Author name code: komm ADS astronomy entries on 2022-09-14 author:"Komm, Rudolf W." OR author:"Komm, Rudi" ------------------------------------------------------------------------ Title: Is the Subsurface Meridional Flow Zero at the Equator? Authors: Komm, R. Bibcode: 2022SoPh..297...99K Altcode: We study the subsurface meridional flow and its divergence from the surface to a depth of about 16 Mm at the equator and its variation with the solar cycle derived with ring-diagram analysis applied to Michelson Doppler Imager (MDI) Dynamics Program, Global Oscillation Network Group (GONG), and Helioseismic and Magnetic Imager (HMI) Dopplergrams. The meridional flow at the equator is small but nonzero and is mainly negative (southward) during Solar Cycle 23 with an average of −1.1 ±0.2 ms−1 at depths shallower than 7 Mm and positive (northward) during Solar Cycle 24 with an average of +1.3 ±0.1 ms−1 over the same depth range derived from supersynoptic maps of combined HMI and GONG data (scaled to match HMI flow amplitudes). The divergence in supersynoptic maps is positive at all times and clearly varies with the solar cycle with large values during cycle maxima and small values during minima. On time scales of synoptic maps, we found that at depths shallower than 10 Mm the cross-equatorial flow is, on average, toward the hemisphere with the larger amount of flux. The meridional flow at the equator has broad distributions with widths that are at least five times larger than the mean values. The distributions of Solar Cycles 23 and 24 overlap but are distinguishable. For a high-activity subset, the cross-equatorial flow is predominantly toward locations with high activity and the divergence is greater than average. The nonzero cross-equatorial flow is in this case a consequence of the inflows present near active regions and the imbalance of activity between the hemispheres. For a quiet-region subset, the cross-equatorial flow is, on average, in the same direction as the average flow over a solar cycle with a similar broad distribution, while the quiet-region divergence is smaller than the grand average. Title: Subsurface Horizontal Flows During Solar Cycles 24 and 25 with Large-Tile Ring-Diagram Analysis Authors: Komm, R. Bibcode: 2021SoPh..296..174K Altcode: We study the large-scale subsurface flows to a depth of about 32 Mm covering the near-surface shear layer (NSSL). The flows were derived with a ring-diagram analysis applied to Helioseismic and Magnetic Imager (HMI) Dopplergrams using tiles with 30∘ diameter instead of the commonly used 15∘ ones. This allows us to determine flows at greater depths in exchange for coarser spatial resolution. We confirm that the average zonal flow increases with increasing depth and reaches a plateau in the NSSL. There is a hint of a local maximum or saddle point much closer to the surface at about 8 Mm. The average meridional flow is poleward at all depths in both hemispheres. The average amplitude is 14.3 ±0.2 m s−1 at 30∘ and 12.4 ±0.2 m s−1 at 15∘ latitude at depths of 20 Mm and shallower, while amplitudes at these latitudes decrease at greater depths. The solar-cycle variation of the zonal and meridional flow are clearly noticeable from the surface throughout the NSSL. The dominant features of the zonal flow are bands of faster-than-average flow associated with Solar Cycles 24 and 25. The onset of the fast bands happens almost simultaneously at all depths. For Cycle 25, the fast bands appear in the southern hemisphere about one year before those in the northern one and both fast bands appear several years before magnetic activity appeared at the surface in either hemisphere. The meridional flow shows a similar pattern after subtracting the temporal mean at each latitude. The bands of converging residual meridional flow move from mid- to low latitudes during a solar cycle. These bands appear at low latitudes almost at the same time at all depths, similar to the fast bands of the zonal flow. However, at 45∘ latitude they appear first in layers near 32 Mm and about two years later at the solar surface, as if the pattern were rising through the outer layers. Title: Subsurface Plasma Flows and the Flare Productivity of Solar Active Regions Authors: Biji, Lekshmi; Jain, Kiran; Komm, Rudolf; Nandy, Dibyendu Bibcode: 2021AGUFMSH54A..07B Altcode: Highly energetic solar events such as solar flares and Coronal Mass Ejections (CMEs) can lead to extreme space weather. Hence, it is essential to understand their physical drivers and explore what governs their occurrence and intensity. By using the near-surface velocities derived by the ring-diagram analysis of active region patches using Global Oscillation Network Group (GONG) Doppler velocity measurements, we seek to explore the connection between subsurface flow properties and solar flares. The temporal evolution of vorticity and kinetic helicity of flaring and non-flaring active regions is investigated. The integrated vorticity, kinetic and current helicities, and magnetic flux one day prior to the flare are observed to be correlated with the integrated flare intensity. We show that active regions with strong subsurface vorticity and kinetic helicity tend to generate high intensity flares. We hypothesize that this is achieved via energy injection into subsurface magnetic flux systems by helical plasmas flows. Title: Subsurface Flow Measurements in the Near Surface Shear Layer over Two Solar Cycles Authors: Tripathy, Sushanta; Jain, Kiran; Komm, Rudolf; Kholikov, Shukirjon Bibcode: 2021AGUFMSH53C..02T Altcode: Helioseismic studies have illustrated that the most significant changes with the solar cycle occur in the near-surface shear layer (NSSL) where the density changes by several orders of magnitude. This layer approximately occupies the outer 5% of the solar interior. It is also believed that a nonlinear alpha-omega dynamo could be operating in the NSSL where the velocity shear converts a part of the poloidal magnetic field into the toroidal field in addition to the global dynamo operating in the tachocline region. With the advent of local helioseismic technique of ring diagram, subsurface flows in the outer 2% have been well studied. Here we extend the measurements of large-scale flows to deeper layers to provide observational constraints on the temporal as well as latitudinal variations of the zonal and meridional flows during the last two solar cycles. The study is based on the GONG data and uses the technique of ring diagram and 30 degree tiles to probe deeper layers. We will also compare GONG with HMI results for solar cycle 24 and beyond. Title: Kinetic and Magnetic Helicity in Solar Active Regions Authors: Liu, Yang; Komm, Rudolf; Brummell, Nicholas; Hoeksema, J. Bibcode: 2021AGUFMSH54A..08L Altcode: Flows and magnetic fields in the Sun interact with each other, especially in the solar interior where flow dominates. Kinetic and magnetic helicity are proxies for links between flows and the magnetic field. Studying magnetic helicity, its evolution, physical scale, and the relationship with flows (kinetic helicity) provides insight for understanding the solar dynamo and magnetic flux emergence. This study explores the relationship between kinetic helicity in the interior and magnetic helicity in the atmosphere in active regions. We investigate 16 active regions to search for a possible sign relationship between the magnetic and kinetic helicity. This sample is representative because it includes active regions with various magnetic properties -- 8 emerging and 8 well developed active regions having simple and complex magnetic configurations, and that exhibit a range of solar activity, including ones with multiple major flares and no flare activity. We determine the relationship between kinetic and magnetic helicity for active regions with various properties and discuss implications for solar interior activity. Title: A Comparative Study of Measurements of the Suns Axisymmetric Flows: A COFFIES Effort Authors: Upton, Lisa; Jain, Kiran; Komm, Rudolf; Mahajan, Sushant; Pevtsov, Alexei; Roudier, Thierry; Tripathy, Sushanta; Ulrich, Roger; Zhao, Junwei; Basu, Sarbani; Chen, Ruizhu; DeRosa, Marc; Hess Webber, Shea; Hoeksema, J. Bibcode: 2021AGUFMSH55D1871U Altcode: Consequence Of Fields and Flows in the Interior and Exterior of the Sun (COFFIES) is a Phase-1 NASA DRIVE Science Center (DSC), with the primary objective of developing a data driven model of solar activity. One of COFFIES five primary science questions is What drives varying large-scale motions in the Sun? To address this question, we are developing a comprehensive catalog of the variable differential rotation and meridional circulation flow patterns. This catalog includes measurements of these flows as obtained by several measurement techniques: Doppler imaging, granule tracking, magnetic pattern tracking, magnetic feature tracking, as well as both time distance and ring diagram helioseismology. We show a comparison of these flows across these varied techniques, with a particular focus on the MDI/HMI/GONG/Mount Wilson overlap period (May-July 2010). We investigate the uncertainties and attempt to reconcile any discrepancies (e.g., due to flow depth or systematics associated with the different measurement techniques). This analysis will pave the way toward accurately determining the global patterns of axisymmetric flows and their regular and irregular variations during the cycle. Title: Global solar flows and their impact on magnetic activity Authors: Dikpati, Mausumi; Braun, Douglas; Featherstone, Nicholas; Hindman, Bradley; Komm, Rudolf; Liu, Yang; Scherrer, Philip; Upton, Lisa; Wang, Haimin Bibcode: 2021AGUFMSH55D1872D Altcode: This poster presents the second year progress report of the LWS focused-science team-4 of 2019. The main science objective is to jointly develop the most comprehensive, dynamically consistent picture of solar flows at the surface, in the convection zone and tachocline, and determine the MHD effects induced by these motions. Our major team-achievements in the second year include: (i) consensus about active regions' flow and their contributions in modifying the global flow; (ii) long-term global flow map from various magnetograms, and their specific properties as function of cycle phase, (iii) impacts of the flows in polar field evolutions, (iv) simulations of global flows with various solar-like interior conditions, (v) roles of simulated flows in driving the nonlinear dynamics of spot-producing magnetic fields and producing their spatio-temporal patterns, which are compared with that manifested as active regions patterns in surface magnetograms. We will describe in detail how these observationally constrained local and global flows are leading us to improved simulations of model-outputs of magnetic activity and flows. In turn, these outputs can reliably be used as inputs to heliospheric models, for example, for simulating properties of reconnection of active regions' magnetic fields, high-speed streams, sector passages, all of which have profound influence on various aspects of space weather and impact on terrestrial atmosphere. Title: Understanding the Consequences Of Fields and Flows in the Interior and Exterior of the Sun (COFFIES) Authors: Hoeksema, J. T.; Brummell, N.; Bush, R.; Hess Webber, S.; Kitiashvili, I.; Komm, R.; Kosovichev, A.; Mendez, B.; Scherrer, P.; Upton, L.; Wray, A.; Zevin, D.; The Coffies Team Bibcode: 2021AAS...23811322H Altcode: The solar activity cycle is the Consequence Of Fields and Flows in the Interior and Exterior of the Sun (COFFIES). As a Phase-1 NASA DRIVE Science Center (DSC), COFFIES ultimately aims to develop a data-driven model of solar activity. To attain this goal COFFIES members are learning to work together effectively to perform the investigations needed to answer five primary science questions:

1) What drives varying large-scale motions in the Sun?

2) How do flows interact with the magnetic field to cause varying activity cycles?

3) Why do active regions emerge when and where they do?

4) What do the manifestations of activity and convection reveal about the internal processes?

5) How does our understanding of the Sun as a star inform us more generally about activity dynamics and structure?

