss recent progress in the helioseismic probing of the subsurface structure of solar magnetic regions. To simulate the interaction of helioseismic waves with magnetic fields and thermal perturbations we use a simple model that is translation invariant in the horizontal directions, has a realistic stratification in the vertical direction, and has physically consistent boundary conditions for the waves at the upper and lower boundaries of the computational domain. Using this model we generate synthetic helioseismic data and subsequently measure time-distance travel times. We evaluate a model for the wave-speed perturbation below sunspots that replaces the sound speed in a non-magnetic model by the fast-mode speed from a magnetic model; our results indicate that this approach is unlikely to be useful in modeling wave-speed perturbations in sunspots. We develop and test an inversion algorithm for inferring the sound-speed perturbation in magnetic regions. We show that this algorithm retrieves the correct sound-speed perturbation only when the sensitivity kernels employed account for the effects of the magnetic field on the waves and the subsurface structure. Title: Helioseismic Inversions For Magnetic Field And Sound-speed Perturbations Authors: Clack, Christopher; Crouch, A. D.; Birch, A. C.; Braun, D. C. Bibcode: 2011SPD....42.1602C Altcode: 2011BAAS..43S.1602C In local helioseismology, inversion methods that can separate magnetic and thermal perturbations are needed, especially for probing the subsurface structure of sunspots. We present a method for performing linear helioseismic inversions that can infer small-amplitude perturbations to both the magnetic field strength and the sound-speed profile in translation-invariant background models permeated by a 3 kG vertical magnetic field, consistent with expectations for sunspot umbrae. We introduce a novel inversion routine that consists of two parts: first; a traditional regularized least squares inversion is utilized to search regularization-parameter space for inversion coefficients and second; an analysis of these inversion coefficients identifies the sets of coefficients that have the required attributes for a pair of inferred sound-speed and magnetic fields models. We show a case study in which this inversion method is able to accurately recover a sound-speed perturbation and a perturbation in the magnetic field strength simultaneously. We will discuss how these results relate to the local helioseismology of sunspots. This work is supported by NASA contracts NNH09CE41C and NNG07EI51C. Title: F-mode Seismology Of Solar Simulations Authors: DeGrave, Kyle; Jackiewicz, J.; Braun, D.; Birch, A. C.; Research Associates, NorthWest Bibcode: 2011SPD....42.1613D Altcode: 2011BAAS..43S.1613D Time-distance helioseismology using f-mode travel times is used to study near-surface regions of realistic numerical magnetohydrodynamic simulations. A fully-consistent inversion procedure is used to analyze the simulation flow field outside of a sunspot. This approach is carried out to validate the time-distance technique, as well as the sensitivity kernels and the inversion algorithm. This work is supported by NASA under the SDO Science Center project (contract NNH09CE41C) as well as well as a NASA EPSCoR award. Title: Local Helioseismology of Small-Scale Magnetic Elements Authors: Crouch, Ashley D.; Braun, D. C.; Felipe, T.; Birch, A. C.; Duvall, T. L. Bibcode: 2011SPD....42.1604C Altcode: 2011BAAS..43S.1604C We will discuss recent progress in the measurement and modeling of the interaction of helioseismic waves with small-scale magnetic elements. We will present measurements of the Hankel analysis phase shifts and absorption coefficients associated with an average small-scale magnetic element, measured using ensemble-averaging techniques. We will show results from theoretical calculations and the numerical simulations of wave interactions with thin magnetic flux tubes. We will compare the Hankel analysis measurements with the predictions from these theoretical models, and discuss how these results pertain to the local helioseismology of magnetic flux concentrations. This work is supported by NASA contract NNH09CE43C. Title: Towards Reliable Physics-based Helioseismic Inversions of Sunspot Structure Authors: Braun, Douglas; Birch, A.; Crouch, A.; Clack, C.; Dombroski, D.; Rempel, M.; Duvall, T., Jr. Bibcode: 2011SPD....42.1603B Altcode: 2011BAAS..43S.1603B Inversion methods capable of reliably probing the subsurface structure beneath regions of strong magnetic fields, such as sunspots, remain elusive. We will review progress of a SDO Science Center project, funded to (among other goals) develop and evaluate new methods for this problem. Progress to date has included extensive production of magneto-convective sunspot models for the testing and validation of existing methods, for which a 27 hour run of artificial photospheric Dopplergrams is available online to the community. We will also summarize progress on the use of magnetostatic models for the development and testing of novel inversion methods designed to distinguish between magnetic field and thermal perturbations.

This work is supported by NASA contracts NNH09CE41C and NNG07EI51C. Title: Local Helioseismology of Magnetoconvective Sunspot Simulations and the Reliability of Standard Inversion Methods Authors: Braun, Douglas; Birch, A.; Rempel, M.; Duvall, T.; J. Bibcode: 2011SPD....42.1607B Altcode: 2011BAAS..43S.1607B Controversy exists in the interpretation and modeling of helioseismic signals in and around magnetic regions like sunspots. We show the results of applying local helioseismic inversions to travel-time shift measurements from realistic magnetoconvective sunspot simulations. We compare travel-time maps made from several simulations, using different measurements (helioseismic holography and center-annulus time distance helioseismology), and made on real sunspots observed with the HMI instrument onboard the Solar Dynamics Observatory. We find remarkable similarities in the travel-time perturbations measured between: 1) simulations extending both 8 and 16 Mm deep, 2) the methodology (holography or time-distance) applied, and 3) the simulated and real sunspots. The application of RLS inversions, using Born approximation kernels, to narrow frequency-band travel-time shifts from the simulations demonstrates that standard methods fail to reliably reproduce the true wave speed structure. These findings emphasize the need for new methods for inferring the subsurface structure of active regions. Artificial Dopplergrams from our simulations are available to the community at www.hao.ucar.edu under "Data" and "Sunspot Models." This work is supported by NASA under the SDO Science Center project (contract NNH09CE41C). Title: Newly Identified Properties of Surface Acoustic Power Authors: Schunker, H.; Braun, D. C. Bibcode: 2011SoPh..268..349S Altcode: 2010SoPh..tmp..146S; 2010SoPh..tmp...76S; 2009arXiv0911.3042S The cause of enhanced acoustic power surrounding active regions, known as the acoustic halo, is not as yet understood. We explore the properties of the enhanced acoustic power observed near disk center from 21 to 27 January 2002, including AR 9787. We find that i) there exists a strong correlation of the enhanced high-frequency power with magnetic-field inclination, with greater power in more horizontal fields, ii) the frequency of the maximum enhancement increases along with magnetic-field strength, and iii) the oscillations contributing to the halos show modal ridges that are shifted to higher wavenumber at constant frequency in comparison to the ridges of modes in the quiet Sun. Title: The Need for Physics-based Inversions of Sunspot Structure and Flows Authors: Braun, D. C.; Birch, A. C.; Crouch, A. D.; Rempel, M. Bibcode: 2011JPhCS.271a2010B Altcode: Current controversy exists in the interpretation and modeling of helioseismic signals in and around magnetic regions like sunspots. Unresolved issues include the dependence of the sign of both the inferred flows and wave speed on the type of filtering used, and the discrepancy between the relatively deep two-layer wave-speed models derived from standard time-distance methods and shallow, positive wave-speed models derived using forward models which include effects of mode conversion To make full use of the year-round, almost limb-to-limb, coverage provided by the Solar Dynamics Observatory, an efficient and reliable inversion method incorporating possible magnetic effects and the currently unexplained sensitivity to methodology is critical. Title: Properties of Near-surface Flows around Active Regions from Helioseismic Holography Authors: Braun, D. C.; Wan, K. Bibcode: 2011JPhCS.271a2007B Altcode: A variety of local-helioseismic analyses have shown ~50 m/s flows converging on active regions (ARs). We have examined the average properties of both the 75 strongest converging and 75 strongest diverging flows present in Carrington rotation CR1988 within the uppermost 3 Mm of the Sun. The flows, averaged over 5 days, were deduced from calibrated helioseismic holography measurements applied to MDI observations of CR1988. Inflows associated with ARs typically have maximum speed of between 20 and 60 m/s at about 3 heliocentric degrees from their centers and fall to zero by a radius of 7 degrees. Similar converging flows, however, are prevalent in the quiet Sun. Outflows of similar spatial extent, but signficantly larger speeds, are present diverging from sunspots (i.e. the moat flows). Many of the converging flows in ARs appear to simply mark the boundaries of the moats while others converge on plage regions. In general, large ARs containing sunspots contain a complex mixture of both inflows and outflows which, aside from sunspot moats, also appear similar in property to convective components of the quiet Sun. Title: Sunspot Seismology with the Solar Dynamics Observatory Helioseismic and Magnetic Imager Authors: Braun, D. C.; Birch, A. C.; Crouch, A. D.; Clack, C.; Dombroski, D.; Rempel, M. Bibcode: 2010AGUFMSH14A..05B Altcode: The Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) promises to yield detailed information about the subsurface dynamics and structure of solar active regions. A SDO Science Center was recently funded and initiated by NASA to (among other goals) enable the reliable measurements of subsurface flow, magnetic field, and sound speed in regions of strong magnetic fields. Using analyses of sunspots observed with HMI/SDO, we illustrate the challenges of this goal and suggest a plan for the development and implementation of new physics-based modeling of the subsurface structure of sunspots. Key components of this effort will be discussed, including numerical forward modeling of the wave propagation through model sunspots. These efforts incorporate both magnetostatic and magneto-convective models. This work is supported by the NASA SDO Science Center and Heliophysics GI programs through contracts NNH09CE41C and NNG07EI51C. Title: An Estimate of the Detectability of Rising Flux Tubes Authors: Birch, A. C.; Braun, D. C.; Fan, Y. Bibcode: 2010ApJ...723L.190B Altcode: The physics of the formation of magnetic active regions (ARs) is one of the most important problems in solar physics. One main class of theories suggests that ARs are the result of magnetic flux that rises from the tachocline. Time-distance helioseismology, which is based on measurements of wave propagation, promises to allow the study of the subsurface behavior of this magnetic flux. Here, we use a model for a buoyant magnetic flux concentration together with the ray approximation to show that the dominant effect on the wave propagation is expected to be from the roughly 100 m s-1 retrograde flow associated with the rising flux. Using a B-spline-based method for carrying out inversions of wave travel times for flows in spherical geometry, we show that at 3 days before emergence the detection of this retrograde flow at a depth of 30 Mm should be possible with a signal-to-noise level of about 8 with a sample of 150 emerging ARs. Title: Modeling the Subsurface Structure of Sunspots Authors: Moradi, H.; Baldner, C.; Birch, A. C.; Braun, D. C.; Cameron, R. H.; Duvall, T. L.; Gizon, L.; Haber, D.; Hanasoge, S. M.; Hindman, B. W.; Jackiewicz, J.; Khomenko, E.; Komm, R.; Rajaguru, P.; Rempel, M.; Roth, M.; Schlichenmaier, R.; Schunker, H.; Spruit, H. C.; Strassmeier, K. G.; Thompson, M. J.; Zharkov, S. Bibcode: 2010SoPh..267....1M Altcode: 2009arXiv0912.4982M; 2010SoPh..tmp..171M While sunspots are easily observed at the solar surface, determining their subsurface structure is not trivial. There are two main hypotheses for the subsurface structure of sunspots: the monolithic model and the cluster model. Local helioseismology is the only means by which we can investigate subphotospheric structure. However, as current linear inversion techniques do not yet allow helioseismology to probe the internal structure with sufficient confidence to distinguish between the monolith and cluster models, the development of physically realistic sunspot models are a priority for helioseismologists. This is because they are not only important indicators of the variety of physical effects that may influence helioseismic inferences in active regions, but they also enable detailed assessments of the validity of helioseismic interpretations through numerical forward modeling. In this article, we provide a critical review of the existing sunspot models and an overview of numerical methods employed to model wave propagation through model sunspots. We then carry out a helioseismic analysis of the sunspot in Active Region 9787 and address the serious inconsistencies uncovered by Gizon et al. (2009a, 2009b). We find that this sunspot is most probably associated with a shallow, positive wave-speed perturbation (unlike the traditional two-layer model) and that travel-time measurements are consistent with a horizontal outflow in the surrounding moat. Title: Erratum: Erratum to: Helioseismology of Sunspots: A Case Study of NOAA Region 9787 Authors: Gizon, L.; Schunker, H.; Baldner, C. S.; Basu, S.; Birch, A. C.; Bogart, R. S.; Braun, D. C.; Cameron, R.; Duvall, T. L.; Hanasoge, S. M.; Jackiewicz, J.; Roth, M.; Stahn, T.; Thompson, M. J.; Zharkov, S. Bibcode: 2010SSRv..156..257G Altcode: 2010SSRv..tmp...99G No abstract at ADS Title: Modeling the Sensitivity of Helioseismic Measurements to Magnetic Fields and Thermal Perturbations Authors: Crouch, Ashley D.; Birch, A.; Braun, D. Bibcode: 2010AAS...21631906C Altcode: 2010BAAS...41Q.910C We will discuss recent progress in modeling the interaction of helioseismic waves with magnetic fields and thermal perturbations. We employ a background model that is translation-invariant in the horizontal directions, has a realistic stratification in the vertical direction, and includes uniform, inclined magnetic fields. Physically consistent boundary conditions for the waves are implemented at the upper and lower boundaries of the model. Using this model we generate synthetic data and subsequently measure time-distance travel times. We will show the sensitivity of these travel times to magnetic fields and changes in sound speed. We will show the effect of magnetic fields on inversions for wave speed. We will discuss how these results relate to the local heliseismology of sunspots. This work is supported by NASA contracts NNH09CE41C and NNG07EI51C. Title: Developing Physics-Based Procedures for Local Helioseismic Probing of Sunspots and Magnetic Regions Authors: Birch, Aaron; Braun, D. C.; Crouch, A.; Rempel, M.; Fan, Y.; Centeno, R.; Toomre, J.; Haber, D.; Hindman, B.; Featherstone, N.; Duvall, T., Jr.; Jackiewicz, J.; Thompson, M.; Stein, R.; Gizon, L.; Cameron, R.; Saidi, Y.; Hanasoge, S.; Burston, R.; Schunker, H.; Moradi, H. Bibcode: 2010AAS...21630805B Altcode: We have initiated a project to test and improve the local helioseismic techniques of time-distance and ring-diagram analysis. Our goals are to develop and implement physics-based methods that will (1) enable the reliable determinations of subsurface flow, magnetic field, and thermal structure in regions of strong magnetic fields and (2) be quantitatively tested with realistic solar magnetoconvection simulations in the presence of sunspot-like magnetic fields. We are proceeding through a combination of improvements in local helioseismic measurements, forward modeling of the helioseismic wavefield, kernel computations, inversions, and validation through numerical simulations. As improvements over existing techniques are made they will be applied to the SDO/HMI observations. This work is funded through the the NASA Heliophysics Science Division through the Solar Dynamics Observatory (SDO) Science Center program. Title: Tests of Helioseismic Holography Sound-Speed Inversions Using Synthetic Data Authors: Birch, Aaron; Braun, D.; Crouch, A.; Parchevsky, K.; Kosovichev, A. Bibcode: 2010AAS...21640006B Altcode: 2010BAAS...41..855B Helioseismic holography is an important method for measuring physical conditions in the solar interior. Synthetic data is a powerful tool for validating the methods of local helioseismology. Here we show some example inversions of surface-focusing holography measurements of synthetic data sets. We show that Born-approximation based inversions of phase-speed and ridge-filtered measurements yield models that are consistent with the true sound-speed structure in some simple test cases. This work is supported by NASA contracts NNH09CE41C and NNG07EI51C. Title: How Much Data Do We Need to Detect the Deep Solar Meridional Circulation? Authors: Braun, D. C.; Birch, A. C. Bibcode: 2009ASPC..416..131B Altcode: We assess the noise in p-mode travel-time shifts which would form the basis of inferences of large-scale flows throughout the solar convection zone. We derive the expected travel times from a parameterized return flow component of the meridional circulation. We show that a helioseismic detection of the return component may not be possible using data spanning an interval less than a solar cycle. Title: The Internal Dynamics and Magnetism of the Sun -- the Perspective from Local Helioseismology (Invited) Authors: Braun, D. C. Bibcode: 2009AGUFMSH11B..03B Altcode: The application of innovative local helioseismic methods to solar observations made with GONG, MDI, and other instruments over the past two decades has shed light on dynamical and magnetic processes in the solar interior. The community now stands poised for the onslaught of new data of unprecedented quality and quantity from the SDO mission. However, we are already substantially benefiting from the appearance of sophisticated numerical analyses and artificial data products. I will touch upon three problems in local helioseismology which are subject to substantive renewed efforts: the deep meridional circulation, the detection of magnetic flux prior to its appearance at the photosphere, and the subsurface nature of sunspots. All three problems pose major challenges, but there is considerable hope for breakthroughs within the next few years. DCB acknowledges support from NSF grant AST-0406225; NASA contracts NNH09CE41C, NNG07EI51C, and NNH07CD25C; and a subcontract from the NASA sponsored HMI project at Stanford University. Title: Numerical sunspot models - subsurface structure and helioseismic forward modeling (Invited) Authors: Rempel, M.; Birch, A. C.; Braun, D. C. Bibcode: 2009AGUFMSH11B..02R Altcode: The magnetic and thermal subsurface structure of sunspots has been debated for decades. While local helioseismic inversions allow in principle to constrain the subsurface structure of sunspots, a full inversion is still not possible due to the complicated interaction between waves and magnetic field. As an alternative it is possible to address this problem through forward modeling. Over the past few years numerical MHD models of entire sunspots including radiative transfer and a realistic equation of state have become possible. These simulations include p-modes excited by convection and the full interaction of these modes with the magnetic and thermal structure of the sunspot. In this talk I will present recent progress in MHD modeling of sunspots with special emphasis on the thermal and magnetic structure of numerical sunspot models. It turns out that modeled sunspots so far impose rather shallow perturbations to sound and fast mode speeds in the upper most 2 Mm. Nevertheless the seismic signatures are very similar to observed sunspots. Title: Improving the Prediction Capability of Seismic Far-Side Maps Authors: González Hernández, I.; Scherrer, P.; Hill, F.; Lindsey, C.; Braun, D. Bibcode: 2009ASPC..416...87G Altcode: Both the Michelson Doppler Imager (MDI) and the Global Oscillation Network Group (GONG) projects produce daily seismic maps of surface magnetic activity on the non-visible hemisphere of the Sun. The technique has proven useful to detect and follow large active regions before they appear to face the Earth. This work demonstrates an improvement in the detection capability of the technique by applying the results of new research. We calibrate the daily far-side maps in terms of characteristics of the active region, such as total area and magnetic flux strength, apply a relationship between the strength of the persistent signal and the success rate to automatically highlight possible candidates, and remove solar-cycle variations to stabilize the signal. Title: Absorption of p Modes by Magnetic Plage Authors: Jain, R.; Hindman, B. W.; Braun, D. C.; Birch, A. C. Bibcode: 2009ASPC..416...55J Altcode: The Sun's magnetic active regions, composed of sunspots and plage, are topologically complex. The magnetic field is highly structured, forming a tangle of fibrils within the plage and more compact, regimented bundles within sunspot umbrae. The fragmented nature of the field makes helioseismic observations within active regions rather difficult to interpret. We choose to study the propagation of acoustic waves through regions of plage, modeling the magnetic field therein as a collection of thin flux tubes. In this paper, we present the first results of this research; the computation of the absorption coefficient from an ensemble of many flux tubes. The incoming acoustic waves interact with the magnetic flux tube, exciting sausage and kink tube waves which propagate downward and upward carrying away energy, thereby producing absorption. We calculate the resulting theoretical absorption coefficients and compare with the most recent observations. Title: Detecting, Selecting, And Controlling For Emerging ActiveRegions In The Search For Helioseismic Pre-emergence Signatures. Authors: Leka, K. D.; Dunn, T.; Gonzalez-Hernandez, I.; Barnes, G.; Braun, D.; Birch, A. Bibcode: 2009SPD....40.0708L Altcode: Helioseismology is potentially capable of predicting the emergence of solaractive regions. As part of a search for statistically significant helioseismic predictors of active region emergence, we have developed methods for the automatic determination of emergence times based on the NOAA/NGDC active region catalog and MDI/SOHO 96 minute magnetograms. We demonstrate the application of this method and its sister task of selecting an appropriate control sample. We show first results from a statistical study investigating the pre-emergence signatures of Solar Active Regions using GONG data. This work was supported by NASA contract NNH07CD25C. Title: A Search for Pre-Emergence Signatures of Active Regions Authors: Birch, Aaron; Braun, D. C.; Leka, K. D.; Barnes, G.; Dunn, T. L.; González Hernández, I. Bibcode: 2009SPD....40.0402B Altcode: Prediction of solar active region emergence is an important goal for helioseismology. As a first step towards developing prediction methods, we are carrying out a search for helioseismic pre-emergence signatures. Using GONG data, we have applied helioseismic holography to about 150 pre-emergence active regions and a control sample of 450 quiet-Sun regions. We will show preliminary results of this study.

