Author name code: hill
ADS astronomy entries on 2022-09-14
author:"Hill, Frank"
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Title: A Compact Full-disk Solar Magnetograph based on miniaturization
of GONG instrument
Authors: Gosain, Sanjay; Harvey, Jack; Martinez-Pillet, Valentin;
Woods, Tom; Hill, Frank
Bibcode: 2022arXiv220707728G
Altcode:
Designing compact instruments is the key for the scientific exploration
by smaller spacecrafts such as cubesats or by deep space missions. Such
missions require compact instrument designs to have minimal instrument
mass. Here we present a proof of concept for miniaturization of the
Global Oscillation Network Group GONG instrument. GONG instrument
routinely obtains solar full disk Doppler and magnetic field maps of
the solar photosphere using Ni 676 nm absorption line. A key concept
for miniaturization of GONG optical design is to replace the bulky
Lyot filter with a narrow-band interference filter and reduce the
length of feed telescope. We present validation of the concept via
numerical modeling as well as by proof of concept observations.
Title: Continuous Solar Observations from the Ground-Assessing Duty
Cycle from GONG Observations
Authors: Jain, Kiran; Tripathy, Sushanta C.; Hill, Frank; Pevtsov,
Alexei A.
Bibcode: 2021PASP..133j5001J
Altcode: 2021arXiv211006319J
Continuous observations play an important role in the studies of solar
variability. While such observations can be achieved from space with
an almost 100% duty cycle, it is difficult to accomplish a very high
duty cycle from the ground. In this context, we assess the duty cycle
that has been achieved from the ground by analyzing the observations of
a six station network of identical instruments, the Global Oscillation
Network Group (GONG). We provide a detailed analysis of the duty cycle
using GONG observations spanning over 18 yr. We also discuss the duty
cycle of individual sites and point out various factors that may impact
individual site or network duty cycles. The mean duty cycle of the
network is 93%, however it reduces by about 5% after all images pass
through the stringent quality-control checks. The standard deviations
in monthly and yearly duty cycle values are found to be 1.9% and 2.2%,
respectively. These results provide a baseline that can be used in
the planning of future ground-based networks.
Title: Divergence and Vorticity of Subsurface Flows During Solar
Cycles 23 and 24
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 2021SoPh..296...73K
Altcode:
We study the solar-cycle variation of the divergence and vorticity
of subsurface horizontal flows from the surface to a depth of 16
Mm. The flows were derived with ring-diagram analysis applied to
Michelson Doppler Imager (MDI) Dynamics Program, Global Oscillation
Network Group (GONG), and Helioseismic and Magnetic Imager (HMI)
Dopplergrams. We study their variation for the complete data set and
for two subsets representing active and quiet regions. All three data
sets show alternating bands of diverging and converging flows and bands
of cyclonic and anticyclonic flows moving from mid-latitudes toward
the equator during a solar cycle. For Solar Cycle 24, these bands are
precursors of the magnetic activity appearing several years before
magnetic activity is present at a given latitude even leading the fast
bands of the flows. The amplitude differences between the cyclonic and
anticyclonic and the converging and diverging bands during a solar
cycle agree within the error bars between the complete data set and
the two subsets. For Solar Cycle 24, the amplitude differences are 6.0
±0.7 10−8s−1 for the bands of vorticity and
−4.9 ±0.6 10−8s−1 for those of divergence
averaged over 2.0 - 11.6 Mm using the complete data set. The amplitude
differences of Solar Cycle 23 are 26 ±3 % smaller than those of Solar
Cycle 24. The flows of the active-region subset are more converging
and cyclonic than those of the quiet-region subset with an extra
vorticity of 1.3 ±0.1 10−8s−1 and an extra
divergence of −6.7 ±0.3 10−8s−1 averaged
over 7.5∘ - 30∘ and all depths and epochs. The
amplitude of the extra divergence of active regions is about a factor of
1.3 larger at depths shallower than 6 Mm and decreases with increasing
depth, while the extra vorticity is nearly constant with depth.
Title: Solar-Cycle Variation of the Subsurface Flows of Active-
and Quiet-Region Subsets
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 2020SoPh..295...47K
Altcode:
We study the solar-cycle variation of subsurface flows for both active
and quiet solar regions. We derive flows from the surface to a depth
of 16 Mm using ring-diagram analysis applied to Dopplergrams obtained
with the Michelson Doppler Imager (MDI) Dynamics Program, the Global
Oscillation Network Group (GONG), and the Helioseismic and Magnetic
Imager (HMI) instrument. We derive the temporal variation of the zonal
and meridional flows in a consistent manner for Solar Cycles 23 and
24 combining the flows from the three data sources scaled to match
HMI-derived flows. The subsurface flows associated with active and quiet
regions show the same variation with the solar cycle with alternating
bands of faster- and slower-than-average zonal and meridional flows
moving from mid-latitudes toward the equator during the course of
a cycle. We derive the differences between the amplitudes of the
extrema of the fast and the slow flows. For Cycle 24, the average
difference between the fast- and slow-flow amplitude is 9.5 ±0.5
ms−1 for the zonal flows and 7.0 ±0.4 ms−1
for the meridional flows of the quiet-region subset averaged over 2
to 12 Mm within ±30∘ latitude. For the active-region
subset, the average difference is 10.4 ±0.9 ms−1 for
the zonal flows and 9.3 ±0.7 ms−1 for the meridional
flows. We subtract the flows of the quiet-region subset from those
of the active-region one to determine the contribution of active
regions to the long-term flow pattern. The resulting meridional flow
associated with active regions has a maximum amplitude near 3.1 Mm and
its amplitude decreases with depth. This implies that the converging
flows attributed to active regions are a shallow-layer phenomenon.
Title: Study of Acoustic Halos in NOAA Active Region 12683
Authors: Tripathy, S. C.; Jain, K.; Kholikov, S.; Hill, F.; Cally, P.
Bibcode: 2020ASSP...57..121T
Altcode:
We characterize the spatio-temporal power distribution around the
active region 12683 as a function of height in the solar atmosphere,
wave frequencies, magnetic field strength and inclination of the
magnetic field.
Title: A Comparison of Global Helioseismic-Instrument Performances:
Solar-SONG, GOLF and VIRGO
Authors: Breton, S. N.; García, R. A.; Pallé, P. L.; Mathur, S.;
Hill, F.; Jain, K.; Jiménez, A.; Tripathy, S. C.; Grundahl, F.;
Fredslund-Andersen, M.; Santos, A. R. G.
Bibcode: 2020ASSP...57..327B
Altcode:
The SONG spectrograph has recently demonstrated its ability to perform
solar radial velocity measurement during the first test run of the
Solar-SONG initiative. A preliminary assessment of its performance
is carried out here by comparing the results of Solar-SONG during
the summer 2018 test run, with GOLF and VIRGO/SPM taken as reference
instruments.
Title: Comparing Solar Activity Minima Using Acoustic Oscillation
Frequencies
Authors: Jain, Kiran; Tripathy, Sushanta C.; Hill, Frank
Bibcode: 2020ASSP...57..137J
Altcode:
Using the variability of solar acoustic oscillation mode frequencies,
we investigate the width and timing of last three solar minima at
various depths in the solar interior. We find that the current minimum
is as deep as the previous minimum, however, more data are needed to
reveal the true depth of the current minimum.
Title: ngGONG: The Next Generation GONG - A New Solar Synoptic
Observational Network
Authors: Hill, Frank; Hammel, Heidi; Martinez-Pillet, Valentin; de
Wijn, A.; Gosain, S.; Burkepile, J.; Henney, C. J.; McAteer, J.; Bain,
H. M.; Manchester, W.; Lin, H.; Roth, M.; Ichimoto, K.; Suematsu, Y.
Bibcode: 2019BAAS...51g..74H
Altcode: 2019astro2020U..74H
The white paper describes a next-generation GONG, a ground-based
geographically distributed network of instrumentation to continually
observe the Sun. This would provide data for solar magnetic field
research and space weather forecasting, and would extend the time
coverage of helioseismology.
Title: Historical astronomical data: urgent need for preservation,
digitization enabling scientific exploration
Authors: Pevtsov, Alexei; Griffin, Elizabeth; Grindlay, Jonathan;
Kafka, Stella; Bartlett, Jennifer; Usoskin, Ilya; Mursula, Kalevi;
Gibson, Sarah; Pillet, Valentín; Burkepile, Joan; Webb, David; Clette,
Frédéric; Hesser, James; Stetson, Peter; Muñoz-Jaramillo, Andres;
Hill, Frank; Bogart, Rick; Osborn, Wayne; Longcope, Dana
Bibcode: 2019BAAS...51c.190P
Altcode: 2019arXiv190304839P; 2019astro2020T.190P
This white paper emphasizes critical importance of preservation,
digitization and scientific exploration of historical astronomical
data. It outlines the rationale, provides examples of new science
with such data, and reviews the potential losses to science if nothing
it done.
Title: Synoptic Studies of the Sun as a Key to Understanding Stellar
Astrospheres
Authors: Martinez Pillet, Valentin; Hill, Frank; Hammel, Heidi B.;
de Wijn, Alfred G.; Gosain, Sanjay; Burkepile, Joan; Henney, Carl;
McAteer, R. T. James; Bain, Hazel; Manchester, Ward; Lin, Haosheng;
Roth, Markus; Ichimoto, Kiyoshi; Suematsu, Yoshinori
Bibcode: 2019BAAS...51c.110M
Altcode: 2019astro2020T.110M; 2019arXiv190306944M
Ground-based solar observations provide key contextual data (i.e., the
"big picture") to produce a complete description of the only astrosphere
we can study in situ: our Sun's heliosphere. This white paper outlines
the current paradigm for ground-based solar synoptic observations,
and indicates those areas that will benefit from focused attention.
Title: Multi-wavelength Observations of Flare-Induced Acoustic Waves
Around Active Regions with SDO AIA
Authors: Monsue, Teresa; Pesnell, W. Dean; Hill, Frank; Kirk, Michael
Bibcode: 2018csc..confE.111M
Altcode:
Active regions on the Sun are abundant with a variety of waves that are
both acoustically helioseismic and magnetohydrodynamic in nature. The
occurrence of a solar flare can disrupt these waves, through MHD
mode-mixing or scattering by the excitation of these waves. We take
a multi-wavelength observational approach to understand the source
of these waves by studying active regions where flaring activity
occurs. Utilizing a Fast Fourier Transform (FFT) algorithm, our approach
is to search for signals within a time series of images by producing
multi-frequency power map movies and spatially sampling the time
series by radial sectors with constant area that minimizes the spatial
variation of the acoustic power. With this application we are able to
study the active region both spatially and temporally and correlate
data over multiple wavelengths, allowing us to observe the behavior
of the waves at different heights within the Solar atmosphere. We
apply multi-wavelength measurements utilizing NASA's SDO AIA 1700
(lower photosphere), 1600 (upper photosphere) and 304 (chromosphere)
passbands. When we run power map movies of the chromosphere we are able
to see a subtle propagating feature moving outward from the center of
the flare; this could be an MHD-wave propagating outward by the flaring
event. With our sector sampling method we observe power variation
around the flaring active region. This power variation corresponds to
the flare induced enhancement of the oscillations around the active
region. Furthermore, there seems to be absorptive properties observed
within the chromospheric line of the AIA 304 Å passband.
Title: Investigation of Acoustic Halos using Multi-Height SDO
Observations
Authors: Tripathy, S. C.; Jain, Kiran; Kholikov, S.; Burtseva, O.;
Hill, F.; Cally, P.
Bibcode: 2018csc..confE.130T
Altcode:
The interpretation of acoustic waves surrounding active regions has
been a challenging task since the influence of magnetic field on the
incident waves is not fully understood. As a result, structure and
dynamics of active regions beneath the surface show significant
uncertainties. Recent numerical simulations and helioseismic
measurements in active regions have demonstrated that the key to the
understanding of these complex processes requires a synergy between
models and helioseismic inferences from observations. In this context,
using data from Helioseismic Magnetic Imager and Atmospheric Imaging
Assembly instruments on board the Solar Dynamics Observatory, we
characterize the spatio-temporal power distribution around active
regions as a function of the height in the solar atmosphere. We
find power enhancements (acoustic halos) occur above the acoustic
cutoff frequency and extends up to 10 mHz in HMI Doppler and AIA
170 nm observations and are strong functions of magnetic field and
their inclination angle. We also examine the relative phases and
cross-coherence spectra and find different wave characteristics at
different heights.
Title: GONG p-Mode Parameters Through Two Solar Cycles
Authors: Kiefer, René; Komm, Rudi; Hill, Frank; Broomhall, Anne-Marie;
Roth, Markus
Bibcode: 2018SoPh..293..151K
Altcode: 2018arXiv181009324K
We investigate the parameters of global solar p-mode oscillations,
namely damping width Γ , amplitude A , mean squared velocity
«v2», energy E , and energy supply rate d E /d t , derived
from two solar cycles' worth (1996 - 2018) of Global Oscillation Network
Group (GONG) time series for harmonic degrees l =0 -150 . We correct for
the effect of fill factor, apparent solar radius, and spurious jumps in
the mode amplitudes. We find that the amplitude of the activity-related
changes of Γ and A depends on both frequency and harmonic degree of the
modes, with the largest variations of Γ for modes with 2400 μ Hz≤ν
≤3300 μ Hz and 31 ≤l ≤60 with a minimum-to-maximum variation of
26.6 ±0.3 % and of A for modes with 2400 μ Hz≤ν ≤3300 μ Hz and
61 ≤l ≤100 with a minimum-to-maximum variation of 27.4 ±0.4 % . The
level of correlation between the solar radio flux F10.7 and
mode parameters also depends on mode frequency and harmonic degree. As
a function of mode frequency, the mode amplitudes are found to follow
an asymmetric Voigt profile with νmax=3073.59 ±0.18 μ
Hz. From the mode parameters, we calculate physical mode quantities
and average them over specific mode frequency ranges. In this way, we
find that the mean squared velocities «v2» and energies
E of p modes are anticorrelated with the level of activity, varying by
14.7 ±0.3 % and 18.4 ±0.3 % , respectively, and that the mode energy
supply rates show no significant correlation with activity. With this
study we expand previously published results on the temporal variation
of solar p-mode parameters. Our results will be helpful to future
studies of the excitation and damping of p modes, i.e., the interplay
between convection, magnetic field, and resonant acoustic oscillations.
Title: Subsurface Flows During Cycle 23 and 24
Authors: Komm, Rudolf; Howe, Rachel; Hill, Frank
Bibcode: 2018csc..confE..54K
Altcode:
We study the solar-cycle variation of subsurface flows from the
surface to a depth of 16 Mm. We have used ring-diagram analysis to
analyze Dopplergrams obtained with the MDI Dynamics Program, the GONG,
and the SDO/HMI instrument. We combine the zonal and meridional flows
from the three data sources and we derive their temporal variation
in a consistent manner for Solar Cycle 23 and 24. For Cycle 24, the
flow patterns are precursors of the magnetic activity. The timing
difference between the occurrence of the flow pattern and the magnetic
one increases almost linearly with increasing latitude. For example,
the fast zonal and meridional flow appear about 2.1 years and 2.5 years
respectively before the magnetic pattern at 30 degree latitude in the
northern hemisphere, while in the southern one the differences are
3.2 years and 2.6 years. The flow patterns of Cycle 25 are present
and have reached 30 degree latitude. The amplitude differences of
Cycle 25 are about 22% smaller than those of Cycle 24 but comparable
to those of Cycle 23. In addition, we divide the data into subsets of
low and high magnetic activity and study the variation of the quiet-
and active-region flows during Solar Cycle 23 and 24.
Title: Variation in Sun's Seismic Radius and its implication on the
TSI variability
Authors: Jain, Kiran; Tripathy, Sushanta; Hill, Frank
Bibcode: 2018csc..confE.131J
Altcode:
Space-borne instruments on-board SoHO and SDO have been collecting
uninterrupted helioseismic data since 1996 and are providing a unique
opportunity to study changes occurring below the surface over two
solar cycles, 23 and 24. Here we study the variation in solar seismic
radius with the changing level of the surface magnetic activity. The
seismic radius is calculated from the fundamental modes of solar
oscillations utilizing the observations from SoHO/MDI and SDO/HMI. Our
study suggests that the sub-surface layers shrinks with increasing
magnetic activity. We interpret these changes in seismic radius to be
caused by the variation of sound speed, temperature or the changes
in the super-adiabatic superficial layers. Our estimated maximum
change in seismic radius during a solar cycle is about 5 kilometers,
and is consistent in both solar cycles 23 and 24. We also explore the
relationship between seismic solar radius and the total solar irradiance
(TSI) and find that the radius variation plays a secondary role in TSI
variability. We further observe that the solar irradiance increases
with decreasing seismic radius, however the anti-correlation between
them is moderately weak.
Title: Subsurface Zonal and Meridional Flow During Cycles 23 and 24
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 2018SoPh..293..145K
Altcode:
We study the solar-cycle variation of subsurface flows from the
surface to a depth of 16 Mm. We have used ring-diagram analysis to
analyze Dopplergrams obtained with the Michelson Doppler Imager (MDI)
Dynamics Program, the Global Oscillation Network Group (GONG), and the
Helioseismic and Magnetic Imager (HMI) instrument. We combined the zonal
and meridional flows from the three data sources and scaled the flows
derived from MDI and GONG to match those from HMI observations. In
this way, we derived their temporal variation in a consistent manner
for Solar Cycles 23 and 24. We have corrected the measured flows for
systematic effects that vary with disk positions. Using time-depth
slices of the corrected subsurface flows, we derived the amplitudes
and times of the extrema of the fast and slow zonal and meridional
flows during Cycles 23 and 24 at every depth and latitude. We find an
average difference between maximum and minimum amplitudes of 8.6 ±0.4
ms−1 for the zonal flows and 7.9 ±0.3 ms−1
for the meridional flows associated with Cycle 24 averaged over a
depth range from 2 to 12 Mm. The corresponding values derived from
GONG data alone are 10.5 ±0.3 ms−1 for the zonal and
10.8 ±0.3 ms−1 for the meridional flow. For Cycle 24,
the flow patterns are precursors of the magnetic activity. The timing
difference between the occurrence of the flow pattern and the magnetic
one increases almost linearly with increasing latitude. For example,
the fast zonal and meridional flow appear 2.1 ±0.6 years and 2.5 ±0.6
years, respectively, before the magnetic pattern at 30∘
latitude in the northern hemisphere, while in the southern hemisphere,
the differences are 3.2 ±1.2 years and 2.6 ±0.6 years. The flow
patterns of Cycle 25 are present and have reached 30∘
latitude. The amplitude differences of Cycle 25 are about 22%
smaller than those of Cycle 24, but are comparable to those of
Cycle 23. Moreover, polynomial fits of meridional flows suggest that
equatorward meridional flows (counter-cells) might exist at about
80∘ latitude except during the declining phase of the
solar cycle.
Title: Roadmap for Reliable Ensemble Forecasting of the Sun-Earth
System
Authors: Nita, Gelu; Angryk, Rafal; Aydin, Berkay; Banda, Juan;
Bastian, Tim; Berger, Tom; Bindi, Veronica; Boucheron, Laura; Cao,
Wenda; Christian, Eric; de Nolfo, Georgia; DeLuca, Edward; DeRosa,
Marc; Downs, Cooper; Fleishman, Gregory; Fuentes, Olac; Gary, Dale;
Hill, Frank; Hoeksema, Todd; Hu, Qiang; Ilie, Raluca; Ireland,
Jack; Kamalabadi, Farzad; Korreck, Kelly; Kosovichev, Alexander;
Lin, Jessica; Lugaz, Noe; Mannucci, Anthony; Mansour, Nagi; Martens,
Petrus; Mays, Leila; McAteer, James; McIntosh, Scott W.; Oria, Vincent;
Pan, David; Panesi, Marco; Pesnell, W. Dean; Pevtsov, Alexei; Pillet,
Valentin; Rachmeler, Laurel; Ridley, Aaron; Scherliess, Ludger; Toth,
Gabor; Velli, Marco; White, Stephen; Zhang, Jie; Zou, Shasha
Bibcode: 2018arXiv181008728N
Altcode:
The authors of this report met on 28-30 March 2018 at the New Jersey
Institute of Technology, Newark, New Jersey, for a 3-day workshop
that brought together a group of data providers, expert modelers, and
computer and data scientists, in the solar discipline. Their objective
was to identify challenges in the path towards building an effective
framework to achieve transformative advances in the understanding
and forecasting of the Sun-Earth system from the upper convection
zone of the Sun to the Earth's magnetosphere. The workshop aimed to
develop a research roadmap that targets the scientific challenge
of coupling observations and modeling with emerging data-science
research to extract knowledge from the large volumes of data (observed
and simulated) while stimulating computer science with new research
applications. The desire among the attendees was to promote future
trans-disciplinary collaborations and identify areas of convergence
across disciplines. The workshop combined a set of plenary sessions
featuring invited introductory talks and workshop progress reports,
interleaved with a set of breakout sessions focused on specific topics
of interest. Each breakout group generated short documents, listing
the challenges identified during their discussions in addition to
possible ways of attacking them collectively. These documents were
combined into this report-wherein a list of prioritized activities
have been collated, shared and endorsed.
Title: Design of a next generation synoptic solar observing network:
solar physics research integrated network group (SPRING)
Authors: Gosain, Sanjay; Roth, Markus; Hill, Frank; Pevtsov, Alexei;
Martinez Pillet, Valentin; Thompson, Michael J.
Bibcode: 2018SPIE10702E..4HG
Altcode:
Long-term synoptic observations of the Sun in different wavelength
regions are essential to understand its secular behavior. Such
observations have proven very important for discovery of 11 year
solar activity cycle, 22 year magnetic cycle, polar field reversals,
Hale's polarity law, Joy's law, that helped Babcock and Leighton
to propose famous solar dynamo model. In more recent decades, the
societal impact of the secular changes in Sun's output has been felt in
terms of solar inputs to terrestrial climate-change and space-weather
hazards. Further, it has been realized that to better understand the
activity phenomena such as flares and coronal mass ejections (CMEs)
one needs synoptic observations in multiple spectral lines to enable
tomographic inference of physical parameters. Currently, there are
both space and ground based synoptic observatories. However, given
the requirements for the long-term stability and reliability of such
synoptic datasets, ground-based facilities are more preferable. Also,
the ground based observatories are easy to maintain or upgrade while
detailed and frequent calibrations are easily possible. The only
ground-based facility that currently provides full-disk velocity and
magnetic field maps of the Sun around the clock and at good cadence,
is the Global Oscillations Network Group (GONG) network of National
Solar Observatory (NSO) which is operational since the mid 90s. Due
to its aging instrumentation, operating for nearly three decades, and
new requirements to obtain multiwavelength observations, a need is felt
in the solar community to build a next generation synoptic observatory
network. A group of international observatories have come together under
the auspices of SOLARNET program, funded by European Union (EU), to
carryout a preliminary design study of such a synoptic solar observing
facility called "SPRING", which stands for Solar Physics Research
Integrated Network Group. In this article we will present concept of
SPRING and the optical design concept of its major instruments.ts.
Title: Signatures of Solar Cycle 25 in Subsurface Zonal Flows
Authors: Howe, R.; Hill, F.; Komm, R.; Chaplin, W. J.; Elsworth, Y.;
Davies, G. R.; Schou, J.; Thompson, M. J.
Bibcode: 2018ApJ...862L...5H
Altcode: 2018arXiv180702398H
The pattern of migrating zonal flow bands associated with the solar
cycle, known as the torsional oscillation, has been monitored with
continuous global helioseismic observations by the Global Oscillations
Network Group (GONG), together with those made by the Michelson
Doppler Imager (MDI) on board the Solar and Heliospheric Observatory
(SOHO) and its successor, the Helioseismic and Magnetic Imager (HMI)
on board the Solar Dynamics Observatory (SDO), since 1995, giving us
nearly two full solar cycles of observations. We report that the flows
now show traces of the mid-latitude acceleration that is expected to
become the main equatorward-moving branch of the zonal flow pattern for
Cycle 25. Based on the current position of this branch, we speculate
that the onset of widespread activity for Cycle 25 is unlikely to be
earlier than the middle of 2019.
Title: The Sun's Seismic Radius as Measured from the Fundamental
Modes of Oscillations and Its Implications for the TSI Variations
Authors: Jain, Kiran; Tripathy, S. C.; Hill, F.
Bibcode: 2018ApJ...859L...9J
Altcode: 2018arXiv180505307J
In this Letter we explore the relationship between the solar seismic
radius and total solar irradiance (TSI) during the last two solar
cycles using the uninterrupted data from space-borne instruments on
board the Solar and Heliospheric Observatory (SoHO) and the Solar
Dynamics Observatory (SDO). The seismic radius is calculated from the
fundamental (f) modes of solar oscillations utilizing the observations
from SoHO/Michelson Doppler Imager (MDI) and SDO/Helioseismic and
Magnetic Imager (HMI), and the TSI measurements are obtained from
SoHO/VIRGO. Our study suggests that the major contribution to the TSI
variation arises from the changes in magnetic field, while the radius
variation plays a secondary role. We find that the solar irradiance
increases with decreasing seismic radius; however, the anti-correlation
between them is moderately weak. The estimated maximum change in seismic
radius during a solar cycle is about 5 km, and is consistent in both
solar cycles 23 and 24. Previous studies ;suggest a radius change at
the surface of the order of 0.06 arcsec to explain the 0.1% variation
in the TSI values during the solar cycle; however, our inferred seismic
radius change is significantly smaller, hence the TSI variations cannot
be fully explained by the temporal changes in seismic radius.
Title: Un-interrupted Sun-as-a-star Helioseismic Observations over
Multiple Solar Cycles
Authors: Jain, Kiran; Tripathy, Sushanta; Hill, Frank; Salabert,
David; García, Rafael A.; Broomhall, Anne-Marie
Bibcode: 2018IAUS..340...27J
Altcode: 2018arXiv180505298J
We analyze Sun-as-a-star observations spanning over solar cycles
22 - 24 from the ground-based network BiSON and solar cycles 23 -
24 collected by the space-based VIRGO and GOLF instruments on board
the SoHO satellite. Using simultaneous observations from all three
instruments, our analysis suggests that the structural and magnetic
changes responsible for modifying the frequencies remained comparable
between cycle 23 and cycle 24 but differ from cycle 22. Thus we
infer that the magnetic layer of the Sun has become thinner since the
beginning of cycle 23 and continues during the current cycle.
Title: 22 Year Solar Magnetic Cycle and its relation to Convection
Zone Dynamics
Authors: Jain, Kiran; Tripathy, Sushanta; Komm, Rudolf; Hill, Frank;
Simoniello, Rosaria
Bibcode: 2018IAUS..340....9J
Altcode: 2018arXiv180505371J
Using continuous observations for 22 years from ground-based network
GONG and space-borne instruments MDI onboard SoHO and HMI onboard SDO,
we report both global and local properties of the convection zone and
their variations with time.
Title: A study of acoustic halos in active region NOAA 11330 using
multi-height SDO observations
Authors: Tripathy, S. C.; Jain, K.; Kholikov, S.; Hill, F.; Rajaguru,
S. P.; Cally, P. S.
Bibcode: 2018AdSpR..61..691T
Altcode: 2017arXiv171101259T
We analyze data from the Helioseismic Magnetic Imager (HMI) and the
Atmospheric Imaging Assembly (AIA) instruments on board the Solar
Dynamics Observatory (SDO) to characterize the spatio-temporal acoustic
power distribution in active regions as a function of the height in
the solar atmosphere. For this, we use Doppler velocity and continuum
intensity observed using the magnetically sensitive line at 6173 Å
as well as intensity at 1600 Å and 1700 Å. We focus on the power
enhancements seen around AR 11330 as a function of wave frequency,
magnetic field strength, field inclination and observation height. We
find that acoustic halos occur above the acoustic cutoff frequency and
extends up to 10 mHz in HMI Doppler and AIA 1700 Å observations. Halos
are also found to be strong functions of magnetic field and their
inclination angle. We further calculate and examine the spatially
averaged relative phases and cross-coherence spectra and find different
wave characteristics at different heights.
Title: Multi-wavelength Observations of Solar Acoustic Waves Near
Active Regions
Authors: Monsue, Teresa; Pesnell, Dean; Hill, Frank
Bibcode: 2018AAS...23115807M
Altcode:
Active region areas on the Sun are abundant with a variety of waves
that are both acoustically helioseismic and magnetohydrodynamic in
nature. The occurrence of a solar flare can disrupt these waves, through
MHD mode-mixing or scattering by the excitation of these waves. We take
a multi-wavelength observational approach to understand the source
of theses waves by studying active regions where flaring activity
occurs. Our approach is to search for signals within a time series of
images using a Fast Fourier Transform (FFT) algorithm, by producing
multi-frequency power map movies. We study active regions both spatially
and temporally and correlate this method over multiple wavelengths using
data from NASA’s Solar Dynamics Observatory. By surveying the active
regions on multiple wavelengths we are able to observe the behavior
of these waves within the Solar atmosphere, from the photosphere up
through the corona. We are able to detect enhancements of power around
active regions, which could be acoustic power halos and of an MHD-wave
propagating outward by the flaring event. We are in the initial stages
of this study understanding the behaviors of these waves and could one
day contribute to understanding the mechanism responsible for their
formation; that has not yet been explained.
Title: Probing Subsurface Flows in NOAA Active Region 12192:
Comparison with NOAA 10486
Authors: Jain, Kiran; Tripathy, S. C.; Hill, F.
Bibcode: 2017ApJ...849...94J
Altcode: 2017arXiv171002137J
NOAA Active Region (AR) 12192 is the biggest AR observed in solar cycle
24 so far. This was a long-lived AR that survived for four Carrington
rotations (CRs) and exhibited several unusual phenomena. We measure
the horizontal subsurface flows in this AR in multiple rotations using
the ring-diagram technique of local helioseismology and the Global
Oscillation Network Group (GONG+) Dopplergrams, and we investigate how
different was the plasma flow in AR 12192 from that in AR 10486. Both
regions produced several high M- and X-class flares, but they had
different coronal mass ejection (CME) productivity. Our analysis
suggests that these ARs had unusually large horizontal flow amplitude
with distinctly different directions. While meridional flow in AR
12192 was poleward that supports the flux transport to poles, it was
equatorward in AR 10486. Furthermore, there was a sudden increase in the
magnitude of estimated zonal flow in shallow layers in AR 12192 during
the X3.1 flare; however, it reversed direction in AR 10486 with the
X17.2 flare. These flow patterns produced strong twists in horizontal
velocity with depth in AR 10486 that persisted throughout the disk
passage, as opposed to AR 12192, which produced a twist only after
the eruption of the X3.1 flare that disappeared soon after. Our study
indicates that the sunspot rotation combined with the reorganization
of magnetic field in AR 10486 was not sufficient to decrease the flow
energy even after several large flares that might have triggered
CMEs. Furthermore, in the absence of sunspot rotation in AR 12192,
this reorganization of magnetic field contributed significantly to
the substantial release of flow energy after the X3.1 flare.
Title: Solar-Cycle Variation of Subsurface-Flow Divergence: A Proxy
of Magnetic Activity?
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 2017SoPh..292..122K
Altcode:
We study the solar-cycle variation of subsurface flows from the surface
to a depth of 16 Mm. We have analyzed Global Oscillation Network Group
(GONG) Dopplergrams with a ring-diagram analysis covering about 15
years and Helioseismic and Magnetic Imager (HMI) Dopplergrams covering
more than 6 years. After subtracting the average rotation rate and
meridional flow, we have calculated the divergence of the horizontal
residual flows from the maximum of Solar Cycle 23 through the declining
phase of Cycle 24. The subsurface flows are mainly divergent at quiet
regions and convergent at locations of high magnetic activity. The
relationship is essentially linear between divergence and magnetic
activity at all activity levels at depths shallower than about 10
Mm. At greater depths, the relationship changes sign at locations of
high activity; the flows are increasingly divergent at locations with
a magnetic activity index (MAI) greater than about 24 G. The flows are
more convergent by about a factor of two during the rising phase of
Cycle 24 than during the declining phase of Cycle 23 at locations of
medium and high activity (about 10 to 40 G MAI) from the surface to at
least 10 Mm. The subsurface divergence pattern of Solar Cycle 24 first
appears during the declining phase of Cycle 23 and is present during
the extended minimum. It appears several years before the magnetic
pattern of the new cycle is noticeable in synoptic maps. Using linear
regression, we estimate the amount of magnetic activity that would be
required to generate the precursor pattern and find that it should be
almost twice the amount of activity that is observed.
Title: Acoustic Oscillation Properties of Active Region 12193
Authors: Monsue, Teresa; Pesnell, William D.; Hill, Frank
Bibcode: 2017SPD....4810904M
Altcode:
Solar flares are dynamic objects occurring randomly and yet unannounced
in nature. In order to find an efficient detection method, we require
a greater breadth of knowledge of the system. One path to such a
method is to observe the solar atmosphere in a region around a flare
in different wavelengths of light and acoustic frequency bands. This
provides information from different altitudes in the solar atmosphere
and allows us to study the temporal evolution of each altitude through
the flaring event. A more complete understanding of the time evolution
may lead to yet undiscovered precursors of the flare. In this project,
we study Active Region 12192 using acoustic observations near an
X3 flare occurring on October 24, 2014 at 21:41UT. Our wavelet
analysis utilizes time series data to create Fourier power spectra
of individual pixels spatially resolved around the flare region, to
study the frequency bands. In order to study the power distribution
in regions around the flare and to search for any correlation we
apply several methods. One method we partition sub-regions in our
main flaring region and take a survey of the oscillations for each
frequency band within power maps. Another method we average the FFT
to take measurements within the p-modes (2-4 mHz) and chromospheric
(4-6 mHz) frequencies. The application of these methods should be able
to get us closer to tracking waveforms within power maps.
Title: The Virtual Solar Observatory: Progress and Diversions
Authors: Gurman, Joseph B.; Bogart, R. S.; Amezcua, A.; Hill, Frank;
Oien, Niles; Davey, Alisdair R.; Hourcle, Joseph; Mansky, E.; Spencer,
Jennifer L.
Bibcode: 2017SPD....4811501G
Altcode:
The Virtual Solar Observatory (VSO) is a known and useful method for
identifying and accessing solar physics data online. We review current
"behind the scenes" work on the VSO, including the addition of new
data providers and the return of access to data sets to which service
was temporarily interrupted. We also report on the effect on software
development efforts when government IT “security” initiatives
impinge on finite resoruces. As always, we invite SPD members to
identify data sets, services, and interfaces they would like to see
implemented in the VSO.
Title: The Importance of Long-Term Synoptic Observations and Data
Sets for Solar Physics and Helioseismology
Authors: Elsworth, Yvonne; Broomhall, Anne-Marie; Gosain, Sanjay;
Roth, Markus; Jefferies, Stuart M.; Hill, Frank
Bibcode: 2017hdsi.book..143E
Altcode:
No abstract at ADS
Title: Helioseismology with Solar Orbiter
Authors: Löptien, Björn; Birch, Aaron C.; Gizon, Laurent; Schou,
Jesper; Appourchaux, Thierry; Blanco Rodríguez, Julián; Cally,
Paul S.; Dominguez-Tagle, Carlos; Gandorfer, Achim; Hill, Frank;
Hirzberger, Johann; Scherrer, Philip H.; Solanki, Sami K.
