Author name code: snodgrass ADS astronomy entries on 2022-09-14 author:"Snodgrass, Herschel B." ------------------------------------------------------------------------ Title: Obituary: Peter Robert Wilson, 1929-2007 Authors: Snodgrass, Herschel B. Bibcode: 2009BAAS...41..583S Altcode: It is with great sadness that I report the passing of Peter Robert Wilson, a well-known and well-loved figure in the solar physics community. Peter was on the faculty of the Department of Applied Mathematics at the University of Sydney for 39 years, and Chair of the department for 24 of these years. He was the author or co-author of more than 80 scientific research papers and a book, Solar and Stellar Activity Cycles (1994), published by Cambridge University Press. He died suddenly of a heart attack, at his home in Glebe, Australia, in the early morning of 11 November 2007.

Peter was an organizer of, and participant in, many international conferences and workshops. He traveled extensively, holding visiting appointments at the University of Colorado (JILA), at Cambridge University, at the College de France (Paris), and at the California Institute of Technology [CalTech]. Most of his work was in the field of solar physics, but he also did some work on the philosophy of science and on tides.

Peter came from a line of mathematicians. His father, Robert Wilson, immigrated to Australia from Glasgow in 1911, and became a mathematics teacher at Scotch College, a private school in Melbourne. There his name was changed to 'Bill' because 'Bob' was already taken."

Peter's enjoyment of this story as characteristic of Australian academia (as any fan of Monty Python would understand) is indicative of his infectious sense of humor. In a similar vein, he claimed ancestry traced back to the eighteenth-century Scottish mathematician Alexander Wilson, Professor of Astronomy at the University of Glasgow. That Wilson is famous in the solar physics community for his discovery, known as the "Wilson Effect," of the photospheric depressions associated with sunspots. Peter himself could not resist writing a paper on this subject, and was delighted when the bait was taken by some less-informed colleagues who chided him for "naming an effect after himself."

"Bill" Wilson married Naomi Christian, a Melbourne native, and together they had three children. Peter was the eldest; he was born on 17 October 1929. He attended Scotch College, where his father taught, and went on to the University of Melbourne where he eventually earned an M. Sc. in experimental physics. This was not his cup of tea, however, and he first endeavored to follow in his father's footsteps, taking short-term appointments teaching mathematics at the secondary-school level abroad, in England, and in Scotland. After a few years Peter returned to Melbourne and took a post at Scotch College following his father's retirement. He soon decided, however, that teaching young boys in a private school was not his cup of tea either, and in 1959 he secured a position in applied mathematics at the University of Sydney. He had just married his first wife, Margaret, and they moved north together to start their family.

Peter flourished at the University of Sydney, but his advancement in rank was hampered by the lack of a Ph. D. The problem was solved by Ron Giovanelli, Chief of the Division of Physics at Australia's Commonwealth Scientific and Industrial Research Organization [CSIRO], an astrophysicist whose interest lay in the transfer of radiation through the outer layers in the Sun. Giovanelli took Peter on as a thesis student. This both earned him the needed Ph. D. and started him on his research career in solar physics. He now began to move up the academic ladder at Sydney.

To satisfy his love of adventure, Peter was also able to take a series of visiting positions in the United States, working with Dick Thomas and others at JILA and Sacramento Peak Observatory (National Solar Observatory) in New Mexico. During this time he created a framework for further collaborations that became known as the Sydney-Boulder Astrophysics Association [SBAA].

In 1971 Peter was appointed Professor and Chair of the Department of Applied Mathematics at Sydney, and for the next two decades he worked hard to strengthen this department. He was very successful in this endeavor; he had a reputation for fairness and honesty and was well liked. Under his leadership the department grew in both size and quality. Peter fostered a group of outstanding students, including Chris Cannon, David Rees, and Lawrence Cram. One of his proudest accomplishments was to recruit several women onto the faculty and to increase the number of female students. One of these, Nalini Joshi, is presently Head of School. After Peter resigned as Chair, he went on to several other positions associated with the governance of the University, including the Academic Senate, the Governing Council of the Women's College, and the Board of Trustees.

Peter and his first wife were divorced in 1982, after their two children, Sally and Michael, had grown up and left home. A few years later he met and married Geraldine Barnes, a Senior Lecturer in the English Department. This proved to be a fabulous match; they supported each other's academic pursuits, attended each other's conferences, enjoyed a rich social life centered around the university, and traveled extensively together. Their marriage helped both of them refocus their careers. Geraldine steadily advanced in rank, and is now Head of the School of Letters, Arts and the Media. Peter became one of the chief organizers of a series of workshops focused on the solar activity cycle.

The first solar cycle workshop was held in 1986 at CalTech's Big Bear Solar Observatory [BBSO], and it was at this meeting that I first met Peter. There were three subsequent meetings, roughly a year apart, held at the University of Sydney, at Stanford's Fallen Leaf Lake in the Sierras, and at Sacramento Peak Observatory, and these were very successful in bringing together the main players in this research field. My subsequent association with Peter involved several trips back and forth between Portland (Oregon), Boulder, and Sydney and collaborations on about a dozen controversial research papers. Together with Peter Fox and Pat McIntosh, we became the solar-physics "gang of four."

A dinner in Sydney with Geraldine, Peter, and their friends always meant liberal amounts of fine Australian wine, lively conversations on every imaginable topic (except physics), much laughter, and a deliciously endless meal. A weekend at their beach house in Killcare was even better, featuring long walks on the golden-sand beach and in the nearby bush. Kookaburras, Currawongs, and Rainbow Lorikeets frequented the outdoor deck, and the bush teemed with large and fascinating spiders. Back in Sydney, short-term visitors enjoyed lodgings and excellent breakfasts at the University of Sydney's Women's College, with Peter on the Council.