This work was supported by NASA contract NNH07CD25C Title: Helioseismology of a Realistic MHD Sunspot Simulation Authors: Braun, Douglas; Birch, A. C.; Rempel, M. Bibcode: 2009SPD....40.0303B Altcode: We have recently measured travel times and absorption of p modes propagating through a realistic numerical model of solar convection in the presence of a sunspot-like structure. Both the mean travel-time perturbations and the absorption in the simulation are remarkably similar to those observed in typical sunspots. Therefore, simulations of this type provide both the means to understand the physics behind the helioseismic observations and the opportunity to validate existing and future models of the subsurface structure of sunspots. We will compare helioseismic measurements made with the simulation with those of a typical sunspot observed with MDI. We will discuss the implications of these comparisons for structural inversions of sunspots and understanding the role of MHD mode conversion in interpreting helioseismic observations. This work is supported by NASA contracts NNH09CE41C and NNG07EI51C. Title: Statistical Analysis of the Success Rate of the Far-Side Seismic Mapping of Active Regions. Authors: Gonzalez-Hernandez, Irene; Scherrer, P.; Lindsey, C.; Hill, F.; Braun, D. Bibcode: 2009SPD....40.0707G Altcode: Seismic maps of the non-visible side of the Sun (far side) have been used for almost a decade to follow large active regions before they rotate to face the Earth. Preliminary efforts to quantify the success rate of the used technique (seismic holography) have been published with limited data. However, a thorough study is needed to further understand the limitations of the technique in terms of size and strength of the active regions detected and to reveal clues as to how to improve it.

We have analyzed three complete years of far-side seismic maps calculated using both Global Oscillation Newtwork group (GONG) and Michelson Doppler Imager (MDI) data and matched the far-side candidates with associated active regions as recorded by the NOAA database. Here we present the results. Title: Helioseismic Inversions applied to a Realistic MHD Sunspot Simulation Authors: Birch, Aaron; Braun, D. C.; Rempel, M. Bibcode: 2009SPD....40.0713B Altcode: Local helioseismology applied to the realistic magneto-convection sunspot simulations of Rempel et al. produces solar-like wave travel times. We apply standard ray-theory based inversions to infer subsurface wave speed from these travel times. We find that the inferred wave-speed perturbations are similar to the wave-speed perturbations found from the analysis of typical sunspots observed with MDI. We show, however, that the ray theory inversions fail to retrieve the true time-averaged sound speed or fast-mode speed from the simulations. We propose some alternative strategies for inferring the subsurface structure of sunspots.

This work is supported by NASA contracts NNH09CE41C and NNG07EI51C. Title: Helioseismology of Sunspots: A Case Study of NOAA Region 9787 Authors: Gizon, L.; Schunker, H.; Baldner, C. S.; Basu, S.; Birch, A. C.; Bogart, R. S.; Braun, D. C.; Cameron, R.; Duvall, T. L.; Hanasoge, S. M.; Jackiewicz, J.; Roth, M.; Stahn, T.; Thompson, M. J.; Zharkov, S. Bibcode: 2009SSRv..144..249G Altcode: 2008SSRv..tmp..188G; 2010arXiv1002.2369G Various methods of helioseismology are used to study the subsurface properties of the sunspot in NOAA Active Region 9787. This sunspot was chosen because it is axisymmetric, shows little evolution during 20-28 January 2002, and was observed continuously by the MDI/SOHO instrument. AR 9787 is visible on helioseismic maps of the farside of the Sun from 15 January, i.e. days before it crossed the East limb. Oscillations have reduced amplitudes in the sunspot at all frequencies, whereas a region of enhanced acoustic power above 5.5 mHz (above the quiet-Sun acoustic cutoff) is seen outside the sunspot and the plage region. This enhanced acoustic power has been suggested to be caused by the conversion of acoustic waves into magneto-acoustic waves that are refracted back into the interior and re-emerge as acoustic waves in the quiet Sun. Observations show that the sunspot absorbs a significant fraction of the incoming p and f modes around 3 mHz. A numerical simulation of MHD wave propagation through a simple model of AR 9787 confirmed that wave absorption is likely to be due to the partial conversion of incoming waves into magneto-acoustic waves that propagate down the sunspot. Wave travel times and mode frequencies are affected by the sunspot. In most cases, wave packets that propagate through the sunspot have reduced travel times. At short travel distances, however, the sign of the travel-time shifts appears to depend sensitively on how the data are processed and, in particular, on filtering in frequency-wavenumber space. We carry out two linear inversions for wave speed: one using travel-times and phase-speed filters and the other one using mode frequencies from ring analysis. These two inversions give subsurface wave-speed profiles with opposite signs and different amplitudes. The travel-time measurements also imply different subsurface flow patterns in the surface layer depending on the filtering procedure that is used. Current sensitivity kernels are unable to reconcile these measurements, perhaps because they rely on imperfect models of the power spectrum of solar oscillations. We present a linear inversion for flows of ridge-filtered travel times. This inversion shows a horizontal outflow in the upper 4 Mm that is consistent with the moat flow deduced from the surface motion of moving magnetic features. From this study of AR 9787, we conclude that we are currently unable to provide a unified description of the subsurface structure and dynamics of the sunspot. Title: Surface-Focused Seismic Holography of Sunspots: II. Expectations from Numerical Simulations Using Sound-Speed Perturbations Authors: Birch, A. C.; Braun, D. C.; Hanasoge, S. M.; Cameron, R. Bibcode: 2009SoPh..254...17B Altcode: 2008SoPh..tmp..186B Helioseismic observations of sunspots show that wave travel times, at fixed horizontal phase speed, depend on the temporal frequency of the waves employed in the data analysis. This frequency variation has been suggested to be consistent with near-surface (vertical length scales of order one Mm or smaller) changes in wave propagation properties relative to the quiet Sun. We investigate this suggestion by employing numerical simulations of acoustic-wave propagation through models with horizontally and vertically inhomogeneous structure. Standard methods of surface-focused helioseismic holography are applied to the resulting simulated wave fields. We find that the travel-time shifts measured using holography from the simulations with deep sound-speed perturbations (relative to a plane-parallel quiet-Sun model) do not show a systematic frequency dependence at phase speeds above about 20 km s−1. However, shallow sound-speed perturbations, similar to those proposed to model the acoustic scattering properties of sunspots observed with Hankel analysis, produce systematic frequency dependence at these phase speeds. In both cases, positive travel-time shifts can be caused by positive sound-speed perturbations. The details of the travel-time shifts are, however, model dependent. Title: Magnetic flux emergence on the Sun and Sun-like stars Authors: Rempel, Matthias; Fan, Yuhong; Birch, Aaron; Braun, Douglas Bibcode: 2009astro2010S..74R Altcode: 2009astro2010S..74F No abstract at ADS Title: Helioseismology of Sunspots: A Case Study of NOAA Region 9787 Authors: Gizon, L.; Schunker, H.; Baldner, C. S.; Basu, S.; Birch, A. C.; Bogart, R. S.; Braun, D. C.; Cameron, R.; Duvall, T. L.; Hanasoge, S. M.; Jackiewicz, J.; Roth, M.; Stahn, T.; Thompson, M. J.; Zharkov, S. Bibcode: 2009odsm.book..249G Altcode: Various methods of helioseismology are used to study the subsurface properties of the sunspot in NOAA Active Region 9787. This sunspot was chosen because it is axisymmetric, shows little evolution during 20-28 January 2002, and was observed continuously by the MDI/SOHO instrument. AR 9787 is visible on helioseismic maps of the farside of the Sun from 15 January, i.e. days before it crossed the East limb. Title: Prospects for the Detection of the Deep Solar Meridional Circulation Authors: Braun, Douglas; Birch, A. C. Bibcode: 2009AAS...21349202B Altcode: 2009BAAS...41..471B We perform helioseismic holography to assess the noise in p-mode travel-time shifts which would form the basis of inferences of large-scale flows throughout the solar convection zone. We also derive the expected travel times from a parameterized return (equatorward) flow component of the meridional circulation at the base of the convection zone from forward models under the assumption of the Born approximation. From estimations of the signal-to-noise ratio for measurements focused near the base of the convection zone, we conclude that the helioseismic detection of the deep meridional flow including the return component may not be possible using data spanning an interval less than a solar cycle. Title: Prospects for the Detection of the Deep Solar Meridional Circulation Authors: Braun, D. C.; Birch, A. C. Bibcode: 2008ApJ...689L.161B Altcode: 2008arXiv0810.0284B We perform helioseismic holography to assess the noise in p-mode travel-time shifts which would form the basis of inferences of large-scale flows throughout the solar convection zone. We also derive the expected travel times from a parameterized return (equatorward) flow component of the meridional circulation at the base of the convection zone from forward models under the assumptions of the ray and Born approximations. From estimates of the signal-to-noise ratio for measurements focused near the base of the convection zone, we conclude that the helioseismic detection of the deep meridional flow including the return component may not be possible using travel-time measurements spanning an interval less than a solar cycle. We speculate that this conclusion may be generally true for other helioseismic methods under the assumption that the underlying measurements are equivalently limited by solar realization noise. Title: Physical Properties of Wave Motion in Inclined Magnetic Fields within Sunspot Penumbrae Authors: Schunker, H.; Braun, D. C.; Lindsey, C.; Cally, P. S. Bibcode: 2008SoPh..251..341S Altcode: 2008arXiv0801.4448S; 2008SoPh..tmp...41S At the surface of the Sun, acoustic waves appear to be affected by the presence of strong magnetic fields in active regions. We explore the possibility that the inclined magnetic field in sunspot penumbrae may convert primarily vertically-propagating acoustic waves into elliptical motion. We use helioseismic holography to measure the modulus and phase of the correlation between incoming acoustic waves and the local surface motion within two sunspots. These correlations are modeled by assuming the surface motion to be elliptical, and we explore the properties of the elliptical motion on the magnetic-field inclination. We also demonstrate that the phase shift of the outward-propagating waves is opposite to the phase shift of the inward-propagating waves in stronger, more vertical fields, but similar to the inward phase shifts in weaker, more-inclined fields. Title: Surface-Focused Seismic Holography of Sunspots: I. Observations Authors: Braun, D. C.; Birch, A. C. Bibcode: 2008SoPh..251..267B Altcode: 2008arXiv0802.2652B; 2008SoPh..tmp...46B We present a comprehensive set of observations of the interaction of p-mode oscillations with sunspots using surface-focused seismic holography. Maps of travel-time shifts, relative to quiet-Sun travel times, are shown for incoming and outgoing p modes as well as their mean and difference. We compare results using phase-speed filters with results obtained with filters that isolate single p-mode ridges, and we further divide the data into multiple temporal frequency bandpasses. The f mode is removed from the data. The variations of the resulting travel-time shifts with magnetic-field strength and with the filter parameters are explored. We find that spatial averages of these shifts within sunspot umbrae, penumbrae, and surrounding plage often show strong frequency variations at fixed phase speed. In addition, we find that positive values of the mean and difference travel-time shifts appear exclusively in waves observed with phase-speed filters that are dominated by power in the low-frequency wing of the p1 ridge. We assess the ratio of incoming to outgoing p-mode power using the ridge filters and compare surface-focused holography measurements with the results of earlier published p-mode scattering measurements using Fourier - Hankel decomposition. Title: Combining far-side maps from MDI and GONG to improve the prediction capability Authors: Gonzalez Hernandez, I.; Scherrer, P.; Lindsey, C.; Braun, D.; Hill, F. Bibcode: 2008AGUSMSP41A..04G Altcode: Both the Michaelson Doppler Imager (MDI) and the Global Oscillation Network Group (GONG) projects produce daily seismic maps of surface magnetic activity at the non-visible hemisphere the Sun. The technique has proven useful in order to detect and follow large active regions before they appear to face the Earth. This work explores the possibility of improving the detection capability of the technique by combining the results from both instruments. The research should lead to a better understanding of the spurious, non persistent seismic signal associated with the far-side images and better discrimination between solar and instrumental noise. Title: Helioseismic Holography of Simulated Solar Convection and Prospects for the Detection of Small-Scale Subsurface Flows Authors: Braun, D. C.; Birch, A. C.; Benson, D.; Stein, R. F.; Nordlund, Å. Bibcode: 2007ApJ...669.1395B Altcode: 2007arXiv0708.0214B We perform helioseismic holography on realistic solar convection simulations and compare the observed travel-time perturbations with the expected travel times from the horizontal flows in the simulations computed from forward models under the assumption of the Born approximation. We demonstrate reasonable agreement between the observed and model travel times, which reinforces the validity of helioseismic holography in the detection of subsurface horizontal flows. An assessment is made of the uncertainty of the measured p-mode travel times from the rms of the residuals. From the variation of the signal-to-noise ratio with depth we conclude that the helioseismic detection of individual flow structures with spatial scales of supergranulation or smaller is not possible for depths below about 5 Mm below the surface over timescales of less than a day. The travel-time noise estimated from these simulations appears to be similar to noise in measurements made using solar observations. We therefore suggest that similar limitations exist regarding the detection of analogous subsurface flows in the Sun. A study of the depth dependence of the contribution to the travel-time perturbations for focus depths between 3 and 7 Mm is made, showing that approximately half of the observed signal originates within the first 2 Mm below the surface. A consequence of this is a rapid decrease (and reversal in some cases) of the travel-time perturbations with depth due to the contribution to the measurements of oppositely directed surface flows in neighboring convective cells. This confirms an earlier interpretation of similar effects reported from observations of supergranulation. Title: Helioseismic Holography of Simulated Solar Convection and Prospects for the Detection of Small-Scale Subsurface Flows Authors: Braun, Douglas; Birch, A. C.; Benson, D.; Stein, R. F.; Nordlund, A. Bibcode: 2007AAS...210.2201B Altcode: 2007BAAS...39..124B We perform helioseismic holography on the solar convection simulations of Benson, Stein, and Nordlund and compare the observed acoustic travel-time perturbations with the expected travel times from the horizontal flows in the simulations computed from forward models under the assumption of the Born approximation. The agreement between the observed and model travel times reinforces the validity of helioseismic holography in the detection of subsurface horizontal flows. However, from the variation of the signal-to-noise ratio with depth, we conclude that the local helioseismic detection of individual supergranule-size (or smaller) flow patterns is not possible for depths below about 5 Mm below the surface over time scales less than a day. We suggest that similar limitations exist regarding the detection of analogous subsurface flows in the Sun. We also study the depth dependence of the contribution to the travel-time perturbations for the simulated flows. For holography measurements focused down to 7 Mm, we find that approximately half of the observed signal originates within the first 2 Mm below the surface. A consequence of this is a a rapid decrease (and possible reversal) of the travel-time perturbations with increasing focus depth due to the contribution to the measurements of oppositely directed surface flows in neighboring convective cells. This confirms an earlier interpretation of similar effects reported from holographic analyses of observations of supergranulation.

