Author name code: cadavid ADS astronomy entries on 2022-09-14 author:"Cadavid, Ana Cristina" ------------------------------------------------------------------------ Title: Plasma Flows in the Atmospheric Layers of Coronal Hole and Quiet-Sun Regions in the Context of Their Magnetic Field Environment Authors: Shannon, Scott; Cadavid, Ana; Miralles, Mari Paz Bibcode: 2021AGUFMSH45B2363S Altcode: Recent work (Kayshap et al. (2018), Tripathi et al. (2021)) have identified similarities and differences in coronal hole and adjacent quiet-Sun intensities and Doppler velocities depending on their magnetic field distributions. In our present study, we improve on this work by investigating the relation between plasma flows in different atmospheric layers, chromosphere and transition region, in the context of their magnetic field environment. We use UV spectroscopic data from the Interface Region Imaging Spectrograph (IRIS) to calculate Doppler and non-thermal velocities and spectral line profile asymmetries in order to characterize the plasma flows. Contemporaneous line-of-sight magnetic images obtained with the SDO/Helioseismic and Magnetic Imager (HMI) are used to classify the plasma flow data according to their associated magnetic field strengths. In addition, we also produce potential field extrapolations to gain an insight on the topology associated with the plasma flows in the different solar atmospheric layers. This work is supported by NASA grant 80NSSC21K0725 to the Smithsonian Astrophysical Observatory. Title: The Relation Between Plasma Properties And UV Intensity Fluctuations In Equatorial Coronal Holes Authors: Shannon, S. D.; Cadavid, A. C.; Miralles, M. P.; Wells, L. Bibcode: 2021AAS...23832812S Altcode: While the origin of the solar wind is still an open problem, observations indicate that fast, and sometimes slow, wind originates from equatorial coronal holes. However, the exact locations within them, and the mechanisms that cause the heating and outward acceleration of solar plasmas, are not understood. In the present study, we investigate the relation between the plasma properties in the chromosphere, transition region, and corona and the properties of UV intensity fluctuations in equatorial coronal holes. We analyzed UV spectroscopic and imaging data from the Interface Region Imaging Spectrograph (IRIS) in the lower atmosphere and EUV coronal images from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) spacecraft. Doppler and non-thermal velocities in the lower atmosphere and contemporaneous UV emission time series are used to identify sites of turbulent (or persistent) processes in the solar atmosphere. The line-of-sight SDO/Helioseismic and Magnetic Imager (HMI) magnetic field measurements provide a context for the physical environment. Title: A Machine Learning Approach to Identify Solar Stokes Profiles in Flaring and Non-Flaring Active Regions Authors: Venkatesan, V.; Cadavid, A. C.; Romich, K.; Choudhary, D. P. Bibcode: 2020AGUFMNG0040001V Altcode: Solar flares are explosive events on the surface of the Sun that release electromagnetic radiation, which can disrupt the earth's atmosphere and cause havoc in our communication system. Models for flare forecasting use properties of active region (AR) magnetic fields as predictors of flare occurrence. The magnetic field properties are obtained using inversion models that decode the information contained in Stokes Profiles (SP) as the radiation passes through the solar atmosphere. The inversion techniques ignore the rich information contained in the SP since they tend to use line fitting methods and derive average magnetic field properties. The line parameters can give better information on the magnetic field complexity of the AR atmosphere. We apply a modified K-means clustering method to Hinode spectropolarimetric data to identify and classify the Stokes V profiles in flaring and non-flaring ARs. The modified K-means method leads to a stable result, in which random initializations converge to comparable clustering. The profiles which characterize the centroids of the clusters are used to calculate three-line parameters: the amplitude asymmetry, the area asymmetry (associated with the degree of non-linear polarization), and the percentage of atypical profiles inside and outside the polarity inversion lines (PIL). We find that the amplitude asymmetry is higher in non-flaring vs. flaring regions; the area asymmetry is greater in flaring ARs vs. non-flaring ARs, and inside the PIL vs. outside. Our results indicate that flaring ARs, harbor a higher percentage of atypical profiles compared to non-flaring ARs & outside the PIL. These results are compatible with those found using the individual pixel profiles in the calculations. They indicate that the three parameters can be used to distinguish flaring from non-flaring ARs. Title: Four Solar Cycle Spectrum Variation of the Sun-as-a-Star Authors: Choudhary, D. P.; Chapman, G. A.; Cadavid, A. C.; Cookson, A. Bibcode: 2020AGUFMA227.0008C Altcode: The chromospheric activity of the Sun is governed by the magnetic field anchored in the photosphere. The solar cycle 23 was a smaller cycle compared to the recent cycles, in terms of sunspot number and total disk integrated magnetic field. Comparison of the chromospheric lines in past cycles may provide insight of the effect of magnetic field on solar atmosphere. In this paper, we study the dependence of chromospheric activity on magnetic field of the Sun-as-a-star in four solar cycles during 1977-2018. The study is conducted by merging the data obtained by Dr. W. Livingston and the observations by Integrated Sunlight Spectrometer (ISS) and Vector Spectromagnetograph (VSM) of Synoptic Optical Long-term Investigations of the Sun (SOLIS) instrument. The chromospheric activity is measured as the line depth and equivalent width (EW) of spectral lines in Hα, He I 10830 nm, Ca II 854.2 nm, Ca II H and K, and Na D I 589.6 nm obtained with the ISS. The full disk mean total magnetic flux (FDMTMF) observed with the VSM is used as the measure of magnetic activity of the Sun. The equivalent width of Ca II K and He I 10830 nm measured by Livingston along with the Magnetic Plage Strength Index (MPSI) value and a Mount Wilson Sunspot Index (MWSI) obtained with 150-Foot Solar Tower in Mt. Wilson Observatory are used to further study the relationship between the magnetic field and chromospheric activity. Title: Variability in Irradiance and Photometric Indices During the Last Two Solar Cycles Authors: Choudhary, Debi Prasad; Cadavid, Ana Cristina; Cookson, Angela; Chapman, Gary A. Bibcode: 2020SoPh..295...15C Altcode: The Total Solar Irradiance (TSI) primarily varies on an 11-year time scale and is governed by features such as sunspots and associated decay products such as plage and faculae. These short-lived physical features can also modulate the solar irradiance at intermediate and short temporal scales. Here we investigate the periodic variations, at solar-surface-rotation time scales, of photometric indices derived from images obtained at the San Fernando Observatory (SFO), and we compare them to the properties of the contemporaneous TSI as measured by the Total Irradiance Monitor (TIM) onboard the SOlar Radiation and Climate Experiment (SORCE) spacecraft. Both the daily ground- and space-based data, which span from early 2003 to late 2018, present missing pixels. We use an autoregressive gap-filling method to construct continuous time series to be analyzed via Fourier and wavelet spectral techniques. Lomb-Scargle periodograms, which can handle time series with missing data, are used for comparison. Both the Fourier spectral power and the periodograms yield compatible results with statistically significant periodicities in the range 25 - 35 days. All of the time series have maximum power at 27 days. Significant secondary periods are found at 29 - 30 days and 34 - 35 days. Wavelet analyses of the full time series show that the photometric index resulting from the red-continuum photometric sum [Σr] and the TSI exhibit common high power at surface-solar-rotation scales during the active part of the solar cycle. The phase relation at the surface-solar-rotation scales is not definite. During the solar minimum interval between Solar Cycles (SCs) 23 and 24, variations in the TSI are found to be related to variations both in the photometric index ΣK, calculated from Ca II K-line photometric sums and in the magnetic flux in the solar activity latitudinal band (as found in previous work). This suggests that the TSI changes during the minimum are caused by the reduced line-blanketing effect of diffused magnetic field. Title: Comparison of the Scaling Properties of EUV Intensity Fluctuations in Coronal Hole and Quiet-Sun Regions Authors: Cadavid, Ana Cristina; Miralles, Mari Paz; Romich, Kristine Bibcode: 2019ApJ...886..143C Altcode: 2019arXiv191009541C Using detrended fluctuation analysis and rescaled range analysis, we investigate the scaling properties of extreme ultraviolet (EUV) intensity fluctuations of low-latitude coronal holes (CHs) and neighboring quiet-Sun (QS) regions in signals obtained with the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly instrument. Contemporaneous line-of-sight SDO/Helioseismic and Magnetic Imager magnetic fields provide a context for the physical environment. We find that the intensity fluctuations in the time series of EUV images present at each spatial point a scaling symmetry over the range ∼20 minute to ∼1 hr. Thus we are able to calculate a generalized Hurst exponent and produce image maps, not of physical quantities like intensity or temperature, but of a single dynamical parameter that sums up the statistical nature of the intensity fluctuations at each pixel. In QS regions and in CHs with magnetic bipoles, the scaling exponent (1.0 < α ≤ 1.5) corresponds to anticorrelated turbulent-like processes. In CHs, and in QS regions primarily associated with (open) magnetic field of dominant polarity, the generalized exponent (0.5 < α < 1) corresponds to positively correlated (persistent) processes. We identify a tendency for α ∼ 1 near CH boundaries and in other regions in which open and closed magnetic fields are in proximity. This is a signature of an underlying 1/f type process that is characteristic for self-organized criticality and shot-noise models. Title: Stokes Line Parameters as Possible Indicators of Flaring Activity: A Comparison of Flaring and Non-Flaring Active Regions Authors: Romich, K.; Cadavid, A. C.; Choudhary, D. P.; Beck, C. Bibcode: 2019AGUFMSH31D3338R Altcode: While the association between solar active regions (ARs) and solar flares is well-established, there is currently no reliable means of determining when (or if) a given AR will flare. Much of flare forecasting is based on the application of machine-learning statistical techniques that use parameters derived from the local magnetic field as predictors; these are commonly obtained through spectropolarimetric inversions using Stokes profiles from the observed radiation. The standard inversion codes, such as those based on the Milne-Eddington approximation, yield the average magnetic field values at or near flare locations. However, this fails to utilize the rich information contained in the shape of Stokes profiles, such as the existence of line-of-sight (LOS) magnetic and velocity gradients and multiple magnetic components along the LOS or within the resolving element. The resulting loss of information can potentially lead to inaccurate forecasts. We propose a novel approach, in which line parameters derived from spectrally-resolved Stokes profiles are considered as possible precursors to flare events. Using data from the spectropolarimeter onboard the Hinode satellite, we examine the amplitude asymmetry, net circular polarization, and degree of complexity of Stokes V profiles from several flaring and non-flaring ARs. Particular attention is given to regions near the polarity inversion line (PIL) due to its documented role in flare initiation. We define the PIL using the magnetic field vector relative to the solar surface, which we calculate from the Stokes Q, U, and V profiles; this corrects for projection effects arising from LOS observations of magnetic flux from ARs off disc center. In light of the shortcomings of existing methods, we hope to expand the set of viable indicators of flaring activity with the long-term goal of improving flare forecasting models. Title: Temporal relations between total solar irradiance and photometric indices during the last two solar cycles. Authors: Cadavid, A. C.; Choudhary, D. P.; Chapman, G. A.; Cookson, A. Bibcode: 2019AGUFMSH11D3391C Altcode: Our present understanding, from both empirical and semi-empirical models, indicates that the variations in the Total Solar Irradiance (TSI) on time scales of days to the solar cycle are primarily associated with solar surface magnetic activity, which encompasses sunspots, faculae, and the network. In previous work, approximately seven years of TSI measurements from the Total Irradiance Monitor (TIM) on board the SOlar Radiation and Climate Experiment (SORCE) spacecraft were compared with photometric indices derived from red and K-line images obtained on a daily basis at the San Fernando Observatory (SFO), California State University Northridge (CSUN). The best linear regression model yielded a coefficient of multiple determination, R2, of 0.9495. Expanding on this earlier work and employing additional analysis techniques not previously used, we consider 16 years of SORCE and SFO data, from early 2003 to late 2018. We use an autoregressive gap filling method to construct continuous series which can be analyzed via Fourier and wavelet spectral techniques in order to investigate the characteristics of the time signals on short temporal scales. Lomb-Scargle periodograms, which can handle time series with missing data, are used for comparison. Both the Fourier spectral power and the periodograms yield compatible results with significant periodicities on the solar rotation time scales. For both active and quiet Sun periods, cross-wavelet transforms between the TSI and the photometric indices signals are used to identify regions of high common power in the time-frequency maps. The wavelet transform coherence indicates local periods and times during which the photometric indices signals and TSI have significant coherence and phase locking, independent of the power. Title: Classification of Active-Region Stokes Profiles with Possible Applications for Flare Forecasting Authors: Romich, Kristine; Cadavid, Ana Cristina; Choudhary, Debi Prasad Bibcode: 2019shin.confE.164R Altcode: While the association between solar active regions (ARs) and solar flares is well-established, there is currently no reliable means of determining when (or if) a given AR will flare. Much of flare forecasting is based on the application of machine-learning statistical techniques that use quantities derived from the local magnetic field as predictors. These properties, in turn, are derived from dopplergrams obtained at different polarizations or through spectropolarimetric inversions using Stokes profiles from the observed radiation. The standard inversion techniques, such as those based on the Milne-Eddington approximation, give the average magnetic field values of flare locations. However, this fails to utilize the rich information contained in the shape of Stokes profiles, such as the existence of line-of-sight (LOS) magnetic and velocity gradients and multiple magnetic components along the LOS or within the resolving element. This results in loss of information and potentially inaccurate forecasts. Here we outline a novel approach, in which parameters derived from the raw Stokes profiles are examined as possible precursors to flare events. Using data from the spectropolarimeter onboard the Hinode satellite, we examine the amplitude asymmetry, net circular polarization, and degree of complexity of Stokes profiles from flaring and non-flaring ARs. Particular attention is given to regions near the polarity inversion line due to its documented role in flare initiation. In light of the shortcomings of existing methods, we hope to expand the set of viable indicators of flaring activity with the long-term goal of improving flare forecasting models. Title: EUV Intensity Fluctuations in Equatorial Coronal Holes, Boundaries, and Adjacent Quiet-Sun Regions Authors: Romich, Kristine; Cadavid, Ana Cristina; Miralles, Mari Paz Bibcode: 2018shin.confE..42R Altcode: To quantify differences in the long-term dynamics of equatorial coronal holes (CH) and neighboring quiet-Sun (QS) regions, we investigate the scaling properties and long-term correlations of the fluctuations of SDO/AIA EUV intensity signals. Contemporaneous SDO/HMI magnetic images provide a physical context for these signals. We apply the methods of rescaled range (R/S) analysis and detrended fluctuation analysis (DFA) to generate image maps of Hurst exponents and generalized Hurst exponents, respectively; these sum up the statistical nature of the intensity fluctuations at each pixel. We also discuss similarities and differences between CH interiors, adjacent QS regions, and the boundaries between them. Title: Comparison of the Scaling Properties of EUV Intensity Fluctuations in Coronal Holes to those in Regions of Quiet Sun Authors: Cadavid, Ana Cristina; Lawrence, John K.; Jennings, Peter John Bibcode: 2017SPD....4810613C Altcode: We investigate the scaling properties of EUV intensity fluctuations seen in low-latitude coronal holes (CH) and in regions of Quiet Sun (QS), in signals obtained with the SDO/AIA instrument in the 193 Å waveband. Contemporaneous time series in the 171 and 211 Å wavebands are used for comparison among emissions at different heights in the transition region and low corona. Potential-field extrapolations of contemporaneous SDO/HMI line-of-sight magnetic fields provide a context in the physical environment. Detrended fluctuation analysis (DFA) shows that the variance of the fluctuations obeys a power-law as a function of temporal scales with periods in the range ~15-60 min. This scaling is characterized by a generalized Hurst exponent α. In QS regions, and in regions within CHs that include magnetic bipoles, the scaling exponent lies in the range 1.0 < α < 1.5, and it thus corresponds to anti-correlated, turbulent-like, dynamical processes. Regions inside the coronal holes primarily associated with magnetic field of a dominant single polarity, have a generalized exponent (0.5 < α < 1) corresponding to positively correlated (“persistent”) processes. The results indicate the influence of the magnetic fields on the dynamics of the emission. Title: Multi-scaling Properties of EUV Intensity Fluctuations and Models for Impulsive Heating Authors: Cadavid, A. C.; Rivera, Y.; Lawrence, J. K.; Christian, D. J.; Jennings, P.; Rappazzo, A. F. Bibcode: 2016AGUFMSH42B..05C Altcode: There is wide agreement on the importance of impulsive processes ("nanoflares") to explain coronal heating. Diagnostics of observational data are necessary to uncover signatures of the underlying mechanisms, and, by comparing to those of simulated data, to determine whether a model explains the observations. We have investigated the multi-scaling properties that characterize the intermittency of AIA/SDO radiance fluctuations. Lags between pairs of wavebands were used to distinguish coronal from transition region (TR) signals. Noise degrades the signals, so the 171Å emission, with the highest signal-to-noise ratio, provides the best information. In an active region core, for both loops and for diffuse emission, the probability distribution functions (PDFs) of the increments of both TR and coronal signals are "quasi-Gaussian" for large temporal scales and "leptokurtic" (peaked with heavy tails) for small time increments, as expected for turbulent systems. Multifractal Detrended Fluctuation Analysis (MF-DFA) shows that the variance of the fluctuations obeys a power law as a function of temporal scales in the range 15-45 min. The value of the scaling exponent indicates that, on average, the time series are nonstationary and anti-persistent with small fluctuations following large fluctuations and vice versa. Other moments of the fluctuations obey corresponding power laws and the multi-scaling exponents quantify the degree of the intermittency in the context of multifractality. The variation in the scaling exponents results from long term correlation in the time series. The multiscaling of the EUV data agrees qualitatively with simulated intensity from a simple model of impulsive bursts plus noise, and also with the ohmic dissipation in a Reduced Magnetohydrodynamic (RMHD) model for coronal loop heating. However, the observational data were found to disagree with the modeled PDFs of increments. There is indication that the multifractal properties in the observations could be related to a modified multiplicative cascade model characterized by two parameters. Title: Multifractal Solar EUV Intensity Fluctuations and their Implications for Coronal Heating Models Authors: Cadavid, A. C.; Rivera, Y. J.; Lawrence, J. K.; Christian, D. J.; Jennings, P. J.; Rappazzo, A. F. Bibcode: 2016ApJ...831..186C Altcode: 2016arXiv160902625C We investigate the scaling properties of the long-range temporal evolution and intermittency of Atmospheric Imaging Assembly/Solar Dynamics Observatory intensity observations in four solar environments: an active region core, a weak emission region, and two core loops. We use two approaches: the probability distribution function (PDF) of time series increments and multifractal detrended fluctuation analysis (MF-DFA). Noise taints the results, so we focus on the 171 Å waveband, which has the highest signal-to-noise ratio. The lags between pairs of wavebands distinguish between coronal versus transition region (TR) emission. In all physical regions studied, scaling in the range of 15-45 minutes is multifractal, and the time series are anti-persistent on average. The degree of anti-correlation in the TR time series is greater than that for coronal emission. The multifractality stems from long-term correlations in the data rather than the wide distribution of intensities. Observations in the 335 Å waveband can be described in terms of a multifractal with added noise. The multiscaling of the extreme-ultraviolet data agrees qualitatively with the radiance from a phenomenological model of impulsive bursts plus noise, and also from ohmic dissipation in a reduced magnetohydrodynamic model for coronal loop heating. The parameter space must be further explored to seek quantitative agreement. Thus, the observational “signatures” obtained by the combined tests of the PDF of increments and the MF-DFA offer strong constraints that can systematically discriminate among models for coronal heating. Title: Photoelectric instability and debris disk rings: One theory to rule them all Authors: Lyra, Wladimir; Cadavid, Ana Cristina; Choudhary, Debi Prasad; Christian, Damian; Kuchner, Marc Jason; Richert, Alexander John Wolf Bibcode: 2016hst..prop14572L Altcode: HST images of circumstellar debris disks have helped advance tremendously our understanding of these disks, thought to represent planetary systems during the late stages of planet formation as the gas clears and the system becomes optically thin. These systems are analogs of the Kuiper belt in the solar system, and show a variety of non-trivial structures attributed to planetary perturbations and utilized to constrain the properties of the planets. However, analyses of these systems have largely ignored the fact that, increasingly, debris disks are found to contain small quantities of gas. We have recently shown that dust-gas interactions with photoelectric heating can produce some of the key patterns seen in debris disks that were previously