The virtual COFFIES center brings together a broad spectrum of observers, data analysts, theorists, computational scientists, and educators who collaborate through interacting working groups of four principal science teams. The principal objectives of the four primary science teams are to 1) understand the generation of quasi-periodic stellar magnetic cycles, 2) further develop 3D physical models of interior dynamics and convection, 3) establish clear physical links between solar flow fields and near-surface observations, and 4) develop more robust helioseismic techniques to resolve solar interior flows. Additional cross-team activities are facilitated by teams for numerical modeling, center effectiveness, outreach and eduction, and diversity, equity, inclusion and access (DEIA). Title: Divergence and Vorticity of Subsurface Flows During Solar Cycles 23 and 24 Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 2021SoPh..296...73K Altcode: We study the solar-cycle variation of the divergence and vorticity of subsurface horizontal flows from the surface to a depth of 16 Mm. The flows were derived with ring-diagram analysis applied to Michelson Doppler Imager (MDI) Dynamics Program, Global Oscillation Network Group (GONG), and Helioseismic and Magnetic Imager (HMI) Dopplergrams. We study their variation for the complete data set and for two subsets representing active and quiet regions. All three data sets show alternating bands of diverging and converging flows and bands of cyclonic and anticyclonic flows moving from mid-latitudes toward the equator during a solar cycle. For Solar Cycle 24, these bands are precursors of the magnetic activity appearing several years before magnetic activity is present at a given latitude even leading the fast bands of the flows. The amplitude differences between the cyclonic and anticyclonic and the converging and diverging bands during a solar cycle agree within the error bars between the complete data set and the two subsets. For Solar Cycle 24, the amplitude differences are 6.0 ±0.7 10−8s−1 for the bands of vorticity and −4.9 ±0.6 10−8s−1 for those of divergence averaged over 2.0 - 11.6 Mm using the complete data set. The amplitude differences of Solar Cycle 23 are 26 ±3 % smaller than those of Solar Cycle 24. The flows of the active-region subset are more converging and cyclonic than those of the quiet-region subset with an extra vorticity of 1.3 ±0.1 10−8s−1 and an extra divergence of −6.7 ±0.3 10−8s−1 averaged over 7.5∘ - 30∘ and all depths and epochs. The amplitude of the extra divergence of active regions is about a factor of 1.3 larger at depths shallower than 6 Mm and decreases with increasing depth, while the extra vorticity is nearly constant with depth. Title: COFFIES - Developing a Reliable Physical Model of the Solar Activity Cycle Authors: Hoeksema, J. T.; Brummell, N.; Bush, R. I.; Komm, R.; Kosovichev, A. G.; Mendez, B.; Scherrer, P. H.; Upton, L.; Wray, A. A.; Zevin, D. Bibcode: 2020AGUFMSH0020007H Altcode: The solar activity cycle is the Consequence Of Fields and Flows in the Interior and Exterior of the Sun (COFFIES). The COFFIES Drive Science Center ultimately aims to develop a data driven model of solar activity. The challenging goals are 1) to understand the generation of the quasi-periodic stellar magnetic cycles, 2) further develop 3D physical models of interior dynamics and convection, 3) establish the physical links between solar flow fields and near-surface observations, and 4) develop more robust helioseismic techniques to resolve solar interior flows. To reach these goals the COFFIES team is focusing on what is needed to answer five primary science questions: 1) What drives varying large-scale motions in the Sun? 2) How do flows interact with the magnetic field to cause varying activity cycles? 3) Why do active regions emerge when and where they do? 4) What do the manifestations of activity and convection reveal about the internal processes? And 5) How does our understanding of the Sun as a star inform us more generally about activity dynamics and structure? The virtual COFFIES center is bringing together a broad spectrum of observers, analysts, theorists, computational scientists, and educators who collaborate through interacting teams focused on helioseismology, dynamos, solar convection, surface links, numerical modeling, center effectiveness, outreach, education, diversity and inclusion. Title: Global Solar Flows and Magnetic Fields: Observing, Simulating and Predicting Their Impact on the Heliosphere and Terrestrial Atmosphere Authors: Dikpati, M.; Braun, D. C.; Featherstone, N. A.; Komm, R.; Liu, Y.; Scherrer, P. H.; Upton, L.; Wang, H. Bibcode: 2020AGUFMSH0020008D Altcode: Understanding origins and evolution of solar magnetic activity occurring on a wide range of time-scales, and the space weather effects caused by the particles and electromagnetic outputs that reach the Earth, requires knowledge of the physical origins of this activity below photosphere. Despite much progress, our knowledge of processes responsible for driving the magnetohydrodynamics of flows and fields below photosphere and their relation to observed flows and magnetic activity is far from complete. For example, there is no consensus as to the number of meridional circulation-cells that exist in the Sun and the depth at which the poleward-flow switches direction to equatorward. Main objective of our LWS focused-science team is to jointly develop the most comprehensive, dynamically consistent picture of solar flows at the surface, in the convection zone and tachocline, and determine the MHD effects induced by these motions. We will present how we are developing consensus sets of observational constraints and simulating model-outputs of magnetic activity and flows, which can reliably be used as inputs to heliospheric and terrestrial- atmospheric models. The ultimate success will be in our ability to predict the features of solar cycle 25, including the active-latitudes and -longitudes, global- and localized-flows several months to years ahead. Title: Helioseismic Constraints on the Solar Interior Dynamics and Dynamo Authors: Kosovichev, A. G.; Brummell, N.; Dikpati, M.; Guerrero, G.; Kitiashvili, I.; Komm, R.; Korzennik, S.; Pipin, V.; Reiter, J.; Stejko, A.; Ulrich, R. K.; Warnecke, J. Bibcode: 2020AGUFMSH007..04K Altcode: Uninterrupted helioseismic observations from the SoHO/MDI, SDO/HMI and GONG instruments for more than two decades provide unique observational data for studying the solar-cycle variations of the differential rotation, large-scale and meridional flows. The data also allows us to investigate changes in the thermodynamic structure associated with dynamo-generated magnetic fields. The wealth of global and local helioseismic data provides theoretical constraints on the solar dynamics and dynamo models. The synergy of helioseismic inferences with advanced MHD modeling sheds light on the origin of the solar activity cycles. It helps to understand better the physical processes that control the strength and duration of the cyclic magnetic activity and leads to new physics-based approaches for prediction of the solar cycles. We briefly overview the current status, discuss the solar dynamical structure and evolution revealed by helioseismic inversions and the forward-modeling method, and focus on the most critical points of the problem. In particular, we discuss recent advances in measurements and modeling of the solar-cycle variations of the meridional circulation and migrating zonal flows (torsional oscillations) on the solar surface and in the subsurface layers, the deep convection zone, and the solar tachocline. The relationships between the internal dynamics and the evolution of global magnetic fields lead to new ideas of how magnetic fields are generated and affect the solar flows and structure. Title: Solar-Cycle Variation of the Subsurface Flows of Active and Quiet Regions Authors: Komm, R. Bibcode: 2020AGUFMSH007..03K Altcode: We study the solar-cycle variation of subsurface flows for both active and quiet solar regions. We derive the temporal variation of the zonal and meridional flows from the surface to a depth of 16 Mm using ring-diagram analysis applied to Dopplergrams obtained with the Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory (SDO) spacecraft. We use thresholds in magnetic activity to separate the flows into subsets of active and quiet regions. In addition, we derive the subset of intermediate regions that are excluded from either the quiet- or active-region subset. The subsurface flows associated with active and quiet regions show the same variation with the solar cycle with alternating bands of faster- and slower-than-average zonal and meridional flows moving from mid-latitudes toward the equator during the course of a cycle but with different amplitudes. We will derive the flow patterns of the intermediate-region subset as well and compare their amplitudes with those of the other subsets. We will study the north-south variation of the resulting flow patterns and their implications on the activity of solar cycle 25. Title: Solar-Cycle Variation of the Subsurface Flows of Active- and Quiet-Region Subsets Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 2020SoPh..295...47K Altcode: We study the solar-cycle variation of subsurface flows for both active and quiet solar regions. We derive flows from the surface to a depth of 16 Mm using ring-diagram analysis applied to Dopplergrams obtained with the Michelson Doppler Imager (MDI) Dynamics Program, the Global Oscillation Network Group (GONG), and the Helioseismic and Magnetic Imager (HMI) instrument. We derive the temporal variation of the zonal and meridional flows in a consistent manner for Solar Cycles 23 and 24 combining the flows from the three data sources scaled to match HMI-derived flows. The subsurface flows associated with active and quiet regions show the same variation with the solar cycle with alternating bands of faster- and slower-than-average zonal and meridional flows moving from mid-latitudes toward the equator during the course of a cycle. We derive the differences between the amplitudes of the extrema of the fast and the slow flows. For Cycle 24, the average difference between the fast- and slow-flow amplitude is 9.5 ±0.5 ms−1 for the zonal flows and 7.0 ±0.4 ms−1 for the meridional flows of the quiet-region subset averaged over 2 to 12 Mm within ±30∘ latitude. For the active-region subset, the average difference is 10.4 ±0.9 ms−1 for the zonal flows and 9.3 ±0.7 ms−1 for the meridional flows. We subtract the flows of the quiet-region subset from those of the active-region one to determine the contribution of active regions to the long-term flow pattern. The resulting meridional flow associated with active regions has a maximum amplitude near 3.1 Mm and its amplitude decreases with depth. This implies that the converging flows attributed to active regions are a shallow-layer phenomenon. Title: Kinetic Helicity and Lifetime of Activity Complexes During Solar Cycle 24 Authors: Komm, R.; Gosain, S. Bibcode: 2019ApJ...887..192K Altcode: We study magnetic features on the solar surface that exist for several rotations during solar cycle 24. To identify them, we average synoptic maps over a range in latitude and stack the resulting longitudinal strips in time. We use synoptic maps of magnetograms obtained with the NSO/Synoptic Optical Long-term Investigations of the Sun instrument and create synoptic maps of the kinetic helicity of subsurface flows integrated over 2.0-7.1 Mm based on Solar Dynamics Observatory/Helioseismic and Magnetic Imager Dopplergrams. To distinguish between active and quiet regions, we sort the grid points of the synoptic maps by their activity level and divide the data into four subsets with 25% of activity each and into two subsets with the highest or lowest 12.5% of activity values. The kinetic helicity of these six subsets follows the hemispheric helicity rule with, on average, positive values in the southern and negative values in the northern hemisphere. However, the helicity of the subset with the highest activity is about four times higher than that of the other subsets, and the mid-quartile subsets show the weakest hemispheric helicity rule. We define the lifetime of complexes in each subset and find that for the high-activity subset, the amplitude of magnetic activity and kinetic helicity increases almost linearly with the lifetime of complexes. The distribution of flares closely resembles that of the high-activity subset. The flare-productive locations in long-lived complexes produce, on average, the same number of flares as those of short-lived complexes. However, long-lived complexes have a higher fractional number of these locations than the short-lived complexes and thus produce more flares not just because they live longer. Title: Long-Lived Activity Complexes, their Kinetic Helicity, Lifetime, and Flare Activity Authors: Komm, Rudolf W.; Gosain, Sanjay Bibcode: 2019shin.confE..53K Altcode: We study long-lived activity complexes using stackplots of magnetic activity derived from NSO/SOLIS synoptic magnetograms. We focus on the kinetic helicity below the surface determined with ring-diagram analysis applied to full-disk Dopplergrams from SDO/HMI during Solar Cycle 24. The kinetic helicity of activity complexes follows the hemispheric helicity rule with mainly positive values in the southern hemisphere and negative ones in the northern hemisphere. To distinguish between active and quiet regions, we divide the data into subsets with high and low levels of activity and create stackplots of surface magnetic activity and subsurface kinetic helicity for each subset. The distribution of flares in a stackplot resembles closely that of the high-activity subset. The flare-productive locations in long-lived complexes produce, on average, the same number of flares as those of short-lived ones. However, long-lived complexes have a larger number of these locations and thus a higher flare-production rate than short-lived ones. We will present the latest results. Title: Kinetic and Current Helicity of Long-Lived Activity Complexes During Solar Cycle 24 Authors: Komm, Rudolf; Gosain, Sanjay Bibcode: 2018csc..confE...6K Altcode: We study long-lived activity complexes during Solar Cycle 24. We focus on the kinetic helicity below the surface determined with ring-diagram analysis applied to full-disk Dopplergrams from SDO/HMI. In addition, we study the current helicity at the solar surface of these activity complexes determined from synoptic vector magnetograms. Current and kinetic helicity of activity complexes follow the hemispheric helicity rule with mainly positive values in the southern hemisphere and negative ones in the northern hemisphere. The locations with the dominant sign of kinetic helicity are more organized than those of secondary sign even if they are not part of an activity complex, while locations with the secondary sign are more fragmented. We will present the latest results. Title: GONG p-Mode Parameters Through Two Solar Cycles Authors: Kiefer, René; Komm, Rudi; Hill, Frank; Broomhall, Anne-Marie; Roth, Markus Bibcode: 2018SoPh..293..151K Altcode: 2018arXiv181009324K We investigate the parameters of global solar p-mode oscillations, namely damping width Γ , amplitude A , mean squared velocity «v2», energy E , and energy supply rate d E /d t , derived from two solar cycles' worth (1996 - 2018) of Global Oscillation Network Group (GONG) time series for harmonic degrees l =0 -150 . We correct for the effect of fill factor, apparent solar radius, and spurious jumps in the mode amplitudes. We find that the amplitude of the activity-related changes of Γ and A depends on both frequency and harmonic degree of the modes, with the largest variations of Γ for modes with 2400 μ Hz≤ν ≤3300 μ Hz and 31 ≤l ≤60 with a minimum-to-maximum variation of 26.6 ±0.3 % and of A for modes with 2400 μ Hz≤ν ≤3300 μ Hz and 61 ≤l ≤100 with a minimum-to-maximum variation of 27.4 ±0.4 % . The level of correlation between the solar radio flux F10.7 and mode parameters also depends on mode frequency and harmonic degree. As a function of mode frequency, the mode amplitudes are found to follow an asymmetric Voigt profile with νmax=3073.59 ±0.18 μ Hz. From the mode parameters, we calculate physical mode quantities and average them over specific mode frequency ranges. In this way, we find that the mean squared velocities «v2» and energies E of p modes are anticorrelated with the level of activity, varying by 14.7 ±0.3 % and 18.4 ±0.3 % , respectively, and that the mode energy supply rates show no significant correlation with activity. With this study we expand previously published results on the temporal variation of solar p-mode parameters. Our results will be helpful to future studies of the excitation and damping of p modes, i.e., the interplay between convection, magnetic field, and resonant acoustic oscillations. Title: Subsurface Flows During Cycle 23 and 24 Authors: Komm, Rudolf; Howe, Rachel; Hill, Frank Bibcode: 2018csc..confE..54K Altcode: We study the solar-cycle variation of subsurface flows from the surface to a depth of 16 Mm. We have used ring-diagram analysis to analyze Dopplergrams obtained with the MDI Dynamics Program, the GONG, and the SDO/HMI instrument. We combine the zonal and meridional flows from the three data sources and we derive their temporal variation in a consistent manner for Solar Cycle 23 and 24. For Cycle 24, the flow patterns are precursors of the magnetic activity. The timing difference between the occurrence of the flow pattern and the magnetic one increases almost linearly with increasing latitude. For example, the fast zonal and meridional flow appear about 2.1 years and 2.5 years respectively before the magnetic pattern at 30 degree latitude in the northern hemisphere, while in the southern one the differences are 3.2 years and 2.6 years. The flow patterns of Cycle 25 are present and have reached 30 degree latitude. The amplitude differences of Cycle 25 are about 22% smaller than those of Cycle 24 but comparable to those of Cycle 23. In addition, we divide the data into subsets of low and high magnetic activity and study the variation of the quiet- and active-region flows during Solar Cycle 23 and 24. Title: Subsurface Zonal and Meridional Flow During Cycles 23 and 24 Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 2018SoPh..293..145K Altcode: We study the solar-cycle variation of subsurface flows from the surface to a depth of 16 Mm. We have used ring-diagram analysis to analyze Dopplergrams obtained with the Michelson Doppler Imager (MDI) Dynamics Program, the Global Oscillation Network Group (GONG), and the Helioseismic and Magnetic Imager (HMI) instrument. We combined the zonal and meridional flows from the three data sources and scaled the flows derived from MDI and GONG to match those from HMI observations. In this way, we derived their temporal variation in a consistent manner for Solar Cycles 23 and 24. We have corrected the measured flows for systematic effects that vary with disk positions. Using time-depth slices of the corrected subsurface flows, we derived the amplitudes and times of the extrema of the fast and slow zonal and meridional flows during Cycles 23 and 24 at every depth and latitude. We find an average difference between maximum and minimum amplitudes of 8.6 ±0.4 ms−1 for the zonal flows and 7.9 ±0.3 ms−1 for the meridional flows associated with Cycle 24 averaged over a depth range from 2 to 12 Mm. The corresponding values derived from GONG data alone are 10.5 ±0.3 ms−1 for the zonal and 10.8 ±0.3 ms−1 for the meridional flow. For Cycle 24, the flow patterns are precursors of the magnetic activity. The timing difference between the occurrence of the flow pattern and the magnetic one increases almost linearly with increasing latitude. For example, the fast zonal and meridional flow appear 2.1 ±0.6 years and 2.5 ±0.6 years, respectively, before the magnetic pattern at 30∘ latitude in the northern hemisphere, while in the southern hemisphere, the differences are 3.2 ±1.2 years and 2.6 ±0.6 years. The flow patterns of Cycle 25 are present and have reached 30∘ latitude. The amplitude differences of Cycle 25 are about 22% smaller than those of Cycle 24, but are comparable to those of Cycle 23. Moreover, polynomial fits of meridional flows suggest that equatorward meridional flows (counter-cells) might exist at about 80∘ latitude except during the declining phase of the solar cycle. Title: Signatures of Solar Cycle 25 in Subsurface Zonal Flows Authors: Howe, R.; Hill, F.; Komm, R.; Chaplin, W. J.; Elsworth, Y.; Davies, G. R.; Schou, J.; Thompson, M. J. Bibcode: 2018ApJ...862L...5H Altcode: 2018arXiv180702398H The pattern of migrating zonal flow bands associated with the solar cycle, known as the torsional oscillation, has been monitored with continuous global helioseismic observations by the Global Oscillations Network Group (GONG), together with those made by the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO) and its successor, the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO), since 1995, giving us nearly two full solar cycles of observations. We report that the flows now show traces of the mid-latitude acceleration that is expected to become the main equatorward-moving branch of the zonal flow pattern for Cycle 25. Based on the current position of this branch, we speculate that the onset of widespread activity for Cycle 25 is unlikely to be earlier than the middle of 2019. Title: 22 Year Solar Magnetic Cycle and its relation to Convection Zone Dynamics Authors: Jain, Kiran; Tripathy, Sushanta; Komm, Rudolf; Hill, Frank; Simoniello, Rosaria Bibcode: 2018IAUS..340....9J Altcode: 2018arXiv180505371J Using continuous observations for 22 years from ground-based network GONG and space-borne instruments MDI onboard SoHO and HMI onboard SDO, we report both global and local properties of the convection zone and their variations with time. Title: The Sun in transition? Persistence of near-surface structural changes through Cycle 24 Authors: Howe, R.; Davies, G. R.; Chaplin, W. J.; Elsworth, Y.; Basu, S.; Hale, S. J.; Ball, W. H.; Komm, R. W. Bibcode: 2017MNRAS.470.1935H Altcode: 2017arXiv170509099H We examine the frequency shifts in low-degree helioseismic modes from the Birmingham Solar-Oscillations Network covering the period from 1985 to 2016, and compare them with a number of global activity proxies well as a latitudinally resolved magnetic index. As well as looking at frequency shifts in different frequency bands, we look at a parametrization of the shift as a cubic function of frequency. While the shifts in the medium- and high-frequency bands are very well correlated with all of the activity indices (with the best correlation being with the 10.7-cm radio flux), we confirm earlier findings that there appears to have been a change in the frequency response to activity during solar Cycle 23, and the low-frequency shifts are less correlated with activity in the last two cycles than they were in Cycle 22. At the same time, the more recent cycles show a slight increase in their sensitivity to activity levels at medium and higher frequencies, perhaps because a greater proportion of activity is composed of weaker or more ephemeral regions. This lends weight to the speculation that a fundamental change in the nature of the solar dynamo may be in progress. Title: Solar-Cycle Variation of Subsurface-Flow Divergence: A Proxy of Magnetic Activity? Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 2017SoPh..292..122K Altcode: We study the solar-cycle variation of subsurface flows from the surface to a depth of 16 Mm. We have analyzed Global Oscillation Network Group (GONG) Dopplergrams with a ring-diagram analysis covering about 15 years and Helioseismic and Magnetic Imager (HMI) Dopplergrams covering more than 6 years. After subtracting the average rotation rate and meridional flow, we have calculated the divergence of the horizontal residual flows from the maximum of Solar Cycle 23 through the declining phase of Cycle 24. The subsurface flows are mainly divergent at quiet regions and convergent at locations of high magnetic activity. The relationship is essentially linear between divergence and magnetic activity at all activity levels at depths shallower than about 10 Mm. At greater depths, the relationship changes sign at locations of high activity; the flows are increasingly divergent at locations with a magnetic activity index (MAI) greater than about 24 G. The flows are more convergent by about a factor of two during the rising phase of Cycle 24 than during the declining phase of Cycle 23 at locations of medium and high activity (about 10 to 40 G MAI) from the surface to at least 10 Mm. The subsurface divergence pattern of Solar Cycle 24 first appears during the declining phase of Cycle 23 and is present during the extended minimum. It appears several years before the magnetic pattern of the new cycle is noticeable in synoptic maps. Using linear regression, we estimate the amount of magnetic activity that would be required to generate the precursor pattern and find that it should be almost twice the amount of activity that is observed. Title: Parametrizing the time variation of the `surface term' of stellar p-mode frequencies: application to helioseismic data Authors: Howe, R.; Basu, S.; Davies, G. R.; Ball, W. H.; Chaplin, W. J.; Elsworth, Y.; Komm, R. Bibcode: 2017MNRAS.464.4777H Altcode: 2016arXiv161004113H The solar-cycle variation of acoustic mode frequencies has a frequency dependence related to the inverse mode inertia. The discrepancy between model predictions and measured oscillation frequencies for solar and solar-type stellar acoustic modes includes a significant frequency-dependent term known as the surface term, which is also related to the inverse mode inertia. We parametrize both the surface term and the frequency variations for low-degree solar data from Birmingham Solar-Oscillations Network (BiSON) and medium-degree data from the Global Oscillations Network Group (GONG) using the mode inertia together with cubic and inverse frequency terms. We find that for the central frequency of rotationally split multiplets, the cubic term dominates both the average surface term and the temporal variation, but for the medium-degree case, the inverse term improves the fit to the temporal variation. We also examine the variation of the even-order splitting coefficients for the medium-degree data and find that, as for the central frequency, the latitude-dependent frequency variation, which reflects the changing latitudinal distribution of magnetic activity over the solar cycle, can be described by the combination of a cubic and an inverse function of frequency scaled by inverse mode inertia. The results suggest that this simple parametrization could be used to assess the activity-related frequency variation in solar-like asteroseismic targets. Title: Sub-photosphere to Solar Atmosphere Connection Authors: Komm, Rudolf; De Moortel, Ineke; Fan, Yuhong; Ilonidis, Stathis; Steiner, Oskar Bibcode: 2017hdsi.book..173K Altcode: No abstract at ADS Title: Subsurface Zonal and Meridional Flows from SDO/HMI Authors: Komm, Rudolf; Howe, Rachel; Hill, Frank Bibcode: 2016usc..confE..55K Altcode: We study the solar-cycle variation of the zonal and meridional flows in the near-surface layers of the solar convection zone from the surface to a depth of about 16 Mm. The flows are determined from SDO/HMI Dopplergrams using the HMI ring-diagram pipeline. The zonal and meridional flows vary with the solar cycle. Bands of faster-than-average zonal flows together with more-poleward-than-average meridional flows move from mid-latitudes toward the equator during the solar cycle and are mainly located on the equatorward side of the mean latitude of solar magnetic activity. Similarly, bands of slower-than-average zonal flows together with less-poleward-than-average meridional flows are located on the poleward side of the mean latitude of activity. Here, we will focus on the variation of these flows at high latitudes (poleward of 50 degree) that are now accessible using HMI data. We will present the latest results. Title: Solar origins of space weather Authors: Jain, Kiran; Komm, Rudolf W. Bibcode: 2016AsJPh..25..363J Altcode: Space weather refers to the varying conditions in the space environment near Earth that are driven by the Sun and its changing magnetic field. The magnetic field originates in the interior of the Sun and extends throughout the solar atmosphere. We discuss the solar sources of space weather and focus on coronal mass ejections (CMEs), flares, and solar energetic particles (SEP) and on the on-going efforts to predict these eruptive events and their effect on space weather. Title: Are subsurface flows evidence of hidden magnetic flux during cycle minimum? Authors: Komm, Rudolf; Howe, Rachel; Hill, Frank Bibcode: 2016SPD....47.0708K Altcode: Subsurface flows vary during the course of a solar cycle showing bands of faster- and slower-than-average rotation and bands of converging meridional flow. These flow patterns migrate with latitude; they first appear during the declining phase of a solar cycle and are present during cycle minimum. They appear several years before the magnetic pattern of a new cycle is apparent in synoptic maps and the values of magnetic flux at these locations are comparable to other quiet-Sun locations without such flow patterns. Do the precursory flow patterns thus indicate the presence of magnetic flux that is too small-scale or short-lived to be noticed in synoptic maps? How much flux would be required to generate these flow patterns?We quantify the relationship between subsurface flow patterns and magnetic activity during Cycles 23 and 24 and address these questions. We have analyzed GONG and SDO/HMI Dopplergrams using a dense-pack ring-diagram analysis and determined flows in the near-surface layers of the solar convection zone to a depth of about 16 Mm. Title: Horizontal Flows in Active Regions from Ring-diagram and Local Correlation Tracking Methods Authors: Jain, Kiran; Tripathy, S. C.; Ravindra, B.; Komm, R.; Hill, F. Bibcode: 2016ApJ...816....5J Altcode: 2015arXiv151103208J Continuous high-cadence and high spatial resolution Dopplergrams allow us to study subsurface dynamics that may be further extended to explore precursors of visible solar activity on the surface. Since the p-mode power is absorbed in the regions of high magnetic field, the inferences in these regions are often presumed to have large uncertainties. In this paper, using the Dopplergrams from space-borne Helioseismic Magnetic Imager, we compare horizontal flows in a shear layer below the surface and the photospheric layer in and around active regions. The photospheric flows are calculated using the local correlation tracking (LCT) method, while the ring-diagram technique of helioseismology is used to infer flows in the subphotospheric shear layer. We find a strong positive correlation between flows from both methods near the surface. This implies that despite the absorption of acoustic power in the regions of strong magnetic field, the flows inferred from the helioseismology are comparable to those from the surface measurements. However, the magnitudes are significantly different; the flows from the LCT method are smaller by a factor of 2 than the helioseismic measurements. Also, the median difference between the direction of corresponding vectors is 49°. Title: Sub-photosphere to Solar Atmosphere Connection Authors: Komm, Rudolf; De Moortel, Ineke; Fan, Yuhong; Ilonidis, Stathis; Steiner, Oskar Bibcode: 2015SSRv..196..167K Altcode: 2013SSRv..tmp...93K Magnetic fields extend from the solar interior through the atmosphere. The formation and evolution of active regions can be studied by measuring subsurface flows with local helioseismology. The emergence of magnetic flux from the solar convection zone is associated with acoustic perturbation signatures. In near-surface layers, the average dynamics can be determined for emerging regions. MHD simulations of the emergence of a twisted flux tube show how magnetic twist and free energy are transported from the interior into the corona and the dynamic signatures associated with such transport in the photospheric and sub-photospheric layers. The subsurface twisted flux tube does not emerge into the corona as a whole in emerging active regions. Shear flows at the polarity inversion line and coherent vortical motions in the subsurface flux tubes are the major means by which twist is transported into the corona, leading to the formation of sigmoid-shaped coronal magnetic fields capable of driving solar eruptions. The transport of twist can be followed from the interior by using the kinetic helicity of subsurface flows as a proxy of magnetic helicity; this quantity holds great promise for improving the understanding of eruptive phenomena. Waves are not only vital for studying the link between the solar interior and the surface but for linking the photosphere with the corona as well. Acoustic waves that propagate from the surface into the magnetically structured, dynamic atmosphere undergo mode conversion and refraction. These effects enable atmospheric seismology to determine the topography of magnetic canopies in the solar atmosphere. Inclined magnetic fields lower the cut-off frequency so that low frequency waves can leak into the outer atmosphere. Recent high resolution, high cadence observations of waves and oscillations in the solar atmosphere, have lead to a renewed interest in the potential role of waves as a heating mechanism. In light of their potential contribution to the heating of the solar atmosphere, some of the recent observations of waves and oscillations and ongoing modelling efforts are reviewed. Title: Solar Subsurface Flows During Solar Cycle 24 Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 2015AGUFMSH23A2420K Altcode: We study the variation of subsurface flows in the presence of magnetic activity during the current solar cycle. To determine flows in the near-surface layers of the solar convection zone from the surface to a depth of about 16 Mm, we have analyzed Dopplergrams obtained with the Global Oscillation Network Group (GONG) and the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) using a dense-pack ring-diagram analysis. We will compare the zonal and meridional flows during Cycle 24 with those during Cycle 23. The zonal and meridional flows at high latitudes are now accessible thanks to HMI data. The zonal- and meridional-flow patterns track the mean latitude of activity and are precursors of magnetic activity appearing about three years before activity is visible in synoptic maps of the solar surface. The poleward branch of the zonal-flow pattern is noticeable during Cycle 24 but is considerably weaker than during the previous cycle. We will also present the latest results from global helioseismology for comparison. Title: Persistent Near-Surface Flow Structures from Local Helioseismology Authors: Howe, Rachel; Komm, R. W.; Baker, D.; Harra, L.; van Driel-Gesztelyi, L.; Bogart, R. S. Bibcode: 2015SoPh..290.3137H Altcode: 2015arXiv150706525H; 2015SoPh..tmp..115H Near-surface flows measured by the ring-diagram technique of local helioseismology show structures that persist over multiple rotations. We examine these phenomena using data from the Global Oscillation Network Group (GONG) and the Helioseismic and Magnetic Imager (HMI) and show that a correlation analysis of the structures can be used to estimate the rotation rate as a function of latitude, giving a result consistent with the near-surface rate from global helioseismology and slightly slower than that obtained from a similar analysis of the surface magnetic field strength. At latitudes of 60∘ and above, the HMI flow data reveal a strong signature of a two-sided zonal flow structure. This signature may be related to recent reports of "giant cells" in solar convection. Title: Solar-Cycle Variation of Subsurface Meridional Flow Derived with Ring-Diagram Analysis Authors: Komm, R.; González Hernández, I.; Howe, R.; Hill, F. Bibcode: 2015SoPh..290.3113K Altcode: 2015SoPh..tmp...83K We study the solar-cycle variation of the meridional flow in the near-surface layers of the solar convection zone from the surface to a depth of 16 Mm. We have analyzed Global Oscillation Network Group (GONG) Dopplergrams with a ring-diagram analysis covering about 13 years (July 2001 - October 2014), from the maximum of Cycle 23 through the rising phase of Cycle 24, and Helioseismic and Magnetic Imager (HMI) Dopplergrams covering more than four years (May 2010 - January 2015). GONG and HMI lead to similar meridional flows during common epochs and latitudes. The meridional flow averaged over a Carrington rotation is poleward up to about 70∘ in both hemispheres at all depths after correcting for systematic effects. The flow amplitude peaks at about 40∘ latitude with an amplitude of about 16 to 20 ms−1 depending on depth. The meridional flow varies with the solar cycle; the flow amplitudes are larger during cycle minimum than during maximum at low- and mid-latitudes. The flows are mainly faster or more-poleward-than-average on the equatorward side of the mean latitude of activity and slower or less-poleward-than-average on its poleward side. The residual meridional flow converges near the mean latitude of activity. A comparison with the corresponding zonal flow derived from GONG and HMI data shows that the bands of more-poleward-than-average meridional flow coincide with the bands of faster-than-average zonal flow and that the bands of less-poleward-than-average meridional flow coincide with the bands of slower-than-average zonal flow. This implies that the residual flows are cyclonic. The bands of fast meridional flow appear at mid-latitudes about three years before magnetic activity of Cycle 24 is present in synoptic maps. Title: Temporal evolution of the solar torsional oscillation and implications for cycle 25 Authors: Hill, Frank; Howe, Rachel; Komm, Rudolf; Schou, Jesper; Thompson, Michael; Larson, Timothy Bibcode: 2015TESS....110502H Altcode: The zonal flow known as the torsional oscillation has been observed on the Sun’s surface since 1980 and in its interior since 1995. It has two branches that migrate during the solar cycle, with one moving towards the equator and the other towards the poles. The rate at which these branches migrate in latitude is tightly correlated with the timing of the solar cycle, as seen during the long minimum between cycles 23 and 24. The poleward branch generally becomes visible 10 to 12 years before the appearance of the magnetic activity associated with the corresponding sunspot cycle as it did for the current cycle 24. However, the poleward flow for cycle 25, which was expected to appear in 2008-2010, was not observed. Subsequent analysis showed that it is a very weak flow, and is masked by an apparent change in the background solar differential rotation rate. We will present the latest observations of the zonal flow as determined from global helioseismology, and will discuss the implications for the strength and timing of cycle 25. Title: Subsurface Zonal and Meridional Flow Derived from GONG and SDO/HMI: A Comparison of Systematics Authors: Komm, R.; González Hernández, I.; Howe, R.; Hill, F. Bibcode: 2015SoPh..290.1081K Altcode: 2015SoPh..tmp...22K We study the subsurface flows in the near-surface layers of the solar convection zone from the surface to a depth of 16 Mm derived from Global Oscillation Network Group (GONG) and Helioseismic and Magnetic Imager (HMI) Dopplergrams using a ring-diagram analysis. We characterize the systematic east-west and north-south variations present in the zonal and meridional flows and compare flows derived from GONG and HMI data before and after the correction. The average east-west variation with depth of one flow component resembles the average north-south variation with depth of the other component. The east-west variation of the zonal flow together with the north-south variation of the meridional flow can be modeled as a systematic radial velocity. This indicates a solar center-to-limb variation as the underlying cause. The north-south variation of the zonal flow and the east-west variation of the meridional flow require two separate functions. The east-west variation of the meridional flow consists mainly of an annual variation with the B0 angle, while the north-south trend of the zonal flow consists of a constant non-zero component in addition to an annual variation. This indicates a geometric projection artifact. After compensating for these systematic effects, the meridional and zonal flows derived from HMI data agree well with those derived from GONG data. An offset remains between the zonal flow derived from GONG and HMI data. The equatorward meridional flows at high latitude that appear episodically depending on the B0 angle are absent from the corrected flows. Title: Solar-cycle variation of subsurface flows during 20 years Authors: Komm, Rudolf; Howe, Rachel; Hill, Frank Bibcode: 2015TESS....121406K Altcode: We study the solar-cycle variation of the zonal and meridional flow in the near-surface layers of the solar convection zone from the surface to a depth of about 16 Mm. We have analyzed Dopplergrams obtained with the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO), the Global Oscillation Network Group (GONG),and the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) with a dense-pack ring-diagram analysis. The three data sets combined cover almost two solar cycles. The zonal and meridional flows vary with the solar cycle. Their amplitude variation tracks the mean latitude of activity and appears about three years before magnetic activity is visible in synoptic maps of the solar surface. We focus on the variation of the zonal and meridional flows, including their long-term variation at mid- and low-latitudes using GONG and MDI data and their variation at the high latitudes that are now accessible using HMI data. We will present the latest results. Title: Subsurface helicity of active regions 12192 and 10486 Authors: Komm, Rudolf; Tripathy, Sushant; Howe, Rachel; Hill, Frank Bibcode: 2015TESS....110506K Altcode: The active region 10486 that produced the Halloween flares in 2003 initiated our interest in the kinetic helicity of subsurface flows associated with active regions. This lead to the realization that the helicity of subsurface flows is related to the flare activity of active regions. Eleven years later, a similarly enormous active region (12192) appeared on the solar surface. We plan to study the kinetic helicity of the subsurface flows associated with region 12192 and compare it to that of region 10486. For 10486, we have analyzed Dopplergrams obtained with the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO) and the Global Oscillation Network Group (GONG) with a dense-pack ring-diagram analysis. For 12192, we have analyzed Dopplergrams from GONG and the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We will present the latest results. Title: Current and Kinetic Helicity of Long-lived Activity Complexes Authors: Komm, Rudolf; Gosain, Sanjay Bibcode: 2015ApJ...798...20K Altcode: We study long-lived activity complexes and their current helicity at the solar surface and their kinetic helicity below the surface. The current helicity has been determined from synoptic vector magnetograms from the NSO/SOLIS facility, and the kinetic helicity of subsurface flows has been determined with ring-diagram analysis applied to full-disk Dopplergrams from NSO/GONG and SDO/HMI. Current and kinetic helicity of activity complexes follow the hemispheric helicity rule with mainly positive values (78%; 78%, respectively, with a 95% confidence level of 31%) in the southern hemisphere and negative ones (80%; 93%, respectively, with a 95% confidence level of 22% and 14%, respectively) in the northern hemisphere. The locations with the dominant sign of kinetic helicity derived from Global Oscillation Network Group (GONG) and SDO/HMI data are more organized than those of the secondary sign even if they are not part of an activity complex, while locations with the secondary sign are more fragmented. This is the case for both hemispheres even for the northern one where it is not as obvious visually due to the large amount of magnetic activity present as compared to the southern hemisphere. The current helicity shows a similar behavior. The dominant sign of current helicity is the same as that of kinetic helicity for the majority of the activity complexes (83% with a 95% confidence level of 15%). During the 24 Carrington rotations analyzed here, there is at least one longitude in each hemisphere where activity complexes occur repeatedly throughout the epoch. These "active" longitudes are identifiable as locations of strong current and kinetic helicity of the same sign. Title: Solar Meridional Flow from Helioseismic Observations Authors: Komm, R. Bibcode: 2014AGUFMSH44A..03K Altcode: The meridional flow in the solar interior has been studied with helioseismic techniques applied to observations from the ground-based Global Oscillation Network Group (GONG), the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO), and most recently from the Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory (SDO). The observed meridional flow is on average poleward in the near-surface layers of the Sun and its amplitude varies with the solar cycle. The meridional circulation plays an important role in dynamo theories. For example, the structure and the strength of the meridional flow might determine the duration of the solar cycle and set the timing of the reversals of the Sun's polar fields in flux-transport dynamo models. To improve the understanding of the relationship between dynamo and meridional flow, major topics that need to be addressed are the variation of the meridional flow with the solar cycle, its variation with depth, and the meridional flow at high latitudes. I will discuss recent results from helioseismic observations. Title: Current and Kinetic Helicity of Long-Lived Activity Complexes Authors: Komm, R.; Gosain, S. Bibcode: 2014AGUFMSH41B4137K Altcode: We focus on long-lived activity complexes and their helicity below and above the solar surface. These locations of recurrent flux emergence in or close to a pre-existing active region, last for typically five to seven solar rotations. It is known that emergence of new magnetic flux in pre-existing magnetic region causes an increase in topological complexity of the magnetic field which leads to flares and Coronal Mass Ejections (CMEs). A quantitative measure of topological complexity of magnetic fields is given by the magnetic helicity which measures twisting and linking of the magnetic field. The current helicity determined from vector magnetograms is the equivalent of the kinetic helicity determined from subsurface flows. The helicity is thus an ideal quantity to investigate the linkage of magnetic fields in the solar atmosphere with flows in the upper solar convection zone. The subsurface flows from the surface to a depth of 16 Mm are determined with a ring-diagram analysis of GONG and SDO/HMI Dopplergrams and the current helicity density is determined from SOLIS vector magnetograms. We will study the kinetic and current helicity as a function of time and Carrington longitude, averaged over a suitable range of latitudes in either hemisphere. We will present the latest results. Title: A Combined Study of Photospheric Magnetic and Current Helicities and Subsurface Kinetic Helicities of Solar Active Regions during 2006-2013 Authors: Seligman, D.; Petrie, G. J. D.; Komm, R. Bibcode: 2014ApJ...795..113S Altcode: 2014arXiv1409.0764S We compare the average photospheric current helicity Hc , photospheric twist parameter α (a well-known proxy for the full relative magnetic helicity), and subsurface kinetic helicity Hk for 194 active regions observed between 2006-2013. We use 2440 Hinode photospheric vector magnetograms, and the corresponding subsurface fluid velocity data derived from GONG (2006-2012) and Helioseismic and Magnetic Imager (2010-2013) dopplergrams. We find a significant hemispheric bias in all three parameters. The subsurface kinetic helicity is preferentially positive in the southern hemisphere and negative in the northern hemisphere. The photospheric current helicity and the α parameter have the same bias for strong fields (|B| > 1000 G) and no significant bias for weak fields (100 G <|B| < 500 G). We find no significant region-by-region correlation between the subsurface kinetic helicity and either the strong-field current helicity or α. Subsurface fluid motions of a given handedness correspond to photospheric helicities of both signs in approximately equal numbers. However, common variations appear in annual averages of these quantities over all regions. Furthermore, in a subset of 77 regions, we find significant correlations between the temporal profiles of the subsurface and photospheric helicities. In these cases, the sign of the linear correlation coefficient matches the sign relationship between the helicities, indicating that the photospheric magnetic field twist is sensitive to the twisting motions below the surface. Title: Solar-Cycle Variation of Subsurface Zonal Flow Authors: Komm, R.; Howe, R.; González Hernández, I.; Hill, F. Bibcode: 2014SoPh..289.3435K Altcode: 2014SoPh..tmp...29K We study the solar-cycle variation of the zonal flow in the near-surface layers of the solar convection zone from the surface to a depth of 16 Mm covering the period from mid-2001 to mid-2013 or from the maximum of Cycle 23 through the rising phase of Cycle 24. We have analyzed Global Oscillation Network Group (GONG) and Helioseismic and Magnetic Imager (HMI) Dopplergrams with a ring-diagram analysis. The zonal flow varies with the solar cycle showing bands of faster-than-average flows equatorward of the mean latitude of activity and slower-than-average flows on the poleward side. The fast band of the zonal flow and the magnetic activity appear first in the northern hemisphere during the beginning of Cycle 24. The bands of fast zonal flow appear at mid-latitudes about three years in the southern and four years in the northern hemisphere before magnetic activity of Cycle 24 is present. This implies that the flow pattern is a direct precursor of magnetic activity. The solar-cycle variation of the zonal flow also has a poleward branch, which is visible as bands of faster-than-average zonal flow near 50° latitude. This band appears first in the southern hemisphere during the rising phase of the Cycle 24 and migrates slowly poleward. These results are in good agreement with corresponding results from global helioseismology. Title: Hemispheric Distribution of Subsurface Kinetic Helicity and Its Variation with Magnetic Activity Authors: Komm, R.; Gosain, S.; Pevtsov, A. A. Bibcode: 2014SoPh..289.2399K Altcode: 2014SoPh..tmp...25K We study the hemispheric distribution of the kinetic helicity of subsurface flows in the near-surface layers of the solar convection zone and its variation with magnetic activity. We determine subsurface flows with a ring-diagram analysis applied to Global Oscillation Network Group (GONG) Dopplergrams and Dynamics Program data from the Michelson Doppler Imager (MDI) instrument onboard the Solar and Heliospheric Observatory (SOHO). We determine the average kinetic helicity density as a function of Carrington rotation and latitude. The average kinetic helicity density at all depths and the kinetic helicity, integrated over 2 - 7 Mm, follow the same hemispheric rule as the current/magnetic helicity proxies with predominantly positive values in the southern and negative ones in the northern hemisphere. This holds true for all levels of magnetic activity from quiet to active regions. However, this is a statistical result; only about 55 % of all locations follow the hemispheric rule. But these locations have larger helicity values than those that do not follow the rule. The average values of helicity density increase with depth for all levels of activity, which might reflect an increase of the characteristic size of convective motions with greater depth. The average helicity of subsets of high magnetic activity is about five times larger than that of subsets of low activity. The solar-cycle variation of helicity is thus mainly due to the presence or absence of active regions. During the rising phase of cycle 24, locations of high magnetic activity at low latitudes show a weaker hemispheric behavior compared to the rising phase of cycle 23. Title: Daily Normalized Helicity of Subsurface Flows Authors: Komm, Rudolf; Reinard, Alysha; Hill, Frank Bibcode: 2014AAS...22421801K Altcode: Flare-productive active regions are associated with subsurface flows with large values of kinetic helicity density. Kinetic helicity is related to mixing and turbulence of fluids. Reinard et al. 2010 have developed a parameter that captures the variation of kinetic helicity with depth and time, the so-called Normalized Helicity Gradient Variance (NHGV). This parameter increases 2-3 days before a flare occurs and the NHGV values for flaring and non-flaring active regions represent clearly separate populations. We derive subsurface flows from the surface to a depth of 16 Mm using GONG and SDO/HMI Dopplergrams analyzed with the ring-diagram technique and calculate kinetic helicity density as a function of position on the solar disk. We will then calculate the NHGV parameter exploring different normalization schemes and depth ranges. We will present cases studies of active regions observed with GONG and SDO/HMI. Title: Current and Kinetic Helicity of Long-Lived Activity Complexes Authors: Komm, Rudolf; Gosain, S. Bibcode: 2014shin.confE..60K Altcode: We focus on long-lived activity complexes and their helicity below and above the solar surface. These locations of recurrent flux emergence in or close to a pre-existing active region, last for typically five to seven solar rotations. It is known that emergence of new magnetic flux in pre-existing magnetic region causes an increase in topological complexity of the magnetic field which leads to flares and Coronal Mass Ejections (CMEs). A quantitative measure of topological complexity of magnetic fields is given by the magnetic helicity which measures twisting and linking of the magnetic field. The current helicity determined from vector magnetograms is the equivalent of the kinetic helicity determined from subsurface flows. The helicity is thus an ideal quantity to investigate the linkage of magnetic fields in the solar atmosphere with flows in the upper solar convection zone. The subsurface flows from the surface to a depth of 16 Mm are determined with a ring-diagram analysis of GONG and SDO/HMI Dopplergrams and the current helicity density is determined from SOLIS vector magnetograms. We will study the kinetic and current helicity as a function of time and Carrington longitude, averaged over a suitable range of latitudes in either hemisphere. We will present the latest results. Title: Daily Normalized Kinetic Helicity of Subsurface Flows Authors: Komm, Rudolf; Reinard, A.; Hill, F. Bibcode: 2014shin.confE.163K Altcode: Flare-productive active regions are associated with subsurface flows with large values of kinetic helicity density. Kinetic helicity is related to mixing and turbulence of fluids. Reinard et al. 2010 have developed a parameter that captures the variation of kinetic helicity with depth and time, the so-called Normalized Helicity Gradient Variance (NHGV). This parameter increases 2-3 days before a flare occurs and the NHGV values for flaring and non-flaring active regions represent clearly separate populations. We derive subsurface flows from the surface to a depth of 16 Mm using GONG and SDO/HMI Dopplergrams analyzed with the ring-diagram technique and calculate kinetic helicity density as a function of position on the solar disk. We will then calculate the NHGV parameter exploring different normalization schemes and depth ranges. We will present cases studies of active regions observed with GONG and SDO/HMI. Title: Photospheric and sub-photospheric Flows in Active Regions Authors: Jain, Kiran; Komm, Rudolf W; Tripathy, Sushanta; Ravindra, B.; Hill, Frank Bibcode: 2014AAS...22421821J Altcode: The availability of continuous high-cadence and high-spatial resolution Dopplergrams allows us to study sub-surface dynamics that may be further extended to explore precursors of the solar activity. Since p-mode power is absorbed in high magnetic field regions, the helioseismic inferences in these regions are associated with large errors. In order to validate results, we use Dopplergrams from both space-borne (Helioseismic Magnetic Imager-HMI) and ground-based (Global Oscillation Network Group-GONG) observations to infer horizontal flows in photospheric and sub-photospheric layers in and around several active regions with different characteristics. The photospheric flows are calculated using local correlation tracking (LCT) method while ring-diagram analysis technique is used to infer flows in the sub-photospheric regions. A detailed comparison between flows in shear layer and photospheric layer will be made in order to study similarities and discrepancies in these results. Title: Active Regions with Superpenumbral Whirls and Their Subsurface Kinetic Helicity Authors: Komm, R.; Gosain, S.; Pevtsov, A. Bibcode: 2014SoPh..289..475K Altcode: We search for a signature of helicity flow from the solar interior to the photosphere and chromosphere. For this purpose, we study two active regions, NOAA 11084 and 11092, that show a regular pattern of superpenumbral whirls in chromospheric and coronal images. These two regions are good candidates for comparing magnetic/current helicity with subsurface kinetic helicity because the patterns persist throughout the disk passage of both regions. We use photospheric vector magnetograms from SOLIS/VSM and SDO/HMI to determine a magnetic helicity proxy, the spatially averaged signed shear angle (SASSA). The SASSA parameter produces consistent results leading to positive values for NOAA 11084 and negative ones for NOAA 11092 consistent with the clockwise and counter-clockwise orientation of the whirls. We then derive the properties of the subsurface flows associated with these active regions. We measure subsurface flows using a ring-diagram analysis of GONG high-resolution Doppler data and derive their kinetic helicity, hz. Since the patterns persist throughout the disk passage, we analyze synoptic maps of the subsurface kinetic helicity density. The sign of the subsurface kinetic helicity is negative for NOAA 11084 and positive for NOAA 11092; the sign of the kinetic helicity is thus anticorrelated with that of the SASSA parameter. As a control experiment, we study the subsurface flows of six active regions without a persistent whirl pattern. Four of the six regions show a mixture of positive and negative kinetic helicity resulting in small average values, while two regions are clearly dominated by kinetic helicity of one sign or the other, as in the case of regions with whirls. The regions without whirls follow overall the same hemispheric rule in their kinetic helicity as in their current helicity with positive values in the southern and negative values in the northern hemisphere. Title: Solar Origins of Space Weather and Space Climate: Preface Authors: González Hernández, I.; Komm, R.; Pevtsov, A.; Leibacher, J. W. Bibcode: 2014SoPh..289..437G Altcode: No abstract at ADS Title: A Combined Study of Photospheric Magnetic and Current Helicities and Subsurface Kinetic Helicities of Solar Active Regions during 2006-2012 Authors: Seligman, Darryl; Petrie, G.; Komm, R. Bibcode: 2014AAS...22315801S Altcode: We compare the average photospheric current helicity H_c, photospheric twist parameter α (a well-known proxy for the full relative magnetic helicity), and subsurface kinetic helicity K_h for 128 active regions observed between 2006-2012. We use 1436 Hinode photospheric vector magnetograms and subsurface fluid velocity data from GONG Dopplergrams. We find a significant hemispheric bias in all three parameters. The K_h parameter is preferentially positive/negative in the southern/northern hemisphere. The H_c and α parameters have the same bias for strong fields |{B}|>1000 G). We examine the temporal variability of each parameter for each active region and identify a significant subset of regions whose three helicity parameters all exhibit clear increasing or decreasing trends. The temporal profiles of these regions have the same bias: positive/negative helicity in the northern/southern hemisphere. The results are consistent with Longcope et al.'s Σ-effect. This work is carried out through the National Solar Observatory Research Experiences for Undergraduate (REU) site program, which is co-funded by the Department of Defense in partnership with the NSF REU Program. The National Solar Observatory is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation. Title: Subsurface Flows in Active Region 11158 Authors: Jain, K.; Tripathy, S. C.; Komm, R.; González Hernández, I.; Hill, F. Bibcode: 2013ASPC..478..225J Altcode: We apply the ring-diagram technique to study the temporal evolution of horizontal velocity in sub-photospheric layers beneath active regions as they move across the solar disk. Here we present results for the AR 11158 for six days and investigate how flows get organized within the active region by the morphology of individual sunspots or vice versa. We find abrupt changes in depth profiles for smaller regions in going from one day to another, however the average flows for the active region do not show significant temporal variation. Title: Medium-Degree Global-Mode Frequency Shifts in Solar Cycles 23 and 24: Is There Any Difference? Authors: Howe, R.; Komm, R.; Hill, F. Bibcode: 2013ASPC..478..155H Altcode: It is well established that the frequencies of acoustic modes vary with the solar cycle, being strongly correlated with the temporal and spatial distribution of magnetic activity as measured by the magnetic field strength or by intensity proxies. With nearly eighteen years of data from GONG and MDI, we check for differences between the sensitivity to the Kitt Peak magnetic index between the rising phases of Solar Cycles 23 and 24. We find no significant difference. Title: Solar Cycle Variation of High-Degree Acoustic Mode Frequencies Authors: Tripathy, S. C.; Jain, K.; Komm, R. W.; Hill, F. Bibcode: 2013ASPC..478..221T Altcode: We investigate the temporal variations of the high-degree mode frequencies measured over localized regions of the Sun though the technique of ring-diagrams. We observe that the high-degree mode frequencies have a solar cycle variation similar to those of intermediate-degree modes but ten times greater. We also find that the averaged frequency shifts are linearly correlated with routinely measured solar activity indices e.g. 10.7 cm radio flux. We do not, however, find any evidence of a quadratic relation between the frequencies of individual multiplets and solar activity indices as reported earlier from the study of global high-degree modes. Title: Solar-Cycle Variation of Subsurface Zonal Flow Derived from Ring-Diagram Analysis Authors: Komm, R.; Howe, R.; González Hernández, I.; Hill, F.; Bogart, R. S.; Haber, D. Bibcode: 2013ASPC..478..217K Altcode: We study the solar-cycle variation of the zonal flow in the near-surface layers of the solar convection zone from the surface to a depth of 16 Mm. We have analyzed Global Oscillation Network Group (GONG) and Helioseismic and Magnetic Imager (HMI) Dopplergrams with the ring-diagram analysis covering about 12 years combined. The zonal flow varies with the solar cycle showing faster-than-average flows equatorward of the mean latitude of activity and slower-than-average flows on the poleward side. The bands of fast zonal flow appear at mid-latitudes about two years before magnetic activity of cycle 24 is seen. The poleward branch of this variation is visible as bands of fast zonal flow near 50° latitude in both HMI and GONG data. Title: The Torsional Oscillation and the Timing of the Solar Cycle: Is it Maximum Yet? Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.; Larson, T. P.; Schou, J.; Thompson, M. J. Bibcode: 2013ASPC..478..303H Altcode: After the late start to Cycle 24 there are some indications that activity may have peaked as early as late 2011 and that the polar-field reversal has already occurred in the North. We use helioseismic measurements of the migrating zonal flow pattern known as the torsional oscillation to estimate the length of the solar cycle, and find that it has held steady at about 12.3 years since late 2009, which would point to solar maximum in 2013 as expected. Title: Magnetic Polarity Streams and Subsurface Flows Authors: Howe, R.; Baker, D.; Harra, L.; van Driel-Gesztelyi, L.; Komm, R.; Hill, F.; González Hernández, I. Bibcode: 2013ASPC..478..291H Altcode: An important feature of the solar cycle is the transport of unbalanced magnetic flux from active regions towards the poles, which eventually results in polarity reversal. This transport takes the form of distinct “polarity streams” that are visible in the magnetic butterfly diagram. We compare the poleward migration rate estimated from such streams to that derived from the subsurface meridional flows measured in helioseismic data from the GONG network since 2001, and find that the results are in reasonable agreement. Title: Subsurface Meridional Flow from HMI Using the Ring-Diagram Pipeline Authors: Komm, R.; González Hernández, I.; Hill, F.; Bogart, R.; Rabello-Soares, M. C.; Haber, D. Bibcode: 2013SoPh..287...85K Altcode: 2012SoPh..tmp..177K We have determined the meridional flows in subsurface layers for 18 Carrington rotations (CR 2097 to 2114) analyzing high-resolution Dopplergrams obtained with the Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory (SDO). We are especially interested in flows at high latitudes up to 75∘ in order to address the question whether the meridional flow remains poleward or reverses direction (so-called counter cells). The flows have been determined in depth from near-surface layers to about 16 Mm using the HMI ring-diagram pipeline. The measured meridional flows show systematic effects, such as a variation with the B0-angle and a variation with central meridian distance (CMD). These variations have been taken into account to lead to more reliable flow estimates at high latitudes. The corrected average meridional flow is poleward at most depths and latitudes with a maximum amplitude of about 20~m s^{-1} near 37.5∘ latitude. The flows are more poleward on the equatorward side of the mean latitude of magnetic activity at 22∘ and less poleward on the poleward side, which can be interpreted as convergent flows near the mean latitude of activity. The corrected meridional flow is poleward at all depths within ± 67.5∘ latitude. The corrected flow is equatorward only at 75∘ latitude in the southern hemisphere at depths between about 4 and 8 Mm and at 75∘ latitude in the northern hemisphere only when the B0 angle is barely large enough to measure flows at this latitude. These counter cells are most likely the remains of an insufficiently corrected B0-angle variation and not of solar origin. Flow measurements and B0-angle corrections are difficult at the highest latitude because these flows are only determined during limited periods when the B0 angle is sufficiently large. Title: Latest Results Found with Ring-Diagram Analysis Authors: Baldner, C. S.; Basu, S.; Bogart, R. S.; Burtseva, O.; González Hernández, I.; Haber, D.; Hill, F.; Howe, R.; Jain, K.; Komm, R. W.; Rabello-Soares, M. C.; Tripathy, S. Bibcode: 2013SoPh..287...57B Altcode: 2012SoPh..tmp..294B Ring-diagram analysis is a helioseismic tool useful for studying the near-surface layers of the Sun. It has been employed to study near-surface shear, meridional circulation, flows around sunspots, and thermal structure beneath active regions. We review recent results obtained using ring-diagram analysis, state some of the more important outstanding difficulties in the technique, and point out several extensions to the technique that are just now beginning to bear fruit. Title: Preface Authors: Mansour, Nagi N.; Kosovichev, Alexander G.; Komm, Rudolf; Longcope, Dana; Leibacher, John W. Bibcode: 2013SoPh..287....1M Altcode: No abstract at ADS Title: Are subsurface flows and coronal holes related? Authors: Komm, R.; Howe, R.; González Hernández, I.; Harra, L.; Baker, D.; van Driel-Gesztelyi, L. Bibcode: 2013JPhCS.440a2022K Altcode: We study synoptic maps of solar subsurface flows covering six Carrington rotations (2050 to 2055). The subsurface flows are determined with a ring-diagram analysis of GONG high-resolution Doppler data. We identify the locations of coronal holes in synoptic maps of EUV images at 195Å from the EIT instrument and determine the characteristics of associated subsurface flows. We study two long-lived coronal holes that are present during this epoch. We find that large-scale patterns are present in the subsurface flows but appear to be unrelated to these coronal holes. The horizontal subsurface flows associated with the two long-lived coronal holes are weakly divergent (upflows) with small cyclonic vorticity. These flows are thus similar to subsurface flows of quiet regions with regard to the vertical flows and similar to flows of active regions with regard to vorticity. Title: How do the active region subsurface flow properties differ based on hemisphere and CME association? Authors: Reinard, Alysha; Komm, R.; Hill, F. Bibcode: 2013shin.confE..60R Altcode: The investigation of subsurface flows beneath active regions offers insight into the processes that occur prior to and during flare/CME eruptions. We present new research on this topic that considers both the flare location (specifically northern vs southern hemisphere) and the presence or absence of an associated CME to determine whether there is any difference in the subsurface flow pattern. We find essentially no difference in subsurface flows below eruptive (i.e. CME associated) and non-eruptive flares, indicating that the underlying processes are similar in each case and the magnetic configuration of the active region determines the eruptive potential. We do find a difference in events originating in the northern and southern hemisphere with the kinetic helicity density at the deepest layers being of opposite signs in each hemisphere. This effect is stronger for CME-associated flares, perhaps because such flares tend to be larger. Title: Helicity of Subsurface Flows and Magnetic Activity in the Photosphere Authors: Komm, Rudolf; Gosain, S.; Pevtsov, A. A. Bibcode: 2013shin.confE..43K Altcode: Subsurface flows associated with active regions show generally large values of kinetic helicity density. The vertical component of kinetic helicity is defined as the product of the curl of the horizontal velocities and the vertical velocity component. It is thus the equivalent of current helicity determined from vector magnetograms. The vertical component of kinetic helicity follows on average the hemispheric rule established for current helicity with negative values in the northern hemisphere and positive values in the southern one. We analyze 11 years of GONG Dopplergrams and derive subsurface flows from the surface to a depth of 16 Mm with the ring-diagram technique. From these velocities, we calculate the kinetic helicity density and integrate it over selected depth ranges. We will study the kinetic helicity as a function of time and latitude for different levels of magnetic activity, such as active and quiet regions. We will present the latest results. Title: Subsurface flows associated with non-Joy oriented active regions: a case study Authors: González Hernández, Irene; Komm, Rudolf; van Driel-Gesztelyi, Lidia; Baker, Deborah; Harra, Louise; Howe, Rachel Bibcode: 2013JPhCS.440a2050G Altcode: Non-Joy oriented active regions (ARs) are a challenge for solar magnetic field modelers. Although significant deviations from Joy's law are relatively rare for simple bipolar ARs, understanding the causes of their particularity could be critical for the big picture of the solar dynamo. We explore the possibility of the sub-surface local dynamics being responsible for the significant rotation of these ARs. We apply the ring-diagram technique, a local helioseismology method, to infer the flows under and surrounding a non-Joy oriented AR and present the results of a case study in this paper. Title: Daily Normalized Helicity of Subsurface Flows Authors: Komm, Rudolf; Reinard, A.; Hill, F. Bibcode: 2013shin.confE..44K Altcode: Flare-productive active regions are associated with subsurface flows with large values of kinetic helicity density. Kinetic helicity is related to mixing and turbulence of fluids. Reinard et al. 2010 have developed a parameter that captures the variation of kinetic helicity with depth and time, the so-called Normalized Helicity Gradient Variance (NHGV). This parameter increases 2-3 days before a flare occurs and the NHGV values for flaring and non-flaring active regions represent clearly separate populations. We derive subsurface flows from the surface to a depth of 16 Mm using GONG Dopplergrams analyzed with the ring-diagram technique. From the measured velocities, we calculate kinetic helicity density as a function of position on the solar disk. We will then calculate the NHGV parameter exploring different normalization schemes and depth ranges. We will calculate daily NHGV maps of the solar disk for different levels of magnetic activity. We will present the latest results. Title: The High-latitude Branch of the Solar Torsional Oscillation in the Rising Phase of Cycle 24 Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.; Larson, T. P.; Rempel, M.; Schou, J.; Thompson, M. J. Bibcode: 2013ApJ...767L..20H Altcode: We use global heliseismic data from the Global Oscillation Network Group, the Michelson Doppler Imager on board the Solar and Heliospheric Observatory, and the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, to examine the behavior, during the rising phase of Solar Cycle 24, of the migrating zonal flow pattern known as the torsional oscillation. Although the high-latitude part of the pattern appears to be absent in the new cycle when the flows are derived by subtracting a mean across a full solar cycle, it can be seen if we subtract the mean over a shorter period in the rising phase of each cycle, and these two mean rotation profiles differ significantly at high latitudes. This indicates that the underlying high-latitude rotation has changed; we speculate that this is in response to weaker polar fields, as suggested by a recent model. Title: Subsurface Flows in and Around Active Regions with Rotating and Non-rotating Sunspots Authors: Jain, K.; Komm, R. W.; González Hernández, I.; Tripathy, S. C.; Hill, F. Bibcode: 2012SoPh..279..349J Altcode: 2012arXiv1205.2356J The temporal variation of the horizontal velocity in sub-surface layers beneath three different types of active region is studied using the technique of ring diagrams. In this study, we select active regions (ARs) 10923, 10930, 10935 from three consecutive Carrington rotations: AR 10930 contains a fast-rotating sunspot in a strong emerging active region while other two have non-rotating sunspots with emerging flux in AR 10923 and decaying flux in AR 10935. The depth range covered is from the surface to about 12 Mm. In order to minimize the influence of systematic effects, the selection of active and quiet regions is made so that these were observed at the same heliographic locations on the solar disk. We find a significant variation in both components of the horizontal velocity in active regions as compared to quiet regions. The magnitude is higher in emerging-flux regions than in the decaying-flux region, in agreement with earlier findings. Further, we clearly see a significant temporal variation in depth profiles of both zonal and meridional flow components in AR 10930, with the variation in the zonal component being more pronounced. We also notice a significant influence of the plasma motion in areas closest to the rotating sunspot in AR 10930, while areas surrounding the non-rotating sunspots in all three cases are least affected by the presence of the active region in their neighborhood. Title: Subsurface flows associated with eruptive and non-eruptive flares Authors: Reinard, Alysha; Krista, Larisza; Komm, Rudi; Hill, Frank Bibcode: 2012shin.confE.144R Altcode: Subsurface flows beneath active regions offer insight into the processes that occur prior to and during flare/CME eruptions. We have developed a technique to forecast solar flares based on subsurface flows. We present new research on this topic that involves comparing eruptive and non-eruptive flares to determine whether there is any difference in the flow pattern. We also look at active region characteristics associated with these events. Title: Active regions with superpenumbral whirls and their subsurface flow vorticity Authors: Komm, Rudolf W.; Gosain, S.; Pevtsov, A. Bibcode: 2012shin.confE.119K Altcode: We search for a signature of helicity flow from the solar interior to the photosphere and chromosphere. We study two active regions NOAA 11084 and NOAA 11092 that show a regular pattern of superpenumbral whirls in H-alpha. The pattern persists throughout the disk passage of both regions. We use photospheric vector magnetograms from SOLIS/VSM to determine two helicity proxies: vertical component of the current helicity density (Hc_z=Jz.Bz) and the mean twist parameter (alpha_z=<Jz/Bz>), and to study their evolution. We compare the two proxies of magnetic helicity with the properties of the subsurface flows below the active regions. For this purpose, we analyze subsurface flows measured with a ring-diagram analysis of GONG high-resolution Doppler data and derive their vorticity. As a control experiment, we study the subsurface flows of six active regions that do not show a regular whirl pattern in the chromosphere. Title: Are subsurface flows and coronal holes related? Authors: Komm, Rudolf W.; Howe, R.; González Hernández, I.; Harra, L.; Baker, D.; van Driel-Gesztelyi, L. Bibcode: 2012shin.confE.120K Altcode: We study subsurface flows measured with a ring-diagram analysis of GONG high-resolution Doppler data. In previous studies, we have focused on the relationship between active regions and subsurface flows associated with them. Synoptic subsurface flow maps show also large-scale patterns that are not obviously associated with active regions. It is unknown whether these flow patterns correlate with any large-scale magnetic features. Here, we explore whether there is a relationship between subsurface flows and coronal features. We analyze synoptic maps of subsurface flows covering 18 Carrington rotations during the years 2006 and 2007 (CR 2038-2055). Long-lived coronal holes are present during this epoch at low latitudes, which are accessible by ring-diagram analysis of GONG data. We compare subsurface flow maps with EIT synoptic maps of EUV images at 195A (http://sun.stanford.edu/synop/EIT/) and will present the latest results. Title: Temporal Variation of Subsurface Flows in Active Regions Authors: Komm, Rudolf W.; Jain, K.; Tripathy, S. C.; Gonzalez Hernandez, I.; Hill, F. Bibcode: 2012shin.confE.121K Altcode: We apply the ring-diagram technique to study the temporal variation of horizontal velocity in sub-photospheric layers beneath active regions as they move across the solar disk. We categorize these active regions on the basis of their dynamical characteristics and investigate how velocity components beneath rotating sunspots differ from that in non-rotating sunspots. Our study clearly shows that there is a singnificant temporal variation in depth profiles of both zonal and meridional components in active regions with rotating sunspots while these variations remain small for non-rotating sunspots. Title: Coronal relative magnetic helicities and subsurface kinetic helicities of active regions Authors: Petrie, Gordon; Komm, Rudolf; Amari, Tahar Bibcode: 2012shin.confE.117P Altcode: Excess of helicity in coronal magnetic structures has often been linked to their instability and eruption. Moreover, active regions associated with subphotospheric patterns of strong subsurface kinetic helicity have been found to be more flare productive. How are these atmospheric magnetic and subsurface fluid helicities related? Using SOLIS vector magnetic magnetograms, the XTRAPOL nonlinear force-free field extrapolation code and GONG helioseismic data we study the coronal relative magnetic helicities of a set of active regions in combination with their subsurface kinetic helicities in order to better understand the transport processes of helicity in solar activity. Title: The Evolution of Large-Scale Subsurface Flow Patterns in the Sun Authors: Bogart, Richard S.; Baldner, C. S.; Basu, S.; Burtseva, O.; Gonzalez-Hernandez, I.; Haber, D. A.; Hill, F.; Howe, R.; Jain, K.; Komm, R. W.; Rabello-Soares, M. C.; Tripathy, S. Bibcode: 2012AAS...22020509B Altcode: Ring-diagram analysis permits us to infer large-scale flow fields at the photosphere and down to depths of about 0.95 R. We present comparisons of the mean zonal and meridional velocity profiles determined from uniform analysis techniques applied to three observational data sets, those from the SDO/HMI and SOHO/MDI missions and the GONG project, over the last 18 years. We pay special attention to measurements obtained during the summer of 2010, when observations from all three observatories were available. We discuss systematic effects affecting the individual datasets in order to analyse evolution of global flows over the time scale of the solar cycle. Title: Data From The HMI Ring-Diagram Pipelines Authors: Bogart, Richard S.; Baldner, C. S.; Basu, S.; Gonzalez-Hernandez, I.; Haber, D. A.; Hill, F.; Howe, R.; Jain, K.; Komm, R. W.; Rabello-Soares, M. C.; Tripathy, S. Bibcode: 2012AAS...22020512B Altcode: The HMI data pipeline for measurement of sub-surface flows with ring-diagram analysis has been running for nearly two years, and virtually all HMI Doppler data have been analyzed. Nearly 5 million local-area power spectra have been produced and fitted for regions of various sizes, and inversions for the depth structure of flows have been performed for over 150,000 of the larger regions. The pipeline for determination of the sub-surface thermal structure is still under active development, with test results for a number of strong active regions currently available for analysis. We describe the ring-diagram pipelines, report on their performance, describe the data products available, and discuss outstanding problems and issues for further development. Title: Latest Results on the Torsional Oscillation and Solar Cycle 25 Authors: Hill, Frank; Howe, R.; Schou, J.; Thompson, M.; Larson, T.; Komm, R. Bibcode: 2012AAS...22012302H Altcode: The Torsional Oscillation in the Sun is a zonal (East-West) flow that is slightly faster than the background differential rotation profile. The location of this flow slowly migrates in latitude over a period of several years. There are two branches of the flow: an equatorward branch that underlies the active regions, and a poleward branch. The timing of the equatorward migration is correlated with the timing of the solar cycle such that the activity for a cycle appears when the center of the flow reaches latitude 25 degrees. In addition, the poleward branch appears about 12 years prior to the activity for a cycle. Thus we should have observed the onset of Cycle 25 in 2008, but did not. This poster will update the observations to 2012, and present a new analysis that shows that the Cycle 25 flow appeared in 2010, but was hidden by a change in the background differential rotation profile. These results suggest that the next minimum will be two years longer than average, and that Cycle 25 will begin in 2022. Title: Vorticity of Subsurface Flows of Emerging and Decaying Active Regions Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 2012SoPh..277..205K Altcode: We study the temporal variation of the vorticity of subsurface flows of 828 active regions and 977 quiet regions. The vorticity of these flows is derived from measured subsurface velocities. The horizontal flows are determined by analyzing high-resolution Global Oscillation Network Group Doppler data with ring-diagram analysis covering a range of depths from the surface to about 16 Mm. The vertical velocity component is derived from the divergence of the measured horizontal flows using mass conservation. We determine the change in unsigned magnetic flux density during the disk passage of each active region using Michelson Doppler Imager (MDI) magnetograms binned to the ring-diagram grid with centers spaced by 7.5° ranging ± 52.5° in latitude and central meridian distance with an effective diameter of 15° after apodization. We then sort the data by their flux change from decaying to emerging flux and divide the data into five subsets of equal size. We find that the vorticity of subsurface flows increases during flux emergence and decreases when active regions decay. For flux emergence, the absolute values of the zonal and meridional vorticity components show the most coherent variation with activity, while for flux decrease the strongest signature is in the absolute values of the meridional and vertical vorticity components. The temporal variation of the enstrophy (residual vorticity squared) is thus a good indicator for either flux increase or decrease. There are some indications that the increase in vorticity during flux emergence happens about a day later at depths below about 8 Mm compared to layers shallower than about 4 Mm. This timing difference might imply that the vorticity signal analyzed here is caused by the interaction between magnetic flux and turbulent flows near the solar surface. There are also hints that the vorticity decrease during flux decay begins about a day earlier at layers deeper than about 8 Mm compared to shallower ones. However, the timing difference between the change at different depths is comparable to the time step of the analysis. Title: The Global Context of Solar Activity During the Whole Heliosphere Interval Campaign Authors: Webb, D. F.; Cremades, H.; Sterling, A. C.; Mandrini, C. H.; Dasso, S.; Gibson, S. E.; Haber, D. A.; Komm, R. W.; Petrie, G. J. D.; McIntosh, P. S.; Welsch, B. T.; Plunkett, S. P. Bibcode: 2011SoPh..274...57W Altcode: The Whole Heliosphere Interval (WHI) was an international observing and modeling effort to characterize the 3-D interconnected "heliophysical" system during this solar minimum, centered on Carrington Rotation 2068, March 20 - April 16, 2008. During the latter half of the WHI period, the Sun presented a sunspot-free, deep solar minimum type face. But during the first half of CR 2068 three solar active regions flanked by two opposite-polarity, low-latitude coronal holes were present. These departures from the quiet Sun led to both eruptive activity and solar wind structure. Most of the eruptive activity, i.e., flares, filament eruptions and coronal mass ejections (CMEs), occurred during this first, active half of the interval. We determined the source locations of the CMEs and the type of associated region, such as active region, or quiet sun or active region prominence. To analyze the evolution of the events in the context of the global solar magnetic field and its evolution during the three rotations centered on CR 2068, we plotted the CME source locations onto synoptic maps of the photospheric magnetic field, of the magnetic and chromospheric structure, of the white light corona, and of helioseismological subsurface flows. Most of the CME sources were associated with the three dominant active regions on CR 2068, particularly AR 10989. Most of the other sources on all three CRs appear to have been associated with either isolated filaments or filaments in the north polar crown filament channel. Although calculations of the flux balance and helicity of the surface magnetic features did not clearly identify a dominance of one region over the others, helioseismological subsurface flows beneath these active regions did reveal a pronounced difference among them. These preliminary results suggest that the "twistedness" (i.e., vorticity and helicity) of subsurface flows and its temporal variation might be related to the CME productivity of active regions, similar to the relationship between flares and subsurface flows. Title: Solar dynamics at high latitudes and deep in the convection zone Authors: Gonzalez Hernandez, I.; Komm, R.; Howe, R.; Kholikov, S.; Hill, F.; Bogart, R. S.; Rabello-Soares, M. Bibcode: 2011AGUFMSH33A2041G Altcode: For a long time, helioseismic inferences have provided a window into the solar interior. In the last two decades, the development of local helioseismology tools has extended the capability of helioseismology by allowing the study of localized structure changes and dynamics. In particular, it has revealed the subsurface flows and its variation throughout the solar cycle. Both the torsional oscillation and the meridional circulation present interesting patterns leading to solar cycle 24, which continue during the onset of this cycle. Yet, many questions related to the behavior of such flows at high latitudes as well as deep down in the convection zone that are key to solar dynamo models remain unanswered. Long-term helioseismic studies using both Global Oscillation Network Group (GONG) and Michelson Doppler Imager (MDI)data have uncovered the difficulties of properly interpreting data far from disk center due to systematics and solar effects, limiting the helioseismic inferences to only specific areas. The Helioseismic and Magnetic Imager (HMI) instrument on board the Solar Dynamics Observatory (SDO) provides an excellent opportunity to explore the until now unreachable territories thanks to its higher resolution. In addition, newly available artificial data sets offer an unprecedented opportunity for disentangling and modeling the different effects. We present here a review of the main features observed in the subsurface flows in the recent years and discuss future plans to extend the inferences at higher latitudes and deep down in the convection zone. Title: Multi-spectral Analysis of Heliseismic Acoustic Mode Parameters Authors: Jain, Kiran; Tripathy, S.; Basu, S.; Bogart, R.; Gonzalez Hernandez, I.; Hill, F.; Howe, R.; Kholikov, S.; Komm, R. Bibcode: 2011sdmi.confE..33J Altcode: Simultaneous measurements at different wavelengths from SDO offer the prospect of studying the sensitivity of helioseismic inferences to the choice of observing height both in quiet-Sun and magnetically active regions. In this poster, we present comparison of mode parameters obtained with different observables, quantify differences, and interpret results in the context of the formation height and the anticipated phase relationships between the oscillations at those heights. This work is expected to enhance our understanding of the excitation and damping of the oscillations and the uncertainties in helioseismic inferences. Title: Subsurface kinetic helicity of flows near active regions Authors: Komm, R.; Jain, K.; Petrie, G.; Pevtsov, A.; González Hernández I.; Hill, F. Bibcode: 2011sdmi.confE..68K Altcode: We study the temporal variation of subsurface flows associated with emerging and decaying active regions on the Sun. We measure the subsurface flows analyzing GONG high-resolution Doppler data with ring-diagram analysis. We can detect the emergence of magnetic flux in these flows when averaging over a sufficiently large sample. In a previous study, we have found that emerging flux has a faster rotation than the ambient fluid and pushes it up, as indicated by enhanced vertical velocity and faster-than-average zonal flow. Here, we show that the kinetic helicity density of subsurface flows increases when new flux emerges and decreases when flux decays. Title: Latest Results Found With Ring-Diagram Analysis Authors: Haber, D. A.; Baldner, C.; Basu, S.; Bogart, R. S.; González-Hernández, I.; Hill, F.; Howe, R.; Jain, K.; Komm, R. W.; . Rabello-Soares, C.; Pinkerton, S.; Tripathy, S. Bibcode: 2011sdmi.confE..51H Altcode: This talk will mainly be a preview of the posters generated by the HMI Rings Team on large-scale (meridional and zonal) flows; characterizations of active regions at various stages of evolution using data from AIA as well as from HMI; systematic changes in frequencies, flows, and other fitted parameters as a function of disk placement, underlying magnetism, B angle, etc.; and the status of the Rings pipeline. It will also include any new ring-diagram results from GONG and MDI. Title: Large-scale flows from HMI using the ring-diagram pipeline Authors: Komm, R.; González Hernández, I.; Hill, F.; Bogart, R. S.; Rabello-Soares, M. C. Bibcode: 2011sdmi.confE..72K Altcode: We determine the zonal and meridional flows in subsurface layers derived from HMI Doppler data processed with the HMI ring-diagram pipeline. We analyze subsurface flow measurements obtained during Carrington rotation 2097 to 2113. We are especially interested in flows at latitudes of 60 degree and higher, since previous observations have been limited to lower latitudes (using local helioseismic techniques). Systematic effects, such as B0-angle variations, have to be taken into account to lead to reliable flow estimates at high latitudes. We will present the latest results. Title: Subsurface flows associated with rotating sunspots Authors: Jain, Kiran; Komm, Rudolf; Hernández, Irene González; Tripathy, Sushant C.; Hill, Frank Bibcode: 2011IAUS..273..356J Altcode: 2011arXiv1107.5032J In this paper, we compare components of the horizontal flow below the solar surface in and around regions consisting of rotating and non-rotating sunspots. Our analysis suggests that there is a significant variation in both components of the horizontal flow at the beginning of sunspot rotation as compared to the non-rotating sunspot. The flows in surrounding areas are in most cases relatively small. However, there is a significant influence of the motion on flows in an area closest to the sunspot rotation. Title: Solar subsurface flows of active regions: flux emergence and flare activity Authors: Komm, Rudolf; Howe, Rachel; Hill, Frank; Jain, Kiran Bibcode: 2011IAUS..273..148K Altcode: We study the temporal variation of subsurface flows associated with active regions within 16 Mm of the solar surface. We have analyzed the subsurface flows of nearly 1000 active and quiet regions applying ring-diagram analysis to Global Oscillation Network Group (GONG) Dopplergram data. We find that newly emerging active regions are characterized by enhanced upflows and fast zonal flows in the near-surface layers, as expected for a flux tube rising from deeper layers of the convection zone. The subsurface flows associated with strong active regions are highly twisted, as indicated by their large vorticity and helicity values. The dipolar pattern exhibited by the zonal and meridional vorticity component leads to the interpretation that these subsurface flows resemble vortex rings, when measured on the spatial scales of the standard ring-diagram analysis. Title: Helioseismic Observations of Solar Convection Zone Dynamics Authors: Hill, Frank; Howe, Rachel; Komm, Rudi; Hernández, Irene González; Kholikov, Shukur; Leibacher, John Bibcode: 2011IAUS..271...15H Altcode: The large-scale dynamics of the solar convection zone have been inferred using both global and local helioseismology applied to data from the Global Oscillation Network Group (GONG) and the Michelson Doppler Imager (MDI) on board SOHO. The global analysis has revealed temporal variations of the ``torsional oscillation'' zonal flow as a function of depth, which may be related to the properties of the solar cycle. The horizontal flow field as a function of heliographic position and depth can be derived from ring diagrams, and shows near-surface meridional flows that change over the activity cycle. Time-distance techniques can be used to infer the deep meridional flow, which is important for flux-transport dynamo models. Temporal variations of the vorticity can be used to investigate the production of flare activity. This paper summarizes the state of our knowledge in these areas. Title: Subsurface kinetic helicity of flows near active regions Authors: Komm, Rudolf; Jain, K.; Petrie, G.; Pevtsov, A.; González Hernández, I.; Hill, F. Bibcode: 2011shin.confE.142K Altcode: We study the flows in the upper solar convection zone determined from GONG data using the standard dense-pack ring-diagram analysis and derive daily and synoptic maps of the velocity components. We also calculate the vorticity and the kinetic helicity density of the flows. Previous studies have shown that the vorticity is enhanced near locations of active regions and that the kinetic helicity density associated with active regions correlates well with the X-ray flare intensity of active regions. These fluid dynamics descriptors are thus promising indicators for investigating the relation between active regions and associated subsurface flows. Here, we focus on the temporal evolution of subsurface kinetic helicity density during flux emergence and decay. We will present the latest results. Title: Large-scale Zonal Flows During the Solar Minimum -- Where Is Cycle 25? Authors: Hill, Frank; Howe, R.; Komm, R.; Christensen-Dalsgaard, J.; Larson, T. P.; Schou, J.; Thompson, M. J. Bibcode: 2011SPD....42.1610H Altcode: 2011BAAS..43S.1610H The so-called torsional oscillation is a pattern of migrating zonal flow bands that move from mid-latitudes towards the equator and poles as the magnetic cycle progresses. Helioseismology allows us to probe these flows below the solar surface. The prolonged solar minimum following Cycle 23 was accompanied by a delay of 1.5 to 2 years in the migration of bands of faster rotation towards the equator. During the rising phase of Cycle 24, while the lower-level bands match those seen in the rising phase of Cycle 23, the rotation rate at middle and higher latitudes remains slower than it was at the corresponding phase in earlier cycles, perhaps reflecting the weakness of the polar fields. In addition, there is no evidence of the poleward flow associated with Cycle 25. We will present the latest results based on nearly sixteen years of global helioseismic observations from GONG and MDI, with recent results from HMI, and discuss the implications for the development of Cycle 25. Title: Subsurface Vorticity of Flaring versus Flare-Quiet Active Regions Authors: Komm, R.; Ferguson, R.; Hill, F.; Barnes, G.; Leka, K. D. Bibcode: 2011SoPh..268..389K Altcode: 2010SoPh..tmp...78K We apply discriminant analysis to 1023 active regions and their subsurface-flow parameters, such as vorticity and kinetic helicity density, with the goal of distinguishing between flaring and non-flaring active regions. We derive synoptic subsurface flows by analyzing GONG high-resolution Doppler data with ring-diagram analysis. We include magnetic-flux values in the discriminant analysis derived from NSO Kitt Peak and SOLIS synoptic maps binned to the same spatial scale as the helioseismic analysis. For each active region, we determine the flare information from GOES and include all flares within 60° central meridian distance to match the coverage of the ring-diagram analysis. The subsurface-flow characteristics improve the ability to distinguish between flaring and non-flaring active regions. For the C- and M-class flare category, the most important subsurface parameter is the so-called structure vorticity, which estimates the horizontal gradient of the horizontal-vorticity components. The no-event skill score, which measures the improvement over predicting that no events occur, reaches 0.48 for C-class flares and 0.32 for M-class flares, when the structure vorticity at three depths combined with total magnetic flux are used. The contributions come mainly from shallow layers within about 2 Mm of the surface and layers deeper than about 7 Mm. Title: Subsurface Velocity of Emerging and Decaying Active Regions Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 2011SoPh..268..407K Altcode: 2011SoPh..tmp....6K We study the temporal variation of subsurface flows of 828 active regions and 977 quiet regions. The horizontal flows cover a range of depths from the surface to about 16 Mm and are determined by analyzing Global Oscillation Network Group high-resolution Doppler data with ring-diagram analyses. The vertical velocity component is derived from the divergence of the measured horizontal flows using mass conservation. For comparison, we analyze Michelson Doppler Imager (MDI) Dynamics Run data covering 68 active regions common to both data sets. We determine the change in unsigned magnetic flux during the disk passage of each active region using MDI magnetograms binned to the ring-diagram grid. We then sort the data by their flux change from decaying to emerging flux and divide the data into five subsets of equal size. We find that emerging flux has a faster rotation than the ambient fluid and pushes it up, as indicated by enhanced vertical velocity and faster-than-average zonal flow. After active regions are formed, downflows are established within two days of emergence in shallow layers between about 4 and 10 Mm. Emerging flux in existing active regions shows a similar scenario, where the upflows at depths greater than about 10 Mm are enhanced and the already established downflows at shallower depths are weakened. When active regions decay, the corresponding flow pattern disappears as well; the zonal flow slows down to values comparable to that of quiet regions and the upflows become weaker at deeper layers. The residual meridional velocity is mainly poleward and shows no obvious variation. The magnitude of the residual velocity, defined as the sum of the squares of the residual velocity components, increases with increasing magnetic flux and decreases with decreasing flux. Title: Solar-cycle variation of zonal and meridional flow Authors: Komm, R.; Howe, R.; Hill, F.; González Hernández, I.; Haber, D. Bibcode: 2011JPhCS.271a2077K Altcode: We study the variation with the solar cycle of the zonal and meridional flows in the near-surface layers of the solar convection zone. We have analyzed MDI Dynamics-Program data with ring-diagram analysis covering the rising phase of cycle 23, while the analyzed GONG high-resolution data cover the maximum and declining phase of cycle 23. For the zonal flow, the migration with latitude of the flow pattern is apparent in the deeper layers, while for the meridional flow, a migration with latitude is apparent only in the layers close to the surface. The faster-than-average bands of the zonal flow associated with the new cycle are clearly visible. Similarly, a pattern related to the new cycle appears in the residual meridional flow. We also study the flow differences between the hemispheres during the course of the solar cycle. The difference pattern of the meridional flow is slanted in latitude straddling the faster-than-average band of the torsional oscillation pattern in the zonal flow. The difference pattern of the zonal flow, on the other hand, resembles the cycle variation of the meridional flow. In addition, the meridional flow during the minimum of cycle 23/24 appears to be slightly stronger than during the previous minimum of cycle 22/23. Title: Solar flares and temporal changes in subsurface vorticity measurements Authors: Komm, R.; Jain, K.; Reinard, A.; Howe, R.; Hill, F. Bibcode: 2011JPhCS.271a2019K Altcode: We derive the kinetic helicity density of subsurface flows applying ring-diagram analysis to Global Oscillation Network Group (GONG) data. Here, we focus on flows derived from times series of 8 hours and compare them to daily values for a high- and a low-activity sample. Compared with daily values, the horizontal flows derived from 8-hour time series are reasonable near disk center and less reliable near the limb. Also, the errors are larger for shorter time series. A dipolar helicity pattern is present in the flows derived from 8-hour and 24-hour time series of flare-productive active region 10808. For the quiet-Sun sample, the subsurface kinetic helicity is considerably smaller without any pattern. Title: First Global Rotation Inversions of HMI Data Authors: Howe, R.; Larson, T. P.; Schou, J.; Hill, F.; Komm, R.; Christensen-Dalsgaard, J.; Thompson, M. J. Bibcode: 2011JPhCS.271a2061H Altcode: We present the first 2-dimensional global rotational inversions of medium-degree p-mode data from the Helioseismic and Magnetic Imager, and compare the results with inversions of Michelson Doppler Imager data for the same time period. The inferred rotation profiles show good agreement between the two instruments. Title: Comparison of HMI Dopplergrams with GONG and MDI data Authors: Howe, R.; Jain, K.; Hill, F.; Komm, R.; González Hernández, I.; Bogart, R. Bibcode: 2011JPhCS.271a2060H Altcode: We compare sample Dopplergrams from the Helioseismic and Magnetic Imager, the Michelson Doppler Imager and the Global Oscillation Network Group. Each instrument has a distinct static velocity patterm across the disk; once this has been subtracted and the images interpolated to a common grid, the agreement is satisfactory. Title: The torsional oscillation and the new solar cycle Authors: Howe, R.; Hill, F.; Komm, R.; Christensen-Dalsgaard, J.; Larson, T. P.; Schou, J.; Thompson, M. J.; Ulrich, R. Bibcode: 2011JPhCS.271a2074H Altcode: We present updated observations of the pattern of migrating solar zonal flows known as the torsional oscillation, covering 15 years of helioseismic measurements with GONG and MDI and 30 years of surface Doppler observations from Mount Wilson. We compare the behavior of the flows during the extended solar minimum following Cycle 23 with that in earlier minima. We demonstrate that the timing of the migration of the zonal flow belts may be of some use in predicting the start of the new cycle. We also note that the behavior of the high-latitude part of the pattern currently differs from that seen early in the previous cycle, with the high-latitude poleward-migrating branch still not established. Title: Local helioseismology of sunspot regions: Comparison of ring-diagram and time-distance results Authors: Kosovichev, A. G.; Basu, S.; Bogart, R.; Duvall, T. L., Jr.; Gonzalez-Hernandez, I.; Haber, D.; Hartlep, T.; Howe, R.; Komm, R.; Kholikov, S.; Parchevsky, K. V.; Tripathy, S.; Zhao, J. Bibcode: 2011JPhCS.271a2005K Altcode: 2010arXiv1011.0799K Local helioseismology provides unique information about the subsurface structure and dynamics of sunspots and active regions. However, because of complexity of sunspot regions local helioseismology diagnostics require careful analysis of systematic uncertainties and physical interpretation of the inversion results. We present new results of comparison of the ring-diagram analysis and time-distance helioseismology for active region NOAA 9787, for which a previous comparison showed significant differences in the subsurface sound-speed structure, and discuss systematic uncertainties of the measurements and inversions. Our results show that both the ring-diagram and time-distance techniques give qualitatively similar results, revealing a characteristic two-layer seismic sound-speed structure consistent with the results for other active regions. However, a quantitative comparison of the inversion results is not straightforward. It must take into account differences in the sensitivity, spatial resolution and the averaging kernels. In particular, because of the acoustic power suppression, the contribution of the sunspot seismic structure to the ring-diagram signal can be substantially reduced. We show that taking into account this effect reduces the difference in the depth of transition between the negative and positive sound-speed variations inferred by these methods. Further detailed analysis of the sensitivity, resolution and averaging properties of the local helioseismology methods is necessary for consolidation of the inversion results. It seems to be important that both methods indicate that the seismic structure of sunspots is rather deep and extends to at least 20 Mm below the surface, putting constraints on theoretical models of sunspots. Title: Rotation-rate variations at the tachocline: An update Authors: Howe, R.; Komm, R.; Hill, F.; Christensen-Dalsgaard, J.; Larson, T. P.; Schou, J.; Thompson, M. J.; Toomre, J. Bibcode: 2011JPhCS.271a2075H Altcode: After 15 years of GONG and MDI observations of the solar interior rotation, we revisit the issue of variations in the rotation rate near the base of the convection zone. The 1.3-year period seen in the first few years of the observations disappeared after 2000 and has still not returned. On the other hand, the agreement between GONG and MDI observations suggests that variations seen in this region have some solar origin, whether a true rotation-rate change or possibly mere stochastic variation; we present a numerical experiment supporting this contention. Title: A search for coherent structures in subsurface flows Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 2011JPhCS.271a2065K Altcode: We search for coherent patterns in horizontal subsurface flows obtained from Global Oscillation Network Group (GONG) Dopplergram data using ring-diagram analysis. The existence of north-south aligned downflow patterns near the equator has been predicted by numerical models of the solar convection zone. We analyze time series of daily flow measurements near the solar equator focusing on the vertical velocity component and the derivative of the zonal flow in the east-west direction. To reduce the influence of surface magnetic activity, we analyze observations during the minimum phase of the solar cycle. We find coherent equatorial structures that persist for several days in the zonal velocity derivative and the vertical velocity component and are not associated with surface magnetic activity. We use a cross-correlation analysis to measure the strength and rotation rate of these coherent patterns. Our results are consistent with other studies that have observed north-south aligned patterns in supergranulation. Title: Ring-diagram parameter comparisons for GONG, MDI and HMI Authors: Howe, R.; Tripathy, S.; González Hernández, I.; Komm, R.; Hill, F.; Bogart, R.; Haber, D. Bibcode: 2011JPhCS.271a2015H Altcode: We examine the differences between ring-diagram mode frequency estimates from samples of Global Oscillation Network Group [GONG], Michelson Doppler Imager [MDI] and Helioseismic and Magnetic Imager [HMI] data, and find that different instruments and analysis pipelines do result in small systematic differences which may not be uniform across the solar disk. Title: Low-degree helioseismology with AIA Authors: Howe, R.; Hill, F.; Komm, R.; Broomhall, A. -M.; Chaplin, W. J.; Elsworth, Y. Bibcode: 2011JPhCS.271a2058H Altcode: We form unresolved-sun time series from the 1600 and 1700 Angstrom images produced by the Atmospheric Imaging Assembly, and find a clean low-degree p-mode spectrum at each wavelength. The time series and spectra are compared with Doppler velocity and continuum intensity time series from the Helioseismic and Magnetic Imager and velocity series from the Birmingham Solar Oscillation Network. The UV data have a slight phase shift with respect to the velocity, and show more sensitivity to high-frequency and less to low-frequency modes. Unlike the HMI (visible) continuum observations, the UV spectra show little or no granulation noise at low frequencies and thus potentially allow more low-frequency modes to be recovered. These results suggest that asteroseismology at near-UV wavelengths should be very feasible and even an improvement on visible-wavelength intensity measurements, at least in low-activity stars. Title: Meridional Flow Observations: Implications for the current Flux Transport Models Authors: González Hernández, Irene; Komm, Rudolf; Kholikov, Shukur; Howe, Rachel; Hill, Frank Bibcode: 2011JPhCS.271a2073G Altcode: Meridional circulation has become a key element in the solar dynamo flux transport models. Available helioseismic observations from several instruments, Taiwan Oscillation Network (TON), Global Oscillation Network Group (GONG) and Michelson Doppler Imager (MDI), have made possible a continuous monitoring of the solar meridional flow in the subphotospheric layers for the last solar cycle, including the recent extended minimum. Here we review some of the meridional circulation observations using local helioseismology techniques and relate them to magnetic flux transport models. Title: Testing the GONG ring-diagram pipeline with HMI Dopplergrams Authors: Jain, Kiran; Tripathy, S. C.; González Hernández, I.; Kholikov, S.; Hill, F.; Komm, R.; Bogart, R.; Haber, D. Bibcode: 2011JPhCS.271a2017J Altcode: The GONG ring-diagram pipeline was developed to analyze GONG+ Dopplergrams in order to extract information about solar subsurface flows and has been extensively tested for this purpose. Here we present preliminary results obtained by analyzing the HMI Dopplergrams with the GONG pipeline and compare them with those obtained from the HMI ring-diagram pipeline. Title: Helioseismic Studies of a Sunspot using HMI Data Authors: Tripathy, S. C.; Jain, K.; Gonzalez Hernandez, I.; Komm, R.; Hill, F.; McManus, S.; Bogart, R.; Rabello-Soares, M. C.; Basu, S.; Baldner, C.; Haber, D. A. Bibcode: 2010AGUFMSH11A1603T Altcode: We study the mode parameters and sub-surface properties of the sunspot in NOAA active region 10093 during its disk passage between August 6-14, 2010. This is one of the major active regions recorded so far during the cycle 24 and continuous observations are available from the Helioseismic and Magnetic Imager (HMI). We will present the results using the HMI data processed through the HMI ring-diagram pipeline and compare those obtained with the GONG pipeline. We will also present results by analyzing the GONG observations through GONG pipeline. Title: The acoustic and magnetic solar cycle Authors: Komm, R. Bibcode: 2010AN....331..873K Altcode: The frequency variation of global modes provides information about the solar structure and the rotation rate of the solar interior. The solar-cycle variation of the rotation rate, the so-called torsional oscillation, extends throughout the convection zone. Alternating bands of faster- and slower-than-average rotation move from mid-latitudes toward the equator during the solar cycle. The variation of the meridional flow, measured with local helioseismic techniques, is of similar amplitude. The zonal- and the meridional-flow variation related to a new cycle are noticeable years before magnetic activity of the new cycle is present at the surface. The sound-speed variations show a small, but significant variation with the solar cycle near the base of the convection zone, which might be interpreted as a change in magnetic field strength. The mode characteristics, such as acoustic radius and frequency shifts, provide information about changes in the near-surface layers, where acoustic modes are excited. Title: Predictions of active region flaring probability using subsurface helicity measurements Authors: Reinard, A. A.; Komm, R.; Hill, F. Bibcode: 2010AGUFMSH43B1818R Altcode: Solar flares are responsible for a number of hazardous effects on the earth such as disabling high-frequency radio communications, interfering with GPS measurements, and disrupting satellites. However, forecasting flare occurrence is currently very difficult. One possible means for predicting flare occurrence lies in helioseismology, i.e. analysis of the region below the active region for signs of an impending flare. Time series helioseismic data collected by the Global Oscillation Network Group (GONG) has been analyzed for a subset of active regions that produce large flares and a subset with very high magnetic field strength that produce no flares. A predictive parameter has been developed and analyzed using discriminant analysis as well as traditional forecasting tools such as the Heidke skill score. Preliminary results show that this parameter predicts the flaring probability of an active region 2-3 days in advance with a relatively high degree of success. Title: Solar Subsurface Flows derived with Ring-Diagram Analysis Authors: Komm, R.; Howe, R.; Gonzalez Hernandez, I.; Hill, F.; Haber, D. A. Bibcode: 2010AGUFM.S32A..06K Altcode: Local helioseismology makes it possible to map the horizontal flows in the outer convection zone of the Sun. For the ring-diagram analysis, we start from full-disk Doppler velocity images of the Sun and track a region at about the surface rotation rate for a period of a day. Each tracked data cube of velocity is then Fourier transformed. The resulting 3-D power spectrum shows structures that correspond to the acoustic waves. These structures appear as rings in a 2-D plane at a given temporal frequency. Since acoustic waves are advected by subsurface flows, the velocity of these horizontal flows can be determined from the offset of the ring centers. Using ring-diagram analysis of Doppler images of the Sun obtained with the ground-based Global Oscillation Network Group (GONG) and the Michelson Doppler Imager (MDI) instrument on board the Solar and Heliospheric Observatory spacecraft (SOHO), we are studying, for example, the large-scale subsurface flows (E-W rotation and N-S meridional flow) and their variation with the solar cycle of magnetic activity. We are also studying subsurface flows associated with active regions on the Sun focusing on their evolution (emergence and decay). In addition, we have started to analyze data from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) spacecraft. We will present some recent results. Title: Subsurface Flows from SDO, SOHO, and GONG (Invited) Authors: Komm, R. Bibcode: 2010AGUFMSH21C..01K Altcode: Active regions (magnetic fields, in general) provide a point of contact between helioseismic studies of the upper convection zone and studies of the solar atmosphere as well as the whole heliophysics system. Helioseismic observations allow us to derive subsurface flows and sound-speed structures associated with active regions. For example, recent helioseismic studies have shown that the emergence and decay of active regions can be observed as changes in subsurface flow patterns and sound-speed variations on time scales of days. SDO will allow us to study these phenomena in unprecedented detail and the comparison with GONG and SOHO data sets will provide cross-calibration. On time scales of years, the intercomparison of the SDO, SOHO, and GONG data sets will allow us to study large-scale subsurface flows and their variation during two (or more) solar cycles. The cycle-related patterns of the zonal and the meridional flow appeared before magnetic activity of cycle 24 was present at the solar surface. With SDO and GONG, we will be able to observe these patterns during the current cycle and compare them with the patterns of the previous one observed by GONG and SOHO. Subsurface flows of active regions are also highly twisted and this appears to be related to the flare production of active regions. Helicity-loaded fields are very probably responsible for the most geoeffective solar phenomena such as coronal mass ejections and flares. It is thus of interest, for example, to find out how the kinetic helicity of subsurface flows derived from SDO and GONG Dopplergrams relates to the magnetic helicity of flux tubes derived from SDO vector magnetograms. I will discuss some of the plans for intercomparison of SDO data sets with SOHO and GONG data. Title: Global and Local Helioseismology from HMI and AIA Authors: Howe, R.; Komm, R.; Gonzalez Hernandez, I.; Jain, K.; Hill, F.; Haber, D. A.; Bogart, R. Bibcode: 2010AGUFMSH11A1601H Altcode: Data from the HMI [Helioseismic and Magnetic Imager] and AIA [Atmospheric Imaging Assembly] instruments aboard the Solar Dynamics observatory have been available for some months. We present some preliminary results from these data, including subsurface flow maps and activity-related local mode parameter shifts from helioseismic ring-diagram analysis of HMI data, HMI helioseismic sensing of the far side of the Sun, and low-degree p-mode spectra from the high-photosphere bands on AIA as well as from HMI velocity and continuum intensity. The results will be compared with those from the Michelson Doppler Imager and the Global Oscillation Network Group. Title: Modeling the Subsurface Structure of Sunspots Authors: Moradi, H.; Baldner, C.; Birch, A. C.; Braun, D. C.; Cameron, R. H.; Duvall, T. L.; Gizon, L.; Haber, D.; Hanasoge, S. M.; Hindman, B. W.; Jackiewicz, J.; Khomenko, E.; Komm, R.; Rajaguru, P.; Rempel, M.; Roth, M.; Schlichenmaier, R.; Schunker, H.; Spruit, H. C.; Strassmeier, K. G.; Thompson, M. J.; Zharkov, S. Bibcode: 2010SoPh..267....1M Altcode: 2009arXiv0912.4982M; 2010SoPh..tmp..171M While sunspots are easily observed at the solar surface, determining their subsurface structure is not trivial. There are two main hypotheses for the subsurface structure of sunspots: the monolithic model and the cluster model. Local helioseismology is the only means by which we can investigate subphotospheric structure. However, as current linear inversion techniques do not yet allow helioseismology to probe the internal structure with sufficient confidence to distinguish between the monolith and cluster models, the development of physically realistic sunspot models are a priority for helioseismologists. This is because they are not only important indicators of the variety of physical effects that may influence helioseismic inferences in active regions, but they also enable detailed assessments of the validity of helioseismic interpretations through numerical forward modeling. In this article, we provide a critical review of the existing sunspot models and an overview of numerical methods employed to model wave propagation through model sunspots. We then carry out a helioseismic analysis of the sunspot in Active Region 9787 and address the serious inconsistencies uncovered by Gizon et al. (2009a, 2009b). We find that this sunspot is most probably associated with a shallow, positive wave-speed perturbation (unlike the traditional two-layer model) and that travel-time measurements are consistent with a horizontal outflow in the surrounding moat. Title: Using helioseismology to understand and predict the solar cycle Authors: Hill, Frank; Komm, Rudi; Howe, Rachel; Gonzalez Hernandez, Irene; Kholikov, Shukur; Leibacher, John Bibcode: 2010shin.confE.156H Altcode: Helioseismology is now being used to investigate the subsurface flows that are related to the solar cycle. The relevant flows are the east-west zonal flows (torsional oscillation), and the north-south meridional flows. This poster will summarize the relationship of the timing of the solar cycle with the characteristics of the zonal and meridional flows; as well as what we know about the nature of the deep meridional flows that play a role in the dynamo. Title: What Solar Oscillation Tell Us About the Solar Minimum Authors: Jain, K.; Tripathy, S. C.; Burtseva, O.; H´Ndez, I. G.; Hill, F.; Howe, R.; Kholikov, S.; Komm, R.; Leibacher, J. Bibcode: 2010ASPC..428...57J Altcode: 2010arXiv1002.2411J The availability of continuous helioseismic data for two consecutive solar minima has provided a unique opportunity to study the changes in the solar interior that might have led to this unusual minimum. We present preliminary analysis of intermediate-degree mode frequencies in the 3 mHz band during the current period of minimal solar activity and show that the mode frequencies are significantly lower than those during the previous activity minimum. Our analysis does not show any signature of the beginning of cycle 24 until the end of 2008. In addition, the zonal and meridional flow patterns inferred from inverting frequencies also hint at a delayed onset of a new cycle. The estimates of travel time are higher than the previous minimum confirming a relatively weak solar activity during the current minimum. Title: Meridional Circulation During the Extended Solar Minimum: Another Component of the Torsional Oscillation? Authors: González Hernández, I.; Howe, R.; Komm, R.; Hill, F. Bibcode: 2010ApJ...713L..16G Altcode: 2010arXiv1003.1685G We show here a component of the meridional circulation developing at medium-high latitudes (40°-50°) before the new solar cycle starts. Like the torsional oscillation of the zonal flows, this extra circulation seems to precede the onset of magnetic activity at the solar surface and moves slowly toward lower latitudes. However, the behavior of this component differs from that of the torsional oscillation regarding location and convergence toward the equator at the end of the cycle. The observation of this component before the magnetic regions appear at the solar surface has only been possible due to the prolonged solar minimum. The results could settle the discussion as to whether the extra component of the meridional circulation around the activity belts, which has been known for some time, is or is not an effect of material motions around the active regions. Title: Evidence That Temporal Changes in Solar Subsurface Helicity Precede Active Region Flaring Authors: Reinard, A. A.; Henthorn, J.; Komm, R.; Hill, F. Bibcode: 2010ApJ...710L.121R Altcode: We report on the analysis of subsurface vorticity/helicity measurements for flare producing and quiet active regions. We have developed a parameter to investigate whether large, decreasing kinetic helicity density commonly occurs prior to active region flaring. This new parameter is effective at separating flaring and non-flaring active regions and even separates among C-, M-, and X-class flare producing regions. In addition, this parameter provides advance notice of flare occurrence, as it increases 2-3 days before the flare occurs. These results are striking on an average basis, though on an individual basis there is still considerable overlap between flare associated and non-flare associated values. We propose the following qualitative scenario for flare production: subsurface rotational kinetic energy twists the magnetic field lines into an unstable configuration, resulting in explosive reconnection and a flare. Title: Subsurface Flow Properties of Flaring versus Flare-Quiet Active Regions Authors: Ferguson, R.; Komm, R.; Hill, F.; Barnes, G.; Leka, K. D. Bibcode: 2009ASPC..416..127F Altcode: We apply discriminant analysis to 1009 active regions and their subsurface flow parameters, such as vorticity and kinetic helicity density, with the goal of distinguishing between flaring and non-flaring active regions. Flow and flux variables lead to better classification rates than a no-event prediction. The Heidke skill score, which measures the improvement over predicting that no events occur, increases by about 25% and 50% for C- and M-class flares when several subsurface characteristics are included compared to using a single magnetic flux measure. Title: Subsurface Zonal Flows of Active and Quiet Regions Authors: Komm, R.; Howe, R.; Hill, F.; González Hernández, I. Bibcode: 2009ASPC..416..123K Altcode: We study the zonal flow in solar subsurface layers, analyzing about six years of GONG+ high-resolution Doppler data with a ring-diagram analysis. We focus on the variation of the zonal flow with magnetic activity over a range of depths from the surface to about 16 Mm. We calculate the average zonal flow for a quiet- and an active-region subset defined as dense-pack locations with an unsigned magnetic flux less than 3.4 G and locations with greater than 65.0 G respectively. The average zonal flow of active regions is about 4 ms-1 faster than the average flow of quiet regions and this difference increases slightly with increasing depth at depths greater than about 5 Mm. The difference shows no apparent pattern in time and latitude; it shows no variation with the solar cycle. Title: Temporal Variation of Subsurface Flows of Active Regions Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 2009ASPC..416..115K Altcode: We study the temporal variation of subsurface flows associated with 955 active regions. The subsurface kinetic helicity density varies with the magnetic flux and its values at deeper layers are correlated with the total flare intensity. The average vertical velocity shows a downflow at depths shallower than about 12 Mm and upflows at greater depth. Daily ring-diagram measurements thus confirm previous synoptic measurements. In addition we find, that at some depths, the crosscorrelation between the vertical velocity and the unsigned magnetic flux is positive at negative lag time. This implies that the temporal variation of the vertical velocity might be a precursor of flux changes. Title: The internal dynamics and magnetism of the sun -- the perspective from global helioseismology (Invited) Authors: Howe, R.; Hill, F.; Komm, R.; Christensen-Dalsgaard, J.; Schou, J.; Thompson, M. J. Bibcode: 2009AGUFMSH11B..04H Altcode: Helioseismology allows us to probe the interior dynamics of the Sun. Observations over the past three decades reveal the interior rotation profile, with a near-surface shear layer, differential rotation throughout the convection zone, a strong shear layer -- the tachocline -- at the base of the convection zone, and approximately uniform rotation in the radiative interior. Since the mid 1990's, continuous observations from the Global Oscillations Network Group and the Michelson Doppler Imager have allowed the study of subtle temporal variations in the rotation within the convection zone. The so-called "torsional oscillation" pattern of migrating zonal flows accompanying the surface activity migration during the solar cycle has been shown to penetrate deep within the convection zone. During the current extended solar minimum, the flow bands can be seen to migrate more slowly towards the equator than was seen in the previous minimum. There have also been (still unconfirmed) findings of shorter-term variations in the rotation rate close to the tachocline during the early years of the previous solar cycle. This review will describe the important results and give an update on the most recent observations of the interior dynamics as we await the rise of solar cycle 24. Title: Ring Diagram Analysis of an Artificial 96 × 96 × 20 Mm Data Set Authors: Howe, R.; González Hernández, I.; Komm, R.; Hill, F. Bibcode: 2009ASPC..416..151H Altcode: A 16-hour time series of data from a 96 × 96 × 20 Mm hydrodynamic convection simulation has recently been made available. We will present the preliminary results of applying the ring-diagram technique of local helioseismology to this dataset, in comparison with similar quiet-Sun observations from GONG and MDI, and show that it is possible to recover the underlying horizontal flow profile, at least in the upper half of the region. Title: Using subsurface helicity measurements to predict flare occurrence Authors: Reinard, A. A.; Henthorn, J.; Komm, R.; Hill, F. Bibcode: 2009AGUFMSH21C..06R Altcode: Solar flares are responsible for a number of hazardous effects including disabling high-frequency radio communications, interfering with GPS measurements, and disrupting satellites. Forecasting flare occurrence is very difficult, giving little advanced notice of these events. One possible means for predicting flare occurrence lies in helioseismology, i.e. analysis of the region below the active region for signs of an impending flare. Time series helioseismic data collected by the Global Oscillation Network Group (GONG) have been analyzed for a subset of active regions that produce large flares and a subset with very high magnetic field strength that produce no flares. A predictive parameter has been developed and analyzed using discriminant analysis as well as traditional forecasting tools such as the Heidke skill score. Preliminary results indicate this parameter predicts flare occurrence with a high success rate. Title: Large-Scale Solar Subsurface Flows During Solar Cycle Minimum Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 2009AGUFMSH11A1482K Altcode: The long solar minimum between cycles 23/24 allows us to study large-scale flows, such as rotation and meridional flow, as a dynamical process without bias due to magnetic fields. We study the subsurface flows in the near-surface layers of the convection zone with a local helioseismic technique, called ring-diagram analysis, using Global Oscillation Network Group (GONG) data obtained during the years 2008 and early 2009. We focus on the meridional flow and the divergence and vorticity of subsurface flows during this exceptional solar minimum. We also search for large-scale coherent structures that might be present in the convection zone but might be easily obscured by the effect of surface magnetic fields during other epochs of the solar cycle. We will present the most recent results. Title: The Torsional Oscillation and the Solar Minimum Authors: Howe, R.; Hill, F.; Komm, R.; Christensen-Dalsgaard, J.; Schou, J.; Thompson, M. J. Bibcode: 2009AGUFM.U34A..03H Altcode: The so-called torsional oscillation is a pattern of zonal flow bands, detected at the solar surface by direct Doppler measurements and within the convection zone by helioseismic measurements such as those carried out by the Global Oscillations Network Group and the Michelson Doppler Imager, that migrates from mid-latitudes towards the equator and poles with each solar cycle. In the current minimum the low-latitude branch of the pattern can be seen to have taken at least a year longer to migrate towards the equator than was the case in the previous minimum. A flow configuration matching that of the previous minimum was reached during 2008, and by early 2009 the fast-rotating belt associated with the new cycle had reached the latitude at which the onset of activity was seen in Cycle 23, but magnetic activity has remained low. We will present the most recent results and consider the implications for the new solar cycle. Title: The Torsional Oscillation and the Solar Cycle: Is it Minimum Yet? Authors: Howe, R.; Komm, R.; Hill, F.; Larson, T.; Schou, J.; Thompson, M. J.; Ulrich, R. K. Bibcode: 2009ASPC..416..269H Altcode: The torsional oscillation pattern of migrating zonal flows is related to the solar activity cycle. In the approach to solar minimum, we compare the current flow profile with that seen at the previous minimum, using Global Oscillation Network Group (GONG) and Michelson Doppler Imager (MDI) data as well as Mount Wilson Doppler observations that reach further back in time. Will the flow pattern at the upcoming minimum match that for the previous one? Title: A Note on the Torsional Oscillation at Solar Minimum Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.; Schou, J.; Thompson, M. J. Bibcode: 2009ApJ...701L..87H Altcode: 2009arXiv0907.2965H We examine the evolution of the zonal flow pattern in the upper solar convection zone during the current extended solar minimum, and compare it with that during the previous minimum. The results suggest that a configuration matching that at the previous minimum was reached during 2008, but that the flow band corresponding to the new cycle has been moving more slowly toward the equator than was observed in the previous cycle, resulting in a gradual increase in the apparent length of the cycle during the 2007-2008 period. The current position of the lower-latitude fast-rotating belt corresponds to that seen around the onset of activity in the previous cycle. Title: Emerging and Decaying Magnetic Flux and Subsurface Flows Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 2009SoPh..258...13K Altcode: We study the temporal variation of subsurface flows of 788 active regions and 978 quiet regions. The vertical-velocity component used in this study is derived from the divergence of the measured horizontal flows using mass conservation. The horizontal flows cover a range of depths from the surface to about 16 Mm and are determined by analyzing about five years of GONG high-resolution Doppler data with ring-diagram analysis. We determine the change in unsigned magnetic flux during the disk passage of each active region using MDI magnetograms binned to the ring-diagram grid. We then sort the data by their flux change from decaying to emerging flux and divide the data into five subsets of equal size. The average vertical flows of the emerging-flux subset are systematically shifted toward upflows compared to the grand average values of the complete data set, whereas the average flows of the decaying-flux subset show comparably more pronounced downflows especially near 8 Mm. For flux emergence, upflows become stronger with time with increasing flux at depths greater than about 10 Mm. At layers shallower than about 4 Mm, the flows might start to change from downflows to upflows, when flux emerges, and then back to downflows after the active regions are established. The flows in the layers between these two depth ranges show no response to the emerging flux. In the case of decaying flux, the flows change from strong upflows to downflows at depths greater than about 10 Mm, whereas the flows do not change systematically at other depths. A cross-correlation analysis shows that the flows in the near-surface and the deeper layers might change about one day before flux emerges. The flows associated with the quiet regions fluctuate with time but do not show any systematic variation. Title: Solar flares and solar subphotospheric vorticity Authors: Komm, R.; Hill, F. Bibcode: 2009JGRA..114.6105K Altcode: 2009JGRA..11406105K We explore the relation between surface magnetic flux of the sun and subsurface flow vorticity for flaring and nonflaring solar active regions. For this purpose, we use a data set consisting of 1009 active regions, including the vorticity measurements of their subsurface flows derived from high-resolution global oscillation network group (GONG) helioseismology data and the corresponding X-ray flare data from the geostationary operation environmental satellite (GOES). Using quantities averaged over the disk passage of active regions, we find that, while there is a considerable spread of the flux and vorticity values, they are more or less linearly related. We distinguish the level of flare activity by X-ray flare class and find that large flux or large vorticity values are sufficient for an active region to produce low-intensity C-class flares. Active regions that produce high-intensity X-class flares are characterized by large values of both flux and vorticity. Active regions that produce M-class flares of intermediate intensity are characterized by large vorticity values. The inclusion of solar subsurface vorticity thus helps to distinguish between flaring and nonflaring active regions. Title: Subsurface Flow Properties of Flaring Versus Flare-quiet Active Regions Authors: Ferguson, Ryan M.; Komm, R.; Hill, F.; Barnes, G.; Leka, K. D. Bibcode: 2009SPD....40.1908F Altcode: Previous studies have shown that the flare activity of active regions is intrinsically linked with the vorticity of subsurface flows on temporal and spatial scales comparable to the size and lifetime of active regions. We begin to address the question whether the measured vorticity of subsurface flows associated with active regions can help to improve flare forecasting. For this purpose, we apply statistical tests based on discriminant analysis to several subsurface flow parameters with the goal to differentiate between flaring and non-flaring active regions.