This work is supported by NASA contracts NNH05CC76C and NNH04CC05C, NSF grant AST-0406225 , and a subcontract through the HMI project at Stanford University awarded to NWRA, and by NASA grant NNG04GB92G and NSF grant AST-0605738 to MSU. Title: Sunspot Seismology: Testing Surface Effects with Numerical Simulations Authors: Braun, Douglas; Birch, A. C.; Hanasoge, S. M. Bibcode: 2007AAS...210.2206B Altcode: 2007BAAS...39..125B The discovery that sunspots absorb acoustic waves was first announced twenty years ago at a previous SPD meeting in Honolulu. A considerable effort has been made to understand the physics of the interaction between acoustic waves and sunspots. However, the implications of this two-decade old discovery are still being explored in helioseismology. An ongoing controversy involves the role of surface effects, including absorption, in modeling the subsurface structure of sunspots. Braun and Birch recently suggested that observed frequency variations, at fixed phase speeds, of acoustic travel-time perturbations through sunspots offers evidence for a strong contribution to travel times from structures with vertical scales smaller than about one Mm near the solar surface. We test this suggestion with the numerical simulations of acoustic-wave propagation hrough specified sound-speed perturbations of a background solar model. An important finding is that travel times measured using helioseismic holography from simulations employing sound-speed perturbations typical of recent time-distance inversions do not predict the strong frequency variations observed in with solar data. We are in the process of evaluating whether shallow sound-speed perturbations, such as that proposed by Fan, Braun and Chou to explain the acoustic scattering propertis of sunspots observed with Hankel analysis, can reproduce the frequency variations observed in sunspots.