attributed to planets. We propose to code software and run a suite of models to develop the theory of photoelectric instability in gas-rich optically thin disks in light of the observational constrains set by HST observations and its interaction with other dynamically important processes such as hydromagnetic turbulence, radiation forces, planetary perturbers, and stellar flares. Title: Scaling and Long Term Correlation Properties of EUV Intensity Fluctuations and Implications for Impulsive Heating Mechanisms of the Solar Corona Authors: Rivera, Y.; Cadavid, A. C.; Lawrence, J. K. Bibcode: 2015AGUFMSH13B2445R Altcode: Scaling properties of the stochastic component of EUV intensity fluctuations from AIA/SDO observations show long-term correlations and can carry information about the energetics of coronal loops. Power spectra indicate that the stochastic time series are nonstationary. Thus we apply the method of detrended fluctuation analysis (DFA), which was designed to determine the true scaling properties of a signal. It can identify the long-term correlations in noisy and nonstationary time series after accounting for external influences. The scaling exponents encountered in the solar fluctuation functions indicate long-time correlations of the series. We study to what degree the properties may correspond to those of fractional Brownian motion (fBm) or fractional Gaussian noise (fGn) processes. Analysis of a non-flaring active region (AR) indicates that the EUV emission in the hot 131 Å (Fe XXI), hot 94 Å (Fe XVIII) and 335 Å intensity bands has different properties from the warm emission in the 211, 193 and 171 Å bands. Further differences are found in the quiet vs AR core regions. The intensity values satisfy probability distribution functions (pdf)s corresponding to superposed lognormal and Gaussian functions. The pdfs of the increments are Gaussian. The properties of the data can be reproduced by a physically motivated phenomenological model for impulsive heating with added noise. We propose that DFA, complemented with the identification of the pdfs, can be a useful tool to constrain more realistic models of coronal heating. Title: Correlation and scaling properties of non-stationary intensity fluctuations in coronal EUVtime series in different physical environments Authors: Cadavid, Ana Cristina; Lawrence, John; Rivera, Yeimy Bibcode: 2015TESS....120307C Altcode: Previously we have used EUV observations from AIA/SDO to examine properties of energy deposition into coronal-loops in non-flaring active region (AR) cores. The evolution of the loop apex intensity, temperature, and electron density indicate that the loops are impulsively heated in a mode compatible with high intensity nanoflare storms characterized by a progressive cooling pattern in the EUV lines with the hot channels leading the emission. Spectra of the hot 131 Å intensity (basically Fe XXI) and of the energy dissipation in a 2D model of loop magneto-turbulence compatible with nanoflare statistics, both exhibit three scaling regimes with low frequencies corresponding to 1/f noise, the intermediate range indicating a persistent process, and high frequencies corresponding to white noise. The varying power law behavior in these spectra indicates that both the observational and the simulated time series are not stationary. Therefore to extend the analysis beyond the AR loops we apply the method of detrended fluctuation analysis (DFA) that was developed to study the long-range correlations in non-stationary signals. DFA provides a scaling exponent that characterizes the correlation properties of the signal and which can be related both to the spectral exponents and to the Hurst exponent. In areas of diffuse emission and for all the spectral channels the time series of intensity fluctuations are characterized by scaling exponents that indicate a weak positive correlation across all time scales. In regions with intermittent intensity brightenings a cross-over occurs at timescales near 10 - 20 min with different exponents describing the degree of positive correlation of the intensity fluctuations at short and long time scales. Qualitative differences exist between the exponents of the hotter and the cooler channels. We have further compared the scaling properties of the time series associated with different physical environments distinguished by the possibility of underlying nanoflare storms, or by the strength of the magnetic field in contemporaneous HMI images. Another comparison is made to the scaling properties of simulations of energy dissipation in magnetoturbulence. Title: Heating Mechanisms for Intermittent Loops in Active Region Cores from AIA/SDO EUV Observations Authors: Cadavid, A. C.; Lawrence, J. K.; Christian, D. J.; Jess, D. B.; Nigro, G. Bibcode: 2014ApJ...795...48C Altcode: 2014arXiv1404.7824C We investigate intensity variations and energy deposition in five coronal loops in active region cores. These were selected for their strong variability in the AIA/SDO 94 Å intensity channel. We isolate the hot Fe XVIII and Fe XXI components of the 94 Å and 131 Å by modeling and subtracting the "warm" contributions to the emission. HMI/SDO data allow us to focus on "inter-moss" regions in the loops. The detailed evolution of the inter-moss intensity time series reveals loops that are impulsively heated in a mode compatible with a nanoflare storm, with a spike in the hot 131 Å signals leading and the other five EUV emission channels following in progressive cooling order. A sharp increase in electron temperature tends to follow closely after the hot 131 Å signal confirming the impulsive nature of the process. A cooler process of growing emission measure follows more slowly. The Fourier power spectra of the hot 131 Å signals, when averaged over the five loops, present three scaling regimes with break frequencies near 0.1 min-1 and 0.7 min-1. The low frequency regime corresponds to 1/f noise; the intermediate indicates a persistent scaling process and the high frequencies show white noise. Very similar results are found for the energy dissipation in a 2D "hybrid" shell model of loop magneto-turbulence, based on reduced magnetohydrodynamics, that is compatible with nanoflare statistics. We suggest that such turbulent dissipation is the energy source for our loops. Title: Different Periodicities in the Sunspot Area and the Occurrence of Solar Flares and Coronal Mass Ejections in Solar Cycle 23 - 24 Authors: Choudhary, D. P.; Lawrence, J. K.; Norris, M.; Cadavid, A. C. Bibcode: 2014SoPh..289..649C Altcode: In order to investigate the relationship between magnetic-flux emergence, solar flares, and coronal mass ejections (CMEs), we study the periodicity in the time series of these quantities. It has been known that solar flares, sunspot area, and photospheric magnetic flux have a dominant periodicity of about 155 days, which is confined to a part of the phase of the solar cycle. These periodicities occur at different phases of the solar cycle during successive phases. We present a time-series analysis of sunspot area, flare and CME occurrence during Cycle 23 and the rising phase of Cycle 24 from 1996 to 2011. We find that the flux emergence, represented by sunspot area, has multiple periodicities. Flares and CMEs, however, do not occur with the same period as the flux emergence. Using the results of this study, we discuss the possible activity sources producing emerging flux. Title: Non-steady, Intermittent, Hot Loops in an Active Region Observed with the SDO/AIA Authors: Cadavid, Ana C.; Lawrence, J. K.; Christian, D. J. Bibcode: 2013SPD....44...48C Altcode: While there is accumulated evidence of high temperature coronal emission in active region cores that corresponds to structures in equilibrium, other studies have found of evolving loops. We investigate the EUV intensity variations of two low and short coronal loops observed in the core of NOAA AR 11250 on 13 July 2011 between UT 12:02 and 16:32. The loops (32 Mm loop 1, 23 Mm loop 2), run directly between the AR opposite polarities, and are first detectable in the 94Å band (effective temperature ~ 7 MK). Space-time slices present intermittent brightenings evocative of turbulence. Spatial averages over the intermoss loop region lead to light curves used to analyze the temporal evolution of the loops. We find quantities with scaling regimes that are characteristic of intermittent processes. In particular intensity histograms display scaling ranges with slopes ~ -1.8, and spectra also show a scaling region for frequencies 1-8 mHz, with slopes - 3.8 (loop 1) and -2.8 (loop 2). We further investigate the time evolution of the loops in five other AIA EUV channels. The results are separated into two classes. Group A (94Å, 335Å, 211Å) characterized by hotter temperatures 2-6 MK), and group B (193Å, 171Å, 131Å) by cooler temperatures (0.4 - 1.6 MK). In loop 1 (group A) the intensity peaks in the 94Å channel are followed by maxima in the 335 Å channel with a time lag of ~10 min, suggestive of a cooling pattern with an exponential decay. The 211Å maxima follow those in the 335 Å channel, but there is no systematic relation which would indicate a progressive cooling process. In group B the signals in the 171 and 131Å channels track each other closely, and tend to lag behind the 193Å. The three signals follow a general gradual increase reaching a maximum at about the middle of the time series and then decrease. An exponential cooling model can also be associated with the 193 and 171Å pair. For loop 2 the observations in the group B light curves present similar properties as in loop 1. In contrast the intensity curves in group A only show one distinct case which could be a candidate for exponential decay via a 94 Å to 335 Å cooling process.Abstract (2,250 Maximum Characters): While there is accumulated evidence of high temperature coronal emission in active region cores that corresponds to structures in equilibrium, other studies have found of evolving loops. We investigate the EUV intensity variations of two low and short coronal loops observed in the core of NOAA AR 11250 on 13 July 2011 between UT 12:02 and 16:32. The loops (32 Mm loop 1, 23 Mm loop 2), run directly between the AR opposite polarities, and are first detectable in the 94Å band (effective temperature ~ 7 MK). Space-time slices present intermittent brightenings evocative of turbulence. Spatial averages over the intermoss loop region lead to light curves used to analyze the temporal evolution of the loops. We find quantities with scaling regimes that are characteristic of intermittent processes. In particular intensity histograms display scaling ranges with slopes ~ -1.8, and spectra also show a scaling region for frequencies 1-8 mHz, with slopes - 3.8 (loop 1) and -2.8 (loop 2). We further investigate the time evolution of the loops in five other AIA EUV channels. The results are separated into two classes. Group A (94Å, 335Å, 211Å) characterized by hotter temperatures 2-6 MK), and group B (193Å, 171Å, 131Å) by cooler temperatures (0.4 - 1.6 MK). In loop 1 (group A) the intensity peaks in the 94Å channel are followed by maxima in the 335 Å channel with a time lag of ~10 min, suggestive of a cooling pattern with an exponential decay. The 211Å maxima follow those in the 335 Å channel, but there is no systematic relation which would indicate a progressive cooling process. In group B the signals in the 171 and 131Å channels track each other closely, and tend to lag behind the 193Å. The three signals follow a general gradual increase reaching a maximum at about the middle of the time series and then decrease. An exponential cooling model can also be associated with the 193 and 171Å pair. For loop 2 the observations in the group B light curves present similar properties as in loop 1. In contrast the intensity curves in group A only show one distinct case which could be a candidate for exponential decay via a 94 Å to 335 Å cooling process. Title: 2nd ATST-EAST Workshop in Solar Physics: Magnetic Fields from the Photosphere to the Corona Authors: Rimmele, T. R.; Tritschler, A.; Wöger, F.; Collados Vera, M.; Socas-Navarro, H.; Schlichenmaier, R.; Carlsson, M.; Berger, T.; Cadavid, A.; Gilbert, P. R.; Goode, P. R.; Knölker, M. Bibcode: 2012ASPC..463.....R Altcode: No abstract at ADS Title: Coupled Effects of a Perturbation in a Complex Structure Observed with SDO/AIA, SDO/HMI and ROSA/HARDcam Authors: Cadavid, A. C.; Lawrence, J. K.; Christian, D. J.; Jess, D. B.; Mathioudakis, M. Bibcode: 2012AGUFMSH51A2197C Altcode: We study properties of intensity fluctuations in NOAA Active Region 11250 observed on 13 July 2011 starting at UT 13:32. Included are data obtained in the EUV bands of the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory (SDO/AIA) as well as nearly simultaneous observations of the chromosphere made, at much higher spatial and temporal resolution, with the Rapid Oscillations in the Solar Atmosphere (ROSA) and Hydrogen-Alpha Rapid Dynamics camera (HARDcam) systems at the Dunn Solar Telescope. A complex structure seen in both the ROSA/HARDcam and SDO data sets comprises a system of loops extending outward from near the boundary of the leading sunspot umbra. It is visible in the ROSA Ca II K and HARDcam Hα images, as well as the SDO 304 Å, 171 Å and 193 Å channels, and it thus couples the chromosphere, transition region and corona. In the ground-based images the loop structure is 4.1 Mm long. Some 17.5 Mm, can be traced in the SDO/AIA data. The chromospheric emissions observed by ROSA and HARDcam appear to occupy the inner, and apparently cooler and lower, quarter of the loop. We compare the intensity fluctuations of two points within the structure. From alignment with SDO/HMI images we identify a point "A" near the loop structure, which sits directly above a bipolar magnetic feature in the photosphere. Point "B" is characteristic of locations within the loops that are visible in both the ROSA/HARDcam and the SDO/AIA data. The intensity traces for point A are quiet during the first part of the data string. At time ~ 19 min they suddenly begin a series of impulsive brightenings. In the 171 Å and 193 Å coronal lines the brightenings are localized impulses in time, but in the transition region line at 304 Å they are more extended in time. The intensity traces in the 304 Å line for point B shows a quasi-periodic signal that changes properties at about 19 min. The wavelet power spectra are characterized by two periodicities. A 6.7 min period extends from the beginning of the series until about 25 minutes, and another signal with period ~3 min starts at about 20 min. The 193 Å power spectrum has a characteristic period of 5 min, before the 20 min transition and a 2.5 min periodicity afterward. In the case of HARDcam Hα data a localized 4 min periodicity can be found until about 7 min, followed by a quiet regime. After ~20 min a 2.3 min periodicity appears. Interestingly a coronal loop visible in the 94 Å line that is centrally located in the AR, running from the leading umbra to the following polarity, at about time 20 min undergoes a strong brightening beginning at the same moment all along 15 Mm of its length. The fact that these different signals all experience a clear-cut change at time about 20 min suggests an underlying organizing mechanism. Given that point A has a direct connection to the photospheric magnetic bipole, we conjecture that the whole extended structure is connected in a complex manner to the underlying magnetic field. The periodicities in these features may favor the wave nature rather than upflows and interpretations will be discussed. Title: Coupled Intensity Variations in Hot Coronal Loops Observed with SDO/AIA Authors: Lawrence, J. K.; Cadavid, A. C.; Christian, D. J. Bibcode: 2012AGUFMSH33D2265L Altcode: Data from the AIA on board SDO allow us to study EUV intensity variations of coronal loops. Here we study strong EUV brightenings of coronal loops in NOAA Active Region 11250 on 13 July 2011 between UT 13:32 and 14:32. The brightenings are seen only in the 94Å band of Fe XVIII, implying an effective temperature ~ 8 MK. The relevant loops run directly between the AR opposite polarities and are low and short. One example is an apparently single loop north of the AR midline. At UT 13:50 (18 min into the observational sequence - see the image) it began a strong brightening in the 94 Å band. This occurred at the same moment all along 15 Mm of its length to ~ 12 s accuracy. This suggests the presence of stored free energy along the loop that was released by an instability that must have propagated along it at 1500 km/s or faster. The maximum rate of increase of the 94 Å intensity occurred at 20 min into the sequence, and the maximum was reached at 23 min. It then decayed, reaching its former level at time 40 min. Another example lay south of the AR midline (see the image). On its trailing end this loop had two feet, suggesting that it is a superposition of two loops seen in projection. This structure showed two strong 94 Å brightenings peaking at 32 min and 37 min into the data sequence. The first brightening was associated with an intensity increase in the northern trailing foot, while the second was associated with an intensity increase in the southern foot. Again, this points to the presence of two superimposed loops. Brightenings in the loop feet indicate upward motion of intensity features toward the loop center at various speeds from 50 - 200 km/s. The intensity in the central loop section shows a sequence of weaker increases at 4 min intervals preceding the strong brightenings and a still weaker sequence at 5 min intervals afterward. These indicate releases of stored energy along a 10 Mm loop segment by a periodically repeating instability. The onset of the periodic energy releases in Example 2 and also the start of the loop brightening in Example 1 both occur at time 18 min into the data sequence. This coincides with the time of disturbances in other features of AR 11250 and suggests a complex coupling among its various structures.; SDO/AIA images of AR11250 made in the EUV 94 Å band at UT 13:53 and 14:03 on 13 July 2011. The images are 94 Mm wide. The grayscale is reversed. Title: Turbulent Fluctuations in G-band and K-line Intensities Observed with the Rapid Oscillations in the Solar Atmosphere (ROSA) Instrument Authors: Cadavid, A. C.; Lawrence, J. K.; Christian, D. J.; Jess, D. B.; Mathioudakis, M. Bibcode: 2012ASPC..463...75C Altcode: Using the Rapid Oscillation in the Solar Atmosphere (ROSA) instrument at the Dunn Solar Telescope we have found that the spectra of fluctuations of the G-band (cadence 1.05 s) and Ca II K-line (cadence 4.2 s) intensities show correlated fluctuations above white noise out to frequencies beyond 300 mHz and up to 70 mHz, respectively. The noise-corrected G-band spectrum presents a scaling range (Ultra High Frequency “UHF”) for f = 25-100 mHz, with an exponent consistent with the presence of turbulent motions. The UHF power, is concentrated at the locations of magnetic bright points in the intergranular lanes, it is highly intermittent in time and characterized by a positive kurtosis κ. Combining values of G-band and K-line intensities, the UHF power, and κ, reveals two distinct “states” of the internetwork solar atmosphere. State 1, with κ ≍ 6, which includes almost all the data, is characterized by low intensities and low UHF power. State 2, with κ ≍ 3, including a very small fraction of the data, is characterized by high intensities and high UHF power. Superposed epoch analysis shows that for State 1, the K-line intensity presents 3.5 min chromospheric oscillations with maxima occurring 21 s after G-band intensity maxima implying a 150-210 km effective height difference. For State 2, the G-band and K-line intensity maxima are simultaneous, suggesting that in the highly magnetized environment sites of G-band and K-line emission may be spatially close together. Analysis of observations obtained with Hinode/SOT confirm a scaling range in the G-band spectrum up to 53 mHz also consistent with turbulent motions as well as the identification of two distinct states in terms of the H-line intensity and G-band power as functions of G-band intensity. Title: Observed Effect of Magnetic Fields on the Propagation of Magnetoacoustic Waves in the Lower Solar Atmosphere Authors: Lawrence, J. K.; Cadavid, A. C. Bibcode: 2012SoPh..280..125L Altcode: 2012SoPh..tmp..159L; 2012arXiv1206.4360L We study Hinode/SOT-FG observations of intensity fluctuations in Ca II H-line and G-band image sequences and their relation to simultaneous and co-spatial magnetic field measurements. We explore the G-band and H-line intensity oscillation spectra both separately and comparatively via their relative phase differences, time delays and cross-coherences. In the non-magnetic situations, both sets of fluctuations show strong oscillatory power in the 3 - 7 mHz band centered at 4.5 mHz, but this is suppressed as magnetic field increases. A relative phase analysis gives a time delay of H-line after G-band of 20±1 s in non-magnetic situations implying a mean effective height difference of 140 km. The maximum coherence is at 4 - 7 mHz. Under strong magnetic influence the measured delay time shrinks to 11 s with the peak coherence near 4 mHz. A second coherence maximum appears between 7.5 - 10 mHz. Investigation of the locations of this doubled-frequency coherence locates it in diffuse rings outside photospheric magnetic structures. Some possible interpretations of these results are offered. Title: Rapid Fluctuations in the Lower Solar Atmosphere Authors: Lawrence, J. K.; Cadavid, A. C.; Christian, D. J.; Jess, D. B.; Mathioudakis, M. Bibcode: 2011ApJ...743L..24L Altcode: 2011arXiv1111.4253L The Rapid Oscillations in the Solar Atmosphere instrument reveals solar atmospheric fluctuations at high frequencies. Spectra of variations of the G-band intensity (IG ) and Ca II K-line intensity (IK ) show correlated fluctuations above white noise to frequencies beyond 300 mHz and 50 mHz, respectively. The noise-corrected G-band spectrum for f = 28-326 mHz shows a power law with exponent -1.21 ± 0.02, consistent with the presence of turbulent motions. G-band spectral power in the 25-100 mHz ("UHF") range is concentrated at the locations of magnetic bright points in the intergranular lanes and is highly intermittent in time. The intermittence of the UHF G-band fluctuations, shown by a positive kurtosis κ, also suggests turbulence. Combining values of IG , IK , UHF power, and κ reveals two distinct states of the solar atmosphere. State 1, including almost all the data, is characterized by low IG , IK , and UHF power and κ ≈ 6. State 2, including only a very small fraction of the data, is characterized by high IG , IK , and UHF power and κ ≈ 3. Superposed epoch analysis shows that the UHF power peaks simultaneously with spatio-temporal IG maxima in either state. For State 1, IK shows 3.5 minute chromospheric oscillations with maxima occurring 21 s after IG maxima implying a 150-210 km effective height difference. However, for State 2 the IK and IG maxima are simultaneous; in this highly magnetized environment sites of G-band and K-line emission may be spatially close together. Title: Effect of Magnetic Fields on Wave Propagation in the Solar Atmosphere Authors: Lawrence, John K.; Cadavid, A. C.; Christian, D. J. Bibcode: 2011SPD....42.1729L Altcode: 2011BAAS..43S.1729L We studied 1 - 24 mHz intensity fluctuations in 3-hour sequences of high-cadence, high-resolution, broad-band filtergram images taken by the SOT-FG on board the Hinode spacecraft. The observations consist of near simultaneous, co-registered G-band (GB), Ca II H-line (HL) intensity images, and line-of-sight magnetic images calibrated to Gauss with MDI magnetograms. GB is typically used as a proxy for magnetic fields while HL is a diagnostic of chromospheric heating.