We will present the latest results. This work is carried out through the National Solar Observatory Research Experiences for Undergraduate (REU) site program, which is co-funded by the Department of Defense in partnership with the National Science Foundation REU Program. Title: A Helioseismic Comparison of the Solar Minima Preceding Cycles 23 and 24 Authors: Hill, Frank; Howe, R.; Komm, R.; Gonzallez Hernandez, I.; Tripathy, S.; Jain, K. Bibcode: 2009SPD....40.2401H Altcode: The current solar minimum is clearly unusual in a variety of ways, including length, solar wind pressure, cosmic ray flux, and marked absence of sunspots. This talk will compare the current minimum with the previous one in terms of its helioseismic and subsurface flow characteristics. The helioseismic characteristics are primarily activity-related changes in the frequencies, amplitudes and lifetimes. The relevant flows are the torsional oscillation, meridional flow, subsurface vorticity, and the subsurface rotation rate. Title: Subsurface Zonal Flows Authors: Komm, R.; Howe, R.; Hill, F.; González Hernández, I. Bibcode: 2009SoPh..254....1K Altcode: 2008SoPh..tmp..189K We study the zonal flow in solar subsurface layers, analyzing about six years of GONG++ high-resolution Doppler data with ring-diagram analysis. We focus on the variation of zonal flow with magnetic activity over a range of depths from the surface to about 16 Mm. There is a positive correlation between unsigned magnetic flux and zonal flow at most depths. We calculate the average zonal flow for a quiet- and an active-region subset defined as dense-pack locations with an unsigned magnetic flux less than 3.4 G and locations with greater than 65.0 G, respectively. The average zonal flow of active regions is about 4 m s−1 larger than the average flow of quiet regions. This difference increases slightly with increasing depth, which might be explained by a nonradial inclination of the flux tubes or a different extent in depth of different magnetic features. The difference shows no apparent pattern in time and latitude, which makes it unlikely that it is simply a manifestation of the torsional-oscillation pattern. As a byproduct, we find that the size of the North - South asymmetry of the rotation rate decreases during the same epoch. Title: Subsurface Meridional Circulation in the Active Belts Authors: González Hernández, I.; Kholikov, S.; Hill, F.; Howe, R.; Komm, R. Bibcode: 2008SoPh..252..235G Altcode: 2008SoPh..tmp..167G; 2008arXiv0808.3606G Temporal variations of the subsurface meridional flow with the solar cycle have been reported by several authors. The measurements are typically averaged over periods of time during which surface magnetic activity existed in the regions where the velocities are calculated. The present work examines the possible contamination of these measurements due to the extra velocity fields associated with active regions plus the uncertainties in the data obtained where strong magnetic fields are present. We perform a systematic analysis of more than five years of GONG data and compare meridional flows obtained by ring-diagram analysis before and after removing the areas of strong magnetic field. The overall trend of increased amplitude of the meridional flow towards solar minimum remains after removal of large areas associated with surface activity. We also find residual circulation toward the active belts that persists even after the removal of the surface magnetic activity, suggesting the existence of a global pattern or longitudinally-located organized flows. Title: Kinetic helicity of subsurface flows and magnetic flux Authors: Komm, Rudolf; Hill, Frank; Howe, Rachel Bibcode: 2008JPhCS.118a2035K Altcode: We study the relation between the vorticty of solar subsurface flows and surface magnetic activity, analyzing more than five years of GONG+ data with ring-diagram analysis. We focus on the enstrophy, defined as the square of vorticity, and the kinetic helicity density, defined as the scalar product of velocity and vorticity, and derive them from the surface to a depth of about 16 Mm. We find that enstrophy and helicity density of subsurface flows are rather constant at low flux values (less than about 10 G), while at higher flux values there is a linear relation between flux and the logarithm of enstrophy or unsigned helicity. In addition, we analyze the temporal variation of thirteen emerging active regions. At the locations of these active regions, there is little enstrophy or helicity before the regions emerge, while after flux emergence the vorticity and helicity values are large. The crosscorrelation in time between flux and enstrophy shows that they are correlated and that shallow layers lag behind deeper layers. This signal might be a hint of the emergence of active regions. Title: Rotation Rate of Sunspots and Subsurface Zonal Flows Authors: Komm, R.; Howe, R.; Hill, F.; González Hernández, I. Bibcode: 2008AGUSMSP41A..08K Altcode: From surface observations, it is well known that sunspots rotate faster than the surrounding plasma. Helioseismic observations have confirmed this behavior for near-surface layers. Here, we study the zonal flow of active regions in solar subsurface layers over a range of depths from the surface to about 16 Mm. We have analyzed about six years of GONG+ high-resolution Doppler data with the dense-pack ring-diagram analysis. We calculate the average zonal flow for a quiet- and an active-region subset defined as dense-pack patches (of 15 degree diameter) with an unsigned magnetic flux less than 3.4 G and greater than 65.0 G respectively. The average zonal flow of active regions is about 4m/s larger than the average flow of quiet regions on dense-pack length scales. This difference increases slightly with increasing depth and shows no apparent pattern in time and latitude. As a byproduct, we study the north-south asymmetry of the rotation rate in these subsurface layers and find that the asymmetry decreases during the declining phase of solar cycle 23. Title: Views of the Solar Torsional Oscillation Authors: Howe, R.; Komm, R. W.; Hill, F.; Schou, J.; Thompson, M. J. Bibcode: 2008AGUSMSP41A..05H Altcode: The pattern of zonal flows migrating towards the equator over the solar cycle, known as the torsional oscillation, is well established from both helioseismology and surface Doppler measurements. However, the exact appearance of the pattern will vary depending on the form of the overall rotation profile that has been subtracted, even when the data cover a full eleven-year cycle. Here we compare the appearance of the flow pattern when applying several different methods to the MDI and GONG data for Solar Cycle 23. Title: Space Weather with GONG+ Data Authors: Hill, F.; Komm, R.; Gonzalez-Hernandez, I.; Petrie, G.; Harvey, J. W. Bibcode: 2008AGUSMSP54A..08H Altcode: The Global Oscillation Network Group (GONG) is now routinely producing several data products that are useful for space weather predictions. These products are one-minute cadence full-disk magnetograms obtained continually; ten-miniute averages of these magnetograms; one-hour cadence synoptic magnetic field maps and potential field source-surface extrapolations; and twelve-hour far-side maps that show the presence of large active regions. Most of these these products are made available over the Internet in near-real time. In addition, we are developing flare predictors based on subsurface vorticity obtained from helioseismic ring diagrams in conjunction with surface magnetic field observations. We find that, when both the subsurface vorticity and the surface magnetic field are above certain thresholds for a specific active region, then that active region has a very high probability of producing vigorous flare activity. We will present the quantitative results for this predictor and also report on progress developing a predictor based on the temporal evolution of the vorticity. Title: Emerging Active Regions Studied with Ring-Diagram Analysis Authors: Komm, R.; Morita, S.; Howe, R.; Hill, F. Bibcode: 2008ApJ...672.1254K Altcode: We study the temporal variation of subsurface flows associated with emerging active regions, focusing on four regions in detail. Two of them, AR 10314 and AR 10488, emerge near disk center and the other two, AR 10365 and AR 10375, are older regions where new flux emerges during their disk passage. We measure the horizontal subsurface flows from high-resolution Global Oscillation Network Group (GONG) data using ring-diagram analysis and derive the vertical flow component. Before flux emergence, we find upflows in AR 10314, while the other emerging region, AR 10488, shows mainly weak vertical flows. Both aging regions, AR 10365 and AR 10375, initially show downflows, as expected from already established regions. When new flux emerges, the weaker one of the two, AR 10365, shows upflows, while AR 10375 shows an even stronger downflow. In strong active regions, such as AR 10375 and AR 10488, strong downflows are present after the region has been established. In all four regions, the transition occurs on timescales of about one to two days. As a control experiment, we repeat the analysis for the same locations as those of the four active regions in 53 Carrington rotations and find that it is unlikely that the temporal variations of the vertical velocity are caused by systematics such as a projection effect. We then search our data set for emerging regions with similar characteristics to AR 10314 and AR 10488, i.e., emergence near disk center and large flux increase. From an analysis of 13 emerging regions, we conclude that there is a small preference for upflows before the emergence of new flux and for a transition toward downflows after flux emergence. Title: Helioseismic Frequency Shifts in Active Regions Authors: Howe, R.; Haber, D. A.; Hindman, B. W.; Komm, R.; Hill, F.; Gonzalez Hernandez, I. Bibcode: 2008ASPC..383..305H Altcode: The variation in the frequencies of solar acoustic modes over the activity cycle is well established. We discuss some of the historical findings, and present some recent results obtained using both global and local helioseismic analysis of data from the Global Oscillation Network Group and the Michelson Doppler Imager. The results are consistent with earlier work; the frequencies of modes in the five-minute band generally show a positive correlation with the local surface magnetic field strength, while those above the acoustic cutoff show an anticorrelation. Title: Subsurface and Atmospheric Influences on Solar Activity Authors: Howe, R.; Komm, R. W.; Balasubramaniam, K. S.; Petrie, G. J. D. Bibcode: 2008ASPC..383.....H Altcode: No abstract at ADS Title: Subsurface Flows near Four Emerging Active Regions Studied with Ring-Diagram Analysis Authors: Komm, R.; Howe, R.; Hill, F.; Morita, S. Bibcode: 2008ASPC..383...83K Altcode: We study the temporal variation of subsurface flows associated with four emerging active regions. Two of them, AR~10314 and AR~10488, emerge near disk center and the other two, AR~10365 and AR~10375, are older regions where new flux emerges during their disk passage. We measure the horizontal subsurface flows from high-resolution Global Oscillation Network Group (GONG+) data using ring-diagram analysis and derive the vertical flow component. Before flux emergence, we find upflows in AR~10314, while the other emerging region, AR~10488, shows only weak vertical flows hinting at upflows. Both aging regions, AR~10365 and AR~10375, show initially downflows, as expected from already established regions. When new flux emerges, the weaker one of the two, AR~10365, shows upflows, while AR~10375 shows stronger downflows. In strong active regions, such as AR~10375 and AR~10488, strong downflows are present after the region has been established. Title: Divergence and Vorticity of Solar Subsurface Flows Derived from Ring-Diagram Analysis of MDI and GONG Data Authors: Komm, R.; Howe, R.; Hill, F.; Miesch, M.; Haber, D.; Hindman, B. Bibcode: 2007ApJ...667..571K Altcode: We measure the relation between divergence and vorticity of subsurface horizontal flows as a function of unsigned surface magnetic flux. Observations from the Michelson Doppler Imager (MDI) Dynamics Program and Global Oscillation Network Group (GONG) have been analyzed with a standard ring-diagram technique to measure subsurface horizontal flows from the surface to a depth of about 16 Mm. We study residual horizontal flows after subtracting large-scale trends (low-order polynomial fits in latitude) from the measured velocities. On average, quiet regions are characterized by weakly divergent horizontal flows and small anticyclonic vorticity (clockwise in the northern hemisphere), while locations of high activity show convergent horizontal flows combined with cyclonic vorticity (counterclockwise in the northern hemisphere). Divergence and vorticity of horizontal flows are anticorrelated (correlated) in the northern (southern) hemisphere. This is especially noticeable at greater depth, where the relation between divergence and vorticity of horizontal flows is nearly linear. These trends show a slight reversal at the highest levels of magnetic flux; the vorticity amplitude decreases at the highest flux levels, while the divergence changes sign at depths greater than about 10 Mm. The product of divergence and vorticity of the horizontal flows, a proxy of the vertical contribution to the kinetic helicity density, is on average negative (positive) in the northern (southern) hemisphere. The helicity proxy values are greater at locations of high magnetic activity than at quiet locations. Title: Solar Cycle Changes Over 11 Years of Medium-Degree Helioseismic Observations Authors: Howe, Rachel; Komm, R. W.; Hill, F.; Christensen-Dalsgaard, J.; Schou, J.; Thompson, M. J. Bibcode: 2007AAS...210.2218H Altcode: 2007BAAS...39..127H The Global Oscillations Network Group (GONG) has now completed, and the Michelson Doppler Imager (MDI) aboard SOHO will soon complete, a full eleven years of continuous observations of the medium-degree solar oscillations. This enables us to follow changes in the acoustic mode parameters and interior dynamics over a full solar cycle. We present results from observations of convection-zone dynamics, in which the torsional oscillation pattern seen at the surface can be followed throughout most of the bulk of the convection zone, and also changes in the frequency, lifetime and amplitude of the modes which can be shown to be closely related in space and time to the migrating pattern of surface activity.

