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. <P />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. <P />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." <P />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." <P />"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. <P
  />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. <P />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]. <P />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. <P />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. <P />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." <P />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. <P />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. <P />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. <P />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: <P />"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 Km<SUP>2</SUP>
  s<SUP>-1</SUP>, 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<SUP>-1</SUP>) 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 D<SUB>m</SUB>=530+/-100 km<SUP>2</SUP>
  s<SUP>-1</SUP>. Our value for D<SUB>m</SUB> agrees with that required
  in the model of Sheeley, Nash, &amp; 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 D<SUB>s</SUB>~=250 km<SUP>2</SUP>
  s<SUP>-1</SUP>. 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 &amp; 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<SUP>−1</SUP>, 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 &amp; 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
  R<SUB>1</SUB> = 2.14 solar radius and R<SUB>2</SUB> = 2.24 solar radius
  and M<SUB>1</SUB> = 2.20 solar mass and M<SUB>2</SUB> = 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<SUP>-1</SUP>,
  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 cells<SUP>1</SUP> 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
  LaBonte<SUP>2,3</SUP> 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<SUP>-1</SUP>. 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 data<SUP>4</SUP> and in latitude variations of the limb
  temperature<SUP>5</SUP>. 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 Gilman<SUP>6</SUP>, and from the poleward propagating
  rolls reported by Ribes et al.<SUP>7</SUP>.

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<SUP>−1</SUP> 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<SUP>−1</SUP> 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