We estimate the height z1 of the "magnetic canopy,” where magnetic and gas pressures balance, using potential field extrapolation and the Fontenla 2006 model atmosphere. When z1 is above the height of formation of both signals, the coherence of the GB and HL oscillations is strong for frequencies between 3 mHz and 6 mHz and maximal near 5 mHz, around the acoustic cutoff frequency. Near 3 mHz there is no time delay between the HL and GB signals indicating a pure standing wave. Above 7 mHz the time delay settles near 20 sec indicating an upward propagating acoustic wave. When z1 is below the GB and HL heights of formation the coherence between the signals drops and has a maximum near 4 mHz. The time delay remains zero at 3 mHz, but above 7 mHz it is less than 20 sec and decreases with frequency, suggesting that the original acoustic fluctuations have undergone mode conversion.

A similar analysis of ground-based data acquired with the Rapid Oscillations in the Solar Atmosphere (ROSA) instrument at the Dunn Solar Telescope finds longer time delays of 34 sec when z1 is high and 21 sec when z1 is low. This is consistent with the greater effective formation height of the ROSA narrowband (1 Å) Ca II K-line core compared to the more broadband (3 Å) H-line in the Hinode data. Title: Rapid Oscillations in the Solar Atmosphere: Spectra and Physical Effects Authors: Lawrence, John K.; Christian, D. J.; Cadavid, A. C.; Jess, D. B.; Mathioudakis, M. Bibcode: 2011SPD....42.1727L Altcode: 2011BAAS..43S.1727L High-frequency fluctuations are observed with the Rapid Oscillations in the Solar Atmosphere (ROSA) instrument (Jess et al. 2010, Solar Phys, 261, 363) at the Dunn Solar Telescope. This can produce simultaneous observations in up to six channels, at different heights in the photosphere and chromosphere, at an unprecedentedly high cadence of 0.5 seconds, and at a spatial resolution of 100 km after photometrically correct speckle reconstruction.