This work utilizes data obtained by the Global Oscillation Network Group (GONG) program, managed by the National Solar Observatory, which is operated by AURA, Inc. under a cooperative agreement with the National Science Foundation. SOHO is a mission of international cooperation between ESA and NASA. Title: Value-added maps: fluid-dynamics descriptors from ring diagrams Authors: Komm, R. W. Bibcode: 2007AN....328..269K Altcode: We describe fluid-dynamics descriptors derived from maps of the horizontal flow components measured with ring-diagram analysis. Here, we focus on quantities, such as vorticity and kinetic helicity density, and discuss three examples of results derived from them: subsurface flows associated with active regions, subsurface flows and flare activity, and large-scale behavior of horizontal flows. Title: Temporal variations in solar rotation at the bottom of the convection zone: The current status Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.; Schou, J.; Thompson, M. J.; Toomre, J. Bibcode: 2007AdSpR..40..915H Altcode: We present the most recent results on the short-period variations in the solar rotation rate near the base of the convection zone. The 1.3-year period which was reported in the early years of solar cycle 23 appears not to persist after 2001, but there are hints of fluctuations at a different period during the declining phase of the cycle. Title: Peak parameter shifts from large-aperture ring diagram analysis Authors: Howe, R.; González Hernández, I.; Hill, F.; Komm, R. Bibcode: 2006ESASP.624E..68H Altcode: 2006soho...18E..68H No abstract at ADS Title: B0-angle effect on zonal and meridional flow determinations from 3 years ring diagram analysis of GONG++ data Authors: Zaatri, A.; Komm, R.; González Hernández, I.; Howe, R.; Corbard, T. Bibcode: 2006ESASP.624E..55Z Altcode: 2006soho...18E..55Z No abstract at ADS Title: Solar Convection Zone Dynamics: How Sensitive Are Inversions to Subtle Dynamo Features? Authors: Howe, R.; Rempel, M.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.; Larsen, R. M.; Schou, J.; Thompson, M. J. Bibcode: 2006ApJ...649.1155H Altcode: The nearly 10 year span of medium-degree helioseismic data from the Global Oscillation Network Group and the Michelson Doppler Imager has allowed us to study the evolving flows in the solar convection zone over most of solar cycle 23. Using two independent two-dimensional rotation inversion techniques and extensive studies of the resolution using artificial data from different assumed flow profiles, including those generated from sample mean field dynamo models, we attempt to assess the reality of certain features seen in the inferred rotation profiles. Our results suggest that the findings from observations of a substantial depth dependence of the phase of the zonal flow pattern in the low latitudes, and the penetration of the flows deep into the convection zone, are likely to be real rather than artifacts of the inversion process. Title: Subsurface flows from numerical simulations compared with flows from ring analysis Authors: Ustyugov, S.; Komm, R.; Burtseva, O.; Howe, R.; Kholikov, S. Bibcode: 2006ESASP.624E..54U Altcode: 2006soho...18E..54U No abstract at ADS Title: Subsurface flows measured with big rings Authors: Komm, R.; González Hernández, I.; Howe, R.; Hill, F. Bibcode: 2006ESASP.624E..53K Altcode: 2006soho...18E..53K No abstract at ADS Title: Divergence and Vorticity of Subsurface Flows Derived from Ring-Diagram Analysis of MDI and GONG Data Authors: Komm, R.; Howe, R.; Hill, F.; Miesch, M.; Haber, D.; Hundman, B. Bibcode: 2006ESASP.617E..42K Altcode: 2006soho...17E..42K No abstract at ADS Title: Flares, Magnetic Fields, and Subsurface Vorticity: A Survey of GONG and MDI Data Authors: Mason, D.; Komm, R.; Hill, F.; Howe, R.; Haber, D.; Hindman, B. W. Bibcode: 2006ApJ...645.1543M Altcode: We search for a relation between flows below active regions and flare events occurring in those active regions. For this purpose, we determine the subsurface flows from high-resolution Global Oscillation Network Group (GONG) and Michelson Doppler Imager (MDI) Dynamics Program data using the ring-diagram technique. We then calculate the vorticity of the flows associated with active regions and compare it with a proxy of the total X-ray flare intensity of these regions using data from the Geostationary Operation Environmental Satellite (GOES). We have analyzed 408 active regions with X-ray flare activity from GONG and 159 active regions from MDI data. Both data sets lead to similar results. The maximum unsigned zonal and meridional vorticity components of active regions are correlated with the total flare intensity; this behavior is most apparent at values greater than 3.2×10-5 W m-2. These vorticity components show a linear relation with the logarithm of the flare intensity that is dependent on the maximum unsigned magnetic flux; vorticity values are proportional to the product of total flare intensity and maximum unsigned magnetic flux for flux values greater than about 36 G. Active regions with strong flare intensity show a dipolar pattern in the zonal and meridional vorticity component that reverses at depths between ~2 and 5 Mm. A measure of this pattern shows the same kind of relation with total flare intensity as the vorticity components. The vertical vorticity component shows no clear relation to flare activity. Title: North South Asymmetry of Zonal and Meridional Flows Determined From Ring Diagram Analysis of Gong ++ Data Authors: Zaatri, A.; Komm, R.; González Hernández, I.; Howe, R.; Corbard, T. Bibcode: 2006SoPh..236..227Z Altcode: We study the North-South asymmetry of zonal and meridional components of horizontal, solar subsurface flows during the years 2001-2004, which cover the declining phase of solar cycle 23. We measure the horizontal flows from the near-surface layers to 16 Mm depth by analyzing 44 consecutive Carrington rotations of Global Oscillation Network Group (GONG) Doppler images with a ring-diagram analysis technique. The meridional flow and the errors of both flow components show an annual variation related to the B0-angle variation, while the zonal flow is less affected by the B0-angle variation. After correcting for this effect, the meridional flow is mainly poleward but it shows a counter cell close to the surface at high latitudes in both hemispheres. During the declining phase of the solar cycle, the meridional flow mainly increases with time at latitudes poleward of about 20˚, while it mainly decreases at more equatorward latitudes. The temporal variation of the zonal flow in both hemispheres is significantly correlated at latitudes less than about 20˚. The zonal flow is larger in the southern hemisphere than the northern one, and this North-South asymmetry increases with depth. Details of the North-South asymmetry of zonal and meridional flow reflect the North-South asymmetry of the magnetic flux. The North-South asymmetries of the flows show hints of a variation with the solar cycle. Title: MDI and GONG Inferences of the Changing Sun Authors: Burtseva, O.; González Hernández, I.; Hill, F.; Howe, R.; Jain, K.; Kholikov, S.; Komm, R.; Leibacher, J.; Toner, C.; Tripathy, S.; Haber, D.; Hindman, B.; Ladenkov, O.; Chou, D. -Y. Bibcode: 2006ESASP.617E..41B Altcode: 2006soho...17E..41B No abstract at ADS Title: Anomalous variations in low-degree helioseismic mode frequencies Authors: Howe, R.; Chaplin, W. J.; Elsworth, Y.; Hill, F.; Komm, R. W.; Isaak, G. R.; New, R. Bibcode: 2006MNRAS.369..933H Altcode: 2006MNRAS.tmp..504H We compare changes in the frequencies of solar acoustic modes with degree between 0 and 2, as derived from Global Oscillation Network Group (GONG), Birmingham Solar Oscillations Network (BiSON) and Michelson Doppler Imager (MDI) spectra obtained between 1995 and 2003. We find that, after the solar-activity dependence has been removed from the frequencies, there remain variations that appear to be significant, and are often well correlated between the different data sets. We consider possible explanations for these fluctuations, and conclude that they are likely to be related to the stochastic excitation of the modes. The existence of such fluctuations has possible relevance to the analysis of other low-degree acoustic mode spectra such as those from solar-type stars. Title: Solar Flares, Magnetic Fields, And Subsurface Vorticity. A Survey Of Gong And Mdi Data Authors: Mason, Douglas J.; Komm, R.; Howe, R.; Hill, F.; Haber, D.; Hindman, B. Bibcode: 2006SPD....37.0506M Altcode: 2006BAAS...38..224M We search for a relation between flare events and magnetic fields in active regions and the subsurface flows associated with these regions. For this purpose, we determine the solar subsurface flows from high-resolution Global Oscillation Network Group (GONG) and and Michelson Doppler Imager (MDI) Dynamics Program data using ring-diagram analysis (a local helioseismology technique). For the first time, we have been able to search out these connections with a statistical analysis of consecutive data that encompass many years. We have found that the vorticity of the flow field below the solar surface, specifically the maximum flow vorticity within each active region, correlates well with the total X-ray flare intensity data for the region (provided by GOES, the Geostationary Operation Environmental Satellite). Above a certain threshold of flare activity, vorticity values exhibit a linear relationship with total flare activity that is dependent on the magnetic flux of the active region.This work is carried out through the National Solar Observatory Research Experiences for Undergraduate (REU) site program, which is co-funded by the Department of Defense in partnership with the National Science Foundation REU Program. Title: Large-Scale Zonal Flows Near the Solar Surface Authors: Howe, R.; Komm, R.; Hill, F.; Ulrich, R.; Haber, D. A.; Hindman, B. W.; Schou, J.; Thompson, M. J. Bibcode: 2006SoPh..235....1H Altcode: Migrating bands of weak, zonal flow, associated with the activity bands in the solar cycle, have been observed at the solar surface for some time. More recently, these flows have been probed deep within the convection zone using global helioseismology and examined in more detail close to the surface with the techniques of local helioseismology. We compare the near-surface results from global and local helioseismology using data from the Michelson Doppler Imager and the Global Oscillation Network Group with surface Doppler velocity measurements from the Mount Wilson 150-foot tower and find that the results are in reasonable agreement, with some explicable differences in detail. All of the data sets show zones of faster rotation approaching the equator from mid-latitudes during the solar cycle, with a variation at any given location that can be approximately, but not completely, described by a single sinusoid and an amplitude that does not drop off steeply below the surface. Title: Meridional Circulation Variability from Large-Aperture Ring-Diagram Analysis of Global Oscillation Network Group and Michelson Doppler Imager Data Authors: González Hernández, I.; Komm, R.; Hill, F.; Howe, R.; Corbard, T.; Haber, D. A. Bibcode: 2006ApJ...638..576G Altcode: Ring-diagram analysis, a local helioseismology technique, has proven to be very useful for studying solar subsurface velocity flows down to a depth of about 0.97 Rsolar. The depth range is determined by the modes used in this type of analysis, and thus depends on the size of the area analyzed. Extending the area allows us to detect lower spherical harmonic degree (l) modes which, at a constant frequency, penetrate deeper in the Sun. However, there is a compromise between the size of the area and the validity of the plane-wave approximation used by the technique. We present the results of applying the ring diagrams to 30° diameter areas over the solar surface in an attempt to reach deeper into the solar interior. Meridional flows for 25 consecutive Carrington rotations (1985-2009) are derived by applying this technique to Global Oscillation Network Group (GONG) and Michelson Doppler Imager (MDI) data. This covers a time span of almost 2 yr, starting at the beginning of 2002. The amplitude of the meridional flow shows a variation of the order of 5 m s-1 during this period. Our results indicate that the flows increase toward the interior of the Sun for the depth range studied. We find a 1 yr periodicity in the appearance of an equatorward meridional cell at high latitudes that coincides with maximum values of the solar inclination toward the Earth (B0 angle). Title: Helioseismic sensing of the solar cycle Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 2006AdSpR..38..845K Altcode: All quantities observed with helioseismic methods, such as frequencies, width, and amplitudes of acoustic waves, vary with the solar cycle. However, they relate to the dynamics and structure in different parts of the solar convection zone. The rotation rate varies with the solar cycle, showing the so-called torsional oscillation pattern, from the surface throughout most of the convection zone. Near the tachocline, the current observations do not show this solar-cycle variation, but there is some evidence that there is a 1.3-year variation of the rotation rate. The meridional flow, observed in the outer 2% of the solar radius, varies with the solar cycle showing flows converging toward the mean latitude of magnetic activity at depths less than about 10 Mm and flows diverging at greater depth. There is some evidence for a counter-cell in the northern hemisphere during epochs of high activity. Structure inversions show variations in asphericity near the surface where the sound speed varies with the distribution of surface activity. There are hints but no conclusive evidence that such variations exist in the convection zone. The damping of acoustic modes increases and the mode energy decreases with increasing activity. Their variation with time and latitude shows that even global modes sense the local distribution of the surface magnetic activity. Title: Large-scale Flows in Subsurface Layers Authors: Komm, R.; Howe, R.; González Hernández, I.; Hill, F.; Toner, C. Bibcode: 2005ASPC..346...33K Altcode: We analyze Global Oscillation Network Group (GONG) observations obtained during 14 consecutive Carrington rotations CR 1979--1992. We use a ring-diagram technique in order to measure the zonal and meridional flow components in the upper solar convection zone from the near-surface layers to 16 Mm in depth and derive the vertical velocity component assuming mass conservation. The average flows show the patterns that are expected as solar-cycle related variations. For example, the vertical flow shows downflows near the mean latitude of activity and upflows near the equator. This long-term pattern seems to be the net effect of flows at locations that do not coincide with strong active regions. Locations of strong active regions show downflows at depths less than about 12 Mm on average and strong upflows at greater depths independent of latitude. At these locations, the zonal flow is faster on average than the average flow over regions with less magnetic activity. Title: Solar Convection-Zone Dynamics, 1995-2004 Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.; Schou, J.; Thompson, M. J. Bibcode: 2005ApJ...634.1405H Altcode: The nine-year span of medium-degree helioseismic data from the Global Oscillation Network Group (GONG) and the Michelson Doppler Imager (MDI) allows us to study the evolving zonal flows in the solar convection zone over the rising phase, maximum, and early declining phase of solar cycle 23. Using two independent two-dimensional rotation inversion techniques, we investigate the depth profile of the flow pattern known as the torsional oscillation. The observations suggest that the flows penetrate deep within the convection zone-perhaps to its base-even at low latitudes, and that the phase of the pattern is approximately constant along lines of constant rotation rather than lines of constant latitude. Title: How Sensitive are Rotation Inversions to Subtle Features of the Dynamo? Authors: Howe, R.; Rempel, M.; Christensen-Dalsgaard, J.; Schou, J.; Thompson, M. J.; Komm, R.; Hill, F. Bibcode: 2005ASPC..346...99H Altcode: Global rotation inversions can probe the pattern of zonal flows well into the convection zone. In this paper, we test the ability of the inversions to constrain the predictions of dynamo models. A flux-transport dynamo model, including a mean-field theory of differential rotation and allowing for feedback of the Lorentz force on differential rotation and meridional flow, was used to produce a 22-year cycle of simulated rotation profiles. These were then subjected to simulated inversions with realistic mode sets and errors, in order to test how well the subtle subsurface features of the input profile could be recovered. The preliminary results are quite encouraging. Title: Solar Flares, Magnetic Fields, and Subsurface Vorticity. A survey of GONG data Authors: Mason, D.; Komm, R.; Hill, F.; Howe, R. Bibcode: 2005AAS...20711103M Altcode: 2005BAAS...37.1341M We search for a relation between flows below active regions on the Sun and flare events in those active regions. For this purpose, we determine the solar subsurface flows from high-resolution Global Oscillation Network Group (GONG) data using the ring-diagram technique. We then calculate the vorticity of the flows associated with active regions and compare it with the X-ray flare intensity of these regions from the Geostationary Operation Environmental Satellite (GOES). The maximum unsigned vorticity of an active region is correlated with its maximum magnetic flux and the maximum unsigned zonal and meridional vorticity component are also correlated with flare intensity greater than 3.2 × 10-5 W/m2. Above this threshold, large vorticity values will accompany large magnetic flux for a given flare intensity and larger flare activity will accompany lower magnetic field for a given vorticity value. Active regions with strong flare intensity additionally show a dipolar pattern in the zonal and meridional vorticity component. We define a structure component as a measure of this dipolar pattern and find that it can be represented as a linear function of the logarithm of flare intensity where the slope is linearly dependent on the unsigned flux.

