scherrer

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Author name code: scherrer
ADS astronomy entries on 2022-09-14
author:"Scherrer, Philip H."

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Title: Solar Toroidal Field Evolution Spanning Four Sunspot Cycles
Seen by the Wilcox Solar Observatory, the Solar and Heliospheric
Observatory/Michelson Doppler Imager, and the Solar Dynamics
Observatory/Helioseismic and Magnetic Imager
Authors: Liu, Allison L.; Scherrer, Philip H.
2022ApJ...927L...2L Altcode: 2022arXiv220406012L
Forty-four years of Wilcox Solar Observatory, 14 years of Michelson
Doppler Imager on the Solar and Heliospheric Observatory, and 11 years
of Helioseismic and Magnetic Imager on the Solar Dynamics Observatory
magnetic field data have been studied to determine the east-west
inclination-the toroidal component-of the magnetic field. Maps of the
zonal averaged inclination show that each toroidal field cycle begins
at around the same time at high latitudes in the northern and southern
hemispheres, and ends at the equator. Observation of these maps also
shows that each instance of a dominant toroidal field direction starts
at high latitudes near sunspot maximum and is still visible near the
equator well past the minimum of its cycle, indicating that the toroidal
field cycle spans approximately two sunspot cycles. The length of the
extended activity cycle is measured to be approximately 16.8 yr.

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Title: Solar Toroidal Field Evolution Spanning Four Sunspot Cycles
Seen By WSO, SOHO/MDI, and SDO/HMI
Authors: Scherrer, Philip; Liu, Allison
2021AGUFMSH55D1874S Altcode:
Forty-four years of Wilcox Solar Observatory (WSO), fourteen years of
Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory
(SOHO), and eleven years of Helioseismic and Magnetic Imager (HMI)
on the Solar Dynamics Observatory (SDO) magnetogram data have been
studied to determine the east-west inclination, the toroidal component
of the magnetic field. Maps of the east-west zonal averaged inclination
produced by this study shows that each toroidal field cycle begins at
around the same time at high latitudes in the Northern and Southern
Hemispheres, and ends at the equator. Observation of these maps also
show that each instance of a dominant toroidal field direction starts
at high latitudes near sunspot maximum and is still visible near the
equator well past the minimum of its cycle, indicating that the toroidal
field cycle spans approximately 2 sunspot cycles. This supports earlier
reports of the extended magnetic cycles.

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Title: The Multiview Observatory for Solar Terrestrial Science (MOST)
Authors: Gopalswamy, Nat; Kucera, Therese; Leake, James; MacDowall,
Robert; Wilson, Lynn; Kanekal, Shrikanth; Shih, Albert; Christe,
Steven; Gong, Qian; Viall, Nicholeen; Tadikonda, Sivakumar; Fung,
Shing; Yashiro, Seiji; Makela, Pertti; Golub, Leon; DeLuca, Edward;
Reeves, Katharine; Seaton, Daniel; Savage, Sabrina; Winebarger, Amy;
DeForest, Craig; Desai, Mihir; Bastian, Tim; Lazio, Joseph; Jensen,
P. E., C. S. P., Elizabeth; Manchester, Ward; Wood, Brian; Kooi,
Jason; Wexler, David; Bale, Stuart; Krucker, Sam; Hurlburt, Neal;
DeRosa, Marc; Pevtsov, Alexei; Tripathy, Sushanta; Jain, Kiran;
Gosain, Sanjay; Petrie, Gordon; Kholikov, Shukirjon; Zhao, Junwei;
Scherrer, Philip; Woods, Thomas; Chamberlin, Philip; Kenny, Megan
2021AGUFMSH12A..07G Altcode:
The Multiview Observatory for Solar Terrestrial Science (MOST) is a
comprehensive mission concept targeting the magnetic coupling between
the solar interior and the heliosphere. The wide-ranging imagery and
time series data from MOST will help understand the solar drivers and
the heliospheric responses as a system, discerning and tracking 3D
magnetic field structures, both transient and quiescent in the inner
heliosphere. MOST will have seven remote-sensing and three in-situ
instruments: (1) Magnetic and Doppler Imager (MaDI) to investigate
surface and subsurface magnetism by exploiting the combination of
helioseismic and magnetic-field measurements in the photosphere; (2)
Inner Coronal Imager in EUV (ICIE) to study large-scale structures
such as active regions, coronal holes and eruptive structures by
capturing the magnetic connection between the photosphere and the
corona to about 3 solar radii; (3) Hard X-ray Imager (HXI) to image
the non-thermal flare structure; (4) White-light Coronagraph (WCOR) to
seamlessly study transient and quiescent large-scale coronal structures
extending from the ICIE field of view (FOV); (5) Faraday Effect
Tracker of Coronal and Heliospheric structures (FETCH), a novel radio
package to determine the magnetic field structure and plasma column
density, and their evolution within 0.5 au; (6) Heliospheric Imager
with Polarization (HIP) to track solar features beyond the WCOR FOV,
study their impact on Earth, and provide important context for FETCH;
(7) Radio and Plasma Wave instrument (M/WAVES) to study electron beams
and shocks propagating into the heliosphere via passive radio emission;
(8) Solar High-energy Ion Velocity Analyzer (SHIVA) to determine spectra
of electrons, and ions from H to Fe at multiple spatial locations
and use energetic particles as tracers of magnetic connectivity; (9)
Solar Wind Magnetometer (MAG) to characterize magnetic structures at
1 au; (10) Solar Wind Plasma Instrument (SWPI) to characterize plasma
structures at 1 au. MOST will have two large spacecraft with identical
payloads deployed at L4 and L5 and two smaller spacecraft ahead of L4
and behind L5 to carry additional FETCH elements. MOST will build upon
SOHO and STEREO achievements to expand the multiview observational
approach into the first half of the 21st Century.

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Title: Global solar flows and their impact on magnetic activity
Authors: Dikpati, Mausumi; Braun, Douglas; Featherstone, Nicholas;
Hindman, Bradley; Komm, Rudolf; Liu, Yang; Scherrer, Philip; Upton,
Lisa; Wang, Haimin
2021AGUFMSH55D1872D Altcode:
This poster presents the second year progress report of the LWS
focused-science team-4 of 2019. The main science objective is to
jointly develop the most comprehensive, dynamically consistent picture
of solar flows at the surface, in the convection zone and tachocline,
and determine the MHD effects induced by these motions. Our major
team-achievements in the second year include: (i) consensus about active
regions' flow and their contributions in modifying the global flow;
(ii) long-term global flow map from various magnetograms, and their
specific properties as function of cycle phase, (iii) impacts of the
flows in polar field evolutions, (iv) simulations of global flows with
various solar-like interior conditions, (v) roles of simulated flows
in driving the nonlinear dynamics of spot-producing magnetic fields
and producing their spatio-temporal patterns, which are compared with
that manifested as active regions patterns in surface magnetograms. We
will describe in detail how these observationally constrained local and
global flows are leading us to improved simulations of model-outputs of
magnetic activity and flows. In turn, these outputs can reliably be used
as inputs to heliospheric models, for example, for simulating properties
of reconnection of active regions' magnetic fields, high-speed streams,
sector passages, all of which have profound influence on various
aspects of space weather and impact on terrestrial atmosphere.

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Title: Understanding the Consequences Of Fields and Flows in the
Interior and Exterior of the Sun (COFFIES)
Authors: Hoeksema, J. T.; Brummell, N.; Bush, R.; Hess Webber, S.;
Kitiashvili, I.; Komm, R.; Kosovichev, A.; Mendez, B.; Scherrer, P.;
Upton, L.; Wray, A.; Zevin, D.; The Coffies Team
2021AAS...23811322H Altcode:
The solar activity cycle is the Consequence Of Fields and Flows in the
Interior and Exterior of the Sun (COFFIES). As a Phase-1 NASA DRIVE
Science Center (DSC), COFFIES ultimately aims to develop a data-driven
model of solar activity. To attain this goal COFFIES members are
learning to work together effectively to perform the investigations
needed to answer five primary science questions: 1) What drives
varying large-scale motions in the Sun? 2) How do flows interact
with the magnetic field to cause varying activity cycles? 3) Why
do active regions emerge when and where they do? 4) What do the
manifestations of activity and convection reveal about the internal
processes? 5) How does our understanding of the Sun as a star
inform us more generally about activity dynamics and structure? The
virtual COFFIES center brings together a broad spectrum of observers,
data analysts, theorists, computational scientists, and educators
who collaborate through interacting working groups of four principal
science teams. The principal objectives of the four primary science
teams are to 1) understand the generation of quasi-periodic stellar
magnetic cycles, 2) further develop 3D physical models of interior
dynamics and convection, 3) establish clear physical links between solar
flow fields and near-surface observations, and 4) develop more robust
helioseismic techniques to resolve solar interior flows. Additional
cross-team activities are facilitated by teams for numerical modeling,
center effectiveness, outreach and eduction, and diversity, equity,
inclusion and access (DEIA).

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Title: COFFIES - Developing a Reliable Physical Model of the Solar
Activity Cycle
Authors: Hoeksema, J. T.; Brummell, N.; Bush, R. I.; Komm, R.;
Kosovichev, A. G.; Mendez, B.; Scherrer, P. H.; Upton, L.; Wray,
A. A.; Zevin, D.
2020AGUFMSH0020007H Altcode:
The solar activity cycle is the Consequence Of Fields and Flows in
the Interior and Exterior of the Sun (COFFIES). The COFFIES Drive
Science Center ultimately aims to develop a data driven model of solar
activity. The challenging goals are 1) to understand the generation
of the quasi-periodic stellar magnetic cycles, 2) further develop 3D
physical models of interior dynamics and convection, 3) establish the
physical links between solar flow fields and near-surface observations,
and 4) develop more robust helioseismic techniques to resolve solar
interior flows. To reach these goals the COFFIES team is focusing on
what is needed to answer five primary science questions: 1) What drives
varying large-scale motions in the Sun? 2) How do flows interact with
the magnetic field to cause varying activity cycles? 3) Why do active
regions emerge when and where they do? 4) What do the manifestations
of activity and convection reveal about the internal processes? And
5) How does our understanding of the Sun as a star inform us more
generally about activity dynamics and structure? The virtual COFFIES
center is bringing together a broad spectrum of observers, analysts,
theorists, computational scientists, and educators who collaborate
through interacting teams focused on helioseismology, dynamos, solar
convection, surface links, numerical modeling, center effectiveness,
outreach, education, diversity and inclusion.

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Title: Global Solar Flows and Magnetic Fields: Observing, Simulating
and Predicting Their Impact on the Heliosphere and Terrestrial
Atmosphere
Authors: Dikpati, M.; Braun, D. C.; Featherstone, N. A.; Komm, R.;
Liu, Y.; Scherrer, P. H.; Upton, L.; Wang, H.
2020AGUFMSH0020008D Altcode:
Understanding origins and evolution of solar magnetic activity occurring
on a wide range of time-scales, and the space weather effects caused
by the particles and electromagnetic outputs that reach the Earth,
requires knowledge of the physical origins of this activity below
photosphere. Despite much progress, our knowledge of processes
responsible for driving the magnetohydrodynamics of flows and fields
below photosphere and their relation to observed flows and magnetic
activity is far from complete. For example, there is no consensus as to
the number of meridional circulation-cells that exist in the Sun and the
depth at which the poleward-flow switches direction to equatorward. Main
objective of our LWS focused-science team is to jointly develop the
most comprehensive, dynamically consistent picture of solar flows
at the surface, in the convection zone and tachocline, and determine
the MHD effects induced by these motions. We will present how we are
developing consensus sets of observational constraints and simulating
model-outputs of magnetic activity and flows, which can reliably be
used as inputs to heliospheric and terrestrial- atmospheric models. The
ultimate success will be in our ability to predict the features of
solar cycle 25, including the active-latitudes and -longitudes, global-
and localized-flows several months to years ahead.

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Title: A Method for the Estimation of f- and p-mode Parameters and
Rotational Splitting Coefficients from Un-averaged Solar Oscillation
Power Spectra
Authors: Reiter, J.; Rhodes, E. J., Jr.; Kosovichev, A. G.; Scherrer,
P. H.; Larson, T. P.; , S. F. Pinkerton, II
2020ApJ...894...80R Altcode:
We present a new methodology for the fitting of the peaks in
solar oscillation power spectra that is equally well-suited for the
estimation of low-, medium, and high-degree f- and p-mode parameters and
frequency-splitting coefficients. The method can provide accurate input
data over a wide portion of the dispersion plane for both structural and
rotational inversions. This method, which we call the Multiple-Peak,
Tesseral-Spectrum (MPTS) method, operates directly upon of all of the
modes in a multiplet (n, l) of radial order n and degree l, and employs
a fitting profile that consists of the sum of numerous individual
overlapping profiles whose relative amplitudes are determined by the
leakage matrix appropriate to the targeted mode. Hence, 2l + 1 sets
of modal parameters are obtained simultaneously for each multiplet
(n, l). By fitting an appropriate polynomial to the run of the
fitted frequencies versus the azimuthal order, frequency-splitting
coefficients are also obtained for the same multiplet. Using power
spectra obtained from the 66 day long 2010 MDI Dynamics Run, we
present sample structural and rotational inversions that employed
frequencies and frequency-splitting coefficients from modes in the
degree range of 0-1000 and the frequency range of 965-4600 μHz. The
structural inversion confirms evidence for a pronounced departure of
the sound speed in the outer solar convection zone from the radial
sound-speed profile contained in Model S of Christensen-Dalsgaard
and his collaborators that we obtained previously using a different
fitting method.

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Title: Observations about Observations of the Sun
Authors: Scherrer, Philip H.
2019AAS...23412701S Altcode:
After more than 50 years as an observer of the Sun, of the process of
observing the Sun, and of the people who participate in the adventure
I will offer some comments about what I have learned.

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Title: What do we reliably know about how fast the Sun's core spins?
Authors: Scherrer, Philip H.; Gough, Douglas
2019AAS...23430206S Altcode:
Fossat et al. (2017) and Fossat &amp; Schmider (2018) have attempted
to use solar p-mode frequency perturbations to detect rotational
splitting of g-modes. They claim that this approach detected the
Sun's core to be rotating about 3.8 times faster than the surrounding
radiative interior and the convection zone. We report an independent
study of the technique, the inconsistencies with the well-established
p-mode determinations of rotation, and with their assumption of which
g-modes might be sensed. Additionally we used both the same calibrated
80s SOHO/GOLF data used in the 2017 study and the then only publically
available GOLF 60s cadence data and verified the findings of Schunker et
al. (2018) that the g-mode detection was fragile: It vanished when the
GOLF data was sampled at the 60s vs 80s cadence and when the starting
point was shifted by 2 hours of the 15 years studied. We also applied
the same technique to all other available long duration low-degree data
collections including SOHO/MDI, SOHO/LOI, SDO/HMI, GONG, and BiSON and
found no evidence of the Fossat et al. (2017) reported signals. We note
that a second independent study by Appourchaux &amp; Corbard (2019) came
to the same conclusions. Thus we doubt the validity of the 2017 findings
and conclude that there is no useful information about the rotation of
the solar core yet determined using these techniques (Scherrer &amp;
Gough, 2019). References: Appourchaux, T., &amp; Corbard, T. 2019,
Submitted to A&amp;A, Fossat, E., Boumier, P., Corbard, T., et al. 2017,
A&amp;A, 604, A40, Fossat, E., &amp; Schmider, F. X. 2018, A&amp;A,
612, L1, Scherrer, P. &amp; Gough, D., Accepted by ApJ, 2019, Schunker,
H., Schou, J., Gaulme, P., &amp; Gizon, L. 2018, SoPh, 293, 95

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Title: A Makeover for HMI Magnetic Field Data
Authors: Hoeksema, Jon Todd; Liu, Yang; Scherrer, Philip H.
2019AAS...23410613H Altcode:
HMI, the Helioseismic and Magnetic Imager on the Solar Dynamics
Observatory (SDO) has measured the Sun's vector magnetic field
nearly every 135 or 90 seconds since May 2010. The Stokes parameters
are determined from sets of filtergrams every 720 seconds over the
full disk. The quality of the images is remarkably uniform and the
measurements are reliable for many types of analysis. However, the
inverted and disambiguated magnetic field values are occasionally
incorrect, show small periodic variations with time and spacecraft
velocity, or depend in a systematic way on disk position or
magnitude. Estimates of uncertainties in the inversion are provided for
each point, but for some kinds of analysis having a smoother and more
uniform time series is necessary. Sources of some errors are well
understood and well characterized, but others are not. Statistical and
empirical techniques have been developed by the HMI Team and others
to improve both the calibration and appearance of the observations,
to increase consistency, and minimize undesirable variability. Effects
addressed include issues related to field inversion, disambiguation,
sensitivity, optical distortion, instrument characteristics, and
systematic errors due to spacecraft velocity and viewing angle. Some
of the most reliable and affordable corrections are included in the
regular analysis pipeline. Some corrections are too compute intensive
to implement routinely. For others the resulting 'corrections' depend
on assumptions about the typical behavior of the solar magnetic field,
so care must be taken when using such results.

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Title: A Critical Evaluation of Recent Claims Concerning Solar
Rotation
Authors: Scherrer, P. H.; Gough, D. O.
2019ApJ...877...42S Altcode: 2019arXiv190402820S
Fossat et al. recently reported detecting rotational splitting of
g-modes indirectly via the interaction with p-modes observed directly
by the Global Oscillations at Low Frequency (GOLF) instrument on
the Solar and Heliospheric Observatory (SOHO). They concluded that
the core of the Sun is rotating 3.8 ± 0.1 times faster than the
surrounding radiative envelope. This is startling, partly because
such rapid rotation almost contradicts direct inferences from the
p-mode rotational splitting inferred from the same data. Moreover,
the inferred amplitudes of the g-modes appear to exceed the upper
bound reported by Appourchaux et al. It is also suspect because the
theory of the procedure implies that the principal modes claimed to
have been measured should be undetectable. We point out that there are
other interpretations: one leads to a core rotation about twice as fast
as the surrounding envelope; another, to a core rotating more slowly
than the envelope. Here we also report on an independent assessment
of the Fossat et al. analysis by applying their procedure to different
representations of the GOLF data, expanding on Schunker et al. We also
analyze seismic data obtained from LOI and MDI (both also on SOHO),
from HMI (on SDO), and from the ground-based BiSON and GONG, and
we find the evidence reported by Fossat et al. not to be robust. We
also illustrate that merely fitting model spectra to observations,
which Fossat et al. do to support their g-mode detections, and as
Fossat &amp; Schmider do for extracting additional g-mode splittings,
is not necessarily reliable. We are therefore led to doubt the claim.

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Title: HMI Data Corrected for Scattered Light Compared to Hinode
SOT-SP Data
Authors: Norton, A. A.; Duvall, T. L., Jr.; Schou, J.; Cheung,
M. C. M.; Scherrer, P. H.; Chu, K. C.; Sommers, J.
2018csc..confE.101N Altcode:
In March 2018, the Helioseismic Magnetic Imager (HMI) team began
providing full-disk data to the public on a daily basis that were
corrected for scattered light. In addition to the intensity and
magnetogram data, the improved vector magnetic field maps are also
provided. The process uses a Richardson-Lucy algorithm and a known
PSF. The deconvolution results in a few percent decrease in umbral
intensity corresponding to a 200 K decrease in temperature, a doubling
of the intensity contrast of granulation from 3.6 to 7.2%, an increase
in total field strength values (not only line-of-sight B) in plage by
1.4, faculae brightening and network darkening, and a partial correction
for the convective blue-shift. The new data series can be found in
JSOC with names similar to the original but with the qualifying term
'_dcon' or '_dconS' appended (denoting whether the deconvolution
was applied to the filtergrams or Stokes images). Comparisons to
near-simultaneous Hinode SOT-SP data demonstrate that the correction
brings the two instruments into much better agreement, including the
inverted magnetic field parameters. We compare our results to similar
efforts in the literature such as work by Diaz Baso and Asensio Ramos
(2018) in which HMI intensity and magnetogram data was enhanced using
neural networks and super-resolution.

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Title: Soothing Massage of HMI Magnetic Field Data
Authors: Hoeksema, J. Todd; Liu, Yang; Sun, Xudong; Scherrer, Philip;
HMI Science Team
2018csc..confE...7H Altcode:
The Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics
Observatory (SDO) has measured solar polarization at six wavelengths
across the Fe I 6173 spectral line with one arc second resolution
nearly every 90 or 135 seconds since May 2010, and the Stokes
parameters are determined every 720 seconds over the full disk. The
quality of the filtergrams is remarkably uniform, but the inverted
and disambiguated magnetic field values are sometime incorrect or
show small systematic variations with time and space. Estimates of
the numerical uncertainties are provided for each pixel, but, for some
kinds of analysis, having a smoother and more uniform time series can
be useful. This report describes methods that can be used to 'massage'
the observations to improve consistency and appearance and minimize
unwanted variability. Effects considered include issues related to field
inversion, disambiguation, instrument sensitivity, optical distortion,
and systematic errors due to spacecraft velocity. The resulting
'corrections' typically depend on assumptions about the behavior of
the solar magnetic field, so care must be taken when using such results.

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Title: Statistical Analysis of Acoustic Wave Power and Flows around
Solar Active Regions
Authors: Rabello-Soares, M. Cristina; Bogart, Richard S.; Scherrer,
Philip H.
2018csc..confE..51R Altcode:
We analyze the effect of a sunspot in its quiet surroundings applying
a helioseismic technique on almost three years of Helioseismic and
Magnetic Imager (HMI) observations obtained during solar cycle 24
to further study the sunspot structure below the solar surface. The
attenuation of acoustic waves with frequencies lower than 4.2 mHz
depends more strongly on the wave direction at a distance of 6°-7°
from the sunspot center. The amplification of higher frequency waves is
highest 6° away from the active region and is largely independent of
the wave's direction. We observe a mean clockwise flow around active
regions, the angular speed of which decreases exponentially with
distance and has a coefficient close to -0.7 degree-1. The observed
horizontal flow in the direction of the nearby active region agrees with
a large-scale circulation around the sunspot in the shape of cylindrical
shell. The center of the shell seems to be centered around 7° from the
sunspot center, where we observe an inflow close to the surface down
to ∼2 Mm, followed by an outflow at deeper layers until at least 7 Mm.

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Title: Classifying Signatures of Sudden Ionospheric Disturbances
Authors: Hegde, Sahil; Bobra, Monica G.; Scherrer, Philip H.
2018RNAAS...2..162H Altcode: 2018RNAAS...2c.162H; 2018arXiv180902742H
Solar activity, such as flares, produce bursts of high-energy
radiation that temporarily enhance the D-region of the ionosphere and
attenuate low-frequency radio waves. To track these Sudden Ionospheric
Disturbances (SIDs), which disrupt communication signals and perturb
satellite orbits, Scherrer et al. (2008) developed an international,
ground-based network of around 500 SID monitors that measure the signal
strength of low-frequency radio waves. However, these monitors suffer
from a host of noise contamination issues that preclude their use for
rigorous scientific analysis. As such, we attempt to create an algorithm
to automatically identify noisy, contaminated SID data sets from clean
ones. To do so, we develop a set of features to characterize times
series measurements from SID monitors and use these features, along with
a binary classifer called a support vector machine, to automatically
assess the quality of the SID data. We compute the True Skill Score,
a metric that measures the performance of our classifier, and find that
it is ~0.75+/-0.06. We find features characterizing the difference
between the daytime and nighttime signal strength of low-frequency
radio waves most effectively discern noisy data sets from clean ones.

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Title: Statistical Analysis of Acoustic Wave Power and Flows around
Solar Active Regions
Authors: Rabello-Soares, M. Cristina; Bogart, Richard S.; Scherrer,
Philip H.
2018ApJ...859....7R Altcode: 2018arXiv180407791R
We analyze the effect of a sunspot in its quiet surroundings applying
a helioseismic technique on almost three years of Helioseismic and
Magnetic Imager (HMI) observations obtained during solar cycle 24
to further study the sunspot structure below the solar surface. The
attenuation of acoustic waves with frequencies lower than 4.2 mHz
depends more strongly on the wave direction at a distance of 6°-7°
from the sunspot center. The amplification of higher frequency waves
is highest 6° away from the active region and is largely independent
of the wave’s direction. We observe a mean clockwise flow around
active regions, the angular speed of which decreases exponentially with
distance and has a coefficient close to -0.7 degree-1. The
observed horizontal flow in the direction of the nearby active region
agrees with a large-scale circulation around the sunspot in the shape
of cylindrical shell. The center of the shell seems to be centered
around 7° from the sunspot center, where we observe an inflow close
to the surface down to ∼2 Mm, followed by an outflow at deeper layers
until at least 7 Mm.

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Title: On-Orbit Performance of the Helioseismic and Magnetic Imager
Instrument onboard the Solar Dynamics Observatory
Authors: Hoeksema, J. T.; Baldner, C. S.; Bush, R. I.; Schou, J.;
Scherrer, P. H.
2018SoPh..293...45H Altcode: 2018arXiv180201731H
The Helioseismic and Magnetic Imager (HMI) instrument is a major
component of NASA's Solar Dynamics Observatory (SDO) spacecraft. Since
commencement of full regular science operations on 1 May 2010, HMI
has operated with remarkable continuity, e.g. during the more than
five years of the SDO prime mission that ended 30 September 2015, HMI
collected 98.4% of all possible 45-second velocity maps; minimizing gaps
in these full-disk Dopplergrams is crucial for helioseismology. HMI
velocity, intensity, and magnetic-field measurements are used in
numerous investigations, so understanding the quality of the data is
important. This article describes the calibration measurements used
to track the performance of the HMI instrument, and it details trends
in important instrument parameters during the prime mission. Regular
calibration sequences provide information used to improve and update the
calibration of HMI data. The set-point temperature of the instrument
front window and optical bench is adjusted regularly to maintain
instrument focus, and changes in the temperature-control scheme have
been made to improve stability in the observable quantities. The
exposure time has been changed to compensate for a 20% decrease in
instrument throughput. Measurements of the performance of the shutter
and tuning mechanisms show that they are aging as expected and continue
to perform according to specification. Parameters of the tunable
optical-filter elements are regularly adjusted to account for drifts
in the central wavelength. Frequent measurements of changing CCD-camera
characteristics, such as gain and flat field, are used to calibrate the
observations. Infrequent expected events such as eclipses, transits,
and spacecraft off-points interrupt regular instrument operations and
provide the opportunity to perform additional calibration. Onboard
instrument anomalies are rare and seem to occur quite uniformly in
time. The instrument continues to perform very well.

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Title: Measuring the Large-scale Solar Magnetic Field
Authors: Hoeksema, J. T.; Scherrer, P. H.; Peterson, E.; Svalgaard, L.
2017AGUFMSH51C2497H Altcode:
The Sun's large-scale magnetic field is important for determining
global structure of the corona and for quantifying the evolution of
the polar field, which is sometimes used for predicting the strength
of the next solar cycle. Having confidence in the determination of the
large-scale magnetic field of the Sun is difficult because the field is
often near the detection limit, various observing methods all measure
something a little different, and various systematic effects can be
very important. We compare resolved and unresolved observations of
the large-scale magnetic field from the Wilcox Solar Observatory,
Heliseismic and Magnetic Imager (HMI), Michelson Doppler Imager
(MDI), and Solis. Cross comparison does not enable us to establish an
absolute calibration, but it does allow us to discover and compensate
for instrument problems, such as the sensitivity decrease seen in the
WSO measurements in late 2016 and early 2017.

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Title: Stray Light Correction of HMI Data
Authors: Norton, Aimee Ann; Duvall, Thomas; Schou, Jesper; Cheung,
Mark; Scherrer, Philip H.
2017SPD....4820705N Altcode:
The point spread function (PSF) for HMI is an Airy function convolved
with a Lorentzian. The parameters are bound by ground-based testing
before launch, then post-launch off-limb light curves, lunar eclipse
and Venus transit data. The PSF correction is programmed in C and runs
within the HMI data processing pipeline environment. A single full-disk
intensity image can be processed in less than one second. Deconvolution
of the PSF on the Stokes profile data (a linear combination of
original filtergrms) is less computationally expensive and is shown
to be equivalent to deconvolution applied at the original filtergram
level. Results include a decrease in umbral darkness of a few percent
(~200 K cooler), a doubling of the granulation contrast in intensity
from 3.6 to 7.2%, an increase in plage field strengths by a factor of
1.5, and a partial correction of the convective blueshift in Doppler
velocities. Requests for data corrected for stray light are welcome
and will be processed by the HMI team.

---------------------------------------------------------
Title: Status update of the effort to correct the SDO/HMI systemmatic
errors in Doppler velocity and derived data products
Authors: Scherrer, Philip H.
2017SPD....4811003S Altcode:
This poster provides an update of the status of the efforts to
understand and correct the leakage of the SDO orbit velocity into most
HMI data products. The following is extracted from the abstract for the
similar topic presented at the 2016 SPD meeting: “The Helioseismic
and Magnetic Imager (HMI) instrument on the Solar Dynamics Observatory
(SDO) measures sets of filtergrams which are converted into velocity
and magnetic field maps. In addition to solar photospheric motions the
velocity measurements include a direct component from the line-of-sight
component of the SDO orbit. Since the magnetic field is computed as the
difference between the velocity measured in left and right circular
polarization, the orbit velocity is canceled only if the velocity
is properly calibrated. When the orbit velocity is subtracted the
remaining "solar" velocity shows a residual signal which is equal
to about 2% of the c. +- 3000 m/s orbit velocity in a nearly linear
relationship. This implies an error in our knowledge of some of the
details of as-built filter components. This systematic error is the
source of 12- and 24-hour variations in most HMI data products. While
the instrument as presently calibrated (Couvidat et al. 2012 and 2016)
meets all of the “Level-1” mission requirements it fails to meet
the stated goal of 10 m/s accuracy for velocity data products. For the
velocity measurements this has not been a significant problem since
the prime HMI goals of obtaining data for helioseismology are not
affected by this systematic error. However the orbit signal leaking
into the magnetograms and vector magnetograms degrades the ability to
accomplish some of the mission science goals at the expected levels
of accuracy. This poster presents the current state of understanding
of the source of this systematic error and prospects for near term
improvement in the accuracy of the filter profile model.”

---------------------------------------------------------
Title: Variation of acoustic mode parameters with distance from a
nearby active region
Authors: Rabello-Soares, M. Cristina; Bogart, Richard S.; Scherrer,
Philip H.
2017SPD....4810905R Altcode:
In a previous paper (Rabello-Soares, Bogart &amp; Scherrer 2016), we
quantified the influence of magnetic fields on acoustic mode parameters
and flows in and around active regions by comparing the differences in
the parameters in magnetically quiet regions when there is an active
region in their vicinity with those of quiet regions at the same disc
locations for which there are no neighboring active regions. Here we
detail further our analysis by estimating how these differences vary
with distance from the active region. We use ring diagram analysis
from almost five years of HMI observations.In our first paper, we
observed that the power reduction has a strong dependence on the wave
direction but the amplitude enhacement (the `acoustic halo effect')
has a very weak dependence on the wave propagation direction. We find
that the effect on the amplitude decreases as the distance increases
as expected. However, the dependence on the wave direction seems
to reach a peak around 70 Mm from the active region. Very near the
active region, the amplitude effects are independent of the direction
of mode propagation.

---------------------------------------------------------
Title: The Olsen Rotating Dipole, Revisited
Authors: Svalgaard, L.; Gough, D. O.; Scherrer, P. H.
2016AGUFMSH31B2548S Altcode:
Olsen (1948) and Wilcox &amp; Gonzales (1971) reported evidence
of a solar equatorial magnetic dipole with a stable (synodic)
rotation period of 26 7/8 days maintaining its phase over 15 years
(1926-1941, Olsen) and possibly to 1968 as well (1963-1968, Wilcox &amp;
Gonzales). Using a composite series of Interplanetary Magnetic Sector
Polarities covering the interval 1844-2016 (derived from geomagnetic
data before the space age and direct measurements during 1963-2016)
we find that 1) the response of geomagnetic activity to passage (at
Earth) of a sector boundary has been consistently the same in every
solar cycle from 9 through 24, thus validating the inferred times of
sector boudary passages over the past 173 years, and 2) the 'Olsen'
dipole can be traced back the 16 cycles to the year 1844, albeit
with a slightly different synodic rotation period of 26.86 days (431
nHz). Olsen ended his paper with "The persistence of a fixed period
during 15 years points to the possibility that the origin of the effect
is to be found in a layer on the Sun with a fixed rotation-period during
a long time" and Wilcox &amp; Gonzales noted that "A rotating magnetic
dipole may be lurking within the sun". We compare the Olsen-period
with other evidence for rotation periods in the deep interior and for
the existence of a relic magnetic field.

---------------------------------------------------------
Title: Achieving Consistent Vector Magnetic Field Measurements
from SDO/HMI
Authors: Schuck, P. W.; Antiochos, S. K.; Scherrer, P. H.; Hoeksema,
J. T.; Leka, K. D.; Barnes, G.
2016AGUFMSH31B2575S Altcode:
NASA's Solar Dynamics Observatory (SDO) is delivering vector magnetic
field observations of the full solar disk with unprecedented temporal
and spatial resolution; however, the satellite is in a highly inclined
geosynchronous orbit. The relative spacecraft-Sun velocity varies by ±3
km/s over a day which introduces significant orbital artifacts in the
Helioseismic Magnetic Imager (HMI) data. We have recently demonstrated
that the orbital artifacts contaminate all spatial and temporal scales
in the data and developed a procedure for mitigating these artifacts
in the Doppler data obtained from the Milne-Eddington inversions in the
HMI Pipeline. Simultaneously, we have found that the orbital artifacts
may be introduced by inaccurate estimates for the free-spectral ranges
(FSRs) of the optical elements in HMI. We describe our approach and
attempt to minimize orbital artifacts in the hmi.V_720 Dopplergram
series by adjusting the FSRs for the optical elements of HMI within
their measurement uncertainties of ±1%.

---------------------------------------------------------
Title: HMI Data Corrected for Stray Light Now Available
Authors: Norton, A. A.; Duvall, T. L.; Schou, J.; Cheung, M. C. M.;
Scherrer, P. H.
2016usc..confE..95N Altcode:
The form of the point spread function (PSF) derived for HMI is an
Airy function convolved with a Lorentzian. The parameters are bound
by observational ground-based testing of the instrument conducted
prior to launch (Wachter et al., 2012), by full-disk data used to
evaluate the off-limb behavior of the scattered light, as well as by
data obtained during the Venus transit. The PSF correction has been
programmed in both C and cuda C and runs within the JSOC environment
using either a CPU or GPU. A single full-disk intensity image can
be deconvolved in less than one second. The PSF is described in more
detail in Couvidat et al. (2016) and has already been used by Hathaway
et al. (2015) to forward-model solar-convection spectra, by Krucker et
al. (2015) to investigate footpoints of off-limb solar flares and by
Whitney, Criscuoli and Norton (2016) to examine the relations between
intensity contrast and magnetic field strengths. In this presentation,
we highlight the changes to umbral darkness, granulation contrast
and plage field strengths that result from stray light correction. A
twenty-four hour period of scattered-light corrected HMI data from
2010.08.03, including the isolated sunspot NOAA 11092, is currently
available for anyone. Requests for additional time periods of interest
are welcome and will be processed by the HMI team.

---------------------------------------------------------
Title: MHD Waves at Umbral-Penumbral Boundary Observed with
Hinode/SOT-SP and SDO/HMI
Authors: Norton, A. A.; Tarbell, T. D.; Scherrer, P. H.; Baldner, C. S.
2016usc..confE.114N Altcode:
The conversion of p-modes and other perturbations in the near-surface
layers into MHD waves that can propagate along and across magnetic field
lines is a topic of interest for energy transport. The photospheric
signatures of MHD waves are weak due to low amplitudes at the
beta=1 equipartion level where mode-conversion occurs. We report on
oscillations observed with Hinode SOT/SP and HMI in which we have time
series for sunspots 12186 (11.10.2014) and 12434 (17.10.2015). In
the Milne-Eddington inversion results from SP, oscillations in the
inclination angle and velocity are found at the umbral-penumbral
boundary with 5 minute periods. HMI data also shows distinct
umbral-penumbral boundary oscillations consistent with the SP data. We
discuss surface versus body modes that might explain these observations.

---------------------------------------------------------
Title: Observables Processing for the Helioseismic and Magnetic
Imager Instrument on the Solar Dynamics Observatory
Authors: Couvidat, S.; Schou, J.; Hoeksema, J. T.; Bogart, R. S.;
Bush, R. I.; Duvall, T. L.; Liu, Y.; Norton, A. A.; Scherrer, P. H.
2016SoPh..291.1887C Altcode: 2016SoPh..tmp..120C; 2016arXiv160602368C
NASA's Solar Dynamics Observatory (SDO) spacecraft was launched
11 February 2010 with three instruments onboard, including the
Helioseismic and Magnetic Imager (HMI). After commissioning, HMI
began normal operations on 1 May 2010 and has subsequently observed
the Sun's entire visible disk almost continuously. HMI collects
sequences of polarized filtergrams taken at a fixed cadence with two
4096 ×4096 cameras, from which are computed arcsecond-resolution maps
of photospheric observables that include line-of-sight velocity and
magnetic field, continuum intensity, line width, line depth, and the
Stokes polarization parameters [I ,Q ,U ,V ]. Two processing pipelines
have been implemented at the SDO Joint Science Operations Center (JSOC)
at Stanford University to compute these observables from calibrated
Level-1 filtergrams, one that computes line-of-sight quantities every
45 seconds and the other, primarily for the vector magnetic field, that
computes averages on a 720-second cadence. Corrections are made for
static and temporally changing CCD characteristics, bad pixels, image
alignment and distortion, polarization irregularities, filter-element
uncertainty and nonuniformity, as well as Sun-spacecraft velocity. We
detail the functioning of these two pipelines, explain known issues
affecting the measurements of the resulting physical quantities,
and describe how regular updates to the instrument calibration impact
them. We also describe how the scheme for computing the observables
is optimized for actual HMI observations. Initial calibration of
HMI was performed on the ground using a variety of light sources and
calibration sequences. During the five years of the SDO prime mission,
regular calibration sequences have been taken on orbit to improve and
regularly update the instrument calibration, and to monitor changes
in the HMI instrument. This has resulted in several changes in the
observables processing that are detailed here. The instrument more
than satisfies all of the original specifications for data quality and
continuity. The procedures described here still have significant room
for improvement. The most significant remaining systematic errors are
associated with the spacecraft orbital velocity.

---------------------------------------------------------
Title: Statistical Analysis of Acoustic Wave Parameters Near Solar
Active Regions
Authors: Rabello-Soares, M. Cristina; Bogart, Richard S.; Scherrer,
Philip H.
2016ApJ...827..140R Altcode: 2016arXiv160608068R
In order to quantify the influence of magnetic fields on acoustic
mode parameters and flows in and around active regions, we analyze
the differences in the parameters in magnetically quiet regions nearby
an active region (which we call “nearby regions”), compared with
those of quiet regions at the same disk locations for which there are
no neighboring active regions. We also compare the mode parameters in
active regions with those in comparably located quiet regions. Our
analysis is based on ring-diagram analysis of all active regions
observed by the Helioseismic and Magnetic Imager (HMI) during almost
five years. We find that the frequency at which the mode amplitude
changes from attenuation to amplification in the quiet nearby regions is
around 4.2 mHz, in contrast to the active regions, for which it is about
5.1 mHz. This amplitude enhacement (the “acoustic halo effect”)
is as large as that observed in the active regions, and has a very
weak dependence on the wave propagation direction. The mode energy
difference in nearby regions also changes from a deficit to an excess
at around 4.2 mHz, but averages to zero over all modes. The frequency
difference in nearby regions increases with increasing frequency
until a point at which the frequency shifts turn over sharply, as in
active regions. However, this turnover occurs around 4.9 mHz, which
is significantly below the acoustic cutoff frequency. Inverting the
horizontal flow parameters in the direction of the neigboring active
regions, we find flows that are consistent with a model of the thermal
energy flow being blocked directly below the active region.

---------------------------------------------------------
Title: On HMI's Mod-L Sequence: Test and Evaluation
Authors: Liu, Yang; Baldner, Charles; Bogart, R. S.; Bush, R.;
Couvidat, S.; Duvall, Thomas L.; Hoeksema, Jon Todd; Norton, Aimee Ann;
Scherrer, Philip H.; Schou, Jesper
2016SPD....47.0810L Altcode:
HMI Mod-L sequence can produce full Stokes parameters at a cadence of 90
seconds by combining filtergrams from both cameras, the front camera and
the side camera. Within the 90-second, the front camera takes two sets
of Left and Right Circular Polarizations (LCP and RCP) at 6 wavelengths;
the side camera takes one set of Linear Polarizations (I+/-Q and I+/-U)
at 6 wavelengths. By combining two cameras, one can obtain full Stokes
parameters of [I,Q,U,V] at 6 wavelengths in 90 seconds. In norminal
Mod-C sequence that HMI currently uses, the front camera takes LCP and
RCP at a cadence of 45 seconds, while the side camera takes observation
of the full Stokes at a cadence of 135 seconds. Mod-L should be
better than Mod-C for providing vector magnetic field data because
(1) Mod-L increases cadence of full Stokes observation, which leads
to higher temporal resolution of vector magnetic field measurement;
(2) decreases noise in vector magnetic field data because it uses
more filtergrams to produce [I,Q,U,V]. There are two potential issues
in Mod-L that need to be addressed: (1) scaling intensity of the two
cameras’ filtergrams; and (2) if current polarization calibration
model, which is built for each camera separately, works for the combined
data from both cameras. This presentation will address these questions,
and further place a discussion here.

---------------------------------------------------------
Title: The Processing of Observables Made by the HMI Instrument on SDO
Authors: Hoeksema, Jon Todd; Schou, Jesper; Couvidat, Sebastien;
Bogart, Richard S.; Bush, Rock; Duvall, Thomas L.; Liu, Yang; Norton,
Aimee Ann; Scherrer, Philip H.
2016SPD....47.0808H Altcode:
The Helioseismic and Magnetic Imager (HMI) acquires sequences of
polarized filtergrams of the Sun from which observable quantities
are computed. The observables include five line-of-sight quantities -
magnetic field, velocity, continuum intensity, line depth, and line
width - as well as Stokes polarization parameters. The process of
turning a set of filtergrams into calibrated measurements is quite
involved. Since May 2010 the streams of data from HMI’s two cameras
have been treated separately. The frame list for the Doppler camera
repeats every 45 seconds and the images are combined to determine
the line-of-sight observables. The Vector camera sequence measures
additional polarizations and so requires 135s; images from ten sequences
are combined every 720s to determine the four Stokes polarization
parameters at each of six wavelengths, as well as the LoS observables. A
variety of calibration corrections are made to the Level-1 filtergrams
to account for distortion, image motion and alignment, polarization,
wavelength and intensity irregularities, camera issues, solar rotation,
and other effects. Residual random variations in the final observables
are consistent with photon noise levels, but systematic errors remain
that have not been fully corrected. Of particular concern are those
associated with the velocity of the instrument relative to the Sun
due to the geosynchronous orbit of the Solar Dynamics Observatory
(SDO) spacecraft. This presentation describes the creation of the
observables, characterizes the residual errors, and indicates plans
for future improvements - including correction for the instrument point
spread function. All HMI data are available at http://jsoc.stanford.edu.

---------------------------------------------------------
Title: HMI Measured Doppler Velocity Contamination from the SDO
Orbit Velocity
Authors: Scherrer, Philip H.; SDO HMI Team
2016SPD....47.0812S Altcode:
The Helioseismic and Magnetic Imager (HMI) instrument on the Solar
Dynamics Observatory (SDO) measures sets of filtergrams which are
converted into velocity and magnetic field maps each 45-seconds with its
front camera and each 12 minutes with its side camera. In addition to
solar phototspheric motions the velocity measurements include a direct
component from the line-of-sight component of the SDO orbit. Since
the magnetic field is computed as the difference between the velocity
measured in left and right circular polarization the orbit velocity is
canceled only if the celocity is properly calibrated. When the orbit
component of the velocity is subtracted for each pixel the remaining
"solar" velocity shows a residual signal which is equal to about 2% of
the c. +- 3000 m/s orbit velocity in a nearly linear relationship. This
implies an error in our knowledge of some of the details of as-built
filter components. The model instrument transmission profile is
required for calibration of all HMI level 1.5 “observable”
quantities. This systematic error is very likely the source of 12-
and 24-hour variations in most HMI data products. Over the years since
launch a substantial effort has been dedicated to understanding the
origin of this problem. While the instrument as presently calibrated
(Couvidat et al. 2012 and 2016) meets all of the “Level-1” mission
requirements it fails to meet the stated goal of 10 m/s accuracy for
velocity data products and some not stated but generally assumed goals
for other products. For the velocity measurements this has not been a
significant problem since the prime HMI goals of obtaining data for
helioseismology are not affected by this systematic error. However
the orbit signal leaking into the magnetograms and vector magnetograms
degrades the ability to accomplish some of the mission science goals at
the expected levels of accuracy. This poster presents the current state
of understanding of the source of this systematic error and prospects
for near term improvement in the accuracy of the filter profile model.

---------------------------------------------------------
Title: Amplitudes of MHD Waves in Sunspots
Authors: Norton, Aimee Ann; Cally, Paul; Baldner, Charles; Kleint,
Lucia; Tarbell, Theodore D.; De Pontieu, Bart; Scherrer, Philip H.;
Rajaguru, Paul
2016SPD....47.1009N Altcode:
The conversion of p-modes into MHD waves by strong magnetic fields
occurs mainly in the sub-photospheric layers. The photospheric
signatures of MHD waves are weak due to low amplitudes at the beta=1
equipartion level where mode-conversion occurs. We report on small
amplitude oscillations observed in the photosphere with Hinode SOT/SP
in which we analyze time series for sunspots ARs 12186 (11.10.2014)
and 12434 (17.10.2015). No significant magnetic field oscillations
are recovered in the umbra or penumbra in the ME inversion. However,
periodicities in the inclination angle are found at the umbral/penumbral
boundary with 5 minute periods. Upward propagating waves are indicated
in the intensity signals correlated between HMI and AIA at different
heights. We compare SP results with the oscillations observed in HMI
data. Simultaneous IRIS data shows transition region brightening above
the umbral core.

---------------------------------------------------------
Title: Helioseismology with Solar Orbiter
Authors: Löptien, Björn; Birch, Aaron C.; Gizon, Laurent; Schou,
Jesper; Appourchaux, Thierry; Blanco Rodríguez, Julián; Cally,
Paul S.; Dominguez-Tagle, Carlos; Gandorfer, Achim; Hill, Frank;
Hirzberger, Johann; Scherrer, Philip H.; Solanki, Sami K.
2015SSRv..196..251L Altcode: 2014arXiv1406.5435L; 2014SSRv..tmp...31L
The Solar Orbiter mission, to be launched in July 2017, will
carry a suite of remote sensing and in-situ instruments, including
the Polarimetric and Helioseismic Imager (PHI). PHI will deliver
high-cadence images of the Sun in intensity and Doppler velocity
suitable for carrying out novel helioseismic studies. The orbit of
the Solar Orbiter spacecraft will reach a solar latitude of up to
21∘ (up to 34∘ by the end of the extended
mission) and thus will enable the first local helioseismology studies of
the polar regions. Here we consider an array of science objectives to be
addressed by helioseismology within the baseline telemetry allocation
(51 Gbit per orbit, current baseline) and within the science observing
windows (baseline 3×10 days per orbit). A particularly important
objective is the measurement of large-scale flows at high latitudes
(rotation and meridional flow), which are largely unknown but play an
important role in flux transport dynamos. For both helioseismology
and feature tracking methods convection is a source of noise in
the measurement of longitudinally averaged large-scale flows, which
decreases as T -1/2 where T is the total duration of the
observations. Therefore, the detection of small amplitude signals (e.g.,
meridional circulation, flows in the deep solar interior) requires long
observation times. As an example, one hundred days of observations at
lower spatial resolution would provide a noise level of about three m/s
on the meridional flow at 80∘ latitude. Longer time-series
are also needed to study temporal variations with the solar cycle. The
full range of Earth-Sun-spacecraft angles provided by the orbit will
enable helioseismology from two vantage points by combining PHI with
another instrument: stereoscopic helioseismology will allow the study
of the deep solar interior and a better understanding of the physics
of solar oscillations in both quiet Sun and sunspots. We have used a
model of the PHI instrument to study its performance for helioseismology
applications. As input we used a 6 hr time-series of realistic solar
magneto-convection simulation (Stagger code) and the SPINOR radiative
transfer code to synthesize the observables. The simulated power
spectra of solar oscillations show that the instrument is suitable for
helioseismology. In particular, the specified point spread function,
image jitter, and photon noise are no obstacle to a successful mission.

---------------------------------------------------------
Title: The Sun From the Perspective of an Observer
Authors: Sibeck, D. G.; Scherrer, P. H.
2015AGUFMSH34A..01S Altcode:
This talk will reflect on issues and pleasures of observing the Sun
from the Earth and from space over four sunspot cycles. Parker and
those who preceded and follow his early estimates of how our star
should/might/could work need to compare their models with the real
Sun. The true test of a model is how well it explains reality. Observers
try to make their own estimates of how the Sun does work based on
observable proxies for the physical quantities of interest. It the best
of times, the models match the observations. The results are seldom
simple due to, at least, limitations of both models and observations.