Peter was a man of many interests. He was an expert sailor, a small-plane pilot who took colleagues and friends on adventurous flights, and a lover of sports. He was a skier, a hiker, and a good tennis player who disdained proper form but usually won the point. In 1994, one day after his 65th birthday, Peter suffered a serious stroke. Recovery from this was extremely difficult, painful, and slow; he did, however, recover to a remarkable degree. He had to learn to walk all over again and his vocal chords were partially paralyzed, but after several years of determined work, Peter was able to play a little tennis and squash, and he could bowl and hike. During the last decade of his life he traveled to Easter Island, to the Galapagos, and to the Ross Ice Shelf in Antarctica.

Peter continued to take pleasure in his research to the end, in collaboration with close colleagues who were always among his closest friends. Among these was Chris Durrant, who had been Head of the School of Mathematics and Statistics from 1994 to 1998. They were writing a series of papers on the mechanism of the Sun's polar field reversals. I was looking forward to joining them this coming summer. My last visit with Peter was in Phoenix, Arizona, where Geraldine was participating in a conference. We hiked into the Superstition Mountains, and I remember him walking slowly, being careful of his balance, but going the whole distance with pride and in good spirits.

Peter was a truly remarkable man with, as Geraldine has put it, "a genuine gift for leadership and the encouragement of team spirit." He was a creative and productive scientist with a tremendous life force, a great sense of adventure, and a warm heart. My own collaborations with him were a joy. His death is a sad loss to all who knew him, and he will be sorely missed, but Peter R. Wilson lived life to the fullest and gave his best to the world. We should be glad for him. At the end of his (unpublished) autobiography, where he describes his recovery from the stroke, he writes:

"So as I forecast in 1994, I have continued to 'soldier on', and must admit that a miracle has indeed occurred, at least 80%; I wouldn't have missed the past ten years for anything. Who knows what the inevitable advance of old age may hold, but I cannot complain that I have been 'short changed' in any way." Title: Patterns of vorticity on the solar surface Authors: Brown, Benjamin P.; Snodgrass, Herschel B. Bibcode: 2003ESASP.517..109B Altcode: 2003soho...12..109B Local Correlation tracking of Hydrogen-alpha images taken at one minute intervals at Big Bear Solar Observatory is used to make flow maps that reveal large-scale, high-velocity patterns that appear to be associated with the Sun's magnetic activity. We discuss the possible connections of these patterns to the azimuthally averaged meridional flow and torsional oscillations. We then use the flow maps to compute global maps of vorticity at the solar surface. The vorticity maps contain plume-like patterns of alternation resembling the patterns seen in the maps of the Sun's background magnetic field. The vorticity plumes may account for the disparity in diffusion constants determined for the dispersal of the field and the polar field reversals. Title: Properties and Motions of Photospheric Magnetic Features away from Active Regions Authors: Tucker, J. F.; Snodgrass, H. B. Bibcode: 2001AAS...198.7106T Altcode: 2001BAAS...33..893T Analysis of the Pearson correlation amplitude as a function of latitude, lag in longitude and time separation of correlated magnetograms reveals interesting mean properties of the magnetic field features seen in the photosphere. Small features decorrelate after a few days, but correlations persist at all latitudes for lag times spanning several rotations, revealing the ubiquitous presence of concentrated aggregates of small features that (1) differentially rotate like the small features, (2) have very long lifetimes, and (3) have areal sizes an order of magnitude larger than supergranules. These ``meso-scale" features comprise the unipolar plumes extending poleward from the active regions, and the more rigid rotation of the plumes stems from the poleward meridional drift and random walk of these features. The random walk is consistent with a diffusion constant of 600 Km2 s-1, but these features are too large for this to be propelled by supergranular convection. We discuss the evolution of the properties and motions of these features, or aggregates, during the activity cycle. This work is supported through NSF Grant ATM98-14145. Title: Torsional Oscillations: Vorticity; Solar Cycle Predictions Authors: Snodgrass, H. B. Bibcode: 2001AAS...198.7102S Altcode: 2001BAAS...33Q.893S The azimuthal wind bands known as the torsional oscillations have been revealed primarily by studying the longitudinally averaged solar rotation over a period spanning several full solar rotations. This averaging yields what look like broad but slow, oppositely-moving ( ~ 5 m s-1) bands lying to either side of the centroid of the sunspot butterfly, making the activity band appear to be a zone of weakly enhanced shear. In most discussions, the pattern has been characterized as axially symmetric, but such longitudinal averages could equally well arise from a system of large-scale vortices associated with the active regions, if such vortices rotated counterclockwise in the Northern hemisphere and clockwise in the Southern hemisphere. For some time Doppler charts made from the Mount Wilson data, though noisy, have indicated that the torsional pattern is not axially symmetric, at least during the active phase of the cycle; and recent maps of local velocities determined from short-term tracer tracking at Big Bear Solar Observatory suggest that there are large vortical motions superposed on the mean differential rotation. In any case, it is evident that the torsional pattern tells us something about the cycle, and since it precedes the onset of activity, it might be useful as a predictor of the level of activity to come. For the present cycle 23, the torsional pattern did not emerge until just before solar minimum, whereas for cycles 21 and 22 it appeared several years earlier. This would have suggested by 