This work is carried out through the National Solar Observatory Research Experiences for Undergraduate (REU) site program, which is co-funded by the Department of Defense in partnership with the National Science Foundation REU Program. Travel is funded by the University of Southern California. Title: Ring Analysis of Solar Subsurface Flows and Their Relation to Surface Magnetic Activity Authors: Komm, R.; Howe, R.; Hill, F.; González-Hernández, I.; Toner, C.; Corbard, T. Bibcode: 2005ApJ...631..636K Altcode: We measure the horizontal flows in the outer 2% of the Sun by analyzing 14 consecutive Carrington rotations of Global Oscillation Network Group (GONG) Doppler images and two of Michelson Doppler Imager (MDI) Dynamics Program data with the ring-diagram technique. The zonal and meridional flows show no variation with activity at low to medium activity levels (below 71 G). At active region locations, the zonal flow increases with increasing activity; active regions rotate faster than their quieter surroundings. The meridional flow at active region locations is more equatorward than on average at depths less than about 10 Mm; the flow converges toward the mean latitude of activity. At depths greater than about 10 Mm, some active region locations show poleward and others equatorward motions indicating strong outflows from active regions. The estimated vertical flow decreases with increasing activity levels except at active region locations at depths greater than about 10 Mm; active regions show downflows near the surface and upflows at depths greater than about 10 Mm. The velocity errors increase somewhat with increasing activity at flux levels below 71 G, but they increase rapidly up to about 2 times the median error at higher flux values. This increase occurs at all depths. The flows averaged over all longitudes show the patterns expected from solar cycle variations. The quiet and the intermediate activity subsets show the same flow pattern, while the active region subset shows a mixture of solar cycle flow pattern and local flow behavior. Title: Kinetic Helicity Density in Solar Subsurface Layers and Flare Activity of Active Regions Authors: Komm, R.; Howe, R.; Hill, F.; González Hernández, I.; Toner, C. Bibcode: 2005ApJ...630.1184K Altcode: We search for a relation between subsurface flows below active regions and flare events occurring in those regions. For this purpose, we use a ring-diagram analysis to determine the subsurface flows from high-resolution Global Oscillation Network Group (GONG) and Michelson Doppler Imager (MDI) data and derive the kinetic helicity as a measure of the topology of the subsurface flows. We compare it with X-ray flare data from the Geostationary Operational Environmental Satellite (GOES). We study active regions in three Carrington rotations (CR 1982, 1988, and 2009), which represent different levels of flare activity. The maximum value of the unsigned kinetic helicity density associated with each active region correlates remarkably well with the total flare X-ray intensity of the active regions; active regions with strong flare activity show large values of kinetic helicity density in subsurface flows. Title: Kinetic Helicity in Solar Subsurface Layers and Flare Activity of Active Regions Authors: Komm, R.; Howe, R.; Hill, F.; González Hernández, I.; Toner, C. G. Bibcode: 2005AGUSMSP43B..03K Altcode: We search for a relation between subsurface flows below active regions and flare events occuring in those regions. For this purpose, we use a ring-diagram analysis to determine the subsurface flows from high-resolution Global Oscillation Network Group (GONG) and Michelson Doppler Imager (MDI) data and derive the kinetic helicity as a measure of the topology of the subsurface flows. We compare it with X-ray flare data from Geostationary Operational Environmental Satellite (GOES). We study active regions in three Carrington rotations (CR~1982, 1988, and 2009), which represent different levels of flare activity. The maximum value of the unsigned kinetic helicity density associated with each active region correlates remarkably well with the total flare X-ray intensity of the active regions; active regions with strong flare activity show large values of kinetic helicity density in subsurface flows. This work has ben supported by NASA grant NAG 5-11703. Title: Global, Local and Surface Measurements of Large-Scale Zonal Flows Near the Solar Surface Authors: Howe, R.; Komm, R. W.; Haber, D. A.; Hindman, B. W.; Ulrich, R. K.; Schou, J.; Thompson, M. J.; Hill, F. Bibcode: 2005AGUSMSP32A..03H Altcode: Migrating bands of weak zonal flow, associated with the activity bands in the solar cycle, have been observed at the solar surface for some time. More recently, these flows have been probed deep within the convection zone using global helioseismology, and examined in more detail close to the surface with the techniques of local helioseismology. We compare the results from global and local helioseismology using data from the Michelson Doppler Imager and the GONG network and also Doppler measurements from Mount Wilson, and find that the results are in reasonable agreement, with some explicable differences in detail. This was work was supported by the National Science Foundation and NASA. Title: 2 Years of Meridional Circulation from GONG Ring Diagrams Authors: Gonzalez Hernandez, I.; Komm, R.; Corbard, T.; Hill, F.; Howe, R.; Haber, D. A. Bibcode: 2005AGUSMSP32A..01G Altcode: Large Aperture Ring Diagram analysis has been used to search for meridional circulation variability using a 2-year GONG data series. This technique uses patches that are four times the size of the typically studied sections of 15 degrees in diameter, so we are able to recover information about lower l modes that penetrate deeper into the Sun. Although extending the working area allow us to reach further into the solar interior, there is a compromise between the size of the patch and the validity of the plane wave approximation used by the technique. In this particular study, we search for variability of the meridional flows as a function of depth for 25 consecutive Carrington rotations. We have studied patches of 30-degree diameter over the solar surface as they crossed the solar central meridian. The range of modes recovered with these larger regions goes down to l~100 and reach a maximum depth of approximately 0.96Rsun. A set of 15 overlapping sections, centered at latitudes 0,+/-7.5,+/-15,+/-22.5,+/-30.0,+/-37.5,+/-45.0 and +/-52.5, has been analyzed for 24 intervals of 1664 minutes covering each Carrington rotation from CR1985 to CR2009 (Jan-2002 to Dec-2003). Meridional circulation results from standard ring diagram analysis and this large-aperture technique are compared, as well as results obtained from two different instruments GONG and MDI. This work was supported in part by NASA grant NAG5-11703. SOHO is a project of international cooperation between ESA and NASA. This work utilizes data obtained by the Global Oscillation Network Group (GONG) Program, managed by the National Solar Observatory, which is operated by AURA, Inc. under a cooperative agreement with the National Science Foundation. The data were acquired by instruments operated by the Big Bear Solar Observatory, High Altitude Observatory, Learmonth Solar Observatory, Udaipur Solar Observatory, Instituto de Astrofisico de Canarias, and Cerro Tololo Interamerican Observatory. Title: Local Helioseismic Mode Frequency Shifts With Magnetic Activity, From GONG and MDI Authors: Howe, R.; Komm, R. W.; Gonzalez Hernandez, I.; Hill, F.; Haber, D. A.; Hindman, B. W. Bibcode: 2005AGUSMSP11B..06H Altcode: We use the ring-diagram technique of local helioseismology to study the frequency shifts of high-degree solar acoustic modes from over 600 days of data from the Global Oscillations Network Group (GONG), covering the period 2001-2004. The data are compared with contemporaneous data from the Michelson Doppler Imager (MDI) dynamics program, where available. We examine both synoptic charts and the day-to-day variations in selected active regions. The results, once instrumental effects have been removed, show strong dependence of the mode frequency on the local magnetic flux, with the frequencies generally increasing with magnetic index. We relate these findings to results from global modes. This work was supported by the National Science Foundation and NASA Title: Comparison of Mode Parameters Between Velocity and Intensity Acoustic Spectra via Ring Diagrams Authors: Tripathy, S. C.; Hill, F.; González Hernández, I.; Howe, R.; Komm, R. W.; Toner, C. G. Bibcode: 2005AGUSMSP24A..03T Altcode: We analyse the local acoustic spectra at different locations over the solar disk using both velocity and intensity images from MDI. These spectra were fitted to obtain different mode parameters: e.g., acoustic frequencies, mode amplitudes and life time using symmetric fits. We find differences between frequencies derived from velocity and intensity filtergrams, and it appears that the mode frequencies vary as a function of location on the disk. Since the apparent frequency shift between an oscillation observed in velocity and intensity can not be a property of the mode, the analysis is expected to provide important information about the driving and damping of local acoustic oscillations. Title: Five-Minute Power Maps From GONG and MDI. Authors: Howe, R.; Komm, R. W.; Hill, F.; Haber, D. A.; Hindman, B. W. Bibcode: 2005AGUSMSP13A..01H Altcode: The presence of magnetic active regions on the solar surface is well known to influence the detected power of the oscillation signal. We consider maps of the five-minute power in the velocity signal from Global Oscillations Network Group (GONG) observations covering much of the disk over multiple Carrington Rotations, and compare these in detail with magnetic and continuum intensity images, with estimates of the velocity power from ring diagram helioseismic analysis, and also with a small sample of contemporaneous MDI (Michelson Doppler Imager) data. The comparison of power maps with magnetograms is carried out at a pixel-by-pixel level, for averages over patches of 16× 16 degrees in heliographic latitude and longitude, and at some intermediate scales. This research was supported by the National Science Foundation and NASA. Title: Vorticity and Kinetic Helicity in Solar Subsurface Layers from GONG and MDI data Authors: Komm, R.; Howe, R.; Hill, F.; Haber, D. A.; González Hernández, I. Bibcode: 2005AGUSMSP43B..04K Altcode: We use a ring-diagram analysis to determine the subsurface flows from high-resolution Global Oscillation Network Group (GONG) and Michelson Doppler Imager (MDI) data and derive the vorticity and the kinetic helicity of the subsurface flows in the upper 16~Mm of the convection zone. We separate the contributions of large-scale horizontal flows, such as differential rotation, from those of small-scale variations, such as the ones due to active regions, and analyze the large-scale and the residual component independently. We study the relation between magnetic activity and subsurface flows by comparing synoptic maps of the derived residual quantities with maps of photospheric magnetic activity. By comparing synoptic maps derived from GONG and MDI data, we are able to cross-validate the results. We will present the latest findings. This work has been supported by NASA and NSF. Title: Solar Subsurface Flows of Active Region AR~0696 Authors: Komm, R.; Howe, R.; Donaldson Hanna, K.; Hill, F.; Sheeley, N. Bibcode: 2005AGUSMSP24A..02K Altcode: We use a ring-diagram analysis to determine the subsurface flows in the upper 16~Mm of the convection zone from high-resolution Global Oscillation Network Group (GONG) data obtained during the first two weeks of November 2004. The active region AR~0696 emerges near the eastern limb and moves across the disk during this time period. The region produced several terrestrially effective flares and halo CMEs during its transit across the disk. During its disk passage, AR~0696 is the only large active region in the northern hemisphere and almost the only flare producing region on the sun. This makes it a good candidate for investigating the relation between active regions, their flare activity, and associated subsurface flows. We will present the latest results. This work was supported by NASA grant NAG 5-11703. Title: The Effects of Magnetically-Induced Spectral Line Profile Changes on Helioseismic and Flare Observations Authors: Edelman, F.; Hill, F.; Howe, R.; Komm, R. Bibcode: 2005AGUSMSP13A..03E Altcode: We have modeled the effect of changes in the shape of the spectral line used for the GONG and MDI observations, and we investigate the consequences for measurements of properties of oscillations and flares. We find that magnetic field measurements are not very sensitive to line shape changes, but velocity estimates do strongly depend on line variations. Using simulated observations of a flare we find that recently observed associated magnetic field changes are not due to line shape changes. On the other hand, a simulation of an oscillation indicates that at least part of the observed amplitude suppression in an active region is due to variations in the line shape. We also report preliminary results of the effect of vertical phase variations across the line profile on the helioseismic observations. This work is carried out through the National Solar Observatory Research Experiences for Undergraduate (REU) site program, which is co-funded by the Department of Defense in partnership with the National Science Foundation REU Program. This work utilizes data obtained by the Global Oscillation Network Group (GONG) project, managed by the National Solar Observatory, which is operated by AURA, Inc. under a cooperative agreement with the National Science Foundation. The data were acquired by instruments operated by the Big Bear Solar Observatory, High Altitude Observatory, Learmonth Solar Observatory, Udaipur Solar Observatory, Instituto de Astrofísica de Canarias, and Cerro Tololo Interamerican Observatory. Title: How Sensitive are Rotation Inversions to Subtle Features of the Dynamo? Authors: Howe, R.; Rempel, M.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.; Schou, J.; Thompson, M. J. Bibcode: 2004ESASP.559..468H Altcode: 2004soho...14..468H No abstract at ADS Title: Searching for Subsurface Signatures of X-Class Flares Authors: Komm, R.; Howe, R.; González Hernández, I.; Hill, F.; Sudol, J.; Toner, C. Bibcode: 2004ESASP.559..158K Altcode: 2004soho...14..158K No abstract at ADS Title: Solar Subsurface Flows and Vorticity Authors: Komm, R.; Howe, R.; González Hernández, I.; Hill, F.; Haber, D.; Hindman, B.; Corbard, T. Bibcode: 2004ESASP.559..520K Altcode: 2004soho...14..520K No abstract at ADS Title: Local Frequency Shifts from GONG and MDI Authors: Howe, R.; Komm, R. W.; González Hernández, I.; Hill, F.; Haber, D. A.; Hindman, B. W. Bibcode: 2004ESASP.559..484H Altcode: 2004soho...14..484H No abstract at ADS Title: The Phase of the Torsional Oscillation Pattern Authors: Howe, R.; Komm, R. W.; Hill, F.; Christensen-Dalsgaard, J.; Schou, J.; Thompson, M. J. Bibcode: 2004ESASP.559..476H Altcode: 2004soho...14..476H No abstract at ADS Title: Meridional Variability from Large-Aperture Ring Diagrams Authors: González Hernández, I.; Komm, R.; Hill, F.; Howe, R.; Corbard, T. Bibcode: 2004ESASP.559..444G Altcode: 2004soho...14..444G No abstract at ADS Title: A tale of Two Regions: Acoustic Power Maps and Magnetic Activity in AR 10486 and AR 10488 Authors: Howe, R.; Komm, R. W.; González Hernández, I.; Hill, F.; Haber, D. A.; Hindman, B. W. Bibcode: 2004ESASP.559..480H Altcode: 2004soho...14..480H No abstract at ADS Title: Flowmaps Covering Six Consecutive Carrington Rotations Authors: Komm, R.; Howe, R.; Bolding, J.; Donaldson Hanna, K.; González Hernández, I.; Hill, F.; Toner, C. Bibcode: 2004ESASP.559..516K Altcode: 2004soho...14..516K No abstract at ADS Title: The Effect of Spectral Line Shape Changes on GONG Observations of Oscillations and Flares Authors: Edelman, F.; Hill, F.; Howe, R.; Komm, R. Bibcode: 2004ESASP.559..416E Altcode: 2004soho...14..416E No abstract at ADS Title: An Automated Image Rejection System for GONG Authors: Clark, R.; Toner, C.; Hill, F.; Hanna, K.; Ladd, G.; Komm, R.; Howe, R.; Gonzalez-Hernandez, I.; Kholikov, S. Bibcode: 2004ESASP.559..381C Altcode: 2004soho...14..381C No abstract at ADS Title: Convection-Zone Dynamics from GONG and MDI, 1995-2004 Authors: Howe, R.; Komm, R. W.; Hill, F.; Christensen-Dalsgaard, J.; Haber, D. A.; Schou, J.; Thompson, M. J. Bibcode: 2004ESASP.559..472H Altcode: 2004soho...14..472H No abstract at ADS Title: Activity-related Changes in Local Solar Acoustic Mode Parameters from Michelson Doppler Imager and Global Oscillations Network Group Authors: Howe, R.; Komm, R. W.; Hill, F.; Haber, D. A.; Hindman, B. W. Bibcode: 2004ApJ...608..562H Altcode: We use the ring-diagram technique of local helioseismology to study the amplitude and line width of high-degree solar acoustic modes from 474 days of data from the Michelson Doppler Imager Dynamics program, covering the period 1996-2002. The 2002 data are compared with contemporaneous data from the Global Oscillations Network Group network. The results, once instrumental effects have been removed, show a strong dependence of the amplitude and lifetime of the modes on the local magnetic flux, with the amplitude and lifetime decreasing in the 5 minute band and a reversed trend at high frequencies. We relate these findings to results from global modes and from other approaches for analyzing high-degree local oscillations. Title: Vorticity of Solar Subsurface Flows and Torsional Oscillations Authors: Komm, R.; Howe, R.; Gonzalez-Hernandez, I.; Hill, F.; Haber, D.; Hindman, B.; Corbard, T. Bibcode: 2004AAS...204.5308K Altcode: 2004BAAS...36Q.757K We study horizontal flows in the upper solar convection zone derived from GONG and MDI Dynamics Program data using ring-diagram analysis. We start exploring the dynamics of the near surface layers and the interaction between flows and magnetic flux by deriving the vorticity of the horizontal flow components. A preliminary analysis of synoptic flow maps shows that the vorticity is enhanced near locations of active regions. In this study, we focus on the question of how these flows with vorticity near active regions are related to the so-called torsional oscillation pattern shown by zonal flows. During a solar cycle, alternating bands of faster- and slower-than-average rotation move from high latitudes toward the solar equator with the faster-than-average band being equatorward of active regions. The solar-cycle variation of the zonal flows thus contributes to the vorticity measured in daily or synoptic flow maps. We plan to determine the size of this contribution and will present our latest results.