---------------------------------------------------------
Title: A Method for the Estimation of p-Mode Parameters from Averaged
Solar Oscillation Power Spectra
Authors: Reiter, J.; Rhodes, E. J., Jr.; Kosovichev, A. G.; Schou,
J.; Scherrer, P. H.; Larson, T. P.
2015ApJ...803...92R Altcode: 2015arXiv150407493R
A new fitting methodology is presented that is equally well suited for
the estimation of low-, medium-, and high-degree mode parameters from
m-averaged solar oscillation power spectra of widely differing spectral
resolution. This method, which we call the “Windowed, MuLTiple-Peak,
averaged-spectrum” or WMLTP Method, constructs a theoretical profile
by convolving the weighted sum of the profiles of the modes appearing
in the fitting box with the power spectrum of the window function of
the observing run, using weights from a leakage matrix that takes into
account observational and physical effects, such as the distortion of
modes by solar latitudinal differential rotation. We demonstrate that
the WMLTP Method makes substantial improvements in the inferences of
the properties of the solar oscillations in comparison with a previous
method, which employed a single profile to represent each spectral
peak. We also present an inversion for the internal solar structure,
which is based upon 6366 modes that we computed using the WMLTP method
on the 66 day 2010 Solar and Heliospheric Observatory/MDI Dynamics
Run. To improve both the numerical stability and reliability of the
inversion, we developed a new procedure for the identification and
correction of outliers in a frequency dataset. We present evidence
for a pronounced departure of the sound speed in the outer half of the
solar convection zone and in the subsurface shear layer from the radial
sound speed profile contained in Model S of Christensen-Dalsgaard and
his collaborators that existed in the rising phase of Solar Cycle 24
during mid-2010.

---------------------------------------------------------
Title: SDO/HMI Highlights After Five Years
Authors: Scherrer, Philip H.
2015TESS....140303S Altcode:
The SDO five year Prime Mission ends during thisTESS meeting. The
HMI isntrument has operated as designed for these five years and
has produced data used in more than 600 refereed articles. Some
of the highlights from these articles and some not yet published
are discussed. The SDO JSOC-SDP (Joint Science Operations Center -
Science Data Processing) facility at Stanford status is also reviewed
with hints to help with access to SDO HMI and AIA data.

---------------------------------------------------------
Title: The Interface Region Imaging Spectrograph (IRIS)
Authors: De Pontieu, B.; Title, A. M.; Lemen, J. R.; Kushner, G. D.;
Akin, D. J.; Allard, B.; Berger, T.; Boerner, P.; Cheung, M.; Chou,
C.; Drake, J. F.; Duncan, D. W.; Freeland, S.; Heyman, G. F.; Hoffman,
C.; Hurlburt, N. E.; Lindgren, R. W.; Mathur, D.; Rehse, R.; Sabolish,
D.; Seguin, R.; Schrijver, C. J.; Tarbell, T. D.; Wülser, J. -P.;
Wolfson, C. J.; Yanari, C.; Mudge, J.; Nguyen-Phuc, N.; Timmons,
R.; van Bezooijen, R.; Weingrod, I.; Brookner, R.; Butcher, G.;
Dougherty, B.; Eder, J.; Knagenhjelm, V.; Larsen, S.; Mansir, D.;
Phan, L.; Boyle, P.; Cheimets, P. N.; DeLuca, E. E.; Golub, L.;
Gates, R.; Hertz, E.; McKillop, S.; Park, S.; Perry, T.; Podgorski,
W. A.; Reeves, K.; Saar, S.; Testa, P.; Tian, H.; Weber, M.; Dunn, C.;
Eccles, S.; Jaeggli, S. A.; Kankelborg, C. C.; Mashburn, K.; Pust, N.;
Springer, L.; Carvalho, R.; Kleint, L.; Marmie, J.; Mazmanian, E.;
Pereira, T. M. D.; Sawyer, S.; Strong, J.; Worden, S. P.; Carlsson,
M.; Hansteen, V. H.; Leenaarts, J.; Wiesmann, M.; Aloise, J.; Chu,
K. -C.; Bush, R. I.; Scherrer, P. H.; Brekke, P.; Martinez-Sykora,
J.; Lites, B. W.; McIntosh, S. W.; Uitenbroek, H.; Okamoto, T. J.;
Gummin, M. A.; Auker, G.; Jerram, P.; Pool, P.; Waltham, N.
2014SoPh..289.2733D Altcode: 2014arXiv1401.2491D; 2014SoPh..tmp...25D
The Interface Region Imaging Spectrograph (IRIS) small explorer
spacecraft provides simultaneous spectra and images of the photosphere,
chromosphere, transition region, and corona with 0.33 - 0.4 arcsec
spatial resolution, two-second temporal resolution, and 1 km
s−1 velocity resolution over a field-of-view of up to
175 arcsec × 175 arcsec. IRIS was launched into a Sun-synchronous
orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a
19-cm UV telescope that feeds a slit-based dual-bandpass imaging
spectrograph. IRIS obtains spectra in passbands from 1332 - 1358 Å,
1389 - 1407 Å, and 2783 - 2834 Å, including bright spectral lines
formed in the chromosphere (Mg II h 2803 Å and Mg II k 2796 Å) and
transition region (C II 1334/1335 Å and Si IV 1394/1403 Å). Slit-jaw
images in four different passbands (C II 1330, Si IV 1400, Mg II k
2796, and Mg II wing 2830 Å) can be taken simultaneously with spectral
rasters that sample regions up to 130 arcsec × 175 arcsec at a variety
of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to
emission from plasma at temperatures between 5000 K and 10 MK and will
advance our understanding of the flow of mass and energy through an
interface region, formed by the chromosphere and transition region,
between the photosphere and corona. This highly structured and dynamic
region not only acts as the conduit of all mass and energy feeding
into the corona and solar wind, it also requires an order of magnitude
more energy to heat than the corona and solar wind combined. The
IRIS investigation includes a strong numerical modeling component
based on advanced radiative-MHD codes to facilitate interpretation of
observations of this complex region. Approximately eight Gbytes of data
(after compression) are acquired by IRIS each day and made available
for unrestricted use within a few days of the observation.

---------------------------------------------------------
Title: The Availability of Higher Level SDO/HMI Data Products
Authors: Scherrer, Philip H.
2014AAS...22421842S Altcode:
The Solar Dynamics Observatory Helioseismic and Magnetic Imager
(SDO/HMI) investigation proposed to generate a set of "high level" data
products. These are data products that require processing and analysis
well beyond the traditional products prepared by Heliophysics mission
teams. That is, these are not simply images nor what the HMI team
calls "Observables" which are e.g. magnetograms or Dopplergrams. The
traditional deliverd data products are often referred to as "Level-1"
data products and are the highest level of processing required by
contract with NASA. The HMI team planned to also produce higher level
products such as flows in the solar interior, solar oscillation mode
frequencies and inversions for interior rotation, magnetic vector
field inversions with disambiguation, derived indices that may have
space-weather applications, et cetera. Most of these products are
now in regular production and a series of recent papers and papers in
progress describe them in detail. This poster is to bring attention
to the availability of these products and describe where and how to
get the needed information to use them for new research objectives.

---------------------------------------------------------
Title: Identifying Potential Markers of the Sun's Giant Convective
Scale
Authors: McIntosh, Scott W.; Wang, Xin; Leamon, Robert J.; Scherrer,
Philip H.
2014ApJ...784L..32M Altcode: 2014arXiv1403.0692M
Line-of-sight magnetograms from the Helioseismic and Magnetic Imager
(HMI) of the Solar Dynamics Observatory (SDO) are analyzed using a
diagnostic known as the magnetic range of influence (MRoI). The MRoI
is a measure of the length over which a photospheric magnetogram
is balanced and so its application gives the user a sense of the
connective length scales in the outer solar atmosphere. The MRoI maps
and histograms inferred from the SDO/HMI magnetograms primarily exhibit
four scales: a scale of a few megameters that can be associated with
granulation, a scale of a few tens of megameters that can be associated
with super-granulation, a scale of many hundreds to thousands of
megameters that can be associated with coronal holes and active regions,
and a hitherto unnoticed scale that ranges from 100 to 250 Mm. We
infer that this final scale is an imprint of the (rotationally driven)
giant convective scale on photospheric magnetism. This scale appears
in MRoI maps as well-defined, spatially distributed concentrations that
we have dubbed "g-nodes." Furthermore, using coronal observations from
the Atmospheric Imaging Assembly on SDO, we see that the vicinity of
these g-nodes appears to be a preferred location for the formation of
extreme-ultraviolet (and likely X-Ray) brightpoints. These observations
and straightforward diagnostics offer the potential of a near real-time
mapping of the Sun's largest convective scale, a scale that possibly
reaches to the very bottom of the convective zone.

---------------------------------------------------------
Title: SDO/HMI Status and Recent Findings
Authors: Scherrer, Philip H.; SDO/HMI Science Team; SDO/JSOC Team
2013SPD....44..153S Altcode:
Calibrated HMI basic observable quantities have been available for
almost 3 years. Higher level standard HMI data products for magnetic
fields and helioseismic derived parameters have been available for
more than a year. This talk will give a brief status update on the
standard products and describe a few groundbreaking findings based on
these products.

---------------------------------------------------------
Title: Using Solar Dynamics Observatory Data in the Classroom to Do
Real Science -- A Community College Astronomy Laboratory Investigation
Authors: Scherrer, Deborah K.; Hildreth, S.; Lee, S.; Dave, T.;
Scherrer, P. H.
2013SPD....44..156S Altcode:
A partnership between Stanford University and Chabot Community College
(Hayward, CA) has developed a series of laboratory exercises using
SDO (AIA, HMI) data, targeted for community college students in an
introductory astronomy lab class. The labs lead students to explore what
SDO can do via online resources and videos. Students investigate their
chosen solar events, generate their own online videos, prepare their
own hypotheses relating to the events, and explore outcomes. Final
assessment should be completed by the end of summer 2013. Should the
labs prove valuable, they may be adapted for high school use.

---------------------------------------------------------
Title: Far-side helioseismic maps: the next generation
Authors: González Hernández, Irene; Lindsey, Charles; Braun,
Douglas C.; Bogart, Richard S.; Scherrer, Philip H.; Hill, Frank
2013JPhCS.440a2029G Altcode:
For more than a decade, far-side seismic maps of medium-to-large active
regions have proven their capability as a space weather forecasting
tool. In the last few years, these maps have started to serve another
purpose: complementing the front side observations that are input to
different solar models. Photospheric flux transport as well as solar
spectral irradiance models have been shown to produce improved results
when incorporating the far-side seismic maps as well as providing
better forecasting. The challenge for the future is twofold: Far-side
seismic monitoring needs to be more sensitive, and it needs to offer
more information. We present here initial steps towards fulfilling
these goals using higher resolution input images, adding extra skips
to the analysis and changing the presentation of the maps.

---------------------------------------------------------
Title: Perturbations in the wave parameters near active regions
Authors: Rabello-Soares, M. C.; Bogart, R. S.; Scherrer, P. H.
2013JPhCS.440a2008R Altcode:
The wave characteristics derived from ring-diagram analysis of HMI
Doppler data in magnetically quiet regions near active regions
are compared with those with no nearby active regions using 5°
patches during 2.5 years of cycle 24 ascending phase. We search for
perturbations that may be associated with propagation of the acoustic
oscillations through the nearby sunspot. We observe significant
variations in the mode parameters and flows. We analyse their dependence
on the direction of the wave propagation. The observed mode dependence
of the variations in mode amplitude, line width and frequency does
not have the same functional form as that observed for the differences
between quiet and active regions.

---------------------------------------------------------
Title: Using Solar Dynamics Observatory Data in the Classroom to
Do Real Science - A Community College Astronomy Laboratory Class
Investigation
Authors: Hildreth, Scott; Lee, Shannon; Dave, Timothy; Scherrer,
Deborah; Scherrer, Philip
2013enss.confE..90H Altcode:
The incredible accessibility of extremely high spatial and temporal
resolution data from the Solar Dynamics Observatory creates an
opportunity for students to do near real-time solar investigations
in an astronomy lab environment. We are developing a short series
of laboratory exercises using SDO (AIA, HMI) data, targeted for
Community College students in an introductory astronomy lab class,
extendable to high school and university students. The labs initially
lead students to explore what SDO can do, online, through existing
SDO video clips taken on specific dates. Students then investigate
solar events using the Heliophysics Events Knowledgebase (HEK),
and make their own online movies of events, to discuss and share
with classmates. Finally, students can investigate specific events
and areas, selecting specific dates, locations, wavelength regions,
and time cadences to create and gather their own SDO datasets for
more detailed investigation. In exploring the Sun using actual data,
students actually do real science. We are in the process of beta testing
the sequence of labs, and are seeking interested community college,
university, and high school astronomy lab teachers who might consider
trying the labs themselves.

---------------------------------------------------------
Title: Approach to Integrate Global-Sun Models of Magnetic Flux
Emergence and Transport for Space Weather Studies
Authors: Mansour, Nagi Nicolas; Wray, A.; Mehrotra, P.; Henney, C.;
arge, N.; Manchester, C.; Godinez, H.; Koller, J.; Kosovichev, A.;
Scherrer, P.; Zhao, J.; Stein, R.; Duvall, T.; Fan, Y.
2013enss.confE.125M Altcode:
The Sun lies at the center of space weather and is the source of its
variability. The primary input to coronal and solar wind models is
the activity of the magnetic field in the solar photosphere. Recent
advancements in solar observations and numerical simulations provide
a basis for developing physics-based models for the dynamics of
the magnetic field from the deep convection zone of the Sun to the
corona with the goal of providing robust near real-time boundary
conditions at the base of space weather forecast models. The goal is
to develop new strategic capabilities that enable characterization
and prediction of the magnetic field structure and flow dynamics of
the Sun by assimilating data from helioseismology and magnetic field
observations into physics-based realistic magnetohydrodynamics (MHD)
simulations. The integration of first-principle modeling of solar
magnetism and flow dynamics with real-time observational data via
advanced data assimilation methods is a new, transformative step in
space weather research and prediction. This approach will substantially
enhance an existing model of magnetic flux distribution and transport
developed by the Air Force Research Lab. The development plan is to use
the Space Weather Modeling Framework (SWMF) to develop Coupled Models
for Emerging flux Simulations (CMES) that couples three existing models:
(1) an MHD formulation with the anelastic approximation to simulate
the deep convection zone (FSAM code), (2) an MHD formulation with
full compressible Navier-Stokes equations and a detailed description
of radiative transfer and thermodynamics to simulate near-surface
convection and the photosphere (Stagger code), and (3) an MHD
formulation with full, compressible Navier-Stokes equations and an
approximate description of radiative transfer and heating to simulate
the corona (Module in BATS-R-US). CMES will enable simulations of the
emergence of magnetic structures from the deep convection zone to the
corona. Finally, a plan will be summarized on the development of a
Flux Emergence Prediction Tool (FEPT) in which helioseismology-derived
data and vector magnetic maps are assimilated into CMES that couples
the dynamics of magnetic flux from the deep interior to the corona.

---------------------------------------------------------
Title: HMI Status and Highlights
Authors: Scherrer, P. H.
2013enss.confE..98S Altcode:
Calibrated HMI basic observable quantities have been available for
almost 2.5 years. Higher level standard HMI data products for magnetic
fields and helioseismic derived parameters have been available for
about a year. This talk will give a brief status update on the standard
products and describe a few findings based on these products.

---------------------------------------------------------
Title: Comparison Between Line-Of-Sight Observables And
Milne-Eddington Inversion Results From HMI: 24- And 12-hour Period
Oscillations
Authors: Couvidat, Sebastien; Liu, Yang; Scherrer, Philip H.; Schou,
Jesper; HMI Team
2013enss.confE..84C Altcode:
Oscillations with 12 and 24 hour periods are visible in sunspots
on line-of-sight (LOS) observables and, to a lesser extent, on
Milne-Eddington (ME) inversion results from the SDO/HMI instrument.Such
oscillations are artifacts produced by the LOS algorithm and ME
inversion procedure, and are not of solar origin. For instance, the LOS
algorithm depends on an Fe I line profile and on HMI filter transmission
profiles to convert the HMI intensities into Doppler velocities and LOS
magnetic-field strengths: one of the issues we encountered is that in
the presence of strong fields the Fe I profile used is inappropriate
and results in errors in the left and right circular polarization
velocity estimates. Here we present some properties of these 12-
and 24-hour period oscillations, and we discuss their origin and the
possibility of improving the LOS algorithm and ME inversion procedure
to reduce their amplitudes.

---------------------------------------------------------
Title: Three 2012 Transits of Venus: From Earth, Jupiter, and Saturn
Authors: Pasachoff, Jay M.; Schneider, G.; Babcock, B. A.; Lu, M.;
Edelman, E.; Reardon, K.; Widemann, T.; Tanga, P.; Dantowitz, R.;
Silverstone, M. D.; Ehrenreich, D.; Vidal-Madjar, A.; Nicholson,
P. D.; Willson, R. C.; Kopp, G. A.; Yurchyshyn, V. B.; Sterling,
A. C.; Scherrer, P. H.; Schou, J.; Golub, L.; McCauley, P.; Reeves, K.
2013AAS...22131506P Altcode:
We observed the 2012 June 6/5 transit seen from Earth (E/ToV),
simultaneously with Venus Express and several other spacecraft
not only to study the Cytherean atmosphere but also to provide an
exoplanet-transit analog. From Haleakala, the whole transit was visible
in coronal skies; among our instruments was one of the world-wide Venus
Twilight Experiment's nine coronagraphs. Venus's atmosphere became
visible before first contact. SacPeak/IBIS provided high-resolution
images at Hα/carbon-dioxide. Big Bear's NST also provided
high-resolution observations of the Cytherean atmosphere and black-drop
evolution. Our liaison with UH's Mees Solar Observatory scientists
provided magneto-optical imaging at calcium and potassium. Solar
Dynamics Observatory's AIA and HMI, and the Solar Optical Telescope
(SOT) and X-ray Telescope (XRT) on Hinode, and total-solar-irradiance
measurements with ACRIMSAT and SORCE/TIM, were used to observe the
event as an exoplanet-transit analog. On September 20, we imaged
Jupiter for 14 Hubble Space Telescope orbits, centered on a 10-hour
ToV visible from Jupiter (J/ToV), as an exoplanet-transit analog in
our own solar system, using Jupiter as an integrating sphere. Imaging
was good, although much work remains to determine if we can detect
the expected 0.01% solar irradiance decrease at Jupiter and the even
slighter differential effect between our violet and near-infrared
filters caused by Venus's atmosphere. We also give a first report on our
currently planned December 21 Cassini UVIS observations of a transit of
Venus from Saturn (S/ToV). Our E/ToV expedition was sponsored by the
Committee for Research and Exploration/National Geographic Society;
supplemented: NASA/AAS's Small Research Grant Program. We thank Rob
Ratkowski, Stan Truitt, Rob Lucas, Aram Friedman, and Eric Pilger
'82 at Haleakala, and Joseph Gangestad '06 at Big Bear for assistance,
and Lockheed Martin Solar and Astrophysics Lab and Hinode science and
operations teams for support for coordinated observations with NASA
satellites. Our J/ToV observations were based on observations made
with HST, operated by AURA, Inc., under NASA contract NAS 5-26555;
these observations are associated with program #13067.

---------------------------------------------------------
Title: The 2012 Transit of Venus for Cytherean Atmospheric Studies
and as an Exoplanet Analog
Authors: Pasachoff, Jay M.; Schneider, G.; Babcock, B. A.; Lu, M.;
Reardon, K. P.; Widemann, T.; Tanga, P.; Dantowitz, R.; Willson,
R.; Kopp, G.; Yurchyshyn, V.; Sterling, A.; Scherrer, P.; Schou, J.;
Golub, L.; Reeves, K.
2012DPS....4450806P Altcode:
We worked to assemble as complete a dataset as possible for the
Cytherean atmosphere in collaboration with Venus Express in situ
and to provide an analog of spectral and total irradiance exoplanet
measurements. From Haleakala, the whole transit was visible in
coronal skies; our B images showed the evolution of the visibility
of Venus's atmosphere and of the black-drop effect, as part of the
Venus Twilight Experiment's 9 coronagraphs distributed worldwide
with BVRI. We imaged the Cytherean atmosphere over two minutes before
first contact, with subarcsecond resolution, with the coronagraph and
a separate refractor. The IBIS imaging spectrometer at Sacramento
Peak Observatory at H-alpha and carbon-dioxide also provided us
high-resolution imaging. The NST of Big Bear Solar Observatory
also provided high-resolution vacuum observations of the Cytherean
atmosphere and black drop evolution. Our liaison with UH's Mees Solar
Observatory scientists provided magneto-optical imaging at calcium
and potassium. Spaceborne observations included the Solar Dynamics
Observatory's AIA and HMI, and the Solar Optical Telescope (SOT)
and X-ray Telescope (XRT) on Hinode, and total-solar-irradiance
measurements with ACRIMSAT and SORCE/TIM, to characterize the
event as an exoplanet-transit analog. Our expedition was sponsored
by the Committee for Research and Exploration/National Geographic
Society. Some of the funds for the carbon-dioxide filter for IBIS were
provided by NASA through AAS's Small Research Grant Program. We thank
Rob Lucas, Aram Friedman, and Eric Pilger '82 for assistance with
Haleakala observing, Rob Ratkowski of Haleakala Amateur Astronomers
for assistance with equipment and with the site, Stan Truitt for the
loan of his Paramount ME, and Steve Bisque/Software Bisque for TheSky
X controller. We thank Joseph Gangestad '06 of Aerospace Corp., a
veteran of our 2004 expedition, for assistance at Big Bear. We thank
the Lockheed Martin Solar and Astrophysics Laboratory and Hinode
science and operations teams for planning and support.

---------------------------------------------------------
Title: Comparison of Line-of-Sight Magnetograms Taken by the Solar
Dynamics Observatory/Helioseismic and Magnetic Imager and Solar and
Heliospheric Observatory/Michelson Doppler Imager
Authors: Liu, Y.; Hoeksema, J. T.; Scherrer, P. H.; Schou, J.;
Couvidat, S.; Bush, R. I.; Duvall, T. L.; Hayashi, K.; Sun, X.;
Zhao, X.
2012SoPh..279..295L Altcode: 2012SoPh..tmp...75L
We compare line-of-sight magnetograms from the Helioseismic and
Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) and
the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric
Observatory (SOHO). The line-of-sight magnetic signal inferred from
the calibrated MDI data is greater than that derived from the HMI data
by a factor of 1.40. This factor varies somewhat with center-to-limb
distance. An upper bound to the random noise for the 1” resolution
HMI 720-second magnetograms is 6.3 Mx cm−2, and 10.2 Mx
cm−2 for the 45-second magnetograms. Virtually no p-mode
leakage is seen in the HMI magnetograms, but it is significant in
the MDI magnetograms. 12-hour and 24-hour periodicities are detected
in strong fields in the HMI magnetograms. The newly calibrated
MDI full-disk magnetograms have been corrected for the zero-point
offset and underestimation of the flux density. The noise is 26.4 Mx
cm−2 for the MDI one-minute full-disk magnetograms and
16.2 Mx cm−2 for the five-minute full-disk magnetograms
observed with four-arcsecond resolution. The variation of the noise over
the Sun's disk found in MDI magnetograms is likely due to the different
optical distortions in the left- and right-circular analyzers, which
allows the granulation and p-mode to leak in as noise. Saturation
sometimes seen in sunspot umbrae in MDI magnetograms is caused by
the low intensity and the limitation of the onboard computation. The
noise in the HMI and MDI line-of-sight magnetic-field synoptic charts
appears to be fairly uniform over the entire map. The noise is 2.3 Mx
cm−2 for HMI charts and 5.0 Mx cm−2 for MDI
charts. No evident periodicity is found in the HMI synoptic charts.

---------------------------------------------------------
Title: Line-of-Sight Observables Algorithms for the Helioseismic
and Magnetic Imager (HMI) Instrument Tested with Interferometric
Bidimensional Spectrometer (IBIS) Observations
Authors: Couvidat, Sébastien; Rajaguru, S. P.; Wachter, Richard;
Sankarasubramanian, K.; Schou, Jesper; Scherrer, Philip H.
2012SoPh..278..217C Altcode:
The Helioseismic and Magnetic Imager (HMI) instrument onboard the
Solar Dynamics Observatory produces line-of-sight (LOS) observables
(Doppler velocity, magnetic-field strength, Fe I line width, line
depth, and continuum intensity) as well as vector magnetic-field maps
at the solar surface. The accuracy of LOS observables is dependent
on the algorithm used to translate a sequence of HMI filtergrams into
the corresponding observables. Using one hour of high-cadence imaging
spectropolarimetric observations of a sunspot in the Fe I line at 6173
Å through the Interferometric Bidimensional Spectrometer installed
at the Dunn Solar Telescope, and the Milne-Eddington inversion of the
corresponding Stokes vectors, we test the accuracy of the observables
algorithm currently implemented in the HMI data-analysis pipeline:
the MDI-like algorithm. In an attempt to improve the accuracy of
HMI observables, we also compare this algorithm to others that may be
implemented in the future: a least-squares fit with a Gaussian profile,
a least-squares fit with a Voigt profile, and the use of second Fourier
coefficients in the MDI-like algorithm.

---------------------------------------------------------
Title: A First Look at Magnetic Field Data Products from SDO/HMI
Authors: Liu, Y.; Scherrer, P. H.; Hoeksema, J. T.; Schou, J.; Bai,
T.; Beck, J. G.; Bobra, M.; Bogart, R. S.; Bush, R. I.; Couvidat,
S.; Hayashi, K.; Kosovichev, A. G.; Larson, T. P.; Rabello-Soares,
C.; Sun, X.; Wachter, R.; Zhao, J.; Zhao, X. P.; Duvall, T. L., Jr.;
DeRosa, M. L.; Schrijver, C. J.; Title, A. M.; Centeno, R.; Tomczyk,
S.; Borrero, J. M.; Norton, A. A.; Barnes, G.; Crouch, A. D.; Leka,
K. D.; Abbett, W. P.; Fisher, G. H.; Welsch, B. T.; Muglach, K.;
Schuck, P. W.; Wiegelmann, T.; Turmon, M.; Linker, J. A.; Mikić,
Z.; Riley, P.; Wu, S. T.
2012ASPC..455..337L Altcode:
The Helioseismic and Magnetic Imager (HMI; Scherrer &amp; Schou 2011)
is one of the three instruments aboard the Solar Dynamics Observatory
(SDO) that was launched on February 11, 2010 from Cape Canaveral,
Florida. The instrument began to acquire science data on March 24. The
regular operations started on May 1. HMI measures the Doppler velocity
and line-of-sight magnetic field in the photosphere at a cadence of
45 seconds, and the vector magnetic field at a 135-second cadence,
with a 4096× 4096 pixels full disk coverage. The vector magnetic
field data is usually averaged over 720 seconds to suppress the p-modes
and increase the signal-to-noise ratio. The spatial sampling is about
0".5 per pixel. HMI observes the Fe i 6173 Å absorption line, which
has a Landé factor of 2.5. These data are further used to produce
higher level data products through the pipeline at the HMI-AIA Joint
Science Operations Center (JSOC) - Science Data Processing (Scherrer et
al. 2011) at Stanford University. In this paper, we briefly describe the
data products, and demonstrate the performance of the HMI instrument. We
conclude that the HMI is working extremely well.

---------------------------------------------------------
Title: Wavelength Dependence of the Helioseismic and Magnetic Imager
(HMI) Instrument onboard the Solar Dynamics Observatory (SDO)
Authors: Couvidat, Sébastien; Schou, Jesper; Shine, Richard A.;
Bush, Rock I.; Miles, John W.; Scherrer, Philip H.; Rairden, Richard L.
2012SoPh..275..285C Altcode: 2011SoPh..tmp..150C; 2011SoPh..tmp..219C; 2011SoPh..tmp...33C;
2011SoPh..tmp..110C
The Helioseismic and Magnetic Imager (HMI) instrument will produce
Doppler-velocity and vector-magnetic-field maps of the solar surface,
whose accuracy is dependent on a thorough knowledge of the transmission
profiles of the components of the HMI optical-filter system. Here we
present a series of wavelength-dependence calibration tests, performed
on the instrument from 2005 onwards, to obtain these profiles. We
obtained the transmittances as a function of wavelength for the tunable
and non-tunable filter elements, as well as the variation of these
transmittances with temperature and the angle of incidence of rays of
light. We also established the presence of fringe patterns produced by
interferences inside the blocking filter and the front window, as well
as a change in transmitted intensity with the tuning position. This
thorough characterization of the HMI-filter system confirmed the very
high quality of the instrument, and showed that its properties are
well within the required specifications to produce superior data with
high spatial and temporal resolution.

---------------------------------------------------------
Title: Implementation and Comparison of Acoustic Travel-Time
Measurement Procedures for the Solar Dynamics Observatory/Helioseismic
and Magnetic Imager Time - Distance Helioseismology Pipeline
Authors: Couvidat, S.; Zhao, J.; Birch, A. C.; Kosovichev, A. G.;
Duvall, T. L.; Parchevsky, K.; Scherrer, P. H.
2012SoPh..275..357C Altcode:
The Helioseismic and Magnetic Imager (HMI) instrument onboard the
Solar Dynamics Observatory (SDO) satellite is designed to produce
high-resolution Doppler-velocity maps of oscillations at the solar
surface with high temporal cadence. To take advantage of these
high-quality oscillation data, a time - distance helioseismology
pipeline (Zhao et al., Solar Phys. submitted, 2010) has been
implemented at the Joint Science Operations Center (JSOC) at Stanford
University. The aim of this pipeline is to generate maps of acoustic
travel times from oscillations on the solar surface, and to infer
subsurface 3D flow velocities and sound-speed perturbations. The wave
travel times are measured from cross-covariances of the observed
solar oscillation signals. For implementation into the pipeline we
have investigated three different travel-time definitions developed in
time - distance helioseismology: a Gabor-wavelet fitting (Kosovichev
and Duvall, SCORE'96: Solar Convection and Oscillations and Their
Relationship, ASSL, Dordrecht, 241, 1997), a minimization relative to a
reference cross-covariance function (Gizon and Birch, Astrophys. J.571,
966, 2002), and a linearized version of the minimization method (Gizon
and Birch, Astrophys. J.614, 472, 2004). Using Doppler-velocity data
from the Michelson Doppler Imager (MDI) instrument onboard SOHO,
we tested and compared these definitions for the mean and difference
travel-time perturbations measured from reciprocal signals. Although
all three procedures return similar travel times in a quiet-Sun region,
the method of Gizon and Birch (Astrophys. J.614, 472, 2004) gives travel
times that are significantly different from the others in a magnetic
(active) region. Thus, for the pipeline implementation we chose the
procedures of Kosovichev and Duvall (SCORE'96: Solar Convection and
Oscillations and Their Relationship, ASSL, Dordrecht, 241, 1997)
and Gizon and Birch (Astrophys. J.571, 966, 2002). We investigated
the relationships among these three travel-time definitions, their
sensitivities to fitting parameters, and estimated the random errors
that they produce.

---------------------------------------------------------
Title: The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics
Observatory (SDO)
Authors: Lemen, James R.; Title, Alan M.; Akin, David J.; Boerner,
Paul F.; Chou, Catherine; Drake, Jerry F.; Duncan, Dexter W.; Edwards,
Christopher G.; Friedlaender, Frank M.; Heyman, Gary F.; Hurlburt, Neal
E.; Katz, Noah L.; Kushner, Gary D.; Levay, Michael; Lindgren, Russell
W.; Mathur, Dnyanesh P.; McFeaters, Edward L.; Mitchell, Sarah; Rehse,
Roger A.; Schrijver, Carolus J.; Springer, Larry A.; Stern, Robert A.;
Tarbell, Theodore D.; Wuelser, Jean-Pierre; Wolfson, C. Jacob; Yanari,
Carl; Bookbinder, Jay A.; Cheimets, Peter N.; Caldwell, David; Deluca,
Edward E.; Gates, Richard; Golub, Leon; Park, Sang; Podgorski, William
A.; Bush, Rock I.; Scherrer, Philip H.; Gummin, Mark A.; Smith, Peter;
Auker, Gary; Jerram, Paul; Pool, Peter; Soufli, Regina; Windt, David
L.; Beardsley, Sarah; Clapp, Matthew; Lang, James; Waltham, Nicholas
2012SoPh..275...17L Altcode: 2011SoPh..tmp..106L; 2011SoPh..tmp..172L; 2011SoPh..tmp..241L;
2011SoPh..tmp..115L
The Atmospheric Imaging Assembly (AIA) provides multiple simultaneous
high-resolution full-disk images of the corona and transition region
up to 0.5 R⊙ above the solar limb with 1.5-arcsec spatial
resolution and 12-second temporal resolution. The AIA consists of four
telescopes that employ normal-incidence, multilayer-coated optics to
provide narrow-band imaging of seven extreme ultraviolet (EUV) band
passes centered on specific lines: Fe XVIII (94 Å), Fe XVII, XXI
(131 Å), Fe IX (171 Å), Fe XII, XXIV (193 Å), Fe XIV (211 Å),
He II (304 Å), and Fe XVI (335 Å). One telescope observes C IV
(near 1600 Å) and the nearby continuum (1700 Å) and has a filter
that observes in the visible to enable coalignment with images from
other telescopes. The temperature diagnostics of the EUV emissions
cover the range from 6×104 K to 2×107 K. The
AIA was launched as a part of NASA's Solar Dynamics Observatory (SDO)
mission on 11 February 2010. AIA will advance our understanding of the
mechanisms of solar variability and of how the Sun's energy is stored
and released into the heliosphere and geospace.

---------------------------------------------------------
Title: Time-Distance Helioseismology Data-Analysis Pipeline for
Helioseismic and Magnetic Imager Onboard Solar Dynamics Observatory
(SDO/HMI) and Its Initial Results
Authors: Zhao, J.; Couvidat, S.; Bogart, R. S.; Parchevsky, K. V.;
Birch, A. C.; Duvall, T. L.; Beck, J. G.; Kosovichev, A. G.; Scherrer,
P. H.
2012SoPh..275..375Z Altcode: 2011SoPh..tmp...86Z; 2011SoPh..tmp..163Z; 2011arXiv1103.4646Z;
2011SoPh..tmp..232Z
The Helioseismic and Magnetic Imager onboard the Solar Dynamics
Observatory (SDO/HMI) provides continuous full-disk observations
of solar oscillations. We develop a data-analysis pipeline based
on the time-distance helioseismology method to measure acoustic
travel times using HMI Doppler-shift observations, and infer solar
interior properties by inverting these measurements. The pipeline
is used for routine production of near-real-time full-disk maps of
subsurface wave-speed perturbations and horizontal flow velocities
for depths ranging from 0 to 20 Mm, every eight hours. In addition,
Carrington synoptic maps for the subsurface properties are made from
these full-disk maps. The pipeline can also be used for selected target
areas and time periods. We explain details of the pipeline organization
and procedures, including processing of the HMI Doppler observations,
measurements of the travel times, inversions, and constructions of the
full-disk and synoptic maps. Some initial results from the pipeline,
including full-disk flow maps, sunspot subsurface flow fields, and
the interior rotation and meridional flow speeds, are presented.

---------------------------------------------------------
Title: Design and Ground Calibration of the Helioseismic and Magnetic
Imager (HMI) Instrument on the Solar Dynamics Observatory (SDO)
Authors: Schou, J.; Scherrer, P. H.; Bush, R. I.; Wachter, R.;
Couvidat, S.; Rabello-Soares, M. C.; Bogart, R. S.; Hoeksema, J. T.;
Liu, Y.; Duvall, T. L.; Akin, D. J.; Allard, B. A.; Miles, J. W.;
Rairden, R.; Shine, R. A.; Tarbell, T. D.; Title, A. M.; Wolfson,
C. J.; Elmore, D. F.; Norton, A. A.; Tomczyk, S.
2012SoPh..275..229S Altcode:
The Helioseismic and Magnetic Imager (HMI) investigation (Solar
Phys. doi:10.1007/s11207-011-9834-2, 2011) will study the solar
interior using helioseismic techniques as well as the magnetic field
near the solar surface. The HMI instrument is part of the Solar
Dynamics Observatory (SDO) that was launched on 11 February 2010. The
instrument is designed to measure the Doppler shift, intensity, and
vector magnetic field at the solar photosphere using the 6173 Å Fe I
absorption line. The instrument consists of a front-window filter, a
telescope, a set of waveplates for polarimetry, an image-stabilization
system, a blocking filter, a five-stage Lyot filter with one tunable
element, two wide-field tunable Michelson interferometers, a pair
of 40962 pixel cameras with independent shutters, and
associated electronics. Each camera takes a full-disk image roughly
every 3.75 seconds giving an overall cadence of 45 seconds for the
Doppler, intensity, and line-of-sight magnetic-field measurements
and a slower cadence for the full vector magnetic field. This article
describes the design of the HMI instrument and provides an overview of
the pre-launch calibration efforts. Overviews of the investigation,
details of the calibrations, data handling, and the science analysis
are provided in accompanying articles.

---------------------------------------------------------
Title: The Helioseismic and Magnetic Imager (HMI) Investigation for
the Solar Dynamics Observatory (SDO)
Authors: Scherrer, P. H.; Schou, J.; Bush, R. I.; Kosovichev, A. G.;
Bogart, R. S.; Hoeksema, J. T.; Liu, Y.; Duvall, T. L.; Zhao, J.;
Title, A. M.; Schrijver, C. J.; Tarbell, T. D.; Tomczyk, S.
2012SoPh..275..207S Altcode:
The Helioseismic and Magnetic Imager (HMI) instrument and investigation
as a part of the NASA Solar Dynamics Observatory (SDO) is designed
to study convection-zone dynamics and the solar dynamo, the origin
and evolution of sunspots, active regions, and complexes of activity,
the sources and drivers of solar magnetic activity and disturbances,
links between the internal processes and dynamics of the corona and
heliosphere, and precursors of solar disturbances for space-weather
forecasts. A brief overview of the instrument, investigation objectives,
and standard data products is presented.

---------------------------------------------------------
Title: Far-side seismic maps with HMI
Authors: Gonzalez Hernandez, I.; Lindsey, C. A.; Bogart, R. S.;
Scherrer, P. H.; Hill, F.
2011AGUFMSH12A..01G Altcode:
Seismic maps of the far side of the Sun have proven their capability
to locate and track medium to large active regions on the non-visible
hemisphere. Waves that travel all the way from the far side to the
front side carry information of the magnetic perturbations that they
encounter. The seismic holography technique makes use of the observation
of waves at the front side of the Sun and compares them to a model to
map areas of strong magnetic field on the far side. Recent improvements
to these maps include a more accurate determination of the location of
the active region, automatic highlighting of candidates, and calibration
in terms of the magnetic field strength. Since the launch of SDO,
the Helioseismic Magnetic Imager(HMI) has been providing maps of the
far-side activity. We discuss here strategies to optimize these far-side
maps as well as how to include extra information (such as realistic
error estimates and area determination) in order to use these maps as
input to irradiance and photospheric flux-transport models. Far-side
direct observations from STEREO will help to reach these goals.

---------------------------------------------------------
Title: Perturbations in the wave parameters near active regions
Authors: Rabello-Soares, M. Cristina; Bogart, Richard S.; Scherrer;
Philip H.
2011sdmi.confE..84R Altcode:
The wave characteristics in magnetically quiet regions with a nearby
active region are compared with those of quiet regions at the
same solar disk positions, but with no nearby active regions. We
search for perturbations in the wave characteristics as the solar
acoustic oscillations are affected as they propagate inside the
nearby sunspot. The wave parameters were derived from ring-diagram
analysis of HMI/SDO data. We find perturbations in several parameters,
specially in the amplitude, width and frequency. The frequency observed
in a five-degree quiet tile seems to be smaller if there is an active
region nearby than if there is not by as much as 6%. We also describe
the level of anisotropy in these perturbations in relation to direction
of the nearby sunspot.

---------------------------------------------------------
Title: Temporal changes in the frequencies of the solar p-mode
oscillations during solar cycle 23
Authors: Rhodes, E. J.; Reiter, J.; Schou, J.; Larson, T.; Scherrer,
P.; Brooks, J.; McFaddin, P.; Miller, B.; Rodriguez, J.; Yoo, J.
2011IAUS..273..389R Altcode:
We present a study of the temporal changes in the sensitivities of the
frequencies of the solar p-mode oscillations to corresponding changes in
the levels of solar activity during Solar Cycle 23. From MDI and GONG++
full-disk Dopplergram three-day time series obtained between 1996 and
2008 we have computed a total of 221 sets of m-averaged power spectra
for spherical harmonic degrees ranging up to 1000. We have then fit
these 284 sets of m-averaged power spectra using our WMLTP fitting
code and both symmetric Lorentzian profiles for the peaks as well as
the asymmetric profile of Nigam and Kosovichev to obtain 568 tables
of p-mode parameters. We then inter-compared these 568 tables, and
we performed linear regression analyses of the differences in p-mode
frequencies, widths, amplitudes, and asymmetries as functions of the
differences in as many as ten different solar activity indices. From the
linear regression analyses that we performed on the frequency difference
data sets, we have discovered a new signature of the frequency shifts
of the p-modes. Specifically, we have discovered that the temporal
shifts of the solar oscillation frequencies are positively correlated
with the changes in solar activity below a limiting frequency. They
then become anti-correlated with the changes in activity for a range of
frequencies before once again becoming positively-correlated with the
activity changes at very high frequencies. We have also discovered
that the two frequencies where the sensitivities of the temporal
frequency shifts change sign also change in phase with the average
level of solar activity.

---------------------------------------------------------
Title: SDO/HMI - The First Year
Authors: Scherrer, Philip H.
2011SPD....42.0901S Altcode: 2011BAAS..43S.0901S
The Solar Dynamics Observatory (SDO) science operations phase began a
year ago. During that time the Helioseismic and Magnetic Imager (HMI)
team has made significant progress in developing calibration and data
processing procedures. The new view of the Sun provided by SDO/HMI
allows direct viewing of dynamic processes both in the interior and
photospheric magnetic fields and brightness features. The extended
team is now spending as much or even more time exploring the Sun than
developing calibration and processing codes. Some highlights of the
former and a quick status of the latter will be presented.

---------------------------------------------------------
Title: Imaging Spectroscopy of a White-Light Solar Flare
Authors: Martínez Oliveros, J. C.; Couvidat, S.; Schou, J.; Krucker,
S.; Lindsey, C.; Hudson, H. S.; Scherrer, P.
2011SoPh..269..269M Altcode: 2011SoPh..tmp....7M; 2010arXiv1012.0344M
We report observations of a white-light solar flare
(SOL2010-06-12T00:57, M2.0) observed by the Helioseismic Magnetic
Imager (HMI) on the Solar Dynamics Observatory (SDO) and the Reuven
Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The HMI data
give us the first space-based high-resolution imaging spectroscopy
of a white-light flare, including continuum, Doppler, and magnetic
signatures for the photospheric Fe I line at 6173.34 Å and its
neighboring continuum. In the impulsive phase of the flare, a bright
white-light kernel appears in each of the two magnetic footpoints. When
the flare occurred, the spectral coverage of the HMI filtergrams (six
equidistant samples spanning ±172 mÅ around nominal line center)
encompassed the line core and the blue continuum sufficiently far from
the core to eliminate significant Doppler crosstalk in the latter, which
is otherwise a possibility for the extreme conditions in a white-light
flare. RHESSI obtained complete hard X-ray and γ-ray spectra (this
was the first γ-ray flare of Cycle 24). The Fe I line appears to be
shifted to the blue during the flare but does not go into emission; the
contrast is nearly constant across the line profile. We did not detect
a seismic wave from this event. The HMI data suggest stepwise changes
of the line-of-sight magnetic field in the white-light footpoints.

---------------------------------------------------------
Title: Temporal changes in the frequencies and widths of the solar
p-mode oscillations
Authors: Rhodes, E. J., Jr.; Reiter, J.; Schou, J.; Larson, T.;
Scherrer, P.; Brooks, J.; McFaddin, P.; Miller, B.; Rodriguez, J.;
Yoo, J.
2011JPhCS.271a2029R Altcode:
We present a study of the temporal changes in the sensitivities of the
frequencies and widths of the solar p-mode oscillations to corresponding
changes in the levels of solar activity during Solar Cycle 23. From MDI
and GONG++ full-disk Dopplergram three-day time series obtained between
1996 and 2008 we have computed a total of 221 sets of m-averaged power
spectra for spherical harmonic degrees ranging up to 1000. We have then
fit these 221 sets of m-averaged power spectra using our WMLTP fitting
code and both symmetric Lorentzian profiles for the peaks as well as
the asymmetric profile of Nigam and Kosovichev to obtain 442 tables
of p-mode parameters. We then inter-compared these 442 tables which
comprise in excess of 5.3 million p-mode parameters, and we performed
linear regression analyses of the differences in p-mode frequencies
and widths as functions of the differences in as many as ten different
solar activity indices. From these linear regression analyses we have
discovered new signatures of the frequency shifts of the p-modes and
a similar, but slightly different, signature of the temporal shifts
in the widths of the oscillations.

---------------------------------------------------------
Title: Access to Solar Dynamics Observatory HMI and AIA Data via
the Joint Science Operations Center (JSOC)
Authors: Scherrer, P. H.; Amezcua, A.; Bogart, R. S.
2010AGUFMSH23C1867S Altcode:
The Solar Dynamics Observatory (SDO) Helioseismic and Magnetic Imager
(HMI) and Atmospheric Imaging Assembly (AIA) instruments have recently
begun regular production of science level standard data products. While
the primary data access for SDO is via the Virtual Solar Observatory
(VSO) system, special data products are only available from the
instrument team web sites. Both instruments share the Joint Science
Operations Center (JSOC) components for instrument operations (the
Instrument Operations Center) and data processing, archiving, and export
(Science Data Processing - SDP) This poster provides an overview of
the JSOC/SDP data access tools and provides examples of using these
tools for typical HMI data browse and export purposes. A description
of the JSOC services to the AIA web site is also provided.

---------------------------------------------------------
Title: Estimating the Energy Flux of Acoustic-Gravity Waves in the
Solar Atmosphere from SDO/HMI Data
Authors: Fleck, B.; Straus, T.; Jefferies, S.; Scherrer, P.
2010AGUFMSH11A1602F Altcode:
Straus et al. (2008, 2009) demonstrated the existence of internal
gravity waves in the solar atmosphere and showed that they are a
key mediator of mechanical energy in the middle/upper photosphere,
transporting even more energy than high-frequency acoustic waves. Here
we repeat this analysis with data from SDO/HMI, which offers several
distinct advantages, which are particularly relevant for the study
of internal gravity waves (which have long periods and small spatial
scales): excellent image stability over long time intervals, high
spatial resolution, large field-of-view, and good temporal cadence.

---------------------------------------------------------
Title: Three Cycles of the Solar Toroidal Magnetic Field and This
Peculiar Minimum
Authors: Lo, L.; Hoeksema, J. T.; Scherrer, P. H.
2010ASPC..428..109L Altcode: 2010arXiv1003.3981L
Thirty-four years of WSO (Wilcox Solar Observatory) and thirteen years
of SOHO/MDI (Michelson Doppler Imager on the Solar and Heliospheric
Observatory) magnetograms have been studied to measure the east-west
inclination angle, indicating the toroidal component of the photospheric
magnetic field. This analysis reveals that the large-scale toroidal
component of the global magnetic field is antisymmetric around the
equator and reverses direction in regions associated with flux from
one solar cycle compared to the next. The toroidal field revealed the
first early signs of Cycle 24 at high latitudes, especially in the
northern hemisphere, appearing as far back as 2003 in the WSO data
and 2004 in MDI. As in previous cycles, the feature moves gradually
equatorward. Cycles overlap and the pattern associated with each
cycle lasts about 17 years. Even though the polar field at the current
solar minimum is significantly lower than the three previous minima,
the toroidal field pattern is similar.

---------------------------------------------------------
Title: Helioseismic and Magnetic Imager Investigation on SDO -
Current Status
Authors: Scherrer, Philip H.; HMI Team
2010AAS...21640204S Altcode: 2010BAAS...41..873S
The Helioseismic and Magnetic Imager (HMI) instrument on the Solar
Dynamics Observatory (SDO) is expected to be providing data on a routine
basis by the time of this meeting. A brief summary of the status of the
several high level data products and of the data access procedures and
rules will be discussed. Current status of the investigation can be
obtained at http://hmi.stanford.edu. Data access information via the
HMI-AIA Joint Science Operations Center - Science Data Processing can
be found at at http://jsoc.stanford.edu. This work was supported
by NASA through contract NAS5-02139 with Stanford University.

---------------------------------------------------------
Title: Improving the Prediction Capability of Seismic Far-Side Maps
Authors: González Hernández, I.; Scherrer, P.; Hill, F.; Lindsey,
C.; Braun, D.
2009ASPC..416...87G Altcode:
Both the Michelson Doppler Imager (MDI) and the Global Oscillation
Network Group (GONG) projects produce daily seismic maps of surface
magnetic activity on the non-visible hemisphere of the Sun. The
technique has proven useful to detect and follow large active regions
before they appear to face the Earth. This work demonstrates an
improvement in the detection capability of the technique by applying
the results of new research. We calibrate the daily far-side maps in
terms of characteristics of the active region, such as total area and
magnetic flux strength, apply a relationship between the strength of
the persistent signal and the success rate to automatically highlight
possible candidates, and remove solar-cycle variations to stabilize
the signal.