Bibcode: 2017hdsi.book..257L
Altcode:
No abstract at ADS
Title: Five Years of Synthesis of Solar Spectral Irradiance from
SDID/SISA and SDO/AIA Images
Authors: Fontenla, J. M.; Codrescu, M.; Fedrizzi, M.; Fuller-Rowell,
T.; Hill, F.; Landi, E.; Woods, T.
Bibcode: 2017ApJ...834...54F
Altcode:
In this paper we describe the synthetic solar spectral irradiance (SSI)
calculated from 2010 to 2015 using data from the Atmospheric Imaging
Assembly (AIA) instrument, on board the Solar Dynamics Observatory
spacecraft. We used the algorithms for solar disk image decomposition
(SDID) and the spectral irradiance synthesis algorithm (SISA) that
we had developed over several years. The SDID algorithm decomposes
the images of the solar disk into areas occupied by nine types of
chromospheric and 5 types of coronal physical structures. With this
decomposition and a set of pre-computed angle-dependent spectra for
each of the features, the SISA algorithm is used to calculate the
SSI. We discuss the application of the basic SDID/SISA algorithm to a
subset of the AIA images and the observed variation occurring in the
2010-2015 period of the relative areas of the solar disk covered by the
various solar surface features. Our results consist of the SSI and total
solar irradiance variations over the 2010-2015 period. The SSI results
include soft X-ray, ultraviolet, visible, infrared, and far-infrared
observations and can be used for studies of the solar radiative forcing
of the Earth’s atmosphere. These SSI estimates were used to drive
a thermosphere-ionosphere physical simulation model. Predictions of
neutral mass density at low Earth orbit altitudes in the thermosphere
and peak plasma densities at mid-latitudes are in reasonable agreement
with the observations. The correlation between the simulation results
and the observations was consistently better when fluxes computed by
SDID/SISA procedures were used.
Title: Temporal Evolution of Chromospheric Oscillations in Flaring
Regions: A Pilot Study
Authors: Monsue, T.; Hill, F.; Stassun, K. G.
Bibcode: 2016AJ....152...81M
Altcode: 2018arXiv180302506M
We have analyzed Hα intensity images obtained at a 1 minute cadence
with the Global Oscillation Network Group (GONG) system to investigate
the properties of oscillations in the 0-8 mHz frequency band at the
location and time of strong M- and X-class flares. For each of three
subregions within two flaring active regions, we extracted time
series from multiple distinct positions, including the flare core
and quieter surrounding areas. The time series were analyzed with a
moving power-map analysis to examine power as a function of frequency
and time. We find that, in the flare core of all three subregions, the
low-frequency power (∼1-2 mHz) is substantially enhanced immediately
prior to and after the flare, and that power at all frequencies up to
8 mHz is depleted at flare maximum. This depletion is both frequency-
and time-dependent, which probably reflects the changing depths visible
during the flare in the bandpass of the filter. These variations are
not observed outside the flare cores. The depletion may indicate that
acoustic energy is being converted into thermal energy at flare maximum,
while the low-frequency enhancement may arise from an instability in the
chromosphere and provide an early warning of the flare onset. Dark lanes
of reduced wave power are also visible in the power maps, which may
arise from the interaction of the acoustic waves and the magnetic field.
Title: Cross-Spectral Fitting of HMI Velocity and Intensity Data
Authors: Tripathy, Sushanta C.; Barban, Caroline; Jain, Kiran;
Kholikov, Shukur; Hill, Frank
Bibcode: 2016usc..confE..84T
Altcode:
The simultaneous HMI velocity and intensity observations are used
to obtain better estimates of solar acoustic mode parameters. This
is achieved by fitting four spectra simultaneously viz. velocity,
intensity, the phase difference and the coherence between the
intensity and velocity spectra. We further compare the oscillation mode
parameters obtained from the single-observable fitting and those from
the cross-spectral fitting method. We find that the mode frequencies
derived from the cross-spectral procedure are lower than those derived
from the velocity spectrum fitted with an asymmetrical profile. We
further note a clear solar cycle dependence in the mode frequencies
while other mode parameters e.g. amplitudes and line widths do not show
significant variation with solar activity. This corroborates earlier
findings that the interpretation of model fit parameters based on
measurements of a single spectra should be examined critically.
Title: Magnetoseismology of Active Regions using Multi-wavelength
Observations from SDO
Authors: Tripathy Sushanta C.; Jain, Kiran; Kholikov, Shukur; Hill,
Frank; Cally, Paul S.
Bibcode: 2016usc..confE..85T
Altcode:
The structure and dynamics of active regions beneath the surface show
significant uncertainties due to our limited understanding of the
wave interaction with magnetic field. Recent numerical simulations
further demonstrate that the atmosphere above the photospheric
levels also modifies the seismic observables at the surface. Thus
the key to improve helioseismic interpretation beneath the active
regions requires a synergy between models and helioseismic inferences
from observations. In this context, using data from Helioseismic
Magnetic Imager and Atmospheric Imaging Assembly onboard Solar
Dynamics Observatory, we characterize the spatio-temporal power
distribution in and around active regions. Specifically, we focus on
the power enhancements seen around active regions as a function of wave
frequencies, strength, inclination of magnetic field and observation
height as well as the relative phases of the observables and their
cross-coherence functions. It is expected that these effects will help
us to comprehend the interaction of acoustic waves with fast and slow
MHD waves in the solar photosphere.
Title: Subsurface Zonal and Meridional Flows from SDO/HMI
Authors: Komm, Rudolf; Howe, Rachel; Hill, Frank
Bibcode: 2016usc..confE..55K
Altcode:
We study the solar-cycle variation of the zonal and meridional
flows in the near-surface layers of the solar convection zone from
the surface to a depth of about 16 Mm. The flows are determined from
SDO/HMI Dopplergrams using the HMI ring-diagram pipeline. The zonal and
meridional flows vary with the solar cycle. Bands of faster-than-average
zonal flows together with more-poleward-than-average meridional flows
move from mid-latitudes toward the equator during the solar cycle and
are mainly located on the equatorward side of the mean latitude of solar
magnetic activity. Similarly, bands of slower-than-average zonal flows
together with less-poleward-than-average meridional flows are located
on the poleward side of the mean latitude of activity. Here, we will
focus on the variation of these flows at high latitudes (poleward of
50 degree) that are now accessible using HMI data. We will present
the latest results.
Title: Solar Acoustic Oscillations Observations in SDO AIA and HMI
around AR 12192
Authors: Monsue, Teresa; Pesnell, W. Dean; Hill, Frank
Bibcode: 2016usc..confE..89M
Altcode:
Solar flares are dynamic objects occurring randomly and yet unannounced
in nature. In order to find an efficient detection method, we require a
greater breadth of knowledge of the system. One such mode is to observe
flares in different frequency bands at different depths and study
their temporal evolution through the flaring event. In this project we
obtain acoustic observations of an X3 flare occurring on October 24,
2014 at 21:41UT. We employ the study of active regions, near sunspots,
in which flaring activity is taking place. Our wavelet analysis utilizes
time series data to create Fourier power spectra of individual pixels
spatially resolved around the flare region, to study the frequency
bands. In order to study the power distribution in regions around the
flare and compare the measurements to magnetograms to search for any
correlation, we combine observations of oscillations in three SDO AIA
wavelengths: the 1600Å, 1700 Å and 304Å, and combine them with HMI
data. We then study how the frequency distribution evolves temporally
by constructing a Power Map Movie (PMM) of the regions. From these
PMMs we can partition sub-regions in our main flaring region and take
a survey of the oscillations for each frequency band.
Title: A New Challenge to Solar Dynamo Models from Helioseismic
Observations: The Latitudinal Dependence of the Progression of the
Solar Cycle
Authors: Simoniello, R.; Tripathy, S. C.; Jain, K.; Hill, F.
Bibcode: 2016ApJ...828...41S
Altcode: 2016arXiv160603037S
The onset of the solar cycle at mid-latitudes, the slowdown in the
drift of sunspots toward the equator, the tail-like attachment, and
the overlap of successive cycles at the time of minimum activity are
delicate issues in models of the αΩ dynamo wave and the flux transport
dynamo. Very different parameter values produce similar results, making
it difficult to understand the origin of the properties of these solar
cycles. We use helioseismic data from the Global Oscillation Network
Group to investigate the progression of the solar cycle as observed
in intermediate-degree global p-mode frequency shifts at different
latitudes and subsurface layers, from the beginning of solar cycle
23 up to the maximum of the current solar cycle. We also analyze
those for high-degree modes in each hemisphere obtained through
the ring-diagram technique of local helioseismology. The analysis
highlights differences in the progression of the cycle below 15°
compared to higher latitudes. While the cycle starts at mid-latitudes
and then migrates equatorward/poleward, the sunspot eruptions of the old
cycle are still ongoing below 15° latitude. This prolonged activity
causes a delay in the onset of the cycle and an overlap of successive
cycles, whose extent differs in the two hemispheres. Then the activity
level rises faster, reaching a maximum characterized by a single-peak
structure as opposed to the double peak at higher latitudes. Afterwards
the descending phase shows up with a slower decay rate. The latitudinal
properties of the progression of the solar cycle highlighted in this
study provide useful constraints for discerning among the multitude
of solar dynamo models.
Title: Transitioning GONG data processing to NOAA SWPC operations
Authors: Reinard, Alysha; Berger, Thomas; Marble, Andrew; Hill, Frank
Bibcode: 2016shin.confE..26R
Altcode:
The NOAA Space Weather Prediction Center (SWPC) is the nation's official
source of space weather watches, warnings, and alerts, providing 24x7
forecasting and support to critical infrastructure operators around
the world. Observations of the conditions on the Sun are crucial for
determining when and if a warning is needed. The Global Oscillation
Network Group (GONG) operated by the National Solar Observatory (NSO)
consists of six ground stations, allowing continuous observations of the
Sun. Of particular interest for space weather purposes are the H-alpha
images and magnetograms. H-alpha data is used to identify filaments and
their eruptions, to assess active region evolution and plage extent,
and to help localize flare locations. Magnetograms are used to identify
neutral lines, examine potential shearing areas and characterize the
magnetic structure of active regions. GONG magnetograms also provide
the initial condition for models of solar wind expansion such as
the WSA-Enlil model. GONG helioseismology products, in particular
far-side imaging, are being examined for operational use in the near
future. NSO has operated GONG as a science facility since 1995
and has provided processed space weather data products to NOAA via
public internet connections for the past several years. In 2014 the
White House Office of Management and Budget (OMB) requested that NOAA
transition the GONG network to an operational space weather asset
in order to ensure the continued flow of critical magnetogram data
for solar wind models. NSO will continue to operate and manage the
instruments and sites, but the H-alpha images and 10 minute averaged
magnetogram data will be sent directly to SWPC for processing and use
in space weather modeling. SWPC will make these data available to NSO
and the public via the new NOAA Integrated Dissemination Program (IDP)
network. We discuss the progress and details of this change.
Title: Seismic Mapping of the Sun's Far Hemisphere for Applications
in Space-Weather Forecasting
Authors: Lindsey, Charles; Werne, Joseph; Hill, Frank
Bibcode: 2016shin.confE..36L
Altcode:
Magnetic regions in the Sun's outer atmosphere exert a major impact
on space weather at Earth. Magnetic regions in the far hemisphere
appear to exert relatively little immediate impact, but, because the
Sun rotates, these regions cross into the near hemisphere somewhat
suddenly and without warning--except for our ability to monitor the
Sun's far hemisphere. Monitoring of the Sun's far hemisphere therefore
becomes crucial to space-weather forecasting on time scales ranging from
a few days to a few weeks. For the past several years, this need has
been well served by NASA's twin STEREO spacecraft, which, since 2011,
have been in positions to view the entirety of the Sun's far hemisphere
directly. Beginning in about 2019, STEREO coverage of the far hemisphere
will begin to diminish, as both of the STEREO spacecraft drift back to
Earth's side of the solar system. For most of the succeeding decade,
solar seismology will be the only means of detecting and accurately
locating large, newly emerging active regions that covers the entirety
of the Sun's far hemisphere. We will review the development of
seismology of the Sun's far hemisphere from the 1990s to present. We
will summarize recent developments in seismic sensing of the Sun's
far hemisphere, describing its basic capabilities and limitations as a
tool for detecting and locating new emerging magnetic flux in the Sun's
far hemisphere and forecasting its subsequent transit across the Sun's
eastern limb. We will also offer projections on coming improvements in
far-side solar seismology of likely value to space-weather forecasters.
Title: Magnetoseismology of Active Regions using Multi-wavelength
Observations from GONG and SDO
Authors: Tripathy, Sushanta; Jain, Kiran; Kholikov, Shukur; Hill,
Frank; Cally, Paul
Bibcode: 2016SPD....47.0721T
Altcode:
The structure and dynamics of active regions beneath the surface show
significant uncertainties due to our limited understanding of the wave
interaction with magnetic field. Recent numerical simulations further
demonstrate that the atmosphere above the photospheric levels also
modifies the seismic observables at the surface. Thus the key to improve
helioseismic interpretation beneath the active regions requires a
synergy between models and helioseismic inferences from observations. In
this context, using data from Global Oscillation Network Group and from
Helioseismic Magnetic Imager and Atmospheric Imaging Assembly onboard
Solar Dynamics Observatory, we characterize the spatio-temporal power
distribution in and around active regions. Specifically, we focus on
the power enhancements seen around active regions as a function of wave
frequencies, strength, inclination of magnetic field and observation
height as well as the relative phases of the observables and their
cross-coherence functions. It is expected that these effects will help
us to comprehend the interaction of acoustic waves with magnetic field
in the solar photosphere.
Title: The Discriminant Analysis Flare Forecasting System (DAFFS)
Authors: Leka, K. D.; Barnes, Graham; Wagner, Eric; Hill, Frank;
Marble, Andrew R.
Bibcode: 2016SPD....4720701L
Altcode:
The Discriminant Analysis Flare Forecasting System (DAFFS) has been
developed under NOAA/Small Business Innovative Research funds to
quantitatively improve upon the NOAA/SWPC flare prediction. In the
Phase-I of this project, it was demonstrated that DAFFS could indeed
improve by the requested 25% most of the standard flare prediction
data products from NOAA/SWPC. In the Phase-II of this project, a
prototype has been developed and is presently running autonomously
at NWRA.DAFFS uses near-real-time data from NOAA/GOES, SDO/HMI, and
the NSO/GONG network to issue both region- and full-disk forecasts
of solar flares, based on multi-variable non-parametric Discriminant
Analysis. Presently, DAFFS provides forecasts which match those provided
by NOAA/SWPC in terms of thresholds and validity periods (including
1-, 2-, and 3- day forecasts), although issued twice daily. Of
particular note regarding DAFFS capabilities are the redundant system
design, automatically-generated validation statistics and the large
range of customizable options available. As part of this poster, a
description of the data used, algorithm, performance and customizable
options will be presented, as well as a demonstration of the DAFFS
prototype.DAFFS development at NWRA is supported by NOAA/SBIR contracts
WC-133R-13-CN-0079 and WC-133R-14-CN-0103, with additional support
from NASA contract NNH12CG10C, plus acknowledgment to the SDO/HMI and
NSO/GONG facilities and NOAA/SWPC personnel for data products, support,
and feedback. DAFFS is presently ready for Phase-III development.
Title: Solar Indices Forecasting Tool
Authors: Henney, Carl John; Shurkin, Kathleen; Arge, Charles; Hill,
Frank
Bibcode: 2016SPD....47.1303H
Altcode:
Progress to forecast key space weather parameters using SIFT
(Solar Indices Forecasting Tool) with the ADAPT (Air Force Data
Assimilative Photospheric flux Transport) model is highlighted in
this presentation. Using a magnetic flux transport model, ADAPT, we
estimate the solar near-side field distribution that is used as input
into empirical models for predicting F10.7(solar 10.7 cm, 2.8 GHz, radio
flux), the Mg II core-to-wing ratio, and selected bands of solar far
ultraviolet (FUV) and extreme ultraviolet (EUV) irradiance. Input to the
ADAPT model includes the inferred photospheric magnetic field from the
NISP ground-based instruments, GONG & VSM. Besides a status update
regarding ADAPT and SIFT models, we will summarize the findings that:
1) the sum of the absolute value of strong magnetic fields, associated
with sunspots, is shown to correlate well with the observed daily
F10.7 variability (Henney et al. 2012); and 2) the sum of the absolute
value of weak magnetic fields, associated with plage regions, is shown
to correlate well with EUV and FUV irradiance variability (Henney et
al. 2015). This work utilizes data produced collaboratively between Air
Force Research Laboratory (AFRL) and the National Solar Observatory
(NSO). The ADAPT model development is supported by AFRL. The input
data utilized by ADAPT is obtained by NISP (NSO Integrated Synoptic
Program). NSO is operated by the Association of Universities for
Research in Astronomy (AURA), Inc., under a cooperative agreement with
the National Science Foundation (NSF). The 10.7 cm solar radio flux
data service, utilized by the ADAPT/SIFT F10.7 forecasting model,
is operated by the National Research Council of Canada and National
Resources Canada, with the support of the Canadian Space Agency.
Title: Solar Activity in Cycle 24 - What do Acoustic Oscillations
tell us?
Authors: Jain, Kiran; Tripathy, Sushant; Simoniello, Rosaria; Hill,
Frank
Bibcode: 2016SPD....47.0716J
Altcode:
Solar Cycle 24 is the weakest cycle in modern era of space- and
ground-based observations. The number of sunspots visible on solar disk
and other measures of magnetic activity have significantly decreased
from the last cycle. It was also preceeded by an extended phase of low
activity, a period that raised questions on our understanding of the
solar activity cycle and its origin. This unusual behavior was not only
limited to the visible features in Sun's atmosphere, the helioseismic
observations also revealed peculiar behavior in the interior. It
was suggested that the changes in magnetic activity were confined
to shallower layers only, as a result low-degree mode frequencies
were found to be anti-correlated with solar activity. Here we present
results on the progression of Cycle 24 by analyzing the uninterrupted
helioseismic data from GONG and SDO/HMI, and discuss differences and
similarity between cycles 23 and 24 in relation to the solar activity.
Title: The Virtual Solar Observatiory: Where Do We Go From Here?
Authors: Gurman, Joseph B.; Bogart, R. S.; Amezcua, A.; Hill, Frank;
Oien, Niles; Hourcle, Joseph; Spencer, Jennifer L.; Davey, Alisdair R.
Bibcode: 2016SPD....47.0202G
Altcode:
The Virtual Solar Observatory (VSO) is a known and useful method for
identifying and accessing solar phsyics data online. We review current
"behind the scenes" work on the VSO and invite SPD members to identify
data sets, services, and interfaces they would like to see implemented
in the VSO.
Title: Are subsurface flows evidence of hidden magnetic flux during
cycle minimum?
Authors: Komm, Rudolf; Howe, Rachel; Hill, Frank
Bibcode: 2016SPD....47.0708K
Altcode:
Subsurface flows vary during the course of a solar cycle showing bands
of faster- and slower-than-average rotation and bands of converging
meridional flow. These flow patterns migrate with latitude; they first
appear during the declining phase of a solar cycle and are present
during cycle minimum. They appear several years before the magnetic
pattern of a new cycle is apparent in synoptic maps and the values
of magnetic flux at these locations are comparable to other quiet-Sun
locations without such flow patterns. Do the precursory flow patterns
thus indicate the presence of magnetic flux that is too small-scale
or short-lived to be noticed in synoptic maps? How much flux would be
required to generate these flow patterns?We quantify the relationship
between subsurface flow patterns and magnetic activity during Cycles 23
and 24 and address these questions. We have analyzed GONG and SDO/HMI
Dopplergrams using a dense-pack ring-diagram analysis and determined
flows in the near-surface layers of the solar convection zone to a
depth of about 16 Mm.
Title: Horizontal Flows in Active Regions from Ring-diagram and
Local Correlation Tracking Methods
Authors: Jain, Kiran; Tripathy, S. C.; Ravindra, B.; Komm, R.; Hill, F.
Bibcode: 2016ApJ...816....5J
Altcode: 2015arXiv151103208J
Continuous high-cadence and high spatial resolution Dopplergrams allow
us to study subsurface dynamics that may be further extended to explore
precursors of visible solar activity on the surface. Since the p-mode
power is absorbed in the regions of high magnetic field, the inferences
in these regions are often presumed to have large uncertainties. In
this paper, using the Dopplergrams from space-borne Helioseismic
Magnetic Imager, we compare horizontal flows in a shear layer below the
surface and the photospheric layer in and around active regions. The
photospheric flows are calculated using the local correlation tracking
(LCT) method, while the ring-diagram technique of helioseismology
is used to infer flows in the subphotospheric shear layer. We find
a strong positive correlation between flows from both methods near
the surface. This implies that despite the absorption of acoustic
power in the regions of strong magnetic field, the flows inferred
from the helioseismology are comparable to those from the surface
measurements. However, the magnitudes are significantly different;
the flows from the LCT method are smaller by a factor of 2 than the
helioseismic measurements. Also, the median difference between the
direction of corresponding vectors is 49°.
Title: The Importance of Long-Term Synoptic Observations and Data
Sets for Solar Physics and Helioseismology
Authors: Elsworth, Yvonne; Broomhall, Anne-Marie; Gosain, Sanjay;
Roth, Markus; Jefferies, Stuart M.; Hill, Frank
Bibcode: 2015SSRv..196..137E
Altcode: 2015SSRv..tmp..106E
A casual single glance at the Sun would not lead an observer to conclude
that it varies. The discovery of the 11-year sunspot cycle was only
made possible through systematic daily observations of the Sun over
150 years and even today historic sunspot drawings are used to study
the behavior of past solar cycles. The origin of solar activity is
still poorly understood as shown by the number of different models
that give widely different predictions for the strength and timing
of future cycles. Our understanding of the rapid transient phenomena
related to solar activity, such as flares and coronal mass ejections
(CMEs) is also insufficient and making reliable predictions of these
events, which can adversely impact technology, remains elusive. There
is thus still much to learn about the Sun and its activity that requires
observations over many solar cycles. In particular, modern helioseismic
observations of the solar interior currently span only 1.5 cycles,
which is far too short to adequately sample the characteristics of
the plasma flows that govern the dynamo mechanism underlying solar
activity. In this paper, we review some of the long-term solar and
helioseismic observations and outline some future directions.
Title: Transitioning GONG data processing to NOAA SWPC operations
Authors: Reinard, A.; Marble, A.; Hill, F.; Berger, T. E.
Bibcode: 2015AGUFMSH21B2394R
Altcode:
The NOAA Space Weather Prediction Center (SWPC) is the nation's official
source of space weather watches, warnings, and alerts, providing 24x7
forecasting and support to critical infrastructure operators around
the world. Observations of the conditions on the Sun are crucial for
determining when and if a warning is needed. The Global Oscillation
Network Group (GONG) operated by the National Solar Observatory (NSO)
consists of six ground stations, allowing continuous observations of the
Sun. Of particular interest for space weather purposes are the H-alpha
images and magnetograms. The H-alpha data are used to identify filaments
and their eruptions, to assess active region evolution and plage extent,
and to help localize flare locations. The magnetograms are used to
identify neutral lines, to examine potential shearing areas and to
characterize the magnetic structure of active regions. GONG magnetograms
also provide the initial condition for models of solar wind expansion
through the heliosphere such as the WSA-Enlil model. Although beyond
the scope of current space weather applications, GONG helioseismology
products can be used to assess active region emergence on the far
side of the Sun and to indicate the flaring potential of a front-side
active region. These products are being examined as future tools in
flare prediction. NSO has operated GONG as a science facility since
1995 and has provided processed space weather data products to NOAA
via public internet connections for the past several years. In 2014
the White House Office of Management and Budget (OMB) requested that
NOAA transition the GONG network to an operational space weather asset
in order to ensure the continued flow of critical magnetogram data
for solar wind models. NSO will continue to operate and manage the
instruments and sites, but the H-alpha images and 10 minute averaged
magnetogram data will be sent directly to SWPC for processing and use
in space weather modeling. SWPC will make these data available to NSO
and the public via the new NOAA Integrated Dissemination Program (IDP)
network. We discuss the progress and details of this change.
Title: Helioseismology with Solar Orbiter
Authors: Löptien, Björn; Birch, Aaron C.; Gizon, Laurent; Schou,
Jesper; Appourchaux, Thierry; Blanco Rodríguez, Julián; Cally,
Paul S.; Dominguez-Tagle, Carlos; Gandorfer, Achim; Hill, Frank;
Hirzberger, Johann; Scherrer, Philip H.; Solanki, Sami K.
Bibcode: 2015SSRv..196..251L
Altcode: 2014arXiv1406.5435L; 2014SSRv..tmp...31L
The Solar Orbiter mission, to be launched in July 2017, will
carry a suite of remote sensing and in-situ instruments, including
the Polarimetric and Helioseismic Imager (PHI). PHI will deliver
high-cadence images of the Sun in intensity and Doppler velocity
suitable for carrying out novel helioseismic studies. The orbit of
the Solar Orbiter spacecraft will reach a solar latitude of up to
21∘ (up to 34∘ by the end of the extended
mission) and thus will enable the first local helioseismology studies of
the polar regions. Here we consider an array of science objectives to be
addressed by helioseismology within the baseline telemetry allocation
(51 Gbit per orbit, current baseline) and within the science observing
windows (baseline 3×10 days per orbit). A particularly important
objective is the measurement of large-scale flows at high latitudes
(rotation and meridional flow), which are largely unknown but play an
important role in flux transport dynamos. For both helioseismology
and feature tracking methods convection is a source of noise in
the measurement of longitudinally averaged large-scale flows, which
decreases as T -1/2 where T is the total duration of the
observations. Therefore, the detection of small amplitude signals (e.g.,
meridional circulation, flows in the deep solar interior) requires long
observation times. As an example, one hundred days of observations at
lower spatial resolution would provide a noise level of about three m/s
on the meridional flow at 80∘ latitude. Longer time-series
are also needed to study temporal variations with the solar cycle. The
full range of Earth-Sun-spacecraft angles provided by the orbit will
enable helioseismology from two vantage points by combining PHI with
another instrument: stereoscopic helioseismology will allow the study
of the deep solar interior and a better understanding of the physics
of solar oscillations in both quiet Sun and sunspots. We have used a
model of the PHI instrument to study its performance for helioseismology
applications. As input we used a 6 hr time-series of realistic solar
magneto-convection simulation (Stagger code) and the SPINOR radiative
transfer code to synthesize the observables. The simulated power
spectra of solar oscillations show that the instrument is suitable for
helioseismology. In particular, the specified point spread function,
image jitter, and photon noise are no obstacle to a successful mission.
Title: Solar Subsurface Flows During Solar Cycle 24
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 2015AGUFMSH23A2420K
Altcode:
We study the variation of subsurface flows in the presence of magnetic
activity during the current solar cycle. To determine flows in the
near-surface layers of the solar convection zone from the surface to
a depth of about 16 Mm, we have analyzed Dopplergrams obtained with
the Global Oscillation Network Group (GONG) and the Helioseismic and
Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO)
using a dense-pack ring-diagram analysis. We will compare the zonal
and meridional flows during Cycle 24 with those during Cycle 23. The
zonal and meridional flows at high latitudes are now accessible thanks
to HMI data. The zonal- and meridional-flow patterns track the mean
latitude of activity and are precursors of magnetic activity appearing
about three years before activity is visible in synoptic maps of
the solar surface. The poleward branch of the zonal-flow pattern is
noticeable during Cycle 24 but is considerably weaker than during the
previous cycle. We will also present the latest results from global
helioseismology for comparison.
Title: Response of Solar Oscillations to Magnetic Activity in Cycle 24
Authors: Jain, K.; Tripathy, S. C.; Hill, F.
Bibcode: 2015AGUFMSH23A2422J
Altcode:
Acoustic mode parameters are generally used to study the variability
of the solar interior in response to changing magnetic activity. While
oscillation frequencies do vary in phase with the solar activity,
the mode amplitudes are anti-correlated. Now, continuous measurements
from ground and space allow us study the origin of such variability
in detail. Here we use intermediate-dgree mode frequencies computed
from a ground-based 6-site network ( GONG), covering almost two solar
cycles from the minimum of cycle 23 to the declining phase of cycle
24, to investigate the effect of remarkably low solar activity on
the solar oscillations in current cycle and the preceding minimum;
is the response of acoustic oscillations to magnetic activity in cycle
24 similar to cycle 23 or there are differences between cycles 23 and
24? In this paper, we analyze results for both solar cycles, and try
to understand the origin of similarities/differences between them. We
will also compare our findings with the contemporaneous observations
from space (SOHO/MDI and SDO/HMI).
Title: Solar-Cycle Variation of Subsurface Meridional Flow Derived
with Ring-Diagram Analysis
Authors: Komm, R.; González Hernández, I.; Howe, R.; Hill, F.
Bibcode: 2015SoPh..290.3113K
Altcode: 2015SoPh..tmp...83K
We study the solar-cycle variation of the meridional flow in the
near-surface layers of the solar convection zone from the surface to
a depth of 16 Mm. We have analyzed Global Oscillation Network Group
(GONG) Dopplergrams with a ring-diagram analysis covering about 13
years (July 2001 - October 2014), from the maximum of Cycle 23 through
the rising phase of Cycle 24, and Helioseismic and Magnetic Imager
(HMI) Dopplergrams covering more than four years (May 2010 - January
2015). GONG and HMI lead to similar meridional flows during common
epochs and latitudes. The meridional flow averaged over a Carrington
rotation is poleward up to about 70∘ in both hemispheres at
all depths after correcting for systematic effects. The flow amplitude
peaks at about 40∘ latitude with an amplitude of about 16
to 20 ms−1 depending on depth. The meridional flow varies
with the solar cycle; the flow amplitudes are larger during cycle
minimum than during maximum at low- and mid-latitudes. The flows are
mainly faster or more-poleward-than-average on the equatorward side of
the mean latitude of activity and slower or less-poleward-than-average
on its poleward side. The residual meridional flow converges near
the mean latitude of activity. A comparison with the corresponding
zonal flow derived from GONG and HMI data shows that the bands
of more-poleward-than-average meridional flow coincide with the
bands of faster-than-average zonal flow and that the bands of
less-poleward-than-average meridional flow coincide with the bands of
slower-than-average zonal flow. This implies that the residual flows
are cyclonic. The bands of fast meridional flow appear at mid-latitudes
about three years before magnetic activity of Cycle 24 is present in
synoptic maps.
Title: Variations in High Degree Acoustic Mode Frequencies of the
Sun during Solar Cycles 23 and 24
Authors: Tripathy, S. C.; Jain, K.; Hill, F.
Bibcode: 2015ApJ...812...20T
Altcode: 2015arXiv150905474T
We examine continuous measurements of the high-degree acoustic mode
frequencies of the Sun covering the period from 2001 July to 2014
June. These are obtained through the ring-diagram technique applied
to the full-disk Doppler observations made by the Global Oscillation
Network Group. The frequency shifts in the degree range of 180
≤slant {\ell } ≤slant 1200 are correlated with different proxies
of solar activity, e.g., 10.7 cm radio flux, the International Sunspot
Number, and the strength of the local magnetic field. In general,
a good agreement is found between the shifts and activity indices,
and the correlation coefficients are found to be comparable with
intermediate-degree mode frequencies. Analyzing the frequency shifts
separately for the two cycles, we find that cycle 24 is weaker than
cycle 23. Since the magnetic activity is known to be different in the
two hemispheres, for the first time, we compute the frequency shifts
over the two hemispheres separately and find that the shifts also
display hemispheric asymmetry; the amplitude of shifts in the northern
hemisphere peaked during late 2011, more than two years earlier than
in the south. We further correlate the hemispheric frequency shifts
with the hemispheric sunspot number and mean magnetic activity index
(MAI). Since the frequency shifts and the hemispheric activity indices
are found to be significantly correlated, we suggest that the shifts
be used as an indicator of hemispheric activity since not many indices
are measured over the two hemispheres separately. We also investigate
the variation at different latitudinal bands and conclude that the
shifts in active latitudes correlate well with the local MAI.
Title: Divergent Horizontal Sub-surface Flows within Active Region
11158
Authors: Jain, Kiran; Tripathy, S. C.; Hill, F.
Bibcode: 2015ApJ...808...60J
Altcode: 2015arXiv150800519J
We measure the horizontal subsurface flow in a fast emerging
active region (AR; NOAA 11158) using the ring-diagram technique
and the Helioseismic and Magnetic Imager high spatial resolution
Dopplergrams. This AR had a complex magnetic structure and displayed
significant changes in morphology during its disk passage. Over a
period of six days from 2011 February 11 to 16, the temporal variation
in the magnitude of the total velocity is found to follow the trend
of magnetic field strength. We further analyze regions of individual
magnetic polarity within AR 11158 and find that the horizontal velocity
components in these sub-regions have significant variation with time and
depth. The leading and trailing polarity regions move faster than the
mixed-polarity region. Furthermore, both zonal and meridional components
have opposite signs for trailing and leading polarity regions at all
depths showing divergent flows within the AR. We also find a sharp
decrease in the magnitude of total horizontal velocity in deeper
layers around major flares. It is suggested that the re-organization
of magnetic fields during flares, combined with the sunspot rotation,
decreases the magnitude of horizontal flows or that the flow kinetic
energy has been converted into the energy released by flares. After
the decline in flare activity and sunspot rotation, the flows tend
to follow the pattern of magnetic activity. We also observe less
variation in the velocity components near the surface but these tend
to increase with depth, further demonstrating that the deeper layers
are more affected by the topology of ARs.
Title: Temporal evolution of the solar torsional oscillation and
implications for cycle 25
Authors: Hill, Frank; Howe, Rachel; Komm, Rudolf; Schou, Jesper;
Thompson, Michael; Larson, Timothy
Bibcode: 2015TESS....110502H
Altcode:
The zonal flow known as the torsional oscillation has been observed
on the Sun’s surface since 1980 and in its interior since 1995. It
has two branches that migrate during the solar cycle, with one moving
towards the equator and the other towards the poles. The rate at which
these branches migrate in latitude is tightly correlated with the
timing of the solar cycle, as seen during the long minimum between
cycles 23 and 24. The poleward branch generally becomes visible 10
to 12 years before the appearance of the magnetic activity associated
with the corresponding sunspot cycle as it did for the current cycle
24. However, the poleward flow for cycle 25, which was expected to
appear in 2008-2010, was not observed. Subsequent analysis showed
that it is a very weak flow, and is masked by an apparent change
in the background solar differential rotation rate. We will present
the latest observations of the zonal flow as determined from global
helioseismology, and will discuss the implications for the strength
and timing of cycle 25.
Title: A Novel Analysis of Acoustic Oscillations in Chromospheric
Active Regions
Authors: Monsue, Teresa; Hill, Frank; Stassun, Keivan G.