1996 that that the present cycle would be weaker than the previous two (as it apparently is), while other predictors as late as 1998 forecasted a very strong cycle. This work is supported through NSF Grant ATM98-14145. Title: On the Use of Correlations to Determine the Motions and Properties of Mesoscale Magnetic Features in the Solar Photosphere Authors: Snodgrass, Herschel B.; Smith, Adam A. Bibcode: 2001ApJ...546..528S Altcode: The use of correlations to determine both intrinsic properties and collective motions of patterns is investigated, and the results are applied to the study of the magnetic features in the solar photosphere. Simulations with artificial data are used as a bridge between theory and practical correlation calculations. It is shown that the correlation amplitude as a function of lag can be used to determine not only pattern displacement, but also feature sizes and lifetimes. It is found that reliable results are obtained only when a normalized correlation function is employed, and then only when the signal-to-noise level is greater than ~1.5. For weak correlations, we show that this ratio must be enhanced by averaging the correlation amplitudes, but when applied to the photospheric magnetic field patterns, this gives a result different from that obtained by averaging the individual correlation results. We find this to be the root of the differences between the magnetic rotation rates that have been reported and resolve this long-standing puzzle. The correlations indicate the ubiquitous presence of differentially rotating magnetic features of two types: small-scale features that have lifetimes of ~1 day, and ``mesoscale'' features with lifetimes of many solar rotations. The latter are estimated to have diameters on the order of 100 Mm, and their motions relative to the ambient plasma are consistent with a random walk with diffusion constant Dm=530+/-100 km2 s-1. Our value for Dm agrees with that required in the model of Sheeley, Nash, & Wang, but these features are too large to have their random walks propelled by the supergranular convection. Furthermore, analysis of their relative contributions to the background field implies they decay at a rate consistent with a smaller diffusion constant Ds~=250 km2 s-1. This agrees with the value determined in high-resolution studies, which suggests that the mesoscale features are aggregates of small-scale features undergoing random walks as well, like those observed in these studies. Title: The effects of meridional motion on the determination of rotation by tracer tracking Authors: Snodgrass, Herschel B.; Smith, Adam A. Bibcode: 2000SoPh..191...21S Altcode: We explore a systematic error that arises in feature-tracking measurements of time-average rotation. It stems from the flows of features across latitudes, and as these flows vary with the solar activity cycle, the error has a pattern of variation which mocks the torsional oscillation. We develop a series expansion for this error and evaluate the leading terms for the example case of cycle 21. It grows with the time lag; for a 30 day lag it is ≲1%, depending on how the correlations are done and interpreted. We conclude that the mock pattern cannot, however, account for the magnetic-rotation torsional oscillations pattern found in recent analyses of magnetograms from Kitt Peak and Mount Wilson. For the 1-day time lag in the Kitt Peak study, the error is negligible, and for the ∼30-day time lag in the Mount Wilson study, it represents at most about 30% of the signal. Title: Observations of the Polar Magnetic Fields During the Polarity Reversals of Cycle 22 Authors: Snodgrass, H. B.; Kress, J. M.; Wilson, P. R. Bibcode: 2000SoPh..191....1S Altcode: The Mount Wilson synoptic magnetic data for the period September 1987 through March 1996 are completely revised and used to provide polar plots of the solar magnetic fields for both hemispheres. This period, from Carrington rotations 1793 to 1906, covers the reversals of the polar magnetic fields in cycle 22. Comparison of our plots with the presently available Hα filtergrams for this period shows that the polarity boundaries are consistent in these two data sets where they overlap. The Mount Wilson plots show that the polar field reversals involve a complex sequence of events. Although the details differ slightly, the basic patterns are similar in each hemisphere. First the old polarity becomes isolated at the pole, then shortly thereafter, the isolation is broken, and the polar field includes unipolar regions of both polarities. The old polarity then reclaims the polar region, but when the isolation of this field is established for a second time, it declines in both area and strength. We take the reversal to be complete when the old polarity field is no longer observed in the Mount Wilson plots. With this criterion we find that the polar field reversal is completed in the north by CR 1836, i.e., by December 1990, and in the south by CR 1853, i.e., March 1992. Title: Comment on ``Absence of Correlation between the Solar Neutrino Flux and the Sunspot Number'' Authors: Snodgrass, H. B.; Oakley, D. S. Bibcode: 1999PhRvL..83.1894S Altcode: A Comment on the Letter by Guenther Walther, Phys. Rev. Lett. 79, 4522 (1997). The authors of the Letter offer a Reply. Title: Observations of 44i Bootis. Authors: Jurgenson, C.; Price, M. E.; Pereira, M.; Macinnes, D.; Snodgrass, H. B. Bibcode: 1999BAAS...31..954J Altcode: No abstract at ADS Title: Observations of 44i Bootis Authors: Jurgenson, C.; Price, M. E.; Pereira, M.; Macinnes, D.; Snodgrass, H. B. Bibcode: 1999AAS...194.7505J Altcode: Seven times of minimum were obtained for the W Ursae Majoris type system 44i Bootis; three primary and four secondary. These observations were taken using a 10-inch Newtonian reflector and 1P21 photomultiplier at Lewis & Clark College. Our times of minimum are used with previously observed minimum times for plotting an (o-c) curve to generate a function that describes how the system's ~ 6.5 hr. period is changing over time. After applying a parabolic least squares fit to the (o-c) curve we obtain a quadratic function F(E), where E is the eclipse number. Adding this to the 1991 ephemeris of Oprescu, we obtain a corrected non-linear