Author name code: scherrer ADS astronomy entries on 2022-09-14 author:"Scherrer, Philip H." ------------------------------------------------------------------------ Title: Solar Toroidal Field Evolution Spanning Four Sunspot Cycles Seen by the Wilcox Solar Observatory, the Solar and Heliospheric Observatory/Michelson Doppler Imager, and the Solar Dynamics Observatory/Helioseismic and Magnetic Imager Authors: Liu, Allison L.; Scherrer, Philip H. Bibcode: 2022ApJ...927L...2L Altcode: 2022arXiv220406012L Forty-four years of Wilcox Solar Observatory, 14 years of Michelson Doppler Imager on the Solar and Heliospheric Observatory, and 11 years of Helioseismic and Magnetic Imager on the Solar Dynamics Observatory magnetic field data have been studied to determine the east-west inclination-the toroidal component-of the magnetic field. Maps of the zonal averaged inclination show that each toroidal field cycle begins at around the same time at high latitudes in the northern and southern hemispheres, and ends at the equator. Observation of these maps also shows that each instance of a dominant toroidal field direction starts at high latitudes near sunspot maximum and is still visible near the equator well past the minimum of its cycle, indicating that the toroidal field cycle spans approximately two sunspot cycles. The length of the extended activity cycle is measured to be approximately 16.8 yr. Title: Solar Toroidal Field Evolution Spanning Four Sunspot Cycles Seen By WSO, SOHO/MDI, and SDO/HMI Authors: Scherrer, Philip; Liu, Allison Bibcode: 2021AGUFMSH55D1874S Altcode: Forty-four years of Wilcox Solar Observatory (WSO), fourteen years of Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO), and eleven years of Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) magnetogram data have been studied to determine the east-west inclination, the toroidal component of the magnetic field. Maps of the east-west zonal averaged inclination produced by this study shows that each toroidal field cycle begins at around the same time at high latitudes in the Northern and Southern Hemispheres, and ends at the equator. Observation of these maps also show that each instance of a dominant toroidal field direction starts at high latitudes near sunspot maximum and is still visible near the equator well past the minimum of its cycle, indicating that the toroidal field cycle spans approximately 2 sunspot cycles. This supports earlier reports of the extended magnetic cycles. Title: The Multiview Observatory for Solar Terrestrial Science (MOST) Authors: Gopalswamy, Nat; Kucera, Therese; Leake, James; MacDowall, Robert; Wilson, Lynn; Kanekal, Shrikanth; Shih, Albert; Christe, Steven; Gong, Qian; Viall, Nicholeen; Tadikonda, Sivakumar; Fung, Shing; Yashiro, Seiji; Makela, Pertti; Golub, Leon; DeLuca, Edward; Reeves, Katharine; Seaton, Daniel; Savage, Sabrina; Winebarger, Amy; DeForest, Craig; Desai, Mihir; Bastian, Tim; Lazio, Joseph; Jensen, P. E., C. S. P., Elizabeth; Manchester, Ward; Wood, Brian; Kooi, Jason; Wexler, David; Bale, Stuart; Krucker, Sam; Hurlburt, Neal; DeRosa, Marc; Pevtsov, Alexei; Tripathy, Sushanta; Jain, Kiran; Gosain, Sanjay; Petrie, Gordon; Kholikov, Shukirjon; Zhao, Junwei; Scherrer, Philip; Woods, Thomas; Chamberlin, Philip; Kenny, Megan Bibcode: 2021AGUFMSH12A..07G Altcode: The Multiview Observatory for Solar Terrestrial Science (MOST) is a comprehensive mission concept targeting the magnetic coupling between the solar interior and the heliosphere. The wide-ranging imagery and time series data from MOST will help understand the solar drivers and the heliospheric responses as a system, discerning and tracking 3D magnetic field structures, both transient and quiescent in the inner heliosphere. MOST will have seven remote-sensing and three in-situ instruments: (1) Magnetic and Doppler Imager (MaDI) to investigate surface and subsurface magnetism by exploiting the combination of helioseismic and magnetic-field measurements in the photosphere; (2) Inner Coronal Imager in EUV (ICIE) to study large-scale structures such as active regions, coronal holes and eruptive structures by capturing the magnetic connection between the photosphere and the corona to about 3 solar radii; (3) Hard X-ray Imager (HXI) to image the non-thermal flare structure; (4) White-light Coronagraph (WCOR) to seamlessly study transient and quiescent large-scale coronal structures extending from the ICIE field of view (FOV); (5) Faraday Effect Tracker of Coronal and Heliospheric structures (FETCH), a novel radio package to determine the magnetic field structure and plasma column density, and their evolution within 0.5 au; (6) Heliospheric Imager with Polarization (HIP) to track solar features beyond the WCOR FOV, study their impact on Earth, and provide important context for FETCH; (7) Radio and Plasma Wave instrument (M/WAVES) to study electron beams and shocks propagating into the heliosphere via passive radio emission; (8) Solar High-energy Ion Velocity Analyzer (SHIVA) to determine spectra of electrons, and ions from H to Fe at multiple spatial locations and use energetic particles as tracers of magnetic connectivity; (9) Solar Wind Magnetometer (MAG) to characterize magnetic structures at 1 au; (10) Solar Wind Plasma Instrument (SWPI) to characterize plasma structures at 1 au. MOST will have two large spacecraft with identical payloads deployed at L4 and L5 and two smaller spacecraft ahead of L4 and behind L5 to carry additional FETCH elements. MOST will build upon SOHO and STEREO achievements to expand the multiview observational approach into the first half of the 21st Century. 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: 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: A Method for the Estimation of f- and p-mode Parameters and Rotational Splitting Coefficients from Un-averaged Solar Oscillation Power Spectra Authors: Reiter, J.; Rhodes, E. J., Jr.; Kosovichev, A. G.; Scherrer, P. H.; Larson, T. P.; , S. F. Pinkerton, II Bibcode: 2020ApJ...894...80R Altcode: We present a new methodology for the fitting of the peaks in solar oscillation power spectra that is equally well-suited for the estimation of low-, medium, and high-degree f- and p-mode parameters and frequency-splitting coefficients. The method can provide accurate input data over a wide portion of the dispersion plane for both structural and rotational inversions. This method, which we call the Multiple-Peak, Tesseral-Spectrum (MPTS) method, operates directly upon of all of the modes in a multiplet (n, l) of radial order n and degree l, and employs a fitting profile that consists of the sum of numerous individual overlapping profiles whose relative amplitudes are determined by the leakage matrix appropriate to the targeted mode. Hence, 2l + 1 sets of modal parameters are obtained simultaneously for each multiplet (n, l). By fitting an appropriate polynomial to the run of the fitted frequencies versus the azimuthal order, frequency-splitting coefficients are also obtained for the same multiplet. Using power spectra obtained from the 66 day long 2010 MDI Dynamics Run, we present sample structural and rotational inversions that employed frequencies and frequency-splitting coefficients from modes in the degree range of 0-1000 and the frequency range of 965-4600 μHz. The structural inversion confirms evidence for a pronounced departure of the sound speed in the outer solar convection zone from the radial sound-speed profile contained in Model S of Christensen-Dalsgaard and his collaborators that we obtained previously using a different fitting method. Title: Observations about Observations of the Sun Authors: Scherrer, Philip H. Bibcode: 2019AAS...23412701S Altcode: After more than 50 years as an observer of the Sun, of the process of observing the Sun, and of the people who participate in the adventure I will offer some comments about what I have learned. Title: What do we reliably know about how fast the Sun's core spins? Authors: Scherrer, Philip H.; Gough, Douglas Bibcode: 2019AAS...23430206S Altcode: Fossat et al. (2017) and Fossat & Schmider (2018) have attempted to use solar p-mode frequency perturbations to detect rotational splitting of g-modes. They claim that this approach detected the Sun's core to be rotating about 3.8 times faster than the surrounding radiative interior and the convection zone. We report an independent study of the technique, the inconsistencies with the well-established p-mode determinations of rotation, and with their assumption of which g-modes might be sensed. Additionally we used both the same calibrated 80s SOHO/GOLF data used in the 2017 study and the then only publically available GOLF 60s cadence data and verified the findings of Schunker et al. (2018) that the g-mode detection was fragile: It vanished when the GOLF data was sampled at the 60s vs 80s cadence and when the starting point was shifted by 2 hours of the 15 years studied. We also applied the same technique to all other available long duration low-degree data collections including SOHO/MDI, SOHO/LOI, SDO/HMI, GONG, and BiSON and found no evidence of the Fossat et al. (2017) reported signals. We note that a second independent study by Appourchaux & Corbard (2019) came to the same conclusions. Thus we doubt the validity of the 2017 findings and conclude that there is no useful information about the rotation of the solar core yet determined using these techniques (Scherrer & Gough, 2019). References: Appourchaux, T., & Corbard, T. 2019, Submitted to A&A, Fossat, E., Boumier, P., Corbard, T., et al. 2017, A&A, 604, A40, Fossat, E., & Schmider, F. X. 2018, A&A, 612, L1, Scherrer, P. & Gough, D., Accepted by ApJ, 2019, Schunker, H., Schou, J., Gaulme, P., & Gizon, L. 2018, SoPh, 293, 95 Title: A Makeover for HMI Magnetic Field Data Authors: Hoeksema, Jon Todd; Liu, Yang; Scherrer, Philip H. Bibcode: 2019AAS...23410613H Altcode: HMI, the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory (SDO) has measured the Sun's vector magnetic field nearly every 135 or 90 seconds since May 2010. The Stokes parameters are determined from sets of filtergrams every 720 seconds over the full disk. The quality of the images is remarkably uniform and the measurements are reliable for many types of analysis. However, the inverted and disambiguated magnetic field values are occasionally incorrect, show small periodic variations with time and spacecraft velocity, or depend in a systematic way on disk position or magnitude. Estimates of uncertainties in the inversion are provided for each point, but for some kinds of analysis having a smoother and more uniform time series is necessary.

Sources of some errors are well understood and well characterized, but others are not. Statistical and empirical techniques have been developed by the HMI Team and others to improve both the calibration and appearance of the observations, to increase consistency, and minimize undesirable variability. Effects addressed include issues related to field inversion, disambiguation, sensitivity, optical distortion, instrument characteristics, and systematic errors due to spacecraft velocity and viewing angle. Some of the most reliable and affordable corrections are included in the regular analysis pipeline. Some corrections are too compute intensive to implement routinely. For others the resulting 'corrections' depend on assumptions about the typical behavior of the solar magnetic field, so care must be taken when using such results. Title: A Critical Evaluation of Recent Claims Concerning Solar Rotation Authors: Scherrer, P. H.; Gough, D. O. Bibcode: 2019ApJ...877...42S Altcode: 2019arXiv190402820S Fossat et al. recently reported detecting rotational splitting of g-modes indirectly via the interaction with p-modes observed directly by the Global Oscillations at Low Frequency (GOLF) instrument on the Solar and Heliospheric Observatory (SOHO). They concluded that the core of the Sun is rotating 3.8 ± 0.1 times faster than the surrounding radiative envelope. This is startling, partly because such rapid rotation almost contradicts direct inferences from the p-mode rotational splitting inferred from the same data. Moreover, the inferred amplitudes of the g-modes appear to exceed the upper bound reported by Appourchaux et al. It is also suspect because the theory of the procedure implies that the principal modes claimed to have been measured should be undetectable. We point out that there are other interpretations: one leads to a core rotation about twice as fast as the surrounding envelope; another, to a core rotating more slowly than the envelope. Here we also report on an independent assessment of the Fossat et al. analysis by applying their procedure to different representations of the GOLF data, expanding on Schunker et al. We also analyze seismic data obtained from LOI and MDI (both also on SOHO), from HMI (on SDO), and from the ground-based BiSON and GONG, and we find the evidence reported by Fossat et al. not to be robust. We also illustrate that merely fitting model spectra to observations, which Fossat et al. do to support their g-mode detections, and as Fossat & Schmider do for extracting additional g-mode splittings, is not necessarily reliable. We are therefore led to doubt the claim. Title: HMI Data Corrected for Scattered Light Compared to Hinode SOT-SP Data Authors: Norton, A. A.; Duvall, T. L., Jr.; Schou, J.; Cheung, M. C. M.; Scherrer, P. H.; Chu, K. C.; Sommers, J. Bibcode: 2018csc..confE.101N Altcode: In March 2018, the Helioseismic Magnetic Imager (HMI) team began providing full-disk data to the public on a daily basis that were corrected for scattered light. In addition to the intensity and magnetogram data, the improved vector magnetic field maps are also provided. The process uses a Richardson-Lucy algorithm and a known PSF. The deconvolution results in a few percent decrease in umbral intensity corresponding to a 200 K decrease in temperature, a doubling of the intensity contrast of granulation from 3.6 to 7.2%, an increase in total field strength values (not only line-of-sight B) in plage by 1.4, faculae brightening and network darkening, and a partial correction for the convective blue-shift. The new data series can be found in JSOC with names similar to the original but with the qualifying term '_dcon' or '_dconS' appended (denoting whether the deconvolution was applied to the filtergrams or Stokes images). Comparisons to near-simultaneous Hinode SOT-SP data demonstrate that the correction brings the two instruments into much better agreement, including the inverted magnetic field parameters. We compare our results to similar efforts in the literature such as work by Diaz Baso and Asensio Ramos (2018) in which HMI intensity and magnetogram data was enhanced using neural networks and super-resolution. Title: Soothing Massage of HMI Magnetic Field Data Authors: Hoeksema, J. Todd; Liu, Yang; Sun, Xudong; Scherrer, Philip; HMI Science Team Bibcode: 2018csc..confE...7H Altcode: The Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) has measured solar polarization at six wavelengths across the Fe I 6173 spectral line with one arc second resolution nearly every 90 or 135 seconds since May 2010, and the Stokes parameters are determined every 720 seconds over the full disk. The quality of the filtergrams is remarkably uniform, but the inverted and disambiguated magnetic field values are sometime incorrect or show small systematic variations with time and space. Estimates of the numerical uncertainties are provided for each pixel, but, for some kinds of analysis, having a smoother and more uniform time series can be useful. This report describes methods that can be used to 'massage' the observations to improve consistency and appearance and minimize unwanted variability. Effects considered include issues related to field inversion, disambiguation, instrument sensitivity, optical distortion, and systematic errors due to spacecraft velocity. The resulting 'corrections' typically depend on assumptions about the behavior of the solar magnetic field, so care must be taken when using such results. Title: Statistical Analysis of Acoustic Wave Power and Flows around Solar Active Regions Authors: Rabello-Soares, M. Cristina; Bogart, Richard S.; Scherrer, Philip H. Bibcode: 2018csc..confE..51R Altcode: We analyze the effect of a sunspot in its quiet surroundings applying a helioseismic technique on almost three years of Helioseismic and Magnetic Imager (HMI) observations obtained during solar cycle 24 to further study the sunspot structure below the solar surface. The attenuation of acoustic waves with frequencies lower than 4.2 mHz depends more strongly on the wave direction at a distance of 6°-7° from the sunspot center. The amplification of higher frequency waves is highest 6° away from the active region and is largely independent of the wave's direction. We observe a mean clockwise flow around active regions, the angular speed of which decreases exponentially with distance and has a coefficient close to -0.7 degree-1. The observed horizontal flow in the direction of the nearby active region agrees with a large-scale circulation around the sunspot in the shape of cylindrical shell. The center of the shell seems to be centered around 7° from the sunspot center, where we observe an inflow close to the surface down to ∼2 Mm, followed by an outflow at deeper layers until at least 7 Mm. Title: Classifying Signatures of Sudden Ionospheric Disturbances Authors: Hegde, Sahil; Bobra, Monica G.; Scherrer, Philip H. Bibcode: 2018RNAAS...2..162H Altcode: 2018RNAAS...2c.162H; 2018arXiv180902742H Solar activity, such as flares, produce bursts of high-energy radiation that temporarily enhance the D-region of the ionosphere and attenuate low-frequency radio waves. To track these Sudden Ionospheric Disturbances (SIDs), which disrupt communication signals and perturb satellite orbits, Scherrer et al. (2008) developed an international, ground-based network of around 500 SID monitors that measure the signal strength of low-frequency radio waves. However, these monitors suffer from a host of noise contamination issues that preclude their use for rigorous scientific analysis. As such, we attempt to create an algorithm to automatically identify noisy, contaminated SID data sets from clean ones. To do so, we develop a set of features to characterize times series measurements from SID monitors and use these features, along with a binary classifer called a support vector machine, to automatically assess the quality of the SID data. We compute the True Skill Score, a metric that measures the performance of our classifier, and find that it is ~0.75+/-0.06. We find features characterizing the difference between the daytime and nighttime signal strength of low-frequency radio waves most effectively discern noisy data sets from clean ones. Title: Statistical Analysis of Acoustic Wave Power and Flows around Solar Active Regions Authors: Rabello-Soares, M. Cristina; Bogart, Richard S.; Scherrer, Philip H. Bibcode: 2018ApJ...859....7R Altcode: 2018arXiv180407791R We analyze the effect of a sunspot in its quiet surroundings applying a helioseismic technique on almost three years of Helioseismic and Magnetic Imager (HMI) observations obtained during solar cycle 24 to further study the sunspot structure below the solar surface. The attenuation of acoustic waves with frequencies lower than 4.2 mHz depends more strongly on the wave direction at a distance of 6°-7° from the sunspot center. The amplification of higher frequency waves is highest 6° away from the active region and is largely independent of the wave’s direction. We observe a mean clockwise flow around active regions, the angular speed of which decreases exponentially with distance and has a coefficient close to -0.7 degree-1. The observed horizontal flow in the direction of the nearby active region agrees with a large-scale circulation around the sunspot in the shape of cylindrical shell. The center of the shell seems to be centered around 7° from the sunspot center, where we observe an inflow close to the surface down to ∼2 Mm, followed by an outflow at deeper layers until at least 7 Mm. Title: On-Orbit Performance of the Helioseismic and Magnetic Imager Instrument onboard the Solar Dynamics Observatory Authors: Hoeksema, J. T.; Baldner, C. S.; Bush, R. I.; Schou, J.; Scherrer, P. H. Bibcode: 2018SoPh..293...45H Altcode: 2018arXiv180201731H The Helioseismic and Magnetic Imager (HMI) instrument is a major component of NASA's Solar Dynamics Observatory (SDO) spacecraft. Since commencement of full regular science operations on 1 May 2010, HMI has operated with remarkable continuity, e.g. during the more than five years of the SDO prime mission that ended 30 September 2015, HMI collected 98.4% of all possible 45-second velocity maps; minimizing gaps in these full-disk Dopplergrams is crucial for helioseismology. HMI velocity, intensity, and magnetic-field measurements are used in numerous investigations, so understanding the quality of the data is important. This article describes the calibration measurements used to track the performance of the HMI instrument, and it details trends in important instrument parameters during the prime mission. Regular calibration sequences provide information used to improve and update the calibration of HMI data. The set-point temperature of the instrument front window and optical bench is adjusted regularly to maintain instrument focus, and changes in the temperature-control scheme have been made to improve stability in the observable quantities. The exposure time has been changed to compensate for a 20% decrease in instrument throughput. Measurements of the performance of the shutter and tuning mechanisms show that they are aging as expected and continue to perform according to specification. Parameters of the tunable optical-filter elements are regularly adjusted to account for drifts in the central wavelength. Frequent measurements of changing CCD-camera characteristics, such as gain and flat field, are used to calibrate the observations. Infrequent expected events such as eclipses, transits, and spacecraft off-points interrupt regular instrument operations and provide the opportunity to perform additional calibration. Onboard instrument anomalies are rare and seem to occur quite uniformly in time. The instrument continues to perform very well. Title: Measuring the Large-scale Solar Magnetic Field Authors: Hoeksema, J. T.; Scherrer, P. H.; Peterson, E.; Svalgaard, L. Bibcode: 2017AGUFMSH51C2497H Altcode: The Sun's large-scale magnetic field is important for determining global structure of the corona and for quantifying the evolution of the polar field, which is sometimes used for predicting the strength of the next solar cycle. Having confidence in the determination of the large-scale magnetic field of the Sun is difficult because the field is often near the detection limit, various observing methods all measure something a little different, and various systematic effects can be very important. We compare resolved and unresolved observations of the large-scale magnetic field from the Wilcox Solar Observatory, Heliseismic and Magnetic Imager (HMI), Michelson Doppler Imager (MDI), and Solis. Cross comparison does not enable us to establish an absolute calibration, but it does allow us to discover and compensate for instrument problems, such as the sensitivity decrease seen in the WSO measurements in late 2016 and early 2017. Title: Stray Light Correction of HMI Data Authors: Norton, Aimee Ann; Duvall, Thomas; Schou, Jesper; Cheung, Mark; Scherrer, Philip H. Bibcode: 2017SPD....4820705N Altcode: The point spread function (PSF) for HMI is an Airy function convolved with a Lorentzian. The parameters are bound by ground-based testing before launch, then post-launch off-limb light curves, lunar eclipse and Venus transit data. The PSF correction is programmed in C and runs within the HMI data processing pipeline environment. A single full-disk intensity image can be processed in less than one second. Deconvolution of the PSF on the Stokes profile data (a linear combination of original filtergrms) is less computationally expensive and is shown to be equivalent to deconvolution applied at the original filtergram level. Results include a decrease in umbral darkness of a few percent (~200 K cooler), a doubling of the granulation contrast in intensity from 3.6 to 7.2%, an increase in plage field strengths by a factor of 1.5, and a partial correction of the convective blueshift in Doppler velocities. Requests for data corrected for stray light are welcome and will be processed by the HMI team. Title: Status update of the effort to correct the SDO/HMI systemmatic errors in Doppler velocity and derived data products Authors: Scherrer, Philip H. Bibcode: 2017SPD....4811003S Altcode: This poster provides an update of the status of the efforts to understand and correct the leakage of the SDO orbit velocity into most HMI data products. The following is extracted from the abstract for the similar topic presented at the 2016 SPD meeting: “The Helioseismic and Magnetic Imager (HMI) instrument on the Solar Dynamics Observatory (SDO) measures sets of filtergrams which are converted into velocity and magnetic field maps. In addition to solar photospheric motions the velocity measurements include a direct component from the line-of-sight component of the SDO orbit. Since the magnetic field is computed as the difference between the velocity measured in left and right circular polarization, the orbit velocity is canceled only if the velocity is properly calibrated. When the orbit velocity is subtracted the remaining "solar" velocity shows a residual signal which is equal to about 2% of the c. +- 3000 m/s orbit velocity in a nearly linear relationship. This implies an error in our knowledge of some of the details of as-built filter components. This systematic error is the source of 12- and 24-hour variations in most HMI data products. While the instrument as presently calibrated (Couvidat et al. 2012 and 2016) meets all of the “Level-1” mission requirements it fails to meet the stated goal of 10 m/s accuracy for velocity data products. For the velocity measurements this has not been a significant problem since the prime HMI goals of obtaining data for helioseismology are not affected by this systematic error. However the orbit signal leaking into the magnetograms and vector magnetograms degrades the ability to accomplish some of the mission science goals at the expected levels of accuracy. This poster presents the current state of understanding of the source of this systematic error and prospects for near term improvement in the accuracy of the filter profile model.” Title: Variation of acoustic mode parameters with distance from a nearby active region Authors: Rabello-Soares, M. Cristina; Bogart, Richard S.; Scherrer, Philip H. Bibcode: 2017SPD....4810905R Altcode: In a previous paper (Rabello-Soares, Bogart & Scherrer 2016), we quantified the influence of magnetic fields on acoustic mode parameters and flows in and around active regions by comparing the differences in the parameters in magnetically quiet regions when there is an active region in their vicinity with those of quiet regions at the same disc locations for which there are no neighboring active regions. Here we detail further our analysis by estimating how these differences vary with distance from the active region. We use ring diagram analysis from almost five years of HMI observations.In our first paper, we observed that the power reduction has a strong dependence on the wave direction but the amplitude enhacement (the `acoustic halo effect') has a very weak dependence on the wave propagation direction. We find that the effect on the amplitude decreases as the distance increases as expected. However, the dependence on the wave direction seems to reach a peak around 70 Mm from the active region. Very near the active region, the amplitude effects are independent of the direction of mode propagation. Title: Helioseismology with Solar Orbiter Authors: Löptien, Björn; Birch, Aaron C.; Gizon, Laurent; Schou, Jesper; Appourchaux, Thierry; Blanco Rodríguez, Julián; Cally, Paul S.; Dominguez-Tagle, Carlos; Gandorfer, Achim; Hill, Frank; Hirzberger, Johann; Scherrer, Philip H.; Solanki, Sami K. Bibcode: 2017hdsi.book..257L Altcode: No abstract at ADS Title: The Olsen Rotating Dipole, Revisited Authors: Svalgaard, L.; Gough, D. O.; Scherrer, P. H. Bibcode: 2016AGUFMSH31B2548S Altcode: Olsen (1948) and Wilcox & Gonzales (1971) reported evidence of a solar equatorial magnetic dipole with a stable (synodic) rotation period of 26 7/8 days maintaining its phase over 15 years (1926-1941, Olsen) and possibly to 1968 as well (1963-1968, Wilcox & Gonzales). Using a composite series of Interplanetary Magnetic Sector Polarities covering the interval 1844-2016 (derived from geomagnetic data before the space age and direct measurements during 1963-2016) we find that 1) the response of geomagnetic activity to passage (at Earth) of a sector boundary has been consistently the same in every solar cycle from 9 through 24, thus validating the inferred times of sector boudary passages over the past 173 years, and 2) the 'Olsen' dipole can be traced back the 16 cycles to the year 1844, albeit with a slightly different synodic rotation period of 26.86 days (431 nHz). Olsen ended his paper with "The persistence of a fixed period during 15 years points to the possibility that the origin of the effect is to be found in a layer on the Sun with a fixed rotation-period during a long time" and Wilcox & Gonzales noted that "A rotating magnetic dipole may be lurking within the sun". We compare the Olsen-period with other evidence for rotation periods in the deep interior and for the existence of a relic magnetic field. Title: Achieving Consistent Vector Magnetic Field Measurements from SDO/HMI Authors: Schuck, P. W.; Antiochos, S. K.; Scherrer, P. H.; Hoeksema, J. T.; Leka, K. D.; Barnes, G. Bibcode: 2016AGUFMSH31B2575S Altcode: NASA's Solar Dynamics Observatory (SDO) is delivering vector magnetic field observations of the full solar disk with unprecedented temporal and spatial resolution; however, the satellite is in a highly inclined geosynchronous orbit. The relative spacecraft-Sun velocity varies by ±3 km/s over a day which introduces significant orbital artifacts in the Helioseismic Magnetic Imager (HMI) data. We have recently demonstrated that the orbital artifacts contaminate all spatial and temporal scales in the data and developed a procedure for mitigating these artifacts in the Doppler data obtained from the Milne-Eddington inversions in the HMI Pipeline. Simultaneously, we have found that the orbital artifacts may be introduced by inaccurate estimates for the free-spectral ranges (FSRs) of the optical elements in HMI. We describe our approach and attempt to minimize orbital artifacts in the hmi.V_720 Dopplergram series by adjusting the FSRs for the optical elements of HMI within their measurement uncertainties of ±1%. Title: HMI Data Corrected for Stray Light Now Available Authors: Norton, A. A.; Duvall, T. L.; Schou, J.; Cheung, M. C. M.; Scherrer, P. H. Bibcode: 2016usc..confE..95N Altcode: The form of the point spread function (PSF) derived for HMI is an Airy function convolved with a Lorentzian. The parameters are bound by observational ground-based testing of the instrument conducted prior to launch (Wachter et al., 2012), by full-disk data used to evaluate the off-limb behavior of the scattered light, as well as by data obtained during the Venus transit. The PSF correction has been programmed in both C and cuda C and runs within the JSOC environment using either a CPU or GPU. A single full-disk intensity image can be deconvolved in less than one second. The PSF is described in more detail in Couvidat et al. (2016) and has already been used by Hathaway et al. (2015) to forward-model solar-convection spectra, by Krucker et al. (2015) to investigate footpoints of off-limb solar flares and by Whitney, Criscuoli and Norton (2016) to examine the relations between intensity contrast and magnetic field strengths. In this presentation, we highlight the changes to umbral darkness, granulation contrast and plage field strengths that result from stray light correction. A twenty-four hour period of scattered-light corrected HMI data from 2010.08.03, including the isolated sunspot NOAA 11092, is currently available for anyone. Requests for additional time periods of interest are welcome and will be processed by the HMI team. Title: MHD Waves at Umbral-Penumbral Boundary Observed with Hinode/SOT-SP and SDO/HMI Authors: Norton, A. A.; Tarbell, T. D.; Scherrer, P. H.; Baldner, C. S. Bibcode: 2016usc..confE.114N Altcode: The conversion of p-modes and other perturbations in the near-surface layers into MHD waves that can propagate along and across magnetic field lines is a topic of interest for energy transport. The photospheric signatures of MHD waves are weak due to low amplitudes at the beta=1 equipartion level where mode-conversion occurs. We report on oscillations observed with Hinode SOT/SP and HMI in which we have time series for sunspots 12186 (11.10.2014) and 12434 (17.10.2015). In the Milne-Eddington inversion results from SP, oscillations in the inclination angle and velocity are found at the umbral-penumbral boundary with 5 minute periods. HMI data also shows distinct umbral-penumbral boundary oscillations consistent with the SP data. We discuss surface versus body modes that might explain these observations. Title: Observables Processing for the Helioseismic and Magnetic Imager Instrument on the Solar Dynamics Observatory Authors: Couvidat, S.; Schou, J.; Hoeksema, J. T.; Bogart, R. S.; Bush, R. I.; Duvall, T. L.; Liu, Y.; Norton, A. A.; Scherrer, P. H. Bibcode: 2016SoPh..291.1887C Altcode: 2016SoPh..tmp..120C; 2016arXiv160602368C NASA's Solar Dynamics Observatory (SDO) spacecraft was launched 11 February 2010 with three instruments onboard, including the Helioseismic and Magnetic Imager (HMI). After commissioning, HMI began normal operations on 1 May 2010 and has subsequently observed the Sun's entire visible disk almost continuously. HMI collects sequences of polarized filtergrams taken at a fixed cadence with two 4096 ×4096 cameras, from which are computed arcsecond-resolution maps of photospheric observables that include line-of-sight velocity and magnetic field, continuum intensity, line width, line depth, and the Stokes polarization parameters [I ,Q ,U ,V ]. Two processing pipelines have been implemented at the SDO Joint Science Operations Center (JSOC) at Stanford University to compute these observables from calibrated Level-1 filtergrams, one that computes line-of-sight quantities every 45 seconds and the other, primarily for the vector magnetic field, that computes averages on a 720-second cadence. Corrections are made for static and temporally changing CCD characteristics, bad pixels, image alignment and distortion, polarization irregularities, filter-element uncertainty and nonuniformity, as well as Sun-spacecraft velocity. We detail the functioning of these two pipelines, explain known issues affecting the measurements of the resulting physical quantities, and describe how regular updates to the instrument calibration impact them. We also describe how the scheme for computing the observables is optimized for actual HMI observations. Initial calibration of HMI was performed on the ground using a variety of light sources and calibration sequences. During the five years of the SDO prime mission, regular calibration sequences have been taken on orbit to improve and regularly update the instrument calibration, and to monitor changes in the HMI instrument. This has resulted in several changes in the observables processing that are detailed here. The instrument more than satisfies all of the original specifications for data quality and continuity. The procedures described here still have significant room for improvement. The most significant remaining systematic errors are associated with the spacecraft orbital velocity. Title: Statistical Analysis of Acoustic Wave Parameters Near Solar Active Regions Authors: Rabello-Soares, M. Cristina; Bogart, Richard S.; Scherrer, Philip H. Bibcode: 2016ApJ...827..140R Altcode: 2016arXiv160608068R In order to quantify the influence of magnetic fields on acoustic mode parameters and flows in and around active regions, we analyze the differences in the parameters in magnetically quiet regions nearby an active region (which we call “nearby regions”), compared with those of quiet regions at the same disk locations for which there are no neighboring active regions. We also compare the mode parameters in active regions with those in comparably located quiet regions. Our analysis is based on ring-diagram analysis of all active regions observed by the Helioseismic and Magnetic Imager (HMI) during almost five years. We find that the frequency at which the mode amplitude changes from attenuation to amplification in the quiet nearby regions is around 4.2 mHz, in contrast to the active regions, for which it is about 5.1 mHz. This amplitude enhacement (the “acoustic halo effect”) is as large as that observed in the active regions, and has a very weak dependence on the wave propagation direction. The mode energy difference in nearby regions also changes from a deficit to an excess at around 4.2 mHz, but averages to zero over all modes. The frequency difference in nearby regions increases with increasing frequency until a point at which the frequency shifts turn over sharply, as in active regions. However, this turnover occurs around 4.9 mHz, which is significantly below the acoustic cutoff frequency. Inverting the horizontal flow parameters in the direction of the neigboring active regions, we find flows that are consistent with a model of the thermal energy flow being blocked directly below the active region. Title: On HMI's Mod-L Sequence: Test and Evaluation Authors: Liu, Yang; Baldner, Charles; Bogart, R. S.; Bush, R.; Couvidat, S.; Duvall, Thomas L.; Hoeksema, Jon Todd; Norton, Aimee Ann; Scherrer, Philip H.; Schou, Jesper Bibcode: 2016SPD....47.0810L Altcode: HMI Mod-L sequence can produce full Stokes parameters at a cadence of 90 seconds by combining filtergrams from both cameras, the front camera and the side camera. Within the 90-second, the front camera takes two sets of Left and Right Circular Polarizations (LCP and RCP) at 6 wavelengths; the side camera takes one set of Linear Polarizations (I+/-Q and I+/-U) at 6 wavelengths. By combining two cameras, one can obtain full Stokes parameters of [I,Q,U,V] at 6 wavelengths in 90 seconds. In norminal Mod-C sequence that HMI currently uses, the front camera takes LCP and RCP at a cadence of 45 seconds, while the side camera takes observation of the full Stokes at a cadence of 135 seconds. Mod-L should be better than Mod-C for providing vector magnetic field data because (1) Mod-L increases cadence of full Stokes observation, which leads to higher temporal resolution of vector magnetic field measurement; (2) decreases noise in vector magnetic field data because it uses more filtergrams to produce [I,Q,U,V]. There are two potential issues in Mod-L that need to be addressed: (1) scaling intensity of the two cameras’ filtergrams; and (2) if current polarization calibration model, which is built for each camera separately, works for the combined data from both cameras. This presentation will address these questions, and further place a discussion here. Title: The Processing of Observables Made by the HMI Instrument on SDO Authors: Hoeksema, Jon Todd; Schou, Jesper; Couvidat, Sebastien; Bogart, Richard S.; Bush, Rock; Duvall, Thomas L.; Liu, Yang; Norton, Aimee Ann; Scherrer, Philip H. Bibcode: 2016SPD....47.0808H Altcode: The Helioseismic and Magnetic Imager (HMI) acquires sequences of polarized filtergrams of the Sun from which observable quantities are computed. The observables include five line-of-sight quantities - magnetic field, velocity, continuum intensity, line depth, and line width - as well as Stokes polarization parameters. The process of turning a set of filtergrams into calibrated measurements is quite involved. Since May 2010 the streams of data from HMI’s two cameras have been treated separately. The frame list for the Doppler camera repeats every 45 seconds and the images are combined to determine the line-of-sight observables. The Vector camera sequence measures additional polarizations and so requires 135s; images from ten sequences are combined every 720s to determine the four Stokes polarization parameters at each of six wavelengths, as well as the LoS observables. A variety of calibration corrections are made to the Level-1 filtergrams to account for distortion, image motion and alignment, polarization, wavelength and intensity irregularities, camera issues, solar rotation, and other effects. Residual random variations in the final observables are consistent with photon noise levels, but systematic errors remain that have not been fully corrected. Of particular concern are those associated with the velocity of the instrument relative to the Sun due to the geosynchronous orbit of the Solar Dynamics Observatory (SDO) spacecraft. This presentation describes the creation of the observables, characterizes the residual errors, and indicates plans for future improvements - including correction for the instrument point spread function. All HMI data are available at http://jsoc.stanford.edu. Title: HMI Measured Doppler Velocity Contamination from the SDO Orbit Velocity Authors: Scherrer, Philip H.; SDO HMI Team Bibcode: 2016SPD....47.0812S Altcode: The Helioseismic and Magnetic Imager (HMI) instrument on the Solar Dynamics Observatory (SDO) measures sets of filtergrams which are converted into velocity and magnetic field maps each 45-seconds with its front camera and each 12 minutes with its side camera. In addition to solar phototspheric motions the velocity measurements include a direct component from the line-of-sight component of the SDO orbit. Since the magnetic field is computed as the difference between the velocity measured in left and right circular polarization the orbit velocity is canceled only if the celocity is properly calibrated. When the orbit component of the velocity is subtracted for each pixel the remaining "solar" velocity shows a residual signal which is equal to about 2% of the c. +- 3000 m/s orbit velocity in a nearly linear relationship. This implies an error in our knowledge of some of the details of as-built filter components. The model instrument transmission profile is required for calibration of all HMI level 1.5 “observable” quantities. This systematic error is very likely the source of 12- and 24-hour variations in most HMI data products. Over the years since launch a substantial effort has been dedicated to understanding the origin of this problem. While the instrument as presently calibrated (Couvidat et al. 2012 and 2016) meets all of the “Level-1” mission requirements it fails to meet the stated goal of 10 m/s accuracy for velocity data products and some not stated but generally assumed goals for other products. For the velocity measurements this has not been a significant problem since the prime HMI goals of obtaining data for helioseismology are not affected by this systematic error. However the orbit signal leaking into the magnetograms and vector magnetograms degrades the ability to accomplish some of the mission science goals at the expected levels of accuracy. This poster presents the current state of understanding of the source of this systematic error and prospects for near term improvement in the accuracy of the filter profile model. Title: Amplitudes of MHD Waves in Sunspots Authors: Norton, Aimee Ann; Cally, Paul; Baldner, Charles; Kleint, Lucia; Tarbell, Theodore D.; De Pontieu, Bart; Scherrer, Philip H.; Rajaguru, Paul Bibcode: 2016SPD....47.1009N Altcode: The conversion of p-modes into MHD waves by strong magnetic fields occurs mainly in the sub-photospheric layers. The photospheric signatures of MHD waves are weak due to low amplitudes at the beta=1 equipartion level where mode-conversion occurs. We report on small amplitude oscillations observed in the photosphere with Hinode SOT/SP in which we analyze time series for sunspots ARs 12186 (11.10.2014) and 12434 (17.10.2015). No significant magnetic field oscillations are recovered in the umbra or penumbra in the ME inversion. However, periodicities in the inclination angle are found at the umbral/penumbral boundary with 5 minute periods. Upward propagating waves are indicated in the intensity signals correlated between HMI and AIA at different heights. We compare SP results with the oscillations observed in HMI data. Simultaneous IRIS data shows transition region brightening above the umbral core. Title: Helioseismology with Solar Orbiter Authors: Löptien, Björn; Birch, Aaron C.; Gizon, Laurent; Schou, Jesper; Appourchaux, Thierry; Blanco Rodríguez, Julián; Cally, Paul S.; Dominguez-Tagle, Carlos; Gandorfer, Achim; Hill, Frank; Hirzberger, Johann; Scherrer, Philip H.; Solanki, Sami K. Bibcode: 2015SSRv..196..251L Altcode: 2014arXiv1406.5435L; 2014SSRv..tmp...31L The Solar Orbiter mission, to be launched in July 2017, will carry a suite of remote sensing and in-situ instruments, including the Polarimetric and Helioseismic Imager (PHI). PHI will deliver high-cadence images of the Sun in intensity and Doppler velocity suitable for carrying out novel helioseismic studies. The orbit of the Solar Orbiter spacecraft will reach a solar latitude of up to 21 (up to 34 by the end of the extended mission) and thus will enable the first local helioseismology studies of the polar regions. Here we consider an array of science objectives to be addressed by helioseismology within the baseline telemetry allocation (51 Gbit per orbit, current baseline) and within the science observing windows (baseline 3×10 days per orbit). A particularly important objective is the measurement of large-scale flows at high latitudes (rotation and meridional flow), which are largely unknown but play an important role in flux transport dynamos. For both helioseismology and feature tracking methods convection is a source of noise in the measurement of longitudinally averaged large-scale flows, which decreases as T -1/2 where T is the total duration of the observations. Therefore, the detection of small amplitude signals (e.g., meridional circulation, flows in the deep solar interior) requires long observation times. As an example, one hundred days of observations at lower spatial resolution would provide a noise level of about three m/s on the meridional flow at 80 latitude. Longer time-series are also needed to study temporal variations with the solar cycle. The full range of Earth-Sun-spacecraft angles provided by the orbit will enable helioseismology from two vantage points by combining PHI with another instrument: stereoscopic helioseismology will allow the study of the deep solar interior and a better understanding of the physics of solar oscillations in both quiet Sun and sunspots. We have used a model of the PHI instrument to study its performance for helioseismology applications. As input we used a 6 hr time-series of realistic solar magneto-convection simulation (Stagger code) and the SPINOR radiative transfer code to synthesize the observables. The simulated power spectra of solar oscillations show that the instrument is suitable for helioseismology. In particular, the specified point spread function, image jitter, and photon noise are no obstacle to a successful mission. Title: The Sun From the Perspective of an Observer Authors: Sibeck, D. G.; Scherrer, P. H. Bibcode: 2015AGUFMSH34A..01S Altcode: This talk will reflect on issues and pleasures of observing the Sun from the Earth and from space over four sunspot cycles. Parker and those who preceded and follow his early estimates of how our star should/might/could work need to compare their models with the real Sun. The true test of a model is how well it explains reality. Observers try to make their own estimates of how the Sun does work based on observable proxies for the physical quantities of interest. It the best of times, the models match the observations. The results are seldom simple due to, at least, limitations of both models and observations. Title: A Method for the Estimation of p-Mode Parameters from Averaged Solar Oscillation Power Spectra Authors: Reiter, J.; Rhodes, E. J., Jr.; Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Larson, T. P. Bibcode: 2015ApJ...803...92R Altcode: 2015arXiv150407493R A new fitting methodology is presented that is equally well suited for the estimation of low-, medium-, and high-degree mode parameters from m-averaged solar oscillation power spectra of widely differing spectral resolution. This method, which we call the “Windowed, MuLTiple-Peak, averaged-spectrum” or WMLTP Method, constructs a theoretical profile by convolving the weighted sum of the profiles of the modes appearing in the fitting box with the power spectrum of the window function of the observing run, using weights from a leakage matrix that takes into account observational and physical effects, such as the distortion of modes by solar latitudinal differential rotation. We demonstrate that the WMLTP Method makes substantial improvements in the inferences of the properties of the solar oscillations in comparison with a previous method, which employed a single profile to represent each spectral peak. We also present an inversion for the internal solar structure, which is based upon 6366 modes that we computed using the WMLTP method on the 66 day 2010 Solar and Heliospheric Observatory/MDI Dynamics Run. To improve both the numerical stability and reliability of the inversion, we developed a new procedure for the identification and correction of outliers in a frequency dataset. We present evidence for a pronounced departure of the sound speed in the outer half of the solar convection zone and in the subsurface shear layer from the radial sound speed profile contained in Model S of Christensen-Dalsgaard and his collaborators that existed in the rising phase of Solar Cycle 24 during mid-2010. Title: SDO/HMI Highlights After Five Years Authors: Scherrer, Philip H. Bibcode: 2015TESS....140303S Altcode: The SDO five year Prime Mission ends during thisTESS meeting. The HMI isntrument has operated as designed for these five years and