Bibcode: 2015TESS....130304M
Altcode:
A helioseismic analysis of the chromosphere is employed in H-alpha
to study how solar flares around active regions affect the behavior
of acoustic oscillations. Our analysis deals with flares directly
over sunspots, where the region is highly magnetized. In our current
study of analyzing these oscillations in the chromosphere we study the
temporal evolution of the oscillatory behavior from data taken from
the Global Oscillation Network Group (GONG) H-alpha detectors. We
investigate the wave behavior across different frequency bands (1
< ν < 8.33 mHz). In order to analyze the frequency bands of
the oscillations, our analysis utilizes time series data to create
Fourier power spectra of individual pixels spatially resolved and
temporally evolved around the flare region; thereby creating a movie
of each frequency band. This study entails three active regions,
directly over sunspots, in which flaring activity is taking place
from two solar flares, which occurred on June 13th and July 12th,
2012. We found that the intensity of the flare has an effect on the
oscillations within different frequency bands. A suppression of power
was observed in dark anomalous structures across the total frequency
bands and in other regions there was an observed boost in power due to
flaring activity. We find that, in the heart of all three regions, the
low-frequency power (∼1-2 mHz) is substantially enhanced immediately
prior to and after the flare, and that power at all frequencies up to
8 mHz is depleted at flare maximum. This depletion is both frequency
and time dependent, which probably reflects the changing depths visible
during the flare in the bandpass of the filter. These variations are
not observed outside the flaring region. The depletion may indicate that
acoustic energy is being converted into thermal energy at flare maximum,
while the low-frequency enhancement may arise from an instability in
the chromosphere and provide an early warning of the flare onset.
Title: Subsurface Zonal and Meridional Flow Derived from GONG and
SDO/HMI: A Comparison of Systematics
Authors: Komm, R.; González Hernández, I.; Howe, R.; Hill, F.
Bibcode: 2015SoPh..290.1081K
Altcode: 2015SoPh..tmp...22K
We study the subsurface flows in the near-surface layers of the
solar convection zone from the surface to a depth of 16 Mm derived
from Global Oscillation Network Group (GONG) and Helioseismic and
Magnetic Imager (HMI) Dopplergrams using a ring-diagram analysis. We
characterize the systematic east-west and north-south variations
present in the zonal and meridional flows and compare flows derived
from GONG and HMI data before and after the correction. The average
east-west variation with depth of one flow component resembles the
average north-south variation with depth of the other component. The
east-west variation of the zonal flow together with the north-south
variation of the meridional flow can be modeled as a systematic
radial velocity. This indicates a solar center-to-limb variation as
the underlying cause. The north-south variation of the zonal flow and
the east-west variation of the meridional flow require two separate
functions. The east-west variation of the meridional flow consists
mainly of an annual variation with the B0 angle, while the
north-south trend of the zonal flow consists of a constant non-zero
component in addition to an annual variation. This indicates a geometric
projection artifact. After compensating for these systematic effects,
the meridional and zonal flows derived from HMI data agree well with
those derived from GONG data. An offset remains between the zonal flow
derived from GONG and HMI data. The equatorward meridional flows at
high latitude that appear episodically depending on the B0
angle are absent from the corrected flows.
Title: Solar-cycle variation of subsurface flows during 20 years
Authors: Komm, Rudolf; Howe, Rachel; Hill, Frank
Bibcode: 2015TESS....121406K
Altcode:
We study the solar-cycle variation of the zonal and meridional flow
in the near-surface layers of the solar convection zone from the
surface to a depth of about 16 Mm. We have analyzed Dopplergrams
obtained with the Michelson Doppler Imager (MDI) onboard the Solar and
Heliospheric Observatory (SOHO), the Global Oscillation Network Group
(GONG),and the Helioseismic and Magnetic Imager (HMI) onboard the Solar
Dynamics Observatory (SDO) with a dense-pack ring-diagram analysis. The
three data sets combined cover almost two solar cycles. The zonal and
meridional flows vary with the solar cycle. Their amplitude variation
tracks the mean latitude of activity and appears about three years
before magnetic activity is visible in synoptic maps of the solar
surface. We focus on the variation of the zonal and meridional flows,
including their long-term variation at mid- and low-latitudes using
GONG and MDI data and their variation at the high latitudes that are
now accessible using HMI data. We will present the latest results.
Title: Helioseismic Mode Parameters from 20 Years of Global
Oscillation Network Group (GONG) Observations
Authors: Jain, Kiran; Tripathy, Sushant C.; Hill, Frank; Simoniello,
Rosaria
Bibcode: 2015TESS....110305J
Altcode:
The intermediate-degree mode parameters are used to study the
variability of solar oscillations and their dependence on the
magnetic-activity. We use uninterrupted observations from the 6-site
network, Global Oscillation Network Group (GONG), for about 20 years
that covers a period from the minimum of cycle 23 to the declining
phase of cycle 24. Using the observations for cycle 23, it was
demonstrated that the frequencies do vary in phase with the solar
activity indices. However, the degree of correlation differs from phase
to phase of the cycle; the mode frequency shifts are strongly correlated
with the activity proxies during the rising and declining phases whereas
this correlation is significantly lower during the high-activity
period. Here we present and compare results for two solar cycles,
and try to understand the origin of the differences between both cycles.
Title: Brief History of Using GONG for Space Weather Forecasting
Authors: Arge, Nick; Henney, Carl; Hill, Frank
Bibcode: 2015TESS....121403A
Altcode:
In 2006 the National Solar Observatory’s (NSO) Global Oscillation
Network Group (GONG) completed the upgrade of their magnetographs with
new polarization modulators permitting, for the first time, proper
inter-calibration of the magnetic field data from a global network
of six different instruments. This development was ground breaking
for at least three reasons. First, it allowed the magnetograms from
the different magnetographs to be merged together into global maps
of the photospheric magnetic field. Second, it was the first ground
based system that could monitor the full-disk solar magnetic field
24/7 at moderate spatial resolution (2 arcsec) and high temporal
cadence (60 seconds). Third, techniques for merging magnetic
field data from the six (technically identical but practically)
different instruments were developed, which can now be applied to
future ground based networks. Approximately one year after the GONG
upgrade, NOAA/SWPC began routinely using the new GONG maps as input
to the Wang-Sheeley-Arge (WSA) coronal and solar wind model. Since
this time, use of GONG data for space weather applications has grown
rapidly. For example, GONG photospheric field maps are now the primary
data driving the operational WSA+Enlil model at NOAA/SWPC. In addition,
GONG magnetograph and helioseismic farside data are beginning to be
used as input to the ADAPT flux transport model to generate synchronic
maps and forecast F10.7 and EUV. This talk provides a brief history
of the use of GONG for practical space weather forecasting purposes.
Title: Subsurface helicity of active regions 12192 and 10486
Authors: Komm, Rudolf; Tripathy, Sushant; Howe, Rachel; Hill, Frank
Bibcode: 2015TESS....110506K
Altcode:
The active region 10486 that produced the Halloween flares in 2003
initiated our interest in the kinetic helicity of subsurface flows
associated with active regions. This lead to the realization that the
helicity of subsurface flows is related to the flare activity of active
regions. Eleven years later, a similarly enormous active region (12192)
appeared on the solar surface. We plan to study the kinetic helicity of
the subsurface flows associated with region 12192 and compare it to that
of region 10486. For 10486, we have analyzed Dopplergrams obtained with
the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric
Observatory (SOHO) and the Global Oscillation Network Group (GONG)
with a dense-pack ring-diagram analysis. For 12192, we have analyzed
Dopplergrams from GONG and the Helioseismic and Magnetic Imager (HMI)
onboard the Solar Dynamics Observatory (SDO). We will present the
latest results.
Title: Tracking Active Region NOAA 12192 in Multiple Carrington
Rotations
Authors: Jain, Kiran; Tripathy, Sushant C.; Hill, Frank
Bibcode: 2015TESS....110306J
Altcode:
Active region NOAA 12192 appeared on the visible solar disk on
October 18, 2014 and grew rapidly into the largest such region since
1990. During its entire transit across the Earth facing side of the
Sun, it produced a significant number of X- and M-class flares. The
combination of front-side and helioseismic far-side images clearly
indicated that it lived through several Carrington rotations. In this
paper, using Dopplergrams from GONG and HMI, we present a study on mode
parameters, viz. oscillation frequencies, amplitude, and sub-surface
flows and investigate how these vary with the evolution of active
region in multiple rotations. We also present a detailed comparison
between NOAA 10486 (the biggest active region in cycle 23) and NOAA
12192, and discuss the similarities/differences between them.
Title: Fitting of Intensity-Velocity Cross Spectrum using GONG and
HMI Oscillation Data
Authors: Tripathy, S. C.; Barban, C.; Jain, K.; Kholikov, S.; Hill, F.
Bibcode: 2014AGUFMSH13B4096T
Altcode:
The fitting of solar intensity-velocity cross spectrum together with
coherence and intensity-velocity phase difference provides us with
better estimates of the oscillation mode parameters. This also serves
as a diagnostic tool to improve our understanding of the excitation of
the p-modes by convection by estimating the contribution of the solar
backgrounds which may or may not be correlated with the acoustic
modes. Using both GONG and HMI data, we will present our results
of fitting four spectra simultaneously viz. velocity, intensity,
the phase difference and the coherence between the intensity and
velocity spectra. We will compare the mode parameters obtained from
a single-observable and those from cross-spectral fitting method and
comment on the solar cycle variation of mode parameters. We will also
characterize and compare the contribution from different background
components.
Title: Chromospheric Acoustic Oscillations in Active Flaring Regions
Authors: Monsue, T.; Hill, F.; Stassun, K.
Bibcode: 2014AGUFMSH51C4168M
Altcode:
Chromospheric p-mode oscillations are studied in Hα to obtain
helioseismic information regarding the local structural conditions
around highly magnetic regions such as sunspots. Solar flares commonly
occur in active regions where these sunspots exist therefore boosting
the p-mode power. In our current study of analyzing p-modes in the
chromosphere we study the time evolution of acoustic p-mode oscillation
data taken from the Global Oscillation Network Group (GONG) Hα, and
investigate the p-modes across the frequency band (1 < ν < 8.33
mHz). This study entails three active regions directly over sunspots,
with accompanying flaring activity from two solar flares, occurring on
June 13th and July 12th, 2012. Our analysis utilizes time series data
to create Fourier power spectra of individual pixels spatially resolved
around the flare region, to study the frequency bands. We then study
how the frequency distribution evolves temporally by constructing a
Power Map Movie (PMM) of the regions. From these PMMs we can take a
survey of the chromospheric oscillations for each frequency band. We
found that the intensity of the flare has an effect on the behavior of
the p-modes within different frequency bands. The suppression of power
was observed in dark anomalous structures within the PMMs and in other
regions there was an observed boost in power due to flaring activity.
Title: Solar-Cycle Variation of Subsurface Zonal Flow
Authors: Komm, R.; Howe, R.; González Hernández, I.; Hill, F.
Bibcode: 2014SoPh..289.3435K
Altcode: 2014SoPh..tmp...29K
We study the solar-cycle variation of the zonal flow in the near-surface
layers of the solar convection zone from the surface to a depth of 16
Mm covering the period from mid-2001 to mid-2013 or from the maximum
of Cycle 23 through the rising phase of Cycle 24. We have analyzed
Global Oscillation Network Group (GONG) and Helioseismic and Magnetic
Imager (HMI) Dopplergrams with a ring-diagram analysis. The zonal flow
varies with the solar cycle showing bands of faster-than-average flows
equatorward of the mean latitude of activity and slower-than-average
flows on the poleward side. The fast band of the zonal flow and the
magnetic activity appear first in the northern hemisphere during
the beginning of Cycle 24. The bands of fast zonal flow appear
at mid-latitudes about three years in the southern and four years
in the northern hemisphere before magnetic activity of Cycle 24 is
present. This implies that the flow pattern is a direct precursor of
magnetic activity. The solar-cycle variation of the zonal flow also
has a poleward branch, which is visible as bands of faster-than-average
zonal flow near 50° latitude. This band appears first in the southern
hemisphere during the rising phase of the Cycle 24 and migrates slowly
poleward. These results are in good agreement with corresponding
results from global helioseismology.
Title: A New Ground-Based Network for Synoptic Solar Observations:
The Solar Physics Research Integrated Network Group (SPRING)
Authors: Hill, Frank; Roth, Markus; Thompson, Michael; Gusain, Sanjay
Bibcode: 2014AAS...22412354H
Altcode:
SPRING is a project to develop a geographically distributed network
of instrumentation to obtain synoptic solar observations. Building
on the demonstrated success of networks to provide nearly-continuous
long-term data for helioseismology, SPRING will provide data for a wide
range of solar research areas. Scientific objectives include internal
solar dynamics and structure; wave transport in the solar atmosphere;
the evolution of the magnetic field over the activity cycle; irradiance
fluctuations; and space weather origins. Anticipated data products
include simultaneous full-disk multi-wavelength Doppler and vector
magnetic field images; filtergrams in H-Alpha, CaK, and white light;
and PSPT-type irradiance support. The data will be obtained with a duty
cycle of around 90% and at a cadence no slower than one minute. The
current concept is a multi-instrument platform installed in at least
six locations, and which will also provide context information for
large-aperture solar telescopes such as EST and the DKIST. There is
wide support for the idea within the EU and the US solar research
communities. The project is in the early planning stages, and we are
open to and looking for participants in the science and instrument
definition.
Title: Daily Normalized Helicity of Subsurface Flows
Authors: Komm, Rudolf; Reinard, Alysha; Hill, Frank
Bibcode: 2014AAS...22421801K
Altcode:
Flare-productive active regions are associated with subsurface flows
with large values of kinetic helicity density. Kinetic helicity is
related to mixing and turbulence of fluids. Reinard et al. 2010 have
developed a parameter that captures the variation of kinetic helicity
with depth and time, the so-called Normalized Helicity Gradient Variance
(NHGV). This parameter increases 2-3 days before a flare occurs and the
NHGV values for flaring and non-flaring active regions represent clearly
separate populations. We derive subsurface flows from the surface to
a depth of 16 Mm using GONG and SDO/HMI Dopplergrams analyzed with
the ring-diagram technique and calculate kinetic helicity density as
a function of position on the solar disk. We will then calculate the
NHGV parameter exploring different normalization schemes and depth
ranges. We will present cases studies of active regions observed with
GONG and SDO/HMI.
Title: Daily Normalized Kinetic Helicity of Subsurface Flows
Authors: Komm, Rudolf; Reinard, A.; Hill, F.
Bibcode: 2014shin.confE.163K
Altcode:
Flare-productive active regions are associated with subsurface flows
with large values of kinetic helicity density. Kinetic helicity is
related to mixing and turbulence of fluids. Reinard et al. 2010 have
developed a parameter that captures the variation of kinetic helicity
with depth and time, the so-called Normalized Helicity Gradient Variance
(NHGV). This parameter increases 2-3 days before a flare occurs and the
NHGV values for flaring and non-flaring active regions represent clearly
separate populations. We derive subsurface flows from the surface to
a depth of 16 Mm using GONG and SDO/HMI Dopplergrams analyzed with
the ring-diagram technique and calculate kinetic helicity density as
a function of position on the solar disk. We will then calculate the
NHGV parameter exploring different normalization schemes and depth
ranges. We will present cases studies of active regions observed with
GONG and SDO/HMI.
Title: Photospheric and sub-photospheric Flows in Active Regions
Authors: Jain, Kiran; Komm, Rudolf W; Tripathy, Sushanta; Ravindra,
B.; Hill, Frank
Bibcode: 2014AAS...22421821J
Altcode:
The availability of continuous high-cadence and high-spatial resolution
Dopplergrams allows us to study sub-surface dynamics that may be further
extended to explore precursors of the solar activity. Since p-mode power
is absorbed in high magnetic field regions, the helioseismic inferences
in these regions are associated with large errors. In order to validate
results, we use Dopplergrams from both space-borne (Helioseismic
Magnetic Imager-HMI) and ground-based (Global Oscillation Network
Group-GONG) observations to infer horizontal flows in photospheric
and sub-photospheric layers in and around several active regions with
different characteristics. The photospheric flows are calculated using
local correlation tracking (LCT) method while ring-diagram analysis
technique is used to infer flows in the sub-photospheric regions. A
detailed comparison between flows in shear layer and photospheric
layer will be made in order to study similarities and discrepancies
in these results.
Title: Meridional-Flow Measurements from Global Oscillation Network
Group Data
Authors: Kholikov, S.; Hill, F.
Bibcode: 2014SoPh..289.1077K
Altcode:
We present measurements of the solar meridional flow using time-distance
analysis based on Global Oscillation Network Group (GONG) data. In
an attempt to detect the deep equatorward flow, which is believed
to be a very small amplitude motion, we averaged time-difference
measurements over a 15-year period and utilized both phase-velocity
and high-m filtering techniques. These method seem to be capable of
extending the meridional-flow measurements to the deep layers of the
convection zone, down to 0.7 R⊙. Typical uncertainties
for most depths within ± 35∘ latitude are less than 0.03
s. At higher latitudes, the uncertainties are about 0.06 s. There is a
significant abrupt decrease in the nature of the travel-time differences
for measurements that probe the bottom of the convection zone.
Title: A Full-Sun Magnetic Index from Helioseismology Inferences
Authors: González Hernández, I.; Díaz Alfaro, M.; Jain, K.; Tobiska,
W. K.; Braun, D. C.; Hill, F.; Pérez Hernández, F.
Bibcode: 2014SoPh..289..503G
Altcode:
Solar magnetic indices are used to model the solar irradiance and
ultimately to forecast it. However, the observation of such indices is
generally limited to the Earth-facing hemisphere of the Sun. Seismic
maps of the far side of the Sun have proven their capability to locate
and track medium-large active regions at the non-visible hemisphere. We
present here the possibility of using the average signal from these
seismic far-side maps, combined with similarly calculated near-side
maps, as a proxy to the full-Sun magnetic activity.
Title: Assessing Ring-Diagram Fitting Methods
Authors: Jain, K.; Tripathy, S. C.; Basu, S.; Baldner, C. S.; Bogart,
R. S.; Hill, F.; Howe, R.
Bibcode: 2013ASPC..478..193J
Altcode:
The ring-diagram technique is widely used to study oscillation mode
parameters and dynamics of the sub-surface layers of the Sun. In
this technique, the three-dimensional power spectrum is fitted to a
model to calculate mode parameters. The fitted velocities are then
inverted to infer the depth dependence of sub-surface flows. Here,
we examine the influence of various models on inferred quantities and
also compare results obtained with contemporaneous Dopplergrams from
SDO/HMI and GONG.
Title: Subsurface Flows in Active Region 11158
Authors: Jain, K.; Tripathy, S. C.; Komm, R.; González Hernández,
I.; Hill, F.
Bibcode: 2013ASPC..478..225J
Altcode:
We apply the ring-diagram technique to study the temporal evolution of
horizontal velocity in sub-photospheric layers beneath active regions
as they move across the solar disk. Here we present results for the
AR 11158 for six days and investigate how flows get organized within
the active region by the morphology of individual sunspots or vice
versa. We find abrupt changes in depth profiles for smaller regions
in going from one day to another, however the average flows for the
active region do not show significant temporal variation.
Title: Medium-Degree Global-Mode Frequency Shifts in Solar Cycles
23 and 24: Is There Any Difference?
Authors: Howe, R.; Komm, R.; Hill, F.
Bibcode: 2013ASPC..478..155H
Altcode:
It is well established that the frequencies of acoustic modes vary
with the solar cycle, being strongly correlated with the temporal
and spatial distribution of magnetic activity as measured by the
magnetic field strength or by intensity proxies. With nearly eighteen
years of data from GONG and MDI, we check for differences between the
sensitivity to the Kitt Peak magnetic index between the rising phases
of Solar Cycles 23 and 24. We find no significant difference.
Title: Are We Entering a Period of Reduced Activity or a Grand
Minima State?
Authors: Simoniello, R.; Jain, K.; Tripathy, S. C.; Baldner, C. S.;
Turck-Chièze, S.; Hill, F.
Bibcode: 2013ASPC..478..167S
Altcode:
Solar cycle 23 has been characterized by an unpredicted deepest
minimum in nearly a century, and solar cycle 24 has turned out to be
20% less strong than the previous cycle, against expectations. Are
the current solar dynamics indicative that we might enter a period
of reduced activity or even a Grand Minima state? To answer this
question, we investigated the properties of the cyclic behavior
of solar magnetic activity, characterized by the 11- and 2-year
periodicity, the latter also known as the quasi-biennial periodicity
(QBP). Recently it has been shown that the QBP signal might be the
cycle period related to the quadrupolar component of the magnetic
dynamo configuration. Observationally and theoretically, it has been
shown that this component might play a key role over period of reduced
activity by inducing a strong North-South asymmetry. We, therefore,
wonder if the QBP signatures might be used as a precursor of solar
magnetic activity. To this aim we used 17 years of Global Oscillation
Network Group (GONG) observations to investigate the signatures and
properties of the QBP in the dipolar and quadrupolar component of
p-mode frequency shifts and in the even-order splitting coefficients
of spherical degree ℓ = 0 - 120, as the latter are related to the
magnetic field strength and oblateness. The observational findings
seem to indicate that the QBP signal strength has been particularly
strong over the ascending phase of solar cycle 23, but suddenly in
2003 became weaker and has remained weak over the ascending phase of
solar cycle 24. We argue that the QBP, since 2003, suggested a week
solar cycle 24 compared to cycle 23.
Title: Solar Cycle Variation of High-Degree Acoustic Mode Frequencies
Authors: Tripathy, S. C.; Jain, K.; Komm, R. W.; Hill, F.
Bibcode: 2013ASPC..478..221T
Altcode:
We investigate the temporal variations of the high-degree mode
frequencies measured over localized regions of the Sun though
the technique of ring-diagrams. We observe that the high-degree
mode frequencies have a solar cycle variation similar to those of
intermediate-degree modes but ten times greater. We also find that
the averaged frequency shifts are linearly correlated with routinely
measured solar activity indices e.g. 10.7 cm radio flux. We do not,
however, find any evidence of a quadratic relation between the
frequencies of individual multiplets and solar activity indices as
reported earlier from the study of global high-degree modes.
Title: Solar-Cycle Variation of Subsurface Zonal Flow Derived from
Ring-Diagram Analysis
Authors: Komm, R.; Howe, R.; González Hernández, I.; Hill, F.;
Bogart, R. S.; Haber, D.
Bibcode: 2013ASPC..478..217K
Altcode:
We study the solar-cycle variation of the zonal flow in the near-surface
layers of the solar convection zone from the surface to a depth of
16 Mm. We have analyzed Global Oscillation Network Group (GONG)
and Helioseismic and Magnetic Imager (HMI) Dopplergrams with the
ring-diagram analysis covering about 12 years combined. The zonal
flow varies with the solar cycle showing faster-than-average flows
equatorward of the mean latitude of activity and slower-than-average
flows on the poleward side. The bands of fast zonal flow appear at
mid-latitudes about two years before magnetic activity of cycle 24
is seen. The poleward branch of this variation is visible as bands of
fast zonal flow near 50° latitude in both HMI and GONG data.
Title: Where to go from here: The Future of Helio- and
Astero-seismology
Authors: Hill, F.; Baldner, C. S.; García, R. A.; Roth, M.;
Schunker, H.
Bibcode: 2013ASPC..478..401H
Altcode:
While this conference is partly a look back over 50 years of
helioseismology, we also look forward into the future. Upcoming
paths of research in the near-term include understanding the effects
due to strong surface magnetic fields, including mode conversion, in
the solar atmosphere and how they affect subsurface inferences; the
place of the Sun in the asteroseismic universe, and the relationship
of subsurface dynamics and solar activity as forecast tools for
space weather. These paths will motivate new technical approaches of
multi-height/multi-wavelength solar observations; numerical models
of wave propagation in magnetized plasmas; further understanding of
systematic errors; and combined analyses of vector magnetic field
measurements and helioseismic data. The next major programmatic
steps will be the advent of multi-viewpoint solar space missions,
and the development of a new multi-purpose solar synoptic observing
network on the ground. For asteroseismology, the PLATO mission and
the ground-based SONG program will provide a wealth of new data.
Title: Variation of solar oscillation frequencies in solar cycle 23
and their relation to sunspot area and number (Corrigendum)
Authors: Jain, R.; Tripathy, S. C.; Watson, F. T.; Fletcher, L.;
Jain, K.; Hill, F.
Bibcode: 2013A&A...560C...1J
Altcode:
No abstract at ADS
Title: Analysis of Active Region 11339 using Multi-Spectral Data
Authors: Tripathy, S. C.; Jain, K.; Howe, R.; Bogart, R. S.; Basu,
S.; Hill, F.
Bibcode: 2013ASPC..478..237T
Altcode:
We apply the local helioseismic technique of ring-diagrams to Doppler
and intensity images from Helioseismic Magnetic Imager and Atmospheric
Imaging Assembly on board the Solar Dynamics Observatory and investigate
the variation in high-degree mode frequencies and sub-surface flows of
a complex active region 11339. After subtracting the frequencies of the
quiet region from the active region, we find a reasonable agreement
between the frequencies measured from different observables. We also
observe that the depth profiles of zonal and meridional components
of the horizontal subsurface flow agree with each other within three
sigma if the contribution of quiet regions is removed.
Title: Fifty Years of Seismology of the Sun and Stars
Authors: Jain, K.; Tripathy, S. C.; Hill, F.; Leibacher, J. W.;
Pevtsov, A. A.
Bibcode: 2013ASPC..478.....J
Altcode:
No abstract at ADS
Title: The Torsional Oscillation and the Timing of the Solar Cycle:
Is it Maximum Yet?
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
Larson, T. P.; Schou, J.; Thompson, M. J.
Bibcode: 2013ASPC..478..303H
Altcode:
After the late start to Cycle 24 there are some indications that
activity may have peaked as early as late 2011 and that the polar-field
reversal has already occurred in the North. We use helioseismic
measurements of the migrating zonal flow pattern known as the torsional
oscillation to estimate the length of the solar cycle, and find that
it has held steady at about 12.3 years since late 2009, which would
point to solar maximum in 2013 as expected.
Title: Magnetic Polarity Streams and Subsurface Flows
Authors: Howe, R.; Baker, D.; Harra, L.; van Driel-Gesztelyi, L.;
Komm, R.; Hill, F.; González Hernández, I.
Bibcode: 2013ASPC..478..291H
Altcode:
An important feature of the solar cycle is the transport of unbalanced
magnetic flux from active regions towards the poles, which eventually
results in polarity reversal. This transport takes the form of distinct
“polarity streams” that are visible in the magnetic butterfly
diagram. We compare the poleward migration rate estimated from such
streams to that derived from the subsurface meridional flows measured
in helioseismic data from the GONG network since 2001, and find that
the results are in reasonable agreement.
Title: Subsurface Meridional Flow from HMI Using the Ring-Diagram
Pipeline
Authors: Komm, R.; González Hernández, I.; Hill, F.; Bogart, R.;
Rabello-Soares, M. C.; Haber, D.
Bibcode: 2013SoPh..287...85K
Altcode: 2012SoPh..tmp..177K
We have determined the meridional flows in subsurface layers for 18
Carrington rotations (CR 2097 to 2114) analyzing high-resolution
Dopplergrams obtained with the Helioseismic and Magnetic Imager
(HMI) instrument onboard the Solar Dynamics Observatory (SDO). We are
especially interested in flows at high latitudes up to 75∘
in order to address the question whether the meridional flow remains
poleward or reverses direction (so-called counter cells). The flows
have been determined in depth from near-surface layers to about 16 Mm
using the HMI ring-diagram pipeline. The measured meridional flows show
systematic effects, such as a variation with the B0-angle
and a variation with central meridian distance (CMD). These variations
have been taken into account to lead to more reliable flow estimates
at high latitudes. The corrected average meridional flow is poleward
at most depths and latitudes with a maximum amplitude of about 20~m
s^{-1} near 37.5∘ latitude. The flows are more poleward
on the equatorward side of the mean latitude of magnetic activity at
22∘ and less poleward on the poleward side, which can be
interpreted as convergent flows near the mean latitude of activity. The
corrected meridional flow is poleward at all depths within ±
67.5∘ latitude. The corrected flow is equatorward only at
75∘ latitude in the southern hemisphere at depths between
about 4 and 8 Mm and at 75∘ latitude in the northern
hemisphere only when the B0 angle is barely large enough to
measure flows at this latitude. These counter cells are most likely the
remains of an insufficiently corrected B0-angle variation
and not of solar origin. Flow measurements and B0-angle
corrections are difficult at the highest latitude because these flows
are only determined during limited periods when the B0
angle is sufficiently large.
Title: Latest Results Found with Ring-Diagram Analysis
Authors: Baldner, C. S.; Basu, S.; Bogart, R. S.; Burtseva, O.;
González Hernández, I.; Haber, D.; Hill, F.; Howe, R.; Jain, K.;
Komm, R. W.; Rabello-Soares, M. C.; Tripathy, S.
Bibcode: 2013SoPh..287...57B
Altcode: 2012SoPh..tmp..294B
Ring-diagram analysis is a helioseismic tool useful for studying
the near-surface layers of the Sun. It has been employed to study
near-surface shear, meridional circulation, flows around sunspots,
and thermal structure beneath active regions. We review recent results
obtained using ring-diagram analysis, state some of the more important
outstanding difficulties in the technique, and point out several
extensions to the technique that are just now beginning to bear fruit.
Title: Solar cycle and quasi-biennial variations in helioseismic
frequencies
Authors: Tripathy, Sushanta C.; Jain, Kiran; Simoniello, Rosaria;
Hill, Frank; Turck-Chièze, Sylvaine
Bibcode: 2013IAUS..294...73T
Altcode:
The prolonged period of solar minimum between cycles 23 and 24 has
invoked a great deal of interest to understand the origin of the
unusually low solar activity. Even though the origin of solar activity
is believed to lie in the shear layer at the base of the convection
zone, the analysis of helioseismic data seem to orientate us toward
the near surface. In this context, we analyze the signature of the
quasi-biennial periodicity seen in the oscillation frequencies which
may provide additional constraints on the solar dynamo models.
Title: Validating the Ring-diagram Flows through Numerical Simulations
Authors: Tripathy, Sushanta; Jain, K.; Basu, S.; Bogart, R. S.; Howe,
R.; Hill, F.
Bibcode: 2013SPD....44...90T
Altcode:
Among many techniques of local helioseismology, the ring-diagram
method has been quite popular because of its ability to quickly analyze
vast amounts of high-resolution data. In ring analysis, the speed and
direction of horizontal flows beneath the solar surface are assessed
by inverting fitted surface velocities for a given set of modes. Here
we discuss the validationof the inversion technique through the use
of supergranulation scale hydrodynamic numerical simulations.
Title: Solar oscillations in cycle 24 ascending
Authors: Jain, Kiran; Tripathy, Sushanta; Hill, Frank; Larson, Timothy
Bibcode: 2013JPhCS.440a2023J
Altcode:
Solar oscillation frequencies are known to follow the trend of
solar cycle and show a strong correlation with various activity
indices. However, the extended minimum between cycles 23 and 24 has
raised several questions on the correlation between frequencies and
solar activity where frequencies with different mode sets sensed
different minima. In this paper, we analyze intermediate-degree mode
frequencies as the Sun emerges from the unusually long period of minimal
magnetic activity to study their behaviour with activity indices and
compare results with the corresponding phase of cycle 23. We show that
a model based on the rising phase of cycle 23 is a good predictor for
behaviour in the rising phase of cycle 24.
Title: Temporal Variations of High-Degree Solar p-Modes using
Ring-Diagram Analysis
Authors: Burtseva, Olga; Tripathy, Sushant; Bogart, Richard; Jain,
Kiran; Howe, Rachel; Hill, Frank; Rabello-Soares, Maria Cristina
Bibcode: 2013JPhCS.440a2027B
Altcode: 2013arXiv1303.6722B
We study temporal variations in the amplitudes and widths of high-degree
acoustic modes by applying the ring-diagram technique to the GONG+,
MDI and HMI Dopplergrams during the declining phase of cycle 23 and
rising phase of cycle 24. The mode parameters from all three instruments
respond similarly to the varying magnetic activity. The mode amplitudes
and widths show consistently lower variation due to smaller magnetic
activity in cycle 24 as compared to the previous solar cycle.
Title: Far-side helioseismic maps: the next generation
Authors: González Hernández, Irene; Lindsey, Charles; Braun,
Douglas C.; Bogart, Richard S.; Scherrer, Philip H.; Hill, Frank
Bibcode: 2013JPhCS.440a2029G
Altcode:
For more than a decade, far-side seismic maps of medium-to-large active
regions have proven their capability as a space weather forecasting
tool. In the last few years, these maps have started to serve another
purpose: complementing the front side observations that are input to
different solar models. Photospheric flux transport as well as solar
spectral irradiance models have been shown to produce improved results
when incorporating the far-side seismic maps as well as providing
better forecasting. The challenge for the future is twofold: Far-side
seismic monitoring needs to be more sensitive, and it needs to offer
more information. We present here initial steps towards fulfilling
these goals using higher resolution input images, adding extra skips
to the analysis and changing the presentation of the maps.
Title: How do the active region subsurface flow properties differ
based on hemisphere and CME association?
Authors: Reinard, Alysha; Komm, R.; Hill, F.
Bibcode: 2013shin.confE..60R
Altcode:
The investigation of subsurface flows beneath active regions offers
insight into the processes that occur prior to and during flare/CME
eruptions. We present new research on this topic that considers both
the flare location (specifically northern vs southern hemisphere) and
the presence or absence of an associated CME to determine whether there
is any difference in the subsurface flow pattern. We find essentially
no difference in subsurface flows below eruptive (i.e. CME associated)
and non-eruptive flares, indicating that the underlying processes
are similar in each case and the magnetic configuration of the active
region determines the eruptive potential. We do find a difference in
events originating in the northern and southern hemisphere with the
kinetic helicity density at the deepest layers being of opposite signs
in each hemisphere. This effect is stronger for CME-associated flares,
perhaps because such flares tend to be larger.
Title: Multi-spectral study of acoustic mode parameters and
sub-surface flows
Authors: Jain, Kiran; Tripathy, S.; Basu, S.; Bogart, R.; González
Hernández, I.; Hill, F.; Howe, R.
Bibcode: 2013JPhCS.440a2012J
Altcode:
Simultaneous measurements at different wavelengths offer the prospect
of studying the sensitivity of helioseismic inferences to the choice of
observing height both in quiet-Sun and magnetically active regions. In
this context, we use observations from space-borne measurements from
the Solar Dynamics Observatory and ground-based Global Oscillation
Network Group to analyze high-degree acoustic mode parameters and
sub-surface flows obtained with different observables. We also quantify
differences and interpret results in the framework of the formation
height in solar atmosphere.
Title: Multi-wavelength analysis of active regions using ring-diagram
technique
Authors: Tripathy, S. C.; Jain, K.; Howe, R.; Bogart, R.; Basu, S.;
Rabello-Soares, M. C.; Hill, F.