ephemeris JD 2443604.5919 + 0.26781665 E + 5.9 x10(-11) E(2) . From this we find, in agreement with past observations, that the period of 44i Bootis is increasing over time, and determine the rate of increase. This work was supported by Partners in Science Grant HS0485, an M. J. Murdock Charitable Trust Award of Research Corporation. Title: Simulations of Photospheric Magnetic Fields Authors: Smith, A. A.; Snodgrass, H. B. Bibcode: 1999AAS...194.9402S Altcode: 1999BAAS...31Q.991S We have run plots of artificial data, which mimic solar magnetograms, through standard algorithms to critique several results reported in the literature. In studying correlation algorithms, we show that the differences in the profiles for the differential rotation of the photospheric magnetic field stem from different methods of averaging. We verify that the lifetimes of small magnetic features, or of small patterns of these features in the large-scale background field, are on the order of months, rather than a few days. We also show that a meridional flow which is cycle dependent creates an artifact in the correlation-determined magnetic rotation which looks like a torsional oscillation; and we compare this artifact to the torsional patterns that have been reported. Finally, we simulate the time development of a large-scale background field created solely from an input of artifical, finite-lifetime 'sunspot' bipoles. In this simulation, we separately examine the effects of differential rotation, meridional flow and Brownian motion (random walk, which we use rather than diffusion), and the inclination angles of the sunspot bipoles (Joy's law). We find, concurring with surface transport equation models, that a critical factor for producing the patterns seen on the Sun is the inclination angle of the bipolar active regions. This work was supported by NSF grant 9416999. Title: Multipole Decomposition of the Solar Magnetic Field Authors: Collord, J.; Snodgrass, H. B. Bibcode: 1999AAS...194.9401C Altcode: 1999BAAS...31..991C We do a multipole expansion of the photospheric magnetic field, determined by least-squares fits to the radial component plotted on Carrington maps of Mount Wilson magnetograph data. We study these moments in each hemisphere separately and also for the Sun as a whole, and follow their evolution over three solar cycles. The axial and equatorial components of the dipole each have a roughly 21-yr. sinusoidal variation and, as expected, are 90(o) out of phase. The equatorial component is strongest around solar maximum, and its direction can suddenly shift. Between such shifts, it rotates at a rate that varies during the cycle. The north and south axial components reflect the different times of the north and south polar field reversals, and also a persistent north-south asymmetry, for the southern axial dipole lags in its time development, but is stronger at maximum. Although the polar reversals seem to involve some `redirecting' of the hemispheric dipoles, our evidence suggests that the field reversals cannot be thought of as rotations of these dipoles. The behavior of the quadrupole moments is also discussed, as is the overall method for doing this expansion. This work was supported by NSF Grant AST9416999. Title: Interactions between solar neutrinos and solar magnetic fields Authors: Oakley, D. S.; Snodgrass, Herschel B. Bibcode: 1997APh.....7..297O Altcode: 1996hep.ph....4252O We attempt to correlate all of the available solar-neutrino data with the strong magnetic fields these neutrinos encounter in the solar interior along their Earth-bound path. We approximate these fields using the photospheric, magnetograph-measured flux from central latitude bands, time delayed to proxy the magnetic fields in the solar interior. Our strongest evidence for anticorrelation is for magnetic fields within the central ±5° solar-latitude band that have been delayed by 0.85 ± 0.55 yr. Assuming a neutrino-magnetic interaction, this might indicate that interior fields travel to the solar surface in this period of time. As more solar-neutrino flux information is gathered, the question of whether this result arises from a physical process or is merely a statistical fluke should be resolved, providing that new data are obtained spanning additional solar cycles and that correlation studies focus on these same regions of the solar magnetic field. Title: Meridional Motions of Magnetic Features in the Solar Photosphere Authors: Snodgrass, Herschel B.; Dailey, Sara B. Bibcode: 1996SoPh..163...21S Altcode: We cross-correlate pairs of Mt. Wilson magnetograms spaced at intervals of 24-38 days to investigate the meridional motions of small magnetic features in the photosphere. Our study spans the 26-yr period July 1967-August 1993, and the correlations determine longitude averages of these motions, as functions of latitude and time. The time-average of our results over the entire 26-yr period is, as expected, antisymmetric about the equator. It is poleward between ∼ 10° and ∼ 60°, with a maximum rate of 13 m s−1, but for latitudes below ±10° it is markedly equatorward, and it is weakly equatorward for latitudes above 60°. A running 1-yr average shows that this complex latitude dependence of the long-term time average comes from a pattern of motions that changes dramatically during the course of the activity cycle. At low latitudes the motion is equatorward during the active phase of the cycle. It tends to increase as the zones of activity move toward the equator, but it reverses briefly to become poleward at solar minimum. On the poleward sides of the activity zones the motion is most strongly poleward when the activity is greatest. At high latitudes, where the results are more uncertain, the motion seems to be equatorward except around the times of polar field reversal. The difference-from-average meridional motions pattern is remarkably similar to the pattern of the magnetic rotation torsional oscillations. The correspondence is such that the zones in which the difference-from-average motion is poleward are the zones where the magnetic rotation is slower than average, and the zones in which it is equatorward are the zones where the rotation is faster. Title: Meridional Flow, Torsional