has produced data used in more than 600 refereed articles. Some of the highlights from these articles and some not yet published are discussed. The SDO JSOC-SDP (Joint Science Operations Center - Science Data Processing) facility at Stanford status is also reviewed with hints to help with access to SDO HMI and AIA data. Title: The Interface Region Imaging Spectrograph (IRIS) Authors: De Pontieu, B.; Title, A. M.; Lemen, J. R.; Kushner, G. D.; Akin, D. J.; Allard, B.; Berger, T.; Boerner, P.; Cheung, M.; Chou, C.; Drake, J. F.; Duncan, D. W.; Freeland, S.; Heyman, G. F.; Hoffman, C.; Hurlburt, N. E.; Lindgren, R. W.; Mathur, D.; Rehse, R.; Sabolish, D.; Seguin, R.; Schrijver, C. J.; Tarbell, T. D.; Wülser, J. -P.; Wolfson, C. J.; Yanari, C.; Mudge, J.; Nguyen-Phuc, N.; Timmons, R.; van Bezooijen, R.; Weingrod, I.; Brookner, R.; Butcher, G.; Dougherty, B.; Eder, J.; Knagenhjelm, V.; Larsen, S.; Mansir, D.; Phan, L.; Boyle, P.; Cheimets, P. N.; DeLuca, E. E.; Golub, L.; Gates, R.; Hertz, E.; McKillop, S.; Park, S.; Perry, T.; Podgorski, W. A.; Reeves, K.; Saar, S.; Testa, P.; Tian, H.; Weber, M.; Dunn, C.; Eccles, S.; Jaeggli, S. A.; Kankelborg, C. C.; Mashburn, K.; Pust, N.; Springer, L.; Carvalho, R.; Kleint, L.; Marmie, J.; Mazmanian, E.; Pereira, T. M. D.; Sawyer, S.; Strong, J.; Worden, S. P.; Carlsson, M.; Hansteen, V. H.; Leenaarts, J.; Wiesmann, M.; Aloise, J.; Chu, K. -C.; Bush, R. I.; Scherrer, P. H.; Brekke, P.; Martinez-Sykora, J.; Lites, B. W.; McIntosh, S. W.; Uitenbroek, H.; Okamoto, T. J.; Gummin, M. A.; Auker, G.; Jerram, P.; Pool, P.; Waltham, N. Bibcode: 2014SoPh..289.2733D Altcode: 2014arXiv1401.2491D; 2014SoPh..tmp...25D The Interface Region Imaging Spectrograph (IRIS) small explorer spacecraft provides simultaneous spectra and images of the photosphere, chromosphere, transition region, and corona with 0.33 - 0.4 arcsec spatial resolution, two-second temporal resolution, and 1 km s−1 velocity resolution over a field-of-view of up to 175 arcsec × 175 arcsec. IRIS was launched into a Sun-synchronous orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a 19-cm UV telescope that feeds a slit-based dual-bandpass imaging spectrograph. IRIS obtains spectra in passbands from 1332 - 1358 Å, 1389 - 1407 Å, and 2783 - 2834 Å, including bright spectral lines formed in the chromosphere (Mg II h 2803 Å and Mg II k 2796 Å) and transition region (C II 1334/1335 Å and Si IV 1394/1403 Å). Slit-jaw images in four different passbands (C II 1330, Si IV 1400, Mg II k 2796, and Mg II wing 2830 Å) can be taken simultaneously with spectral rasters that sample regions up to 130 arcsec × 175 arcsec at a variety of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to emission from plasma at temperatures between 5000 K and 10 MK and will advance our understanding of the flow of mass and energy through an interface region, formed by the chromosphere and transition region, between the photosphere and corona. This highly structured and dynamic region not only acts as the conduit of all mass and energy feeding into the corona and solar wind, it also requires an order of magnitude more energy to heat than the corona and solar wind combined. The IRIS investigation includes a strong numerical modeling component based on advanced radiative-MHD codes to facilitate interpretation of observations of this complex region. Approximately eight Gbytes of data (after compression) are acquired by IRIS each day and made available for unrestricted use within a few days of the observation. Title: The Availability of Higher Level SDO/HMI Data Products Authors: Scherrer, Philip H. Bibcode: 2014AAS...22421842S Altcode: The Solar Dynamics Observatory Helioseismic and Magnetic Imager (SDO/HMI) investigation proposed to generate a set of "high level" data products. These are data products that require processing and analysis well beyond the traditional products prepared by Heliophysics mission teams. That is, these are not simply images nor what the HMI team calls "Observables" which are e.g. magnetograms or Dopplergrams. The traditional deliverd data products are often referred to as "Level-1" data products and are the highest level of processing required by contract with NASA. The HMI team planned to also produce higher level products such as flows in the solar interior, solar oscillation mode frequencies and inversions for interior rotation, magnetic vector field inversions with disambiguation, derived indices that may have space-weather applications, et cetera. Most of these products are now in regular production and a series of recent papers and papers in progress describe them in detail. This poster is to bring attention to the availability of these products and describe where and how to get the needed information to use them for new research objectives. Title: Identifying Potential Markers of the Sun's Giant Convective Scale Authors: McIntosh, Scott W.; Wang, Xin; Leamon, Robert J.; Scherrer, Philip H. Bibcode: 2014ApJ...784L..32M Altcode: 2014arXiv1403.0692M Line-of-sight magnetograms from the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO) are analyzed using a diagnostic known as the magnetic range of influence (MRoI). The MRoI is a measure of the length over which a photospheric magnetogram is balanced and so its application gives the user a sense of the connective length scales in the outer solar atmosphere. The MRoI maps and histograms inferred from the SDO/HMI magnetograms primarily exhibit four scales: a scale of a few megameters that can be associated with granulation, a scale of a few tens of megameters that can be associated with super-granulation, a scale of many hundreds to thousands of megameters that can be associated with coronal holes and active regions, and a hitherto unnoticed scale that ranges from 100 to 250 Mm. We infer that this final scale is an imprint of the (rotationally driven) giant convective scale on photospheric magnetism. This scale appears in MRoI maps as well-defined, spatially distributed concentrations that we have dubbed "g-nodes." Furthermore, using coronal observations from the Atmospheric Imaging Assembly on SDO, we see that the vicinity of these g-nodes appears to be a preferred location for the formation of extreme-ultraviolet (and likely X-Ray) brightpoints. These observations and straightforward diagnostics offer the potential of a near real-time mapping of the Sun's largest convective scale, a scale that possibly reaches to the very bottom of the convective zone. Title: SDO/HMI Status and Recent Findings Authors: Scherrer, Philip H.; SDO/HMI Science Team; SDO/JSOC Team Bibcode: 2013SPD....44..153S Altcode: Calibrated HMI basic observable quantities have been available for almost 3 years. Higher level standard HMI data products for magnetic fields and helioseismic derived parameters have been available for more than a year. This talk will give a brief status update on the standard products and describe a few groundbreaking findings based on these products. Title: Using Solar Dynamics Observatory Data in the Classroom to Do Real Science -- A Community College Astronomy Laboratory Investigation Authors: Scherrer, Deborah K.; Hildreth, S.; Lee, S.; Dave, T.; Scherrer, P. H. Bibcode: 2013SPD....44..156S Altcode: A partnership between Stanford University and Chabot Community College (Hayward, CA) has developed a series of laboratory exercises using SDO (AIA, HMI) data, targeted for community college students in an introductory astronomy lab class. The labs lead students to explore what SDO can do via online resources and videos. Students investigate their chosen solar events, generate their own online videos, prepare their own hypotheses relating to the events, and explore outcomes. Final assessment should be completed by the end of summer 2013. Should the labs prove valuable, they may be adapted for high school use. Title: Far-side helioseismic maps: the next generation Authors: González Hernández, Irene; Lindsey, Charles; Braun, Douglas C.; Bogart, Richard S.; Scherrer, Philip H.; Hill, Frank Bibcode: 2013JPhCS.440a2029G Altcode: For more than a decade, far-side seismic maps of medium-to-large active regions have proven their capability as a space weather forecasting tool. In the last few years, these maps have started to serve another purpose: complementing the front side observations that are input to different solar models. Photospheric flux transport as well as solar spectral irradiance models have been shown to produce improved results when incorporating the far-side seismic maps as well as providing better forecasting. The challenge for the future is twofold: Far-side seismic monitoring needs to be more sensitive, and it needs to offer more information. We present here initial steps towards fulfilling these goals using higher resolution input images, adding extra skips to the analysis and changing the presentation of the maps. Title: Perturbations in the wave parameters near active regions Authors: Rabello-Soares, M. C.; Bogart, R. S.; Scherrer, P. H. Bibcode: 2013JPhCS.440a2008R Altcode: The wave characteristics derived from ring-diagram analysis of HMI Doppler data in magnetically quiet regions near active regions are compared with those with no nearby active regions using 5° patches during 2.5 years of cycle 24 ascending phase. We search for perturbations that may be associated with propagation of the acoustic oscillations through the nearby sunspot. We observe significant variations in the mode parameters and flows. We analyse their dependence on the direction of the wave propagation. The observed mode dependence of the variations in mode amplitude, line width and frequency does not have the same functional form as that observed for the differences between quiet and active regions. Title: Using Solar Dynamics Observatory Data in the Classroom to Do Real Science - A Community College Astronomy Laboratory Class Investigation Authors: Hildreth, Scott; Lee, Shannon; Dave, Timothy; Scherrer, Deborah; Scherrer, Philip Bibcode: 2013enss.confE..90H Altcode: The incredible accessibility of extremely high spatial and temporal resolution data from the Solar Dynamics Observatory creates an opportunity for students to do near real-time solar investigations in an astronomy lab environment. We are developing a short series of laboratory exercises using SDO (AIA, HMI) data, targeted for Community College students in an introductory astronomy lab class, extendable to high school and university students. The labs initially lead students to explore what SDO can do, online, through existing SDO video clips taken on specific dates. Students then investigate solar events using the Heliophysics Events Knowledgebase (HEK), and make their own online movies of events, to discuss and share with classmates. Finally, students can investigate specific events and areas, selecting specific dates, locations, wavelength regions, and time cadences to create and gather their own SDO datasets for more detailed investigation. In exploring the Sun using actual data, students actually do real science. We are in the process of beta testing the sequence of labs, and are seeking interested community college, university, and high school astronomy lab teachers who might consider trying the labs themselves. Title: Approach to Integrate Global-Sun Models of Magnetic Flux Emergence and Transport for Space Weather Studies Authors: Mansour, Nagi Nicolas; Wray, A.; Mehrotra, P.; Henney, C.; arge, N.; Manchester, C.; Godinez, H.; Koller, J.; Kosovichev, A.; Scherrer, P.; Zhao, J.; Stein, R.; Duvall, T.; Fan, Y. Bibcode: 2013enss.confE.125M Altcode: The Sun lies at the center of space weather and is the source of its variability. The primary input to coronal and solar wind models is the activity of the magnetic field in the solar photosphere. Recent advancements in solar observations and numerical simulations provide a basis for developing physics-based models for the dynamics of the magnetic field from the deep convection zone of the Sun to the corona with the goal of providing robust near real-time boundary conditions at the base of space weather forecast models. The goal is to develop new strategic capabilities that enable characterization and prediction of the magnetic field structure and flow dynamics of the Sun by assimilating data from helioseismology and magnetic field observations into physics-based realistic magnetohydrodynamics (MHD) simulations. The integration of first-principle modeling of solar magnetism and flow dynamics with real-time observational data via advanced data assimilation methods is a new, transformative step in space weather research and prediction. This approach will substantially enhance an existing model of magnetic flux distribution and transport developed by the Air Force Research Lab. The development plan is to use the Space Weather Modeling Framework (SWMF) to develop Coupled Models for Emerging flux Simulations (CMES) that couples three existing models: (1) an MHD formulation with the anelastic approximation to simulate the deep convection zone (FSAM code), (2) an MHD formulation with full compressible Navier-Stokes equations and a detailed description of radiative transfer and thermodynamics to simulate near-surface convection and the photosphere (Stagger code), and (3) an MHD formulation with full, compressible Navier-Stokes equations and an approximate description of radiative transfer and heating to simulate the corona (Module in BATS-R-US). CMES will enable simulations of the emergence of magnetic structures from the deep convection zone to the corona. Finally, a plan will be summarized on the development of a Flux Emergence Prediction Tool (FEPT) in which helioseismology-derived data and vector magnetic maps are assimilated into CMES that couples the dynamics of magnetic flux from the deep interior to the corona. Title: HMI Status and Highlights Authors: Scherrer, P. H. Bibcode: 2013enss.confE..98S Altcode: Calibrated HMI basic observable quantities have been available for almost 2.5 years. Higher level standard HMI data products for magnetic fields and helioseismic derived parameters have been available for about a year. This talk will give a brief status update on the standard products and describe a few findings based on these products. Title: Comparison Between Line-Of-Sight Observables And Milne-Eddington Inversion Results From HMI: 24- And 12-hour Period Oscillations Authors: Couvidat, Sebastien; Liu, Yang; Scherrer, Philip H.; Schou, Jesper; HMI Team Bibcode: 2013enss.confE..84C Altcode: Oscillations with 12 and 24 hour periods are visible in sunspots on line-of-sight (LOS) observables and, to a lesser extent, on Milne-Eddington (ME) inversion results from the SDO/HMI instrument.Such oscillations are artifacts produced by the LOS algorithm and ME inversion procedure, and are not of solar origin. For instance, the LOS algorithm depends on an Fe I line profile and on HMI filter transmission profiles to convert the HMI intensities into Doppler velocities and LOS magnetic-field strengths: one of the issues we encountered is that in the presence of strong fields the Fe I profile used is inappropriate and results in errors in the left and right circular polarization velocity estimates. Here we present some properties of these 12- and 24-hour period oscillations, and we discuss their origin and the possibility of improving the LOS algorithm and ME inversion procedure to reduce their amplitudes. Title: Three 2012 Transits of Venus: From Earth, Jupiter, and Saturn Authors: Pasachoff, Jay M.; Schneider, G.; Babcock, B. A.; Lu, M.; Edelman, E.; Reardon, K.; Widemann, T.; Tanga, P.; Dantowitz, R.; Silverstone, M. D.; Ehrenreich, D.; Vidal-Madjar, A.; Nicholson, P. D.; Willson, R. C.; Kopp, G. A.; Yurchyshyn, V. B.; Sterling, A. C.; Scherrer, P. H.; Schou, J.; Golub, L.; McCauley, P.; Reeves, K. Bibcode: 2013AAS...22131506P Altcode: We observed the 2012 June 6/5 transit seen from Earth (E/ToV), simultaneously with Venus Express and several other spacecraft not only to study the Cytherean atmosphere but also to provide an exoplanet-transit analog. From Haleakala, the whole transit was visible in coronal skies; among our instruments was one of the world-wide Venus Twilight Experiment's nine coronagraphs. Venus's atmosphere became visible before first contact. SacPeak/IBIS provided high-resolution images at Hα/carbon-dioxide. Big Bear's NST also provided high-resolution observations of the Cytherean atmosphere and black-drop evolution. Our liaison with UH's Mees Solar Observatory scientists provided magneto-optical imaging at calcium and potassium. Solar Dynamics Observatory's AIA and HMI, and the Solar Optical Telescope (SOT) and X-ray Telescope (XRT) on Hinode, and total-solar-irradiance measurements with ACRIMSAT and SORCE/TIM, were used to observe the event as an exoplanet-transit analog. On September 20, we imaged Jupiter for 14 Hubble Space Telescope orbits, centered on a 10-hour ToV visible from Jupiter (J/ToV), as an exoplanet-transit analog in our own solar system, using Jupiter as an integrating sphere. Imaging was good, although much work remains to determine if we can detect the expected 0.01% solar irradiance decrease at Jupiter and the even slighter differential effect between our violet and near-infrared filters caused by Venus's atmosphere. We also give a first report on our currently planned December 21 Cassini UVIS observations of a transit of Venus from Saturn (S/ToV). Our E/ToV expedition was sponsored by the Committee for Research and Exploration/National Geographic Society; supplemented: NASA/AAS's Small Research Grant Program. We thank Rob Ratkowski, Stan Truitt, Rob Lucas, Aram Friedman, and Eric Pilger '82 at Haleakala, and Joseph Gangestad '06 at Big Bear for assistance, and Lockheed Martin Solar and Astrophysics Lab and Hinode science and operations teams for support for coordinated observations with NASA satellites. Our J/ToV observations were based on observations made with HST, operated by AURA, Inc., under NASA contract NAS 5-26555; these observations are associated with program #13067. Title: The 2012 Transit of Venus for Cytherean Atmospheric Studies and as an Exoplanet Analog Authors: Pasachoff, Jay M.; Schneider, G.; Babcock, B. A.; Lu, M.; Reardon, K. P.; Widemann, T.; Tanga, P.; Dantowitz, R.; Willson, R.; Kopp, G.; Yurchyshyn, V.; Sterling, A.; Scherrer, P.; Schou, J.; Golub, L.; Reeves, K. Bibcode: 2012DPS....4450806P Altcode: We worked to assemble as complete a dataset as possible for the Cytherean atmosphere in collaboration with Venus Express in situ and to provide an analog of spectral and total irradiance exoplanet measurements. From Haleakala, the whole transit was visible in coronal skies; our B images showed the evolution of the visibility of Venus's atmosphere and of the black-drop effect, as part of the Venus Twilight Experiment's 9 coronagraphs distributed worldwide with BVRI. We imaged the Cytherean atmosphere over two minutes before first contact, with subarcsecond resolution, with the coronagraph and a separate refractor. The IBIS imaging spectrometer at Sacramento Peak Observatory at H-alpha and carbon-dioxide also provided us high-resolution imaging. The NST of Big Bear Solar Observatory also provided high-resolution vacuum observations of the Cytherean atmosphere and black drop evolution. Our liaison with UH's Mees Solar Observatory scientists provided magneto-optical imaging at calcium and potassium. Spaceborne observations included the Solar Dynamics Observatory's AIA and HMI, and the Solar Optical Telescope (SOT) and X-ray Telescope (XRT) on Hinode, and total-solar-irradiance measurements with ACRIMSAT and SORCE/TIM, to characterize the event as an exoplanet-transit analog. Our expedition was sponsored by the Committee for Research and Exploration/National Geographic Society. Some of the funds for the carbon-dioxide filter for IBIS were provided by NASA through AAS's Small Research Grant Program. We thank Rob Lucas, Aram Friedman, and Eric Pilger '82 for assistance with Haleakala observing, Rob Ratkowski of Haleakala Amateur Astronomers for assistance with equipment and with the site, Stan Truitt for the loan of his Paramount ME, and Steve Bisque/Software Bisque for TheSky X controller. We thank Joseph Gangestad '06 of Aerospace Corp., a veteran of our 2004 expedition, for assistance at Big Bear. We thank the Lockheed Martin Solar and Astrophysics Laboratory and Hinode science and operations teams for planning and support. Title: Comparison of Line-of-Sight Magnetograms Taken by the Solar Dynamics Observatory/Helioseismic and Magnetic Imager and Solar and Heliospheric Observatory/Michelson Doppler Imager Authors: Liu, Y.; Hoeksema, J. T.; Scherrer, P. H.; Schou, J.; Couvidat, S.; Bush, R. I.; Duvall, T. L.; Hayashi, K.; Sun, X.; Zhao, X. Bibcode: 2012SoPh..279..295L Altcode: 2012SoPh..tmp...75L We compare line-of-sight magnetograms from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) and the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO). The line-of-sight magnetic signal inferred from the calibrated MDI data is greater than that derived from the HMI data by a factor of 1.40. This factor varies somewhat with center-to-limb distance. An upper bound to the random noise for the 1'' resolution HMI 720-second magnetograms is 6.3 Mx cm−2, and 10.2 Mx cm−2 for the 45-second magnetograms. Virtually no p-mode leakage is seen in the HMI magnetograms, but it is significant in the MDI magnetograms. 12-hour and 24-hour periodicities are detected in strong fields in the HMI magnetograms. The newly calibrated MDI full-disk magnetograms have been corrected for the zero-point offset and underestimation of the flux density. The noise is 26.4 Mx cm−2 for the MDI one-minute full-disk magnetograms and 16.2 Mx cm−2 for the five-minute full-disk magnetograms observed with four-arcsecond resolution. The variation of the noise over the Sun's disk found in MDI magnetograms is likely due to the different optical distortions in the left- and right-circular analyzers, which allows the granulation and p-mode to leak in as noise. Saturation sometimes seen in sunspot umbrae in MDI magnetograms is caused by the low intensity and the limitation of the onboard computation. The noise in the HMI and MDI line-of-sight magnetic-field synoptic charts appears to be fairly uniform over the entire map. The noise is 2.3 Mx cm−2 for HMI charts and 5.0 Mx cm−2 for MDI charts. No evident periodicity is found in the HMI synoptic charts. Title: Line-of-Sight Observables Algorithms for the Helioseismic and Magnetic Imager (HMI) Instrument Tested with Interferometric Bidimensional Spectrometer (IBIS) Observations Authors: Couvidat, Sébastien; Rajaguru, S. P.; Wachter, Richard; Sankarasubramanian, K.; Schou, Jesper; Scherrer, Philip H. Bibcode: 2012SoPh..278..217C Altcode: The Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory produces line-of-sight (LOS) observables (Doppler velocity, magnetic-field strength, Fe I line width, line depth, and continuum intensity) as well as vector magnetic-field maps at the solar surface. The accuracy of LOS observables is dependent on the algorithm used to translate a sequence of HMI filtergrams into the corresponding observables. Using one hour of high-cadence imaging spectropolarimetric observations of a sunspot in the Fe I line at 6173 Å through the Interferometric Bidimensional Spectrometer installed at the Dunn Solar Telescope, and the Milne-Eddington inversion of the corresponding Stokes vectors, we test the accuracy of the observables algorithm currently implemented in the HMI data-analysis pipeline: the MDI-like algorithm. In an attempt to improve the accuracy of HMI observables, we also compare this algorithm to others that may be implemented in the future: a least-squares fit with a Gaussian profile, a least-squares fit with a Voigt profile, and the use of second Fourier coefficients in the MDI-like algorithm. Title: A First Look at Magnetic Field Data Products from SDO/HMI Authors: Liu, Y.; Scherrer, P. H.; Hoeksema, J. T.; Schou, J.; Bai, T.; Beck, J. G.; Bobra, M.; Bogart, R. S.; Bush, R. I.; Couvidat, S.; Hayashi, K.; Kosovichev, A. G.; Larson, T. P.; Rabello-Soares, C.; Sun, X.; Wachter, R.; Zhao, J.; Zhao, X. P.; Duvall, T. L., Jr.; DeRosa, M. L.; Schrijver, C. J.; Title, A. M.; Centeno, R.; Tomczyk, S.; Borrero, J. M.; Norton, A. A.; Barnes, G.; Crouch, A. D.; Leka, K. D.; Abbett, W. P.; Fisher, G. H.; Welsch, B. T.; Muglach, K.; Schuck, P. W.; Wiegelmann, T.; Turmon, M.; Linker, J. A.; Mikić, Z.; Riley, P.; Wu, S. T. Bibcode: 2012ASPC..455..337L Altcode: The Helioseismic and Magnetic Imager (HMI; Scherrer & Schou 2011) is one of the three instruments aboard the Solar Dynamics Observatory (SDO) that was launched on February 11, 2010 from Cape Canaveral, Florida. The instrument began to acquire science data on March 24. The regular operations started on May 1. HMI measures the Doppler velocity and line-of-sight magnetic field in the photosphere at a cadence of 45 seconds, and the vector magnetic field at a 135-second cadence, with a 4096× 4096 pixels full disk coverage. The vector magnetic field data is usually averaged over 720 seconds to suppress the p-modes and increase the signal-to-noise ratio. The spatial sampling is about 0".5 per pixel. HMI observes the Fe i 6173 Å absorption line, which has a Landé factor of 2.5. These data are further used to produce higher level data products through the pipeline at the HMI-AIA Joint Science Operations Center (JSOC) - Science Data Processing (Scherrer et al. 2011) at Stanford University. In this paper, we briefly describe the data products, and demonstrate the performance of the HMI instrument. We conclude that the HMI is working extremely well. Title: Wavelength Dependence of the Helioseismic and Magnetic Imager (HMI) Instrument onboard the Solar Dynamics Observatory (SDO) Authors: Couvidat, Sébastien; Schou, Jesper; Shine, Richard A.; Bush, Rock I.; Miles, John W.; Scherrer, Philip H.; Rairden, Richard L. Bibcode: 2012SoPh..275..285C Altcode: 2011SoPh..tmp..150C; 2011SoPh..tmp..219C; 2011SoPh..tmp...33C; 2011SoPh..tmp..110C The Helioseismic and Magnetic Imager (HMI) instrument will produce Doppler-velocity and vector-magnetic-field maps of the solar surface, whose accuracy is dependent on a thorough knowledge of the transmission profiles of the components of the HMI optical-filter system. Here we present a series of wavelength-dependence calibration tests, performed on the instrument from 2005 onwards, to obtain these profiles. We obtained the transmittances as a function of wavelength for the tunable and non-tunable filter elements, as well as the variation of these transmittances with temperature and the angle of incidence of rays of light. We also established the presence of fringe patterns produced by interferences inside the blocking filter and the front window, as well as a change in transmitted intensity with the tuning position. This thorough characterization of the HMI-filter system confirmed the very high quality of the instrument, and showed that its properties are well within the required specifications to produce superior data with high spatial and temporal resolution. Title: Implementation and Comparison of Acoustic Travel-Time Measurement Procedures for the Solar Dynamics Observatory/Helioseismic and Magnetic Imager Time - Distance Helioseismology Pipeline Authors: Couvidat, S.; Zhao, J.; Birch, A. C.; Kosovichev, A. G.; Duvall, T. L.; Parchevsky, K.; Scherrer, P. H. Bibcode: 2012SoPh..275..357C Altcode: The Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory (SDO) satellite is designed to produce high-resolution Doppler-velocity maps of oscillations at the solar surface with high temporal cadence. To take advantage of these high-quality oscillation data, a time - distance helioseismology pipeline (Zhao et al., Solar Phys. submitted, 2010) has been implemented at the Joint Science Operations Center (JSOC) at Stanford University. The aim of this pipeline is to generate maps of acoustic travel times from oscillations on the solar surface, and to infer subsurface 3D flow velocities and sound-speed perturbations. The wave travel times are measured from cross-covariances of the observed solar oscillation signals. For implementation into the pipeline we have investigated three different travel-time definitions developed in time - distance helioseismology: a Gabor-wavelet fitting (Kosovichev and Duvall, SCORE'96: Solar Convection and Oscillations and Their Relationship, ASSL, Dordrecht, 241, 1997), a minimization relative to a reference cross-covariance function (Gizon and Birch, Astrophys. J.571, 966, 2002), and a linearized version of the minimization method (Gizon and Birch, Astrophys. J.614, 472, 2004). Using Doppler-velocity data from the Michelson Doppler Imager (MDI) instrument onboard SOHO, we tested and compared these definitions for the mean and difference travel-time perturbations measured from reciprocal signals. Although all three procedures return similar travel times in a quiet-Sun region, the method of Gizon and Birch (Astrophys. J.614, 472, 2004) gives travel times that are significantly different from the others in a magnetic (active) region. Thus, for the pipeline implementation we chose the procedures of Kosovichev and Duvall (SCORE'96: Solar Convection and Oscillations and Their Relationship, ASSL, Dordrecht, 241, 1997) and Gizon and Birch (Astrophys. J.571, 966, 2002). We investigated the relationships among these three travel-time definitions, their sensitivities to fitting parameters, and estimated the random errors that they produce. Title: The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) Authors: Lemen, James R.; Title, Alan M.; Akin, David J.; Boerner, Paul F.; Chou, Catherine; Drake, Jerry F.; Duncan, Dexter W.; Edwards, Christopher G.; Friedlaender, Frank M.; Heyman, Gary F.; Hurlburt, Neal E.; Katz, Noah L.; Kushner, Gary D.; Levay, Michael; Lindgren, Russell W.; Mathur, Dnyanesh P.; McFeaters, Edward L.; Mitchell, Sarah; Rehse, Roger A.; Schrijver, Carolus J.; Springer, Larry A.; Stern, Robert A.; Tarbell, Theodore D.; Wuelser, Jean-Pierre; Wolfson, C. Jacob; Yanari, Carl; Bookbinder, Jay A.; Cheimets, Peter N.; Caldwell, David; Deluca, Edward E.; Gates, Richard; Golub, Leon; Park, Sang; Podgorski, William A.; Bush, Rock I.; Scherrer, Philip H.; Gummin, Mark A.; Smith, Peter; Auker, Gary; Jerram, Paul; Pool, Peter; Soufli, Regina; Windt, David L.; Beardsley, Sarah; Clapp, Matthew; Lang, James; Waltham, Nicholas Bibcode: 2012SoPh..275...17L Altcode: 2011SoPh..tmp..106L; 2011SoPh..tmp..172L; 2011SoPh..tmp..241L; 2011SoPh..tmp..115L The Atmospheric Imaging Assembly (AIA) provides multiple simultaneous high-resolution full-disk images of the corona and transition region up to 0.5 R above the solar limb with 1.5-arcsec spatial resolution and 12-second temporal resolution. The AIA consists of four telescopes that employ normal-incidence, multilayer-coated optics to provide narrow-band imaging of seven extreme ultraviolet (EUV) band passes centered on specific lines: Fe XVIII (94 Å), Fe XVII, XXI (131 Å), Fe IX (171 Å), Fe XII, XXIV (193 Å), Fe XIV (211 Å), He II (304 Å), and Fe XVI (335 Å). One telescope observes C IV (near 1600 Å) and the nearby continuum (1700 Å) and has a filter that observes in the visible to enable coalignment with images from other telescopes. The temperature diagnostics of the EUV emissions cover the range from 6×104 K to 2×107 K. The AIA was launched as a part of NASA's Solar Dynamics Observatory (SDO) mission on 11 February 2010. AIA will advance our understanding of the mechanisms of solar variability and of how the Sun's energy is stored and released into the heliosphere and geospace. Title: Time-Distance Helioseismology Data-Analysis Pipeline for Helioseismic and Magnetic Imager Onboard Solar Dynamics Observatory (SDO/HMI) and Its Initial Results Authors: Zhao, J.; Couvidat, S.; Bogart, R. S.; Parchevsky, K. V.; Birch, A. C.; Duvall, T. L.; Beck, J. G.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 2012SoPh..275..375Z Altcode: 2011SoPh..tmp...86Z; 2011SoPh..tmp..163Z; 2011arXiv1103.4646Z; 2011SoPh..tmp..232Z The Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory (SDO/HMI) provides continuous full-disk observations of solar oscillations. We develop a data-analysis pipeline based on the time-distance helioseismology method to measure acoustic travel times using HMI Doppler-shift observations, and infer solar interior properties by inverting these measurements. The pipeline is used for routine production of near-real-time full-disk maps of subsurface wave-speed perturbations and horizontal flow velocities for depths ranging from 0 to 20 Mm, every eight hours. In addition, Carrington synoptic maps for the subsurface properties are made from these full-disk maps. The pipeline can also be used for selected target areas and time periods. We explain details of the pipeline organization and procedures, including processing of the HMI Doppler observations, measurements of the travel times, inversions, and constructions of the full-disk and synoptic maps. Some initial results from the pipeline, including full-disk flow maps, sunspot subsurface flow fields, and the interior rotation and meridional flow speeds, are presented. Title: Design and Ground Calibration of the Helioseismic and Magnetic Imager (HMI) Instrument on the Solar Dynamics Observatory (SDO) Authors: Schou, J.; Scherrer, P. H.; Bush, R. I.; Wachter, R.; Couvidat, S.; Rabello-Soares, M. C.; Bogart, R. S.; Hoeksema, J. T.; Liu, Y.; Duvall, T. L.; Akin, D. J.; Allard, B. A.; Miles, J. W.; Rairden, R.; Shine, R. A.; Tarbell, T. D.; Title, A. M.; Wolfson, C. J.; Elmore, D. F.; Norton, A. A.; Tomczyk, S. Bibcode: 2012SoPh..275..229S Altcode: The Helioseismic and Magnetic Imager (HMI) investigation (Solar Phys. doi:10.1007/s11207-011-9834-2, 2011) will study the solar interior using helioseismic techniques as well as the magnetic field near the solar surface. The HMI instrument is part of the Solar Dynamics Observatory (SDO) that was launched on 11 February 2010. The instrument is designed to measure the Doppler shift, intensity, and vector magnetic field at the solar photosphere using the 6173 Å Fe I absorption line. The instrument consists of a front-window filter, a telescope, a set of waveplates for polarimetry, an image-stabilization system, a blocking filter, a five-stage Lyot filter with one tunable element, two wide-field tunable Michelson interferometers, a pair of 40962 pixel cameras with independent shutters, and associated electronics. Each camera takes a full-disk image roughly every 3.75 seconds giving an overall cadence of 45 seconds for the Doppler, intensity, and line-of-sight magnetic-field measurements and a slower cadence for the full vector magnetic field. This article describes the design of the HMI instrument and provides an overview of the pre-launch calibration efforts. Overviews of the investigation, details of the calibrations, data handling, and the science analysis are provided in accompanying articles. Title: The Helioseismic and Magnetic Imager (HMI) Investigation for the Solar Dynamics Observatory (SDO) Authors: Scherrer, P. H.; Schou, J.; Bush, R. I.; Kosovichev, A. G.; Bogart, R. S.; Hoeksema, J. T.; Liu, Y.; Duvall, T. L.; Zhao, J.; Title, A. M.; Schrijver, C. J.; Tarbell, T. D.; Tomczyk, S. Bibcode: 2012SoPh..275..207S Altcode: The Helioseismic and Magnetic Imager (HMI) instrument and investigation as a part of the NASA Solar Dynamics Observatory (SDO) is designed to study convection-zone dynamics and the solar dynamo, the origin and evolution of sunspots, active regions, and complexes of activity, the sources and drivers of solar magnetic activity and disturbances, links between the internal processes and dynamics of the corona and heliosphere, and precursors of solar disturbances for space-weather forecasts. A brief overview of the instrument, investigation objectives, and standard data products is presented. Title: Far-side seismic maps with HMI Authors: Gonzalez Hernandez, I.; Lindsey, C. A.; Bogart, R. S.; Scherrer, P. H.; Hill, F. Bibcode: 2011AGUFMSH12A..01G Altcode: Seismic maps of the far side of the Sun have proven their capability to locate and track medium to large active regions on the non-visible hemisphere. Waves that travel all the way from the far side to the front side carry information of the magnetic perturbations that they encounter. The seismic holography technique makes use of the observation of waves at the front side of the Sun and compares them to a model to map areas of strong magnetic field on the far side. Recent improvements to these maps include a more accurate determination of the location of the active region, automatic highlighting of candidates, and calibration in terms of the magnetic field strength. Since the launch of SDO, the Helioseismic Magnetic Imager(HMI) has been providing maps of the far-side activity. We discuss here strategies to optimize these far-side maps as well as how to include extra information (such as realistic error estimates and area determination) in order to use these maps as input to irradiance and photospheric flux-transport models. Far-side direct observations from STEREO will help to reach these goals. Title: Perturbations in the wave parameters near active regions Authors: Rabello-Soares, M. Cristina; Bogart, Richard S.; Scherrer; Philip H. Bibcode: 2011sdmi.confE..84R Altcode: The wave characteristics in magnetically quiet regions with a nearby active region are compared with those of quiet regions at the same solar disk positions, but with no nearby active regions. We search for perturbations in the wave characteristics as the solar acoustic oscillations are affected as they propagate inside the nearby sunspot. The wave parameters were derived from ring-diagram analysis of HMI/SDO data. We find perturbations in several parameters, specially in the amplitude, width and frequency. The frequency observed in a five-degree quiet tile seems to be smaller if there is an active region nearby than if there is not by as much as 6%. We also describe the level of anisotropy in these perturbations in relation to direction of the nearby sunspot. Title: Temporal changes in the frequencies of the solar p-mode oscillations during solar cycle 23 Authors: Rhodes, E. J.; Reiter, J.; Schou, J.; Larson, T.; Scherrer, P.; Brooks, J.; McFaddin, P.; Miller, B.; Rodriguez, J.; Yoo, J. Bibcode: 2011IAUS..273..389R Altcode: We present a study of the temporal changes in the sensitivities of the frequencies of the solar p-mode oscillations to corresponding changes in the levels of solar activity during Solar Cycle 23. From MDI and GONG++ full-disk Dopplergram three-day time series obtained between 1996 and 2008 we have computed a total of 221 sets of m-averaged power spectra for spherical harmonic degrees ranging up to 1000. We have then fit these 284 sets of m-averaged power spectra using our WMLTP fitting code and both symmetric Lorentzian profiles for the peaks as well as the asymmetric profile of Nigam and Kosovichev to obtain 568 tables of p-mode parameters. We then inter-compared these 568 tables, and we performed linear regression analyses of the differences in p-mode frequencies, widths, amplitudes, and asymmetries as functions of the differences in as many as ten different solar activity indices. From the linear regression analyses that we performed on the frequency difference data sets, we have discovered a new signature of the frequency shifts of the p-modes. Specifically, we have discovered that the temporal shifts of the solar oscillation frequencies are positively correlated with the changes in solar activity below a limiting frequency. They then become anti-correlated with the changes in activity for a range of frequencies before once again becoming positively-correlated with the activity changes at very high frequencies. We have also discovered that the two frequencies where the sensitivities of the temporal frequency shifts change sign also change in phase with the average level of solar activity. Title: SDO/HMI - The First Year Authors: Scherrer, Philip H. Bibcode: 2011SPD....42.0901S Altcode: 2011BAAS..43S.0901S The Solar Dynamics Observatory (SDO) science operations phase began a year ago. During that time the Helioseismic and Magnetic Imager (HMI) team has made significant progress in developing calibration and data processing procedures. The new view of the Sun provided by SDO/HMI allows direct viewing of dynamic processes both in the interior and photospheric magnetic fields and brightness features. The extended team is now spending as much or even more time exploring the Sun than developing calibration and processing codes. Some highlights of the former and a quick status of the latter will be presented. Title: Imaging Spectroscopy of a White-Light Solar Flare Authors: Martínez Oliveros, J. C.; Couvidat, S.; Schou, J.; Krucker, S.; Lindsey, C.; Hudson, H. S.; Scherrer, P. Bibcode: 2011SoPh..269..269M Altcode: 2011SoPh..tmp....7M; 2010arXiv1012.0344M We report observations of a white-light solar flare (SOL2010-06-12T00:57, M2.0) observed by the Helioseismic Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The HMI data give us the first space-based high-resolution imaging spectroscopy of a white-light flare, including continuum, Doppler, and magnetic signatures for the photospheric Fe I line at 6173.34 Å and its neighboring continuum. In the impulsive phase of the flare, a bright white-light kernel appears in each of the two magnetic footpoints. When the flare occurred, the spectral coverage of the HMI filtergrams (six equidistant samples spanning ±172 mÅ around nominal line center) encompassed the line core and the blue continuum sufficiently far from the core to eliminate significant Doppler crosstalk in the latter, which is otherwise a possibility for the extreme conditions in a white-light flare. RHESSI obtained complete hard X-ray and γ-ray spectra (this was the first γ-ray flare of Cycle 24). The Fe I line appears to be shifted to the blue during the flare but does not go into emission; the contrast is nearly constant across the line profile. We did not detect a seismic wave from this event. The HMI data suggest stepwise changes of the line-of-sight magnetic field in the white-light footpoints. Title: Temporal changes in the frequencies and widths of the solar p-mode oscillations Authors: Rhodes, E. J., Jr.; Reiter, J.; Schou, J.; Larson, T.; Scherrer, P.; Brooks, J.; McFaddin, P.; Miller, B.; Rodriguez, J.; Yoo, J. Bibcode: 2011JPhCS.271a2029R Altcode: We present a study of the temporal changes in the sensitivities of the frequencies and widths of the solar p-mode oscillations to corresponding changes in the levels of solar activity during Solar Cycle 23. From MDI and GONG++ full-disk Dopplergram three-day time series obtained between 1996 and 2008 we have computed a total of 221 sets of m-averaged power spectra for spherical harmonic degrees ranging up to 1000. We have then fit these 221 sets of m-averaged power spectra using our WMLTP fitting code and both symmetric Lorentzian profiles for the peaks as well as the asymmetric profile of Nigam and Kosovichev to obtain 442 tables of p-mode parameters. We then inter-compared these 442 tables which comprise in excess of 5.3 million p-mode parameters, and we performed linear regression analyses of the differences in p-mode frequencies and widths as functions of the differences in as many as ten different solar activity indices. From these linear regression analyses we have discovered new signatures of the frequency shifts of the p-modes and a similar, but slightly different, signature of the temporal shifts in the widths of the oscillations. Title: Access to Solar Dynamics Observatory HMI and AIA Data via the Joint Science Operations Center (JSOC) Authors: Scherrer, P. H.; Amezcua, A.; Bogart, R. S. Bibcode: 2010AGUFMSH23C1867S Altcode: The Solar Dynamics Observatory (SDO) Helioseismic and Magnetic Imager (HMI) and Atmospheric Imaging Assembly (AIA) instruments have recently begun regular production of science level standard data products. While the primary data access for SDO is via the Virtual Solar Observatory (VSO) system, special data products are only available from the instrument team web sites. Both instruments share the Joint Science Operations Center (JSOC) components for instrument operations (the Instrument Operations Center) and data processing, archiving, and export (Science Data Processing - SDP) This poster provides an overview of the JSOC/SDP data access tools and provides examples of using these tools for typical HMI data browse and export purposes. A description of the JSOC services to the AIA web site is also provided. Title: Estimating the Energy Flux of Acoustic-Gravity Waves in the Solar Atmosphere from SDO/HMI Data Authors: Fleck, B.; Straus, T.; Jefferies, S.; Scherrer, P. Bibcode: 2010AGUFMSH11A1602F Altcode: Straus et al. (2008, 2009) demonstrated the existence of internal gravity waves in the solar atmosphere and showed that they are a key mediator of mechanical energy in the middle/upper photosphere, transporting even more energy than high-frequency acoustic waves. Here we repeat this analysis with data from SDO/HMI, which offers several distinct advantages, which are particularly relevant for the study of internal gravity waves (which have long periods and small spatial scales): excellent image stability over long time intervals, high spatial resolution, large field-of-view, and good temporal cadence. Title: Three Cycles of the Solar Toroidal Magnetic Field and This Peculiar Minimum Authors: Lo, L.; Hoeksema, J. T.; Scherrer, P. H. Bibcode: 2010ASPC..428..109L Altcode: 2010arXiv1003.3981L Thirty-four years of WSO (Wilcox Solar Observatory) and thirteen years of SOHO/MDI (Michelson Doppler Imager on the Solar and Heliospheric Observatory) magnetograms have been studied to measure the east-west inclination angle, indicating the toroidal component of the photospheric magnetic field. This analysis reveals that the large-scale toroidal component of the global magnetic field is antisymmetric around the equator and reverses direction in regions associated with flux from one solar cycle compared to the next. The toroidal field revealed the first early signs of Cycle 24 at high latitudes, especially in the northern hemisphere, appearing as far back as 2003 in the WSO data and 2004 in MDI. As in previous cycles, the feature moves gradually equatorward. Cycles overlap and the pattern associated with each cycle lasts about 17 years. Even though the polar field at the current solar minimum is significantly lower than the three previous minima, the toroidal field pattern is similar. Title: Helioseismic and Magnetic Imager Investigation on SDO - Current Status Authors: Scherrer, Philip H.; HMI Team Bibcode: 2010AAS...21640204S Altcode: 2010BAAS...41..873S The Helioseismic and Magnetic Imager (HMI) instrument on the Solar Dynamics Observatory (SDO) is expected to be providing data on a routine basis by the time of this meeting. A brief summary of the status of the several high level data products and of the data access procedures and rules will be discussed. Current status of the investigation can be obtained at http://hmi.stanford.edu. Data access information via the HMI-AIA Joint Science Operations Center - Science Data Processing can be found at at http://jsoc.stanford.edu.

This work was supported by NASA through contract NAS5-02139

with Stanford University. Title: Improving the Prediction Capability of Seismic Far-Side Maps Authors: González Hernández, I.; Scherrer, P.; Hill, F.; Lindsey, C.; Braun, D. Bibcode: 2009ASPC..416...87G Altcode: Both the Michelson Doppler Imager (MDI) and the Global Oscillation Network Group (GONG) projects produce daily seismic maps of surface magnetic activity on the non-visible hemisphere of the Sun. The technique has proven useful to detect and follow large active regions before they appear to face the Earth. This work demonstrates an improvement in the detection capability of the technique by applying the results of new research. We calibrate the daily far-side maps in terms of characteristics of the active region, such as total area and magnetic flux strength, apply a relationship between the strength of the persistent signal and the success rate to automatically highlight possible candidates, and remove solar-cycle variations to stabilize the signal. Title: NetDRMS: A Shared Data Management System for SDO and VSO Authors: Bogart, Richard S.; Aloise, J. J.; Amezcua, A. B.; Hourclé, J. A.; Scherrer, P. H.; Spencer, J. L.; Suarez-Sola, F. I. Bibcode: 2009SPD....40.1705B Altcode: The Joint Science Operations Center of the Solar Dynamic Observatory has built an integrated Data Record Management System (DRMS) and Storage Unit Management System (SUMS) to manage the analysis, archiving, and distribution of the massive amount of data flowing from the AIA and HMI instruments. Both DRMS and SUMS use the open source PostgreSQL database to manage the metadata. Locally developed Unix tools and C and Fortran libraries are used by DRMS and SUMS to manage data storage, retrieval, and transfer. They also provide an Applications Programming Interface to the databases. NetDRMS has been designed as an extension of DRMS/SUMS to simplify the automatic sharing of metadata and transport of image data among multiple data servers. It uses Slony, an open-source PostgreSQL replication system, and the DRMS/SUMS API. It has been adopted by the Virtual Solar Observatory as the mechanism for mirroring of key SDO data sets for distribution throughout the scientific community. In this paper we present a description of the architecture and features of NetDRMS, the mechanisms for data distribution, requirements for installation and operation, and the current status of the system. Title: Statistical Analysis of the Success Rate of the Far-Side Seismic Mapping of Active Regions. Authors: Gonzalez-Hernandez, Irene; Scherrer, P.; Lindsey, C.; Hill, F.; Braun, D. Bibcode: 2009SPD....40.0707G Altcode: Seismic maps of the non-visible side of the Sun (far side) have been used for almost a decade to follow large active regions before they rotate to face the Earth. Preliminary efforts to quantify the success rate of the used technique (seismic holography) have been published with limited data. However, a thorough study is needed to further understand the limitations of the technique in terms of size and strength of the active regions detected and to reveal clues as to how to improve it.