Bibcode: 2013JPhCS.440a2026T
Altcode:
With the availability of high-cadence and high-resolution Doppler and
intensity images from the Solar Dynamics Observatory's Helioseismic
Magnetic Imager (HMI) and Atmospheric Imager Assembly (AIA), we analyze
the characteristics of high-degree solar acoustic modes in active
regions. We apply the ring-diagram technique to Doppler, continuum
intensity measurements from HMI, and intensity images from AIA 1600
Å and 1700 Å passband to examine the high-degree mode parameters
and sub-surface horizontal flows.
Title: Daily Normalized Helicity of Subsurface Flows
Authors: Komm, Rudolf; Reinard, A.; Hill, F.
Bibcode: 2013shin.confE..44K
Altcode:
Flare-productive active regions are associated with subsurface flows
with large values of kinetic helicity density. Kinetic helicity is
related to mixing and turbulence of fluids. Reinard et al. 2010 have
developed a parameter that captures the variation of kinetic helicity
with depth and time, the so-called Normalized Helicity Gradient Variance
(NHGV). This parameter increases 2-3 days before a flare occurs and
the NHGV values for flaring and non-flaring active regions represent
clearly separate populations. We derive subsurface flows from the
surface to a depth of 16 Mm using GONG Dopplergrams analyzed with the
ring-diagram technique. From the measured velocities, we calculate
kinetic helicity density as a function of position on the solar
disk. We will then calculate the NHGV parameter exploring different
normalization schemes and depth ranges. We will calculate daily NHGV
maps of the solar disk for different levels of magnetic activity. We
will present the latest results.
Title: The High-latitude Branch of the Solar Torsional Oscillation
in the Rising Phase of Cycle 24
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
Larson, T. P.; Rempel, M.; Schou, J.; Thompson, M. J.
Bibcode: 2013ApJ...767L..20H
Altcode:
We use global heliseismic data from the Global Oscillation Network
Group, the Michelson Doppler Imager on board the Solar and Heliospheric
Observatory, and the Helioseismic and Magnetic Imager on board the Solar
Dynamics Observatory, to examine the behavior, during the rising phase
of Solar Cycle 24, of the migrating zonal flow pattern known as the
torsional oscillation. Although the high-latitude part of the pattern
appears to be absent in the new cycle when the flows are derived by
subtracting a mean across a full solar cycle, it can be seen if we
subtract the mean over a shorter period in the rising phase of each
cycle, and these two mean rotation profiles differ significantly
at high latitudes. This indicates that the underlying high-latitude
rotation has changed; we speculate that this is in response to weaker
polar fields, as suggested by a recent model.
Title: A New Multi-Wavelength Synoptic Network for Solar Physics
and Space Weather
Authors: Hill, Frank; Roth, Markus; Thompson, Michael
Bibcode: 2013EGUGA..1511892H
Altcode:
Continuous solar observations are important for many research topics
in solar physics, such as magnetic field evolution, flare and CME
characteristics, and p-mode oscillation measurements. In addition,
space weather operations require constant streams of solar data as
input. The deployment of a number of identical instruments around
the world in a network has proven to be a very effective strategy for
obtaining nearly continuous solar observations. The financial costs of
a network are 1-2 orders of magnitude lower than space-based platforms;
network instrumentation can be easily accessed for maintenance and
upgrades; and telemetry bandwidth is readily available. Currently,
there are two solar observing networks with consistent instruments:
BiSON and GONG, both designed primarily for helioseismology. In
addition, GONG has been augmented with continual magnetic field
measurements and H-alpha imagery, with both being used for space
weather operational purposes. However, GONG is now 18 years old and
getting increasingly more challenging to maintain. There are also at
least three scientific motivations for a multi-wavelength network:
Recent advances in helioseismology have demonstrated the need for
multi-wavelength observations to allow more accurate interpretation
of the structure and dynamics below sunspots. Vector magnetometry
would greatly benefit from multi-wavelength observations to provide
height information and resolve the azimuthal ambiguity. Finally,
space weather operations always need a consistent reliable source of
continual solar data. This presentation will outline the scientific
need for a multi-wavelength network, and discuss some concepts for
the design of the instrumentation. A workshop on the topic will be
held in Boulder this April.
Title: The Quasi-biennial Periodicity as a Window on the Solar
Magnetic Dynamo Configuration
Authors: Simoniello, R.; Jain, K.; Tripathy, S. C.; Turck-Chièze,
S.; Baldner, C.; Finsterle, W.; Hill, F.; Roth, M.
Bibcode: 2013ApJ...765..100S
Altcode: 2012arXiv1210.6796S
Manifestations of the solar magnetic activity through periodicities
of about 11 and 2 years are now clearly seen in all solar activity
indices. In this paper, we add information about the mechanism driving
the 2-year period by studying the time and latitudinal properties of
acoustic modes that are sensitive probes of the subsurface layers. We
use almost 17 years of high-quality resolved data provided by the Global
Oscillation Network Group to investigate the solar cycle changes in
p-mode frequencies for spherical degrees l from 0 to 120 and 1600 μHz
<=ν <= 3500 μHz. For both periodic components of solar activity,
we locate the origin of the frequency shift in the subsurface layers
and find evidence that a sudden enhancement in amplitude occurs in just
the last few hundred kilometers. We also show that, in both cases, the
size of the shift increases toward equatorial latitudes and from minimum
to maximum solar activity, but, in agreement with previous findings,
the quasi-biennial periodicity (QBP) causes a weaker shift in mode
frequencies and a slower enhancement than that caused by the 11-year
cycle. We compare our observational findings with the features predicted
by different models, that try to explain the origin of this QBP and
conclude that the observed properties could result from the beating
between a dipole and quadrupole magnetic configuration of the dynamo.
Title: Ring-Diagram Analysis of Active Regions using HMI and AIA data
Authors: Tripathy, S. C.; Jain, K.; Howe, R.; Bogart, R.; Basu, S.;
Hill, F.
Bibcode: 2013enss.confE..42T
Altcode:
With the launch of the Helioseismic and Magnetic Imager on board the
Solar Dynamics Observatory, high-resolution observations of the Sun are
available in Doppler velocity and continuum intensity. In addition,
data is also available from the Atmospheric Imaging Assembly in 160
and 170 nm bands, which are useful for helioseismic studies. Here
we use the ring-diagram technique and analyze six active regions,
simple and complex, observed simultaneously in different wavelengths,
and focus on the characteristics of high-degree modes e.g. frequencies
and asymmetry parameters. We further investigate the dependence of
sub-surface flows on the choice of the observables to comprehend
the effect of the observing heights, which may be important in
multi-wavelength local helioseismic studies.
Title: Acoustic Mode Frequencies of the Sun During the Minimum Phase
Between Solar Cycles 23 and 24
Authors: Tripathy, S. C.; Jain, K.; Hill, F.
Bibcode: 2013SoPh..282....1T
Altcode: 2012SoPh..tmp..239T; 2012arXiv1210.0060T
We investigate the spatial and temporal variations of the high-degree
mode frequencies calculated over localized regions of the Sun during the
extended minimum phase between solar cycles 23 and 24. The frequency
shifts measured relative to the spatial average over the solar disk
indicate that the correlation between the frequency shift and magnetic
field strength during the low-activity phase is weak. The disk-averaged
frequency shifts computed relative to a minimal activity period also
reveal a moderate correlation with different activity indices, with
a maximum linear correlation of about 72 %. From the investigation of
the frequency shifts at different latitudinal bands, we do not find a
consensus period for the onset of solar cycle 24. The frequency shifts
corresponding to most of the latitudes in the northern hemisphere and
30° south of the equator indicate the minimum epoch to be February
2008, which is earlier than inferred from solar activity indices.
Title: Helioseismic analysis of active regions using HMI and AIA data
Authors: Tripathy, S. C.; Jain, K.; Howe, R.; Bogart, R. S.; Hill, F.
Bibcode: 2012AN....333.1013T
Altcode:
We apply the ring-diagram technique to analyze three active regions
located near the central meridian. Using Doppler, continuum intensity,
and line depth images from the Helioseismic Magnetic Imager (HMI),
we investigate the variation in the high-degree mode asymmetry,
frequencies, and horizontal flows. We find that the sub-surface zonal
and meridional flows do not change significantly with the choice of
different observables representing different heights in the solar
photosphere, while the mode frequencies differ. We also examine the
2-d acoustic power distribution using data from HMI and the Atmospheric
Imaging Assembly (AIA) 1600 and 1700 Å, bands.
Title: No Evidence Supporting Flare-Driven High-Frequency Global
Oscillations
Authors: Richardson, M.; Hill, F.; Stassun, K. G.
Bibcode: 2012SoPh..281...21R
Altcode: 2012SoPh..tmp..168R; 2012arXiv1206.6010R
The underlying physics that generates the excitations in the
global low-frequency (< 5.3 mHz) solar acoustic power spectrum
is a well-known process that is attributed to solar convection;
however, a definitive explanation as to what causes excitations in
the high-frequency regime (> 5.3 mHz) has yet to be found. Karoff
and Kjeldsen (Astrophys. J. 678, 73 - 76, 2008) concluded that there
is a correlation between solar flares and the global high-frequency
solar acoustic waves. We have used Global Oscillation Network Group
(GONG) helioseismic data in an attempt to verify the Karoff and Kjeldsen
(2008) results as well as compare the post-flare acoustic power spectrum
to the pre-flare acoustic power spectrum for 31 solar flares. Among
the 31 flares analyzed, we observe that a decrease in acoustic power
after the solar flare is just as likely as an increase. Furthermore,
while we do observe variations in acoustic power that are most likely
associated with the usual p-modes associated with solar convection,
these variations do not show any significant temporal association with
flares. We find no evidence that consistently supports flare-driven
high-frequency waves.
Title: Variation of solar oscillation frequencies in solar cycle 23
and their relation to sunspot area and number
Authors: Jain, R.; Tripathy, S. C.; Watson, F. T.; Fletcher, L.;
Jain, K.; Hill, F.
Bibcode: 2012A&A...545A..73J
Altcode:
Aims: Studying the long term evolution of the solar acoustic
oscillations is necessary for understanding how the large-scale solar
dynamo operates. In particular, an understanding of the solar cycle
variation in the frequencies of solar oscillations can provide a
powerful diagnostic tool for constraining various dynamo models. In
this work, we report the temporal evolution of solar oscillations
for the solar cycle 23, and correlate with solar magnetic activity
indices.
Methods: We use solar oscillation frequencies obtained
from the Michelson Doppler Imager on board the Solar and Heliospheric
Observatory, correlate them with the sunspot number provided by the
international sunspot number, RI, and compare them with the
sunspot number calculated with the Sunspot Tracking And Recognition
Algorithm (STARA).
Results: We find that the mean frequency
shifts correlate very well with the sunspot numbers obtained from
two different datasets. We also find a hysteresis-type behaviour
for the STARA sunspot area and mean magnetic field strength for the
different phases of the solar cycle. The increase in solar oscillation
frequencies precedes slightly the increase in total sunspot area and
the mean magnetic field strength for the solar cycle 23. We briefly
discuss the cyclic behaviour in the context of p-mode frequencies.
Title: Subsurface Flows in and Around Active Regions with Rotating
and Non-rotating Sunspots
Authors: Jain, K.; Komm, R. W.; González Hernández, I.; Tripathy,
S. C.; Hill, F.
Bibcode: 2012SoPh..279..349J
Altcode: 2012arXiv1205.2356J
The temporal variation of the horizontal velocity in sub-surface layers
beneath three different types of active region is studied using the
technique of ring diagrams. In this study, we select active regions
(ARs) 10923, 10930, 10935 from three consecutive Carrington rotations:
AR 10930 contains a fast-rotating sunspot in a strong emerging active
region while other two have non-rotating sunspots with emerging flux
in AR 10923 and decaying flux in AR 10935. The depth range covered is
from the surface to about 12 Mm. In order to minimize the influence
of systematic effects, the selection of active and quiet regions is
made so that these were observed at the same heliographic locations
on the solar disk. We find a significant variation in both components
of the horizontal velocity in active regions as compared to quiet
regions. The magnitude is higher in emerging-flux regions than in the
decaying-flux region, in agreement with earlier findings. Further,
we clearly see a significant temporal variation in depth profiles
of both zonal and meridional flow components in AR 10930, with the
variation in the zonal component being more pronounced. We also notice
a significant influence of the plasma motion in areas closest to the
rotating sunspot in AR 10930, while areas surrounding the non-rotating
sunspots in all three cases are least affected by the presence of the
active region in their neighborhood.
Title: Subsurface flows associated with eruptive and non-eruptive
flares
Authors: Reinard, Alysha; Krista, Larisza; Komm, Rudi; Hill, Frank
Bibcode: 2012shin.confE.144R
Altcode:
Subsurface flows beneath active regions offer insight into the processes
that occur prior to and during flare/CME eruptions. We have developed
a technique to forecast solar flares based on subsurface flows. We
present new research on this topic that involves comparing eruptive
and non-eruptive flares to determine whether there is any difference
in the flow pattern. We also look at active region characteristics
associated with these events.
Title: Temporal Variation of Subsurface Flows in Active Regions
Authors: Komm, Rudolf W.; Jain, K.; Tripathy, S. C.; Gonzalez
Hernandez, I.; Hill, F.
Bibcode: 2012shin.confE.121K
Altcode:
We apply the ring-diagram technique to study the temporal variation of
horizontal velocity in sub-photospheric layers beneath active regions
as they move across the solar disk. We categorize these active regions
on the basis of their dynamical characteristics and investigate
how velocity components beneath rotating sunspots differ from that
in non-rotating sunspots. Our study clearly shows that there is a
singnificant temporal variation in depth profiles of both zonal and
meridional components in active regions with rotating sunspots while
these variations remain small for non-rotating sunspots.
Title: Multi-Wavelength Helioseismology: Power and Phase Maps in an
Active Region
Authors: Hill, Frank; Howe, R.; Jain, K.; Tripathy, S.; Bogart, R.;
Baldner, C.; Haber, D.
Bibcode: 2012AAS...22020504H
Altcode:
The phase and amplitude of acoustic waves in the solar atmosphere is
modified in the presence of magnetic regions. Waves at frequencies
above the acoustic cutoff show a complex pattern of changes depending
on both temporal frequency and the height of formation of the quantity
observed, with phase shifts as well as enhancement and suppression of
power surrounding the active region. We show some examples of these
effects in Doppler and intensity observations from the Helioseismic
and Magnetic Imager and in the 1600 and 1700 Angstrom bands of the
Atmospheric Imaging Array aboard the Solar Dynamics Observatory,
probing the photosphere and lower chromosphere.
Title: The Evolution of Large-Scale Subsurface Flow Patterns in
the Sun
Authors: Bogart, Richard S.; Baldner, C. S.; Basu, S.; Burtseva, O.;
Gonzalez-Hernandez, I.; Haber, D. A.; Hill, F.; Howe, R.; Jain, K.;
Komm, R. W.; Rabello-Soares, M. C.; Tripathy, S.
Bibcode: 2012AAS...22020509B
Altcode:
Ring-diagram analysis permits us to infer large-scale flow fields at the
photosphere and down to depths of about 0.95 R. We present comparisons
of the mean zonal and meridional velocity profiles determined from
uniform analysis techniques applied to three observational data sets,
those from the SDO/HMI and SOHO/MDI missions and the GONG project,
over the last 18 years. We pay special attention to measurements
obtained during the summer of 2010, when observations from all three
observatories were available. We discuss systematic effects affecting
the individual datasets in order to analyse evolution of global flows
over the time scale of the solar cycle.
Title: Solar Tiling And Tracking Extraction Service Using The VSO
API As The Backend
Authors: Davey, Alisdair R.; Suarez Sola, I.; Gonzalez Suarez, E.;
Gonzalez Hernandez, I.; Hill, F.; Hourcle, J.; VSO Team
Bibcode: 2012AAS...22020125D
Altcode:
In solar research it is often necessary to isolate areas of the
Sun for further studies. Most scientists develop their own set of
tools to extract the areas in which they are interested and build
temporal series that include selected solar phenomena, however the
overwhelming amount of available solar data, especially since the
launch of SDO (Solar Dynamics Observatory), makes it difficult for
researchers to access selected sets of data without downloading very
large images. With the help of one of the modules of the GONG
(Global Oscillation Network Group) "ring-diagram'"pipeline and the VSO
(Virtual Solar Observatory) API (Application Programming Interface),
we build an asynchronous Solar data cube extraction service for GONG,
SOLIS (Synoptic Optical Long-term Investigations of the Sun) and SDO
data. The service has a simple ad-hoc HTML front end for researchers
to access it. The data cube extraction service takes as input as
set of solar coordinates, a period of time, the size of the requested
area, the spatial resolution needed, projection to use (cylindrical or
postel) and the images to work on. The service then tracks the sun and
corrects for standard solar rotation effects. The extracted files are
saved to a staging area and the user is notified via email or a SOAP
callback function that the processed images are available for download.
Title: Data From The HMI Ring-Diagram Pipelines
Authors: Bogart, Richard S.; Baldner, C. S.; Basu, S.;
Gonzalez-Hernandez, I.; Haber, D. A.; Hill, F.; Howe, R.; Jain, K.;
Komm, R. W.; Rabello-Soares, M. C.; Tripathy, S.
Bibcode: 2012AAS...22020512B
Altcode:
The HMI data pipeline for measurement of sub-surface flows with
ring-diagram analysis has been running for nearly two years, and
virtually all HMI Doppler data have been analyzed. Nearly 5 million
local-area power spectra have been produced and fitted for regions of
various sizes, and inversions for the depth structure of flows have
been performed for over 150,000 of the larger regions. The pipeline
for determination of the sub-surface thermal structure is still under
active development, with test results for a number of strong active
regions currently available for analysis. We describe the ring-diagram
pipelines, report on their performance, describe the data products
available, and discuss outstanding problems and issues for further
development.
Title: The Virtual Solar Observatory: What Are We Up To Now?
Authors: Gurman, Joseph B.; Hill, F.; Suàrez-Solà, F.; Bogart, R.;
Amezcua, A.; Martens, P.; Hourclé, J.; Hughitt, K.
Bibcode: 2012AAS...22020124G
Altcode:
In the nearly ten years of a functional Virtual Solar Observatory (VSO),
http://virtualsolar.org/, we have made it possible to query and access
sixty-seven distinct solar data products and several event lists from
nine spacecraft and fifteen observatories or observing networks. We
have used existing VSO technology, and developed new software, for
a distributed network of sites caching and serving SDO HMI and/or
AIA data. We have also developed an application programming interface
(API) that has enabled VSO search and data access capabilities in IDL,
Python, and Java. We also have quite a bit of work yet to do,
including completion of the implementation of access to SDO EVE data,
and access to some nineteen other data sets from space- and ground-based
observatories. In addition, we have been developing a new graphic user
interface that will enable the saving of user interface and search
preferences. We solicit advice from the community input prioritizing
our task list, and adding to it.
Title: Latest Results on the Torsional Oscillation and Solar Cycle 25
Authors: Hill, Frank; Howe, R.; Schou, J.; Thompson, M.; Larson, T.;
Komm, R.
Bibcode: 2012AAS...22012302H
Altcode:
The Torsional Oscillation in the Sun is a zonal (East-West) flow
that is slightly faster than the background differential rotation
profile. The location of this flow slowly migrates in latitude over
a period of several years. There are two branches of the flow: an
equatorward branch that underlies the active regions, and a poleward
branch. The timing of the equatorward migration is correlated with the
timing of the solar cycle such that the activity for a cycle appears
when the center of the flow reaches latitude 25 degrees. In addition,
the poleward branch appears about 12 years prior to the activity for
a cycle. Thus we should have observed the onset of Cycle 25 in 2008,
but did not. This poster will update the observations to 2012, and
present a new analysis that shows that the Cycle 25 flow appeared
in 2010, but was hidden by a change in the background differential
rotation profile. These results suggest that the next minimum will be
two years longer than average, and that Cycle 25 will begin in 2022.
Title: Vorticity of Subsurface Flows of Emerging and Decaying
Active Regions
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 2012SoPh..277..205K
Altcode:
We study the temporal variation of the vorticity of subsurface flows
of 828 active regions and 977 quiet regions. The vorticity of these
flows is derived from measured subsurface velocities. The horizontal
flows are determined by analyzing high-resolution Global Oscillation
Network Group Doppler data with ring-diagram analysis covering
a range of depths from the surface to about 16 Mm. The vertical
velocity component is derived from the divergence of the measured
horizontal flows using mass conservation. We determine the change in
unsigned magnetic flux density during the disk passage of each active
region using Michelson Doppler Imager (MDI) magnetograms binned to
the ring-diagram grid with centers spaced by 7.5° ranging ± 52.5°
in latitude and central meridian distance with an effective diameter
of 15° after apodization. We then sort the data by their flux change
from decaying to emerging flux and divide the data into five subsets
of equal size. We find that the vorticity of subsurface flows increases
during flux emergence and decreases when active regions decay. For flux
emergence, the absolute values of the zonal and meridional vorticity
components show the most coherent variation with activity, while for
flux decrease the strongest signature is in the absolute values of the
meridional and vertical vorticity components. The temporal variation of
the enstrophy (residual vorticity squared) is thus a good indicator for
either flux increase or decrease. There are some indications that the
increase in vorticity during flux emergence happens about a day later
at depths below about 8 Mm compared to layers shallower than about
4 Mm. This timing difference might imply that the vorticity signal
analyzed here is caused by the interaction between magnetic flux and
turbulent flows near the solar surface. There are also hints that the
vorticity decrease during flux decay begins about a day earlier at
layers deeper than about 8 Mm compared to shallower ones. However, the
timing difference between the change at different depths is comparable
to the time step of the analysis.
Title: Far-side seismic maps with HMI
Authors: Gonzalez Hernandez, I.; Lindsey, C. A.; Bogart, R. S.;
Scherrer, P. H.; Hill, F.
Bibcode: 2011AGUFMSH12A..01G
Altcode:
Seismic maps of the far side of the Sun have proven their capability
to locate and track medium to large active regions on the non-visible
hemisphere. Waves that travel all the way from the far side to the
front side carry information of the magnetic perturbations that they
encounter. The seismic holography technique makes use of the observation
of waves at the front side of the Sun and compares them to a model to
map areas of strong magnetic field on the far side. Recent improvements
to these maps include a more accurate determination of the location of
the active region, automatic highlighting of candidates, and calibration
in terms of the magnetic field strength. Since the launch of SDO,
the Helioseismic Magnetic Imager(HMI) has been providing maps of the
far-side activity. We discuss here strategies to optimize these far-side
maps as well as how to include extra information (such as realistic
error estimates and area determination) in order to use these maps as
input to irradiance and photospheric flux-transport models. Far-side
direct observations from STEREO will help to reach these goals.
Title: Comparison of STEREO's Farside Observations of Solar Activity
and Predictions from the Global Oscillations Network Group (GONG)
Authors: Liewer, P. C.; Hall, J. R.; Misrak, A.; Gonzalez Hernandez,
I.; Hill, F.; Thompson, W. T.; De Jong, E. M.
Bibcode: 2011AGUFMSH13A1926L
Altcode:
Beginning February 18, 2011, the STEREO mission, for the first
time, gave us an "All Sun" view of the entire corona in extreme
ultraviolet (EUV) light. Here, we compare STEREO/EUVI views of
solar activity on the farside to predictions of far side strong
magnetic field regions from helioseismology using National Solar
Observatory/ Global Oscillation Network Group (GONG) observations
(see http://gong.nso.edu/data/farside/). The GONG project produces
"All Sun" Carrington maps of strong magnetic field regions; farside
regions with a probability of 70% or higher are labeled. We have
produced "All Sun" Carrington maps of coronal magnetic activity by
combining nearly simultaneous STEREO A & B EUVI data and SDO
AIA data at each of the four EUVI wavelengths. We then visually
determine whether or not magnetic activity is seen in the corona
(as evidenced by brightening in EUV) at the locations predicted by
GONG. We have analyzed all GONG farside predictions from February to
June 2011. For 139 of 157 comparisons (89%), activity is observed in
the corona by STEREO A or B. For 18 predictions, no activity was seen
at the predicted region. Results from the analysis of the location of
the false predictions relative to Earth will also be presented.
Title: Obituary: Clifford G. Toner (1959-2009)
Authors: Hill, Frank
Bibcode: 2011BAAS...43..022H
Altcode:
Cliff Toner passed away unexpectedly at home in Tucson, Arizona on
March 29, 2009. For most of his career, Cliff was involved with the
Global Oscillation Network Group (GONG), a facility of the National
Solar Observatory in Tucson, Arizona. GONG is a set of instruments
around the world to observe the inside of the sun using the sound
that is trapped below the solar surface. This science is called
helioseismology. Cliff Toner was born on December 8, 1959 in New
Westminster, British Columbia near the western coast of Canada. After
receiving his B.Sc. in Physics & Astronomy at the University of
British Columbia at Vancouver in 1981, he headed east to the University
of Western Ontario in London. His graduate school period was spent
in collaboration with David F. Gray, with whom he received both an
M.Sc. in Astronomy in 1984, and a Ph.D. in Astronomy in 1988. Toner
actually wrote two theses at UWO, one on "Line Asymmetries in F, G,
and K Supergiants and Bright Giants" for his M.Sc., and the other on
"The Time Variability of Spectral Line Asymmetries and Equivalent
Widths for the G8 Dwarf ? Boo A: Evidence for a Starpatch" for his
Ph.D. After graduate school, Cliff Toner left the cool climate
of Canada in 1988 and accepted a postdoctoral position in the warmer
temperatures of Hawai'i at the Institute for Astronomy located at the
University of Hawai'i in Honolulu. There he worked primarily with Barry
LaBonte. At first, he continued his work on ? Boo A, but he became
interested in the sun and helioseismology. This led to the discovery
of halos of enhanced high-frequency acoustic power surrounding solar
active regions (Ap.J. 415, 847). At the end of his post-doc,
Cliff Toner was hired by the GONG project as a Data Scientist in
1991. He quickly tackled the problem of merging the data from the
six GONG sites, which was the major data reduction challenge facing
GONG at the time. In parallel, he and Stuart Jefferies developed
an algorithm to measure the radii of full-disk solar images to a
relative precision of 0.01% by determining the zero points of the
Hankel transform of the image. As a by-product of the algorithm, the
modulation transfer function (MTF) of each image was also obtained,
and this led Toner to develop a merging scheme based on the MTF of
every image. It proved to be a very effective approach, and both the
radii measurement and the merging algorithm remain in daily use in the
GONG processing pipeline. However, there was one remaining challenge to
assembling the GONG time series in a seamless manner. Each of the six
GONG instruments is slightly and unavoidably misaligned with geographic
North, producing an angular misregistration of the solar image between
sites. Cliff Toner developed a sophisticated optimization scheme that
determined a network-wide solution to the relative orientations of the
images, and then pinned down the absolute value with drift scans. He
further refined the solutions to compensate for gear irregularities in
the camera rotator units at the sites. As a result of these algorithms,
Toner was able to co-align all of the GONG images to a precision and
accuracy of 0.02∘, as verified by his observations of
the transits of Mercury and Venus. Without this complex and clever
strategy and these extremely important algorithms, it would have been
impossible for the GONG data to be merged into a single uniform time
series of adequate accuracy for precision helioseismology. Cliff Toner's
tireless, selfless, and generally unseen work behind the scenes was
essential for the success of GONG. Toner also developed the scheme for
merging together the GONG high-cadence magnetograms, and was working
on determining the radii of the forthcoming GONG Ha data at the time of
his untimely death. Cliff Toner was a very tall man, and colleagues
at Hawai'i enjoyed the sight of him riding around the campus on a small
moped. Everyone who met him loved him for his patience and willingness
to help out. One of his colleagues from his stay in Hawai'i, K.D. Leka,
recalls that "Cliff was the embodiment of a "gentle giant"; so tall,
yet so soft-spoken and patient, and I just recall a sense of his always
being ready to help any living thing. Cliff was out with a back injury
in March 1991, and it was under his temporarily-abandoned desk that
Betsy, the IfA cat had her one (and only) litter (when my cat Audrey,
whom many of you know, was born). As the littermates grew, Cliff, Matt
Penn and I had kittens crawling over us; I can still hear his chuckles,
"well helloooh, who are you there now?" as they would scramble up
his chair to his desk. It was always with a smile that he'd greet me
when we ran into each other after the "Hawai'i days"; we'd swap some
stories, kid updates but only recently we were more in touch as I'm
now playing with GONG data. I was heartened to hear he was working on
the magnetogram merging, because I knew it'd be done really well with
his attention." Cliff Toner was a caring and loving person, an
excellent scientist, and a hero of GONG. He will be sorely missed by
everyone who knew him. He is survived by his wife, Nelsey, children,
Ariel, Nathaniel, Miranda, and Kayla, sister Gloria, brothers Ethan
(Heather) and Emanuel (Lisa).
Title: Solar dynamics at high latitudes and deep in the convection
zone
Authors: Gonzalez Hernandez, I.; Komm, R.; Howe, R.; Kholikov, S.;
Hill, F.; Bogart, R. S.; Rabello-Soares, M.
Bibcode: 2011AGUFMSH33A2041G
Altcode:
For a long time, helioseismic inferences have provided a window into
the solar interior. In the last two decades, the development of local
helioseismology tools has extended the capability of helioseismology
by allowing the study of localized structure changes and dynamics. In
particular, it has revealed the subsurface flows and its variation
throughout the solar cycle. Both the torsional oscillation and the
meridional circulation present interesting patterns leading to solar
cycle 24, which continue during the onset of this cycle. Yet, many
questions related to the behavior of such flows at high latitudes as
well as deep down in the convection zone that are key to solar dynamo
models remain unanswered. Long-term helioseismic studies using both
Global Oscillation Network Group (GONG) and Michelson Doppler Imager
(MDI)data have uncovered the difficulties of properly interpreting data
far from disk center due to systematics and solar effects, limiting
the helioseismic inferences to only specific areas. The Helioseismic
and Magnetic Imager (HMI) instrument on board the Solar Dynamics
Observatory (SDO) provides an excellent opportunity to explore the
until now unreachable territories thanks to its higher resolution. In
addition, newly available artificial data sets offer an unprecedented
opportunity for disentangling and modeling the different effects. We
present here a review of the main features observed in the subsurface
flows in the recent years and discuss future plans to extend the
inferences at higher latitudes and deep down in the convection zone.
Title: Comparison of STEREO's Far-side Observations of Solar Activity
and Predictions from the Global Oscillations Network Group (GONG)
Authors: Liewer, P. C.; Hall, J. R.; Hernandez Gonzalez, I.; Hill,
F.; Thompson, W. T.; Misrak, A.; De Jong, E. M.
Bibcode: 2011sdmi.confE..97L
Altcode:
Beginning February 18, 2011, the STEREO mission in conjunction with SDO,
for the first time, gave us an “All Sun” view of the entire corona
in extreme ultraviolet (EUV) light. Here, we compare STEREO/EUVI views
of solar activity on the far side to predictions of far-side strong
magnetic field regions from helioseismology using National Solar
Observatory/ Global Oscillation Network Group (GONG) observations
(see http://gong.nso.edu/data/farside/). The GONG project produces
“All Sun” Carrington maps of strong magnetic field regions; far
side regions with a probability of 70% or higher are labeled. We have
produced “All Sun” EUV Carrington maps of coronal magnetic activity
by combining nearly simultaneous STEREO A & B EUVI data and SDO AIA
data at each of the four EUVI wavelengths. We then visually determine
whether or not magnetic activity is seen in the corona (as evidenced
by brightening in EUV) at the locations predicted by GONG. We have
analyzed all GONG far-side predictions from February through June
2011. For 139 of 157 comparisons (89%), activity is observed in the
corona by STEREO A or B. For 18 predictions, no activity was seen
at the predicted region. We have also analyzed GONG’s success at
predicting 15 large active regions that appear on the East limb (as
viewed from Earth) during this stime period. For those not predicted,
we use STEREO B EUVI data to determine whether or not the regions had
significant activity during the time when GONG should have been able
to predict them.
Title: Solar cycle variations of the Interior
Authors: Hill, Frank
Bibcode: 2011sdmi.confE..47H
Altcode:
It has been known for some time that the properties of the solar
oscillations evolve in parallel with the activity cycle. Today, these
properties can be used to infer how the solar interior changes as the
cycle waxes and wanes. The subsurface behavior of both the meridional
flow, which is thought to set the amplitude of the solar cycle in
flux-transport dynamos, and the zonal flow or torsional oscillation
that appears to be tightly correlated with the timing of the cycle have
now been followed Using 16 years of data from GONG, SOHO, and SDO. The
flows have been observed over all of cycle 23, and the start of the
peculiar cycle 24. In addition, changes in the frequencies have recently
exhibited an unusual double minimum that may reflect the progression of
the cycle from deep to shallow layers. These results will be reviewed
and possible future avenues of future research will be presented.
Title: Multi-spectral Analysis of Heliseismic Acoustic Mode Parameters
Authors: Jain, Kiran; Tripathy, S.; Basu, S.; Bogart, R.; Gonzalez
Hernandez, I.; Hill, F.; Howe, R.; Kholikov, S.; Komm, R.
Bibcode: 2011sdmi.confE..33J
Altcode:
Simultaneous measurements at different wavelengths from SDO offer
the prospect of studying the sensitivity of helioseismic inferences
to the choice of observing height both in quiet-Sun and magnetically
active regions. In this poster, we present comparison of mode parameters
obtained with different observables, quantify differences, and interpret
results in the context of the formation height and the anticipated phase
relationships between the oscillations at those heights. This work is
expected to enhance our understanding of the excitation and damping
of the oscillations and the uncertainties in helioseismic inferences.
Title: Subsurface kinetic helicity of flows near active regions
Authors: Komm, R.; Jain, K.; Petrie, G.; Pevtsov, A.; González
Hernández I.; Hill, F.
Bibcode: 2011sdmi.confE..68K
Altcode:
We study the temporal variation of subsurface flows associated with
emerging and decaying active regions on the Sun. We measure the
subsurface flows analyzing GONG high-resolution Doppler data with
ring-diagram analysis. We can detect the emergence of magnetic flux
in these flows when averaging over a sufficiently large sample. In a
previous study, we have found that emerging flux has a faster rotation
than the ambient fluid and pushes it up, as indicated by enhanced
vertical velocity and faster-than-average zonal flow. Here, we show
that the kinetic helicity density of subsurface flows increases when
new flux emerges and decreases when flux decays.
Title: A Global Solar Wind Model Based on Surface Measurements of
Magnetic Field and Transverse Velocity from GONG
Authors: Wu, S. T.; Wang, A. H.; Wu, C. -C.; Hill, F.; Hernández,
I. G.; Feng, X. S.; Dryer, M.
Bibcode: 2011ASPC..444..143W
Altcode:
We present a solar wind model based on a three-dimensional (3D)
data-driven, time-dependent, magnetohydrodynamic (MHD) model. The inputs
to the model are the measured line-of-sight (LOS) magnetic field of
SOLIS and transverse velocity from the Global Oscillation Network Group
(GONG) on the lower boundary without heating and momentum additions. The
results show that both slow and fast components of the solar wind
are produced without arbitrarily specifying additional heating and
momentum due to the employment of multiple sets of observations. In
addition, the global distribution of the coronal holes responsible
for the formation of co-rotating interaction regions (CIRs) is also
consistently presented.