Here we concentrate on observations at two levels. The first is in the G-band of the CH radical at 4305.5Å, bandpass 9.2Å, with height of formation z < 250 km at a cadence of 0.525 sec corresponding to Nyquist frequency 950 mHz. The second is in the Ca II K-line core at 3933.7Å, bandpass 1.0Å, with height of formation z < 1300 km, and cadence 4.2 sec giving Nyquist frequency 120 mHz. The data span 53 min, and the maximum field of view is 45 Mm. The data were taken on 28 May 2009 in internetwork and network near disk center.

Using both Fourier and Morlet wavelet methods we find evidence in the G-band spectra for intensity fluctuations above noise out to frequencies f >> 100 mHz. The K-line signal is noisier and is seen only for f < 50 mHz. With wavelet techniques we find that G-band spectral power with 20 < f < 100 mHz is clearly concentrated in the intergranular lanes and especially at the locations of magnetic elements indicated by G-band bright points. This wavelet power is highly intermittent in time. By cross-correlating the data we find that pulses of high-frequency G-band power in the photosphere tend to be followed by increases in K-line emission in the chromosphere with a time lag of about 2 min. Title: Space - Time Distribution of G-band and Ca II H-line Intensity Oscillations in Hinode/SOT - FG Observations Authors: Lawrence, J. K.; Cadavid, A. C. Bibcode: 2010SoPh..261...35L Altcode: 2009arXiv0907.5001L We study the space - time distributions of intensity fluctuations in 2 - 3 hour sequences of multi-spectral, high-resolution, high-cadence, broad-band filtergram images of the Sun made by the SOT - FG system aboard the Hinode spacecraft. In the frequency range 5.5<f<8.0 mHz both G-band and Ca II H-line oscillations are suppressed in the presence of magnetic fields, but the suppression disappears for f>10 mHz. By looking at G-band frequencies above 10 mHz we find that the oscillatory power, both at these frequencies and at lower frequencies, lies in a mesh pattern with cell scale 2 - 3 Mm, clearly larger than normal granulation, and with correlation times on the order of hours. The mesh pattern lies in the dark lanes between stable cells found in time-integrated G-band intensity images. It also underlies part of the bright pattern in time-integrated H-line emission. This discovery may reflect dynamical constraints on the sizes of rising granular convection cells together with the turbulence created in strong intercellular downflows. Title: Magnetic and Dynamical Properties of Intensity Oscillations in the Lower Solar Atmosphere Authors: Cadavid, A. C.; Lawrence, J. K. Bibcode: 2009AGUFMSH51A1259C Altcode: We study 1 - 24 mHz intensity fluctuations in 2-3 hour sequences of high-cadence, high-resolution images taken by the SOT-FG on board Hinode. The observations consist of near simultaneous, co-registered G-Band (GB), Ca II H-Line (HL), and line-of-sight polarization density (V/I) images. MDI full-disk and high-resolution magnetograms are used to calibrate the V/I to magnetic field in Gauss. This equips us to compare fluctuations in magnetic and non-magnetic regions, as well as to study recently discovered patterns of enhanced oscillatory power in the photosphere and chromosphere. Oscillatory power in non-magnetic regions of HL images peaks at ~5 mHz, characteristic of an acoustic signal. As magnetic field increases up to ~ 200 G the spectrum is significantly diminished in strength, with a shift toward lower frequencies ~ 4 mHz starting between 100 - 200 G. In GB images the magnetic spectrum is dominant below ~3 mHz, perhaps due to contributions from GB bright points, while in non-magnetic regions the acoustic contribution peaks at ~ 4 mHz. To further investigate these effects we estimate the height of the “magnetic canopy,” where plasma β≈1, via potential field extrapolation from calibrated magnetic images and the VAL 3C or more recent model atmospheres. We then segregate the various contributions to the power according to whether the signal originates above or below the canopy. We have found previously that GB oscillatory power at frequencies above 10 mHz lies in a mesh-like pattern with characteristic cell scale 2 - 3 Mm, larger than normal granulation, and with correlation times on the order of hours. By appropriate segregation of image pixels we find that at the sites of enhanced > 10 mHz GB spectral power, there is in fact excess spectral power at all frequencies, both in GB and HL. Title: G-Band Bright Point Oscillations Underlying Chromospheric Ca II H-Line Emission Authors: Lawrence, John K.; Cadavid, A. C. Bibcode: 2009SPD....40.1004L Altcode: We study the spatial distributions of oscillatory power and of emission in two sequences of high-cadence, high-resolution images taken by the Solar Optical Telescope on board Hinode. The sequences consist of simultaneous, co-registered G-Band (GB) and Ca II H-Line (HL) images with pixel scale 80 km and fields of view 40 x 40 Mm and 80 x 40 Mm. The first sequence has cadence 21 s over 3 hours on 2007 April 14; the other has cadence 24 s over 2 hours on 2007 March 30. Both sequences include network and internetwork at heliocentric angle 35 degrees.

The G-Band images were filtered to emphasize the smallest features and thus to isolate phenomena connected to the G-Band bright points (GBPs). These appear in intergranular lanes and are associated with magnetic elements. The filtered G-Band images serve to segment areas in H-Line and magnetic images and therefore to explore their connections to the GBPs.

Time averaged Morlet wavelet transforms give smoothed Fourier spectra for each spatial location in the data. Averaging over four different frequency bands highlights different physical regimes: "evolutionary” timescales (f < 1.2 mHz); evanescent frequencies just below the acoustic cutoff (2.6 mHz < f < 4.2 mHz); high frequencies just above the cutoff (5.5 mHz <f 10mHz). These last frequencies require data cadences < 50 s. Spectral images for the filtered GBP data show that the associated spectral power is greatest in the evanescent frequency band. The apparent absence of magnetic shadowing suggests non-acoustic waves. An image of time-integrated H-Line emission shows strong and detailed correlation with the spatial distribution of spectral power in the GBP data, thus suggesting a possible energy source. Title: Sources and Propagation of High Frequency Waves in the Solar Photosphere and Chromosphere Authors: Lawrence, John K.; Cadavid, A. C. Bibcode: 2009SPD....40.1002L Altcode: We study the spatial distribution of oscillatory power in two sequences of high-cadence, high-resolution images taken by the Solar Optical Telescope on board Hinode. The sequences consist of simultaneous, co-registered G-Band (GB) and Ca II H-Line (HL) images with pixel scale 80 km and fields of view 40 x 40 Mm and 80 x 40 Mm. The first sequence has cadence 21 s over 3 hours on 2007 April 14; the other has cadence 24 s over 2 hours on 2007 March 30. Both sequences include network and internetwork at heliocentric angle 35 degrees.

Time averaging of Morlet wavelet transforms gives smoothed Fourier spectra for each spatial location in the GB and HL data. We averaged over four different frequency bands to highlight different physical regimes: "evolutionary” timescales (f < 1.2 mHz); evanescent frequencies just below the acoustic cutoff ( 2.6 mHz < f < 4.2 mHz); high frequencies just above the cutoff (5.5 mHz <f 10mHz) These last frequencies require data cadences < 50 s.

The evanescent and high frequency spectral images display clear magnetic shadowing in both GB and HL channels, though more strongly in the HL. Thus the heights at which the GB and HL are formed must both straddle the magnetic canopy, with the HL higher up. Interestingly, in the VHF band the magnetic shadowing is markedly weakened. The VHF case shows GB power in the internetwork that is arranged in the boundary web of a cellular pattern with scales 2 - 3 Mm. These are found to coincide with the boundaries of stable clusters of granules. These dark boundaries may correspond to downflows that control the cell structuring and that could be the source of acoustic power. Title: Phase And Time Lags Between G-band, H-line And Magnetic Fluctuations In The Photosphere And Chromosphere Authors: Cadavid, Ana Cristina; Lawrence, J. Bibcode: 2009SPD....40.1003C Altcode: We study the oscillatory power in two sequences of high-cadence, high-resolution images taken by the SOT on board Hinode. The sequences consist of simultaneous, co-registered G-Band (GB), Ca II H-Line (HL), and the absolute value of line-of-sight magnetic field (|B|) images, with pixel scale 80 km and fields of view 40 x 40 Mm and 80 x 40 Mm. The first sequence has cadence 21 s over 3 hours on 2007 April 14; the other has cadence 24 s over 2 hours on 2007 March 30. Both sequences include network and internetwork at heliocentric angle 35 degrees.