Oscillations and Random Walk of Photospheric Magnetic Features Authors: Snodgrass, H. B.; Dailey, S. B. Bibcode: 1995AAS...18710110S Altcode: 1995BAAS...27.1427S We have used two-dimensional cross-correlations of Mount Wilson coarse-array magnetograms, spaced at 24-38 days, to determine the pattern of meridional drifts for photospheric features in the large-scale background field during the period 1967-1993. The flow pattern is linked to the butterfly diagram, and varies markedly during the activity cycle. The dominant trend is motion away from regions of high flux concentration. Our results are consistent with a picture in which magnetic features of size comparable to a few supergranules behave like 'particles' undergoing a Brownian motion on the solar surface. They appear neither to be tightly bound to subsurface field structures, nor to evaporate, and the diffusion that appears to propel them about evidently does not extend to small enough scales to take them apart. Comparison with the magnetic torsional oscillation suggests that the torsional pattern is an artifact of the meridional drift pattern rather than an actual East-West flow. {abstract} Title: On the Correlation of Solar Surface Magnetic Flux with Solar Neutrino Capture Rate Authors: Oakley, David S.; Snodgrass, Herschel B.; Ulrich, Roger K.; Vandekop, Toni L. Bibcode: 1994ApJ...437L..63O Altcode: We correlate the Homestake solar neutrino capture rate with magnetograph measured photospheric magnetic flux, using all available data from 1970-1991. We find that the anticorrelation of the capture rate with the flux is stronger than the (previously studied) anticorrelation with sunspot number, and that the anticorrelation and its significance improve markedly when the flux is taken from near the center of the solar disk. Furthermore, we find that there is no significant correlation when the near-disk-center flux is excluded. This supports an hypothesis that there is an interaction between the outgoing solar neutrinos and the magnetic fields they encounter along their flight paths. We find the suggestion of a similar pattern with the Kamiokande neutrino data, although noise level and time span do not permit conclusive results. Title: Real and Virtual Unipolar Regions Authors: Snodgrass, H. B.; Wilson, P. R. Bibcode: 1993SoPh..148..179S Altcode: Difficulties in relating magnetograph measurements to the actual solar magnetic field are discussed. After a brief review both of problems inherent in the nature of the measurements and of sources of instrumental error, we show that field measurements taken within the photosphere can map out large-scale regions of a single magnetic polarity even though these regions contain no footpoints of large-scale magnetic structures, but instead only aggregates of small, unresolved bipoles. This may occur wherever the density of unresolved bipoles has a preferred orientation and a spatial variation along the direction of that orientation. We call these regionsvirtual unipolar regions, as they are not connected to regions of opposite polarity by field loops or lines passing through the corona. Investigation of these regions shows that they can arise at widely separated locations, and that they may evolve into real unipolar magnetic regions which are connected to the chromospheric and coronal fields. These results can explain a number of puzzling aspects of magnetograph observations of the solar background magnetic field. Title: A Photometric Investigation of the Eclipsing Binary V505 Sagittarii Authors: Chambliss, C. R.; Walker, R. L.; Karle, J. H.; Snodgrass, H. B.; Vracko, Y. A. Bibcode: 1993AJ....106.2058C Altcode: V505 Sgr is a classical Algol system consisting of an A2 V primary and a G5 IV secondary that fills its Roche lobe. New times of minimum light are presented. The period of the eclipsing system (1.18287d) varies, due in part to an orbital light-time effect. A third component has been detected that orbits the eclipsing pair. This investigation uses the SIMPLEX algorithm (Kallrath & Linnell, 1987) and the Differential Correction code (Wilson, 1979) to analyze two separate datasets. The results indicate the third component, an F8 V star, contirbutes about 5% of the light to the system. The minimum projected distance between the third component and the eclipsing pair is 37 AU. This implies an orbital period of about 105 years, a value that differs with the O-C data. The photometric solution, combined with recent spectroscopic data yields R1 = 2.14 solar radius and R2 = 2.24 solar radius and M1 = 2.20 solar mass and M2 = 1.15 solar mass. Title: Is the Flux of Solar Neutrinos Correlated with the Solar Magnetic Activity Cycle? Authors: Vandekop, T.; Snodgrass, H. B. Bibcode: 1993BAAS...25.1194V Altcode: No abstract at ADS Title: Full-Disk Magnetogram Cross-correlations at Long Time Lags Authors: Snodgrass, H. B.; Metcalf, T.; Vandekop, T. Bibcode: 1993BAAS...25.1194S Altcode: No abstract at ADS Title: Telluric water vapor contamination of the Mount Wilson solar Doppler measurements Authors: Carter, Christopher S.; Snodgrass, Herschel B.; Bryja, Claia Bibcode: 1992SoPh..139...13C Altcode: It has been shown that the solar line λ5250.2 (FeI) is weakly blended with a telluric line in the water vapor spectrum, and that magnetograms taken using this line are therefore inaccurate. We investigate the effects of this contamination on the Mount Wilson synoptic magnetograph data, which is based on λ5250.2. Using spectrum scans taken at Kitt Peak, we model the contamination and develop a procedure that would correct for it, whenever the slant water vapor along the line of sight to the Sun is known. As this information is not available for the data collected thus far at Mount Wilson, we use the variation of determined quantities with airmass to obtain an average, or first-order, correction. Concentrating on the fitted coefficients for the solar rotation, the correction is found to be very slight, ∼ 0.5%, raising the value for the A coefficient, averaged over the period 3 December, 1985 to 22 July, 1990, from 2.8289 to 2.8422 μrad s-1, The correction also removes a slight annual variation that has become discernible in the data collected since 1986. Title: Smokestacks and