We have analyzed three complete years of far-side seismic maps calculated using both Global Oscillation Newtwork group (GONG) and Michelson Doppler Imager (MDI) data and matched the far-side candidates with associated active regions as recorded by the NOAA database. Here we present the results. Title: Cycle 24 - An Inside Perspective Authors: Scherrer, Philip H. Bibcode: 2009SPD....40.3501S Altcode: One of the prime goals for SDO is to increase understanding of the processes that generate dynamical magnetic disturbances that are the proximate cause of "space weather." Existing helioseismic series from GONG and SOHO/MDI cover the full span of cycle 23. One must ask what can we accomplish with another five years. Solar minimum is a good time to begin a new set of observations. Due to extreme patience on the part of the Sun, SDO is scheduled to be in place to allow observations near the beginning of cycle 24. SDO/HMI should provide modest improvement for global scale measurements and significant improvement for near surface studies. This talk will provide a brief overview of what we know about magnetic fields in the interior and what we hope to learn with SDO. Title: The HMI Magnetic Field Pipeline Authors: Hoeksema, Jon Todd; Liu, Y.; Schou, J.; Scherrer, P.; HMI Science Team Bibcode: 2009SPD....40.1701H Altcode: The Helioseismic and Magnetic Imager (HMI) will provide frequent full-disk magnetic field data after launch of the Solar Dynamics Observatory (SDO), currently scheduled for fall 2009. 16 megapixel line-of-sight magnetograms (Blos) will be recorded every 45 seconds. A full set of polarized filtergrams needed to determine the vector magnetic field requires 90 seconds. Quick-look data will be available within a few minutes of observation. Quick-look space weather and browse products must have identified users, and the list currently includes full disk magnetograms, feature identification and movies, 12-minute disambiguated vector fields in active region patches, time evolution of AR indices, synoptic synchronic frames, potential and MHD model results, and 1 AU predictions. A more complete set of definitive science data products will be offered about a day later and come in three types. "Pipeline” products, such as full disk vector magnetograms, will be computed for all data on an appropriate cadence. A larger menu of "On Demand” products, such as Non-Linear Force Free Field snapshots of an evolving active region, will be produced whenever a user wants them. Less commonly needed "On Request” products that require significant project resources, such as a high resolution MHD simulation of the global corona, will be created subject to availability of resources. Further information can be found at the SDO Joint Science Operations Center web page, jsoc.stanford.edu Title: A New Way to Infer Variations of the Seismic Solar Radius Authors: González Hernández, I.; Scherrer, P.; Hill, F. Bibcode: 2009ApJ...691L..87G Altcode: 2009arXiv0902.1002G; 2009ApJ...691L..87H We show that the mean phase of waves propagating all the way from the far side of the Sun to the front side, as measured by seismic holography, varies with time. The change is highly anticorrelated with solar cycle activity and is consistent with other recent results on the variation of the seismic radius of the Sun. The phase change that we observe corresponds to a few kilometers difference in the seismic solar radius from solar maximum to solar minimum in agreement with inferences from global helioseismology studies. Title: Distributing space weather monitoring instruments and educational materials worldwide for IHY 2007: The AWESOME and SID project Authors: Scherrer, Deborah; Cohen, Morris; Hoeksema, Todd; Inan, Umran; Mitchell, Ray; Scherrer, Philip Bibcode: 2008AdSpR..42.1777S Altcode: The International Heliophysical Year (IHY) aims to advance our understanding of the fundamental processes that govern the Sun, Earth, and heliosphere. The IHY Education and Outreach Program is dedicated to inspiring the next generation of space and Earth scientists as well as spreading the knowledge, beauty, and relevance of our solar system to the people of the world. In our Space Weather Monitor project we deploy a global network of sensors to high schools and universities to provide quantitative diagnostics of solar-induced ionospheric disturbances, thunderstorm intensity, and magnetospheric activity. We bring real scientific instruments and data in a cost-effective way to students throughout the world. Instruments meet the objectives of being sensitive enough to produce research-quality data, yet inexpensive enough for placement in high schools and universities. The instruments and data have been shown to be appropriate to, and usable by, high school age and early university students. Data contributed to the Stanford data center is openly shared and partnerships between groups in different nations develop naturally. Students and teachers have direct access to scientific expertise. The result is a world-wide collaboration of scientists, teachers, and students to investigate the variability of the ionosphere. The research-quality AWESOME (Atmospheric Weather Electromagnetic System of Observation, Modeling, and Education) instruments have been selected as a participating program by the United Nations Basic Space Science Initiative (UNBSSI). The IHY Committee for International Education and Public Outreach has designated the simpler SID (Sudden Ionospheric Disturbance) monitors to be provided to teacher/student teams in each of the 192 countries of the world. Title: Development of Time-Distance Helioseismology Data Analysis Pipeline for SDO/HMI Authors: Duvall, T. L.; Zhao, J.; Couvidat, S.; Parchevsky, K. V.; Beck, J.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 2008AGUSMSP51B..15D Altcode: The Helioseismic and Magnetic Imager of SDO will provide uninterrupted 4kx4k-pixel Doppler-shift images of the Sun with ~45 sec cadence. These data will have a unique potential for advancing local helioseismic diagnostics of the Sun's interior structure and dynamics. They will help to understanding the basics mechanisms of solar activity and developing predictive capabilities for the NASA's Living with a Star Program. Because of the tremendous amount of data the HMI team is developing a data analysis pipeline, which will provide maps of subsurface flows and sound-speed distributions inferred from the Doppler data by the time-distance technique. We discuss the development plan, methods and algorithms, and present the status of the pipeline, testing results and examples of the data products. Title: Combining far-side maps from MDI and GONG to improve the prediction capability Authors: Gonzalez Hernandez, I.; Scherrer, P.; Lindsey, C.; Braun, D.; Hill, F. Bibcode: 2008AGUSMSP41A..04G Altcode: Both the Michaelson Doppler Imager (MDI) and the Global Oscillation Network Group (GONG) projects produce daily seismic maps of surface magnetic activity at the non-visible hemisphere the Sun. The technique has proven useful in order to detect and follow large active regions before they appear to face the Earth. This work explores the possibility of improving the detection capability of the technique by combining the results from both instruments. The research should lead to a better understanding of the spurious, non persistent seismic signal associated with the far-side images and better discrimination between solar and instrumental noise. Title: A Changing Solar Shape Authors: Kuhn, Jeffrey R.; Emilio, M.; Bush, R.; Scherrer, P. Bibcode: 2007AAS...21012001K Altcode: 2007BAAS...39..245K The Sun's shape is sensitive to the influence of gravity, rotation, and local turbulence and magnetic fields in its outer atmosphere. In 1997 the Michelson Doppler Imager (MDI) aboard the Solar and Heliospheric Observatory (SOHO) allowed a precise measurement of the oblateness from above the atmosphere. In 2001 this technique was repeated and we report here on the detection of a time-variable solar shape from these data. Title: Radiative Transfer Effects On Doppler Measurements As Sources Of Surface Effects In Sunspot Seismology Authors: Rajaguru, Paul; Sankarasubramanian, K.; Wachter, R.; Scherrer, P. H. Bibcode: 2007AAS...210.2208R Altcode: 2007BAAS...39..125R We show that the use of Doppler shifts of Zeeman sensitive spectral lines to observe waves in sunspots is subject to measurement specific phase shifts arising from, 1) altered height range of spectral line formation and the propagating character of p mode waves in penumbrae, and 2) Zeeman broadening and splitting. We also show that these phase shifts depend on wave frequencies, strengths and line of sight inclination of magnetic field, and the polarization state used for Doppler measurements. We discuss how these phase shifts could contribute to local helioseismic measurements of 'surface effects' in sunspot seismology. Title: A Changing Solar Shape Authors: Emilio, M.; Bush, R. I.; Kuhn, J.; Scherrer, P. Bibcode: 2007ApJ...660L.161E Altcode: The Sun's shape is sensitive to the influence of gravity, rotation, and local turbulence and magnetic fields in its outer atmosphere. A careful measurement of this shape has long been sought to better understand the solar structure and its change during the 11 yr solar cycle. Numerous disparate measurements of the solar oblateness or the fractional difference between equatorial and polar radii have been difficult to interpret, in part because this quantity is much smaller than terrestrial atmospheric seeing and most instrumental noise sources. In 1997 the Michelson Doppler Imager (MDI) aboard the Solar and Heliospheric Observatory (SOHO) obtained a precise measurement of the oblateness from above the atmosphere by utilizing a spacecraft roll procedure to remove instrumental influences. In 2001 this technique was repeated, and we report here on the detection of a time-variable solar shape from these data. The changing oblateness we find from 1997 to 2001 is smaller than the apparent discrepancy between earlier ground-based observations, but is significantly larger than MDI's astrometric measurement uncertainty. The shape change appears to be anticorrelated with the observed helioseismic variability. This fact and our MDI measurements suggest that the outer solar atmosphere expands nonhomologously during the cycle. It is possible that solar cycle changes in the turbulent pressure in the outer atmosphere can account for both the optical limb change and the helioseismic acoustic global solar shape change. Title: Analytical Models for Cross-Correlation Signal in Time-Distance Helioseismology Authors: Nigam, R.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 2007ApJ...659.1736N Altcode: 2007astro.ph..2499N In time-distance helioseismology, the time signals (Doppler shifts) at two points on the solar surface separated by a fixed angular distance are cross-correlated, and this leads to a wave packet signal. Accurately measuring the travel times of these wave packets is crucial for inferring the subsurface properties in the Sun. The observed signal is quite noisy, and to improve the signal-to-noise ratio and make the cross-correlation more robust, the temporal oscillation signal is phase-speed filtered at the two points in order to select waves that travel a fixed horizontal distance. Hence a new formula to estimate the travel times is derived in the presence of a phase-speed filter, and it includes both the radial and horizontal component of the oscillation displacement signal. It generalizes the previously used Gabor wavelet that was derived without a phase-speed filter and included only the radial component of the displacement. This is important since it will be consistent with the observed cross-correlation that is computed using a phase-speed filter, and it also accounts for both the components of the displacement. The new formula depends on the location of the two points on the solar surface that are being cross-correlated and accounts for the travel time shifts at different locations on the solar surface. Title: A Note on Saturation Seen in the MDI/SOHO Magnetograms Authors: Liu, Y.; Norton, A. A.; Scherrer, P. H. Bibcode: 2007SoPh..241..185L Altcode: A type of saturation is sometimes seen in sunspot umbrae in MDI/SOHO magnetograms. In this paper, we present the underlying cause of such saturation. By using a set of MDI circular polarization filtergrams taken during an MDI line profile campaign observation, we derive the MDI magnetograms using two different approaches: the on-board data processing and the ground data processing, respectively. The algorithms for processing the data are the same, but the former is limited by a 15-bit lookup table. Saturation is clearly seen in the magnetogram from the on-board processing simulation, which is comparable to an observed MDI magnetogram taken one and a half hours before the campaign data. We analyze the saturated pixels and examine the on-board numerical calculation method. We conclude that very low intensity in sunspot umbrae leads to a very low depth of the spectral line that becomes problematic when limited to the 15-bit on-board numerical treatment. This 15-bit on-board treatment of the values is the reason for the saturation seen in sunspot umbrae in the MDI magnetogram. Although it is possible for a different type of saturation to occur when the combination of a strong magnetic field and high velocity moves the spectral line out of the effective sampling range, this saturation is not observed. Title: Magnetic Field Vector Retrieval With the Helioseismic and Magnetic Imager Authors: Borrero, J. M.; Tomczyk, S.; Norton, A.; Darnell, T.; Schou, J.; Scherrer, P.; Bush, R.; Liu, Y. Bibcode: 2007SoPh..240..177B Altcode: 2006astro.ph.11565B We investigate the accuracy to which we can retrieve the solar photospheric magnetic field vector using the Helioseismic and Magnetic Imager (HMI) that will fly onboard of the Solar Dynamics Observatory by inverting simulated HMI profiles. The simulated profiles realistically take into account the effects of the photon noise, limited spectral resolution, instrumental polarization modulation, solar p modes, and temporal averaging. The accuracy of the determination of the magnetic field vector is studied by considering the different operational modes of the instrument. Title: Radiative Transfer Effects on Doppler Measurements as Sources of Surface Effects in Sunspot Seismology Authors: Rajaguru, S. P.; Sankarasubramanian, K.; Wachter, R.; Scherrer, P. H. Bibcode: 2007ApJ...654L.175R Altcode: 2006astro.ph.11897R We show that the use of Doppler shifts of Zeeman-sensitive spectral lines to observe waves in sunspots is subject to measurement-specific phase shifts arising from (1) the altered height range of spectral line formation and the propagating character of p-mode waves in penumbrae and (2) Zeeman broadening and splitting. We also show that these phase shifts depend on wave frequencies, strengths and line-of-sight inclinations of magnetic fields, and the polarization state used for Doppler measurements. We discuss how these phase shifts could contribute to local helioseismic measurements of ``surface effects'' in sunspot seismology. Title: Spectral Line Selection for HMI Authors: Norton, A. A.; Pietarila Graham, J. D.; Ulrich, R. K.; Schou, J.; Tomczyk, S.; Liu, Y.; Lites, B. W.; López Ariste, A.; Bush, R. I.; Socas-Navarro, H.; Scherrer, P. H. Bibcode: 2006ASPC..358..193N Altcode: We present information on two spectral lines, Fe I 6173 Å and Ni I 6768 Å, that were candidates for use in the Helioseismic and Magnetic Imager (HMI) instrument. Both Fe I and Ni I profiles have clean continuum and no blends that threaten performance. The higher Landé factor of Fe I means its operational velocity range in regions of strong magnetic field is smaller than for Ne I. Fe I performs better than Ni I for vector magnetic field retrieval. Inversion results show that Fe I consistently determines field strength and flux more accurately than the Ni I line. Inversions show inclination and azimuthal errors are recovered to ≈2° above 600 Mx/cm2 for Fe I and above 1000 Mx/cm2 for Ni I. The Fe I line was recommended, and ultimately chosen, for use in HMI. Title: Magnetic Field Vector Retrieval with HMI Authors: Borrero, J. M.; Tomczyk, S.; Norton, A. A.; Darnell, T.; Schou, J.; Scherrer, P.; Bush, R. I.; Lui, Y. Bibcode: 2006ASPC..358..144B Altcode: The Helioseismic and Magnetic Imager (HMI), on board the Solar Dynamics Observatory (SDO), will begin data acquisition in 2008. It will provide the first full-disk, high temporal cadence observations of the full Stokes vector with a 0.5 arcsec pixel size. This will allow for a continuous monitoring of the Solar magnetic-field vector. HMI data will advance our understanding of the small- and large-scale magnetic field evolution, its relation to the solar and global dynamic processes, coronal field extrapolations, flux emergence, magnetic helicity, and the nature of the polar magnetic fields. We summarize HMI's expected operation modes, focusing on the polarization cross-talk induced by the solar oscillations, and how this affects the magnetic-field vector determination. Title: Spectral Line Selection for HMI: A Comparison of Fe I 6173 Å and Ni I 6768 Å Authors: Norton, A. A.; Graham, J. Pietarila; Ulrich, R. K.; Schou, J.; Tomczyk, S.; Liu, Y.; Lites, B. W.; Ariste, A. López; Bush, R. I.; Socas-Navarro, H.; Scherrer, P. H. Bibcode: 2006SoPh..239...69N Altcode: 2006SoPh..tmp...88N; 2006astro.ph..8124N We present a study of two spectral lines, Fe I 6173 Å and Ni I 6768 Å, that were candidates to be used in the Helioseismic and Magnetic Imager (HMI) for observing Doppler velocity and the vector magnetic field. The line profiles were studied using the Mt. Wilson Observatory, the Advanced Stokes Polarimeter and the Kitt Peak-McMath Pierce telescope and one-meter Fourier transform spectrometer atlas. Both Fe I and Ni I profiles have clean continua and no blends that threaten instrument performance. The Fe I line is 2% deeper, 15% narrower, and has a 6% smaller equivalent width than the Ni I line. The potential of each spectral line to recover pre-assigned solar conditions is tested using a least-squares minimization technique to fit Milne-Eddington models to tens of thousands of line profiles that have been sampled at five spectral positions across the line. Overall, the Fe I line has a better performance than the Ni I line for vector-magnetic-field retrieval. Specifically, the Fe I line is able to determine field strength, longitudinal and transverse flux four times more accurately than the Ni I line in active regions. Inclination and azimuthal angles can be recovered to ≈2° above 600 Mx cm−2 for Fe I and above 1000 Mx cm−2 for Ni I. Therefore, the Fe I line better determines the magnetic-field orientation in plage, whereas both lines provide good orientation determination in penumbrae and umbrae. We selected the Fe I spectral line for use in HMI due to its better performance for magnetic diagnostics while not sacrificing velocity information. The one exception to the better performance of the Fe I line arises when high field strengths combine with high velocities to move the spectral line beyond the effective sampling range. The higher geff of Fe I means that its useful range of velocity values in regions of strong magnetic field is smaller than Ni I. Title: Quantitative Study of Solar Farside Observations to Predict Active Regions Authors: Buder, I.; Scherrer, P. H. Bibcode: 2006AGUFMSH33B0412B Altcode: Estimates of sunspots on the far side of the Sun have been obtained for several years with SOHO/MDI and recently with GONG observations. E.g. http://soi.stanford.edu/data/full_farside/. We have examined the predictive usefulness of far-side images of regions within a few days of the East limb by comparing the far-side images with subsequent magnetograms. We developed a quantitative measure of success based on the frequency of true positives and false alarms. We can detect about 75% of strong magnetic regions with a false alarm rate of less than 20%. Title: VLF Remote -Sensing of the Lower Ionosphere with AWESOME Receivers: Solar Flares, Lightning-induced Electron Precipitation, Sudden Ionospheric Disturbances, Sprites, Gravity Waves and Gamma-ray Flares Authors: Inan, U. S.; Cohen, M.; Scherrer, P.; Scherrer, D. Bibcode: 2006ihy..workE..66I Altcode: Stanford University Very Low Frequency (VLF) radio receivers have been used extensively for remote sensing of the ionosphere and the magnetosphere. Among the phenomena that can be uniquely measured via VLF receivers are radio atmospherics, whistlers, electron precipitation, solar flares, sudden ionospheric disturbances, gravity waves, sprites, and cosmic gamma-ray flares. With the use of simple square air-core magnetic loop antennas of a couple of meters in size, the sensitivity of these instruments allows the measurement of magnetic fields as low as several tens of femtoTesla per root Hz, in the frequency range of ~300 Hz to 50 kHz. This sensitivity well exceeds that required to detect any event above the ambient atmospheric noise floor, determined by the totality of lightning activity on this planet. In recent years, as cost of production, timing accuracy (due to low cost GPS cards), and data handling flexibility of the systems has improved, it has become possible to distribute many of these instruments in the form of arrays, to perform interferometric and holographic imaging of the lower ionosphere. These goals can be achieved using the newest version of the Stanford VLF receiver, known as AWESOME: Atmospheric Weather Educational System for Observation and Modeling of Electromagnetics. In the context of the IHY/UNBSS program for 2007, the AWESOME receivers can be used extensively as part of the United Nations initiative to place scientific instruments in developing countries. Drawing on the Stanford experiences from setting up arrays of VLF receivers, including an interferometer in Alaska, the Holographic Array for Ionospheric and Lightning research (HAIL) consisting of instruments at 13 different high schools in mid-western United States, a broader set of ELF/VLF receivers in Alaska, and various receivers abroad, including in France, Japan, Greece, Turkey, and India, a global network of ELF/VLF receivers offer possibilities for a wide range of scientific topics, as well as serving as a means for educational outreach. Most recently, AWESOME receivers were placed in several North African countries, including Tunisia, Algeria, and Morocco. The new AWESOME version is substantially lower in cost, and easier to set-up and use. Nevertheless, the receivers offer the same ultimate levels of resolution in time, sensitivity and dynamic range, as well as ease of handling of data that is used by researchers conducting cutting edge ionospheric and Space Weather research. In this context, the placement of these systems at underdeveloped host countries provides an open-ended potential for exploration, limited only by the imagination and drive of the users. Title: Farside helioseismic holography: recent advances Authors: González Hernández, I.; Hill, F.; Lindsey, C.; Braun, D.; Scherrer, P.; Hanasoge, S. M. Bibcode: 2006ESASP.624E...3G Altcode: 2006soho...18E...3G No abstract at ADS Title: Success rate of predicting the heliospheric magnetic field polarity with Michelson Doppler Imager (MDI) synoptic charts Authors: Zhao, X. P.; Hoeksema, J. T.; Liu, Y.; Scherrer, P. H. Bibcode: 2006JGRA..11110108Z Altcode: The photospheric and heliospheric magnetic fields have been continuously observed at the L1 point by the Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO) and Wind and the Advanced Composition Explorer (ACE) spacecraft since 1996. The combined observations of the photospheric and heliospheric magnetic fields make it possible to more reliably predict the heliospheric magnetic field and more accurately estimate the success rate of the prediction. On the basis of the latitude dependence of the zonal polar field inferred from high-resolution MDI synoptic charts between 1996 and 2003 we fill in the polar data gaps in the MDI synoptic charts. To assess the influence of synoptic charts from different data sources on the prediction of the coronal and heliospheric magnetic fields, we compare the success rate of the heliospheric magnetic field (HMF) polarity predicted over 107 Carrington rotations from June 1996 to June 2004. We used the potential field source surface model and the synoptic charts from the Kitt Peak National Observatory, MDI, and the Wilcox Solar Observatory. The mean success rate of the HMF polarity predicted using MDI synoptic charts over 8 years is 0.862 ± 0.101, the best among the three photospheric data sources, although the difference among the three sources is small. This result validates the MDI synoptic charts in modeling coronal and heliospheric magnetic fields. Title: The Helioseismic and Magnetic Imager for the Solar Dynamics Observatory Authors: Rabello-Soares, M. C.; Scherrer, P. H.; Hmi Team Bibcode: 2006IAUJD..17E..30R Altcode: The Solar Dynamics Observatory (SDO) is the first mission in the NASA Living With a Star (LWS) Program. SDO is set to launch in August of 2008 and it will be placed into an inclined geosynchronous orbit. SDO is being designed to help us understand the origin of solar variability and its impact on the geospace environment. SDO has three instruments: HMI (Helioseismic and Magnetic Imager), AIA (Atmospheric Imaging Assembly) and EVE (Extreme Ultraviolet Variability Experiment). The primary goal of the Helioseismic and Magnetic Imager (HMI) investigation is to study the origin of solar variability and to characterize and understand the Sun's interior and the various components of magnetic activity. HMI makes measurements of the motion of the solar photosphere to study solar oscillations and measurements of the polarization in a spectral line to study all three components of the photospheric magnetic field. The instrument has significant heritage from the Solar and Heliospheric Observatory (SOHO) Michelson Doppler Imager (MDI) with enhancements to achieve higher resolution, higher cadence, and the addition of a second channel to provide full Stokes polarization measurements. In this presentation, we will give a brief overview of the HMI instrument and describe its science goals. stabilized 1"-resolution full-disk Doppler velocity and line-of-sight magnetic flux images every 45 seconds, and vector-magnetic field maps every 90 seconds. In this presentation , we will give a brief overview of the HMI instrument and describe its science goals. Title: The Sun's Polar Magnetic Flux from 1996-2006 Observed With SOHO/MDI Authors: Hoeksema, Jon T.; Benevolenskaya, E. E.; Liu, Y.; Scherrer, P. H.; Zhao, X. Bibcode: 2006SPD....37.0702H Altcode: 2006BAAS...38..228H Observations of the Sun's magnetic field using nearly 10 years of full-disk SOHO/MDI data are used to investigate the net flux and total flux of the polar regions.The northern pole above 78 degrees changed polarity in April 2001 (CR 1974), five rotations before the southern pole (August, 2001, CR 1979). These dates are a little earlier than those found by Durrant and Wilson (2003): CR 1975 in the north and CR 1981 in the south.Solar cycle changes in the total polar magnetic flux are more difficult to determine. Most of the polar measurements are near the noise level due to the extreme reduction in the line-of-sight component due to projection effects near the limb. Determination of the total flux is highly sensitive to changes in noise due to the different MDI observing modes, to systematic errors in the instrument, and to the exact method of processing the data (e.g. spatial and temporal averaging). Periodic orientation changes of the SOHO spacecraft in recent years allow better characterization of the systematic errors. Observations taken at different inclinations of the solar rotation axis also help characterize the known errors to provide a better estimate of the solar polar flux with time. Title: Farside Helioseismic Holography: Recent Advances Authors: Gonzalez-Hernandez, Irene; Braun, D. C.; Hanasoge, S. M.; Hill, F.; Lindsey, C. A.; Scherrer, P. H. Bibcode: 2006SPD....37.0502G Altcode: 2006BAAS...38Q.223G Both MDI and GONG have been calculating partial farside maps for some time, showing a high degree of agreement in detecting large active regions within approximately 45 degrees around the antipode of disk center.Recently, the full-hemisphere capability has been added to the farside pipelines of both instruments. We show here the capability of detecting large active regions and tracking them through out the full farside hemisphere by applying the technique to active region 10808.We also report on efforts underway to calibrate the farside signal in terms of equivalent magnetic field, including some preliminary maps obtained from artificial helioseismic data. Title: Helioseismic and Magnetic Imager for the Solar Dynamics Observatory Authors: Scherrer, P. H.; Hoeksema, J. T.; Hmi Team Bibcode: 2006cosp...36.1469S Altcode: 2006cosp.meet.1469S The primary goal of the Helioseismic and Magnetic Imager HMI investigation is to study the origin of solar variability and to characterize and understand the Sun s interior and the various components of magnetic activity The HMI instrument is part of the Living With a Star LWS Solar Dynamics Observatory SDO HMI determines the motion of the solar photosphere to study solar oscillations and measures the polarization in a spectral line to study all three components of the photospheric magnetic field This presentation gives an overview of the science goals the instrument and its expected performance the science products produced and the ways in which the science community and public will be able to use HMI data Title: Characteristics of the Sun's polar magnetic flux from 1996-2005 using SOHO/MDI observations Authors: Benevolenskaya, E. E.; Hoeksema, J. T.; Liu, Y.; Zhao, X.; Scherrer, P. H. Bibcode: 2005AGUFMSH41A1120B Altcode: We have studied the Sun's polar magnetic field using nearly 10 years of full-disk SOHO/MDI data. We have estimated the time of the polar magnetic field reversals above 78 degrees. The net flux in the southern cap changed polarity in CR 1979 (August, 2001), five rotations later than the north (CR 1974; April, 2001). These are just a little earlier than the times identified by Durrant and Wilson (2003): CR 1981 in the south and CR 1975 in the north. We also investigate apparent solar cycle changes in the total magnetic flux observed in the polar caps. The total flux determination is highly sensitive to changes in random noise due to the different MDI observing modes, to systematic errors in the instrument, and to the exact method of processing the data (e.g. spatial and temporal averaging). This is because nearly all of the flux measurements are near the noise level due to the extreme reduction in the line-of-sight component due to projection effects near the limb. In recent years the SOHO spacecraft has periodically been rotated and this allows us to better characterize the systematic errors. Using observations taken when the inclination of the solar equator provides the best viewing of each pole, we correct for all known errors to provide the best estimate of the solar polar flux with time. Title: VLF Remote Sensing of the Lower Ionosphere: Solar Flares, Electron Precipitation, Sudden Ionospheric Disturbances, Sprites, Gravity Waves and Gamma-ray Flares Authors: Tan, J. H.; Cohen, M.; Inan, U. S.; Scherrer, P. H.; Scherrer, D. Bibcode: 2005AGUFMSM33D..03T Altcode: Stanford University Very Low Frequency (VLF) and Extremely Low Frequency (ELF) radio receivers have been used extensively for remote sensing of the ionosphere and the magnetosphere. Among the phenomena that can be uniquely measured via ELF/VLF receivers are radio atmospherics, whistlers, electron precipitation, solar flares, sudden ionospheric disturbances, gravity waves, sprites, and cosmic gamma-ray flares. With the use of simple square air-core magnetic loop antennas of a couple of meters in size, the sensitivity of these instruments allows the measurement of magnetic fields as low as several tens of femtoTesla per root-Hz, in the frequency range of ~30 Hz to 50 kHz. This sensitivity well exceeds that required to detect any event above the ambient atmospheric noise floor, determined by the totality of lightning activity on the planet. In recent years, as cost of production, timing accuracy (due to low cost GPS clocks), and data handling flexibility of the systems has improved, it has become possible to distribute many of these instruments in the form of arrays, to perform interferometric and holographic imaging of the lower ionosphere. In the context of the IHY in 2007, the ELF/VLF receiver can used extensively as part of the United Nations initiative to place scientific instruments in developing countries. Stanford University's past experiences setting up arrays of ELF/VLF receivers include an interferometer in Alaska, the Holographic Array for Ionospheric and Lightning research (HAIL) consisting of instruments at 13 different high schools in mid-western United States, a broader set of ELF/VLF receivers in Alaska, and various receivers abroad, including in France, Japan, Greece, Turkey, Ireland, and India. A global network of ELF/VLF receivers offer possibilities for a wide range of scientific topics, as well as serving as a means for educational outreach. These goals will be achieved using the newest version of the Stanford VLF receiver, known as AWESOME: Atmospheric Weather Educational System for Observation and Modeling of Electromagnetics. This new version is substantially lower in cost, and easier to set-up and use. Nevertheless, the receivers offer the same ultimate levels of resolution in time, sensitivity and dynamic range, as well as ease of handling of data that is used by researchers conducting cutting edge ionospheric and magnetospheric research. In this context, the placement of these systems at underdeveloped host countries provides an open-ended potential for exploration, limited only by the imagination and drive of the users. AWESOME monitors can be placed at schools, or universities, where they will serve the dual purpose of advancing scientific research, as well as providing a valuable tool for scientific education. Data collected can be pooled and publicly available to all the sites, strengthening the potential for both cooperative education and collaboration on the science between various regions and locations. Title: Magnetic topologies and two-class coronal mass ejections: a numerical magnetohydrodynamic study Authors: Liu, W.; Zhao, X. P.; Wu, S. T.; Scherrer, P. H. Bibcode: 2005astro.ph.11023L Altcode: White-light observations of the solar corona show that there are two characteristic types of Coronal Mass Ejections (CMEs) in terms of speed-height profiles: so-called fast CMEs that attain high speeds low in the corona and slow CMEs that gradually accelerate from low initial speeds. Low and Zhang (2002) have recently proposed that fast and slow CMEs result from initial states with magnetic configurations characterized by normal prominences (NPs) and inverse prominences (IPs), respectively. To test their theory, we employed a two-dimensional, time-dependent, resistive magnetohydrodynamic code to simulate the expulsion of CMEs in these two different prominence environments. Our numerical simulations demonstrate that (i) a CME-like expulsion is more readily produced in an NP than in an IP environment, and, (ii) a CME originating from an NP environment tends to have a higher speed early in the event than one originating from an IP environment. Magnetic reconnection plays distinct roles in the two different field topologies of these two environments to produce their characteristic CME speed-height profiles. Our numerical simulations support the proposal of Low and Zhang (2002) although the reconnection development for the NP associated CME is different from the one sketched in their theory. Observational implications of our simulations are discussed. Title: Prediction and understanding of the north-south displacement of the heliospheric current sheet Authors: Zhao, X. P.; Hoeksema, J. T.; Scherrer, P. H. Bibcode: 2005JGRA..11010101Z Altcode: On the basis of Wilcox Solar Observatory observations of the photospheric magnetic field and the potential field-source surface model, we compare the solid angles occupied by the positive source surface field with that of the negative. We develop an algorithm to quantitatively estimate and understand the positive-negative displacement of the heliospheric current sheet (HCS) about Sun's magnetic dipole equator and the north-south displacement of the HCS about the heliographic equator. The north-south HCS displacement predicted using the algorithm quantitatively agrees with that observed by Ulysses and Wind in 1994-1995. The predicted positive-negative and north-south HCS displacement for 362 Carrington rotations between 1976 and 2001 show that in addition to the two long southward HCS displacement intervals that are consistent with earlier observations and statistical results, there are several short north-south HCS displacement intervals in the rising and early declining solar activity phases. All the positive-negative HCS displacements about the Sun's magnetic dipole equator determined for the 25 years can be understood using the positive-negative asymmetry in the characteristics of coronal holes or open field regions between two hemispheres, such as the area, field strength, or the outward expansion factor of the coronal holes. To understand the north-south HCS displacement about the heliographic equator, the effect of the Sun's magnetic dipole tilt angle relative to the Sun's rotation axis must be taken into consideration as well. Title: The GONG Farside Project Authors: Leibacher, J. W.; Braun, D.; González Hernández, I.; Goodrich, J.; Kholikov, S.; Lindsey, C.; Malanushenko, A.; Scherrer, P. Bibcode: 2005AGUSMSP11B..14L Altcode: The GONG program is currently providing near-real-time helioseismic images of the farside of the Sun. The continuous stream of low resolution images, obtained from the 6 earth based GONG stations, are merged into a single data series that are the input to the farside pipeline. In order to validate the farside images, it is crucial to compare the results obtained from different instruments. We show comparisons between the farside images provided by the MDI instrument and the GONG ones. New aditions to the pipeline will allow us to create full-hemisphere farside images, examples of the latest are shown in this poster. Our efforts are now concentrated in calibrating the farside signal so it became a reliable solar activity forecasting tool. We are also testing single-skip acoustic power holography at 5-7 mHz as a prospective means of reinforcing the signatures of active regions crossing the the east and west limb and monitoring acoustic emission in the neighborhoods of Sun's the poles. This work utilizes data obtained by the Global Oscillation Network Group (GONG) Program, managed by the National Solar Observatory, which is operated by AURA, Inc. under a cooperative agreement with the National Science Foundation. The data were acquired by instruments operated by the Big Bear Solar Observatory, High Altitude Observatory, Learmonth Solar Observatory, Udaipur Solar Observatory, Instituto de Astrofisico de Canarias, and Cerro Tololo Interamerican Observatory, as well as the Michaelson Doppler Imager on SoHO, a mission of international cooperation between ESA and NASA. This work has been supported by the NASA Living with a Star - Targeted Research and Technology program. Title: The Helioseismic and Magnetic Imager for the Solar Dynamics Observatory Authors: Scherrer, P. H.; HMI Team Bibcode: 2005AGUSMSP43A..05S Altcode: The primary goal of the Helioseismic and Magnetic Imager (HMI) investigation is to study the origin of solar variability and to characterize and understand the Sun's interior and the various components of magnetic activity. The HMI investigation is based on measurements obtained with the HMI instrument as part of the Solar Dynamics Observatory (SDO) mission. HMI makes measurements of the motion of the solar photosphere to study solar oscillations and measurements of the polarization in a spectral line to study all three components of the photospheric magnetic field. Here we will give an overview of the HMI science goals, the HMI instrument and its expected performance, the science products produced and the ways in which the science community and public will be able to utilize HMI data. Title: Designing Sudden Ionospheric Disturbance Monitors -- a Unique Collaboration Between Scientists and Educators Authors: Scherrer, D.; Mitchell, R.; Clark, W.; Styner, R.; Scherrer, P.; Inan, U.; Cohen, M.; Tan, J.; Lee, S.; Khanal, S.; Winegarden, S.; Mortfield, P. Bibcode: 2005AGUSMED12A..05S Altcode: Funding agencies such as NASA and NSF encourage E/PO programs to provide local educators with research experience. However, many researchers have neither the time nor the expertize nor the training resources to effectively incorporate an educator into their computer- and numerical-analysis-based research environments. Stanford's Solar Center has been experimenting with a unique project that teams community college and high school educators with research groups to develop a hands-on instrument that the educators's students can, in turn, use to conduct their own research. With support from the researchers, the Educators design, develop, and classroom-test a VLF radio receiver that monitors changes to the Earth's ionosphere caused by solar activity. The educators bring to the table their knowledge of classroom needs plus their amateur background in electronics. Stanford's Electrical Engineering Department's Very Low Frequency Group provides EE resources and knowledge of ionospheric research. Stanford's Solar Observatories Group completes the team with their expertize on the Sun and solar activity. Together, the project team has designed and developed two forms of monitors: 1) an inexpensive Sudden Ionospheric Disturbance (SID) monitor that can be produced in quantity and made available to high schools and community colleges around the nation; and 2) a research quality SID monitor, nicknamed AWESOME, that can be placed in selected schools and will return data of sufficient quality and sensitivity that it can be used both by the students and for ionospheric research. Title: Designing Data Services for the SDO AIA/HMI Joint Science Operations Center Authors: Larsen, R. M.; Bogart, R. S.; Scherrer, P. H.; Schou, J.; Tian, K. Q. Bibcode: 2005AGUSMSH51B..04L Altcode: The Joint Science Operations Center (JSOC) is designed to provide data capture, archive, analysis, and distribution functions for both the Helioseismic and Magnetic Imager and the Atmospheric Imaging Array on the Solar Dynamics Observatory. These instruments are notable for the large quantity of raw data they will generate, more than doubling the total volume of all existing solar data in the first few months alone. In addition, the JSOC will be required to handle a larger component of higher-level data products than most previous missions. The fundamental concept of the JSOC architecture is that the metadata and bulk image data are stored separately, not being combined until the time of use or export. This enables all metadata to be rapidly accessible through a relational database. It permits flexible organization of the data into virtual data sets or series, and the use of an abstracted syntax, such as a URL, for data description and querying. Furthermore, data organization details dictated by the requirements of efficient mass storage can be hidden from the user. Multiple classes of access to the processing and data are envisioned, ranging from production pipeline modules generating standard mission products to workstation users analyzing self-contained data products exported from the archive. The JSOC design provides a rich set of primitives upon which VSO-like services can be built, and should allow us to provide a unified view of the data and data services to all classes of users. Title: The Effect of the Differential Rotation of Photospheric Magnetic Features on Synoptic Frames of the Photospheric Magnetic Field Authors: Zhao, X.; Scherrer, P. H.; Hoeksema, J. T. Bibcode: 2004AGUFMSH21B0419Z Altcode: To model the time-dependent heliosphere we need the instantaneous global distribution of the photospheric magnetic field. As a proxy for the instantaneous global distribution of the photospheric magnetic field at a particular time of interest, the synoptic frame of the photospheric magnetic field is constructed by inserting into the associated monthly Carrington map of the photospheric magnetic field a remapped magnetogram observed as close as possible to the time of interest. In such a synoptic frame, the observation time of magnetic features in pixels outside the inserted magnetogram may differ from the time of the magnetogram by as much as 14 days. During the interval the magnetic features move significantly due to differential rotation, though it may be acceptable to neglect the effects of meridian flow and random walk diffusion. We improve the synoptic frame by accounting for the differential rotation of the magnetic features in the synoptic background frame and consider how changes in the boundary around the inserted magnetogram due to the differential rotation lead to significant effects on the predicted chromospheric and coronal structures. Title: On the Constancy of the Solar Diameter. II. Authors: Kuhn, J. R.; Bush, R. I.; Emilio, M.; Scherrer, P. H. Bibcode: 2004ApJ...613.1241K Altcode: The Michelson Doppler Imager instrument on board SOHO has operated for most of a solar cycle. Here we present a careful analysis of solar astrometric data obtained with it from above the Earth's turbulent atmosphere. These data yield the most accurate direct constraint on possible solar radius variations on timescales from minutes to years and the first accurate determination of the solar radius obtained in the absence of atmospheric seeing. Title: On the Constancy of the Solar Diameter Authors: Kuhn, J. R.; Bush, R.; Emilio, M.; Scherrer, P. Bibcode: 2004AAS...204.8801K Altcode: 2004BAAS...36..819K The solar radius and its variation have now been measured during most of a solar cycle from the Solar and Heliospheric Observatory, using the Michelson Doppler Imager. These instruments provide unique astrometric data from above the Earth's atmosphere. A new analysis based on MDI data yields a refined measurement of the solar radius and no evidence of secular or solar cycle size variations. Title: On the constancy of the solar radius Authors: Kuhn, J.; Bush, R.; Emilio, M.; Scherrer, P. Bibcode: 2004cosp...35.1918K Altcode: 2004cosp.meet.1918K The MDI experiment aboard SOHO has operated for most of a solar cycle. From it we have obtained the most sensitive constraints on possible solar radius variations and changes in the solar limb darkening function over a solar cycle timescale. Here we describe the new measurements and their implications for our understanding of the mechanisms of solar cycle variability. Title: The Stanford Solar Observatory Group E/PO Program Authors: Scherrer, P. H. Bibcode: 2003AGUFMED41E..03S Altcode: As PI for the SOHO/MDI and SDO/HMI investigations and a Co-I in the NSF CISM STC program I have had the opportunity to help in the formulation and development of a multifaceted education and public outreach program. Our E/PO effort began with a web page and press relations but has grown to include the development of an inexpensive spectrometer with supporting materials, poster development and distribution, and a series of webcasts in collaboration with NASA. The present program, with the support of a dedicated E/PO team, includes the development of a solar planetarium program, and a space weather monitor that can be made available through traditional distribution methods. In collaboration with the Stanford Haas Center for Public Service we are also developing a university course that will teach the essentials of science education as part of a lifetime commitment to public service. The development of the Stanford solar E/PO program and involvement of science professionals in that program will be discussed. (The Michelson Doppler Imager (MDI) is an instrument on the Joint ESA & NASA Solar and Heliospheric Observatory (SOHO) mission. The Helioseismic and Magnetic Imager (HMI), is an instrument on the NASA Solar Dynamics Observatory (SDO) mission which is under development. The Center for Space Weather Modeling (CISM) led by Jeff Hughes at Boston University is an NSF Science and Technology Center.) Title: Effects of magnetic topology on CME kinematic properties Authors: Liu, Wei; Zhao, Xue Pu; Wu, S. T.; Scherrer, Philip Bibcode: 2003ESASP.535..459L Altcode: 2003iscs.symp..459L Coronal Mass Ejections (CMEs) exhibit two types of kinematic property: fast CMEs with high initial speeds and slow CMEs with low initial speeds but gradual accelerations. To account for this dual character. Low and Zhang (LZ 2002) proposed that fast and slow CMEs result from initial states with magnetic configurations characterized by normal and inverse quiescent prominences, respectively. To test their theory and further explore the effects of topology on the kinematic properties of CMEs we employed a self-consistent magnetohydrodynamic (MHD) model [Guo, Wu, et al.] to simulate the evolution of CMEs respectively in the normal and inverse prominence environments. The numerical results show that CMEs originating from a normal prominence environment do have higher initial speeds than those from an inverse one. In addition, our simulations demonstrate the distinct roles played by magnetic reconnection in these two topologically different magnetic environments to produce the two different CME height-time profiles as suggested by LZ 2002. Title: Optimal Masks for Solar g-Mode Detection Authors: Wachter, R.; Schou, J.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 2003ApJ...588.1199W Altcode: The detection of gravity (g) modes of solar oscillations is important for probing the physical conditions in the Sun's energy-generating core. We have developed a new method of spatial masks optimized to reveal solar g-modes of angular degree l=1-3 and applied it to Michelson Doppler Imager data in the frequency range of 50-500 μHz. These masks take into account the horizontal component of g-mode velocity eigenfunctions and the variations in the level of noise across the solar disk and adjust for the time-dependent mode projection properties caused by the inclination of the Sun's axis of rotation. They allow us to optimize the signal-to-noise ratio in the oscillation power spectra for potential g-modes of various angular order and degree. The peaks in the resulting spectra are analyzed in terms of their instrumental origin, long-term stability, and correspondence to the theoretically predicted g-mode spectrum. As a consequence of failing to detect any g-mode candidates, new upper limits for the surface amplitude of g-modes are obtained. The lowest upper limits in the range of 5-6 mm s-1 are found for sectorial g-modes (l=m). These limits are an order of magnitude higher than the theoretical prediction of Kumar et al. in 1996. Title: The North-South Offset of the Heliospheric Current Sheet Authors: Zhao, Xuepu; Hoeksema, J. T.; Scherrer, P. H. Bibcode: 2003IAUJD...7E..43Z Altcode: In situ measurements of the heliospheric magnetic field from the Ulysses' fast latitude scan and Wind have shown the offset of the heliospheric current sheet (HCS) southward from the Sun's heliographic equator during early 1995 (Crooker et al. 1997). This southward offset of the HCS can be reproduced using the WSO magnetic synoptic chart and the potential-field source-surface model and has been suggested to be the cause of the north-south hemispherical asymmetry of the galactic cosmic ray flux observed by Ulysses (Simpson et al. 1996).