This work is supported by contracts NAS5-02139, NNH05CC76C and NNH04CC05C from NASA, and grant AST-0406225 from the NSF. Title: Surface magnetic field effects in local helioseismology Authors: Schunker, H.; Braun, D. C.; Cally, P. S. Bibcode: 2007AN....328..292S Altcode: 2010arXiv1002.2379S Using helioseismic holography strong evidence is presented that the phase (or equivalent travel-time) of helioseismic signatures in Dopplergrams within sunspots depend upon the line-of-sight angle in the plane containing the magnetic field and vertical directions. This is shown for the velocity signal in the penumbrae of two sunspots at 3, 4 and 5 mHz. Phase-sensitive holography demonstrates that they are significantly affected in a strong, moderately inclined magnetic field. This research indicates that the effects of the surface magnetic field are potentially very significant for local helioseismic analysis of active regions. Title: The Role of MHD Mode Conversion in Sunspot Seismology Authors: Crouch, A. P.; Cally, P. S.; Charbonneau, P.; Braun, D. C.; Desjardins, M. Bibcode: 2006ASPC..354..161C Altcode: Sunspots absorb energy from and shift the phase of f and p modes incident upon them. Understanding the mechanism causing each of these effects is vital to the local helioseismology of sunspots (and magnetic flux concentrations in general). Because the beta-equals-unity layer typically lies in the near surface layers below the photospheres of sunspot umbrae, MHD mode conversion can occur. Mode conversion provides a promising absorption mechanism because the slow magnetoacoustic-gravity waves and Alfvén waves guide energy along the magnetic field away from the acoustic cavity. Our previous mode conversion calculations have shown that simple sunspot models with non-vertical magnetic fields can produce ample absorption to explain the Hankel analysis measurements, along with phase shift predictions that agree well with the observations. Those calculations only considered the possibility of MHD waves propagating down the magnetic field into the interior. In this contribution, we consider a second additional possibility -- waves propagating up into the atmosphere overlying sunspots. Title: Behaviour of Acoustic Waves in Sunspots Authors: Schunker, H.; Braun, D. C.; Cally, P. S.; Lindsey, C. Bibcode: 2006ASPC..354..244S Altcode: Because helioseismology uses surface signals to calculate subsurface characteristics the behaviour of surface acoustic oscillations in sunspots is important in interpreting helioseismic results. SOHO-MDI Doppler velocity analysis of AR9026 and AR9033 at 3, 4, and 5 mHz, using helioseismic holography, show that the amplitude and the phase in the correlation of the acoustic ingression with the observed surface velocity are found to be sensitive to the relative line-of-sight angle in the penumbra of both sunspots. This is consistent with a conversion of vertically propagating acoustic waves into magneto-acoustic waves with motion described by ellipses. Title: Farside helioseismic holography: recent advances Authors: González Hernández, I.; Hill, F.; Lindsey, C.; Braun, D.; Scherrer, P.; Hanasoge, S. M. Bibcode: 2006ESASP.624E...3G Altcode: 2006soho...18E...3G No abstract at ADS Title: The interaction between acoustic waves and inclined magnetic fields near the β~1 layer Authors: Schunker, H.; Braun, D. C.; Cally, P. S.; Lindsey, C. Bibcode: 2006IAUJD..17E..16S Altcode: The acoustic showerglass effect may be hindering our helioseismic renditions of the solar subsurface. We present the results of near -surface wave conversion of acoustic waves in a model polytropic atmosphere by a uniform, inclined magnetic field. The upcoming fast, acoustic wave undergoes conversion to a slow, magnetic wave at the β ~ 1 layer where the sound speed and Alfven speed are comparable. The conversion is dependent upon the " attack angle" between the ray path and the magnetic field. The angle of the wave vectors at the polytropic " surface" is compared to observations of surface velocity vectors in sunspot penumbrae. AR9026 and AR9057 both have well- defined, static penumbrae and their Doppler velocities are viewed from different angles by SOHO-MDI as they cross the solar disk. The phase of the correlation between the ingression and surface velocity, determined by helioseismic holography, is used to assess the effect the penumbral magnetic field has on incoming acoustic waves. The phase is found to be dependent upon the line-of-sight of observation indicating that this is a surface phenomenon, which could otherwise be interpreted as subsurface travel-time perturbations of up to one minute. Furthermore, using vector magnetograms from the IVM at the Mees Observatory, the phase of the correlation is found to be dependent on the magnetic field tilt from vertical, and the dependence is consistent across the two sunspots. Comparing the results from the polytropic model with the observations show strong support for the near-surface wave conversion theory, although many questions still remain. Title: Observed Frequency Variations of Solar p-Mode Travel Times as Evidence for Surface Effects in Sunspot Seismology Authors: Braun, D. C.; Birch, A. C. Bibcode: 2006ApJ...647L.187B Altcode: Using helioseismic holography, we measure acoustic (p-mode) travel-time perturbations, observed within solar active regions, as functions of frequency and phase speed. We find evidence for a frequency variation, at fixed phase speed, of the travel times that has not previously been reported. This variation is not expected from typical sound-speed models of sunspots, which result from the inversion of travel times and may indicate a significant contribution to the travel times from structures with vertical scales smaller than about 1 Mm near the solar surface. Title: Farside Helioseismic Holography: Recent Advances Authors: Gonzalez-Hernandez, Irene; Braun, D. C.; Hanasoge, S. M.; Hill, F.; Lindsey, C. A.; Scherrer, P. H. Bibcode: 2006SPD....37.0502G Altcode: 2006BAAS...38Q.223G Both MDI and GONG have been calculating partial farside maps for some time, showing a high degree of agreement in detecting large active regions within approximately 45 degrees around the antipode of disk center.Recently, the full-hemisphere capability has been added to the farside pipelines of both instruments. We show here the capability of detecting large active regions and tracking them through out the full farside hemisphere by applying the technique to active region 10808.We also report on efforts underway to calibrate the farside signal in terms of equivalent magnetic field, including some preliminary maps obtained from artificial helioseismic data. Title: Genetic magnetohelioseismology with Hankel analysis data Authors: Crouch, A. D.; Cally, P. S.; Charbonneau, P.; Braun, D. C.; Desjardins, M. Bibcode: 2005MNRAS.363.1188C Altcode: 2005MNRAS.tmp..856C Hankel analysis determined that sunspots absorb energy from and shift the phase of f- and p-modes incident upon them. One promising mechanism that can explain the absorption is partial conversion to slow magnetoacoustic-gravity (MAG) waves and Alfvén waves, which guide energy along the magnetic field away from the acoustic cavity. Our recent mode conversion calculations demonstrated that simple sunspot models, which roughly account for the radial variation of the magnetic field strength and inclination, can produce ample absorption to explain the observations, along with phase shifts that agree remarkably well with the Hankel analysis data. In this paper, we follow the same approach, but adopt a more realistic model for the solar convection zone that includes the thermal perturbation associated with a sunspot's magnetic field. Consistent with our earlier findings, we show that a moderately inclined, uniform magnetic field exhibits significantly enhanced absorption (mode conversion) in comparison to a vertical field (depending on the frequency and radial order of the mode). A genetic algorithm is employed to adjust the parameters that control the radial structure of our sunspot models, in order to minimize the discrepancy between the theoretical predictions and the Hankel analysis measurements. For models that best fit the phase shifts, the agreement with the Hankel analysis data is excellent, and the corresponding absorption coefficients are generally in excess of the observed levels. On the other hand, for models that best fit the phase shift and absorption data simultaneously, the overall agreement is very good but the phase shifts agree less well. This is most likely caused by the different sizes of the regions responsible for the absorption and phase shift. Typically, the field strengths required by such models lie in the range 1-3kG, compatible with observations for sunspots and active regions. While there remain some uncertainties, our results provide further evidence that mode conversion is the predominant mechanism responsible for the observed absorption in sunspots; and that field inclination away from vertical is a necessary ingredient for any model that aims to simultaneously explain the phase shift and absorption data. Title: The GONG Farside Project Authors: Leibacher, J. W.; Braun, D.; González Hernández, I.; Goodrich, J.; Kholikov, S.; Lindsey, C.; Malanushenko, A.; Scherrer, P. Bibcode: 2005AGUSMSP11B..14L Altcode: The GONG program is currently providing near-real-time helioseismic images of the farside of the Sun. The continuous stream of low resolution images, obtained from the 6 earth based GONG stations, are merged into a single data series that are the input to the farside pipeline. In order to validate the farside images, it is crucial to compare the results obtained from different instruments. We show comparisons between the farside images provided by the MDI instrument and the GONG ones. New aditions to the pipeline will allow us to create full-hemisphere farside images, examples of the latest are shown in this poster. Our efforts are now concentrated in calibrating the farside signal so it became a reliable solar activity forecasting tool. We are also testing single-skip acoustic power holography at 5-7 mHz as a prospective means of reinforcing the signatures of active regions crossing the the east and west limb and monitoring acoustic emission in the neighborhoods of Sun's the poles. This work utilizes data obtained by the Global Oscillation Network Group (GONG) Program, managed by the National Solar Observatory, which is operated by AURA, Inc. under a cooperative agreement with the National Science Foundation. The data were acquired by instruments operated by the Big Bear Solar Observatory, High Altitude Observatory, Learmonth Solar Observatory, Udaipur Solar Observatory, Instituto de Astrofisico de Canarias, and Cerro Tololo Interamerican Observatory, as well as the Michaelson Doppler Imager on SoHO, a mission of international cooperation between ESA and NASA. This work has been supported by the NASA Living with a Star - Targeted Research and Technology program. Title: Flow Inversions for Phase-Sensitive Helioseismic Holography Authors: Birch, A. C.; Braun, D. C. Bibcode: 2005AGUSMSP24A..05B Altcode: Phase-sensitive holography has been used extensively to study solar subsurface mass flows. To date though, the ingression-egression correlation phases measured using phase-sensitive holography data have never been inverted. We present an inversion procedure, based on Born-approximation sensitivity functions and the MCD algorithm, for estimating subsurface flows from phase-sensitive holography measurements. We present some simple validation tests and example flow maps resulting from inversions of SOHO/MDI data. Title: Comparison of Solar Subsurface Velocities Using Small-Scale Ring Analysis, Time-Distance and Holography Authors: Haber, D. A.; Featherstone, N. A.; Braun, D. C.; Hindman, B. W.; Bogart, R. S. Bibcode: 2005AGUSMSP24A..01H Altcode: For the first time we compare subsurface horizontal velocity flows determined by all three common local helioseismic analysis methods on a very small scale (approximately 1-2 degrees). Holographic and time-distance techniques have been compared on small scales, however, ring analysis techniques have mainly been performed with 15 degree size tiles spaced 7.5 degrees apart. Here we use tiles approximately 2 degrees in size with a spacing of 1 degree and compare the results with those of time-distance and holography. All three techniques have been applied to full-disc Doppler velocity data with 4" resolution (0.2 deg at disc center) taken with the Michelson Doppler Imager instrument aboard SOHO during Carrington Rotation 1988 in March-April of 2002. Title: Towards Assessing, Understanding, and Correcting the Influence of Surface Magnetism in Local Helioseismology Authors: Braun, D. C.; Schunker, H.; Lindsey, C.; Cally, P. S. Bibcode: 2005AGUSMSP23C..03B Altcode: Efforts to probe subsurface wave-speed variations and mass flows near and under solar active regions are complicated and potentially compromised by strong phase and amplitude perturbations introduced in the photosphere by magnetic fields. Recently it has been shown that the phase distortions correlate with surface magnetic field strength and may be corrected to image wave-speed variations underlying active regions. A strong phase asymmetry between waves arriving into and departing from a magnetic region is also shown to produce spurious signatures of horizontal outflows below active regions. Further evidence of the photospheric origin of these phase distortions, as well as a key to their physical origin, is also presented. Using MDI observations, from the SOHO spacecraft, we perform ingression control correlations in the inclined magnetic fields of sunspot penumbra and demonstrate that incoming acoustic waves produce photospheric motion that describes an ellipse tilted towards the inclination of the magnetic field. A consequence is that the phase of the correlation varies with the viewing angle with respect to the field direction. Observations of the vector components of the photospheric fields could be used to correct these phase perturbations analogous to the procedures already developed using line-of-sight magnetograms. A physical understanding of surface distortions will come through MHD modeling, including simulations of the interaction of acoustic and magneto-acoustic-gravity waves with prescribed magnetic and sound-speed perturbations and flows (artificial data). The development of appropriate tools for assessing and correcting the effects of the surface magnetism will be vital for the interpretation of helioseismic data from the upcoming HMI mission on SDO. DCB and CL gratefully acknowledge support from the NSF (SAA/AST) and NASA (LWS, SR&T). Title: The Local Helioseismology of Inclined Magnetic Fields and the Showerglass Effect Authors: Schunker, H.; Braun, D. C.; Cally, P. S.; Lindsey, C. Bibcode: 2005ApJ...621L.149S Altcode: We present evidence for the dependence of helioseismic Doppler signatures in active regions on the line-of-sight angle in inclined magnetic fields. Using data from the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory, we performed phase-sensitive holography in the penumbrae of sunspots over the course of several days as the spots traversed the solar disk. Control correlations, which comprise a correlation of the surface wave amplitude with the incoming acoustic wave amplitude from a surrounding region, were mapped. There is a direct dependence of control-correlation phase signatures on the line-of-sight angle in the plane defined by the vertical and magnetic field vectors. The phase shift of waves observed along directions close to the orientation of the magnetic field is smaller than the phase shift observed when the line of sight is at a significant angle with respect to the field orientation. These findings have important implications for local helioseismology. The variation in phase shift (or the equivalent acoustic travel-time perturbations) with line-of-sight direction suggests that a substantial portion of the phase shift occurs in the photospheric magnetic field. Observations of the vector components of the field may be used to develop a proxy to correct these phase perturbations (known as the acoustic showerglass) that introduce uncertainties in the signatures of acoustic perturbations below the surface. Title: The Acoustic Showerglass. I. Seismic Diagnostics of Photospheric Magnetic Fields Authors: Lindsey, Charles; Braun, D. C. Bibcode: 2005ApJ...620.1107L Altcode: A problem of major interest in the helioseismology of active regions is the acoustics of magnetic photospheres and shallow subphotospheres. Magnetic fields suppress the photospheric signatures of acoustic waves impinging onto them from the underlying solar interior and shift their phases. The phase shifts function as a sort of acoustic showerglass that impairs the coherence of seismic waves arriving from below, degrading images of subsurface anomalies derived by mechanical reconstruction of phase-coherent waves. The purpose of this study is to characterize the ``acoustic showerglass'' in general optical terms and make a rough practical assessment of its impact on local seismic diagnostics of the shallow subphotospheres of active regions. We compile statistics comparing the acoustic field in magnetic photospheres with holographic projections of waves arriving from distant surrounding pupils. These ``local control correlations'' are consistent with an acoustic anomaly in the shallow subphotosphere of the active region that is strong but predominantly superficial; we call this the ``acoustic Wilson depression.'' The local control correlations also exhibit a phenomenon we call the ``penumbral acoustic anomaly,'' characterized by a conspicuous phase shift in regions of inclined magnetic field. This appears to be consistent with a fairly straightforward hydromechanical interpretation of the interaction of acoustic waves with photospheric magnetic forces. Detailed numerical simulations of the interaction of acoustic waves with magnetic forces can greatly facilitate our understanding of the acoustic showerglass and the thermal structure of the top few hundred kilometers of active region subphotospheres. Title: The Acoustic Showerglass. II. Imaging Active Region Subphotospheres Authors: Lindsey, Charles; Braun, D. C. Bibcode: 2005ApJ...620.1118L Altcode: Seismic diagnostics of the shallow subphotospheres of strong active regions are substantially impacted by large amplitude and phase perturbations introduced by overlying surface magnetic fields. These function as an ``acoustic showerglass'' that impairs the coherence of acoustic waves impinging onto the solar surface from below, degrading images of subsurface anomalies derived by phase-coherent seismic reconstruction. In an independent study we have developed a rough proxy to characterize showerglass phase errors based on maps of the square magnitude of the vector magnetic field at the surface. In this study we apply the proxy to correct helioseismic observations of active region photospheres from the Michelson Doppler Imager aboard the Solar and Heliospheric Observatory. We apply phase-correlation seismic holography to the corrected observations to image the underlying 5-10 Mm subphotosphere. The corrected phase maps show no consistent evidence for sound-speed anomalies more than 5 Mm beneath a moderately large, isolated sunspot. Forward-modeling computations applied to simple models suggest sound-speed anomalies limited to approximately +/-250 m s-1 for depths from 5 to 10 Mm, averaged over the horizontal extent of the sunspot. For complex active regions, uncertainties are considerably greater. However, results of this study suggest that more careful modeling of the acoustic showerglass will lead to substantially improved seismic diagnostics of active region subphotospheres. Detailed hydromechanical computations of acoustics models of active region photospheres and subphotospheres are needed to facilitate the interpretation of showerglass-corrected holographic signatures. Title: Principles of Seismic Holography for Diagnostics of the Shallow Subphotosphere Authors: Lindsey, Charles; Braun, D. C. Bibcode: 2004ApJS..155..209L Altcode: We develop the wave-mechanical formalism for phase-correlation computational seismic holography of the shallow subphotosphere under the plane-parallel approximation and apply it to helioseismic Doppler observations from the Michelson Doppler Imager on the SOHO spacecraft of both the quiet Sun and active regions. We compare holographic signatures computed wave-mechanically with similar signatures computed under the widely used eikonal approximation. The major difference between the hydromechanical and eikonal computations can be expressed in terms of acoustic dispersion effects within a few Mm of the solar surface. With an appropriate account for dispersion, the eikonal computations are remarkably accurate over a broad range of practical applications. A major imposition that confronts local diagnostics of the shallow subphotosphere is a phenomenon we call ``ghost signatures,'' artifacts introduced by a local ambiguity in the origin of the waves that give rise to the helioseismic signatures observed in the photosphere. Phase-correlation holographic signatures of the shallow subphotospheres of active regions are predominated by strong, stochastic phase shifts associated with magnetic fields at the solar surface. These introduce effects similar to those of an optical showerglass, significantly impairing the coherence of waves impinging into the magnetic photosphere from beneath, smearing the holographic signatures of possible subphotospheric anomalies. Title: Local Helioseismology of Inclined Magnetic Fields and the Showerglass Effect Authors: Schunker, H.; Braun, D. C.; Lindsey, C.; Cally, P. S. Bibcode: 2004ESASP.559..227S Altcode: 2004soho...14..227S No abstract at ADS Title: Local Helioseismology of Near-Surface Flows Authors: Braun, D. C.; Birch, A. C.; Lindsey, C. Bibcode: 2004ESASP.559..337B Altcode: 2004soho...14..337B No abstract at ADS Title: The Penumbral Acoustic Anomaly Authors: Lindsey, C.; Braun, D. C. Bibcode: 2004ESASP.559..552L Altcode: 2004soho...14..552L No abstract at ADS Title: Local Helioseismology of Solar Dynamics Authors: Braun, D. C.; Lindsey, C.; Birch, A. C. Bibcode: 2004AAS...204.5309B Altcode: 2004BAAS...36..757B We have initiated a systematic exploration of the dynamics of the solar interior, applying Doppler-sensitive seismic holography to data from the MDI instrument onboard the SOHO spacecraft and the Global Oscillations Network Group (GONG). Goals of this comprehensive project include understanding the nature of supergranulation, monitoring the subsurface variations of the meridional circulation, and understanding other subsurface flows and their relation to solar activity. We present initial results on our inference of subsurface flows due with an emphasis on control work, including comparisons between MDI and GONG datasets and other local seismic procedures such as ring diagrams. The project will develop and test data analysis tools and a forward (and inverse) modeling formalism based on the Born approximation, in preparation for their routine application to the next generation of helioseismic data from the Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observer. This work is supported by funding from NASA SR&T and Living With a Star programs and the NSF Stellar Astronomy and Astrophysics program. Title: The Acoustic Showerglass and Diagnostics of Active Region Subphotospheres Authors: Lindsey, C.; Braun, D. C. Bibcode: 2004AAS...204.5310L Altcode: 2004BAAS...36..757L Magnetic fields introduce large phase shifts into acoustic waves passing through the upper 400 km of an active region subphotosphere, impairing the phase coherence of time-distance correlation measurements, including seismic images of the underlying subphotosphere. We call this the "acoustic showerglass" effect. Reliable diagnostics of active region subphotospheres require a careful account of the interaction of acoustic waves with showerglass magnetic fields. A clear understanding of the acoustics of shallow magnetic fields offers the facility for detailed thermal modeling of the showerglass layer. It also opens the possibility of a high-quality magnetic proxy to correct showerglass phase errors, greatly improving our view of the underlying magnetic subphotosphere. The research reported in this poster is supported by grants from the National Aeronautics and Space Administration and the National Science Foundation. Title: Acoustic Holographic Studies of Solar Active Regions Authors: Malanushenko, A.; Braun, D.; Kholikov, S.; Leibacher, J.; Lindsey, C. Bibcode: 2004IAUS..223..283M Altcode: 2005IAUS..223..283M We present results of a study of the morphology and evolution of active regions using solar acoustic holography. These include acoustic signatures of large far-side active regions and their relationship to near-side activity indices a half rotation before and after the farside image, and the direct comparison of near-side acoustic signatures with the standard activity indicators, not only in their own right but also to calibrate the farside acoustic signature. Title: Microfluidic Experiments exploring Thermal Force approaches to the Origin of Life Authors: Braun, D. Bibcode: 2004cosp...35..781B Altcode: 2004cosp.meet..781B Microfluidic experiments are discussed where temperature gradients across mesoscopic pores provide essential boundary conditions for autonomous molecular evolution: (1) Laminar thermal convection can drive exponential DNA replication as the molecules are continuously cycled between hot and cold regions of a chamber. (2) Thermophoresis can induce strong accumulation of charged biopolymers such as DNA in the same convection settings. Combined, the experiments demonstrate a robust nonequilibrium boundary condition for the replication and accumulation of evolving molecules. The experimental conditions are comparable to conditions in porous rocks near submarine hydrothermal mounds. It is expected that further studies of microscopic open systems can reveal further unexpected connecting pieces in the fascinating puzzle on the origins of life. 1. D. Braun, N.L. Goddard and A. Libchaber, Exponential DNA Replication by Laminar Convection, Physical Review Letters 91:158103 (2003) 2. D. Braun & A. Libchaber, Trapping of DNA by Thermophoretic Depletion and Convection, Physical Review Letters 89:188103 (2002) 3. D. Braun & A. Libchaber, Thermal force approach to molecular evolution, Physical Biology, accepted Title: Probing sunspot magnetic fields with p-mode absorption and phase shift data Authors: Cally, P. S.; Crouch, A. D.; Braun, D. C. Bibcode: 2003MNRAS.346..381C Altcode: Long-standing observations of incoming and outgoing f- and p-modes in annuli around sunspots reveal that the spots partially absorb and substantially shift the phase of waves incident upon them. The commonly favoured absorption mechanism is partial conversion to slow magneto-acoustic waves that disappear into the solar interior channelled by the magnetic field of the sunspot. However, up until now, only f-mode absorption could be accounted for quantitatively by this means. Based on vertical magnetic field models, the absorption of p-modes was insufficient. In this paper, we use the new calculations of Crouch & Cally for inclined fields, and a simplified model of the interaction between spot interior and exterior. We find excellent agreement with phase shift data assuming field angles from the vertical in excess of 30° and Alfvén/acoustic equipartition depths of around 600-800 km. The absorption of f-modes produced by such models is considerably larger than is observed, but consistent with numerical simulations. On the other hand, p-mode absorption is generally consistent with observed values, up to some moderate frequency dependent on radial order. Thereafter, it is too large, assuming absorbing regions comparable in size to the inferred phase-shifting region. The excess absorption produced by the models is in stark contrast with previous calculations based on a vertical magnetic field, and is probably due to finite mode lifetimes and excess emission in acoustic glories. The excellent agreement of phase shift predictions with observational data allows some degree of probing of subsurface field strengths, and opens up the possibility of more accurate inversions using improved models. Most importantly, though, we have confirmed that slow mode conversion is a viable, and indeed the likely, cause of the observed absorption and phase shifts. Title: Computational Seismic Holography of Active Region Subphotospheres Authors: Lindsey, C.; Braun, D. C. Bibcode: 2003SPD....34.0808L Altcode: 2003BAAS...35Q.823L We apply phase-correlation seismic holography to SOHO/MDI observations of large sunspots to render signatures of local sound-speed anomalies in their shallow subphotospheres. In the computations reported here, a magnetic proxy we call the ``showerglass correction'' was applied to correct large phase errors introduced by surface magnetic fields. Preliminary results suggest a general sound speed enhancement in the range 1--4% up to depths of 10 Mm over horizontally extended regions surrounding large sunspots. These regions cover diameters roughly in the range 30--50 Mm. Phase maps of large active region complexes show signatures that tend to blanket most of the active region. The correlation between the phase shift and the magnetic field strength is generally high, but there are localized regions in which the phase signature departs significantly from the magnetic. The signature of the sunspot itself tends to be subtle with a maximum that may be significantly displaced towards the periphery of the active region. The research reported here is supported by funding from the Supporting Research and Technology and the Living with a Star Programs of the National Aeronautics and Space Administration, and from the Astronomical Sciences Division of the National Science Foundation. Title: The showerglass effect in seismic diagnostics of active region subphotospehres Authors: Lindsey, Charles; Braun, D. C. Bibcode: 2003ESASP.517...23L Altcode: 2003soho...12...23L A major obstacle that encumbers local seismic diagnostics of the shallow subphotospheres of strong active regions is phase errors introduced by overlying surface magnetic fields. These errors function as a sort of "acoustic showerglass" that obscures subphotospheric acoustic anomalies, scrambling computational images of these derived by phase-coherent seismic reconstruction. We develop a proxy based on the surface magnetic field to correct the showerglass phase errors and image acoustic scatterers beneath it. Preliminary applications of this correction give us signatures that appear to signify strong, sharply outlined acoustic anomalies 3-9 Mm beneath large growing active regions. Correction of the showerglass correction appears to be important, if not essential, for diffraction-limited diagnostics of acoustic anomalies in the shallow subphotospheres of strong active regions. Title: Helioseismic imaging of the farside and the interior Authors: Braun, D. C.; Lindsey, C. Bibcode: 2003ESASP.517...15B Altcode: 2003soho...12...15B Helioseismic holography is a highly efficient and flexible procedure with a wide range of utility, from mapping sound wave travel times over the entire far solar hemisphere to imaging small scale scatterers and flows beneath solar active regions. Seismic images covering the entire far hemisphere of the Sun have been constructed using data from the recently upgraded Global Oscillation Network Group (GONG+) network and compare favorably with those made using simultaneous data from the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observer (SOHO). We are also continuing our comprehensive exploration of diffraction-limited seismic imaging of active regions. We have recently extended our applications of helioseismic holography to include Doppler diagnostics of active regions and quiet Sun. A major finding presented here is that the horizontal velocity field in supergranules and sunspot moats appears to be concentrated at the surface. Another recent, but vital, contribution to local helioseismology has been a study of what is termed the "showerglass effect". Magnetic fields in the photosphere produce large, local amplitude and phase perturbations to the observed acoustic wave field which may be quantified and removed prior to the holographic computations. Removal of the showerglass from local helioseismic images of active regions is proving to be a crucial step in the detection of compact subsurface scatterers. Title: MDI and GONG inferences of the changing solar interior Authors: Barban, C.; Howe, R.; Hill, F.; Komm, R. W.; Leibacher, J.; Toner, C.; Bogart, R.; Braun, D.; Haber, D.; Hindman, B.; Lindsey, C. Bibcode: 2002ESASP.508...55B Altcode: 2002soho...11...55B The Global Oscillation Network Group (GONG) and the Solar Oscillations Investigation (SOI) using the Michelson Doppler Imager (MDI) instrument aboard the SOHO spacecraft provide combined data sets that now cover more than six years and allow us to probe the changing dynamics of the convection zone in unprecedented detail. Here we present the latest combined results from both projects, showing the evolution of the migrating zonal flows close to the surface and also changes close to and below the base of the convection zone, as well as changes in the mode parameters related to surface magnetic activity variation in time and latitude. Title: The First Seismic Images of the Solar Interior and Far Side from the GONG+ Network Authors: Braun, D. C.; Lindsey, C. Bibcode: 2002AAS...200.8906B Altcode: 2002BAAS...34..791B Since mid-2001, the upgraded GONG+ network has been providing high-resolution Doppler images of the Sun. We are now analyzing GONG+ data as part of our program in local helioseismology and acoustic holography. The bulk of the results shown here are derived from data obtained during a 24-hour period in 2001 September, when simultaneous full-disk observations from the MDI instrument onboard the SOHO spacecraft were available for comparison. Images showing the acoustic travel-time perturbations over the entire far hemisphere obtained from GONG+ and MDI data are essentially identical. This demonstrates that the GONG+ network may be used as the basis of a synoptic far-side imaging program of comparable quality to that now provided by MDI. Holographic depth-diagnostics of travel-time perturbations below several active regions on the solar front side are also presented. These phase-sensitive holographic images from GONG+ and MDI have similar noise characteristics when computed using acoustic modes with degree (wavenumber) below about 300, which implies that the r.m.s. fluctuations in these images are solar in nature. At higher wavenumbers, atmospheric seeing introduces an excess r.m.s., which increases with mode degree, to the images derived from GONG+ data. However, acceptable images are possible using modes with degrees up to at least 700. We will discuss how GONG+ data may be advantageously utilized in detailed, continuous, and long-term local-helioseismic analyses of the far side and deep interior of the Sun. This work is supported by awards AST-9987286 from NSF, and awards NASW-01007 and NAG5-10984 from NASA. Title: Computational Seismic Holography of the Deep Interior and Far Surface of the Sun Authors: Lindsey, C.; Braun, D. C. Bibcode: 2002AAS...200.7903L Altcode: 2002BAAS...34..780L Computational seismic holography has given us a remarkably flexible and powerful new utility for local diagnostics of the solar interior. Major results to date include the following: - Seismic signatures surrounding sunspots up to 100 Mm in diameter, called ``acoustic moats.'' - Enhancements of locally stochastic seismic emission, called ``acoustic glories,'' surrounding complex active regions. - Chromatic siesmic emission maps of a solar flare. - Signatures suggesting compact thermal enhancements in the shallow subphotospheres of surface magnetic regions. - Synoptic phase-correlation maps of active regions on the far surface of the Sun. Prospects for deep interior diagnostics of the solar interior are highly encouraging. Seismic holography applied to the database we expect from the Solar Dynamics Observatory is nearly certain to give us a synoptic view of the local structure of flows and torsional oscillations down to the base of the convection zone. Cooperative seismic observations of both near and far surfaces of the Sun offer high quality holographic diagnostics of the solar core. Holographic diagnostics promise deep insight into the operation of the solar dynamo, and may give us indications of emerging magnetic fields significantly in advance of their appearance at the solar surface. This research has been supported by funding from the National Science Foundation and the National Aeronautics and Space Administration. Title: Helioseismological observations of active regions Authors: Braun, Douglas Bibcode: 2002ocnd.confE...3B Altcode: No abstract at ADS Title: Seismic forecasting of solar activity Authors: Braun, D. C.; Lindsey, C. Bibcode: 2002HiA....12..378B Altcode: No abstract at ADS Title: Seismic Imaging of the Far Hemisphere of the Sun Authors: Braun, D. C.; Lindsey, C. Bibcode: 2001ApJ...560L.189B Altcode: We apply phase-sensitive helioseismic holography to Solar and Heliospheric Observatory/Michelson Dopper Imager data to demonstrate how acoustic travel-time perturbations may be mapped over the entire portion of the Sun facing away from the Earth, including the polar regions. In addition to offering significant improvements to ongoing space weather forecasting efforts, the procedure offers the possibility of local seismic monitoring of both the temporal and spatial variations in the acoustic properties of the Sun over all of the far surface. Title: Helioseismic Holography and a Study of the Process of Magnetic Flux Disappearance in Canceling Bipoles Authors: Lindsey, Charles; Harvey, Karen L.; Braun, D.; Jones, H. P.; Penn, M.; Hassler, D. Bibcode: 2001STIN...0156300L Altcode: Project 1: We have developed and applied a technique of helioseismic holography along the lines of originally set out in our proposal. The result of the application of this diagnostic technique to solar activity and the quiet Sun has produced a number of important discoveries: (1) acoustic moats surrounding sunspots; (2) acoustic glories surround large active regions; (3) acoustic condensations beneath active regions; and (4) temporally-resolve acoustic images of a solar flare. These results have been published in a series of papers in the Astrophysical Journal. We think that helioseismic holography is now established as the most powerful and discriminating diagnostic in local helioseismology. Project 2: We conducted a collaborative observational program to define the physical character and magnetic geometry of canceling magnetic bipoles aimed at determining if the cancellation process is the result of submergence of magnetic fields. This assessment is based on ground-based observations combining photospheric and chromospheric magnetograms from NSO/KP, BBSO, and SOHO-MDI, and EUV and X-ray images from SOHO EIT/CDS, Yohkoh/SXT, and TRACE. Our study involves the analysis of data taken during three observing campaigns to define the height structure of canceling bipoles inferred from magnetic field and intensity images, and how this varies with time. We find that some canceling bipoles can be explained by the submerge of their magnetic flux. A paper on the results of this analysis will be presented at an upcoming scientific meeting and be written up for publication. Title: Progress in Helioseismic Holography Authors: Braun, D. C. Bibcode: 2001AGUSM..SP21C07B Altcode: Local Helioseismology uses acoustic waves to probe small-scale structures in the solar interior down to a spatial resolution imposed by wave diffraction. Although its practitioners, including this author, may sometimes employ measurements of the acoustic wave field made over a local area of the Sun's surface to examine its shallow layers, local helioseismology generally has a much broader utility. For example, some applications of helioseismic holography (and other local diagnostics) require global acoustic modes, observed over large portions of the surface, to produce diffraction-limited images of the far side or deep interior of the Sun. In this review, I will summarize recent progress achieved in seismic holography in collaboration with C. Lindsey (SPRC). With P. Scherrer and the SOI-MDI team at Stanford, we have helped to realize a daily synoptic monitor of far-side activity using medium-resolution MDI images obtained within 24 hours of their acquisition by the SOHO spacecraft. In addition, we have laid out the basic theoretical groundwork for the application of computational seismic holography to the deep solar interior to image the tachocline and underlying radiative core of the Sun. Taking advantage of the substantial depth sensitivity of horizontal-flow diagnostics, we have recently adapted our holographic software to test the basic techniques on the shallow subphotospheres of active regions. The utility of both ground- and space-based instruments is usually enhanced by their combination and comparison. I will present the results of holographic analyses of simultaneous GONG+ prototype and SOI-MDI observations of a large flare-producing active region. The general similarity of the helioseismic images from both instruments is noteworthy. This demonstrates the feasibility of increasing the temporal and spatial coverage available to local analyses by combining SOHO data with that obtained from the GONG+ network. We gratefully acknowledge recent support from the National Science Foundation (AST-9987286) and a contract (PY-0184) from the NASA-funded SOI-MDI project at Stanford University. Title: Prospects for Helioseismic Holography in the Deep Solar Interior Authors: Lindsey, C.; Braun, D. C. Bibcode: 2001AGUSM..SP21C08L Altcode: Holographic seismic imaging of low-degree acoustic noise opens new prospects for solar interior diagnostics that are most encouraging. Seismic imaging of the near solar interior has given us the discoveries of ``acoustic moats,'' surrounding sunspots, of anomalous emission from ``acoustic glories'' surrounding large active regions, acoustic images of solar flares, and the signatures of apparent acoustic perturbations up to 20~Mm beneath active region photospheres. Low-degree seismic holography is now giving us images of large magnetic regions on the far surface of the Sun, a utility with valuable space-weather forecasting and general synoptic applications. Extensions of the foregoing applications promise insight into the deep solar interior, to the base of the convection zone and into the Sun's nuclear-burning core. Diffraction-limited imaging of low-degree noise over pupils covering most of the near solar hemisphere offer the most discriminating probe of the deep solar interior. Earth-based helioseismic observations coordinated with seismic observations of the far side of the Sun at frequencies in the range 6--7 mHz would allow us to resolve local thermal and Doppler structure in the solar core with a resolution of 75~Mm. Coordinated seismic observations of both near and far sides of the Sun are essential to take advantage of the superior spatial resolution offered by high-frequency waves. Title: Seismic Holography of the Solar Interior and Far Side Authors: Braun, D. C.; Lindsey, C. Bibcode: 2001IAUS..203..167B Altcode: The development of solar acoustic holography has opened a major new diagnostic avenue in local helioseismology. Its application to SOI-MDI data from SOHO has revealed ``acoustic moats'' surrounding sunspots, ``acoustic glories'' surrounding complex active-regions, and ``acoustic condensations'' suggesting the existence of significant seismic anomalies up to 20 Mm beneath active-region photospheres. It has given us the first seismic images of a solar flare, and has uncovered a remarkable anomaly in the statistical distribution of seismic emission from acoustic glories. Phase-sensitive seismic holography is now producing high-resolution maps of sound travel-time anomalies caused by magnetic forces in the immediate subphotosphere, apparent thermal enhancements in acoustic moats, and Doppler signatures of subsurface flows. It has also produced the first seismic images of active regions on the far-side of the Sun, giving us a powerful tool for forecasting more than a week in advance their arrival at the east limb. This diagnostic now promises a new insight into the hydromechanical and thermal environments of the solar interior in the local perspective. Title: Seismic Holography of the Deep Solar Interior Authors: Lindsey, C.; Braun, D. C. Bibcode: 2000SPD....31.0503L Altcode: 2000BAAS...32R.836L The first images of magnetic regions on the far solar surface were recently secured by applying seismic holography to five-minute oscillations with spherical harmonic degrees roughly in the range 20 to 40 in SOHO-MDI observations. These waves penetrate up to half way to the sun's center, and can therefore sample the base of the convection zone with a resolution similar to that of the aforementioned far-side images, approximately 10o in longitude at the solar equator. However, by far the best seismic diagnostics are invariably offered by the highest possible frequencies, 6 mHz and above, if possible. Because these waves are efficiently absorbed by the solar surface, helioseismic observations that can compare the far side of the sun with earth-based observations of the near side are needed for coherent phase-sensitive imaging of the deep solar interior. Coordinated near- and far-side seismic observations of the sun at frequencies in the range 6--7 mHz would allow us to examine the thermal and Doppler profile of the solar core with a resolution of 75 Mm. This presentation is based on research supported by grants NAG5-7236 from NASA and AST-9528249 from NSF, and by a contract, PY-0184, with Stanford University. Title: Seismic Imaging of the Far Side and Interior of the Sun Authors: Braun, D. C.; Lindsey, C. Bibcode: 2000SPD....3102112B Altcode: 2000BAAS...32Q.831B Images of active regions on the far side of the Sun were derived by applying seismic holography to observations from the SOI-MDI instrument on the SOHO spacecraft. Synoptic seismic imaging of far-side solar activity will allow anticipation of the appearance of large active regions more than a week ahead of their arrival on the east limb. The technical requirements for a synoptic monitor appear to be quite modest, given real time access to observations from the Global Oscillations Network Group, for example. Currently, seismic images of the solar far side are easily computed in less than a day using a single-processor Pentium-based PC running Linux. In addition to providing new applications for space weather prediction, the development of solar acoustic holography is opening major new diagnostic avenues in the study of the solar interior. Phase-sensitive seismic holography is producing high-resolution maps of sound travel-time anomalies caused by magnetic forces in the immediate subphotosphere, apparent thermal enhancements in acoustic moats around sunspots, and Doppler signatures of subsurface flows. Seismic holography applied to global modes, such as those used to image the far side, has directly demonstrated the influence of active regions on these modes. This reinforces a growing consensus that reduced sound travel times in magnetic regions explain the entirety of the frequency shifts of global modes with the solar cycle. Phase-sensitive holography will also be used to probe thermal and Doppler perturbations deep in the solar convection zone and the tachocline. This work is supported by grants NAG5-7236 from NASA and AST-9528249 from NSF, and by a contract, PY-0184, from Stanford University. Title: Stochastic Seismic Emission from Acoustic Glories and the Quiet Sun Authors: Donea, A. -C.; Lindsey, C.; Braun, D. C. Bibcode: 2000SoPh..192..321D Altcode: Helioseismic images of multipolar active regions show enhanced seismic emission in 5-mHz oscillations in a halo surrounding the active region called the `acoustic glory'. The acoustic glories contain elements that sustain an average seismic emission 50% greater than similar elements in the quiet Sun. The most intense seismic emitters tend to form strings in non-magnetic regions, sometimes marking the borders of weak magnetic regions and the separation between weak magnetic regions of opposite polarity. This study compares the temporal character of seismic emission from acoustic glories with that from the quiet Sun. The power distribution of quiet-Sun seismic emission far from solar activity is exponential, as for random Gaussian noise, and therefore not perceivably episodic. The distribution of seismic power emanating from the most intense elements that comprise the acoustic glories is exponential out to approximately 4 times the average power emitted by the quiet Sun. Above this threshold the latter distribution shows significant saturation, suggesting the operation of a hydromechanical non-linearity that sets limits on the acoustic power generated by the convection zone. This could give us considerable insight into the physical mechanism of seismic emission from the near subphotosphere. Title: Helioseismic Holography of Active-Region Subphotospheres - (Invited Review) Authors: Braun, D. C.; Lindsey, C. Bibcode: 2000SoPh..192..285B Altcode: The development of solar acoustic holography has opened a major new diagnostic avenue in local helioseismology. It has revealed `acoustic moats' surrounding sunspots, `acoustic glories' surrounding complex active regions, and `acoustic condensations' suggesting the existence of significant seismic anomalies up to 20 Mm beneath active-region photospheres. Phase-sensitive seismic holography is now yielding high-resolution maps of sound travel-time anomalies caused by magnetic forces in the immediate subphotosphere, apparent thermal enhancements in acoustic moats, and Doppler signatures of subsurface flows. It has given us the first seismic images of a solar flare, and has uncovered a remarkable anomaly in the statistical distribution of seismic emission from acoustic glories. Seismic holography will probably give us the means for early detection of large active regions on the far-surface of the Sun, and possibly of deep subsurface activity as well. This powerful diagnostic now promises a new insight into the hydromechanical and thermal environments of the solar interior in the local perspective. Title: Seismic Images of the Far Side of the Sun Authors: Lindsey, C.; Braun, D. C. Bibcode: 2000Sci...287.1799L Altcode: Images of an active region on the far side of the sun were derived by applying seismic holography to recent helioseismic observations from space. Active regions are the centers of energetic phenomena such as solar flares and coronal mass ejections, whose resulting electromagnetic and particle radiation interfere with telecommunications and power transmissions on Earth and can pose significant hazards to astronauts and spacecraft. Synoptic seismic imaging of far-side solar activity will now allow anticipation of the appearance of large active regions more than a week ahead of their arrival on the east solar limb. Title: Phase-sensitive Holography of Solar Activity Authors: Braun, D. C.; Lindsey, C. Bibcode: 2000SoPh..192..307B Altcode: Phase-correlation statistics comparing acoustic radiation coming out of a particular point on the solar photosphere with acoustic radiation going into it show considerably reduced sound travel times through the subphotospheres of active regions. We have now applied techniques in phase-sensitive seismic holography to data from the Solar Oscillations Investigation - Michelson Doppler Imager (SOI-MDI) on the Solar and Heliospheric Observatory (SOHO) spacecraft to obtain high resolution phase-correlation maps of a large, complex active region and the `acoustic moat' which surrounds it. We report the following new results: First, the reduced sound travel-time perturbations in sunspots, acoustic moats, and isolated plages increase approximately in proportion to the logarithm of the surface magnetic flux density, for flux densities above 10 G. This is consistent with an interpretation of the travel-time anomalies, observed with holographic and other local-helioseismic procedures, as caused by acoustic Wilson-like depressions in photospheres of magnetic regions. Second, we find that, compared with isolated plages, the acoustic moats have an additional sound travel-time reduction on the order of 3-5 s which may be explained by a thermal excess due to the blockage of convective transport by the sunspot photosphere. Third, the combined effect of the Wilson depression in plages, acoustic moats, and sunspots may explain the observed variation of global p-mode frequencies with the solar cycle. Fourth, we find that active regions, including sunspots, acoustic moats, and plages, significantly reflect p modes above the acoustic cut-off frequency, where the surface of the quiet Sun acts as a nearly perfect absorber of incident acoustic radiation. Title: Basic Principles of Solar Acoustic Holography - (Invited Review) Authors: Lindsey, C.; Braun, D. C. Bibcode: 2000SoPh..192..261L Altcode: We summarize the basic principles of holographic seismic imaging of the solar interior, drawing on familiar principles in optics and parallels with standard optical holography. Computational seismic holography is accomplished by the phase-coherent wave-mechanical reconstruction of the p-mode acoustic field into the solar interior based on helioseismic observations at the solar surface. It treats the acoustic field at the solar surface in a way broadly analogous to how the eye treats electromagnetic radiation at the surface of the cornea, wave-mechanically refocusing radiation from submerged sources to render stigmatic images that can be sampled over focal surfaces at any desired depth. Holographic diagnostics offer a straight-forward assessment of the informational content of the observed p-mode spectrum independent of prospective physical models of the local interior anomalies that it represents. Computational holography was proposed as the optimum approach whereby to address the severe diffraction effects that confront standard tomography in the solar p-mode environment. It has given us a number of remarkable discoveries in the last two years and now promises a new insight into solar interior structure and dynamics in the local perspective. We compare the diagnostic roles of simple acoustic-power holography and phase-sensitive holography, and anticipate approaches to solar interior modeling based on holographic signatures. We identify simple computational principles that, applied to high-quality helioseismic observations, make it easy for prospective analysts to produce high-quality holographic images for practical applications in local helioseismology. Title: Seismic Forecasting of Solar Activity Authors: Lindsey, C.; Braun, D. C. Bibcode: 2000IAUJD...7E...4L Altcode: from SOHO, has recently given us the first images of an active region on the far side of the Sun. The advent of phase-coherent seismic imaging is now allowing us quite literally to look into the solar interior from a local perspective, indeed to see through the solar interior acoustically to its far surface. Space and ground-based helioseismic observatories will soon have the capability for ``real-time helioseismology,'' and will be routinely monitoring the far surface of the Sun. This will greatly facilitate medium-range forecasts important to space weather, allowing us to anticipate more than a week in advance the arrival of large far-side active regions at the Sun's east limb to within a few hours. Title: The MVACS soil temperature probe. Authors: Wood, S. E.; Paige, D. A.; Nguyen, A.; Crisp, D.; Alleruzzo, R.; Labaw, C.; Mahoney, C.; Vargas, R.; Gunderson, H.; Braun, D.; Slostad, J.; Manvi, R.; Brown, K.; Oakes, E. Bibcode: 1999BAAS...31.1146W Altcode: No abstract at ADS Title: The MVACS Soil Temperature Probe Authors: Wood, S. E.; Paige, D. A.; Nguyen, A.; Crisp, D.; Alleruzzo, R.; Labaw, C.; Mahoney, C.; Vargas, R.; Gunderson, H.; Braun, D.; Slostad, J.; Manvi, R.; Brown, K.; Oakes, E. Bibcode: 1999DPS....31.4711W Altcode: As part of the Mars Volatiles and Climate Surveyor (MVACS) payload on Mars Polar Lander, currently on its way to a Dec. 3, 1999 landing on the south polar layered deposits, the Soil Temperature Probe (STP) will make direct measurements of the temperatures and thermophysical properties of soils and/or ices accessible by the Robotic Arm (RA). The STP consists of a thin, rigid fiberglass tube 15 cm long containing 2 platinum resistance temperature sensors; one in the metal tip which can be heated (PRT-1), and another inside the tube (PRT-2). It is mounted on the side of the scoop at the end of the RA. To make measurements, the RA places the STP in the desired location on or beneath the surface, and Robotic Arm Camera (RAC) image(s) are taken to verify its position, using ruler markings on the STP to measure its depth. The temperatures of both PRT's are recorded every 3 seconds. Data and commanding are handled through the meteorology instruments (MET) electronics package. Measurement of thermophysical properties can be done actively or passively. In active mode, PRT-1 is heated at a constant rate ( 10 mW). The thermal conductivity of the surrounding soil can be derived from the asymptotic temperature rise. The thermal diffusivity (alpha ) can be derived from the transient response. In passive mode alpha can also be determined by measuring the change in the amplitude and phase of the diurnal thermal wave at different depths. The temperature and thermophysical property measurements obtained with the STP will be very useful for interpreting other MVACS observations including air temperature and humidity, the presence or absence of subsurface ice, the identity of any surface frosts (CO_2 or H_2O), and Thermal Evolved Gas Analyzer soil sample analysis. These STP measurements will also provide invaluable "ground truth" for comparison with data from orbiting spacecraft such as Mars Global Surveyor and Mars Climate Orbiter. Title: New Results from Helioseismic Holography Authors: Braun, D. C. Bibcode: 1999AAS...194.4202B Altcode: 1999BAAS...31..882B The application of helioseismic holography (also called seismic imaging) to solar data is among the latest developments in local helioseismology. This procedure applies helioseismic observations at the solar surface in time-reverse to a model of the solar interior, coherently regressing the surface disturbances downward to render acoustic images of subsurface structure. I will describe the basic concept, first developed ten years ago by C. Lindsey and D. Braun (1990 Solar Physics, 126, 101), and present new results from our recent application of the method to SOHO/MDI data. Notable discoveries include the ``acoustic moat'' (extended 3-mHz absorption surrounding all active regions), ``acoustic glories'' (high frequency halos of emission around complex active regions), acoustic condensations up to 20 Mm beneath active regions, and the 6-mHz acoustic reflectivity of active regions. Recent results obtained with phase-sensitive seismic holography demonstrate a wave-speed perturbation beneath acoustic moats, which may be a manifestation of a localized convection cell predicted by theoretical models of sunspot convection and energy transport. The development of seismic-imaging procedures sensitive to Doppler and thermal perturbations promises to provide considerable insight into the physical conditions underlying active regions. This research is supported by NSF Grants AST 9521637 and AST 9528249, and NASA Grants NAGW-97029 and NAG5-7236. Title: Phase-Sensitive Holography of Acoustic Moats Authors: Braun, D. C.; Lindsey, C. Bibcode: 1999AAS...194.5610B Altcode: 1999BAAS...31..913B Phase-correlation statistics comparing acoustic radiation coming out of a particular point on the solar photosphere with acoustic radiation going into it show considerably reduced sound travel times through the subphotospheres of active regions. This is already well established by time-distance correlations measured by Duvall et al., and is consistent with earlier measurements of scattering phase shifts of single sunspots by Braun and Fan. We have now applied techniques in phase-sensitive seismic holography to obtain high resolution phase-correlation maps of active regions and the ``acoustic moats'' that surround them. The important new result which the holographic correlation maps give us is that the seismic perturbation manifested by the acoustic moats is generally quite significant and in large active-region complexes predominant. Indeed, the acoustic moat surrounding the large active region complex NOAA AR 8179 (1998 March 16) manifests a one-way travel-time reduction of ~ 30s over an area of some 10(4) Mm(2) , encompassing all of the significant sunspots in the region. Onto this phase perturbation the major sunspots impose an additional localized contribution of ~ 30s. These results strongly reinforce an interpretation of the acoustic moat as a well integrated convection cell driven by the thermal perturbation that results from the local blockage of convective heat transport by the sunspot photosphere. The remarkable lateral extent of the acoustic moat, some 100 Mm in latitude and more than 150 Mm in longitude, suggests a convective flow that undertakes to spread the thermal perturbation into a relatively thin layer, such that the excess heat contained therein can access the solar surface through normal supergranular and granular diffusion. We expect holographic Doppler diagnostics, now under development, to shed considerable light very soon on the flows that are needed to explain the extended dimensions of the thermal perturbations that surround large active regions. This research is supported by NSF Grants AST 9521637 and AST 9528249, and NASA Grants NAGW-97029 and NAG5-7236. Title: Seismic Images of a Solar Flare Authors: Donea, A. -C.; Braun, D. C.; Lindsey, C. Bibcode: 1999ApJ...513L.143D Altcode: We have used helioseismic holography to render seismic images of the solar flare of 1996 July 9, whose helioseismic signature was recently reported by Kosovichev & Zharkova. We computed time series of ``egression power maps'' in 2 mHz bands centered at 3.5 and 6 mHz. These images suggest an oblong acoustic source associated with the flare some 18 Mm in the north-south direction and approximately 15 Mm in the east-west direction. The considerable preponderance of the flare acoustic power emanates in the 3.5 mHz band. However, because the ambient noise in the 6 mHz band is much lower and the diffraction limit for 6 mHz waves is much finer, the flare is rendered far more clearly in the 6 mHz band. The 6 mHz flare signature lags the 3.5 mHz by approximately 4 minutes. Title: Helioseismic Images of an Active Region Complex Authors: Braun, D. C.; Lindsey, C. Bibcode: 1999ApJ...513L..79B Altcode: Helioseismic images of a large active region complex at a frequency of 5 mHz show a prominent halo of acoustic emission, which we call the ``acoustic glory,'' surrounding the active region. This feature is remarkably intense and contains small-scale elements of concentrated seismic emission which cluster in strings in nonmagnetic regions. Subsurface images show condensations of acoustic deficit that appear to represent acoustic perturbations located in excess of 10 Mm beneath the photosphere. The analysis of this complex active region suggests that these features are common in the neighborhoods of large active regions and can appear tens of megameters horizontally separated from sunspots. We propose that acoustic condensations are the result of refraction or scattering by subsurface thermal or Doppler perturbations below active regions. The appearance of acoustic glories and condensations strongly suggests that complex active regions have acoustic properties that are fundamentally different from those of single isolated sunspots. Title: Chromatic Holography of the Sunspot Acoustic Environment Authors: Lindsey, C.; Braun, D. C. Bibcode: 1999ApJ...510..494L Altcode: We use helioseismic holography to obtain seismic images of a sunspot and its local environment over the 3-8 mHz acoustic spectrum. We are particularly interested in the acoustic deficit brought about by strong acoustic absorption by the sunspot itself in the 3-4 mHz range and in the helioseismic character of the ``acoustic moat'' recently discovered by Braun et al. The holographic images computed here clearly show that over a broad range in frequency the sunspot replaces the acoustic radiation impinging into it from the ambient solar interior with an outgoing acoustic flux that is only a fraction of that which it receives. This acoustic deficit persists uniformly over the 3-7 mHz spectrum, even as the reflectivity of the quiet-Sun photosphere goes from being an almost perfect, specular reflector at 4 mHz to an almost perfect absorber at 5 mHz. As far as we can judge, the acoustic moat surrounding the sunspot need not require a helioseismic absorption mechanism of its own. Its signature in 3-4 mHz images could arise from simple scattering of an acoustic deficit that originates in the nearby sunspot. Such scattering may be the result of a thermal perturbation resulting from the blockage of convective heat transport through the sunspot photosphere. Alternatively, it could be the signature of a Doppler perturbation attendant to the rapid convective outflow that might be driven by such a thermal accumulation. While the results presented here do not rule out the possibility that the acoustic moat has its own absorption mechanism, they show little independent evidence to indicate that the acoustic moat otherwise behaves very differently from the quiet Sun where absorption and reemission of acoustic flux are concerned.