---------------------------------------------------------
Title: NetDRMS: A Shared Data Management System for SDO and VSO
Authors: Bogart, Richard S.; Aloise, J. J.; Amezcua, A. B.; Hourclé,
J. A.; Scherrer, P. H.; Spencer, J. L.; Suarez-Sola, F. I.
2009SPD....40.1705B Altcode:
The Joint Science Operations Center of the Solar Dynamic Observatory has
built an integrated Data Record Management System (DRMS) and Storage
Unit Management System (SUMS) to manage the analysis, archiving, and
distribution of the massive amount of data flowing from the AIA and HMI
instruments. Both DRMS and SUMS use the open source PostgreSQL database
to manage the metadata. Locally developed Unix tools and C and Fortran
libraries are used by DRMS and SUMS to manage data storage, retrieval,
and transfer. They also provide an Applications Programming Interface to
the databases. NetDRMS has been designed as an extension of DRMS/SUMS to
simplify the automatic sharing of metadata and transport of image data
among multiple data servers. It uses Slony, an open-source PostgreSQL
replication system, and the DRMS/SUMS API. It has been adopted by the
Virtual Solar Observatory as the mechanism for mirroring of key SDO
data sets for distribution throughout the scientific community. In
this paper we present a description of the architecture and features
of NetDRMS, the mechanisms for data distribution, requirements for
installation and operation, and the current status of the system.

---------------------------------------------------------
Title: Statistical Analysis of the Success Rate of the Far-Side
Seismic Mapping of Active Regions.
Authors: Gonzalez-Hernandez, Irene; Scherrer, P.; Lindsey, C.; Hill,
F.; Braun, D.
2009SPD....40.0707G Altcode:
Seismic maps of the non-visible side of the Sun (far side) have been
used for almost a decade to follow large active regions before they
rotate to face the Earth. Preliminary efforts to quantify the success
rate of the used technique (seismic holography) have been published
with limited data. However, a thorough study is needed to further
understand the limitations of the technique in terms of size and
strength of the active regions detected and to reveal clues as to how
to improve it. We have analyzed three complete years of far-side
seismic maps calculated using both Global Oscillation Newtwork group
(GONG) and Michelson Doppler Imager (MDI) data and matched the far-side
candidates with associated active regions as recorded by the NOAA
database. Here we present the results.

---------------------------------------------------------
Title: Cycle 24 - An Inside Perspective
Authors: Scherrer, Philip H.
2009SPD....40.3501S Altcode:
One of the prime goals for SDO is to increase understanding of the
processes that generate dynamical magnetic disturbances that are the
proximate cause of "space weather." Existing helioseismic series from
GONG and SOHO/MDI cover the full span of cycle 23. One must ask what
can we accomplish with another five years. Solar minimum is a good time
to begin a new set of observations. Due to extreme patience on the part
of the Sun, SDO is scheduled to be in place to allow observations near
the beginning of cycle 24. SDO/HMI should provide modest improvement for
global scale measurements and significant improvement for near surface
studies. This talk will provide a brief overview of what we know about
magnetic fields in the interior and what we hope to learn with SDO.

---------------------------------------------------------
Title: The HMI Magnetic Field Pipeline
Authors: Hoeksema, Jon Todd; Liu, Y.; Schou, J.; Scherrer, P.; HMI
Science Team
2009SPD....40.1701H Altcode:
The Helioseismic and Magnetic Imager (HMI) will provide frequent
full-disk magnetic field data after launch of the Solar Dynamics
Observatory (SDO), currently scheduled for fall 2009. 16 megapixel
line-of-sight magnetograms (Blos) will be recorded every 45 seconds. A
full set of polarized filtergrams needed to determine the vector
magnetic field requires 90 seconds. Quick-look data will be available
within a few minutes of observation. Quick-look space weather and
browse products must have identified users, and the list currently
includes full disk magnetograms, feature identification and movies,
12-minute disambiguated vector fields in active region patches,
time evolution of AR indices, synoptic synchronic frames, potential
and MHD model results, and 1 AU predictions. A more complete set of
definitive science data products will be offered about a day later and
come in three types. "Pipeline” products, such as full disk vector
magnetograms, will be computed for all data on an appropriate cadence. A
larger menu of "On Demand” products, such as Non-Linear Force Free
Field snapshots of an evolving active region, will be produced whenever
a user wants them. Less commonly needed "On Request” products that
require significant project resources, such as a high resolution MHD
simulation of the global corona, will be created subject to availability
of resources. Further information can be found at the SDO Joint Science
Operations Center web page, jsoc.stanford.edu

---------------------------------------------------------
Title: A New Way to Infer Variations of the Seismic Solar Radius
Authors: González Hernández, I.; Scherrer, P.; Hill, F.
2009ApJ...691L..87G Altcode: 2009arXiv0902.1002G; 2009ApJ...691L..87H
We show that the mean phase of waves propagating all the way from
the far side of the Sun to the front side, as measured by seismic
holography, varies with time. The change is highly anticorrelated with
solar cycle activity and is consistent with other recent results on
the variation of the seismic radius of the Sun. The phase change that
we observe corresponds to a few kilometers difference in the seismic
solar radius from solar maximum to solar minimum in agreement with
inferences from global helioseismology studies.

---------------------------------------------------------
Title: Distributing space weather monitoring instruments and
educational materials worldwide for IHY 2007: The AWESOME and
SID project
Authors: Scherrer, Deborah; Cohen, Morris; Hoeksema, Todd; Inan,
Umran; Mitchell, Ray; Scherrer, Philip
2008AdSpR..42.1777S Altcode:
The International Heliophysical Year (IHY) aims to advance our
understanding of the fundamental processes that govern the Sun, Earth,
and heliosphere. The IHY Education and Outreach Program is dedicated to
inspiring the next generation of space and Earth scientists as well as
spreading the knowledge, beauty, and relevance of our solar system to
the people of the world. In our Space Weather Monitor project we deploy
a global network of sensors to high schools and universities to provide
quantitative diagnostics of solar-induced ionospheric disturbances,
thunderstorm intensity, and magnetospheric activity. We bring real
scientific instruments and data in a cost-effective way to students
throughout the world. Instruments meet the objectives of being sensitive
enough to produce research-quality data, yet inexpensive enough for
placement in high schools and universities. The instruments and data
have been shown to be appropriate to, and usable by, high school age
and early university students. Data contributed to the Stanford data
center is openly shared and partnerships between groups in different
nations develop naturally. Students and teachers have direct access
to scientific expertise. The result is a world-wide collaboration of
scientists, teachers, and students to investigate the variability of
the ionosphere. The research-quality AWESOME (Atmospheric Weather
Electromagnetic System of Observation, Modeling, and Education)
instruments have been selected as a participating program by the United
Nations Basic Space Science Initiative (UNBSSI). The IHY Committee
for International Education and Public Outreach has designated the
simpler SID (Sudden Ionospheric Disturbance) monitors to be provided
to teacher/student teams in each of the 192 countries of the world.

---------------------------------------------------------
Title: Development of Time-Distance Helioseismology Data Analysis
Pipeline for SDO/HMI
Authors: Duvall, T. L.; Zhao, J.; Couvidat, S.; Parchevsky, K. V.;
Beck, J.; Kosovichev, A. G.; Scherrer, P. H.
2008AGUSMSP51B..15D Altcode:
The Helioseismic and Magnetic Imager of SDO will provide uninterrupted
4kx4k-pixel Doppler-shift images of the Sun with ~45 sec cadence. These
data will have a unique potential for advancing local helioseismic
diagnostics of the Sun's interior structure and dynamics. They
will help to understanding the basics mechanisms of solar activity
and developing predictive capabilities for the NASA's Living with
a Star Program. Because of the tremendous amount of data the HMI
team is developing a data analysis pipeline, which will provide maps
of subsurface flows and sound-speed distributions inferred from the
Doppler data by the time-distance technique. We discuss the development
plan, methods and algorithms, and present the status of the pipeline,
testing results and examples of the data products.

---------------------------------------------------------
Title: Combining far-side maps from MDI and GONG to improve the
prediction capability
Authors: Gonzalez Hernandez, I.; Scherrer, P.; Lindsey, C.; Braun,
D.; Hill, F.
2008AGUSMSP41A..04G Altcode:
Both the Michaelson Doppler Imager (MDI) and the Global Oscillation
Network Group (GONG) projects produce daily seismic maps of surface
magnetic activity at the non-visible hemisphere the Sun. The technique
has proven useful in order to detect and follow large active regions
before they appear to face the Earth. This work explores the possibility
of improving the detection capability of the technique by combining
the results from both instruments. The research should lead to a better
understanding of the spurious, non persistent seismic signal associated
with the far-side images and better discrimination between solar and
instrumental noise.

---------------------------------------------------------
Title: A Changing Solar Shape
Authors: Kuhn, Jeffrey R.; Emilio, M.; Bush, R.; Scherrer, P.
2007AAS...21012001K Altcode: 2007BAAS...39..245K
The Sun's shape is sensitive to the influence of gravity, rotation, and
local turbulence and magnetic fields in its outer atmosphere. In 1997
the Michelson Doppler Imager (MDI) aboard the Solar and Heliospheric
Observatory (SOHO) allowed a precise measurement of the oblateness from
above the atmosphere. In 2001 this technique was repeated and we report
here on the detection of a time-variable solar shape from these data.

---------------------------------------------------------
Title: Radiative Transfer Effects On Doppler Measurements As Sources
Of Surface Effects In Sunspot Seismology
Authors: Rajaguru, Paul; Sankarasubramanian, K.; Wachter, R.; Scherrer,
P. H.
2007AAS...210.2208R Altcode: 2007BAAS...39..125R
We show that the use of Doppler shifts of Zeeman sensitive spectral
lines to observe waves in sunspots is subject to measurement specific
phase shifts arising from, 1) altered height range of spectral
line formation and the propagating character of p mode waves in
penumbrae, and 2) Zeeman broadening and splitting. We also show that
these phase shifts depend on wave frequencies, strengths and line of
sight inclination of magnetic field, and the polarization state used
for Doppler measurements. We discuss how these phase shifts could
contribute to local helioseismic measurements of 'surface effects'
in sunspot seismology.

---------------------------------------------------------
Title: A Changing Solar Shape
Authors: Emilio, M.; Bush, R. I.; Kuhn, J.; Scherrer, P.
2007ApJ...660L.161E Altcode:
The Sun's shape is sensitive to the influence of gravity, rotation,
and local turbulence and magnetic fields in its outer atmosphere. A
careful measurement of this shape has long been sought to better
understand the solar structure and its change during the 11 yr solar
cycle. Numerous disparate measurements of the solar oblateness or
the fractional difference between equatorial and polar radii have
been difficult to interpret, in part because this quantity is much
smaller than terrestrial atmospheric seeing and most instrumental
noise sources. In 1997 the Michelson Doppler Imager (MDI) aboard
the Solar and Heliospheric Observatory (SOHO) obtained a precise
measurement of the oblateness from above the atmosphere by utilizing
a spacecraft roll procedure to remove instrumental influences. In 2001
this technique was repeated, and we report here on the detection of a
time-variable solar shape from these data. The changing oblateness we
find from 1997 to 2001 is smaller than the apparent discrepancy between
earlier ground-based observations, but is significantly larger than
MDI's astrometric measurement uncertainty. The shape change appears
to be anticorrelated with the observed helioseismic variability. This
fact and our MDI measurements suggest that the outer solar atmosphere
expands nonhomologously during the cycle. It is possible that solar
cycle changes in the turbulent pressure in the outer atmosphere can
account for both the optical limb change and the helioseismic acoustic
global solar shape change.

---------------------------------------------------------
Title: Analytical Models for Cross-Correlation Signal in Time-Distance
Helioseismology
Authors: Nigam, R.; Kosovichev, A. G.; Scherrer, P. H.
2007ApJ...659.1736N Altcode: 2007astro.ph..2499N
In time-distance helioseismology, the time signals (Doppler shifts) at
two points on the solar surface separated by a fixed angular distance
are cross-correlated, and this leads to a wave packet signal. Accurately
measuring the travel times of these wave packets is crucial for
inferring the subsurface properties in the Sun. The observed signal
is quite noisy, and to improve the signal-to-noise ratio and make
the cross-correlation more robust, the temporal oscillation signal is
phase-speed filtered at the two points in order to select waves that
travel a fixed horizontal distance. Hence a new formula to estimate the
travel times is derived in the presence of a phase-speed filter, and it
includes both the radial and horizontal component of the oscillation
displacement signal. It generalizes the previously used Gabor wavelet
that was derived without a phase-speed filter and included only the
radial component of the displacement. This is important since it will be
consistent with the observed cross-correlation that is computed using
a phase-speed filter, and it also accounts for both the components of
the displacement. The new formula depends on the location of the two
points on the solar surface that are being cross-correlated and accounts
for the travel time shifts at different locations on the solar surface.

---------------------------------------------------------
Title: A Note on Saturation Seen in the MDI/SOHO Magnetograms
Authors: Liu, Y.; Norton, A. A.; Scherrer, P. H.
2007SoPh..241..185L Altcode:
A type of saturation is sometimes seen in sunspot umbrae in MDI/SOHO
magnetograms. In this paper, we present the underlying cause of such
saturation. By using a set of MDI circular polarization filtergrams
taken during an MDI line profile campaign observation, we derive
the MDI magnetograms using two different approaches: the on-board
data processing and the ground data processing, respectively. The
algorithms for processing the data are the same, but the former
is limited by a 15-bit lookup table. Saturation is clearly seen in
the magnetogram from the on-board processing simulation, which is
comparable to an observed MDI magnetogram taken one and a half hours
before the campaign data. We analyze the saturated pixels and examine
the on-board numerical calculation method. We conclude that very low
intensity in sunspot umbrae leads to a very low depth of the spectral
line that becomes problematic when limited to the 15-bit on-board
numerical treatment. This 15-bit on-board treatment of the values
is the reason for the saturation seen in sunspot umbrae in the MDI
magnetogram. Although it is possible for a different type of saturation
to occur when the combination of a strong magnetic field and high
velocity moves the spectral line out of the effective sampling range,
this saturation is not observed.

---------------------------------------------------------
Title: Magnetic Field Vector Retrieval With the Helioseismic and
Magnetic Imager
Authors: Borrero, J. M.; Tomczyk, S.; Norton, A.; Darnell, T.; Schou,
J.; Scherrer, P.; Bush, R.; Liu, Y.
2007SoPh..240..177B Altcode: 2006astro.ph.11565B
We investigate the accuracy to which we can retrieve the solar
photospheric magnetic field vector using the Helioseismic and Magnetic
Imager (HMI) that will fly onboard of the Solar Dynamics Observatory by
inverting simulated HMI profiles. The simulated profiles realistically
take into account the effects of the photon noise, limited spectral
resolution, instrumental polarization modulation, solar p modes, and
temporal averaging. The accuracy of the determination of the magnetic
field vector is studied by considering the different operational modes
of the instrument.

---------------------------------------------------------
Title: Radiative Transfer Effects on Doppler Measurements as Sources
of Surface Effects in Sunspot Seismology
Authors: Rajaguru, S. P.; Sankarasubramanian, K.; Wachter, R.;
Scherrer, P. H.
2007ApJ...654L.175R Altcode: 2006astro.ph.11897R
We show that the use of Doppler shifts of Zeeman-sensitive spectral
lines to observe waves in sunspots is subject to measurement-specific
phase shifts arising from (1) the altered height range of spectral line
formation and the propagating character of p-mode waves in penumbrae
and (2) Zeeman broadening and splitting. We also show that these
phase shifts depend on wave frequencies, strengths and line-of-sight
inclinations of magnetic fields, and the polarization state used
for Doppler measurements. We discuss how these phase shifts could
contribute to local helioseismic measurements of “surface effects”
in sunspot seismology.

---------------------------------------------------------
Title: Spectral Line Selection for HMI
Authors: Norton, A. A.; Pietarila Graham, J. D.; Ulrich, R. K.;
Schou, J.; Tomczyk, S.; Liu, Y.; Lites, B. W.; López Ariste, A.;
Bush, R. I.; Socas-Navarro, H.; Scherrer, P. H.
2006ASPC..358..193N Altcode:
We present information on two spectral lines, Fe I 6173 Å and Ni I 6768
Å, that were candidates for use in the Helioseismic and Magnetic Imager
(HMI) instrument. Both Fe I and Ni I profiles have clean continuum and
no blends that threaten performance. The higher Landé factor of Fe
I means its operational velocity range in regions of strong magnetic
field is smaller than for Ne I. Fe I performs better than Ni I for
vector magnetic field retrieval. Inversion results show that Fe I
consistently determines field strength and flux more accurately than
the Ni I line. Inversions show inclination and azimuthal errors are
recovered to ≈2° above 600 Mx/cm2 for Fe I and above
1000 Mx/cm2 for Ni I. The Fe I line was recommended, and
ultimately chosen, for use in HMI.

---------------------------------------------------------
Title: Magnetic Field Vector Retrieval with HMI
Authors: Borrero, J. M.; Tomczyk, S.; Norton, A. A.; Darnell, T.;
Schou, J.; Scherrer, P.; Bush, R. I.; Lui, Y.
2006ASPC..358..144B Altcode:
The Helioseismic and Magnetic Imager (HMI), on board the Solar Dynamics
Observatory (SDO), will begin data acquisition in 2008. It will provide
the first full-disk, high temporal cadence observations of the full
Stokes vector with a 0.5 arcsec pixel size. This will allow for a
continuous monitoring of the Solar magnetic-field vector. HMI data will
advance our understanding of the small- and large-scale magnetic field
evolution, its relation to the solar and global dynamic processes,
coronal field extrapolations, flux emergence, magnetic helicity, and
the nature of the polar magnetic fields. We summarize HMI's expected
operation modes, focusing on the polarization cross-talk induced
by the solar oscillations, and how this affects the magnetic-field
vector determination.

---------------------------------------------------------
Title: Spectral Line Selection for HMI: A Comparison of Fe I 6173
Å and Ni I 6768 Å
Authors: Norton, A. A.; Graham, J. Pietarila; Ulrich, R. K.; Schou,
J.; Tomczyk, S.; Liu, Y.; Lites, B. W.; Ariste, A. López; Bush,
R. I.; Socas-Navarro, H.; Scherrer, P. H.
2006SoPh..239...69N Altcode: 2006SoPh..tmp...88N; 2006astro.ph..8124N
We present a study of two spectral lines, Fe I 6173 Å and Ni I 6768 Å,
that were candidates to be used in the Helioseismic and Magnetic Imager
(HMI) for observing Doppler velocity and the vector magnetic field. The
line profiles were studied using the Mt. Wilson Observatory, the
Advanced Stokes Polarimeter and the Kitt Peak-McMath Pierce telescope
and one-meter Fourier transform spectrometer atlas. Both Fe I and Ni
I profiles have clean continua and no blends that threaten instrument
performance. The Fe I line is 2% deeper, 15% narrower, and has a 6%
smaller equivalent width than the Ni I line. The potential of each
spectral line to recover pre-assigned solar conditions is tested
using a least-squares minimization technique to fit Milne-Eddington
models to tens of thousands of line profiles that have been sampled
at five spectral positions across the line. Overall, the Fe I line
has a better performance than the Ni I line for vector-magnetic-field
retrieval. Specifically, the Fe I line is able to determine field
strength, longitudinal and transverse flux four times more accurately
than the Ni I line in active regions. Inclination and azimuthal angles
can be recovered to ≈2° above 600 Mx cm−2
for Fe I and above 1000 Mx cm−2 for Ni I. Therefore, the
Fe I line better determines the magnetic-field orientation in plage,
whereas both lines provide good orientation determination in penumbrae
and umbrae. We selected the Fe I spectral line for use in HMI due to
its better performance for magnetic diagnostics while not sacrificing
velocity information. The one exception to the better performance of the
Fe I line arises when high field strengths combine with high velocities
to move the spectral line beyond the effective sampling range. The
higher geff of Fe I means that its useful range of velocity
values in regions of strong magnetic field is smaller than Ni I.

---------------------------------------------------------
Title: Quantitative Study of Solar Farside Observations to Predict
Active Regions
Authors: Buder, I.; Scherrer, P. H.
2006AGUFMSH33B0412B Altcode:
Estimates of sunspots on the far side of the Sun have been
obtained for several years with SOHO/MDI and recently with GONG
observations. E.g. http://soi.stanford.edu/data/full_farside/. We
have examined the predictive usefulness of far-side images of regions
within a few days of the East limb by comparing the far-side images
with subsequent magnetograms. We developed a quantitative measure of
success based on the frequency of true positives and false alarms. We
can detect about 75% of strong magnetic regions with a false alarm
rate of less than 20%.

---------------------------------------------------------
Title: VLF Remote -Sensing of the Lower Ionosphere with AWESOME
Receivers: Solar Flares, Lightning-induced Electron Precipitation,
Sudden Ionospheric Disturbances, Sprites, Gravity Waves and Gamma-ray
Flares
Authors: Inan, U. S.; Cohen, M.; Scherrer, P.; Scherrer, D.
2006ihy..workE..66I Altcode:
Stanford University Very Low Frequency (VLF) radio receivers have
been used extensively for remote sensing of the ionosphere and the
magnetosphere. Among the phenomena that can be uniquely measured via
VLF receivers are radio atmospherics, whistlers, electron precipitation,
solar flares, sudden ionospheric disturbances, gravity waves, sprites,
and cosmic gamma-ray flares. With the use of simple square air-core
magnetic loop antennas of a couple of meters in size, the sensitivity of
these instruments allows the measurement of magnetic fields as low as
several tens of femtoTesla per root Hz, in the frequency range of ~300
Hz to 50 kHz. This sensitivity well exceeds that required to detect
any event above the ambient atmospheric noise floor, determined by
the totality of lightning activity on this planet. In recent years,
as cost of production, timing accuracy (due to low cost GPS cards),
and data handling flexibility of the systems has improved, it has
become possible to distribute many of these instruments in the form
of arrays, to perform interferometric and holographic imaging of the
lower ionosphere. These goals can be achieved using the newest version
of the Stanford VLF receiver, known as AWESOME: Atmospheric Weather
Educational System for Observation and Modeling of Electromagnetics. In
the context of the IHY/UNBSS program for 2007, the AWESOME receivers
can be used extensively as part of the United Nations initiative to
place scientific instruments in developing countries. Drawing on the
Stanford experiences from setting up arrays of VLF receivers, including
an interferometer in Alaska, the Holographic Array for Ionospheric and
Lightning research (HAIL) consisting of instruments at 13 different
high schools in mid-western United States, a broader set of ELF/VLF
receivers in Alaska, and various receivers abroad, including in
France, Japan, Greece, Turkey, and India, a global network of ELF/VLF
receivers offer possibilities for a wide range of scientific topics,
as well as serving as a means for educational outreach. Most recently,
AWESOME receivers were placed in several North African countries,
including Tunisia, Algeria, and Morocco. The new AWESOME version is
substantially lower in cost, and easier to set-up and use. Nevertheless,
the receivers offer the same ultimate levels of resolution in time,
sensitivity and dynamic range, as well as ease of handling of data that
is used by researchers conducting cutting edge ionospheric and Space
Weather research. In this context, the placement of these systems at
underdeveloped host countries provides an open-ended potential for
exploration, limited only by the imagination and drive of the users.

---------------------------------------------------------
Title: Farside helioseismic holography: recent advances
Authors: González Hernández, I.; Hill, F.; Lindsey, C.; Braun, D.;
Scherrer, P.; Hanasoge, S. M.
2006ESASP.624E...3G Altcode: 2006soho...18E...3G
No abstract at ADS

---------------------------------------------------------
Title: Success rate of predicting the heliospheric magnetic field
polarity with Michelson Doppler Imager (MDI) synoptic charts
Authors: Zhao, X. P.; Hoeksema, J. T.; Liu, Y.; Scherrer, P. H.
2006JGRA..11110108Z Altcode:
The photospheric and heliospheric magnetic fields have been
continuously observed at the L1 point by the Michelson Doppler Imager
(MDI) on the Solar and Heliospheric Observatory (SOHO) and Wind and
the Advanced Composition Explorer (ACE) spacecraft since 1996. The
combined observations of the photospheric and heliospheric magnetic
fields make it possible to more reliably predict the heliospheric
magnetic field and more accurately estimate the success rate of the
prediction. On the basis of the latitude dependence of the zonal polar
field inferred from high-resolution MDI synoptic charts between 1996
and 2003 we fill in the polar data gaps in the MDI synoptic charts. To
assess the influence of synoptic charts from different data sources
on the prediction of the coronal and heliospheric magnetic fields,
we compare the success rate of the heliospheric magnetic field (HMF)
polarity predicted over 107 Carrington rotations from June 1996 to
June 2004. We used the potential field source surface model and the
synoptic charts from the Kitt Peak National Observatory, MDI, and the
Wilcox Solar Observatory. The mean success rate of the HMF polarity
predicted using MDI synoptic charts over 8 years is 0.862 ± 0.101, the
best among the three photospheric data sources, although the difference
among the three sources is small. This result validates the MDI synoptic
charts in modeling coronal and heliospheric magnetic fields.

---------------------------------------------------------
Title: The Helioseismic and Magnetic Imager for the Solar Dynamics
Observatory
Authors: Rabello-Soares, M. C.; Scherrer, P. H.; Hmi Team
2006IAUJD..17E..30R Altcode:
The Solar Dynamics Observatory (SDO) is the first mission in the NASA
Living With a Star (LWS) Program. SDO is set to launch in August of
2008 and it will be placed into an inclined geosynchronous orbit. SDO is
being designed to help us understand the origin of solar variability and
its impact on the geospace environment. SDO has three instruments: HMI
(Helioseismic and Magnetic Imager), AIA (Atmospheric Imaging Assembly)
and EVE (Extreme Ultraviolet Variability Experiment). The primary goal
of the Helioseismic and Magnetic Imager (HMI) investigation is to study
the origin of solar variability and to characterize and understand the
Sun's interior and the various components of magnetic activity. HMI
makes measurements of the motion of the solar photosphere to study solar
oscillations and measurements of the polarization in a spectral line
to study all three components of the photospheric magnetic field. The
instrument has significant heritage from the Solar and Heliospheric
Observatory (SOHO) Michelson Doppler Imager (MDI) with enhancements
to achieve higher resolution, higher cadence, and the addition of a
second channel to provide full Stokes polarization measurements. In this
presentation, we will give a brief overview of the HMI instrument and
describe its science goals. stabilized 1"-resolution full-disk Doppler
velocity and line-of-sight magnetic flux images every 45 seconds, and
vector-magnetic field maps every 90 seconds. In this presentation ,
we will give a brief overview of the HMI instrument and describe its
science goals.

---------------------------------------------------------
Title: The Sun's Polar Magnetic Flux from 1996-2006 Observed With
SOHO/MDI
Authors: Hoeksema, Jon T.; Benevolenskaya, E. E.; Liu, Y.; Scherrer,
P. H.; Zhao, X.
2006SPD....37.0702H Altcode: 2006BAAS...38..228H
Observations of the Sun's magnetic field using nearly 10 years of
full-disk SOHO/MDI data are used to investigate the net flux and total
flux of the polar regions.The northern pole above 78 degrees changed
polarity in April 2001 (CR 1974), five rotations before the southern
pole (August, 2001, CR 1979). These dates are a little earlier than
those found by Durrant and Wilson (2003): CR 1975 in the north and CR
1981 in the south.Solar cycle changes in the total polar magnetic flux
are more difficult to determine. Most of the polar measurements are
near the noise level due to the extreme reduction in the line-of-sight
component due to projection effects near the limb. Determination of the
total flux is highly sensitive to changes in noise due to the different
MDI observing modes, to systematic errors in the instrument, and to
the exact method of processing the data (e.g. spatial and temporal
averaging). Periodic orientation changes of the SOHO spacecraft
in recent years allow better characterization of the systematic
errors. Observations taken at different inclinations of the solar
rotation axis also help characterize the known errors to provide a
better estimate of the solar polar flux with time.

---------------------------------------------------------
Title: Farside Helioseismic Holography: Recent Advances
Authors: Gonzalez-Hernandez, Irene; Braun, D. C.; Hanasoge, S. M.;
Hill, F.; Lindsey, C. A.; Scherrer, P. H.
2006SPD....37.0502G Altcode: 2006BAAS...38Q.223G
Both MDI and GONG have been calculating partial farside maps for some
time, showing a high degree of agreement in detecting large active
regions within approximately 45 degrees around the antipode of disk
center.Recently, the full-hemisphere capability has been added to the
farside pipelines of both instruments. We show here the capability of
detecting large active regions and tracking them through out the full
farside hemisphere by applying the technique to active region 10808.We
also report on efforts underway to calibrate the farside signal in
terms of equivalent magnetic field, including some preliminary maps
obtained from artificial helioseismic data.

---------------------------------------------------------
Title: Helioseismic and Magnetic Imager for the Solar Dynamics
Observatory
Authors: Scherrer, P. H.; Hoeksema, J. T.; Hmi Team
2006cosp...36.1469S Altcode: 2006cosp.meet.1469S
The primary goal of the Helioseismic and Magnetic Imager HMI
investigation is to study the origin of solar variability and
to characterize and understand the Sun s interior and the various
components of magnetic activity The HMI instrument is part of the Living
With a Star LWS Solar Dynamics Observatory SDO HMI determines the motion
of the solar photosphere to study solar oscillations and measures
the polarization in a spectral line to study all three components of
the photospheric magnetic field This presentation gives an overview
of the science goals the instrument and its expected performance the
science products produced and the ways in which the science community
and public will be able to use HMI data

---------------------------------------------------------
Title: Characteristics of the Sun's polar magnetic flux from 1996-2005
using SOHO/MDI observations
Authors: Benevolenskaya, E. E.; Hoeksema, J. T.; Liu, Y.; Zhao, X.;
Scherrer, P. H.
2005AGUFMSH41A1120B Altcode:
We have studied the Sun's polar magnetic field using nearly 10 years
of full-disk SOHO/MDI data. We have estimated the time of the polar
magnetic field reversals above 78 degrees. The net flux in the southern
cap changed polarity in CR 1979 (August, 2001), five rotations later
than the north (CR 1974; April, 2001). These are just a little earlier
than the times identified by Durrant and Wilson (2003): CR 1981 in
the south and CR 1975 in the north. We also investigate apparent
solar cycle changes in the total magnetic flux observed in the polar
caps. The total flux determination is highly sensitive to changes in
random noise due to the different MDI observing modes, to systematic
errors in the instrument, and to the exact method of processing the
data (e.g. spatial and temporal averaging). This is because nearly all
of the flux measurements are near the noise level due to the extreme
reduction in the line-of-sight component due to projection effects
near the limb. In recent years the SOHO spacecraft has periodically
been rotated and this allows us to better characterize the systematic
errors. Using observations taken when the inclination of the solar
equator provides the best viewing of each pole, we correct for all known
errors to provide the best estimate of the solar polar flux with time.

---------------------------------------------------------
Title: VLF Remote Sensing of the Lower Ionosphere: Solar Flares,
Electron Precipitation, Sudden Ionospheric Disturbances, Sprites,
Gravity Waves and Gamma-ray Flares
Authors: Tan, J. H.; Cohen, M.; Inan, U. S.; Scherrer, P. H.;
Scherrer, D.
2005AGUFMSM33D..03T Altcode:
Stanford University Very Low Frequency (VLF) and Extremely Low Frequency
(ELF) radio receivers have been used extensively for remote sensing
of the ionosphere and the magnetosphere. Among the phenomena that can
be uniquely measured via ELF/VLF receivers are radio atmospherics,
whistlers, electron precipitation, solar flares, sudden ionospheric
disturbances, gravity waves, sprites, and cosmic gamma-ray flares. With
the use of simple square air-core magnetic loop antennas of a couple
of meters in size, the sensitivity of these instruments allows the
measurement of magnetic fields as low as several tens of femtoTesla per
root-Hz, in the frequency range of ~30 Hz to 50 kHz. This sensitivity
well exceeds that required to detect any event above the ambient
atmospheric noise floor, determined by the totality of lightning
activity on the planet. In recent years, as cost of production, timing
accuracy (due to low cost GPS clocks), and data handling flexibility
of the systems has improved, it has become possible to distribute many
of these instruments in the form of arrays, to perform interferometric
and holographic imaging of the lower ionosphere. In the context of
the IHY in 2007, the ELF/VLF receiver can used extensively as part
of the United Nations initiative to place scientific instruments in
developing countries. Stanford University's past experiences setting
up arrays of ELF/VLF receivers include an interferometer in Alaska,
the Holographic Array for Ionospheric and Lightning research (HAIL)
consisting of instruments at 13 different high schools in mid-western
United States, a broader set of ELF/VLF receivers in Alaska, and various
receivers abroad, including in France, Japan, Greece, Turkey, Ireland,
and India. A global network of ELF/VLF receivers offer possibilities
for a wide range of scientific topics, as well as serving as a
means for educational outreach. These goals will be achieved using
the newest version of the Stanford VLF receiver, known as AWESOME:
Atmospheric Weather Educational System for Observation and Modeling
of Electromagnetics. This new version is substantially lower in cost,
and easier to set-up and use. Nevertheless, the receivers offer the same
ultimate levels of resolution in time, sensitivity and dynamic range, as
well as ease of handling of data that is used by researchers conducting
cutting edge ionospheric and magnetospheric research. In this context,
the placement of these systems at underdeveloped host countries provides
an open-ended potential for exploration, limited only by the imagination
and drive of the users. AWESOME monitors can be placed at schools,
or universities, where they will serve the dual purpose of advancing
scientific research, as well as providing a valuable tool for scientific
education. Data collected can be pooled and publicly available to all
the sites, strengthening the potential for both cooperative education
and collaboration on the science between various regions and locations.

---------------------------------------------------------
Title: Magnetic topologies and two-class coronal mass ejections:
a numerical magnetohydrodynamic study
Authors: Liu, W.; Zhao, X. P.; Wu, S. T.; Scherrer, P. H.
2005astro.ph.11023L Altcode:
White-light observations of the solar corona show that there are two
characteristic types of Coronal Mass Ejections (CMEs) in terms of
speed-height profiles: so-called fast CMEs that attain high speeds
low in the corona and slow CMEs that gradually accelerate from low
initial speeds. Low and Zhang (2002) have recently proposed that fast
and slow CMEs result from initial states with magnetic configurations
characterized by normal prominences (NPs) and inverse prominences (IPs),
respectively. To test their theory, we employed a two-dimensional,
time-dependent, resistive magnetohydrodynamic code to simulate the
expulsion of CMEs in these two different prominence environments. Our
numerical simulations demonstrate that (i) a CME-like expulsion is more
readily produced in an NP than in an IP environment, and, (ii) a CME
originating from an NP environment tends to have a higher speed early
in the event than one originating from an IP environment. Magnetic
reconnection plays distinct roles in the two different field
topologies of these two environments to produce their characteristic
CME speed-height profiles. Our numerical simulations support the
proposal of Low and Zhang (2002) although the reconnection development
for the NP associated CME is different from the one sketched in their
theory. Observational implications of our simulations are discussed.

---------------------------------------------------------
Title: Prediction and understanding of the north-south displacement
of the heliospheric current sheet
Authors: Zhao, X. P.; Hoeksema, J. T.; Scherrer, P. H.
2005JGRA..11010101Z Altcode:
On the basis of Wilcox Solar Observatory observations of the
photospheric magnetic field and the potential field-source surface
model, we compare the solid angles occupied by the positive source
surface field with that of the negative. We develop an algorithm
to quantitatively estimate and understand the positive-negative
displacement of the heliospheric current sheet (HCS) about Sun's
magnetic dipole equator and the north-south displacement of the
HCS about the heliographic equator. The north-south HCS displacement
predicted using the algorithm quantitatively agrees with that observed
by Ulysses and Wind in 1994-1995. The predicted positive-negative and
north-south HCS displacement for 362 Carrington rotations between
1976 and 2001 show that in addition to the two long southward HCS
displacement intervals that are consistent with earlier observations
and statistical results, there are several short north-south HCS
displacement intervals in the rising and early declining solar activity
phases. All the positive-negative HCS displacements about the Sun's
magnetic dipole equator determined for the 25 years can be understood
using the positive-negative asymmetry in the characteristics of coronal
holes or open field regions between two hemispheres, such as the area,
field strength, or the outward expansion factor of the coronal holes. To
understand the north-south HCS displacement about the heliographic
equator, the effect of the Sun's magnetic dipole tilt angle relative
to the Sun's rotation axis must be taken into consideration as well.

---------------------------------------------------------
Title: The GONG Farside Project
Authors: Leibacher, J. W.; Braun, D.; González Hernández, I.;
Goodrich, J.; Kholikov, S.; Lindsey, C.; Malanushenko, A.; Scherrer, P.
2005AGUSMSP11B..14L Altcode:
The GONG program is currently providing near-real-time helioseismic
images of the farside of the Sun. The continuous stream of low
resolution images, obtained from the 6 earth based GONG stations, are
merged into a single data series that are the input to the farside
pipeline. In order to validate the farside images, it is crucial
to compare the results obtained from different instruments. We show
comparisons between the farside images provided by the MDI instrument
and the GONG ones. New aditions to the pipeline will allow us to create
full-hemisphere farside images, examples of the latest are shown in
this poster. Our efforts are now concentrated in calibrating the
farside signal so it became a reliable solar activity forecasting
tool. We are also testing single-skip acoustic power holography
at 5-7 mHz as a prospective means of reinforcing the signatures of
active regions crossing the the east and west limb and monitoring
acoustic emission in the neighborhoods of Sun's the poles. This work
utilizes data obtained by the Global Oscillation Network Group (GONG)
Program, managed by the National Solar Observatory, which is operated
by AURA, Inc. under a cooperative agreement with the National Science
Foundation. The data were acquired by instruments operated by the Big
Bear Solar Observatory, High Altitude Observatory, Learmonth Solar
Observatory, Udaipur Solar Observatory, Instituto de Astrofisico de
Canarias, and Cerro Tololo Interamerican Observatory, as well as
the Michaelson Doppler Imager on SoHO, a mission of international
cooperation between ESA and NASA. This work has been supported by the
NASA Living with a Star - Targeted Research and Technology program.

---------------------------------------------------------
Title: The Helioseismic and Magnetic Imager for the Solar Dynamics
Observatory
Authors: Scherrer, P. H.; HMI Team
2005AGUSMSP43A..05S Altcode:
The primary goal of the Helioseismic and Magnetic Imager (HMI)
investigation is to study the origin of solar variability and to
characterize and understand the Sun's interior and the various
components of magnetic activity. The HMI investigation is based on
measurements obtained with the HMI instrument as part of the Solar
Dynamics Observatory (SDO) mission. HMI makes measurements of the motion
of the solar photosphere to study solar oscillations and measurements
of the polarization in a spectral line to study all three components of
the photospheric magnetic field. Here we will give an overview of the
HMI science goals, the HMI instrument and its expected performance, the
science products produced and the ways in which the science community
and public will be able to utilize HMI data.

---------------------------------------------------------
Title: Designing Sudden Ionospheric Disturbance Monitors -- a Unique
Collaboration Between Scientists and Educators
Authors: Scherrer, D.; Mitchell, R.; Clark, W.; Styner, R.; Scherrer,
P.; Inan, U.; Cohen, M.; Tan, J.; Lee, S.; Khanal, S.; Winegarden,
S.; Mortfield, P.
2005AGUSMED12A..05S Altcode:
Funding agencies such as NASA and NSF encourage E/PO programs to
provide local educators with research experience. However, many
researchers have neither the time nor the expertize nor the training
resources to effectively incorporate an educator into their computer-
and numerical-analysis-based research environments. Stanford's
Solar Center has been experimenting with a unique project that teams
community college and high school educators with research groups to
develop a hands-on instrument that the educators's students can,
in turn, use to conduct their own research. With support from the
researchers, the Educators design, develop, and classroom-test a VLF
radio receiver that monitors changes to the Earth's ionosphere caused
by solar activity. The educators bring to the table their knowledge of
classroom needs plus their amateur background in electronics. Stanford's
Electrical Engineering Department's Very Low Frequency Group provides
EE resources and knowledge of ionospheric research. Stanford's Solar
Observatories Group completes the team with their expertize on the
Sun and solar activity. Together, the project team has designed and
developed two forms of monitors: 1) an inexpensive Sudden Ionospheric
Disturbance (SID) monitor that can be produced in quantity and made
available to high schools and community colleges around the nation;
and 2) a research quality SID monitor, nicknamed AWESOME, that can
be placed in selected schools and will return data of sufficient
quality and sensitivity that it can be used both by the students and
for ionospheric research.

---------------------------------------------------------
Title: Designing Data Services for the SDO AIA/HMI Joint Science
Operations Center
Authors: Larsen, R. M.; Bogart, R. S.; Scherrer, P. H.; Schou, J.;
Tian, K. Q.
2005AGUSMSH51B..04L Altcode:
The Joint Science Operations Center (JSOC) is designed to provide data
capture, archive, analysis, and distribution functions for both the
Helioseismic and Magnetic Imager and the Atmospheric Imaging Array
on the Solar Dynamics Observatory. These instruments are notable
for the large quantity of raw data they will generate, more than
doubling the total volume of all existing solar data in the first few
months alone. In addition, the JSOC will be required to handle a larger
component of higher-level data products than most previous missions. The
fundamental concept of the JSOC architecture is that the metadata and
bulk image data are stored separately, not being combined until the time
of use or export. This enables all metadata to be rapidly accessible
through a relational database. It permits flexible organization of the
data into virtual data sets or series, and the use of an abstracted
syntax, such as a URL, for data description and querying. Furthermore,
data organization details dictated by the requirements of efficient mass
storage can be hidden from the user. Multiple classes of access to the
processing and data are envisioned, ranging from production pipeline
modules generating standard mission products to workstation users
analyzing self-contained data products exported from the archive. The
JSOC design provides a rich set of primitives upon which VSO-like
services can be built, and should allow us to provide a unified view
of the data and data services to all classes of users.

---------------------------------------------------------
Title: The Effect of the Differential Rotation of Photospheric
Magnetic Features on Synoptic Frames of the Photospheric Magnetic
Field
Authors: Zhao, X.; Scherrer, P. H.; Hoeksema, J. T.
2004AGUFMSH21B0419Z Altcode:
To model the time-dependent heliosphere we need the instantaneous
global distribution of the photospheric magnetic field. As a proxy for
the instantaneous global distribution of the photospheric magnetic
field at a particular time of interest, the synoptic frame of the
photospheric magnetic field is constructed by inserting into the
associated monthly Carrington map of the photospheric magnetic field
a remapped magnetogram observed as close as possible to the time of
interest. In such a synoptic frame, the observation time of magnetic
features in pixels outside the inserted magnetogram may differ from the
time of the magnetogram by as much as 14 days. During the interval the
magnetic features move significantly due to differential rotation,
though it may be acceptable to neglect the effects of meridian
flow and random walk diffusion. We improve the synoptic frame by
accounting for the differential rotation of the magnetic features in
the synoptic background frame and consider how changes in the boundary
around the inserted magnetogram due to the differential rotation lead
to significant effects on the predicted chromospheric and coronal
structures.

---------------------------------------------------------
Title: On the Constancy of the Solar Diameter. II.
Authors: Kuhn, J. R.; Bush, R. I.; Emilio, M.; Scherrer, P. H.
2004ApJ...613.1241K Altcode:
The Michelson Doppler Imager instrument on board SOHO has operated for
most of a solar cycle. Here we present a careful analysis of solar
astrometric data obtained with it from above the Earth's turbulent
atmosphere. These data yield the most accurate direct constraint on
possible solar radius variations on timescales from minutes to years
and the first accurate determination of the solar radius obtained in
the absence of atmospheric seeing.

---------------------------------------------------------
Title: On the Constancy of the Solar Diameter
Authors: Kuhn, J. R.; Bush, R.; Emilio, M.; Scherrer, P.
2004AAS...204.8801K Altcode: 2004BAAS...36..819K
The solar radius and its variation have now been measured during
most of a solar cycle from the Solar and Heliospheric Observatory,
using the Michelson Doppler Imager. These instruments provide unique
astrometric data from above the Earth's atmosphere. A new analysis
based on MDI data yields a refined measurement of the solar radius
and no evidence of secular or solar cycle size variations.

---------------------------------------------------------
Title: On the constancy of the solar radius
Authors: Kuhn, J.; Bush, R.; Emilio, M.; Scherrer, P.
2004cosp...35.1918K Altcode: 2004cosp.meet.1918K
The MDI experiment aboard SOHO has operated for most of a solar
cycle. From it we have obtained the most sensitive constraints
on possible solar radius variations and changes in the solar limb
darkening function over a solar cycle timescale. Here we describe the
new measurements and their implications for our understanding of the
mechanisms of solar cycle variability.

---------------------------------------------------------
Title: The Stanford Solar Observatory Group E/PO Program
Authors: Scherrer, P. H.
2003AGUFMED41E..03S Altcode:
As PI for the SOHO/MDI and SDO/HMI investigations and a Co-I in the NSF
CISM STC program I have had the opportunity to help in the formulation
and development of a multifaceted education and public outreach
program. Our E/PO effort began with a web page and press relations but
has grown to include the development of an inexpensive spectrometer
with supporting materials, poster development and distribution, and
a series of webcasts in collaboration with NASA. The present program,
with the support of a dedicated E/PO team, includes the development of a
solar planetarium program, and a space weather monitor that can be made
available through traditional distribution methods. In collaboration
with the Stanford Haas Center for Public Service we are also developing
a university course that will teach the essentials of science education
as part of a lifetime commitment to public service. The development of
the Stanford solar E/PO program and involvement of science professionals
in that program will be discussed. (The Michelson Doppler Imager (MDI)
is an instrument on the Joint ESA &amp; NASA Solar and Heliospheric
Observatory (SOHO) mission. The Helioseismic and Magnetic Imager (HMI),
is an instrument on the NASA Solar Dynamics Observatory (SDO) mission
which is under development. The Center for Space Weather Modeling
(CISM) led by Jeff Hughes at Boston University is an NSF Science and
Technology Center.)

---------------------------------------------------------
Title: Effects of magnetic topology on CME kinematic properties
Authors: Liu, Wei; Zhao, Xue Pu; Wu, S. T.; Scherrer, Philip
2003ESASP.535..459L Altcode: 2003iscs.symp..459L
Coronal Mass Ejections (CMEs) exhibit two types of kinematic property:
fast CMEs with high initial speeds and slow CMEs with low initial speeds
but gradual accelerations. To account for this dual character. Low and
Zhang (LZ 2002) proposed that fast and slow CMEs result from initial
states with magnetic configurations characterized by normal and inverse
quiescent prominences, respectively. To test their theory and further
explore the effects of topology on the kinematic properties of CMEs we
employed a self-consistent magnetohydrodynamic (MHD) model [Guo, Wu, et
al.] to simulate the evolution of CMEs respectively in the normal and
inverse prominence environments. The numerical results show that CMEs
originating from a normal prominence environment do have higher initial
speeds than those from an inverse one. In addition, our simulations
demonstrate the distinct roles played by magnetic reconnection in
these two topologically different magnetic environments to produce
the two different CME height-time profiles as suggested by LZ 2002.

---------------------------------------------------------
Title: Optimal Masks for Solar g-Mode Detection
Authors: Wachter, R.; Schou, J.; Kosovichev, A. G.; Scherrer, P. H.
2003ApJ...588.1199W Altcode:
The detection of gravity (g) modes of solar oscillations is important
for probing the physical conditions in the Sun's energy-generating
core. We have developed a new method of spatial masks optimized to
reveal solar g-modes of angular degree l=1-3 and applied it to Michelson
Doppler Imager data in the frequency range of 50-500 μHz. These
masks take into account the horizontal component of g-mode velocity
eigenfunctions and the variations in the level of noise across the
solar disk and adjust for the time-dependent mode projection properties
caused by the inclination of the Sun's axis of rotation. They allow us
to optimize the signal-to-noise ratio in the oscillation power spectra
for potential g-modes of various angular order and degree. The peaks
in the resulting spectra are analyzed in terms of their instrumental
origin, long-term stability, and correspondence to the theoretically
predicted g-mode spectrum. As a consequence of failing to detect
any g-mode candidates, new upper limits for the surface amplitude of
g-modes are obtained. The lowest upper limits in the range of 5-6 mm
s-1 are found for sectorial g-modes (l=m). These limits
are an order of magnitude higher than the theoretical prediction of
Kumar et al. in 1996.

---------------------------------------------------------
Title: The North-South Offset of the Heliospheric Current Sheet
Authors: Zhao, Xuepu; Hoeksema, J. T.; Scherrer, P. H.
2003IAUJD...7E..43Z Altcode:
In situ measurements of the heliospheric magnetic field from the
Ulysses' fast latitude scan and Wind have shown the offset of the
heliospheric current sheet (HCS) southward from the Sun's heliographic
equator during early 1995 (Crooker et al. 1997). This southward offset
of the HCS can be reproduced using the WSO magnetic synoptic chart
and the potential-field source-surface model and has been suggested
to be the cause of the north-south hemispherical asymmetry of the
galactic cosmic ray flux observed by Ulysses (Simpson et al. 1996). We examine the distribution of magnetic polarities on the source
surface obtained using the WSO magnetic observations between 1976 and
2001 and the potential field-source surface model and find that (1)
southward and northward offsets of the HCS occur alternately all over
25 years and each offset lasts for several solar rotations; (2) there
are two long intervals of southward offset of the HCS occurred between
March 1983 and July 1986 and between April 1992 and June 1995; (3)
The north-south offset of the HCS is mainly caused by the north-south
hemispherical asymmetry of the magnetic strength in open field regions
and the orientation of Sun's dipole moment

---------------------------------------------------------
Title: Evolution of Large-scale Coronal Structure with the Solar
Cycle from EUV Data
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.
2002ASPC..277..419B Altcode: 2002sccx.conf..419B
No abstract at ADS

---------------------------------------------------------
Title: Solar cycle in the photosphere and corona
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.
2002ESASP.506..831B Altcode: 2002svco.conf..831B; 2002ESPM...10..831B
EIT/SOHO data in four EUV lines and MDI/SOHO (1996-2002), and soft X-ray
YOHKOH data (1991-2001) are analyzed in the form of coronal synoptic
maps for the investigation of solar cycle variations of the corona
and magnetic field. The evolution of coronal structures is closely
related to sunspot activity, photospheric magnetic field, and topology
of the large-scale magnetic field. The coronal structures visible in
extreme ultraviolet and soft X-rays as extended bright loops, reflect
the non-axisymmetrical magnetic structure of the Sun, changing with the
solar cycle. The long-living coronal structures are related to complexes
of solar activity and display the quasiperiodic behavior (impulses of
coronal activity) with periods of 1.0-1.5 year in the axisymmetrical
distribution of EUV and X-ray fluxes during the current cycle.