Title: Latest Results Found With Ring-Diagram Analysis
Authors: Haber, D. A.; Baldner, C.; Basu, S.; Bogart, R. S.;
González-Hernández, I.; Hill, F.; Howe, R.; Jain, K.; Komm, R. W.;
. Rabello-Soares, C.; Pinkerton, S.; Tripathy, S.
Bibcode: 2011sdmi.confE..51H
Altcode:
This talk will mainly be a preview of the posters generated by
the HMI Rings Team on large-scale (meridional and zonal) flows;
characterizations of active regions at various stages of evolution using
data from AIA as well as from HMI; systematic changes in frequencies,
flows, and other fitted parameters as a function of disk placement,
underlying magnetism, B angle, etc.; and the status of the Rings
pipeline. It will also include any new ring-diagram results from GONG
and MDI.
Title: The HMI Ring-Diagram Pipelines: A Status Report
Authors: Bogart, R. S.; Baldner, C. S.; Basu, S.; Haber, D. A.; Howe,
R.; Gonzalez Hernandez, I.; Hill, F.; Jain, K.; Rabello-Soares, M. C.;
Tripathy, S.
Bibcode: 2011sdmi.confE..55B
Altcode:
The HMI analysis pipeline for determination of sub-surface flows
has been running for nearly one year, and virtually all HMI Doppler
data from the beginning of the mission have been analyzed. Over 3.5
million local-area power spectra of regions of various sizes have
been produced and fitted, and inversions for the depth structure of
flows have been produced for over 130,000 of the larger regions. The
pipeline for determination of the sub-surface thermal structure is still
under active development, with test results available for analysis
for a number of strong active regions. We describe the ring-diagram
pipelines, report on their performance as part of the overall HMI data
analysis pipeline, describe the data products available, and discuss
outstanding problems and issues for further development.
Title: Large-scale flows from HMI using the ring-diagram pipeline
Authors: Komm, R.; González Hernández, I.; Hill, F.; Bogart, R. S.;
Rabello-Soares, M. C.
Bibcode: 2011sdmi.confE..72K
Altcode:
We determine the zonal and meridional flows in subsurface layers derived
from HMI Doppler data processed with the HMI ring-diagram pipeline. We
analyze subsurface flow measurements obtained during Carrington rotation
2097 to 2113. We are especially interested in flows at latitudes of
60 degree and higher, since previous observations have been limited
to lower latitudes (using local helioseismic techniques). Systematic
effects, such as B0-angle variations, have to be taken into account
to lead to reliable flow estimates at high latitudes. We will present
the latest results.
Title: How Peculiar Was the Recent Extended Minimum: A Hint toward
Double Minima
Authors: Jain, Kiran; Tripathy, S. C.; Hill, F.
Bibcode: 2011ApJ...739....6J
Altcode: 2011arXiv1107.0049J
In this paper, we address the controversy regarding the recent extended
solar minimum as seen in helioseismic low- and intermediate-degree
mode frequencies: studies from different instruments identify different
epochs of seismic minima. Here we use mode frequencies from a network
of six identical instruments, the Global Oscillation Network Group,
continuously collecting data for more than 15 years, to investigate the
epoch of minimum in solar oscillation frequencies prior to the beginning
of solar cycle 24. We include both low- and intermediate-degree
modes in the l range of 0-120 and frequency range of 2.0-3.5 mHz. In
this analysis, we demonstrate that there were indeed two minima in
oscillation frequencies, depending upon the degree of modes, or more
precisely the lower turning point radius of the propagating wave. We
also analyze frequencies as a function of latitude to identify the
beginning of solar cycle 24. We observe two minima at high latitudes
and a single minimum at mid/low latitudes. This scenario is in contrast
to cycle 23 where the epoch of seismic minimum did not change with
latitude or depth. Our results also hint at a possible role of the
relic magnetic field in modifying the oscillation frequencies of modes
sampling deeper layers.
Title: Subsurface flows associated with rotating sunspots
Authors: Jain, Kiran; Komm, Rudolf; Hernández, Irene González;
Tripathy, Sushant C.; Hill, Frank
Bibcode: 2011IAUS..273..356J
Altcode: 2011arXiv1107.5032J
In this paper, we compare components of the horizontal flow below
the solar surface in and around regions consisting of rotating and
non-rotating sunspots. Our analysis suggests that there is a significant
variation in both components of the horizontal flow at the beginning
of sunspot rotation as compared to the non-rotating sunspot. The flows
in surrounding areas are in most cases relatively small. However,
there is a significant influence of the motion on flows in an area
closest to the sunspot rotation.
Title: Solar subsurface flows of active regions: flux emergence and
flare activity
Authors: Komm, Rudolf; Howe, Rachel; Hill, Frank; Jain, Kiran
Bibcode: 2011IAUS..273..148K
Altcode:
We study the temporal variation of subsurface flows associated
with active regions within 16 Mm of the solar surface. We have
analyzed the subsurface flows of nearly 1000 active and quiet regions
applying ring-diagram analysis to Global Oscillation Network Group
(GONG) Dopplergram data. We find that newly emerging active regions
are characterized by enhanced upflows and fast zonal flows in the
near-surface layers, as expected for a flux tube rising from deeper
layers of the convection zone. The subsurface flows associated with
strong active regions are highly twisted, as indicated by their large
vorticity and helicity values. The dipolar pattern exhibited by the
zonal and meridional vorticity component leads to the interpretation
that these subsurface flows resemble vortex rings, when measured on
the spatial scales of the standard ring-diagram analysis.
Title: Helioseismic Observations of Solar Convection Zone Dynamics
Authors: Hill, Frank; Howe, Rachel; Komm, Rudi; Hernández, Irene
González; Kholikov, Shukur; Leibacher, John
Bibcode: 2011IAUS..271...15H
Altcode:
The large-scale dynamics of the solar convection zone have been inferred
using both global and local helioseismology applied to data from the
Global Oscillation Network Group (GONG) and the Michelson Doppler
Imager (MDI) on board SOHO. The global analysis has revealed temporal
variations of the ``torsional oscillation'' zonal flow as a function of
depth, which may be related to the properties of the solar cycle. The
horizontal flow field as a function of heliographic position and depth
can be derived from ring diagrams, and shows near-surface meridional
flows that change over the activity cycle. Time-distance techniques
can be used to infer the deep meridional flow, which is important for
flux-transport dynamo models. Temporal variations of the vorticity can
be used to investigate the production of flare activity. This paper
summarizes the state of our knowledge in these areas.
Title: Using SONG to probe rapid variability and evolution of
starspots
Authors: Neff, James E.; Hakkila, Jon; Hill, Frank; Jackiewicz, Jason;
Metcalfe, Travis S.; Christensen-Dalsgaard, Jørgen; Frandsen, Søren;
Grundahl, Frank; Kjeldsen, Hans; Jørgensen, Uffe Gråe; Rasmussen,
Per Kjærgaard; Gu, Sheng-Hong
Bibcode: 2011IAUS..273..451N
Altcode:
The Stellar Observations Network Group (SONG) is being developed
as a network of 1-meter spectroscopic telescopes designed for and
primarily dedicated to asteroseismology. It is patterned after the
highly successful GONG project. The Danish prototype telescope will
be installed in Tenerife in early 2011. Ultimately we hope to have
as many as 8 identical nodes providing continuous high-resolution
spectroscopic observations for targets anywhere in the sky. The
primary scientific goals of SONG are asteroseismology and the search
for Earth-mass exoplanets. The spectroscopic requirements for these
programs push the limits of current technology, but the resulting
spectrograph design will enable many secondary science programs
with less stringent requirements. Doppler imaging of starspots can
be accomplished using continuous observations over several stellar
rotations using identical instrumentation at each node. It should be
possible to observe the evolution of starspot morphology in real-time,
for example. We discuss the design and status of the SONG project
in general, and we describe how SONG could be used to probe short
timescale changes in stellar surface structure.
Title: Subsurface kinetic helicity of flows near active regions
Authors: Komm, Rudolf; Jain, K.; Petrie, G.; Pevtsov, A.; González
Hernández, I.; Hill, F.
Bibcode: 2011shin.confE.142K
Altcode:
We study the flows in the upper solar convection zone determined from
GONG data using the standard dense-pack ring-diagram analysis and derive
daily and synoptic maps of the velocity components. We also calculate
the vorticity and the kinetic helicity density of the flows. Previous
studies have shown that the vorticity is enhanced near locations
of active regions and that the kinetic helicity density associated
with active regions correlates well with the X-ray flare intensity of
active regions. These fluid dynamics descriptors are thus promising
indicators for investigating the relation between active regions and
associated subsurface flows. Here, we focus on the temporal evolution of
subsurface kinetic helicity density during flux emergence and decay. We
will present the latest results.
Title: Deep Meridional Flow Measurements from GONG: Temporal and
Depth Variations
Authors: Kholikov, Shukur; Leibacher, J.; Hill, F.
Bibcode: 2011SPD....42.1618K
Altcode: 2011BAAS..43S.1618K
We present measurements of meridional flow using time-distance analysis
of GONG data. To push the depth profile of the flow deeper, we average
time-difference measurements over 15 years. In order to increase the
signal-to-noise ratio, and to reduce contamination from other modes,
we utilized both phase velocity and low-m filtering. This approach
seems to be capable of extending the meridional-flow measurements
down to 0.7 Rsun. Our preliminary results indicate that the precision
achieved is very close to that required to measure the reverse flow
down to the base of the solar convection zone where it is expected to be
situated. Typical uncertainties for most depths within mid-latitudes are
less than 0.02 seconds. At high latitudes, due to projection effects,
error bars increase up to 0.06 seconds. There is a significant change in
the nature of the time differences at the bottom of the convection zone.
Title: Utilization of Multiple Measurements for Global
Three-dimensional Magnetohydrodynamic Simulations
Authors: Wang, A. H.; Wu, S. T.; Tandberg-Hanssen, E.; Hill, Frank
Bibcode: 2011ApJ...732...19W
Altcode:
Magnetic field measurements, line of sight (LOS) and/or vector
magnetograms, have been used in a variety of solar physics
studies. Currently, the global transverse velocity measurements near
the photosphere from the Global Oscillation Network Group (GONG) are
available. We have utilized these multiple observational data, for
the first time, to present a data-driven global three-dimensional and
resistive magnetohydrodynamic (MHD) simulation, and to investigate
the energy transport across the photosphere to the corona. The
measurements of the LOS magnetic field and transverse velocity reflect
the effects of convective zone dynamics and provide information from the
sub-photosphere to the corona. In order to self-consistently include
the observables on the lower boundary as the inputs to drive the
model, a set of time-dependent boundary conditions is derived by using
the method of characteristics. We selected GONG's global transverse
velocity measurements of synoptic chart CR2009 near the photosphere
and SOLIS full-resolution LOS magnetic field maps of synoptic chart
CR2009 on the photosphere to simulate the equilibrium state and compute
the energy transport across the photosphere. To show the advantage
of using both observed magnetic field and transverse velocity data,
we have studied two cases: (1) with the inputs of the LOS magnetic
field and transverse velocity measurements, and (2) with the input of
the LOS magnetic field and without the input of transverse velocity
measurements. For these two cases, the simulation results presented
here are a three-dimensional coronal magnetic field configuration,
density distributions on the photosphere and at 1.5 solar radii, and the
solar wind in the corona. The deduced physical characteristics are the
total current helicity and the synthetic emission. By comparing all the
physical parameters of case 1 and case 2 and their synthetic emission
images with the EIT image, we find that using both the measured magnetic
field and the velocity distribution would give more cohesive results.
Title: Helioseismic Studies With Multi-wavelength Data From HMI And
AIA Onboard SDO
Authors: Hill, Frank; Jain, K.; Tripathy, S.; Kholikov, S.; Gonzalez
Hernandez, I.; Leibacher, J.; Howe, R.; Baudin, F.; Carlsson, M.;
Chaplin, W.; Tarbell, T.
Bibcode: 2011SPD....42.2111H
Altcode: 2011BAAS..43S.2111H
The successful launch of the Solar Dynamics Observatory (SDO) in
February 2010 opens important, new possibilities for helioseismic
exploration of the solar interior and atmosphere using multi-wavelength
observations from multiple instruments. In order to better understand
the solar interior and atmosphere, as well as the physics of the
helioseismic modes and waves themselves, we exploit the potential of
the Atmospheric Imaging Assembly (AIA) 1600 and 1700 Angstrom continuum
measurements and the contemporaneous Helioseismic and Magnetic Imager
(HMI) Fe I 6173.3 Angstrom velocity and intensity observations. Standard
techniques of helioseismology e.g Sun-as-a-star, spherical harmonic
analysis, ring diagrams, and time- distance analysis are applied to
obtain acoustic mode parameters and other characteristics. Here we
present our preliminary results, and interpret these in the context
of the differences in the heights of formation of the lines.
Title: Subsurface Vorticity of Emerging Active Regions
Authors: Komm, Rudolph; Howe, R.; Hill, F.
Bibcode: 2011SPD....42.1601K
Altcode: 2011BAAS..43S.1601K
We study the temporal variation of subsurface flows associated with
emerging active regions. We have analyzed the flows of nearly 1000
active and quiet regions analyzing GONG high-resolution Doppler
data with ring-diagram analysis. We determine the change in unsigned
magnetic flux during the disk passage of each active region using MDI
magnetograms binned to the ring-diagram grid. In a previous study, we
have found that emerging flux has a faster rotation than the ambient
fluid and pushes it up, as indicated by enhanced vertical velocity and
faster-than-average zonal flow. In this study, we are focusing on the
vorticity of subsurface flows associated with newly emerging active
regions. We will present the latest results.
Title: Comparison of Ring Diagram Fitting Techniques
Authors: Baldner, Charles; Basu, S.; Bogart, R.; Haber, D.; Hill,
F.; Howe, R.; Rabello-Soares, C.
Bibcode: 2011SPD....42.1608B
Altcode: 2011BAAS..43S.1608B
Ring diagrams are used to study the structure and dynamics of the
near-surface layers of the Sun. The parameters of primary interest
are frequencies and velocities in both the zonal and merridional
direction as a function of wavenumber and of radial order n. These
parameters are recovered by fitting a model of the spectral profile
to three-dimensional power spectra of small regions of the Sun. In
this work, we examine the systematic differences between fits assuming
an asymmetric profile and fits assuming a symmetric profile. We also
explore the coupling between the parameters of interest and certain
secondary parameters such as amplitude, width, and asymmetry.
Title: Comparison of Farside Observations of Solar Activity from
STEREO's Extreme UltraViolet Imager and the Global Oscillations
Network Group (GONG)
Authors: Liewer, Paulett C.; Gonzalez-Hernandez, I.; Thompson, W. T.;
Hall, J. R.; Hill, F.
Bibcode: 2011SPD....42.1802L
Altcode: 2011BAAS..43S.1802L
Beginning February 18, 2011, the STEREO mission, for the first time,
gave us a "whole Sun” view of the entire corona in extreme ultraviolet
(EUV) light. At this time, the twin STEREO spacecraft were 180°
apart and roughly ±90° from Earth. For the next several years,
as the STEREO spacecraft drift further from Earth, EUV images from
STEREO combined with the Earth-side images from the Solar Dynamics
Observatory will continue to show the solar activity in the chromosphere
and corona for the full Sun. Here, we compare these three-spacecraft
EUV observations of farside solar activity with the prediction of far
side active regions from helioseismology using NSO GONG observations
(see http://stereo-ssc.nascom.nasa.gov/beacon/beacon_farside.shtml). We
compare cases where (1) a known active region persists throughout
its farside passage, and (2) where a new active region emerges on the
farside and rotates around to the Earth-side. We also discuss tools
developed to help further in-depth comparison of solar observations
utilizing far-side data.
Title: Meridional Circulation Measurements from 15 Years of GONG
Authors: Serebryanskiy, Aleksander; Kholikov, S.; Hill, F.;
Jackiewicz, J.
Bibcode: 2011SPD....42.1614S
Altcode: 2011BAAS..43S.1614S
We present results of meridional flow measurements utilizing
the GONG spherical harmonic time series for the 1995-2009 time
period. Travel-time differences were obtained from cross-correlation
measurements in the North-South direction using traditional
time-distance helioseismology procedures. The travel times were used as
input to an inversion procedure based on ray-path approximation kernels
to infer the velocity amplitude of the meridional flow throughout
the solar convection zone. Also presented are studies of well-known
projection and systematic errors of these types of measurements.
Title: Solar Flare Detection With SWIFT and Real-time GONG H-alpha
Images
Authors: Henney, Carl John; MacKenzie, D.; Hill, F.; Mills, B.;
Pietrzak, J.
Bibcode: 2011SPD....42.2233H
Altcode: 2011BAAS..43S.2233H
The Air Force Weather Agency (AFWA) has begun the process of
upgrading the Solar Observing Optical Network (SOON) with an
Improved-SOON (ISOON). During the interim period, AFWA is supporting
the addition and operation of a solar H-alpha (Hydrogen-alpha, 656.3
nm) full-disk image network utilizing the light feed from the National
Solar Observatory's existing GONG (Global Oscillation Network Group)
instruments. The H-alpha instruments at the GONG sites have been in
operation collectively since the beginning of 2011, providing one to
three H-alpha images per minute. Cross-site comparison and calibration
of flare detection has begun using an image analysis tool called SWIFT
(SWFL/ISOON Flare-cast Tool). SWIFT is a unique and versatile software
package, designed originally for ISOON data, that has been attuned to
ingest and display GONG H-alpha images in real-time. The SWIFT software
allows a user to detect and analyze optical flares from solar active
regions. The SWIFT software is in the process of being beta-tested at
AFWA in collaboration with the Space Weather Center of Excellence's SWFL
(Space Weather Forecasting Laboratory) to better forecast space weather
events. Solar flares are of great interest to the Air Force Research
Laboratory's Space Vehicles Directorate because they can trigger
energetic particle events or coronal mass ejection events that impact
the Earth's magnetosphere creating geomagnetic storms. Such events
can result in satellite charging damage, increased satellite drag,
power grid disruption, navigation system anomalies, and communication
fadeouts. An overview of SWIFT, along with preliminary flare detection
comparisons between GONG sites and the SOON flare reports, will be
presented.
Title: The B0-angle Effect in Local Helioseismology Inferences of
Meridional Circulation
Authors: Gonzalez-Hernandez, Irene; Hartlep, T.; Kholikov, S.; Hill, F.
Bibcode: 2011SPD....42.1615G
Altcode: 2011BAAS..43S.1615G
Meridional circulation has become a key ingredient in flux-transport
solar-dynamo models. The development of local-helioseismology methods,
combined with medium-high continuous observations from the Global
Oscillation Network Group (GONG) and the Michelson Doppler Imager (MDI)
has allowed the monitoring of the meridional circulation below the solar
surface during the last solar cycle. However, the inferences have been
limited in latitude as well as in depth, due mainly to the uncertainties
in the analysis methods and the resolution of the observation. Here we
investigate the effect of the B0 angle on the inferences of meridional
circulation flows and explore the possibility of modeling such effect
by using artificial data, a numerical simulation of helioseismic wave
propagation in the whole solar interior.
Title: Large-scale Zonal Flows During the Solar Minimum -- Where Is
Cycle 25?
Authors: Hill, Frank; Howe, R.; Komm, R.; Christensen-Dalsgaard, J.;
Larson, T. P.; Schou, J.; Thompson, M. J.
Bibcode: 2011SPD....42.1610H
Altcode: 2011BAAS..43S.1610H
The so-called torsional oscillation is a pattern of migrating zonal flow
bands that move from mid-latitudes towards the equator and poles as the
magnetic cycle progresses. Helioseismology allows us to probe these
flows below the solar surface. The prolonged solar minimum following
Cycle 23 was accompanied by a delay of 1.5 to 2 years in the migration
of bands of faster rotation towards the equator. During the rising phase
of Cycle 24, while the lower-level bands match those seen in the rising
phase of Cycle 23, the rotation rate at middle and higher latitudes
remains slower than it was at the corresponding phase in earlier cycles,
perhaps reflecting the weakness of the polar fields. In addition,
there is no evidence of the poleward flow associated with Cycle 25. We
will present the latest results based on nearly sixteen years of global
helioseismic observations from GONG and MDI, with recent results from
HMI, and discuss the implications for the development of Cycle 25.
Title: Full-disk Solar H-alpha Images From GONG
Authors: Harvey, J. W.; Bolding, J.; Clark, R.; Hauth, D.; Hill, F.;
Kroll, R.; Luis, G.; Mills, N.; Purdy, T.; Henney, C.; Holland, D.;
Winter, J.
Bibcode: 2011SPD....42.1745H
Altcode: 2011BAAS..43S.1745H
Since mid-2010 the Global Oscillation Network Group (GONG) has collected
H-alpha images at six sites around the world. These images provide
a near real-time solar activity patrol for use in space weather
applications and also an archive for research purposes. Images are
collected once per minute, dark, smear, and flat corrected, compressed
and then sent via the Internet to a 'cloud' server where reduction
is completed. Various reduced images are usually available within a
minute after exposure. The H-alpha system is an add-on to the normal
GONG helioseismology instrument and does not interfere with regular
observations. A polarizing beamsplitter sends otherwise unused 656 nm
light through two lenses to a Daystar 0.04 nm mica etalon filter. The
filter is matched to an image of the GONG light feed entrance pupil
and sees an image of the Sun at infinity. Two lenses behind the filter
form the solar image on a DVC-4000 2k x 2k interline transfer CCD
camera. Exposure times are automatically adjusted to maintain the
quiet disk center at 20% of full dynamic range to avoid saturation
by bright flares. Image resolution is limited by diffraction,
seeing and some high-order wavefront errors in the filters. A unique
dual-heater system was developed by Daystar to homogenize the passband
characteristics of the mica etalons. The data are in regular use for
space weather forecasting by the U.S. Air Force Weather Agency, which
funded construction and installation of the instruments. Operational and
reduction improvements are underway and archived data are already being
used for research projects. The Web site URL is http://halpha.nso.edu.
Title: Subsurface Vorticity of Flaring versus Flare-Quiet Active
Regions
Authors: Komm, R.; Ferguson, R.; Hill, F.; Barnes, G.; Leka, K. D.
Bibcode: 2011SoPh..268..389K
Altcode: 2010SoPh..tmp...78K
We apply discriminant analysis to 1023 active regions and their
subsurface-flow parameters, such as vorticity and kinetic helicity
density, with the goal of distinguishing between flaring and non-flaring
active regions. We derive synoptic subsurface flows by analyzing GONG
high-resolution Doppler data with ring-diagram analysis. We include
magnetic-flux values in the discriminant analysis derived from NSO
Kitt Peak and SOLIS synoptic maps binned to the same spatial scale
as the helioseismic analysis. For each active region, we determine
the flare information from GOES and include all flares within 60°
central meridian distance to match the coverage of the ring-diagram
analysis. The subsurface-flow characteristics improve the ability to
distinguish between flaring and non-flaring active regions. For the C-
and M-class flare category, the most important subsurface parameter
is the so-called structure vorticity, which estimates the horizontal
gradient of the horizontal-vorticity components. The no-event skill
score, which measures the improvement over predicting that no events
occur, reaches 0.48 for C-class flares and 0.32 for M-class flares, when
the structure vorticity at three depths combined with total magnetic
flux are used. The contributions come mainly from shallow layers within
about 2 Mm of the surface and layers deeper than about 7 Mm.
Title: Subsurface Velocity of Emerging and Decaying Active Regions
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 2011SoPh..268..407K
Altcode: 2011SoPh..tmp....6K
We study the temporal variation of subsurface flows of 828 active
regions and 977 quiet regions. The horizontal flows cover a range of
depths from the surface to about 16 Mm and are determined by analyzing
Global Oscillation Network Group high-resolution Doppler data with
ring-diagram analyses. The vertical velocity component is derived
from the divergence of the measured horizontal flows using mass
conservation. For comparison, we analyze Michelson Doppler Imager
(MDI) Dynamics Run data covering 68 active regions common to both
data sets. We determine the change in unsigned magnetic flux during
the disk passage of each active region using MDI magnetograms binned
to the ring-diagram grid. We then sort the data by their flux change
from decaying to emerging flux and divide the data into five subsets
of equal size. We find that emerging flux has a faster rotation than
the ambient fluid and pushes it up, as indicated by enhanced vertical
velocity and faster-than-average zonal flow. After active regions
are formed, downflows are established within two days of emergence in
shallow layers between about 4 and 10 Mm. Emerging flux in existing
active regions shows a similar scenario, where the upflows at depths
greater than about 10 Mm are enhanced and the already established
downflows at shallower depths are weakened. When active regions decay,
the corresponding flow pattern disappears as well; the zonal flow slows
down to values comparable to that of quiet regions and the upflows
become weaker at deeper layers. The residual meridional velocity is
mainly poleward and shows no obvious variation. The magnitude of the
residual velocity, defined as the sum of the squares of the residual
velocity components, increases with increasing magnetic flux and
decreases with decreasing flux.
Title: Meridional-Flow Measurements from 15 Years of GONG
Spherical-Harmonic Time Series
Authors: Kholikov, S.; González Hernández, I.; Hill, F.; Leibacher,
J.
Bibcode: 2011JPhCS.271a2052K
Altcode:
We present results of meridional-flow measurements for 1995-2009, using
travel-time differences from velocity images reconstructed using GONG
spherical harmonic (SH) coefficients after applying phase-velocity and
low-m filters. This filtering technique increases the signal-to-noise
ratio and thus extends travel-time measurements to relatively high
latitudes and deep into the convection zone. Preliminary analyses shows
a strong one-year periodicity presumably due to solar pole misalignment
and B0-angle artifacts, which makes it difficult to see
underlying temporal variations. Removing a simple one-year-period sine
wave fit reveals long-term temporal variations of the flow on top
of this yearly periodicity. High-latitude measurements are affected
more stronger by foreshortening and B0 -angle artifacts. We
analyze different B0-angle intervals separately, so in each
hemisphere better high-latitude visibility comes six months apart. This
approach suggests why at high latitudes travel-time measurements of
meridional flow shows a tendency to change sign instead of continuing
towards the poles.
Title: The far-side solar magnetic index
Authors: González Hernández, Irene; Jain, Kiran; Tobiska, W. Kent;
Hill, Frank
Bibcode: 2011JPhCS.271a2028G
Altcode:
Several magnetic indices are used to model the solar irradiance and
ultimately to forecast it. However, the observation of such indices are
generally limited to the Earth-facing hemisphere of the Sun. Seismic
maps of the far side of the Sun have proven their capability to locate
and track medium-large active regions at the non-visible hemisphere. We
present here the possibility of using the average signal from these
seismic far-side maps as a proxy to the non-visible solar activity
which can complement the current front-side solar activity indices.
Title: Solar-cycle variation of zonal and meridional flow
Authors: Komm, R.; Howe, R.; Hill, F.; González Hernández, I.;
Haber, D.
Bibcode: 2011JPhCS.271a2077K
Altcode:
We study the variation with the solar cycle of the zonal and meridional
flows in the near-surface layers of the solar convection zone. We have
analyzed MDI Dynamics-Program data with ring-diagram analysis covering
the rising phase of cycle 23, while the analyzed GONG high-resolution
data cover the maximum and declining phase of cycle 23. For the zonal
flow, the migration with latitude of the flow pattern is apparent in
the deeper layers, while for the meridional flow, a migration with
latitude is apparent only in the layers close to the surface. The
faster-than-average bands of the zonal flow associated with the new
cycle are clearly visible. Similarly, a pattern related to the new
cycle appears in the residual meridional flow. We also study the flow
differences between the hemispheres during the course of the solar
cycle. The difference pattern of the meridional flow is slanted in
latitude straddling the faster-than-average band of the torsional
oscillation pattern in the zonal flow. The difference pattern of the
zonal flow, on the other hand, resembles the cycle variation of the
meridional flow. In addition, the meridional flow during the minimum
of cycle 23/24 appears to be slightly stronger than during the previous
minimum of cycle 22/23.
Title: Solar flares and temporal changes in subsurface vorticity
measurements
Authors: Komm, R.; Jain, K.; Reinard, A.; Howe, R.; Hill, F.
Bibcode: 2011JPhCS.271a2019K
Altcode:
We derive the kinetic helicity density of subsurface flows applying
ring-diagram analysis to Global Oscillation Network Group (GONG)
data. Here, we focus on flows derived from times series of 8 hours
and compare them to daily values for a high- and a low-activity
sample. Compared with daily values, the horizontal flows derived from
8-hour time series are reasonable near disk center and less reliable
near the limb. Also, the errors are larger for shorter time series. A
dipolar helicity pattern is present in the flows derived from 8-hour
and 24-hour time series of flare-productive active region 10808. For
the quiet-Sun sample, the subsurface kinetic helicity is considerably
smaller without any pattern.
Title: First Global Rotation Inversions of HMI Data
Authors: Howe, R.; Larson, T. P.; Schou, J.; Hill, F.; Komm, R.;
Christensen-Dalsgaard, J.; Thompson, M. J.
Bibcode: 2011JPhCS.271a2061H
Altcode:
We present the first 2-dimensional global rotational inversions of
medium-degree p-mode data from the Helioseismic and Magnetic Imager,
and compare the results with inversions of Michelson Doppler Imager
data for the same time period. The inferred rotation profiles show
good agreement between the two instruments.
Title: Comparison of HMI Dopplergrams with GONG and MDI data
Authors: Howe, R.; Jain, K.; Hill, F.; Komm, R.; González Hernández,
I.; Bogart, R.
Bibcode: 2011JPhCS.271a2060H
Altcode:
We compare sample Dopplergrams from the Helioseismic and Magnetic
Imager, the Michelson Doppler Imager and the Global Oscillation Network
Group. Each instrument has a distinct static velocity patterm across
the disk; once this has been subtracted and the images interpolated
to a common grid, the agreement is satisfactory.
Title: Variation of high-degree mode frequencies during the declining
phase of solar cycle 23
Authors: Tripathy, S. C.; Jain, K.; Hill, F.
Bibcode: 2011JPhCS.271a2024T
Altcode:
We investigate the spatial and temporal variation of the high-degree
mode frequencies during the declining phase of the solar cycle
23 and the extended minimum between the cycle 23 and 24. We find
that the frequency shifts of high-degree modes obtained through the
ring-diagram analysis in different phases of the solar cycle are not
equally correlated with the local magnetic activity index.
Title: Towards near real time high-resolution Dopplergrams from GONG
Authors: Jain, Kiran; McManus, S.; González Hernández, I.; Tripathy,
S. C.; Bolding, J.; Hill, F.; Wentzel, T. M.
Bibcode: 2011JPhCS.271a2018J
Altcode:
The GONG network, consisting of six sites around the globe, provides
continuous observations of the Sun. The processing and merging of
Dopplergrams from various sites usually takes several months before
these are made available to the community for analysis. In this paper,
we discuss our recent attempts to reduce the delay between observations
and the availability of merged Dopplergrams. Our analysis indicates that
the modified approach does not influence mode parameters and inferred
helioseismic flows. However, the duty cycle plays a significant role in
inferring the sub-surface flows and a low duty cycle, if less stations
contribute, may lead to qualitatively different results.
Title: An Introduction to Wave-Trapping in Supergranulation
Authors: Allen, W.; Hill, F.
Bibcode: 2011JPhCS.271a2069A
Altcode:
This paper is an introduction to modelling waves trapped in
a supergranular cell. The supergranular cell is generalized to the
form of a hexagon with a cylinder inscribed within its boundaries. A
cylindrical wave equation is implemented and solved and we account
for the edges of the hexagon through boundary conditions. Plots are
created of the solution and will serve as a test as to whether the model
reflects actual wave conditions inside a single supergranular cell.
Title: The torsional oscillation and the new solar cycle
Authors: Howe, R.; Hill, F.; Komm, R.; Christensen-Dalsgaard, J.;
Larson, T. P.; Schou, J.; Thompson, M. J.; Ulrich, R.
Bibcode: 2011JPhCS.271a2074H
Altcode:
We present updated observations of the pattern of migrating solar
zonal flows known as the torsional oscillation, covering 15 years of
helioseismic measurements with GONG and MDI and 30 years of surface
Doppler observations from Mount Wilson. We compare the behavior of the
flows during the extended solar minimum following Cycle 23 with that in
earlier minima. We demonstrate that the timing of the migration of the
zonal flow belts may be of some use in predicting the start of the new
cycle. We also note that the behavior of the high-latitude part of the
pattern currently differs from that seen early in the previous cycle,
with the high-latitude poleward-migrating branch still not established.
Title: Angular-degree dependence of p-mode frequencies during solar
cycle 23
Authors: Tripathy, S. C.; Jain, K.; Salabert, D.; Garcia, R. A.;
Hill, F.; Leibacher, J. W.
Bibcode: 2011JPhCS.271a2055T
Altcode:
We analyze simultaneous helioseismic observations collected by the
ground- and space-based instruments during solar cycle 23 by computing
oscillation frequencies for low- and intermediate-degree p-modes on a
time scale of 36 days. We find that the frequency shifts corresponding
to different angular degree, ell, indicate different epochs for the
onset of the solar cycle 24. The analysis also indicates the presence
of double minima between cycles 23 and 24 for some range of ell values.
Title: Rotation-rate variations at the tachocline: An update
Authors: Howe, R.; Komm, R.; Hill, F.; Christensen-Dalsgaard, J.;
Larson, T. P.; Schou, J.; Thompson, M. J.; Toomre, J.
Bibcode: 2011JPhCS.271a2075H
Altcode:
After 15 years of GONG and MDI observations of the solar interior
rotation, we revisit the issue of variations in the rotation rate near
the base of the convection zone. The 1.3-year period seen in the first
few years of the observations disappeared after 2000 and has still
not returned. On the other hand, the agreement between GONG and MDI
observations suggests that variations seen in this region have some
solar origin, whether a true rotation-rate change or possibly mere
stochastic variation; we present a numerical experiment supporting
this contention.
Title: A search for coherent structures in subsurface flows
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 2011JPhCS.271a2065K
Altcode:
We search for coherent patterns in horizontal subsurface flows obtained
from Global Oscillation Network Group (GONG) Dopplergram data using
ring-diagram analysis. The existence of north-south aligned downflow
patterns near the equator has been predicted by numerical models of the
solar convection zone. We analyze time series of daily flow measurements
near the solar equator focusing on the vertical velocity component and
the derivative of the zonal flow in the east-west direction. To reduce
the influence of surface magnetic activity, we analyze observations
during the minimum phase of the solar cycle. We find coherent
equatorial structures that persist for several days in the zonal
velocity derivative and the vertical velocity component and are not
associated with surface magnetic activity. We use a cross-correlation
analysis to measure the strength and rotation rate of these coherent
patterns. Our results are consistent with other studies that have
observed north-south aligned patterns in supergranulation.