This work was supported by grants from NASA and NSF. Title: Meridional Circulation Variability from Large-Aperture Ring Diagrams Authors: Gonzalez-Hernandez, I.; Komm, R.; Corbard, T.; Hill, F.; Howe, R. Bibcode: 2004AAS...204.5307G Altcode: 2004BAAS...36..756G Ring Diagram analysis, a local helioseismology technique, has proven very useful in the study of solar subsurface velocity flows to a depth of about 0.97Rsun. The depth range is determined by the modes recovered with this method and thus depends on the size of the area analyzed. Extending the working area allows us to detect lower l modes that penetrate deeper into the Sun. However, there is a compromise between the size of the patch and the validity of the plane wave approximation used by the technique.

Here we search for variability of the meridional flows as a function of depth for three consecutive Carrington rotations. We have studied patches of 30-degree diameter over the solar surface as they crossed the solar central meridian. These patches are twice the size of the typically studied sections of 15 degrees in diameter. The range of modes recovered with these larger regions goes down to l 100. A set of 15 overlapping sections, centered at latitudes 0 +/-7.5,+/-15,+/-22.5,+/-30.0,+/-37.5,+/-45.0 and +/-52.5, has been analyzed for 25 intervals of 1664 minutes in each Carrington rotation: CR1987, CR1988 and CR1989. Both GONG and MDI full disk Dopplergrams have been used for the work.

This work was supported in part by NASA grant NAG5-11703. SOHO is a project of international cooperation between ESA and NASA. This work utilizes data obtained by the Global Oscillation Network Group (GONG) Program, managed by the National Solar Observatory, which is operated by AURA, Inc. under a cooperative agreement with the National Science Foundation. The data were acquired by instruments operated by the Big Bear Solar Observatory, High Altitude Observatory, Learmonth Solar Observatory, Udaipur Solar Observatory, Instituto de Astrofisica de Canarias, and Cerro Tololo Interamerican Observatory. Title: Acoustic Power Maps of High Spatial Resolution Sunspot Data Authors: Astley, V.; Komm, R.; Howe, R. Bibcode: 2004AAS...204.5311A Altcode: 2004BAAS...36..757A We analyzed a time series of high spatial resolution (.04" per pixel) intensity images of a sunspot region observed on July 15, 2002 with the Swedish Solar Telescope to study the interaction of acoustic modes with small-scale features, such as granules near a sunspot, and their evolution over short time-scales (approximately one hour). The images were taken in G-band intensity with a cadence of 22 seconds. The time series were filtered with Empirical Mode Decomposition to eliminate low frequency power generated by the evolution of solar surface features and a simple 1-D FFT was used to obtain the power spectra in temporal frequency at each spatial location. Preliminary results show a correlation between small-scale structure and frequency-dependent acoustic power emission. Granules show increased power output in the 3 mHz range while the same area shows acoustic suppression at higher frequencies confirming results by other authors. We find that the distribution of acoustic power is spatially very localized especially in penumbral filaments and umbral sub-structures of the sunspot.

This work is carried out through the National Solar Observatory Research Experiences for Undergraduate (REU) site program, which is co-funded by the Department of Defense in partnership with the National Science Foundation REU Program. Title: Solar Subsurface Fluid Dynamics Descriptors Derived from Global Oscillation Network Group and Michelson Doppler Imager Data Authors: Komm, R.; Corbard, T.; Durney, B. R.; González Hernández, I.; Hill, F.; Howe, R.; Toner, C. Bibcode: 2004ApJ...605..554K Altcode: We analyze Global Oscillation Network Group (GONG) and Michelson Doppler Imager (MDI) observations obtained during Carrington rotation 1988 (2002 March 30-April 26) with a ring-diagram technique in order to measure the zonal and meridional flow components in the upper solar convection zone. We derive daily flow maps over a range of depths up to 16 Mm on a spatial grid of 7.5d in latitude and longitude covering +/-60° in latitude and central meridian distance and combine them to make synoptic flow maps. We begin exploring the dynamics of the near-surface layers and the interaction between flows and magnetic flux by deriving fluid dynamics descriptors such as divergence and vorticity from these flow maps. Using these descriptors, we derive the vertical velocity component and the kinetic helicity density. For this particular Carrington rotation, we find that the vertical velocity component is anticorrelated with the unsigned magnetic flux. Strong downflows are more likely associated with locations of strong magnetic activity. The vertical vorticity is positive in the northern hemisphere and negative in the southern hemisphere. At locations of magnetic activity, we find an excess vorticity of the same sign as that introduced by differential rotation. The vertical gradient of the zonal flow is mainly negative except within 2 Mm of the surface at latitudes poleward of about 20°. The zonal-flow gradient appears to be related to the unsigned magnetic flux in the sense that locations of strong activity are also locations of large negative gradients. The vertical gradient of the meridional flow changes sign near about 7 Mm, marking a clear distinction between near-surface and deeper layers. GONG and MDI data show very similar results. Differences occur mainly at high latitudes, especially in the northern hemisphere, where MDI data show a counter cell in the meridional flow that is not present in the corresponding GONG data. Title: Helioseismic sensing of the solar cycle Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 2004cosp...35.1397K Altcode: 2004cosp.meet.1397K In the last decade, great progress has been made in understanding the activity-cycle variation of the dynamics and structure of the solar interior. Observations from SoHO/MDI, GONG, BiSON, and Mt. Wilson have now provided detailed helioseismic information over two decades. Parameters such as frequency, width, and amplitude describing global acoustic modes sense the varying local distribution of the surface magnetic activity with the solar cycle. Mode width and amplitude contain information about the damping and excitation of acoustic modes and hence have implications for the understanding of the near-surface layers where the acoustic modes are generated. The frequency variation of the global modes provides information about the solar structure and interior rotation rate. The rotation rate in the upper convection zone varies with the solar cycle: the zonal flows are detectable in at least the upper third of the convection zone. At the base of the convection zone, the rotation rate varies with a period of about 1.3 yr which might indicate an exchange of angular momentum between the radiative interior and the convection zone. With local helioseismology techniques such as ring-diagram or time-distance analysis, it is possible to measure the flow component in the meridional direction. Its variation with depth and solar cycle can provide insights into the operation of the solar dynamo. Title: A Comparison of Solar p-Mode Parameters from MDI and GONG: Mode Frequencies and Structure Inversions Authors: Basu, S.; Christensen-Dalsgaard, J.; Howe, R.; Schou, J.; Thompson, M. J.; Hill, F.; Komm, R. Bibcode: 2003ApJ...591..432B Altcode: Helioseismic analysis of solar global oscillations allows investigation of the internal structure of the Sun. One important test of the reliability of the inferences from helioseismology is that the results from independent sets of contemporaneous data are consistent with one another. Here we compare mode frequencies from the Global Oscillation Network Group and Michelson Doppler Imager on board SOHO and resulting inversion results on the Sun's internal structure. The average relative differences between the data sets are typically less than 1×10-5, substantially smaller than the formal errors in the differences; however, in some cases the frequency differences show a systematic behavior that might nonetheless influence the inversion results. We find that the differences in frequencies are not a result of instrumental effects but are almost entirely related to the data pipeline software. Inversion of the frequencies shows that their differences do not result in any significant effects on the resulting inferences on solar structure. We have also experimented with fitting asymmetric profiles to the oscillation power spectra and find that, compared with the symmetric fits, this causes no significant change in the inversion results. Title: Flow maps from GONG+ ring diagrams Authors: Komm, R.; Bolding, J.; Corbard, T.; Hill, F.; Howe, R.; Toner, C. Bibcode: 2003SPD....34.0811K Altcode: 2003BAAS...35..823K We show first results derived from one month or more of GONG++ data analyzed with a ring-diagram technique as part of the GONG++ local helioseimology analysis pipeline. We focus on observations obtained during spring 2002 and especially on Carrington rotation 1988 (2002/3/30 - 2002/4/26) and measure horizontal flow components over a range of depths up to 16 Mm on a spatial grid of 7.5 degree in latitude and longitude. We calculate zonal and meridional flow components and compare the average zonal flows with corresponding results of a global rotation inversion. We create and analyze synoptic maps of large-scale flows and compare them with corresponding synoptic maps of magnetic activity. We will present the latest results.

RH and RK are partially supported by NASA Grant S-92698-F. NSO is operated by AURA, Inc under a co-operative agreement with the National Science Foundation. Title: A Comparison of Low-Degree Solar p-Mode Parameters from BiSON and GONG: Underlying Values and Temporal Variations Authors: Howe, R.; Chaplin, W. J.; Elsworth, Y. P.; Hill, F.; Komm, R.; Isaak, G. R.; New, R. Bibcode: 2003ApJ...588.1204H Altcode: Approximately 5 years of the l=0 time series from the GONG project have been analyzed using the algorithm developed for the BiSON zero-dimensional data. The data cover the period 1995-2000. The results are compared with those from a parallel analysis of contemporaneous BiSON data and also with the results of the traditional GONG analysis of the low-degree time series. The spectra analyzed were prepared using the multitaper spectral analysis technique used in the recent reanalysis of the GONG data. We consider both solar cycle trends and temporally averaged values for mode frequencies, line widths, amplitudes, and asymmetry parameters. Title: The LoHCo Project. 1 -- Comparison of Ring-Diagram Local Helioseismology on GONG++, MDI and Mt. Wilson Data Sets Authors: Bogart, R. S.; Schou, J.; Basu, S.; Bolding, J.; Hill, F.; Howe, R.; Komm, R. W.; Leibacher, J. W.; Toner, C. G.; Corbard, T.; Haber, D. A.; Hindman, B. W.; Toomre, J.; Rhodes, E. J.; Rose, P. J.; LoHCo Project Team Bibcode: 2003SPD....34.0804B Altcode: 2003BAAS...35..822B Full deployment of the GONG+ enhanced observing network in October 2001 and implementation of ring-diagram helioseismology in the GONG++ analysis pipeline this year has enabled us to make a detailed intercomparison of results obtained through multiple paths, from observation through each of the analysis steps. Such comparisons can provide a certain degree of validation of the implementations of the analysis procedures, hints of systematic errors, and better characterization of the observations, possibly leading to improved calibrations. The Local Helioseismology Comparison (LoHCo) Project has been established to provide standards for intercomparison of results obtained with different local helioseismic analysis techniques applied to the available observational data sources. We present here a detailed comparison of ring-diagram determinations of localized sub-surface flows and frequency shifts obtained from both MDI and GONG in common observing intervals during Carrington Rotation 1988 (2002/3/30 -- 2002/4/26), using both the MDI and the GONG analysis pipelines. We also present preliminary results of similar analyses of data obtained by the Mt. Wilson MOF during the same times.

This work is partially supported by grants from NASA and NSF. Title: Localized Frequency Shifts from GONG+ Authors: Howe, R.; Komm, R. W.; Hill, F.; Bolding, John; Toner, Cliff; Corbard, Thierry Bibcode: 2003SPD....34.0802H Altcode: 2003BAAS...35Q.822H Ring Diagram analysis uses 3-dimensional power spectra from small areas of the solar disk to measure the local frequency of high-degree modes and follow local flows below the surface. The pipeline for processing ring diagrams from the 1024x 1024 pixel data generated by the GONG+ network has now been implemented and the first data has been analyzed. We will present our latest initial results on the local variations in the mode frequency and their correlation with the local magnetic index over a month or more of observations.