---------------------------------------------------------
Title: Vector Magnetic Field Measurement Capabiliity of the
Helioseismic and Magnetic Imager on SDO
Authors: Bush, R.; Scherrer, P.; Schou, J.; Liu, Y.; Tomczyk, S.;
Graham, J.; Norton, A.
2002AGUFMSH52A0464B Altcode:
The Helioseismic and Magnetic Imager (HMI) instrument has been selected
as part of the payload complement of the Solar Dynamics Observatory
Spacecraft. In this poster we describe the observing technique for
measuring solar vector magnetic fields. The expected performance of
the HMI instrument will be discussed including results of modeling
the observing lines and instrument.

---------------------------------------------------------
Title: The Helioseismic and Magnetic Imager for the Solar Dynamics
Observatory
Authors: Scherrer, P. H.
2002AGUFMSH52A0494S Altcode:
The NASA Living With a Star (LWS) Solar Dynamics Observatory (SDO)
mission is now in Phase-A of its development. The instrument complement
has been selected and includes the Helioseismic and Magnetic Imager
(HMI). The primary goal the HMI investigation is to study the origin
of solar variability and to characterize and understand the Sun's
interior and the various components of magnetic activity. HMI will
make measurements of the motion of the solar photosphere to study solar
oscillations and measurements of the polarization in a spectral line to
study all three components of the photospheric magnetic field. HMI will
produce data to determine the interior sources and mechanisms of solar
variability and how the physical processes inside the Sun are related to
surface magnetic field and activity. It also will produce data to enable
estimates of the coronal magnetic field for studies of variability in
the extended solar atmosphere. HMI observations will enable establishing
the relationships between the internal dynamics and magnetic activity
in order to understand solar variability and its effects, leading to
predictive capability, one of the key elements of the Living With a
Star (LWS) program. The broad goals described above will be addressed
in a coordinated investigation in a number of parallel studies. These
segments of the HMI investigation are to observe and understand these
interlinked processes: Convection- zone dynamics and the solar dynamo;
Origin and evolution of sunspots, active regions and complexes of
activity; Sources and drivers of solar activity and disturbances;
Links between the internal processes and dynamics of the corona and
heliosphere; and Precursors of solar disturbances for space-weather
forecasts. All HMI data will be available to all for analysis after only
minutes to days of automated processing. The dedicated efforts of many
in the solar community will be needed to exploit the full potential of
HMI and every effort will be made to make such contributions possible.

---------------------------------------------------------
Title: Solar mean magnetic field variability: A wavelet approach
to Wilcox Solar Observatory and SOHO/Michelson Doppler Imager
observations
Authors: Boberg, Fredrik; Lundstedt, Henrik; Hoeksema, J. Todd;
Scherrer, Philip H.; Liu, Wei
2002JGRA..107.1318B Altcode:
Solar mean magnetic field (SMMF) measurements from the Wilcox
Solar Observatory and with the SOHO/MDI instrument are described and
analyzed. Even though two completely different methods of observation
are used, the two data sets obtained show a strong similarity. Using
continuous wavelet transforms, SMMF variability is found at a number
of temporal scales. Detected SMMF signals with a 1-2 year period are
considered to be linked to variations in the internal rotation of the
Sun. Intermediate SMMF oscillations with a period of 80-200 days are
probably connected to the evolution of large active regions. We also
find evidence for 90 min variations with coronal mass ejections as a
suggested origin.

---------------------------------------------------------
Title: A new method for measuring frequencies and splittings of
high-degree modes
Authors: Reiter, Johann; Rhodes, E. J., Jr.; Kosovichev, A. G.; Schou,
J.; Scherrer, P. H.
2002ESASP.508...91R Altcode: 2002soho...11...91R
A novel peak-bagging method is presented that operates by fitting a
theoretical profile (symmetric or asymmetric) to the separate peaks of
each multiplet within each unaveraged power spectrum. This new approach
allows a separate frequency, width, and amplitude to be obtained for
each m value at each value of l, n. Hence, the frequency splittings
due to solar rotation for each multiplet can be measured directly. We
present some of our initial results obtained with this new method
in the range 45 &lt;= l &lt;= 300, ν &lt;= 7 mHz when applied to
data from the Michelson Doppler Imager (MDI) onboard the Solar and
Heliospheric Observatory (SOHO). Also discussed are some instrumental
and methodological problems of high-degree mode measurements.

---------------------------------------------------------
Title: Effect of line asymmetry on determination of high-degree
mode frequencies
Authors: Reiter, Johann; Rhodes, E. J., Jr.; Kosovichev, A. G.; Schou,
J.; Scherrer, P. H.
2002ESASP.508...87R Altcode: 2002soho...11...87R
Accurate measurements of frequencies of high-degree p-modes are
important for diagnostics of the structure and dynamics of the
upper convective boundary layer, and understanding the nature of
the solar-cycle variations detected in low- and medium-degree mode
frequencies. Neglecting line asymmetry in the peak-bagging approach
may lead to systematic errors in the determination of the mode
characteristics and, hence, may affect the results of inversions. Here
we demonstrate how the p-mode frequencies are systematically changed in
the range of l &lt;= 1000, ν &lt;= 7mHz when line asymmetry is taken
into account in the fitting of the spectral power peaks. The results
reported are based upon spectra that were created from observations
obtained from the MDI Full-Disk Program during the 1996 SOHO/MDI
Dynamics Run.

---------------------------------------------------------
Title: Large-Scale Solar Coronal Structures in Soft X-Rays and Their
Relationship to the Magnetic Flux
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Lemen, J. R.;
Scherrer, P. H.; Slater, G. L.
2002ApJ...571L.181B Altcode:
We have investigated the relationship between magnetic activity
and coronal structures using soft X-ray data from the Yohkoh soft
X-ray telescope and magnetic field data from the Kitt Peak Solar
Observatory for the period of 1991-2001 and EUV data from the Solar
and Heliospheric Observatory EUV Imaging Telescope for 1996-2001. The
data are reduced to Carrington synoptic maps, which reveal two types of
migrating structures of coronal activity at low and high latitudes in
the time-latitudinal distribution. The low-latitude coronal structures,
migrating equatorward, correspond to photospheric sunspot activity,
and the high-latitude structures migrating toward the poles reflect
polar activity of the Sun. We present the following new results:1. The
migrating high-latitude coronal magnetic structures are revealed in the
soft X-ray data as complete bright giant loops connecting the magnetic
field of the following part of active regions with the polar field. They
appear during the rising phase and maximum of the solar cycle and show
quasi-periodic impulsive variations with a 1-1.5 yr period.2. The soft
X-ray intensity of these loops has a strong power-law correlation with
the photospheric magnetic flux. The power-law index, which on average
is close to 2, shows variations with the solar cycle: it is higher
for the period of the declining phase and minimum of solar activity
than for the rising phase and maximum.

---------------------------------------------------------
Title: Large-scale coronal structures in EUV and soft X-rays in
solar cycle 23
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.;
Lemen, J. R.; Slater, G. L.
2002ESASP.508..367B Altcode: 2002soho...11..367B
We have analyzed the EIT/SOHO data in four EUV lines (171 Å, 195 Å,
284 Å and 304 Å) and soft X-ray YOHKOH data in two filters (AlMg and
Al) in the form of coronal synoptic maps for the period 1996 - 2001
yrs. Two types of the bright structures have been detected in EUV in
the axisymmetrically averaged synoptic maps. The structures of the first
type migrate equatorward as the solar cycle progresses. They are related
to complexes of sunspot activity and display the "butterfly"-type
distribution. The structures of the second type migrate polarward
and are associated with footpoints of giant coronal loops, which
connect the polar regions and the following parts of the active
complexes. These structures of coronal activity are also pronounced in
the soft X-ray maps. However, the whole structure of the giant polar
loops is visible in X-rays, and reveals connections to the low-latitude
coronal structures. The relationship between the soft X-rays emission
and the photospheric magnetic flux obtained from SOHO/MDI and Kitt
Peak Solar Observatory has been investigated. It has been found that
the relationship depends on the phase of the solar cycle. We discuss
the role of the magnetic flux in the formation and evolution of the
stable coronal structures during the rising phase of cycle 23.

---------------------------------------------------------
Title: Optimal masks for g-mode detection in MIDI velocity data
Authors: Wachter, R.; Schou, J.; Kosovichev, A.; Scherrer, P. H.
2002ESASP.508..115W Altcode: 2002soho...11..115W
We are applying spatial masks to MDI velocity data that are optimized
for revealing g-modes in the frequency range 50 through 500 μHz. These
masks take into account the horizontal component of g-mode velocity
eigenfunctions as well as the time dependent mode projection properties
due to the changing solar B angle, and the varying noise level across
the solar disk. The solar noise, which is likely to be caused by
supergranulation in this frequency range is assumed to be uniformly
distributed over the solar surface, consisting of a dominant horizontal
component and a small radial component. The resulting time series are
examined for possible g-mode candidates and new upper limits for the
surface amplitude of g-modes are obtained.

---------------------------------------------------------
Title: Optimal masks for g-mode detection in MDI velocity data
Authors: Wachter, R.; Schou, J.; Kosovichev, A.; Scherrer, P. H.;
Phoebus Team
2002AAS...200.0412W Altcode: 2002BAAS...34..645W
We are applying spatial masks for MDI velocity data that are optimized
for revealing g-modes in the frequency range 50 through 500 μ
Hz. These masks take into account the horizontal component of g-mode
velocity eigenfunctions as well as the time dependent mode projection
properties due to the changing solar B angle, and the varying noise
level across the solar disk. The solar noise, which is likely to be
caused by supergranulation in this frequency range is assumed to be
uniformly distributed over the solar surface, consisting of a dominant
horizontal component and a smaller radial component. The optimal masks
are applied to the image and the resulting time series are examined
for possible g-mode candidates. Because no mode peak has been detected,
firm upper limits for the surface visibility of individual low degree
modes can be given.

---------------------------------------------------------
Title: Effects of Topology on CME Kinematic Properties
Authors: Liu, W.; Zhao, X. P.; Wu, S. T.; Scherrer, P. H.
2002AAS...200.3602L Altcode: 2002BAAS...34Q.693L
Coronal Mass Ejections (CMEs) exhibit two types of kinematic property:
fast CMEs with high initial speeds and slow CMEs with low initial speeds
but gradual accelerations. Efforts have been made for years to probe
the underlying physics responsible for this dual character. Within
these efforts, magnetic topology has gained much attention. Low and
Zhang (ApJ, 564, L53, 2002) proposed that fast or slow CMEs result from
initial states with magnetic configurations characterized by the normal
or inverse quiescent prominences, respectively. To test their theory
and further explore the effects of topology on kinematic properties
of CMEs, we employed a 2-D, axisymmetric, resistive MHD model to
simulate the evolution of CMEs in the normal and inverse prominence
environments, respectively. The numerical results show that the CMEs
originating from a normal prominence environment do have higher initial
speeds than those from an inverse one. In addition, our simulations
demonstrate the distinct roles played by magnetic reconnection in
these two topologically different magnetic environments to produce
the two different CME height-time profiles as suggested by Low and
Zhang. The implication of the results and discussion on future work
are described. SOHO is a project of international cooperation between
ESA and NASA.

---------------------------------------------------------
Title: The Helioseismic and Magnetic Imager for the Solar Dynamics
Observatory
Authors: Scherrer, P. H.; SDO/HMI Team
2002AAS...200.5604S Altcode: 2002BAAS...34..735S
The Solar Dynamics Observatory, the first mission of the Living
With a Star program, will provide a new look at the solar interior,
photospheric magnetic fields, and the atmosphere. One of the high
priority goals for SDO is to develop new observations and analysis
tools to better understand the origin of solar variability and its
impact the geospace environment. The HMI instrument as proposed by a
consortium led by Stanford University will provide the solar interior
and magnetic field observations necessary to meet the goals of SDO.

---------------------------------------------------------
Title: On Formation of the Sigmoidal Structure in Solar Active Region
NOAA 8100
Authors: Liu, Y.; Zhao, X. P.; Hoeksema, J. T.; Scherrer, P. H.;
Wang, J.; Yan, Y.
2002SoPh..206..333L Altcode:
Using soft X-ray images taken by the Soft X-ray Telescope on board
Yohkoh, line-of-sight magnetograms taken by SOHO/MDI and vector
magnetograms taken at Beijing Astronomical Observatory, we have
studied the formation of the sigmoidal structure in active region NOAA
8100 on 3-4 November 1997. The sigmoidal structure appeared after
the occurrences of a series of flares accompanied by new magnetic
flux emergence. This implies that reconnection may play a role in
formation of this sigmoid structure. We calculated the self-helicity
(twist) and mutual helicity of the active region before and after the
formation of the sigmoidal structure and found that the mutual helicity
decreased. The twist of the sigmoidal structure was higher than the
twist of the emerging magnetic flux and exceeded the critical twist for
kink in stability. This result suggests that the reconnection increased
the twist of magnetic flux tubes by converting mutual helicity to
self-helicity, supporting the previous studies by Berger (1998, 1999).

---------------------------------------------------------
Title: Coronal Patterns of Activity from Yohkoh and SOHO/EIT Data
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.;
Lemen, J. R.; Slater, G. L.
2002mwoc.conf..329B Altcode:
We have studied the evolution of large-scale coronal structures using
soft X-ray data from YOHKOH and EUV data from SOHO/EIT during the
rising phase of the current solar cycle 23, and compared with the
evolution of the photospheric magnetic field. During this period the
distribution of the coronal structures generally reflects the evolution
of the magnetic fields. However, the data from EIT and YOHKOH reveal
large-scale magnetic connections in the corona which probably play
significant role in the solar cycle. In particular, we have found that
coronal structures such as high-latitude giant loops may be important
for the topological evolution of magnetic structures during the solar
cycle and for polar magnetic field reversals. We discuss possible
mechanisms of the polar magnetic field reversals and their relations
to the observed coronal structures.

---------------------------------------------------------
Title: Solar Coronal Activity and Evolution of the Magnetic Field
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.
2002stma.conf...27B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Active longitudes and coronal structures during the rising
phase of the solar cycle
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.
2002AdSpR..29..389B Altcode:
The longitudinal structure of the solar corona has been investigated
during the transition period between solar cycles 22 and 23 and at the
beginning of the current cycle 23 using the SOHO/EIT data obtained
in 171 Å, 195 Å, 284 Å and 304 Å EUV lines. The EIT images
were transformed into synoptic maps for each of the spectral lines,
and for the 195Å/171Å line ratio, which is an index of the coronal
temperature. The synoptic maps reveal stable longitudinal structures in
the coronal intensities and temperature, that are related to large-scale
magnetic field structures. We discuss the relation between the coronal
and photospheric magnetic structures obtained from the SOHO and Kitt
Peak Solar Observatory data, and compare the rotation rates of these
structures with the rotation profile of the solar interior in order
to determine the possible origin of the coronal structures.

---------------------------------------------------------
Title: The solar interior
Authors: Gough, D. O.; Scherrer, P. H.
2002css1.book.1035G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Local-area helioseismology as a diagnostic tool for solar
variability
Authors: Kosovichev, A. G.; Duvall, T. L.; Birch, A. C.; Gizon, L.;
Scherrer, P. H.; Zhao, Junwei
2002AdSpR..29.1899K Altcode:
Dynamical and thermal variations of the internal structure of the Sun
can affect the energy flow and result in variations in irradiance
at the surface. Studying variations in the interior is crucial for
understanding the mechanisms of the irradiance variations. "Global"
helioseismology based on analysis of normal mode frequencies, has helped
to reveal radial and latitudinal variations of the solar structure
and dynamics associated with the solar cycle in the deep interior. A
new technique, - "local-area" helioseismology or heliotomography,
offers additional potentially important diagnostics by providing
three-dimensional maps of the sound speed and flows in the upper
convection zone. These diagnostics are based on inversion of travel
times of acoustic waves which propagate between different points on the
solar surface through the interior. The most significant variations
in the thermodynamic structure found by this method are associated
with sunspots and complexes of solar activity. The inversion results
provide evidence for areas of higher sound speed beneath sunspot regions
located at depths of 4-20 Mm, which may be due to accumulated heat or
magnetic field concentrations. However, the physics of these structures
is not yet understood. Heliotomography also provides information about
large-scale stable longitudinal structures in the solar interior,
which can be used in irradiance models. This new diagnostic tool for
solar variability is currently under development. It will require both
a substantial theoretical and modeling effort and high-resolution
data to develop new capabilities for understanding mechanisms of
solar variability.

---------------------------------------------------------
Title: The Largest Active Region of the Solar Cycle
Authors: Kosovichev, A. G.; Bush, R. I.; Duvall, T. L.; Scherrer, P. H.
2001AGUFMSH11C0730K Altcode:
The largest and most active sunspot region of the current solar
cycle (known as AR 9393) was observed by the MDI instrument on SOHO
continuously during three solar rotations in March-May 2001. On April
2 this active region produced the largest solar flare of the last 25
years. By using time-distance helioseismology we have investigated
the development of the active region in the solar interior during that
period starting from the processes of emergence. We present tomographic
images of the sound-speed structures associated with this active region
up to 100 Mm below the solar surface, and discuss their relation to
the evolution of the surface magnetic field.

---------------------------------------------------------
Title: Solar Coronal Structures in Extreme Ultraviolet and Soft
X-rays and Their Relation to Magnetic Flux
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Lemen, J. R.;
Scherrer, P. H.; Slater, G. L.
2001AGUFMSH11C0720B Altcode:
The large-scale coronal structures are ultimately related to internal
magnetic fields and thus provide important information about the solar
dynamo. We have investigated the relationship between magnetic activity
and coronal structures using EUV data from SOHO/EIT and X-ray data
from Yohkoh/SXT, and magnetic field data from Kitt Peak and Wilcox
Solar Observatories for the period 1996-2000 years. We discuss the
non-uniform distribution of coronal heating and its connection with
long-lived complexes of solar activity during the current cycle. EUV
images reveal two sets of migrating structures of coronal activity
in the time-latitudinal distribution of the EUV intensity in 171A,
195A, 284A and 304A EIT wavelength channels. The low-latitude coronal
structures, migrating equatorward, correspond to photospheric sunspot
activity, and the high-latitude structures migrating towards the poles
reflect polar activity of the sun. The polar branches are cooler then
the equatorial branches. This is reflected in the time-latitudinal
distribution of the soft X-rays in two filters (Al and AlMg). We
discuss the physical properties and nature of these structures of
coronal activity and their role in the solar cycle.

---------------------------------------------------------
Title: Observed and Predicted Ratios of the Horizontal and Vertical
Components of the Solar p-Mode Velocity Eigenfunctions
Authors: Rhodes, Edward J., Jr.; Reiter, Johann; Schou, Jesper;
Kosovichev, Alexander G.; Scherrer, Philip H.
2001ApJ...561.1127R Altcode:
We present evidence that the observed ratios of the horizontal
and vertical components of the solar intermediate-degree p-mode
velocity eigenfunctions closely match theoretical predictions of
these ratios. This evidence comes from estimates of the observed
eigenfunction component ratios that were obtained from the fitting
of the p-mode oscillation peaks in low- and intermediate-degree
(l&lt;=200) m-averaged power spectra computed from two different
60.75 day time series of Global Oscillation Network Group (GONG)
project Dopplergrams obtained in late 1996 and early 1998. These fits
were carried out using a peak-fitting method in which we fitted each
observed p-mode multiplet with a model profile that included both the
target mode and its six nearest spatial sidelobes and which incorporated
the effects of the incomplete observational time series through the
convolution of the fitted profiles with the temporal window functions,
which were computed using the two actual GONG observing histories. The
fitted profile also included the effects of the spatial leakage of
the modes of differing degrees into the target spectrum through the
use of different sets of m-averaged spatial leakage matrices. In
order to study the sensitivity of the estimated component ratios to
the details of the computation of the m-averaged power spectra and of
the image-masking schemes employed by the GONG project, we generated
a total of 22 different sets of modal fits. We found that the best
agreement between the predicted and inferred ratios came from the use
of unweighted averaged power spectra that were computed using so-called
n-averaged frequency-splitting coefficients, which had been computed
by cross-correlating the 2l+1 zonal, tesseral, and sectoral power
spectra at each l over a wide range of frequencies. This comparison
yielded a total of 1906 pairs of predicted ct,theory and
fitted ct,fit eigenfunction component ratios. A linear
regression analysis of these pairs of ratios resulted in the following
regression equation: ct,fit=(0.0088+/-0.0013)+(0.9940+/-
0.0044)ct,theory. The resulting correlation coefficient
was 0.9817. This agreement between the predicted and inferred ratios
suggests that the predicted ratios should be used in the fitting of
high-degree power spectra where the ratios cannot be inferred because
of the blending together of individual modal peaks into broad ridges
of power.

---------------------------------------------------------
Title: Time-distance helioseismology and the Solar Orbiter mission
Authors: Gizon, L.; Birch, A. C.; Bush, R. I.; Duvall, T. L., Jr.;
Kosovichev, A. G.; Scherrer, P. H.; Zhao, Junwei
2001ESASP.493..227G Altcode: 2001sefs.work..227G
No abstract at ADS

---------------------------------------------------------
Title: Detection of High-Latitude Waves of Solar Coronal Activity in
Extreme-Ultraviolet Data from the Solar and Heliospheric Observatory
EUV Imaging Telescope
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.
2001ApJ...554L.107B Altcode:
We present the results of an investigation of EUV coronal structures
in 1996-2000 using the Solar and Heliospheric Observatory EIT data
in 171, 195, 284, and 304 Å lines. During this period, poleward-
and equatorward-migrating waves of solar activity have been found
in axisymmetrical distributions of EUV intensity in all four
lines. In the axisymmetrical distribution of the ratio of 195 Å
to 171 Å intensities, which is a proxy of coronal temperature from
1×106 to 2×106 K, the polar branches are less
prominent. The high-latitude activity waves are caused by giant coronal
magnetic loops connecting the polar magnetic field (formed during the
preceding solar cycle) with the magnetic field of the “following”
parts of active regions that emerged during the rising phase of the
current cycle. We suggest that these coronal loops play an important
role in the topological evolution of the magnetic structure of the
Sun during the solar cycle.

---------------------------------------------------------
Title: Polar Activity Wave in the Solar Corona
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.
2001AGUSM..SP61A05B Altcode:
We present the results of investigation of EUV coronal structures in
1996-2000 using SOHO/EIT data in 171A, 195A, 284A and 304A. During
this period polarward and equatorward migrating waves of activity
have been found in axysymmetrical distributions of EUV intensity in
all four lines. In the ratio of 195A and 171A intensities, which is
a proxy of coronal temperature from 1 MK to 2 MK, the polar branch
is not present. We discuss the physical nature of the polar wave
of activity and conclude that it is related to dense plasma loops
which are cooler then the loops related to the equatorward migrating
wave. The latter reflects coronal structures connected with active
regions and complexies of solar activity. The polar activity wave
is caused by reconnection between the polar magnetic field and the
magnetic field of `following' parts of active regions, and, probably,
plays an important role in the solar cycle.

---------------------------------------------------------
Title: Are the Signals in the Sun's Mean Magnetic Field Associated
With Coronal Mass Ejections?
Authors: Liu, W.; Liu, Y.; Zhao, X.; Scherrer, P.
2001AGUSM..SH41A06L Altcode:
A study on time-frequency variability of the solar mean magnetic field
(SMMF) using wavelet analysis is presented. The SMMF data of Michelson
Doppler Imager (MDI) contain an offset most likely introduced by the
random error of the exposure time of MDI. Without the offset correction,
the peaks of wavelet power spectra for the full-disk SMMF time series
coincide with the onset of coronal mass ejections. It has thus been
suggested that the peak of wavelet power spectra is associated with
coronal mass ejections [Boberg and Lundstedt 2000]. To localize the
source of the peak, the full solar disk has been divided into four
quadrants. It turns out unexpectedly that the time series for each
quadrant closely resembles that of the full-disk series. In addition,
all the five series are nearly in phase. On the other hand, the peaks
of wavelet power spectra that coincide with coronal mass ejections
disappear for the full-disk SMMF series obtained after the offset
correction, suggesting that the signal actually occurs in the offset
series. These results give rise to the question -- what is the cause
of the signals detected in the offset series by the wavelet technique?

---------------------------------------------------------
Title: Helioseismology - What is Next?
Authors: Scherrer, P. H.; Fleck, B.; Ulrich, R. K.
2001AGUSM..SP22A09S Altcode:
The helioseismology instruments on SOHO have produced a rich set of
new insights into the solar interior. Combined with GONG and other
ground-based networks these instruments have, for the most part, met the
goals set for them. These instruments have demonstrated the usefulness
of helioseismic techniques for imaging solar interior structure and
motions but do not have all the capabilities necessary to fully exploit
the method. Future mission plans call for pushing helioseismic imaging
to regions nearer the surface, to higher latitudes, and deeper into the
interior. The capabilities of the planned or possible instruments on the
Solar Dynamics Observatory, Solar Orbiter, and Farside/Safari missions
will enable these presently inaccessible domains to be exploited.

---------------------------------------------------------
Title: Challenges in High-Degree Helioseismology
Authors: Rhodes, E. J.; Reiter, J.; Schou, J.; Kosovichev, A. G.;
Scherrer, P. H.
2001AGUSM..SP21C06R Altcode:
Some of the most exciting results that the field of helioseismology
has provided in recent years have come from numerical inversions of
different properties of the solar p-mode oscillations. Such inversions
have been primarily of three types: 1) structural inversions which
have employed tables of the frequencies of various p-modes and
their associated uncertainties to infer different thermodynamic
properties of the solar interior as functions of radius and latitude,
2) rotational inversions which have employed tables of the frequency
splittings of the modes of different azimuthal order to measure the
internal angular velocity as functions of radius and latitude, and 3)
horizontal flow inversions which have employed sets of frequencies
of the rings that are observed in three-dimensional power spectra to
infer sub-photospheric horizontal flow vectors as functions of depth,
latitude and longitude. Unfortunately, the vast majority of such
inversions have only included frequencies or frequency splittings
of the low- and the intermediate-degree oscillations. Furthermore,
the horizontal flow inversions have been somewhat limited by the
difficulties in accurately fitting the rings of the higher-degree
power spectra. These limitations have prevented helioseismologists from
accurately inferring the sound speed, density, adiabatic gradient, and
helium abundance in the outermost three to four percent (by radius)
of the solar interior. In addition, the absence of high-l frequency
splittings from most past rotational inversions has limited the
accuracy with which we have been able to estimate the angular velocity
of the solar surface layers. These limitations have mainly come about
because for l&gt;= 200 the individual modal peaks blend together into
broad ridges of power. Fitting such ridges requires knowledge of the
amount of power which leaks into the sidelobes that are adjacent to
the true spectral peaks. Such leakage information requires detailed
knowledge of the spatial behavior of each different intrument, of
the ratio of horizontal and vertical components of the solar p-mode
eigenfunctions, and of the temporal window function of each dataset. In
this presentation we will demonstrate the high-l frequencies which we
have obtained from a new fitting technique which employs m-averaged
power spectra, temporal window functions, and spatial leakage matrices
to fit each mode or ridge with a total of seven peaks. We will also
demonstrate that we have obtained evidence from the fitting of GONG
power spectra that the true ratios of the eigenfunction components
match the theoretical predictions of these ratios. Finally, we will
also demonstrate that cross-correlations of the peaks and ridges in
the 2l+1 individual spectra at each l result in systematic jumps in the
frequency-splitting coefficients for l&gt;=200 due to the blending of
the peaks into ridges. We will point out that, unless some method can
be found which overcomes these detrimental effects of peak-blending,
we will not be able to provide measures of the latitudinal behavior
of the solar angular velocity close to the photosphere which will
be independent of the horizontal flow mesurements obtained with the
so-called “ring and trumpet” technique.

---------------------------------------------------------
Title: The Long-Term Variation of the Sun's Magnetic Field
Authors: Zhao, X.; Scherrer, P. H.; Hoeksema, J. T.; Sommers, J.
2001AGUSM..SH52A01Z Altcode:
Measurements of the near-Earth interplanetary magnetic field (IMF)
has been examined and it is revealed that the least-squares-fit line
of the annual means of the amplitude of the radial IMF component has
risen by a factor of 1.4 from 1964 to 1995 (Stamper et al., JGR, 104,
28325, 1999). This changes in the interplanetary magnetic field have
been linked with long-term changes in geomagnetic activity and in
total cloud cover over the Earth (Lockwood et al., Nature, 399, 437,
1999). Is the changes in the interplanetary magnetic field caused
by changes in Sun's magnetic field? We examine the photospheric
magnetic field observed by the Wilcox Solar Observatory and the Kitt
Peak Solar Observatory over 26 years and find that the change of the
total magnetic flux in the photosphere follows closely the change of
sunspot number. The coronal magnetic field computed near the Alfven
critical point using the three-layer coronal magnetic field model does
show a trend of increase from 1976 to the end of 1991, similar to the
trend found in the interplanetary magnetic field. However, the trend
after 1992 appears to be decreasing. The cause of the discrepancy
is discussed.

---------------------------------------------------------
Title: Probing Magnetic Structures in the Solar Interior by
Helioseismic Tomography
Authors: Kosovichev, A. G.; Duvall, T. L., Jr.; Scherrer, P. H.
2001ASPC..248..169K Altcode: 2001mfah.conf..169K
No abstract at ADS

---------------------------------------------------------
Title: Heliotomography of the outer layers of the Sun
Authors: Kosovichev, A. G.; Duvall, T. L., Jr.; Birch, A. C.; Gizon,
L.; Scherrer, P. H.; Zhao, Junwei
2001ESASP.464..701K Altcode: 2001soho...10..701K
Heliotomography offers important diagnostics of the solar interior
by providing three-dimensional maps of the sound speed and flows in
the upper convection zone. These diagnostics are based on inversion
of travel times of acoustic waves which propagate between different
points on the solar surface through the interior. The most significant
variations in the thermodynamic structure found by this method
are associated with sunspots and complexes of solar activity. The
inversion results provide evidence for areas of higher sound speed
beneath sunspot regions located at depths of 4 - 20 Mm, which may be
due to accumulated heat or magnetic field concentrations. The results
reveal structures and flows associated with active regions and sunspots
at various stages of their evolution, and provide important constraints
for theories of solar dynamics and activity.

---------------------------------------------------------
Title: Large-Scale Patterns of Solar Magnetic Field and Activity
Cycles
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.
2001ASPC..248..135B Altcode: 2001mfah.conf..135B
No abstract at ADS

---------------------------------------------------------
Title: Local-area helioseismology by SOT on-board Solar-B
Authors: Sekii, T.; Shibahashi, H.; Kosovichev, A. G.; Duvall, T. L.,
Jr.; Berger, T. E.; Bush, R.; Scherrer, P. H.
2001ESASP.464..327S Altcode: 2001soho...10..327S
Solar-B satellite, a successor to Yohkoh, will be launched
in 2005. Placed in a sun-synchronous orbit, it will carry out
multi-wavelength observation in optical, EUV and X-ray ranges. One of
the instruments on Solar-B, Solar Optical Telescope (SOT), a Japan/US
collaboration, aims at measuring the magnetic field and the Doppler
velocity field in the solar photosphere. Although it is not specifically
designed for helioseismic observations, the high-resolution Dopplergram
produced by SOT is potentially a very powerful tool for detailed
seismic investigation of subsurface magnetic and thermal structures
and associated mass flows. If successful, these measurements will be
an important contribution to the main goal of the Solar-B project:
understanding the origin and dynamics of the basic magnetic structures
and their effects on the solar corona. We discuss the prospect and
challenges of local-area helioseismology by SOT.

---------------------------------------------------------
Title: MDI-SOHO Measures of Solar Radius Variation
Authors: Emilio, M.; Kuhn, J. R.; Bush, R. I.; Scherrer, P.
2001IAUS..203..101E Altcode:
Why does the solar luminosity vary and could it change on human
timescales by enough to affect terrestrial climate? As important as
these questions are, we lack answers because we do not understand the
physical mechanisms which are responsible for the solar irradiance
cycle. Progress here depends on discovering how changes in the solar
interior affect energy flow from the radiative and convection zones out
through the photosphere. Measurements of small changes in the solar
radius are a critical probe of the Sun's interior stratification and
can tell us how and where the solar luminosity is gated or stored. Here
we report results from a sensitive 3 year satellite experiment designed
to detect solar diameter fluctuations.

---------------------------------------------------------
Title: Active Longitudinal Structures of the Sun from MDI and EIT
Observations
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.
2001IAUS..203..251B Altcode:
Using data from the EIT and MDI instruments on SOHO and from Kitt
Peak Observatory we have studied the non-axisymmetrical structure
and dynamics of solar activity at different levels of the solar
atmosphere. The data were reduced to synoptic maps of the photospheric
magnetic field and coronal structures in the EUV lines: 171Å, 195Å,
284Å, and 304Å. In addition, the coronal temperature maps were
obtained using the ration of the 171Å and 195Å lines. The results
reveal long-living longitudinal structures in the photosphere and
corona during the transition from Cycle 22 to 23 and the rising
phase of Cycle 23. We have found the Hale magnetic field polarity
reversal first occured at the active longitudes. Thus, the stable
longitudinal structures play an important role in the mechanism of
the solar cycle. These structures are also revealed in the large-scale
structure of the corona. We study the relation between the magnetic and
coronal longitudinal structures, and their role in formation of coronal
holes. We discuss the relations between rotation of the longitudinal
structures in the photosphere and corona and compare with the rotation
rate of the solar interior using helioseismic data. This work was
carried out in the collaboration with J. T. Hoeksema, A. G. Kosovichev
and P. H. Scherrer of Stanford University.

---------------------------------------------------------
Title: Solar Active Longitudes and Their Rotations Using SOHO-MDI Data
(CD-ROM Directory: contribs/benevo2)
Authors: Benevolenskaya, E. E.; Hoeksema, J. T.; Kosovichev, A. G.;
Scherrer, P. H.
2001ASPC..223..583B Altcode: 2001csss...11..583B
No abstract at ADS

---------------------------------------------------------
Title: g-mode detection: Where do we stand?
Authors: Appourchaux, T.; Andersen, B.; Berthomieu, G.; Chaplin, W.;
Elsworth, Y.; Finsterle, W.; Frölich, C.; Gough, D. O.; Hoeksema,
T.; Isaak, G.; Kosovichev, A.; Provost, J.; Scherrer, P.; Sekii, T.;
Toutain, T.
2001ESASP.464..467A Altcode: 2001soho...10..467A
We review the recent developments in determining the upper limits to
g-mode amplitudes obtained by SOHO instruments, GONG and BiSON. We
address how this limit can be improved by way of new helioseismic
instruments and/or new collaborations, hopefully providing in the not
too distant future unambiguous g-mode detection.

---------------------------------------------------------
Title: On the Constancy of the Solar Diameter
Authors: Emilio, M.; Kuhn, J. R.; Bush, R. I.; Scherrer, P.
2000ApJ...543.1007E Altcode:
Why does the solar luminosity vary and could it change on human
timescales by enough to affect terrestrial climate? As important as
these questions are, we lack answers because we do not understand the
physical mechanisms responsible for the solar irradiance cycle. Progress
here depends on discovering how changes in the solar interior affect
energy flow from the radiative and convection zones out through the
photosphere. Measurements of small changes in the solar radius are a
critical probe of the Sun's interior stratification; they can tell us
how and where the solar luminosity is gated or stored. Here we report
results from a sensitive 3 yr satellite experiment designed to detect
solar diameter fluctuations.

---------------------------------------------------------
Title: Modeling the 1994 April 14 Polar Crown SXR Arcade Using
Three-Dimensional Magnetohydrostatic Equilibrium Solutions
Authors: Zhao, X. P.; Hoeksema, J. T.; Scherrer, P. H.
2000ApJ...538..932Z Altcode:
The coronal magnetic field in the polar crown soft X-ray (SXR) arcade
of 1994 April 14 has been computed using the global photospheric
magnetic field distribution constructed for the time of interest and
the three-dimensional magnetohydrostatic equilibrium solutions. In
the solutions there are two free parameters, α and a, respectively,
characterizing the effect of the field-aligned and horizontal electric
currents. Magnetic field configurations have been determined for various
combinations of α and a. The magnetic arcade computed with α--&gt;0
and a=0.9 agrees best in shape and size with the well-developed polar
crown SXR arcade. This suggests that the well-developed SXR arcade
has a potential-like magnetic configuration with non-field-aligned
currents. The computed loci of the apexes of lines of force that
close above 1.3 Rsolar match the shape of the bright axial
features superposed on the well-developed SXR arcade. This suggests
that newly opened lines of force may have reconnected only above 1.3
Rsolar, and consequently the pre-eruption closed lines of
force may not be completely opened up during the eruption phase. The
SXT images before the formation of the SXR loop show the occurrence
of dimmings, supporting the inference of partially “transient”
coronal opening.

---------------------------------------------------------
Title: Observational Upper Limits to Low-Degree Solar g-Modes
Authors: Appourchaux, T.; Fröhlich, C.; Andersen, B.; Berthomieu, G.;
Chaplin, W. J.; Elsworth, Y.; Finsterle, W.; Gough, D. O.; Hoeksema,
J. T.; Isaak, G. R.; Kosovichev, A. G.; Provost, J.; Scherrer, P. H.;
Sekii, T.; Toutain, T.
2000ApJ...538..401A Altcode:
Observations made by the Michelson Doppler Imager (MDI) and Variability
of solar IRradiance and Gravity Oscillations (VIRGO) on the Solar and
Heliospheric Observatory (SOHO) and by the ground-based Birmingham
Solar Oscillations Network (BiSON) and Global Oscillations Network
Group (GONG) have been used in a concerted effort to search for solar
gravity oscillations. All spectra are dominated by solar noise in the
frequency region from 100 to 1000 μHz, where g-modes are expected to be
found. Several methods have been used in an effort to extract any g-mode
signal present. These include (1) the correlation of data-both full-disk
and imaged (with different spatial-mask properties)-collected over
different time intervals from the same instrument, (2) the correlation
of near-contemporaneous data from different instruments, and (3) the
extraction-through the application of complex filtering techniques-of
the coherent part of data collected at different heights in the solar
atmosphere. The detection limit is set by the loss of coherence
caused by the temporal evolution and the motion (e.g., rotation)
of superficial structures. Although we cannot identify any g-mode
signature, we have nevertheless set a firm upper limit to the amplitudes
of the modes: at 200 μHz, they are below 10 mm s-1 in
velocity, and below 0.5 parts per million in intensity. The velocity
limit corresponds very approximately to a peak-to-peak vertical
displacement of δR/Rsolar=2.3×10-8 at the
solar surface. These levels which are much lower than prior claims,
are consistent with theoretical predictions.

---------------------------------------------------------
Title: Comparison of Frequencies and Rotational Splittings of Solar
Acoustic Modes of Low Angular Degree from Simultaneous MDI and
GOLF Observations
Authors: Bertello, L.; Henney, C. J.; Ulrich, R. K.; Varadi, F.;
Kosovichev, A. G.; Scherrer, P. H.; Roca Cortés, T.; Thiery, S.;
Boumier, P.; Gabriel, A. H.; Turck-Chièze, S.
2000ApJ...535.1066B Altcode:
During the years 1996 through 1998 the Michelson Doppler Imager (MDI)
and the Global Oscillations at Low Frequency (GOLF) experiments on the
Solar and Heliospheric Observatory (SOHO) mission have provided unique
and nearly uninterrupted sequences of helioseismic observations. This
paper describes the analysis carried out on power spectra from 759
days of calibrated disk-averaged velocity signals provided by these two
experiments. The period investigated in this work is from 1996 May 25
to 1998 June 22. We report the results of frequency determination of
low-degree (l&lt;=3) acoustic modes in the frequency range between 1.4
mHz and 3.7 mHz. Rotational splittings are also measured for nonradial
modes up to 3.0 mHz. The power spectrum estimation of the signals
is performed using classical Fourier analysis and the line-profile
parameters of the modes are determined by means of a maximum likelihood
method. All parameters have been estimated using both symmetrical and
asymmetrical line profile-fitting formula. The line asymmetry parameter
of all modes with frequency higher than 2.0 mHz is systematically
negative and independent of l. This result is consistent with the
fact that both MDI and GOLF data sets investigated in this paper are
predominantly velocity signals, in agreement with previous results. A
comparison of the results between the symmetric and asymmetric fits
shows that there is a systematic shift in the frequencies for modes
above 2.0 mHz. Below this frequency, the line width of the modes
is very small and the time base of the data does not provide enough
statistics to reveal an asymmetry. In general, the results show that
frequency and rotational splitting values obtained from both the
MDI and GOLF signals are in excellent agreement, and no significant
differences exist between the two data sets within the accuracy of the
measurements. Our results are consistent with a uniform rotation of
the solar core at the rate of about 435 nHz and show only very small
deviations of the core structure from the standard solar model.

---------------------------------------------------------
Title: Rossby waves on the Sun as revealed by solar `hills'
Authors: Kuhn, J. R.; Armstrong, J. D.; Bush, R. I.; Scherrer, P.
2000Natur.405..544K Altcode:
It is a long-standing puzzle that the Sun's photosphere-its visible
surface-rotates differentially, with the equatorial regions rotating
faster than the poles. It has been suggested that waves analogous to
terrestrial Rossby waves, and known as r-mode oscillations, could
explain the Sun's differential rotation: Rossby waves are seen in
the oceans as large-scale (hundreds of kilometres) variations of
sea-surface height (5-cm-high waves), which propagate slowly either
east or west (they could take tens of years to cross the Pacific
Ocean). Calculations show that the solar r-mode oscillations have
properties that should be strongly constrained by differential
rotation. Here we report the detection of 100-m-high `hills' in the
photosphere, spaced uniformly over the Sun's surface with a spacing of
(8.7 +/- 0.6) × 104km. If convection under the photosphere
is organized by the r-modes, the observed corrugated photosphere is
a probable surface manifestation of these solar oscillations.

---------------------------------------------------------
Title: Synoptic Magnetic Field Measurements
Authors: Hoeksema, J. T.; Bush, R. I.; Chu, K. -C.; Liu, Y.; Scherrer,
P. H.; Sommers, J.; Zhao, X. P.; SOHO/MDI Team
2000SPD....31.0139H Altcode: 2000BAAS...32R.808H
Frequent MDI measurements of the photospheric magnetic field make
possible new kinds of synoptic data sets that provide insight into the
global evolution of solar activity. Synoptic charts can be constructed
at central meridian or at other disk longitudes to characterize the
development of the surface field and to compare with other kinds of
synoptic measurements. Individual magnetograms inserted into a synoptic
chart provide a better snapshot of the field configuration and provide
a clearer record of changes in the global field. Daily changes can
be used for prediction. Development of structures during the rising
phase of Solar Cycle 23 are compared with data from other sources and
other cycles. Issues of accuracy, precision, and magnetogram merging
are discussed. SOHO is a project of international cooperation between
ESA and NASA.

---------------------------------------------------------
Title: Active Longitudes in Solar Corona
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.
2000SPD....31.0226B Altcode: 2000BAAS...32..815B
We present the results of the investigation of the large-scale
structure of the solar corona during the transition period between
solar cycles 22 and 23 and at the beginning of the current cycle 23
using the SOHO/EIT EUV data obtained in 171 Angstroms, 195 Angstroms,
284 Angstroms and 304 Angstroms lines. For this analysis the data
were transformed into synoptic maps for each of the spectral lines,
and for the 195 Angstroms/171 Angstroms line ratio which is an
index of the coronal temperature. The synoptic maps reveal stable
longitudinal structures in the coronal intensities and temperature,
which are related to large-scale magnetic field structures. We discuss
the relation between the coronal and photospheric magnetic structures
obtained from the SOHO/MDI data, and compare the rotation rates of
these structures with the rotation profile of the solar interior in
order to determine the possible origin of the coronal structures.

---------------------------------------------------------
Title: Sunspots: Frontside and Backside Measurements with
Time-Distance Helioseismology
Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H.
2000SPD....31.0505D Altcode: 2000BAAS...32..837D
In time-distance helioseismology, travel times measured between
different surface locations are used to infer subsurface flows,
temperature inhomogeneities and magnetic fields. It has been suggested
that most of the travel time reduction near sunspots may be due to the
lowered reflection layer associated with the Wilson depression. This
will be examined by looking at rays that travel below the sunspot but do
not begin or end in the spot. A time-distance method of imaging sunspots
on the backside will be compared with that of Lindsey and Braun.

---------------------------------------------------------
Title: Sunspots: frontside and backside measurements with
time-distance helioseismology.
Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H.
2000BAAS...32Q.837D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Plasma Flows within and around Sunspots
Authors: Bai, T. A.; Scherrer, P. H.
2000SPD....31.0121B Altcode: 2000BAAS...32Q.804B
It is essential to know plasma flows within and around sunspots for
understanding the evolution and stability of sunspots. By analyzing data
obtained by the Michelson Doppler Imager aboard SOHO, we have studied
plasma flows within and around four sunspots in the decay phase. We
have confirmed the existence of a downward component in the Evershed
flow, which has been recognized until recently, mainly as horizontal
outflows in the penumbra. The downward component reaches its peak value
of about 500 m/s near the outer edge of the penumbra. Additionally,
we have discovered plasma flows within umbrae. In two sunspots (in AR
7981 and AR 8194), we have found evidence for radial inflows within the
umbra, which are in the opposite direction of Evershed flows. In two
other sunspots under this study (in AR 8402 and AR 8403), we have found
evidence for outflows within the umbra. The speeds of such horizontal
flows are about 300 m/s.

---------------------------------------------------------
Title: US Mission of Opportunity on MONS
Authors: Schou, J.; Scherrer, P. H.; Bogart, R. S.;
Christensen-Dalsgaard, J.; Kjeldsen, H.; Buzasi, D. L.
2000mons.proc..123S Altcode:
The Measuring Oscillations in Nearby Stars (MONS) Survey Telescope
(MONS-ST) is a Mission of Opportunity that will study the interior
of a large number of stars using stellar oscillations. MONS-ST will
provide additional hardware and/or extend the lifetime of the Danish
MONS micro satellite, which has been selected for flight in 2003. The
additional hardware provided by MONS-ST will enhance the MONS mission
by increasing the number of stars observable and extending the lifetime
of the mission. A Guest Investigator program, allowing a number of
scientists to propose targets and analyze data, will be part of the
mission.

---------------------------------------------------------
Title: The Magnetic Connectivity of Moss Regions
Authors: Zhao, X. P.; Hoeksema, J. T.; Kosovichev, A. G.; Bush, R.;
Scherrer, P. H.
2000SoPh..193..219Z Altcode:
A novel emission feature resembling moss was first identified in
high-resolution TRACE Fe ix/x 171 Å images by Berger et al. (1999). The
moss emission is characterized by dynamic arc-second scale, bright
elements surrounding dark inclusions in images of solar active
regions. Patches of moss elements, called moss regions, have a scale
of 20-30 Mm. Moss regions occur only above some of magnetic plages
that underlie soft X-ray coronal loops. Using the potential field
extrapolation of the photospheric magnetic field into the corona, we
find that the magnetic field lines in moss-associated magnetic plages
connect with adjacent plages with opposite polarity; however, all field
lines from mossless plages end in surrounding `quiet regions'. This
result is consistent with the idea that the TRACE moss is the emission
from the upper transition region due to heating of low-lying plasma
by field-aligned thermal conduction from overlying hot plasma (Berger
et al., 1999).

---------------------------------------------------------
Title: Time-Distance Inversion Methods and Results - (Invited Review)
Authors: Kosovichev, A. G.; Duvall, T. L. _Jr., Jr.; Scherrer, P. H.
2000SoPh..192..159K Altcode:
The current interpretations of the travel-time measurements in quiet
and active regions on the Sun are discussed. These interpretations
are based on various approximations to the 3-D wave equation such as
the Fermat principle for acoustic rays and the Born approximation. The
ray approximation and its modifications have provided the first view
of the 3-D structures and flows in the solar interior. However, more
accurate and computationally efficient approximations describing the
relation between the wave travel times and the internal properties
are required to study the structures and flows in detail. Inversion
of the large three-dimensional datasets is efficiently carried
out by regularized iterative methods. Some results of time-distance
inversions for emerging active regions, sunspots, meridional flows and
supergranulation are presented. An active region which emerged on the
solar disk in January 1998, was studied from SOHO/MDI for eight days,
both before and after its emergence at the surface. The results show
a complicated structure of the emerging region in the interior, and
suggest that the emerging flux ropes travel very quickly through the
depth range of our observations. The estimated speed of emergence is
about 1.3 km s−1. Tomographic images of a large sunspot
reveal sunspot `fingers' - long narrow structures at a depth of about
4 Mm, which connect the sunspot with surrounding pores of the same
polarity.