Helioseismic images of conspicuous halos that appear in 6 mHz acoustic power maps show no significant enhancement of acoustic emission from these regions. A fairly broad region surrounding the sunspot appears to render a weak enhancement, ~2.5%, in the local generation of 5 mHz acoustic power. This seems to explain peculiarities in the spectrum of acoustic flux balance measurements based on Hankel analysis. The distribution of the 5 mHz ``acoustic egression'' excess is fairly diffuse and does not seem to be spatially correlated with the strong acoustic power halos seen in 6 mHz acoustic power maps. Title: Erratum: Helioseismic Measurements of the Subsurface Meridional Flow Authors: Braun, D. C.; Fan, Y. Bibcode: 1999ApJ...510L..81B Altcode: In the Letter ``Helioseismic Measurements of the Subsurface Meridional Flow'' by D. C. Braun and Y. Fan (ApJ, 508, L105 [1998]), equation (4) was misprinted and should appear as follows:<Uθ>≡-(θmax-θmin)-1θminθmaxU\b.dot θ̂dθ. (4) Title: Comparative Results from Seismic Imaging and Hankel Analysis Authors: Braun, D. C. Bibcode: 1999soho....9E..27B Altcode: Studies of solar active regions using Hankel-decomposition techniques have clearly demonstrated over the past decade that sunspots and plage are efficient absorbers of acoustic waves, and that the wave speeds below sunspots are generally greater than that of the surrounding quiet Sun. These results have been consistently confirmed by more recent applications of both seismic-imaging and time-distance correlation analyses. The development of seismic imaging (or helioseismic holography), originally conceived ten years ago by C. Lindsey and D. Braun, and recently applied to SOHO/MDI data, has additionally provided important insights regarding the spatial (horizontal and vertical) structure of the acoustic perturbations first detected with Hankel analysis. Moreover, holography has enabled a number of remarkable new discoveries including the "acoustic moat," "acoustic glories," acoustic condensations up to 20 Mm beneath active regions, and the reflectivity of active regions above the quiet-Sun acoustic cut-off frequency. Recent application of phase-sensitive holographic procedures have also revealed a subsurface wave-speed perturbation extending tens of Mm beyond the sunspots, possibly associated with a convection cell driven by the local blockage of heat transport by the spots. A significant controversy still remains regarding the depth of the primary acoustic perturbation below sunspots. Modeling of scattering phase-shifts and seismic-imaging observations suggests that the perturbations are strongly concentrated within depths of a few Mm or less, in contrast to the deeper signatures implied by inversions of time-distance correlation measurements. Simple, but straightforward theoretical considerations, imply that the burden of proof rests with proponents of the latter scenario. Complexities introduced by the use of the photospheric signals within sunspots themselves also contribute to uncertainties in the interpretations. Careful control work and comparisons among diverse techniques, coupled with a continued theory-based effort in understanding and modeling local-helioseismic techniques and results, are crucial in providing a full understanding of the physics of solar active regions and their interaction with acoustic radiation. Title: Seismic images of the solar flare of July 9, 1996. Authors: Donea, A. -C.; Braun, D. C.; Lindsey, C. Bibcode: 1999joso.proc..124D Altcode: The helioseismic holography is a new method useful for rendering seismic images of the solar flare of July 9, 1996. Time series of the "egression power map" are computed in 2 mHz bands centered at 3.5 mHz and 6 mHz. The images show an acoustic source associated with the flare some 18 mm in the N-S direction and approximately 15 mm in the E-W. The flare is rendered far more clearly in the 6 mHz band. The 6 mHz flare signature lags the 3.5 mHz by approximately 6 minutes. Title: Phase-Sensitive Seismic Holography of the Photospheres and Near Subphotospheres of Active Regions Authors: Lindsey, C.; Braun, D. C. Bibcode: 1999soho....9E..71L Altcode: The discovery of acoustic power halos surrounding active regions by Braun, et al., Brown et al., and Toner and LaBonte, suggested that surface regions with weak magnetic fields were enhanced emitters of high-frequency seismic noise. Seismic holography of these regions by Lindsey and Braun showed clearly that this was not generally the case. Phase-sensitive holography of these features shows that these are regions in which the Doppler signatures of seismic waves from distant sources are locally enhanced, but the local seismic emission is not enhanced. On the other hand, acoustic glories are regions of strongly enhanced seismic emission from the quiet Sun just outside of magnetic regions. Moreover, regions of strong magnetic field show suppressed seismic emission. We examine the phase relation between the acoustic ingressions, acoustic egressions, and local acoustic amplitudes of these regions and consider how these can be treated as diagnostic of the photospheres and near subphotospheres of active regions. Title: Helioseismic Holography - a Technique for Understanding Solar Flares Authors: Donea, A. C.; Lindsey, C.; Braun, D. Bibcode: 1999RoAJ....9S..71D Altcode: The helioseismic holography is a technique which allows the analysis of the photosphere of the Sun from the point of view of the acoustics. In this paper we shall discuss mainly the seismic image of the flare of July 9, 1996 which produced the largest sunquake observed by MDI-SOHO instrument. We emphasize the fact that the kernel-like structure observed in the seismic signature at both 3.5 mHz and 6 mHz egression power maps are not side lobes effect. The seismic signature reveals the presence of an extended acoustic source, much larger than the Doppler redshift motion observed in the MDI-SOHO Dopplergrams. Title: Seismic Imaging of Acoustic Moats around Active Regions Authors: Braun, D. C.; Lindsey, C. Bibcode: 1999soho....9E..46B Altcode: Phase-correlation statistics comparing acoustic radiation coming out of a particular point on the solar photosphere with acoustic radiation going into it show considerably reduced sound travel times through the subphotospheres of active regions. This is already well established by scattering phase shifts of single sunspots by Braun and Fan, and by time-distance correlations measured by Duvall et al. We have now applied techniques in phase-sensitive seismic holography to obtain high resolution phase-correlation maps of active regions and the "acoustic moats" that surround them. Correlation maps obtained for several active regions show that the seismic perturbation manifested by the acoustic moats extends 30 Mm or so beyond the visible sunspots, and in large active-region complexes is quite predominate. Indeed, the acoustic moat surrounding the large active region complex NOAA AR 8179 (1998 March 15) manifests a one-way travel-time reduction of approximately 30s over an area of some 10,000 sq. Mm, encompassing all of the significant sunspots in the region. Onto this phase perturbation the major sunspots impose an additional localized contribution of about 30s. These results strongly reinforce an interpretation of the acoustic moat as a well integrated convection cell driven by the thermal perturbation that results from the local blockage of convective heat transport by the sunspot photosphere. Title: Acoustic Signatures of Subphotospheric Structure Underlying Sunspots Authors: Lindsey, C.; Braun, D. C. Bibcode: 1998ApJ...509L.129L Altcode: Helioseismic holography of active regions at frequencies in the range of 5-6 mHz renders acoustic signatures that we think signify acoustic perturbations several megameters beneath the photosphere. The application of holographic diagnostics at 5-6 mHz gives us images with considerably finer horizontal spatial resolution, and likewise much finer depth resolution with respect to focus, than the 3 mHz diagnostics we have recently published. This Letter reports comparative results of standard focus-defocus diagnostics of a single sunspot at 3 and 6 mHz. Images of the ``acoustic egression power'' at 6 mHz show a remarkable, compact acoustic deficit that persists in acoustic focal planes submerged up to 11.2 Mm beneath the solar surface. We propose that this and other similar features associated with other active regions are the result of refraction or scattering by submerged thermal or Doppler perturbations of an acoustic deficit that is caused by strong wave absorption in the overlying photosphere of the active region. Title: Helioseismic Measurements of the Subsurface Meridional Flow Authors: Braun, D. C.; Fan, Y. Bibcode: 1998ApJ...508L.105B Altcode: We measure the mean frequencies of acoustic (p-mode) waves propagating toward and away from the poles of the Sun from observations made with the Solar Oscillations Investigation-Michelson Doppler Imager on board the Solar and Heliospheric Observatory and the ground-based Global Oscillations Network Group. We demonstrate that there is a significant frequency shift between poleward- and equatorward-traveling waves measured over solar latitudes 20°-60°, which is consistent with the Doppler effect of a poleward meridional flow on the order of 10 m s-1. From the variation of the frequency shifts of p-modes with degree l between 72 and 882 as a function of the lower turning point depth, we infer the speed of the meridional flow, averaged over these latitudes, over a range in depth extending over the top half of the solar convection zone. We find no evidence for a significant equatorward return flow within this depth range. Title: Seismic Holography of Solar Activity Authors: Braun, D. C.; Lindsey, C.; Fan, Y.; Fagan, M. Bibcode: 1998ApJ...502..968B Altcode: Helioseismic images of sunspots show a remarkable acoustic anomaly surrounding the sunspot. We applied the computational formalism of ``helioseismic holography'' to SOHO-MDI observations to render acoustic images of NOAA AR 7973, an active region containing a moderately large sunspot. The results of this study are based on simple ``acoustic power holography,'' to image the absorption of p-mode waves by the sunspot. These images clearly show a strong, compact acoustic deficit representing the sunspot, as well as plages in the neighborhood of the sunspot, consistent with earlier results of ``Hankel analysis.'' However, they also show surrounding the sunspot a conspicuous acoustic halo extending out to a radius of approximately 35,000 km. We propose that this ``acoustic moat'' is the helioseismic manifestation of a single convection eddy that is driven by the thermal disturbance resulting from the local blockage of convective transport in the sunspot subphotosphere. Depth diagnostics based on acoustic focus show a rapidly defocusing sunspot image as the focal plane is submerged. Acoustic noise models in which absorption by the sunspot is entirely superficial yield images that defocus significantly more slowly with increasing focal-plane depth than the SOHO-MDI images of NOAA AR 7973. Extending the absorption significantly beneath the model photosphere enhances the discrepancy. More recent tests tentatively suggest that this ``focus anomaly'' is the result of neglect of image smearing introduced into the MDI instrument to suppress aliasing, and that a proper account of the instrumental MTF will render defocus profiles roughly consistent with superficial absorption. Our holographic images roughly indicate that the sunspot in NOAA AR 7973 absorbs low-l waves with approximately the same efficiency as it does high-l waves. Contrary to widely held opinion, this result is entirely consistent with that of the Hankel analysis, given that the absorption of waves by magnetic regions is indeed superficial. We expect that the efficient absorption of low-l waves will make it possible to image large active regions on the far side of the Sun by the acoustic-absorption signatures they render at their antipodes. Title: The Acoustic Moat and Thermal Transport in the Neighborhoods of Sunspots Authors: Lindsey, C.; Braun, D. C. Bibcode: 1998ApJ...499L..99L Altcode: Helioseismic holography of sunspots shows a remarkable acoustic anomaly surrounding the sunspot, which we call an ``acoustic moat.'' We used Solar and Heliospheric Observatory (SOHO) Michelson Doppler Imager observations of NOAA Active Region 7973 to render acoustic images of a typical sunspot. These images show a conspicuous halo, 70,000 km in diameter, surrounding the sunspot, in which there appears a predominant acoustic deficit. This ``acoustic moat'' may be terminated by a sharp outer boundary, which appears to circumscribe the sunspot completely in some instances. The outer boundary of the acoustic moat coincides conspicuously with plages in the neighborhood of the sunspot. Depth diagnostics based on acoustic focus suggest that the acoustic perturbations characterizing both the sunspot and the acoustic are predominantly superficial, within a few thousand kilometers of the solar surface. Following work by Meyer et al., we propose that the acoustic moat is the helioseismic manifestation of a single, integrated convection eddy that is driven by heat accumulation resulting from the local blockage of convective transport from the solar interior into the sunspot subphotosphere. We propose that the acoustic deficit predominantly characterizing the halo is the result of thermal refraction or Doppler scattering by the eddy outflow of an acoustic deficit originating in the helioseismic absorption by the nearby sunspot and possibly neighboring plages. With the advent of SOHO and the Global Oscillation Network Group, helioseismic holography promises considerable insight into the general subject of convective flows surrounding sunspots, an issue that is certain to be critical to the long-standing problem of thermal transport in the neighborhoods of sunspots. Title: The Seismology of Sunspots: A Comparison of Time-Distance and Frequency-Wavenumber Methods Authors: Bogdan, T. J.; Braun, D. C.; Lites, B. W.; Thomas, John H. Bibcode: 1998ApJ...492..379B Altcode: A pair of formulae are developed that relate the absorption coefficient and partial-wave phase shift concepts of frequency-wavenumber local helioseismology to the center-annulus cross-correlation function of time-distance helioseismology, under the general circumstances that both induced and spontaneous sunspot oscillations may be present. These formulae show that spontaneous emission of p-modes by magnetic and Reynolds stresses within the spot and the mode mixing between incoming and outgoing p-modes affect only the outgoing center-annulus cross-correlation time τ+, and they caution that real or spurious phase lags of the umbral oscillation signal lead to differences in the incoming and outgoing correlation times, resulting in τ- ≠ τ+. The application of these methods to actual helioseismic data obtained by the Global Oscillation Network Group (GONG) project is carried out in order to provide a tangible illustration of how time-distance and frequency-wavenumber ideas can profitably be combined to yield deeper insight into the seismic probing of sunspots.