Balloonmen: A Magnetic Rotation Controversy Authors: Snodgrass, Herschel B. Bibcode: 1992ASPC...27...71S Altcode: 1992socy.work...71S No abstract at ADS Title: Synoptic Observations of Large Scale Velocity Patterns on the Sun Authors: Snodgrass, Herschel B. Bibcode: 1992ASPC...27..205S Altcode: 1992socy.work..205S No abstract at ADS Title: A Torsional Oscillation in the Rotation of the Solar Magnetic Field Authors: Snodgrass, Herschel B. Bibcode: 1991ApJ...383L..85S Altcode: The pattern rotation rate for the sun's magnetic field, determined by cross-correlating Mount Wilson full disk 5250.2 (Fe I) magnetograms spaced a full solar rotation apart, closely parallels at all latitudes the photospheric plasma rotation profile determined from the Doppler shifts of the same spectral line. When an 11-yr running mean is subtracted, a torsional oscillation is revealed, in the form of an equatorward-migrating pattern of fast and slow zones. Although the magnetic rotation torsional pattern is similar enough to its much-studied Doppler counterpart to provide confirmation, there are significant differences between the two - the magnetic pattern is strongest (about 20 m/s) at high latitudes, weakens at sunspot latitudes where the Doppler pattern is strongest, and is offset at all latitudes by about 10 deg toward the equator, so that its slow zones approximately coincide with the maximal shear zones of the Doppler pattern. These zones appear to be fore-runners to the wings of the magnetic flux (sunspot) butterflies of the activity cycle. Title: The CUREA 1992 Summer Program in Astrophysics at Mount Wilson Observatory Authors: Snider, J.; Bracher, K.; Briggs, J.; Mickelson, M.; Mitchell, W., Jr.; Pasachoff, J.; Snodgrass, H.; Yorka, S. Bibcode: 1991BAAS...23.1437S Altcode: No abstract at ADS Title: A Torsional Pattern in the Rotation of the Solar Magnetic Field Authors: Snodgrass, H. B. Bibcode: 1990BAAS...22.1233S Altcode: No abstract at ADS Title: The Reversal of the Solar Polar Magnetic Fields - Part One Authors: Wilson, P. R.; McIntosh, P. S.; Snodgrass, H. B. Bibcode: 1990SoPh..127....1W Altcode: Some theoretical difficulties confronting the current model of the polar magnetic reversal by cancellation with the flux remnants of decaying active regions are discussed. It is shown that the flux transport equation does not adequately describe the essential physical consequences of the transport of large-scale fields, linked to deep subsurface toroids, over distances comparable with the solar radius. The possibility that subsurface reconnections may release these fields to form U-loops is discussed but it is shown that, in this event, the loops will quickly rise to the surface. Mechanisms whereby the flux may escape through the surface are considered. Title: Rotation of Doppler Features in the Solar Photosphere Authors: Snodgrass, Herschel B.; Ulrich, Roger K. Bibcode: 1990ApJ...351..309S Altcode: The pattern rotation rate for the line-of-sight velocity features in the solar photosphere is determined by cross-correlating Doppler residual coarse arrays from magnetograph observations. From the latitude dependence and the approximately one-day lifetime of the correlation amplitudes, it is concluded that the dominant velocity pattern producing the correlation is the supergranulation network. The rotation rate average over the entire period is determined. The rate at all latitudes is about 2 percent faster than the magnetic and sunspot rates and about 4 percent faster than the Mount Wilson spectroscopic rate. Comparing this coarse array determination with Duvall's (1988) earlier result indicates that the supergranulation pattern may be a very sensitive indicator of large-scale motions at the top of the solar convection zone. Title: Photometric Observations of Short-Period Eclipsing Binaries Authors: Vracko, Y. A.; Snodgrass, H. B.; Karle, J. H. Bibcode: 1990BAAS...22..831V Altcode: No abstract at ADS Title: An Extended Activity Cycle Picture of the Sun's Polar Magnetic Fields Authors: Snodgrass, H. B.; Wilson, P. R. Bibcode: 1990BAAS...22Q.855S Altcode: No abstract at ADS Title: CUREA: The Consortium for Undergraduate Research and Education in Astronomy Authors: Snider, J.; Bracher, K.; Meyers, K.; Mickelson, M.; Mitchell, W., Jr.; Naftilan, S.; Pasachoff, J.; Snodgrass, H.; Yorka, S.; Zook, A. Bibcode: 1989BAAS...21.1065S Altcode: No abstract at ADS Title: SYSTEMATIC OBSERVATIONS OF THE SUN (In honour of Helen Dodson Prince): Observations Authors: McIntosh, P.; Snodgrass, H.; Mouradian, Z.; Harvey, K.; Altrock, R.; Simon, P.; Legrand, J. -P.; Alissandrakis, G.; Neckel, H.; Petropoulos, P.; Poulakis, X.; Gokhale, M. H.; Sivaraman, K. R.; Pap, J. Bibcode: 1989HiA.....8..672M Altcode: No abstract at ADS Title: Solar Rotation Measurements at MT.WILSON - Part Five Authors: Ulrich, Roger K.; Boyden, John E.; Webster, Larry; Snodgrass, Herschel B.; Padilla, Steven P.; Gilman, Pamela; Shieber, Tom Bibcode: 1988SoPh..117..291U Altcode: This paper describes a thorough reevaluation of the procedures for reducing the data acquired at the Mt. Wilson Observatory synoptic program of solar observations at the 150-foot tower. We also describe a new program of acquiring as many scans per day as possible of the solar magnetic and velocity fields. We give a new fitting formula which removes the background velocity field from each scan. An important new feature of our reduction algorithm is our treatment of the limb shift which permits time variation in this function. We identify the difference between the limb shift along the north-south axis and the east-west axis as potentially being a result of meridional circulation. Our analysis interprets the time variation in the east-west limb shift as being the result of changes in a vertical component of the meridional circulation. Title: The extended solar activity cycle Authors: Wilson, P. R.; Altrocki, R. C.; Harvey, K. L.; Martin, S. F.; Snodgrass, H. B. Bibcode: 1988Natur.333..748W Altcode: The solar cycle has been defined in terms of a sequential periodic variation in sunspot numbers, the period being the interval between successive minima, currently averaging 11.2 years. But a number of observations have indicated that the activity cycle may begin at