---------------------------------------------------------
Title: New and Old Magnetic Fluxes at the Beginning of Solar Cycle 23
Authors: Benevolenskaya, E. E.; Hoeksema, J. T.; Kosovichev, A. G.;
Scherrer, P. H.
1999ESASP.448...69B Altcode: 1999ESPM....9...69B; 1999mfsp.conf...69B
No abstract at ADS

---------------------------------------------------------
Title: Stellar and Planetary Explorer (SPEX)
Authors: Schou, J.; Bogart, R. S.; Bush, R. I.; Hoeksema, J. T.;
Scherrer, P. H.; Brown, T. M.; Buzasi, D. L.; Horner, S. D.; Korzennik,
S. G.
1999AAS...195.8808S Altcode: 1999BAAS...31.1506S
The Stellar and Planetary Explorer (SPEX) mission will search for
terrestrial inner planets around Sun-like (FGK, main sequence) stars
using photometric techniques as well as provide very long time series
for asteroseismology. If every Sun-like star had a planetary system
similar to ours, the proposed instrumentation would detect at least
100 terrestrial planets similar to the Earth or Venus and be able to
provide statistics on their diameters and orbital periods. SPEX will
accomplish this by continuously observing a large number of field stars
to detect planetary transits. The instrument consists of a fast Schmidt
camera with a mosaic of large CCD detectors. SPEX will observe a field
near the galactic plane from a geosynchronous orbit for a minimum of 3
years. The very long asteroseismic time series will allow inferences
on the interiors of more than 100 Sun-like stars with a variety of
masses and ages. This will allow us to substantially refine stellar
model calculations and in particular improve on the age estimates of
stars. This in turn is of considerable interest for the understanding
of the evolution of our galaxy and the universe as a whole. SPEX will
also provide new data for stellar activity and will be able to detect
the reflected light from large inner planets, such as those detected
using ground based Doppler velocity searches.

---------------------------------------------------------
Title: Structure and Dynamics of Interconnecting Loops and Coronal
Holes in Active Longitudes
Authors: Benevolenskaya, Elena E.; Kosovichev, A. G.; Scherrer, P. H.
1999SoPh..190..145B Altcode:
Using SOHO/MDI and SOHO/EIT data we study properties and dynamics
of interconnected active regions, and the relations between the
photospheric magnetic fields and coronal structures in active longitudes
during the beginning of solar cycle 23. The emergence of new magnetic
flux results in appearance of new interconnecting loops. The existence
of stable coronal structures strongly depends on the photospheric
magnetic fluxes and their variations. We present some initial results
for a complex of solar activity observed in April 1997, and discuss
the role of reconnection in the formation of the interconnected loops
and coronal holes.

---------------------------------------------------------
Title: Frequencies and splittings of low-degree acoustic modes:
a comparison between MDI and GOLF observations
Authors: Bertello, L.; Henney, C. J.; Ulrich, R. K.; Varadi, F.;
Kosovichev, A. G.; Roca Cortes, T.; Garcia, R. A.; Scherrer, P. H.
1999AAS...19410805B Altcode:
During the years 1996 through 1998 the MDI and GOLF experiments on the
SOHO mission have provided unique and nearly uninterrupted sequences of
helioseismic observations. This paper describes the analysis carried out
on power spectra from 759 days of calibrated velocity signals provided
by these two experiments. The time series investigated in this work are
from 25 May, 1996 to 22 June, 1998. We report the results of frequency
and splitting determination of low-degree (l &lt; 4) acoustic modes
in the frequency range between 1.5 mHz and 4.0 mHz. The power spectrum
estimation of the signals is performed using classical Fourier analysis
and the line-profile parameters of the modes are determined by means of
a maximum likelihood method. All parameters have been estimated using
both symmetrical and asymmetrical line profile-fitting formula. The
line asymmetry parameter of all modes with frequency higher than 2.0
mHz is systematically negative and independent from l. This result is
consistent with the fact that both MDI and GOLF data sets investigated
in this paper are predominantly velocity signals. A comparison of the
results between symmetric fit and asymmetric one shows that there
is a systematic shift in the eigenfrequencies for modes above 2.0
mHz. The results show that eigenfrequency and rotational splitting
values obtained from both the MDI and GOLF signals are in excellent
agreement, and no significant differences exist between the two data
sets within the indetermination of the measurement.

---------------------------------------------------------
Title: Power spectra comparison between GOLF and MDI velocity
observations
Authors: Henney, C. J.; Ulrich, R. K.; Bertello, L.; Bogart,
R. S.; Bush, R. I.; Scherrer, P. H.; Palle, P. L.; Roca Cortes, T.;
Turck-Chieze, S.
1999AAS...194.5617H Altcode: 1999BAAS...31..914H
We present a comparison of the velocity power spectra between the GOLF
and MDI instruments. In addition, this poster outlines work towards
creating a GOLF-simulated signal utilizing MDI velocity images. The
simulation of the GOLF signal is achieved by integrating spatially
weighted masks with MDI LOI-proxy velocity images. The GOLF-simulated
signal and a selection of additional spatially masked MDI velocity
signals are compared with the observed GOLF signal for a 759 day period
from May 25, 1996 through June 22, 1998. Ultimately, a cross-analysis
process between GOLF and MDI signals could lead to an enhancement
of our ability to detect low frequency solar oscillations. The
signal-to-background ratio (S/B) for the GOLF and the spatially masked
MDI velocity data is presented for low degree (l &lt;= 3) and low
frequency p-modes. We find that signals from both MDI and GOLF are
beneficial for detecting low degree (l &lt;= 3) and low frequency
(&lt; 2000 mu Hz) p-modes. For the frequency range and the signals
compared in this poster, the GOLF signal has the highest S/B for l=0
p-modes. The S/B of the GOLF and MDI central region masked signals
is good for detecting l=1 p-modes. For l &gt;= 2 p-modes, the central
region masked signals have the highest S/B of the power spectra compared
here. In addition, the S/B of the preliminary GOLF-simulated signal
is found to be more similar to the GOLF signal than the MDI LOI-proxy
signal without spatial masking for the modes investigated here.

---------------------------------------------------------
Title: Power spectra comparison between GOLF and spatially masked
MDI velocity signals
Authors: Henney, C. J.; Ulrich, R. K.; Bertello, L.; Bogart, R. S.;
Bush, R. I.; Scherrer, P. H.; Roca Cortés, T.; Turck-Chièze, S.
1999A&A...348..627H Altcode:
The Global Oscillations at Low Frequency (GOLF) and the Michelson
Doppler Imager (MDI) instruments aboard the Solar and Heliospheric
Observatory (SOHO) give an excellent opportunity to search for solar
low frequency oscillation modes previously undetected from ground
based experiments. Presented here is a comparison of the velocity power
spectra between the two instruments. In addition, this paper outlines
work towards creating a GOLF-simulated signal utilizing MDI velocity
images. The simulation of the GOLF signal is achieved by integrating
spatially weighted masks with MDI full-disk Doppler images. The
GOLF-simulated signal and a selection of additional spatially masked
MDI velocity signals are compared with the observed GOLF signal for a
759 day period from May 25, 1996 through June 22, 1998. Ultimately,
a cross-analysis process between GOLF and MDI signals could lead
to an enhancement of our ability to detect low frequency solar
oscillations. For low degree (l&lt;= 3) and low frequency acoustic
modes, the signal-to-background ratio between GOLF and the spatially
masked MDI velocity data is compared here.

---------------------------------------------------------
Title: The Interaction of New and Old Magnetic Fluxes at the Beginning
of Solar Cycle 23
Authors: Benevolenskaya, E. E.; Hoeksema, J. T.; Kosovichev, A. G.;
Scherrer, P. H.
1999ApJ...517L.163B Altcode: 1999astro.ph..3404B
The 11 yr cycle of solar activity follows Hale's law by reversing
the magnetic polarity of leading and following sunspots in bipolar
regions during the minima of activity. In the 1996-1997 solar minimum,
most solar activity emerged in narrow longitudinal zones--“active
longitudes” but over a range in latitude. Investigating the
distribution of solar magnetic flux, we have found that the Hale
sunspot polarity reversal first occurred in these active zones. We have
estimated the rotation rates of the magnetic flux in the active zones
before and after the polarity reversal. Comparing these rotation rates
with the internal rotation inferred by helioseismology, we suggest
that both “old” and “new” magnetic fluxes were probably generated
in a low-latitude zone near the base of the solar convection zone. The
reversal of active region polarity observed in certain longitudes at the
beginning of a new solar cycle suggests that the phenomenon of active
longitudes may give fundamental information about the mechanism of
the solar cycle. The nonrandom distribution of old-cycle and new-cycle
fluxes presents a challenge for dynamo theories, most of which assume
a uniform longitudinal distribution of solar magnetic fields.

---------------------------------------------------------
Title: Measuring Local Short-Term Changes in the Global Solar
Magnetic Field
Authors: Hoeksema, J. T.; Zhao, X. P.; Chu, K. -C.; Scherrer, P. H.
1999AAS...194.9405H Altcode: 1999BAAS...31Q.991H
Global evolution of the solar magnetic field is driven by local magnetic
flux changes. We have systematically measured the small-scale magnetic
field on the visible surface over an extended time interval. The
MDI instrument on SOHO has made 2" full-disk observations of the
photospheric field every 96 minutes since May 1996, except for a
several-month gap in 1998 and early 1999 caused by problems with
the SOHO spacecraft. We are now developing tools to characterize
the local variations and relate them to their global effects. MDI
magnetograms compare well with KPNO and WSO observations at higher
and lower resolution. Several MDI magnetograms are available in near
real time each day. MDI daily synoptic charts show the evolution of
large-scale coronal structures. Daily updates and archival records of
individual magnetograms and synoptic charts can be found on the www
at http://soi.stanford.edu.

---------------------------------------------------------
Title: Changes of the boot-shaped coronal hole boundary during Whole
Sun Month near sunspot minimum
Authors: Zhao, X. P.; Hoeksema, J. T.; Scherrer, P. H.
1999JGR...104.9735Z Altcode:
The August 27, 1996, boot-shaped coronal hole is shown to rotate nearly
rigidly at a rate of 13.25°/day, greater than the equatorial rotation
rate of bipolar magnetic regions such as active regions and plages. The
day-to-day variation of the coronal hole border is determined by
comparing the rigid rotation projection of the disk-center hole
boundary to coronal hole boundaries observed in successive daily coronal
images. To determine the influence of the changing photospheric field
on the location of the coronal hole boundary, a better approximation
of the instantaneous global magnetic field distribution is developed
and used as input to a potential-field source-surface model to compute
the foot-point areas of open field lines. Day-to-day variations of
the coronal hole boundary may be caused by changes of the magnetic
field and plasma properties in the corona, as well as by the changing
photospheric field.

---------------------------------------------------------
Title: Imaging of Emerging Magnetic Flux by Time-Distance
Helioseismology
Authors: Kosovichev, A. G.; Duvall, T. L., Jr.; Scherrer, P. H.
1999AAS...194.5901K Altcode: 1999BAAS...31..917K
We have used measurements of acoustic travel time in the convection
zone to infer local perturbations of the sound speed and 3D flow
velocities associated with emerging active regions in July 1996 and
January 1998. Both regions were observed with the MDI instrument on
SOHO before and after emergence continuously for 9 days. The first
active region emerged in a long-lived complex of activity and produced
a strong X-class flare. The second active region was a high-latitude
region of the new solar cycle. The time-distance inversion results show
complicated dynamics of the magnetic flux in the convection zone, and
indicate that the emerging flux travels faster in the convection zone
than predicted by theory. We discuss the differences in the dynamics
of these active regions.

---------------------------------------------------------
Title: Solar Internal Rotation as Measured by the SOHO SOI/MDI
Full-Disk Program
Authors: Rhodes, E. J., Jr.; Reiter, J.; Kosovichev, A. G.; Schou,
J.; Scherrer, P. H.
1999AAS...194.5602R Altcode: 1999BAAS...31..911R
We present estimates of the solar internal angular velocity obtained
from p-mode frequency splittings computed from observations of the
SOHO SOI/MDI Experiment's Full-Disk Program. Specifically, a time
series of full-disk Dopplergrams which was obtained during the 61-day
long 1996 Dynamics Run of the SOI/MDI Experiment were converted into
time series of spherical harmonic coeffificients for degrees ranging
up to 1000. These time series of spherical harmonic coefficients
were then converted into 1001 sets of zonal, sectoral, and tesseral
power spectra. Estimates of the rotationally-induced p-mode frequency
splittings for every degree between 1 and 1000 were then obtained from
these sets of power spectra through a cross-correlation of the 2l+1
spectra within each set. Because this cross-correlation was carried
out between the frequency limits of 1800 to 4800 mu Hz for each set
of spectra, the resulting splitting coefficients were effectively
averaged over the radial order, n, at each degree. Due to the blending
of individual p-mode spectral peaks for degrees above 200, the raw
frequency splitting coefficients for all degrees between 200 and 1000
had to be corrected before an inversion could be performed. We will
describe the method we adopted for correcting the raw splittings and
we will present both the raw and corrected splitting coefficients. We
will also present a two-dimensional inversion of the corrected
coefficients. Finally, we will also demonstrate how the inclusion of
the high-degree splittings allows us to obtain better estimates of the
solar internal angular velocity in the shallow sub-photospheric part
of the solar convection zone than have been possible in past studies
which included only the splittings of the low- and intermediate-degree
p-modes.

---------------------------------------------------------
Title: The SOI-MDI Dynamics Program: Observing the Solar Cycle
Authors: Bush, R. I.; Beck, J. G.; Bogart, R. S.; Hoeksema, J. T.;
Kosovichev, A. G.; Scherrer, P. H.; Schou, J.; Sommers, J.; Duvall,
T. L.
1999AAS...194.9205B Altcode: 1999BAAS...31..987B
The Michelson Doppler Imager instrument on the SOHO spacecraft has been
observing the Sun over the last three years. The MDI Dynamics Program
provides nearly continuous full disk Doppler measurements of the solar
photosphere with 4 arc-second resolution for periods of 60 to 90 days
each year. Three of these Dynamics periods have been completed: 23 May
to 24 July 1996, 13 April to 14 July 1997, 9 January to 10 April 1998. A
fourth Dynamics observing period began on 13 March and is scheduled to
continue through mid July. These observations provide a unique view
of the evolution of the Sun in the early part of the solar cycle,
both from interior flows deduced by helioseimic analysis and changes
in large scale surface motion. Details of the Dynamics programs will
be presented along with an overview of current results. This research
is supported by the SOI-MDI NASA grant NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: SONAR - Solar Near-surface Active Region Rendering
Authors: Scherrer, P. H.; Hoeksema, J. T.; Kosovichev, A. G.; Duvall,
T. L.; Schrijver, K. J.; Title, A. M.
1999AAS...194.7606S Altcode: 1999BAAS...31Q.957S
The processes in the top 20,000-km of the Sun's convection zone govern
the growth and decay of active regions and provide the magnetic flux and
energy for the active phenomena of the upper solar atmosphere. The MDI
experiment on SOHO has demonstrated that this region is now accessible
to study by means of local helioseismology. However, SOHO provides
neither the temporal nor spatial resolution and coverage necessary
to exploit these techniques to study the eruption and evolution of
active region magnetic structures. The SONAR mission with moderate
resolution full disk Doppler and vector magnetic field observations,
and atmospheric magnetic connectivity observations via EUV imaging
can provide the necessary data. The science motivation and general
instrumentation requirements for the mission are presented.

---------------------------------------------------------
Title: New Views of Active Regions
Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H.
1999AAS...194.4203D Altcode: 1999BAAS...31..882D
3-d acoustic tomography of the region below the photosphere is providing
qualitatively new insights about solar active regions. This tomography
is based on the measurement of travel times between different surface
locations and is sensitive to subsurface flows and to wave-speed
inhomogeneities caused by temperature and magnetic field variations. A
flow cell has been seen below sunspots similar to the model of Parker
(Ap.J. 230,905-913,1979) in which there is a horizontal inflow near
the top of the convection zone, a downflow directly below the sunspot
and a horizontal outflow below. This flow may be what stabilizes the
sunspot. A wave-speed reduction is seen in the 2 Mm below the surface
sunspot and a wave-speed enhancement is seen below to at least 10 Mm
depth for a reasonably large spot. At 10 Mm depth, a wave-speed increase
of 3% could be caused by a 10 kG magnetic field or a temperature
excess of 6%. At present we cannot distinguish between temperature
and magnetic field effects on the wave speed, but we will present a
comparison between the wave speed as predicted from a sunspot model
and that measured with the tomography. This research is supported by
NASA contract NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: Needs for Future of Visible Light Observation
Authors: Scherrer, P. H.
1999AAS...194.6502S Altcode: 1999BAAS...31..927S
There are a number of both recent and long-standing questions that
require space-based visible light observations of the Sun. These fit
into several general categories including total irradiance measurements,
coronal and heliospheric structures, high resolution vector magnetic
fields, high resolution photospheric structures, and the structure and
dynamics of the solar interior for both global and local phenomena. Much
progress has been made lately or is in development for the near
future. In particular solar interior studies have had significant
development with SOHO and GONG observations, Solar-B will address
moderately high-resolution structures and fields, STEREO will address
dynamic structures in the corona, etc. Nevertheless there will remain
many very important questions after these missions are complete. The
interior dynamics near the rotation axis and near the poles remains
elusive. Detecting magnetic fields at the base of the convection
zone remains beyond reach. Imaging the motions in the upper part of
the convection zone beneath active regions has been demonstrated but
detailed study is not possible with current instrumentation. Full
disk moderate resolution and small region high resolution magnetic
field observations just serve to point to the need for full disk high
resolution magnetic observations. And observations of magnetoconvective
fine scale structures remain just beyond reach. These needs and some
possible observing scenarios will be discussed.

---------------------------------------------------------
Title: Large-Scale Solar Flows From Time-Distance Helioseismology
Authors: Giles, P. M.; Duvall, T. L., Jr.; Scherrer, P. H.
1999AAS...194.2102G Altcode: 1999BAAS...31..858G
Over the past thirty years, helioseismology has proven to be an
extremely useful tool for probing the solar interior. Using global
mode frequencies, the structure and the rotation of the Sun have been
determined with unprecedented accuracy. More recently, there has been
rapid evolution of so-called "local" methods in helioseismology. These
techniques are able to examine aspects of the Sun's structure and
dynamics which are otherwise inaccessible. One of the most successful
of these techniques is time-distance helioseismology, which relies
on the determination of wave travel times to infer properties of the
subsurface region. This approach has been particularly successful
in measuring flows in the solar convection zone which were previously
observable only at the surface. In this paper we present our most recent
results in these investigations, including our latest determination
of the meridional circulation as a function of depth, and our search
for large-scale nonaxisymmetric velocity structures. Data for this
research was obtained by the MDI instrument on SOHO. This research is
supported by NASA contract NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: The Magnetic Structure of the Sun at the Beginning of Solar
Cycle 23
Authors: Benevolenskaya, E. E.; Hoeksema, J. T.; Kosovichev, A. G.;
Scherrer, P. H.
1999AAS...194.9201B Altcode: 1999BAAS...31R.986B
The 11-year cycle of solar activity follows Hale's law by reversing the
magnetic polarity of leading and following sunspots in bipolar regions
during the minima of activity. In the 1996-97 solar minimum, most solar
activity emerged in narrow longitudinal zones - `active longitudes'
but over a range in latitude. Investigating the distribution of solar
magnetic flux, we have found that the Hale sunspot polarity reversal
first occurred in these active zones. We have estimated the rotation
rates of the magnetic flux in the active zones before and after the
polarity reversal. Comparing these rotation rates with the internal
rotation inferred by helioseismology, we suggest that both `old' and
`new' magnetic fluxes were probably generated in a low-latitude zone
near the base of the solar convection zone. The reversal of active
region polarity observed in certain longitudes at the beginning of
a new solar cycle suggests that the phenomenon of active longitudes
may give fundamental information about the mechanism of the solar
cycle. The non-random distribution of old-cycle and new-cycle fluxes
presents a challenge for dynamo theories, most of which assume a
uniform longitudinal distribution of solar magnetic fields. We have
used accurate measurements of solar oscillation frequencies from the
GONG and SOHO/MDI to infer the latitudinal dependence of the solar
structure associated with magnetic fields beneath the surface. The
results show significant variations of the aspherical structure of
the Sun at the beginning of the new cycle. These variations correlate
with the latitudinal distribution of the surface magnetic flux. We
discuss possible variations at the base of the convection zone and
their relation to the dynamo mechanism.

---------------------------------------------------------
Title: Subsurface Observations of Sunspots and Solar Supergranulation
Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H.
1999AAS...194.5606D Altcode: 1999BAAS...31..912D
3-d acoustic tomography of the region below the photosphere is providing
new insights into sunspots and the apparently convective flow observed
at the surface called supergranulation. The tomography is based on
the measurement of travel times between different surface locations
and is sensitive to subsurface flows and to wave-speed inhomogeneities
caused by temperature and magnetic field variations. This study uses
dopplergrams from the MDI instrument on the SOHO spacecraft. A flow
cell has been seen below sunspots similar to the model of Parker
(Ap.J. 230,905-913,1979) in which there is a horizontal inflow near
the top of the convection zone, a downflow directly below the sunspot
and a horizontal outflow below. The depth of the supergranulation
flow will be discussed. This research is supported by NASA contract
NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: Time-distance Measurements of Meridional Circulation Deep in
the Convection Zone
Authors: Giles, P. M.; Duvall, T. L., Jr.; Scherrer, P. H.
1999soho....9E..23G Altcode:
Explaining the solar cycle is one of the central goals of solar
physics. Some of the most successful models of the cycle fall under
the broad category of Babcock-Leighton dynamo theories. Babcock
and Leighton developed this model in the 1960s, making use of the
most recent observations of the Sun's magnetic field and surface
motions. The model reproduces the large-scale properties of the cycle
by invoking both differential rotation and supergranular diffusion of
magnetic elements. Although the original work predates the birth of
helioseismology, it still underlies much of our current understanding
of the solar cycle. The development of helioseismology has, however,
necessitated some evolution of the theory. For example, dynamo theorists
now must match their models to the observed differential rotation
profile in the solar interior. Prodded by more sophisticated surface
measurements, several groups have also proposed models including
a meridional circulation. Until recently, theorists were free to
speculate on the characteristics of this flow below the surface. In
the past few years, however, several helioseismic techniques have been
used to successfully measure the meridional circulation in the solar
interior. In this paper, the authors present their latest measurements
of the meridional flow using the time-distance technique on MDI
data. These measurements now reach far enough into the convection zone
that they might be a useful constraint on solar dynamo theories. This
research is supported by NASA contract NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: Time-distance helioseismology
Authors: Kosovichev, A. G.; Duvall, T. L.; Scherrer, P. H.
1999AdSpR..24..163K Altcode:
The time-distance helioseismology (or helioseismic tomography) is a new
promising method for probing 3-D structures and flows beneath the solar
surface, which is potentially important for studying the birth of active
regions in the sun's interior and for understanding the relation between
the internal dynamics of active regions and chromospheric and coronal
activity. In this method, the time for waves to travel along subsurface
ray paths is determined from the temporal cross correlation of signals
at two separated surface points. By measuring the times for many
pairs of points from Dopplergrams covering the visible hemisphere, a
tremendous quantity of information about the state of the solar interior
is derived. As an example, we present the results for supergranular
flows and for an active region which emerged near the center of the
solar disk in July 1996, and was studied from SOHO/MDI for nine days,
both before and after its emergence at the surface. Initial results
show a complicated structure of the emerging region in the interior,
and suggest that the emerging flux ropes travel very quickly through
the depth range of our observations.

---------------------------------------------------------
Title: Power spectra comparison between GOLF and MDI velocity
observations.
Authors: Henney, C. J.; Ulrich, R. K.; Bertello, L.; Bogart, R. S.;
Bush, R. I.; Scherrer, P. H.; Pallé, P. L.; Roca Cortés, T.;
Turck-Chièze, S.
1999BAAS...31Q1237H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Prospects for Future Helioseismology Missions
Authors: Scherrer, Philip H.
1999soho....9E..31S Altcode:
The progress afforded by present and past helioseismology missions has
been the topic of this and numerous previous conferences. The primary
conclusion of the 1983 NASA study on prospects for solar oscillations
have been basically confirmed. That is, part of the job can be done on
the ground but a significant part can only be done from space. While
we have made significant progress, it is also clear that additional
opportunities to use helioseismic techniques to better understand
stellar interiors remain. Recent advances in local helioseismology in
particular point to additional observing requirements. These include
larger field of view at high resolution in order to follow magnetic
region development, longer baselines in longitude to probe the bottom
of the convection zone and below, and a high latitude vantage point to
examine processes near the rotation axis. Several possible missions
have been discussed recently to address these issues. They include
SONAR, Farside Observer, Solar Polar Imager, and Solar Probe. The basic
concepts of these missions will be discussed along with the continuing
role for enhanced ground based observations.

---------------------------------------------------------
Title: Plasma Flows in Growing Active Regions
Authors: Bai, T.; Scherrer, P. H.
1999soho....9E..34B Altcode:
Around mature spots plasma outflows are often observed. Moving magnetic
features are also often observed. However, plasma flows around growing
sunspots have not been studied in detail. MDI aboard SOHO provides
high-quality data for such studies. AR 7968 was growing when it passed
near the central meridian on June 6, 1996. It passed near the disk
center because of its very low latitudes (N02). Analyzing dopplergrams
and magnetograms of this active region, we have observed vertical
downward flows of about 100 m/s surrounding the sunspots. Around the
area of downward flow, we find a ring of upward flow area. Similar
behavior was observed in AR 7978, which was rapidly growing while
passing the central meridian on July 5, 1996. This research is supported
by NASA grant NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: APT: an astrometric and photometric telescope
Authors: Kuhn, Jeff R.; Bush, Rock I.; Coulter, Roy; Froehlich, Claus;
Gwo, Dz-Hung; Jones, A.; Pap, Judit M.; Scherrer, Philip H.; Sofia,
Sabatino; Ulrich, Roger
1998SPIE.3442..203K Altcode:
Helioseismic and precise solar photometric measurements reveal that the
Sun varies globally as a start during the source of an 11 year solar
cycle. To understand the physical mechanisms of the magnetic cycle in
the solar interior we must learn how to measure the tiny changes in
the Sun's global properties, like its radius, internal temperature
distribution and surface luminosity. The SoHO/MDI experimental has
proven that exceedingly small solar shape fluctuations are measurable
from outside our atmosphere. We describe here an instrument which
will not only measure limb shape oscillations with unprecedented
accuracy, but it will also detect solar radius changes with heretofore
unachieved accuracy and precision. Variations in these parameters are
caused by physical changes, both in the photosphere and the deep solar
interior. Solar radius and shape observations will teach us how the
Sun's convective envelope responds to emergent energy fluctuations. The
determination of this outer boundary condition is essential to
understand the solar total irradiance and luminosity variations.

---------------------------------------------------------
Title: New Observations of the Sun: Helioseismology and the
Photospheric Magnetic Field
Authors: Scherrer, Philip
1998APS..DPPH4I202S Altcode:
In the past several years the interior of the Sun has become accessible
to direct observation via helioseismology. The Michelson Doppler Imager
(MDI) experiment aboard the Solar and Heliosperic Observatory (SOHO)
spacecraft has allowed inferrences of solar interior conditions from
the upper few thousand km to near the solar core. In addition to global
scale observations, the MDI instrument allows local helioseismology
techniques to be used to probe local sound speed variations and
flows in the near surface regions just beneath supergranulation and
sunspots. The MDI instrument also obtains a near continuous record of
the photospheric magnetic field without degradation from the Earht's
atmosphere. These observations reveal a new picture of magnetic
field evolution. This paper will review the observational methods,
basic analysis techniques, and present results obtained from the
first two years of operation of MDI. Further information about the
SOHO mission and MDI observations in particular can be found at &lt;A
HREF=http://soi.stanford.edu&gt;http://soi.stanford.edu&lt;/A&gt;.

---------------------------------------------------------
Title: Asymmetry and Frequencies of Low-Degree p-Modes and the
Structure of the Sun's Core
Authors: Toutain, T.; Appourchaux, T.; Fröhlich, C.; Kosovichev,
A. G.; Nigam, R.; Scherrer, P. H.
1998ApJ...506L.147T Altcode:
An accurate determination of the frequencies of low-degree solar
p-modes is an important task of helioseismology. Using 679 days of
solar oscillation data observed in Doppler velocity and continuum
intensity from two Solar and Heliospheric Observatory instruments
(the Michelson Doppler Imager and the SunPhotoMeter), we show that
fitting the spectra with Lorentzian profiles leads to systematic
differences between intensity and velocity frequencies as large as
0.1 μHz for angular degrees l=0, 1, and 2 because of the opposite
asymmetry between intensity and velocity. We use a physics-based
asymmetrical line shape to fit p-mode lines, and we demonstrate
that their asymmetry is statistically significant and that frequency
differences are considerably reduced. These measurements provide more
accurate estimates of the solar eigenfrequencies. We discuss inferences
of the structure of the solar core.

---------------------------------------------------------
Title: Helioseismic Studies of Differential Rotation in the Solar
Envelope by the Solar Oscillations Investigation Using the Michelson
Doppler Imager
Authors: Schou, J.; Antia, H. M.; Basu, S.; Bogart, R. S.; Bush,
R. I.; Chitre, S. M.; Christensen-Dalsgaard, J.; Di Mauro, M. P.;
Dziembowski, W. A.; Eff-Darwich, A.; Gough, D. O.; Haber, D. A.;
Hoeksema, J. T.; Howe, R.; Korzennik, S. G.; Kosovichev, A. G.;
Larsen, R. M.; Pijpers, F. P.; Scherrer, P. H.; Sekii, T.; Tarbell,
T. D.; Title, A. M.; Thompson, M. J.; Toomre, J.
1998ApJ...505..390S Altcode:
The splitting of the frequencies of the global resonant acoustic modes
of the Sun by large-scale flows and rotation permits study of the
variation of angular velocity Ω with both radius and latitude within
the turbulent convection zone and the deeper radiative interior. The
nearly uninterrupted Doppler imaging observations, provided by the
Solar Oscillations Investigation (SOI) using the Michelson Doppler
Imager (MDI) on the Solar and Heliospheric Observatory (SOHO) spacecraft
positioned at the L1 Lagrangian point in continuous sunlight,
yield oscillation power spectra with very high signal-to-noise ratios
that allow frequency splittings to be determined with exceptional
accuracy. This paper reports on joint helioseismic analyses of
solar rotation in the convection zone and in the outer part of the
radiative core. Inversions have been obtained for a medium-l mode set
(involving modes of angular degree l extending to about 250) obtained
from the first 144 day interval of SOI-MDI observations in 1996. Drawing
inferences about the solar internal rotation from the splitting data
is a subtle process. By applying more than one inversion technique
to the data, we get some indication of what are the more robust
and less robust features of our inversion solutions. Here we have
used seven different inversion methods. To test the reliability and
sensitivity of these methods, we have performed a set of controlled
experiments utilizing artificial data. This gives us some confidence
in the inferences we can draw from the real solar data. The inversions
of SOI-MDI data have confirmed that the decrease of Ω with latitude
seen at the surface extends with little radial variation through much
of the convection zone, at the base of which is an adjustment layer,
called the tachocline, leading to nearly uniform rotation deeper
in the radiative interior. A prominent rotational shearing layer in
which Ω increases just below the surface is discernible at low to
mid latitudes. Using the new data, we have also been able to study the
solar rotation closer to the poles than has been achieved in previous
investigations. The data have revealed that the angular velocity
is distinctly lower at high latitudes than the values previously
extrapolated from measurements at lower latitudes based on surface
Doppler observations and helioseismology. Furthermore, we have found
some evidence near latitudes of 75° of a submerged polar jet which
is rotating more rapidly than its immediate surroundings. Superposed
on the relatively smooth latitudinal variation in Ω are alternating
zonal bands of slightly faster and slower rotation, each extending
some 10° to 15° in latitude. These relatively weak banded flows
have been followed by inversion to a depth of about 5% of the solar
radius and appear to coincide with the evolving pattern of “torsional
oscillations” reported from earlier surface Doppler studies.

---------------------------------------------------------
Title: Long-lived giant cells detected at the surface of the Sun
Authors: Beck, J. G.; Duvall, T. L.; Scherrer, P. H.
1998Natur.394..653B Altcode:
Giant convective cells have been predicted to exist in the Sun. Such
cells should span the entire zone unstable to convective motions - now
known to cover the outer 29 per cent of the Sun's radius - and could
be dredging up the magnetic flux that is thought to be the source of
solar activity (sunspots). Several studies have failed to detect these
giant cells, although there have been hints of their existence. We have
detected long-lived velocity cells, which we identify as the elusive
giant convective cells, extending over 40-50 degrees of longitude but
less than 10 degrees of latitude. The large aspect ratio (&gt;4) is
surprising (although predicted by one model) and may be a consequence
of the Sun's differential rotation, whereby features with a larger
extent in latitude are broken up by rotational shear.

---------------------------------------------------------
Title: Oscillations of sunspot magnetic fields
Authors: Rueedi, I.; Solanki, S. K.; Stenflo, J. O.; Tarbell, T.;
Scherrer, P. H.
1998A&A...335L..97R Altcode:
We report on velocity and magnetic field oscillations observed
in sunspots using the MDI instrument onboard SOHO. In addition to
the well-known velocity oscillations, the data clearly show highly
localised oscillations of the magnetogram signal in different parts
of the sunspots. We show that only oscillations of the magnetic field
vector can produce the observed magnetogram oscillations, and that the
observed phase relations suggest an origin in terms of magnetoacoustic
gravity waves.

---------------------------------------------------------
Title: Magnetic Field of the Sun as a Star: The Mount Wilson
Observatory Catalog 1970-1982
Authors: Kotov, V. A.; Scherrer, P. H.; Howard, R. F.; Haneychuk, V. I.
1998ApJS..116..103K Altcode:
Measurements of the mean magnetic field of the Sun (MMFS) seen as
a star were regularly conducted at the Mount Wilson Observatory
from 1970 October through 1982 December. A listing is presented of
all these data (2457 daily values) suitable for comparison with
similar data of other observatories and for studies of magnetic
variability and rotation of the Sun. The scatter-plot diagrams and
power spectra of the Mount Wilson data and also of the total data
1968-1991 (collected from three observatories: Crimean Astrophysical
Observatory, Mount Wilson Observatory, and Wilcox Solar Observatory)
are also presented. Time variations of the MMFS connected with solar
rotation at periods ~27-28 days and also an enigmatic 1 yr variation
are briefly discussed. The power spectrum of the 24 yr data set
shows that the most significant and phase-coherent synodic periods of
the MMFS variations are 26.92 +/- 0.02 and 27.13 +/- 0.02 days (both
are thought to be associated with rotation of the large-scale surface
magnetic field near equator of the Sun) and 28.13 +/- 0.02 days. It
is suggested that the latter period reflects “rigid” rotation of
the global magnetic field concentrated under the bottom of the solar
convection zone. The arguments are given in favor of reality and high
confidence level of major periodicities exhibited by MMFS variations.

---------------------------------------------------------
Title: Initial High-Degree p-Mode Frequencies and Rotational Frequency
Splittings from the SOHO SOI/MDI Experiment
Authors: Rhodes, E. J., Jr.; Reiter, J.; Kosovichev, A. G.; Schou,
J.; Scherrer, P. H.
1998AAS...192.1901R Altcode: 1998BAAS...30..845R
We present the first high-degree p-mode frequencies and
rotationally-induced frequency splittings obtained from the Full-Disk
Program of the SOHO Solar Oscillation Investigation/Michelson
Doppler Imager experiment. The frequencies and splittings which we
present here were computed from power spectra obtained during the
1996 SOI/MDI Dynamics Run. Specifically, a 60.75-day time series of
full-disk Dopplergrams was converted into sets of zonal, tesseral,
and sectoral power spectra covering the degree range of 0 through
1000. Estimates of the n-averaged frequency splittings were computed
for the frequency range of 1800 to 4800 microhertz at each degree and
these averaged splitting coefficients were then employed to compute an
average power spectrum for that degree. From these 1001 average power
spectra estimates were made of the frequencies, frequency uncertainties,
widths, peak power densities, and background power densities of a total
of 13664 separate peaks in the set of 1001 average power spectra. A
total of 2554 of these peaks were isolated enough in their respective
spectra to be fit as single p-modes. However, for the remaining 11110
peaks (mostly those above l =200), the individual p-mode peaks and
their spatial sidelobes were located so close together in frequency
that they appeared as ridges rather than as isolated modal peaks in the
average power spectra. For these p-mode ridges we obtained so-called
“ridge-fit” parameter estimates. Observed asymmetries in the p-mode
ridge shapes altered the fitted peak frequencies from their “true”
values and required that we correct the raw ridge-fit frequencies. Forty
sets of these power spectra were also processed to yield estimates of
the rotational splitting coefficients for individual p-mode ridges
for every 25th degree between l =25 and 1000. For l between 25
and 175 we will compare these Full-Disk program splittings with the
previously-published splittings from the 1996 SOI/MDI Medium-l Program
(Kosovichev et al., Solar Physics, 170, 43-61,1997).

---------------------------------------------------------
Title: Asymmetry in Velocity and Intensity Helioseismic Spectra:
A Solution to a Long-standing Puzzle
Authors: Nigam, R.; Kosovichev, A. G.; Scherrer, P. H.; Schou, J.
1998ApJ...495L.115N Altcode:
We give an explanation for the opposite sense of asymmetry of the
solar acoustic mode lines in velocity and intensity oscillation
power spectra, thereby solving the half-decade-old puzzle of Duvall
and coworkers. The solution came after comparing the velocity and
intensity oscillation data of medium angular degree l obtained from the
Michelson Doppler Imager instrument on board the Solar and Heliospheric
Observatory with the theoretical power spectra. We conclude that the
solar noise in the velocity and intensity spectra is made up of two
components: one is correlated to the source that is responsible for
driving the solar p-modes, and the other is an additive uncorrelated
background. The correlated component of the noise affects the line
profiles. The asymmetry of the intensity spectrum is reversed because
the correlated component is of a sufficiently large level, while the
asymmetry of the velocity spectrum remains unreversed because the
correlated component is smaller. This also explains the high-frequency
shift between velocity and intensity at and above the acoustic cutoff
frequency. A composite source consisting of a monopole term (mass term)
and a dipole term (force due to Reynolds stress) is found to explain
the observed spectra when it is located in the zone of superadiabatic
convection at a depth of 75+/-50 km below the photosphere.

---------------------------------------------------------
Title: The sun's shape and brightness
Authors: Kuhn, J. R.; Bush, R. I.; Scherrer, P.; Scheick, X.
1998Natur.392..155K Altcode:
We present satellite data that show that the sun's shape and temperature
vary with latitude in an unexpectedly complex way. Although the solar
oblateness shows no evidence of varying with the solar cycle, we find
a significant hexadecapole shape term which may vary. We also see a
variation of about 1.5 K in the surface temperature with latitude. Based
on these results, we suggest that sensitive observations of brightness
variations be used as a record of the surface 'shadow' of cyclical
changes in the solar interior.

---------------------------------------------------------
Title: A New Method for Diagnostics of Solar Magnetic Fields and
Flows from Time-Distance Analysis
Authors: Ryutova, Margarita; Scherrer, Philip
1998ApJ...494..438R Altcode:
We propose a new method to obtain information on plasma flows and
magnetic fields below the visible solar surface using time-distance
measurements. The method is based on sine and cosine transforms of
propagation times measured as a function of direction. The method allows
one to sort out various characteristics of the subsurface medium, the
flows, magnetic fields and their nonuniformities, and is less sensitive
to the measurement errors. We discuss the parity properties of various
contributions to the propagation times with respect to forward and
backward directions and show how these properties allow separation of
the effects of magnetic field and flows, as well as separation of the
horizontal components from the vertical. It is shown that the first
harmonics contain information on the direction and absolute value of the
velocity, while the second harmonics are sensitive to the orientation
and absolute value of horizontal magnetic fields and spatial gradients
of the flow velocity. We discuss the effects of discrete mesh on the
accuracy of measurements of the propagation time. An advantage of the
method is in its intrinsic invariance with respect to the choice of the
coordinate frame. The method provides an automatic rule of assigning
proper weights to every observation points. We give estimates of
the accuracy of the reconstruction of the flow field over distances
comparable with the scale of the convection. We also present the
“magnetic” corrections to the propagation time in a vertically
stratified medium.

---------------------------------------------------------
Title: The Comparison of Simultaneous SOI/MDI and Mt. Wilson 60-foot
Tower Power Spectra and p-Mode Parameters
Authors: Rhodes, E. J., Jr.; Reiter, J.; Kosovichev, A. G.; Schou,
J.; Scherrer, P. H.; Rose, P. J.; Irish, S.; Jones, A. R.
1998ESASP.418..311R Altcode: 1998soho....6..311R
We present the results of the first detailed comparison between the
1996 SOHO SOI/MDI Dynamics Run program of full-disk Ni I Dopplergram
observations and a simultaneous time series of ground-based
observations obtained in the Na D lines at the 60-Foot Solar Tower
of the Mt. Wilson Observatory (MWO). Specifically, we will compare
sets of simultaneously-observed SOHO/MDI and MWO power spectra and
the high-degree p-mode frequencies, frequency splittings, widths, and
power densities which we obtained by fitting these two sets of power
spectra. Beginning on May 23, 1996, the SOI/MDI experiment began its
first high duty cycle run of 1024x1024 pixel images. this was the
1996 Dynamics Run. On all but three of the days of this 60.75-day
time series a second time series of simultaneous 1024x1024 pixel
full-disk Dopplergrams was obtained at MWO. From these simultaneous MWO
observations we have computed 601 sets of zonal, tesseral, and sectoral
power spectra which covered the degree range of 0 to 600. These sets
of power spectra were then analyzed in two different ways to yield
both frequencies and frequency splittings. First, estimates of the
frequency splittings were computed for the frequency range of 1800 to
4800 microhertz at each degree and these n-averaged splittings were
employed to compute an average power spectrum for that degree. Estimates
were then made of the frequencies, frequency uncertainties, widths, peak
power densities, and background power densities of the set of peaks in
these 601 average power spectra. As is described in our companion paper
on the MDI ridge-fit frequency measurements (Rhodes et al.,1998), we
also had to correct our raw MWO ridge-fit frequencies for the effects
the merger of individual p-mode peaks and sidelobes into ridges. We
could also directly compare the frequency dependence of the observed
power density in both the MDI and MWO power spectra. We have found
that there is a systematic difference such that the power density in
the chromospheric-level power spectra from MWO tends to be below that
of the photosheric-level MDI spectra at low frequencies and to rise
above the MDI power density as the frequency increases. All but the l
= 0 MWO power spectra were also processed to yield estimates of the
rotational splitting coefficients for individual p-mode ridges for
every degree between l = 4 and 600. We will compare these splittings
with both the previously-published splittings from the 1996 SOI/MDI
Medium-l Program (Kosovichev et al., 1997) and with the MDI high-degree
splittings presented in our companion MDI paper.

---------------------------------------------------------
Title: Line Asymmetry of VIRGO and MDI Low-Degree p Modes
Authors: Toutain, T.; Appourchaux, T.; Frohlich, C.; Kosovichev, A.;
Rakesh, N.; Scherrer, P.
1998ESASP.418..973T Altcode: 1998soho....6..973T
Using continuous time series of 610 days of velocity (MDI, LOI-proxy)
and intensity (VIRGO, SPM and LOI) we show that Lorentzian profiles as
a model of low-degree p-mode line leads to systematic differences in
the determination of intensity and velocity mode frequencies. These
differences, as large as 0.1 muHz for degrees l = 0, 1, 2 and 3,
are frequency-dependent. The use of a physics-based asymmetrical line
shape (Rakesh et al., 1998) to fit the same lines has allowed us to
significantly reduce differences in the frequency determination. P-mode
lines in velocity exhibit a significant negative asymmetry (excess
of power in the left wing) whereas p-modes lines in intensity have a
positive asymmetry (excess of power in the right wing). The magnitude
and sign of this asymmetry are directly related to the location of
the source of p-mode excitation and to the correlation between mode
and solar noise.

---------------------------------------------------------
Title: Time-Distance Measurements of Subsurface Rotation and
Meridional Flow
Authors: Giles, P. M.; Duvall, T. L., Jr.; Scherrer, P. H.
1998ESASP.418..775G Altcode: 1998soho....6..775G
One of the most promising applications of time-distance helioseismology
is the measurement of flows beneath the solar surface. In some
cases the time-distance approach can yield information which cannot
be obtained with more traditional helioseismology. Recently this
technique has been used to measure the global meridional circulation
(Giles et al., 1997) and differential rotation (Giles &amp; Duvall,
1997). So far, these meaurements have only been able to penetrate a
short distance into the solar interior --- up to a few percent of the
solar radius. We will present the results of work which extends these
measurements to greater depths, with a special focus on the meridional
circulation. Probing this deeper region, while simple in principle,
offers significant practical challenges. We will present a brief
analysis of these difficulties along with our new results.

---------------------------------------------------------
Title: Comparison of SOHO-SOI/MDI and GONG Spectra
Authors: Komm, R. W.; Anderson, E.; Hill, F.; Howe, R.; Kosovichev,
A. G.; Scherrer, P. H.; Schou, J.; Fodor, I.; Stark, P.
1998ESASP.418..253K Altcode: 1998soho....6..253K
We compare solar p-mode parameters, such as central frequency, width,
and amplitude, derived from GONG and SOHO-SOI/MDI Medium-l Program
time series obtained during the same time period. With the excellent
data available now from GONG and SOHO-SOI/MDI, there exist data
sets long enough to make such a comparison useful. For this study,
we have chosen time series of three ell values (ell = 30, 65, and 100)
corresponding to GONG month 16 (Oct 28 -- Dec 2, 1996). For each time
series, we calculated multitaper power spectra using generalized
sine tapers to reduce the influence of the gap structure, which is
different for the two data sets. Then, we applied the GONG peakfitting
algorithm to the spectra to derive mode parameters and selected `good'
fits common to both MDI and GONG spectra, according to three selection
criteria. Preliminary results show that mode frequencies determined
from MDI spectra are essentially the same as the frequencies from
GONG spectra and that the difference is, in general, well within one
formal error bar. The background slope at frequencies above 5mHz is
different between MDI and GONG spectra depending on ell. At present,
we are analyzing 3-month time series of ell = 0 to ell = 150. We intend
to present the results of the on-going comparison.

---------------------------------------------------------
Title: Helio-Atmospheric Links Explorer (HALE): A MIDEX Experiment
for Exploring the Emergence of Magnetic Flux from Below the Solar
Photosphere through the Corona
Authors: Scherrer, P. H.; Title, A. M.; Bush, R. I.; Duvall, T. L.,
Jr.; Gurman, J. B.; Kosovichev, J. T.; Hoeksema, A. G.; Poland, A. I.;
Tarbell, T. D.
1998ESASP.417..285S Altcode: 1998cesh.conf..285S
No abstract at ADS

---------------------------------------------------------
Title: Initial SOI/MDI High-Degree Frequencies and Frequency
Splittings
Authors: Rhodes, E. J., Jr.; Reiter, J.; Kosovichev, A. G.; Schou,
J.; Scherrer, P. H.
1998ESASP.418...73R Altcode: 1998soho....6...73R
We present the first high-degree p-mode frequencies and frequency
splittings obtained from the Full-Disk Program of the SOHO Solar
Oscillation Investigation/Michelson Doppler Imager experiment. The
frequencies and splittings which we present here were computed
from power spectra obtained during the 1996 SOI/MDI Dynamics
Run. Specifically, a time series of full-disk Dopplergrams, which
began on May 23, 1996, and which covered 87480 minutes (60.75 days),
was converted into sets of zonal, tesseral, and sectoral power spectra
covering the degree range of 0 through 1000. These sets of power spectra
were then analyzed in two different ways to yield both frequencies and
frequency splittings. First, estimates of the frequency splittings
were computed for the frequency range of 1800 to 4800 microhertz at
each degree and these n-averaged splittings were employed to compute an
average power spectrum for that degree. Estimates were then made of the
frequencies, frequency uncertainties, widths, peak power densities,
and background power densities of a total of 13664 separate peaks
in these 1001 average power spectra. A total of 2554 of these peaks
were isolated enough in their respective spectra to be fit as single
p-modes. However, for the remaining 11110 peaks (mostly those above l
= 200), the individual p-mode peaks and their spatial sidelobes were
located so close together in frequency that they appeared as ridges
rather than as isolated modal peaks in the average power spectra. For
these cases we were forced to employ a wider fitting range for our
frequency-estimation code and in so doing we obtained so-called
“ridge-fit” parameter estimates. Due to a degree-dependence in
the measured velocity power density, the observed p-mode ridges were
asymmetric in shape. These asymmetries in the p-mode ridge shapes,
which are in addition to the intinsic asymmetries caused by the
excitation mechanism of the p-modes themselves, alter the fitted peak
frequencies from their “true” values. For this reason, we had to
develop a mechanism which we then used to correct the raw ridge-fit
frequencies. Forty sets of these power spectra were also processed to
yield estimates of the rotational splitting coefficients for individual
p-mode ridges for every 25th degree between l = 25 and 1000. For l
between 25 and 175 we will compare these Full-Disk program splittings
with the previously-published splittings from the 1996 SOI/MDI Medium-l
Program (Kosovichev et al., Solar Physics, 170, 43-61,1997).

---------------------------------------------------------
Title: The Stellar and Planetary Explorer (SPEX) Mission
Authors: Schou, J.; Scherrer, P. H.; Brown, T. M.; Frandsen, S.;
Horner, S. D.; Korzennik, S. G.; Noyes, R. W.; Tarbell, T. D.; Title,
A. M.; Walker, A. B. C., II; Weiss, W. W.; Bogart, R. S.; Bush, R. I.;
Christensen-Dalsgaard, J.; Hoeksema, J. T.; Jones, A.; Kjeldsen, H.
1998ESASP.418..401S Altcode: 1998soho....6..401S
The Stellar and Planetary Explorer (SPEX) is a mission designed
to search for terrestrial sized planets around sun-like stars using
precise photometry. The planets will be detected by searching for the
decrease in brightness associated with transits of the planets in front
of their parent stars. One of the secondary scientific objective of
SPEX is to do asteroseismology on a number of sun-like stars. SPEX
is designed as a secondary payload on a commercial communications
satellite and will have a design life time of three years. We will
provide an overview of the SPEX scientific objectives and design,
with particular emphasis on the prospects for doing asteroseismology.