By using the helioseismic GONG data in conjunction with concurrent observations of Doppler velocities and vector magnetic fields obtained by the High Altitude Observatory/National Solar Observatory (HAO/NSO) Advanced Stokes Polarimeter (ASP) for the 1995 October disk passage of active region NOAA 7912, we demonstrate that the inferred GONG umbral signal actually originates from the umbra-penumbra boundary about 6 Mm distant from the center of the spot. Further, the ASP observations show that the 5 minute oscillations at the umbra-penumbra boundary lag behind those in the center of the umbra by approximately 1 minute, which is precisely the difference between the incoming and outgoing correlation times for NOAA 7912 recently determined by Braun. This remarkable result underscores the perils of using umbral oscillations in time-distance helioseismology, and it calls into question previous claims that correlation time differences constitute direct evidence for the existence of a steady downflow in and around sunspots. Taken together, the observational and theoretical evidence suggest that the p-mode forcing of the spot leads to the generation of upwardly propagating slow magnetoatmospheric waves. These waves are in turn responsible for the decreased amplitudes of the outwardly propagating p-modes in the surrounding quiet Sun, and the dispersion in their travel times between the hidden subsurface layer where they are forced and the overlying level where the Doppler signals originate leads to the observed phase lag between the umbral and penumbral oscillations and the corresponding correlation time differences.