We examine the distribution of magnetic polarities on the source surface obtained using the WSO magnetic observations between 1976 and 2001 and the potential field-source surface model and find that (1) southward and northward offsets of the HCS occur alternately all over 25 years and each offset lasts for several solar rotations; (2) there are two long intervals of southward offset of the HCS occurred between March 1983 and July 1986 and between April 1992 and June 1995; (3) The north-south offset of the HCS is mainly caused by the north-south hemispherical asymmetry of the magnetic strength in open field regions and the orientation of Sun's dipole moment Title: Evolution of Large-scale Coronal Structure with the Solar Cycle from EUV Data Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 2002ASPC..277..419B Altcode: 2002sccx.conf..419B No abstract at ADS Title: Solar cycle in the photosphere and corona Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 2002ESASP.506..831B Altcode: 2002svco.conf..831B; 2002ESPM...10..831B EIT/SOHO data in four EUV lines and MDI/SOHO (1996-2002), and soft X-ray YOHKOH data (1991-2001) are analyzed in the form of coronal synoptic maps for the investigation of solar cycle variations of the corona and magnetic field. The evolution of coronal structures is closely related to sunspot activity, photospheric magnetic field, and topology of the large-scale magnetic field. The coronal structures visible in extreme ultraviolet and soft X-rays as extended bright loops, reflect the non-axisymmetrical magnetic structure of the Sun, changing with the solar cycle. The long-living coronal structures are related to complexes of solar activity and display the quasiperiodic behavior (impulses of coronal activity) with periods of 1.0-1.5 year in the axisymmetrical distribution of EUV and X-ray fluxes during the current cycle. Title: Vector Magnetic Field Measurement Capabiliity of the Helioseismic and Magnetic Imager on SDO Authors: Bush, R.; Scherrer, P.; Schou, J.; Liu, Y.; Tomczyk, S.; Graham, J.; Norton, A. Bibcode: 2002AGUFMSH52A0464B Altcode: The Helioseismic and Magnetic Imager (HMI) instrument has been selected as part of the payload complement of the Solar Dynamics Observatory Spacecraft. In this poster we describe the observing technique for measuring solar vector magnetic fields. The expected performance of the HMI instrument will be discussed including results of modeling the observing lines and instrument. Title: The Helioseismic and Magnetic Imager for the Solar Dynamics Observatory Authors: Scherrer, P. H. Bibcode: 2002AGUFMSH52A0494S Altcode: The NASA Living With a Star (LWS) Solar Dynamics Observatory (SDO) mission is now in Phase-A of its development. The instrument complement has been selected and includes the Helioseismic and Magnetic Imager (HMI). The primary goal the HMI investigation is to study the origin of solar variability and to characterize and understand the Sun's interior and the various components of magnetic activity. HMI will make measurements of the motion of the solar photosphere to study solar oscillations and measurements of the polarization in a spectral line to study all three components of the photospheric magnetic field. HMI will produce data to determine the interior sources and mechanisms of solar variability and how the physical processes inside the Sun are related to surface magnetic field and activity. It also will produce data to enable estimates of the coronal magnetic field for studies of variability in the extended solar atmosphere. HMI observations will enable establishing the relationships between the internal dynamics and magnetic activity in order to understand solar variability and its effects, leading to predictive capability, one of the key elements of the Living With a Star (LWS) program. The broad goals described above will be addressed in a coordinated investigation in a number of parallel studies. These segments of the HMI investigation are to observe and understand these interlinked processes: Convection- zone dynamics and the solar dynamo; Origin and evolution of sunspots, active regions and complexes of activity; Sources and drivers of solar activity and disturbances; Links between the internal processes and dynamics of the corona and heliosphere; and Precursors of solar disturbances for space-weather forecasts. All HMI data will be available to all for analysis after only minutes to days of automated processing. The dedicated efforts of many in the solar community will be needed to exploit the full potential of HMI and every effort will be made to make such contributions possible. Title: Solar mean magnetic field variability: A wavelet approach to Wilcox Solar Observatory and SOHO/Michelson Doppler Imager observations Authors: Boberg, Fredrik; Lundstedt, Henrik; Hoeksema, J. Todd; Scherrer, Philip H.; Liu, Wei Bibcode: 2002JGRA..107.1318B Altcode: Solar mean magnetic field (SMMF) measurements from the Wilcox Solar Observatory and with the SOHO/MDI instrument are described and analyzed. Even though two completely different methods of observation are used, the two data sets obtained show a strong similarity. Using continuous wavelet transforms, SMMF variability is found at a number of temporal scales. Detected SMMF signals with a 1-2 year period are considered to be linked to variations in the internal rotation of the Sun. Intermediate SMMF oscillations with a period of 80-200 days are probably connected to the evolution of large active regions. We also find evidence for 90 min variations with coronal mass ejections as a suggested origin. Title: A new method for measuring frequencies and splittings of high-degree modes Authors: Reiter, Johann; Rhodes, E. J., Jr.; Kosovichev, A. G.; Schou, J.; Scherrer, P. H. Bibcode: 2002ESASP.508...91R Altcode: 2002soho...11...91R A novel peak-bagging method is presented that operates by fitting a theoretical profile (symmetric or asymmetric) to the separate peaks of each multiplet within each unaveraged power spectrum. This new approach allows a separate frequency, width, and amplitude to be obtained for each m value at each value of l, n. Hence, the frequency splittings due to solar rotation for each multiplet can be measured directly. We present some of our initial results obtained with this new method in the range 45 <= l <= 300, ν <= 7 mHz when applied to data from the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO). Also discussed are some instrumental and methodological problems of high-degree mode measurements. Title: Effect of line asymmetry on determination of high-degree mode frequencies Authors: Reiter, Johann; Rhodes, E. J., Jr.; Kosovichev, A. G.; Schou, J.; Scherrer, P. H. Bibcode: 2002ESASP.508...87R Altcode: 2002soho...11...87R Accurate measurements of frequencies of high-degree p-modes are important for diagnostics of the structure and dynamics of the upper convective boundary layer, and understanding the nature of the solar-cycle variations detected in low- and medium-degree mode frequencies. Neglecting line asymmetry in the peak-bagging approach may lead to systematic errors in the determination of the mode characteristics and, hence, may affect the results of inversions. Here we demonstrate how the p-mode frequencies are systematically changed in the range of l <= 1000, ν <= 7mHz when line asymmetry is taken into account in the fitting of the spectral power peaks. The results reported are based upon spectra that were created from observations obtained from the MDI Full-Disk Program during the 1996 SOHO/MDI Dynamics Run. Title: Large-Scale Solar Coronal Structures in Soft X-Rays and Their Relationship to the Magnetic Flux Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Lemen, J. R.; Scherrer, P. H.; Slater, G. L. Bibcode: 2002ApJ...571L.181B Altcode: We have investigated the relationship between magnetic activity and coronal structures using soft X-ray data from the Yohkoh soft X-ray telescope and magnetic field data from the Kitt Peak Solar Observatory for the period of 1991-2001 and EUV data from the Solar and Heliospheric Observatory EUV Imaging Telescope for 1996-2001. The data are reduced to Carrington synoptic maps, which reveal two types of migrating structures of coronal activity at low and high latitudes in the time-latitudinal distribution. The low-latitude coronal structures, migrating equatorward, correspond to photospheric sunspot activity, and the high-latitude structures migrating toward the poles reflect polar activity of the Sun. We present the following new results:1. The migrating high-latitude coronal magnetic structures are revealed in the soft X-ray data as complete bright giant loops connecting the magnetic field of the following part of active regions with the polar field. They appear during the rising phase and maximum of the solar cycle and show quasi-periodic impulsive variations with a 1-1.5 yr period.2. The soft X-ray intensity of these loops has a strong power-law correlation with the photospheric magnetic flux. The power-law index, which on average is close to 2, shows variations with the solar cycle: it is higher for the period of the declining phase and minimum of solar activity than for the rising phase and maximum. Title: Large-scale coronal structures in EUV and soft X-rays in solar cycle 23 Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.; Lemen, J. R.; Slater, G. L. Bibcode: 2002ESASP.508..367B Altcode: 2002soho...11..367B We have analyzed the EIT/SOHO data in four EUV lines (171 Å, 195 Å, 284 Å and 304 Å) and soft X-ray YOHKOH data in two filters (AlMg and Al) in the form of coronal synoptic maps for the period 1996 - 2001 yrs. Two types of the bright structures have been detected in EUV in the axisymmetrically averaged synoptic maps. The structures of the first type migrate equatorward as the solar cycle progresses. They are related to complexes of sunspot activity and display the "butterfly"-type distribution. The structures of the second type migrate polarward and are associated with footpoints of giant coronal loops, which connect the polar regions and the following parts of the active complexes. These structures of coronal activity are also pronounced in the soft X-ray maps. However, the whole structure of the giant polar loops is visible in X-rays, and reveals connections to the low-latitude coronal structures. The relationship between the soft X-rays emission and the photospheric magnetic flux obtained from SOHO/MDI and Kitt Peak Solar Observatory has been investigated. It has been found that the relationship depends on the phase of the solar cycle. We discuss the role of the magnetic flux in the formation and evolution of the stable coronal structures during the rising phase of cycle 23. Title: Optimal masks for g-mode detection in MIDI velocity data Authors: Wachter, R.; Schou, J.; Kosovichev, A.; Scherrer, P. H. Bibcode: 2002ESASP.508..115W Altcode: 2002soho...11..115W We are applying spatial masks to MDI velocity data that are optimized for revealing g-modes in the frequency range 50 through 500 μHz. These masks take into account the horizontal component of g-mode velocity eigenfunctions as well as the time dependent mode projection properties due to the changing solar B angle, and the varying noise level across the solar disk. The solar noise, which is likely to be caused by supergranulation in this frequency range is assumed to be uniformly distributed over the solar surface, consisting of a dominant horizontal component and a small radial component. The resulting time series are examined for possible g-mode candidates and new upper limits for the surface amplitude of g-modes are obtained. Title: Optimal masks for g-mode detection in MDI velocity data Authors: Wachter, R.; Schou, J.; Kosovichev, A.; Scherrer, P. H.; Phoebus Team Bibcode: 2002AAS...200.0412W Altcode: 2002BAAS...34..645W We are applying spatial masks for MDI velocity data that are optimized for revealing g-modes in the frequency range 50 through 500 μ Hz. These masks take into account the horizontal component of g-mode velocity eigenfunctions as well as the time dependent mode projection properties due to the changing solar B angle, and the varying noise level across the solar disk. The solar noise, which is likely to be caused by supergranulation in this frequency range is assumed to be uniformly distributed over the solar surface, consisting of a dominant horizontal component and a smaller radial component. The optimal masks are applied to the image and the resulting time series are examined for possible g-mode candidates. Because no mode peak has been detected, firm upper limits for the surface visibility of individual low degree modes can be given. Title: Effects of Topology on CME Kinematic Properties Authors: Liu, W.; Zhao, X. P.; Wu, S. T.; Scherrer, P. H. Bibcode: 2002AAS...200.3602L Altcode: 2002BAAS...34Q.693L Coronal Mass Ejections (CMEs) exhibit two types of kinematic property: fast CMEs with high initial speeds and slow CMEs with low initial speeds but gradual accelerations. Efforts have been made for years to probe the underlying physics responsible for this dual character. Within these efforts, magnetic topology has gained much attention. Low and Zhang (ApJ, 564, L53, 2002) proposed that fast or slow CMEs result from initial states with magnetic configurations characterized by the normal or inverse quiescent prominences, respectively. To test their theory and further explore the effects of topology on kinematic properties of CMEs, we employed a 2-D, axisymmetric, resistive MHD model to simulate the evolution of CMEs in the normal and inverse prominence environments, respectively. The numerical results show that the CMEs originating from a normal prominence environment do have higher initial speeds than those from an inverse one. In addition, our simulations demonstrate the distinct roles played by magnetic reconnection in these two topologically different magnetic environments to produce the two different CME height-time profiles as suggested by Low and Zhang. The implication of the results and discussion on future work are described. SOHO is a project of international cooperation between ESA and NASA. Title: The Helioseismic and Magnetic Imager for the Solar Dynamics Observatory Authors: Scherrer, P. H.; SDO/HMI Team Bibcode: 2002AAS...200.5604S Altcode: 2002BAAS...34..735S The Solar Dynamics Observatory, the first mission of the Living With a Star program, will provide a new look at the solar interior, photospheric magnetic fields, and the atmosphere. One of the high priority goals for SDO is to develop new observations and analysis tools to better understand the origin of solar variability and its impact the geospace environment. The HMI instrument as proposed by a consortium led by Stanford University will provide the solar interior and magnetic field observations necessary to meet the goals of SDO. Title: On Formation of the Sigmoidal Structure in Solar Active Region NOAA 8100 Authors: Liu, Y.; Zhao, X. P.; Hoeksema, J. T.; Scherrer, P. H.; Wang, J.; Yan, Y. Bibcode: 2002SoPh..206..333L Altcode: Using soft X-ray images taken by the Soft X-ray Telescope on board Yohkoh, line-of-sight magnetograms taken by SOHO/MDI and vector magnetograms taken at Beijing Astronomical Observatory, we have studied the formation of the sigmoidal structure in active region NOAA 8100 on 3-4 November 1997. The sigmoidal structure appeared after the occurrences of a series of flares accompanied by new magnetic flux emergence. This implies that reconnection may play a role in formation of this sigmoid structure. We calculated the self-helicity (twist) and mutual helicity of the active region before and after the formation of the sigmoidal structure and found that the mutual helicity decreased. The twist of the sigmoidal structure was higher than the twist of the emerging magnetic flux and exceeded the critical twist for kink in stability. This result suggests that the reconnection increased the twist of magnetic flux tubes by converting mutual helicity to self-helicity, supporting the previous studies by Berger (1998, 1999). Title: Coronal Patterns of Activity from Yohkoh and SOHO/EIT Data Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.; Lemen, J. R.; Slater, G. L. Bibcode: 2002mwoc.conf..329B Altcode: We have studied the evolution of large-scale coronal structures using soft X-ray data from YOHKOH and EUV data from SOHO/EIT during the rising phase of the current solar cycle 23, and compared with the evolution of the photospheric magnetic field. During this period the distribution of the coronal structures generally reflects the evolution of the magnetic fields. However, the data from EIT and YOHKOH reveal large-scale magnetic connections in the corona which probably play significant role in the solar cycle. In particular, we have found that coronal structures such as high-latitude giant loops may be important for the topological evolution of magnetic structures during the solar cycle and for polar magnetic field reversals. We discuss possible mechanisms of the polar magnetic field reversals and their relations to the observed coronal structures. Title: Solar Coronal Activity and Evolution of the Magnetic Field Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 2002stma.conf...27B Altcode: No abstract at ADS Title: Active longitudes and coronal structures during the rising phase of the solar cycle Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 2002AdSpR..29..389B Altcode: The longitudinal structure of the solar corona has been investigated during the transition period between solar cycles 22 and 23 and at the beginning of the current cycle 23 using the SOHO/EIT data obtained in 171 Å, 195 Å, 284 Å and 304 Å EUV lines. The EIT images were transformed into synoptic maps for each of the spectral lines, and for the 195Å/171Å line ratio, which is an index of the coronal temperature. The synoptic maps reveal stable longitudinal structures in the coronal intensities and temperature, that are related to large-scale magnetic field structures. We discuss the relation between the coronal and photospheric magnetic structures obtained from the SOHO and Kitt Peak Solar Observatory data, and compare the rotation rates of these structures with the rotation profile of the solar interior in order to determine the possible origin of the coronal structures. Title: The solar interior Authors: Gough, D. O.; Scherrer, P. H. Bibcode: 2002css1.book.1035G Altcode: No abstract at ADS Title: Local-area helioseismology as a diagnostic tool for solar variability Authors: Kosovichev, A. G.; Duvall, T. L.; Birch, A. C.; Gizon, L.; Scherrer, P. H.; Zhao, Junwei Bibcode: 2002AdSpR..29.1899K Altcode: Dynamical and thermal variations of the internal structure of the Sun can affect the energy flow and result in variations in irradiance at the surface. Studying variations in the interior is crucial for understanding the mechanisms of the irradiance variations. "Global" helioseismology based on analysis of normal mode frequencies, has helped to reveal radial and latitudinal variations of the solar structure and dynamics associated with the solar cycle in the deep interior. A new technique, - "local-area" helioseismology or heliotomography, offers additional potentially important diagnostics by providing three-dimensional maps of the sound speed and flows in the upper convection zone. These diagnostics are based on inversion of travel times of acoustic waves which propagate between different points on the solar surface through the interior. The most significant variations in the thermodynamic structure found by this method are associated with sunspots and complexes of solar activity. The inversion results provide evidence for areas of higher sound speed beneath sunspot regions located at depths of 4-20 Mm, which may be due to accumulated heat or magnetic field concentrations. However, the physics of these structures is not yet understood. Heliotomography also provides information about large-scale stable longitudinal structures in the solar interior, which can be used in irradiance models. This new diagnostic tool for solar variability is currently under development. It will require both a substantial theoretical and modeling effort and high-resolution data to develop new capabilities for understanding mechanisms of solar variability. Title: The Largest Active Region of the Solar Cycle Authors: Kosovichev, A. G.; Bush, R. I.; Duvall, T. L.; Scherrer, P. H. Bibcode: 2001AGUFMSH11C0730K Altcode: The largest and most active sunspot region of the current solar cycle (known as AR 9393) was observed by the MDI instrument on SOHO continuously during three solar rotations in March-May 2001. On April 2 this active region produced the largest solar flare of the last 25 years. By using time-distance helioseismology we have investigated the development of the active region in the solar interior during that period starting from the processes of emergence. We present tomographic images of the sound-speed structures associated with this active region up to 100 Mm below the solar surface, and discuss their relation to the evolution of the surface magnetic field. Title: Solar Coronal Structures in Extreme Ultraviolet and Soft X-rays and Their Relation to Magnetic Flux Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Lemen, J. R.; Scherrer, P. H.; Slater, G. L. Bibcode: 2001AGUFMSH11C0720B Altcode: The large-scale coronal structures are ultimately related to internal magnetic fields and thus provide important information about the solar dynamo. We have investigated the relationship between magnetic activity and coronal structures using EUV data from SOHO/EIT and X-ray data from Yohkoh/SXT, and magnetic field data from Kitt Peak and Wilcox Solar Observatories for the period 1996-2000 years. We discuss the non-uniform distribution of coronal heating and its connection with long-lived complexes of solar activity during the current cycle. EUV images reveal two sets of migrating structures of coronal activity in the time-latitudinal distribution of the EUV intensity in 171A, 195A, 284A and 304A EIT wavelength channels. The low-latitude coronal structures, migrating equatorward, correspond to photospheric sunspot activity, and the high-latitude structures migrating towards the poles reflect polar activity of the sun. The polar branches are cooler then the equatorial branches. This is reflected in the time-latitudinal distribution of the soft X-rays in two filters (Al and AlMg). We discuss the physical properties and nature of these structures of coronal activity and their role in the solar cycle. Title: Observed and Predicted Ratios of the Horizontal and Vertical Components of the Solar p-Mode Velocity Eigenfunctions Authors: Rhodes, Edward J., Jr.; Reiter, Johann; Schou, Jesper; Kosovichev, Alexander G.; Scherrer, Philip H. Bibcode: 2001ApJ...561.1127R Altcode: We present evidence that the observed ratios of the horizontal and vertical components of the solar intermediate-degree p-mode velocity eigenfunctions closely match theoretical predictions of these ratios. This evidence comes from estimates of the observed eigenfunction component ratios that were obtained from the fitting of the p-mode oscillation peaks in low- and intermediate-degree (l<=200) m-averaged power spectra computed from two different 60.75 day time series of Global Oscillation Network Group (GONG) project Dopplergrams obtained in late 1996 and early 1998. These fits were carried out using a peak-fitting method in which we fitted each observed p-mode multiplet with a model profile that included both the target mode and its six nearest spatial sidelobes and which incorporated the effects of the incomplete observational time series through the convolution of the fitted profiles with the temporal window functions, which were computed using the two actual GONG observing histories. The fitted profile also included the effects of the spatial leakage of the modes of differing degrees into the target spectrum through the use of different sets of m-averaged spatial leakage matrices. In order to study the sensitivity of the estimated component ratios to the details of the computation of the m-averaged power spectra and of the image-masking schemes employed by the GONG project, we generated a total of 22 different sets of modal fits. We found that the best agreement between the predicted and inferred ratios came from the use of unweighted averaged power spectra that were computed using so-called n-averaged frequency-splitting coefficients, which had been computed by cross-correlating the 2l+1 zonal, tesseral, and sectoral power spectra at each l over a wide range of frequencies. This comparison yielded a total of 1906 pairs of predicted ct,theory and fitted ct,fit eigenfunction component ratios. A linear regression analysis of these pairs of ratios resulted in the following regression equation: ct,fit=(0.0088+/-0.0013)+(0.9940+/- 0.0044)ct,theory. The resulting correlation coefficient was 0.9817. This agreement between the predicted and inferred ratios suggests that the predicted ratios should be used in the fitting of high-degree power spectra where the ratios cannot be inferred because of the blending together of individual modal peaks into broad ridges of power. Title: Time-distance helioseismology and the Solar Orbiter mission Authors: Gizon, L.; Birch, A. C.; Bush, R. I.; Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H.; Zhao, Junwei Bibcode: 2001ESASP.493..227G Altcode: 2001sefs.work..227G No abstract at ADS Title: Detection of High-Latitude Waves of Solar Coronal Activity in Extreme-Ultraviolet Data from the Solar and Heliospheric Observatory EUV Imaging Telescope Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 2001ApJ...554L.107B Altcode: We present the results of an investigation of EUV coronal structures in 1996-2000 using the Solar and Heliospheric Observatory EIT data in 171, 195, 284, and 304 Å lines. During this period, poleward- and equatorward-migrating waves of solar activity have been found in axisymmetrical distributions of EUV intensity in all four lines. In the axisymmetrical distribution of the ratio of 195 Å to 171 Å intensities, which is a proxy of coronal temperature from 1×106 to 2×106 K, the polar branches are less prominent. The high-latitude activity waves are caused by giant coronal magnetic loops connecting the polar magnetic field (formed during the preceding solar cycle) with the magnetic field of the ``following'' parts of active regions that emerged during the rising phase of the current cycle. We suggest that these coronal loops play an important role in the topological evolution of the magnetic structure of the Sun during the solar cycle. Title: Polar Activity Wave in the Solar Corona Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 2001AGUSM..SP61A05B Altcode: We present the results of investigation of EUV coronal structures in 1996-2000 using SOHO/EIT data in 171A, 195A, 284A and 304A. During this period polarward and equatorward migrating waves of activity have been found in axysymmetrical distributions of EUV intensity in all four lines. In the ratio of 195A and 171A intensities, which is a proxy of coronal temperature from 1 MK to 2 MK, the polar branch is not present. We discuss the physical nature of the polar wave of activity and conclude that it is related to dense plasma loops which are cooler then the loops related to the equatorward migrating wave. The latter reflects coronal structures connected with active regions and complexies of solar activity. The polar activity wave is caused by reconnection between the polar magnetic field and the magnetic field of `following' parts of active regions, and, probably, plays an important role in the solar cycle. Title: Are the Signals in the Sun's Mean Magnetic Field Associated With Coronal Mass Ejections? Authors: Liu, W.; Liu, Y.; Zhao, X.; Scherrer, P. Bibcode: 2001AGUSM..SH41A06L Altcode: A study on time-frequency variability of the solar mean magnetic field (SMMF) using wavelet analysis is presented. The SMMF data of Michelson Doppler Imager (MDI) contain an offset most likely introduced by the random error of the exposure time of MDI. Without the offset correction, the peaks of wavelet power spectra for the full-disk SMMF time series coincide with the onset of coronal mass ejections. It has thus been suggested that the peak of wavelet power spectra is associated with coronal mass ejections [Boberg and Lundstedt 2000]. To localize the source of the peak, the full solar disk has been divided into four quadrants. It turns out unexpectedly that the time series for each quadrant closely resembles that of the full-disk series. In addition, all the five series are nearly in phase. On the other hand, the peaks of wavelet power spectra that coincide with coronal mass ejections disappear for the full-disk SMMF series obtained after the offset correction, suggesting that the signal actually occurs in the offset series. These results give rise to the question -- what is the cause of the signals detected in the offset series by the wavelet technique? Title: Helioseismology - What is Next? Authors: Scherrer, P. H.; Fleck, B.; Ulrich, R. K. Bibcode: 2001AGUSM..SP22A09S Altcode: The helioseismology instruments on SOHO have produced a rich set of new insights into the solar interior. Combined with GONG and other ground-based networks these instruments have, for the most part, met the goals set for them. These instruments have demonstrated the usefulness of helioseismic techniques for imaging solar interior structure and motions but do not have all the capabilities necessary to fully exploit the method. Future mission plans call for pushing helioseismic imaging to regions nearer the surface, to higher latitudes, and deeper into the interior. The capabilities of the planned or possible instruments on the Solar Dynamics Observatory, Solar Orbiter, and Farside/Safari missions will enable these presently inaccessible domains to be exploited. Title: Challenges in High-Degree Helioseismology Authors: Rhodes, E. J.; Reiter, J.; Schou, J.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 2001AGUSM..SP21C06R Altcode: Some of the most exciting results that the field of helioseismology has provided in recent years have come from numerical inversions of different properties of the solar p-mode oscillations. Such inversions have been primarily of three types: 1) structural inversions which have employed tables of the frequencies of various p-modes and their associated uncertainties to infer different thermodynamic properties of the solar interior as functions of radius and latitude, 2) rotational inversions which have employed tables of the frequency splittings of the modes of different azimuthal order to measure the internal angular velocity as functions of radius and latitude, and 3) horizontal flow inversions which have employed sets of frequencies of the rings that are observed in three-dimensional power spectra to infer sub-photospheric horizontal flow vectors as functions of depth, latitude and longitude. Unfortunately, the vast majority of such inversions have only included frequencies or frequency splittings of the low- and the intermediate-degree oscillations. Furthermore, the horizontal flow inversions have been somewhat limited by the difficulties in accurately fitting the rings of the higher-degree power spectra. These limitations have prevented helioseismologists from accurately inferring the sound speed, density, adiabatic gradient, and helium abundance in the outermost three to four percent (by radius) of the solar interior. In addition, the absence of high-l frequency splittings from most past rotational inversions has limited the accuracy with which we have been able to estimate the angular velocity of the solar surface layers. These limitations have mainly come about because for l>= 200 the individual modal peaks blend together into broad ridges of power. Fitting such ridges requires knowledge of the amount of power which leaks into the sidelobes that are adjacent to the true spectral peaks. Such leakage information requires detailed knowledge of the spatial behavior of each different intrument, of the ratio of horizontal and vertical components of the solar p-mode eigenfunctions, and of the temporal window function of each dataset. In this presentation we will demonstrate the high-l frequencies which we have obtained from a new fitting technique which employs m-averaged power spectra, temporal window functions, and spatial leakage matrices to fit each mode or ridge with a total of seven peaks. We will also demonstrate that we have obtained evidence from the fitting of GONG power spectra that the true ratios of the eigenfunction components match the theoretical predictions of these ratios. Finally, we will also demonstrate that cross-correlations of the peaks and ridges in the 2l+1 individual spectra at each l result in systematic jumps in the frequency-splitting coefficients for l>=200 due to the blending of the peaks into ridges. We will point out that, unless some method can be found which overcomes these detrimental effects of peak-blending, we will not be able to provide measures of the latitudinal behavior of the solar angular velocity close to the photosphere which will be independent of the horizontal flow mesurements obtained with the so-called ``ring and trumpet'' technique. Title: The Long-Term Variation of the Sun's Magnetic Field Authors: Zhao, X.; Scherrer, P. H.; Hoeksema, J. T.; Sommers, J. Bibcode: 2001AGUSM..SH52A01Z Altcode: Measurements of the near-Earth interplanetary magnetic field (IMF) has been examined and it is revealed that the least-squares-fit line of the annual means of the amplitude of the radial IMF component has risen by a factor of 1.4 from 1964 to 1995 (Stamper et al., JGR, 104, 28325, 1999). This changes in the interplanetary magnetic field have been linked with long-term changes in geomagnetic activity and in total cloud cover over the Earth (Lockwood et al., Nature, 399, 437, 1999). Is the changes in the interplanetary magnetic field caused by changes in Sun's magnetic field? We examine the photospheric magnetic field observed by the Wilcox Solar Observatory and the Kitt Peak Solar Observatory over 26 years and find that the change of the total magnetic flux in the photosphere follows closely the change of sunspot number. The coronal magnetic field computed near the Alfven critical point using the three-layer coronal magnetic field model does show a trend of increase from 1976 to the end of 1991, similar to the trend found in the interplanetary magnetic field. However, the trend after 1992 appears to be decreasing. The cause of the discrepancy is discussed. Title: Probing Magnetic Structures in the Solar Interior by Helioseismic Tomography Authors: Kosovichev, A. G.; Duvall, T. L., Jr.; Scherrer, P. H. Bibcode: 2001ASPC..248..169K Altcode: 2001mfah.conf..169K No abstract at ADS Title: Heliotomography of the outer layers of the Sun Authors: Kosovichev, A. G.; Duvall, T. L., Jr.; Birch, A. C.; Gizon, L.; Scherrer, P. H.; Zhao, Junwei Bibcode: 2001ESASP.464..701K Altcode: 2001soho...10..701K Heliotomography offers important diagnostics of the solar interior by providing three-dimensional maps of the sound speed and flows in the upper convection zone. These diagnostics are based on inversion of travel times of acoustic waves which propagate between different points on the solar surface through the interior. The most significant variations in the thermodynamic structure found by this method are associated with sunspots and complexes of solar activity. The inversion results provide evidence for areas of higher sound speed beneath sunspot regions located at depths of 4 - 20 Mm, which may be due to accumulated heat or magnetic field concentrations. The results reveal structures and flows associated with active regions and sunspots at various stages of their evolution, and provide important constraints for theories of solar dynamics and activity. Title: Large-Scale Patterns of Solar Magnetic Field and Activity Cycles Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 2001ASPC..248..135B Altcode: 2001mfah.conf..135B No abstract at ADS Title: Local-area helioseismology by SOT on-board Solar-B Authors: Sekii, T.; Shibahashi, H.; Kosovichev, A. G.; Duvall, T. L., Jr.; Berger, T. E.; Bush, R.; Scherrer, P. H. Bibcode: 2001ESASP.464..327S Altcode: 2001soho...10..327S Solar-B satellite, a successor to Yohkoh, will be launched in 2005. Placed in a sun-synchronous orbit, it will carry out multi-wavelength observation in optical, EUV and X-ray ranges. One of the instruments on Solar-B, Solar Optical Telescope (SOT), a Japan/US collaboration, aims at measuring the magnetic field and the Doppler velocity field in the solar photosphere. Although it is not specifically designed for helioseismic observations, the high-resolution Dopplergram produced by SOT is potentially a very powerful tool for detailed seismic investigation of subsurface magnetic and thermal structures and associated mass flows. If successful, these measurements will be an important contribution to the main goal of the Solar-B project: understanding the origin and dynamics of the basic magnetic structures and their effects on the solar corona. We discuss the prospect and challenges of local-area helioseismology by SOT. Title: MDI-SOHO Measures of Solar Radius Variation Authors: Emilio, M.; Kuhn, J. R.; Bush, R. I.; Scherrer, P. Bibcode: 2001IAUS..203..101E Altcode: Why does the solar luminosity vary and could it change on human timescales by enough to affect terrestrial climate? As important as these questions are, we lack answers because we do not understand the physical mechanisms which are responsible for the solar irradiance cycle. Progress here depends on discovering how changes in the solar interior affect energy flow from the radiative and convection zones out through the photosphere. Measurements of small changes in the solar radius are a critical probe of the Sun's interior stratification and can tell us how and where the solar luminosity is gated or stored. Here we report results from a sensitive 3 year satellite experiment designed to detect solar diameter fluctuations. Title: Active Longitudinal Structures of the Sun from MDI and EIT Observations Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 2001IAUS..203..251B Altcode: Using data from the EIT and MDI instruments on SOHO and from Kitt Peak Observatory we have studied the non-axisymmetrical structure and dynamics of solar activity at different levels of the solar atmosphere. The data were reduced to synoptic maps of the photospheric magnetic field and coronal structures in the EUV lines: 171Å, 195Å, 284Å, and 304Å. In addition, the coronal temperature maps were obtained using the ration of the 171Å and 195Å lines. The results reveal long-living longitudinal structures in the photosphere and corona during the transition from Cycle 22 to 23 and the rising phase of Cycle 23. We have found the Hale magnetic field polarity reversal first occured at the active longitudes. Thus, the stable longitudinal structures play an important role in the mechanism of the solar cycle. These structures are also revealed in the large-scale structure of the corona. We study the relation between the magnetic and coronal longitudinal structures, and their role in formation of coronal holes. We discuss the relations between rotation of the longitudinal structures in the photosphere and corona and compare with the rotation rate of the solar interior using helioseismic data. This work was carried out in the collaboration with J. T. Hoeksema, A. G. Kosovichev and P. H. Scherrer of Stanford University. Title: Solar Active Longitudes and Their Rotations Using SOHO-MDI Data (CD-ROM Directory: contribs/benevo2) Authors: Benevolenskaya, E. E.; Hoeksema, J. T.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 2001ASPC..223..583B Altcode: 2001csss...11..583B No abstract at ADS Title: g-mode detection: Where do we stand? Authors: Appourchaux, T.; Andersen, B.; Berthomieu, G.; Chaplin, W.; Elsworth, Y.; Finsterle, W.; Frölich, C.; Gough, D. O.; Hoeksema, T.; Isaak, G.; Kosovichev, A.; Provost, J.; Scherrer, P.; Sekii, T.; Toutain, T. Bibcode: 2001ESASP.464..467A Altcode: 2001soho...10..467A We review the recent developments in determining the upper limits to g-mode amplitudes obtained by SOHO instruments, GONG and BiSON. We address how this limit can be improved by way of new helioseismic instruments and/or new collaborations, hopefully providing in the not too distant future unambiguous g-mode detection. Title: On the Constancy of the Solar Diameter Authors: Emilio, M.; Kuhn, J. R.; Bush, R. I.; Scherrer, P. Bibcode: 2000ApJ...543.1007E Altcode: Why does the solar luminosity vary and could it change on human timescales by enough to affect terrestrial climate? As important as these questions are, we lack answers because we do not understand the physical mechanisms responsible for the solar irradiance cycle. Progress here depends on discovering how changes in the solar interior affect energy flow from the radiative and convection zones out through the photosphere. Measurements of small changes in the solar radius are a critical probe of the Sun's interior stratification; they can tell us how and where the solar luminosity is gated or stored. Here we report results from a sensitive 3 yr satellite experiment designed to detect solar diameter fluctuations. Title: Modeling the 1994 April 14 Polar Crown SXR Arcade Using Three-Dimensional Magnetohydrostatic Equilibrium Solutions Authors: Zhao, X. P.; Hoeksema, J. T.; Scherrer, P. H. Bibcode: 2000ApJ...538..932Z Altcode: The coronal magnetic field in the polar crown soft X-ray (SXR) arcade of 1994 April 14 has been computed using the global photospheric magnetic field distribution constructed for the time of interest and the three-dimensional magnetohydrostatic equilibrium solutions. In the solutions there are two free parameters, α and a, respectively, characterizing the effect of the field-aligned and horizontal electric currents. Magnetic field configurations have been determined for various combinations of α and a. The magnetic arcade computed with α-->0 and a=0.9 agrees best in shape and size with the well-developed polar crown SXR arcade. This suggests that the well-developed SXR arcade has a potential-like magnetic configuration with non-field-aligned currents. The computed loci of the apexes of lines of force that close above 1.3 Rsolar match the shape of the bright axial features superposed on the well-developed SXR arcade. This suggests that newly opened lines of force may have reconnected only above 1.3 Rsolar, and consequently the pre-eruption closed lines of force may not be completely opened up during the eruption phase. The SXT images before the formation of the SXR loop show the occurrence of dimmings, supporting the inference of partially ``transient'' coronal opening. Title: Observational Upper Limits to Low-Degree Solar g-Modes Authors: Appourchaux, T.; Fröhlich, C.; Andersen, B.; Berthomieu, G.; Chaplin, W. J.; Elsworth, Y.; Finsterle, W.; Gough, D. O.; Hoeksema, J. T.; Isaak, G. R.; Kosovichev, A. G.; Provost, J.; Scherrer, P. H.; Sekii, T.; Toutain, T. Bibcode: 2000ApJ...538..401A Altcode: Observations made by the Michelson Doppler Imager (MDI) and Variability of solar IRradiance and Gravity Oscillations (VIRGO) on the Solar and Heliospheric Observatory (SOHO) and by the ground-based Birmingham Solar Oscillations Network (BiSON) and Global Oscillations Network Group (GONG) have been used in a concerted effort to search for solar gravity oscillations. All spectra are dominated by solar noise in the frequency region from 100 to 1000 μHz, where g-modes are expected to be found. Several methods have been used in an effort to extract any g-mode signal present. These include (1) the correlation of data-both full-disk and imaged (with different spatial-mask properties)-collected over different time intervals from the same instrument, (2) the correlation of near-contemporaneous data from different instruments, and (3) the extraction-through the application of complex filtering techniques-of the coherent part of data collected at different heights in the solar atmosphere. The detection limit is set by the loss of coherence caused by the temporal evolution and the motion (e.g., rotation) of superficial structures. Although we cannot identify any g-mode signature, we have nevertheless set a firm upper limit to the amplitudes of the modes: at 200 μHz, they are below 10 mm s-1 in velocity, and below 0.5 parts per million in intensity. The velocity limit corresponds very approximately to a peak-to-peak vertical displacement of δR/Rsolar=2.3×10-8 at the solar surface. These levels which are much lower than prior claims, are consistent with theoretical predictions. Title: Comparison of Frequencies and Rotational Splittings of Solar Acoustic Modes of Low Angular Degree from Simultaneous MDI and GOLF Observations Authors: Bertello, L.; Henney, C. J.; Ulrich, R. K.; Varadi, F.; Kosovichev, A. G.; Scherrer, P. H.; Roca Cortés, T.; Thiery, S.; Boumier, P.; Gabriel, A. H.; Turck-Chièze, S. Bibcode: 2000ApJ...535.1066B Altcode: During the years 1996 through 1998 the Michelson Doppler Imager (MDI) and the Global Oscillations at Low Frequency (GOLF) experiments on the Solar and Heliospheric Observatory (SOHO) mission have provided unique and nearly uninterrupted sequences of helioseismic observations. This paper describes the analysis carried out on power spectra from 759 days of calibrated disk-averaged velocity signals provided by these two experiments. The period investigated in this work is from 1996 May 25 to 1998 June 22. We report the results of frequency determination of low-degree (l<=3) acoustic modes in the frequency range between 1.4 mHz and 3.7 mHz. Rotational splittings are also measured for nonradial modes up to 3.0 mHz. The power spectrum estimation of the signals is performed using classical Fourier analysis and the line-profile parameters of the modes are determined by means of a maximum likelihood method. All parameters have been estimated using both symmetrical and asymmetrical line profile-fitting formula. The line asymmetry parameter of all modes with frequency higher than 2.0 mHz is systematically negative and independent of l. This result is consistent with the fact that both MDI and GOLF data sets investigated in this paper are predominantly velocity signals, in agreement with previous results. A comparison of the results between the symmetric and asymmetric fits shows that there is a systematic shift in the frequencies for modes above 2.0 mHz. Below this frequency, the line width of the modes is very small and the time base of the data does not provide enough statistics to reveal an asymmetry. In general, the results show that frequency and rotational splitting values obtained from both the MDI and GOLF signals are in excellent agreement, and no significant differences exist between the two data sets within the accuracy of the measurements. Our results are consistent with a uniform rotation of the solar core at the rate of about 435 nHz and show only very small deviations of the core structure from the standard solar model. Title: Rossby waves on the Sun as revealed by solar `hills' Authors: Kuhn, J. R.; Armstrong, J. D.; Bush, R. I.; Scherrer, P. Bibcode: 2000Natur.405..544K Altcode: It is a long-standing puzzle that the Sun's photosphere-its visible surface-rotates differentially, with the equatorial regions rotating faster than the poles. It has been suggested that waves analogous to terrestrial Rossby waves, and known as r-mode oscillations, could explain the Sun's differential rotation: Rossby waves are seen in the oceans as large-scale (hundreds of kilometres) variations of sea-surface height (5-cm-high waves), which propagate slowly either east or west (they could take tens of years to cross the Pacific Ocean). Calculations show that the solar r-mode oscillations have properties that should be strongly constrained by differential rotation. Here we report the detection of 100-m-high `hills' in the photosphere, spaced uniformly over the Sun's surface with a spacing of (8.7 +/- 0.6) × 104km. If convection under the photosphere is organized by the r-modes, the observed corrugated photosphere is a probable surface manifestation of these solar oscillations. Title: Synoptic Magnetic Field Measurements Authors: Hoeksema, J. T.; Bush, R. I.; Chu, K. -C.; Liu, Y.; Scherrer, P. H.; Sommers, J.; Zhao, X. P.; SOHO/MDI Team Bibcode: 2000SPD....31.0139H Altcode: 2000BAAS...32R.808H Frequent MDI measurements of the photospheric magnetic field make possible new kinds of synoptic data sets that provide insight into the global evolution of solar activity. Synoptic charts can be constructed at central meridian or at other disk longitudes to characterize the development of the surface field and to compare with other kinds of synoptic measurements. Individual magnetograms inserted into a synoptic chart provide a better snapshot of the field configuration and provide a clearer record of changes in the global field. Daily changes can be used for prediction. Development of structures during the rising phase of Solar Cycle 23 are compared with data from other sources and other cycles. Issues of accuracy, precision, and magnetogram merging are discussed. SOHO is a project of international cooperation between ESA and NASA. Title: Active Longitudes in Solar Corona Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 2000SPD....31.0226B Altcode: 2000BAAS...32..815B We present the results of the investigation of the large-scale structure of the solar corona during the transition period between solar cycles 22 and 23 and at the beginning of the current cycle 23 using the SOHO/EIT EUV data obtained in 171 Angstroms, 195 Angstroms, 284 Angstroms and 304 Angstroms lines. For this analysis the data were transformed into synoptic maps for each of the spectral lines, and for the 195 Angstroms/171 Angstroms line ratio which is an index of the coronal temperature. The synoptic maps reveal stable longitudinal structures in the coronal intensities and temperature, which are related to large-scale magnetic field structures. We discuss the relation between the coronal and photospheric magnetic structures obtained from the SOHO/MDI data, and compare the rotation rates of these structures with the rotation profile of the solar interior in order to determine the possible origin of the coronal structures. Title: Sunspots: Frontside and Backside Measurements with Time-Distance Helioseismology Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 2000SPD....31.0505D Altcode: 2000BAAS...32..837D In time-distance helioseismology, travel times measured between different surface locations are used to infer subsurface flows, temperature inhomogeneities and magnetic fields. It has been suggested that most of the travel time reduction near sunspots may be due to the lowered reflection layer associated with the Wilson depression. This will be examined by looking at rays that travel below the sunspot but do not begin or end in the spot. A time-distance method of imaging sunspots on the backside will be compared with that of Lindsey and Braun. Title: Sunspots: frontside and backside measurements with time-distance helioseismology. Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 2000BAAS...32Q.837D Altcode: No abstract at ADS Title: Plasma Flows within and around Sunspots Authors: Bai, T. A.; Scherrer, P. H. Bibcode: 2000SPD....31.0121B Altcode: 2000BAAS...32Q.804B It is essential to know plasma flows within and around sunspots for understanding the evolution and stability of sunspots. By analyzing data obtained by the Michelson Doppler Imager aboard SOHO, we have studied plasma flows within and around four sunspots in the decay phase. We have confirmed the existence of a downward component in the Evershed flow, which has been recognized until recently, mainly as horizontal outflows in the penumbra. The downward component reaches its peak value of about 500 m/s near the outer edge of the penumbra. Additionally, we have discovered plasma flows within umbrae. In two sunspots (in AR 7981 and AR 8194), we have found evidence for radial inflows within the umbra, which are in the opposite direction of Evershed flows. In two other sunspots under this study (in AR 8402 and AR 8403), we have found evidence for outflows within the umbra. The speeds of such horizontal flows are about 300 m/s. Title: US Mission of Opportunity on MONS Authors: Schou, J.; Scherrer, P. H.; Bogart, R. S.; Christensen-Dalsgaard, J.; Kjeldsen, H.; Buzasi, D. L. Bibcode: 2000mons.proc..123S Altcode: The Measuring Oscillations in Nearby Stars (MONS) Survey Telescope (MONS-ST) is a Mission of Opportunity that will study the interior of a large number of stars using stellar oscillations. MONS-ST will provide additional hardware and/or extend the lifetime of the Danish MONS micro satellite, which has been selected for flight in 2003. The additional hardware provided by MONS-ST will enhance the MONS mission by increasing the number of stars observable and extending the lifetime of the mission. A Guest Investigator program, allowing a number of scientists to propose targets and analyze data, will be part of the mission. Title: The Magnetic Connectivity of Moss Regions Authors: Zhao, X. P.; Hoeksema, J. T.; Kosovichev, A. G.; Bush, R.; Scherrer, P. H. Bibcode: 2000SoPh..193..219Z Altcode: A novel emission feature resembling moss was first identified in high-resolution TRACE Fe ix/x 171 Å images by Berger et al. (1999). The moss emission is characterized by dynamic arc-second scale, bright elements surrounding dark inclusions in images of solar active regions. Patches of moss elements, called moss regions, have a scale of 20-30 Mm. Moss regions occur only above some of magnetic plages that underlie soft X-ray coronal loops. Using the potential field extrapolation of the photospheric magnetic field into the corona, we find that the magnetic field lines in moss-associated magnetic plages connect with adjacent plages with opposite polarity; however, all field lines from mossless plages end in surrounding `quiet regions'. This result is consistent with the idea that the TRACE moss is the emission from the upper transition region due to heating of low-lying plasma by field-aligned thermal conduction from overlying hot plasma (Berger et al., 1999). Title: Time-Distance Inversion Methods and Results - (Invited Review) Authors: Kosovichev, A. G.; Duvall, T. L. _Jr., Jr.; Scherrer, P. H. Bibcode: 2000SoPh..192..159K Altcode: The current interpretations of the travel-time measurements in quiet and active regions on the Sun are discussed. These interpretations are based on various approximations to the 3-D wave equation such as the Fermat principle for acoustic rays and the Born approximation. The ray approximation and its modifications have provided the first view of the 3-D structures and flows in the solar interior. However, more accurate and computationally efficient approximations describing the relation between the wave travel times and the internal properties are required to study the structures and flows in detail. Inversion of the large three-dimensional datasets is efficiently carried out by regularized iterative methods. Some results of time-distance inversions for emerging active regions, sunspots, meridional flows and supergranulation are presented. An active region which emerged on the solar disk in January 1998, was studied from SOHO/MDI for eight days, both before and after its emergence at the surface. The results show a complicated structure of the emerging region in the interior, and suggest that the emerging flux ropes travel very quickly through the depth range of our observations. The estimated speed of emergence is about 1.3 km s−1. Tomographic images of a large sunspot reveal sunspot `fingers' - long narrow structures at a depth of about 4 Mm, which connect the sunspot with surrounding pores of the same polarity. Title: New and Old Magnetic Fluxes at the Beginning of Solar Cycle 23 Authors: Benevolenskaya, E. E.; Hoeksema, J. T.