---------------------------------------------------------
Title: The Evershed Effect: an MDI Investigation
Authors: Bai, T.; Scherrer, P. H.; Bogart, R. S.
1998ESASP.418..607B Altcode: 1998soho....6..607B
Because SOHO/MDI observes the Sun continuously, it provides valuable
data for studying various properties of plasma flows within and around
sunspots. We have studied the plasma flows in a long-lived active
region, which crossed the solar disk for three times. After emerging
in the southern hemisphere on July 4, 1996, AR 7978 developed rapidly,
producing an X-class flare on July 9. After passing over the western
limb on July 13, it rotated into the visible hemisphere for its second
and third disk passages. When it appeared for its second disk passage
on July 26 (AR 7981), leading-polarity (positive) spots remained with
negative spots dispersed into network fields, and only the leader
spot remained by the end of its second disk passage. The leader spot
decayed slowly during its third disk passage after returning to the
visible hemisphere on August 23 (AR 7986). Full-disk dopplergrams were
obtained continuously throughout the first disk passage period, because
the first dynamics program was in operation. Full-disk dopplergrams
were obtained during some parts of the second and third disk passages,
providing enough clue for the characteristics of plasma flows in this
active region. The important results are as follows: (1) Horizontal
out flows seem to be continuous from within sunspot umbrae, penumbrae,
and outside penumbrae. Outflows within the umbra are spatially well
resolved. In a given sunspot, the magnitude of the horizontal outflow
slowly increases as the distance from the center of the spot increases,
reaching its maximum (order of 1500 m/s) in the penumbra. (2) Vertical
down flows are detected, with their magnitude reaching its maximum
value of about 300 m/s outside the penumbra. (3) After such plasma flows
(out and downward flows) weakens, sunspots decay rapidly. Therefore, it
seems that such flows are a main mechanism keeping a sunspot from decay.

---------------------------------------------------------
Title: Line asymmetry and excitation mechanism of solar oscillations
Authors: Nigam, R.; Kosovichev, A. G.; Scherrer, P. H.
1998IAUS..185..195N Altcode:
The width and asymmetry of lines in the power spectrum of solar
oscillations, obtained from the Michelson Doppler Imager (MDI) data,
on board the Solar and Heliospheric Observatory (SOHO), are used to
study the physics of excitation and damping of the oscillations. A
theoretical model for solar oscillations is developed. In this model,
the asymmetry is an effect of interference between the trapped waves
from the source that pass through the region of wave propagation in the
Sun's interior. From this the power spectrum is computed for different
values of the source location and for various values of the angular
degree l. It is seen that there is marked line asymmetry below the
acoustic cut-off frequency, which corresponds to the asymmetry of
bound states in quantum mechanics. The asymmetry is reduced above
the acoustic cut-off frequency, which corresponds to the asymmetry
of scattered states, which is a result of interference between an
outward direct wave from the source and corresponding inward untrapped
waves. The asymmetry is found to depend strongly on the source location
and on the value of l. We discuss the properties of the solar acoustic
source inferred from the MDI data.

---------------------------------------------------------
Title: The Detection of Giant Velocity Cells on the Sun
Authors: Beck, J. G.; Duvall, T. L., Jr.; Scherrer, P. H.; Hocksema,
J. T.
1998ESASP.418..725B Altcode: 1998soho....6..725B
No abstract at ADS

---------------------------------------------------------
Title: VIRGO on SOHO: Status and Future Prospects
Authors: Fröhlich, C.; Scherrer, P.; MDI Team; Virgo Team; Gabriel,
A.; GOLF Team
1998ESASP.418....7F Altcode: 1998soho....6....7F
After two years of nearly uninterrupted operation, the Michelson
Doppler Imager (MDI) instrument has produced many unique data sets
that are being used to address a wide variety of topics in solar
physics. The more than two years of observations from VIRGO (Variability
of solar IRradiance and Gravity Oscillations) yield a unique data set
covering the activity minimum and the rising part of cycle 23. This
allows not only to determine the influence of varying activity on the
solar oscillation frequencies and amplitudes, but also to study the
relationship between oscillations and irradiance variability. Over
2 years of GOLF data with nearly 100% continuity are yielding the
highest ever signal to noise quality, enabling precise measurements of
the frequencies, linewidths and power in the p-modes. The precision
available for the inversion of the frequencies in terms of sound
speed in the solar interior is no longer limited by the quality of the
time-series itself, but rather by questions concerning the most correct
method of fitting the observed spectrum. Unique measurements from the
GOLF p-mode signals include the high-frequency global structure above
the acoustic cut-off and the measurement of the global average magnetic
field of the Sun. Several different techniques are being employed in
searching for the g-mode signals in the GOLF spectrum.

---------------------------------------------------------
Title: Spherical and aspherical structure of the sun: First year of
SOHO/MDI observations
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Goode, P. H.;
Dziembowski, W. A.; Rhodes, E. J., Jr.; SOI Structure Inversion Team
1998IAUS..185..157K Altcode:
We report the results of one year of continuous observations of the
Sun's internal structure using data from the Medium-l Program of
the Michelson Doppler Imager (MDI) on board SOHO. The data provide
continuous coverage of p modes of angular degree l from 0 to 250,
and the f mode from l=100 to 250. The striking stability of solar
Dopplergrams measured by MDI, without an intervening atmosphere,
substantially decreases the noise in the solar oscillations power
spectrum compared with ground-based observations. This permits
detection of lower amplitude oscillations, extending the range and
precision of measured normal mode frequencies. We present new inversion
results for the radial and latitudinal seismic solar structures with
particular attention to zonal asphericity inferred with the high
angular resolution from the data. Using f-mode frequency splitting
we estimate the large-scale structure of the subsurface magnetic
fields. The variations of the solar structure observed during the
first year of MDI observations are also discussed.

---------------------------------------------------------
Title: SOI/MDI: Status and Future Prospects
Authors: Scherrer, P. H.
1998ESASP.418...15S Altcode: 1998soho....6...15S
No abstract at ADS

---------------------------------------------------------
Title: Observational Upper Limits for Low-Degree Solar g-modes
Authors: Fröhlich, C.; Finsterle, W.; Andersen, B.; Appourchaux, T.;
Chaplin, W. J.; Elsworth, Y.; D. O. Gough; Hoeksema, J. T.; Isaak,
G. R.; Kosovichev, A. G.; Provost, J.; Scherrer, P. H.; Sekii, T.;
Toutain, T.
1998ESASP.418...67F Altcode: 1998soho....6...67F
No abstract at ADS

---------------------------------------------------------
Title: Sunspot Oscillations Observed with MDI
Authors: Rüedi, I.; Solanki, S. K.; Stenflo, J. O.; Scherrer, P. H.
1998ESASP.417..281R Altcode: 1998cesh.conf..281R
No abstract at ADS

---------------------------------------------------------
Title: Comparative Studies of Low-Order and Low-Degree Solar p Modes
Authors: Appourchaux, T.; Andersen, B.; Chaplin, W.; Elsworth, Y.;
Finsterle, W.; Frohlich, C.; Gough, D.; Hoeksema, J. T.; Isaak, G.;
Kosovichev, A.; Provost, J.; Scherrer, P.; Sekii, T.; Toutain, T.
1998ESASP.418...95A Altcode: 1998soho....6...95A
The amplitudes of solar p-modes decrease steeply with decreasing
radial order below about 17. The background solar signal (solar noise)
in general increases steadily with decreasing frequency. For the
irradiance and radiance measurements with VIRGO or SOI/MDI on SOHO this
combination makes it difficult to detect low degree modes below about
1.8 mHz. The solar noise as observed in velocity with SOI/MDI or the
ground based BISON network is significantly lower in this region than
in intensity measurements. This allows low degree modes to be observed
close to 1 mHz. We present results of detection and charaterization
of the lowest order observable p-modes both in velocity and intensity
measurements. Where applicable the properties of the modes observed
with the two methods are compared.

---------------------------------------------------------
Title: Calibration and Stability of MDI Velocities
Authors: Beck, J. G.; Scherrer, P. H.; Bush, R. I.; Tarbell, T. D.
1998ESASP.418..105B Altcode: 1998soho....6..105B
No abstract at ADS

---------------------------------------------------------
Title: A Modification to the Calibration of MDI Velocities
Authors: Evans, S.; Ulrich, R. K.; Scherrer, P. H.; Bush, R. I.;
Tarbell, T. D.
1998ESASP.418..157E Altcode: 1998soho....6..157E
The ability of the Michelson Doppler Imager instrument used by the
Solar Oscillations Investigation (Scherrer, et al, 1995) to produce
velocity measurements is affected by center-to-limb effects on the Ni
6768 AA line profile. These effects are removed by special calibration
observations known as detunes. Part of the detune procedure involves the
modelling of center-to-limb line profile changes by fitting a Gaussian
to the line profile and varying both the model profile's depth and
FWHM as a function of center-to-limb angle. However, the functions
used for modelling both line depth and FWHM differ from those derived
from data from both the Mt. Wilson 150' Tower and the Fourier Transform
Spectrometer at Kitt Peak. This variation can produce velocity errors
of ~100 m/s. By modifying the line depth and FWHM functions to conform
to those derived from the data, an improved velocity calibration can
be achieved.

---------------------------------------------------------
Title: Probing the Internal Structure of the Sun with the SOHO
Michelson Doppler Imager
Authors: Kosovichev, A. G.; Nigam, R.; Scherrer, P. H.; Schou, J.;
Reiter, J.; Rhodes, E. J., Jr.; Toutain, T.
1997AAS...191.7311K Altcode: 1997BAAS...29R1322K
The inference of the thermodynamic structure of the Sun from the
observed properties of the solar normal modes of oscillation is a
principal goal of helioseismology. We report the results of the first
year of continuous observations of the Sun's internal structure using
data from the Medium-l Program of the Michelson Doppler Imager (MDI)
on board ESA/NASA spacecraft SOHO. The data provide continuous coverage
of the acoustic (p) modes of angular degree l from 0 to 250, and the
fundamental (f) mode of the Sun from l=100 to 250. During two 2-month
intervals, the high-degree modes, up to l=1000, have been observed. The
great stability of solar Dopplergrams measured by MDI permits detection
of lower amplitude oscillations, extending the range and precision of
measured normal mode frequencies, and thus substantially increasing
the resolution and precision of helioseismic inversions. We present
new inversion results for the radial and latitudinal seismic solar
structures with particular attention to the transition region between
the radiative and convection zones and to the energy-generating core. We
discuss evidence for convective overshoot at the base of the convection
zone, and the significance of deviations in the core structure from
the standard evolutionary model. Comparing the f-mode frequencies
with the corresponding frequencies of the standard solar models, we
argue that the apparent photospheric solar radius (695.99 Mm) used to
calibrate the models should be reduced by approximately 0.3 Mm. The
discrepancy between the `seismic' and apparent photospheric radii is
not explained by the known systematic errors in the helioseismic and
photospheric measurements. If confirmed, this discrepancy represents
a new interesting challenge to theories of solar convection and solar
modeling. Using f-mode frequency splitting we estimate the large-scale
structure of the subsurface magnetic fields. The variations of the solar
oscillation frequencies during the first year of MDI observations are
also discussed.

---------------------------------------------------------
Title: Rotation and Zonal Flows in the Solar Envelope from the
SOHO/MDI Observations
Authors: Scherrer, P. H.; Schou, J.; Bogart, R. S.; Bush, R. I.;
Hoeksema, J. T.; Kosovichev, A. G.; Antia, H. M.; Chitre, S. M.;
Christensen-Dalsgaard, J.; Larsen, R. M.; Pijpers, F. P.; Eff-Darwich,
A.; Korzennik, S. G.; Gough, D. O.; Sekii, T.; Howe, R.; Tarbell,
T.; Title, A. M.; Thompson, M. J.; Toomre, J.
1997AAS...191.7310S Altcode: 1997BAAS...29.1322S
We report on the latest inferences concerning solar differential
rotation that have been drawn from the helioseismic data that are now
available from the Solar Oscillations Investigation (SOI) using the
Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory
(SOHO). That spacecraft is positioned in a halo orbit near the Sun-Earth
Lagrangian point L_1, in order to obtain continuous Doppler-imaged
observations of the sun with high spatial fidelity. Doppler velocity,
intensity and magnetic field images are recorded, based on modulations
of the 676.8 nm Ni I solar absorption line. The high spatial resolution
of MDI thereby permits the study of many millions of global resonant
modes of solar oscillation. Determination and subsequent inversion
of the frequencies of these modes, including the degeneracy-splitting
by the rotation of the sun, enables us to infer how the sun's angular
velocity varies throughout much of the interior. The current MDI data
are providing substantial refinements to the helioseismic deductions
that can be made about differential rotation both within the convection
zone and in its transition to the radiative interior. The shearing
layer evident in the angular velocity Omega just below the solar
surface is becoming better defined, as is the adjustment layer or
tachocline near the base of the convection zone. The MDI data are also
revealing a prominent decrease in Omega at high latitudes from the
rotation rate expressed by a simple three-term expansion in latitude
that was originally deduced from surface Doppler measurements. Further,
there are indications that a submerged polar vortex involving somewhat
faster Omega than its surroundings exists at about 75(deg) in latitudes.

---------------------------------------------------------
Title: A subsurface flow of material from the Sun's equator to
its poles
Authors: Giles, P. M.; Duvall, T. L.; Scherrer, P. H.; Bogart, R. S.
1997Natur.390...52G Altcode:
Gas on the Sun's surface has been observed to flow away from the
equator towards both poles. If the same flow persists to great depths,
it could play an important dynamical role in the eleven-year sunspot
cycle, by carrying the magnetic remnants of the sunspots to high
latitudes. An even deeper counterflow, which would be required
to maintain mass balance, could explain why new sunspots form at
lower latitudes as the cycle progresses. These deep flows would
also redistribute angular momentum within the Sun, and therefore
help to maintain the faster rotation of the equator relative to the
poles. Here we report the detection, using helioseismic tomography,
of the longitude-averaged subsurface flow in the outer 4% of the
Sun. We find that the subsurface flow is approximately constant in
this depth range, and that the speed is similar to that seen on the
surface. This demonstrates that the surface flow penetrates deeply,
so that it is likely to be an important factor in solar dynamics.

---------------------------------------------------------
Title: Measurements of Frequencies of Solar Oscillations from the
MDI Medium-l Program
Authors: Rhodes, E. J., Jr.; Kosovichev, A. G.; Schou, J.; Scherrer,
P. H.; Reiter, J.
1997SoPh..175..287R Altcode:
Inversions of solar internal structure employ both the frequencies
and the associated uncertainties of the solar oscillation modes
as input parameters. In this paper we investigate how systematic
errors in these input parameters may affect the resulting inferences
of the sun's internal structure. Such systematic errors are likely
to arise from inaccuracies in the theoretical models which are used
to represent the spectral lines in the observational power spectra,
from line blending, from asymmetries in the profiles of these lines,
and from other factors. In order to study such systematic effects we
have employed two different duration observing runs (one of 60 days
and the second of 144 days) obtained with the Medium-l Program of the
Michelson Doppler Imager experiment onboard the SOHO spacecraft. This
observing program provides continuous observations of solar oscillation
modes having angular degrees, l, ranging from 0 to ∼ 300. For this
study intermediate- and high-degree p-mode oscillations having degrees
less than 251 were employed.

---------------------------------------------------------
Title: Tri-Phonic Helioseismology: Comparison of Solar P Modes
Observed by the Helioseismology Instruments Aboard SOHO
Authors: Toutain, T.; Appourchaux, T.; Baudin, F.; Fröhlich, C.;
Gabriel, A.; Scherrer, P.; Andersen, B. N.; Bogart, R.; Bush, R.;
Finsterle, W.; García, R. A.; Grec, G.; Henney, C. J.; Hoeksema,
J. T.; Jiménez, A.; Kosovichev, A.; Roca Cortés, T.; Turck-Chièze,
S.; Ulrich, R.; Wehrli, C.
1997SoPh..175..311T Altcode:
The three helioseismology instruments aboard SOHO observe solar p modes
in velocity (GOLF and MDI) and in intensity (VIRGO and MDI). Time series
of two months duration are compared and confirm that the instruments
indeed observe the same Sun to a high degree of precision. Power
spectra of 108 days are compared showing systematic differences between
mode frequencies measured in intensity and in velocity. Data coverage
exceeds 97% for all the instruments during this interval. The weighted
mean differences (V-I) are −0.1 µHz for l=0, and −0.16 µHz for
l=1. The source of this systematic difference may be due to an asymmetry
effect that is stronger for modes seen in intensity. Wavelet analysis
is also used to compare the shape of the forcing functions. In these
data sets nearly all of the variations in mode amplitude are of solar
origin. Some implications for structure inversions are discussed.

---------------------------------------------------------
Title: Solar Meridional Circulation and Rotation Determined by
Time-Distance Helioseismology using MDI Data From SOHO
Authors: Giles, P. M.; Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer,
P. H.
1997SPD....28.1002G Altcode: 1997BAAS...29..914G
Using the technique of time-distance helioseismology, acoustic wave
travel times can be measured between pairs of points on the solar
surface. The travel time of the waves depends primarily on the wave
group velocity and on the component of flow velocity which is parallel
to the direction of wave propagation. By choosing pairs of points which
share a common longitude, it is possible to use these waves to probe
the meridional flow beneath the surface. Any flows present will cause
a difference between the northward and southward travel times along
the meridian. Varying the distance between points allows isolation
of waves which propagate to different depths beneath the surface,
and thus the flow velocity can be measured as a function of latitude
and depth. Similarly, by choosing pairs of points which share a common
latitude it is possible to measure the effects of solar rotation using
an analogous procedure. This technique could provide high resolution
in latitude and allows study of the northern and southern hemispheres
independently. Using velocity images taken by the Michelson Doppler
Imager during June 1996, we have detected meridional flows in the
uppermost layers of the sun. Measurements of this flow velocity
and of the rotation rate as functions of latitude and depth will be
presented. This research is supported by NASA contract NAG5-3077 at
Stanford University.

---------------------------------------------------------
Title: Photospheric Differential Rotation from Full-Disk SOI/MDI
Dopplergrams
Authors: Bogart, R. S.; Bai, T.; Scherrer, P. H.; Strous, L. H.;
Simon, G. W.; Tarbell, T. D.
1997SPD....28.0258B Altcode: 1997BAAS...29..903B
We report on measurements of the solar surface differential rotation
made from SOI/MDI full-disk Dopplergrams obtained once per minute during
the 2-month Dynamics Program from 23 May through 26 July 1996. We infer
the rotation profile both from the direct photospheric Doppler signal
and also by tracking Doppler features (supergranules) across the solar
disk. We study the rotation curve as a function of latitude, feature
size, and tracking method, and look for global scale flows. This work
was supported by NASA Grant NAG5-3077 at Stanford and Lockheed Martin,
and by AFOSR and the Fellows Program of AF Phillips Lab at NSO/SP.

---------------------------------------------------------
Title: Surface Flows in Active Regions
Authors: Bai, T.; Bogart, R. S.; Scherrer, P. H.; Tarbell, T. D.
1997SPD....28.1701B Altcode: 1997BAAS...29..921B
Plasma flows around sunspots must influence the stability and
development of sunspots. We have been studying photospheric flows
around sunspots by analyzing dopplergrams and magneto- grams obtained
by the MDI (Michelson Doppler Imager) aboard SOHO. We have found some
interesting phenomena. First, during the growing phase of an active
region, plasmas around sunspots seem to draft downward with a speed of
order of 100 m/s. Second, during the decaying phase of an active region,
plasmas around sunspots flow outward. Outflow speeds range up to several
hundred m/s. Such outflows are prominent during the decaying phase of
a long-lived big active region. Third, there is evidence for flows
within sunspots. Such flows are presumed to be along magnetic field
lines. We will present the details of these results and discuss their
implications on the dynamics and stability of sunspots. MDI research
is supported by NASA contract NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: Analysis of Velocity and Intensity Helioseismic Spectra
from SOHO/MDI
Authors: Nigam, R.; Kosovichev, A. G.; Scherrer, P. H.; Schou, J.
1997SPD....28.0904N Altcode: 1997BAAS...29..913N
We give an explanation for the cause of the asymmetry of spectral lines
of solar oscillation power spectrum. We also explain the cause of the
opposite sense of asymmetry in velocity and intensity oscillation power
spectra, thereby resolving a half-decade old puzzle. The motivation for
the investigation came after comparing the velocity and intensity data
obtained from the Michelson Doppler Imager (MDI) instrument on board the
Solar and Heliospheric Observatory (SOHO). The analysis is based on a
theoretical model of wave excitation with viscous damping in conjunction
with a spherically symmetric solar model. Neglecting asymmetry can
lead to systematic errors in the eigenfrequency measurements, which
in turn leads to errors in inversion. This research was supported by
NASA grant NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: Continuous Observations of Solar Magnetic Fields from SOI/MDI
on SOHO
Authors: Hoeksema, J. T.; Bush, R. I.; Scherrer, P. H.; Heck, C.;
Hurlburt, N.; Shine, R.; Tarbell, T.; Title, A.
1997SPD....28.0127H Altcode: 1997BAAS...29..884H
The Solar Oscillations Investigation's Michelson Doppler Imager
instrument (SOI/MDI) on SOHO measures the photospheric magnetic field
over the whole disk nearly every 96 minutes with 4" resolution and a
noise level of a few Gauss. Beginning in April 1996, this unprecedented
continuous series of frequent, uniform quality magnetograms provides
a striking view of the continual emergence, motion, evolution, and
interaction of magnetic flux everywhere on the visible solar surface
near solar minimum. These evolving photospheric fields ultimately
drive the variations of the corona and solar wind that affect the
terrestrial environment. Knowledge of the rapidly evolving photospheric
field provides a crucial input for forecasting conditions in the
corona, heliosphere, and geospace. A few magnetograms are available
each day within hours of observation through the SOHO web site at
http://sohowww.nascom.nasa.gov/. These may be used for planning and
forecasting, e.g. to compute models of the solar corona. The remainder
are generally available within a few weeks. Sometimes more focused
campaigns provide magnetic observations as often as once each minute
for up to 8 hours. Campaigns can be run with either the full disk
resolution or with 0.6" pixels in a limited field near the center of
the disk. The SOI project welcomes collaborations. More information
can be found at http://soi.stanford.edu/.

---------------------------------------------------------
Title: Convective Flow Patterns in Time-Distance Measurements and
"Magnetic Corrections" in Vertically Stratified Atmosphere.
Authors: Ryutova, M.; Scherrer, P.
1997SPD....28.0204R Altcode: 1997BAAS...29..893R
Time-distance measurements for the reconstruction of subsurface flows
and horizontal magnetic fields proved to be very efficient. However,
if one can expect a reasonable accuracy of reconstructed maps for the
annuli of the radius small compared to the characteristic scale of
the convection, the situation changes when annular distances become
comparable with the scale of granular, mezogranular, or supergranular
convective motions: in each of these cases the uncertainty in the
measurements of travel time perturbations increases dramatically. We
present here a quantitative analysis of the problem for a particular
model of convective motions and compute the travel time perturbations as
a function of annular distances and the supergranule radius. It is shown
that at annular sizes close to the size of convective cell there occurs:
(1) the apparent reduction of the local velocity, and (2) appearance
of additional terms in the corrections to perturbation travel time
which cause a large error in reconstruction of the velocity field. We
discuss the importance of "directionally sensitive" measurements and
show that Fourier sin ntheta , cos ntheta transforms of travel times
measured as a function of direction, "kills" the largest source of
errors. We discuss the role of vertical motions. We also present the
expressions for the "magnetic corrections" in a vertically stratified
atmosphere. This research is supported by NASA contract NAG5-3077 at
Stanford University and the MDI contract PR 9162 at Lockheed.

---------------------------------------------------------
Title: Performance of the Michelson Doppler Imager Instrument on SOHO
Authors: Scherrer, P.; Bogart, R.; Bush, R.; Duvall, T.; Hoeksema,
J. T.; Kosovichev, A.; Schou, J.; Morrison, M.; Tarbell, T.; Title, A.
1997SPD....28.0207S Altcode: 1997BAAS...29..894S
Launched on SOHO in December 1995, the MDI instrument took its 10
millionth filtergram in early April, 1997. The instrument and spacecraft
have performed admirably since commissioning, providing over a year
of virtually uninterrupted time series of velocity and intensity
measurements at moderate resolution, a continuous 60-day time series
of full disk 4" velocity and line depth maps, monthly 72+ hour time
series in various observables, a host of daily 8-hour campaigns, and
full-disk magnetograms every 96 minutes. Another uninterrupted 90-day
interval of nearly full data recovery is scheduled to be completed in
mid July. Various scientific results using MDI data are being presented
at this meeting. About a dozen terabytes of data sets have been created
and archived and normal pipeline processing is now completed soon after
retrieving the data, typically less than a month after the observations
are made. Most of the data products are generally available on the WWW,
see http://soi.stanford.edu. Selected data are available in near real
time. The SOI team welcomes collaborations. Routine and extraordinary
calibrations along with analysis of scientific data sets allow us to
make good estimates of the noise and understand many of the sources
of systematic errors in the instrument. In almost every respect the
instrument performs as well or better than expected before launch,
the primary limitations being photon noise on the short term and
fixed or slowly varying offsets on the long term. We have found that
the Michelsons are somewhat more sensitive to operational temperature
variations than was expected, adding some additional constraints on
our observing sequences.

---------------------------------------------------------
Title: The Effects of Systematic Errors in the Estimation of p-Mode
Frequencies on the Inversion of Solar Internal Structure
Authors: Rhodes, E. J., Jr.; Appourchaux, T.; Bachmann, K.; Kosovichev,
A. G.; Scherrer, P. H.; Schou, J.; Reiter, J.
1997SPD....28.0901R Altcode: 1997BAAS...29..913R
The frequencies and associated uncertainties of the low-, intermdeiate-,
and high-degree p-mode oscillations are the input quantities for the
inversion programs which infer the thermodynamic structure of the solar
interior. In this review we will attempt to demonstrate the different
possible systematic errors that are currently present in our estimation
of both the modal frequencies and their uncertainties. We will also
demonstrate the effects of some of these errors upon the inferred
radial profile of the solar internal sound speed. Among the different
possible systematic errors which we will discuss are the effects of:
1)the asymmetric shapes of the peaks in observational power spectra,
2)the realization noise which is present in the case of the low-degree
modes, 3)the different frequency estimation methods used on different
types of power spectra (i.e., on either tesseral power spectra or
on m-averaged power spectra), 4) the differences in the frequencies
which are estimated from velocity- and intensity-based power spectra,
5) the blending of individual p-modes into so-called "ridges" of
observed power at both high degrees and high frequencies, and 6) the
spatial and temporal aliasing which occurs at both high degrees and
at high frequencies. We will demonstrate these different errors using
results obtained with the VIRGO and MDI experiments onboard the SOHO
spacecraft. We will also compare some of these space-based results
with the results of similar estimates obtained from co-temporaneous
ground-based observations, such as from the Mt. Wilson 60-Foot Solar
Tower. We will include the results from different structural inversions
carried out with different sets of input frequencies and uncertainties
in order to demonstrate the effects of these different systematic
errors upon the inverted internal sound speed profile.

---------------------------------------------------------
Title: Structure and Rotation of the Solar Interior: Initial Results
from the MDI Medium-L Program
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.;
Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.; de
Forest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.; Scott,
K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard, J.; Dappen,
W.; Rhodes, E. J., Jr.; Duvall, T. L., Jr.; Howe, R.; Thompson, M. J.;
Gough, D. O.; Sekii, T.; Toomre, J.; Tarbell, T. D.; Title, A. M.;
Mathur, D.; Morrison, M.; Saba, J. L. R.; Wolfson, C. J.; Zayer, I.;
Milford, P. N.
1997SoPh..170...43K Altcode:
The medium-l program of the Michelson Doppler Imager instrument on board
SOHO provides continuous observations of oscillation modes of angular
degree, l, from 0 to ∽ 300. The data for the program are partly
processed on board because only about 3% of MDI observations can be
transmitted continuously to the ground. The on-board data processing,
the main component of which is Gaussian-weighted binning, has been
optimized to reduce the negative influence of spatial aliasing of the
high-degree oscillation modes. The data processing is completed in a
data analysis pipeline at the SOI Stanford Support Center to determine
the mean multiplet frequencies and splitting coefficients. The initial
results show that the noise in the medium-l oscillation power spectrum
is substantially lower than in ground-based measurements. This enables
us to detect lower amplitude modes and, thus, to extend the range of
measured mode frequencies. This is important for inferring the Sun's
internal structure and rotation. The MDI observations also reveal the
asymmetry of oscillation spectral lines. The line asymmetries agree
with the theory of mode excitation by acoustic sources localized in the
upper convective boundary layer. The sound-speed profile inferred from
the mean frequencies gives evidence for a sharp variation at the edge
of the energy-generating core. The results also confirm the previous
finding by the GONG (Gough et al., 1996) that, in a thin layer just
beneath the convection zone, helium appears to be less abundant than
predicted by theory. Inverting the multiplet frequency splittings from
MDI, we detect significant rotational shear in this thin layer. This
layer is likely to be the place where the solar dynamo operates. In
order to understand how the Sun works, it is extremely important to
observe the evolution of this transition layer throughout the 11-year
activity cycle.

---------------------------------------------------------
Title: Modeling Boot-Shaped Coronal Holes using SOHO-MDI Magnetic
Measurements
Authors: Zhao, X. P.; Hoeksema, J. T.; Scherrer, P. H.
1997ESASP.404..751Z Altcode: 1997cswn.conf..751Z
No abstract at ADS

---------------------------------------------------------
Title: Precision solar astrometry from SoHO/MDI
Authors: Kuhn, J. R.; Bogart, R.; Bush, R.; Sá, L.; Scherrer, P.;
Scheick, X.
1997IAUS..181..103K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Internal structure and rotation of the Sun: First results
from MDI data
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.;
Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.;
De Forest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.;
Scott, K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard,
J.; Däppen, W.; Rhodes, E. J., Jr.; Duvall, T. L., Jr.; Howe, R.;
Thompson, M. J.; Gough, D. O.; Sekii, T.; Toomre, J.; Tarbell, T. D.;
Title, A. M.; Mathur, D.; Morrison, M.; Saba, J. L. R.; Wolfson,
C. J.; Zayer, I.; Milford, P. N.
1997IAUS..181..203K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: New Time-distance helioseismology results from the SOI/MDI
experiment
Authors: Duvall, T., Jr.; Kosovichev, A. G.; Scherrer, P. H.
1997IAUS..181...83D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Temporal Variability in the Quiet Sun Transition Region
Authors: Wikstoøl, Ø.; Hansteen, V. H.; Brynildsen, N.; Maltby,
P.; Kyeldseth-Moe, O.; Harrison, R. A.; Wilhelm, K.; Tarbell, T. D.;
Scherrer, P. H.
1997ESASP.404..733W Altcode: 1997cswn.conf..733W
No abstract at ADS

---------------------------------------------------------
Title: Time-Distance Helioseismology with the MDI Instrument:
Initial Results
Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H.;
Bogart, R. S.; Bush, R. I.; de Forest, C.; Hoeksema, J. T.; Schou,
J.; Saba, J. L. R.; Tarbell, T. D.; Title, A. M.; Wolfson, C. J.;
Milford, P. N.
1997SoPh..170...63D Altcode:
In time-distance helioseismology, the travel time of acoustic waves
is measured between various points on the solar surface. To some
approximation, the waves can be considered to follow ray paths that
depend only on a mean solar model, with the curvature of the ray
paths being caused by the increasing sound speed with depth below the
surface. The travel time is affected by various inhomogeneities along
the ray path, including flows, temperature inhomogeneities, and magnetic
fields. By measuring a large number of times between different locations
and using an inversion method, it is possible to construct 3-dimensional
maps of the subsurface inhomogeneities. The SOI/MDI experiment on SOHO
has several unique capabilities for time-distance helioseismology. The
great stability of the images observed without benefit of an intervening
atmosphere is quite striking. It has made it possible for us to detect
the travel time for separations of points as small as 2.4 Mm in the
high-resolution mode of MDI (0.6 arc sec pixel-1). This has
enabled the detection of the supergranulation flow. Coupled with the
inversion technique, we can now study the 3-dimensional evolution of
the flows near the solar surface.

---------------------------------------------------------
Title: Frequencies of solar oscillations and the seismic structure
of the Sun from SOHO/MDI.
Authors: Rhodes, E. J., Jr.; Kosovichev, A. G.; Scherrer, P. H.;
Schou, J.; Reiter, J.
1997AGAb...13..163R Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observation of solar convection with the MDI instrument
on SOHO.
Authors: Kosovichev, A. G.; Scherrer, P. H.; Duvall, T. L., Jr.
1996BAAS...28.1298K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: New Views of the Sun's Interior from the SOHO/MDI Space
Experiment
Authors: Scherrer, P. H.; Bogart, R. S.; Bush, R. I.; Hoeksema, J. T.;
Kosovichev, A. G.; Nigam, R.; Schou, J.; Duvall, T. L., Jr.
1996AAS...189.1803S Altcode: 1996BAAS...28.1298S
The strking stability of solar Dopplergrams measured by the Michelson
Doppler Imager (MDI) instrument on the SOHO spacecraft, without an
intervening atmosphere, substantially decreases the noise in the solar
oscillations power spectrum compared with groundbased observations. This
permits detection of lower amplitude oscillations, extending the range
of measured normal mode frequencies. This is important for improving
resolution and precision of helioseismic inferences about the Sun's
internal structure and dynamics. The MDI observations also reveal the
asymmetries of oscillation spectral lines that until now have been
largely hidden in noise. The line asymmetries agree with a theory of
excitation of solar oscillations by acoustic sources localized in the
upper convective boundary layer. High-resolution MDI images make it
possible to measure the travel time of acoustic waves propagating
inside the Sun by comparing points on the surface as close as 2.4
Mm. This is sufficient to detect supergranulation flows beneath the
surface. Coupled with tomographic inversion techniques, we can now study
the 3-dimensional evolution of the flows near the photosphere. The
sound-speed profile inferred from normal modes frequencies shows a
sharp variation at the edge of the energy-generating core, something
not accounted for by the standard evolution theory. The analysis also
confirms recent GONG results suggesting that helium is less abundant
than theory predicts in a thin layer just beneath the convection
zone. Inversion of the multiplet frequency splittings shows significant
rotational shear in this thin layer. This shear flow probably generates
turbulence that mixes the plasma in the upper radiative zone. This layer
is likely to be the place where the solar dynamo operates. Continuous
observation of the evolution of this transition layer during the entire
11-year activity cycle will be extremely important for understanding
the mechanisms of solar activity.

---------------------------------------------------------
Title: Solar Chromospheric and Coronal Explorer
Authors: Walker, Arthur B.; Scherrer, Philip H.; Hoover, Richard B.;
Tandberg-Hanssen, Einar; Barbee, Troy W.; Ling, James C.; MacQueen,
R. M.; Timothy, J. Gethyn; Adamson, Paul; Mennzel, Mike T.; Petheram,
John C.; Shattuck, Paul L.
1996SPIE.2804..286W Altcode:
The presence of the solar magnetic field has a profound effect on
the structure of the lower chromosphere, and is responsible for the
formation of the upper chromosphere and the corona, and the acceleration
of the solar wind. The variation of the field induces variations in
the chromosphere and the corona on time scales from 0.001 seconds to
centries. SOHO, and subsequent approved solar missions such as TRACE
will bring powerful observational capabilities to bear on critical
questions relating to solar variability. However, the most fundamental
question--how energy is transferred from the magnetic field into the
solar plasma--will require observations of diagnostic quality on a
spatial scale of 50 - 100 kilometers; this is an order of magnitude
beyond the capability of any planned mission. Our mission concept,
the Solar Chromospheric and Coronal Explorer (SCCE) is designed to
investigate the mechanisms underlying the variability of the solar
atmosphere, by attaining spectroscopic observations of the solar
atmosphere over a wide range of temperatures (4,500 K to 100,000,000 K),
with very high angular (0.1 arcseconds) and temporal (0.001 seconds)
resolution, that will permit models of the physical processes that
underlie the phenomena of solar activity to be formulated and tested
at the scale, 50 - 75 kilometers that appears to be fundamental. The
architecture of the SCCE is based on advances in multilayer optics,
which permit broad spectral response, and high angular and spectral
resolution to be achieved in a volume, and at a cost that is compatible
with deployment within the fiscal and physical constraints of the
MIDEX program.

---------------------------------------------------------
Title: Prediction of coronal and heliospheric magnetic fields:
the promise of SOI-MDI on SOHO.
Authors: Hoeksema, J. T.; Zhao, Xuepu; Scherrer, P. H.
1996AIPC..382...76H Altcode:
Coronal magnetic field models reproduce the static characteristics of
coronal and heliospheric structures fairly well; however, limitations
of spatial and temporal resolution and nonuniform quality of the
input data are important factors limiting investigations of the
response of the corona to rapidly changing photospheric conditions. The
Solar Oscillations Investigation (SOI) Michelson Doppler Imager (MDI)
experiment on SOHO produces a series of full-disk photospheric magnetic
field observations with 4″resolution about every 96 minutes for the
next several years. To suggest the potential of the MDI photospheric
magnetic field data, the authors show calculations of the steady
coronal magnetic field using low spatial resolution data and compare
results with various observations.

---------------------------------------------------------
Title: Coordinated SOHO Observations of Polar Plumes
Authors: Deforest, C. E.; Scherrer, P. H.; Tarbell, T.; Harrison,
R. A.; Fludra, A.; Delaboudiniere, J. P.; Gurman, J. B.; Wilhelm,
K.; Lemaire, P.; Hassler, D. M.; Kohl, J. L.; Noci, G.; Fineschi,
S.; Brueckner, G. E.; Howard, R. A.; Cyr, O. C. St.
1996AAS...188.4909D Altcode: 1996BAAS...28R.898D
On 7 and 8 March 1996, SOHO instruments engaged in their first
joint science operation, a 12-hr observation of polar plumes
over the South polar coronal hole. The observing mini-campaign
included observations from SOHO, other spacecraft, and ground-based
observatories. Contributing SOHO instruments -- in order of altitude,
MDI, CDS, SUMER, EIT, UVCS, and LASCO -- made overlapping, simultaneous
observations of plume structures from the photosphere out to the
LASCO C3 limit of 32 solar radii. MDI provided line-of-sight surface
magnetograms with a one-min cadence and 0.6 arcsec resolution;
CDS, SUMER, and EIT supplied temperature-sensitive images of the
lower corona with varying cadences and resolutions; UVCS measured
fluctuations in Ly B intensity across the coronal hole with a one-min
cadence at 1.4 R0; and LASCO imaged the entire corona out to 30 R0 in
various visible passbands. Plume footpoints in the lower corona are
observed by EIT and CDS to vary by a factor of two in EUV brightness
with a timescale of tens of minutes, while the structures above are
(as as been previously observed) quiescent on at least a ten-hr time
scale. We present preliminary results of cross-instrument analysis
of the observed plumes, and suggest how this and similar future data
sets can be used to constrain quiet-sun wind acceleration and coronal
heating models for the coronal hole. This research is supported by
the SOI-MDI NASA contract NAG5-3077 at Stanford University. SOHO is
project of international cooperation between NASA and ESA.

---------------------------------------------------------
Title: The MDI Structure Program: Continuous Monitoring of the
Solar Interior
Authors: Bush, R. I.; Bogart, R. S.; Hoeksema, J. T.; Kosovichev,
A. G.; Scherrer, P. H.; Mathur, D.; Morrison, M.; Tarbell, T. D.
1996AAS...188.3708B Altcode: 1996BAAS...28..878B
The Structure Program for the Michelson Doppler Imager instrument
on SOHO is designed to provide valuable helioseismic observations
through a continuously operating 5 kbps telemetry channel. Only about
3% of the total MDI raw data can be transmitted without interruption
to the ground. Therefore, extensive data processing must be performed
by the MDI instrument in order produce data products that will fit
into the restricted telemetry and to meet the scientific observing
requirements. The Structure Program consists of five observing programs:
the Medium-l Velocity, Low-l (LOI) Velocity and Intensity, Limb Figure,
Flux Budget, and Magnetic Proxy. These programs generate spatial
and temporal averages of three of the MDI full disk observables:
the velocity, computed continuum intensity, and the computed line
depth. The performance of these filters will be described. The
goal of the Medium-l Program is to provide reliable measurements
of solar p-modes in the range of the angular degree, l, from 0 to
300, by generating a 23,000 bin spatial average of the full disk
velocity. The Low-l Program re-bins the velocity and continuum intensity
images into 180 bins, with the intent of observing long period global
oscillations. The other three Structure Observations are averaged over
24 minutes with a 12 minute sample time. The Limb Figure extracts a 14
arcsecond annulus at the Sun's limb in order to study long wavelength
oscillations in the observed limb. The Flux Budget and Magnetic Proxy
are 128 by 128 pixel re-bins of the continuum intensity and line depth
observables respectively, to study the solar luminosity and large
scale features. Extensive tests of the individual components of the
Structure Program have been performed during the commissioning phase of
the SOHO operation. Uninterrupted operation started in April 1996. This
research is supported by NASA contract NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: Perspectives in Helioseismology
Authors: Gough, D. O.; Leibacher, J. W.; Scherrer, P. H.; Toomre, J.
1996Sci...272.1281G Altcode:
Helioseismology is probing the interior structure and dynamics of
the sun with ever-increasing precision, providing a well-calibrated
laboratory in which physical processes can be studied under conditions
that are unattainable on Earth. Nearly 10 million resonant modes
of oscillation are observable in the solar atmosphere, and their
frequencies need to be known with great accuracy in order to gauge the
sun's interior. The advent of nearly continuous imaged observations
from the complementary ground-based Global Oscillation Network Group
(GONG) observatories and the space-based Solar and Heliospheric
Observatory instruments augurs a new era of discovery. The flow of
early results from GONG resolves some issues and raises a number of
theoretical questions whose answers are required for understanding
how a seemingly ordinary star actually operates.

---------------------------------------------------------
Title: Detection of Subsurface Supergranulation Structure and Flows
from MDI High-Resolution Data using Time-Distance Techniques
Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H.;
Milford, P. N.
1996AAS...188.4908D Altcode: 1996BAAS...28Q.898D
The supergranulation is seen at the surface of the sun in the doppler
shift of spectrum lines as an apparent cellular convection pattern
with a scale of about 4% of the solar radius. This scale is about
30 times larger than the granulation, seen in white light. Why these
distinct scales would be present (and possibly a third intermediate
scale mesogranulation) is somewhat of a mystery. Also unknown is
the depth structure of the convection. We have used acoustic wave
measurements from the MDI experiment on SOHO to address these
questions. By crosscorrelating the signal at one location with
that on annuli centered on the location, it is possible to measure
times for waves to travel over known subsurface ray paths. With some
variations on this theme, it is possible to measure horizontal and
vertical flows and sound speed variations. Of course, the resulting
measurements refer to quantities integrated along these ray paths. An
inversion technique based on Fermat's principle has been developed
and used to map the flow velocities and sound speed variations as
a function of horizontal position and depth. The MDI experiment on
SOHO makes doppler shift maps with 1Kx1K points in two choices of
image scale, 2 and 0.6 arcsec/pixel. For the present study, we have
used the higher resolution mode to observe 8.5 hours of doppler maps
sampled once per minute. In order to average enough crosscorrelations
to see time-distance effects, the resultant time-distance maps are
reduced in resolution by a factor of 10 from the initial data. This
still yields about 7 samples across a single supergranulation cell,
or 49 over the area of a square cell. Our initial inversions based
on the ray theory suggest that the supergranulation flow extends at
least to 0.5% of the solar radius below the surface. This research is
supported by the SOI-MDI NASA contract NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: TRACE: the Transition Region and Coronal Explorer
Authors: Schrijver, C.; Title, A.; Acton, L.; Bruner, M.; Fischer,
R.; Golub, L.; Harrison, R.; Lemen, J.; Rosner, R.; Scharmer, G.;
Scherrer, P.; Strong, K.; Tarbell, T.; Wolfson, J.
1996AAS...188.6704S Altcode: 1996BAAS...28..934S
The TRACE mission is designed to obtain images of the solar
transition region and corona of unprecedented quality. With these
images we will be able to explore quantitatively the connections
between the photospheric magnetic field and the associated hot and
tenuous structures in the outer atmosphere. The TRACE telescope has
an aperture of 30 cm, and will observe an 8.5 x 8.5 arcminute field of
view with a resolution of one arcsecond. Finely tuned coatings on four
quadrants on the primary and secondary normal--incidence mirrors will
allow observations in narrow EUV and UV spectral bands. The passbands
are set to Fe IX, XII, and XV lines in the EUV band, while filters
allow observations in C IV, Ly alpha , and the UV continuum using
the UV mirror quadrant. The data thus cover temperatures from 10(4)
K up to 10(7) K. The Sun--synchronous orbit allows long intervals of
uninterrupted viewing. Observations at different wavelengths can be
made in rapid succession with an alignment of 0.1 arcsec. Coordinated
observing with TRACE, SoHO and YOHKOH will give us the first opportunity
to observe all temperature regimes in the solar atmosphere, including
magnetograms, simultaneously from space. TRACE is currently scheduled
to be launched in October 1997. More information can be found on the
web at “http://pore1.space.lockheed.com/TRACE/welcome.html”.

---------------------------------------------------------
Title: Initial Results from SOI/MDI High Resolution Magnetograms
Authors: Title, A.; Tarbell, T.; Frank, Z.; Schrijver, C.; Shine,
R.; Wolfson, J.; Zayer, I.; Scherrer, P.; Bush, R.; Deforest, C.;
Hoeksema, T.
1996AAS...188.6915T Altcode: 1996BAAS...28..938T
The Michelson Doppler Imager (MDI) on SoHO takes magnetogram
s with resolutions of 1.2 (high resolution) and 4 (full disk)
arcseconds. Movies of 16 hour duration have been constructed in full
disk and high resolution mode. High resolution movies of the south
polar region also have been obtained. In sums of nine high resolution
magnetograms it is possible to detect fields as low as 5 gauss and
total fluxes as low as 5 10(1) 6 Mx. In mid latitude regions new flux
is observed to emerge everywhere. At all latitudes below 60 degrees
flux is mixed on the scale of supergranulation. In the polar region
above 60 degrees only fields of a single polarity are observed above
the detection limit.

---------------------------------------------------------
Title: Calibration and Performance of the Michelson Doppler Imager
on SOHO.
Authors: Zayer, I.; Morrison, M.; Tarbell, T. D.; Title, A.; Wolfson,
C. J.; MDI Engineering Team; Bogart, R. S.; Bush, R. I.; Hoeksema,
J. T.; Duvall, T.; Sa, L. A. D.; Scherrer, P. H.; Schou, J.
1996AAS...188.3712Z Altcode: 1996BAAS...28..879Z
The Michelson Doppler Imager (MDI) instrument probes the interior
of the Sun by measuring the photospheric manifestations of solar
oscillations. MDI was launched in December, 1995, on the Solar and
Heliospheric Observatory (SOHO) and has been successfully observing the
Sun since then. The instrument images the Sun on a 1024 x 1024 pixel CCD
camera through a series of increasingly narrow spectral filters. The
final elements, a pair of tunable Michelson interferometers, enable
MDI to record filtergrams with FWHM bandwidth of 94 m Angstroms with
a resolution of 4 arcseconds over the whole disk. Images can also be
collected in MDI's higher resolution (1.25 arcsecond) field centered
about 160 arcseconds north of the equator. An extensive calibration
program has verified the end-to-end performance of the instrument
in flight. MDI is working very well; we present the most important
calibration results and a sample of early science observations. The
Image Stabilization System (ISS) maintains overall pointing to
better than ca. 0.01 arcsec, while the ISS' diagnostic mode allows
us to measure spectrally narrow pointing jitter down to less than
1 mili-arcsec. We have confirmed the linearity of each CCD pixel to
lie within 0.5%\ (the FWHM of the distribution is 0.2% ), and have to
date not detected any contamination on the detector, which is cooled
to -72 C. The noise in a single Dopplergram is of the order of 20 m/s,
and initial measurements of transverse velocities are reliable to 100
m/s. The sensitivity of magnetograms reach 5G in a 10 minute average
(15G in a single magnetogram). MDI's primary observable, the p-modes
from full-disk medium-l data, are of very high quality out to l=300
as seen in the initial l-nu diagram. The SOI-MDI program is supported
by NASA contract NAG5-3077.