We investigate phase relations between fluctuations of pairs of the three data sets as functions of their common frequencies. The height Z1 of the "magnetic canopy,” where plasma beta equal 1, is estimated via a potential field extrapolation and the VAL 3C model atmosphere. The phase shifts at each frequency are taken as the maxima of normalized histograms made by binning the phase shifts for all space-time pixels segregated by high or low Z1. We interpret the phase shifts as a constant phase shift plus a constant time shift. For Z1 > 1.3 Mm G leads H with a constant time lag of 10 sec for frequencies above the acoustic cut-off, suggesting propagating acoustic waves. For Z1 < 1.15 Mm the time lag between the G and H signals is smaller. Both G and H lead the |B| fluctuations by a constant phase shift of 100 degrees for all Z1. For Z1 < 1.15 G also leads |B| by 3±1 sec and H trails |B| by 6±1 sec. For Z1 > 1.3 Mm these time lags disappear. Thus we can locate an effective "height” of |B| about 20 km above GB and of HL about 40 km above |B|. Title: Fine Scale, Rapid Dynamics of the Solar Atmosphere from Space-Based Versus Ground- Based Observations Authors: Lawrence, J. K.; Cadavid, A. C. Bibcode: 2008AGUFMSH41A1609L Altcode: We compare analyses of multi-wavelength, high-cadence sequences of high-resolution solar images that are derived from ground-based observations and from space-based observations. The original analyses aim to show the effects of magnetism on the propagation of wave energy from the photosphere into the solar atmosphere. Here we focus on differences that arise from the differing circumstances of the data acquisition. The ground-based data are a 9 hour sequence of Swedish Vacuum Solar Telescope filtergram images made on 1998 May 30 in the photospheric G-band and in the chromospheric CaII K-line with 21 s cadence. Atmospheric distortion was removed by phase diversity reconstruction, and the images were 4 x 4 square averaged to a spatial resolution of 0.24 Mm/px. A sequence of line-of-sight magnetograms had lesser resolution and longer cadence. The primary space-based data are a 6 hour sequence at 1 min cadence of Hinode SOT-FG images in G-band and CaII H-line and line-of-sight magnetic field, made on 2007 May 2. For space-based data phase reconstruction is irrelevant. The spatial scale is 0.08 Mm/px but can be averaged to lower resolutions. The relative phases of oscillations in the different data channels and the correlations between oscillation periods and spectral intensities show significant differences between the space- and ground-based cases. These differences may come partly from terrestrial atmospheric fluctuations that, in spite of phase reconstruction, act to artificially strengthen correlations among the ground-based data channels. For example, the photospheric and the chromospheric intensity fluctuations are more strongly correlated in the ground data than in the space data. The relative phases of oscillations in the three data channels show some different dependences on magnetic field strength between the two cases. This may be attributable to the higher quality of the available space magnetic data. Title: Quasi-periodic patterns coupling the Sun, solar wind and the Earth Authors: Ruzmaikin, Alexander; Cadavid, Ana Cristina; Lawrence, John Bibcode: 2008JASTP..70.2112R Altcode: The spectrum of velocity and magnetic fields in the solar wind is self-similar (power-law type) in the frequency range greater than >1/day indicating well-mixed turbulence. But it loses self-similarity for lower frequencies indicating the presence of large-scale patterns, which are intermittently generated inside the Sun and propagate from the Sun to the Earth. Here we discuss the spatia-temporal characteristics and origin of the 1.3-year quasi-periodic pattern found inside the Sun by helioseismic methods and detected in the solar wind. To identify and characterize this pattern on the Sun we use time series of solar magnetic Carrington maps generated at the Wilcox Solar Observatory and independent component data analysis. This analysis shows the latitudinal distribution of the pattern, its variable frequency and intermittent appearance. Title: Rotational Quasi-Periodicities and the Sun - Heliosphere Connection Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. Bibcode: 2008SoPh..252..179L Altcode: 2008arXiv0803.3260L; 2008SoPh..tmp..138L Mutual quasi-periodicities near the solar-rotation period appear in time series based on the Earth's magnetic field, the interplanetary magnetic field, and signed solar-magnetic fields. Dominant among these is one at 27.03±0.02 days that has been highlighted by Neugebauer et al. (J. Geophys. Res.105, 2315, 2000). Extension of their study in time and to different data reveals decadal epochs during which the ≈ 27.0 days, or a ≈ 28.3 days, or other quasi-periods dominate the signal. Space-time eigenvalue analyses of time series in 30 solar latitude bands, based on synoptic maps of unsigned photospheric fields, lead to two maximally independent modes that account for almost 30% of the data variance. One mode spans 45° of latitude in the northern hemisphere and the other one in the southern. The modes rotate around the Sun rigidly, not differentially, suggesting connection with the subsurface dynamo. Spectral analyses yield familiar dominant quasi-periods 27.04±0.03 days in the North and at 28.24±0.03 days in the South. These are replaced during cycle 23 by one at 26.45±0.03 days in the North. The modes show no tendency for preferred longitudes separated by ≈ 180°. Title: Principal Components and Independent Component Analysis of Solar and Space Data Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. Bibcode: 2008SoPh..248..247C Altcode: 2007arXiv0709.3263C Principal components analysis (PCA) and independent component analysis (ICA) are used to identify global patterns in solar and space data. PCA seeks orthogonal modes of the two-point correlation matrix constructed from a data set. It permits the identification of structures that remain coherent and correlated or that recur throughout a time series. ICA seeks for maximally independent modes and takes into account all order correlations of the data. We apply PCA to the interplanetary magnetic field polarity near 1 AU and to the 3.25R⊙ source-surface fields in the solar corona. The rotations of the two-sector structures of these systems vary together to high accuracy during the active interval of solar cycle 23. We then use PCA and ICA to hunt for preferred longitudes in northern hemisphere Carrington maps of magnetic fields. Title: Search for Persistent Quasi-Periodicities in the Solar and Interplanetary Magnetic Fields Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. Bibcode: 2007AGUFMSH23A1165L Altcode: Previous analysis of the radial component of the interplanetary magnetic field from 1962 - 1998 has revealed a dominant frequency of 27.03 days to 0.02 day accuracy (Neugebauer, et al., 2000). We have repeated and extended this analysis with OMNI data from 1963 - 2007 obtained from the Coordinated Heliospheric Observations (COHO) database. Over this longer data string we find that the 27.03 day Lomb-Scargle periodogram peak is reduced while two side peaks near 26.8 days and 27.6 days become almost as strong. In the interval 1999-2007 there are two dominant periods near 26.5 days and 27.2 days. As a solar counterpart to the above analysis we have searched for persistent rotation periods near 27 days of global patterns of photospheric magnetic fields derived from Wilcox Solar Observatory synoptic Carrington rotation maps. Techniques applied include, principal components analysis, independent component analysis, singular spectrum analysis, wavelet spectral analysis, and complex demodulation. We find a variety of quasi- periodicities between 26 and 29 days that remain coherent for 1 - 2 years. In the southern solar hemisphere the strongest periodicity is at 28.2 days, while in the northern hemisphere it is around 26.5 days. Neugebauer, M., Smith, Smith, E.J., Ruzmaikin, A., Feynman, J., Vaughan, A.H. 2000, J. Geophys. Res., 106, A5, 8363. Title: Quasi-Periodicities, Magnetic Clusters and Solar Activity Authors: Cadavid, A. C.; Lawrence, J. K.; Sandor, C.; Ruzmaikin, A. Bibcode: 2006AGUFMSH21A0325C Altcode: To investigate quasi-periodicities, 12 hour averages of the radial component of the interplanetary magnetic field and the solar wind speed, covering ~ 42 (1963-2005) years were analyzed. A Lomb periodogram for data up to 1998 showed a dominant period of 27.03 days as fpund in earlier results. Including cycle 23, a dominant period of 27.06 days was identified. Analysis of the solar cycles independently showed a dominant period of 27.03 days in solar cycle 20, but not in the other cycles. To investigate the degree of persistency of a particular signal, the technique of complex demodulation was applied since it permits the determination of continuous changes in time of the amplitude and frequency of the signal relative to the test signal. It was found that a period of ~27.6 days gave an overall flat phase function in time, while other periods < ~0.5 day shorter and longer, with comparable but lesser amplitude, come and go. To investigate the solar sources of these periods, the method of principal component analysis (PCA) was applied to ~ 27 years (1976-2003) of synoptic maps obtained with the NSO Kitt Peak Vaccum Telescope. Before the analysis, the original synoptic maps were shifted relative to the previous maps using the period under investigation. Using PCA the Empirical Orthogonal Functions (EOFs) and Pricipal Components (PCs) were found for the set of synoptic maps rescaled to the rotation rate 27.03 days in 1999-2003. The patterns characterized by EOFs 1 and 2 are mostly axisymmetric and PCs 1 and 2 show solar cycle variability. EOF3 shows only one well-localized pattern in the Southern Hemisphere which is markedly non-axisymmetric and PC3 has peaks at times when fast CMEs occur. Title: Solar Cycle Dependence of Solar Wind Geoeffectiveness Authors: Lawrence, J. K.; Cadavid, A. C. Bibcode: 2006AGUFMSH24A..04L Altcode: We find clear solar cycle dependence of the specific ways in which different physical properties of the solar wind (SW) couple to different aspects of geomagnetic activity. Geomagnetic activity is described by orthogonalized versions Kp, PC/Kp, and Dst/Kp/PC of the familiar indices. These represent, respectively, geomagnetic activity measured at mid-latitudes, geomagnetic activity measured in the (North) polar region and forced to be linearly independent of Kp, and finally geomagnetic activity measured at low latitudes and forced to be independent of both Kp and PC. Solar wind inputs are hourly averages of the SW plasma beta, dynamical pressure, the imposed duskward electric field, and a derived parameter related to nonthermally fast SW structures. These were measured by the Wind and ACE spacecraft from 1995 through December 2005. They were obtained from the OMNI2 data set. We connect these quantities using multivatiate factor analysis. During the active phase of Cycle 23 (1998- 2003) we find that Kp is primarily governed by SW dynamical pressure, PC/Kp almost entirely by the imposed electric field, and Dst/Kp/PC by the SW plasma beta and by nonthermal structures. This result holds separately for the rising and falling phases of the active Sun. However, during the preceding quiet Sun period (1995-1997) the nonthermal structures were unimportant. Then Dst/Kp/PC was governed by the SW plasma beta and dynamical pressure. At the same time, Kp was coupled directly to SW pressure and electric field, and negatively to plasma beta. Title: Persistent Peridicities in the Solar Wind and Photospheric Magnetic Field Coherent Structures Authors: Cadavid, Ana C.; Lawrence, J. K.; Ruzmaikin, A. Bibcode: 2006SPD....37.1106C Altcode: 2006BAAS...38..239C To investigate persistent periodicities, 12-hour averages of the radial component of the interplanetary magnetic field and the solar wind speed, covering 42 years (1963-2005), were analyzed. A Lomb periodogram for the data up to 1998 showed maximum spectral power at a period of 27.03 days, as encountered previously by Neugebauer et al. (2000). Including cycle 23 shifted the peak to 27.06 days. Analysis of solar cycles 20 - 23 separately showed a dominant period of 27.03 days in solar cycle 20, but not in the other cycles.To investigate the degree of persistency and phase coherence of a particular signal, the technique of complex demodulation was applied since it permits the determination of continuous changes in time of the amplitude and frequency of the signal relative to a test signal. It was found that for a reference signal of 27.03 days, the phase was a flat function of time during the intervals 1965-1972 and 1995-1997. The phase decreased in time from 1972-1995 and increased after 1997. This implies that for the intervals 1972-1995 and 1997-2005 other periodicities better characterize the data. A period of 27.6 days gave an overall flat phase function in time, while other periods < 0.5 day shorter and longer, with comparable but lesser amplitude, come and go.To investigate the solar sources of these periods, the methods of principal component analysis (PCA) and independent component analysis (ICA) were applied to 27 years (1976-2003) of synoptic maps obtained with the NSO Kitt Peak Vacuum Telescope. Before the analysis, the original synoptic maps were shifted relative to the previous maps using the particular period under investigation. PCA and ICA identified 3 modes for the 27.03 reference period and 2 modes for the 27.6 period that showed clusters of magnetic activity at preferred longitudes. Title: Stellar Objects with Infrared Excess in the \textit{Spitzer Space Telescope} Wide-Area Infrared Extragalactic Survey (SWIRE) Authors: Morales, F. Y.; Werner, M. W.; Padgett, D.; Fajardo-Acosta, S.; Stevens Stern, D.; Chary, R. -R.; Dawson, S.; Dickinson, M.; Stauffer, J. R.; Smith, B.; Walton, S.; Cadavid, A. C.; SWIRE Team; Ana Christina Cadavid Collaboration Bibcode: 2005AAS...207.6344M Altcode: 2005BAAS...37Q1254M We have identified two new debris disk candidates in the \textit{Spitzer Space Telescope} Legacy Project Wide-Area InfraRed Extragalactic Survey (SWIRE). We searched two of the six SWIRE photometric survey fields, and present 3.6-160 μ m photometry obtained with the Infrared Array Camera (IRAC) and the Multiband Imaging Photometer (MIPS) instruments. We followed up the candidates with spectro-photometry from 4-36 μ m using the Infrared Spectrometer (IRS) low resolution modules. The candidates spectral energy distributions (SEDs) were constructed from Keck's LRIS optical spectroscopy, \textit{2MASS} J, H, Ks, \textit{Spitzer's} IRAC 3.6, 4.5, 5.8, 8.0 μ m bands, and MIPS 24 m photometry (70 and 160 μ m when detected). The two candidates, Lockman_tile32_1228 and EN1_tile22_11767, were selected by their 24 μ m emission above photospheric expected levels, an indicator of the Vega phenomenon, or the presence of circumstellar dust at ∼120 K. Object Lockman_tile32_1228 has 70 and 160 μ m surplus in flux, suggesting the presence of cold dust represented by blackbody curves of ∼65 and ∼23 Kelvin. The infrared spectra reveal both sources to have infrared excess at wavelengths shorter than 24 μ m as well. The shape of Lockman_tile32_1228's SED exhibits interesting features from 8 to 20 μ m, possibly due to the composition of the emitting material. To confirm these sources are stellar objects, 0.32-0.95 μ m optical spectra was obtained via W.M. Keck Observatory's LRIS dual spectrometer. LRIS blue and red arm spectroscopy confirms the candidates are K-type main sequence stars about 195 and 160 pc away from the Sun. At high-galactic latitudes, where interstellar material is scarce, the SEDs of these sources illustrate there can exist a diversity of debris disk evolutionary states in foreground stars of the Galaxy.

This work is based on observations made with \textit{Spitzer Space Telescope}, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. Title: Solar Wind Interaction and Orthogonal Magnetospheric Indices Authors: Lawrence, J. K.; Cadavid, A. C. Bibcode: 2005AGUFMSM43A1214L Altcode: Multivariate methods can help to untangle connections between indices of magnetospheric activity and solar wind (SW) parameters. The data are 3-hour resolution time series spanning the period 1996 JAN 25 to 2004 SEP 17. The time series include Kp, the Dst and PC (polar cap) indices and an auroral POES index derived from NOAA satellite observations, plus OMNI SW data. The Kp index correlates with many other indices of magnetospheric activity due to its association with the convection electric field (see the survey in Thomsen 2004). We find correlation coefficients C(Kp,PC)=0.57, C(Dst,Kp)=-0.44 and C(Dst,PC)=-0.37. POES correlations are small. We replace PC with a variable PC/Kp containing that part of PC orthogonal to Kp. Likewise we replace Dst with Dst/KpPC, orthogonal to both Kp and to PC/Kp. The independent indices behave very differently from the original ones. Factor analysis gives five latent factor modes relating the terrestrial and SW sets. (1) The only factor containing the solar cycle connects sunspot number fluctuations to POES and PC/Kp only. This is the only factor containing POES or PC/Kp, so these vary mainly together. (2) Only one factor contains the south IMF, and this connects its fluctuations to Kp only. (3) A third factor relates strong responses in Dst/KpPC to increases in SW ram pressure, temperature and to alpha/proton ratio, an indicator of solar ejecta in the SW. (4) A fourth factor relates strong responses in Dst/KpPC to increases in excess SW coolness, another indicator of solar ejecta, along with drops in mean IMF, SW ram pressure and plasma beta. (5) The fifth factor relates increases in Kp to increased mean IMF, SW speed, coolness and plasma beta. We present a path analysis calculation quantifying the web of causal relations between the SW and the independent terrestrial indices via the intermediate latent factors. Thomsen, M.F. 2004, Space Weather, 2, S11004, doi:10.1029/2004SW000089 Title: Coherent Structures vs Independent Modes of the Axisymmetric Magnetic Field Fluctuations Authors: Cadavid, A. C.; Lawrence, J. K.; McDonald, D. P.; Ruzmaikin, A. Bibcode: 2005ASPC..346...91C Altcode: Quasi periodicities on scales of 1 to 2.5 years have been observed in solar, interplanetary and geomagnetic time series. The relation of these signals to 1 and 1.3 yr fluctuations in the solar interior, suggest the presence of structures or characteristic modes in the magnetic field, generated by the dynamo, that extend into the heliosphere. We have applied the methods of principal component analysis (PCA) and independent component analysis (ICA) to search for the coherent structures (PCA) and independent global modes (ICA) of the axisymmetric solar magnetic field. While PCA is effective in identifying the coherent modes that describe the 22 yr solar cycle, ICA uncovers the independent global modes the with characteristic 1 to 2.5 yr quasi periods observed in heliospheric and helioseismic time series. Five modes capture the salient properties of the data. Two modes describe the polar and high latitude fields, and present 1-1.5 yr quasi periodicities. The other three modes correspond to low and mid-latitude phenomena and show both 1.3 yr and 1.7 yr variations. Title: Quasi periodicities in the Fluctuations of the Axisymmetric Solar Magnetic Field from Independent Component Analysis Authors: McDonald, D. P.; Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. Bibcode: 2005AGUSMSP43B..05M Altcode: Observed solar, interplanetary and geomagnetic time series contain quasi periodicities on the order of 1 to 2.5 years. The further discovery of 1.3 year fluctuations in helioseismic observations suggests that a variety of signals may be related to the underlying dynamo in the Sun. We have applied the methods of principal component analysis (PCA) and independent component analysis (ICA) to search for the coherent structures (PCA) and independent global modes (ICA) of the axisymmetric solar magnetic field. While PCA was shown to be effective in identifying the coherent modes that describe the 22 yr solar cycle, ICA uncovers the independent global modes with characteristic 1 to 2.5 yr quasi periods observed in heliospheric and helioseismic time series. We found that five modes effectively describe the data in both spatial and temporal domains. Two modes describe the polar and high latitude fields, and present 1-1.5 year quasi periodicities. The other three modes correspond to low and mid-latitude phenomena and show both 1.3 year and 1.7 year variations. By comparing the characteristic timescales, dates of occurrence and heliocentric latitudes of these modes, we connect them to their manifestations in heliospheric time series. Title: Coherent Structures and Rotation Rates in Coronal Activity, from Principal Component Analysis Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. Bibcode: 2005AGUSMSP21B..07C Altcode: Principal component analysis (PCA) offers a way to extract those structures that remain spatially coherent throughout a time series. We apply this method to a ~ 28 year time series of Wilcox Solar Observatory Carrington rotation maps (CR) of the 3.25 R coronal source surface field obtained via a potential field extrapolation. We find that over 99% of the variance is contained in the first eight modes. Mode 1, carrying 81.5% of the variance, and modes 2 and 3 containing 13% of the variance, have "dipole" structures. Modes 4-8, with a "quadruple" structure, contain 4.5% of the variance. The principal components (PCs) give the time dependence of the modes. We combine the PCs of modes 2 and 3 to get the amplitude and phase of a structure that behaves essentially as a dipole in the equatorial plane. During activity minima the structure is relatively weak and rotates at the 27.275 day Carrington rate. During the active periods of cycles 21 and 22 the amplitude is large and highly intermittent, and the dipole rotates more rapidly than the Carrington rate with a synodic period of 26.6 days. During cycle 23, however, the dipole moves backward in Carrington longitude with a synodic period of 27.8 days. The average of these is ~ 27.0 days, though this is actually realized only sporadically. The phase changes that occur at shorter time scales and that coincide with intermittent changes in the dipole amplitude seem to represent essentially random effects of the passage of the magnetic field through the convection zone. While the lower modes tend to lock the hemispheres together the higher modes present separate Northern and Southern hemisphere quadrupole-type patterns that drift in Carrington longitude similarly to the equatorial dipole. Over some periods the drift in each hemisphere closely tracks the other over a wide range of timescales. However, there are large, decadal-scale excursions in which first one hemisphere leads in phase by 3 or 4 rotations and then the other leads by a similar amount. Title: Magnetic Topology and Wave Propagation in the Solar Atmosphere Authors: Lawrence, J. K.; Cadavid, A. C.; McIntosh, S. W.; Berger, T. E. Bibcode: 2005AGUSMSH13C..01L Altcode: We analyze a 9 hr sequence of simultaneous, high resolution, 21 s cadence SVST G-band and K-line solar filtergrams plus magnetograms of lower cadence and resolution. The data include both network and internetwork areas (Berger and Title 2001, Cadavid, et al. 2003, Lawrence, et al. 2003). Time series of the G-band and K-line data are compared after filtering by a Morlet wavelet transform of period 2.5 min. On the average, the K-line signal is delayed by several seconds after the G-band signal Δ T = 8.6 ± 0.1 s for weak (|BZ| < 50 G) magnetic field in internetwork but Δ T = 7.2 ± 0.1 s for weak field in an area including network. The internetwork has no strong fields, but in network (|BZ| > 80 G) the mean delay time drops to Δ T = 3.4 ± 0.3 s. This is consistent with results by McIntosh, Fleck and Tarbell (2004) using TRACE 1600Å and 1700Å UV image series. Our principal result is that the time delay is greater in the internetwork than in the network by 1.4 ± 0.1 s, even for the same local magnetic field strength. This suggests that the difference must be an effect of the field topology. Spatial maps of time delays, in comparison to maps of such topological quantities as the height in the solar atmosphere at which the plasma β = 1, offer additional details of the relationship between wave propagation and the magnetic fields in the solar atmosphere. This work was supported in part by grants NSF-ATM 9987305 and NASA-NAG5-10880. The SVST is operated by the Swedish Royal Academy of Sciences at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Berger, T.E. and Title, A.M. 2001, ApJ, 553, 449. Cadavid, A.C., et al. 2003, ApJ, 586, 1409. Lawrence, J.K., et al. 2003, ApJ, 597, 1178. McIntosh, S.W., Fleck, B. and Tarbell, T.D. 2004, ApJ, 609, L95. Title: Independent Global Modes of Solar Magnetic Field Fluctuations Authors: Cadavid, A. C.; Lawrence, J. K.; McDonald, D. P.; Ruzmaikin, A. Bibcode: 2005SoPh..226..359C Altcode: Observed solar, interplanetary and geomagnetic time series contain quasi periodicities on scales of 1-2.5 years. The further discovery of 1.3 year fluctuations in helioseismic observations suggests that a variety of signals may be related to the underlying dynamo in the Sun. We use independent component analysis to study the temporal and spatial variations of a few statistically independent global modes of the axisymmetric solar magnetic field over a period of 25 years. Five modes capture the salient properties of the data. Two modes describe the polar and high latitude fields, and present 1-1.5 year quasi periodicities. The other three modes correspond to low and mid-latitude phenomena and show both 1.3 and 1.7-year variations. By comparing the characteristic time scales, dates of occurrence and heliocentric latitudes of these modes, we connect them to their manifestations in heliospheric time series. Title: Principal Component Analysis of the Latitudinal and Longitudinal Structure of the Photospheric Magnetic Cycle Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. Bibcode: 2004AAS...204.3708L Altcode: 2004BAAS...36Q.710L We average magnetic fields in NSO synoptic maps over longitude and bin the result by sin(latitude). Also, we average over a band of latitudes and bin by longitude. A time stack of one-dimensional latitude "images" resembles the Maunder butterfly diagram. Time stacks of longitude "images" can be re-mapped to arbitrary rotation periods.