RK, CT, and RH in part, are supported by NASA contract S-92698-F. NSO is operated by AURA, Inc under a co-operative agreement with the National Science Foundation. Title: Temporal Variation of Angular Momentum in the Solar Convection Zone Authors: Komm, R.; Howe, R.; Durney, B. R.; Hill, F. Bibcode: 2003ApJ...586..650K Altcode: We derive the angular momentum as a function of radius and time with the help of the rotation rates resulting from inversions of helioseismic data obtained from the Global Oscillation Network Group (GONG) and the Michelson Doppler Imager (MDI) and the density distribution from a model of the Sun. The base of the convection zone can be identified as a local maximum in the relative angular momentum after subtracting the contribution of the solid-body rotation. The angular momentum as a function of radius shows the strongest temporal variation near the tachocline. This variation extends into the lower convection zone and into the radiative interior and is related to the 1.3 yr periodicity found in the equatorial rotation rate of the tachocline. In the upper convection zone, we find a small systematic variation of the angular momentum that is related to torsional oscillations. The angular momentum integrated from the surface to a lower limit in the upper convection zone provides a hint that the torsional oscillation pattern extends deep into the convection zone. This is supported by other quantities such as the coefficients of a fit of Legendre polynomials to the rotation rates as a function of latitude. The temporal variation of the coefficient of P4, indicative of torsional oscillations, suggests that the signature of these flows in the inversion results extend to about r~0.83Rsolar. With the lower limit of integration placed in the middle or lower convection zone, the angular momentum fluctuates about the mean without apparent trend, i.e., the angular momentum is conserved within the measurement errors. However, when integrated over the layers slightly below the convection zone (0.60-0.71Rsolar), the angular momentum shows the 1.3 yr period and hints at a long-term trend that might be related to the solar activity cycle. Title: Temporal variation of angular momentum in the convection zone Authors: Komm, R.; Howe, R.; Durney, B. R.; Hill, F. Bibcode: 2003ESASP.517...97K Altcode: 2003soho...12...97K We derive the angular momentum as a function of radius and time with the help of the rotation rates resulting from inversions of helioseismic data obtained from the Global Oscillation Network Group (GONG) and the Michelson Doppler Imager (MDI) and the density distribution from a model of the Sun. The angular momentum as a function of radius shows the strongest temporal variation near the base of the convection zone. This variation extends into the lower convection zone and into the radiative interior and is related to the 1.3-yr periodicity found in the equatorial rotation rate of the tachocline. In the upper convection zone, we find a small systematic variation of the angular momentum that is related to torsional oscillations. The angular momentum integrated from the surface to a lower limit in the upper convection zone provides a hint that the torsional oscillation pattern extends deep into the convection zone. With the lower limit of integration placed in the lower half of the convection zone, the angular momentum fluctuates about the mean without apparent trend, i.e. the angular momentum is conserved within the measurement errors. However, when integrated over the layers slightly below the convection zone, the angular momentum shows the 1.3-yr period and hints at a long-term trend which might be related to the solar activity cycle. Title: Activity related variation of width and energy of global p-modes Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 2003ESASP.517..325K Altcode: 2003soho...12..325K We derived mode width, energy, and energy supply rate from 66 108-day GONG time series currently processed with multitapers. We show the temporal variation of these mode parameters from the previous minimum to the maximum of the current solar cycle localized in latitude. Mode width and energy of global modes clearly sense the local distribution of surface magnetic activity. The relation between magnetic activity and localized mode energy and width is linear within the measurement uncertainties. The energy supply rate however does not show such a relation with the latitudinal distribution of surface magnetic activity. The results presented here are consistent with previously published results, where we analyzed periodograms instead of multitapered spectra. Title: Comparing results from the GONG l = 0 and BiSON time series Authors: Howe, R.; Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Komm, R. W.; New, R. Bibcode: 2003ESASP.517..303H Altcode: 2003soho...12..303H Approximately 5 years of the l = 0 time series from the GONG project have been analysed using the algorithm developed for the BiSON 0-dimensional data. The data cover the period 1995-2000. The results are compared with those from a parallel analysis of contemporaneous BiSON data, and also with the results of the traditional GONG analysis of the low-degree time series. The spectra analysed were prepared using the multitaper spectral analysis technique used in the recent re-analysis of the GONG data. We consider both solar-cycle trends and temporally averaged values for mode frequencies, linewidths, amplitudes and asymmetry parameters. Title: Transient oscillations near the solar tachocline Authors: Toomre, Juri; Christensen-Dalsgaard, Jorgen; Hill, Frank; Howe, Rachel; Komm, Rudolf W.; Schou, Jesper; Thompson, Michael J. Bibcode: 2003ESASP.517..409T Altcode: 2003soho...12..409T We report on further developments in the 1.3-yr quasi-periodic oscillations reported by Howe et al. (2000). These are small (6 to 8 nHz peak-to-peak) oscillations in the inferred rotation rate near the bottom of the convection zone and in the outer part of the radiative interior. The oscillations are strongest and most coherent at about a fractional radius of 0.72 in the equatorial region. Further monitoring of the oscillations near the equator shows that they continued for a period after the end of the data analyzed by Howe et al., but appear to have now diminished in amplitude. This is reminiscent of the transient behavior of similar (1.3 to 1.4 yr) periodicities in solar-wind and geomagnetic datasets previously reported. We speculate that the near tachocline oscillation is associated with the rising phase of the solar cycle. We discuss tests performed to eliminate various possible explanations of the oscillations due to systematic errors in the data and in their analyses. Title: Localizing the Solar Cycle Frequency Shifts in Global p-Modes Authors: Howe, R.; Komm, R. W.; Hill, F. Bibcode: 2002ApJ...580.1172H Altcode: The 6.5 yr span of observations from the Global Oscillation Network Group and the Michelson Doppler Imager aboard the Solar and Heliospheric Observatory allows a detailed study of the solar cycle-related frequency shifts at the level of central frequencies and a-coefficients from individual multiplets and even of individual modes within a multiplet. We analyze such data and show that the shifts at all levels of averaging are consistent with the hypothesis that the global p-mode frequency shifts are closely related to the surface magnetic field distribution. Furthermore, the evolution of the surface magnetic flux distribution can be reconstructed by an inversion technique operating on the shifts within individual (n, l) multiplets. Title: Detectability of large-scale flows in global helioseismic data - A numerical experiment Authors: Roth, M.; Howe, R.; Komm, R. Bibcode: 2002A&A...396..243R Altcode: Convective motions affect the solar p-modes by shifting their frequencies. In comparison to the frequency splitting caused by the differential rotation, this is only a small additional effect. As the spatial resolution of the inversions for the differential rotation becomes better, it is important to know how these additional frequency shifts modify the splitting coefficients and how these two effects might be disentangled. Therefore we carry out a numerical experiment. We use quasi-degenerate perturbation theory to create frequencies of p-modes that are affected by differential rotation and by large-scale flows. The simulated frequency sets are analyzed and inverted for differential rotation. We use changes in the (l, nu ) coverage, the multiplets, and the inversion results as diagnostics to draw conclusions about the detectability of large-scale flows in global helioseismic data. The result is a detectability limit of the order of 10 m s-1 for large-scale flows in the convection zone. A sectoral poloidal flow with greater amplitude will lead to a noticeable distortion of the rotation rate, while a zonal poloidal flow with greater amplitude will lead to distorted even-a coefficients and disrupted multiplets. Title: MDI and GONG inferences of the changing solar interior Authors: Barban, C.; Howe, R.; Hill, F.; Komm, R. W.; Leibacher, J.; Toner, C.; Bogart, R.; Braun, D.; Haber, D.; Hindman, B.; Lindsey, C. Bibcode: 2002ESASP.508...55B Altcode: 2002soho...11...55B The Global Oscillation Network Group (GONG) and the Solar Oscillations Investigation (SOI) using the Michelson Doppler Imager (MDI) instrument aboard the SOHO spacecraft provide combined data sets that now cover more than six years and allow us to probe the changing dynamics of the convection zone in unprecedented detail. Here we present the latest combined results from both projects, showing the evolution of the migrating zonal flows close to the surface and also changes close to and below the base of the convection zone, as well as changes in the mode parameters related to surface magnetic activity variation in time and latitude. Title: Localizing Width and Energy of Solar Global p-Modes Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 2002ApJ...572..663K Altcode: We present the first attempt at localizing in latitude the temporal variation of mode energy, energy supply rate, and lifetime of global acoustic modes. We use Global Oscillation Network Group (GONG) and Michelson Doppler Imager data analyzed with the GONG peak-fitting algorithm to measure mode width and amplitude of individual (l, n, m) modes. While measured amplitude and width values are inherently noisier than frequency measurements, it is possible to use the (m/l) dependence of these mode parameters to extract their variation in latitude. With the currently analyzed data sets, we construct maps in time and latitude of acoustic mode energy, lifetime (inverse of mode width), and energy supply rate covering the rising phase of the current solar cycle from the previous minimum to the current maximum. We find that the energy and width of global modes vary in latitude as well as in time and that the variation is clearly related to the distribution of magnetic flux. After removing the average quantity, the residual mode width shows a linear correlation with magnetic activity with a correlation coefficient of 0.88, while the corresponding residual mode energy is anticorrelated with magnetic activity with a correlation coefficient of -0.90. These mode parameters derived from global p-modes respond to the local distribution of surface magnetic activity. The energy supply rate shows no correlation with the latitudinal distribution of magnetic activity within the limits of the current measurements. We estimate the variation of global mode energy in response to an individual magnetic feature, such as a plage, and find that the global mode energy and the mode lifetime are reduced by about 40% by an active region compared to the quiet Sun. Title: New Results from GONG `classic' data Authors: Kras, S.; Howe, R.; Komm, R.; Hill, F. Bibcode: 2002AAS...200.0408K Altcode: 2002BAAS...34R.644K We reprocessed all 59 108-day time series obtained during the operation of GONG in `classic' mode (mid-1995--mid-2001) using multitapers. The multitaper method helps to improve the fitting of mode parameters by producing smoothed power spectra. The main benefit is an increase in the number of modes that are fitted well, which leads to an increase of the order of 10%\ in the number of multiplets for each time sample. We will compare multitapered with previous untapered results to show the improvement gained, for example, in the rotation rates of the solar interior by this reprocessing step. In addition, we analyzed 1-year and 3-year GONG classic time series in order to improve the number of well-fitted modes at low frequencies (below 1.5 mHz). Preliminary results show an improvement in the number of modes at low frequencies is gained by increasing the length of the time series from 108 days to three years. We will present our latest results. The Global Oscillation Network Group (GONG) project is managed by the National Solar Observatory, which is operated by AURA, Inc. under a cooperative agreement with the National Science Foundation. Title: Temporal Variation of Angular Momentum in the Solar Convection Zone Authors: Komm, R.; Howe, R.; Durney, B.; Hill, F. Bibcode: 2002AAS...200.0404K Altcode: 2002BAAS...34Q.644K We present the temporal variation of the solar angular momentum derived from helioseismic observations. In the absence of `true' angular momentum inversions, we use the rotation rates resulting from rotation inversions of GONG data and the density distribution from a model of the Sun. We focus especially on the layers near the base of the convection zone and the layers near the solar surface. We derive the angular momentum as a function of depth and the corresponding solid-body rotation. The angular momentum decreases with increasing radius following essentially the product of density times the fourth power of radius. The tachocline can be identified as a local maximum in the radial gradient of the angular momentum and as a local maximum in the relative angular momentum after subtracting the contribution of the solid-body rotation. The angular momentum shows the strongest temporal variation near the tachocline. This variation is reminiscent of the 1.3-yr periodicity found in the equatorial rotation rate of the tachocline, which is not too surprising since the angular momentum of a spherical shell is heavily weighted toward the equator. We discuss the extension of this variation into the convection zone and into the radiative interior. In addition, we fit the rotation rates as functions of latitude with Legendre polynomials to cross-validate the numerical results and to draw conclusions about the zonal flows (`torsional oscillations') in the upper convection zone. This work was supported by NASA Grant S-92698-F. Title: A Comparison of Solar p-Mode Parameters from the Michelson Doppler Imager and the Global Oscillation Network Group: Splitting Coefficients and Rotation Inversions Authors: Schou, J.; Howe, R.; Basu, S.; Christensen-Dalsgaard, J.; Corbard, T.; Hill, F.; Komm, R.; Larsen, R. M.; Rabello-Soares, M. C.; Thompson, M. J. Bibcode: 2002ApJ...567.1234S Altcode: Using contemporaneous helioseismic data from the Global Oscillation Network Group (GONG) and Michelson Doppler Imager (MDI) onboard SOHO, we compare frequency-splitting data and resulting inversions about the Sun's internal rotation. Helioseismology has been very successful in making detailed and subtle inferences about the solar interior. But there are some significant differences between inversion results obtained from the MDI and GONG projects. It is important for making robust inferences about the solar interior that these differences are located and their causes eliminated. By applying the different analysis pipelines developed by the projects not only to their own data but also to the data from the other project, we conclude that the most significant differences arise not from the observations themselves but from the different frequency estimation analyses used by the projects. We find that the GONG pipeline results in substantially fewer fitted modes in certain regions. The most serious systematic differences in the results, with regard to rotation, appear to be an anomaly in the MDI odd-order splitting coefficients around a frequency of 3.5 mHz and an underestimation of the low-degree rotational splittings in the GONG algorithm. Title: Solar-cycle variation of the sound-speed asphericity from GONG and MDI data 1995-2000 Authors: Antia, H. M.; Basu, S.; Hill, F.; Howe, R.; Komm, R. W.; Schou, J. Bibcode: 2001MNRAS.327.1029A Altcode: 2001astro.ph..9326A We study the variation of the frequency splitting coefficients describing the solar asphericity in both GONG and MDI data, and use these data to investigate temporal sound-speed variations as a function of both depth and latitude during the period 1995-2000 and a little beyond. The temporal variations in even splitting coefficients are found to be correlated to the corresponding component of magnetic flux at the solar surface. We confirm that the sound-speed variations associated with the surface magnetic field are superficial. Temporally averaged results show a significant excess in sound speed around r=0.92Rsolar and latitude of 60°. Title: Empirical Mode Decomposition and Hilbert Analysis Applied to Rotation Residuals of the Solar Convection Zone Authors: Komm, R. W.; Hill, F.; Howe, R. Bibcode: 2001ApJ...558..428K Altcode: We apply empirical mode decomposition (EMD) and Hilbert analysis to time series of rotation residuals at all latitudes and at all depths in the convection zone derived from 49 Global Oscillation Network Group data sets covering the period 1995 May 7 to 2000 May 15. Hilbert analysis combined with EMD is a tool to analyze nonlinear and nonstationary signals and is used to localize events in time-frequency space. We calculate Hilbert power spectra, power as a function of time and frequency, for each time series in order to determine whether the rotation rate in the convection zone shows any other systematic temporal variation besides the so-called torsional oscillation pattern in the upper convection zone and the periodicity of 1.3 yr near the base of the convection zone. In other regions of the convection zone, the temporal variations of the rotation residuals are compatible with a noise signal except near about 0.86 Rsolar in radius, where we find indications of a long-term period of about 6 yr. However, it is uncertain whether this signal is of solar origin, since the available data set is too short to rule out the possibility of an artifact. In addition, we calculate the amount of power contained in the torsional oscillation signal as a function of time, latitude, and radius to study the variation of the torsional oscillation pattern. The depth to which the pattern extends apparently changes with time. For example, at midlatitudes the pattern extends to deeper layers with increasing time. The degree of stationarity doubles from the surface to about 0.92 Rsolar in radius, which indicates that the torsional oscillation pattern disappears with increasing depth in agreement with previous results. Title: Asymmetric Line Profiles Applied to Gong Helioseismic Data Authors: Landy, D.; Howe, R.; Komm, R.; Hill, F. Bibcode: 2001AGUSM..SP21C04L Altcode: P-mode frequencies have traditionally been fit using a symmetric Lorentzian profile. Due to clear asymmetries in the peaks, researchers have begun moving toward asymmetric near-Lorentzian profiles; amongst the most popular is the Nigam profile. In this paper, results are presented from a fit of the Nigam profile to two datasets, both taken from GONG data, using a new peak fitting engine (PEAKFIND Mark II). Details of PEAKFIND Mark II are presented. Results of the Nigam model fits are compared with those achieved using a symmetric Lorentzian line profile (those reported by the GONG network). Results are also shown to be largely consistent with other published fits in the low frequency region. Title: Detectability of Large-Scale Convection in Global Helioseismic Data Authors: Roth, M.; Howe, R.; Komm, R. W. Bibcode: 2001AGUSM..SP31A08R Altcode: Convection affects the solar p-modes by additonally shifting the frequencies. This effect is small in comparison to the frequency splitting caused by the differential rotation. But, as the spatial resolution of the inversions for the differential rotation becomes better, it is important to know how these additional frequency shifts are blended into the splitting coefficients and how both might be disentangled. Therefore we carry out a numerical experiment. We calculate with quasi-degenerate perturbation theory the frequencies of p-modes that are affected by differential rotation and large-scale convection cells. This simulated data are inverted for differential rotation, and on that basis upper limits for the detectability of large-scale convection in global helioseismic data are derived. Title: Hilbert Spectral Analysis Applied to Helioseismic Time Series Authors: Komm, R.; Hill, F.; Howe, R. Bibcode: 2001AGUSM..SP31A07K Altcode: We apply Empirical Mode Decomposition and Hilbert spectral analysis to helioseismic time series to study excitation and damping of solar p-modes. We use time series from the Solar Oscillations Investigation (SOI) project using the Michelson Doppler Imager (MDI) aboard the Solar and Heliospheric Observatory (SOHO) spacecraft. The Hilbert spectral analysis is a tool to analyze nonlinear and nonstationary signals and is used to localize events in time-frequency space. The solar acoustic oscillations are thought to be stochastically excited by the release of acoustic energy from sources near the top of the turbulent convection zone of the Sun. Individual modes are present during some time periods and absent during others. We analyze time series of different l and m values in order to detect individual excitation or damping events. In addition, we compare data sets obtained during different levels of solar magnetic activity to study the influence of magnetic activity on solar p-modes. We will present the latest results of this investigation. Title: Comparing Global Solar Rotation Results from MDI and GONG Authors: Howe, R.; Komm, R. W.; Hill, F.; Christensen-Dalsgaard, J.; Schou, J.; Thompson, M. J.; Corbard, T. Bibcode: 2001AGUSM..SP31A14H Altcode: The GONG (Global Oscillations Network Group) project and the Solar Oscillations Investigation (SOI) using the Michelson Doppler Imager (MDI) instrument aboard the SOHO spacecraft have jointly accumulated more than five years of data on medium-degree solar p-modes, including nearly four years of contemporaneous observations. The inferences of interior solar rotation from the two projects are broadly consistent and show similar temporal variations, but there are also significant systematic differences. We report here on the results of an ongoing attempt to cross-compare the results and analysis techniques of the two projects. Three 108-day periods, at low, medium and high solar activity epochs, have been analysed, with both MDI and GONG analysis being applied to each data set, and the results are compared. Title: Solar Cycle Changes in p-Mode Frequencies and Asphericity 1995-2000 Authors: Howe, R.; Hill, F.; Komm, R. W. Bibcode: 2001AGUSM..SP21C03H Altcode: With 5 years of analysed data from the GONG (Global Oscillation Network Group) project and the Solar Oscillations Investigation (SOI) using the Michelson Doppler Imager (MDI) aboard the SOHO spacecraft, we can investigate the solar-cycle changes in the medium-degree solar p-mode frequencies in much more detail than has previously been possible. The quality of the data allows us to study the variations in the central frequencies of individual (l,n) multiplets, and also to demonstrate that the latitudinal variation of the frequency changes within a multiplet correlates closely with the latitudinal distribution of surface magnetic activity. We report here on the latest results of such an investigation, and the implications for our understanding of the relationship between p-mode frequencies and solar activity. Title: Variations in Rotation Rate Within the Solar Convection Zone From GONG and MDI 1995-2000 Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.; Schou, J.; Thompson, M. J.; Toomre, J. Bibcode: 2001AGUSM..SP31A15H Altcode: Helioseismic measurements with the Michelson Doppler Imager (MDI) instrument aboard SOHO, and complementary measurements from the Global Oscillation Network Group (GONG) project, are revealing changes deep within the Sun as the solar cycle progresses. We will present the latest results based on recent data from both experiments, including flows in the upper part of the convection zone and variations in the rotation rate near its base. Title: Hilbert Spectral Analysis Applied to Rotation Residuals of the Solar Convection Zone Authors: Komm, R.; Hill, F.; Howe, R. Bibcode: 2001AGUSM..SP31A06K Altcode: We apply Empirical Mode Decomposition and Hilbert spectral analysis to time series of rotation residuals at all latitudes and at all depths in the solar convection zone derived from 49 data sets obtained by the Global Oscillation Network Group (GONG) project covering the period 1995 May 7 to 2000 May 15. The Hilbert spectral analysis is a tool to analyze nonlinear and nonstationary signals and is used to localize events in time-frequency space. We calculate Hilbert power spectra, power as a function of time and frequency, for each time series in order to determine whether the rotation rate in the solar convection zone shows any other systematic temporal variation besides the torsional oscillation pattern in the upper convection zone and the 1.3-yr periodicity near the base of the convection zone. In addition, we calculate the amount of power contained in the torsional oscillation signal as a function of time, latitude, and radius to study the variation of the torsional oscillation pattern. For example, the degree of stationarity of the torsional oscillation doubles between surface layers and a depth of about 8%\ of the solar radius. This indicates that the torsional oscillation pattern disappears with increasing depth in agreement with previous studies. We will present the latest results of this investigation. Title: Studying asphericity in the solar sound speed from MDI and GONG data Authors: Antia, H. M.; Basu, S.; Hill, F.; Howe, R.; Komm, R. W.; Schou, J. Bibcode: 2001ESASP.464...45A Altcode: 2001soho...10...45A We study the variation of the frequency splitting coefficients describing the solar asphericity in both GONG and MDI data, and use these data to investigate temporal sound-speed variations as a function of both depth and latitude during the period 1995-2000. The temporal variations in even splitting coefficients are found to be correlated with the corresponding component of magnetic flux at the solar surface. The sound-speed variations associated with the surface magnetic field appear to be superficial. Temporally averaged results show a significant excess in sound speed around r = 0.92 Rsolar and latitude of 60°. Title: Comparing mode frequencies from MDI and GONG Authors: Howe, R.; Hill, F.; Basu, S.; Christensen-Dalsgaard, J.; Komm, R. W.; Munk Larsen, R.; Roth, M.; Schou, J.; Thompson, M. J.; Toomre, J. Bibcode: 2001ESASP.464..137H Altcode: 2001soho...10..137H We present results of analyses of MDI and GONG time series covering the same time intervals, and using both the MDI and GONG peakbagging algorithms. We discuss some of the likely causes of differences between the inferred frequencies and frequency splittings. In addition, we consider the effect of these differences on the results of inversions for the solar internal rotation and sound speed. Title: Solar cycle changes in convection zone dynamics from MDI and GONG 1995 - 2000 Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.; Munk Larsen, R.; Schou, J.; Thompson, M. J.; Toomre, J. Bibcode: 2001ESASP.464...19H Altcode: 2001soho...10...19H The combined GONG and MDI medium-degree helioseismic data sets now cover just over 5 years and allow us to probe the changing dynamics of the convection zone in unprecedented detail. Here we present the latest results from both projects, showing the evolution of the migrating zonal flows close to the surface and also changes close to and below the base of the convection zone. Title: Background amplitudes of solar p-modes observed by GONG Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 2001ESASP.464..645K Altcode: 2001soho...10..645K We analyzed the mode background amplitudes, derived from the 45 currently processed 108-day GONG time series. We found that the background amplitudes and their solar-cycle variation qualitatively resembles more the mode amplitude, A, than the quantity mode amplitude times width squared, AΓ2. If the measured background consists only of the tails of p-modes and leaks, then the background amplitude should qualitatively follow the behavior of AΓ2. This unexpected behavior might be a subtle artifact of the temporal window correction or it might indicate that the tails of leaks and modes are not the only contributors to the measured background. Title: Interior Solar-Cycle Changes Detected by Helioseismology Authors: Howe, R.; Hill, F.; Komm, R. W.; Christensen-Dalsgaard, J.; Munk Larsen, R.; Schou, J.; Thompson, M. J.; Toomre, J. Bibcode: 2001IAUS..203...40H Altcode: Helioseismic measurements with the MDI instrument aboard SOHO, and complementary measurements from the GONG network, are revealing changes deep within the Sun as the solar cycle progresses. We will present results based on recent data from both experiments, including variations in the rotation rate deep inside the convection zone. Title: The effect of magnetic flux distribution on individual-m frequencies Authors: Howe, R.; Landy, D. H.; Komm, R. W.; Hill, F. Bibcode: 2001ESASP.464...91H Altcode: 2001soho...10...91H The GONG PEAKFIND algorithm generates a frequency for each m in an l,n multiplet. For most purposes, we then fit orthogonal polynomials to the frequencies to derive α-coefficients. The even-order coefficients are strongly correlated with the distribution of the magnetic flux. With over 4 years of GONG data, we can now demonstrate that the frequencies of individual n, l, m components experience shifts correlated with the surface flux distribution in the region sampled by that mode. At high activity levels, this can give rise to visible distortion of the "S-curve" shape within a multiplet, which in turn means that higher-order α coefficients are needed to correctly represent the shape and estimate the central frequency of the multiplet. Title: Width and energy of solar p-modes observed by GONG 1995 - 1999 Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 2001ESASP.464...33K Altcode: 2001soho...10...33K We present measurements of mode width, mean-square velocity power, the energy per mode, and the energy supply rate, derived from all currently processed 108-day GONG time series and discuss their implications for p-mode excitation and damping. The mode width shows the familiar "plateau" between 2.5 and 3.1 mHz with a "dip" near 2.9 mHz. This dip is most prominent during solar-cycle minimum and disappears with increasing magnetic activity. The mode energy, which reaches a maximum value of about 2.2×1028 erg near 3.15 mHz, decreases with increasing activity. The decrease is frequency dependent and shows a maximum near 3 mHz with a change of about -13% from the previous activity minimum to the currently highest level of activity. The energy supply rate, reaching a maximum value of about 2.5×1023 erg s-1 near 3.6 mHz, decreases on average by about 3% and its solar-cycle variation shows no frequency dependenc which is in marked contrast to the other mode parameters. Therefore, the variation in the energy supply rate might be compatible with a zero change. We speculate that the excess of the supplied energy might be transferred to the increasing number of flux tubes and might, in this way, contribute to the irradiance variation. Title: Exploring time series analysis techniques Authors: Komm, R.; Hill, F.; Howe, R.; Toner, C. Bibcode: 2001ESASP.464..351K Altcode: 2001soho...10..351K Multitaper power spectra show greatly reduced noise compared to single taper spectra, such as periodograms. We performed a random-restart test to show that multitaper spectra do not bias the fitted mode parameters. Then, we show a different way to increase the signal-to-noise ratio of spectra by calculating interleaved shifted cross-spectra. Finally, we start exploring the Hilbert spectral analysis which is a tool to localize events in time-frequency space. Title: Width and Energy of Solar p-Modes Observed by Global Oscillation Network Group Authors: Komm, R. W.; Howe, R.; Hill, F. Bibcode: 2000ApJ...543..472K Altcode: We present measurements of mode width, Γ, and mean square velocity power, 2>, derived from all currently processed 108 day Global Oscillation Network Group (GONG) time series and discuss their implications for p-mode excitation and damping. Assuming stochastic excitation, we estimate the energy per mode, E, and the energy supply rate, dE/dt. For modes with l=9-150, the mean square velocity power and the mode energy peak at about 3.15 mHz reaching values of 2>~1.4×103 cm2 s-2 and E~2.2×1028 ergs. The energy supply rate reaches a maximum value of dE/dt~2.5×1023 ergs s-1 near 3.6 mHz. The mode width shows the familiar ``plateau'' between 2.5 and 3.1 mHz with a ``dip'' near 2.9 mHz, which is strongest for l~40. This dip is most prominent during solar cycle minimum and disappears with increasing magnetic activity. The energy supply rate decreases on average by about 2.7% from the previous activity minimum to the currently highest level of activity. The solar cycle variation of dE/dt shows no frequency dependence, which is in marked contrast to the other mode parameters. The mode parameters are adequately represented by power laws in several frequency ranges, for example, dE/dt~ν6.89+/-0.07 for 2.4 mHz<=ν<3.0 mHz and dE/dt~ν-5.62+/-0.27 for 3.75 mHz<=ν<4.5 mHz. The solar cycle variation of these parameters can then be expressed as changes of a few percent in the power-law exponents and multipliers. Our results agree reasonably well with previous studies of Birmingham Solar-Oscillations Network and Big Bear Solar Observatory data. Title: Studying Asphericity in the Solar Sound Speed from MDI and GONG Data 1995-1999 Authors: Schou, J.; Antia, H. M.; Basu, S.; Howe, R.; Hill, F.; Komm, R. W. Bibcode: 2000SPD....31.0111S Altcode: 2000BAAS...32..803S We study the variation of the frequency splitting coefficients describing the solar asphericity in both GONG and MDI data, and use these data to investigate temporal sound-speed variations as a function of both depth and latitude during the period 1995--99. We confirm that the sound-speed variations associated with the surface magnetic field are superficial. Title: Solar-Cycle Changes in Convection-Zone Dynamics from SOI and GONG Data Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.; Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J. Bibcode: 2000SPD....31.0113H Altcode: 2000BAAS...32..803H The combined GONG and MDI medium-degree helioseismic data sets now cover more than 4.5 years and allow us to probe the changing dynamics of the convection zone in unprecedented detail. Here we present the latest results from both projects, showing the evolution of the migrating zonal flows close to the surface and also changes close to and below the base of the convection zone. This work utilizes data obtained by the Global Oscillation Network Group (GONG) project, managed by the National Solar Observatory, a Division of the National Optical Astronomy Observatories, which is operated by AURA, Inc. under a cooperative agreement with the National Science Foundation. SOHO is a joint project of ESA and NASA. Title: Width and Energy of Solar P-Modes Observed by GONG Authors: Komm, R. W.; Howe, R.; Hill, F. Bibcode: 2000SPD....31.0114K Altcode: 2000BAAS...32..803K We present mode width, Γ , and mean-square velocity power, < v2 >, derived from all currently processed 108-day GONG time series and discuss their implications for p-mode excitation and damping. Assuming stochastic excitation, we estimate the energy per mode, E, and the energy supply rate, dE / dt. For modes with l = 9 - 150, the mean-square velocity power and the mode energy peak at about 3.15 mHz reaching values of < v2 > ≈ 1.4 ; 103 cm2 s-2 and E ≈ 2.2 ; 1028 ergs. The energy supply rate reaches a maximum value of dE / dt ≈ 2.5 ; 1023 ergs s-1 near 3.6 mHz. The mode width shows the familiar `plateau' between 2.5 and 3.1 mHz with a `dip' near 2.9 mHz, which is strongest for l ≈ 40. This dip is most prominent during solar-cycle minimum and disappears with increasing magnetic activity. The energy supply rate decreases on average by about 2.7%\ from the previous activity minimum to the currently highest level of activity. The solar-cycle variation of dE / dt shows no frequency dependence, which is in marked contrast to the other mode parameters. The mode parameters are adequately represented by power laws in several frequency ranges, for example, dE / dt ~ ν 6.89 +/- 0.07 for 2.4 <= ν < 3.0 mHz and dE / dt ~ ν -5.62 +/- 0.27 for 3.75 <= ν < 4.5 mHz. The solar-cycle variation of these parameters can then be expressed as changes of a few percent in the power-law exponents and multipliers. Our results agree reasonably well with previous studies of BiSON and BBSO data. Title: Deeply Penetrating Banded Zonal Flows in the Solar Convection Zone Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.; Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J. Bibcode: 2000ApJ...533L.163H Altcode: 2000astro.ph..3121H Helioseismic observations have detected small temporal variations of the rotation rate below the solar surface that correspond to the so-called ``torsional oscillations'' known from Doppler measurements of the surface. These appear as bands of slower- and faster-than-average rotation moving equatorward. Here we establish, using complementary helioseismic observations over 4 yr from the GONG network and from the MDI instrument on board SOHO, that the banded flows are not merely a near-surface phenomenon: rather, they extend downward at least 60 Mm (some 8% of the total solar radius) and thus are evident over a significant fraction of the nearly 200 Mm depth of the solar convection zone. Title: Variations in solar sub-surface rotation from GONG data 1995-1998 Authors: Howe, R.; Komm, R.; Hill, F. Bibcode: 2000SoPh..192..427H Altcode: We have completed an analysis of the first 35 GONG Months (1 GM = 36 days) covering the last solar minimum and the rising phase of cycle 23. The mode parameters have been estimated from 33 time series, each of 3-GM duration, with centers spaced by 1 GM. We report on the temporal evolution of the rotational splitting coefficients up to 15th order. The coefficients do not correlate well with any surface magnetic flux measure yet considered, but we find small but significant trends in their temporal evolution. Inverting the coefficients for two-dimensional rotation information and looking at deviations from the mean produces a picture of a systematic zonal flow migrating towards lower latitudes during the rising phase of the cycle. This flow is probably associated with the torsional oscillation. Similar trends are seen in the 1986 -1990 BBSO data. Title: Dynamic Variations at the Base of the Solar Convection Zone Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.; Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J. Bibcode: 2000Sci...287.2456H Altcode: We have detected changes in the rotation of the sun near the base of its convective envelope, including a prominent variation with a period of 1.3 years at low latitudes. Such helioseismic probing of the deep solar interior has been enabled by nearly continuous observation of its oscillation modes with two complementary experiments. Inversion of the global-mode frequency splittings reveals that the largest temporal changes in the angular velocity Ω are of the order of 6 nanohertz and occur above and below the tachocline that separates the sun's differentially rotating convection zone (outer 30% by radius) from the nearly uniformly rotating deeper radiative interior beneath. Such changes are most pronounced near the equator and at high latitudes and are a substantial fraction of the average 30-nanohertz difference in Ω with radius across the tachocline at the equator. The results indicate variations of rotation close to the presumed site of the solar dynamo, which may generate the 22-year cycles of magnetic activity. Title: Solar-Cycle Changes in Gong P-Mode Widths and Amplitudes 1995-1998 Authors: Komm, R. W.; Howe, R.; Hill, F. Bibcode: 2000ApJ...531.1094K Altcode: We search for a solar-cycle variation in mode widths and amplitudes derived from 3 month GONG time series. The variation of mode width and amplitude observed in GONG data are the combined effects of fill factor, temporal variation, and measurement uncertainties. The largest variation is caused by the fill factor resulting in modes with increased width and reduced amplitude when fill is lower. We assume that the solar-cycle variation is the only other systematic variation beside the temporal window function effect. We correct all currently available data sets for the fill factor and simultaneously derive the solar-cycle variation. We find an increase of about 3% on average in mode width from the previous minimum to October 1998 and a decrease of about 7% and 6% in mode amplitude and mode area (widthxamplitude). We find no l dependence of the solar-cycle changes. As a function of frequency, these changes show a maximum between 2.7 and 3.3 mHz with about 47% higher than average values for mode width and about 29% and 36% higher ones for mode amplitude and area. We estimate the significance of these rather small changes by a prewhitening method and find that the results are significant at or above the 99.9% level, with mode area showing the highest level of significance and mode width the lowest. The variation in background amplitude is most likely not significant and is consistent with a zero change. Title: The Solar Cycle is More than Skin Deep! Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 2000ESASP.463...15K Altcode: 2000sctc.proc...15K No abstract at ADS Title: Helioseismic detection of temporal variations of solar rotation rate near the base of the convection zone Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.; Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J. Bibcode: 1999AAS...19510702H Altcode: 1999BAAS...31R1530H The differential rotation of the Sun and its ability to generate large-scale magnetic fields through cyclic dynamo action appear to be intimately linked. It is now commonly thought that the global dynamo behavior responsible for the emergence of active regions is derived from strong organized toroidal magnetic fields generated by rotational shear in a thin region (the tachocline) at the base of the convection zone. The magnetic field could well have a feedback effect on the fluid motions in the region. We are thus motivated to use helioseismology to look for changes in rotation profiles near the tachocline as the Sun's magnetic cycle progresses. This approach has become possible using frequency-splitting data for p- and f-mode oscillations derived over four years (from May 1995 to Sept 1999) of full-disk Doppler observations from the ground-based Global Oscillation Network Group (GONG) project and from the Michelson Doppler Imager (MDI) experiment aboard the SOHO spacecraft. Inversions using two different methods of the splittings from these two independent data sets reveal systematic variations of the rotation rate close to the base of the convection zone, with different behavior at low and high latitudes. Notable are variations of order 6 nHz in rotation rates near the equator, to be compared with the radial angular velocity contrast across the tachocline of about 30 nHz. These exhibit several nearly repetitive changes with a period of about 1.2-1.4 years and appear to be real changes in the deep convection zone and tachocline rotation rates that need to be followed as the solar cycle progresses. The GONG project is managed by the National Solar Observatory, a Division of the National Optical Astronomy Observatories, which is operated by AURA, Inc. under a cooperative agreement with the National Science Foundation. SOHO is a joint project of ESA and NASA. Title: Solar Cycle Changes in GONG P-Mode Frequencies, 1995-1998 Authors: Howe, R.; Komm, R.; Hill, F. Bibcode: 1999ApJ...524.1084H Altcode: We have analyzed 27 3 month sets of Global Oscillaiton Network Group (GONG) data from the end of cycle 22 and the beginning of cycle 23 and here present evidence of significant shifts in the central frequencies and the even a-coefficients of the frequency splittings of the modes. The temporal behavior of the even a-coefficients is better reproduced by the corresponding coefficients of a Legendre polynomial decomposition of the surface magnetic field than by the total flux; i.e., the temporal variation is strongly correlated with the latitudinal distribution of the surface magnetic activity. These changes are consistent with available data from previous solar cycles. The even a-coefficients, which sense the asphericity of the solar structure, appear to show similar temporal evolution at all depths. The odd a-coefficients, which sense the internal differential rotation, show no significant variation with time or depth. In particular they show no significant correlation with either the magnetic flux or with the corresponding odd Legendre components of the flux. This suggests that the solar cycle related variation of the oscillation frequencies is not due to contamination of observed Doppler shifts by the surface magnetic fields. Title: Multitaper Spectral Analysis and Wavelet Denoising Applied to Helioseismic Data Authors: Komm, R. W.; Gu, Y.; Hill, F.; Stark, P. B.; Fodor, I. K. Bibcode: 1999ApJ...519..407K Altcode: Estimates of solar normal mode frequencies from helioseismic observations can be improved by using multitaper spectral analysis (MTSA) to estimate spectra from the time series, then using wavelet denoising of the log spectra. MTSA leads to a power spectrum estimate with reduced variance and better leakage properties than the conventional periodogram. Under the assumption of stationarity and mild regularity conditions, the log multitaper spectrum has a statistical distribution that is approximately Gaussian, so wavelet denoising is asymptotically an optimal method to reduce the noise in the estimated spectra. We find that a single m-ν spectrum benefits greatly from MTSA followed by wavelet denoising and that wavelet denoising by itself can be used to improve m-averaged spectra. We compare estimates using two different five-taper estimates (Slepian and sine tapers) and the periodogram estimate for Global Oscillation Network Group (GONG) time series at selected angular degrees l. We compare those three spectra with and without wavelet denoising, both visually and in terms of the mode parameters estimated from the preprocessed spectra using the GONG peak-fitting algorithm. The two multitaper estimates give equivalent results. The number of modes fitted well by the GONG algorithm is 20%-60% larger (depending on l and the temporal frequency) when applied to the multitaper estimates than when applied to the periodogram. The estimated mode parameters (frequency, amplitude, and width) are comparable for the three power spectrum estimates, except for modes with very small mode widths (a few frequency bins), where the multitaper spectra broaden the modes compared with the periodogram. At frequencies below 3 mHz, wavelet denoising of the log multitaper power spectra tends to increase the number of modes for which the GONG peak-fitting algorithm converges well. Close to 3 mHz, where all modes are resolved, wavelet denoising makes little difference. At higher frequencies close to the acoustic cutoff frequency, where modes are blended into ridges, wavelet denoising the multitaper spectra reduces the number of good fits. We tested the influence of the number of tapers used and found that narrow modes at low n-values are broadened to the extent that they can no longer be fitted if the number of tapers is too large. For helioseismic time series of this length and temporal resolution, the optimal number of tapers is less than 10. Title: Solar Cycle Changes in GONG Data 1995-1998 Authors: Komm, R.; Howe, R.; Hill, F. Bibcode: 1999AAS...194.5601K Altcode: 1999BAAS...31..911K The GONG project has now analysed 3-month velocity time series covering the period late 1995 to mid-1998, covering the end of solar cycle 22 and the beginning of cycle 23. We here present an analysis of the highly significant shifts in the central frequencies and the a_2 and a_4 coefficients of the modes, and relate them to magnetic activity indices and to the corresponding coefficients of a Legendre polynomial decomposition of the surface magnetic field. These changes are confirmed by an analysis of the MDI-SOI time series for some of the equivalent time periods using the GONG peakfinding algorithm, and are consistent with available data from previous solar cycles. In addition, we study mode widths and amplitudes derived from the GONG data and search for a variation of these mode parameters with the solar cycle. With increased activity from cycle minimum to mid-1998, we find a small increase in mode width of about 2% on average and about 4% in the frequency range from 2.9 to 3.3 mHz. We find a decrease of similar size in mode amplitude and mode area (width times amplitude). The change in background amplitude is not significant and is consistent with a zero change. Title: Helioseismology and the Solar Cycle Authors: Komm, R. Bibcode: 1999AAS...194.4204K Altcode: 1999BAAS...31R.882K Helioseismic data show temporal variations that are clearly related to the solar cycle. It is well-established that the central frequencies of p-modes vary with solar activity, while it is a recent result that the even-a coefficients vary with the corresponding components of the surface magnetic fields. The frequency variations seem to be mainly due to near surface effects, but the physical relation between these variations and the surface magnetic fields has not been established yet. The solar-cycle variation of other mode parameters, such as mode width and amplitude, which relate to the excitation and damping of p-modes, are less well known. With GONG operating for over 3 years by now and SOHO for 2 years, we have data sets available which continually cover the end of solar cycle 22 and the beginning of solar cycle 23. This allows us to study the solar cycle variation of p-mode parameters with unprecedented detail. I will discuss recent results and some of their implications. Title: Short-term periodicities of the sun's `mean' and differential rotation Authors: Javaraiah, J.; Komm, R. W. Bibcode: 1999SoPh..184...41J Altcode: We have looked for periodicities in solar differential rotation on time scales shorter than the 11-year solar cycle through the power- spectrum analysis of the differential rotation parameters determined from Mt. Wilson velocity data (1969-1994) and Greenwich sunspot group data (1879-1976). We represent the differential rotation by a set of Gegenbauer polynomials (ω(φ)= + (5sin2φ−1)+ (21sin4φ−14sin2φ+1)). For the Mt. Wilson data, we focus on observations obtained after 1981 due to the reduced instrumental noise and have binned the data into intervals of 19 days. We calculated annual averages for the sunspot data to reduce the uncertainty and corrected for outliers occuring during solar cycle minima. The power spectrum of the photospheric `mean rotation' , determined from the velocity data during 1982-1994, shows peaks at the periods of 6.7-4.4 yr, 2.2 ± 0.4 yr, 1.2 ± 0.2 yr, and 243 ± 10 day with ≥99.9% confidence level, which are similar to periods found in other indicators of solar activity suggesting that they are of solar origin. However, this result has to be confirmed with other techniques and longer data sets. The 11-yr periodicity is insignificant or absent in . The power spectra of the differential rotation parameters and , determined from the same subset, show only the solar cycle period with a ≥99.9% confidence level. Title: Solar Cycle Changes in Oscillation Parameters From the First 35 Months of GONG Authors: Hill, F.; Howe, R.; Komm, R. Bibcode: 1999soho....9E..63H Altcode: We have completed an analysis of the first 35 GONG Months (1 GM = 36 days) covering the last solar minimum and the rising phase of Cycle 23. The mode parameters have been estimated from 33 time series, each of 3-GM duration, with centers spaced by 1 GM. We report on the temporal evolution of the frequency, splitting coefficients up to 15th order, widths, and amplitudes. We clearly observe the bulk frequency shift that is well-correlated with the surface magnetic flux, and are able to discern fine details in this evolution. We find that the even frequency splitting coefficients up to 14th order are highly correlated not with the total magnetic surface flux, but instead with the corresponding Legendre components of the average latitudinal surface flux. On the other hand, the odd coefficients do not correlate well with any surface magnetic flux measure yet considered. We find small yet significant trends in the temporal evolution of the odd coefficients up to 15th order. The widths and amplitudes also show evidence of temporal evolution, with widths slightly increasing (up to 10%) and amplitudes similarly decreasing as the activity level rises. Title: Solar-Cycle Changes in SOI and GONG Data for 1996-7 Authors: Anderson, E. R.; Howe, R.; Komm, R. Bibcode: 1998ESASP.418..901A Altcode: 1998soho....6..901A We have analysed two 3-month sets of GONG data from the end of cycle 22 (GONG months 12-14, June-September 1996) and the beginning of cycle 23 (GONG months 21-23, May-August 1997), and here present evidence of small but significant shifts in the central frequencies and the a4 coefficients of the modes, when averaged over all l and over 70-mu Hz frequency bins. These changes are confirmed by an analysis of the MDI-SOI time series for the equivalent time periods using the GONG peakfinding algorithm. Although small, these changes are consistent with what we would expect based on measurements of the activity-dependence of the frequencies in previous solar cycles. (Elsworth et al 1994, Woodard and Libbrecht 1993) We look forward to following the rise of solar cycle 23 in detail. Title: Comparison of SOHO-SOI/MDI and GONG Spectra Authors: Komm, R. W.; Anderson, E.; Hill, F.; Howe, R.; Kosovichev, A. G.; Scherrer, P. H.; Schou, J.; Fodor, I.; Stark, P. Bibcode: 1998ESASP.418..253K Altcode: 1998soho....6..253K We compare solar p-mode parameters, such as central frequency, width, and amplitude, derived from GONG and SOHO-SOI/MDI Medium-l Program time series obtained during the same time period. With the excellent data available now from GONG and SOHO-SOI/MDI, there exist data sets long enough to make such a comparison useful. For this study, we have chosen time series of three ell values (ell = 30, 65, and 100) corresponding to GONG month 16 (Oct 28 -- Dec 2, 1996). For each time series, we calculated multitaper power spectra using generalized sine tapers to reduce the influence of the gap structure, which is different for the two data sets. Then, we applied the GONG peakfitting algorithm to the spectra to derive mode parameters and selected `good' fits common to both MDI and GONG spectra, according to three selection criteria. Preliminary results show that mode frequencies determined from MDI spectra are essentially the same as the frequencies from GONG spectra and that the difference is, in general, well within one formal error bar. The background slope at frequencies above 5mHz is different between MDI and GONG spectra depending on ell. At present, we are analyzing 3-month time series of ell = 0 to ell = 150. We intend to present the results of the on-going comparison. Title: Multitaper Spectral Analysis and Wavelet Denoising Applied to Helioseismic Data Authors: Komm, Rudolf; Gu, Yeming; Hill, Frank; Stark, Phil; Fodor, Imola Bibcode: 1998ASPC..154..783K Altcode: 1998csss...10..783K Our goal is to improve the estimates of mode frequencies, amplitudes, and widths derived from helioseismic observations. To this end, we apply Multitaper Spectral Analysis (MTSA) to the observed time series to derive power spectrum estimates, and then we apply wavelet denoising to the log spectra to further improve the signal-to-noise ratio of the modes. The rationale behind this approach is that MTSA leads to a power spectrum estimate with reduced variance and better leakage properties than the conventional periodogram and that since the log multitaper spectrum is close to Gaussian, distributed wavelet denoising is the optimum method to reduce the noise level in the calculated spectra. We applied MTSA and wavelet denoising to GONG and SOHO-SOI/MDI time series and found that a single m-nu spectrum benefits greatly from MTSA plus wavelet denoising and that wavelet denoising by itself can be used to improve m-averaged spectra. Title: Multitaper Analysis Applied to a 3-month Time Series Authors: Komm, R. W.; Anderson, E.; Hill, F.; Howe, R.; Fodor, I.; Stark, P. Bibcode: 1998ESASP.418..257K Altcode: 1998soho....6..257K We show the benefit of multitapering by applying this technique to a 3-month helioseismic time series, then deriving p-mode parameters using the GONG peakfitting algorithm. A multitaper spectrum is an average over uncorrelated spectra derived from the same time series by applying a set of orthogonal tapers. Thus, a multitaper spectrum has less variance or noise than a single taper spectrum and has better leakage properties than a periodogram. We use generalized sine tapers, which are orthogonal tapers taking the gap structure of the time series into account. We applied this technique with great success to a variety of time series from SOHO-SOI/MDI and GONG. The benefit of multitapering is that more modes can be fitted than in a periodogram due to the reduced noise. The improvement depends on ell and other details of the time series and is typically between 20% and 60% for low to medium ell values for GONG as well as MDI data. For example, for the 3-month GONG time series covering months 12--14, the number of good fits increases by 10% on average for all modes from ell = 0--150, using 5 generalized sine tapers. The largest improvement is at ell <= 70 where at low frequencies one extra ridge can be fitted in the multitaper spectrum. Title: Estimated Mode Parameters from the Fitting of GONG Spectra Authors: Hill, F.; Anderson, E.; Howe, R.; Jefferies, S. M.; Komm, R.; Toner, C. Bibcode: 1998ESASP.418..231H Altcode: 1998soho....6..231H The estimation of mode parameters is a critical step in the helioseismic data reduction process. Several estimation methods are currently in use, and a comparison of the resulting frequencies from a common data set shows small, yet significant, differences. This suggests that the fitting procedures can introduce systematic errors. These errors will affect subsequent inversions of the data. For example, the presence of a high-latitude jet in the solar rotation rate appears to depend on the type of spectral fitting used to estimate the splitting coefficients. In addition, as the available helioseismic observations have improved, it has become apparent that several effects have been neglected in the peak fitting techniques. These effects include line profile asymmetry, coupling between the background and the mode signal, fine details in the leakage matrix, and the differences in the oscillation spectrum when observed in Doppler velocity or total intensity. Here we report on the latest GONG fitting methods and present the resulting mode parameter estimates. The GONG fitting technique now includes improved mode quality assurance checks and asymmetrical line profiles. Currently under development are multi-dimensional fitting, multi-taper time series analysis, background/mode coupling, simultaneous fitting of velocity and intensity spectra, and the inclusion of a leakage matrix. The improvements have resulted in higher-quality frequency estimates that are now being computed for 108-day long time series spaced by 36 days. After completion, each frequency table is made freely available to the helioseismic community. Title: GONG Spectra in three observables: What is a p-mode frequency? Authors: Harvey, J.; Hill, F.; Komm, R.; Leibacher, J.; Pohl, B.; GONG Team Bibcode: 1998IAUS..185...49H Altcode: No abstract at ADS Title: Multitaper Spectral Analysis and Wavelet Analysis of Daily and Monthly Sunspot Numbers Authors: Komm, R. W. Bibcode: 1998ASPC..140..431K Altcode: 1998ssp..conf..431K No abstract at ADS Title: Multitaper Spectral Analysis and Wavelet Denoising Applied to Helioseismic Data Authors: Komm, R.; Gu, Y.; Stark, P.; Hill, F. Bibcode: 1997SPD....28.0215K Altcode: 1997BAAS...29..895K Our goal is to improve the estimates of mode frequencies, amplitudes, and widths derived from helioseismic observations. To this end, we apply Multitaper Spectral Analysis (MTSA) to the observed time series to derive power spectrum estimates, and then we apply wavelet denoising to the spectra to improve the signal-to-noise ratio of the modes. The rationale behind this approach is that MTSA leads to a more accurate and robust power spectrum estimate than the conventional periodogram and that since the log multitaper spectrum is close to Gaussian distributed wavelet denoising is the optimum method to reduce the noise level in the calculated spectra. We have put together a `pipeline' to calculate a multitaper spectral estimate from a given time series, to apply wavelet denoising to the log spectra and then to derive mode parameters using the GONG peak-fitting algorithm. This pipeline was applied to a set of simple artificial data in order to check for systematic errors and consistency. The wavelet denoising method was already applied to m-averaged South Pole spectra and to some GONG spectra of different L values reducing the noise level considerably and improving the fit. At the moment, we apply the pipeline to GONG and SOHO-SOI/MDI time series. We intend to present a comparison of two multitaper estimates using Slepian and Sinusoidal tapers with a conventional periodogram and a comparison of each of the three spectra with the corresponding wavelet denoised spectrum. This comparison will allow us to discuss the benefits of adding these methods to existing helioseismic data analysis packages. Title: A spatial and spectral maximum entropy method as applied to OVRO solar data Authors: Komm, R. W.; Hurford, G. J.; Gary, D. E. Bibcode: 1997A&AS..122..181K Altcode: We present first results of applying a Maximum Entropy Method (MEM) algorithm that acts in both the spatial and spectral domains to data obtained with the frequency-agile solar interferometer at Owens Valley Radio Observatory (OVRO) taken at 45 frequencies in the range 1-18 GHz. The traditional MEM algorithm does not exploit the spatial information available at adjacent frequencies in the OVRO data, but rather applies separately to each frequency. We seek an algorithm that obtains a global solution to the visibilities in both the spatial and spectral domains. To simplify the development process, the algorithm is at present limited to the one-dimensional spatial case. We apply our 1-d algorithm to observations taken with the OVRO frequency-agile interferometer of active region AR 5417 near the solar limb on March 20, 1989 (vernal equinox). The interferometer's two 27 m antennas and 40 m antenna were arranged in a linear east-west array, which at the vernal equinox gives a good match to the 1-d algorithm. Our results show that including the spectral MEM term greatly improves the dynamic range of the reconstructed image compared with a reconstruction without using this information. The derived brightness temperature spectra show that for AR 5417 the dominant radio emission mechanism is thermal gyroresonance and we use this information to deduce the spatial variation of electron temperature and magnetic field strength in the corona above the active region. Title: Spatial/Spectral MEM Applied to OVRO Flare Data Authors: Komm, R. W.; Gary, D. E.; Hurford, G. J. Bibcode: 1996AAS...188.8502K Altcode: 1996BAAS...28..961K We present observations of a flare that occured on 1995 Oct 11, in AR 7912 obtained with the frequency-agile solar interferometer at Owens Valley Radio Observatory (OVRO) made with both high spatial and spectral resolution. We analyzed data at 32 frequencies in the range 1.2-12.4 GHz for both left-handed and right-handed circular polarizations applying the recently completed Spatial/Spectral Maximum Entropy Method (MEM). In contrast to the traditional MEM algorithm, which does not exploit the spatial information available at adjacent frequencies in the OVRO data, the new algorithm obtains a global solution to the visibilities in both the spatial and spectral domains and leads to spectra which are greatly improved in smoothness and dynamic range. A comparison with BBSO data shows that the optical flare is associated with the trailing sunspot of the active region, while the leading sunspot shows no flare related brightning. The reconstructed radio images show two sources; one of them, the primary source, is associated with the optical flare and has its peak emission at about 7.0 GHz, while the other one, the secondary source, is associated with the leading sunspot with a peak emission at about 2.8 GHz. The slopes of the brightness temperature spectra imply that in both cases non-thermal gyrosynchrotron emission is the process responsible for the microwave radiation. A preliminary model fit of the spectra shows that the emission of both sources comes from low-order harmonics and that the estimated magnetic field strength and the estimated density of nonthermal electrons of the primary source are much larger than the corresponding values of the secondary source. The results suggest that the two sources are connected by a large secondary loop and that the emission of the secondary source is caused by nonthermal electrons escaping from the primary source. The time evolution of the two sources within about +/- 3 min of the flux peak time can be described by an increase in the number of nonthermal electrons up to the peak time and by a subsequent decrease. Title: Temperature and velocity fluctuations in the deeper layers of the solar atmosphere. Authors: Vollmoeller, P.; Komm, R.; Mattig, W. Bibcode: 1996A&A...306..294V Altcode: To study temperature and velocity fluctuations in the lower photosphere of the Sun, we analyzed spectrograms obtained with the Vacuum Tower Telescope of the Observatorio del Teide in Tenerife in a spectral range at about 410nm, the secondary minimum of the continuum absorption coefficient. We find much larger temperature fluctuations than deduced by previous investigations at almost all photospheric heights. The velocity fluctuations show the same height dependence as deduced by earlier studies at mid- and upper photospheric layers (at heights larger than about 100km above τ_0_=1), but they do not increase as rapidly with decreasing height in the lower photosphere. The results indicate the existence of a velocity maximum located at the bottom of the photosphere or slightly below in subphotospheric layers. The location of this maximum agrees reasonably well with predictions of convection zone models. Title: Characteristic Size and Diffusion of Quiet Sun Magnetic Patterns Authors: Komm, R. W.; Howard, R. F.; Harvey, J. W. Bibcode: 1995SoPh..158..213K Altcode: We have previously studied large-scale motions using high-resolution magnetograms taken from 1978 to 1990 with the NSO Vacuum Telescope on Kitt Peak. Latitudinal and longitudinal motions were determined by a two-dimensional crosscorrelation analysis of pairs of consecutive daily observations using small magnetic features as tracers. Here we examine the shape and amplitude of the crosscorrelation functions. We find a characteristic length scale as indicated by the FWHM of the crosscorrelation functions of 16.6 ± 0.2 Mm. The length scale is constant within ±45° latitude and decreases by about 5% at 52.5° latitude; i.e., the characteristic size is almost latitude independent. The characteristic scale is within 3% of the average value during most times of the solar cycle, but it increases during cycle maximum at latitudes where active regions are present. For the time period 1978-1981 (solar cycle maximum), the length scale increases up to 1.7 Mm or 10% at 30° latitude. In addition, we derive the average amplitude of the crosscorrelation functions, which reflects the diffusion of magnetic elements and their evolutionary changes (including formation and decay). We find an average value of 0.091 ± 0.003 for the crosscorrelation amplitude at a time lag of one day, which we interpret as being caused by the combined effect of the lifetime of magnetic features and a diffusion process. Assuming a lifetime of one day, we find a value of 120 km2 s−1 for the diffusion constant, while a lifetime of two days leads to 230 km2 s−1. Title: Wavelet Analysis of a Magnetogram Authors: Komm, R. W. Bibcode: 1995SoPh..157...45K Altcode: I analyze a quiet-Sun magnetogram with an orthogonal wavelet transform, which allows me to define an entropy measure. The entropy measure of the magnetogram as a function of spatial scale obeys a scaling law, which leads to a fractal dimension ofDf = 1.7. Furthermore, the entropy scaling law is directly related to the intermittency of magnetic features, which increases for decreasing spatial scales, as expected for a turbulent signal. In this context, the scaling law parameter can be interpreted as a fractional reduction in volume from one step of the turbulent cascade to the next. Title: The Application of Spatial and Spectral MEM to OVRO Solar Data Authors: Komm, R. W.; Hurford, G. J.; Gary, D. E. Bibcode: 1995SPD....26.1301K Altcode: 1995BAAS...27..986K No abstract at ADS Title: Hurst Analysis of Mt. Wilson Rotation Measurements Authors: Komm, R. W. Bibcode: 1995SoPh..156...17K Altcode: I study the temporal variation of the solar rotation on time scales shorter than the 11-year cycle by analyzing the daily Mt. Wilson Doppler measurements from 1967 to 1992. The differential rotation is represented by the three coefficients,A, B, andC, of the following expansion:ω =A +B sin2(θ) +C sin4(θ). TheA, B, andC time series show clearly the 11-year solar cycle and they also show high-frequency fluctuations. The Hurst analysis of these time series shows that a Gaussian random process such as observational noise can only account for fluctuations on time scales shorter than 20 days. For time scales from 20 days to 11 years, the variations of A give rise to a Hurst exponent ofH = 0.83, i.e., the variations ofA are `persistent'. The temporal variations ofB show the same behavior asC, which is different fromA. From one to 11 years, theB andC variations are dominated by the 11-year cycle, while for time lags shorter than about 250 days, theB andC fluctuations give rise to a Hurst exponent ofH = 0.66, which lies betweenH = 1/2, of a Gaussian random process, and the exponent of the persistent process shown byA. An analysis of the equivalent coefficients of the first three even Legendre polynomials, computed usingA, B, andC, provides additional information. For time scales between 100 and 1000 days, the ranges,R/S, of Legendre polynomial coefficients decrease with increasing order of the polynomials which suggests that the persistent process operates mainly on large spatial scales. The Hurst exponent ofH = 0.83 for variations inA is the same asH for monthly sunspot numbers with time scales between 6 months and 200 years and for14C radiocarbon data with time scales between 120 years and 3000 years, previously analyzed by other authors. The combined results imply that the underlying solar process shows the same persistent behavior for time scales as short as about 20 days up to time scales of a few thousand years. Title: The Covariance of Latitudinal and Longitudinal Motions of Small Magnetic Features Authors: Komm, R. W.; Howard, R. F.; Harvey, J. W. Bibcode: 1994SoPh..151...15K Altcode: We study the covariance of longitudinal and latitudinal motions of small magnetic features after subtracting long-term averages of differential rotation and meridional flow. The covariance is generally interpreted as Reynolds stress and linked to the equatorward transport of angular momentum. Using high-resolution magnetograms taken daily with the NSO Vacuum Telescope on Kitt Peak, we determine large-scale motions by a two-dimensional crosscorrelation analysis of pairs of consecutive daily observations from which active regions are excluded, i.e., we analyze the motions of small magnetic features. In the present work, we focus on 107 day pairs obtained during the year 1988 and on 472 day pairs taken in selected intervals from 1978 to 1990. We find that all covariance values are very small (below 250 m2 s−2), which is about one to two orders of magnitude smaller than the values from sunspot measurements derived by other authors. At active region latitudes, the masking process increases the noise, which increases the chance that the covariances at these latitudes are not significantly different from zero. We find that the results depend strongly on the temporal averaging involved. Daily unaveraged crosscorrelations lead to no apparent correlation between the residual velocities, while in the monthly averages of the 1988 data, we find a covariance of −37 ± 15 m2 s−2 at 45° with a linear correlation of −0.59, which is significantly different from zero and has the right sign for an equatorial transport of angular momentum. When we average over longer time periods, the covariance values decrease again. The annual averages of the 1978-1990 data show both no significant covariances and the smallest errors. These small covariances imply that the motions of small magnetic features do not reflect the transport of angular momentum via the mechanism of Reynolds stress. Title: Meridional Flow and Rotation of Active Regions Authors: Komm, R. W. Bibcode: 1994SoPh..149..417K Altcode: Meridional flow and rotation are studied using high-resolution magnetograms taken during the year 1988 with the NSO Vacuum Telescope on Kitt Peak. Motions are determined by a two-dimensional crosscorrelation analysis of 107 pairs of consecutive daily observations. The analysis was done first with active regions included and repeated with active regions excluded. The difference between the two analyses provides an estimate of the motions of active regions. I find that active regions rotate slower than small magnetic features and that active regions show a meridional flow toward the mean latitude of activity. Title: Wavelet Analysis of Active Regions Authors: Komm, Rudolf W. Bibcode: 1994ASPC...68...24K Altcode: 1994sare.conf...24K No abstract at ADS Title: Wavelet Analysis of Solar Magnetic Structures Authors: Komm, Rudolf W. Bibcode: 1994ASPC...64..432K Altcode: 1994csss....8..432K No abstract at ADS Title: Solar non-rotational motions Authors: Komm, R. W.; Howard, R. F.; Harvey, J. W. Bibcode: 1994smf..conf...68K Altcode: No abstract at ADS Title: Dynamics of the solar granulation. Authors: Nesis, A.; Hanslmeier, A.; Hammer, R.; Komm, R.; Mattig, W.; Staiger, J. Bibcode: 1993A&A...279..599N Altcode: This investigation is based on a series of spectrograms of extraordinary spatial resolution taken with the vacuum tower telescope (VTT) at Izana (Tenerife) in 1990. The quantitative analysis of these spectrograms reveals an asymmetrical character of the granular flow (non-Benard like convection). We suggest that a typical granule consists of a region of high intensity and low turbulence in its interior and a region of high turbulence and moderate intensity at its border. In other words, we surmise that reigons of enhanced turbulence outline the borders of granules. By means of power and coherence analyses we found two different scaling laws for the small scale range: both the velocity and intensity power as well as various cross-correlation functions change their behavior near log k approximately = 0.8. Title: Meridional Flow of Small Photospheric Magnetic Features Authors: Komm, R. W.; Howard, R. F.; Harvey, J. W. Bibcode: 1993SoPh..147..207K Altcode: We study the meridional flow of small magnetic features, using high-resolution magnetograms taken from 1978 to 1990 with the NSO Vacuum Telescope on Kitt Peak. Latitudinal motions are determined by a two-dimensional crosscorrelation analysis of 514 pairs of consecutive daily observations from which active regions are excluded. We find a meridional flow of the order of 10 m s−1, which is poleward in each hemisphere, increases in amplitude from 0 at the equator, reaches a maximum at mid-latitude, and slowly decreases poleward. The average observed meridional flow is fit adequately by an expansion of the formM (θ) = 12.9(±0.6) sin(2θ) + 1.4(±0.6) sin(4θ), in m s−1 whereθ is the latitude and which reaches a maximum of 13.2 m s−1 at 39°. We also find a solar-cycle dependence of the meridional flow. The flow remains poleward during the cycle, but the amplitude changes from smaller-than-average during cycle maximum to larger-than-average during cycle minimum for latitudes between about 15° and 45°. The difference in amplitude between the flows at cycle minimum and maximum depends on latitude and is about 25% of the grand average value. The change of the flow amplitude from cycle maximum to minimum occurs rapidly, in about one year, for the 15-45° latitude range. At the highest latitude range analyzed, centered at 52.5°, the flow is more poleward-than-average during minimumand maximum, and less at other times. These data show no equatorward migration of the meridional flow pattern during the solar cycle and no significant hemispheric asymmetry. Our results agree with the meridional flow and its temporal variation derived from Doppler data. They also agree on average with the meridional flow derived from the poleward migration of the weak large-scale magnetic field patterns but differ in the solar-cycle dependence. Our results, however, disagree with the meridional flow derived from sunspots or plages. Title: The Covariance of Latitudinal and Longitudinal Motions of Small Magnetic Features Authors: Komm, R. W.; Howard, R. F.; Harvey, J. W. Bibcode: 1993BAAS...25.1220K Altcode: No abstract at ADS Title: Rotation Rates of Small Magnetic Features from Two-Dimensional and One-Dimensional Cross-Correlation Analyses Authors: Komm, R. W.; Howard, R. F.; Harvey, J. W. Bibcode: 1993SoPh..145....1K Altcode: We present results of an analysis of 628 high-resolution magnetograms taken daily with the NSO Vacuum Telescope on Kitt Peak from 1975 to 1991. Motions in longitude on the solar surface are determined by a two-dimensional cross-correlation analysis of consecutive day pairs. We find that the measured rotation rate of small magnetic features, i.e., excluding active regions, is in excellent agreement with the results of the previous one-dimensional analysis of the same data (Komm, Howard, and Harvey, 1993). The polynomial fits show magnetic torsional oscillations, i.e., a more rigid rotation during cycle maximum and a more differential rotation during cycle minimum, but with smaller amplitudes than the one-dimensional analysis. The full width at half maximum of the cross-correlations is almost constant over latitude which shows that the active regions are effectively excluded. The agreement between the one- and two-dimensional cross-correlation analyses shows that the two different techniques are consistent and that the large-scale motions can be divided into rotational and meridional components that are not affected by each other. Title: Rapid Variations in the Intergranular Space Authors: Nesis, A.; Hanslmeier, A.; Hammer, R.; Komm, R.; Mattig, W.; Staiger, J. Bibcode: 1993ASPC...46..222N Altcode: 1993mvfs.conf..222N; 1993IAUCo.141..222N No abstract at ADS Title: Torsional Oscillations and Internal Rotation Authors: Komm, R. W.; Harvey, J. W.; Howard, R. F. Bibcode: 1993ASPC...42..269K Altcode: 1993gong.conf..269K No abstract at ADS Title: Torsional Oscillation Patterns in Photospheric Magnetic Features Authors: Komm, R. W.; Howard, R. F.; Harvey, J. W. Bibcode: 1993SoPh..143...19K Altcode: We analyzed 689 high-resolution magnetograms taken daily with the NSO Vacuum Telescope on Kitt Peak from 1975 to 1991. Motions in longitude on the solar surface are determined by a one-dimensional crosscorrelation analysis of consecutive day pairs. The main sidereal rotation rate of small magnetic features is best fit byω = 2.913(±0.004) − 0.405(±0.027) sin2φ − 0.422(±0.030) sin4φ, in µrad s−1, whereφ is the latitude. Small features and the large-scale field pattern show the same general cycle dependence; both show a torsional oscillation pattern. Alternating bands of faster and slower rotation travel from higher latitudes toward the equator during the solar cycle in such a way that the faster bands reach the equator at cycle minimum. For the magnetic field pattern, the slower bands coincide with larger widths of the crosscorrelations (corresponding to larger features) and also with zones of enhanced magnetic flux. Active regions thus rotate slower than small magnetic features. This magnetic torsional oscillation resembles the pattern derived from Doppler measurements, but its velocities are larger by a factor of more than 1.5, it lies closer to the equator, and it leads the Doppler pattern by about two years. These differences could be due to different depths at which the different torsional oscillation indicators are rooted. Title: Solar Meridional Flow Detected in Small Magnetic Features Authors: Komm, R. W.; Howard, R. F.; Harvey, J. W. Bibcode: 1992AAS...181.8102K Altcode: 1992BAAS...24.1252K We present results of an analysis of 514 high-resolution magnetograms taken daily with the NSO Vacuum Telescope on Kitt Peak from 1978 to 1990. Motions in latitude on the solar surface are determined by a two-dimensional crosscorrelation analysis of consecutive day pairs after excluding large active regions. We find a meridional flow of the order of 10 ms(-1) , which is poleward in each hemisphere, increases in amplitude from 0 at the equator, reaches a maximum at mid-latitude, and slowly decreases poleward. The average meridional flow is fit by an expansion of derivatives of even Legendre polynomials $M(theta ) = 8.88 (+/- 0.45) {{partial P_2}/{partial theta }} - 0.66 (+/-0.26) {{partial P_4}/{partial theta }} in ms^{-1}\ where \theta is the latitude, which reaches a maximum of 13.2 ms^{-1}\ at 39 deg. We also find a solar cycle dependence of the meridional flow. The flow remains poleward during the cycle, but the amplitude (at latitudes poleward of 20 deg) changes from smaller-than-average during maximum to larger-than-average during minimum. The meridional flow fit of the maximum activity years 1980--1982 peaks at 10.9 ms^{-1}, while the fit of the minimum years 1984--1986 reaches a maximum velocity of 14.5 ms^{-1}$; the difference is about 27% of the average value. Title: Crosscorrelation Analysis of Small Photospheric Magnetic Features Authors: Komm, Rudolf W.; Howard, Robert F.; Harvey, John W. Bibcode: 1992AAS...180.5110K Altcode: 1992BAAS...24..815K We present results of an analysis of high-resolution magnetograms taken daily with the NSO Vacuum Telescope on Kitt Peak from 1975 to 1991. Motions in longitude on the solar surface are determined by a one-dimensional crosscorrelation analysis of consecutive day pairs. The mean sidereal rotation rate of small magnetic features is best fit by $omega = 2.913 (+/- 0.004) -0.405 (+/- 0.027) sin(2phi ) -0.422 (+/- 0.030) sin(4phi ) in \mu rad s^{-1} where \phi$ is the latitude. The small features show a torsional oscillation pattern; alternating bands of faster and slower rotation travel from higher latitudes toward the equator during the solar cycle in such a way that the faster bands reach the equator at cycle minimum. The magnetic torsional oscillation resembles the pattern derived from Doppler measurements, but is different in three respects. Its velocities are larger by a factor of more than 1.5, it lies closer to the equator, and leads the Doppler pattern by about two years. Motions in longitude and also in latitude are determined by a two-dimensional crosscorrelation analysis. The mean sidereal rotation rate of the two-dimensional analysis is in excellent agreement with the one-dimensional rate which assures the robustness of the two-dimensional analysis. In latitude, we find meridional motions of the order of 10 m/s which are poleward in each hemisphere. Title: What are the Boundaries of Solar Granules? Authors: Nesis, A.; Hanslmeier, A.; Hammer, R.; Komm, R.; Mattig, W.; Staiger, J. Bibcode: 1992AAS...180.5109N Altcode: 1992BAAS...24..814N This investigation is based on a series of spectrograms of extraordinary spatial resolution taken with the vacuum tower telescope(VTT) at Iza\ na (Tenerife) in 1990. The quantitative analysis of these spectrograms revealed an asymmetrical character of the granular flow (non-Benard like convection). The intensity maximum and the maximum of the upward line-of-sight velocity do not coincide. In most cases the maximum of the velocity lies near the border of the granule and falls rapidly to the adjacent intergranular lane(from 1.5 to 0.2kmsec(-1) over 200km), but moderately towards the other intergranular lane. In some granules the position with zero velocity coincides with the position of highest intensity, whereas maxima of velocities with different signs lie at their border, thus reflecting a typical velocity profile of a rotating eddy. The low correlation(of less than 0.5) between intensity and Doppler velocity fluctuations along the spectrograph slit reflects the asymmetric character of the solar granular flow. Concerning the border of granules we find that bright regions often exhibit downward, instead of the expected upward velocity. Moreover, by investigating the broadening of a non-magnetically sensitive line, we were able to localize regions with enhanced turbulence within the intergranular space. We find that these regions do not always cover the whole intergranular lane, but are concentrated at the border of the granules, especially where the steep decrease of the velocity takes place. On the basis of these findings we suggest that a typical granule consists of a region of high intensity and low turbulence in its interior and a region of high turbulence and moderate intensity at its border. In other words, we surmise that regions of enhanced turbulence outline the borders of granules. Using our time series of spectrograms, which were taken every 15sec over a total of 5min, we followed the dynamics of these properties and the evolution of the steep intensity and velocity changes along the slit. These changes are connected with shear instabilities and turbulence production. The findings from non-active regions will be compared with those from active regions based on magnetically sensitive lines. Title: Velocity Fluctuations; Energy Dissipation in the Solar Photosphere Authors: Komm, R.; Mattig, W.; Nesis, A. Bibcode: 1992ASPC...26..175K Altcode: 1992csss....7..175K No abstract at ADS Title: Rotation Rate Determined from Small Photospheric Magnetic Features Authors: Komm, R. W.; Howard, R. F.; Harvey, J. W.; Forgach, S. Bibcode: 1992ASPC...27..325K Altcode: 1992socy.work..325K No abstract at ADS Title: Dynamics of the solar granulation. I - A phenomenological approach Authors: Nesis, A.; Hanslmeier, A.; Hammer, R.; Komm, R.; Mattig, W.; Staiger, J. Bibcode: 1992A&A...253..561N Altcode: High-spatial-resolution spectrograms taken with the vacuum tower telescope in Tenerife were used to investigate the dynamics of the deep photospheric layers by tracing the motions of small-scale structures such as granulation. Based on a time series of these spectrograms, traces of line Doppler shifts were detected which show strong asymmetries within solar granules. The results are discussed within the framework of different granulation flow models. Title: The decay of granular motions and the generation of gravity waves in the solar photosphere Authors: Komm, R.; Mattig, W.; Nesis, A. Bibcode: 1991A&A...252..827K Altcode: The solar photosphere was investigated using a coherence analysis of rms-velocities. Results confirm that there is a distiction between the granular structures of the lower photosphere and the secondary structures of the higher photosphere. It is shown that the conversion of motions occurs well below a height of 200 km. In the layers of the higher photosphere (above 170 km) structures are found in the wavenumber range from 2.5 M/m to 7.0 M/m with a dominant scale of about 4.0 M/m. It is concluded that secondary motions are generated by decaying granular motions. Title: The height dependence of velocity-intensity fluctuations and several non-dimensional parameters in the solar photosphere Authors: Komm, R.; Mattig, W.; Nesis, A. Bibcode: 1991A&A...252..812K Altcode: The quiet photosphere was studied using autocorrelation functions (ACFs) of intensity-velocity fluctuations. It is found that all ACFs get broader with height for the whole center-to-limb variation. For the length scale L, there is no significant center-to-limb variation but a general height dependence. In the lower photospheric layers (less than 150 km), L is of the order of 500 km, while in the higher layers L increases to 700 km. The vorticity is found to be 0.025/s in the lower photosphere and 0.001/s in the higher layers. The height dependence of several independent nondimensional parameters has been deduced to study the effect of dissipative processes on the granular motions. The Reynolds number is found to decrease from 5 x 10 exp 9 at the continuum layers to 10 exp 8 at the temperature minimum; the Peclet number decreases from 70 to 1; and the magnetic Reynolds number is of the order of 500,000. It is concluded that granules are buoyantly rising turbulent structures which disintegrate due to turbulent mixing with the environment. Title: Granulation Spectroscopy: First Results from VTT-Tenerife Authors: Nesis, A.; Hanslmeier, A.; Hammer, R.; Komm, R.; Mattig, W.; Staiger, J. Bibcode: 1991BAAS...23R1048N Altcode: No abstract at ADS Title: The small-scale velocity field in the solar photosphere Authors: Komm, R.; Mattig, W.; Nesis, A. Bibcode: 1991A&A...243..251K Altcode: The center-to-limb variation of velocity fluctuations derived from several spectral lines is presented and, from these data, the height dependence of the vertical and horizontal components of the small-scale velocity field is deduced. A strong decrease in the lower photosphere and a flat gradient in the upper photosphere are observed for both the horizontal and vertical velocity. It is concluded that the convective motions decay in the middle photosphere up to a height of about 170 km and so-called secondary motions dominate the upper layers of the photosphere. A stability criterion is used to interpret this conversion of motions and, by utilizing the Richardson number and several length scales, it is shown that the stable stratification of the photosphere causes the decay of the granular convective motions. Title: On the Dynamics of Granulation in Active Regions and the Heating Problem (With 2 Figures) Authors: Nesis, A.; Hanslmeier, A.; Hammer, R.; Komm, R.; Mattig, W. Bibcode: 1991mcch.conf...36N Altcode: No abstract at ADS Title: The height dependence of intensity structures in the solar photosphere Authors: Komm, R.; Mattig, W.; Nesis, A. Bibcode: 1990A&A...239..340K Altcode: The results are presented of a power and coherence analysis of intensity variations derived from the wings of the solar Mg b2 line. It is found that the power spectra can be represented by a power law function in the range of wavenumbers between 2.8/Mm. The deep photosphere shows the Kolmogorov (-5/3)-scaling law. The values of the exponent and also of the rms intensity itself decrease with height, attain a minimum, and increase again. While small structures are coherent up to higher photospheric layers, the coherence of the larger structures breaks down in the same layer where the rms intensity shows its minimum. It is concluded that the large intensity structures reflect the effect of convective overshoot, and the breakdown of the coherence reflects the disappearance of convective structures up to a certain height in the photosphere, while the small structures are of turbulent origin. Title: The decay process of the granulation and its influence on the absorption lines. Authors: Nesis, A.; Hanslmeier, A.; Hammer, R.; Komm, R.; Mattig, W. Bibcode: 1990AGAb....5...33N Altcode: No abstract at ADS Title: The Influence of the Granulation on the Absorption Lines I. Nonactive Regions Authors: Nesis, A.; Hanslmeier, A.; Hammer, R.; Komm, R.; Mattig, W. Bibcode: 1990PDHO....7..108N Altcode: 1990ESPM....6..108N; 1990dysu.conf..108N No abstract at ADS Title: Results on the height dependence of granular velocity fluctuations Authors: Komm, R.; Mattig, W. Bibcode: 1989hsrs.conf..330K Altcode: No abstract at ADS Title: Granulare Overshoot-Schichten als Randbedingungen Authors: Nesis, A.; Komm, R.; Mattig, W. Bibcode: 1986MitAG..67..289N Altcode: No abstract at ADS Title: Einiges zur Streulichtkorrektur Authors: Komm, R.; Hessenbruch, A.; Mattig, W. Bibcode: 1986MitAG..67..286K Altcode: No abstract at ADS Title: Balmerlinien in Sonnenflecken Authors: Komm, R. Bibcode: 1983MitAG..60..279K Altcode: No abstract at ADS