This work utilizes data obtained by the Global Oscillations Network Group (GONG) project, managed by the National Solar Observatory, a Division of the National Optical Astronomy Observatories, which is operated by AURA, Inc., under a cooperative agreement with the National Science Foundation. Title: Helioseismic Signatures of Subphotospheric Structure Beneath Active Regions Authors: Lindsey, C.; Braun, D. C. Bibcode: 1998ESASP.418..641L Altcode: 1998soho....6..641L No abstract at ADS Title: Time-Distance Sunspot Seismology with GONG Data Authors: Braun, D. C. Bibcode: 1997ApJ...487..447B Altcode: We present time-distance analyses of several active regions and a region of quiet Sun observed with the Global Oscillation Network Group (GONG). Analyzing temporal correlations between the p-mode oscillation signal observed within the sunspots with the signals integrated within surrounding annuli, we confirm the recent finding of Duvall and his colleagues that travel times (τ+) for outward propagating p-modes are smaller by approximately 1 minute than corresponding inward travel times (τ-). We also analyze correlations of the oscillation signal integrated within annuli of different radii. By varying the radius of the inner annulus (that which is closer to the target) we show that the radial extent of the region giving rise to the travel time perturbations is coincident with the outer boundary of the sunspot penumbrae.

A comparison of independent methods designed to determine the mean travel time perturbations of p-modes passing through the sunspots is made. We find the surprising result that time-distance correlations that do not utilize the signal within the sunspot itself (employing ``two-skip'' trajectories) yield mean travel times that differ substantially from the average of τ+ and τ- and that are significantly closer in agreement with times predicted from scattering phase shifts measured by Hankel decomposition techniques. These observations suggest that it unlikely that Doppler shifts caused by subsurface flows are responsible for the travel time differences determined from center-annuli correlations targeted on sunspots.

This work utilizes data obtained by the Global Oscillation Network Group (GONG) project, managed by the National Solar Observatory, a Division of the National Optical Astronomy Observatories, which is operated by AURA, Inc., under a cooperative agreement with the National Science Foundation. Title: Helioseismic Holography Authors: Lindsey, C.; Braun, D. C. Bibcode: 1997ApJ...485..895L Altcode: We describe the basic principles of ``helioseismic holography,'' an analytic technique intended for local helioseismology of subsurface structure. The purpose of this technique is to provide depth discrimination of subsurface structure that manifests a surface signature in acoustic waves. It is based on the computational application of spatially resolved helioseismic observations to the surface of an acoustic model of the solar interior that contains no local structure. The observed surface oscillations are applied to the model in time reverse, and the model is then computationally sampled at various depths in its interior. This technique takes advantage of the coherence retained by waves in a smooth acoustic medium following an interaction with subsurface structure, allowing us to extrapolate the acoustic field with high accuracy to the depth where the structure lies. Depth discrimination is then accomplished by focus-defocus diagnostics.

We describe computational approaches to the technique from two different perspectives, the ``spectral'' and the ``spatial.'' For rigorous models of the solar interior, the computational demands of the spectral and spatial approaches are approximately the same. For diagnostics of relatively shallow structure, the plane-parallel approximation of the model is useful. In this case the spectral approach reduces computational holography essentially to Fourier transforms, which can be performed rapidly with very modest hardware. We illustrate the technique in this case, using artificial data characterizing waves in an idealized plane-parallel medium with acoustic absorbers located at various depths.

At present, we prefer to maintain a secure distinction between holography and modeling. While we do not discuss modeling in this paper, we think that it is important to develop an approach to modeling that takes advantage of holographic reconstruction. The prospect of viewing local subsurface magnetic regions and flows opens an entirely new dimension to helioseismology and to solar and stellar physics in general. It may make it possible to anticipate solar activity far in advance of its emergence to the surface. Local acoustic diagnostics could revolutionize our understanding of the solar dynamo and the 22 yr activity cycle. Title: The Seismology of Sunspots: A Comparison of Time-Distance and Frequency-Wavenumber Methods Authors: Bogdan, T. J.; Braun, D. C.; Lites, B. W.; Thomas, J. H. Bibcode: 1997SPD....28.0210B Altcode: 1997BAAS...29..894B A pair of formulae are developed which relate the absorption coefficient and partial wave phase-shift concepts of frequency-wavenumber local helioseismology to the center- annulus cross correlation function of time-distance helioseismology, under the general circumstances that both induced and spontaneous sunspot oscillations may be present. These formulae caution that real or spurious phase lags of the umbral oscillation signal lead to differences in the incoming and outgoing correlation times for sunspots, as first observed by Duvall et al. (1996, Nature, 379, 430) and recently confirmed by Braun (1997, ApJ, submitted). By using helioseismic data obtained by the GONG project in conjunction with concurrent observations of Doppler velocities and magnetic fields obtained by the HAO/NSO Advanced Stokes Polarimeter for the October 1995 disk passage of active region NOAA 7912, we demonstrate that the inferred GONG umbral oscillation signal actually originates from the umbra-penumbra boundary some 6 Mm distant from the center of the spot. Further, the ASP observations show that the 5-min oscillations at the umbra-penumbra boundary lag those in the center of the umbra by approximately 1 min, which is precisely the difference between the incoming and outgoing cross correlation times for NOAA 7912 recently determined by Braun. The evidence suggests that p-mode forcing of the spot results in the generation of upward propagating slow MAG waves. These waves are responsible for the absorption of the p-modes, and the dispersion in their travel times between the subsurface layer where they are forced and the overlying level where the Doppler signals originate leads to the observed phase lag between the umbral and penumbral oscillations, and the corresponding correlation time differences. Title: Doppler Acoustic Diagnostics of Subsurface Solar Magnetic Structure Authors: Lindsey, C.; Braun, D. C.; Jefferies, S. M.; Woodard, M. F.; Fan, Y.; Gu, Y.; Redfield, S. Bibcode: 1996ApJ...470..636L Altcode: We used the Bartol-NSO-NASA South Pole helioseismic observations of 1991 January to probe the subsurface structure of active regions to depths of ∼15,000 km. The helioseismic signature we particularly examine is intended to register acoustic Doppler effects caused by horizontal flows associated with the active region. We propose to show that the Doppler acoustic signature of horizontal flows is particularly well suited for deep subsurface diagnostics in terms of vertical discrimination of the structure. This study is based primarily on observations of NOAA Active Regions 6431, 6432, 6440, and 6442 between 1991 January 1 and January 8. We interpret the acoustic signatures we find in terms of a general outflow of the solar medium surrounding the active region. The acoustic signatures are strongly dependent on wavenumber, which suggests an outflow that is quite weak near the surface, the upper 4000 km of the subphotosphere, but which increases strongly with depth to velocities of several hundred meters per second at 15,000 km. This depth profile evolves rapidly as the active region matures. Young active regions show a strong outflow signature for waves that explore depths between 4000 and 8000 km. As the active region matures, the outflow vacates these intermediate layers and submerges to depths mostly below 8000 km.

We examine the location of AR 6442 for a possible preemergence signature. We also show evidence for extended, relatively superficial flows in the quiet Sun between the active region bands directed roughly into the active region bands. Title: Helioseismic Measurements of Subsurface Outflows From Sunspots Authors: Braun, D. C.; Fan, Y.; Lindsey, C.; Jefferies, S. M. Bibcode: 1996AAS...188.6911B Altcode: 1996BAAS...28Q.937B We measure the mean frequencies of acoustic waves propagating toward and away from sunspots employing a spot-centered Fourier-Hankel decomposition of p-mode amplitudes as measured from observations made at the South Pole in 1988 and 1991. There is a significant frequency shift between the inward and outward traveling waves which is consistent with the Doppler effect of a radial outflow from the sunspots. For p-modes of temporal frequencies of 3 mHz it is observed that the frequency shift decreases slightly with spatial frequency, for modes with degree l between 160 to 600. From the l dependence of the frequency shift, we infer that the mean radial outflow within the observed annular region (which extends between 30 and 137 Mm from the spots) increases nearly linearly with depth, reaching a magnitude of about 200 m/s at a depth of 20 Mm. This outflow exhibits properties similar to flows recently reported by Lindsey, et al. (1996 ApJ submitted) using spatially sensitive local helioseismic techniques. This work is supported by NSF Grant AST 9496171 and NASA Grant NAGW-4143. Title: Doppler Acoustic Diagnostics of Subsurface Solar Magnetic Structure Authors: Lindsey, C.; Braun, D.; Jefferies, S.; Fan, Y.; Gu, Y.; Redfield, S. Bibcode: 1996AAS...188.7903L Altcode: 1996BAAS...28R.955L We used the Bartol-NSO-NASA South Pole helioseismic observations of 1991 January to study the subsurface structure of active regions to depths of ~ 15,000 km. The helioseismic signature we particularly examine is based on acoustic Doppler effects caused by horizontal flows associated with the active region. We demonstrate that the Doppler-acoustic signature of horizontal flows is particularly well suited for deep subsurface diagnostics in terms of vertical discrimination of the structure. This study is based primarily on observations of NOAA active regions 6431, 6432, 6440 and 6442 between 1991 January 1 and January 8. We interpret the Doppler signatures we find in terms of a general outflow of the solar medium surrounding the active region. The existence of deep subsurface structure is indicated by the strong dependence of the Doppler signature on horizontal wavelength. The outflows in surface layers, the upper 4,000 km of the subphotosphere, are quite weak but increase strongly with depth to velocities of several hundred m/s at 15,000 km. This depth profile evolves rapidly as the active region matures. Young active regions show strong outflows at depths between 4,000 and 8,000 km. As the active region matures, the outflow vacates these intermediate layers and submerges to depths mostly below 8,000 km. We examine the location of Region 6442 for a possible pre-emergence signature. We also show strong evidence for extended, relatively superficial flows in the quiet Sun between the active-region bands directed roughly into the active region bands. Title: Diagnostics of a Subsurface Radial Outflow From a Sunspot Authors: Braun, D. C.; Fan, Y.; Lindsey, C.; Jefferies, S. M. Bibcode: 1996astro.ph..3078B Altcode: We measure the mean frequencies of acoustic waves propagating toward and away from a sunspot employing a spot-centered Fourier-Hankel decomposition of p-mode amplitudes as measured from a set of observations made at the South Pole in 1991. We demonstrate that there is a significant frequency shift between the inward and outward traveling waves which is consistent with the Doppler effect of a radial outflow from the sunspot. For p-modes of temporal frequencies of 3 mHz it is observed that the frequency shift decreases slightly with spatial frequency, for modes with degree l between 160 to 600. From the l dependence of the frequency shift, we infer that the mean radial outflow within the observed annular region (which extends between 30 and 137 Mm from the spot) increases nearly linearly with depth, reaching a magnitude of about 200 m/s at a depth of 20 Mm. This outflow exhibits properties similar to flows recently reported by Lindsey, et al. (1996) using spatially sensitive local helioseismic techniques. Title: Scattering of p-Modes by Sunspots. II. Calculations of Phase Shifts from a Phenomenological Model Authors: Fan, Y.; Braun, D. C.; Chou, D. -Y. Bibcode: 1995ApJ...451..877F Altcode: We model the scattering of p-mode waves in a polytropic atmosphere by localized inhomogeneities in wave speed, pressure, and density of the medium. The effect of the inhomogeneities is attributed to a source term in the pressure wave equation. The inhomogeneous wave equation for the scattered waves is solved under the simplification of the Born approximation. From the solution for the scattered waves, we compute the phase shifts between the incoming and outgoing waves of individual modes.

We find that the variations of the computed phase shifts with degree l and radial order n of the modes show different behavior for inhomogeneities with different characteristic depths. Depths significantly shallower than the depth of the modes seem to show a phase shift dependence on l and n that is similar to the qualitative behavior of the observed phase shifts produced by sunspots. Direct quantitative comparison of the computed phase shifts with observations is limited to modes with lower degree (l < 200) in which the observed phase shifts are reasonably small so that the Born approximation is applicable. We find that for inhomogeneities with a wave speed contrast reasonable for sunspots, occupying a volume described by a characteristic depth D 108 cm and horizontal radius R ≍ 2.5 × 109 cm, the computed phase shifts at lower l range are in agreement with the observed phase shifts from sunspots in both their magnitudes as well as their variation with l and frequency (or n). Title: Scattering of p-Modes by Sunspots. I. Observations Authors: Braun, D. C. Bibcode: 1995ApJ...451..859B Altcode: The acoustic scattering properties of two large sunspots and a plage are determined from a Fourier-Hankel decomposition of p-mode amplitudes as measured from 68 hr subsets of a larger set of observations made at the South Pole in 1988. We present measurements of p-mode absorption and scattering phase shifts as functions of the incident mode properties (degree, radial order, and azimuthal order).

In the two sunspots we observe a distinct modulation of the absorption with temporal frequency in a fashion that is very nearly independent of the degree of the mode. In particular, the absorption exhibits a broad peak at 3 mHz, an absence of absorption at 5 mHz, and a rise in absorption at higher temporal frequencies. This variation is in good qualitative agreement with a prediction of a model of p-mode absorption by slow mode conversion described recently by Spruit & Bogdan (see also the recent work of Cally & Bogdan). The spotless plage also shows significant p-mode absorption, at a level of 20% of the value seen in the spots. Control tests made by repeating the analysis in a region of quiet Sun have confirmed the recent observation by Bogdan et al. that the quiet Sun shows an apparent acoustic emission. In particular, we find a significant anticorrelation between the absorption coefficient in the quiet Sun and the values measured in a nearby sunspot.

The scattering phase shifts are shown to increase with the degree of the modes with an increase that is faster than a linear relation. At constant degree the phase shifts increase with temporal frequency (radial order) before leveling off at a roughly constant value. We suggest that this behavior is consistent with a relatively shallow sound-speed perturbation produced by the spots. The variation of the phase shift and the absorption with azimuthal order suggest that the phase shifts are largely produced within the area of the sunspot, while significant absorption is occurring in a more extended region. Related to this observation is the finding that the plage, while absorbing p-modes, produces no measurable phase shifts. Upper limits place any phase shifts caused by the plage to be less than about 5 % of that observed in the spots.