Principal component analysis recombines images in a stack into mutually orthogonal "empirical orthogonal functions" (EOFs). The EOFs are ordered by how well each correlates with the full set of images. The principal components (PCs) give the evolution of each EOF as a function of any ordering parameter, such as time. The original data can be wholly or partially reconstructed from subsets of the EOFs and their PCs.

Our latitudinal EOFs have a few leaders whose PCs show both the 11/22-year cycle and repeating substructure. Following are EOFs whose PCs show the cycle but no repeated substructure. Next are EOFs with small scale structure independent of the cycle. The least correlated EOFs contain high latitude, mostly unipolar fields. We suggest associating these four subsets of the EOFs with, respectively, global dynamo toroidal fields, turbulently disordered structures fed by the toroidal fields, a possible local surface dynamo process, and a global poloidal component.

We also studied a stack of longitudinal images of fields that were averaged over latitude between N25 and N35 degrees. Two especially active longitudes 180 degrees apart rotate with a period of 27.8 days. Structure at these longitudes dominates the leading EOFs. The corresponding PCs are active over the whole span of the data.

This work was supported by NASA Grant NAG5-10880. NSO/Kitt Peak data used here are produced cooperatively by NSF/NOAO, NASA/GSFC, and NOAA/SEL. Title: Two-dimensional Empirical Orthogonal Functions of the Photospheric Magnetic Cycle Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. Bibcode: 2004AAS...204.3707C Altcode: 2004BAAS...36Q.710C We carried out a principal component analysis (PCA) on sequences of NSO magnetic flux synoptic maps by Carrington rotation. Two data sets were investigated: (i) a sequence of 364 images from Carrington rotation 1625 to 2007, with image size 360 x 180 pixels (1 degree/pixel in longitude and sin(latitude)*90 in latitude for both hemispheres); (ii) a sequence of 79 higher resolution maps of size 1800 x 900 pixels starting at Carrington rotation 1913. The PCA of a time series yields an eigenvalue spectrum, the corresponding eigenfunctions (modes or "empirical orthogonal functions" (EOFs)), and the principal components which describe the time evolution of the modes. The dominant EOFs are associated with those structures that remain spatially coherent throughout intervals of the time series, and correspond to the functions with the highest eigenvalues. If the eigenvalue spectrum is dominated by only a few large members, then the corresponding few EOFs will mainly characterize the data. The rest will contain transient fluctuations. We apply the technique to the two dimensional maps and determine which EOFs dominate during different times of the solar cycle. We find that the dominant modes are associated with the active part of the cycle as expected, while the weaker modes characterize the quiet periods. The increasing and declining phases are associated with modes of intermediate eigenvalues. We reconstruct the time series by projecting onto the three classes of modes and investigate the probability distribution function (PDF) of "projected" magnetic flux. We compare these results to the PDFs obtained from artificial data generated by dynamo models. This work was supported in part by Grant NASA-NAG5-10880. NSO/Kitt Peak data used here are produced cooperatively by NSF/NOAO, NASA/GSFC, and NOAA/SEL. Title: A simple model of solar variability influence on climate Authors: Ruzmaikin, Alexander; Lawrence, John K.; Cadavid, Ana Cristina Bibcode: 2004AdSpR..34..349R Altcode: We present a simple dynamic model of solar variability influence on climate, which is truncated from the stratospheric wave-zonal flow interaction dynamics over a β-plane. The model consists of three ordinary differential equations controlled by two parameters: the initial amplitude of planetary waves and the vertical gradient of the zonal wind. The changes associated with the solar UV variability, as well as with seasonal variations, are introduced as periodic modulations of the zonal wind gradient. Influence of the Quasi-Biennial Oscillation is included as a periodic change of the width of the latitudinal extent of the β-plane. The major climate response to these changes is seen through modulation of the number of cold and warm winters. Title: Influence of Photospheric Magnetic Fields and Dynamics on Chromospheric K-Line Emission Authors: Lawrence, J. K.; Cadavid, A. C.; Miccolis, D.; Berger, T. E.; Ruzmaikin, A. Bibcode: 2003ApJ...597.1178L Altcode: We analyze a 9 hr sequence of simultaneous, high-resolution, high-cadence G-band and K-line solar filtergrams plus magnetograms of lower cadence and resolution. Images include both network and internetwork. The magnetic and filtergram intensities, their fluctuations, and relative phases change with progressive strengthening of local magnetic field. At increased flux levels, sudden photospheric downflows create long-lived magnetic elements. For weak magnetic fields the K-line and G-band intensities include an oscillatory component with period 4 minutes. For stronger fields, the K-line period shifts to 5 minutes, while the G-band fluctuations fade due to dissociation of their source, the CH radical. These K-line and G-band fluctuations, whose periods are longer than the acoustic cutoff, are coherent and in phase. They also are coherent with fluctuations of the magnetic field. Weak-field magnetic fluctuations lead the intensity fluctuations by a phase shift of 90°. Strong-field magnetic fluctuations trail the intensities by 100°. These are interpreted as standing waves in the photosphere and low chromosphere. Another class of G-band fluctuations, with periods shorter than the acoustic cutoff, is associated both with stronger magnetic fields and with enhanced K-line emission with fluctuations longer than the cutoff period. This suggests waves excited by rapid photospheric perturbations and propagating up along magnetic flux tubes. Title: Influence of Photospheric Magnetism and Dynamics on Chromospheric K-line Emission Authors: Lawrence, J. K.; Cadavid, A. C.; Miccolis, D.; Berger, T. E.; Ruzmaikin, A. Bibcode: 2003SPD....34.0704L Altcode: 2003BAAS...35..820L We analyze a unique 9 hr sequence of near simultaneous, high resolution and high cadence G-band and K-line SVST solar filtergrams together with magnetograms of lower cadence and resolution. We focus on a region of the solar surface that includes both internetwork and network. We examine how the (temperature minimum/chromospheric) CaII K-line and (photospheric) G-band intensities, their temporal fluctuations and their coherence and phase relations, with each other and with magnetic fluctuations, change as we progress from weak magnetic fields (internetwork) to intermediate and strong fields (network).

As the background level of flux is increased, sudden photospheric downflow events can create long-lived, compact (i.e. network) magnetic elements. For weak magnetic fields the K-line and G-band intensity signals show an oscillatory component with period centered on 4 min. As we pass to strong fields, the K-line signal shifts to a 5 min period while the G-band signal fades, presumably due to dissociation of the CH radical. The K-line and G-band signals are coherent and nearly in-phase. They are both coherent with fluctuations of the magnetic field. For weak field the magnetic signal leads the intensity signals by 90o in phase. For intermediate and strong fields the magnetic signal trails the intensities by 110o. We interpret this as a transition from acoustic standing waves with weak, passive magnetic field to a slow mode trapped magnetoacoustic wave. For intermediate magnetic field we find, in addition to the coherent waves, that G-band fluctuations at frequencies above the acoustic cutoff (period < 3.5 min) are associated with magnetic fields and with K-line emission at periods > 3.5 min. This suggests the presence of flux tube waves excited by rapid photospheric perturbations.