higher latitudes before the emergence of the first sunspots of the new cycle. Here we report results from sunspot cycle 21 concerning the ephemeral active regions, the coronal green-line emission and the torsional oscillation signal, which confirm the earlier suggestions. In particular, we report the appearance of a high-latitude population of ephemeral active regions in the declin-ing phase of sunspot cycle 21, with orientations that tend to favour those for cycle 22 rather than 21. Taken together, these data indicate that sunspot activity is simply the main phase of a more extended cycle that begins at high latitudes before the maximum of a given sunspot cycle and progresses towards the equator during the next 18-22 yr, merging with the conventional 'butterfly diagram' (the plot of the latitudes of emerging sunspots against time) as it enters sunspot latitudes. We suggest that this extended cycle may be understood in the perspective of a model of giant convective rolls that generate dynamo waves propagating from pole to equator. Title: Evidence for a solar cycle. Authors: Snodgrass, H. B. Bibcode: 1988PhT....41a..11S Altcode: No abstract at ADS Title: Photospheric Magnetic and Velocity-Feature Rotation in λ5250.2 Authors: Snodgrass, H. B. Bibcode: 1987BAAS...19R1118S Altcode: No abstract at ADS Title: Telluric Contamination Mount Wilson λ5250. 2 Magnetograph Observations Authors: Carter, C. S.; Snodgrass, H. B. Bibcode: 1987BAAS...19.1117C Altcode: No abstract at ADS Title: Solar torsional oscillations as a signature of giant cells Authors: Snodgrass, H. B.; Wilson, P. R. Bibcode: 1987Natur.328..696S Altcode: Although the existence of giant cells1 as the fundamental mode of solar convection has long been proposed on theoretical grounds, attempts to detect them observationally have been unsuccessful. During one search, using Mount Wilson magnetograph data, Howard and LaBonte2,3 discovered a pattern of latitudinal velocity bands that move from the poles towards the equator in synchrony with the sunspot cycle, and they interpreted this pattern as a torsional wave or 'oscillation' with wavenumber k=2 hemisphere-1. Here we suggest that this signal is not in fact an oscillation but represents a modulation of the mean differential rotation caused by a system of giant convective rolls which start at the poles at 11-yr intervals and migrate to the equator in a period of 18-22 yr. Additional evidence for the presence of these rolls is found in the zero offsets in the Mount Wilson data4 and in latitude variations of the limb temperature5. Thus we argue that the fundamental mode of giant-cell convection in the sun takes the form of equatorward migrating azimuthal rolls. This differs from the 'banana cell' mode suggested by Gilman6, and from the poleward propagating rolls reported by Ribes et al.7. Title: Azimuthal Rolls and the Solar Cycle Authors: Snodgrass, H. B.; Wilson, P. R. Bibcode: 1987BAAS...19Q.935S Altcode: No abstract at ADS Title: Spectroscopic Evidence for a Moving Pattern of Azimuthal Rolls on the Sun Authors: Snodgrass, Herschel B. Bibcode: 1987ApJ...316L..91S Altcode: A migrating pattern of solar surface motions associated with the torsional oscillation is revealed through the analysis of latitudinal 'zero offset' data from Mount Wilson full-disk Dopplergrams taken over the past 19 yr. This new pattern, which registers meridional flow in high latitudes and vertical flow in low latitudes, contains a line-of-sight velocity signal of about + or - 4 m/s. The vertical, meridional, and rotational flows, taken together, constitute the pattern of surface motions expected from a system of giant azimuthal rolls. The implication is that there is a system of from three to four rolls per hemisphere, which migrate from near the poles to the equator over a period of about 18 yr. This observational result provides strong supporting evidence for recent azimuthal convective-roll models of the solar cycle. Title: Torsional Oscillations and the Solar Cycle Authors: Snodgrass, Herschel B. Bibcode: 1987SoPh..110...35S Altcode: Both the net torsional pattern and its derivative, the shear oscillation, are studied in relation to the solar activity cycle using data collected at Mount Wilson from 1967-1986. The shear is seen as the better quantity for study, since it is both more fully determinable with these data and has straighter ties to the zones of activity. The shear zones run from pole to equator, clearly indicating that the cycle begins at the poles. Total transit, roughly at constant speed, takes roughly 18 years, and the active zones emerge to span the zones of shear enhancement after the latter have reached sunspot latitudes. This 18-yr transit time is seen as the proper duration of the cycle: successive cycles begin roughly 11 years apart and thus overlap. The polar origin of the torsional pattern is found to be phenomenologically connected with variations in the polar field amplitude. It is also noted in both the magnetic and torsional patterns that, for the past few cycles, the activity portion begins earlier and thus lasts longer in the northern hemisphere. Title: Correcting for Atmospheric Water Vapour Interference of the λ5250 (Fe I) Solar Line Authors: Bryja, C.; Snodgrass, H. B. Bibcode: 1986BAAS...18..932B Altcode: No abstract at ADS Title: Torsional Oscillation Update and a Search for Longitudinal Structure Authors: Shieber, T. R.; Snodgrass, H. B. Bibcode: 1986BAAS...18R1011S Altcode: No abstract at ADS Title: Polar Genesis and Propagation of the Torsional Shear Oscillation Authors: Snodgrass, H. B. Bibcode: 1986BAAS...18Q1011S Altcode: No abstract at ADS Title: Torsional Oscillations of the Sun Authors: Snodgrass, H. B.; Howard, R. Bibcode: 1985Sci...228..945S Altcode: The sun's differential rotation has a cyclic pattern of change that is tightly correlated with the sunspot, or magnetic activity, cycle. This pattern can be described as a torsional oscillation, in which the solar rotation is periodically sped up or slowed down in certain zones of latitude while elsewhere the rotation remains essentially steady. The zones of anomalous rotation move on the sun in wavelike fashion, keeping pace with and flanking the zones of magnetic activity. It is