---------------------------------------------------------
Title: Diagnostics of Shallow Convective Structures by Time-Distance
Helioseismology
Authors: Kosovichev, A. G.; Duvall, T. L., Jr.; Scherrer, P. H.
1996AAS...188.3709K Altcode: 1996BAAS...28R.878K
We present a new method of 3D helioseismic diagnostics to study
subphotospheric flow and thermal and magnetic structure associated with
turbulent convection. The main difference from the previous studies
by Duvall et al. (1996, Nature, 379, 235) and by Kosovichev (1996,
ApJL, 461, L55) is that the new method can be applied for measuring
solar properties in the shallow layer just beneath the surface. The
shallow layer of superadiabatic convection, which is only few thousand
kilometers deep, is the region of the greatest uncertainty in our
knowledge of the Sun's interior. Recent numerical simulations have
demonstrated substantial deviations of the structure of this layer from
the mixing-length theory commonly used in modeling stellar structure
and evolution. The uncertainty in the physics of turbulent convection
also affects helioseismic inferences about the deep interior. Our method
of 3D diagnostics is based on measuring and inverting anomalies of the
sound-wave travel time between two areas on the solar surface. Because
of the stochastic nature of solar waves, these two areas must
be sufficiently large to provide a good signal-to-noise ratio. In
practice, the travel time can be measured from the cross-correlation
function averaged over several thousand cross-correlations between
individual points on the surface. Therefore, it is essential to have
stable high-resolution series of Doppler images. Such data have been
obtained from the Michelson Doppler Imager instrument on SOHO. In this
paper, we present some details of the cross-correlation time-distance
analysis, and the technique to invert the travel-time measurements using
the optical ray approximation. The travel time of the waves depends
primarily on the wave group velocity and on the velocity of flow along
the ray paths. The effects of the wave speed structure and of flows are
separated by measuring the travel time of waves propagating in opposite
directions along the same ray paths. The effects of magnetic fields are
measured through anisotropy of the wave speed. We discuss the limits
for observing small-scale features beneath the surface. This research is
supported by the SOI-MDI NASA contract NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: The Solar Oscillations Investigation - Michelson Doppler Imager
Authors: Scherrer, P. H.; Bogart, R. S.; Bush, R. I.; Hoeksema, J. T.;
Kosovichev, A. G.; Schou, J.; Rosenberg, W.; Springer, L.; Tarbell,
T. D.; Title, A.; Wolfson, C. J.; Zayer, I.; MDI Engineering Team
1995SoPh..162..129S Altcode:
The Solar Oscillations Investigation (SOI) uses the Michelson Doppler
Imager (MDI) instrument to probe the interior of the Sun by measuring
the photospheric manifestations of solar oscillations. Characteristics
of the modes reveal the static and dynamic properties of the
convection zone and core. Knowledge of these properties will improve
our understanding of the solar cycle and of stellar evolution. Other
photospheric observations will contribute to our knowledge of the
solar magnetic field and surface motions. The investigation consists
of coordinated efforts by several teams pursuing specific scientific
objectives.

---------------------------------------------------------
Title: Soi Data and Information Services on the World-Wide Web
Authors: Bogart, R. S.; Scherrer, P. H.; Stehle, M. B.; Suryanarayanan,
J. K.; Tian, K.
1995ESASP.376b.153B Altcode: 1995help.confP.153B; 1995soho....2..153B
The SOHO Solar Oscillations Investigation (SOI) will use the World
Wide Web in several ways: as a public information service providing
background and sample data to the public; as a source of rapid
access quick-look data for other experimenters and observers; as the
network hub for data distribution services to team members and guest
investigators; as the online library site for documentation; and as
a planning and operational tool to be used by team members in the
definition and conduct of observational and analysis campaigns. The
authors describe those services already on the Web and discuss the
implementation of other planned services.

---------------------------------------------------------
Title: P-Mode Frequencies of Degree L = 3 TO 5
Authors: Pantel, A.; Hoeksema, T.; Fossat, E.; Scherrer, P.; Gelly,
B.; Grec, G.; Loudagh, S.; Schmider, F. X.
1995ESASP.376b.381P Altcode: 1995soho....2..381P; 1995help.confP.381P
No abstract at ADS

---------------------------------------------------------
Title: Prediction of coronal and heliospheric magnetic fields:
The promise of SOI-MDI on SOHO
Authors: Hoeksema, J. T.; Zhao, X. P.; Scherrer, P. H.
1995sowi.confQ..57H Altcode:
Models of the coronal magnetic field have been developed over the years
that reproduce the static characteristics of coronal and heliospheric
structures fairly well. Limitations of spatial and temporal resolution
and nonuniform quality of the input data have made it particularly
difficult to investigate the response of the corona to rapidly changing
photospheric conditions. The Solar Oscillations Investigation (SOI)
experiment on SOHO, scheduled for launch late in 1995, will produce a
series of full-disk photospheric magnetic field observations with 4"
resolution about every 2 hours for the next several years. Higher
resolution observations of the center of the disk will be available
several times per day. These data should provide a basis for predicting
the coronal and heliospheric field and their changes with unprecedented
accuracy during the rising phase of Solar Cycle 23.

---------------------------------------------------------
Title: Soi/mdi Studies of Active-Region Seismology and Evolution
Authors: Tarbell, T. D.; Title, A.; Hoeksema, J. T.; Scherrer, P.;
Zweibel, E.
1995ESASP.376b..99T Altcode: 1995help.confP..99T; 1995soho....2...99T
The Solar Oscillations Investigation (SOI) will study active regions
in many ways using both helioseismic and conventional observing
techniques. The Michelson Doppler Imager (MDI) instrument can
make Doppler, continuum and line depth images and also longitudinal
magnetograms, showing either the full disk or a high resolution field of
view. There will be a Dynamics Program of continuous full disk Doppler
observations for two months per year, many Campaign Programs of 8 hours
continuous observing per day, and a synoptic Magnetic Program of about
15 full disk magnetograms per day. This paper gives a brief description
of some of the scientific plans, measurements, and observing programs.

---------------------------------------------------------
Title: Potential Contribution of MDI to Understanding Large-Scale
Structures in the Corona
Authors: Zhao, X.; Hoeksema, J. T.; Scherrer, P. H.
1995ESASP.376b.509Z Altcode: 1995help.confP.509Z; 1995soho....2..509Z
No abstract at ADS

---------------------------------------------------------
Title: Hot Spots and Active Longitudes: Organization of Solar Activity
as a Probe of the Interior
Authors: Bai, T.; Hoeksema, J. T.; Scherrer, P. H.
1995ESASP.376b.113B Altcode: 1995soho....2..113B; 1995help.confP.113B
In order to investigate how solar activity is organized in longitude,
the authors have analyzed major flares, large sunspot groups,
and large-scale photospheric magnetic field strengths. The main
characteristics of hot spots are outlined.

---------------------------------------------------------
Title: Soi Science Plan and Status
Authors: Scherrer, P. H.
1995ESASP.376a..97S Altcode: 1995soho....1...97S; 1995heli.conf...97S
The Solar Oscillations Investigation (SOI) with the Michelson Doppler
Imager (MDI) is one of the three helioseismology instruments on
SOHO. The SOI program is designed to address a diverse set of solar
questions. The primary goals are to measure and characterize the solar
convection zone. The science investigation will be accomplished in a
set of working teams each focusing on specific problems.

---------------------------------------------------------
Title: Michelson Doppler Imager (MDI) Performance Characteristics
Authors: Zayer, I.; Morrison, M.; Pope, T.; Rosenberg, W.; Tarbell,
T.; Title, A.; Wolfson, J.; Bogart, R. S.; Hoeksema, J. T.; Milford,
P.; Scherrer, P. H.; Schou, J.
1995ASPC...76..456Z Altcode: 1995gong.conf..456Z
No abstract at ADS

---------------------------------------------------------
Title: Status of the Solar Oscillations Investigation - Michelson
Doppler Imager
Authors: Scherrer, P. H.; Bogart, R. S.; Bush, R. I.; Hoeksema,
J. T.; Milford, P.; Schou, J.; Pope, T.; Rosenberg, W.; Springer,
L.; Tarbell, T.; Title, A.; Wolfson, J.; Zayer, I.
1995ASPC...76..402S Altcode: 1995gong.conf..402S
No abstract at ADS

---------------------------------------------------------
Title: The SOHO Solar Oscillations Investigation on the Web
Authors: Tian, K.; Scherrer, P. H.; Bogart, R. S.
1995VA.....39...73T Altcode:
The Solar Oscillations Investigation (SOI) is an international project
to study the Sun's interior using data from the Michelson Doppler Imager
on the Solar and Heliospheric Observatory and the newly developing
techniques of the field of helioseismology. We have committed to using
the World-Wide Web not only to provide information and public data,
but as an active tool for defining science objectives, planning and
conducting the mission operations and attendant data processing, as
well as distribution of data to team members. SOI is organized into a
number of Science Teams with responsibility for various aspects of the
mission. As the team members are widely dispersed geographically, the
Web will be used to provide them with operational views into all aspects
of the data flow from observations through the production of organized
calibrated datasets. The same tools will be available to team members
and guest investigators conducting individual science investigations.

---------------------------------------------------------
Title: Status of the Mt. Wilson-Crimean-Kazakhstan High-Degree
Helioseismology Network
Authors: Rhodes, E. J., Jr.; Didkovsky, L.; Chumak, O. V.; Scherrer,
P. H.
1995ASPC...76..398R Altcode: 1995gong.conf..398R
No abstract at ADS

---------------------------------------------------------
Title: East-west inclination of large-scale photospheric magnetic
fields
Authors: Shrauner, J. A.; Scherrer, P. H.
1994SoPh..153..131S Altcode:
Sixteen years of WSO magnetogram data have been studied to determine
the solar cycle variation and latitude dependence of the east-west
inclination of photospheric magnetic field lines. East-west inclination
is here defined as the angle between a field line and its local
radial vector, as projected onto the plane of the latitude and line of
sight. Inclination is determined by a least-squares fit of observed
magnetic fields to a simple projection model, and is found to depend
on polarity and to change with the solar cycle. Leading and following
polarities are tipped towards each by about 9° and have an overall
net tilt in the direction of rotation (to the west) of 0.6°. New
cycles are seen to begin at high latitudes and to grow through the
lower latitudes over approximately 5 years, providing evidence for an
extended cycle length of 16-18 years.

---------------------------------------------------------
Title: East-West Inclination of Large-Scale Photospheric Magnetic
Fields
Authors: Shrauner, J. A.; Scherrer, P. H.
1993BAAS...25.1182S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Solar Oscillation Investigation - Michelson Doppler Imager
(SOI-MDI)
Authors: Hoeksema, J. T.; Bogart, R. S.; Bush, R. I.; Milford, P. N.;
Pope, T.; Rosenberg, W.; Scherrer, P. H.; Springer, L.; Tarbell, T.;
Title, A.; Wolfson, J.; Zayer, I.
1993BAAS...25.1192H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observations of High Frequency and High Wavenumber Solar
Oscillations
Authors: Fernandes, D.; Scherrer, P.; Tarbell, T.; Title, A.
1993ASPC...42..101F Altcode: 1993gong.conf..101F
No abstract at ADS

---------------------------------------------------------
Title: The High-Frequency P-Mode Spectrum
Authors: Milford, P. N.; Scherrer, P. H.; Frank, Z.; Kosovichev,
A. G.; Gough, D. O.
1993ASPC...42...97M Altcode: 1993gong.conf...97M
No abstract at ADS

---------------------------------------------------------
Title: The Search for 160-MINUTE Oscillations in the Stanford and
Crimean Solar Velocity Observations - 1974-1991
Authors: Kotov, V. A.; Scherrer, P. H.; Hoeksema, J. T.; Haneychuk,
V. I.; Tsap, T. T.
1993ASPC...42..293K Altcode: 1993gong.conf..293K
No abstract at ADS

---------------------------------------------------------
Title: Plans for MT.WILSON - Crimean Observatory High-Degree
Helioseismology Network
Authors: Rhodes, E. J., Jr.; Cacciani, A.; Dappen, W.; Didkovsky,
L. V.; Hill, F.; Korzennik, S. G.; Kosovichev, A. G.; Kotov, V. A.;
Scherrer, P. H.
1993ASPC...42..477R Altcode: 1993gong.conf..477R
No abstract at ADS

---------------------------------------------------------
Title: On the Upper Limit for Detecting G-Mode Oscillations of the Sun
Authors: Scherrer, P. H.; Hoeksema, J. T.; Kotov, V. A.
1993ASPC...42..281S Altcode: 1993gong.conf..281S
No abstract at ADS

---------------------------------------------------------
Title: The solar oscillations investigation - Michelson Doppler
Imager.
Authors: Hoeksema, J. Todd; Scherrer, P. H.; Bush, R. I.; Title, A.;
Tarbell, T.
1992ESASP.348....9H Altcode: 1992cscl.work....9H
The Solar Oscillations Investigation (SOI) has developed the Michelson
Doppler Imager (MDI) to investigate the properties of solar interior
using the tools of helioseismology and of the photosphere and
corona using more conventional techniques. A fundamental goal is
to understand the Sun by determining its structure and observing its
dynamics. The basic observables, velocity, intensity and magnetic field,
are computed on board from up to twenty 1024 by 1024 filtergrams made
each minute. Subsequent analysis will extend the region one can explore
downward into the solar interior and upward into the corona. While
the instrument is dedicated to producing an uninterrupted series
of helioseismology data, several magnetograms will be made each day
and special 8-hour campaigns are being developed to address specific
scientific questions, some in coordination with other SOHO instruments.

---------------------------------------------------------
Title: Observations of High-Frequency and High-Wavenumber Solar
Oscillations
Authors: Fernandes, D. N.; Scherrer, P. H.; Tarbell, T. D.; Title,
A. M.
1992ApJ...392..736F Altcode:
Doppler shift measurements of the Na D1 absorption line reveal solar
oscillations in a new regime of frequency and wavenumber. Oscillations
of vertical velocities in the temperature minimum and low chromosphere
of the sun are observed with frequencies ranging up to 9.5 mHz. The
fundamental modes appear with wavenumbers up to 5.33/Mm (equivalent
spherical harmonic degree 3710). No evidence for chromospheric modes
of 3-minute period is reported.

---------------------------------------------------------
Title: The Solar Oscillation Imager-Michelson Doppler Imager for SoHO
Authors: Title, A.; Tarbell, T.; Wolfson, J.; Scherrer, P.; Bush,
R.; Hoeksema, T.
1992AAS...180.0606T Altcode: 1992BAAS...24Q.737T
No abstract at ADS

---------------------------------------------------------
Title: Optical Components of the Solar Oscillations Imager-Michelson
Doppler Imager
Authors: Tarbell, T.; Rosenberg, W.; Pope, T.; Huff, L.; Torgerson,
D.; Title, A.; Wolfson, J.; Scherrer, P.; Bush, R.; Hoeksema, T.
1992AAS...180.0607T Altcode: 1992BAAS...24R.737T
No abstract at ADS

---------------------------------------------------------
Title: Measurement of the Polar Magnetic Fields at Wilcox Solar
Observatory
Authors: Bogart, R. S.; Hoeksema, J. T.; Scherrer, P. H.
1992AAS...180.5106B Altcode: 1992BAAS...24..814B
A new sequence of regular observations has been initiated at Stanford's
Wilcox Solar Observatory to better measure the projected component of
the photospheric magnetic fields poleward of about 75deg latitude. The
measurements are made in the 5250 Angstroms Fe I line used for both the
regular Stanford magnetograms and meanfield measurements, in a circular
aperture of 2 arc min projected diameter centred on the visible pole
and on both the limb points closest to the poles. Initial results of
observations since the beginning of the year suggest that the fields
measured each day vary between +/- 1.5 gauss at this point in the
cycle, with individual measurement uncertainties of approximately
0.15 gauss. These results are compared with the existing sequence
of polar-field measurements, based on the daily magnetograms and
covering a 30deg latitude range, that extend back to 1976. There is
a suggestion of a rotational modulation of the signal in the limited
dataset obtained so far.

---------------------------------------------------------
Title: Helioseismology from SOHO
Authors: Scherrer, P. H.
1992AAS...180.3309S Altcode: 1992BAAS...24..781S
Three experiments are presently being developed for flight on the
SOHO mission. The combination will provide a significant extension in
capabilities from ground based observations. The VIRGO (Variability of
solar IRadiance and Gravity Oscillations) and GOLF (Global Oscillations
at Low Frequencies) experiments will provide increased sensitivity for
the lowest frequency acoustic modes and should significantly lower
the detection threshhold for gravity mode oscillations below that
obtainable from present ground based efforts. GOLF and VIRGO will be
able to observe modes from spherical harmonic degree l=0 to l=3 and
to l=10 respectively. The SOI-MDI (Solar Oscillations Investigation -
Michelson Doppler Imager) will allow observations to k = 2.2 Mm(-1)
(l=1500) in the full disk mode and k = 6.5 Mm(-1) (equivalent degree l =
4500) in a high resolution mode. The combination of the 3 experiments
will allow low frequency observations in velocity (both photospheric and
chromospheric), total irradiance, broadband and narrow band irradiance,
and limb shape. The intrinsic solar noise will be the limiting factor
in sensitivity for both p-modes and g-modes. The three experiments
will provide the capability to allow seismic probing of the solar
interior from the center of the sun to depths of only a few Km. The
three projects involve the joint efforts of people from at least
15 countries including 43 Investigators, more than 44 associated
investigators, and the efforts of more than 100 on the technical teams.

---------------------------------------------------------
Title: SOI-MDI Onboard Real Time Data Reduction - Requirements
and Design.
Authors: Milford, P.; Lindgren, R.; Tarbell, T.; Bacon, L.; Scherrer,
P.
1992AAS...180.0608M Altcode: 1992BAAS...24..737M
SOI-MDI is a space-based high-resolution helioseismology experiment. To
observe Solar oscillations accurately requires a long time base of
(nearly) continuous observations. Due to telemetry restrictions,
SOI-MDI must carry out onboard data reduction of the high-resolution
observations prior to sending the data to the ground. This paper
summarizes the reduction requirements and discusses the hardware and
software design of the processor built to meet these requirements. The
main computational requirement to be met is the one-minute observing
cadence, required to observe a solar signal with a Nyquist frequency
corresponding to a 2-minute period. The analysis requires computing
dopplergrams from the observed filtergrams and a partial spherical
harmonic decomposition of the full disk dopplergrams. A custom image
processor was designed to meet these specifications. Other requirements
include low power, radiation tolerance and light weight. A design based
on an ASIC, designed around the 2903 bitslice family of processors,
has been developed to meet these requirements. The CPU includes three
memory busses with simultaneous DMA transfers to main memory and a
one-cycle 16 bit multiplier. Simultaneous access to the main memory by
the CCD Camera, via a DMA memory adder (also implemented as an ASIC),
and by the telemetry subsystem give the system sufficient performance
to handle the 30 Mb/minute of input data. This work was supported by
NASA Contract NAS5-30386 and Stanford Contract PR-6209.

---------------------------------------------------------
Title: Observations of high frequency and high wavenumber solar
oscillations
Authors: Fernandes, D. N.; Scherrer, P. H.; Tarbell, T. D.; Title,
A. M.
1992STIN...9232488F Altcode:
Doppler shift measurements of the Na D1 absorption line
have revealed solar oscillations in a new regime of frequency and
wavenumber. Oscillations of vertical velocities in the temperature
minimum and low chromosphere of the Sun are observed with frequencies
ranging up to 9.5 mHz. The fundamental modes appear with wavenumbers
up to 5.33 M/m (equivalent spherical harmonic degree, 3710). We find
no evidence for chromospheric modes of a 3-minute period.

---------------------------------------------------------
Title: The IRIS network site at the Wilcox Solar Observatory
Authors: Hoeksema, J. T.; Scherrer, P. H.
1991SoPh..133...57H Altcode:
The Wilcox Solar Observatory at Stanford University houses one of
the International Research on the Interior of the Sun (IRIS) network
observing stations. The instrument has observed the global oscillations
of the Sun continually since it was installed in August 1987. Each
site and instrument are different; here we report the details unique
to the Stanford site.

---------------------------------------------------------
Title: Report of the solar physics panel
Authors: Withbroe, George L.; Fisher, Richard R.; Antiochos, Spiro;
Brueckner, Guenter; Hoeksema, J. Todd; Hudson, Hugh; Moore, Ronald;
Radick, Richard R.; Rottman, Gary; Scherrer, Philip
1991spsi....1...67W Altcode:
Recent accomplishments in solar physics can be grouped by the
three regions of the Sun: the solar interior, the surface, and the
exterior. The future scientific problems and areas of interest involve:
generation of magnetic activity cycle, energy storage and release,
solar activity, solar wind and solar interaction. Finally, the report
discusses a number of future space mission concepts including: High
Energy Solar Physics Mission, Global Solar Mission, Space Exploration
Initiative, Solar Probe Mission, Solar Variability Explorer, Janus,
as well as solar physics on Space Station Freedom.

---------------------------------------------------------
Title: The solar oscillations investigation - Michelson Doppler
imager for SOHO
Authors: Scherrer, P. H.; Hoeksema, J. T.; Bush, R. I.
1991AdSpR..11d.113S Altcode: 1991AdSpR..11..113S
SOHO offers an unprecedented opportunity to probe the interior of a
star with the techniques of helioseismology. Continuous distortion-free
observations of the Sun will provide unique measurements of its internal
structure and dynamics. The MDI instrument provides the capability
to obtain observations with very high spatial resolution and high
precision at all times, with statistical errors well below the expected
solar noise background at all frequencies. The real limitation will
be gaining a sufficient understanding of the systematic error sources
with characteristic periods longer than several hours.

---------------------------------------------------------
Title: Rotation of the Photospheric Magnetic Fields: A North-South
Asymmetry
Authors: Antonucci, E.; Hoeksema, J. T.; Scherrer, P. H.
1990ApJ...360..296A Altcode:
During most of solar cycle 21 the large-scale photospheric field rotated
more rapidly in the Northern Hemisphere than in the southern. The
large-scale northern field rotated with a 26.9 day period (synodic),
was centered at 15 degrees N, and covered a latitude zone about 24
degrees wide. The large-scale southern field rotated with a periodicity
of 28.1 days, was centered at 26 degrees S, and covered a latitude
zone about 32 degrees wide. Our analysis showed rotational power at
only a few discrete latitudes and frequencies in each hemisphere. The
center of each peak lies near to the sunspot differential rotation
curve. The largest scale field contributes to the configuration of the
coronal and interplanetary magnetic field (IMF). The strength of the
first harmonic of the northern field suggests that this structure may
be related to the 4-sector pattern observed in the IMF polarity. The
southern field had much lower power at the first harmonic of the solar
rotation rate and so would contribute only to a 2-sector structure
in the IMF. These results were discovered in Fourier analysis of
photospheric synoptic charts obtained at the Wilcox Solar Observatory
from 1976 to 1986 and confirmed in higher resolution maps from the
National Solar Observatory. Mt. Wilson magnetic field measurements
from solar cycle 20 show a similar north-south asymmetry.

---------------------------------------------------------
Title: Solar variability influences on weather and climate: Possible
connections through cosmic ray fluxes and storm intensification
Authors: Tinsley, Brian A.; Brown, Geoffrey M.; Scherrer, Philip H.
1989JGR....9414783T Altcode:
The question of the mechanism for solar-variability effects on weather
and climate can be separated into (1) the identification of the carrier
of the solar variability and (2) the identification of the physical link
between the carrier and the meteorological response. The suggestion
that galactic cosmic rays (GCR), as modulated by the solar wind,
are the carriers of the component of solar variability that affects
weather and climate has been discussed in the literatue for 30 years,
and considerable evidence for it has now accumulated. Variations of GCR
occur with the 11-year solar cycle, matching the time scale of recent
results for atmospheric variations, as modulated by the quasi-biennial
oscillation of equatorial stratospheric winds (QBO). Variations in
GCR occur on the time scale of centuries with a well-defined peak in
the coldest decade of the little ice age. Here we present new evidence
on the meteorological responses to variations on the time scale of a
few days. The occurrence of correlations of GCR and meteorological
responses on all three time scales strengthens the hypothesis of
GCR as carriers of solar variability to the lower atmosphere. The
responses reported here include changes in the vertical temperature
profile in the troposphere and lower stratosphere and in the northern
hemisphere vorticity area index, associated with Forbush decreases
in GCR. The meteorological responses to Forbush decreases are in
the opposite sense but otherwise are quite similar to responses that
immediately follow solar flares. This is to be expected, based on
the hypothesis that particles with energy about 100-1000 MeV are the
external forcing function for the tropospheric response, since large
solar flares increase the particle flux and ionization and minor species
production in the lower stratosphere, whereas Forbush decreases reduce
them. The mechanism or mechanisms linking changes in low-energy GCR and
other particles in this energy range of 100-1000 MeV to tropospheric
temperature and dynamic responses have not been identified. This can
be attributed to current uncertainties regarding the microphysical and
electrical properties of aerosols and clouds. One possibility is the
changes in clouds lead to changes in cloud radiative forcing. The height
distribution of the tropospheric response and the amount of energy
involved and the rapidity of the time response suggest that the release
of latent heat could also be involved. These could lead to the observed
tropospheric responses which are understandable in terms of changes in
the intensity of cyclonic disturbances. Theoretical considerations link
such changes to the observed latitudinal movement of the jet stream.

---------------------------------------------------------
Title: Solar activity, the QBO, and tropospheric responses
Authors: Tinsley, Brian A.; Brown, Geoffrey M.; Scherrer, Philip H.
1989maph...29...53T Altcode:
The suggestion that galactic cosmic rays (GCR) as modulated by the
solar wind are the carriers of the component of solar variability that
affects weather and climate has been discussed in the literature for 30
years, and there is now a considerable body of evidence that supports
it. Variations of GCR occur with the 11 year solar cycle, matching the
time scale of recent results for atmospheric variations, as modulated
by the quasibiennial oscillation of equatorial stratospheric winds
(the QBO). Variations in GCR occur on the time scale of centuries
with a well defined peak in the coldest decade of the little ice
age. New evidence is presented on the meteorological responses to GCR
variations on the time scale of a few days. These responses include
changes in the vertical temperature profile in the troposphere and
lower stratosphere in the two days following solar flare related high
speed plasma streams and associated GCR decreases, and in decreases
in Vorticity Area Index (VAI) following Forbush decreases of GCR. The
occurrence of correlations of GCR and meteorological responses on
all three time scales strengthens the hypothesis of GCR as carriers
of solar variability to the lower atmosphere. Both short and long
term tropospheric responses are understandable as changes in the
intensity of cyclonic storms initiated by mechanisms involving cloud
microphysical and cloud electrification processes, due to changes in
local ion production from changes in GCR fluxes and other high energy
particles in the MeV to low GeV range. The nature of these mechanisms
remains undetermined. Possible stratospheric wind (particularly QBO)
effects on the transport of HNO3 and other constituents incorporated
in cluster ions and possible condensation and freezing nuclei are
considered as relevant to the long term variations.

---------------------------------------------------------
Title: Rotation of the photospheric magnetic fields: A north-south
asymmetry
Authors: Antonucci, E.; Hoeksema, J. T.; Scherrer, P. H.
1989STIN...9014177A Altcode:
During most of solar cycle 21 the large-scale photospheric field rotated
more rapidly in the Northern Hemisphere than in the southern. The
large-scale northern field rotated with a 26.9 day period (synodic),
was centered at 15 degress N, and covered a latitude zone about 24
degrees wide. The large-scale southern field rotated with a periodicity
of 28.1 days, was centered at 26 degrees S, and covered a latitude zone
about 32 degrees wide. Our analysis showed rotational power at only a
few discrete latitudes and frequencies in each hemisphere. The center
of each peak lies near the sunspot differential rotation curve. The
largest scale field contributes to the configuration of the coronal
and interplanetary magnetic field (IMF). The strength of the first
harmonic of the northern field suggests that this structure may be
related to the 4-sector pattern observed in the IMF polarity. The
southern field had much lower power at the first harmonic of the solar
rotation rate and so would contribute only to a 2-sector structure
in the IMF. These results were discovered in Fourier analysis of
photospheric synoptic charts obtained at the Wilcox Solar Observatory
from 1976 to 1986 and confirmed in higher resolution maps from the
National Solar Observatory. Mt. Wilson magnetic field measurements
from solar cycle 20 show a similar north-south asymmetry.

---------------------------------------------------------
Title: The Solar Oscillations Imager for SOHO
Authors: Scherrer, P. H.
1989BAAS...21..832S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar g-mode oscillations: Comparison of SMM-ACRIM and
ground-based observations
Authors: Scherrer, Philip H.
1989stan.reptQ....S Altcode:
Progress was made in access to data and in developing programs for
its analysis. The difficulties in completing the work in the planned
time can be traced to several factors. The correction of the Stanford
oscillation using gridded intensity data was not successful. It was
concluded that due to poor continuity of the 1985 and 1986 data due
to clouds, that a joint analysis with the ACRIM data (best solar
oscillation data to date) on the summer 1987 observations should be
performed. The 1988 Stanford oscillation data are being examined and
the cross comparison of the ACRIM spectrum with the Standford spectrum
for 1987 in the g-mode regime will shortly begin.

---------------------------------------------------------
Title: Geomagnetic disturbances
Authors: Scherrer, Philip H.
1989stan.reptR....S Altcode:
Investigations have included observations and analysis of the solar
and interplanetary quantities relevant to geomagnetic activity. The
operation of the Wilcox Solar Observatory and analysis of the synoptic
observations of magnetic fields has constituted a significant part
of the effort. Emphasis has been to attempt to understand the timing
and severity of geomagnetic disturbances by understanding the solar
mechanisms responsible for the origin of solar wind variations.

---------------------------------------------------------
Title: The Michelson Doppler imager for the solar oscillations imager
program on SOHO.
Authors: Hoeksema, J. T.; Scherrer, Philip H.; Title, A. M.; Tarbell,
T. D.
1988ESASP.286..407H Altcode: 1988ssls.rept..407H
The Michelson Doppler Imager (MDI) will be the instrument used
in the Solar Oscillations Imager Program on SOHO. MDI will make a
line-of-sight velocity map of the full solar disk with 2 arc-second
pixels each minute. The instrument will be a modification of the
Fourier Tachometer and will operate by using narrow bandpass solar
images at four wavelengths to measure the line profile of the Ni
I line at 6768 Å. This method is relatively insensitive to line
profile changes and has a linear response to velocity. The instrument
is also capable of making partial maps with 0.7 arc-sec pixels. All
data will be transmitted to the ground for two continuous months
each year and 8 hours each day (160 kilobits/sec). At all times the
on-board computer will compute and transmit a selection of modes
(5 kilobits/sec) to take full advantage of the advantages of a space
based telescope. Line-of-sight magnetic fields will also be measured
regularly. The flight instrument will be built by the Lockheed Palo
Alto Research Laboratory.

---------------------------------------------------------
Title: The search for solar gravity modes.
Authors: Henning, Harald M.; Scherrer, Philip H.
1988ESASP.286..419H Altcode: 1988ssls.rept..419H
The authors have maintained a solar oscillations observing program for
more than 13 years at Stanford. The observations are most sensitive to
low degree solar modes and have been used for the study of long period
p-mode and g-mode oscillations. At the start of the 1987 observing
season (summer) some long-standing problems with the instrument were
corrected which (along with good weather) allowed the cleanest set
of data to date. This paper reports the current state of the search
for evidence of g-modes in this data. Analysis of this data shows good
evidence for g-modes. Various methods were used for mode identification
with a statistical search for a simple pattern of even spacing in
period selected as the most robust. Using this method, a possible
g-mode identification was made with an asymptotic period separation
TO = 37.1 minutes. This identification was consistent with
a rotation splitting of 1.6 microHz. Tests with randomly generated
spectral peaks find as significant a possible set of modes in only 2
out of 100 cases.

---------------------------------------------------------
Title: The solar oscillations imager for SOHO.
Authors: Scherrer, Philip H.; Hoeksema, J. T.; Bogart, R. S.
1988ESASP.286..375S Altcode: 1988ssls.rept..375S
The Solar Oscillations Imager (SOI) programs for SOHO will consist
of a Michelson Doppler Imager (MDI) instrument, a data reduction and
analysis capability, and a coordinated set of investigations designed
to address a set of science objectives.

---------------------------------------------------------
Title: SOI: The Solar Oscillations Imager on SOHO
Authors: Scherrer, P. H.; Hoeksema, J. T.; Bogart, R. S.; Walker,
A. B. C., Jr.; Title, A. M.; Tarbell, T. D.; Wolfson, C. J.; Brown,
T. M., Jr.; Christensen-Dalsgaard, J.; Gough, D. O.
1988sohi.rept...25S Altcode:
The Solar Oscillations Imager (SOI) program for SOHO (solar and
heliospheric observatory) is described. It will consist of a Michelson
Doppler Imager (MDI) instrument, a facility providing data reduction
and analysis capability, and a coordinated set of investigations
designed to address a set of science objectives. The MDI is designed
to take advantage of the anticipated SOHO telemetry by organizing
the observations into four observation programs: structure (at all
times), dynamics (two months per year), campaign (eight hours per day,
ten months per year), and magnetic fields (few minutes per day). The
MDI will measure line-of-sight velocity by Doppler shift, transverse
velocity by local correlation tracking, line and continuum intensity,
and line-of-sight magnetic fields with both 4 and 1.4 arc-second
resolution (2 and 0.7 arc-sec pixels respectively).

---------------------------------------------------------
Title: On the Feasibility of Correlation Tracking at Moderate
Resolution
Authors: Bogart, R. S.; Ferguson, S. H.; Scherrer, P. H.; Tarbell,
T. D.; Title, A. M.
1988SoPh..116..205B Altcode:
The SOUP experiment demonstrated that photospheric surface flows can
be measured by correlation tracking of white-light intensity features
at high resolution (November et al., 1987). In order to assess
the feasibility of this technique with observations made at lower
resolution, we have applied it to the same SOUP data artificially
degraded, but still free of seeing distortion. Comparison with the
velocity structures inferred from the original data shows generally
good agreement when the resolution is better than about 2″. The
radial outflow from a sunspot penumbra, however, can only be seen with
resolution of better than 1″. With resolution of worse than 2″,
the inferred velocity fields rapidly lose coherence, while resolution of
better than 1″ yields little improvement. We conclude that apertures
as small as 10-14 cm on a space-based platform will be useful for the
measurement of large-scale horizontal motions.

---------------------------------------------------------
Title: A New Technique for Measuring Solar Velocity
Authors: Scherrer, P. H.; Tarbell, T. D.
1988BAAS...20..702S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Helioseismic Observations at Stanford 1977-1986
Authors: Henning, H. M.; Scherrer, P. H.
1988IAUS..123...29H Altcode:
Observations of low degree modes of solar oscillation have been made
at The Wilcox Solar Observatory at Stanford University for more than a
decade. The authors are presently re-examining the set of observations
from 1977 through 1986. They have first tested the stability of the
p-mode frequencies for modes of degree l = 2 - 5 in each year. They
find a marginally significant trend of a decrease in p-mode frequencies
of 0.06 μHz per year. They have also examined the continuity of the
observed signal at 160.01 minutes.

---------------------------------------------------------
Title: Long-term variability of solar magnetic fields
Authors: Todd Hoeksema, J.; Scherrer, P. H.
1988AdSpR...8g.177T Altcode: 1988AdSpR...8..177T
The solar magnetic field varies on all time scales. Recent analysis
of 600 million year-old Australian varves shows terrestrial evidence
for not only the familiar 22-year magnetic cycle, but variations
with periods of 300-400 years as well. The Maunder minimum is but
one of several long intervals showing atypical levels of solar
activity. Recently a 151-day periodicity in flare activity has been
found. Active regions, sunspots, ephemeral regions, and flares cover
a broad range of shorter time scale variations in the solar magnetic
field. Long-term variations can be interpreted in at least two
ways. One outlook regards the large-scale and long-term variations of
the photospheric field as more-or-less direct guides to the organization
of the solar field as it evolves through a solar cycle. The slowly
varying field reveals the fundamental interior structure of the Sun. An alternative view interprets the surface manifestation of the
magnetic field primarily as the result of the convective motions in
the solar atmosphere. The evolving distribution of photospheric flux
depends upon the locations of emerging flux and the subsequent motions
and interactions of the fields in the moving plasma. Information about
the interior field comes largely from analysis of emerging flux. We discuss interpretation of the phenomenology of the long-term
variability in the context of these contrasting views.

---------------------------------------------------------
Title: More than a solar cycle of synoptic solar and coronal data:
a video presentation.
Authors: Hoeksema, J. T.; Herant, M.; Scherrer, P. H.; Title, A. M.
1988sscd.conf..376H Altcode:
Color video movies of synoptic observations of the sun and corona
can now be created. Individual analog frames on laser disc can be
referenced digitally and played back at any speed. The authors have
brought together photospheric magnetic field data from the Wilcox Solar
Observatory at Standford and the National Solar Observatory, model
computations of the coronal magnetic field, and coronal data from the
Sacramento Peak coronagraph and the Mauna Loa K-coronameter and made a
series of movies presenting the data sets individually and in comparison
with one another. This paper presents a description of each of the data
sets and movies developed thus far and briefly outlines some of the
more interesting and obvious features observed when viewing the movies.

---------------------------------------------------------
Title: Long-term variability of solar magnetic fields.
Authors: Hoeksema, J. Todd; Scherrer, P. H.
1988AdSpR...8g.177H Altcode: 1988AdSpR...8..177H
In this paper the authors summarize the well known variations of the
solar magnetic field, concentrating on some of the more recent work that
attempts to give an empirical description of the way the field varies.

---------------------------------------------------------
Title: More than a solar cycle of synoptic solar and coronal data:
A video presentation
Authors: Hoeksema, J. T.; Herant, M.; Scherrer, P. H.; Title, A. M.
1987STIN...8829708H Altcode:
Color video movies of synoptic observations of the sun and corona
can now be created. Individual analog frames on laser discs can be
referenced digitally and played back at any speed. We have brought
together photospheric magnetic field data from the Wilcox Solar
Observatory at Stanford and the National Solar Observatory, model
computations of the coronal magnetic field, and coronal data from the
Sacramento Peak coronagraph and the Mauna Loa K-coronameter and made a
series of movies presenting the data sets individually and in comparison
with one another. This paper presents a description of each of the data
sets and movies developed thus far and briefly outlines some of the
more interesting and obvious features observed when viewing the movies.

---------------------------------------------------------
Title: Rotation of the Coronal Magnetic Fields
Authors: Hoeksema, J. T.; Scherrer, P. H.
1987ApJ...318..428H Altcode:
The coronal magnetic field rotates differently than the photosphere. The
field configuration of the corona can be calculated from the observed
photosphpere field using a potential field model. Correlation of
the field patterns at different latitudes with a lag near one solar
rotation shows much less differential rotation than observed in the
photospheric field; however, the peak is very broad and determines
the rotation rate rather poorly. Consideration of longer lags reveals
a more complex rotational structure and indicates different rotation
rates in the Northern and Southern Hemispheres. Spectral analysis
of the equatorial dipole component of the coronal field reveals an
organization into just a few discrete rotation frequencies which
are apparently present simultaneously. Spectral analysis of the
field at different latitudes shows that the frequencies are present
simultaneously. Spectra analysis of the field at different latitudes
shows that the frequencies are present simultaneously, but in different
hemispheres, and that the Southern Hemisphere fields rotate more slowly
than those in the north in solar cycle 21.

---------------------------------------------------------
Title: The Meridional Flow Inferred from the Shape of Large-scale
Magnetic Structures in the Photosphere
Authors: Hoeksema, J. T.; Herant, M.; Scherrer, P. H.; Title, A. M.
1987BAAS...19S.935H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On the Feasibility of Correlation Tracking at Moderate
Resolution
Authors: Bogart, R. S.; Scherrer, P. H.; Ferguson, S. H.; Tarbell,
T. D.; Title, A. M.
1987BAAS...19..941B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The North-South Asymmetry in the Rotation of the Photospheric
Magnetic Field During Solar Cycles 21 and 20
Authors: Scherrer, P. H.; Hoeksema, J. T.; Antonucci, E.
1987BAAS...19S.935S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Helioseismic observations at Stanford, 1977-1986
Authors: Henning, H. M.; Scherrer, P. H.
1986STIN...8714236H Altcode:
Observations of low degree modes of solar oscillations were made
at the Wilcox Solar Observatory for more than a decade. The set of
observations from 1977 through 1986 are reexamined. The stability
of the p-mode frequencies for modes of degree l=2-5 in each year
is tested. A marginally significant trend of a decrease in p-mode
frequencies of 0.06 microHz per year is found. The continuity of the
observed signal at 160.01 minutes are also examined. It was found that
the previously reported phase stability is no longer present. However,
due to uncertainties in calibration, the reality of the reported signal
can not be excluded.

---------------------------------------------------------
Title: Rotation of the coronal magnetic field
Authors: Hoeksema, J. T.; Scherrer, Philip H.
1986STIN...8720163H Altcode:
The coronal magnetic field rotates differently than the photosphere. The
field configuration of the corona can be calculated from the observed
photospheric field using a potential field model. Correlation of
the field patterns at different latitudes with a lag near one solar
rotation shows much less differential rotation than observed in the
photospheric field; however, the peak is very broad and determines
the rotation rate rather poorly. Consideration of longer lags reveals
a more complex rotational structure and indicates different rotation
rates in the northern and southern hemispheres. Spectral analysis
of the equatorial dipole component of the coronal field reveals an
organization into just a few discrete rotation frequencies which
are apparently present simultaneously. Spectral analysis of the
field at different latitudes shows that the frequencies are present
simultaneously. Spectral analysis of the field at different latitudes
shows that the frequencies are present simultaneously, but in different
hemispheres, and that the Southern Hemisphere fields rotate more slowly
than those in the north in solar cycle 21.

---------------------------------------------------------
Title: An atlas of photospheric magnetic field observations and
computed coronal magnetic fields: 1976 1985
Authors: Hoeksema, J. T.; Scherrer, P. H.
1986SoPh..105..205H Altcode:
Daily magnetogram observations of the large-scale photospheric magnetic
field have been made at the John M. Wilcox Solar Observatory at Stanford
since May of 1976. These measurements provide a homogeneous record of
the changing solar field through most of solar cycle 21.

---------------------------------------------------------
Title: Topology of the Heliospheric Current Sheet at the Time of
the Halley's Comet-Giotto Encounter
Authors: Suess, S. T.; O'Farrell, J. M.; Hoeksema, J. T.; Scherrer,
P. H.
1986BAAS...18..678S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Upper Limits on Solar Large-Scale Surface Motions
Authors: Scherrer, P. H.; Bogart, R. S.; Hoeksema, J. T.
1986BAAS...18..702S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar magnetic field, 1976 through 1985: an atlas of
photospheric magnetic field observations and computed coronal magnetic
fields from the John M. Wilcox Solar Observatory at Sanford, 1976-1985
Authors: Hoeksema, J. T.; Scherrer, P. H.
1986STIN...8629760H Altcode:
Daily magnetogram observations of the large-scale photospheric magnetic
field have been made at the John M. Wilcox Solar Observatory at Stanford
since May of 1976. These measurements provide a homogeneous record
of the changing solar field through most of Solar Cycle 21. Using the
photospheric data, the configuration of the coronal and heliospheric
fields can be calculated using a Potential Field - Source Surface
model. This provides a 3-dimensional picture of the heliospheric field
evolution during the solar cycle. In the report the authors present
the complete set of synoptic charts of the measured photospheric
magnetic field, the computed field at the source surface, and the
coefficients of the multipole expansion of the coronal field. The
general underlying structure of the solar and helispheric fields,
which determine the environment for solar terrestrial relations and
provide the context within which solar activity related events occur,
can be approximated from these data.

---------------------------------------------------------
Title: Coments on techniques for spectral deconvolution.
Authors: Scherrer, Philip H.
1986ASIC..169..117S Altcode: 1986ssds.proc..117S
Current observational questions in asteroseismology require high
spectral resolution that can only be obtained with observations
spanning many days or months. The primary constraint in the full
utilization of single mid-latitude observing sites is the presence of
diurnal data gaps. Several methods for removing the effect of these
gaps in the spectra obtained from velocity observations have been
suggested. The limitations of these methods and their applicability
to the helioseismology problem is discussed.

---------------------------------------------------------
Title: An atlas of photospheric magnetic field observations and
computed coronal magnetic fields: 1976 - 1985
Authors: Hoeksema, J. T.; Scherrer, P. H.
1986STIN...8715151H Altcode:
Daily magnetogram observations of the large-scale photospheric magnetic
field have been made at the John M. Wilcox Solar Observatory at Stanford
since May of 1976. These measurements provide a homogeneous record
of the changing solar field through most of solar cycle 21. Using the
photospheric data, the configuration of the coronal and heliospheric
fields can be calculated using a Potential Field-Source Surface
model. This provides a three-dimensional picture of the heliospheric
field evolution during the solar cycle. This paper announces the
publication of UAG Report No. 94, an Atlas containing the complete
set of synoptic charts of the measured photospheric magnetic field,
the computed field at the source surface, and the coefficients of
the multipole expansion of the coronal field. The general underlying
structures of the solar and heliospheric fields, which determine the
environment for solar-terrestrial relations and provide the context
within which solar activity related events occur, can be approximated
from these data.

---------------------------------------------------------
Title: Solar rotation measured at the Wilcox Solar Observatory.
Authors: Bogart, R. S.; Scherrer, P. H.
1986BAAS...18R.848B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Geomagnetic disturbances
Authors: Scherrer, P. H.
1986stan.reptQ....S Altcode:
Recent efforts include the study of the solar dynamics by directly
observing the surface manifestations of giant scale convective
motions. A knowledge of the structure of the convective zone is crucial
to the eventual understanding of the solar magnetic cycle. The origin
and structure of coronal magnetic fields and the origin of solar wind
variability are studied. The static structure of the corona is governed
by the large scale organization of photospheric fields. During times of
low activity, these fields can be used to infer the coronal structure
with reasonable accuracy. Our synoptic series of high accuracy low
resolution magnetic observations continues to provide a useful source
for a number of investigations conducted at Stanford and elsewhere. The
relation between the effects of transient events and the large scale
ambient structure is investigated. Flare accelerated material that
does not cross the heliospheric current sheet has a larger impact on
the terrestrial environment than material from flares that must cross
the current sheet to arrive at the Earth.

---------------------------------------------------------
Title: Solar Wind Speed Azimuthal Variation Along the Heliospheric
Current Sheet
Authors: Suess, S. T.; Scherrer, P. H.; Hoeksema, J. T.
1986ASSL..123..275S Altcode: 1986shtd.symp..275S
The authors report on analysis of the speeds measured by Voyager 1 and
2 while skimming along a horizontal (east-west) portion of the current
sheet over several days in 1977. The results demonstrate that in this
case speed variations exist and are large enough to significantly deform
the sheet within a few AU or less if the current sheet were anything but
perfectly horizontal. The spatial scale of the speed variation ranges
from the smallest measurable scale using 1 hour averaged data up to
tens of degrees in longitude. A deformation example is given under the
assumption that the observed velocity variation exists on a current
sheet that is initially perpendicular to the heliographic equator.

---------------------------------------------------------
Title: Observations of low-degree p-mode oscillations in 1984.
Authors: Henning, Harald M.; Scherrer, Philip H.
1986ASIC..169...55H Altcode: 1986ssds.proc...55H
Analysis of Stanford differential velocity observations has been
extended through the 1984 observing season. Excellent quality
observations were obtained in 1984 on 38 days in a 49 day interval
from June 20th through August 7th. The power spectrum of this data
has been examined and improved frequency determinations have been made
for p-modes of degree 2 through 5 and order 5 through 34. Of special
interest are the modes of the lower orders, n ranging from 5 to 10,
which have not been identified previously.

---------------------------------------------------------
Title: The detection of global convective wave flows on the Sun.
Authors: Scherrer, Philip H.; Bogart, Richard; Hoeksema, J. Todd;
Yoshimura, Hirokazu
1986ASIC..169...93S Altcode: 1986ssds.proc...93S
Global convective flows in the solar convection zone have been predictd
by theoretical interpretations of the global-scale ordering of magnetic
fields and activity centers and by theoretical analyses of rotating
convection zones. The signatures of such flows have now been detected
by analyzing the daily series of low-resoluton Dopplergrams obtained
at the Wilcox Solar Observatory at Stanford University. The signatures
are patterns of alternating east and west flows with amplitudes on
the order of 25 m/s and longitudinal extent of about 30 degrees.

---------------------------------------------------------
Title: The influence of the heliospheric current sheet and angular
separation on flare-accelerated solar wind
Authors: Henning, H. M.; Scherrer, P. H.; Hoeksema, J. T.
1985JGR....9011055H Altcode:
A complete set of major flares has been used to investigate the
effect of the heliospheric current sheet on the magnitude of the
flare-associated disturbance measured at the earth. It was found
that disturbances associated with flares located on the same side of
the current sheet as the earth were of larger magnitude than those
associated with flares located such that the flare-accelerated material
would have to cross the current sheet locus. It was also found that the
angular separation between the flare position and the earth has a strong
effect on the magnitude of the disturbance. A larger angular separation
tended to result in a smaller disturbance. Third, it was determined
that flares tend to occur near the heliospheric current sheet.

---------------------------------------------------------
Title: Observations of low-degree p-mode oscillations in
1984. Comments on techniques for spectral deconvolution
Authors: Henning, H. M.; Scherrer, P. H.
1985STIN...8627174H Altcode:
Global convective flows in the solar convection zone have been predicted
by theoretical interpretations of the global-scale ordering of magnetic
fields and activity centers and by theoretical analyses of rotating
convection zones. Direct evidence of these flows in the photosphere
has not previously been found despite several long-term efforts. The
signatures of such flows have now been detected by analyzing the
daily series of low-resolution Dopplergrams obtained at the Wilcox
Solar Observatory at Stanford Univ. The signatures are patterns of
alternating east and west flows with amplitudes on the order of 25
m/s and longitudinal extent of about 30 degrees. The patterns move
across the solar disc at approximately the solar rotation rate and
have lifetimes of at least several rotations. Boundaries of the fast
and slow flows are often associated with large magnetic active regions.

---------------------------------------------------------
Title: The influence of the heliospheric current sheet and angular
separation on flare accelerated solar wind
Authors: Henning, H. M.; Scherrer, P. H.; Hoeksema, J. T.
1985STIN...8529907H Altcode:
A complete set of major flares was used to investigate the effect
of the heliospheric current sheet on the magnitude of the flare
associated disturbance measured at Earth. It was also found that the
angular separation tended to result in a smaller disturbance. Thirdly,
it was determined that flares tend to occur near the heliospheric
current sheet.