This work was supported by grants NSF-ATM 9987305 and NASA-NAG5-10880. The SVST is operated by the Swedish Royal Academy of Sciences at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Title: Photospheric Sources of Chromospheric Dynamics in the Internetwork Authors: Cadavid, A. C.; Lawrence, J. K.; Berger, T. E.; Ruzmaikin, A. Bibcode: 2003SPD....34.0703C Altcode: 2003BAAS...35..820C We analyze a unique 9 hr sequence of near simultaneous, high resolution and high cadence G-band and K-line solar filtergrams together with magnetograms of lower cadence and resolution, taken with the SVST. We investigate an internetwork region characterized by magnetic fields with strength < 150 Gauss and focus on the phenomena surrounding discrete photospheric darkening ``events'' in G-band intensities. 72 % of the darkenings are followed after 2 min by K-line brightenings. In the remaining cases the darkenings are instead preceded by K-line brightenings 2 min earlier. In both cases the preceding and following G-band minima are each associated with transient magnetic enhancements, and thus, presumably, photospheric inflows followed by outflows. The magnetic field appears to have no role in coupling the photospheric phenomena to the chromosphere, and acts as a passive tracer of horizontal photospheric flows that converge on the photospheric darkening events and then rebound. The timing and coupling of the photospheric darkenings and chromospheric brightenings appear to be regulated by a pre-existing 4 min oscillation of the solar atmosphere. Other oscillations with periods in the range 1-8 min also are present, and in general the wave power is doubled at the time of an event. At short periods temporal structure is resolved. Our results favor an acoustic source for enhanced amplitudes of K-line intensity oscillations. Title: Photospheric Sources and Brightening of the Internetwork Chromosphere Authors: Cadavid, A. C.; Lawrence, J. K.; Berger, T. E.; Ruzmaikin, A. Bibcode: 2003ApJ...586.1409C Altcode: We analyze a unique 9 hr sequence of near-simultaneous, high-resolution and high-cadence G-band and K-line solar filtergrams, together with magnetograms of lower cadence and resolution. Our focus is on the phenomena surrounding discrete photospheric darkening ``events'' in internetwork G-band intensities. 72% of the darkenings are followed after 2 minutes by K-line brightenings. In the remaining cases, the darkenings are instead preceded by K-line brightenings 2 minutes earlier. Equivalent results are found when reference is shifted to K-line brightening events, although these two sets overlap by no more than 15%. The timing and coupling of the photospheric darkenings and chromospheric brightenings appear to be regulated by a preexisting 4 minute oscillation of the solar atmosphere. Other oscillations with periods in the range 1-8 minutes also are present, and in general the wave power is doubled at the time of an event. Our results favor an acoustic source for enhanced amplitudes of K-line intensity oscillations. The magnetic field acts as a passive tracer of horizontal photospheric flows that converge on the photospheric darkening events and then rebound. Title: Mesogranulation from Principal Component Analysis of SVST Photospheric Continuum Images Authors: Bell, E.; Cadavid, A. C.; Lawrence, J. K.; Berger, T. E. Bibcode: 2002AAS...200.3805B Altcode: 2002BAAS...34Q.699B We analyze a sequence of 279 images of the photosphere made with the Swedish Vacuum Solar Telescope on 1997 June 11. The sequence spans 3 hr with cadence 38 s. The images were taken in continuum near 4364 Å, and underwent phase diversity reconstruction. Resolution is ~ 0.2 Mm and field of view 32 X 32 Mm. We carried out a principal component analysis on sequences of 15 images spaced 6 min apart and covering 1.5 hr. The 15 X 15 correlation matrix of each such set of images was diagonalized, giving 15 eigenimages which are linear combinations of the original 15. The eigenimage corresponding to the largest eigenvalue is the linear combination that best resembles the original set as a whole; those with smaller and smaller eigenvalues resemble the overall set less and less well. Fourier spectra of the eigenimages were calculated separately for several sequences and then averaged together to reduce uncertainties. Fourier analysis of the leading eigenimage reveals structure at two scales: one for λ =1/ν ~ 1.5 Mm corresponding to granulation and another for λ ~ 4.5 Mm. Because of their scale and because the time span of the sets lies between the lifetimes of granules and mesogranules, we interpret the latter as mesogranules. The subsequent eigenimages do not show the larger structure, but show the granular peak at successively smaller scales. This indicates a spatio-temporal scaling of the granulation with shorter lifetimes for smaller features. For comparison purposes, simulated granulation images (Cattaneo, Lenz and Weiss 2001) were similarly analyzed and give similar results. Work supported in part by grants NSF-ATM-9987305, NASA-NAG5-10880 and the NASA CSUN/JPL PAIR Program. F. Cattaneo, D. Lenz and N. Weiss 2001, ApJ, 563, L91. Title: High Resolution Spatio-Temporal Study of Photospheric and Chromospheric Energetics Authors: Cadavid, A. C.; Lawrence, J. K.; Berger, T. E. Bibcode: 2002AAS...200.3809C Altcode: 2002BAAS...34..700C We study the photosphere/chromosphere energetic connection using a nine hour sequence of SVST images obtained May 30, 1998. The data consist of co-spatial, nearly simultaneous filtergrams of G-band (4305 Å ), Ca II K (3934 Å ), two (6563 Å) Hα channels offset by 0.35 Å and 0.7 Å , and Fe I (6302 Å) magnetograms. The cadence of the G-band and Ca K observations is ~ 30 s; that of the other images is ~ 2 min. The pixel scale is 0.06 Mm and field of view 48 X 48 Mm on the Sun. The filtergram resolution is > 0.2 Mm; that of the magnetograms > 0.3 Mm with single magnetogram sensitivity < 150 G. We have co-registered the images to 1 or 2 pixel accuracy. The number distribution of Ca brightenings and of localized changes in magnetic field strength, measured in standard deviations (σ ) from the image means, present three different characteristic regimes; that of the magnetic ``free energy'' (a derived measure based on the local variance of magnetic field) presents two. Ca brightenings below 3σ show a weak but significant correlation with local magnetic field and free energy. At 3σ the strength of the correlation abruptly increases. Above 5σ no correlation is apparent, but large magnetic field values appear. Using a mask to remove the network areas, the weakest brightenings (<1.5 σ ) show anti-correlation with the magnetic field. For 1.5 σ to 4.5 σ there is no correlation. For selected network examples we follow the time evolution in all observed lines. We find cases in which an increase and then relaxation in the magnetic free energy just precedes a local rise in Ca emission followed by a drop to a lower background level than initially. Work supported in part by NSF-ATM-9987305 and NASA-NAG5-10880. Title: Observations of the Structure of small scale photospheric fields Authors: Lawrence, J.; Cadavid, A.; Ruzmaikin, A.; Berger, T. Bibcode: 2002ocnd.confE..26L Altcode: No abstract at ADS Title: A simple model of solar variability influence on climate. Authors: Ruzmaikin, A.; Lawrence, J.; Cadavid, A. Bibcode: 2002cosp...34E.336R Altcode: 2002cosp.meetE.336R We introduce and study a simple dynamic model of solar influence on climate. The model is truncated from the stratospheric wave-zonal flow interaction model suggested by Holton and Mass (1976). Our model consists of three ordinary differential equations controlled by two parameters: the initial amplitude of planetary waves and the vertical gradient of the zonal wind. The changes associated with seasonal variations and with the solar variability are introduced as periodic modulations of the zonal wind gradient. The major atmospheric response to these changes is seen through modulation of the number of cold and warm winters. Title: Mesogranulation and Turbulence in Photospheric Flows Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. Bibcode: 2001SoPh..202...27L Altcode: 2001astro.ph..4354L Below the scale of supergranules we find that cellular flows are present in the solar photosphere at two distinct size scales, approximately 2 Mm and 4 Mm, with distinct characteristic times. Simultaneously present in the flow is a non-cellular component, with turbulent scaling properties and containing 30% of the flow energy. These results are obtained by means of wavelet spectral analysis and modeling of vertical photospheric motions in a 2-hour sequence of 120 SOHO/MDI, high-resolution, Doppler images near disk center. The wavelets permit detection of specific local flow patterns corresponding to convection cells. Title: Spatiotemporal Scaling of Solar Surface Flows Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A.; Berger, T. E. Bibcode: 2001PhRvL..86.5894L Altcode: 2001astro.ph..1224L The sun provides an excellent natural laboratory for nonlinear phenomena. We use motions of magnetic bright points on the solar surface, at the smallest scales yet observed, to study the small scale dynamics of the photospheric plasma. The paths of the bright points are analyzed within a continuous time random walk framework. Their spatial and temporal scaling suggests that the observed motions are the walks of imperfectly correlated tracers on a turbulent fluid flow in the lanes between granular convection cells. Title: Mesogranulation and Turbulence in Photospheric Flows Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. Bibcode: 2001AGUSM..SP41C02L Altcode: Cellular flows are present in the solar photosphere at two distinct size scales, 2 Mm and 4 Mm, with distinct characteristic times. Simultaneously present in the flow is a non-cellular component, with turbulent scaling properties between 1 Mm and 64 Mm, and containing 30 % of the flow energy. These results are obtained by means of wavelet spectral analysis and modeling of vertical photospheric motions in a 2-hour sequence of 120 SOHO/MDI, high resolution, Doppler images near disk center. The wavelets permit detection of specific local flow patterns corresponding to convection cells. Standard spectral techniques have difficulty resolving mesogranules for three basic reasons: (1) the mesogranules are near in scale to granules and weaker in velocity and (2) they are hidden by overlying turbulence because (3) global basis functions, such as Fourier waves or spherical harmonics, do not allow attention to be paid to the local topologies that label cellular flows. Title: Response to weak solar forcing in a general circulation model of the atmosphere. Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A. Bibcode: 2000BAAS...32R.832C Altcode: No abstract at ADS Title: Random Walks of Magnetic Bright Points and Coronal Loop Heating Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A. Bibcode: 2000AAS...196.4903L Altcode: 2000BAAS...32..750L The random walks of small-scale ( ~ 0.2 arcsec) magnetic bright points (MBPs) in the lanes between photospheric granules are anomalous. The temporal growth of the q-th moment of the displacement r(t) is a power law with exponent q γ (q)/2. For normal, Gaussian walks γ (q)= 1 for all q. However, for the MBP walks on time scales < 45 minutes we find that γ (2)<1 and that γ (q) is a decreasing function of q. Many viable models for the heating of coronal loops are based on the additon of energy via twisting and braiding of magnetic flux lines by the random motions of their footpoints. If the MBPs are associated with such footpoints, then the statistics of their motions are directly relevant to coronal heating. For example, a number of models derive heating rates based on moments of the displacements and include the standard assumption that γ = 1. However, this assumption is wrong for MBPs, and the actual value of γ depends on exactly which moment enters the expression. All such models are therefore subject to modification. The result γ (2)<1 is a result of pauses in the MBP walks on all time scales (''fractal time'') up to ~ 45 min. This implies that the motions of an individual footpoint are not statistically stationary. This in turn means that the injection of energy into a given loop will be strongly variable and intermittent. This can be related to observations of the details of variability in coronal loop emissions, giving information on the locations of energy deposition and on time scales of energy release. We thus hope to further constrain acceptable heating models. This work was supported in part by NSF Grant ATM-9628882. Title: Response to Weak Solar Forcing in a General Circulation Model of the Atmosphere Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A. Bibcode: 2000SPD....3102117C Altcode: 2000BAAS...32..832C We study the effect of variable external forcing on a dynamical system proposed by Lorenz as a simple general circulation model of the atmosphere. When a strong annual cycle is included, numerical exploration reveals the existence of a variety of multi-year climate states, which fall into two basic types. In the space of external forcing parameters, the different kinds of climate state are interleaved in an intricate pattern at scales < 0.01. This is below the ~ 0.1 level of observed solar cycle irradiance variability which can thus modulate the model climate state. If the solar cycle is accompanied by a steady drift in forcing, it can produce periodic modulation which appears, disappears and even reverses its phase. A parametric drift by itself produces intervals of steady, but sometimes differing, climates punctuated by intermittent bursts of variability. Different forcing parameters for the Northern and Southern Hemispheres produce different responses to variable forcing. Title: Anomalous Diffusion of Solar Magnetic Elements Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A. Bibcode: 1999ApJ...521..844C Altcode: The diffusion properties of photospheric bright points associated with magnetic elements (magnetic bright points) in the granulation network are analyzed. We find that the transport is subdiffusive for times less than 20 minutes but normal for times larger than 25 minutes. The subdiffusive transport is caused by the walkers being trapped at stagnation points in the intercellular pattern. We find that the distribution of waiting times at the trap sites obeys a truncated Lévy type (power-law) distribution. The fractal dimension of the pattern of sites available to the random walk is less than 2 for the subdiffusive range and tends to 2 in the normal diffusion range. We show how the continuous time random walk formalism can give an analytical explanation of the observations. We simulate this random walk by using a version of a phenomenological model of renewing cells introduced originally for supergranules by Simon, Title, & Weiss. We find that the traps that cause the subdiffusive transport arise when the renewed convection cell pattern is neither fixed nor totally uncorrelated from the old pattern, as required in Leighton's model, but in some intermediate state between these extremes. Title: General relativistic solitons. II Authors: Cadavid, A. C.; Finkelstein, R. J. Bibcode: 1999PhRvD..59l4019C Altcode: 1998gr.qc.....7014C We investigate the possible existence of nontopological solitons in stringlike theories, or in other completions of Einstein theory, by examining a simple extension of standard theory that describes a nonlinear scalar field interacting with the Einstein, Maxwell, and Weyl (dilaton) fields. The Einstein and Maxwell couplings are standard while the dilatonic coupling is taken to agree with string models. The nonlinear scalar potential is quite general. It is found to be impossible to satisfy the dilatonic boundary conditions. Excluding the dilaton field we find a variety of solitonic structures differing in ways that depend on the nonlinear potential. In general the excited states exhibit a discrete mass spectrum. At large distances the gravitational field approaches the Reissner-Nordström solution. Title: Anomalous Diffusion of Solar Magnetic Elements Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A. Bibcode: 1999AAS...194.5506C Altcode: 1999BAAS...31..911C The diffusion properties of photospheric bright points associated with magnetic elements (MBP's) in the granulation network are analyzed. We find that the transport is subdiffusive for times less than 20 minutes but normal for times larger than 25 minutes. The subdiffusive transport is caused by the walkers being trapped at stagnation points in the intercellular pattern. We find that the distribution of waiting times at the trap sites obeys a truncated Levy type (power law) distribution. The fractal dimension of the pattern of sites available to the random walk is less than 2 for the subdiffusive range and tends to 2 in the normal diffusion range. We show how the continuous time random walk formalism can give an analytical explanation of the observations. We simulate this random walk by using a version of a phenomenological model of renewing cells introduced originally for supergranules by Simon, Title and Weiss (1995). We find that the traps which cause the subdiffusive transport arise when the renewed convection cell pattern is neither fixed nor is it totally uncorrelated from the old pattern as required in Leighton's model, but in some intermediate state between these extremes. (Work supported in part by NSF grant ATM-9628882). Title: Scaling Universality Classes and Analysis of Solar Data Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A. Bibcode: 1999AAS...194.9301L Altcode: 1999BAAS...31..988L Many solar phenomena display a scaling symmetry associated with random multiplicative cascades. Here a physical measure, initially uniform on a spatial, temporal, or space-time set, is divided among subsets according to randomly determined fractions. This division is repeated on smaller and smaller sub-subsets, so that the resulting measure at the smallest scale is given at any point by the product of a string of random fractions comprising its fragmentation history. Such measures are highly intermittent. They characterize such solar phenomena as the spatial distribution of magnetic flux in an active region and the time distribution of global X-ray emission. The probability distribution functions (PDFs) governing the random fractions fall into universality classes with robust properties (Hentschel 1994). For example, all PDFs which allow for zero fractions lead to measures with local peaks of unlimited strengths which are progressively less and less space filling. The GOES-2 X-ray data belong to this class, which indicates the presence of critical behavior associated with flares (Lu & Hamilton 1991). We investigate a number of time series for the presence or absence of this property. Multifractals in nature may fall into a narrow universality class described by just 3 parameters (Schertzer, et al. 1997). We find that at least some examples of active region magnetic fields do indeed have the conjectured form. Further, we apply a causal space-time version of this class of multiplicative cascade processes to forecasting the evolution of solar velocity fields. This work was supported in part by NSF grant ATM-9628882. Hentschel, H.G.E. 1994, Phys. Rev. E, 50, 243. Lu, E.T. & Hamilton, R.J. 1991, ApJ, 380, L89. Schertzer, D., Lovejoy, S., Schmitt, F., Chigirinskaya, Y. & Marsan, D. 1997, Fractals, 5, 427. Title: Characteristic Scales of Photospheric Flows and Their Magnetic and Temperature Markers Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A. Bibcode: 1999ApJ...513..506L Altcode: We study the characteristic scales of quiet-Sun photospheric velocity fields along with their temperature and magnetic markers in Doppler images from the Michelson Doppler Imager aboard the SOHO satellite (SOHO/MDI) in simultaneous, Doppler, magnetic, and intensity images from the San Fernando Observatory and in full-disk magnetograms and an intensity image from National Solar Observatory (Kitt Peak). Wavelet flatness spectra show that velocity fluctuations are normally distributed (Gaussian). This is often assumed in stochastic models of turbulence but had not yet been verified observationally for the Sun. Temperature fluctuations also are Gaussian distributed, but magnetic fields are intermittent and are gathered into patterns related to flow structures. Wavelet basis functions designed to detect characteristic convection cell-flow topologies in acoustically filtered SOHO/MDI Doppler images reveal granulation scales of 0.7-2.2 Mm and supergranulation scales of 28-40 Mm. Mesogranular flows are weakly but significantly detected in the range 4-8 Mm. The systematic flows account for only 30% of the image variances at granular and supergranular scales and much less in between. The main flows for the intermediate range of 2-15 Mm are self-similar, i.e., chaotic or turbulent. Title: Kerr-Schild Description of a Rotating Dyon Authors: Cadavid, A. C.; Finkelstein, R. J. Bibcode: 1999GReGr..31...31C Altcode: No abstract at ADS Title: Spatiotemporal Correlations and Turbulent Photospheric Flows from SOHO/MDI Velocity Data Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A.; Walton, S. R.; Tarbell, T. Bibcode: 1998ApJ...509..918C Altcode: Time series of high-resolution and full-disk velocity images obtained with the Michelson Doppler Imager (MDI) instrument on board SOHO have been used to calculate the spacetime spectrum of photospheric velocity flow. The effects of different methods for filtering acoustic oscillations have been carefully studied. It is found that the spectra show contributions both from organized structures that have their origin in the convection zone and from the turbulent flow. By considering time series of different duration and cadence in solar regions with different line-of-sight projections, it is possible to distinguish the contributions of the spectra from the two different kinds of flows. The spectra associated with the turbulent velocity fields obey power laws characterized by two scaling parameters whose values can be used to describe the type of diffusion. The first parameter is the spectral exponent of the spatial correlation function and the second is a scaling parameter of the time correlation function. Inclusion of the time parameter is an essential difference between the present work and other solar studies. Within the confidence limits of the data, the values of the two parameters indicate that the turbulent part of the flow in the scale range 16-120 Mm produces superdiffusive transport. Title: General relativistic solitons Authors: Cadavid, A. C.; Finkelstein, R. J. Bibcode: 1998PhRvD..57.7318C Altcode: A general relativistic and nontopological soliton is constructed by coupling a nonlinear scalar field to the standard gravitational field. Our results replicate the basic features of the special relativistic case: namely, a singularity-free lump with a discrete spectrum of eigensolutions. The central singularities and horizon that appear in the black hole solitons of string theory are not present. Title: Dyonic Black Holes and Related Solitons Authors: Cadavid, A. C.; Finkelstein, R. J. Bibcode: 1997gr.qc.....7031C Altcode: There is a growing literature on dyonic black holes as they appear in string theory. Here we examine the correspondence limit of a dyonic black hole which is not supersymmetric. Assuming the existence of a dyon with non-supersymmetric Kerr-Schild structure, we calculate its gravitational and electromagnetic fields and compute its mass and angular momentum to obtain a modified B.P.S. relation. The contributionn of the angular momentum to the mass appears in the condition for the appearance of a horizon. Title: Scale Dependence of Photospheric Magnetic, Velocity and Temperature Structure Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A. Bibcode: 1997SPD....28.0247L Altcode: 1997BAAS...29..901L Time series fluctuations may show different structure when observed at different time scale resolutions. Thus, wavelet analysis reveals that fluctuations in the International Sunspot Number are intermittent (that is, distributed with kurtosis K>0) on scales less than 2 yr, but truncated (K<0) on time scales between 2-8 yr. Terrestrial temperature fluctuations are normally distributed (K=0) over discrete timescale bands (<1 yr, 4-6 yr, 13 yr) interspersed by regimes of intermittence (1-4 yr) and truncation (6-13 yr). Similar effects occur for spatial phenomena. We employ various continuous, two-dimensional wavelets to analyze digital solar images in Cartesian projection (simultaneous, co-registered San Fernando Observatory magnetic, Doppler and continuum images; SOHO/MDI high resolution Doppler images) and full-disk images in hemispheric projection (KPNO magnetograms, SOHO/MDI Doppler images). The temperature and velocity data are normally distributed at all scales up to 64 arc sec, though the temperature gradients are slightly intermittent (K~1). The magnetic data are mostly intermittent. Wavelet power spectra for KPNO full-disk magnetograms are quite featureless and indicate scale invariance of the magnetic structures. Structural spectra of both active and quiet sun images, however, show a strong peak in intermittence at a scale near 8 arc sec. Wavelet analysis permits localization of structures in space as well as in spatial scale. The highly intermittent structures can be mapped and are found to be located not in active regions but in some, though not all, areas of low magnetic activity. We discuss possible physical relationships among the magnetic, velocity and temperature distributions studied. Title: Decorrelation Time of Fourier modes in the Spectrum of Solar Background Velocity Fields Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A. Bibcode: 1997SPD....28.0261C Altcode: 1997BAAS...29..904C We calculate the power-energy spectrum of time series of SOHO/MDI line-of sight high resolution Doppler images near disk center. While the spatial spectrum presents velocity features at characteristic scales and not a cascade in wavenumber space, we investigate the extent to which it is still possible to describe in terms of a scaling exponent the properties of the decorrelation time for each Fourier mode as a function of wavelength. We explore the sensitivity of the result to different methods for removing the contribution of the p-modes to the spectrum. Title: Wavelet and Multifractal Analyses of Spatial and Temporal Solar Activity Variations Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A. Bibcode: 1997scma.conf..421L Altcode: No abstract at ADS Title: Spectral Properties of Solar Convection and Diffusion Authors: Ruzmaikin, A. A.; Cadavid, A. C.; Chapman, G. A.; Lawrence, J. K.; Walton, S. R. Bibcode: 1996ApJ...471.1022R Altcode: We present the results of a study of the scaling properties of solar photo spheric motions. We use time series of Doppler images obtained in good seeing conditions with the San Fernando Observatory 28 cm vacuum telescope and vacuum spectroheliograph in video spectra-spectroheliograph mode. Sixty line-of- sight Doppler images of an area of the quiet Sun near disk center are investigated. They were taken at 60 s intervals over a 1 hr time span at ∼2" resolution.