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 1999ESASP.448...69B Altcode: 1999ESPM....9...69B; 1999mfsp.conf...69B No abstract at ADS Title: Stellar and Planetary Explorer (SPEX) Authors: Schou, J.; Bogart, R. S.; Bush, R. I.; Hoeksema, J. T.; Scherrer, P. H.; Brown, T. M.; Buzasi, D. L.; Horner, S. D.; Korzennik, S. G. Bibcode: 1999AAS...195.8808S Altcode: 1999BAAS...31.1506S The Stellar and Planetary Explorer (SPEX) mission will search for terrestrial inner planets around Sun-like (FGK, main sequence) stars using photometric techniques as well as provide very long time series for asteroseismology. If every Sun-like star had a planetary system similar to ours, the proposed instrumentation would detect at least 100 terrestrial planets similar to the Earth or Venus and be able to provide statistics on their diameters and orbital periods. SPEX will accomplish this by continuously observing a large number of field stars to detect planetary transits. The instrument consists of a fast Schmidt camera with a mosaic of large CCD detectors. SPEX will observe a field near the galactic plane from a geosynchronous orbit for a minimum of 3 years. The very long asteroseismic time series will allow inferences on the interiors of more than 100 Sun-like stars with a variety of masses and ages. This will allow us to substantially refine stellar model calculations and in particular improve on the age estimates of stars. This in turn is of considerable interest for the understanding of the evolution of our galaxy and the universe as a whole. SPEX will also provide new data for stellar activity and will be able to detect the reflected light from large inner planets, such as those detected using ground based Doppler velocity searches. Title: Structure and Dynamics of Interconnecting Loops and Coronal Holes in Active Longitudes Authors: Benevolenskaya, Elena E.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 1999SoPh..190..145B Altcode: Using SOHO/MDI and SOHO/EIT data we study properties and dynamics of interconnected active regions, and the relations between the photospheric magnetic fields and coronal structures in active longitudes during the beginning of solar cycle 23. The emergence of new magnetic flux results in appearance of new interconnecting loops. The existence of stable coronal structures strongly depends on the photospheric magnetic fluxes and their variations. We present some initial results for a complex of solar activity observed in April 1997, and discuss the role of reconnection in the formation of the interconnected loops and coronal holes. Title: Frequencies and splittings of low-degree acoustic modes: a comparison between MDI and GOLF observations Authors: Bertello, L.; Henney, C. J.; Ulrich, R. K.; Varadi, F.; Kosovichev, A. G.; Roca Cortes, T.; Garcia, R. A.; Scherrer, P. H. Bibcode: 1999AAS...19410805B Altcode: During the years 1996 through 1998 the MDI and GOLF experiments on the SOHO mission have provided unique and nearly uninterrupted sequences of helioseismic observations. This paper describes the analysis carried out on power spectra from 759 days of calibrated velocity signals provided by these two experiments. The time series investigated in this work are from 25 May, 1996 to 22 June, 1998. We report the results of frequency and splitting determination of low-degree (l < 4) acoustic modes in the frequency range between 1.5 mHz and 4.0 mHz. The power spectrum estimation of the signals is performed using classical Fourier analysis and the line-profile parameters of the modes are determined by means of a maximum likelihood method. All parameters have been estimated using both symmetrical and asymmetrical line profile-fitting formula. The line asymmetry parameter of all modes with frequency higher than 2.0 mHz is systematically negative and independent from l. This result is consistent with the fact that both MDI and GOLF data sets investigated in this paper are predominantly velocity signals. A comparison of the results between symmetric fit and asymmetric one shows that there is a systematic shift in the eigenfrequencies for modes above 2.0 mHz. The results show that eigenfrequency and rotational splitting values obtained from both the MDI and GOLF signals are in excellent agreement, and no significant differences exist between the two data sets within the indetermination of the measurement. Title: Frequencies and splittings of low-degree acoustic modes: a comparison between MDI and GOLF observations. Authors: Bertello, L.; Henney, C. J.; Ulrich, R. K.; Varadi, F.; Kosovichev, A. G.; Roca Cortes, T.; Garcia, R. A.; Scherrer, P. H. Bibcode: 1999BAAS...31.1242B Altcode: No abstract at ADS Title: Power spectra comparison between GOLF and MDI velocity observations Authors: Henney, C. J.; Ulrich, R. K.; Bertello, L.; Bogart, R. S.; Bush, R. I.; Scherrer, P. H.; Palle, P. L.; Roca Cortes, T.; Turck-Chieze, S. Bibcode: 1999AAS...194.5617H Altcode: 1999BAAS...31..914H We present a comparison of the velocity power spectra between the GOLF and MDI instruments. In addition, this poster outlines work towards creating a GOLF-simulated signal utilizing MDI velocity images. The simulation of the GOLF signal is achieved by integrating spatially weighted masks with MDI LOI-proxy velocity images. The GOLF-simulated signal and a selection of additional spatially masked MDI velocity signals are compared with the observed GOLF signal for a 759 day period from May 25, 1996 through June 22, 1998. Ultimately, a cross-analysis process between GOLF and MDI signals could lead to an enhancement of our ability to detect low frequency solar oscillations. The signal-to-background ratio (S/B) for the GOLF and the spatially masked MDI velocity data is presented for low degree (l <= 3) and low frequency p-modes. We find that signals from both MDI and GOLF are beneficial for detecting low degree (l <= 3) and low frequency (< 2000 mu Hz) p-modes. For the frequency range and the signals compared in this poster, the GOLF signal has the highest S/B for l=0 p-modes. The S/B of the GOLF and MDI central region masked signals is good for detecting l=1 p-modes. For l >= 2 p-modes, the central region masked signals have the highest S/B of the power spectra compared here. In addition, the S/B of the preliminary GOLF-simulated signal is found to be more similar to the GOLF signal than the MDI LOI-proxy signal without spatial masking for the modes investigated here. Title: Power spectra comparison between GOLF and spatially masked MDI velocity signals Authors: Henney, C. J.; Ulrich, R. K.; Bertello, L.; Bogart, R. S.; Bush, R. I.; Scherrer, P. H.; Roca Cortés, T.; Turck-Chièze, S. Bibcode: 1999A&A...348..627H Altcode: The Global Oscillations at Low Frequency (GOLF) and the Michelson Doppler Imager (MDI) instruments aboard the Solar and Heliospheric Observatory (SOHO) give an excellent opportunity to search for solar low frequency oscillation modes previously undetected from ground based experiments. Presented here is a comparison of the velocity power spectra between the two instruments. In addition, this paper outlines work towards creating a GOLF-simulated signal utilizing MDI velocity images. The simulation of the GOLF signal is achieved by integrating spatially weighted masks with MDI full-disk Doppler images. The GOLF-simulated signal and a selection of additional spatially masked MDI velocity signals are compared with the observed GOLF signal for a 759 day period from May 25, 1996 through June 22, 1998. Ultimately, a cross-analysis process between GOLF and MDI signals could lead to an enhancement of our ability to detect low frequency solar oscillations. For low degree (l<= 3) and low frequency acoustic modes, the signal-to-background ratio between GOLF and the spatially masked MDI velocity data is compared here. Title: The Interaction of New and Old Magnetic Fluxes at the Beginning of Solar Cycle 23 Authors: Benevolenskaya, E. E.; Hoeksema, J. T.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 1999ApJ...517L.163B Altcode: 1999astro.ph..3404B The 11 yr cycle of solar activity follows Hale's law by reversing the magnetic polarity of leading and following sunspots in bipolar regions during the minima of activity. In the 1996-1997 solar minimum, most solar activity emerged in narrow longitudinal zones--``active longitudes'' but over a range in latitude. Investigating the distribution of solar magnetic flux, we have found that the Hale sunspot polarity reversal first occurred in these active zones. We have estimated the rotation rates of the magnetic flux in the active zones before and after the polarity reversal. Comparing these rotation rates with the internal rotation inferred by helioseismology, we suggest that both ``old'' and ``new'' magnetic fluxes were probably generated in a low-latitude zone near the base of the solar convection zone. The reversal of active region polarity observed in certain longitudes at the beginning of a new solar cycle suggests that the phenomenon of active longitudes may give fundamental information about the mechanism of the solar cycle. The nonrandom distribution of old-cycle and new-cycle fluxes presents a challenge for dynamo theories, most of which assume a uniform longitudinal distribution of solar magnetic fields. Title: Measuring Local Short-Term Changes in the Global Solar Magnetic Field Authors: Hoeksema, J. T.; Zhao, X. P.; Chu, K. -C.; Scherrer, P. H. Bibcode: 1999AAS...194.9405H Altcode: 1999BAAS...31Q.991H Global evolution of the solar magnetic field is driven by local magnetic flux changes. We have systematically measured the small-scale magnetic field on the visible surface over an extended time interval. The MDI instrument on SOHO has made 2" full-disk observations of the photospheric field every 96 minutes since May 1996, except for a several-month gap in 1998 and early 1999 caused by problems with the SOHO spacecraft. We are now developing tools to characterize the local variations and relate them to their global effects. MDI magnetograms compare well with KPNO and WSO observations at higher and lower resolution. Several MDI magnetograms are available in near real time each day. MDI daily synoptic charts show the evolution of large-scale coronal structures. Daily updates and archival records of individual magnetograms and synoptic charts can be found on the www at http://soi.stanford.edu. Title: Changes of the boot-shaped coronal hole boundary during Whole Sun Month near sunspot minimum Authors: Zhao, X. P.; Hoeksema, J. T.; Scherrer, P. H. Bibcode: 1999JGR...104.9735Z Altcode: The August 27, 1996, boot-shaped coronal hole is shown to rotate nearly rigidly at a rate of 13.25°/day, greater than the equatorial rotation rate of bipolar magnetic regions such as active regions and plages. The day-to-day variation of the coronal hole border is determined by comparing the rigid rotation projection of the disk-center hole boundary to coronal hole boundaries observed in successive daily coronal images. To determine the influence of the changing photospheric field on the location of the coronal hole boundary, a better approximation of the instantaneous global magnetic field distribution is developed and used as input to a potential-field source-surface model to compute the foot-point areas of open field lines. Day-to-day variations of the coronal hole boundary may be caused by changes of the magnetic field and plasma properties in the corona, as well as by the changing photospheric field. Title: Imaging of Emerging Magnetic Flux by Time-Distance Helioseismology Authors: Kosovichev, A. G.; Duvall, T. L., Jr.; Scherrer, P. H. Bibcode: 1999AAS...194.5901K Altcode: 1999BAAS...31..917K We have used measurements of acoustic travel time in the convection zone to infer local perturbations of the sound speed and 3D flow velocities associated with emerging active regions in July 1996 and January 1998. Both regions were observed with the MDI instrument on SOHO before and after emergence continuously for 9 days. The first active region emerged in a long-lived complex of activity and produced a strong X-class flare. The second active region was a high-latitude region of the new solar cycle. The time-distance inversion results show complicated dynamics of the magnetic flux in the convection zone, and indicate that the emerging flux travels faster in the convection zone than predicted by theory. We discuss the differences in the dynamics of these active regions. Title: Solar Internal Rotation as Measured by the SOHO SOI/MDI Full-Disk Program Authors: Rhodes, E. J., Jr.; Reiter, J.; Kosovichev, A. G.; Schou, J.; Scherrer, P. H. Bibcode: 1999AAS...194.5602R Altcode: 1999BAAS...31..911R We present estimates of the solar internal angular velocity obtained from p-mode frequency splittings computed from observations of the SOHO SOI/MDI Experiment's Full-Disk Program. Specifically, a time series of full-disk Dopplergrams which was obtained during the 61-day long 1996 Dynamics Run of the SOI/MDI Experiment were converted into time series of spherical harmonic coeffificients for degrees ranging up to 1000. These time series of spherical harmonic coefficients were then converted into 1001 sets of zonal, sectoral, and tesseral power spectra. Estimates of the rotationally-induced p-mode frequency splittings for every degree between 1 and 1000 were then obtained from these sets of power spectra through a cross-correlation of the 2l+1 spectra within each set. Because this cross-correlation was carried out between the frequency limits of 1800 to 4800 mu Hz for each set of spectra, the resulting splitting coefficients were effectively averaged over the radial order, n, at each degree. Due to the blending of individual p-mode spectral peaks for degrees above 200, the raw frequency splitting coefficients for all degrees between 200 and 1000 had to be corrected before an inversion could be performed. We will describe the method we adopted for correcting the raw splittings and we will present both the raw and corrected splitting coefficients. We will also present a two-dimensional inversion of the corrected coefficients. Finally, we will also demonstrate how the inclusion of the high-degree splittings allows us to obtain better estimates of the solar internal angular velocity in the shallow sub-photospheric part of the solar convection zone than have been possible in past studies which included only the splittings of the low- and intermediate-degree p-modes. Title: The SOI-MDI Dynamics Program: Observing the Solar Cycle Authors: Bush, R. I.; Beck, J. G.; Bogart, R. S.; Hoeksema, J. T.; Kosovichev, A. G.; Scherrer, P. H.; Schou, J.; Sommers, J.; Duvall, T. L. Bibcode: 1999AAS...194.9205B Altcode: 1999BAAS...31..987B The Michelson Doppler Imager instrument on the SOHO spacecraft has been observing the Sun over the last three years. The MDI Dynamics Program provides nearly continuous full disk Doppler measurements of the solar photosphere with 4 arc-second resolution for periods of 60 to 90 days each year. Three of these Dynamics periods have been completed: 23 May to 24 July 1996, 13 April to 14 July 1997, 9 January to 10 April 1998. A fourth Dynamics observing period began on 13 March and is scheduled to continue through mid July. These observations provide a unique view of the evolution of the Sun in the early part of the solar cycle, both from interior flows deduced by helioseimic analysis and changes in large scale surface motion. Details of the Dynamics programs will be presented along with an overview of current results. This research is supported by the SOI-MDI NASA grant NAG5-3077 at Stanford University. Title: SONAR - Solar Near-surface Active Region Rendering Authors: Scherrer, P. H.; Hoeksema, J. T.; Kosovichev, A. G.; Duvall, T. L.; Schrijver, K. J.; Title, A. M. Bibcode: 1999AAS...194.7606S Altcode: 1999BAAS...31Q.957S The processes in the top 20,000-km of the Sun's convection zone govern the growth and decay of active regions and provide the magnetic flux and energy for the active phenomena of the upper solar atmosphere. The MDI experiment on SOHO has demonstrated that this region is now accessible to study by means of local helioseismology. However, SOHO provides neither the temporal nor spatial resolution and coverage necessary to exploit these techniques to study the eruption and evolution of active region magnetic structures. The SONAR mission with moderate resolution full disk Doppler and vector magnetic field observations, and atmospheric magnetic connectivity observations via EUV imaging can provide the necessary data. The science motivation and general instrumentation requirements for the mission are presented. Title: New Views of Active Regions Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 1999AAS...194.4203D Altcode: 1999BAAS...31..882D 3-d acoustic tomography of the region below the photosphere is providing qualitatively new insights about solar active regions. This tomography is based on the measurement of travel times between different surface locations and is sensitive to subsurface flows and to wave-speed inhomogeneities caused by temperature and magnetic field variations. A flow cell has been seen below sunspots similar to the model of Parker (Ap.J. 230,905-913,1979) in which there is a horizontal inflow near the top of the convection zone, a downflow directly below the sunspot and a horizontal outflow below. This flow may be what stabilizes the sunspot. A wave-speed reduction is seen in the 2 Mm below the surface sunspot and a wave-speed enhancement is seen below to at least 10 Mm depth for a reasonably large spot. At 10 Mm depth, a wave-speed increase of 3% could be caused by a 10 kG magnetic field or a temperature excess of 6%. At present we cannot distinguish between temperature and magnetic field effects on the wave speed, but we will present a comparison between the wave speed as predicted from a sunspot model and that measured with the tomography. This research is supported by NASA contract NAG5-3077 at Stanford University. Title: Needs for Future of Visible Light Observation Authors: Scherrer, P. H. Bibcode: 1999AAS...194.6502S Altcode: 1999BAAS...31..927S There are a number of both recent and long-standing questions that require space-based visible light observations of the Sun. These fit into several general categories including total irradiance measurements, coronal and heliospheric structures, high resolution vector magnetic fields, high resolution photospheric structures, and the structure and dynamics of the solar interior for both global and local phenomena. Much progress has been made lately or is in development for the near future. In particular solar interior studies have had significant development with SOHO and GONG observations, Solar-B will address moderately high-resolution structures and fields, STEREO will address dynamic structures in the corona, etc. Nevertheless there will remain many very important questions after these missions are complete. The interior dynamics near the rotation axis and near the poles remains elusive. Detecting magnetic fields at the base of the convection zone remains beyond reach. Imaging the motions in the upper part of the convection zone beneath active regions has been demonstrated but detailed study is not possible with current instrumentation. Full disk moderate resolution and small region high resolution magnetic field observations just serve to point to the need for full disk high resolution magnetic observations. And observations of magnetoconvective fine scale structures remain just beyond reach. These needs and some possible observing scenarios will be discussed. Title: Large-Scale Solar Flows From Time-Distance Helioseismology Authors: Giles, P. M.; Duvall, T. L., Jr.; Scherrer, P. H. Bibcode: 1999AAS...194.2102G Altcode: 1999BAAS...31..858G Over the past thirty years, helioseismology has proven to be an extremely useful tool for probing the solar interior. Using global mode frequencies, the structure and the rotation of the Sun have been determined with unprecedented accuracy. More recently, there has been rapid evolution of so-called "local" methods in helioseismology. These techniques are able to examine aspects of the Sun's structure and dynamics which are otherwise inaccessible. One of the most successful of these techniques is time-distance helioseismology, which relies on the determination of wave travel times to infer properties of the subsurface region. This approach has been particularly successful in measuring flows in the solar convection zone which were previously observable only at the surface. In this paper we present our most recent results in these investigations, including our latest determination of the meridional circulation as a function of depth, and our search for large-scale nonaxisymmetric velocity structures. Data for this research was obtained by the MDI instrument on SOHO. This research is supported by NASA contract NAG5-3077 at Stanford University. Title: The Magnetic Structure of the Sun at the Beginning of Solar Cycle 23 Authors: Benevolenskaya, E. E.; Hoeksema, J. T.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 1999AAS...194.9201B Altcode: 1999BAAS...31R.986B The 11-year cycle of solar activity follows Hale's law by reversing the magnetic polarity of leading and following sunspots in bipolar regions during the minima of activity. In the 1996-97 solar minimum, most solar activity emerged in narrow longitudinal zones - `active longitudes' but over a range in latitude. Investigating the distribution of solar magnetic flux, we have found that the Hale sunspot polarity reversal first occurred in these active zones. We have estimated the rotation rates of the magnetic flux in the active zones before and after the polarity reversal. Comparing these rotation rates with the internal rotation inferred by helioseismology, we suggest that both `old' and `new' magnetic fluxes were probably generated in a low-latitude zone near the base of the solar convection zone. The reversal of active region polarity observed in certain longitudes at the beginning of a new solar cycle suggests that the phenomenon of active longitudes may give fundamental information about the mechanism of the solar cycle. The non-random distribution of old-cycle and new-cycle fluxes presents a challenge for dynamo theories, most of which assume a uniform longitudinal distribution of solar magnetic fields. We have used accurate measurements of solar oscillation frequencies from the GONG and SOHO/MDI to infer the latitudinal dependence of the solar structure associated with magnetic fields beneath the surface. The results show significant variations of the aspherical structure of the Sun at the beginning of the new cycle. These variations correlate with the latitudinal distribution of the surface magnetic flux. We discuss possible variations at the base of the convection zone and their relation to the dynamo mechanism. Title: Subsurface Observations of Sunspots and Solar Supergranulation Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 1999AAS...194.5606D Altcode: 1999BAAS...31..912D 3-d acoustic tomography of the region below the photosphere is providing new insights into sunspots and the apparently convective flow observed at the surface called supergranulation. The tomography is based on the measurement of travel times between different surface locations and is sensitive to subsurface flows and to wave-speed inhomogeneities caused by temperature and magnetic field variations. This study uses dopplergrams from the MDI instrument on the SOHO spacecraft. A flow cell has been seen below sunspots similar to the model of Parker (Ap.J. 230,905-913,1979) in which there is a horizontal inflow near the top of the convection zone, a downflow directly below the sunspot and a horizontal outflow below. The depth of the supergranulation flow will be discussed. This research is supported by NASA contract NAG5-3077 at Stanford University. Title: Time-distance Measurements of Meridional Circulation Deep in the Convection Zone Authors: Giles, P. M.; Duvall, T. L., Jr.; Scherrer, P. H. Bibcode: 1999soho....9E..23G Altcode: Explaining the solar cycle is one of the central goals of solar physics. Some of the most successful models of the cycle fall under the broad category of Babcock-Leighton dynamo theories. Babcock and Leighton developed this model in the 1960s, making use of the most recent observations of the Sun's magnetic field and surface motions. The model reproduces the large-scale properties of the cycle by invoking both differential rotation and supergranular diffusion of magnetic elements. Although the original work predates the birth of helioseismology, it still underlies much of our current understanding of the solar cycle. The development of helioseismology has, however, necessitated some evolution of the theory. For example, dynamo theorists now must match their models to the observed differential rotation profile in the solar interior. Prodded by more sophisticated surface measurements, several groups have also proposed models including a meridional circulation. Until recently, theorists were free to speculate on the characteristics of this flow below the surface. In the past few years, however, several helioseismic techniques have been used to successfully measure the meridional circulation in the solar interior. In this paper, the authors present their latest measurements of the meridional flow using the time-distance technique on MDI data. These measurements now reach far enough into the convection zone that they might be a useful constraint on solar dynamo theories. This research is supported by NASA contract NAG5-3077 at Stanford University. Title: Time-distance helioseismology Authors: Kosovichev, A. G.; Duvall, T. L.; Scherrer, P. H. Bibcode: 1999AdSpR..24..163K Altcode: The time-distance helioseismology (or helioseismic tomography) is a new promising method for probing 3-D structures and flows beneath the solar surface, which is potentially important for studying the birth of active regions in the sun's interior and for understanding the relation between the internal dynamics of active regions and chromospheric and coronal activity. In this method, the time for waves to travel along subsurface ray paths is determined from the temporal cross correlation of signals at two separated surface points. By measuring the times for many pairs of points from Dopplergrams covering the visible hemisphere, a tremendous quantity of information about the state of the solar interior is derived. As an example, we present the results for supergranular flows and for an active region which emerged near the center of the solar disk in July 1996, and was studied from SOHO/MDI for nine days, both before and after its emergence at the surface. Initial results show a complicated structure of the emerging region in the interior, and suggest that the emerging flux ropes travel very quickly through the depth range of our observations. Title: Power spectra comparison between GOLF and MDI velocity observations. Authors: Henney, C. J.; Ulrich, R. K.; Bertello, L.; Bogart, R. S.; Bush, R. I.; Scherrer, P. H.; Pallé, P. L.; Roca Cortés, T.; Turck-Chièze, S. Bibcode: 1999BAAS...31Q1237H Altcode: No abstract at ADS Title: Prospects for Future Helioseismology Missions Authors: Scherrer, Philip H. Bibcode: 1999soho....9E..31S Altcode: The progress afforded by present and past helioseismology missions has been the topic of this and numerous previous conferences. The primary conclusion of the 1983 NASA study on prospects for solar oscillations have been basically confirmed. That is, part of the job can be done on the ground but a significant part can only be done from space. While we have made significant progress, it is also clear that additional opportunities to use helioseismic techniques to better understand stellar interiors remain. Recent advances in local helioseismology in particular point to additional observing requirements. These include larger field of view at high resolution in order to follow magnetic region development, longer baselines in longitude to probe the bottom of the convection zone and below, and a high latitude vantage point to examine processes near the rotation axis. Several possible missions have been discussed recently to address these issues. They include SONAR, Farside Observer, Solar Polar Imager, and Solar Probe. The basic concepts of these missions will be discussed along with the continuing role for enhanced ground based observations. Title: Plasma Flows in Growing Active Regions Authors: Bai, T.; Scherrer, P. H. Bibcode: 1999soho....9E..34B Altcode: Around mature spots plasma outflows are often observed. Moving magnetic features are also often observed. However, plasma flows around growing sunspots have not been studied in detail. MDI aboard SOHO provides high-quality data for such studies. AR 7968 was growing when it passed near the central meridian on June 6, 1996. It passed near the disk center because of its very low latitudes (N02). Analyzing dopplergrams and magnetograms of this active region, we have observed vertical downward flows of about 100 m/s surrounding the sunspots. Around the area of downward flow, we find a ring of upward flow area. Similar behavior was observed in AR 7978, which was rapidly growing while passing the central meridian on July 5, 1996. This research is supported by NASA grant NAG5-3077 at Stanford University. Title: APT: an astrometric and photometric telescope Authors: Kuhn, Jeff R.; Bush, Rock I.; Coulter, Roy; Froehlich, Claus; Gwo, Dz-Hung; Jones, A.; Pap, Judit M.; Scherrer, Philip H.; Sofia, Sabatino; Ulrich, Roger Bibcode: 1998SPIE.3442..203K Altcode: Helioseismic and precise solar photometric measurements reveal that the Sun varies globally as a start during the source of an 11 year solar cycle. To understand the physical mechanisms of the magnetic cycle in the solar interior we must learn how to measure the tiny changes in the Sun's global properties, like its radius, internal temperature distribution and surface luminosity. The SoHO/MDI experimental has proven that exceedingly small solar shape fluctuations are measurable from outside our atmosphere. We describe here an instrument which will not only measure limb shape oscillations with unprecedented accuracy, but it will also detect solar radius changes with heretofore unachieved accuracy and precision. Variations in these parameters are caused by physical changes, both in the photosphere and the deep solar interior. Solar radius and shape observations will teach us how the Sun's convective envelope responds to emergent energy fluctuations. The determination of this outer boundary condition is essential to understand the solar total irradiance and luminosity variations. Title: New Observations of the Sun: Helioseismology and the Photospheric Magnetic Field Authors: Scherrer, Philip Bibcode: 1998APS..DPPH4I202S Altcode: In the past several years the interior of the Sun has become accessible to direct observation via helioseismology. The Michelson Doppler Imager (MDI) experiment aboard the Solar and Heliosperic Observatory (SOHO) spacecraft has allowed inferrences of solar interior conditions from the upper few thousand km to near the solar core. In addition to global scale observations, the MDI instrument allows local helioseismology techniques to be used to probe local sound speed variations and flows in the near surface regions just beneath supergranulation and sunspots. The MDI instrument also obtains a near continuous record of the photospheric magnetic field without degradation from the Earht's atmosphere. These observations reveal a new picture of magnetic field evolution. This paper will review the observational methods, basic analysis techniques, and present results obtained from the first two years of operation of MDI. Further information about the SOHO mission and MDI observations in particular can be found at <A HREF=http://soi.stanford.edu>http://soi.stanford.edu</A>. Title: Asymmetry and Frequencies of Low-Degree p-Modes and the Structure of the Sun's Core Authors: Toutain, T.; Appourchaux, T.; Fröhlich, C.; Kosovichev, A. G.; Nigam, R.; Scherrer, P. H. Bibcode: 1998ApJ...506L.147T Altcode: An accurate determination of the frequencies of low-degree solar p-modes is an important task of helioseismology. Using 679 days of solar oscillation data observed in Doppler velocity and continuum intensity from two Solar and Heliospheric Observatory instruments (the Michelson Doppler Imager and the SunPhotoMeter), we show that fitting the spectra with Lorentzian profiles leads to systematic differences between intensity and velocity frequencies as large as 0.1 μHz for angular degrees l=0, 1, and 2 because of the opposite asymmetry between intensity and velocity. We use a physics-based asymmetrical line shape to fit p-mode lines, and we demonstrate that their asymmetry is statistically significant and that frequency differences are considerably reduced. These measurements provide more accurate estimates of the solar eigenfrequencies. We discuss inferences of the structure of the solar core. Title: Helioseismic Studies of Differential Rotation in the Solar Envelope by the Solar Oscillations Investigation Using the Michelson Doppler Imager Authors: Schou, J.; Antia, H. M.; Basu, S.; Bogart, R. S.; Bush, R. I.; Chitre, S. M.; Christensen-Dalsgaard, J.; Di Mauro, M. P.; Dziembowski, W. A.; Eff-Darwich, A.; Gough, D. O.; Haber, D. A.; Hoeksema, J. T.; Howe, R.; Korzennik, S. G.; Kosovichev, A. G.; Larsen, R. M.; Pijpers, F. P.; Scherrer, P. H.; Sekii, T.; Tarbell, T. D.; Title, A. M.; Thompson, M. J.; Toomre, J. Bibcode: 1998ApJ...505..390S Altcode: The splitting of the frequencies of the global resonant acoustic modes of the Sun by large-scale flows and rotation permits study of the variation of angular velocity Ω with both radius and latitude within the turbulent convection zone and the deeper radiative interior. The nearly uninterrupted Doppler imaging observations, provided by the Solar Oscillations Investigation (SOI) using the Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO) spacecraft positioned at the L1 Lagrangian point in continuous sunlight, yield oscillation power spectra with very high signal-to-noise ratios that allow frequency splittings to be determined with exceptional accuracy. This paper reports on joint helioseismic analyses of solar rotation in the convection zone and in the outer part of the radiative core. Inversions have been obtained for a medium-l mode set (involving modes of angular degree l extending to about 250) obtained from the first 144 day interval of SOI-MDI observations in 1996. Drawing inferences about the solar internal rotation from the splitting data is a subtle process. By applying more than one inversion technique to the data, we get some indication of what are the more robust and less robust features of our inversion solutions. Here we have used seven different inversion methods. To test the reliability and sensitivity of these methods, we have performed a set of controlled experiments utilizing artificial data. This gives us some confidence in the inferences we can draw from the real solar data. The inversions of SOI-MDI data have confirmed that the decrease of Ω with latitude seen at the surface extends with little radial variation through much of the convection zone, at the base of which is an adjustment layer, called the tachocline, leading to nearly uniform rotation deeper in the radiative interior. A prominent rotational shearing layer in which Ω increases just below the surface is discernible at low to mid latitudes. Using the new data, we have also been able to study the solar rotation closer to the poles than has been achieved in previous investigations. The data have revealed that the angular velocity is distinctly lower at high latitudes than the values previously extrapolated from measurements at lower latitudes based on surface Doppler observations and helioseismology. Furthermore, we have found some evidence near latitudes of 75° of a submerged polar jet which is rotating more rapidly than its immediate surroundings. Superposed on the relatively smooth latitudinal variation in Ω are alternating zonal bands of slightly faster and slower rotation, each extending some 10° to 15° in latitude. These relatively weak banded flows have been followed by inversion to a depth of about 5% of the solar radius and appear to coincide with the evolving pattern of ``torsional oscillations'' reported from earlier surface Doppler studies. Title: Long-lived giant cells detected at the surface of the Sun Authors: Beck, J. G.; Duvall, T. L.; Scherrer, P. H. Bibcode: 1998Natur.394..653B Altcode: Giant convective cells have been predicted to exist in the Sun. Such cells should span the entire zone unstable to convective motions - now known to cover the outer 29 per cent of the Sun's radius - and could be dredging up the magnetic flux that is thought to be the source of solar activity (sunspots). Several studies have failed to detect these giant cells, although there have been hints of their existence. We have detected long-lived velocity cells, which we identify as the elusive giant convective cells, extending over 40-50 degrees of longitude but less than 10 degrees of latitude. The large aspect ratio (>4) is surprising (although predicted by one model) and may be a consequence of the Sun's differential rotation, whereby features with a larger extent in latitude are broken up by rotational shear. Title: Oscillations of sunspot magnetic fields Authors: Rueedi, I.; Solanki, S. K.; Stenflo, J. O.; Tarbell, T.; Scherrer, P. H. Bibcode: 1998A&A...335L..97R Altcode: We report on velocity and magnetic field oscillations observed in sunspots using the MDI instrument onboard SOHO. In addition to the well-known velocity oscillations, the data clearly show highly localised oscillations of the magnetogram signal in different parts of the sunspots. We show that only oscillations of the magnetic field vector can produce the observed magnetogram oscillations, and that the observed phase relations suggest an origin in terms of magnetoacoustic gravity waves. Title: Magnetic Field of the Sun as a Star: The Mount Wilson Observatory Catalog 1970-1982 Authors: Kotov, V. A.; Scherrer, P. H.; Howard, R. F.; Haneychuk, V. I. Bibcode: 1998ApJS..116..103K Altcode: Measurements of the mean magnetic field of the Sun (MMFS) seen as a star were regularly conducted at the Mount Wilson Observatory from 1970 October through 1982 December. A listing is presented of all these data (2457 daily values) suitable for comparison with similar data of other observatories and for studies of magnetic variability and rotation of the Sun. The scatter-plot diagrams and power spectra of the Mount Wilson data and also of the total data 1968-1991 (collected from three observatories: Crimean Astrophysical Observatory, Mount Wilson Observatory, and Wilcox Solar Observatory) are also presented. Time variations of the MMFS connected with solar rotation at periods ~27-28 days and also an enigmatic 1 yr variation are briefly discussed.

The power spectrum of the 24 yr data set shows that the most significant and phase-coherent synodic periods of the MMFS variations are 26.92 +/- 0.02 and 27.13 +/- 0.02 days (both are thought to be associated with rotation of the large-scale surface magnetic field near equator of the Sun) and 28.13 +/- 0.02 days. It is suggested that the latter period reflects ``rigid'' rotation of the global magnetic field concentrated under the bottom of the solar convection zone. The arguments are given in favor of reality and high confidence level of major periodicities exhibited by MMFS variations. Title: Initial High-Degree p-Mode Frequencies and Rotational Frequency Splittings from the SOHO SOI/MDI Experiment Authors: Rhodes, E. J., Jr.; Reiter, J.; Kosovichev, A. G.; Schou, J.; Scherrer, P. H. Bibcode: 1998AAS...192.1901R Altcode: 1998BAAS...30..845R We present the first high-degree p-mode frequencies and rotationally-induced frequency splittings obtained from the Full-Disk Program of the SOHO Solar Oscillation Investigation/Michelson Doppler Imager experiment. The frequencies and splittings which we present here were computed from power spectra obtained during the 1996 SOI/MDI Dynamics Run. Specifically, a 60.75-day time series of full-disk Dopplergrams was converted into sets of zonal, tesseral, and sectoral power spectra covering the degree range of 0 through 1000. Estimates of the n-averaged frequency splittings were computed for the frequency range of 1800 to 4800 microhertz at each degree and these averaged splitting coefficients were then employed to compute an average power spectrum for that degree. From these 1001 average power spectra estimates were made of the frequencies, frequency uncertainties, widths, peak power densities, and background power densities of a total of 13664 separate peaks in the set of 1001 average power spectra. A total of 2554 of these peaks were isolated enough in their respective spectra to be fit as single p-modes. However, for the remaining 11110 peaks (mostly those above l =200), the individual p-mode peaks and their spatial sidelobes were located so close together in frequency that they appeared as ridges rather than as isolated modal peaks in the average power spectra. For these p-mode ridges we obtained so-called ``ridge-fit'' parameter estimates. Observed asymmetries in the p-mode ridge shapes altered the fitted peak frequencies from their ``true'' values and required that we correct the raw ridge-fit frequencies. Forty sets of these power spectra were also processed to yield estimates of the rotational splitting coefficients for individual p-mode ridges for every 25th degree between l =25 and 1000. For l between 25 and 175 we will compare these Full-Disk program splittings with the previously-published splittings from the 1996 SOI/MDI Medium-l Program (Kosovichev et al., Solar Physics, 170, 43-61,1997). Title: Asymmetry in Velocity and Intensity Helioseismic Spectra: A Solution to a Long-standing Puzzle Authors: Nigam, R.; Kosovichev, A. G.; Scherrer, P. H.; Schou, J. Bibcode: 1998ApJ...495L.115N Altcode: We give an explanation for the opposite sense of asymmetry of the solar acoustic mode lines in velocity and intensity oscillation power spectra, thereby solving the half-decade-old puzzle of Duvall and coworkers. The solution came after comparing the velocity and intensity oscillation data of medium angular degree l obtained from the Michelson Doppler Imager instrument on board the Solar and Heliospheric Observatory with the theoretical power spectra. We conclude that the solar noise in the velocity and intensity spectra is made up of two components: one is correlated to the source that is responsible for driving the solar p-modes, and the other is an additive uncorrelated background. The correlated component of the noise affects the line profiles. The asymmetry of the intensity spectrum is reversed because the correlated component is of a sufficiently large level, while the asymmetry of the velocity spectrum remains unreversed because the correlated component is smaller. This also explains the high-frequency shift between velocity and intensity at and above the acoustic cutoff frequency. A composite source consisting of a monopole term (mass term) and a dipole term (force due to Reynolds stress) is found to explain the observed spectra when it is located in the zone of superadiabatic convection at a depth of 75+/-50 km below the photosphere. Title: The sun's shape and brightness Authors: Kuhn, J. R.; Bush, R. I.; Scherrer, P.; Scheick, X. Bibcode: 1998Natur.392..155K Altcode: We present satellite data that show that the sun's shape and temperature vary with latitude in an unexpectedly complex way. Although the solar oblateness shows no evidence of varying with the solar cycle, we find a significant hexadecapole shape term which may vary. We also see a variation of about 1.5 K in the surface temperature with latitude. Based on these results, we suggest that sensitive observations of brightness variations be used as a record of the surface 'shadow' of cyclical changes in the solar interior. Title: A New Method for Diagnostics of Solar Magnetic Fields and Flows from Time-Distance Analysis Authors: Ryutova, Margarita; Scherrer, Philip Bibcode: 1998ApJ...494..438R Altcode: We propose a new method to obtain information on plasma flows and magnetic fields below the visible solar surface using time-distance measurements. The method is based on sine and cosine transforms of propagation times measured as a function of direction. The method allows one to sort out various characteristics of the subsurface medium, the flows, magnetic fields and their nonuniformities, and is less sensitive to the measurement errors. We discuss the parity properties of various contributions to the propagation times with respect to forward and backward directions and show how these properties allow separation of the effects of magnetic field and flows, as well as separation of the horizontal components from the vertical. It is shown that the first harmonics contain information on the direction and absolute value of the velocity, while the second harmonics are sensitive to the orientation and absolute value of horizontal magnetic fields and spatial gradients of the flow velocity. We discuss the effects of discrete mesh on the accuracy of measurements of the propagation time. An advantage of the method is in its intrinsic invariance with respect to the choice of the coordinate frame. The method provides an automatic rule of assigning proper weights to every observation points. We give estimates of the accuracy of the reconstruction of the flow field over distances comparable with the scale of the convection. We also present the ``magnetic'' corrections to the propagation time in a vertically stratified medium. Title: The Comparison of Simultaneous SOI/MDI and Mt. Wilson 60-foot Tower Power Spectra and p-Mode Parameters Authors: Rhodes, E. J., Jr.; Reiter, J.; Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Rose, P. J.; Irish, S.; Jones, A. R. Bibcode: 1998ESASP.418..311R Altcode: 1998soho....6..311R We present the results of the first detailed comparison between the 1996 SOHO SOI/MDI Dynamics Run program of full-disk Ni I Dopplergram observations and a simultaneous time series of ground-based observations obtained in the Na D lines at the 60-Foot Solar Tower of the Mt. Wilson Observatory (MWO). Specifically, we will compare sets of simultaneously-observed SOHO/MDI and MWO power spectra and the high-degree p-mode frequencies, frequency splittings, widths, and power densities which we obtained by fitting these two sets of power spectra. Beginning on May 23, 1996, the SOI/MDI experiment began its first high duty cycle run of 1024x1024 pixel images. this was the 1996 Dynamics Run. On all but three of the days of this 60.75-day time series a second time series of simultaneous 1024x1024 pixel full-disk Dopplergrams was obtained at MWO. From these simultaneous MWO observations we have computed 601 sets of zonal, tesseral, and sectoral power spectra which covered the degree range of 0 to 600. These sets of power spectra were then analyzed in two different ways to yield both frequencies and frequency splittings. First, estimates of the frequency splittings were computed for the frequency range of 1800 to 4800 microhertz at each degree and these n-averaged splittings were employed to compute an average power spectrum for that degree. Estimates were then made of the frequencies, frequency uncertainties, widths, peak power densities, and background power densities of the set of peaks in these 601 average power spectra. As is described in our companion paper on the MDI ridge-fit frequency measurements (Rhodes et al.,1998), we also had to correct our raw MWO ridge-fit frequencies for the effects the merger of individual p-mode peaks and sidelobes into ridges. We could also directly compare the frequency dependence of the observed power density in both the MDI and MWO power spectra. We have found that there is a systematic difference such that the power density in the chromospheric-level power spectra from MWO tends to be below that of the photosheric-level MDI spectra at low frequencies and to rise above the MDI power density as the frequency increases. All but the l = 0 MWO power spectra were also processed to yield estimates of the rotational splitting coefficients for individual p-mode ridges for every degree between l = 4 and 600. We will compare these splittings with both the previously-published splittings from the 1996 SOI/MDI Medium-l Program (Kosovichev et al., 1997) and with the MDI high-degree splittings presented in our companion MDI paper. Title: Line Asymmetry of VIRGO and MDI Low-Degree p Modes Authors: Toutain, T.; Appourchaux, T.; Frohlich, C.; Kosovichev, A.; Rakesh, N.; Scherrer, P. Bibcode: 1998ESASP.418..973T Altcode: 1998soho....6..973T Using continuous time series of 610 days of velocity (MDI, LOI-proxy) and intensity (VIRGO, SPM and LOI) we show that Lorentzian profiles as a model of low-degree p-mode line leads to systematic differences in the determination of intensity and velocity mode frequencies. These differences, as large as 0.1 muHz for degrees l = 0, 1, 2 and 3, are frequency-dependent. The use of a physics-based asymmetrical line shape (Rakesh et al., 1998) to fit the same lines has allowed us to significantly reduce differences in the frequency determination. P-mode lines in velocity exhibit a significant negative asymmetry (excess of power in the left wing) whereas p-modes lines in intensity have a positive asymmetry (excess of power in the right wing). The magnitude and sign of this asymmetry are directly related to the location of the source of p-mode excitation and to the correlation between mode and solar noise. Title: Time-Distance Measurements of Subsurface Rotation and Meridional Flow Authors: Giles, P. M.; Duvall, T. L., Jr.; Scherrer, P. H. Bibcode: 1998ESASP.418..775G Altcode: 1998soho....6..775G One of the most promising applications of time-distance helioseismology is the measurement of flows beneath the solar surface. In some cases the time-distance approach can yield information which cannot be obtained with more traditional helioseismology. Recently this technique has been used to measure the global meridional circulation (Giles et al., 1997) and differential rotation (Giles & Duvall, 1997). So far, these meaurements have only been able to penetrate a short distance into the solar interior --- up to a few percent of the solar radius. We will present the results of work which extends these measurements to greater depths, with a special focus on the meridional circulation. Probing this deeper region, while simple in principle, offers significant practical challenges. We will present a brief analysis of these difficulties along with our new results. 