Title: Temporal Variations of High-Degree Solar p-Modes from GONG
and MDI
Authors: Burtseva, Olga; Tripathy, Sushant; Howe, Rachel; Jain, Kiran;
Hill, Frank; Bogart, Richard; Rabello-Soares, Maria Cristina
Bibcode: 2011JPhCS.271a2012B
Altcode: 2010arXiv1012.5128B
We study temporal variations in the amplitudes and widths of high-degree
acoustic modes in the quiet and active Sun by applying ring-diagram
technique to the GONG+ and MDI Dopplergrams during the declining phase
of cycle 23. The increase in amplitudes and decrease in line-widths in
the declining phase of the solar activity is in agreement with previous
studies. A similar solar cycle trend in the mode parameters is also
seen in the quiet-Sun regions but with a reduced magnitude. Moreover,
the amplitudes obtained from GONG+ data show long-term variations on
top of the solar cycle trend.
Title: Ring-diagram parameter comparisons for GONG, MDI and HMI
Authors: Howe, R.; Tripathy, S.; González Hernández, I.; Komm, R.;
Hill, F.; Bogart, R.; Haber, D.
Bibcode: 2011JPhCS.271a2015H
Altcode:
We examine the differences between ring-diagram mode frequency estimates
from samples of Global Oscillation Network Group [GONG], Michelson
Doppler Imager [MDI] and Helioseismic and Magnetic Imager [HMI] data,
and find that different instruments and analysis pipelines do result
in small systematic differences which may not be uniform across the
solar disk.
Title: Low-degree helioseismology with AIA
Authors: Howe, R.; Hill, F.; Komm, R.; Broomhall, A. -M.; Chaplin,
W. J.; Elsworth, Y.
Bibcode: 2011JPhCS.271a2058H
Altcode:
We form unresolved-sun time series from the 1600 and 1700 Angstrom
images produced by the Atmospheric Imaging Assembly, and find a clean
low-degree p-mode spectrum at each wavelength. The time series and
spectra are compared with Doppler velocity and continuum intensity
time series from the Helioseismic and Magnetic Imager and velocity
series from the Birmingham Solar Oscillation Network. The UV data
have a slight phase shift with respect to the velocity, and show more
sensitivity to high-frequency and less to low-frequency modes. Unlike
the HMI (visible) continuum observations, the UV spectra show little
or no granulation noise at low frequencies and thus potentially allow
more low-frequency modes to be recovered. These results suggest that
asteroseismology at near-UV wavelengths should be very feasible and
even an improvement on visible-wavelength intensity measurements,
at least in low-activity stars.
Title: Meridional Flow Observations: Implications for the current
Flux Transport Models
Authors: González Hernández, Irene; Komm, Rudolf; Kholikov, Shukur;
Howe, Rachel; Hill, Frank
Bibcode: 2011JPhCS.271a2073G
Altcode:
Meridional circulation has become a key element in the solar dynamo
flux transport models. Available helioseismic observations from several
instruments, Taiwan Oscillation Network (TON), Global Oscillation
Network Group (GONG) and Michelson Doppler Imager (MDI), have made
possible a continuous monitoring of the solar meridional flow in the
subphotospheric layers for the last solar cycle, including the recent
extended minimum. Here we review some of the meridional circulation
observations using local helioseismology techniques and relate them
to magnetic flux transport models.
Title: Testing the GONG ring-diagram pipeline with HMI Dopplergrams
Authors: Jain, Kiran; Tripathy, S. C.; González Hernández, I.;
Kholikov, S.; Hill, F.; Komm, R.; Bogart, R.; Haber, D.
Bibcode: 2011JPhCS.271a2017J
Altcode:
The GONG ring-diagram pipeline was developed to analyze GONG+
Dopplergrams in order to extract information about solar subsurface
flows and has been extensively tested for this purpose. Here we present
preliminary results obtained by analyzing the HMI Dopplergrams with
the GONG pipeline and compare them with those obtained from the HMI
ring-diagram pipeline.
Title: Helioseismic Studies of a Sunspot using HMI Data
Authors: Tripathy, S. C.; Jain, K.; Gonzalez Hernandez, I.; Komm,
R.; Hill, F.; McManus, S.; Bogart, R.; Rabello-Soares, M. C.; Basu,
S.; Baldner, C.; Haber, D. A.
Bibcode: 2010AGUFMSH11A1603T
Altcode:
We study the mode parameters and sub-surface properties of the sunspot
in NOAA active region 10093 during its disk passage between August
6-14, 2010. This is one of the major active regions recorded so far
during the cycle 24 and continuous observations are available from the
Helioseismic and Magnetic Imager (HMI). We will present the results
using the HMI data processed through the HMI ring-diagram pipeline and
compare those obtained with the GONG pipeline. We will also present
results by analyzing the GONG observations through GONG pipeline.
Title: Predictions of active region flaring probability using
subsurface helicity measurements
Authors: Reinard, A. A.; Komm, R.; Hill, F.
Bibcode: 2010AGUFMSH43B1818R
Altcode:
Solar flares are responsible for a number of hazardous effects on the
earth such as disabling high-frequency radio communications, interfering
with GPS measurements, and disrupting satellites. However, forecasting
flare occurrence is currently very difficult. One possible means for
predicting flare occurrence lies in helioseismology, i.e. analysis of
the region below the active region for signs of an impending flare. Time
series helioseismic data collected by the Global Oscillation Network
Group (GONG) has been analyzed for a subset of active regions that
produce large flares and a subset with very high magnetic field strength
that produce no flares. A predictive parameter has been developed and
analyzed using discriminant analysis as well as traditional forecasting
tools such as the Heidke skill score. Preliminary results show that
this parameter predicts the flaring probability of an active region
2-3 days in advance with a relatively high degree of success.
Title: Solar Subsurface Flows derived with Ring-Diagram Analysis
Authors: Komm, R.; Howe, R.; Gonzalez Hernandez, I.; Hill, F.; Haber,
D. A.
Bibcode: 2010AGUFM.S32A..06K
Altcode:
Local helioseismology makes it possible to map the horizontal flows in
the outer convection zone of the Sun. For the ring-diagram analysis,
we start from full-disk Doppler velocity images of the Sun and track a
region at about the surface rotation rate for a period of a day. Each
tracked data cube of velocity is then Fourier transformed. The resulting
3-D power spectrum shows structures that correspond to the acoustic
waves. These structures appear as rings in a 2-D plane at a given
temporal frequency. Since acoustic waves are advected by subsurface
flows, the velocity of these horizontal flows can be determined from
the offset of the ring centers. Using ring-diagram analysis of Doppler
images of the Sun obtained with the ground-based Global Oscillation
Network Group (GONG) and the Michelson Doppler Imager (MDI) instrument
on board the Solar and Heliospheric Observatory spacecraft (SOHO),
we are studying, for example, the large-scale subsurface flows (E-W
rotation and N-S meridional flow) and their variation with the solar
cycle of magnetic activity. We are also studying subsurface flows
associated with active regions on the Sun focusing on their evolution
(emergence and decay). In addition, we have started to analyze data from
the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics
Observatory (SDO) spacecraft. We will present some recent results.
Title: Accessing SDO data in a pipeline environment using the VSO
WSDL/SOAP interface
Authors: Suarez Sola, F. I.; Hourcle, J. A.; Amezcua, A.; Bogart,
R.; Davey, A. R.; Gurman, J. B.; Hill, F.; Hughitt, V. K.; Martens,
P. C.; Spencer, J.; Vso Team
Bibcode: 2010AGUFMSH23C1869S
Altcode:
As part of the Virtual Solar Observatory (VSO) effort to support the
Solar Dynamics Observatory (SDO) data, the VSO has worked on bringing
up to date its WSDL document and SOAP interface to make it compatible
with most widely used web services core engines. (E.g. axis2, jws,
etc.) In this presentation we will explore the possibilities available
for searching and/or fetching data within pipeline code. We will explain
some of the WSDL/VSO-SDO interface intricacies and show how the vast
amount of data that is available via the VSO can be tapped via IDL,
Java, Perl or C in an uncomplicated way.
Title: Global and Local Helioseismology from HMI and AIA
Authors: Howe, R.; Komm, R.; Gonzalez Hernandez, I.; Jain, K.; Hill,
F.; Haber, D. A.; Bogart, R.
Bibcode: 2010AGUFMSH11A1601H
Altcode:
Data from the HMI [Helioseismic and Magnetic Imager] and AIA
[Atmospheric Imaging Assembly] instruments aboard the Solar Dynamics
observatory have been available for some months. We present some
preliminary results from these data, including subsurface flow maps
and activity-related local mode parameter shifts from helioseismic
ring-diagram analysis of HMI data, HMI helioseismic sensing of the far
side of the Sun, and low-degree p-mode spectra from the high-photosphere
bands on AIA as well as from HMI velocity and continuum intensity. The
results will be compared with those from the Michelson Doppler Imager
and the Global Oscillation Network Group.
Title: Improving the Far-Side Seismic Maps
Authors: Gonzalez Hernandez, I.; Hill, F.; Koller, J.
Bibcode: 2010AGUFMSH41D..04G
Altcode:
Seismic maps of the far side of the Sun have proven their capability
to locate and track medium-to-large active regions at 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 in the far-side. Recent
improvements to the these maps include a more accurate determination of
the location of the active region, automatic highlight of candidates
and calibration in terms of the magnetic field strength. We discuss
here strategies to include extra information in the seismic far-side
maps, such as realistic error estimations and area determination,
in order to use them as input to photospheric flux transport models.
Title: Using helioseismology to understand and predict the solar cycle
Authors: Hill, Frank; Komm, Rudi; Howe, Rachel; Gonzalez Hernandez,
Irene; Kholikov, Shukur; Leibacher, John
Bibcode: 2010shin.confE.156H
Altcode:
Helioseismology is now being used to investigate the subsurface
flows that are related to the solar cycle. The relevant flows are the
east-west zonal flows (torsional oscillation), and the north-south
meridional flows. This poster will summarize the relationship of the
timing of the solar cycle with the characteristics of the zonal and
meridional flows; as well as what we know about the nature of the deep
meridional flows that play a role in the dynamo.
Title: What Solar Oscillation Tell Us About the Solar Minimum
Authors: Jain, K.; Tripathy, S. C.; Burtseva, O.; H´Ndez, I. G.;
Hill, F.; Howe, R.; Kholikov, S.; Komm, R.; Leibacher, J.
Bibcode: 2010ASPC..428...57J
Altcode: 2010arXiv1002.2411J
The availability of continuous helioseismic data for two consecutive
solar minima has provided a unique opportunity to study the changes
in the solar interior that might have led to this unusual minimum. We
present preliminary analysis of intermediate-degree mode frequencies in
the 3 mHz band during the current period of minimal solar activity and
show that the mode frequencies are significantly lower than those during
the previous activity minimum. Our analysis does not show any signature
of the beginning of cycle 24 until the end of 2008. In addition, the
zonal and meridional flow patterns inferred from inverting frequencies
also hint at a delayed onset of a new cycle. The estimates of travel
time are higher than the previous minimum confirming a relatively weak
solar activity during the current minimum.
Title: Acoustic Oscillations During the Extended Solar Minimum
Authors: Tripathy, Sushanta; Jain, K.; Hill, F.
Bibcode: 2010AAS...21631901T
Altcode: 2010BAAS...41..909T
The acoustic oscillation frequencies of the Sun vary with the
progress of the solar cycle and in general, the frequencies increase
as solar magnetic activity increases. Our recent study on frequencies
of intermediate degree modes of the Sun during the extended minimum
phase between cycles 23 and 24 shows a surprising anti-correlation
between the frequencies and the measures of solar activity. In this
paper, we present results of our analysis on the temporal evolution
of frequency shifts measured locally over the solar disk during the
period of 2007-2009 and show that the extended minimum period between
cycles 23 and 24 is rather unusual.
Title: Meridional Flow Measurements from 15 Years of GONG Spherical
Harmonic Time Series
Authors: Leibacher, John W.; Kholikov, S.; Hill, F.
Bibcode: 2010AAS...21640003L
Altcode: 2010BAAS...41..855L
We present the results of a meridional flow time-distance analysis
based on GONG data. In order to increase the signal-to-noise ratio,
and to reduce contamination from other modes, we utilize a low-m
filtering technique, which seems capable of extending the meridional
flow measurements down to the deep layers of the convection zone
(0.7R°). Our preliminary results indicate that the precision
achieved is very close to that required to measure the reverse flow
down to the base of the solar convection zone where it is expected to
be situated. To avoid projection effects at high latitudes, and to
extend the analysis to higher latitudes, we analyze extreme B-angle
time periods separately. We discuss the significance of temporal
variations of meridional flow in the presence of additional flows
around active regions.
Title: SDO Data Access Via The Virtual Solar Observatory
Authors: Hill, Frank; Gurman, J.; Martens, P.; Bogart, R.; Davey, A.;
Hourcle, J.; Suarez Sola, F.; Hughitt, K.; Spencer, J.; Reardon, K.;
Amezcua, A.
Bibcode: 2010AAS...21640218H
Altcode: 2010BAAS...41Q.876H
The launch of SDO brings not only the prospect of new solar physics
discoveries, but also a flood of data. The sustained data rate of
150 Mbs (about 1.6 TB per day) is the highest yet produced by a
solar physics observatory, and the handling of the data requires new
methods. One approach is to distribute the data storage and request
system over a number of distinct sites to reduce the bandwidth
requirements at a single location. The VSO, in conjunction with the
Joint Science and Operations Center (JSOC) at Stanford and a network of
partial archive sites currently at CfA, NSO, ROB, and MPIS, is now able
to provide metadata search and data retrieval services for the SDO AIA
and HMI instruments. EVE data will also be included in the future. This
talk will describe how SDO data can be accessed via the VSO.
Title: Meridional Circulation During the Extended Solar Minimum:
Another Component of the Torsional Oscillation?
Authors: González Hernández, I.; Howe, R.; Komm, R.; Hill, F.
Bibcode: 2010ApJ...713L..16G
Altcode: 2010arXiv1003.1685G
We show here a component of the meridional circulation developing
at medium-high latitudes (40°-50°) before the new solar cycle
starts. Like the torsional oscillation of the zonal flows, this extra
circulation seems to precede the onset of magnetic activity at the solar
surface and moves slowly toward lower latitudes. However, the behavior
of this component differs from that of the torsional oscillation
regarding location and convergence toward the equator at the end
of the cycle. The observation of this component before the magnetic
regions appear at the solar surface has only been possible due to the
prolonged solar minimum. The results could settle the discussion as
to whether the extra component of the meridional circulation around
the activity belts, which has been known for some time, is or is not
an effect of material motions around the active regions.
Title: Unusual Trends in Solar P-Mode Frequencies During the Current
Extended Minimum
Authors: Tripathy, S. C.; Jain, K.; Hill, F.; Leibacher, J. W.
Bibcode: 2010ApJ...711L..84T
Altcode: 2010arXiv1002.1690T
We investigate the behavior of the intermediate-degree mode frequencies
of the Sun during the current extended minimum phase to explore the
time-varying conditions in the solar interior. Using contemporaneous
helioseismic data from the Global Oscillation Network Group (GONG) and
the Michelson Doppler Imager (MDI), we find that the changes in resonant
mode frequencies during the activity minimum period are significantly
greater than the changes in solar activity as measured by different
proxies. We detect a seismic minimum in MDI p-mode frequency shifts
during 2008 July-August but no such signature is seen in mean shifts
computed from GONG frequencies. We also analyze the frequencies of
individual oscillation modes from GONG data as a function of latitude
and observe a signature of the onset of the solar cycle 24 in early
2009. Thus, the intermediate-degree modes do not confirm the onset
of the cycle 24 during late 2007 as reported from the analysis of the
low-degree Global Oscillations at Low Frequency frequencies. Further,
both the GONG and MDI frequencies show a surprising anti-correlation
between frequencies and activity proxies during the current minimum,
in contrast to the behavior during the minimum between cycles 22 and 23.
Title: Inhomogeneous Power Distribution in Magnetic Oscillations
Authors: Jain, Kiran; Tripathy, S. C.; Kholikov, S.; Hill, F.
Bibcode: 2010arXiv1003.5013J
Altcode:
We apply ring-diagram analysis and spherical harmonic decomposition
methods to compute 3-dimensional power spectra of magnetograms obtained
by the Global Oscillation Network Group (GONG) during quiet periods of
solar activity. This allows us to investigate the power distribution
in acoustic waves propagating in localized directions on the solar
disk. We find evidence of the presence of five-minute oscillations
in magnetic signals that suggests a non-homogeneous distribution of
acoustic power. In this paper, we present our results on the asymmetry
in oscillatory power and its behaviour as a function of frequency,
time and magnetic field strength. These characteristics are compared
with simultaneous velocity measurements.
Title: Evidence That Temporal Changes in Solar Subsurface Helicity
Precede Active Region Flaring
Authors: Reinard, A. A.; Henthorn, J.; Komm, R.; Hill, F.
Bibcode: 2010ApJ...710L.121R
Altcode:
We report on the analysis of subsurface vorticity/helicity measurements
for flare producing and quiet active regions. We have developed a
parameter to investigate whether large, decreasing kinetic helicity
density commonly occurs prior to active region flaring. This new
parameter is effective at separating flaring and non-flaring active
regions and even separates among C-, M-, and X-class flare producing
regions. In addition, this parameter provides advance notice of flare
occurrence, as it increases 2-3 days before the flare occurs. These
results are striking on an average basis, though on an individual
basis there is still considerable overlap between flare associated
and non-flare associated values. We propose the following qualitative
scenario for flare production: subsurface rotational kinetic energy
twists the magnetic field lines into an unstable configuration,
resulting in explosive reconnection and a flare.
Title: Do Active Regions Modify Oscillation Frequencies?
Authors: Tripathy, S. C.; Jain, K.; Hill, F.
Bibcode: 2010ASSP...19..374T
Altcode: 2009arXiv0903.2077T; 2010mcia.conf..374T
We investigate the variation of high-degree mode frequencies as a local
response to the active regions in two different phases of the solar
activity cycle. We find that the correlation between frequency shifts
and the surface magnetic activity measured locally are significantly
different during the two activity periods.
Title: Enabling Distributed Search and Access to SDO Data with the
Virtual Solar Observatory
Authors: Davey, Alisdair; Martens, P.; Gurman, J.; Hourcle, J.; Hill,
F.; Suarez-Sola, F.; Amezcua, A.; Bogart, R.; Spencer, J.
Bibcode: 2010cosp...38.2881D
Altcode: 2010cosp.meet.2881D
The Virtual Solar Observatory (VSO) will be an integral part of
distributing Solar Dynamics Observatory (SDO) data to the Solar Physics
community and in enabling it to be searched by scientists. A daily
data volume of 1.5TB presents unique challenges, and the VSO has been
working on enhancing various aspects of its infrastructure to deal with
them. The VSO will provide a dedicated interface to SDO data, providing
common methods users of VSO already know, as well as new methods that
reflect the needs of interacting with AIA, HMI and EVE data. VSO has
created a data distribution architecture based up the Joint Science
Operations Center (JSOC) infrastructure, that in partnership with
NASA Solar Data Analysis Center, National Solar Observatory, Royal
Observatory Belgium, University College Lancashire, Max Planck Institute
for Solar System Research and the Institute d'Astrophysique Spatiale
(Orsay) will enable scientists to retrieve SDO data of interest in
the fastest possible way. VSO is working closely with the Helioviewer
and Heliophysics Event Knowledgebase (HEK) teams to ensure we will
be able to use their efforts and be used by their efforts for data
retrieval. In this manner, graphical, IDL-based and event approaches
to data discovery will be fully supported by the VSO.
Title: Amplitudes of High-Degree p Modes in the Quiet and Active Sun
Authors: Burtseva, O.; Tripathy, S. C.; Hill, F.; Kholikov, S.;
Raouafi, N. -E.; Lindsey, C.
Bibcode: 2009ASPC..416..293B
Altcode: 2009arXiv0904.0440B
We investigate mode amplitudes in the active and quiet Sun in both
maximum and minimum phases of the solar activity cycle. We confirm
previous studies showing that p-mode amplitudes at solar minimum are
higher than at solar maximum. We mask active regions of a certain
magnetic field strength and compare the masked and unmasked acoustic
power. After applying the masks, the preliminary analysis indicates
that the amplitude decreases over all degrees during solar minimum,
compared to the unmasked case, while at solar maximum the amplitude
first decreases up to l∼300 and then increases at higher degrees.
Title: Subsurface Flow Properties of Flaring versus Flare-Quiet
Active Regions
Authors: Ferguson, R.; Komm, R.; Hill, F.; Barnes, G.; Leka, K. D.
Bibcode: 2009ASPC..416..127F
Altcode:
We apply discriminant analysis to 1009 active regions and their
subsurface flow parameters, such as vorticity and kinetic helicity
density, with the goal of distinguishing between flaring and non-flaring
active regions. Flow and flux variables lead to better classification
rates than a no-event prediction. The Heidke skill score, which measures
the improvement over predicting that no events occur, increases by
about 25% and 50% for C- and M-class flares when several subsurface
characteristics are included compared to using a single magnetic
flux measure.
Title: Subsurface Zonal Flows of Active and Quiet Regions
Authors: Komm, R.; Howe, R.; Hill, F.; González Hernández, I.
Bibcode: 2009ASPC..416..123K
Altcode:
We study the zonal flow in solar subsurface layers, analyzing about
six years of GONG+ high-resolution Doppler data with a ring-diagram
analysis. We focus on the variation of the zonal flow with magnetic
activity over a range of depths from the surface to about 16 Mm. We
calculate the average zonal flow for a quiet- and an active-region
subset defined as dense-pack locations with an unsigned magnetic flux
less than 3.4 G and locations with greater than 65.0 G respectively. The
average zonal flow of active regions is about 4 ms-1 faster
than the average flow of quiet regions and this difference increases
slightly with increasing depth at depths greater than about 5 Mm. The
difference shows no apparent pattern in time and latitude; it shows
no variation with the solar cycle.
Title: Temporal Variation of Subsurface Flows of Active Regions
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 2009ASPC..416..115K
Altcode:
We study the temporal variation of subsurface flows associated with
955 active regions. The subsurface kinetic helicity density varies
with the magnetic flux and its values at deeper layers are correlated
with the total flare intensity. The average vertical velocity shows
a downflow at depths shallower than about 12 Mm and upflows at
greater depth. Daily ring-diagram measurements thus confirm previous
synoptic measurements. In addition we find, that at some depths, the
crosscorrelation between the vertical velocity and the unsigned magnetic
flux is positive at negative lag time. This implies that the temporal
variation of the vertical velocity might be a precursor of flux changes.
Title: Variation of Oscillation Mode Parameters over Solar Cycle 23:
An Analysis on Different Time Scales
Authors: Tripathy, S. C.; Hill, F.; Jain, K.; Leibacher, J. W.
Bibcode: 2009ASPC..416..285T
Altcode: 2009arXiv0903.2074T
We investigate the variation in the mode parameters obtained from time
series of length nine, 36, 72 and 108 days to understand the changes
occurring on different time-scales. The regression analysis between
frequency shifts and activity proxies indicates that the correlation
and slopes are correlated and both increase in going from time series
of nine to 108 days. We also observe that the energy of the mode is
anti-correlated with solar activity while the rate at which the energy
is supplied remains constant over the solar cycle.
Title: The internal dynamics and magnetism of the sun -- the
perspective from global helioseismology (Invited)
Authors: Howe, R.; Hill, F.; Komm, R.; Christensen-Dalsgaard, J.;
Schou, J.; Thompson, M. J.
Bibcode: 2009AGUFMSH11B..04H
Altcode:
Helioseismology allows us to probe the interior dynamics of the
Sun. Observations over the past three decades reveal the interior
rotation profile, with a near-surface shear layer, differential
rotation throughout the convection zone, a strong shear layer -- the
tachocline -- at the base of the convection zone, and approximately
uniform rotation in the radiative interior. Since the mid 1990's,
continuous observations from the Global Oscillations Network Group and
the Michelson Doppler Imager have allowed the study of subtle temporal
variations in the rotation within the convection zone. The so-called
"torsional oscillation" pattern of migrating zonal flows accompanying
the surface activity migration during the solar cycle has been shown to
penetrate deep within the convection zone. During the current extended
solar minimum, the flow bands can be seen to migrate more slowly towards
the equator than was seen in the previous minimum. There have also been
(still unconfirmed) findings of shorter-term variations in the rotation
rate close to the tachocline during the early years of the previous
solar cycle. This review will describe the important results and give
an update on the most recent observations of the interior dynamics as
we await the rise of solar cycle 24.
Title: Correlation Analysis of Mode Frequencies with Activity Proxies
at Different Phases of the Solar Cycle
Authors: Jain, K.; Tripathy, S. C.; Hill, F.
Bibcode: 2009ASPC..416..189J
Altcode: 2009arXiv0902.1555J
We analyze intermediate degree p- and f-mode eigenfrequencies measured
by GONG and SoHO/MDI for a complete solar cycle to study their
correlation with solar activity. We demonstrate that the frequencies
do vary linearly with the activity, however the degree of correlation
differs from phase to phase of the cycle. During the rising and the
declining phases, the mode frequencies are strongly correlated with the
activity proxies whereas during the low- and high-activity periods,
the frequencies have significantly lower correlation with all the
activity proxies considered here.
Title: Does the Selection of a Quiet Region Influence the Local
Helioseismic Inferences?
Authors: Tripathy, S. C.; Antia, H. M.; Jain, K.; Hill, F.
Bibcode: 2009ASPC..416..139T
Altcode: 2009arXiv0901.4939T
We apply the ring-diagram technique to high resolution Dopplergrams in
order to estimate the variation in oscillation mode parameters between
active and quiet regions. We demonstrate that the difference in mode
parameters between two quiet regions can be as large as those between
a pair of active and quiet region. This leads us to conclude that the
results derived on the basis of a single quiet region could be biased.
Title: Solar-Stellar Dynamos as Revealed by Helio- and
Asteroseismology: GONG 2008/SOHO 21
Authors: Dikpati, M.; Arentoft, T.; González Hernández, I.; Lindsey,
C.; Hill, F.
Bibcode: 2009ASPC..416.....D
Altcode:
No abstract at ADS
Title: Ring Diagram Analysis of an Artificial 96 × 96 × 20 Mm
Data Set
Authors: Howe, R.; González Hernández, I.; Komm, R.; Hill, F.
Bibcode: 2009ASPC..416..151H
Altcode:
A 16-hour time series of data from a 96 × 96 × 20 Mm hydrodynamic
convection simulation has recently been made available. We will present
the preliminary results of applying the ring-diagram technique of local
helioseismology to this dataset, in comparison with similar quiet-Sun
observations from GONG and MDI, and show that it is possible to recover
the underlying horizontal flow profile, at least in the upper half of
the region.
Title: The Future of Helioseismology
Authors: Hill, F.
Bibcode: 2009ASPC..416..557H
Altcode:
The future of observational helioseismology lies in four areas:
extremely high-degree observations, ground-based multi-wavelength
observations, space-based observations from multiple viewpoints, and
space weather predictive tools. On the theoretical front, advances in
numerical simulations, further understanding of the effect of surface
magnetic fields on the observations, and the development of methods
to detect sub-surface magnetic fields are at the forefront. Finally,
new developments in astrophysical fluid dynamics and dynamo models
will provide new insights into the generation of magnetic fields,
and will motivate new efforts to determine the nature of the internal
solar velocity and magnetic fields.
Title: Using subsurface helicity measurements to predict flare
occurrence
Authors: Reinard, A. A.; Henthorn, J.; Komm, R.; Hill, F.
Bibcode: 2009AGUFMSH21C..06R
Altcode:
Solar flares are responsible for a number of hazardous effects including
disabling high-frequency radio communications, interfering with GPS
measurements, and disrupting satellites. Forecasting flare occurrence
is very difficult, giving little advanced notice of these events. One
possible means for predicting flare occurrence lies in helioseismology,
i.e. analysis of the region below the active region for signs of
an impending flare. Time series helioseismic data collected by the
Global Oscillation Network Group (GONG) have been analyzed for a
subset of active regions that produce large flares and a subset with
very high magnetic field strength that produce no flares. A predictive
parameter has been developed and analyzed using discriminant analysis
as well as traditional forecasting tools such as the Heidke skill
score. Preliminary results indicate this parameter predicts flare
occurrence with a high success rate.
Title: Large-Scale Solar Subsurface Flows During Solar Cycle Minimum
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 2009AGUFMSH11A1482K
Altcode:
The long solar minimum between cycles 23/24 allows us to study
large-scale flows, such as rotation and meridional flow, as a dynamical
process without bias due to magnetic fields. We study the subsurface
flows in the near-surface layers of the convection zone with a local
helioseismic technique, called ring-diagram analysis, using Global
Oscillation Network Group (GONG) data obtained during the years 2008
and early 2009. We focus on the meridional flow and the divergence and
vorticity of subsurface flows during this exceptional solar minimum. We
also search for large-scale coherent structures that might be present
in the convection zone but might be easily obscured by the effect of
surface magnetic fields during other epochs of the solar cycle. We
will present the most recent results.
Title: The Torsional Oscillation and the Solar Minimum
Authors: Howe, R.; Hill, F.; Komm, R.; Christensen-Dalsgaard, J.;
Schou, J.; Thompson, M. J.
Bibcode: 2009AGUFM.U34A..03H
Altcode:
The so-called torsional oscillation is a pattern of zonal flow bands,
detected at the solar surface by direct Doppler measurements and within
the convection zone by helioseismic measurements such as those carried
out by the Global Oscillations Network Group and the Michelson Doppler
Imager, that migrates from mid-latitudes towards the equator and poles
with each solar cycle. In the current minimum the low-latitude branch
of the pattern can be seen to have taken at least a year longer to
migrate towards the equator than was the case in the previous minimum. A
flow configuration matching that of the previous minimum was reached
during 2008, and by early 2009 the fast-rotating belt associated with
the new cycle had reached the latitude at which the onset of activity
was seen in Cycle 23, but magnetic activity has remained low. We will
present the most recent results and consider the implications for the
new solar cycle.
Title: Recent Progress in Detecting Meridional Flows Deep within
the Sun
Authors: Hill, F.; Kholikov, S.; Ehgamberdiev, S.; Serebryanskiy, A.
Bibcode: 2009AGUFMSH11B..10H
Altcode:
The solar meridional flow is observed to be primarily poleward in and
immediately below the photosphere. In order to satisfy the conservation
of mass, there must be an equatorward return flow deep within the
sun. Helioseismology has so far been unable to detect this flow,
but the continual accumulation of high-quality data from SOHO/MDI
and GONG over 14 years has improved the chances of observing the
characteristics of the flow, which are vital for modern flux-transport
dynamo models. Here we report on the latest results of inversions of
deep north-south travel-time differences and their implications.
Title: Improving the Prediction Capability of Seismic Far-Side Maps
Authors: González Hernández, I.; Scherrer, P.; Hill, F.; Lindsey,
C.; Braun, D.
Bibcode: 2009ASPC..416...87G
Altcode:
Both the Michelson Doppler Imager (MDI) and the Global Oscillation
Network Group (GONG) projects produce daily seismic maps of surface
magnetic activity on the non-visible hemisphere of the Sun. The
technique has proven useful to detect and follow large active regions
before they appear to face the Earth. This work demonstrates an
improvement in the detection capability of the technique by applying
the results of new research. We calibrate the daily far-side maps in
terms of characteristics of the active region, such as total area and
magnetic flux strength, apply a relationship between the strength of
the persistent signal and the success rate to automatically highlight
possible candidates, and remove solar-cycle variations to stabilize
the signal.
Title: The Torsional Oscillation and the Solar Cycle: Is it Minimum
Yet?
Authors: Howe, R.; Komm, R.; Hill, F.; Larson, T.; Schou, J.; Thompson,
M. J.; Ulrich, R. K.
Bibcode: 2009ASPC..416..269H
Altcode:
The torsional oscillation pattern of migrating zonal flows is related to
the solar activity cycle. In the approach to solar minimum, we compare
the current flow profile with that seen at the previous minimum, using
Global Oscillation Network Group (GONG) and Michelson Doppler Imager
(MDI) data as well as Mount Wilson Doppler observations that reach
further back in time. Will the flow pattern at the upcoming minimum
match that for the previous one?
Title: Lifetimes of High-Degree p Modes in the Quiet and Active Sun
Authors: Burtseva, O.; Hill, F.; Kholikov, S.; Chou, D. -Y.
Bibcode: 2009SoPh..258....1B
Altcode: 2009arXiv0902.2016B
We study variations of the lifetimes of high-ℓ solar p modes in the
quiet and active Sun with the solar activity cycle. The lifetimes in
the degree range ℓ=300 - 600 and ν=2.5 - 4.5 mHz were computed from
SOHO/MDI data in an area including active regions and quiet Sun using
the time - distance technique. We applied our analysis to the data in
four different phases of solar activity: 1996 (at minimum), 1998 (rising
phase), 2000 (at maximum), and 2003 (declining phase). The results
from the area with active regions show that the lifetime decreases as
activity increases. The maximal lifetime variations are between solar
minimum in 1996 and maximum in 2000; the relative variation averaged
over all ℓ values and frequencies is a decrease of about 13%. The
lifetime reductions relative to 1996 are about 7% in 1998 and about 10%
in 2003. The lifetime computed in the quiet region still decreases
with solar activity, although the decrease is smaller. On average,
relative to 1996, the lifetime decrease is about 4% in 1998, 10% in
2000, and 8% in 2003. Thus, measured lifetime increases when regions
of high magnetic activity are avoided. Moreover, the lifetime computed
in quiet regions also shows variations with the activity cycle.
Title: A Note on the Torsional Oscillation at Solar Minimum
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
Schou, J.; Thompson, M. J.
Bibcode: 2009ApJ...701L..87H
Altcode: 2009arXiv0907.2965H
We examine the evolution of the zonal flow pattern in the upper solar
convection zone during the current extended solar minimum, and compare
it with that during the previous minimum. The results suggest that
a configuration matching that at the previous minimum was reached
during 2008, but that the flow band corresponding to the new cycle has
been moving more slowly toward the equator than was observed in the
previous cycle, resulting in a gradual increase in the apparent length
of the cycle during the 2007-2008 period. The current position of the
lower-latitude fast-rotating belt corresponds to that seen around the
onset of activity in the previous cycle.
Title: Emerging and Decaying Magnetic Flux and Subsurface Flows
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 2009SoPh..258...13K
Altcode:
We study the temporal variation of subsurface flows of 788 active
regions and 978 quiet regions. The vertical-velocity component used in
this study is derived from the divergence of the measured horizontal
flows using mass conservation. The horizontal flows cover a range of
depths from the surface to about 16 Mm and are determined by analyzing
about five years of GONG high-resolution Doppler data with ring-diagram
analysis. We determine the change in unsigned magnetic flux during
the disk passage of each active region using MDI magnetograms binned
to the ring-diagram grid. We then sort the data by their flux change
from decaying to emerging flux and divide the data into five subsets
of equal size. The average vertical flows of the emerging-flux
subset are systematically shifted toward upflows compared to the
grand average values of the complete data set, whereas the average
flows of the decaying-flux subset show comparably more pronounced
downflows especially near 8 Mm. For flux emergence, upflows become
stronger with time with increasing flux at depths greater than about
10 Mm. At layers shallower than about 4 Mm, the flows might start to
change from downflows to upflows, when flux emerges, and then back to
downflows after the active regions are established. The flows in the
layers between these two depth ranges show no response to the emerging
flux. In the case of decaying flux, the flows change from strong upflows
to downflows at depths greater than about 10 Mm, whereas the flows do
not change systematically at other depths. A cross-correlation analysis
shows that the flows in the near-surface and the deeper layers might
change about one day before flux emerges. The flows associated with
the quiet regions fluctuate with time but do not show any systematic
variation.