---------------------------------------------------------
Title: Deconvolution Methods for Analysis of Solar Oscillation
Observations
Authors: Scherrer, P. H.
1985BAAS...17R.643S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observations of Low-Degree P-Mode Oscillations in 1984
Authors: Henning, H. M.; Scherrer, P. H.
1985BAAS...17R.639H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Detection of Global (Giant Cell) Convective Wave Flows
on the Sun
Authors: Yoshimura, H.; Scherrer, P. H.; Bogart, R. S.; Hoeksema, J. T.
1985BAAS...17..639Y Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Detection of solar gravity mode oscillations.
Authors: Scherrer, P. H.
1984sses.nasa..173S Altcode: 1984sss..conf..173S
An analysis of solar velocity data obtained at the Stanford Solar
Observatory has shown the existence of solar global oscillations. The
oscillations are in the range 45 to 105 μHz (160 to 370 minutes)
and are interpreted as internal gravity modes of degree l = 1 and l = 2.

---------------------------------------------------------
Title: Harmonic analysis of the solar magnetic field.
Authors: Hoeksema, J. T.; Scherrer, P. H.
1984ESASP.220..269H Altcode: 1984ESPM....4..269H
The spherical harmonics of the global solar magnetic field have been
calculated using photospheric field measurements from the Stanford
Solar Observatory from 1976 - 1983. The field evolution during the
solar cycle is analyzed.

---------------------------------------------------------
Title: Detection of solar gravity mode oscillations
Authors: Scherrer, P. H.
1984MmSAI..55...83S Altcode:
The detection of g-mode oscillations in solar-velocity data obtained at
Stanford Solar Observatory during 1977-1980 is reported, summarizing
the results of Scherrer and Wilcox (1983) and Delache and Scherrer
(1983). Spectra are shown, and the analysis results are presented in
a table and graph. A total of 14 peaks are identified in the frequency
range 45-105 microhertz, of which seven are assigned to a series with l
= 1 and n = 6-10 and four are assigned to a series with l = 2 and n =
15-20; a peak at 59.52 microhertz can be identified as either l = 1,
n = 10 or as l = 2, n = 17.

---------------------------------------------------------
Title: Harmonic Analysis of the Solar and Heliospheric Magnetic Fields
Authors: Hoeksema, J. T.; Scherrer, P. H.
1984BAAS...16..452H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: John M. Wilcox died 1983 October 14.
Authors: Scherrer, P. H.
1984PhT....37e.103S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Detection of solar gravity mode oscillations
Authors: Delache, P.; Scherrer, P. H.
1983Natur.306..651D Altcode:
An analysis of solar velocity data obtained at the Stanford Solar
Observatory shows the existence of solar global oscillations in the
range 45-105 µHz (160-370 min). These oscillations are interpreted
as internal gravity modes of degree l = 1 and l = 2. A good estimate
of the order of the modes has also been made.

---------------------------------------------------------
Title: The structure of the heliospheric current sheet: 1978-1982
Authors: Hoeksema, J. T.; Wilcox, J. M.; Scherrer, P. H.
1983JGR....88.9910H Altcode:
The structure of the heliospheric magnetic field changes substantially
during the 11-year sunspot cycle. We have calculated its configuration
for the period 1976-1982 by using a potential field model, continuing
our earlier study near solar minimum in 1976-1977 (Hoeksema et al.,
1982). In this paper we concentrate on the structure during the rising
phase, maximum, and early decline of sunspot cycle 21, from 1978 to
1982. Early in this interval there are four warps in the current
sheet (the boundary between interplanetary magnetic field toward
and away from the sun) giving rise to a four-sector structure in the
interplanetary magnetic field observed at earth. The location of the
current sheet changes slowly and extends to a heliographic latitude of
approximately 50°. Near maximum the structure is much more complex,
with the current sheet extending nearly to the poles. Often there are
multiple current sheets. As solar activity decrease, the structure
simplifies until, in most of 1982, there is a single, simply shaped
current sheet corresponding to a two-sector interplanetary magnetic
field structure in the ecliptic plane. The sun's polar fields, not
fully measured by magnetographs such as that at the Stanford Solar
Observatory, substantially influence the calculated position of the
current sheet near sunspot minimum. We have determined the strength
of the polar field correction throughout this period and include it in
our model calculations. The lower latitude magnetic fields become much
stronger as the polar fields weaken and reverse polarity near maximum,
decreasing the influence of the polar field correction. The major model
parameter is in the radius of the source surface, the spherical surface
at which the field lines become radial. Correlations of interplanetary
magnetic field polarity observed by spacecraft with that predicted by
the model calculated at various source surface radii indicate that the
optimum source surface radius is not significantly different from 2.5
Rs during this part of the solar cycle.

---------------------------------------------------------
Title: Detection of solar gravity mode oscillations
Authors: Scherrer, P. H.
1983dsgm.book.....S Altcode:
An analysis of solar velocity data obtained at the Stanford Solar
Observatory has shown the existence of solar global oscillations
(Delache and Scherrer, Nature, in press). The oscillations are in the
range of 45 to 105 microHz (160 to 370 minutes) and are interpreted
as internal gravity modes of degree l=1 and l=2.

---------------------------------------------------------
Title: The structure of the heliospheric current sheet, 1978 - 1982
Authors: Hoeksema, J. T.; Wilcox, J. M.; Scherrer, P. H.
1983STIN...8325645H Altcode:
The structure of the heliospheric magnetic field changes substantially
during the 11 year sunspot cycle. Its configuration for the period
1976 through 1982 using a potential field model was calculated. The
structure during the rising phase, maximum, and early decline of
sunspot cycle 21, from 1978 to 1982 is considered.

---------------------------------------------------------
Title: Detection of solar gravity mode oscillations
Authors: Delache, P.; Scherrer, P. H.
1983dsgm.book.....D Altcode:
An analysis of solar velocity data obtained at the Stanford Solar
Observatory shows the existence of solar global oscillations in the
range 45 to 105 microHz (160 to 370 minutes). These oscillations are
interpreted as internal gravity modes of degree l = 1 and l = 2. A
good estimate of the order of the modes has also been made.

---------------------------------------------------------
Title: Detection of solar five-minute oscillations of low degree
Authors: Scherrer, Philip H.; Wilcox, John M.; Christensen-Dalsgaard,
J.; Gough, D. O.
1983SoPh...82...75S Altcode: 1983IAUCo..66...75S
Solar five-minute oscillations of degree l = 3, 4, and 5 have been
observed at Stanford, in the Doppler shift of the Fe 5124 line. The
frequencies and amplitudes are in broad agreement with previous
observations of modes with l ≤ 3, though we note that there are some
systematic discrepancies between the results of different observers.

---------------------------------------------------------
Title: The spiral sector transition regions in the interplanetary
magnetic fields
Authors: Zhao, X. -P.; Wilcox, J. M.; Scherrer, P. H.
1983ChJSS...3....1Z Altcode:
Based on the large-scale configuration of the magnetic fields in
interplanetary space and the possible association of the solar wind
flow near the sector boundary crossing with the coronal streamer,
it is suggested that in interplanetary space there might be some
spiral sector transition regions which are thicker than the sector
boundaries. In situ observations of interplanetary magnetic field
and solar wind plasma do show the existence of the spiral sector
transition regions. The magnetic strength in the regions does not go
to zero for all the 45 cases studied in this work; most of them have
a magnetic strength either much higher or much lower than the average
of 5 gamma in the adjacent magnetic sectors. The physical properties
in the magnetic depressing (MD) and magnetic enhancement (ME) regions
and the possible causes have also been analyzed and discussed.

---------------------------------------------------------
Title: Structure of the Solar Oscillation with Period Near 160-MINUTES
Authors: Scherrer, P. H.; Wilcox, J. M.
1983SoPh...82...37S Altcode: 1983IAUCo..66...37S
The solar oscillation with period near 160 min is found to be unique
in a spectrum computed over the range of periods from about 71 to
278 min. Our best estimate of the period is 160.0095 ± 0.001 min,
which is different from 160 min (1/9 of a day) by a highly significant
amount. The width of the peak is approximately equal to the limiting
resolution that can be obtained from an observation lasting 6 years,
which suggests that the damping time of the oscillations is considerably
longer than 6 years. A suggestion that this peak might be the result of
a beating phenomenon between the five minute data averages and a solar
oscillation with period near five minutes is shown to be incorrect by
recomputing a portion of the spectrum using 15 s data averages.

---------------------------------------------------------
Title: Interplanetary Magnetic Field and Tropospheric Circulation
Authors: Wilcox, J. M.; Scherrer, P. H.; Hoeksema, J. T.
1983wcrs.proc..365W Altcode:
The relation between interplanetary magnetic sector boundary crossings
and areas of high vorticity in the troposphere that was reported during
1963-1973 cannot be investigated in the years after 1973 because of
changes in the processing of the 500 mb height grids prepared by the
National Meteorological Center. In particular, we cannot say that
the effect disappeared. The same applies to vorticity computed from
NMC winds grids. The Limited Area Fine Mesh grid has a large noise in
computed vorticity after December 3, 1974. Therefore the interesting
analysis of Larsen and Kelley cannot be extended. They had found that
forecasts of Vorticity Area Index were significantly poorer after a
sector boundary. Previously announced in STAR as N83-25251

---------------------------------------------------------
Title: Review of Sun-as-a-Star Observations of Low Degree Oscillations
Authors: Scherrer, P. H.
1983EOSTr..64..303S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Structure of the heliospheric curent sheet in the early
portion of sunspot cycle 21
Authors: Hoeksema, J. T.; Wilcox, J. M.; Scherrer, P. H.
1982JGR....8710331H Altcode:
The structure of the heliospheric current sheet on a spherical source
surface of radius 2.35 Rs has been computed via the use
of a potential field model during the first year and a half after
the last sunspot minimum. The solar polar magnetic field that is
not fully observed in conventional magnetograph scans was included
in the computation. The computed heliospheric current sheet had a
quasi-stationary structure consisting of two northward and two southward
maxima in latitude per solar rotation. The extend in latitude slowly
increased from about 15° near the start of the interval to about 45°
near the end. The magnetic field polarity (away from the sun or toward
the sun) at the subterresrial latitude on the source surface agreed
with the interplanetary magnetic field polarity observed or inferred
at the earth on 82% of the days. The interplanetary field structure
observed at the earth at this time is finely tuned to the structure
of low-latitude fields on the source surface.

---------------------------------------------------------
Title: Solar Velocity Oscillations with Periods Greater than 60
Minutes
Authors: Scherrer, P. H.
1982BAAS...14..922S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Review of observations relevant to solar oscillations
Authors: Scherrer, P. H.
1982pccv.conf...83S Altcode: 1982STIN...8313049S
Recent solar oscillation observations and methods used are
described. Integrated or almost integrated sunlight (Sun as a star
observation) was observed. The most certain observations are in the
5 minute range. The p-mode and g-mode oscillations are expected from
3 to more than 300 minutes. The possible period ranges are described
into the three intervals: (1) the 5 minute range for which the most
dramatic and certain results are reported; (2) the 10 to 20 minute
range for which solar diameter oscillations are reported; and (3) the
160 minute oscillation found in velocity and several other quantities.

---------------------------------------------------------
Title: Observation of additional low-degree 5-min modes of solar
oscillation
Authors: Scherrer, P. H.; Wilcox, J. M.; Christensen-Dalsgaard, J.;
Gough, D.
1982Natur.297..312S Altcode: 1982STIN...8315246S
By measuring the difference between the shifts in the Fe 5,124
spectrum line from light integrated from a central circular portion
of the solar disk and from an annular portion exterior to it,
we have detected high-order solar oscillations with degrees l
= 3, 4 and 5. The frequencies of the octupole modes agree well
with the values obtained from whole-disk measurements at the South
Pole1. A least-squares fit of the observed frequencies to
values interpolated between and extrapolated from the predictions
of a sequence of solar models with different chemical compositions
selects two models. One of these is almost identical to that obtained
by a previous fit15 of modes with l&lt;=2, and has a helium
abundance somewhat greater than 25% by mass.

---------------------------------------------------------
Title: Detection of solar five minute oscillations of low degree
Authors: Scherrer, P. H.; Wilcox, J. M.; Christensen-Dalsgaard, J.;
Gough, D. O.
1982STIN...8317445S Altcode:
Solar five-minute oscillations of degree small = 3, 4 and 5 have been
observed at the Stanford Solar Observatory, in the Doppler shift of the
Fe5124 line. The frequencies and amplitudes are in broad agreement with
previous observations of modes with small less than or 3, though we
note that there are some systematic discrepancies between the results
of different observers.

---------------------------------------------------------
Title: Structure of the heliospheric current sheet in the early
portion of sunspot cycle 21
Authors: Hoeksema, J. T.; Wilcox, J. M.; Scherrer, P. H.
1982STIN...8314059H Altcode:
The structure of the heliospheric current sheet on a spherical
source surface of radius 2.35 R has been computed using a potential
field model during the first year and a half after the last sunspot
minimum. The solar polar magnetic field that is not fully observed in
conventional magnetograph scans was included in the computation. The
computed heliospheric current sheet had a quasi-stationary structure
consisting of two northward and two southward maxima in latitude per
solar rotation. The extent in latitude slowly increased from about
15 degrees near the start of the interval to about 45 degrees near
the end of the interval. The magnetic field polarity (away from
the Sun or toward the Sun) at the subterrestrial latitude on the
source surface agreed with the interplanetary magnetic field polarity
observed or inferred at Earth on 82% of the days. The interplanetary
field structure observed at Earth at this time is finely tuned to the
structure of low-latitude fields on the source surface.

---------------------------------------------------------
Title: Structure of the solar oscillation with period near 160 minutes
Authors: Scherrer, P. H.; Wilcox, J. M.
1982STIN...8225074S Altcode:
The solar oscillation with period near 160 minutes is found to be unique
in a spectrum computed over the range of periods from about 71 to 278
minutes. A best estimate of the period is 160.0095 + or - 0.001 minutes,
which is different from 160 minutes (one ninth of a day) by a highly
significant amount. The width of the peak is approximately equal to the
limiting resolution that can be obtained from an observation lasting
6 years, which suggests that the damping time of the oscillations is
considerably longer than 6 years. A suggestion that this peak might
be the result of a beating phenomenon between the five minute data
averages and a solar oscillation with period near five minutes is
shown to be incorrect by recomputing a portion of the spectrum using
15 second data averages.

---------------------------------------------------------
Title: Effect of flare-site magnetic field on solar wind speed and
geomagnetic activity.
Authors: Lundstedt, H.; Duffy, P. B.; Wilcox, J. M.; Scherrer, P. H.
1982ROLun..18..129L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On the Nature of the Apparent Response of the Vorticity Area
Index to the Solar Magnetic Field
Authors: Wilcox, J. M.; Scherrer, P. H.
1981SoPh...74..421W Altcode:
The apparent response of the vorticity area index to the solar
magnetic field is confined to tropospheric regions of intense
circulation. Discussions and calculations that include larger volumes of
the troposphere would not be expected to show a significant Sun-weather
effect. Analysis of the effect in time intervals outside the original
1963-73 is also discussed. An assessment of this Sun-weather effect
at the present time is given.

---------------------------------------------------------
Title: What causes the warp in the heliospheric current sheet?
Authors: Wilcox, J. M.; Scherrer, P. H.
1981JGR....86.5899W Altcode:
A comparative discussion of the warp in the heliospheric current sheet
is presented. Pioneer 10 and 11 data of the interplanetary magnetic
field compared with earlier data (Helios 1 and 2) show a good agreement
on the phenomenon of the warp; however, the interpretations differ. One
theory (Thomas and Smith, 1980) proposes that fast solar wind streams
associated with interaction regions may move the current sheet higher
to heliospheric latitudes, thus causing the warp; while the earlier
theory (1976) adequately explained the phenomenon by using the observed
photospheric magnetic field and the Zeeman effect but omitted the
solar wind dynamical considerations as part of the computations. It
is shown that the Helios data of the polarity of the interplanetary
magnetic field are in good agreement with the computed location of
the current sheet, confirming the earlier theory.

---------------------------------------------------------
Title: Solar Flare Acceleration of Solar Wind: Influence of Active
Region Magnetic Field
Authors: Lundstedt, H.; Wilcox, J. M.; Scherrer, P. H.
1981Sci...212.1501L Altcode:
The direction of the photospheric magnetic field at the site of a solar
flare is a good predictor of whether the flare will accelerate solar
wind plasma. If the field has a southward component, high-speed solar
wind plasma is usually observed near the earth about 4 days later. If
the field has a northward component, such high-speed solar wind is
almost never observed. Southward-field flares may then be expected to
have much larger terrestrial effects than northward flares.

---------------------------------------------------------
Title: Recent Global-Scale Oscillations and Magnetic Field
Observations
Authors: Scherrer, P. H.
1981BAAS...13R.545S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Global Solar Oscillations: High Order Modes with Degree 3 to 5
Authors: Scherrer, P. H.; Wilcox, J. M.
1981BAAS...13..859S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Recent global scale solar oscillations and magnetic field
observations.
Authors: Scherrer, P. H.
1981BAAS...13..548S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Geomagnetic activity and Hale sector boundaries
Authors: Lundstedt, H.; Scherrer, P. H.; Wilcox, J. M.
1981P&SS...29..167L Altcode:
The variation of the geomagnetic activity index Ap at the
IMF sector boundaries (+ to - and - to +) has been studied for three
solar cycles, separating data into vernal and autumnal equinoxes. It
was found that a reported increase in Ap as an effect of a
Hale boundary can be better attributed to the occurrence of a negative
IMF Bz component in the geocentric solar magnetospheric
coordinate system and to the occurrence of high speed solar wind
streams.

---------------------------------------------------------
Title: The rotation of the sun - Observations at Stanford
Authors: Scherrer, P. H.; Wilcox, J. M.; Svalgaard, L.
1980ApJ...241..811S Altcode:
Daily observations of the photospheric rotation rate using the Doppler
effect have been made at the Stanford Solar Observatory since May
1976. These observations show no daily or long-period variations in
the rotation rate that exceed the observational error of about 1%. The
average rotation rate is the same as that of the sunspots and the
large-scale magnetic field structures.

---------------------------------------------------------
Title: Origin of the warped heliospheric current sheet
Authors: Wilcox, J. M.; Hoeksema, J. T.; Scherrer, P. H.
1980Sci...209..603W Altcode:
The warped heliospheric current sheet for early 1976 is calculated
from the observed photospheric magnetic field by a potential field
method. Comparisons with measurements of the interplanetary magnetic
field polarity for early 1976 obtained at several locations in the
heliosphere by Helios 1, Helios 2, Pioneer 11, and at the earth show
a rather detailed agreement between the computed current sheet and
the observations. It appears that the large-scale structure of the
warped heliospheric current sheet is determined by the structure of
the photospheric magnetic field and that 'ballerina skirt' effects
may add small scale ripples.

---------------------------------------------------------
Title: Doppler observations of solar rotation
Authors: Scherrer, P. H.; Wilcox, J. M.
1980ApJ...239L..89S Altcode:
Daily observations of the photospheric equatorial rotation rate using
the Doppler effect are made at the Stanford Solar Observatory. These
observations show no variations in the rotation rate that exceed
the observational error of about 1%. The average rotation rate is
indistinguishable from that of sunspots and large-scale magnetic
field structures.

---------------------------------------------------------
Title: Further evidence of solar oscillations with a period of
160 minutes
Authors: Scherrer, P. H.; Wilcox, J. M.; Severnyi, A. B.; Kotov,
V. A.; Tsap, T. T.
1980ApJ...237L..97S Altcode:
Observations made at the Crimean Astrophysical Observatory and the
Stanford Solar Observatory during 1979 provide evidence of the existence
of oscillations of the sun with a period near 160 minutes. The new
observations showed the same period with a phase of maximum expansion
as predicted from earlier data; for 1979 the time of maximum expansion
of the center of the solar disk was found to be 01:55 UT for the Crimean
observatories and 01:58 UT for Stanford with a phase uncertainty of plus
or minus 15 minutes. In addition, a new regression line can be found
which yields a period of 160.01 minutes or a drift in phase of 31.5
minutes per year in an analysis at exactly 160 minutes. The continued
agreement in phase (and amplitude) between the two observatories
for four years, as well as the fact that the period of oscillations
determined differs from exactly one-ninth of a day, supports the
interpretation that solar oscillations are indeed being observed.

---------------------------------------------------------
Title: The origin of the warped heliospheric current sheet
Authors: Wilcox, J. M.; Scherrer, P. H.; Hoeksema, J. T.
1980STIN...8133113W Altcode:
The warped heliospheric current sheet in early 1976 was calculated
from the observed photospheric magnetic field using a potential
field method. Comparisons with measurements of the interplanetary
magnetic field polarity in early 1976 obtained at several locations
in the heliosphere at Helios 1, Helios 2, Pioneer 11 and Earth show
a rather detailed agreement between the computed current sheet and
the observations. It appears that the large scale structure of the
warped heliospheric current sheet is determined by the structure of
the photospheric magnetic field, and that "ballerina skirt" effects
may add small scale ripples.

---------------------------------------------------------
Title: A Two-Sector Solar Magnetic Structure with 29 Day Rotation
Authors: Hoeksema, J. T.; Scherrer, P. H.; Wilcox, J. M.
1980BAAS...12..474H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Further Investigation of the Solar Torsional Oscillator with
a Period of 11 Years
Authors: Scherrer, P. H.; Wilcox, J. M.
1980BAAS...12Q.473S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Doppler observations of solar rotation
Authors: Scherrer, P. H.
1980STIN...8021238S Altcode:
Daily observations of the photospheric equatorial rotation rate
using the Doppler effect mode at the Sanford Solar Observatory are
presented. These observations show no variations in the rotation rate
that exceed the observational error of about one percent. The average
rotation rate is indistinguishable from that of sunspots and large
scale magnetic field structures.

---------------------------------------------------------
Title: On the nature of the apparent response of vorticity area
index to the solar magnetic field
Authors: Wilcox, J. M.; Scherrer, P. H.
1980STIN...8021239W Altcode:
The characteristics of tropospheric circulation that are involved
in the apparent response of the vorticity area index (VIA) as the
solar magnetic field is carried past the Earth by the solar wind
are discussed. It is shown that the response is concentrated in the
tropospheric regions of most intense circulation, i.e. the central
portions of well-formed low pressure troughs. Factors that must be
considered when assessing the Sun-weather effect in the years from
1947 to 1978 are included.

---------------------------------------------------------
Title: Geomagnetic activity and Hale sector boundaries
Authors: Lundstedt, H.; Scherrer, P. H.; Wilcox, J. M.
1980STIN...8022222L Altcode:
The variation of the geomagnetic activity index Ap at the IMF sector
boundaries (+ to - and - to +) is examined for three solar cycles,
separating data into vernal and autumnal equinoxes. It is found that
a reported increase in Ap as an effect of a Hale boundary can be
better attributed to the occurrence of a negative IMF Bz component
in the geocentric solar magnetospheric coordinate system and to the
occurrence of high speed solar wind streams.

---------------------------------------------------------
Title: Shaking Down the Sun's Long-Period Vibes
Authors: Kotov, V. A.; Severny, A. B.; Tsap, T. T.; Scherrer, P. H.;
Wilcox, J. M.; Fossat, E.; Grec, G.; Pomerantz, M.
1980SciN..118..100K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Unraveling Solar Magnetism
Authors: Wilcox, J. M.; Scherrer, P. H.; Hoeksema, J. T.; Howard,
R.; Labonte, B.
1980SciN..117..374W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Oscillations with a Period Near 160-Minutes
Authors: Scherrer, P. H.
1979BAAS...11..733S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Variation with time of a Sun-weather effect
Authors: Wilcox, J. M.; Scherrer, P. H.
1979Natur.280..845W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar variability and terrestrial weather.
Authors: Scherrer, P. H.
1979RvGSP..17..724S Altcode: 1979RvGeo..17..724S
The present review article indicates that the past four years have been
very active in the field of sun-weather research in the U.S. Some quite
specific questions which have arisen from recent research include the
time variation of the VAL vs SB effect; the nature of the clear-air
electric field; the relationship of the ionospheric potential to
thunderstorm formation; and the constancy of the solar 'constant'
both in terms of the total luminosity on the climatic time scale and
for near UV radiation on the time scale of days to 11 years.

---------------------------------------------------------
Title: Intensity of tropospheric circulation associated with solar
magnetic sector boundary transits.
Authors: Wilcox, J. M.; Scherrer, P. H.; Svalgaard, L.
1979JATP...41..657W Altcode:
The fractional decrease in the vorticity area index associated
with transits past the earth of interplanetary magnetic sector
boundaries increase as the value of vorticity used to compute the index
increases. This suggests that after the boundary transit there is an
approximately uniform reduction in all the values of vorticity that
are not less than 0.00020/sec. In low altitudes and large absolute
vorticities not less than 0.00020/sec the average change in the
vorticity area index approaches 50%.

---------------------------------------------------------
Title: Interplanetary Magnetic Field Polarity and the Size of
Low-Pressure Troughs Near 180 degrees W Longitude
Authors: Wilcox, J. M.; Duffy, P. B.; Schatten, K. H.; Svalgaard,
L.; Scherrer, P. H.; Roberts, W. O.; Olson, R. H.
1979Sci...204...60W Altcode:
When the interplanetary magnetic field is directed away from the sun,
the area of wintertime low-pressure (300-millibar) troughs near 180
degrees W longitude is significantly larger than when the field is
toward the sun. This relation persists during most of the winters of
1951 to 1973.

---------------------------------------------------------
Title: Average photospheric poloidal and toroidal magnetic field
components near solar minimum.
Authors: Duvall, T. L., Jr.; Scherrer, P. H.; Svalgaard, L.; Wilcox,
J. M.
1979SoPh...61..233D Altcode:
Average (over longitude and time) photospheric magnetic field components
are derived from 3' Stanford magnetograms made near the solar minimum
of cycle 21. The average magnetograph signal is found to behave as
the projection of a vector for measurements made across the disk. The
poloidal field exhibits the familiar dipolar structure near the poles,
with a measured signal in the line Fe I λ 5250 Å of ≈ 1 G. At low
latitudes the poloidal field has the polarity of the poles, but is
of reduced magnitude (≈ 0.1 G). A net photospheric toroidal field
with a broad latitudinal extent is found. The polarity of the toroidal
field is opposite in the nothern and southern hemispheres and has the
same sense as subsurface flux tubes giving rise to active regions of
solar cycle 21.

---------------------------------------------------------
Title: Solar Rotation - Observations at Stanford Since 1976
Authors: Scherrer, P. H.
1979BAAS...11..420S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observations of solar oscillations with periods of 160 minutes
Authors: Scherrer, P. H.; Wilcox, J. M.; Kotov, V. A.; Severny, A. B.;
Tsap, T. T.
1979Natur.277..635S Altcode:
Severny et al. (1976) have reported oscillations of the sun with
a period near 160 min. A description is presented of observations
made at the Stanford Solar Observatory during the time from 1975 to
the present which seem to support the reports by Severny et al. At
Stanford the relative velocity between a central circular area of
radius 0.5 solar radius on the solar disk and most of the remaining
area of the solar disk is measured. A superposed epoch analysis of
the observations using a period of 160 min is discussed. An apparent
agreement in phase between the obtained observational data and those
reported by Severny et al. tends to support the interpretation that
solar oscillations are being observed.

---------------------------------------------------------
Title: The equatorial rotation velocity of the photosphere is measured
to be the same as sunspots
Authors: Svalgaard, L.; Scherrer, P. H.; Wilcox, J. M.
1978soro.work...26S Altcode:
The equatorial rotation rate of the photosphere was measured at effect
data. It was found that scattered light has a large influence and
must be taken into account properly. When this was done it was found
that the rotation rate from Doppler shifts agreed very well with the
rate found for sunspots. Short-term fluctuations in rotation rate
(i.e. from day to day) were less than plus or minus 15 m/s and were
thus within observational errors.

---------------------------------------------------------
Title: The strength of the Sun's polar fields.
Authors: Svalgaard, L.; Duvall, T. L., Jr.; Scherrer, P. H.
1978SoPh...58..225S Altcode:
The magnetic field strength within the polar caps of the Sun is an
important parameter for both the solar activity cycle and for our
understanding of the interplanetary magnetic field. Measurements of the
line-of-sight component of the magnetic field generally yield 0.1 to 0.2
mT near times of sunspot minimum. In this paper we report measurements
of the polar fields made at the Stanford Solar Observatory using the
Fe I line λ 525.02 nm. We find that the average flux density poleward
of 55° latitude is about 0.6 mT peaking to more than 1 mT at the pole
and decreasing to 0.2 mT at the polar cap boundary. The total open
flux through either polar cap thus becomes about 3 × 1014
Wb. We also show that observed magnetic field strengths vary as the
line-of-sight component of nearly radial fields.

---------------------------------------------------------
Title: Using Dynamo Theory to predict the sunspot number during
Solar Cycle 21
Authors: Schatten, K. H.; Scherrer, P. H.; Svalgaard, L.; Wilcox, J. M.
1978GeoRL...5..411S Altcode:
On physical grounds it is suggested that the sun's polar field strength
near a solar minimum is closely related to the following cycle's
solar activity. Four methods of estimating the sun's polar magnetic
field strength near solar minimum are employed to provide an estimate
of cycle 21's yearly mean sunspot number at solar maximum of 140 ±
20. We think of this estimate as a first order attempt to predict the
cycle's activity using one parameter of physical importance based upon
dynamo theory.

---------------------------------------------------------
Title: An observational search for large scale organization of
five-minute oscillations on the sun.
Authors: Dittmer, P. H.; Scherrer, P. H.; Wilcox, J. M.
1978SoPh...57....3D Altcode:
The large-scale solar velocity field has been measured over an
aperture of radius 0.8 R⊙ on 121 days between April
and September, 1976. Measurements are made in the line FeI 5123.730
Å, employing a velocity subtraction technique similar to that of
Severny et al. (1976). Comparisons of the amplitude and frequency of
the five-minute resonant oscillation with the geomagnetic C9 index
and magnetic sector boundaries show no evidence of any relationship
between the oscillations and coronal holes or sector structure.

---------------------------------------------------------
Title: Using Dynamo Theory to Predict the Sunspot Number During
Solar Cycle 21
Authors: Scherrer, P. H.; Schatten, K. H.; Svalgaard, L.; Wilcox, J. M.
1978BAAS...10..415S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A physical mechanism for the prediction of the sunspot number
during solar cycle 21
Authors: Schatten, K. H.; Scherrer, P. H.; Svalgaard, L.; Wilcox, J. M.
1978STIN...7829028S Altcode:
On physical grounds it is suggested that the sun's polar field strength
near a solar minimum is closely related to the following cycle's solar
activity. Four methods of estimating the sun's polar magnetic field
strength near solar minimum are employed to provide an estimate of
cycle 21's yearly mean sunspot number at solar maximum of 140 plus or
minus 20. This estimate is considered to be a first order attempt to
predict the cycle's activity using one parameter of physical importance.

---------------------------------------------------------
Title: The strength of the sun's polar fields
Authors: Svalgaard, L.; Duvall, T. L., Jr.; Scherrer, P. H.
1978STIN...7829029S Altcode:
Observations at Stanford Solar Observatory of solar magnetic fields
in the FeI line lambda 525.02 nm shows that a radial magnetic field
measured at a point where the radius makes an angle rho with the line
of sight is observed to be decreased by a factor cos rho. For field
elements of 150 mT, magnetograph saturation causes the measured field
to be too low by a factor of 1.8. The average field magnitude poleward
55 deg latitude is measured to be near 100 micron T. Variation of the
apparent field over a 3 arc min aperture grazing the limb at central
meridian amounts to a factor of two over the year; the field being
strongest when the pole is tipped the most (7 1/4 deg) towards the
observer. Combination of all the above results leads to the following
picture of the magnetic field within the polar caps. The field is
nearly radial, varying as Bp cos to the 8th power theta
where the field strength Bp at the pole (theta = 0 deg)
is 1.15 mT, and falling off to below 0.2 mT at the polar cap boundary
(theta = 35 deg). Within coronal holes outside of the polar cap the
magnetic field strength at sunspot minimum is rather small (0.15 mT).

---------------------------------------------------------
Title: Comparison of Hα synoptic charts with the large-scale solar
magnetic field as observed at Stanford
Authors: Duvall, T. L., Jr.; Wilcox, J. M.; Svalgaard, L.; Scherrer,
P. H.; McIntosh, P. S.
1977SoPh...55...63D Altcode:
Two methods of observing the neutral line of the large-scale
photospheric magnetic field are compared: (1) neutral line positions
inferred from Hα photographs (McIntosh, 1972a, 1975; McIntosh and
Nolte, 1975) and (2) observations of the photospheric magnetic field
made with low spatial resolution (3') and high sensitivity using the
Stanford magnetograph. The comparison is found to be very favorable.

---------------------------------------------------------
Title: The mean magnetic field of the Sun: observations at Stanford.
Authors: Scherrer, P. H.; Wilcox, J. M.; Svalgaard, L.; Duvall, T. L.,
Jr.; Dittmer, P. H.; Gustafson, E. K.
1977SoPh...54..353S Altcode:
A solar telescope has been built at Stanford University to study
the organization and evolution of large-scale solar magnetic fields
and velocities. The observations are made using a Babcock-type
magnetograph which is connected to a 22.9 m vertical Littrow
spectrograph. Sun-as-a-star integrated light measurements of the mean
solar magnetic field have been made daily since May 1975. The typical
mean field magnitude has been about 0.15 G with typical measurement
error less than 0.05 G. The mean field polarity pattern is essentially
identical to the interplanetary magnetic field sector structure (see
near the Earth with a 4 day lag). The differences in the observed
structures can be understood in terms of a `warped current sheet' model.

---------------------------------------------------------
Title: An observational search for large-scale organization of
five-minute oscillations on the sun
Authors: Dittmer, P. H.; Scherrer, P. H.; Wilcox, J. M.
1977STIN...7822996D Altcode:
The large-scale solar velocity field has been measured over an aperture
of radius 0.8 R on 121 days between April and Sept., 1976. Measurements
are made in the line FeI 5123.730A, employing a velocity subtraction
technique similar to that of Severny et al. (1976). Comparisons of the
amplitude and frequency of the five-minute resonant oscillations with
the geomagnetic C9 index and magnetic sector boundaries show no evidence
of any relationship between the oscillations and coronal holes or sector
structure. The average period measured for the five-minute oscillation
is 312.0 plus or minus 0.9 sec, which is longer than the average 296.1
plus or minus 1.3 sec period originally reported by Noyes and Leighton
(1963) from measurements in the line CaI 6103. The average amplitude
is 2.0 m/s, which agrees reasonably with the 2.4 m/s value reported by
Fossat and Ricort (1975). This amplitude is larger than might have been
expected from an extrapolation of the work of Tanenbaum et al. (1969)
to a large aperture, and is evidence of a large horizontal wavelength
for the oscillations.

---------------------------------------------------------
Title: Comparison of H alpha synoptic charts with the large-scale
solar magnetic field as observed at Stanford
Authors: Duvall, T. L., Jr.; Wilcox, J. M.; Svalgaard, L.; Scherrer,
P. H.; McIntosh, P. S.
1977STIN...7729049D Altcode:
Two methods of observing the neutral line of the large-scale
photospheric magnetic field are compared: (1) neutral line positions
inferred from H alpha photographs and (2) observations of the
photospheric magnetic field made with low spatial resolution (3
arc min.) and high sensitivity using the Stanford magnetograph. The
comparison is found to be very favorable.

---------------------------------------------------------
Title: The mean magnetic field of the sun: Observations at Stanford
Authors: Scherrer, P. H.; Wilcox, J. M.; Svalgaard, L.; Duvall, T. L.,
Jr.; Dittmer, P. H.; Gustafson, E. K.
1977STIN...7726055S Altcode:
A solar telescope was built at Stanford University to study the
organization and evolution of large-scale solar magnetic fields
and velocities. The observations are made using a Babcock-type
magnetograph which is connected to a 22.9 m vertical Littrow
spectrograph. Sun-as-a-star integrated light measurements of the mean
solar magnetic field were made daily since May 1975. The typical mean
field magnitude is about 0.15 gauss with typical measurement error
less than 0.05 gauss. The mean field polarity pattern is essentially
identical to the interplanetary magnetic field sector structure (seen
near the earth with a 4 day lag). The differences in the observed
structures can be understood in terms of a warped current sheet model.

---------------------------------------------------------
Title: The mean magnetic field of the Sun: Method of observation
and relation to the interplanetary magnetic field
Authors: Scherrer, Philip H.; Wilcox, John M.; Kotov, Valeri; Severny,
A. B.; Howard, Robert
1977SoPh...52D...6S Altcode:
The mean solar magnetic field as measured in integrated light has
been observed since 1968. Since 1970 it has been observed both at
Hale Observatories and at the Crimean Astrophysical Observatory. The
observing procedures at both observatories and their implications for
mean field measurements are discussed. A comparison of the two sets
of daily observations shows that similar results are obtained at both
observatories. A comparison of the mean field with the interplanetary
magnetic polarity shows that the IMF sector structure has the same
pattern as the mean field polarity.

---------------------------------------------------------
Title: The mean magnetic field of the sun: method of observation
and relation to the interplanetary magnetic field.
Authors: Scherrer, P. H.; Wilcox, J. M.; Kotov, V.; Severnyi, A. B.;
Howard, R.
1977SoPh...52....3S Altcode:
The mean solar magnetic field as measured in integrated light has
been observed since 1968. Since 1970 it has been observed both at
Hale Observatories and at the Crimean Astrophysical Observatory. The
observing procedures at both observatories and their implications for
mean field measurements are discussed. A comparison of the two sets
of daily observations shows that similar results are obtained at both
observatories. A comparison of the mean field with the interplanetary
magnetic polarity shows that the IMF sector structure has the same
pattern as the mean field polarity.

---------------------------------------------------------
Title: 2h 40m Oscillation Observations at Stanford
Authors: Scherrer, P. H.
1977lsms.proc...12S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Stanford Solar Observatory - The First Year
Authors: Scherrer, P. H.; Duvall, T. L., Jr.; Dittmer, P. H.;
Gustafson, E. K.; Wilcox, J. M.
1976BAAS....8Q.370S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Measurements of Large-Scale Solar Velocity Fields
Authors: Dittmer, P. H.; Scherrer, P. H.; Wilcox, J. M.; Duvall,
T. L., Jr.; Gustafson, E. K.
1976BAAS....8..311D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Measurements of the Photospheric Magnetic Field with 3'
Resolution
Authors: Duvall, T. L., Jr.; Scherrer, P. H.; Wilcox, J. M.; Dittmer,
P. H.; Gustafson, E. K.
1976BAAS....8..344D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On the reality of a sun-weather effect.
Authors: Wilcox, J. M.; Svalgaard, L.; Scherrer, P. H.
1976JAtS...33.1113W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Sun's Magnetic Sector Structure
Authors: Svalgaard, L.; Wilcox, J. M.; Scherrer, P. H.; Howard, R.
1975SoPh...45...83S Altcode:
The synoptic appearance of solar magnetic sectors is studied using 454
sector boundaries observed at Earth during 1959-1973. The sectors are
clearly visible in the photospheric magnetic field. Sector boundaries
can be clearly identified as north-south running demarcation lines
between regions of persistent magnetic polarity imbalances. These
regions extend up to about 35 ° of latitude on both sides of the
equator. They generally do not extend into the polar caps. The polar
cap boundary can be identified as an east-west demarcation line marking
the poleward limit of the sectors. The typical flux imbalance for a
magnetic sector is about 4 × 1021 Mx.

---------------------------------------------------------
Title: On the reality of a sun-weather effect
Authors: Wilcox, J. M.; Svalgaard, L.; Scherrer, P. H.
1975STIN...7624117W Altcode:
An influence of the solar magnetic sector structure on the terrestrial
atmospheric vorticity has been reported. The reported effect persists
when the number of sector boundary passages examined is increased from
54 to 131. The same effect is found independently in the latitude zones
35 N - 55 N and greater than 55 N. The depth of the sector-related
effect is much greater than the depth of any other minimum in an
extended analysis. These results support the reality of the effect.

---------------------------------------------------------
Title: The sun's magnetic sector structure
Authors: Svalgaard, L.; Wilcox, J. M.; Scherrer, P. H.; Howard, R.
1975suiprrept.1959S Altcode:
The synoptic appearance of solar magnetic sectors is studied using 454
sector boundaries observed at earth during 1959-1973. The sectors are
clearly visible in the photospheric magnetic field. Sector boundaries
can be clearly identified as north-south running demarcation lines
between regions of persistent magnetic polarity imbalances. These
regions extend up to about 35 deg of latitude on both sides of the
equator. They generally do not extend into the polar caps. The polar
cap boundary can be identified as an east-west demarcation line marking
the poleward limit of the sectors. The typical flux imbalance for a
magnetic sector is about 4 x 10 to the 21st power Maxwells.

---------------------------------------------------------
Title: Seasonal variation and magnitude of the solar sector
structure-atmospheric vorticity effect
Authors: Wilcox, J. M.; Svalgaard, L.; Scherrer, P. H.
1975Natur.255..539W Altcode:
A RELATIONSHIP between the solar sector structure, as swept past the
Earth by the solar wind, and terrestrial atmospheric vorticity has
been reported by Wilcox et al.1. The solar sector structure
is a large scale property of the Sun that is seen most readily in
its magnetic field. As observed by spacecraft magnetometers near the
Earth, the extended solar magnetic field typically consists of four
sectors within a 27-d synodic solar rotation period. Within each sector
the magnetic field is predominantly either towards or away from the
Sun. The sectors are separated by thin current sheets that reverse
the direction of the field and constitute sector boundaries. Here we
report evidence of a seasonal variation in this effect.

---------------------------------------------------------
Title: The Stanford Solar Observatory
Authors: Scherrer, P. H.; Wilcox, J. M.; Svalgaard, L.; Dittmer,
P. H.; Duvall, T. L.
1975BAAS....7..350S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Seasonal Variation and Magnitude of the Solar Sector Structure
- Atmospheric Vorticity Effect
Authors: Wilcox, J. M.; Svalgaard, L.; Scherrer, P. H.
1975scea.conf..294W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Relationship between the Slowly Varying Component of Solar
Radio Emission and Large Scale Photospheric Magnetic Field Patterns
Authors: Scherrer, P. H.; El-Raey, M.
1974SoPh...35..361S Altcode:
Daily solar radio flux observations have been examined for
a relationship to the large-scale photospheric magnetic field
structure. Interplanetary magnetic field sector boundaries were used
to indicate boundaries between photospheric field regions of opposite
polarity. An enhancement in emission was found about four days before
the boundary central meridian passage. Most of the effect came from
emission near toward-to-away type boundaries. A higher level of
emission appears to be associated with toward field regions than with
away field regions.

---------------------------------------------------------
Title: Solar Sector Boundary Configuration from Comparison of
Synoptic Charts of the Photospheric Magnetic Field with the Observed
Interplanetary Field
Authors: Scherrer, P. H.; Wilcox, J. M.; Howard, R.
1974BAAS....6Q.293S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Influence of Solar Magnetic Sector Structure on Terrestrial
Atmospheric Vorticity.
Authors: Wilcox, John M.; Scherrer, Philip H.; Svalgaard, Leif;
Roberts, Walter Orr; Olson, Roger H.; Jenne, Roy L.
1974JAtS...31..581W Altcode:
The solar magnetic sector structure has a sizable and reproducible
influence on tropospheric and lower stratospheric vorticity. The
average vorticity during winter in the Northern Hemisphere north of
2ON latitude reaches a minimum approximately one day after the passing
of a sector boundary, and then increases during the following two or
three days. The effect is found at all heights within the troposphere,
but is not prominent in the stratosphere, except at the lower levels. No
single longitudinal interval appears to dominate the effect.

---------------------------------------------------------
Title: Solar Magnetic Sector Structure: Relation to Circulation of
the Earth's Atmosphere
Authors: Wilcox, John M.; Scherrer, Philip H.; Svalgaard, Leif;
Roberts, Walter Orr; Olson, Roger H.
1973Sci...180..185W Altcode:
The solar magnetic sector structure appears to be related to the
average area of high positive vorticity centers (low-pressure troughs)
observed during winter in the Northern Hemisphere at the 300-millibar
level. The average area of high vorticity decreases (low-pressure
troughs become less intense) during a few days near the times at which
sector boundaries are carried past the earth by the solar wind. The
amplitude of the effect is about 10 percent.

---------------------------------------------------------
Title: The Mean Solar Magnetic Field Observed at the Mt. Wilson
Solar Observatory
Authors: Scherrer, P. H.; Wilcox, J. M.; Howard, R. F.
1973BAAS....5R.279S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: a Study of the Mean Solar Magnetic Field.
Authors: Scherrer, Philip Hanby
1973PhDT........51S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Differential rotation in the solar atmosphere inferred from
optical, radio, and interplanetary data
Authors: El-Raey, Mohamed; Scherrer, Philip H.
1972SoPh...26...15E Altcode:
Autocorrelation analysis of sunspot number, solar radio flux, and
interplanetary field in the period 1967 to 1970 yields new information
concerning solar atmospheric rotation. The upper chromosphere and the
lower corona are rotating on the average about 5 to 8 % faster than is
either the photosphere or the upper corona. In addition, short-lived
features in the chromosphere and lower corona are found to rotate
sometimes as much as 10% faster than relatively long-lived features at
the same height. Coronal and photospheric features are found to rotate
more or less synchronously. Analysis of yearly data has indicated a
considerable change in rotation periods from one year to another.

---------------------------------------------------------
Title: An Annual and a Solar-Magnetic-Cycle Variation in the Inferred
Interplanetary Magnetic Field, 1926-1971
Authors: Wilcox, J. M.; Scherrer, P. H.
1972BAAS....4Q.396W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Comparisons of the Mean Solar Magnetic Field and the
Interplanetary Field Observed During 1969
Authors: Scherrer, P. H.; Wolcox, J. M.; Severny, A. B.
1972BAAS....4S.390S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Mean Photospheric Magnetic Field from Solar Magnetograms:
Comparisons with the Interplanetary Magnetic Field
Authors: Scherrer, Philip H.; Wilcox, John M.; Howard, Robert
1972SoPh...22..418S Altcode:
Large-scale averages of daily solar magnetograms have been compared by
cross-correlation with the interplanetary magnetic sector pattern during
a 2 1/2 yr interval. A significant correlation was found at a lag of
about 4 1/2 days, with the amplitude of the correlation depending on
the area included in the magnetogram averages. The highest correlation
was found when an area of one quarter of the solar disk was used,
which is consistent with the idea that the photospheric features which
are to be associated with the interplanetary sector pattern are large
scale features.

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Title: Large-Scale Negative Polarity Magnetic Fields on the Sun and
Particle-Emitting Flares - Comments
Authors: Scherrer, P. H.; Howard, Robert; Wilcox, John
1972NASSP.308...39S Altcode: 1972sowi.conf...39S
No abstract at ADS

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Title: Annual and solar-magnetic-cycle variations in the
interplanetary magnetic field, 1926-1971
Authors: Wilcox, John M.; Scherrer, Philip H.
1972JGR....77.5385W Altcode:
The polarity of the interplanetary magnetic field has been inferred
by Svalgaard (1972) from observations of the polar geomagnetic field
during the interval 1926-1971. On the basis of a few years of spacecraft
observations, Rosenberg and Coleman (1969) have suggested that there
may be an annual variation in the predominant polarity (toward or away
from the sun) of the interplanetary field. The present analysis of 45
years of inferred field polarity clearly shows an annual variation
and also a variation of about 20 years, which we associate with the
solar-magnetic cycle. On the average the phase of the annual variation
of the interplanetary field changes about 2 ⅔ years after sunspot
maximum, i.e., for about 10 consecutive years the predominant polarity
of the interplanetary field is away from the sun during the 6-month
interval in which the earth is at southern heliographic latitudes, and
then a change of phase occurs such that for about the next 10 years the
predominant polarity is toward the sun while the earth is at southern
heliographic latitudes. The annual variation changes its predominant
polarity within a few days of the times when the heliographic latitude
of the earth is 0.

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Title: Comparison of the mean photospheric magnetic field and the
interplanetary magnetic field.
Authors: Wilcox, J. M.; Scherrer, P. H.; Severny, A.; Colburn, D. S.
1971BAAS....3R.265W Altcode:
No abstract at ADS

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Title: Determination of solar magnetograph zero level using
interplanetary magnetic field observations.
Authors: Scherrer, P. H.; Wilcox, J. M.; Severny, A.; Colburn, D. S.
1971BAAS....3Q.264S Altcode:
No abstract at ADS

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Title: Comparison of the Mean Photospheric Magnetic Field and the
Interplanetary Magnetic Field
Authors: Severny, A.; Wilcox, J. M.; Scherrer, P. H.; Colburn, D. S.
1970SoPh...15....3S Altcode:
The mean photospheric magnetic field of the sun seen as a star has
been compared with the interplanetary magnetic field observed with
spacecraft near the earth. Each change in polarity of the mean solar
field is followed about 4 1/2 days later by a change in polarity
of the interplanetary field (sector boundary). The scaling of the
field magnitude from sun to near earth is within a factor of two of
the theoretical value, indicating that large areas on the sun have
the same predominant polarity as that of the interplanetary sector
pattern. An independent determination of the zero level of the solar
magnetograph has yielded a value of 0.1±0.05 G. An effect attributed
to a delay of approximately one solar rotation between the appearance
of a new photospheric magnetic feature and the resulting change in
the interplanetary field is observed.

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Title: Multi-Channel Magnetograph Observations. I: Comparison with
Spectroheliograms
Authors: Frazier, Edward N.; Scherrer, Philip H.
1969SoPh...10..297F Altcode:
A new technique for displaying magnetograph observations is
presented and applied to the 12-channel magnetograph at Kitt Peak
National Observatory. Using the data from a raster scan, a digital
`spectroheliogram' is constructed on the face of a cathode ray tube and
photographed. This enables one to recognize patterns in magnetograph
data as easily as with conventional photographs. Comparisons with
simultaneous spectroheliograms show no qualitative differences and
indicate that the magnetograph is quite capable of studying morphology
of individual solar features.