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: Helio-Atmospheric Links Explorer (HALE): A MIDEX Experiment for Exploring the Emergence of Magnetic Flux from Below the Solar Photosphere through the Corona Authors: Scherrer, P. H.; Title, A. M.; Bush, R. I.; Duvall, T. L., Jr.; Gurman, J. B.; Kosovichev, J. T.; Hoeksema, A. G.; Poland, A. I.; Tarbell, T. D. Bibcode: 1998ESASP.417..285S Altcode: 1998cesh.conf..285S No abstract at ADS Title: Initial SOI/MDI High-Degree Frequencies and Frequency Splittings Authors: Rhodes, E. J., Jr.; Reiter, J.; Kosovichev, A. G.; Schou, J.; Scherrer, P. H. Bibcode: 1998ESASP.418...73R Altcode: 1998soho....6...73R We present the first high-degree p-mode frequencies and frequency splittings obtained from the Full-Disk Program of the SOHO Solar Oscillation Investigation/Michelson Doppler Imager experiment. The frequencies and splittings which we present here were computed from power spectra obtained during the 1996 SOI/MDI Dynamics Run. Specifically, a time series of full-disk Dopplergrams, which began on May 23, 1996, and which covered 87480 minutes (60.75 days), was converted into sets of zonal, tesseral, and sectoral power spectra covering the degree range of 0 through 1000. These sets of power spectra were then analyzed in two different ways to yield both frequencies and frequency splittings. First, estimates of the frequency splittings were computed for the frequency range of 1800 to 4800 microhertz at each degree and these n-averaged splittings were employed to compute an average power spectrum for that degree. Estimates were then made of the frequencies, frequency uncertainties, widths, peak power densities, and background power densities of a total of 13664 separate peaks in these 1001 average power spectra. A total of 2554 of these peaks were isolated enough in their respective spectra to be fit as single p-modes. However, for the remaining 11110 peaks (mostly those above l = 200), the individual p-mode peaks and their spatial sidelobes were located so close together in frequency that they appeared as ridges rather than as isolated modal peaks in the average power spectra. For these cases we were forced to employ a wider fitting range for our frequency-estimation code and in so doing we obtained so-called ``ridge-fit'' parameter estimates. Due to a degree-dependence in the measured velocity power density, the observed p-mode ridges were asymmetric in shape. These asymmetries in the p-mode ridge shapes, which are in addition to the intinsic asymmetries caused by the excitation mechanism of the p-modes themselves, alter the fitted peak frequencies from their ``true'' values. For this reason, we had to develop a mechanism which we then used to correct the raw ridge-fit frequencies. Forty sets of these power spectra were also processed to yield estimates of the rotational splitting coefficients for individual p-mode ridges for every 25th degree between l = 25 and 1000. For l between 25 and 175 we will compare these Full-Disk program splittings with the previously-published splittings from the 1996 SOI/MDI Medium-l Program (Kosovichev et al., Solar Physics, 170, 43-61,1997). Title: The Stellar and Planetary Explorer (SPEX) Mission Authors: Schou, J.; Scherrer, P. H.; Brown, T. M.; Frandsen, S.; Horner, S. D.; Korzennik, S. G.; Noyes, R. W.; Tarbell, T. D.; Title, A. M.; Walker, A. B. C., II; Weiss, W. W.; Bogart, R. S.; Bush, R. I.; Christensen-Dalsgaard, J.; Hoeksema, J. T.; Jones, A.; Kjeldsen, H. Bibcode: 1998ESASP.418..401S Altcode: 1998soho....6..401S The Stellar and Planetary Explorer (SPEX) is a mission designed to search for terrestrial sized planets around sun-like stars using precise photometry. The planets will be detected by searching for the decrease in brightness associated with transits of the planets in front of their parent stars. One of the secondary scientific objective of SPEX is to do asteroseismology on a number of sun-like stars. SPEX is designed as a secondary payload on a commercial communications satellite and will have a design life time of three years. We will provide an overview of the SPEX scientific objectives and design, with particular emphasis on the prospects for doing asteroseismology. Title: The Evershed Effect: an MDI Investigation Authors: Bai, T.; Scherrer, P. H.; Bogart, R. S. Bibcode: 1998ESASP.418..607B Altcode: 1998soho....6..607B Because SOHO/MDI observes the Sun continuously, it provides valuable data for studying various properties of plasma flows within and around sunspots. We have studied the plasma flows in a long-lived active region, which crossed the solar disk for three times. After emerging in the southern hemisphere on July 4, 1996, AR 7978 developed rapidly, producing an X-class flare on July 9. After passing over the western limb on July 13, it rotated into the visible hemisphere for its second and third disk passages. When it appeared for its second disk passage on July 26 (AR 7981), leading-polarity (positive) spots remained with negative spots dispersed into network fields, and only the leader spot remained by the end of its second disk passage. The leader spot decayed slowly during its third disk passage after returning to the visible hemisphere on August 23 (AR 7986). Full-disk dopplergrams were obtained continuously throughout the first disk passage period, because the first dynamics program was in operation. Full-disk dopplergrams were obtained during some parts of the second and third disk passages, providing enough clue for the characteristics of plasma flows in this active region. The important results are as follows: (1) Horizontal out flows seem to be continuous from within sunspot umbrae, penumbrae, and outside penumbrae. Outflows within the umbra are spatially well resolved. In a given sunspot, the magnitude of the horizontal outflow slowly increases as the distance from the center of the spot increases, reaching its maximum (order of 1500 m/s) in the penumbra. (2) Vertical down flows are detected, with their magnitude reaching its maximum value of about 300 m/s outside the penumbra. (3) After such plasma flows (out and downward flows) weakens, sunspots decay rapidly. Therefore, it seems that such flows are a main mechanism keeping a sunspot from decay. Title: Line asymmetry and excitation mechanism of solar oscillations Authors: Nigam, R.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 1998IAUS..185..195N Altcode: The width and asymmetry of lines in the power spectrum of solar oscillations, obtained from the Michelson Doppler Imager (MDI) data, on board the Solar and Heliospheric Observatory (SOHO), are used to study the physics of excitation and damping of the oscillations. A theoretical model for solar oscillations is developed. In this model, the asymmetry is an effect of interference between the trapped waves from the source that pass through the region of wave propagation in the Sun's interior. From this the power spectrum is computed for different values of the source location and for various values of the angular degree l. It is seen that there is marked line asymmetry below the acoustic cut-off frequency, which corresponds to the asymmetry of bound states in quantum mechanics. The asymmetry is reduced above the acoustic cut-off frequency, which corresponds to the asymmetry of scattered states, which is a result of interference between an outward direct wave from the source and corresponding inward untrapped waves. The asymmetry is found to depend strongly on the source location and on the value of l. We discuss the properties of the solar acoustic source inferred from the MDI data. Title: The Detection of Giant Velocity Cells on the Sun Authors: Beck, J. G.; Duvall, T. L., Jr.; Scherrer, P. H.; Hocksema, J. T. Bibcode: 1998ESASP.418..725B Altcode: 1998soho....6..725B No abstract at ADS Title: VIRGO on SOHO: Status and Future Prospects Authors: Fröhlich, C.; Scherrer, P.; MDI Team; Virgo Team; Gabriel, A.; GOLF Team Bibcode: 1998ESASP.418....7F Altcode: 1998soho....6....7F After two years of nearly uninterrupted operation, the Michelson Doppler Imager (MDI) instrument has produced many unique data sets that are being used to address a wide variety of topics in solar physics. The more than two years of observations from VIRGO (Variability of solar IRradiance and Gravity Oscillations) yield a unique data set covering the activity minimum and the rising part of cycle 23. This allows not only to determine the influence of varying activity on the solar oscillation frequencies and amplitudes, but also to study the relationship between oscillations and irradiance variability. Over 2 years of GOLF data with nearly 100% continuity are yielding the highest ever signal to noise quality, enabling precise measurements of the frequencies, linewidths and power in the p-modes. The precision available for the inversion of the frequencies in terms of sound speed in the solar interior is no longer limited by the quality of the time-series itself, but rather by questions concerning the most correct method of fitting the observed spectrum. Unique measurements from the GOLF p-mode signals include the high-frequency global structure above the acoustic cut-off and the measurement of the global average magnetic field of the Sun. Several different techniques are being employed in searching for the g-mode signals in the GOLF spectrum. Title: Spherical and aspherical structure of the sun: First year of SOHO/MDI observations Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Goode, P. H.; Dziembowski, W. A.; Rhodes, E. J., Jr.; SOI Structure Inversion Team Bibcode: 1998IAUS..185..157K Altcode: We report the results of one year of continuous observations of the Sun's internal structure using data from the Medium-l Program of the Michelson Doppler Imager (MDI) on board SOHO. The data provide continuous coverage of p modes of angular degree l from 0 to 250, and the f mode from l=100 to 250. The striking stability of solar Dopplergrams measured by MDI, without an intervening atmosphere, substantially decreases the noise in the solar oscillations power spectrum compared with ground-based observations. This permits detection of lower amplitude oscillations, extending the range and precision of measured normal mode frequencies. We present new inversion results for the radial and latitudinal seismic solar structures with particular attention to zonal asphericity inferred with the high angular resolution from the data. Using f-mode frequency splitting we estimate the large-scale structure of the subsurface magnetic fields. The variations of the solar structure observed during the first year of MDI observations are also discussed. Title: SOI/MDI: Status and Future Prospects Authors: Scherrer, P. H. Bibcode: 1998ESASP.418...15S Altcode: 1998soho....6...15S No abstract at ADS Title: Observational Upper Limits for Low-Degree Solar g-modes Authors: Fröhlich, C.; Finsterle, W.; Andersen, B.; Appourchaux, T.; Chaplin, W. J.; Elsworth, Y.; D. O. Gough; Hoeksema, J. T.; Isaak, G. R.; Kosovichev, A. G.; Provost, J.; Scherrer, P. H.; Sekii, T.; Toutain, T. Bibcode: 1998ESASP.418...67F Altcode: 1998soho....6...67F No abstract at ADS Title: Sunspot Oscillations Observed with MDI Authors: Rüedi, I.; Solanki, S. K.; Stenflo, J. O.; Scherrer, P. H. Bibcode: 1998ESASP.417..281R Altcode: 1998cesh.conf..281R No abstract at ADS Title: Comparative Studies of Low-Order and Low-Degree Solar p Modes Authors: Appourchaux, T.; Andersen, B.; Chaplin, W.; Elsworth, Y.; Finsterle, W.; Frohlich, C.; Gough, D.; Hoeksema, J. T.; Isaak, G.; Kosovichev, A.; Provost, J.; Scherrer, P.; Sekii, T.; Toutain, T. Bibcode: 1998ESASP.418...95A Altcode: 1998soho....6...95A The amplitudes of solar p-modes decrease steeply with decreasing radial order below about 17. The background solar signal (solar noise) in general increases steadily with decreasing frequency. For the irradiance and radiance measurements with VIRGO or SOI/MDI on SOHO this combination makes it difficult to detect low degree modes below about 1.8 mHz. The solar noise as observed in velocity with SOI/MDI or the ground based BISON network is significantly lower in this region than in intensity measurements. This allows low degree modes to be observed close to 1 mHz. We present results of detection and charaterization of the lowest order observable p-modes both in velocity and intensity measurements. Where applicable the properties of the modes observed with the two methods are compared. Title: Calibration and Stability of MDI Velocities Authors: Beck, J. G.; Scherrer, P. H.; Bush, R. I.; Tarbell, T. D. Bibcode: 1998ESASP.418..105B Altcode: 1998soho....6..105B No abstract at ADS Title: A Modification to the Calibration of MDI Velocities Authors: Evans, S.; Ulrich, R. K.; Scherrer, P. H.; Bush, R. I.; Tarbell, T. D. Bibcode: 1998ESASP.418..157E Altcode: 1998soho....6..157E The ability of the Michelson Doppler Imager instrument used by the Solar Oscillations Investigation (Scherrer, et al, 1995) to produce velocity measurements is affected by center-to-limb effects on the Ni 6768 AA line profile. These effects are removed by special calibration observations known as detunes. Part of the detune procedure involves the modelling of center-to-limb line profile changes by fitting a Gaussian to the line profile and varying both the model profile's depth and FWHM as a function of center-to-limb angle. However, the functions used for modelling both line depth and FWHM differ from those derived from data from both the Mt. Wilson 150' Tower and the Fourier Transform Spectrometer at Kitt Peak. This variation can produce velocity errors of ~100 m/s. By modifying the line depth and FWHM functions to conform to those derived from the data, an improved velocity calibration can be achieved. Title: Probing the Internal Structure of the Sun with the SOHO Michelson Doppler Imager Authors: Kosovichev, A. G.; Nigam, R.; Scherrer, P. H.; Schou, J.; Reiter, J.; Rhodes, E. J., Jr.; Toutain, T. Bibcode: 1997AAS...191.7311K Altcode: 1997BAAS...29R1322K The inference of the thermodynamic structure of the Sun from the observed properties of the solar normal modes of oscillation is a principal goal of helioseismology. We report the results of the first year of continuous observations of the Sun's internal structure using data from the Medium-l Program of the Michelson Doppler Imager (MDI) on board ESA/NASA spacecraft SOHO. The data provide continuous coverage of the acoustic (p) modes of angular degree l from 0 to 250, and the fundamental (f) mode of the Sun from l=100 to 250. During two 2-month intervals, the high-degree modes, up to l=1000, have been observed. The great stability of solar Dopplergrams measured by MDI permits detection of lower amplitude oscillations, extending the range and precision of measured normal mode frequencies, and thus substantially increasing the resolution and precision of helioseismic inversions. We present new inversion results for the radial and latitudinal seismic solar structures with particular attention to the transition region between the radiative and convection zones and to the energy-generating core. We discuss evidence for convective overshoot at the base of the convection zone, and the significance of deviations in the core structure from the standard evolutionary model. Comparing the f-mode frequencies with the corresponding frequencies of the standard solar models, we argue that the apparent photospheric solar radius (695.99 Mm) used to calibrate the models should be reduced by approximately 0.3 Mm. The discrepancy between the `seismic' and apparent photospheric radii is not explained by the known systematic errors in the helioseismic and photospheric measurements. If confirmed, this discrepancy represents a new interesting challenge to theories of solar convection and solar modeling. Using f-mode frequency splitting we estimate the large-scale structure of the subsurface magnetic fields. The variations of the solar oscillation frequencies during the first year of MDI observations are also discussed. Title: Rotation and Zonal Flows in the Solar Envelope from the SOHO/MDI Observations Authors: Scherrer, P. H.; Schou, J.; Bogart, R. S.; Bush, R. I.; Hoeksema, J. T.; Kosovichev, A. G.; Antia, H. M.; Chitre, S. M.; Christensen-Dalsgaard, J.; Larsen, R. M.; Pijpers, F. P.; Eff-Darwich, A.; Korzennik, S. G.; Gough, D. O.; Sekii, T.; Howe, R.; Tarbell, T.; Title, A. M.; Thompson, M. J.; Toomre, J. Bibcode: 1997AAS...191.7310S Altcode: 1997BAAS...29.1322S We report on the latest inferences concerning solar differential rotation that have been drawn from the helioseismic data that are now available from the Solar Oscillations Investigation (SOI) using the Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO). That spacecraft is positioned in a halo orbit near the Sun-Earth Lagrangian point L_1, in order to obtain continuous Doppler-imaged observations of the sun with high spatial fidelity. Doppler velocity, intensity and magnetic field images are recorded, based on modulations of the 676.8 nm Ni I solar absorption line. The high spatial resolution of MDI thereby permits the study of many millions of global resonant modes of solar oscillation. Determination and subsequent inversion of the frequencies of these modes, including the degeneracy-splitting by the rotation of the sun, enables us to infer how the sun's angular velocity varies throughout much of the interior. The current MDI data are providing substantial refinements to the helioseismic deductions that can be made about differential rotation both within the convection zone and in its transition to the radiative interior. The shearing layer evident in the angular velocity Omega just below the solar surface is becoming better defined, as is the adjustment layer or tachocline near the base of the convection zone. The MDI data are also revealing a prominent decrease in Omega at high latitudes from the rotation rate expressed by a simple three-term expansion in latitude that was originally deduced from surface Doppler measurements. Further, there are indications that a submerged polar vortex involving somewhat faster Omega than its surroundings exists at about 75(deg) in latitudes. Title: A subsurface flow of material from the Sun's equator to its poles Authors: Giles, P. M.; Duvall, T. L.; Scherrer, P. H.; Bogart, R. S. Bibcode: 1997Natur.390...52G Altcode: Gas on the Sun's surface has been observed to flow away from the equator towards both poles. If the same flow persists to great depths, it could play an important dynamical role in the eleven-year sunspot cycle, by carrying the magnetic remnants of the sunspots to high latitudes. An even deeper counterflow, which would be required to maintain mass balance, could explain why new sunspots form at lower latitudes as the cycle progresses. These deep flows would also redistribute angular momentum within the Sun, and therefore help to maintain the faster rotation of the equator relative to the poles. Here we report the detection, using helioseismic tomography, of the longitude-averaged subsurface flow in the outer 4% of the Sun. We find that the subsurface flow is approximately constant in this depth range, and that the speed is similar to that seen on the surface. This demonstrates that the surface flow penetrates deeply, so that it is likely to be an important factor in solar dynamics. Title: Measurements of Frequencies of Solar Oscillations from the MDI Medium-l Program Authors: Rhodes, E. J., Jr.; Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Reiter, J. Bibcode: 1997SoPh..175..287R Altcode: Inversions of solar internal structure employ both the frequencies and the associated uncertainties of the solar oscillation modes as input parameters. In this paper we investigate how systematic errors in these input parameters may affect the resulting inferences of the sun's internal structure. Such systematic errors are likely to arise from inaccuracies in the theoretical models which are used to represent the spectral lines in the observational power spectra, from line blending, from asymmetries in the profiles of these lines, and from other factors. In order to study such systematic effects we have employed two different duration observing runs (one of 60 days and the second of 144 days) obtained with the Medium-l Program of the Michelson Doppler Imager experiment onboard the SOHO spacecraft. This observing program provides continuous observations of solar oscillation modes having angular degrees, l, ranging from 0 to ∼ 300. For this study intermediate- and high-degree p-mode oscillations having degrees less than 251 were employed. Title: Tri-Phonic Helioseismology: Comparison of Solar P Modes Observed by the Helioseismology Instruments Aboard SOHO Authors: Toutain, T.; Appourchaux, T.; Baudin, F.; Fröhlich, C.; Gabriel, A.; Scherrer, P.; Andersen, B. N.; Bogart, R.; Bush, R.; Finsterle, W.; García, R. A.; Grec, G.; Henney, C. J.; Hoeksema, J. T.; Jiménez, A.; Kosovichev, A.; Roca Cortés, T.; Turck-Chièze, S.; Ulrich, R.; Wehrli, C. Bibcode: 1997SoPh..175..311T Altcode: The three helioseismology instruments aboard SOHO observe solar p modes in velocity (GOLF and MDI) and in intensity (VIRGO and MDI). Time series of two months duration are compared and confirm that the instruments indeed observe the same Sun to a high degree of precision. Power spectra of 108 days are compared showing systematic differences between mode frequencies measured in intensity and in velocity. Data coverage exceeds 97% for all the instruments during this interval. The weighted mean differences (V-I) are −0.1 µHz for l=0, and −0.16 µHz for l=1. The source of this systematic difference may be due to an asymmetry effect that is stronger for modes seen in intensity. Wavelet analysis is also used to compare the shape of the forcing functions. In these data sets nearly all of the variations in mode amplitude are of solar origin. Some implications for structure inversions are discussed. Title: Solar Meridional Circulation and Rotation Determined by Time-Distance Helioseismology using MDI Data From SOHO Authors: Giles, P. M.; Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 1997SPD....28.1002G Altcode: 1997BAAS...29..914G Using the technique of time-distance helioseismology, acoustic wave travel times can be measured between pairs of points on the solar surface. The travel time of the waves depends primarily on the wave group velocity and on the component of flow velocity which is parallel to the direction of wave propagation. By choosing pairs of points which share a common longitude, it is possible to use these waves to probe the meridional flow beneath the surface. Any flows present will cause a difference between the northward and southward travel times along the meridian. Varying the distance between points allows isolation of waves which propagate to different depths beneath the surface, and thus the flow velocity can be measured as a function of latitude and depth. Similarly, by choosing pairs of points which share a common latitude it is possible to measure the effects of solar rotation using an analogous procedure. This technique could provide high resolution in latitude and allows study of the northern and southern hemispheres independently. Using velocity images taken by the Michelson Doppler Imager during June 1996, we have detected meridional flows in the uppermost layers of the sun. Measurements of this flow velocity and of the rotation rate as functions of latitude and depth will be presented. This research is supported by NASA contract NAG5-3077 at Stanford University. Title: Photospheric Differential Rotation from Full-Disk SOI/MDI Dopplergrams Authors: Bogart, R. S.; Bai, T.; Scherrer, P. H.; Strous, L. H.; Simon, G. W.; Tarbell, T. D. Bibcode: 1997SPD....28.0258B Altcode: 1997BAAS...29..903B We report on measurements of the solar surface differential rotation made from SOI/MDI full-disk Dopplergrams obtained once per minute during the 2-month Dynamics Program from 23 May through 26 July 1996. We infer the rotation profile both from the direct photospheric Doppler signal and also by tracking Doppler features (supergranules) across the solar disk. We study the rotation curve as a function of latitude, feature size, and tracking method, and look for global scale flows. This work was supported by NASA Grant NAG5-3077 at Stanford and Lockheed Martin, and by AFOSR and the Fellows Program of AF Phillips Lab at NSO/SP. Title: Surface Flows in Active Regions Authors: Bai, T.; Bogart, R. S.; Scherrer, P. H.; Tarbell, T. D. Bibcode: 1997SPD....28.1701B Altcode: 1997BAAS...29..921B Plasma flows around sunspots must influence the stability and development of sunspots. We have been studying photospheric flows around sunspots by analyzing dopplergrams and magneto- grams obtained by the MDI (Michelson Doppler Imager) aboard SOHO. We have found some interesting phenomena. First, during the growing phase of an active region, plasmas around sunspots seem to draft downward with a speed of order of 100 m/s. Second, during the decaying phase of an active region, plasmas around sunspots flow outward. Outflow speeds range up to several hundred m/s. Such outflows are prominent during the decaying phase of a long-lived big active region. Third, there is evidence for flows within sunspots. Such flows are presumed to be along magnetic field lines. We will present the details of these results and discuss their implications on the dynamics and stability of sunspots. MDI research is supported by NASA contract NAG5-3077 at Stanford University. Title: Analysis of Velocity and Intensity Helioseismic Spectra from SOHO/MDI Authors: Nigam, R.; Kosovichev, A. G.; Scherrer, P. H.; Schou, J. Bibcode: 1997SPD....28.0904N Altcode: 1997BAAS...29..913N We give an explanation for the cause of the asymmetry of spectral lines of solar oscillation power spectrum. We also explain the cause of the opposite sense of asymmetry in velocity and intensity oscillation power spectra, thereby resolving a half-decade old puzzle. The motivation for the investigation came after comparing the velocity and intensity data obtained from the Michelson Doppler Imager (MDI) instrument on board the Solar and Heliospheric Observatory (SOHO). The analysis is based on a theoretical model of wave excitation with viscous damping in conjunction with a spherically symmetric solar model. Neglecting asymmetry can lead to systematic errors in the eigenfrequency measurements, which in turn leads to errors in inversion. This research was supported by NASA grant NAG5-3077 at Stanford University. Title: Continuous Observations of Solar Magnetic Fields from SOI/MDI on SOHO Authors: Hoeksema, J. T.; Bush, R. I.; Scherrer, P. H.; Heck, C.; Hurlburt, N.; Shine, R.; Tarbell, T.; Title, A. Bibcode: 1997SPD....28.0127H Altcode: 1997BAAS...29..884H The Solar Oscillations Investigation's Michelson Doppler Imager instrument (SOI/MDI) on SOHO measures the photospheric magnetic field over the whole disk nearly every 96 minutes with 4" resolution and a noise level of a few Gauss. Beginning in April 1996, this unprecedented continuous series of frequent, uniform quality magnetograms provides a striking view of the continual emergence, motion, evolution, and interaction of magnetic flux everywhere on the visible solar surface near solar minimum. These evolving photospheric fields ultimately drive the variations of the corona and solar wind that affect the terrestrial environment. Knowledge of the rapidly evolving photospheric field provides a crucial input for forecasting conditions in the corona, heliosphere, and geospace. A few magnetograms are available each day within hours of observation through the SOHO web site at http://sohowww.nascom.nasa.gov/. These may be used for planning and forecasting, e.g. to compute models of the solar corona. The remainder are generally available within a few weeks. Sometimes more focused campaigns provide magnetic observations as often as once each minute for up to 8 hours. Campaigns can be run with either the full disk resolution or with 0.6" pixels in a limited field near the center of the disk. The SOI project welcomes collaborations. More information can be found at http://soi.stanford.edu/. Title: Convective Flow Patterns in Time-Distance Measurements and "Magnetic Corrections" in Vertically Stratified Atmosphere. Authors: Ryutova, M.; Scherrer, P. Bibcode: 1997SPD....28.0204R Altcode: 1997BAAS...29..893R Time-distance measurements for the reconstruction of subsurface flows and horizontal magnetic fields proved to be very efficient. However, if one can expect a reasonable accuracy of reconstructed maps for the annuli of the radius small compared to the characteristic scale of the convection, the situation changes when annular distances become comparable with the scale of granular, mezogranular, or supergranular convective motions: in each of these cases the uncertainty in the measurements of travel time perturbations increases dramatically. We present here a quantitative analysis of the problem for a particular model of convective motions and compute the travel time perturbations as a function of annular distances and the supergranule radius. It is shown that at annular sizes close to the size of convective cell there occurs: (1) the apparent reduction of the local velocity, and (2) appearance of additional terms in the corrections to perturbation travel time which cause a large error in reconstruction of the velocity field. We discuss the importance of "directionally sensitive" measurements and show that Fourier sin ntheta , cos ntheta transforms of travel times measured as a function of direction, "kills" the largest source of errors. We discuss the role of vertical motions. We also present the expressions for the "magnetic corrections" in a vertically stratified atmosphere. This research is supported by NASA contract NAG5-3077 at Stanford University and the MDI contract PR 9162 at Lockheed. Title: Performance of the Michelson Doppler Imager Instrument on SOHO Authors: Scherrer, P.; Bogart, R.; Bush, R.; Duvall, T.; Hoeksema, J. T.; Kosovichev, A.; Schou, J.; Morrison, M.; Tarbell, T.; Title, A. Bibcode: 1997SPD....28.0207S Altcode: 1997BAAS...29..894S Launched on SOHO in December 1995, the MDI instrument took its 10 millionth filtergram in early April, 1997. The instrument and spacecraft have performed admirably since commissioning, providing over a year of virtually uninterrupted time series of velocity and intensity measurements at moderate resolution, a continuous 60-day time series of full disk 4" velocity and line depth maps, monthly 72+ hour time series in various observables, a host of daily 8-hour campaigns, and full-disk magnetograms every 96 minutes. Another uninterrupted 90-day interval of nearly full data recovery is scheduled to be completed in mid July. Various scientific results using MDI data are being presented at this meeting. About a dozen terabytes of data sets have been created and archived and normal pipeline processing is now completed soon after retrieving the data, typically less than a month after the observations are made. Most of the data products are generally available on the WWW, see http://soi.stanford.edu. Selected data are available in near real time. The SOI team welcomes collaborations. Routine and extraordinary calibrations along with analysis of scientific data sets allow us to make good estimates of the noise and understand many of the sources of systematic errors in the instrument. In almost every respect the instrument performs as well or better than expected before launch, the primary limitations being photon noise on the short term and fixed or slowly varying offsets on the long term. We have found that the Michelsons are somewhat more sensitive to operational temperature variations than was expected, adding some additional constraints on our observing sequences. Title: The Effects of Systematic Errors in the Estimation of p-Mode Frequencies on the Inversion of Solar Internal Structure Authors: Rhodes, E. J., Jr.; Appourchaux, T.; Bachmann, K.; Kosovichev, A. G.; Scherrer, P. H.; Schou, J.; Reiter, J. Bibcode: 1997SPD....28.0901R Altcode: 1997BAAS...29..913R The frequencies and associated uncertainties of the low-, intermdeiate-, and high-degree p-mode oscillations are the input quantities for the inversion programs which infer the thermodynamic structure of the solar interior. In this review we will attempt to demonstrate the different possible systematic errors that are currently present in our estimation of both the modal frequencies and their uncertainties. We will also demonstrate the effects of some of these errors upon the inferred radial profile of the solar internal sound speed. Among the different possible systematic errors which we will discuss are the effects of: 1)the asymmetric shapes of the peaks in observational power spectra, 2)the realization noise which is present in the case of the low-degree modes, 3)the different frequency estimation methods used on different types of power spectra (i.e., on either tesseral power spectra or on m-averaged power spectra), 4) the differences in the frequencies which are estimated from velocity- and intensity-based power spectra, 5) the blending of individual p-modes into so-called "ridges" of observed power at both high degrees and high frequencies, and 6) the spatial and temporal aliasing which occurs at both high degrees and at high frequencies. We will demonstrate these different errors using results obtained with the VIRGO and MDI experiments onboard the SOHO spacecraft. We will also compare some of these space-based results with the results of similar estimates obtained from co-temporaneous ground-based observations, such as from the Mt. Wilson 60-Foot Solar Tower. We will include the results from different structural inversions carried out with different sets of input frequencies and uncertainties in order to demonstrate the effects of these different systematic errors upon the inverted internal sound speed profile. Title: Structure and Rotation of the Solar Interior: Initial Results from the MDI Medium-L Program Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.; Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.; de Forest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.; Scott, K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard, J.; Dappen, W.; Rhodes, E. J., Jr.; Duvall, T. L., Jr.; Howe, R.; Thompson, M. J.; Gough, D. O.; Sekii, T.; Toomre, J.; Tarbell, T. D.; Title, A. M.; Mathur, D.; Morrison, M.; Saba, J. L. R.; Wolfson, C. J.; Zayer, I.; Milford, P. N. Bibcode: 1997SoPh..170...43K Altcode: The medium-l program of the Michelson Doppler Imager instrument on board SOHO provides continuous observations of oscillation modes of angular degree, l, from 0 to ∽ 300. The data for the program are partly processed on board because only about 3% of MDI observations can be transmitted continuously to the ground. The on-board data processing, the main component of which is Gaussian-weighted binning, has been optimized to reduce the negative influence of spatial aliasing of the high-degree oscillation modes. The data processing is completed in a data analysis pipeline at the SOI Stanford Support Center to determine the mean multiplet frequencies and splitting coefficients. The initial results show that the noise in the medium-l oscillation power spectrum is substantially lower than in ground-based measurements. This enables us to detect lower amplitude modes and, thus, to extend the range of measured mode frequencies. This is important for inferring the Sun's internal structure and rotation. The MDI observations also reveal the asymmetry of oscillation spectral lines. The line asymmetries agree with the theory of mode excitation by acoustic sources localized in the upper convective boundary layer. The sound-speed profile inferred from the mean frequencies gives evidence for a sharp variation at the edge of the energy-generating core. The results also confirm the previous finding by the GONG (Gough et al., 1996) that, in a thin layer just beneath the convection zone, helium appears to be less abundant than predicted by theory. Inverting the multiplet frequency splittings from MDI, we detect significant rotational shear in this thin layer. This layer is likely to be the place where the solar dynamo operates. In order to understand how the Sun works, it is extremely important to observe the evolution of this transition layer throughout the 11-year activity cycle. Title: Modeling Boot-Shaped Coronal Holes using SOHO-MDI Magnetic Measurements Authors: Zhao, X. P.; Hoeksema, J. T.; Scherrer, P. H. Bibcode: 1997ESASP.404..751Z Altcode: 1997cswn.conf..751Z No abstract at ADS Title: Precision solar astrometry from SoHO/MDI Authors: Kuhn, J. R.; Bogart, R.; Bush, R.; Sá, L.; Scherrer, P.; Scheick, X. Bibcode: 1997IAUS..181..103K Altcode: No abstract at ADS Title: Internal structure and rotation of the Sun: First results from MDI data Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.; Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.; De Forest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.; Scott, K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard, J.; Däppen, W.; Rhodes, E. J., Jr.; Duvall, T. L., Jr.; Howe, R.; Thompson, M. J.; Gough, D. O.; Sekii, T.; Toomre, J.; Tarbell, T. D.; Title, A. M.; Mathur, D.; Morrison, M.; Saba, J. L. R.; Wolfson, C. J.; Zayer, I.; Milford, P. N. Bibcode: 1997IAUS..181..203K Altcode: No abstract at ADS Title: New Time-distance helioseismology results from the SOI/MDI experiment Authors: Duvall, T., Jr.; Kosovichev, A. G.; Scherrer, P. H. Bibcode: 1997IAUS..181...83D Altcode: No abstract at ADS Title: Temporal Variability in the Quiet Sun Transition Region Authors: Wikstoøl, Ø.; Hansteen, V. H.; Brynildsen, N.; Maltby, P.; Kyeldseth-Moe, O.; Harrison, R. A.; Wilhelm, K.; Tarbell, T. D.; Scherrer, P. H. Bibcode: 1997ESASP.404..733W Altcode: 1997cswn.conf..733W No abstract at ADS Title: Time-Distance Helioseismology with the MDI Instrument: Initial Results Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H.; Bogart, R. S.; Bush, R. I.; de Forest, C.; Hoeksema, J. T.; Schou, J.; Saba, J. L. R.; Tarbell, T. D.; Title, A. M.; Wolfson, C. J.; Milford, P. N. Bibcode: 1997SoPh..170...63D Altcode: In time-distance helioseismology, the travel time of acoustic waves is measured between various points on the solar surface. To some approximation, the waves can be considered to follow ray paths that depend only on a mean solar model, with the curvature of the ray paths being caused by the increasing sound speed with depth below the surface. The travel time is affected by various inhomogeneities along the ray path, including flows, temperature inhomogeneities, and magnetic fields. By measuring a large number of times between different locations and using an inversion method, it is possible to construct 3-dimensional maps of the subsurface inhomogeneities. The SOI/MDI experiment on SOHO has several unique capabilities for time-distance helioseismology. The great stability of the images observed without benefit of an intervening atmosphere is quite striking. It has made it possible for us to detect the travel time for separations of points as small as 2.4 Mm in the high-resolution mode of MDI (0.6 arc sec pixel-1). This has enabled the detection of the supergranulation flow. Coupled with the inversion technique, we can now study the 3-dimensional evolution of the flows near the solar surface. Title: Frequencies of solar oscillations and the seismic structure of the Sun from SOHO/MDI. Authors: Rhodes, E. J., Jr.; Kosovichev, A. G.; Scherrer, P. H.; Schou, J.; Reiter, J. Bibcode: 1997AGAb...13..163R Altcode: No abstract at ADS Title: Observation of solar convection with the MDI instrument on SOHO. Authors: Kosovichev, A. G.; Scherrer, P. H.; Duvall, T. L., Jr. Bibcode: 1996BAAS...28.1298K Altcode: No abstract at ADS Title: New Views of the Sun's Interior from the SOHO/MDI Space Experiment Authors: Scherrer, P. H.; Bogart, R. S.; Bush, R. I.; Hoeksema, J. T.; Kosovichev, A. G.; Nigam, R.; Schou, J.; Duvall, T. L., Jr. Bibcode: 1996AAS...189.1803S Altcode: 1996BAAS...28.1298S The strking stability of solar Dopplergrams measured by the Michelson Doppler Imager (MDI) instrument on the SOHO spacecraft, without an intervening atmosphere, substantially decreases the noise in the solar oscillations power spectrum compared with groundbased observations. This permits detection of lower amplitude oscillations, extending the range of measured normal mode frequencies. This is important for improving resolution and precision of helioseismic inferences about the Sun's internal structure and dynamics. The MDI observations also reveal the asymmetries of oscillation spectral lines that until now have been largely hidden in noise. The line asymmetries agree with a theory of excitation of solar oscillations by acoustic sources localized in the upper convective boundary layer. High-resolution MDI images make it possible to measure the travel time of acoustic waves propagating inside the Sun by comparing points on the surface as close as 2.4 Mm. This is sufficient to detect supergranulation flows beneath the surface. Coupled with tomographic inversion techniques, we can now study the 3-dimensional evolution of the flows near the photosphere. The sound-speed profile inferred from normal modes frequencies shows a sharp variation at the edge of the energy-generating core, something not accounted for by the standard evolution theory. The analysis also confirms recent GONG results suggesting that helium is less abundant than theory predicts in a thin layer just beneath the convection zone. Inversion of the multiplet frequency splittings shows significant rotational shear in this thin layer. This shear flow probably generates turbulence that mixes the plasma in the upper radiative zone. This layer is likely to be the place where the solar dynamo operates. Continuous observation of the evolution of this transition layer during the entire 11-year activity cycle will be extremely important for understanding the mechanisms of solar activity. Title: Solar Chromospheric and Coronal Explorer Authors: Walker, Arthur B.; Scherrer, Philip H.; Hoover, Richard B.; Tandberg-Hanssen, Einar; Barbee, Troy W.; Ling, James C.; MacQueen, R. M.; Timothy, J. Gethyn; Adamson, Paul; Mennzel, Mike T.; Petheram, John C.; Shattuck, Paul L. Bibcode: 1996SPIE.2804..286W Altcode: The presence of the solar magnetic field has a profound effect on the structure of the lower chromosphere, and is responsible for the formation of the upper chromosphere and the corona, and the acceleration of the solar wind. The variation of the field induces variations in the chromosphere and the corona on time scales from 0.001 seconds to centries. SOHO, and subsequent approved solar missions such as TRACE will bring powerful observational capabilities to bear on critical questions relating to solar variability. However, the most fundamental question--how energy is transferred from the magnetic field into the solar plasma--will require observations of diagnostic quality on a spatial scale of 50 - 100 kilometers; this is an order of magnitude beyond the capability of any planned mission. Our mission concept, the Solar Chromospheric and Coronal Explorer (SCCE) is designed to investigate the mechanisms underlying the variability of the solar atmosphere, by attaining spectroscopic observations of the solar atmosphere over a wide range of temperatures (4,500 K to 100,000,000 K), with very high angular (0.1 arcseconds) and temporal (0.001 seconds) resolution, that will permit models of the physical processes that underlie the phenomena of solar activity to be formulated and tested at the scale, 50 - 75 kilometers that appears to be fundamental. The architecture of the SCCE is based on advances in multilayer optics, which permit broad spectral response, and high angular and spectral resolution to be achieved in a volume, and at a cost that is compatible with deployment within the fiscal and physical constraints of the MIDEX program. Title: Prediction of coronal and heliospheric magnetic fields: the promise of SOI-MDI on SOHO. Authors: Hoeksema, J. T.; Zhao, Xuepu; Scherrer, P. H. Bibcode: 1996AIPC..382...76H Altcode: Coronal magnetic field models reproduce the static characteristics of coronal and heliospheric structures fairly well; however, limitations of spatial and temporal resolution and nonuniform quality of the input data are important factors limiting investigations of the response of the corona to rapidly changing photospheric conditions. The Solar Oscillations Investigation (SOI) Michelson Doppler Imager (MDI) experiment on SOHO produces a series of full-disk photospheric magnetic field observations with 4″resolution about every 96 minutes for the next several years. To suggest the potential of the MDI photospheric magnetic field data, the authors show calculations of the steady coronal magnetic field using low spatial resolution data and compare results with various observations. Title: Coordinated SOHO Observations of Polar Plumes Authors: Deforest, C. E.; Scherrer, P. H.; Tarbell, T.; Harrison, R. A.; Fludra, A.; Delaboudiniere, J. P.; Gurman, J. B.; Wilhelm, K.; Lemaire, P.; Hassler, D. M.; Kohl, J. L.; Noci, G.; Fineschi, S.; Brueckner, G. E.; Howard, R. A.; Cyr, O. C. St. Bibcode: 1996AAS...188.4909D Altcode: 1996BAAS...28R.898D On 7 and 8 March 1996, SOHO instruments engaged in their first joint science operation, a 12-hr observation of polar plumes over the South polar coronal hole. The observing mini-campaign included observations from SOHO, other spacecraft, and ground-based observatories. Contributing SOHO instruments -- in order of altitude, MDI, CDS, SUMER, EIT, UVCS, and LASCO -- made overlapping, simultaneous observations of plume structures from the photosphere out to the LASCO C3 limit of 32 solar radii. MDI provided line-of-sight surface magnetograms with a one-min cadence and 0.6 arcsec resolution; CDS, SUMER, and EIT supplied temperature-sensitive images of the lower corona with varying cadences and resolutions; UVCS measured fluctuations in Ly B intensity across the coronal hole with a one-min cadence at 1.4 R0; and LASCO imaged the entire corona out to 30 R0 in various visible passbands. Plume footpoints in the lower corona are observed by EIT and CDS to vary by a factor of two in EUV brightness with a timescale of tens of minutes, while the structures above are (as as been previously observed) quiescent on at least a ten-hr time scale. We present preliminary results of cross-instrument analysis of the observed plumes, and suggest how this and similar future data sets can be used to constrain quiet-sun wind acceleration and coronal heating models for the coronal hole. This research is supported by the SOI-MDI NASA contract NAG5-3077 at Stanford University. SOHO is project of international cooperation between NASA and ESA. Title: The MDI Structure Program: Continuous Monitoring of the Solar Interior Authors: Bush, R. I.; Bogart, R. S.; Hoeksema, J. T.; Kosovichev, A. G.; Scherrer, P. H.; Mathur, D.; Morrison, M.; Tarbell, T. D. Bibcode: 1996AAS...188.3708B Altcode: 1996BAAS...28..878B The Structure Program for the Michelson Doppler Imager instrument on SOHO is designed to provide valuable helioseismic observations through a continuously operating 5 kbps telemetry channel. Only about 3% of the total MDI raw data can be transmitted without interruption to the ground. Therefore, extensive data processing must be performed by the MDI instrument in order produce data products that will fit into the restricted telemetry and to meet the scientific observing requirements. The Structure Program consists of five observing programs: the Medium-l Velocity, Low-l (LOI) Velocity and Intensity, Limb Figure, Flux Budget, and Magnetic Proxy. These programs generate spatial and temporal averages of three of the MDI full disk observables: the velocity, computed continuum intensity, and the computed line depth. The performance of these filters will be described. The goal of the Medium-l Program is to provide reliable measurements of solar p-modes in the range of the angular degree, l, from 0 to 300, by generating a 23,000 bin spatial average of the full disk velocity. The Low-l Program re-bins the velocity and continuum intensity images into 180 bins, with the intent of observing long period global oscillations. The other three Structure Observations are averaged over 24 minutes with a 12 minute sample time. The Limb Figure extracts a 14 arcsecond annulus at the Sun's limb in order to study long wavelength oscillations in the observed limb. The Flux Budget and Magnetic Proxy are 128 by 128 pixel re-bins of the continuum intensity and line depth observables respectively, to study the solar luminosity and large scale features. Extensive tests of the individual components of the Structure Program have been performed during the commissioning phase of the SOHO operation. Uninterrupted operation started in April 1996. This research is supported by NASA contract NAG5-3077 at Stanford University. Title: Perspectives in Helioseismology Authors: Gough, D. O.; Leibacher, J. W.; Scherrer, P. H.; Toomre, J. Bibcode: 1996Sci...272.1281G Altcode: Helioseismology is probing the interior structure and dynamics of the sun with ever-increasing precision, providing a well-calibrated laboratory in which physical processes can be studied under conditions that are unattainable on Earth. Nearly 10 million resonant modes of oscillation are observable in the solar atmosphere, and their frequencies need to be known with great accuracy in order to gauge the sun's interior. The advent of nearly continuous imaged observations from the complementary ground-based Global Oscillation Network Group (GONG) observatories and the space-based Solar and Heliospheric Observatory instruments augurs a new era of discovery. The flow of early results from GONG resolves some issues and raises a number of theoretical questions whose answers are required for understanding how a seemingly ordinary star actually operates. Title: Detection of Subsurface Supergranulation Structure and Flows from MDI High-Resolution Data using Time-Distance Techniques Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H.; Milford, P. N. Bibcode: 1996AAS...188.4908D Altcode: 1996BAAS...28Q.898D The supergranulation is seen at the surface of the sun in the doppler shift of spectrum lines as an apparent cellular convection pattern with a scale of about 4% of the solar radius. This scale is about 30 times larger than the granulation, seen in white light. Why these distinct scales would be present (and possibly a third intermediate scale mesogranulation) is somewhat of a mystery. Also unknown is the depth structure of the convection. We have used acoustic wave measurements from the MDI experiment on SOHO to address these questions. By crosscorrelating the signal at one location with that on annuli centered on the location, it is possible to measure times for waves to travel over known subsurface ray paths. With some variations on this theme, it is possible to measure horizontal and vertical flows and sound speed variations. Of course, the resulting measurements refer to quantities integrated along these ray paths. An inversion technique based on Fermat's principle has been developed and used to map the flow velocities and sound speed variations as a function of horizontal position and depth. The MDI experiment on SOHO makes doppler shift maps with 1Kx1K points in two choices of image scale, 2 and 0.6 arcsec/pixel. For the present study, we have used the higher resolution mode to observe 8.5 hours of doppler maps sampled once per minute. In order to average enough crosscorrelations to see time-distance effects, the resultant time-distance maps are reduced in resolution by a factor of 10 from the initial data. This still yields about 7 samples across a single supergranulation cell, or 49 over the area of a square cell. Our initial inversions based on the ray theory suggest that the supergranulation flow extends at least to 0.5% of the solar radius below the surface. This research is supported by the SOI-MDI NASA contract NAG5-3077 at Stanford University. Title: TRACE: the Transition Region and Coronal Explorer Authors: Schrijver, C.; Title, A.; Acton, L.; Bruner, M.; Fischer, R.; Golub, L.; Harrison, R.; Lemen, J.; Rosner, R.; Scharmer, G.; Scherrer, P.; Strong, K.; Tarbell, T.; Wolfson, J. Bibcode: 1996AAS...188.6704S Altcode: 1996BAAS...28..934S The TRACE mission is designed to obtain images of the solar transition region and corona of unprecedented quality. With these images we will be able to explore quantitatively the connections between the photospheric magnetic field and the associated hot and tenuous structures in the outer atmosphere. The TRACE telescope has an aperture of 30 cm, and will observe an 8.5 x 8.5 arcminute field of view with a resolution of one arcsecond. Finely tuned coatings on four quadrants on the primary and secondary normal--incidence mirrors will allow observations in narrow EUV and UV spectral bands. The passbands are set to Fe IX, XII, and XV lines in the EUV band, while filters allow observations in C IV, Ly alpha , and the UV continuum using the UV mirror quadrant. The data thus cover temperatures from 10(4) K up to 10(7) K. The Sun--synchronous orbit allows long intervals of uninterrupted viewing. Observations at different wavelengths can be made in rapid succession with an alignment of 0.1 arcsec. Coordinated observing with TRACE, SoHO and YOHKOH will give us the first opportunity to observe all temperature regimes in the solar atmosphere, including magnetograms, simultaneously from space. TRACE is currently scheduled to be launched in October 1997. More information can be found on the web at ``http://pore1.space.lockheed.com/TRACE/welcome.html''. Title: Initial Results from SOI/MDI High Resolution Magnetograms Authors: Title, A.; Tarbell, T.; Frank, Z.; Schrijver, C.; Shine, R.; Wolfson, J.; Zayer, I.; Scherrer, P.; Bush, R.; Deforest, C.; Hoeksema, T. Bibcode: 1996AAS...188.6915T Altcode: 1996BAAS...28..938T The Michelson Doppler Imager (MDI) on SoHO takes magnetogram s with resolutions of 1.2 (high resolution) and 4 (full disk) arcseconds. Movies of 16 hour duration have been constructed in full disk and high resolution mode. High resolution movies of the south polar region also have been obtained. In sums of nine high resolution magnetograms it is possible to detect fields as low as 5 gauss and total fluxes as low as 5 10(1) 6 Mx. In mid latitude regions new flux is observed to emerge everywhere. At all latitudes below 60 degrees flux is mixed on the scale of supergranulation. In the polar region above 60 degrees only fields of a single polarity are observed above the detection limit. Title: Calibration and Performance of the Michelson Doppler Imager on SOHO. Authors: Zayer, I.; Morrison, M.; Tarbell, T. D.; Title, A.; Wolfson, C. J.; MDI Engineering Team; Bogart, R. S.; Bush, R. I.; Hoeksema, J. T.; Duvall, T.; Sa, L. A. D.; Scherrer, P. H.; Schou, J. Bibcode: 1996AAS...188.3712Z Altcode: 1996BAAS...28..879Z The Michelson Doppler Imager (MDI) instrument probes the interior of the Sun by measuring the photospheric manifestations of solar oscillations. MDI was launched in December, 1995, on the Solar and Heliospheric Observatory (SOHO) and has been successfully observing the Sun since then. The instrument images the Sun on a 1024 x 1024 pixel CCD camera through a series of increasingly narrow spectral filters. The final elements, a pair of tunable Michelson interferometers, enable MDI to record filtergrams with FWHM bandwidth of 94 m Angstroms with a resolution of 4 arcseconds over the whole disk. Images can also be collected in MDI's higher resolution (1.25 arcsecond) field centered about 160 arcseconds north of the equator. An extensive calibration program has verified the end-to-end performance of the instrument in flight. MDI is working very well; we present the most important calibration results and a sample of early science observations. The Image Stabilization System (ISS) maintains overall pointing to better than ca. 0.01 arcsec, while the ISS' diagnostic mode allows us to measure spectrally narrow pointing jitter down to less than 1 mili-arcsec. We have confirmed the linearity of each CCD pixel to lie within 0.5%\ (the FWHM of the distribution is 0.2% ), and have to date not detected any contamination on the detector, which is cooled to -72 C. The noise in a single Dopplergram is of the order of 20 m/s, and initial measurements of transverse velocities are reliable to 100 m/s. The sensitivity of magnetograms reach 5G in a 10 minute average (15G in a single magnetogram). MDI's primary observable, the p-modes from full-disk medium-l