uncertain whether this torsional oscillation is a globally coherent ringing of the sun or whether it is a local pattern caused by and causing local changes in the magnetic fields. In either case, it may be an important link in the connection between the rotation and the cycle that is widely believed to exist but is not yet understood. Title: Solar torsional oscillations - A net pattern with wavenumber 2 as artifact Authors: Snodgrass, H. B. Bibcode: 1985ApJ...291..339S Altcode: A net solar torsional oscillation pattern is uncovered through a new analysis of Mount Wilson Doppler data. This pattern, found from zonal fits, without subtraction of a global fit, consists of a relative polar spin-up around solar maximum, alternating with a single traveling wave that runs from mid latitude to low latitude during the rest of the cycle. It is suggested that these are separate phenomena, and thus that the previously inferred pole-to-equator traveling pattern with wavenumber 2 per hemisphere may be a mathematical artifact. The new pattern retains aspects of the original pattern's relationship to magnetic activity, and agrees better with model predictions. Title: Torsional Oscillations of Low Mode Authors: Snodgrass, H. B.; Howard, R. Bibcode: 1985SoPh...95..221S Altcode: Standing wave torsional oscillations of wavenumber 1/2 and 1 hemisphere−1 are studied using an improved fit to Mount Wilson magnetograph data. These oscillations are seen to be in phase with each other and with the magnetic activity cycle, and seem best represented as a flexing of the differential rotation curve. Superposing them gives a differential rotation which at solar minimum is slightly flattened at the equator but considerably (∼ 5%) steepened at the poles, and also tends to produce a travelling wave with wavenumber 1 hemisphere−1 that moves from pole to equator as the cycle progresses. Title: Absolute Torsional Oscillations of the Sun Authors: Snodgrass, H. B. Bibcode: 1984BAAS...16..978S Altcode: No abstract at ADS Title: Limits on photospheric Doppler signatures for solar giant cells Authors: Snodgrass, H. B.; Howard, R. Bibcode: 1984ApJ...284..848S Altcode: Mount Wilson solar-velocity data taken since improvement of the spectrograph in May 1982 are analyzed to search for photospheric traces of persistent velocity patterns that are anticipated in recent model predictions. The method involves time-averaged autocorrelations and cross correlations of the residuals that remain after least-squares fits for differential rotation, limb shift, and meridional circulation are extracted from the daily-magnetogram velocity arrays. It is argued that, owing to the supergranular motions in the photosphere, the sensitivity in applying the present method to the new Mount Wilson data is close to the ultimate sensitivity possible for detection of this phenomenon. The following limits are currently established through this analysis: (1) there is no sharply peaked power spectrum with amplitude above about 1 m/s per wavenumber, and (2) there is no broad-band power spectrum for which the total integrated power is greater than about 10 sq m/sq sec. Title: Separation of large-scale photospheric Doppler patterns Authors: Snodgrass, H. B. Bibcode: 1984SoPh...94...13S Altcode: Mount Wilson solar Doppler data spanning January 1967 to March 1984 are refit with an expanded set of functions representing the line-of-sight components of rotation, limbshift and meridional flow. The `ears' are not included, and a constant term, formerly regarded as the relative instrumental zero, is reclassified as representing an aspect of the limbshift. The long-standing problem of crosstalk among the fit-determined coefficients is eliminated by orthonormalization with respect to the solar disk of the function space representing each motion class. Examination of the new coefficients shows clear evidence for their variation over the solar cycle: for the rotation coefficients, this variation is a low mode torsional oscillation, and for the limbshift, it appears consistent with the suppression of small-scale convection by magnetic activity. The meridional flow is found to be poleward and slightly faster at low latitudes. Also seen in all coefficients is a dramatic reduction of day-to-day scatter following recent major modifications to the Mount Wilson 150-ft tower spectrograph. Title: Recalibration of Mount-Wilson Doppler Measurements Authors: Snodgrass, H. B.; Howard, R.; Webster, L. Bibcode: 1984SoPh...90..199S Altcode: A new calibration of the spectrograph at the Mount Wilson 150-foot Tower Telescope demonstrates that all reported solar Doppler rates to date measured at λ5250.2 with this instrument are too high by a factor of 0.55%. Title: Limits on Giant Cell Signatures in the Photosphere Authors: Snodgrass, H. B.; Howard, R. Bibcode: 1983BAAS...15..953S Altcode: No abstract at ADS Title: Magnetic rotation of the solar photosphere Authors: Snodgrass, H. B. Bibcode: 1983ApJ...270..288S Altcode: Magnetograms made at Mt. Wilson Observatory from January 1967 to May 1982 are crosscorrelated in 34 latitude strips at 1-4-day increments to determine the rotation of magnetic features in the solar photosphere. The data are smoothed by averaging corresponding correlations and calculating rotation from the displacement of the averaged-correlation maximum; the usefulness and validity of this procedure are discussed. No significant time variation or field dependence is found for the period of the observations, at least to the accuracy of the calculated means (variance of from about 2 m/sec at low latitudes to about 10 m/sec near the poles). The rotation function omega at solar latitude phi is shown to be 2.902 0.464 sin sq phi - 0.328 sin to the 4th phi microrad/sec, in agreement with the Mt. Wilson Doppler profile near the poles and with the sunspot determination of Newton and Nunn (1951) at sunspot latitudes, where the Doppler estimate is about 30 m/sec slower. Title: Large-Scale Doppler Shifts in the Solar Photosphere Authors: Snodgrass, H. B.; Howard, R. Bibcode: 1983BAAS...15..719S Altcode: No abstract at ADS Title: Rotation of Solar Magnetic Fields Authors: Snodgrass, H. B.; Bruning, D. H. Bibcode: 1981BAAS...13R.906S Altcode: No abstract at ADS