Title: Solar flares and solar subphotospheric vorticity
Authors: Komm, R.; Hill, F.
Bibcode: 2009JGRA..114.6105K
Altcode: 2009JGRA..11406105K
We explore the relation between surface magnetic flux of the sun and
subsurface flow vorticity for flaring and nonflaring solar active
regions. For this purpose, we use a data set consisting of 1009 active
regions, including the vorticity measurements of their subsurface
flows derived from high-resolution global oscillation network group
(GONG) helioseismology data and the corresponding X-ray flare data
from the geostationary operation environmental satellite (GOES). Using
quantities averaged over the disk passage of active regions, we find
that, while there is a considerable spread of the flux and vorticity
values, they are more or less linearly related. We distinguish the
level of flare activity by X-ray flare class and find that large
flux or large vorticity values are sufficient for an active region
to produce low-intensity C-class flares. Active regions that produce
high-intensity X-class flares are characterized by large values of
both flux and vorticity. Active regions that produce M-class flares of
intermediate intensity are characterized by large vorticity values. The
inclusion of solar subsurface vorticity thus helps to distinguish
between flaring and nonflaring active regions.
Title: The Virtual Solar Observatory: Where Do We Go from Here?
Authors: Gurman, Joseph B.; Bogart, R.; Spencer, J.; Hill, F.; Suarez
Sola, I.; Reardon, K.; Hourcle, J.; Hughitt, K.; Martens, P.; Davey, A.
Bibcode: 2009SPD....40.1508G
Altcode:
The Virtual Solar Observatory (VSO) continues to add features in an
effort to broaden the ways in which it can be used to aid research. We
describe and demonstrate plans for SDO data access (see also the poster
Suarez-Sola et al.), multiple catalog access (Hourclé et al.), and
new capabilities of the IDL VSO_SEARCH function, as well as describing
future capabilities in development and under consideration. Since
the VSO is funded by the Solar Data Analysis Center (SDAC), which will
be undergoing a NASA Senior Review in July, we solicit community input
to help us prioritize this new work: what should we do with the limited
resources available?
Title: A New Solar H-alpha Distributed Observing System
Authors: Hill, Frank; Harvey, J. W.; Luis, G.; Purdy, T.; Bolding,
J.; Eliason, P.; Kroll, R.; Lewis, F.; Berman, L.; Parsons, A.
Bibcode: 2009SPD....40.1806H
Altcode:
Space weather forecasts and nowcasts require rapid-cadence, continual,
and robust solar observations. A useful strategy to accomplish this
is to deploy a network of ground-based observing systems distributed
in geographic longitude. The US Air Force Weather Agency (AFWA) has
been operating the Solar Optical Observing Network (SOON) for many
years, and is now replacing SOON with ISOON, an improved SOON. As
a back-up during the development and installation of ISOON, AFWA is
supporting the addition of an H-alpha observing system into the existing
sites of the Global Oscillation Network Group (GONG) program. GONG
comprises six sites in California, Hawaii, Australia, India, Spain,
and Chile, and currently provides one per minute continual magnetic
field, Doppler, and intensity measurements in the Ni 6768 line. The
additional H-alpha capability will comprise a 0.4-A bandpass filter,
a 2kX2k CCD, beamsplitter, transfer optics, and a dedicated data
acquisition system. The observing cadence will be one per minute
at a given site, with the acquisition time shifted between adjacent
sites to potentially provide an image every 20 sec. The data will be
transmitted back to Tucson, processed, and then transferred to AFWA
within one minute of acquisition.
Title: Emerging and Decreasing Magnetic Flux and Subsurface Flows
Authors: Komm, Rudolph; Howe, R.; Hill, F.
Bibcode: 2009SPD....40.0403K
Altcode:
We study the temporal variation of subsurface flows of 778 active
regions and 978 quiet regions. The vertical velocity component,
used in this study, is derived from the divergence of the measured
horizontal flows using mass conservation. The horizontal flows cover
a range of depths from the surface to about 16 Mm and are determined
by analyzing about five years of GONG high-resolution Doppler data with
ring-diagram analysis. We determine the change in unsigned magnetic flux
during the disk passage of each active region using MDI magnetograms
binned to the ring-diagram grid. We then sort the data by their flux
change from decreasing to emerging flux and divide the data into five
subsets of equal size. The average vertical flows of the emerging-flux
subset are systematically shifted toward upflows compared to the grand
average values of the complete data set, while the average flows of
the decreasing-flux subset shows comparably more pronounced downflows
especially near 8 Mm. For flux emergence, upflows become stronger with
time with increasing flux at depths greater than about 10 Mm. At layers
shallower than about 4 Mm, the flows change from downflows to upflows,
when flux emerges, and then back to downflows after the active regions
are established. The flows in the layers between these two depth ranges
show no response to the emerging flux. In the case of decaying flux,
the flows change from strong upflows to downflows at depths greater
than about 10 Mm, while the flows do not change systematically at
other depths.
Title: Solar Minimum and Helioseismic Inferences
Authors: Komm, Rudolph; Howe, R.; Jain, K.; Tripathy, S.; Burtseva,
O.; Hill, F.
Bibcode: 2009SPD....40.0718K
Altcode:
We have analyzed Global Oscillation Network Group (GONG) data of
cycle 23 to the end of the year 2008 covering the last/current solar
minimum. We study the rotation rate in the solar convection zone with a
global helioseismic analysis during this minimum and compare it to the
previous one. We also study the subsurface flows in the near-surface
layers of the convection zone with a ring-diagram analysis focusing on
the meridional flow and the divergence and vorticity of subsurface
flows during this epoch. In addition, we study frequency shifts
(from global and local analyses) and their correlation with magnetic
activity during solar minimum. Latitudinal variations of the p-mode
parameters from ring-diagram analysis during solar minimum will be
investigated. We will present the latest results.
Title: Statistical Analysis of the Success Rate of the Far-Side
Seismic Mapping of Active Regions.
Authors: Gonzalez-Hernandez, Irene; Scherrer, P.; Lindsey, C.; Hill,
F.; Braun, D.
Bibcode: 2009SPD....40.0707G
Altcode:
Seismic maps of the non-visible side of the Sun (far side) have been
used for almost a decade to follow large active regions before they
rotate to face the Earth. Preliminary efforts to quantify the success
rate of the used technique (seismic holography) have been published
with limited data. However, a thorough study is needed to further
understand the limitations of the technique in terms of size and
strength of the active regions detected and to reveal clues as to how
to improve it. We have analyzed three complete years of far-side
seismic maps calculated using both Global Oscillation Newtwork group
(GONG) and Michelson Doppler Imager (MDI) data and matched the far-side
candidates with associated active regions as recorded by the NOAA
database. Here we present the results.
Title: Measurement of Low Signal-To-Noise Ratio Solar p-Modes in
Spatially Resolved Helioseismic Data
Authors: Salabert, D.; Leibacher, J.; Appourchaux, T.; Hill, F.
Bibcode: 2009ApJ...696..653S
Altcode: 2009arXiv0902.2561S
We present an adaptation of the rotation-corrected, m-averaged
spectrum technique designed to observe low signal-to-noise ratio
(S/N), low-frequency solar p-modes. The frequency shift of each
of the 2l + 1 m spectra of a given (n, l) multiplet is chosen that
maximizes the likelihood of the m-averaged spectrum. A high S/N can
result from combining individual low S/N, individual-m spectra, none
of which would yield a strong enough peak to measure. We apply the
technique to Global Oscillation Network Group and Michelson Doppler
Imager data and show that it allows us to measure modes with lower
frequencies than those obtained with classic peak-fitting analysis
of the individual-m spectra. We measure their central frequencies,
splittings, asymmetries, lifetimes, and amplitudes. The low frequency,
low- and intermediate-angular degrees rendered accessible by this
new method correspond to modes that are sensitive to the deep solar
interior down to the core (l <= 3) and to the radiative interior
(4 <= l <= 35). Moreover, the low-frequency modes have deeper
upper turning points, and are thus less sensitive to the turbulence and
magnetic fields of the outer layers, as well as uncertainties in the
nature of the external boundary condition. As a result of their longer
lifetimes (narrower linewidths) at the same S/N the determination of
the frequencies of lower frequency modes is more accurate, and the
resulting inversions should be more precise.
Title: Subsurface Flow Properties of Flaring Versus Flare-quiet
Active Regions
Authors: Ferguson, Ryan M.; Komm, R.; Hill, F.; Barnes, G.; Leka, K. D.
Bibcode: 2009SPD....40.1908F
Altcode:
Previous studies have shown that the flare activity of active regions is
intrinsically linked with the vorticity of subsurface flows on temporal
and spatial scales comparable to the size and lifetime of active
regions. We begin to address the question whether the measured vorticity
of subsurface flows associated with active regions can help to improve
flare forecasting. For this purpose, we apply statistical tests based
on discriminant analysis to several subsurface flow parameters with the
goal to differentiate between flaring and non-flaring active regions. We will present the latest results. This work is carried out through
the National Solar Observatory Research Experiences for Undergraduate
(REU) site program, which is co-funded by the Department of Defense
in partnership with the National Science Foundation REU Program.
Title: A Helioseismic Comparison of the Solar Minima Preceding Cycles
23 and 24
Authors: Hill, Frank; Howe, R.; Komm, R.; Gonzallez Hernandez, I.;
Tripathy, S.; Jain, K.
Bibcode: 2009SPD....40.2401H
Altcode:
The current solar minimum is clearly unusual in a variety of
ways, including length, solar wind pressure, cosmic ray flux, and
marked absence of sunspots. This talk will compare the current
minimum with the previous one in terms of its helioseismic and
subsurface flow characteristics. The helioseismic characteristics are
primarily activity-related changes in the frequencies, amplitudes
and lifetimes. The relevant flows are the torsional oscillation,
meridional flow, subsurface vorticity, and the subsurface rotation rate.
Title: Temporal Variations of High-Degree Solar Acoustic Modes in
the Quiet Sun
Authors: Burtseva, Olga; Tripathy, S. C.; Hill, F.; Jain, K.
Bibcode: 2009SPD....40.0719B
Altcode:
Temporal variations in the quiet Sun can be associated with changes
in the convective properties and magnetic fields connected to the
convective motions. Here we characterize the high-degree acoustic
modes in quiet regions of the Sun during different phases of the solar
cycle. We apply ring-diagram technique to the Global Oscillation
Network Group Dopplergrams and focus on high latitudes above the
activity belts. We also analyze the solar cycle variations of the
magnetic field in the quiet Sun using Michelson Doppler Imager full-disk
magnetograms. The results of this study will be presented.
Title: Oscillatory Power Distribution in Full-disk Magnetograms
Authors: Hill, Frank; Jain, K.; Tripathy, S. C.; Kholikov, S.
Bibcode: 2009SPD....40.0928H
Altcode:
It has been shown that the interaction of p-modes with the magnetic
field modifies the mode's characteristics. The power around the
5-minute band is absorbed while there is an enhancement at higher
frequencies. Here we present recent results showing an inhomogeneous
power distribution in magnetic oscillations which may be useful in
characterizing the energy transport mechanisms in the upper solar
atmosphere. We use data from the high-cadence GONG magnetograms during
the low-activity phase of the solar cycle and compare our results with
simultaneous velocity oscillations.
Title: The Virtual Solar Observatory—A Resource for International
Heliophysics Research
Authors: Hill, Frank; Martens, Piet; Yoshimura, Keji; Gurman, Joseph;
Hourclé, Joseph; Dimitoglou, George; Suárez-Solá, Igor; Wampler,
Steve; Reardon, Kevin; Davey, Alisdair; Bogart, Richard S.; Tian,
Karen Q.
Bibcode: 2009EM&P..104..315H
Altcode: 2008EM&P..tmp...47H
The Virtual Solar Observatory (VSO) has been developed to allow
researchers, educators, and the general public to access data
and images from the major sources of on-line solar data. The VSO
substantially reduces the effort required to locate disparate data
sets, and removes the need for the user to locate the data and
learn multiple interfaces. The VSO provides a single interface to
about 60 geographically distributed data sets including space- and
ground-based sources. These data sets incorporate several physical
variables including magnetic field, intensity, Doppler velocity, etc.,
and all wavelengths from X-ray to radio. All layers of the sun, from
the interior to the corona, are included. In this paper we describe
the system and present the interface that the user will encounter. We
also discuss future enhancements planned for the system.
Title: Solar Activity Phases and Intermediate-Degree Mode Frequencies
Authors: Jain, Kiran; Tripathy, S. C.; Hill, F.
Bibcode: 2009ApJ...695.1567J
Altcode: 2009arXiv0902.1557J
We analyze intermediate-degree p-mode eigenfrequencies measured by
Global Oscillation Network Group and Michelson Doppler Imager/Solar and
Heliospheric Observatory over a solar cycle to study the source of their
variability. We carry out a correlation analysis between the change in
frequencies and several measures of the Sun's magnetic activity that are
sensitive to changes at different levels in the solar atmosphere. The
observations span a period of about 12 years starting from mid-1996
(the minimum of cycle 23) to early-2008 (near minimum of cycle 24),
corresponding to a nearly complete solar activity cycle. We demonstrate
that the frequencies do vary in phase with the solar activity indices,
however, the degree of correlation differs from phase to phase of the
cycle. During the rising and declining phases, the mode frequency shifts
are strongly correlated with the activity proxies whereas during the
high-activity period, the shifts have significantly lower correlation
with all activity proxies, except for the 10.7 cm radio flux. In
particular, the proxies that are only influenced by the variation of
the strong component of the magnetic field in the photosphere have
a much lower correlation at the high-activity period. On the other
hand, the shifts are better correlated with the proxies sensitive to
changes in the weak component of the magnetic field. Our correlation
analysis suggests that more than 90% of the variation in the oscillation
frequencies in all activity phases can be explained by changes in both
components of the magnetic field. Further, the slopes obtained from
the linear regression analysis also differ from phase to phase and
show a strong correlation with the correlation coefficients between
frequency shifts and solar activity.
Title: A New Way to Infer Variations of the Seismic Solar Radius
Authors: González Hernández, I.; Scherrer, P.; Hill, F.
Bibcode: 2009ApJ...691L..87G
Altcode: 2009arXiv0902.1002G; 2009ApJ...691L..87H
We show that the mean phase of waves propagating all the way from
the far side of the Sun to the front side, as measured by seismic
holography, varies with time. The change is highly anticorrelated with
solar cycle activity and is consistent with other recent results on
the variation of the seismic radius of the Sun. The phase change that
we observe corresponds to a few kilometers difference in the seismic
solar radius from solar maximum to solar minimum in agreement with
inferences from global helioseismology studies.
Title: Subsurface Zonal Flows
Authors: Komm, R.; Howe, R.; Hill, F.; González Hernández, I.
Bibcode: 2009SoPh..254....1K
Altcode: 2008SoPh..tmp..189K
We study the zonal flow in solar subsurface layers, analyzing about
six years of GONG++ high-resolution Doppler data with ring-diagram
analysis. We focus on the variation of zonal flow with magnetic activity
over a range of depths from the surface to about 16 Mm. There is a
positive correlation between unsigned magnetic flux and zonal flow at
most depths. We calculate the average zonal flow for a quiet- and an
active-region subset defined as dense-pack locations with an unsigned
magnetic flux less than 3.4 G and locations with greater than 65.0 G,
respectively. The average zonal flow of active regions is about 4 m
s−1 larger than the average flow of quiet regions. This
difference increases slightly with increasing depth, which might be
explained by a nonradial inclination of the flux tubes or a different
extent in depth of different magnetic features. The difference shows
no apparent pattern in time and latitude, which makes it unlikely that
it is simply a manifestation of the torsional-oscillation pattern. As
a byproduct, we find that the size of the North - South asymmetry of
the rotation rate decreases during the same epoch.
Title: Causes of Solar Activity
Authors: Giampapa, Mark S.; Gibson, Sarah; Harvey, J. W.; Hill, Frank;
Norton, Aimee A.; Pevtsov, A.
Bibcode: 2009astro2010S..92G
Altcode:
No abstract at ADS
Title: Asteroseismology: The Next Frontier in Stellar Astrophysics
Authors: Giampapa, Mark S.; Aerts, Conny; Bedding, Tim; Bonanno,
Alfio; Brown, Timothy M.; Christensen-Dalsgaard, Jorgen; Dominik,
Martin; Ge, Jian; Gilliland, Ronald L.; Harvey, J. W.; Hill, Frank;
Kawaler, Steven D.; Kjeldsen, Hans; Kurtz, D. W.; Marcy, Geoffrey W.;
Matthews, Jaymie M.; Monteiro, Mario Joao P. F. G.; Schou, Jesper
Bibcode: 2009astro2010S..91G
Altcode:
No abstract at ADS
Title: Comparison of High-Degree Solar Acoustic Frequencies and
Asymmetry Between Velocity and Intensity Data
Authors: Tripathy, S. C.; Antia, H. M.; Jain, K.; Hill, F.
Bibcode: 2009ApJ...691..365T
Altcode: 2008arXiv0809.4486T
Using the local helioseismic technique of ring diagram we analyze the
frequencies of high-degree f- and p-modes derived from both velocity and
continuum intensity data observed by Michelson Doppler Imager. Fitting
the spectra with asymmetric peak profiles, we find that the asymmetry
associated with velocity line profiles is negative for all frequency
ranges, agreeing with previous observations, while the asymmetry
of the intensity profiles shows a complex and frequency-dependent
behavior. We also observe systematic frequency differences between
intensity and velocity spectra at the high end of the frequency range,
mostly above 4 mHz. We infer that this difference arises from the
fitting of the intensity rather than the velocity spectra. We also
show that the frequency differences between intensity and velocity
do not vary significantly from the disk center to the limb when the
spectra are fitted with the asymmetric profile and conclude that only
a part of the background is correlated with the intensity oscillations.
Title: Solar Dynamo and Magnetic Self-Organization
Authors: Kosovichev, A. G.; Arlt, R.; Bonanno, A.; Brandenburg,
A.; Brun, A. S.; Busse, F.; Dikpati, M.; Hill, F.; Gilman, P. A.;
Nordlund, A.; Ruediger, G.; Stein, R. F.; Sekii, T.; Stenflo, J. O.;
Ulrich, R. K.; Zhao, J.
Bibcode: 2009astro2010S.160K
Altcode:
No abstract at ADS
Title: Stellar Physics of the Solar Interior in the Coming Decade
Authors: Hill, Frank
Bibcode: 2009astro2010S.124H
Altcode:
No abstract at ADS
Title: A Magnetohydrodynamic (MHD) Analyses of Energy and Magnetic
flux Transport from Sub-photosphere to the Corona
Authors: Wu, S.; Wang, A.; Hill, F.; Gonzáles-Hernández, I.
Bibcode: 2008AGUFMSH41A1617W
Altcode:
To understand how the particle (mass) flow transport across the magnetic
boundary, a realistic example will be used to illustrate this process,
which is to simulate the mass, magnetic flux, and energy transport
from the sub-photosphere to the corona. The numerical simulation model
that will be used in this paper is a newly developed data-driven
three-dimensional global magnetohydrodynamic (MHD) model with the
observed magnetic field and velocity field from GONG's data as the
inputs at the photosphere. The difference between this new model and
the model used in Wu, et al. 2005 is to include the effects of radiation
and the transition region. Numerical simulation results to be presented
are mass, total magnetic flux, and energy transport through photosphere
to the corona, also the solar wind for the period of Halloween event.
Title: Subsurface Meridional Circulation in the Active Belts
Authors: González Hernández, I.; Kholikov, S.; Hill, F.; Howe, R.;
Komm, R.
Bibcode: 2008SoPh..252..235G
Altcode: 2008SoPh..tmp..167G; 2008arXiv0808.3606G
Temporal variations of the subsurface meridional flow with the solar
cycle have been reported by several authors. The measurements are
typically averaged over periods of time during which surface magnetic
activity existed in the regions where the velocities are calculated. The
present work examines the possible contamination of these measurements
due to the extra velocity fields associated with active regions plus
the uncertainties in the data obtained where strong magnetic fields
are present. We perform a systematic analysis of more than five years
of GONG data and compare meridional flows obtained by ring-diagram
analysis before and after removing the areas of strong magnetic
field. The overall trend of increased amplitude of the meridional flow
towards solar minimum remains after removal of large areas associated
with surface activity. We also find residual circulation toward the
active belts that persists even after the removal of the surface
magnetic activity, suggesting the existence of a global pattern or
longitudinally-located organized flows.
Title: Latitudinal distribution of travel times in the upper solar
convection zone
Authors: Burtseva, Olga; Kholikov, Shukur; Hill, Frank
Bibcode: 2008JPhCS.118a2080B
Altcode:
We applied the time-distance technique to GONG+ data in 2001 (at
solar maximum) and 2006 (at solar minimum) to study the influence
of surface activity on the latitudinal distribution of travel times
of acoustic waves in the upper solar convection zone. We find that
surface activity is the dominant source of travel time differences
over the solar cycle. Removal of the surface activity with a masking
method reveals a residual travel-time shift of 0.5 sec, corresponding
to a surface temperature change of 0.25° K over the solar cycle.
Title: Kinetic helicity of subsurface flows and magnetic flux
Authors: Komm, Rudolf; Hill, Frank; Howe, Rachel
Bibcode: 2008JPhCS.118a2035K
Altcode:
We study the relation between the vorticty of solar subsurface flows
and surface magnetic activity, analyzing more than five years of GONG+
data with ring-diagram analysis. We focus on the enstrophy, defined
as the square of vorticity, and the kinetic helicity density, defined
as the scalar product of velocity and vorticity, and derive them from
the surface to a depth of about 16 Mm. We find that enstrophy and
helicity density of subsurface flows are rather constant at low flux
values (less than about 10 G), while at higher flux values there is a
linear relation between flux and the logarithm of enstrophy or unsigned
helicity. In addition, we analyze the temporal variation of thirteen
emerging active regions. At the locations of these active regions,
there is little enstrophy or helicity before the regions emerge, while
after flux emergence the vorticity and helicity values are large. The
crosscorrelation in time between flux and enstrophy shows that they
are correlated and that shallow layers lag behind deeper layers. This
signal might be a hint of the emergence of active regions.
Title: Effects of surface magnetic activity on meridional circulation
measurements
Authors: González Hernández, Irene; Kholikov, Shukur; Hill, Frank;
Howe, Rachel; Komm, Rudolph
Bibcode: 2008JPhCS.118a2081G
Altcode:
Temporal variations of the subsurface meridional flow with the solar
cycle have been reported by several authors. This work examines
the possible contamination of the helioseismic measurements by the
extra velocity fields associated with active regions as well as the
uncertainties in the data obtained where strong magnetic fields are
present. We compare meridional flows obtained by both ring-diagram
and time-distance analysis before and after removing the areas of
strong magnetic field. The preliminary results suggest that a careful
examination of the contribution of magnetic regions to the longitude
averaged meridional flow is required.
Title: Acoustic Radius Measurements from MDI and GONG
Authors: Kholikov, S.; Hill, F.
Bibcode: 2008SoPh..251..157K
Altcode: 2008SoPh..tmp..116K
We study the temporal autocorrelation function (ACF) of global solar
oscillations. It is well known that the "large frequency separation"
is proportional to the solar acoustic radius. We analyze the ACF of
MDI and GONG spherical-harmonic-coefficient time series for degrees
ℓ=0−3. Acoustic radius measurements obtained from the first
dominant peak locations of the ACF show a significant anticorrelation
with solar cycle. This technique can be a useful tool to search for
stellar activity.
Title: Moving Beyond Time: New VSO Searches
Authors: Davey, A.; Bogart, R.; Gurman, J.; Hill, F.; Hourcle, J.;
Martens, P.; Suarez Sola, I.; VSO Team
Bibcode: 2008AGUSMSP54A..06D
Altcode:
Since its inception the Virtual Solar Observatory (VSO) has supported
a standard set of search parameters for finding data sets of interest,
including instrument, spectral range and observable, all keyed on
a defined time range. The VSO also allows users to derive search
periods based on feature or event catalogs. Recent work on the catalog
infrastructure will enable far more complex science based queries to
derive both stand alone results and also starting points for querying
other data sets. The technical side of this work is presented at
this meeting in 'Event and Feature Catalogs in the Virtual Solar
Observatory' by Joe Hourcle et al. This abstract focuses on the
science made possible by this catalog work and from work to extend
the standard query mechanisms. In the future we will be able to answer
queries such as 'show me data sets suitable for DEM analysis' or 'give
me an image every ten minutes from this instrument.' This effort has
obvious application to handling SDO data.
Title: Rotation Rate of Sunspots and Subsurface Zonal Flows
Authors: Komm, R.; Howe, R.; Hill, F.; González Hernández, I.
Bibcode: 2008AGUSMSP41A..08K
Altcode:
From surface observations, it is well known that sunspots rotate faster
than the surrounding plasma. Helioseismic observations have confirmed
this behavior for near-surface layers. Here, we study the zonal flow
of active regions in solar subsurface layers over a range of depths
from the surface to about 16 Mm. We have analyzed about six years of
GONG+ high-resolution Doppler data with the dense-pack ring-diagram
analysis. We calculate the average zonal flow for a quiet- and an
active-region subset defined as dense-pack patches (of 15 degree
diameter) with an unsigned magnetic flux less than 3.4 G and greater
than 65.0 G respectively. The average zonal flow of active regions is
about 4m/s larger than the average flow of quiet regions on dense-pack
length scales. This difference increases slightly with increasing depth
and shows no apparent pattern in time and latitude. As a byproduct,
we study the north-south asymmetry of the rotation rate in these
subsurface layers and find that the asymmetry decreases during the
declining phase of solar cycle 23.
Title: Still Virtual After All These Years: Recent Developments in
the Virtual Solar Observatory
Authors: Gurman, J. B.; Bogart, R. S.; Davey, A. R.; Hill, F.; Martens,
P. C.; Zarro, D. M.; Team, T. v.
Bibcode: 2008AGUSMSP51B..17G
Altcode:
While continuing to add access to data from new missions, including
Hinode and STEREO, the Virtual Solar Observatory is also being enhanced
as a research tool by the addition of new features such as the unified
representation of catalogs and event lists (to allow joined searches
in two or more catalogs) and workable representation and manipulation
of large numbers of search results (as are expected from the Solar
Dynamics Observatory database). Working with our RHESSI colleagues,
we have also been able to improve the performance of IDL-callable
vso_search and vso_get functions, to the point that use of those
routines is a practical alternative to reproducing large subsets of
mission data on one's own LAN.
Title: The global solar magnetic field according to GONG during WHI
Authors: Petrie, G. J.; Bolding, J.; Clark, R.; Donaldson-Hanna, K.;
Harvey, J. W.; Hill, F.; Toner, C.; Thomas, W. M.
Bibcode: 2008AGUSMSH53A..03P
Altcode:
Line-of-sight photospheric magnetograms are produced every minute at
GONG's six sites. Based on these low- noise images, near-real-time
synoptic full-surface magnetograms are produced hourly around
the clock. In the usual way, potential-field models for the global
coronal field are then extrapolated from the photospheric maps hourly,
giving a description of large-scale magnetic structure including field
changes caused by quasi-static evolution and by flares and coronal
mass ejections. This study focuses on the large-scale features of the
corona during WHI that have consequences for the heliosphere and space
weather: coronal holes, the streamer belt, magnetic flux open to the
ecliptic plane and large-scale changes in the field topology. GONG is
the official provider of magnetograms for NASA's STEREO mission.
Title: Views of the Solar Torsional Oscillation
Authors: Howe, R.; Komm, R. W.; Hill, F.; Schou, J.; Thompson, M. J.
Bibcode: 2008AGUSMSP41A..05H
Altcode:
The pattern of zonal flows migrating towards the equator over the
solar cycle, known as the torsional oscillation, is well established
from both helioseismology and surface Doppler measurements. However,
the exact appearance of the pattern will vary depending on the form of
the overall rotation profile that has been subtracted, even when the
data cover a full eleven-year cycle. Here we compare the appearance
of the flow pattern when applying several different methods to the
MDI and GONG data for Solar Cycle 23.
Title: Space Weather with GONG+ Data
Authors: Hill, F.; Komm, R.; Gonzalez-Hernandez, I.; Petrie, G.;
Harvey, J. W.
Bibcode: 2008AGUSMSP54A..08H
Altcode:
The Global Oscillation Network Group (GONG) is now routinely
producing several data products that are useful for space weather
predictions. These products are one-minute cadence full-disk
magnetograms obtained continually; ten-miniute averages of these
magnetograms; one-hour cadence synoptic magnetic field maps and
potential field source-surface extrapolations; and twelve-hour far-side
maps that show the presence of large active regions. Most of these these
products are made available over the Internet in near-real time. In
addition, we are developing flare predictors based on subsurface
vorticity obtained from helioseismic ring diagrams in conjunction
with surface magnetic field observations. We find that, when both the
subsurface vorticity and the surface magnetic field are above certain
thresholds for a specific active region, then that active region has
a very high probability of producing vigorous flare activity. We will
present the quantitative results for this predictor and also report
on progress developing a predictor based on the temporal evolution of
the vorticity.
Title: Combining far-side maps from MDI and GONG to improve the
prediction capability
Authors: Gonzalez Hernandez, I.; Scherrer, P.; Lindsey, C.; Braun,
D.; Hill, F.
Bibcode: 2008AGUSMSP41A..04G
Altcode:
Both the Michaelson Doppler Imager (MDI) and the Global Oscillation
Network Group (GONG) projects produce daily seismic maps of surface
magnetic activity at the non-visible hemisphere the Sun. The technique
has proven useful in order to detect and follow large active regions
before they appear to face the Earth. This work explores the possibility
of improving the detection capability of the technique by combining
the results from both instruments. The research should lead to a better
understanding of the spurious, non persistent seismic signal associated
with the far-side images and better discrimination between solar and
instrumental noise.
Title: Selection of Quiet Regions in Local Helioseismic Analysis
Authors: Tripathy, S. C.; Jain, K.; Hill, F.
Bibcode: 2008AGUSMSP41A..01T
Altcode:
In local helioseismic studies, the mode characteristics of an active
region are compared with those of a quiet region to estimate the
influence of the magnetic field or differences in structure. Hence the
selection of a proper quiet region is important in order to estimate
the true variations. There are at least three possible ways in which
a quiet region can be selected: (i) a common quiet region for all the
events analyzed (ii) a quiet region at the same heliographic longitude
and latitude within the same Carrington rotation, and (iii) an ensemble
average of quiet regions. The first choice minimizes the differences
that may arise from different quiet regions, but neglects the effect
of temporal variations. On the other hand, the second choice introduces
inherent variations present between quiet regions. It is believed that
the differences in mode parameters between two quiet regions are small
compared to a pair of active and quiet regions. However our analysis
indicates that the differences in mode parameters between two quiet
regions can be significantly large. In this paper we will illustrate the
variations between quiet regions and their effect on the mode properties
of the active region by selecting quiet regions in all three categories.
Title: Low-Frequency Solar p Modes in GONG and MDI Observations
using m-Averaged Spectra
Authors: Leibacher, J.; Salabert, D.; Appourchaux, T.; Hill, F.
Bibcode: 2008AGUSMSP41A..06L
Altcode:
The GONG and MDI global helioseismology pipelines provide solar acoustic
mode parameters for 108- and 72-day time series respectively by fitting
the 2 ℓ + 1 individual-m spectra of a given (n, ℓ/) multiplet
either individually (GONG) or simultaneously (MDI). Our knowledge of
the variable solar interior through helioseismic observations derives
primarily from these two analysis pipelines. We have developed a
new method to extract the mode parameters by adjusting the rotation-
and structure-induced frequency shift for each m-spectrum to minimize
the mode width in the m-averaged spectrum. The m-averaged spectrum
appears to be a powerful tool for low signal-to-noise-ratio modes in the
low-frequency range where the modes have very long lifetimes. Indeed,
in the case of spatially-resolved helioseismic data (MDI, GONG, HMI),
for a given multiplet (n, ℓ/), there exist 2 ℓ + 1 individual-m
spectra, which can result in an average spectrum with a SNR ≫ 1 even
when the individual-m spectra have a SNR < 1. We show here that
the m-averaged spectrum technique, applied to the GONG 108-day and MDI
72-day time series, gives us access to a whole new range of predicted,
low-SNR modes that had not been successfully fitted by the current
MDI and GONG peak-fitting pipelines. We show that the modes that are
measured by both techniques are extracted without bias. We apply this
technique to 360-, 720-, 1080-, and 1440-day long GONG time series to
infer the variability of the mode parameters with solar activity in
the low-frequency range below ~ 1500 μHz.
Title: Helioseismic ring analysis of CME source regions
Authors: Tripathy, S. C.; Wet, S.; Jain, K.; Clark, R.; Hill, F.
Bibcode: 2008JApA...29..207T
Altcode: 2007arXiv0712.1995T
We apply the ring diagram technique to source regions of halo coronal
mass ejections (CMEs) to study changes in acoustic mode parameters
before, during, and after the onset of CMEs. We find that CME regions
associated with a low value of magnetic flux have line widths smaller
than the quiet regions implying a longer life-time for the oscillation
modes. We suggest that this criterion may be used to forecast the
active regions which may trigger CMEs.
Title: Helioseismology and the solar cycle: Past, present and future
Authors: Hill, Frank
Bibcode: 2008JApA...29...75H
Altcode:
No abstract at ADS
Title: Externally Induced or Internally Produced: What is the Source
of the Extreme Magnetic Activity Observed in Very Low Mass Stars?
Authors: Howell, Steve B.; Giampapa, Mark; Harrison, Thomas; Hawley,
Suzanne; Hill, Frank; Honeycutt, Kent; Kafka, Stella; Silvestri,
Nicole; Szkody, Paula; Walter, Fred; West, Andrew
Bibcode: 2008noao.prop...95H
Altcode:
Recent observations of the very low mass donor stars in short
period interacting binaries have revealed the presence of active
chromospheres. Our group has obtained initial spectra for five such
systems to date and found evidence of stellar activity in all of
them, including a brown dwarf mass (0.055 M-sun) donor star. The
Washington group has obtained a SDSS sample of a number of close, but
non-interacting white dwarf + red dwarf binaries and find H(alpha)
emission related to activity. We plan to perform the first detailed
phase-resolved spectroscopic study of the active chromospheres in
this set of rapidly rotating (<0.3 day), low mass (<0.25 M-sun),
fully convective late-type stars and brown dwarfs. Our observational
goals are to study the extent, nature and short-term changes of these
active chromospheres on the low mass stars of close binaries. Is
the extreme activity caused by the low mass star itself or externally
driven by tidal or magnetic forces? The long term goals are to complete
a large enough sample (~10 systems) to provide statistically useful
measurements and to use the extended time allocation to obtain long term
``coverage" spectra of each system to monitor, measure, and understand
the solar-type cycles likely to be present.