data, are of very high quality out to l=300 as seen in the initial l-nu diagram. The SOI-MDI program is supported by NASA contract NAG5-3077. Title: Diagnostics of Shallow Convective Structures by Time-Distance Helioseismology Authors: Kosovichev, A. G.; Duvall, T. L., Jr.; Scherrer, P. H. Bibcode: 1996AAS...188.3709K Altcode: 1996BAAS...28R.878K We present a new method of 3D helioseismic diagnostics to study subphotospheric flow and thermal and magnetic structure associated with turbulent convection. The main difference from the previous studies by Duvall et al. (1996, Nature, 379, 235) and by Kosovichev (1996, ApJL, 461, L55) is that the new method can be applied for measuring solar properties in the shallow layer just beneath the surface. The shallow layer of superadiabatic convection, which is only few thousand kilometers deep, is the region of the greatest uncertainty in our knowledge of the Sun's interior. Recent numerical simulations have demonstrated substantial deviations of the structure of this layer from the mixing-length theory commonly used in modeling stellar structure and evolution. The uncertainty in the physics of turbulent convection also affects helioseismic inferences about the deep interior. Our method of 3D diagnostics is based on measuring and inverting anomalies of the sound-wave travel time between two areas on the solar surface. Because of the stochastic nature of solar waves, these two areas must be sufficiently large to provide a good signal-to-noise ratio. In practice, the travel time can be measured from the cross-correlation function averaged over several thousand cross-correlations between individual points on the surface. Therefore, it is essential to have stable high-resolution series of Doppler images. Such data have been obtained from the Michelson Doppler Imager instrument on SOHO. In this paper, we present some details of the cross-correlation time-distance analysis, and the technique to invert the travel-time measurements using the optical ray approximation. The travel time of the waves depends primarily on the wave group velocity and on the velocity of flow along the ray paths. The effects of the wave speed structure and of flows are separated by measuring the travel time of waves propagating in opposite directions along the same ray paths. The effects of magnetic fields are measured through anisotropy of the wave speed. We discuss the limits for observing small-scale features beneath the surface. This research is supported by the SOI-MDI NASA contract NAG5-3077 at Stanford University. Title: The Solar Oscillations Investigation - Michelson Doppler Imager Authors: Scherrer, P. H.; Bogart, R. S.; Bush, R. I.; Hoeksema, J. T.; Kosovichev, A. G.; Schou, J.; Rosenberg, W.; Springer, L.; Tarbell, T. D.; Title, A.; Wolfson, C. J.; Zayer, I.; MDI Engineering Team Bibcode: 1995SoPh..162..129S Altcode: The Solar Oscillations Investigation (SOI) uses the Michelson Doppler Imager (MDI) instrument to probe the interior of the Sun by measuring the photospheric manifestations of solar oscillations. Characteristics of the modes reveal the static and dynamic properties of the convection zone and core. Knowledge of these properties will improve our understanding of the solar cycle and of stellar evolution. Other photospheric observations will contribute to our knowledge of the solar magnetic field and surface motions. The investigation consists of coordinated efforts by several teams pursuing specific scientific objectives. Title: Soi Data and Information Services on the World-Wide Web Authors: Bogart, R. S.; Scherrer, P. H.; Stehle, M. B.; Suryanarayanan, J. K.; Tian, K. Bibcode: 1995ESASP.376b.153B Altcode: 1995help.confP.153B; 1995soho....2..153B The SOHO Solar Oscillations Investigation (SOI) will use the World Wide Web in several ways: as a public information service providing background and sample data to the public; as a source of rapid access quick-look data for other experimenters and observers; as the network hub for data distribution services to team members and guest investigators; as the online library site for documentation; and as a planning and operational tool to be used by team members in the definition and conduct of observational and analysis campaigns. The authors describe those services already on the Web and discuss the implementation of other planned services. Title: P-Mode Frequencies of Degree L = 3 TO 5 Authors: Pantel, A.; Hoeksema, T.; Fossat, E.; Scherrer, P.; Gelly, B.; Grec, G.; Loudagh, S.; Schmider, F. X. Bibcode: 1995ESASP.376b.381P Altcode: 1995soho....2..381P; 1995help.confP.381P No abstract at ADS Title: Prediction of coronal and heliospheric magnetic fields: The promise of SOI-MDI on SOHO Authors: Hoeksema, J. T.; Zhao, X. P.; Scherrer, P. H. Bibcode: 1995sowi.confQ..57H Altcode: Models of the coronal magnetic field have been developed over the years that reproduce the static characteristics of coronal and heliospheric structures fairly well. Limitations of spatial and temporal resolution and nonuniform quality of the input data have made it particularly difficult to investigate the response of the corona to rapidly changing photospheric conditions. The Solar Oscillations Investigation (SOI) experiment on SOHO, scheduled for launch late in 1995, will produce a series of full-disk photospheric magnetic field observations with 4" resolution about every 2 hours for the next several years. Higher resolution observations of the center of the disk will be available several times per day. These data should provide a basis for predicting the coronal and heliospheric field and their changes with unprecedented accuracy during the rising phase of Solar Cycle 23. Title: Soi/mdi Studies of Active-Region Seismology and Evolution Authors: Tarbell, T. D.; Title, A.; Hoeksema, J. T.; Scherrer, P.; Zweibel, E. Bibcode: 1995ESASP.376b..99T Altcode: 1995help.confP..99T; 1995soho....2...99T The Solar Oscillations Investigation (SOI) will study active regions in many ways using both helioseismic and conventional observing techniques. The Michelson Doppler Imager (MDI) instrument can make Doppler, continuum and line depth images and also longitudinal magnetograms, showing either the full disk or a high resolution field of view. There will be a Dynamics Program of continuous full disk Doppler observations for two months per year, many Campaign Programs of 8 hours continuous observing per day, and a synoptic Magnetic Program of about 15 full disk magnetograms per day. This paper gives a brief description of some of the scientific plans, measurements, and observing programs. Title: Potential Contribution of MDI to Understanding Large-Scale Structures in the Corona Authors: Zhao, X.; Hoeksema, J. T.; Scherrer, P. H. Bibcode: 1995ESASP.376b.509Z Altcode: 1995help.confP.509Z; 1995soho....2..509Z No abstract at ADS Title: Hot Spots and Active Longitudes: Organization of Solar Activity as a Probe of the Interior Authors: Bai, T.; Hoeksema, J. T.; Scherrer, P. H. Bibcode: 1995ESASP.376b.113B Altcode: 1995soho....2..113B; 1995help.confP.113B In order to investigate how solar activity is organized in longitude, the authors have analyzed major flares, large sunspot groups, and large-scale photospheric magnetic field strengths. The main characteristics of hot spots are outlined. Title: Soi Science Plan and Status Authors: Scherrer, P. H. Bibcode: 1995ESASP.376a..97S Altcode: 1995soho....1...97S; 1995heli.conf...97S The Solar Oscillations Investigation (SOI) with the Michelson Doppler Imager (MDI) is one of the three helioseismology instruments on SOHO. The SOI program is designed to address a diverse set of solar questions. The primary goals are to measure and characterize the solar convection zone. The science investigation will be accomplished in a set of working teams each focusing on specific problems. Title: Michelson Doppler Imager (MDI) Performance Characteristics Authors: Zayer, I.; Morrison, M.; Pope, T.; Rosenberg, W.; Tarbell, T.; Title, A.; Wolfson, J.; Bogart, R. S.; Hoeksema, J. T.; Milford, P.; Scherrer, P. H.; Schou, J. Bibcode: 1995ASPC...76..456Z Altcode: 1995gong.conf..456Z No abstract at ADS Title: Status of the Solar Oscillations Investigation - Michelson Doppler Imager Authors: Scherrer, P. H.; Bogart, R. S.; Bush, R. I.; Hoeksema, J. T.; Milford, P.; Schou, J.; Pope, T.; Rosenberg, W.; Springer, L.; Tarbell, T.; Title, A.; Wolfson, J.; Zayer, I. Bibcode: 1995ASPC...76..402S Altcode: 1995gong.conf..402S No abstract at ADS Title: The SOHO Solar Oscillations Investigation on the Web Authors: Tian, K.; Scherrer, P. H.; Bogart, R. S. Bibcode: 1995VA.....39...73T Altcode: The Solar Oscillations Investigation (SOI) is an international project to study the Sun's interior using data from the Michelson Doppler Imager on the Solar and Heliospheric Observatory and the newly developing techniques of the field of helioseismology. We have committed to using the World-Wide Web not only to provide information and public data, but as an active tool for defining science objectives, planning and conducting the mission operations and attendant data processing, as well as distribution of data to team members. SOI is organized into a number of Science Teams with responsibility for various aspects of the mission. As the team members are widely dispersed geographically, the Web will be used to provide them with operational views into all aspects of the data flow from observations through the production of organized calibrated datasets. The same tools will be available to team members and guest investigators conducting individual science investigations. Title: Status of the Mt. Wilson-Crimean-Kazakhstan High-Degree Helioseismology Network Authors: Rhodes, E. J., Jr.; Didkovsky, L.; Chumak, O. V.; Scherrer, P. H. Bibcode: 1995ASPC...76..398R Altcode: 1995gong.conf..398R No abstract at ADS Title: East-west inclination of large-scale photospheric magnetic fields Authors: Shrauner, J. A.; Scherrer, P. H. Bibcode: 1994SoPh..153..131S Altcode: Sixteen years of WSO magnetogram data have been studied to determine the solar cycle variation and latitude dependence of the east-west inclination of photospheric magnetic field lines. East-west inclination is here defined as the angle between a field line and its local radial vector, as projected onto the plane of the latitude and line of sight. Inclination is determined by a least-squares fit of observed magnetic fields to a simple projection model, and is found to depend on polarity and to change with the solar cycle. Leading and following polarities are tipped towards each by about 9° and have an overall net tilt in the direction of rotation (to the west) of 0.6°. New cycles are seen to begin at high latitudes and to grow through the lower latitudes over approximately 5 years, providing evidence for an extended cycle length of 16-18 years. Title: East-West Inclination of Large-Scale Photospheric Magnetic Fields Authors: Shrauner, J. A.; Scherrer, P. H. Bibcode: 1993BAAS...25.1182S Altcode: No abstract at ADS Title: The Solar Oscillation Investigation - Michelson Doppler Imager (SOI-MDI) Authors: Hoeksema, J. T.; Bogart, R. S.; Bush, R. I.; Milford, P. N.; Pope, T.; Rosenberg, W.; Scherrer, P. H.; Springer, L.; Tarbell, T.; Title, A.; Wolfson, J.; Zayer, I. Bibcode: 1993BAAS...25.1192H Altcode: No abstract at ADS Title: Observations of High Frequency and High Wavenumber Solar Oscillations Authors: Fernandes, D.; Scherrer, P.; Tarbell, T.; Title, A. Bibcode: 1993ASPC...42..101F Altcode: 1993gong.conf..101F No abstract at ADS Title: The High-Frequency P-Mode Spectrum Authors: Milford, P. N.; Scherrer, P. H.; Frank, Z.; Kosovichev, A. G.; Gough, D. O. Bibcode: 1993ASPC...42...97M Altcode: 1993gong.conf...97M No abstract at ADS Title: The Search for 160-MINUTE Oscillations in the Stanford and Crimean Solar Velocity Observations - 1974-1991 Authors: Kotov, V. A.; Scherrer, P. H.; Hoeksema, J. T.; Haneychuk, V. I.; Tsap, T. T. Bibcode: 1993ASPC...42..293K Altcode: 1993gong.conf..293K No abstract at ADS Title: Plans for MT.WILSON - Crimean Observatory High-Degree Helioseismology Network Authors: Rhodes, E. J., Jr.; Cacciani, A.; Dappen, W.; Didkovsky, L. V.; Hill, F.; Korzennik, S. G.; Kosovichev, A. G.; Kotov, V. A.; Scherrer, P. H. Bibcode: 1993ASPC...42..477R Altcode: 1993gong.conf..477R No abstract at ADS Title: On the Upper Limit for Detecting G-Mode Oscillations of the Sun Authors: Scherrer, P. H.; Hoeksema, J. T.; Kotov, V. A. Bibcode: 1993ASPC...42..281S Altcode: 1993gong.conf..281S No abstract at ADS Title: The solar oscillations investigation - Michelson Doppler Imager. Authors: Hoeksema, J. Todd; Scherrer, P. H.; Bush, R. I.; Title, A.; Tarbell, T. Bibcode: 1992ESASP.348....9H Altcode: 1992cscl.work....9H The Solar Oscillations Investigation (SOI) has developed the Michelson Doppler Imager (MDI) to investigate the properties of solar interior using the tools of helioseismology and of the photosphere and corona using more conventional techniques. A fundamental goal is to understand the Sun by determining its structure and observing its dynamics. The basic observables, velocity, intensity and magnetic field, are computed on board from up to twenty 1024 by 1024 filtergrams made each minute. Subsequent analysis will extend the region one can explore downward into the solar interior and upward into the corona. While the instrument is dedicated to producing an uninterrupted series of helioseismology data, several magnetograms will be made each day and special 8-hour campaigns are being developed to address specific scientific questions, some in coordination with other SOHO instruments. Title: Observations of High-Frequency and High-Wavenumber Solar Oscillations Authors: Fernandes, D. N.; Scherrer, P. H.; Tarbell, T. D.; Title, A. M. Bibcode: 1992ApJ...392..736F Altcode: Doppler shift measurements of the Na D1 absorption line reveal solar oscillations in a new regime of frequency and wavenumber. Oscillations of vertical velocities in the temperature minimum and low chromosphere of the sun are observed with frequencies ranging up to 9.5 mHz. The fundamental modes appear with wavenumbers up to 5.33/Mm (equivalent spherical harmonic degree 3710). No evidence for chromospheric modes of 3-minute period is reported. Title: The Solar Oscillation Imager-Michelson Doppler Imager for SoHO Authors: Title, A.; Tarbell, T.; Wolfson, J.; Scherrer, P.; Bush, R.; Hoeksema, T. Bibcode: 1992AAS...180.0606T Altcode: 1992BAAS...24Q.737T No abstract at ADS Title: Optical Components of the Solar Oscillations Imager-Michelson Doppler Imager Authors: Tarbell, T.; Rosenberg, W.; Pope, T.; Huff, L.; Torgerson, D.; Title, A.; Wolfson, J.; Scherrer, P.; Bush, R.; Hoeksema, T. Bibcode: 1992AAS...180.0607T Altcode: 1992BAAS...24R.737T No abstract at ADS Title: Measurement of the Polar Magnetic Fields at Wilcox Solar Observatory Authors: Bogart, R. S.; Hoeksema, J. T.; Scherrer, P. H. Bibcode: 1992AAS...180.5106B Altcode: 1992BAAS...24..814B A new sequence of regular observations has been initiated at Stanford's Wilcox Solar Observatory to better measure the projected component of the photospheric magnetic fields poleward of about 75deg latitude. The measurements are made in the 5250 Angstroms Fe I line used for both the regular Stanford magnetograms and meanfield measurements, in a circular aperture of 2 arc min projected diameter centred on the visible pole and on both the limb points closest to the poles. Initial results of observations since the beginning of the year suggest that the fields measured each day vary between +/- 1.5 gauss at this point in the cycle, with individual measurement uncertainties of approximately 0.15 gauss. These results are compared with the existing sequence of polar-field measurements, based on the daily magnetograms and covering a 30deg latitude range, that extend back to 1976. There is a suggestion of a rotational modulation of the signal in the limited dataset obtained so far. Title: Helioseismology from SOHO Authors: Scherrer, P. H. Bibcode: 1992AAS...180.3309S Altcode: 1992BAAS...24..781S Three experiments are presently being developed for flight on the SOHO mission. The combination will provide a significant extension in capabilities from ground based observations. The VIRGO (Variability of solar IRadiance and Gravity Oscillations) and GOLF (Global Oscillations at Low Frequencies) experiments will provide increased sensitivity for the lowest frequency acoustic modes and should significantly lower the detection threshhold for gravity mode oscillations below that obtainable from present ground based efforts. GOLF and VIRGO will be able to observe modes from spherical harmonic degree l=0 to l=3 and to l=10 respectively. The SOI-MDI (Solar Oscillations Investigation - Michelson Doppler Imager) will allow observations to k = 2.2 Mm(-1) (l=1500) in the full disk mode and k = 6.5 Mm(-1) (equivalent degree l = 4500) in a high resolution mode. The combination of the 3 experiments will allow low frequency observations in velocity (both photospheric and chromospheric), total irradiance, broadband and narrow band irradiance, and limb shape. The intrinsic solar noise will be the limiting factor in sensitivity for both p-modes and g-modes. The three experiments will provide the capability to allow seismic probing of the solar interior from the center of the sun to depths of only a few Km. The three projects involve the joint efforts of people from at least 15 countries including 43 Investigators, more than 44 associated investigators, and the efforts of more than 100 on the technical teams. Title: SOI-MDI Onboard Real Time Data Reduction - Requirements and Design. Authors: Milford, P.; Lindgren, R.; Tarbell, T.; Bacon, L.; Scherrer, P. Bibcode: 1992AAS...180.0608M Altcode: 1992BAAS...24..737M SOI-MDI is a space-based high-resolution helioseismology experiment. To observe Solar oscillations accurately requires a long time base of (nearly) continuous observations. Due to telemetry restrictions, SOI-MDI must carry out onboard data reduction of the high-resolution observations prior to sending the data to the ground. This paper summarizes the reduction requirements and discusses the hardware and software design of the processor built to meet these requirements. The main computational requirement to be met is the one-minute observing cadence, required to observe a solar signal with a Nyquist frequency corresponding to a 2-minute period. The analysis requires computing dopplergrams from the observed filtergrams and a partial spherical harmonic decomposition of the full disk dopplergrams. A custom image processor was designed to meet these specifications. Other requirements include low power, radiation tolerance and light weight. A design based on an ASIC, designed around the 2903 bitslice family of processors, has been developed to meet these requirements. The CPU includes three memory busses with simultaneous DMA transfers to main memory and a one-cycle 16 bit multiplier. Simultaneous access to the main memory by the CCD Camera, via a DMA memory adder (also implemented as an ASIC), and by the telemetry subsystem give the system sufficient performance to handle the 30 Mb/minute of input data. This work was supported by NASA Contract NAS5-30386 and Stanford Contract PR-6209. Title: Observations of high frequency and high wavenumber solar oscillations Authors: Fernandes, D. N.; Scherrer, P. H.; Tarbell, T. D.; Title, A. M. Bibcode: 1992STIN...9232488F Altcode: Doppler shift measurements of the Na D1 absorption line have revealed solar oscillations in a new regime of frequency and wavenumber. Oscillations of vertical velocities in the temperature minimum and low chromosphere of the Sun are observed with frequencies ranging up to 9.5 mHz. The fundamental modes appear with wavenumbers up to 5.33 M/m (equivalent spherical harmonic degree, 3710). We find no evidence for chromospheric modes of a 3-minute period. Title: The IRIS network site at the Wilcox Solar Observatory Authors: Hoeksema, J. T.; Scherrer, P. H. Bibcode: 1991SoPh..133...57H Altcode: The Wilcox Solar Observatory at Stanford University houses one of the International Research on the Interior of the Sun (IRIS) network observing stations. The instrument has observed the global oscillations of the Sun continually since it was installed in August 1987. Each site and instrument are different; here we report the details unique to the Stanford site. Title: Report of the solar physics panel Authors: Withbroe, George L.; Fisher, Richard R.; Antiochos, Spiro; Brueckner, Guenter; Hoeksema, J. Todd; Hudson, Hugh; Moore, Ronald; Radick, Richard R.; Rottman, Gary; Scherrer, Philip Bibcode: 1991spsi....1...67W Altcode: Recent accomplishments in solar physics can be grouped by the three regions of the Sun: the solar interior, the surface, and the exterior. The future scientific problems and areas of interest involve: generation of magnetic activity cycle, energy storage and release, solar activity, solar wind and solar interaction. Finally, the report discusses a number of future space mission concepts including: High Energy Solar Physics Mission, Global Solar Mission, Space Exploration Initiative, Solar Probe Mission, Solar Variability Explorer, Janus, as well as solar physics on Space Station Freedom. Title: The solar oscillations investigation - Michelson Doppler imager for SOHO Authors: Scherrer, P. H.; Hoeksema, J. T.; Bush, R. I. Bibcode: 1991AdSpR..11d.113S Altcode: 1991AdSpR..11..113S SOHO offers an unprecedented opportunity to probe the interior of a star with the techniques of helioseismology. Continuous distortion-free observations of the Sun will provide unique measurements of its internal structure and dynamics. The MDI instrument provides the capability to obtain observations with very high spatial resolution and high precision at all times, with statistical errors well below the expected solar noise background at all frequencies. The real limitation will be gaining a sufficient understanding of the systematic error sources with characteristic periods longer than several hours. Title: Rotation of the Photospheric Magnetic Fields: A North-South Asymmetry Authors: Antonucci, E.; Hoeksema, J. T.; Scherrer, P. H. Bibcode: 1990ApJ...360..296A Altcode: During most of solar cycle 21 the large-scale photospheric field rotated more rapidly in the Northern Hemisphere than in the southern. The large-scale northern field rotated with a 26.9 day period (synodic), was centered at 15 degrees N, and covered a latitude zone about 24 degrees wide. The large-scale southern field rotated with a periodicity of 28.1 days, was centered at 26 degrees S, and covered a latitude zone about 32 degrees wide. Our analysis showed rotational power at only a few discrete latitudes and frequencies in each hemisphere. The center of each peak lies near to the sunspot differential rotation curve. The largest scale field contributes to the configuration of the coronal and interplanetary magnetic field (IMF). The strength of the first harmonic of the northern field suggests that this structure may be related to the 4-sector pattern observed in the IMF polarity. The southern field had much lower power at the first harmonic of the solar rotation rate and so would contribute only to a 2-sector structure in the IMF. These results were discovered in Fourier analysis of photospheric synoptic charts obtained at the Wilcox Solar Observatory from 1976 to 1986 and confirmed in higher resolution maps from the National Solar Observatory. Mt. Wilson magnetic field measurements from solar cycle 20 show a similar north-south asymmetry. Title: Solar variability influences on weather and climate: Possible connections through cosmic ray fluxes and storm intensification Authors: Tinsley, Brian A.; Brown, Geoffrey M.; Scherrer, Philip H. Bibcode: 1989JGR....9414783T Altcode: The question of the mechanism for solar-variability effects on weather and climate can be separated into (1) the identification of the carrier of the solar variability and (2) the identification of the physical link between the carrier and the meteorological response. The suggestion that galactic cosmic rays (GCR), as modulated by the solar wind, are the carriers of the component of solar variability that affects weather and climate has been discussed in the literatue for 30 years, and considerable evidence for it has now accumulated. Variations of GCR occur with the 11-year solar cycle, matching the time scale of recent results for atmospheric variations, as modulated by the quasi-biennial oscillation of equatorial stratospheric winds (QBO). Variations in GCR occur on the time scale of centuries with a well-defined peak in the coldest decade of the little ice age. Here we present new evidence on the meteorological responses to variations on the time scale of a few days. The occurrence of correlations of GCR and meteorological responses on all three time scales strengthens the hypothesis of GCR as carriers of solar variability to the lower atmosphere. The responses reported here include changes in the vertical temperature profile in the troposphere and lower stratosphere and in the northern hemisphere vorticity area index, associated with Forbush decreases in GCR. The meteorological responses to Forbush decreases are in the opposite sense but otherwise are quite similar to responses that immediately follow solar flares.

This is to be expected, based on the hypothesis that particles with energy about 100-1000 MeV are the external forcing function for the tropospheric response, since large solar flares increase the particle flux and ionization and minor species production in the lower stratosphere, whereas Forbush decreases reduce them. The mechanism or mechanisms linking changes in low-energy GCR and other particles in this energy range of 100-1000 MeV to tropospheric temperature and dynamic responses have not been identified. This can be attributed to current uncertainties regarding the microphysical and electrical properties of aerosols and clouds. One possibility is the changes in clouds lead to changes in cloud radiative forcing. The height distribution of the tropospheric response and the amount of energy involved and the rapidity of the time response suggest that the release of latent heat could also be involved. These could lead to the observed tropospheric responses which are understandable in terms of changes in the intensity of cyclonic disturbances. Theoretical considerations link such changes to the observed latitudinal movement of the jet stream. Title: Solar activity, the QBO, and tropospheric responses Authors: Tinsley, Brian A.; Brown, Geoffrey M.; Scherrer, Philip H. Bibcode: 1989maph...29...53T Altcode: The suggestion that galactic cosmic rays (GCR) as modulated by the solar wind are the carriers of the component of solar variability that affects weather and climate has been discussed in the literature for 30 years, and there is now a considerable body of evidence that supports it. Variations of GCR occur with the 11 year solar cycle, matching the time scale of recent results for atmospheric variations, as modulated by the quasibiennial oscillation of equatorial stratospheric winds (the QBO). Variations in GCR occur on the time scale of centuries with a well defined peak in the coldest decade of the little ice age. New evidence is presented on the meteorological responses to GCR variations on the time scale of a few days. These responses include changes in the vertical temperature profile in the troposphere and lower stratosphere in the two days following solar flare related high speed plasma streams and associated GCR decreases, and in decreases in Vorticity Area Index (VAI) following Forbush decreases of GCR. The occurrence of correlations of GCR and meteorological responses on all three time scales strengthens the hypothesis of GCR as carriers of solar variability to the lower atmosphere. Both short and long term tropospheric responses are understandable as changes in the intensity of cyclonic storms initiated by mechanisms involving cloud microphysical and cloud electrification processes, due to changes in local ion production from changes in GCR fluxes and other high energy particles in the MeV to low GeV range. The nature of these mechanisms remains undetermined. Possible stratospheric wind (particularly QBO) effects on the transport of HNO3 and other constituents incorporated in cluster ions and possible condensation and freezing nuclei are considered as relevant to the long term variations. Title: Rotation of the photospheric magnetic fields: A north-south asymmetry Authors: Antonucci, E.; Hoeksema, J. T.; Scherrer, P. H. Bibcode: 1989STIN...9014177A Altcode: During most of solar cycle 21 the large-scale photospheric field rotated more rapidly in the Northern Hemisphere than in the southern. The large-scale northern field rotated with a 26.9 day period (synodic), was centered at 15 degress N, and covered a latitude zone about 24 degrees wide. The large-scale southern field rotated with a periodicity of 28.1 days, was centered at 26 degrees S, and covered a latitude zone about 32 degrees wide. Our analysis showed rotational power at only a few discrete latitudes and frequencies in each hemisphere. The center of each peak lies near the sunspot differential rotation curve. The largest scale field contributes to the configuration of the coronal and interplanetary magnetic field (IMF). The strength of the first harmonic of the northern field suggests that this structure may be related to the 4-sector pattern observed in the IMF polarity. The southern field had much lower power at the first harmonic of the solar rotation rate and so would contribute only to a 2-sector structure in the IMF. These results were discovered in Fourier analysis of photospheric synoptic charts obtained at the Wilcox Solar Observatory from 1976 to 1986 and confirmed in higher resolution maps from the National Solar Observatory. Mt. Wilson magnetic field measurements from solar cycle 20 show a similar north-south asymmetry. Title: The Solar Oscillations Imager for SOHO Authors: Scherrer, P. H. Bibcode: 1989BAAS...21..832S Altcode: No abstract at ADS Title: Solar g-mode oscillations: Comparison of SMM-ACRIM and ground-based observations Authors: Scherrer, Philip H. Bibcode: 1989stan.reptQ....S Altcode: Progress was made in access to data and in developing programs for its analysis. The difficulties in completing the work in the planned time can be traced to several factors. The correction of the Stanford oscillation using gridded intensity data was not successful. It was concluded that due to poor continuity of the 1985 and 1986 data due to clouds, that a joint analysis with the ACRIM data (best solar oscillation data to date) on the summer 1987 observations should be performed. The 1988 Stanford oscillation data are being examined and the cross comparison of the ACRIM spectrum with the Standford spectrum for 1987 in the g-mode regime will shortly begin. Title: Geomagnetic disturbances Authors: Scherrer, Philip H. Bibcode: 1989stan.reptR....S Altcode: Investigations have included observations and analysis of the solar and interplanetary quantities relevant to geomagnetic activity. The operation of the Wilcox Solar Observatory and analysis of the synoptic observations of magnetic fields has constituted a significant part of the effort. Emphasis has been to attempt to understand the timing and severity of geomagnetic disturbances by understanding the solar mechanisms responsible for the origin of solar wind variations. Title: The Michelson Doppler imager for the solar oscillations imager program on SOHO. Authors: Hoeksema, J. T.; Scherrer, Philip H.; Title, A. M.; Tarbell, T. D. Bibcode: 1988ESASP.286..407H Altcode: 1988ssls.rept..407H The Michelson Doppler Imager (MDI) will be the instrument used in the Solar Oscillations Imager Program on SOHO. MDI will make a line-of-sight velocity map of the full solar disk with 2 arc-second pixels each minute. The instrument will be a modification of the Fourier Tachometer and will operate by using narrow bandpass solar images at four wavelengths to measure the line profile of the Ni I line at 6768 Å. This method is relatively insensitive to line profile changes and has a linear response to velocity. The instrument is also capable of making partial maps with 0.7 arc-sec pixels. All data will be transmitted to the ground for two continuous months each year and 8 hours each day (160 kilobits/sec). At all times the on-board computer will compute and transmit a selection of modes (5 kilobits/sec) to take full advantage of the advantages of a space based telescope. Line-of-sight magnetic fields will also be measured regularly. The flight instrument will be built by the Lockheed Palo Alto Research Laboratory. Title: The search for solar gravity modes. Authors: Henning, Harald M.; Scherrer, Philip H. Bibcode: 1988ESASP.286..419H Altcode: 1988ssls.rept..419H The authors have maintained a solar oscillations observing program for more than 13 years at Stanford. The observations are most sensitive to low degree solar modes and have been used for the study of long period p-mode and g-mode oscillations. At the start of the 1987 observing season (summer) some long-standing problems with the instrument were corrected which (along with good weather) allowed the cleanest set of data to date. This paper reports the current state of the search for evidence of g-modes in this data. Analysis of this data shows good evidence for g-modes. Various methods were used for mode identification with a statistical search for a simple pattern of even spacing in period selected as the most robust. Using this method, a possible g-mode identification was made with an asymptotic period separation TO = 37.1 minutes. This identification was consistent with a rotation splitting of 1.6 microHz. Tests with randomly generated spectral peaks find as significant a possible set of modes in only 2 out of 100 cases. Title: The solar oscillations imager for SOHO. Authors: Scherrer, Philip H.; Hoeksema, J. T.; Bogart, R. S. Bibcode: 1988ESASP.286..375S Altcode: 1988ssls.rept..375S The Solar Oscillations Imager (SOI) programs for SOHO will consist of a Michelson Doppler Imager (MDI) instrument, a data reduction and analysis capability, and a coordinated set of investigations designed to address a set of science objectives. Title: SOI: The Solar Oscillations Imager on SOHO Authors: Scherrer, P. H.; Hoeksema, J. T.; Bogart, R. S.; Walker, A. B. C., Jr.; Title, A. M.; Tarbell, T. D.; Wolfson, C. J.; Brown, T. M., Jr.; Christensen-Dalsgaard, J.; Gough, D. O. Bibcode: 1988sohi.rept...25S Altcode: The Solar Oscillations Imager (SOI) program for SOHO (solar and heliospheric observatory) is described. It will consist of a Michelson Doppler Imager (MDI) instrument, a facility providing data reduction and analysis capability, and a coordinated set of investigations designed to address a set of science objectives. The MDI is designed to take advantage of the anticipated SOHO telemetry by organizing the observations into four observation programs: structure (at all times), dynamics (two months per year), campaign (eight hours per day, ten months per year), and magnetic fields (few minutes per day). The MDI will measure line-of-sight velocity by Doppler shift, transverse velocity by local correlation tracking, line and continuum intensity, and line-of-sight magnetic fields with both 4 and 1.4 arc-second resolution (2 and 0.7 arc-sec pixels respectively). Title: On the Feasibility of Correlation Tracking at Moderate Resolution Authors: Bogart, R. S.; Ferguson, S. H.; Scherrer, P. H.; Tarbell, T. D.; Title, A. M. Bibcode: 1988SoPh..116..205B Altcode: The SOUP experiment demonstrated that photospheric surface flows can be measured by correlation tracking of white-light intensity features at high resolution (November et al., 1987). In order to assess the feasibility of this technique with observations made at lower resolution, we have applied it to the same SOUP data artificially degraded, but still free of seeing distortion. Comparison with the velocity structures inferred from the original data shows generally good agreement when the resolution is better than about 2″. The radial outflow from a sunspot penumbra, however, can only be seen with resolution of better than 1″. With resolution of worse than 2″, the inferred velocity fields rapidly lose coherence, while resolution of better than 1″ yields little improvement. We conclude that apertures as small as 10-14 cm on a space-based platform will be useful for the measurement of large-scale horizontal motions. Title: A New Technique for Measuring Solar Velocity Authors: Scherrer, P. H.; Tarbell, T. D. Bibcode: 1988BAAS...20..702S Altcode: No abstract at ADS Title: Helioseismic Observations at Stanford 1977-1986 Authors: Henning, H. M.; Scherrer, P. H. Bibcode: 1988IAUS..123...29H Altcode: Observations of low degree modes of solar oscillation have been made at The Wilcox Solar Observatory at Stanford University for more than a decade. The authors are presently re-examining the set of observations from 1977 through 1986. They have first tested the stability of the p-mode frequencies for modes of degree l = 2 - 5 in each year. They find a marginally significant trend of a decrease in p-mode frequencies of 0.06 μHz per year. They have also examined the continuity of the observed signal at 160.01 minutes. Title: Long-term variability of solar magnetic fields Authors: Todd Hoeksema, J.; Scherrer, P. H. Bibcode: 1988AdSpR...8g.177T Altcode: 1988AdSpR...8..177T The solar magnetic field varies on all time scales. Recent analysis of 600 million year-old Australian varves shows terrestrial evidence for not only the familiar 22-year magnetic cycle, but variations with periods of 300-400 years as well. The Maunder minimum is but one of several long intervals showing atypical levels of solar activity. Recently a 151-day periodicity in flare activity has been found. Active regions, sunspots, ephemeral regions, and flares cover a broad range of shorter time scale variations in the solar magnetic field.

Long-term variations can be interpreted in at least two ways. One outlook regards the large-scale and long-term variations of the photospheric field as more-or-less direct guides to the organization of the solar field as it evolves through a solar cycle. The slowly varying field reveals the fundamental interior structure of the Sun.

An alternative view interprets the surface manifestation of the magnetic field primarily as the result of the convective motions in the solar atmosphere. The evolving distribution of photospheric flux depends upon the locations of emerging flux and the subsequent motions and interactions of the fields in the moving plasma. Information about the interior field comes largely from analysis of emerging flux.

We discuss interpretation of the phenomenology of the long-term variability in the context of these contrasting views. Title: More than a solar cycle of synoptic solar and coronal data: a video presentation. Authors: Hoeksema, J. T.; Herant, M.; Scherrer, P. H.; Title, A. M. Bibcode: 1988sscd.conf..376H Altcode: Color video movies of synoptic observations of the sun and corona can now be created. Individual analog frames on laser disc can be referenced digitally and played back at any speed. The authors have brought together photospheric magnetic field data from the Wilcox Solar Observatory at Standford and the National Solar Observatory, model computations of the coronal magnetic field, and coronal data from the Sacramento Peak coronagraph and the Mauna Loa K-coronameter and made a series of movies presenting the data sets individually and in comparison with one another. This paper presents a description of each of the data sets and movies developed thus far and briefly outlines some of the more interesting and obvious features observed when viewing the movies. Title: Long-term variability of solar magnetic fields. Authors: Hoeksema, J. Todd; Scherrer, P. H. Bibcode: 1988AdSpR...8g.177H Altcode: 1988AdSpR...8..177H In this paper the authors summarize the well known variations of the solar magnetic field, concentrating on some of the more recent work that attempts to give an empirical description of the way the field varies. Title: More than a solar cycle of synoptic solar and coronal data: A video presentation Authors: Hoeksema, J. T.; Herant, M.; Scherrer, P. H.; Title, A. M. Bibcode: 1987STIN...8829708H Altcode: Color video movies of synoptic observations of the sun and corona can now be created. Individual analog frames on laser discs can be referenced digitally and played back at any speed. We have brought together photospheric magnetic field data from the Wilcox Solar Observatory at Stanford and the National Solar Observatory, model computations of the coronal magnetic field, and coronal data from the Sacramento Peak coronagraph and the Mauna Loa K-coronameter and made a series of movies presenting the data sets individually and in comparison with one another. This paper presents a description of each of the data sets and movies developed thus far and briefly outlines some of the more interesting and obvious features observed when viewing the movies. Title: Rotation of the Coronal Magnetic Fields Authors: Hoeksema, J. T.; Scherrer, P. H. Bibcode: 1987ApJ...318..428H Altcode: The coronal magnetic field rotates differently than the photosphere. The field configuration of the corona can be calculated from the observed photosphpere field using a potential field model. Correlation of the field patterns at different latitudes with a lag near one solar rotation shows much less differential rotation than observed in the photospheric field; however, the peak is very broad and determines the rotation rate rather poorly. Consideration of longer lags reveals a more complex rotational structure and indicates different rotation rates in the Northern and Southern Hemispheres. Spectral analysis of the equatorial dipole component of the coronal field reveals an organization into just a few discrete rotation frequencies which are apparently present simultaneously. Spectral analysis of the field at different latitudes shows that the frequencies are present simultaneously. Spectra analysis of the field at different latitudes shows that the frequencies are present simultaneously, but in different hemispheres, and that the Southern Hemisphere fields rotate more slowly than those in the north in solar cycle 21. Title: The Meridional Flow Inferred from the Shape of Large-scale Magnetic Structures in the Photosphere Authors: Hoeksema, J. T.; Herant, M.; Scherrer, P. H.; Title, A. M. Bibcode: 1987BAAS...19S.935H Altcode: No abstract at ADS Title: On the Feasibility of Correlation Tracking at Moderate Resolution Authors: Bogart, R. S.; Scherrer, P. H.; Ferguson, S. H.; Tarbell, T. D.; Title, A. M. Bibcode: 1987BAAS...19..941B Altcode: No abstract at ADS Title: The North-South Asymmetry in the Rotation of the Photospheric Magnetic Field During Solar Cycles 21 and 20 Authors: Scherrer, P. H.; Hoeksema, J. T.; Antonucci, E. Bibcode: 1987BAAS...19S.935S Altcode: No abstract at ADS Title: Helioseismic observations at Stanford, 1977-1986 Authors: Henning, H. M.; Scherrer, P. H. Bibcode: 1986STIN...8714236H Altcode: Observations of low degree modes of solar oscillations were made at the Wilcox Solar Observatory for more than a decade. The set of observations from 1977 through 1986 are reexamined. The stability of the p-mode frequencies for modes of degree l=2-5 in each year is tested. A marginally significant trend of a decrease in p-mode frequencies of 0.06 microHz per year is found. The continuity of the observed signal at 160.01 minutes are also examined. It was found that the previously reported phase stability is no longer present. However, due to uncertainties in calibration, the reality of the reported signal can not be excluded. Title: Rotation of the coronal magnetic field Authors: Hoeksema, J. T.; Scherrer, Philip H. Bibcode: 1986STIN...8720163H Altcode: The coronal magnetic field rotates differently than the photosphere. The field configuration of the corona can be calculated from the observed photospheric field using a potential field model. Correlation of the field patterns at different latitudes with a lag near one solar rotation shows much less differential rotation than observed in the photospheric field; however, the peak is very broad and determines the rotation rate rather poorly. Consideration of longer lags reveals a more complex rotational structure and indicates different rotation rates in the northern and southern hemispheres. Spectral analysis of the equatorial dipole component of the coronal field reveals an organization into just a few discrete rotation frequencies which are apparently present simultaneously. Spectral analysis of the field at different latitudes shows that the frequencies are present simultaneously. Spectral analysis of the field at different latitudes shows that the frequencies are present simultaneously, but in different hemispheres, and that the Southern Hemisphere fields rotate more slowly than those in the north in solar cycle 21. Title: An atlas of photospheric magnetic field observations and computed coronal magnetic fields: 1976 1985 Authors: Hoeksema, J. T.; Scherrer, P. H. Bibcode: 1986SoPh..105..205H Altcode: Daily magnetogram observations of the large-scale photospheric magnetic field have been made at the John M. Wilcox Solar Observatory at Stanford since May of 1976. These measurements provide a homogeneous record of the changing solar field through most of solar cycle 21. Title: Topology of the Heliospheric Current Sheet at the Time of the Halley's Comet-Giotto Encounter Authors: Suess, S. T.; O'Farrell, J. M.; Hoeksema, J. T.; Scherrer, P. H. Bibcode: 1986BAAS...18..678S Altcode: No abstract at ADS Title: Upper Limits on Solar Large-Scale Surface Motions Authors: Scherrer, P. H.; Bogart, R. S.; Hoeksema, J. T. Bibcode: 1986BAAS...18..702S Altcode: No abstract at ADS Title: Solar magnetic field, 1976 through 1985: an atlas of photospheric magnetic field observations and computed coronal magnetic fields from the John M. Wilcox Solar Observatory at Sanford, 1976-1985 Authors: Hoeksema, J. T.; Scherrer, P. H. Bibcode: 1986STIN...8629760H Altcode: Daily magnetogram observations of the large-scale photospheric magnetic field have been made at the John M. Wilcox Solar Observatory at Stanford since May of 1976. These measurements provide a homogeneous record of the changing solar field through most of Solar Cycle 21. Using the photospheric data, the configuration of the coronal and heliospheric fields can be calculated using a Potential Field - Source Surface model. This provides a 3-dimensional picture of the heliospheric field evolution during the solar cycle. In the report the authors present the complete set of synoptic charts of the measured photospheric magnetic field, the computed field at the source surface, and the coefficients of the multipole expansion of the coronal field. The general underlying structure of the solar and helispheric fields, which determine the environment for solar terrestrial relations and provide the context within which solar activity related events occur, can be approximated from these data. Title: Coments on techniques for spectral deconvolution. Authors: Scherrer, Philip H. Bibcode: 1986ASIC..169..117S Altcode: 1986ssds.proc..117S Current observational questions in asteroseismology require high spectral resolution that can only be obtained with observations spanning many days or months. The primary constraint in the full utilization of single mid-latitude observing sites is the presence of diurnal data gaps. Several methods for removing the effect of these gaps in the spectra obtained from velocity observations have been suggested. The limitations of these methods and their applicability to the helioseismology problem is discussed. Title: An atlas of photospheric magnetic field observations and computed coronal magnetic fields: 1976 - 1985 Authors: Hoeksema, J. T.; Scherrer, P. H. Bibcode: 1986STIN...8715151H Altcode: Daily magnetogram observations of the large-scale photospheric magnetic field have been made at the John M. Wilcox Solar Observatory at Stanford since May of 1976. These measurements provide a homogeneous record of the changing solar field through most of solar cycle 21. Using the photospheric data, the configuration of the coronal and heliospheric fields can be calculated using a Potential Field-Source Surface model. This provides a three-dimensional picture of the heliospheric field evolution during the solar cycle. This paper announces the publication of UAG Report No. 94, an Atlas containing the complete set of synoptic charts of the measured photospheric magnetic field, the computed field at the source surface, and the coefficients of the multipole expansion of the coronal field. The general underlying structures of the solar and heliospheric fields, which determine the environment for solar-terrestrial relations and provide the context within which solar activity related events occur, can be approximated from these data. Title: Solar rotation measured at the Wilcox Solar Observatory. Authors: Bogart, R. S.; Scherrer, P. H. Bibcode: 1986BAAS...18R.848B Altcode: No abstract at ADS Title: Geomagnetic disturbances Authors: Scherrer, P. H. Bibcode: 1986stan.reptQ....S Altcode: Recent efforts include the study of the solar dynamics by directly observing the surface manifestations of giant scale convective motions. A knowledge of the structure of the convective zone is crucial to the eventual understanding of the solar magnetic cycle. The origin and structure of coronal magnetic fields and the origin of solar wind variability are studied. The static structure of the corona is governed by the large scale organization of photospheric fields. During times of low activity, these fields can be used to infer the coronal structure with reasonable accuracy. Our synoptic series of high accuracy low resolution magnetic observations continues to provide a useful source for a number of investigations conducted at Stanford and elsewhere. The relation between the effects of transient events and the large scale ambient structure is investigated. Flare accelerated material that does not cross the heliospheric current sheet has a larger impact on the terrestrial environment than material from flares that must cross the current sheet to arrive at the Earth. Title: Solar Wind Speed Azimuthal Variation Along the Heliospheric Current Sheet Authors: Suess, S. T.; Scherrer, P. H.; Hoeksema, J. T. Bibcode: 1986ASSL..123..275S Altcode: 1986shtd.symp..275S The authors report on analysis of the speeds measured by Voyager 1 and 2 while skimming along a horizontal (east-west) portion of the current sheet over several days in 1977. The results demonstrate that in this case speed variations exist and are large enough to significantly deform the sheet within a few AU or less if the current sheet were anything but perfectly horizontal. The spatial scale of the speed variation ranges from the smallest measurable scale using 1 hour averaged data up to tens of degrees in longitude. A deformation example is given under the assumption that the observed velocity variation exists on a current sheet that is initially perpendicular to the heliographic equator. Title: Observations of low-degree p-mode oscillations in 1984. Authors: Henning, Harald M.; Scherrer, Philip H. Bibcode: 1986ASIC..169...55H Altcode: 1986ssds.proc...55H Analysis of Stanford differential velocity observations has been extended through the 1984 observing season. Excellent quality observations were obtained in 1984 on 38 days in a 49 day interval from June 20th through August 7th. The power spectrum of this data has been examined and improved frequency determinations have been made for p-modes of degree 2 through 5 and order 5 through 34. Of special interest are the modes of the lower orders, n ranging from 5 to 10, which have not been identified previously. Title: The detection of global convective wave flows on the Sun. Authors: Scherrer, Philip H.; Bogart, Richard; Hoeksema, J. Todd; Yoshimura, Hirokazu Bibcode: 1986ASIC..169...93S Altcode: 1986ssds.proc...93S Global convective flows in the solar convection zone have been predictd by theoretical interpretations of the global-scale ordering of magnetic fields and activity centers and by theoretical analyses of rotating convection zones. The signatures of such flows have now been detected by analyzing the daily series of low-resoluton Dopplergrams obtained at the Wilcox Solar Observatory at Stanford University. The signatures are patterns of alternating east and west flows with amplitudes on the order of 25 m/s and longitudinal extent of about 30 degrees. Title: The influence of the heliospheric current sheet and angular separation on flare-accelerated solar wind Authors: Henning, H. M.; Scherrer, P. H.; Hoeksema, J. T. Bibcode: 1985JGR....9011055H Altcode: A complete set of major flares has been used to investigate the effect of the heliospheric current sheet on the magnitude of the flare-associated disturbance measured at the earth. It was found that disturbances associated with flares located on the same side of the current sheet as the earth were of larger magnitude than those associated with flares located such that the flare-accelerated material would have to cross the current sheet locus. It was also found that the angular separation between the flare position and the earth has a strong effect on the magnitude of the disturbance. A larger angular separation tended to result in a smaller disturbance. Third, it was determined that flares tend to occur near the heliospheric current sheet. Title: Observations of low-degree p-mode oscillations in 1984. Comments on techniques for spectral deconvolution Authors: Henning, H. M.; Scherrer, P. H. Bibcode: 1985STIN...8627174H Altcode: Global convective flows in the solar convection zone have been predicted by theoretical interpretations of the global-scale ordering of magnetic fields and activity centers and by theoretical analyses of rotating convection zones. Direct evidence of these flows in the photosphere has not previously been found despite several long-term efforts. The signatures of such flows have now been detected by analyzing the daily series of low-resolution Dopplergrams obtained at the Wilcox Solar Observatory at Stanford Univ. The signatures are patterns of alternating east and west flows with amplitudes on the order of 25 m/s and longitudinal extent of about 30 degrees. The patterns move across the solar disc at