Finally, we find strong evidence of mode mixing in the two sunspots, as demonstrated by a significant correlation of the phases of incident p-modes of a given radial order with the phases of outgoing modes of adjacent orders at the same temporal frequency. Title: Observations and Models of p-Mode Scattering by Sunspots Authors: Braun, D. C.; Fan, Y. Bibcode: 1995SPD....26..403B Altcode: 1995BAAS...27..954B No abstract at ADS Title: Active Region Seismology Authors: Bogdan, T. J.; Braun, D. C. Bibcode: 1995ESASP.376a..31B Altcode: 1995heli.conf...31B; 1995soho....1...31B Active region seismology is concerned with the determination and interpretation of the interaction of the solar acoustic oscillations with near-surface target structures, such as magnetic flux concentrations, sunspots, and plages. Observations with high spatial resolution and long temporal duration have enabled the measurement of the scattering matrix for sunspots and solar active regions as a function of the mode properties (wavenumber, frequency and azimuthal order). From this information one may determine the amount of p-mode absorption, partial-wave phase shift, and mode mixing introduced by the sunspot. In addition, the possibility of detecting the presence of completely submerged magnetic fields has been raised and new procedures for performing acoustic holography of the solar interior are being developed. The accumulating evidence points to the mode conversion of p-modes to various magneto-atmospheric waves within the magnetic flux concentration as the unifying physical mechanism responsible for these diverse phenomena. Title: Sunspot Seismology: New Observations and Prospects Authors: Braun, D. C. Bibcode: 1995ASPC...76..250B Altcode: 1995gong.conf..250B No abstract at ADS Title: A Model of P-mode Scattering by Sunspots Authors: Fan, Y.; Braun, D. C. Bibcode: 1994AAS...185.4406F Altcode: 1994BAAS...26.1377F It has recently been discovered that sunspots scatter intermediate and high-degree p-modes. The scattering may be characterized by a shift in phase between modes travelling toward and away from the spot. These observations offer the hope that suitable models of the scattering may yield important clues about the subsurface evolution and structure of magnetic regions. We model the scattering of p-mode waves in a polytropic atmosphere by localized inhomogeneities in compressibility (the wave speed), density and pressure of the media. The effect of the inhomogeneities is to introduce a source term in the pressure wave equation. We solve this inhomogeneous equation for the scattered wave amplitudes using standard Green's function techniques under the simplification of the Born approximation. We found that with reasonable strength (or contrast) of the inhomogeneities we can obtain phase shifts between the outgoing and the in-going waves similar to observations of p-modes in both the magnitude and degree (l) dependence. We discuss how the strength of the scattered waves may depend on the depth distribution of the inhomogeneities. This work is supported by a NSF grant AST-9496171 and NASA grant NAGW-4143 awarded to DCB. YF is supported by ONR grant N00014-91-J-1040. Title: An active solar prominence in 1.3 MM radiation Authors: Harrison, R. A.; Carter, M. K.; Clark, T. A.; Lindsey, C.; Jefferies, J. T.; Sime, D. G.; Watt, G.; Roellig, T. L.; Becklin, E. E.; Naylor, D. A.; Tompkins, G. J.; Braun, D. Bibcode: 1993A&A...274L...9H Altcode: We present new millimetre-wavelength observations of an active solar prominence. Observations made over a two-day period with the James Clerk Maxwell Telescope on Manna Kea, Hawaii, give a unique view in 1.3 mm radiation of the spectacular prominence that appeared on the west solar limb in the total solar eclipse of 11 July 1991. Title: Prospects in Helioseismic Holography Authors: Lindsey, C. A.; Braun, D. C.; Jefferies, S. M. Bibcode: 1993BAAS...25.1220L Altcode: No abstract at ADS Title: The P-Mode Scattering Properties of a Sunspot Authors: Braun, D. C.; Labonte, B. J.; Duvall, T. L., Jr.; Jefferies, S. M.; Harvey, M. A.; Pomerantz, J. W. Bibcode: 1993ASPC...42...77B Altcode: 1993gong.conf...77B No abstract at ADS Title: Local Helioseismology of Subsurface Structure Authors: Lindsey, C.; Braun, D. C.; Jefferies, S. M. Bibcode: 1993ASPC...42...81L Altcode: 1993gong.conf...81L No abstract at ADS Title: Measurement of the Height of the Solar CO Layer During the 11 July 1991 Eclipse Authors: Clark, T. A.; Naylor, D. A.; Tompkins, G. J.; Lindsey, C. A.; Becklin, E. E.; Jefferies, J. T.; Harrison, R. A.; Roellig, T. L.; Carter, M.; Braun, D. C.; Watt, G. Bibcode: 1992AAS...181.8108C Altcode: 1992BAAS...24.1253C No abstract at ADS Title: Extreme-infrared brightness profile of the solar chromosphere obtained during the total eclipse of 1991 Authors: Lindsey, C.; Jefferies, J. T.; Clark, T. A.; Harrison, R. A.; Carter, M. K.; Watt, G.; Becklin, E. E.; Roellig, T. L.; Braun, D. C.; Naylor, D. A. Bibcode: 1992Natur.358..308L Altcode: THE solar chromosphere is a thin layer of gas that is several thousand degrees hotter than the underlying photosphere, and responsible for most of the Sun's ultraviolet emission. The mechanism by which it is heated to temperatures exceeding 10,000 K is not understood. Millimetre and submillimetre radiometry can be used to obtain the chromospheric temperature profile, but the diffraction-limited resolution for the largest telescopes is at best 17 arcsec, or ~12,500 km at the Sun's distance. This is greater than the thickness of the quiet chromosphere itself. The total eclipse of July 1991, which passed over the Mauna Kea Observatory in Hawaii, provided a rare opportunity to make limb occultation observations with a large submillimetrewavelength telescope, the 15-m James Clerk Maxwell Telescope, and in this way we obtained a temperature profile in 1.3-mm radiation with ~300 km resolution at the Sun. Our observations indicate that spicules (magnetically entrained funnels of gas) reach a temperature of 8,000 K at 3,000-4,000 km above the photosphere, a temperature lower than those of many spicule models. Title: Local Acoustic Diagnostics of the Solar Interior Authors: Braun, D. C.; Lindsey, C.; Fan, Y.; Jefferies, S. M. Bibcode: 1992ApJ...392..739B Altcode: Two diagnostic utilities, acoustic power maps, and surface acoustic flux maps are used to explore the local diagnostics of magnetic field structure in the solar interior. The acoustic power maps, constructed from 50 hr of continuous K-line intensity images, show three general features: acoustic power deficits at 3 mHz corresponding to surface magnetic flux, acoustic power enhancements at 6 mHz surrounding the exterior of magnetic regions, and occasional power deficits at 3 mHz which extend beyond magnetic regions visible on the surface to regions of quiet-sun. Surface acoustic flux vector maps of two active regions were constructed for two 6-hr time-series of Dopplergrams. Both maps show the divergence of 3-mHz acoustic flux into surface magnetic structures and also sources and sinks of wave energy which are not associated with surface features. Title: Scattering of p-Modes by a Sunspot Authors: Braun, D. C.; Duvall, T. L., Jr.; Labonte, B. J.; Jefferies, S. M.; Harvey, J. W.; Pomerantz, M. A. Bibcode: 1992ApJ...391L.113B Altcode: The acoustic scattering properties of a large sunspot are determined from a Fourier-Hankel decomposition of p-mode amplitudes as measured from a 68-hr subset of a larger set of observations made at the South Pole in 1988. It is shown that significant improvement in the measurement of p-mode scattering amplitudes results from the increased temporal frequency resolution provided by these data. Scattering phase shifts are unambiguously determined for the first time, and the dependence of the p-mode phase shift and absorption with wavenumber and frequency is presented. Title: Prospects in Acoustic Holography of the Solar Interior Authors: Lindsey, C.; Braun, D. C.; Fan, Y.; Jefferies, S. M. Bibcode: 1992AAS...180.1703L Altcode: 1992BAAS...24..753L Acoustic power maps of the solar surface show strong evidence of magnetic structure crossing the solar equator not far beneath the photosphere to connect the active latitude bands. These maps, generated using the Bartol-NSO-NASA South Pole Observations show long finger-like acoustic shadows we think are caused by absorption of acoustic energy by the submerged magnetic structure. These features suggest a solar interior magnetic structure quite different from any previously expected. These new results open the prospect of a new and powerful solar interior diagnostic based on acoustic holography. Title: Scattering of p-Modes by a Sunspot Authors: Braun, D. C.; Duvall, T. L., Jr.; Labonte, B. J.; Jefferies, S. M.; Harvey, J. W.; Pomerantz, M. A. Bibcode: 1992AAS...180.0604B Altcode: 1992BAAS...24..737B For the first time the scattering phase shifts of solar p-modes from a sunspot have been unambiguously determined. This is made possible by the recent availability of long duration, high duty cycle observations. The results presented here are determined from a Fourier-Hankel decomposition of p-mode amplitudes as measured from a 68 hr subset of a larger set of observations made at the South Pole in 1988. In addition to the detection of the phase shifts, the quality of the data allows the dependence of the p-mode scattering and absorption with azimuthal order, spatial wavenumber and temporal frequency to be independently determined. Thus, unlike previous observations, our measurements of absorption and phase shifts do not represent averages over a range of p-modes. With this information we have for the first time a complete description of the acoustic scattering amplitudes from a large sunspot. Interpretation of these observations requires a suitable theory of the interaction of p-modes and sunspots. However, with the complete scattering amplitudes now available one may apply inverse scattering algorithms, based on a few simplifying assumptions, to deduce a 3-dimensional map of the scattering strength of the active region. This offers the hope that general information about subsurface morphology of active regions might be gained even without a detailed understanding of the physical scattering processes involved. DCB is supported by Air Force URI grant AFOSR-90-0116. The South Pole program is supported in part by National Science Foundation grants DPP87-15791 and 89-17626, and by the Solar Physics Branch of the Space Physics Division of NASA. Title: Power Spectra of Solar Convection Authors: Chou, D. -Y.; Labonte, B. J.; Braun, D. C.; Duvall, T. L., Jr. Bibcode: 1991ApJ...372..314C Altcode: The properties of convective motions on the sun are studied using Kitt Peak Doppler images and power spectra of convection. The power peaks at a scale of about 29,000 km and drops off smoothly with wavenumber. There is no evidence of apparent energy excess at the scale of the mesogranulation proposed by other authors. The vertical and horizontal power for each wavenumber are obtained and used to calculate the vertical and horizontal velocities of the supergranulation. The amplitude of vertical and horizontal velocities of the supergranulation are 0.034 (+ or - 0.002) km/s and 0.38 (+ or - 0.01) km/s, respectively. The corresponding rms values are 0.024 (+ or - 0.002) km/s and 0.27 (+ or - 0.01) km/s. Title: An Acoustic Poynting Vector for Solar p-mode Oscillations Authors: Braun, D. C.; Lindsey, C. Bibcode: 1991BAAS...23.1049B Altcode: No abstract at ADS Title: p-mode absorption in the giant active region of 10 March, 1989 Authors: Braun, D. C.; Duvall, T. L., Jr. Bibcode: 1990SoPh..129...83B Altcode: A time series of velocity oscillations is observed in the vicinity of NOAA region 5395 with the Kitt Peak vacuum telescope for 6.8 hours on 1989 March 10 as part of a program to study the interaction of solar p-mode oscillations with solar active regions. The data is transformed in a cylindrical coordinate system centered on the visible sunspot, then Hankel- and Fourier-transformed to produce the power spectra of in- and outgoing acoustic waves. It is observed that a maximum of nearly 70% of the power of incident high-degree modes is absorbed by this unusually large sunspot group. The absorptive properties of this active region are compared with those of more typical regions studied previously. Title: The Spatial Distribution of p-Mode Absorption in Active Regions Authors: Braun, D. C.; Labonte, B. J.; Duvall, T. L., Jr. Bibcode: 1990ApJ...354..372B Altcode: The interaction of solar p-mode waves and active regions has been the subject of recent observational and theoretical investigations. Observations show that up to one-half of the power of incident high-degree acoustic may be absorbed in and around sunspots. In this paper the horizontal spatial distribution of high-degree p-mode absorption in solar active regions is explored. An appropriate Fourier-Hankel transform can be used to detect the mean absorption of waves passing through any given point on the solar surface. By repeating the analysis at multiple positions a map of the absorption can be constructed. A technique for optimal computation of absorption maps is developed and applied to observations of several active regions and an area of quiet sun near disk center. By comparing the distribution of p-mode absorption with magnetograms and line-wing intensity images, it is directly observed that the absorption is not limited to the location of the visible sunspots but is also associated with magnetic fields in the surrounding plage. It is estimated that the absorption efficiency scales roughly with the magnetic flux density, although the absorption appears to saturate inside the strongest fields. Title: Helioseismic Imaging of Sunspots at Their Antipodes Authors: Lindsey, Charles; Braun, Douglas C. Bibcode: 1990SoPh..126..101L Altcode: Recent work by Braun, Duvall, and LaBonte has shown that sunspots absorb helioseismic waves. We propose that sunspot absorption causes a seismic deficit that should be imaged at the antipode of the sunspot. If these images are observable, it should be possible to produce seismic maps of magnetic regions on the far side of the Sun. This possibility opens a broad range of synoptic and diagnostic applications. Diagnostic applications would include lifetimes of higher-frequency modes, and possibly rotation of the solar interior and detection of subsurface magnetic structure. We outline elements of the theory of seismic imaging and consider some applications. We propose the extention of acoustic holography to solar interior diagnostics in the context of antipodal imaging. Title: Far-Infrared Intensity Variations Caused by 5 Minute Oscillations Authors: Lindsey, C.; Kopp, G.; Becklin, E. E.; Roellig, T.; Werner, M. W.; Jefferies, J. T.; Orrall, F. Q.; Braun, D.; Mickey, D. L. Bibcode: 1990ApJ...350..475L Altcode: Observations of solar IR intensity variations at 50, 100, and 200 microns were made simultaneously and cospatially with Doppler measurements in the sodium D1 line at 5896 A. Brightness temperature variations of several K in amplitude are highly correlated with five minute Doppler oscillations. The brightness variations are attributed to work done on the chromospheric medium by compression, driven by the five minute oscillations. The Doppler oscillations lead the brightness variations by about 47 deg in phase at 50 and 100 microns and by about 72 deg in phase at 200 microns. Title: Observations of p-Mode Absorption in Active Regions Authors: Braun, D. C.; Duvall, T. L., Jr.; Jefferies, S. M. Bibcode: 1990LNP...367..181B Altcode: 1990psss.conf..181B We present here a summary of results on the interaction of p-modes with solar active regions based on observations made at the Kitt Peak Solar Vacuum Telescope and the geographic South Pole. A travelling wave decomposition of p-modes is performed in a cylindrical coordinate system centered on the active regions. Significant absorption of p-mode wave power is observed to occur in all of the regions and is a function of horizontal wavenumber () - increasing linearly with k up to some maximum value and remaining constant for higher wavenumbers. The maximum fractional absorption of incident power is about 0.2 for small pores and 0.4 for typical isolated sunspots (radius = 15 Mm). A maximum of 70% absorption is seen in the large sunspot group of March 1989 (radius = 60 Mm). No convincing variation of the absorption with temporal frequency (i.e. radial order) is seen, although not entirely ruled out considering the relative errors involved with the power measurements. No significant difference in the amount of p-mode absorption is detected between equal 3-hour time intervals before and after a class X4 flare in the March 1989 region. No excess of outgoing waves following the time of the flare is detected. These observations do not support the suggestion that large flares may excite observable acoustic waves in the photosphere. Title: The interaction of high-degree p-mode oscillations with solar active regions Authors: Braun, Douglas C Doug Bibcode: 1988PhDT.......201B Altcode: No abstract at ADS Title: The Absorption of High-Degree p-Mode Oscillations in and around Sunspots Authors: Braun, D. C.; Duvall, T. L., Jr.; Labonte, B. J. Bibcode: 1988ApJ...335.1015B Altcode: The direct interaction of p-modes and sunspots is investigated in four observed active regions using a partial wave analysis in a cylindrical coordinate system centered on the spots. Up to half the power of incident p-modes is absorbed by the sunspots. By measuring the magnitude of absorption as a function of horizontal wavenumber and azimuthal order the authors have determined that the absorption is not only from the umbrae of the spots but is also significant within the penumbrae, and in some cases it appears to be associated with the presence of extended magnetic fields surrounding the sunspots. The amount of p-mode energy removed by magnetic fields is estimated for each of the regions observed. Title: Tomography of Solar Active Regions Authors: Braun, D. C.; Labonte, B. J.; Duvall, T. L., Jr. Bibcode: 1988BAAS...20..701B Altcode: No abstract at ADS Title: A Solar Chromosphere and Spicule Model Based on Far-Infrared Limb Observations Authors: Braun, D.; Lindsey, C. Bibcode: 1987ApJ...320..898B Altcode: Techniques developed for LTE radiative transfer problems in a rough atmosphere were used to compute a model chromosphere containing spicules consistent with high-resolution solar limb observations from 100 microns to 2.6 mm. The model consists of a smooth, plane-parallel temperature minimum region extending from the photosphere to a height of 1000 km and randomly distributed cylindrical spicules above this height. It is found that the observed limb brightness profiles are well fitted by spicules with electron temperatures on the order of 7000 K. Title: Acoustic Absorption by Sunspots Authors: Braun, D. C.; Duvall, T. L., Jr.; Labonte, B. J. Bibcode: 1987ApJ...319L..27B Altcode: The paper presents the initial results of a series of observations designed to probe the nature of sunspots by detecting their influence on high-degree p-mode oscillations in the surrounding photosphere. The analysis decomposes the observed oscillations into radially propagating waves described by Hankel functions in a cylindrical coordinate system centered on the sunspot. From measurements of the differences in power between waves traveling outward and inward, it is demonstrated that sunspots appear to absorb as much as 50 percent of the incoming acoustic waves. It is found that for all three sunspots observed, the amount of absorption increases linearly with horizontal wavenumber. The effect is present in p-mode oscillations with wavelengths both significantly larger and smaller than the diameter of the sunspot umbrae. Actual absorption of acoustic energy of the magnitude observed may produce measurable decreases in the power and lifetimes of high-degree p-mode oscillations during periods of high solar activity. Title: The Absorption of 5-Minute Oscillations by Sunspots Authors: Braun, D. C.; Labonte, B. J.; Duvall, T. L., Jr. Bibcode: 1987BAAS...19..936B Altcode: No abstract at ADS Title: Sunspots as Sinks of P-Mode Wave Energy Authors: Duvall, T. L., Jr.; Harvey, J. W.; Braun, D. C.; Labonte, B. J.; Pomerantz, M. A. Bibcode: 1987BAAS...19R.934D Altcode: No abstract at ADS Title: The Solar Irradiance From January to February, 1981 Authors: Braun, D. C.; Labonte, B. J. Bibcode: 1985BAAS...17..756B Altcode: No abstract at ADS Title: Observations of the Ca II K spectral line in He 10830 Å dark points. Authors: Holt, R.; Fortune, N.; Braun, D.; Mullan, D. Bibcode: 1985BAAS...17..760H Altcode: No abstract at ADS Title: Observations of the Ca II K spectral line in He 10830 Å dark points. Authors: Holt, R.; Fortune, N.; Braun, D.; Mullan, D. Bibcode: 1985BAAS...17..933H Altcode: No abstract at ADS Title: Planet Size Stars or Star Size Planets Authors: McCarthy, D.; Low, F.; Kleinmann, S.; Lippincott, S. L.; Braun, D. Bibcode: 1983S&T....66..114M Altcode: No abstract at ADS Title: Astrometric and infrared speckle analysis of the visually unresolved binary BD +41 328. Authors: Lippincott, S. L.; Braun, D.; McCarthy, D. W., Jr. Bibcode: 1983PASP...95..271L Altcode: BD +41°328 (PCC 372), a solar-type 5th magnitude star at a distance of 14 parsecs was discovered to have an unseen companion from proper-motion analysis of astrometric plates taken with the Sproul 61-cm refractor, thus excluding it as a candidate for a solar planetary-type system. The combination of an improved photocentric orbit from recent astrometry and measurement of the companion's separation and brightness by infrared speckle interferometry at 2.2 microns indicates that the companion is a red dwarf with a mass of 0.38 ± 0.07Msun. It revolves around the primary with a period of 19.5 years and a semimajor axis of 8.9 ± 0.5 AU.