After filtering to remove 5 minute acoustic oscillations, the time-spatial spectrum of the velocity is calculated. To study the turbulence of photospheric flows in the mesogranulation scale range, we estimate two scaling parameters in the spectrum: the exponent of the spatial part of the power spectrum and the exponent governing the scaling of time correlations of each spatial mode. These parameters characterize the type of diffusion involved and the fractal dimension of the diffusion front. Our results indicate that the turbulent diffusion produced by motions in this scale range is not normal diffusion but superdiffusion. Title: On the Multifractal Distribution of Solar Magnetic Fields: Erratum Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A. Bibcode: 1996ApJ...467..473L Altcode: Many studies have pointed out fractal and multifractal properties of photospheric magnetic fields, but placing the various approaches into context has proved difficult. Although fractal quantities are defined mathematically in the asymptotic limit of infinite resolution, real data cannot approach this limit. Instead, one must compute fractal dimensions or multifractal spectra within a limited range at finite scales. The consequent effects of this are explored by calculation of fractal quantities in finite images generated from analytically known measures and also from solar data. We find that theorems relating asymptotic quantities need not hold for their finite counterparts, that different definitions of fractal dimension that merge asymptotically give different values at finite scales, and that apparently elementary calculations of dimensions of simple fractals can lead to incorrect results. We examine the limits of accuracy of multifractal spectra from finite data and point out that a recent criticism of one approach to such problems is incorrect. Title: On the Multifractal Distribution of Solar Magnetic Fields Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A. Bibcode: 1996ApJ...465..425L Altcode: Many studies have pointed out fractal and multifractal properties of photospheric magnetic fields, but placing the various approaches into context has proved difficult. Although fractal quantities are defined mathematically in the asymptotic limit of infinite resolution, real data cannot approach this limit. Instead, one must compute fractal dimensions or multifractal spectra within a limited range at finite scales. The consequent effects of this are explored by calculation of fractal quantities in finite images generated from analytically known measures and also from solar data. We find that theorems relating asymptotic quantities need not hold for their finite counterparts, that different definitions of fractal dimension that merge asymptotically give different values at finite scales, and that apparently elementary calculations of dimensions of simple fractals can lead to incorrect results. We examine the limits of accuracy of multifractal spectra from finite data and point out that a recent criticism of one approach to such problems is incorrect. Title: Spectral Properties of the Solar Background Velocity Field Authors: Cadavid, A. C.; Chapman, G. A.; Lawrence, J. K.; Ruzmaikin, A. A.; Walton, S. R. Bibcode: 1996AAS...188.3506C Altcode: 1996BAAS...28Q.872C We study the scaling properties of time series of Doppler images obtained in good seeing conditions with the San Fernando Observatory 28 cm vacuum telescope and vacuum spectroheliograph in video spectra-spectroheliograph mode. The images correspond to two areas of quiet Sun near disk center taken at 60 second intervals from one hour to six hour spans at ~ 2 arcsec resolution. After removal of 5 min acoustic oscillations the time-spatial spectrum of the velocity is calculated. To study the turbulence of photospheric flows we estimate two scaling parameters: the exponent of the spatial part of the power spectrum and the exponent governing the scaling of time correlations of each spatial mode. The implied diffusive behavior produced by the solar convection in the mesogranulation scale range is discussed. This includes characterization of the type of diffusion involved and the fractal dimension of the diffusion front. Title: Turbulent and Chaotic Dynamics Underlying Solar Magnetic Variability Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A. Bibcode: 1995ApJ...455..366L Altcode: We examine the temporal scaling properties of solar magnetic activity on timescales from days to decades. Because of more than 63,000 usable data points, we concentrate on the daily International Sunspot Number. Some results have been checked with other data sets, primarily the 10.7 cm microwave flux with about 16,000 data points. Such time series provide a measure whose scaling and intermittency properties are analyzed.

By means of correlation analysis and both Fourier and wavelet spectral analysis, we distinguish two regimes of temporal behavior of the magnetic variability. The scaling of the time series is analyzed in terms of multiplicative cascade processes which prove to be invariant over more than two decades of scale from about 2 yr down to about 2 days or less. We interpret this result to indicate generic turbulent structuring of the magnetic fields as they rise through the convection zone. We find that a low-dimensional, chaotic behavior in the sunspot number operates entirely at timescales longer than a transition threshold scale of about 8 yr. Magnetic variability on timescales between 2 yr and 8 yr apparently requires handling by direct simulation. Title: Turbulence and Chaos in Solar Variability Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A. Bibcode: 1995SPD....26..514C Altcode: 1995BAAS...27..960C No abstract at ADS Title: Multiplicative cascade models of multifractal solar magnetic fields Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A. Bibcode: 1995PhRvE..51..316L Altcode: We present a multifractal analysis of digital, photoelectric images of line-of-sight magnetic fields in solar active regions and quiet photosphere. We study a positive definite measure related to the Ohmic dissipation of magnetic energy. After calculation of the multifractal spectrum directly and by scaling of the moments of the measure, we focus on a multiplicative cascade approach. We infer a scale-invariant rule by which the Ohmic dissipation measure is allocated among subsets of its support through a hierarchy of scales. Knowledge of this rule, which is hampered to some extent by image noise, permits the calculation of the multifractal spectrum to great accuracy. The scaling of the solar dissipation field resembles that of fully developed turbulence in an atmospheric boundary layer. The cascade multiplier probability distribution is itself a very useful quantity. It allows a convenient display of image properties, such as self-similarity. Further, it is more closely related than the multifractal spectrum to the physics of the turbulent field evolution, and it thus can be used to impose stronger constraints on turbulent dynamo models of magnetic field generation. Title: Spectra of Solar Magnetic Fields and Diffusion Authors: Ruzmaikin, A. A.; Cadavid, A. C.; Chapman, G. A.; Lawrence, J. K.; Walton, S. R. Bibcode: 1995ASPC...76..292R Altcode: 1995gong.conf..292R No abstract at ADS Title: Multifractal Models of Small-Scale Solar Magnetic Fields Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A.; Kayleng-Knight, A. Bibcode: 1994ApJ...429..391C Altcode: We generate, both analytically and numerically, artifical, two-dimensional images composed of a known self-similar, and thus multifractal measured with added Gaussian white noise. These are used to interpret observed, line-of-sight, solar magnetic field distributions noisy multifractals. The range of self-similar scaling of observed, distributions is extended beyond that of previous work. Our interpretation of the data is then used to confront theoretical models for the generation of small-scale solar magnetic fields. We investigate the multifractial structure of the field generated by two-dimensional, random cell dynamos and find that self-similarity is relatively enhanced for more intermittent distributions and strong correlations between cells. An optimum value of the intercellular diffusion coefficient maximizes the degree of intermittency. The simulated field from a linear, kinematic, fast dynamo with two-dimensional, chaotic, 'ABC' flow displays scaling properties resembling those of observed solar fields. We suggest that the chaotic element of this model is the crucial ingredient for the long-range correlations that lead to multifractal scaling. Title: Scaling properties of photospheric magnetic fields Authors: Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A. Bibcode: 1994ASIC..433..279L Altcode: No abstract at ADS Title: Multifractal Measure of the Solar Magnetic Field Authors: Lawrence, J. K.; Ruzmaikin, A. A.; Cadavid, A. C. Bibcode: 1993ApJ...417..805L Altcode: We analyze high-resolution, digital, photoelectric images of solar photospheric magnetic fields. The line-of-sight fields are found to scale in a self-similar way with resolution and thus can be expressed in the form of a signed multifractal measure. The scaling properties of the measure are used to extrapolate field integrals, such as moments of the magnetic field, below resolvable limits. The scaling of the field moments is characteristic of highly intermittent fields. We suggest that the quiet-Sun photospheric fields are generated by local dynamo action based on random convective motions at high magnetic Reynolds number. The properties of active region images are determined by the presence of fields generated by the global, mean field dynamo. Title: Self-Similarity in Solar Magnetic Images Authors: Lawrence, J. K.; Ruzmaikin, A. A.; Cadavid, A. C. Bibcode: 1993BAAS...25.1219L Altcode: No abstract at ADS Title: Multiscale Measure of the Solar Magnetic Field Authors: Ruzmaikin, A. A.; Lawrence, J. K.; Cadavid, A. C. Bibcode: 1993BAAS...25.1219R Altcode: No abstract at ADS Title: Solar Magnetic Fields, Multifractals and Dynamos Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A.; Kayleng-Knight, A. Bibcode: 1993BAAS...25R1206C Altcode: No abstract at ADS Title: (2,2) vacuum configurations for type IIA superstrings: N=2 supergravity Lagrangians and algebraic geometry Authors: Bodner, M.; Cadavid, A. C.; Ferrara, S. Bibcode: 1991CQGra...8..789B Altcode: No abstract at ADS Title: Dimensional reduction of type IIB supergravity and exceptional quaternionic manifolds Authors: Bodner, M.; Cadavid, A. C. Bibcode: 1990CQGra...7..829B Altcode: No abstract at ADS