approximately the solar rotation rate and have lifetimes of at least several rotations. Boundaries of the fast and slow flows are often associated with large magnetic active regions. Title: The influence of the heliospheric current sheet and angular separation on flare accelerated solar wind Authors: Henning, H. M.; Scherrer, P. H.; Hoeksema, J. T. Bibcode: 1985STIN...8529907H Altcode: A complete set of major flares was used to investigate the effect of the heliospheric current sheet on the magnitude of the flare associated disturbance measured at Earth. It was also found that the angular separation tended to result in a smaller disturbance. Thirdly, it was determined that flares tend to occur near the heliospheric current sheet. Title: Deconvolution Methods for Analysis of Solar Oscillation Observations Authors: Scherrer, P. H. Bibcode: 1985BAAS...17R.643S Altcode: No abstract at ADS Title: Observations of Low-Degree P-Mode Oscillations in 1984 Authors: Henning, H. M.; Scherrer, P. H. Bibcode: 1985BAAS...17R.639H Altcode: No abstract at ADS Title: The Detection of Global (Giant Cell) Convective Wave Flows on the Sun Authors: Yoshimura, H.; Scherrer, P. H.; Bogart, R. S.; Hoeksema, J. T. Bibcode: 1985BAAS...17..639Y Altcode: No abstract at ADS Title: Detection of solar gravity mode oscillations. Authors: Scherrer, P. H. Bibcode: 1984sses.nasa..173S Altcode: 1984sss..conf..173S An analysis of solar velocity data obtained at the Stanford Solar Observatory has shown the existence of solar global oscillations. The oscillations are in the range 45 to 105 μHz (160 to 370 minutes) and are interpreted as internal gravity modes of degree l = 1 and l = 2. Title: Harmonic analysis of the solar magnetic field. Authors: Hoeksema, J. T.; Scherrer, P. H. Bibcode: 1984ESASP.220..269H Altcode: 1984ESPM....4..269H The spherical harmonics of the global solar magnetic field have been calculated using photospheric field measurements from the Stanford Solar Observatory from 1976 - 1983. The field evolution during the solar cycle is analyzed. Title: Detection of solar gravity mode oscillations Authors: Scherrer, P. H. Bibcode: 1984MmSAI..55...83S Altcode: The detection of g-mode oscillations in solar-velocity data obtained at Stanford Solar Observatory during 1977-1980 is reported, summarizing the results of Scherrer and Wilcox (1983) and Delache and Scherrer (1983). Spectra are shown, and the analysis results are presented in a table and graph. A total of 14 peaks are identified in the frequency range 45-105 microhertz, of which seven are assigned to a series with l = 1 and n = 6-10 and four are assigned to a series with l = 2 and n = 15-20; a peak at 59.52 microhertz can be identified as either l = 1, n = 10 or as l = 2, n = 17. Title: Harmonic Analysis of the Solar and Heliospheric Magnetic Fields Authors: Hoeksema, J. T.; Scherrer, P. H. Bibcode: 1984BAAS...16..452H Altcode: No abstract at ADS Title: John M. Wilcox died 1983 October 14. Authors: Scherrer, P. H. Bibcode: 1984PhT....37e.103S Altcode: No abstract at ADS Title: Detection of solar gravity mode oscillations Authors: Delache, P.; Scherrer, P. H. Bibcode: 1983Natur.306..651D Altcode: An analysis of solar velocity data obtained at the Stanford Solar Observatory shows the existence of solar global oscillations in the range 45-105 µHz (160-370 min). These oscillations are interpreted as internal gravity modes of degree l = 1 and l = 2. A good estimate of the order of the modes has also been made. Title: The structure of the heliospheric current sheet: 1978-1982 Authors: Hoeksema, J. T.; Wilcox, J. M.; Scherrer, P. H. Bibcode: 1983JGR....88.9910H Altcode: The structure of the heliospheric magnetic field changes substantially during the 11-year sunspot cycle. We have calculated its configuration for the period 1976-1982 by using a potential field model, continuing our earlier study near solar minimum in 1976-1977 (Hoeksema et al., 1982). In this paper we concentrate on the structure during the rising phase, maximum, and early decline of sunspot cycle 21, from 1978 to 1982. Early in this interval there are four warps in the current sheet (the boundary between interplanetary magnetic field toward and away from the sun) giving rise to a four-sector structure in the interplanetary magnetic field observed at earth. The location of the current sheet changes slowly and extends to a heliographic latitude of approximately 50°. Near maximum the structure is much more complex, with the current sheet extending nearly to the poles. Often there are multiple current sheets. As solar activity decrease, the structure simplifies until, in most of 1982, there is a single, simply shaped current sheet corresponding to a two-sector interplanetary magnetic field structure in the ecliptic plane. The sun's polar fields, not fully measured by magnetographs such as that at the Stanford Solar Observatory, substantially influence the calculated position of the current sheet near sunspot minimum. We have determined the strength of the polar field correction throughout this period and include it in our model calculations. The lower latitude magnetic fields become much stronger as the polar fields weaken and reverse polarity near maximum, decreasing the influence of the polar field correction. The major model parameter is in the radius of the source surface, the spherical surface at which the field lines become radial. Correlations of interplanetary magnetic field polarity observed by spacecraft with that predicted by the model calculated at various source surface radii indicate that the optimum source surface radius is not significantly different from 2.5 Rs during this part of the solar cycle. Title: Detection of solar gravity mode oscillations Authors: Scherrer, P. H. Bibcode: 1983dsgm.book.....S Altcode: An analysis of solar velocity data obtained at the Stanford Solar Observatory has shown the existence of solar global oscillations (Delache and Scherrer, Nature, in press). The oscillations are in the range of 45 to 105 microHz (160 to 370 minutes) and are interpreted as internal gravity modes of degree l=1 and l=2. Title: The structure of the heliospheric current sheet, 1978 - 1982 Authors: Hoeksema, J. T.; Wilcox, J. M.; Scherrer, P. H. Bibcode: 1983STIN...8325645H Altcode: The structure of the heliospheric magnetic field changes substantially during the 11 year sunspot cycle. Its configuration for the period 1976 through 1982 using a potential field model was calculated. The structure during the rising phase, maximum, and early decline of sunspot cycle 21, from 1978 to 1982 is considered. Title: Detection of solar gravity mode oscillations Authors: Delache, P.; Scherrer, P. H. Bibcode: 1983dsgm.book.....D Altcode: An analysis of solar velocity data obtained at the Stanford Solar Observatory shows the existence of solar global oscillations in the range 45 to 105 microHz (160 to 370 minutes). These oscillations are interpreted as internal gravity modes of degree l = 1 and l = 2. A good estimate of the order of the modes has also been made. Title: Detection of solar five-minute oscillations of low degree Authors: Scherrer, Philip H.; Wilcox, John M.; Christensen-Dalsgaard, J.; Gough, D. O. Bibcode: 1983SoPh...82...75S Altcode: 1983IAUCo..66...75S Solar five-minute oscillations of degree l = 3, 4, and 5 have been observed at Stanford, in the Doppler shift of the Fe 5124 line. The frequencies and amplitudes are in broad agreement with previous observations of modes with l ≤ 3, though we note that there are some systematic discrepancies between the results of different observers. Title: The spiral sector transition regions in the interplanetary magnetic fields Authors: Zhao, X. -P.; Wilcox, J. M.; Scherrer, P. H. Bibcode: 1983ChJSS...3....1Z Altcode: Based on the large-scale configuration of the magnetic fields in interplanetary space and the possible association of the solar wind flow near the sector boundary crossing with the coronal streamer, it is suggested that in interplanetary space there might be some spiral sector transition regions which are thicker than the sector boundaries. In situ observations of interplanetary magnetic field and solar wind plasma do show the existence of the spiral sector transition regions. The magnetic strength in the regions does not go to zero for all the 45 cases studied in this work; most of them have a magnetic strength either much higher or much lower than the average of 5 gamma in the adjacent magnetic sectors. The physical properties in the magnetic depressing (MD) and magnetic enhancement (ME) regions and the possible causes have also been analyzed and discussed. Title: Structure of the Solar Oscillation with Period Near 160-MINUTES Authors: Scherrer, P. H.; Wilcox, J. M. Bibcode: 1983SoPh...82...37S Altcode: 1983IAUCo..66...37S The solar oscillation with period near 160 min is found to be unique in a spectrum computed over the range of periods from about 71 to 278 min. Our best estimate of the period is 160.0095 ± 0.001 min, which is different from 160 min (1/9 of a day) by a highly significant amount. The width of the peak is approximately equal to the limiting resolution that can be obtained from an observation lasting 6 years, which suggests that the damping time of the oscillations is considerably longer than 6 years. A suggestion that this peak might be the result of a beating phenomenon between the five minute data averages and a solar oscillation with period near five minutes is shown to be incorrect by recomputing a portion of the spectrum using 15 s data averages. Title: Interplanetary Magnetic Field and Tropospheric Circulation Authors: Wilcox, J. M.; Scherrer, P. H.; Hoeksema, J. T. Bibcode: 1983wcrs.proc..365W Altcode: The relation between interplanetary magnetic sector boundary crossings and areas of high vorticity in the troposphere that was reported during 1963-1973 cannot be investigated in the years after 1973 because of changes in the processing of the 500 mb height grids prepared by the National Meteorological Center. In particular, we cannot say that the effect disappeared. The same applies to vorticity computed from NMC winds grids. The Limited Area Fine Mesh grid has a large noise in computed vorticity after December 3, 1974. Therefore the interesting analysis of Larsen and Kelley cannot be extended. They had found that forecasts of Vorticity Area Index were significantly poorer after a sector boundary. Previously announced in STAR as N83-25251 Title: Review of Sun-as-a-Star Observations of Low Degree Oscillations Authors: Scherrer, P. H. Bibcode: 1983EOSTr..64..303S Altcode: No abstract at ADS Title: Structure of the heliospheric curent sheet in the early portion of sunspot cycle 21 Authors: Hoeksema, J. T.; Wilcox, J. M.; Scherrer, P. H. Bibcode: 1982JGR....8710331H Altcode: The structure of the heliospheric current sheet on a spherical source surface of radius 2.35 Rs has been computed via the use of a potential field model during the first year and a half after the last sunspot minimum. The solar polar magnetic field that is not fully observed in conventional magnetograph scans was included in the computation. The computed heliospheric current sheet had a quasi-stationary structure consisting of two northward and two southward maxima in latitude per solar rotation. The extend in latitude slowly increased from about 15° near the start of the interval to about 45° near the end. The magnetic field polarity (away from the sun or toward the sun) at the subterresrial latitude on the source surface agreed with the interplanetary magnetic field polarity observed or inferred at the earth on 82% of the days. The interplanetary field structure observed at the earth at this time is finely tuned to the structure of low-latitude fields on the source surface. Title: Solar Velocity Oscillations with Periods Greater than 60 Minutes Authors: Scherrer, P. H. Bibcode: 1982BAAS...14..922S Altcode: No abstract at ADS Title: Review of observations relevant to solar oscillations Authors: Scherrer, P. H. Bibcode: 1982pccv.conf...83S Altcode: 1982STIN...8313049S Recent solar oscillation observations and methods used are described. Integrated or almost integrated sunlight (Sun as a star observation) was observed. The most certain observations are in the 5 minute range. The p-mode and g-mode oscillations are expected from 3 to more than 300 minutes. The possible period ranges are described into the three intervals: (1) the 5 minute range for which the most dramatic and certain results are reported; (2) the 10 to 20 minute range for which solar diameter oscillations are reported; and (3) the 160 minute oscillation found in velocity and several other quantities. Title: Observation of additional low-degree 5-min modes of solar oscillation Authors: Scherrer, P. H.; Wilcox, J. M.; Christensen-Dalsgaard, J.; Gough, D. Bibcode: 1982Natur.297..312S Altcode: 1982STIN...8315246S By measuring the difference between the shifts in the Fe 5,124 spectrum line from light integrated from a central circular portion of the solar disk and from an annular portion exterior to it, we have detected high-order solar oscillations with degrees l = 3, 4 and 5. The frequencies of the octupole modes agree well with the values obtained from whole-disk measurements at the South Pole1. A least-squares fit of the observed frequencies to values interpolated between and extrapolated from the predictions of a sequence of solar models with different chemical compositions selects two models. One of these is almost identical to that obtained by a previous fit15 of modes with l<=2, and has a helium abundance somewhat greater than 25% by mass. Title: Detection of solar five minute oscillations of low degree Authors: Scherrer, P. H.; Wilcox, J. M.; Christensen-Dalsgaard, J.; Gough, D. O. Bibcode: 1982STIN...8317445S Altcode: Solar five-minute oscillations of degree small = 3, 4 and 5 have been observed at the Stanford Solar Observatory, in the Doppler shift of the Fe5124 line. The frequencies and amplitudes are in broad agreement with previous observations of modes with small less than or 3, though we note that there are some systematic discrepancies between the results of different observers. Title: Structure of the heliospheric current sheet in the early portion of sunspot cycle 21 Authors: Hoeksema, J. T.; Wilcox, J. M.; Scherrer, P. H. Bibcode: 1982STIN...8314059H Altcode: The structure of the heliospheric current sheet on a spherical source surface of radius 2.35 R has been computed using a potential field model during the first year and a half after the last sunspot minimum. The solar polar magnetic field that is not fully observed in conventional magnetograph scans was included in the computation. The computed heliospheric current sheet had a quasi-stationary structure consisting of two northward and two southward maxima in latitude per solar rotation. The extent in latitude slowly increased from about 15 degrees near the start of the interval to about 45 degrees near the end of the interval. The magnetic field polarity (away from the Sun or toward the Sun) at the subterrestrial latitude on the source surface agreed with the interplanetary magnetic field polarity observed or inferred at Earth on 82% of the days. The interplanetary field structure observed at Earth at this time is finely tuned to the structure of low-latitude fields on the source surface. Title: Structure of the solar oscillation with period near 160 minutes Authors: Scherrer, P. H.; Wilcox, J. M. Bibcode: 1982STIN...8225074S Altcode: The solar oscillation with period near 160 minutes is found to be unique in a spectrum computed over the range of periods from about 71 to 278 minutes. A best estimate of the period is 160.0095 + or - 0.001 minutes, which is different from 160 minutes (one ninth of a day) by a highly significant amount. The width of the peak is approximately equal to the limiting resolution that can be obtained from an observation lasting 6 years, which suggests that the damping time of the oscillations is considerably longer than 6 years. A suggestion that this peak might be the result of a beating phenomenon between the five minute data averages and a solar oscillation with period near five minutes is shown to be incorrect by recomputing a portion of the spectrum using 15 second data averages. Title: Effect of flare-site magnetic field on solar wind speed and geomagnetic activity. Authors: Lundstedt, H.; Duffy, P. B.; Wilcox, J. M.; Scherrer, P. H. Bibcode: 1982ROLun..18..129L Altcode: No abstract at ADS Title: On the Nature of the Apparent Response of the Vorticity Area Index to the Solar Magnetic Field Authors: Wilcox, J. M.; Scherrer, P. H. Bibcode: 1981SoPh...74..421W Altcode: The apparent response of the vorticity area index to the solar magnetic field is confined to tropospheric regions of intense circulation. Discussions and calculations that include larger volumes of the troposphere would not be expected to show a significant Sun-weather effect. Analysis of the effect in time intervals outside the original 1963-73 is also discussed. An assessment of this Sun-weather effect at the present time is given. Title: What causes the warp in the heliospheric current sheet? Authors: Wilcox, J. M.; Scherrer, P. H. Bibcode: 1981JGR....86.5899W Altcode: A comparative discussion of the warp in the heliospheric current sheet is presented. Pioneer 10 and 11 data of the interplanetary magnetic field compared with earlier data (Helios 1 and 2) show a good agreement on the phenomenon of the warp; however, the interpretations differ. One theory (Thomas and Smith, 1980) proposes that fast solar wind streams associated with interaction regions may move the current sheet higher to heliospheric latitudes, thus causing the warp; while the earlier theory (1976) adequately explained the phenomenon by using the observed photospheric magnetic field and the Zeeman effect but omitted the solar wind dynamical considerations as part of the computations. It is shown that the Helios data of the polarity of the interplanetary magnetic field are in good agreement with the computed location of the current sheet, confirming the earlier theory. Title: Solar Flare Acceleration of Solar Wind: Influence of Active Region Magnetic Field Authors: Lundstedt, H.; Wilcox, J. M.; Scherrer, P. H. Bibcode: 1981Sci...212.1501L Altcode: The direction of the photospheric magnetic field at the site of a solar flare is a good predictor of whether the flare will accelerate solar wind plasma. If the field has a southward component, high-speed solar wind plasma is usually observed near the earth about 4 days later. If the field has a northward component, such high-speed solar wind is almost never observed. Southward-field flares may then be expected to have much larger terrestrial effects than northward flares. Title: Recent Global-Scale Oscillations and Magnetic Field Observations Authors: Scherrer, P. H. Bibcode: 1981BAAS...13R.545S Altcode: No abstract at ADS Title: Global Solar Oscillations: High Order Modes with Degree 3 to 5 Authors: Scherrer, P. H.; Wilcox, J. M. Bibcode: 1981BAAS...13..859S Altcode: No abstract at ADS Title: Recent global scale solar oscillations and magnetic field observations. Authors: Scherrer, P. H. Bibcode: 1981BAAS...13..548S Altcode: No abstract at ADS Title: Geomagnetic activity and Hale sector boundaries Authors: Lundstedt, H.; Scherrer, P. H.; Wilcox, J. M. Bibcode: 1981P&SS...29..167L Altcode: The variation of the geomagnetic activity index Ap at the IMF sector boundaries (+ to - and - to +) has been studied for three solar cycles, separating data into vernal and autumnal equinoxes. It was found that a reported increase in Ap as an effect of a Hale boundary can be better attributed to the occurrence of a negative IMF Bz component in the geocentric solar magnetospheric coordinate system and to the occurrence of high speed solar wind streams. Title: The rotation of the sun - Observations at Stanford Authors: Scherrer, P. H.; Wilcox, J. M.; Svalgaard, L. Bibcode: 1980ApJ...241..811S Altcode: Daily observations of the photospheric rotation rate using the Doppler effect have been made at the Stanford Solar Observatory since May 1976. These observations show no daily or long-period variations in the rotation rate that exceed the observational error of about 1%. The average rotation rate is the same as that of the sunspots and the large-scale magnetic field structures. Title: Origin of the warped heliospheric current sheet Authors: Wilcox, J. M.; Hoeksema, J. T.; Scherrer, P. H. Bibcode: 1980Sci...209..603W Altcode: The warped heliospheric current sheet for early 1976 is calculated from the observed photospheric magnetic field by a potential field method. Comparisons with measurements of the interplanetary magnetic field polarity for early 1976 obtained at several locations in the heliosphere by Helios 1, Helios 2, Pioneer 11, and at the earth show a rather detailed agreement between the computed current sheet and the observations. It appears that the large-scale structure of the warped heliospheric current sheet is determined by the structure of the photospheric magnetic field and that 'ballerina skirt' effects may add small scale ripples. Title: Doppler observations of solar rotation Authors: Scherrer, P. H.; Wilcox, J. M. Bibcode: 1980ApJ...239L..89S Altcode: Daily observations of the photospheric equatorial rotation rate using the Doppler effect are made at the Stanford Solar Observatory. These observations show no variations in the rotation rate that exceed the observational error of about 1%. The average rotation rate is indistinguishable from that of sunspots and large-scale magnetic field structures. Title: Further evidence of solar oscillations with a period of 160 minutes Authors: Scherrer, P. H.; Wilcox, J. M.; Severnyi, A. B.; Kotov, V. A.; Tsap, T. T. Bibcode: 1980ApJ...237L..97S Altcode: Observations made at the Crimean Astrophysical Observatory and the Stanford Solar Observatory during 1979 provide evidence of the existence of oscillations of the sun with a period near 160 minutes. The new observations showed the same period with a phase of maximum expansion as predicted from earlier data; for 1979 the time of maximum expansion of the center of the solar disk was found to be 01:55 UT for the Crimean observatories and 01:58 UT for Stanford with a phase uncertainty of plus or minus 15 minutes. In addition, a new regression line can be found which yields a period of 160.01 minutes or a drift in phase of 31.5 minutes per year in an analysis at exactly 160 minutes. The continued agreement in phase (and amplitude) between the two observatories for four years, as well as the fact that the period of oscillations determined differs from exactly one-ninth of a day, supports the interpretation that solar oscillations are indeed being observed. Title: The origin of the warped heliospheric current sheet Authors: Wilcox, J. M.; Scherrer, P. H.; Hoeksema, J. T. Bibcode: 1980STIN...8133113W Altcode: The warped heliospheric current sheet in early 1976 was calculated from the observed photospheric magnetic field using a potential field method. Comparisons with measurements of the interplanetary magnetic field polarity in early 1976 obtained at several locations in the heliosphere at Helios 1, Helios 2, Pioneer 11 and Earth show a rather detailed agreement between the computed current sheet and the observations. It appears that the large scale structure of the warped heliospheric current sheet is determined by the structure of the photospheric magnetic field, and that "ballerina skirt" effects may add small scale ripples. Title: A Two-Sector Solar Magnetic Structure with 29 Day Rotation Authors: Hoeksema, J. T.; Scherrer, P. H.; Wilcox, J. M. Bibcode: 1980BAAS...12..474H Altcode: No abstract at ADS Title: Further Investigation of the Solar Torsional Oscillator with a Period of 11 Years Authors: Scherrer, P. H.; Wilcox, J. M. Bibcode: 1980BAAS...12Q.473S Altcode: No abstract at ADS Title: Doppler observations of solar rotation Authors: Scherrer, P. H. Bibcode: 1980STIN...8021238S Altcode: Daily observations of the photospheric equatorial rotation rate using the Doppler effect mode at the Sanford Solar Observatory are presented. These observations show no variations in the rotation rate that exceed the observational error of about one percent. The average rotation rate is indistinguishable from that of sunspots and large scale magnetic field structures. Title: On the nature of the apparent response of vorticity area index to the solar magnetic field Authors: Wilcox, J. M.; Scherrer, P. H. Bibcode: 1980STIN...8021239W Altcode: The characteristics of tropospheric circulation that are involved in the apparent response of the vorticity area index (VIA) as the solar magnetic field is carried past the Earth by the solar wind are discussed. It is shown that the response is concentrated in the tropospheric regions of most intense circulation, i.e. the central portions of well-formed low pressure troughs. Factors that must be considered when assessing the Sun-weather effect in the years from 1947 to 1978 are included. Title: Geomagnetic activity and Hale sector boundaries Authors: Lundstedt, H.; Scherrer, P. H.; Wilcox, J. M. Bibcode: 1980STIN...8022222L Altcode: The variation of the geomagnetic activity index Ap at the IMF sector boundaries (+ to - and - to +) is examined for three solar cycles, separating data into vernal and autumnal equinoxes. It is found that a reported increase in Ap as an effect of a Hale boundary can be better attributed to the occurrence of a negative IMF Bz component in the geocentric solar magnetospheric coordinate system and to the occurrence of high speed solar wind streams. Title: Shaking Down the Sun's Long-Period Vibes Authors: Kotov, V. A.; Severny, A. B.; Tsap, T. T.; Scherrer, P. H.; Wilcox, J. M.; Fossat, E.; Grec, G.; Pomerantz, M. Bibcode: 1980SciN..118..100K Altcode: No abstract at ADS Title: Unraveling Solar Magnetism Authors: Wilcox, J. M.; Scherrer, P. H.; Hoeksema, J. T.; Howard, R.; Labonte, B. Bibcode: 1980SciN..117..374W Altcode: No abstract at ADS Title: Solar Oscillations with a Period Near 160-Minutes Authors: Scherrer, P. H. Bibcode: 1979BAAS...11..733S Altcode: No abstract at ADS Title: Variation with time of a Sun-weather effect Authors: Wilcox, J. M.; Scherrer, P. H. Bibcode: 1979Natur.280..845W Altcode: No abstract at ADS Title: Solar variability and terrestrial weather. Authors: Scherrer, P. H. Bibcode: 1979RvGSP..17..724S Altcode: 1979RvGeo..17..724S The present review article indicates that the past four years have been very active in the field of sun-weather research in the U.S. Some quite specific questions which have arisen from recent research include the time variation of the VAL vs SB effect; the nature of the clear-air electric field; the relationship of the ionospheric potential to thunderstorm formation; and the constancy of the solar 'constant' both in terms of the total luminosity on the climatic time scale and for near UV radiation on the time scale of days to 11 years. Title: Intensity of tropospheric circulation associated with solar magnetic sector boundary transits. Authors: Wilcox, J. M.; Scherrer, P. H.; Svalgaard, L. Bibcode: 1979JATP...41..657W Altcode: The fractional decrease in the vorticity area index associated with transits past the earth of interplanetary magnetic sector boundaries increase as the value of vorticity used to compute the index increases. This suggests that after the boundary transit there is an approximately uniform reduction in all the values of vorticity that are not less than 0.00020/sec. In low altitudes and large absolute vorticities not less than 0.00020/sec the average change in the vorticity area index approaches 50%. Title: Interplanetary Magnetic Field Polarity and the Size of Low-Pressure Troughs Near 180 degrees W Longitude Authors: Wilcox, J. M.; Duffy, P. B.; Schatten, K. H.; Svalgaard, L.; Scherrer, P. H.; Roberts, W. O.; Olson, R. H. Bibcode: 1979Sci...204...60W Altcode: When the interplanetary magnetic field is directed away from the sun, the area of wintertime low-pressure (300-millibar) troughs near 180 degrees W longitude is significantly larger than when the field is toward the sun. This relation persists during most of the winters of 1951 to 1973. Title: Average photospheric poloidal and toroidal magnetic field components near solar minimum. Authors: Duvall, T. L., Jr.; Scherrer, P. H.; Svalgaard, L.; Wilcox, J. M. Bibcode: 1979SoPh...61..233D Altcode: Average (over longitude and time) photospheric magnetic field components are derived from 3' Stanford magnetograms made near the solar minimum of cycle 21. The average magnetograph signal is found to behave as the projection of a vector for measurements made across the disk. The poloidal field exhibits the familiar dipolar structure near the poles, with a measured signal in the line Fe I λ 5250 Å of ≈ 1 G. At low latitudes the poloidal field has the polarity of the poles, but is of reduced magnitude (≈ 0.1 G). A net photospheric toroidal field with a broad latitudinal extent is found. The polarity of the toroidal field is opposite in the nothern and southern hemispheres and has the same sense as subsurface flux tubes giving rise to active regions of solar cycle 21. Title: Solar Rotation - Observations at Stanford Since 1976 Authors: Scherrer, P. H. Bibcode: 1979BAAS...11..420S Altcode: No abstract at ADS Title: Observations of solar oscillations with periods of 160 minutes Authors: Scherrer, P. H.; Wilcox, J. M.; Kotov, V. A.; Severny, A. B.; Tsap, T. T. Bibcode: 1979Natur.277..635S Altcode: Severny et al. (1976) have reported oscillations of the sun with a period near 160 min. A description is presented of observations made at the Stanford Solar Observatory during the time from 1975 to the present which seem to support the reports by Severny et al. At Stanford the relative velocity between a central circular area of radius 0.5 solar radius on the solar disk and most of the remaining area of the solar disk is measured. A superposed epoch analysis of the observations using a period of 160 min is discussed. An apparent agreement in phase between the obtained observational data and those reported by Severny et al. tends to support the interpretation that solar oscillations are being observed. Title: The equatorial rotation velocity of the photosphere is measured to be the same as sunspots Authors: Svalgaard, L.; Scherrer, P. H.; Wilcox, J. M. Bibcode: 1978soro.work...26S Altcode: The equatorial rotation rate of the photosphere was measured at effect data. It was found that scattered light has a large influence and must be taken into account properly. When this was done it was found that the rotation rate from Doppler shifts agreed very well with the rate found for sunspots. Short-term fluctuations in rotation rate (i.e. from day to day) were less than plus or minus 15 m/s and were thus within observational errors. Title: The strength of the Sun's polar fields. Authors: Svalgaard, L.; Duvall, T. L., Jr.; Scherrer, P. H. Bibcode: 1978SoPh...58..225S Altcode: The magnetic field strength within the polar caps of the Sun is an important parameter for both the solar activity cycle and for our understanding of the interplanetary magnetic field. Measurements of the line-of-sight component of the magnetic field generally yield 0.1 to 0.2 mT near times of sunspot minimum. In this paper we report measurements of the polar fields made at the Stanford Solar Observatory using the Fe I line λ 525.02 nm. We find that the average flux density poleward of 55° latitude is about 0.6 mT peaking to more than 1 mT at the pole and decreasing to 0.2 mT at the polar cap boundary. The total open flux through either polar cap thus becomes about 3 × 1014 Wb. We also show that observed magnetic field strengths vary as the line-of-sight component of nearly radial fields. Title: Using Dynamo Theory to predict the sunspot number during Solar Cycle 21 Authors: Schatten, K. H.; Scherrer, P. H.; Svalgaard, L.; Wilcox, J. M. Bibcode: 1978GeoRL...5..411S Altcode: On physical grounds it is suggested that the sun's polar field strength near a solar minimum is closely related to the following cycle's solar activity. Four methods of estimating the sun's polar magnetic field strength near solar minimum are employed to provide an estimate of cycle 21's yearly mean sunspot number at solar maximum of 140 ± 20. We think of this estimate as a first order attempt to predict the cycle's activity using one parameter of physical importance based upon dynamo theory. Title: An observational search for large scale organization of five-minute oscillations on the sun. Authors: Dittmer, P. H.; Scherrer, P. H.; Wilcox, J. M. Bibcode: 1978SoPh...57....3D Altcode: The large-scale solar velocity field has been measured over an aperture of radius 0.8 R on 121 days between April and September, 1976. Measurements are made in the line FeI 5123.730 Å, employing a velocity subtraction technique similar to that of Severny et al. (1976). Comparisons of the amplitude and frequency of the five-minute resonant oscillation with the geomagnetic C9 index and magnetic sector boundaries show no evidence of any relationship between the oscillations and coronal holes or sector structure. Title: Using Dynamo Theory to Predict the Sunspot Number During Solar Cycle 21 Authors: Scherrer, P. H.; Schatten, K. H.; Svalgaard, L.; Wilcox, J. M. Bibcode: 1978BAAS...10..415S Altcode: No abstract at ADS Title: A physical mechanism for the prediction of the sunspot number during solar cycle 21 Authors: Schatten, K. H.; Scherrer, P. H.; Svalgaard, L.; Wilcox, J. M. Bibcode: 1978STIN...7829028S Altcode: On physical grounds it is suggested that the sun's polar field strength near a solar minimum is closely related to the following cycle's solar activity. Four methods of estimating the sun's polar magnetic field strength near solar minimum are employed to provide an estimate of cycle 21's yearly mean sunspot number at solar maximum of 140 plus or minus 20. This estimate is considered to be a first order attempt to predict the cycle's activity using one parameter of physical importance. Title: The strength of the sun's polar fields Authors: Svalgaard, L.; Duvall, T. L., Jr.; Scherrer, P. H. Bibcode: 1978STIN...7829029S Altcode: Observations at Stanford Solar Observatory of solar magnetic fields in the FeI line lambda 525.02 nm shows that a radial magnetic field measured at a point where the radius makes an angle rho with the line of sight is observed to be decreased by a factor cos rho. For field elements of 150 mT, magnetograph saturation causes the measured field to be too low by a factor of 1.8. The average field magnitude poleward 55 deg latitude is measured to be near 100 micron T. Variation of the apparent field over a 3 arc min aperture grazing the limb at central meridian amounts to a factor of two over the year; the field being strongest when the pole is tipped the most (7 1/4 deg) towards the observer. Combination of all the above results leads to the following picture of the magnetic field within the polar caps. The field is nearly radial, varying as Bp cos to the 8th power theta where the field strength Bp at the pole (theta = 0 deg) is 1.15 mT, and falling off to below 0.2 mT at the polar cap boundary (theta = 35 deg). Within coronal holes outside of the polar cap the magnetic field strength at sunspot minimum is rather small (0.15 mT). Title: Comparison of Hα synoptic charts with the large-scale solar magnetic field as observed at Stanford Authors: Duvall, T. L., Jr.; Wilcox, J. M.; Svalgaard, L.; Scherrer, P. H.; McIntosh, P. S. Bibcode: 1977SoPh...55...63D Altcode: Two methods of observing the neutral line of the large-scale photospheric magnetic field are compared: (1) neutral line positions inferred from Hα photographs (McIntosh, 1972a, 1975; McIntosh and Nolte, 1975) and (2) observations of the photospheric magnetic field made with low spatial resolution (3') and high sensitivity using the Stanford magnetograph. The comparison is found to be very favorable. Title: The mean magnetic field of the Sun: observations at Stanford. Authors: Scherrer, P. H.; Wilcox, J. M.; Svalgaard, L.; Duvall, T. L., Jr.; Dittmer, P. H.; Gustafson, E. K. Bibcode: 1977SoPh...54..353S Altcode: A solar telescope has been built at Stanford University to study the organization and evolution of large-scale solar magnetic fields and velocities. The observations are made using a Babcock-type magnetograph which is connected to a 22.9 m vertical Littrow spectrograph. Sun-as-a-star integrated light measurements of the mean solar magnetic field have been made daily since May 1975. The typical mean field magnitude has been about 0.15 G with typical measurement error less than 0.05 G. The mean field polarity pattern is essentially identical to the interplanetary magnetic field sector structure (see near the Earth with a 4 day lag). The differences in the observed structures can be understood in terms of a `warped current sheet' model. Title: An observational search for large-scale organization of five-minute oscillations on the sun Authors: Dittmer, P. H.; Scherrer, P. H.; Wilcox, J. M. Bibcode: 1977STIN...7822996D Altcode: The large-scale solar velocity field has been measured over an aperture of radius 0.8 R on 121 days between April and Sept., 1976. Measurements are made in the line FeI 5123.730A, employing a velocity subtraction technique similar to that of Severny et al. (1976). Comparisons of the amplitude and frequency of the five-minute resonant oscillations with the geomagnetic C9 index and magnetic sector boundaries show no evidence of any relationship between the oscillations and coronal holes or sector structure. The average period measured for the five-minute oscillation is 312.0 plus or minus 0.9 sec, which is longer than the average 296.1 plus or minus 1.3 sec period originally reported by Noyes and Leighton (1963) from measurements in the line CaI 6103. The average amplitude is 2.0 m/s, which agrees reasonably with the 2.4 m/s value reported by Fossat and Ricort (1975). This amplitude is larger than might have been expected from an extrapolation of the work of Tanenbaum et al. (1969) to a large aperture, and is evidence of a large horizontal wavelength for the oscillations. Title: Comparison of H alpha synoptic charts with the large-scale solar magnetic field as observed at Stanford Authors: Duvall, T. L., Jr.; Wilcox, J. M.; Svalgaard, L.; Scherrer, P. H.; McIntosh, P. S. Bibcode: 1977STIN...7729049D Altcode: Two methods of observing the neutral line of the large-scale photospheric magnetic field are compared: (1) neutral line positions inferred from H alpha photographs and (2) observations of the photospheric magnetic field made with low spatial resolution (3 arc min.) and high sensitivity using the Stanford magnetograph. The comparison is found to be very favorable. Title: The mean magnetic field of the sun: Observations at Stanford Authors: Scherrer, P. H.; Wilcox, J. M.; Svalgaard, L.; Duvall, T. L., Jr.; Dittmer, P. H.; Gustafson, E. K. Bibcode: 1977STIN...7726055S Altcode: A solar telescope was built at Stanford University to study the organization and evolution of large-scale solar magnetic fields and velocities. The observations are made using a Babcock-type magnetograph which is connected to a 22.9 m vertical Littrow spectrograph. Sun-as-a-star integrated light measurements of the mean solar magnetic field were made daily since May 1975. The typical mean field magnitude is about 0.15 gauss with typical measurement error less than 0.05 gauss. The mean field polarity pattern is essentially identical to the interplanetary magnetic field sector structure (seen near the earth with a 4 day lag). The differences in the observed structures can be understood in terms of a warped current sheet model. Title: The mean magnetic field of the Sun: Method of observation and relation to the interplanetary magnetic field Authors: Scherrer, Philip H.; Wilcox, John M.; Kotov, Valeri; Severny, A. B.; Howard, Robert Bibcode: 1977SoPh...52D...6S Altcode: The mean solar magnetic field as measured in integrated light has been observed since 1968. Since 1970 it has been observed both at Hale Observatories and at the Crimean Astrophysical Observatory. The observing procedures at both observatories and their implications for mean field measurements are discussed. A comparison of the two sets of daily observations shows that similar results are obtained at both observatories. A comparison of the mean field with the interplanetary magnetic polarity shows that the IMF sector structure has the same pattern as the mean field polarity. Title: The mean magnetic field of the sun: method of observation and relation to the interplanetary magnetic field. Authors: Scherrer, P. H.; Wilcox, J. M.; Kotov, V.; Severnyi, A. B.; Howard, R. Bibcode: 1977SoPh...52....3S Altcode: The mean solar magnetic field as measured in integrated light has been observed since 1968. Since 1970 it has been observed both at Hale Observatories and at the Crimean Astrophysical Observatory. The observing procedures at both observatories and their implications for mean field measurements are discussed. A comparison of the two sets of daily observations shows that similar results are obtained at both observatories. A comparison of the mean field with the interplanetary magnetic polarity shows that the IMF sector structure has the same pattern as the mean field polarity. Title: 2h 40m Oscillation Observations at Stanford Authors: Scherrer, P. H. Bibcode: 1977lsms.proc...12S Altcode: No abstract at ADS Title: Stanford Solar Observatory - The First Year Authors: Scherrer, P. H.; Duvall, T. L., Jr.; Dittmer, P. H.; Gustafson, E. K.; Wilcox, J. M. Bibcode: 1976BAAS....8Q.370S Altcode: No abstract at ADS Title: Measurements of Large-Scale Solar Velocity Fields Authors: Dittmer, P. H.; Scherrer, P. H.; Wilcox, J. M.; Duvall, T. L., Jr.; Gustafson, E. K. Bibcode: 1976BAAS....8..311D Altcode: No abstract at ADS Title: Measurements of the Photospheric Magnetic Field with 3' Resolution Authors: Duvall, T. L., Jr.; Scherrer, P. H.; Wilcox, J. M.; Dittmer, P. H.; Gustafson, E. K. Bibcode: 1976BAAS....8..344D Altcode: No abstract at ADS Title: On the reality of a sun-weather effect. Authors: Wilcox, J. M.; Svalgaard, L.; Scherrer, P. H. Bibcode: 1976JAtS...33.1113W Altcode: No abstract at ADS Title: The Sun's Magnetic Sector Structure Authors: Svalgaard, L.; Wilcox, J. M.; Scherrer, P. H.; Howard, R. Bibcode: 1975SoPh...45...83S Altcode: The synoptic appearance of solar magnetic sectors is studied using 454 sector boundaries observed at Earth during 1959-1973. The sectors are clearly visible in the photospheric magnetic field. Sector boundaries can be clearly identified as north-south running demarcation lines between regions of persistent magnetic polarity imbalances. These regions extend up to about 35 ° of latitude on both sides of the equator. They generally do not extend into the polar caps. The polar cap boundary can be identified as an east-west demarcation line marking the poleward limit of the sectors. The typical flux imbalance for a magnetic sector is about 4 × 1021 Mx. Title: On the reality of a sun-weather effect Authors: Wilcox, J. M.; Svalgaard, L.; Scherrer, P. H. Bibcode: 1975STIN...7624117W Altcode: An influence of the solar magnetic sector structure on the terrestrial atmospheric vorticity has been reported. The reported effect persists when the number of sector boundary passages examined is increased from 54 to 131. The same effect is found independently in the latitude zones 35 N - 55 N and greater than 55 N. The depth of the sector-related effect is much greater than the depth of any other minimum in an extended analysis. These results support the reality of the effect. Title: The sun's magnetic sector structure Authors: Svalgaard, L.; Wilcox, J. M.; Scherrer, P. H.; Howard, R. Bibcode: 1975suiprrept.1959S Altcode: The synoptic appearance of solar magnetic sectors is studied using 454 sector boundaries observed at earth during 1959-1973. The sectors are clearly visible in the photospheric magnetic field. Sector boundaries can be clearly identified as north-south running demarcation lines between regions of persistent magnetic polarity imbalances. These regions extend up to about 35 deg of latitude on both sides of the equator. They generally do not extend into the polar caps. The polar cap boundary can be identified as an east-west demarcation line marking the poleward limit of the sectors. The typical flux imbalance for a magnetic sector is about 4 x 10 to the 21st power Maxwells. Title: Seasonal variation and magnitude of the solar sector structure-atmospheric vorticity effect Authors: Wilcox, J. M.; Svalgaard, L.; Scherrer, P. H. Bibcode: 1975Natur.255..539W Altcode: A RELATIONSHIP between the solar sector structure, as swept past the Earth by the solar wind, and terrestrial atmospheric vorticity has been reported by Wilcox et al.1. The solar sector structure is a large scale property of the Sun that is seen most readily in its magnetic field. As observed by spacecraft magnetometers near the Earth, the extended solar magnetic field typically consists of four sectors within a 27-d synodic solar rotation period. Within each sector the magnetic field is predominantly either towards or away from the Sun. The sectors are separated by thin current sheets that reverse the direction of the field and constitute sector boundaries. Here we report evidence of a seasonal variation in this effect. Title: The Stanford Solar Observatory Authors: Scherrer, P. H.; Wilcox, J. M.; Svalgaard, L.; Dittmer, P. H.; Duvall, T. L. Bibcode: 1975BAAS....7..350S Altcode: No abstract at ADS Title: Seasonal Variation and Magnitude of the Solar Sector Structure - Atmospheric Vorticity Effect Authors: Wilcox, J. M.; Svalgaard, L.; Scherrer, P. H. Bibcode: 1975scea.conf..294W Altcode: No abstract at ADS Title: The Relationship between the Slowly Varying Component of Solar Radio Emission and Large Scale Photospheric Magnetic Field Patterns Authors: Scherrer, P. H.; El-Raey, M. Bibcode: 1974SoPh...35..361S Altcode: Daily solar radio flux observations have been examined for a relationship to the large-scale photospheric magnetic field structure. Interplanetary magnetic field sector boundaries were used to indicate boundaries between photospheric field regions of opposite polarity. An enhancement in emission was found about four days before the boundary central meridian passage. Most of the effect came from emission near toward-to-away type boundaries. A higher level of emission appears to be associated with toward field regions than with away field regions. Title: Solar Sector Boundary Configuration from Comparison of Synoptic Charts of the Photospheric Magnetic Field with the Observed Interplanetary Field Authors: Scherrer, P. H.; Wilcox, J. M.; Howard, R. Bibcode: 1974BAAS....6Q.293S Altcode: No abstract at ADS Title: Influence of Solar Magnetic Sector Structure on Terrestrial Atmospheric Vorticity. Authors: Wilcox, John M.; Scherrer, Philip H.; Svalgaard, Leif; Roberts, Walter Orr; Olson, Roger H.; Jenne, Roy L. Bibcode: 1974JAtS...31..581W Altcode: The solar magnetic sector structure has a sizable and reproducible influence on tropospheric and lower stratospheric vorticity. The average vorticity during winter in the Northern Hemisphere north of 2ON latitude reaches a minimum approximately one day after the passing of a sector boundary, and then increases during the following two or three days. The effect is found at all heights within the troposphere, but is not prominent in the stratosphere, except at the lower levels. No single longitudinal interval appears to dominate the effect. Title: Solar Magnetic Sector Structure: Relation to Circulation of the Earth's Atmosphere Authors: Wilcox, John M.; Scherrer, Philip H.; Svalgaard, Leif; Roberts, Walter Orr; Olson, Roger H. Bibcode: 1973Sci...180..185W Altcode: The solar magnetic sector structure appears to be related to the average area of high positive vorticity centers (low-pressure troughs) observed during winter in the Northern Hemisphere at the 300-millibar level. The average area of high vorticity decreases (low-pressure troughs become less intense) during a few days near the times at which sector boundaries are carried past the earth by the solar wind. The amplitude of the effect is about 10 percent. Title: The Mean Solar Magnetic Field Observed at the Mt. Wilson Solar Observatory Authors: Scherrer, P. H.; Wilcox, J. M.; Howard, R. F. Bibcode: 1973BAAS....5R.279S Altcode: No abstract at ADS Title: a Study of the Mean Solar Magnetic Field. Authors: Scherrer, Philip Hanby Bibcode: 1973PhDT........51S Altcode: No abstract at ADS Title: Differential rotation in the solar atmosphere inferred from optical, radio, and interplanetary data Authors: El-Raey, Mohamed; Scherrer, Philip H. Bibcode: 1972SoPh...26...15E Altcode: Autocorrelation analysis of sunspot number, solar radio flux, and interplanetary field in the period 1967 to 1970 yields new information concerning solar atmospheric rotation. The upper chromosphere and the lower corona are rotating on the average about 5 to 8 % faster than is either the photosphere or the upper corona. In addition, short-lived features in the chromosphere and lower corona are found to rotate sometimes as much as 10% faster than relatively long-lived features at the same height. Coronal and photospheric features are found to rotate more or less synchronously. Analysis of yearly data has indicated a considerable change in rotation periods from one year to another. Title: An Annual and a Solar-Magnetic-Cycle Variation in the Inferred Interplanetary Magnetic Field, 1926-1971 Authors: Wilcox, J. M.; Scherrer, P. H. Bibcode: 1972BAAS....4Q.396W Altcode: No abstract at ADS Title: Comparisons of the Mean Solar Magnetic Field and the Interplanetary Field Observed During 1969 Authors: Scherrer, P. H.; Wolcox, J. M.; Severny, A. B. Bibcode: 1972BAAS....4S.390S Altcode: No abstract at ADS Title: The Mean Photospheric Magnetic Field from Solar Magnetograms: Comparisons with the Interplanetary Magnetic Field Authors: Scherrer, Philip H.; Wilcox, John M.; Howard, Robert Bibcode: 1972SoPh...22..418S Altcode: Large-scale averages of daily solar magnetograms have been compared by cross-correlation with the interplanetary magnetic sector pattern during a 2 1/2 yr interval. A significant correlation was found at a lag of about 4 1/2 days, with the amplitude of the correlation depending on the area included in the magnetogram averages. The highest correlation was found when an area of one quarter of the solar disk was used, which is consistent with the idea that the photospheric features which are to be associated with the interplanetary sector pattern are large scale features. Title: Large-Scale Negative Polarity Magnetic Fields on the Sun and Particle-Emitting Flares - Comments Authors: Scherrer, P. H.; Howard, Robert; Wilcox, John Bibcode: 1972NASSP.308...39S Altcode: 1972sowi.conf...39S No abstract at ADS Title: Annual and solar-magnetic-cycle variations in the interplanetary magnetic field, 1926-1971 Authors: Wilcox, John M.; Scherrer, Philip H. Bibcode: 1972JGR....77.5385W Altcode: The polarity of the interplanetary magnetic field has been inferred by Svalgaard (1972) from observations of the polar geomagnetic field during the interval 1926-1971. On the basis of a few years of spacecraft observations, Rosenberg and Coleman (1969) have suggested that there may be an annual variation in the predominant polarity (toward or away from the sun) of the interplanetary field. The present analysis of 45 years of inferred field polarity clearly shows an annual variation and also a variation of about 20 years, which we associate with the solar-magnetic cycle. On the average the phase of the annual variation of the interplanetary field changes about 2 ⅔ years after sunspot maximum, i.e., for about 10 consecutive years the predominant polarity of the interplanetary field is away from the sun during the 6-month interval in which the earth is at southern heliographic latitudes, and then a change of phase occurs such that for about the next 10 years the predominant polarity is toward the sun while the earth is at southern heliographic latitudes. The annual variation changes its predominant polarity within a few days of the times when the heliographic latitude of the earth is 0. Title: Comparison of the mean photospheric magnetic field and the interplanetary magnetic field. Authors: Wilcox, J. M.; Scherrer, P. H.; Severny, A.; Colburn, D. S. Bibcode: 1971BAAS....3R.265W Altcode: No abstract at ADS Title: Determination of solar magnetograph zero level using interplanetary magnetic field observations. Authors: Scherrer, P. H.; Wilcox, J. M.; Severny, A.; Colburn, D. S. Bibcode: 1971BAAS....3Q.264S Altcode: No abstract at ADS Title: Comparison of the Mean Photospheric Magnetic Field and the Interplanetary Magnetic Field Authors: Severny, A.; Wilcox, J. M.; Scherrer, P. H.; Colburn, D. S. Bibcode: 1970SoPh...15....3S Altcode: The mean photospheric magnetic field of the sun seen as a star has been compared with the interplanetary magnetic field observed with spacecraft near the earth. Each change in polarity of the mean solar field is followed about 4 1/2 days later by a change in polarity of the interplanetary field (sector boundary). The scaling of the field magnitude from sun to near earth is within a factor of two of the theoretical value, indicating that large areas on the sun have the same predominant polarity as that of the interplanetary sector pattern. An independent determination of the zero level of the solar magnetograph has yielded a value of 0.1±0.05 G. An effect attributed to a delay of approximately one solar rotation between the appearance of a new photospheric magnetic feature and the resulting change in the interplanetary field is observed. Title: Multi-Channel Magnetograph Observations. I: Comparison with Spectroheliograms Authors: Frazier, Edward N.; Scherrer, Philip H. Bibcode: 1969SoPh...10..297F Altcode: A new technique for displaying magnetograph observations is presented and applied to the 12-channel magnetograph at Kitt Peak National Observatory. Using the data from a raster scan, a digital `spectroheliogram' is constructed on the face of a cathode ray tube and photographed. This enables one to recognize patterns in magnetograph data as easily as with conventional photographs. Comparisons with simultaneous spectroheliograms show no qualitative differences and indicate that the magnetograph is quite capable of studying morphology of individual solar features.