Title: Active regions: Evolution and Effect on Time-Distance
Measurements
Authors: Burtseva, O.; Hill, F.; Kholikov, S.
Bibcode: 2008ASPC..383..365B
Altcode:
Using SOHO-MDI velocity data, we study the influence of the active
region that emerged on the solar surface in October 2003 on travel
time measurements. We computed travel time maps for waves with two
different phase speeds and investigated the spatial distribution of
the travel times. Changes in the spatial power spectrum of the travel
times may be useful for detecting an emerging active region.
Title: Temporal Variations of High-Cadence GONG+ Magnetic Field Images
Authors: Hill, F.; Bolding, J.; Clark, R.; Donaldson-Hanna, K.;
Harvey, J. W.; Petrie, G. J. D.; Toner, C. G.; Wentzel, T. M.
Bibcode: 2008ASPC..383..227H
Altcode:
The Global Oscillation Network Group (GONG) program now produces
full-disk line-of-sight magnetic field images at the rate of one per
minute. These high-cadence data enable unprecedented studies of the
rapid variations of the solar magnetic field over the entire disk. We
present samples of the data, and power spectra of the magnetic field in
three different types of areas (sunspot, network, and quiet Sun). The
power spectra can be used to measure velocities of moving magnetic
features.
Title: GONG Synoptic Magnetogram Program: Near-real-time Coronal
Magnetic Field Model
Authors: Petrie, G. J. D.; Bolding, J.; Clark, R.; Donaldson-Hanna,
K.; Harvey, J. W.; Hill, F.; Toner, C.; Wentzel, T. M.
Bibcode: 2008ASPC..383..181P
Altcode:
Line-of-sight photospheric magnetograms are produced every minute
at GONG's six sites. All modulators and driving circuitry have
recently been replaced, improving the sensitivity, accuracy and zero
point by orders of magnitude. Information on the solar atmospheric
field can most reliably be derived from such photospheric data,
from which model coronal fields are then extrapolated. Two types of
near-real-time synoptic magnetogram are produced by GONG every hour:
one representing the steady-state field and the other designed to
capture hour-by-hour field changes on the earthward side of the
Sun. Potential-field source-surface (PFSS) models are produced from
the standard steady-state magnetogram every hour yielding insight into
large-scale coronal field changes caused by quasi-static evolution and
by flares and coronal mass ejections. GONG is the official provider
of magnetograms for NASA's STEREO mission.}
Title: Emerging Active Regions Studied with Ring-Diagram Analysis
Authors: Komm, R.; Morita, S.; Howe, R.; Hill, F.
Bibcode: 2008ApJ...672.1254K
Altcode:
We study the temporal variation of subsurface flows associated with
emerging active regions, focusing on four regions in detail. Two of
them, AR 10314 and AR 10488, emerge near disk center and the other two,
AR 10365 and AR 10375, are older regions where new flux emerges during
their disk passage. We measure the horizontal subsurface flows from
high-resolution Global Oscillation Network Group (GONG) data using
ring-diagram analysis and derive the vertical flow component. Before
flux emergence, we find upflows in AR 10314, while the other emerging
region, AR 10488, shows mainly weak vertical flows. Both aging regions,
AR 10365 and AR 10375, initially show downflows, as expected from
already established regions. When new flux emerges, the weaker one of
the two, AR 10365, shows upflows, while AR 10375 shows an even stronger
downflow. In strong active regions, such as AR 10375 and AR 10488,
strong downflows are present after the region has been established. In
all four regions, the transition occurs on timescales of about one
to two days. As a control experiment, we repeat the analysis for the
same locations as those of the four active regions in 53 Carrington
rotations and find that it is unlikely that the temporal variations of
the vertical velocity are caused by systematics such as a projection
effect. We then search our data set for emerging regions with similar
characteristics to AR 10314 and AR 10488, i.e., emergence near disk
center and large flux increase. From an analysis of 13 emerging regions,
we conclude that there is a small preference for upflows before the
emergence of new flux and for a transition toward downflows after
flux emergence.
Title: Multi-Spectral Analysis of Acoustic Mode Characteristics in
Active Regions
Authors: Jain, K.; Hill, F.; Tripathy, S. C.; González-Hernández,
I.; Armstrong, J. D.; Jefferies, S. M.; Rhodes, E. J., Jr.; Rose, P.
Bibcode: 2008ASPC..383..389J
Altcode:
We study the relative differences in acoustic mode parameters
in regions of high magnetic fields at different heights in the
solar atmosphere. The data sets include simultaneous Dopplergrams
obtained with the Ni I 676.8~nm from Global Oscillation Network Group
(GONG+) and K I 769.9 nm from Magneto-Optical Filters at Two Heights
(MOTH). The technique used here is the ring-diagram analysis, which has
been proven to be a powerful tool to study the localized regions on the
solar surface. We find that there is a difference in power suppression
and relative changes in frequencies in active regions with increasing
height. This is explained in terms of the expanding magnetic flux tubes.
Title: Helioseismic Frequency Shifts in Active Regions
Authors: Howe, R.; Haber, D. A.; Hindman, B. W.; Komm, R.; Hill, F.;
Gonzalez Hernandez, I.
Bibcode: 2008ASPC..383..305H
Altcode:
The variation in the frequencies of solar acoustic modes over the
activity cycle is well established. We discuss some of the historical
findings, and present some recent results obtained using both global and
local helioseismic analysis of data from the Global Oscillation Network
Group and the Michelson Doppler Imager. The results are consistent with
earlier work; the frequencies of modes in the five-minute band generally
show a positive correlation with the local surface magnetic field
strength, while those above the acoustic cutoff show an anticorrelation.
Title: Subsurface Flows near Four Emerging Active Regions Studied
with Ring-Diagram Analysis
Authors: Komm, R.; Howe, R.; Hill, F.; Morita, S.
Bibcode: 2008ASPC..383...83K
Altcode:
We study the temporal variation of subsurface flows associated with
four emerging active regions. Two of them, AR~10314 and AR~10488,
emerge near disk center and the other two, AR~10365 and AR~10375, are
older regions where new flux emerges during their disk passage. We
measure the horizontal subsurface flows from high-resolution Global
Oscillation Network Group (GONG+) data using ring-diagram analysis
and derive the vertical flow component. Before flux emergence, we
find upflows in AR~10314, while the other emerging region, AR~10488,
shows only weak vertical flows hinting at upflows. Both aging regions,
AR~10365 and AR~10375, show initially downflows, as expected from
already established regions. When new flux emerges, the weaker one
of the two, AR~10365, shows upflows, while AR~10375 shows stronger
downflows. In strong active regions, such as AR~10375 and AR~10488,
strong downflows are present after the region has been established.
Title: The Virtual Solar Observatory -- An Operational Resource for
Heliophysics Informatics
Authors: Hill, Frank
Bibcode: 2008cosp...37.1241H
Altcode: 2008cosp.meet.1241H
The Virtual Solar Observatory (VSO) has been operating since December
2004, and is designed to provide seamless and unified access to
heliophysics data sets. The VSO concentrates on the solar end of the
sun-earth system, and includes data from all of the major spaceand
ground-based solar observatories. Currently, the user can search 13
archives with access to data from 62 instruments, and on the basis of
time, data source, observable, spectral range or any combination of
these. In addition, several catalogs of events are provided and searches
can be constructed using the catalog information. The interface is
freely available on the web, and access to the data is completely open.
Title: Calibration of the Far Side Seismic-Holography Signature of
Active Regions
Authors: González Hernández, I.; Hill, F.; Lindsey, C.
Bibcode: 2008ASPC..383..155G
Altcode:
We compare helioseismic maps of large active regions on the far side
of the Sun, calculated from Global Oscillation Network Group (GONG)
data, with magnetic and visible-continuum images of the same active
regions on the visible hemisphere before and after their passage
across the far hemisphere. We find a significant correlation between
the far-side signature and both the total area of the active region as
viewed on the near hemisphere and the total area of sunspots within
the active region. We have also studied the relationship between the
magnetic field strength and the phase shift for six of the larger,
more stable active regions.
Title: Callable Virtual Observatory Functionality: Sample Use Cases
Authors: Gurman, J. B.; Hourclé, J. A.; Bogart, R. S.; Tian, K.;
Hill, F.; Suárez-Solá, I.; Zarro, D. M.; Davey, A. R.; Martens,
P. C.; Yoshimura, K.
Bibcode: 2007AGUFMSH51A0259G
Altcode:
A virtual observatory with an Application Programming Interface
(API) can become a powerful tool in analysis and modeling. In
particular, an API that integrates time selection on such criteria
as "most recent" and closest to a given absolute time simplifies the
user-end programming considerably. We examine three types of use cases
(nowcasting, data assimilation input, and user-defined sampling rates)
for such functionality in the Virtual Solar Observatory (VSO).
Title: Design Considerations for Data Catalogs
Authors: Hourcle, J.; Suarez-Sola, I.; Davey, A.; Tian, K.; Yoshimura,
K.; Martens, P.; Gurman, J.; Hill, F.; Bogart, R.
Bibcode: 2007AGUFMSH51A0261H
Altcode:
Mission data catalogs are typically built with the specific mission in
mind. This can create challenges when trying to abstract the metadata
to make it useful to other researchers. The deluge of data from new
missions such as STEREO and Hinode have brought in not only issues
in scale, but also complexities due to the difference in these new
experiments in the context of existing norms. We will discuss issues
and use cases to be considered in designing a mission's data systems
in order to better serve the Heliospheric community.
Title: GONG Synoptic Magnetograms and Coronal Magnetic Field Modeling
Authors: Petrie, G. J.; Bolding, J.; Clark, R.; Donaldson-Hanna, K.;
Harvey, J. W.; Hill, F.; Toner, C.; Wentzel, T. M.
Bibcode: 2007AGUFMSH53A1068P
Altcode:
Line-of-sight photospheric magnetograms are produced every minute at
GONG's six sites. All modulators and driving circuitry have recently
been replaced, improving the sensitivity, accuracy and zero point
by orders of magnitude. Information on the solar atmospheric field
can most reliably be derived from such photospheric data, from
which model coronal fields are then extrapolated. Near-real-time
synoptic magnetogram are produced by GONG every hour. Potential-field
source-surface (PFSS) models are then produced every hour yielding
insight into large-scale coronal field changes caused by quasi-static
evolution and by flares and coronal mass ejections. We also provide
a synoptic map and model summarizing each integral Carrington
rotation. Features highlighted in the plots and movies include coronal
holes, the streamer belt, magnetic flux open to the ecliptic plane
and large-scale changes in the field topology. GONG is the official
provider of magnetograms for NASA's STEREO mission.
Title: Dealing with Large Dataset Queries in the Virtual Solar
Observatory
Authors: Suarez-Sola, F. I.; Bogart, R.; Davey, A.; Gurman, J. B.;
Hill, F.; Hourcle, J.; Martens, P. C.; Tian, K.; Yoshimura, K.
Bibcode: 2007AGUFMSH51A0260S
Altcode:
The Virtual Solar Observatory (VSO) project presents a solution for
dealing with large dataset queries. One of the main problems arising
from the VSO user community has been managing queries that generate
a large amount of metadata records spanning several providers. Until
now the only way to do this was through painstakingly repeating the
same query for smaller time periods and collecting the information
at each pass. With the solution presented here we are making possible
for users to access data over any arbitrary time period in one single
query, minimizing the metadata generated, and yet allowing the user
to sample either a small subset or the whole.
Title: Mexican Virtual Solar Observatory
Authors: Santillan, A.; Hernandez-Cervantes, L.; Gonzalez-Ponce, A.;
Hill, F.; Blanco-Cano, X.
Bibcode: 2007AGUFMSH51A0263S
Altcode:
The Virtual Solar Observatory (VSO) concept contains software tools
for searching, manipulating, and analyzing data from archives of solar
data at many different observatories around the world (Hill 2000). The
VSO not only provides fast and reliable access to the existing solar
data, but also represents a powerful and unique machinery to perform
numerical simulations for the evolution of a variety of different
phenomena associated with solar activity. Two Mexican Universities,
Universidad Nacional Autónoma de México and the Universidad de Sonora,
are working together to create the Mexican Virtual Solar Observatory
(MVSO) that will be part of a wider National effort. In this work we
present a general description of the MVSO project, as well as the
advances obtained in the development of Graphical User Interfaces
(GUI) to Remotely Perform Numerical Simulation of the Evolution of
Coronal Mass Ejection in the Interplanetary Medium.
Title: Calibration of Seismic Signatures of Active Regions on the
Far Side of the Sun
Authors: González Hernández, I.; Hill, F.; Lindsey, C.
Bibcode: 2007ApJ...669.1382G
Altcode:
Synoptic maps of the far hemisphere of the Sun calculated from seismic
holography have proven to be very reliable in localizing large active
regions before they rotate onto the visible hemisphere. We show here
the first results toward a calibration of the far-side signatures
of active regions in terms of active region size and magnetic field
strength. We compare helioseismic maps of large active regions on the
far side of the Sun, calculated from Global Oscillation Network Group
(GONG) Doppler observations, with magnetic and visible-continuum images
of the same active regions on the visible hemisphere before and after
their far-side passage. The far-side seismic signature is expressed as a
phase shift that a far-side active region introduces to waves from the
near hemisphere as they are reflected into the solar interior on their
way back to the near hemisphere. There is a significant correlation
between this far-side signature and both the total area of the active
region, as viewed on the near hemisphere, and the area of the sunspots
contained in the active region. We have studied the relationship
between the magnetic field strength and the phase signature for six
of the larger, more stable active regions. We find an approximately
logarithmic increase in the seismic phase signature with increasing
magnetic field strengths above a critical field of ~10 G. This is
roughly consistent with similar helioseismic signatures measured on
the near solar hemisphere concurrent with associated magnetic fields.
Title: Astronomical Data Analysis Software and Systems XVI
Authors: Shaw, R. A.; Hill, F.; Bell, D. J.
Bibcode: 2007ASPC..376.....S
Altcode: 2007adass..16.....S
No abstract at ADS
Title: Divergence and Vorticity of Solar Subsurface Flows Derived
from Ring-Diagram Analysis of MDI and GONG Data
Authors: Komm, R.; Howe, R.; Hill, F.; Miesch, M.; Haber, D.;
Hindman, B.
Bibcode: 2007ApJ...667..571K
Altcode:
We measure the relation between divergence and vorticity of
subsurface horizontal flows as a function of unsigned surface magnetic
flux. Observations from the Michelson Doppler Imager (MDI) Dynamics
Program and Global Oscillation Network Group (GONG) have been analyzed
with a standard ring-diagram technique to measure subsurface horizontal
flows from the surface to a depth of about 16 Mm. We study residual
horizontal flows after subtracting large-scale trends (low-order
polynomial fits in latitude) from the measured velocities. On average,
quiet regions are characterized by weakly divergent horizontal flows and
small anticyclonic vorticity (clockwise in the northern hemisphere),
while locations of high activity show convergent horizontal flows
combined with cyclonic vorticity (counterclockwise in the northern
hemisphere). Divergence and vorticity of horizontal flows are
anticorrelated (correlated) in the northern (southern) hemisphere. This
is especially noticeable at greater depth, where the relation between
divergence and vorticity of horizontal flows is nearly linear. These
trends show a slight reversal at the highest levels of magnetic flux;
the vorticity amplitude decreases at the highest flux levels, while
the divergence changes sign at depths greater than about 10 Mm. The
product of divergence and vorticity of the horizontal flows, a proxy
of the vertical contribution to the kinetic helicity density, is on
average negative (positive) in the northern (southern) hemisphere. The
helicity proxy values are greater at locations of high magnetic activity
than at quiet locations.
Title: Joint Discussion 17 Highlights of recent progress in the
seismology of the Sun and Sun-like stars
Authors: Bedding, Timothy R.; Brun, Allan S.; Christensen-Dalsgaard,
Jørgen; Crouch, Ashley; De Cat, Peter; García, Raphael A.; Gizon,
Laurent; Hill, Frank; Kjeldsen, Hans; Leibacher, John W.; Maillard,
Jean-Pierre; Mathis, S.; Rabello-Soares, M. Cristina; Rozelot,
Jean-Pierre; Rempel, Matthias; Roxburgh, Ian W.; Samadi, Réza; Talon,
Suzanne; Thompson, Michael J.
Bibcode: 2007HiA....14..491B
Altcode:
The seismology and physics of localized structures beneath the surface
of the Sun takes on a special significance with the completion in
2006 of a solar cycle of observations by the ground-based Global
Oscillation Network Group (GONG) and by the instruments on board the
Solar and Heliospheric Observatory (SOHO). Of course, the spatially
unresolved Birmingham Solar Oscillation Network (BiSON) has been
observing for even longer. At the same time, the testing of models of
stellar structure moves into high gear with the extension of deep probes
from the Sun to other solar-like stars and other multi-mode pulsators,
with ever-improving observations made from the ground, the success of
the MOST satellite, and the recently launched CoRoT satellite. Here
we report the current state of the two closely related and rapidly
developing fields of helio- and asteroseimology.
Title: Solar physics with the Virtual Solar Observatory
Authors: Hill, Frank
Bibcode: 2007HiA....14..612H
Altcode: 2006IAUSS...3E...9H
The Virtual Solar Observatory (VSO) is a lightweight web service
unifying twelve major solar data archives. With the VSO, users
can simultaneously search for data from 50 space- and ground-based
instruments covering the time period from 1915 to the present.
Title: Solar Oscillation Frequency Changes on Time Scales of Nine Days
Authors: Tripathy, S. C.; Hill, F.; Jain, K.; Leibacher, J. W.
Bibcode: 2007SoPh..243..105T
Altcode: 2006astro.ph..8348T
We establish that global solar p-mode frequencies can be measured with
sufficient precision on time scales as short as nine days to detect
activity-related shifts. Using ten years of GONG data, we report
that mode-mass and error-weighted frequency shifts derived from nine
days are significantly correlated with the strength of solar activity
and are consistent with long-duration measurements from GONG and the
SOHO/MDI instrument. The analysis of the year-wise distribution of the
frequency shifts with change in activity indices shows that both the
linear-regression slopes and the magnitude of the correlation varies
from year to year and they are well correlated with each other. The
study also indicates that the magnetic indices behave differently in the
rising and falling phases of the activity cycle. For the short-duration
nine-day observations, we report a higher sensitivity to activity.
Title: Solar Cycle Changes Over 11 Years of Medium-Degree Helioseismic
Observations
Authors: Howe, Rachel; Komm, R. W.; Hill, F.; Christensen-Dalsgaard,
J.; Schou, J.; Thompson, M. J.
Bibcode: 2007AAS...210.2218H
Altcode: 2007BAAS...39..127H
The Global Oscillations Network Group (GONG) has now completed, and
the Michelson Doppler Imager (MDI) aboard SOHO will soon complete,
a full eleven years of continuous observations of the medium-degree
solar oscillations. This enables us to follow changes in the acoustic
mode parameters and interior dynamics over a full solar cycle. We
present results from observations of convection-zone dynamics, in
which the torsional oscillation pattern seen at the surface can be
followed throughout most of the bulk of the convection zone, and also
changes in the frequency, lifetime and amplitude of the modes which
can be shown to be closely related in space and time to the migrating
pattern of surface activity. This work utilizes data obtained by
the Global Oscillation Network Group (GONG) program, managed by the
National Solar Observatory, which is operated by AURA, Inc. under a
cooperative agreement with the National Science Foundation. SOHO is
a mission of international cooperation between ESA and NASA.
Title: Rotation Of The Deep Solar Interior From A Solar Cycle Of
Gong Data
Authors: Leibacher, John W.; Salabert, D.; Appourchaux, T.; Hill,
F.; Howe, R.
Bibcode: 2007AAS...210.2219L
Altcode: 2007BAAS...39..127L
We use 3960 days of Global Oscillation Network Group (GONG) data
to derive the rotation of the deep solar interior. We obtain the
splitting of low signal-to-noise multiplets - at low radial order
and low spherical harmonic degree - using the m-averaged spectra - a
technique that works well even when none of the individual-m spectra are
clean enough to be fit. Central frequencies and rotational splittings
are estimated down to l = 1 and 1 mHz. We illustrate here the validity
of our method and infer the radial rotation profile down to 0.2 solar
radius. This work utilizes data obtained by the Global Oscillation
Network Group (GONG) program, managed by the National Solar Observatory,
which is operated by AURA, Inc. under a cooperative agreement with
the National Science Foundation. The data were acquired by instruments
operated by the Big Bear Solar Observatory, High Altitude Observatory,
Learmonth Solar Observatory, Udaipur Solar Observatory, Instituto de
Astrofisica de Canarias, and Cerro Tololo Interamerican Observatory.
Title: Science With the Virtual Solar Observatory: Today and Tomorrow
Authors: Hill, F.; Bogart, R. S.; Davey, A. R.; Gurman, J. B.; Hourcle,
J. A.; Martens, P. C.; Reardon, K. M.; Suarez-Sola, I.; Tian, K. Q.;
Yoshimura, K.
Bibcode: 2007AGUSMSM33D..05H
Altcode:
The Virtual Solar Observatory (VSO) was released to the community in
December 2004. It is designed to provide solar physicists with a tool
that allows them to locate and access solar data in an efficient manner,
thus facilitating science studies involving multiple data sets. Examples
of science projects that have been done with the VSO are a study of
halo CME speeds and their visibility in a variety of SOHO data sets,
and the calibration between helioseismic farside signals and the
characteristics of active regions. Future possible projects include
studies of farside coronal mass ejections; the relationship between
subsurface flows and solar wind speeds; statistics of the active region
life cycle; sunspot energetics, and space weather predictors.
Title: Suppression Of Acoustic Power In Solar Active Regions: An
Analysis At Different Heights
Authors: Tripathy, Sushanta; Jain, K.; Hill, F.; Gonzalez-Hernandez,
I.; Armstrong, J. D.; Jefferies, S. M.; Rhodes, E. J., Jr.; Rose, P. J.
Bibcode: 2007AAS...210.2411T
Altcode: 2007BAAS...39..130T
The presence of enhanced magnetic fields in active regions is known to
suppress acoustic power and modify oscillation frequencies. Applying
the ring diagram technique to data from three different spectral lines
at different heights in the solar atmosphere, we analyze the variation
of the acoustic power with height. The data sets include simultaneous
Dopplergrams obtained with the Ni I 676.8 nm from Global Oscillation
Network Group (GONG), K I 769.9 nm from Magneto-Optical Filters at Two
Heights (MOTH) and Na I 589.0 nm from MOTH and Mount Wilson Observatory
(MWO). It should be noted that the Ni and K lines are formed in the
photosphere while Na line is formed in lower chromosphere. Preliminary
results suggest a difference in power suppression with increasing
height, which can be explained in terms of the expanding magnetic
flux tubes.
Title: Recent Advances From The GONG Time-distance Helioseismology
Team
Authors: Hill, Frank; Kholikov, S.; Burtseva, O.; Leibacher, J. W.
Bibcode: 2007AAS...210.2213H
Altcode: 2007BAAS...39..126H
We present some recent work using the time-distance method of local
helioseismology as applied to Global Oscillation Network Group (GONG)
data. Four projects will be included: 1) North-south travel time
differences for zonal modes (m=0) have been computed for the period
1995-2006. These measurements provide information on the meridional
flow, and can be used to study temporal variations over the activity
cycle. 2) The autocorrelations of the low-degree (l=0, 1, 2, 3)
time series have been computed. These functions have been analyzed
to obtain a very precise measurement of the large splitting and solar
acoustic radius. A significant temporal variation correlated with the
activity level can be clearly seen. 3) The lifetimes of high-degree
modes have been estimated with the time-distance method. The results for
high and low activity will be discussed. 4) A project to search
for active regions prior to their emergence has been initiated. Some
approaches to the problem will be outlined. The National Solar
Observatory is operated by the Association of Universities for Research
in Astronomy under a cooperative agreement with the National Science
Foundation, for the benefit of the astronomical community.
Title: GONG Synoptic Magnetograms and Coronal Magnetic Field Modeling
Authors: Petrie, Gordon; Bolding, J.; Clark, R.; Donaldson-Hanna,
K.; Hill, F.; Harvey, J. W.; Toner, C.; Wentzel, T. M.
Bibcode: 2007AAS...210.9107P
Altcode: 2007BAAS...39..205P
Line-of-sight photospheric magnetograms are produced every minute
at GONG’s six sites. All modulators and driving circuitry have
recently been replaced, improving the sensitivity, accuracy and zero
point by orders of magnitude. Information on the solar atmospheric
field can most reliably be derived from such photospheric data,
from which model coronal fields are then extrapolated. Two types of
near-real-time synoptic magnetogram are produced by GONG every hour:
one representing the steady-state field and the other designed to
capture hour-by-hour field changes on the earthward side of the
Sun. Potential-field source-surface (PFSS) models are produced from
each type of magnetogram every hour yielding insight into large-scale
coronal field changes caused by quasi-static evolution and by flares and
coronal mass ejections. GONG is the official provider of magnetograms
for NASA’s STEREO mission
Title: Far-side Helioseismic Holography: Calibrating The Signature
Of Active Regions.
Authors: Gonzalez-Hernandez, Irene; Lindsey, C.; Hill, F.
Bibcode: 2007AAS...210.2212G
Altcode: 2007BAAS...39..126G
Synoptic maps of the far hemisphere of the Sun calculated from seismic
holography have proven to be very reliable in localizing large active
regions before they rotate onto the visible hemisphere. Both the
Michelson Doppler Imager (MDI) and the Global Oscillation Network Group
(GONG) provide daily far-side maps of magnetic activity using this
technique. We show here the first results towards a calibration
of the far-side signatures of active regions in terms of active
region size and magnetic field strength. We compare helioseismic
maps of large active regions on the far side of the Sun, calculated
from GONG Doppler observations, with magnetic and visible-continuum
images of the same active regions on the visible hemisphere before
and after their far-side passage. We find a significant correlation
between the far-side signature and both the total area of the active
region, as viewed on the near hemisphere, and the area of the sunspots
contained in the active region. We have studied the relationship
between the magnetic field strength and the phase signature for six
of the larger, more stable active regions. We find an approximately
logarithmic increase in the seismic phase signature with increasing
magnetic field strengths above a critical field of 10 Gauss.
Title: Helioseismic Analysis Of Mode Parameters In The Source Regions
Of CMEs
Authors: DeWet, Stephanie; Tripathy, S. C.; Jain, K.; Clark, R.;
Hill, F.
Bibcode: 2007AAS...210.2909D
Altcode: 2007BAAS...39..138D
We apply ring-diagram technique to high-resolution Global Oscillation
Network Group (GONG) Dopplergrams in order to examine the source regions
of halo coronal mass ejections (CMEs). We study the changes in acoustic
mode parameters such as frequency, line width, and amplitude before,
during, and after CMEs. The CMEs were chosen to have a wide variety
of source regions, including active regions, filament regions, and
transequatorial filament regions. We find that regions associated
with low magnetic flux that produce CMEs have shorter line widths
than corresponding quiet regions. This implies a longer lifetime
or slow damping process for the oscillation modes. We suggest that
this characteristic could be useful in modeling CMEs or forecasting
regions in which CMEs may occur. This work is carried out through
the National Solar Observatory Research Experiences for Undergraduate
(REU) site program, which is co-funded by the Department of Defense
in partnership with the National Science Foundation REU Program.
Title: Temporal variations in solar rotation at the bottom of the
convection zone: The current status
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
Schou, J.; Thompson, M. J.; Toomre, J.
Bibcode: 2007AdSpR..40..915H
Altcode:
We present the most recent results on the short-period variations
in the solar rotation rate near the base of the convection zone. The
1.3-year period which was reported in the early years of solar cycle 23
appears not to persist after 2001, but there are hints of fluctuations
at a different period during the declining phase of the cycle.
Title: The current and future roles of virtual observatories serving
the heliophysical data environment
Authors: Davey, A. R.; Bogart, R. S.; Dimitoglou, G.; Gurman, J. B.;
Hill, F.; Hourcle, J. A.; Martens, P. C.; Suarez-Sola, I.; Tian, K.;
Yoshimura, K.
Bibcode: 2006AGUFMSM11C..05D
Altcode:
The Virtual Solar Observatory is just one of a growing number of
virtual observatories that serve heliophysics data. We discuss the
current capabilities of these virtual observatories, their roles in
data archiving, discovery, quality assurance, assimilation, encouraging
standards and in facilitating science. We also discuss the realistic
goals virtual observatories should have, in fulfilling the demands of
the current and near future heliophysics data environment.
Title: The Virtual Solar Observatory and the Heliophysics Meta-Virtual
Observatory
Authors: Gurman, J. B.; Hourclé, J. A.; Bogart, R. S.; Tian, K.;
Hill, F.; Suàrez-Sola, I.; Zarro, D. M.; Davey, A. R.; Martens,
P. C.; Yoshimura, K.; Reardon, K. M.
Bibcode: 2006AGUFMSM21A0246G
Altcode:
The Virtual Solar Observatory (VSO) has survived its infancy and
provides metadata search and data identification for measurements from
45 instrument data sets held at 12 online archives, as well as flare
and coronal mass ejection (CME) event lists. Like any toddler, the VSO
is good at getting into anything and everything, and is now extending
its grasp to more data sets, new missions, and new access methods
using its application programming interface (API). We discuss and
demonstrate recent changes, including developments for STEREO and SDO,
and an IDL-callable interface for the VSO API. We urge the heliophysics
community to help civilize this obstreperous youngster by providing
input on ways to make the VSO even more useful for system science
research in its role as part of the growing cluster of Heliophysics
Virtual Observatories.
Title: Comparison of solar p-mode lifetimes from GONG, MDI and
TON data
Authors: Burtseva, O.; Kholikov, S.; Hill, F.; Bolding, J.; Ladenkov,
O.; Chou, D. -Y.
Bibcode: 2006ESASP.624E.102B
Altcode: 2006soho...18E.102B
No abstract at ADS
Title: Peak parameter shifts from large-aperture ring diagram analysis
Authors: Howe, R.; González Hernández, I.; Hill, F.; Komm, R.
Bibcode: 2006ESASP.624E..68H
Altcode: 2006soho...18E..68H
No abstract at ADS
Title: A comparison of acoustic mode parameters using multi-spectral
data
Authors: Jain, K.; Hill, F.; Tripathy, S. C.; Antia, H. M.; Armstrong,
J. D.; Jefferies, S. M.; Rhodes, E. J., Jr.; Rose, P. J.
Bibcode: 2006ESASP.624E.103J
Altcode: 2006soho...18E.103J
No abstract at ADS
Title: Comparison of local frequency shifts between MDI velocity
and intensity data
Authors: Tripathy, S. C.; Antia, H. M.; Hill, F.; Jain, K.; González
Hernández, I.
Bibcode: 2006ESASP.624E.104T
Altcode: 2006soho...18E.104T
No abstract at ADS
Title: Does the inference of solar subsurface flow change with choice
of the spectral line?
Authors: Jain, K.; Hill, F.; González Hernández, I.; Toner, C. G.;
Tripathy, S. C.; Armstrong, J. D.; Jefferies, S. M.
Bibcode: 2006ESASP.624E.127J
Altcode: 2006soho...18E.127J
No abstract at ADS
Title: Farside helioseismic holography: recent advances
Authors: González Hernández, I.; Hill, F.; Lindsey, C.; Braun, D.;
Scherrer, P.; Hanasoge, S. M.
Bibcode: 2006ESASP.624E...3G
Altcode: 2006soho...18E...3G
No abstract at ADS
Title: Solar Convection Zone Dynamics: How Sensitive Are Inversions
to Subtle Dynamo Features?
Authors: Howe, R.; Rempel, M.; Christensen-Dalsgaard, J.; Hill, F.;
Komm, R.; Larsen, R. M.; Schou, J.; Thompson, M. J.
Bibcode: 2006ApJ...649.1155H
Altcode:
The nearly 10 year span of medium-degree helioseismic data from the
Global Oscillation Network Group and the Michelson Doppler Imager has
allowed us to study the evolving flows in the solar convection zone
over most of solar cycle 23. Using two independent two-dimensional
rotation inversion techniques and extensive studies of the resolution
using artificial data from different assumed flow profiles, including
those generated from sample mean field dynamo models, we attempt to
assess the reality of certain features seen in the inferred rotation
profiles. Our results suggest that the findings from observations of
a substantial depth dependence of the phase of the zonal flow pattern
in the low latitudes, and the penetration of the flows deep into the
convection zone, are likely to be real rather than artifacts of the
inversion process.
Title: Changes to global mode parameters over a solar cycle
Authors: Tripathy, S. C.; Hill, F.; Jain, K.; Leibacher, J. W.
Bibcode: 2006ESASP.624E..93T
Altcode: 2006soho...18E..93T
No abstract at ADS
Title: Subsurface flows measured with big rings
Authors: Komm, R.; González Hernández, I.; Howe, R.; Hill, F.
Bibcode: 2006ESASP.624E..53K
Altcode: 2006soho...18E..53K
No abstract at ADS
Title: Time variations of internal structure deduced from
helioseismology
Authors: Hill, F.
Bibcode: 2006IAUJD..17E...2H
Altcode:
Solar cycle 23 is the first cycle to be fully and continuously sampled
by modern helioseismology experiments. This talk will present results
from the analysis of global measurements from SOHO/MDI and GONG,
focussing on torsional oscillation evolution, tachocline variations,
polar accelerations, the extended solar cycle, and short time scale
evolution.
Title: Divergence and Vorticity of Subsurface Flows Derived from
Ring-Diagram Analysis of MDI and GONG Data
Authors: Komm, R.; Howe, R.; Hill, F.; Miesch, M.; Haber, D.;
Hundman, B.
Bibcode: 2006ESASP.617E..42K
Altcode: 2006soho...17E..42K
No abstract at ADS
Title: Flares, Magnetic Fields, and Subsurface Vorticity: A Survey
of GONG and MDI Data
Authors: Mason, D.; Komm, R.; Hill, F.; Howe, R.; Haber, D.; Hindman,
B. W.
Bibcode: 2006ApJ...645.1543M
Altcode:
We search for a relation between flows below active regions and flare
events occurring in those active regions. For this purpose, we determine
the subsurface flows from high-resolution Global Oscillation Network
Group (GONG) and Michelson Doppler Imager (MDI) Dynamics Program data
using the ring-diagram technique. We then calculate the vorticity
of the flows associated with active regions and compare it with a
proxy of the total X-ray flare intensity of these regions using data
from the Geostationary Operation Environmental Satellite (GOES). We
have analyzed 408 active regions with X-ray flare activity from GONG
and 159 active regions from MDI data. Both data sets lead to similar
results. The maximum unsigned zonal and meridional vorticity components
of active regions are correlated with the total flare intensity; this
behavior is most apparent at values greater than 3.2×10-5
W m-2. These vorticity components show a linear relation
with the logarithm of the flare intensity that is dependent on the
maximum unsigned magnetic flux; vorticity values are proportional to
the product of total flare intensity and maximum unsigned magnetic flux
for flux values greater than about 36 G. Active regions with strong
flare intensity show a dipolar pattern in the zonal and meridional
vorticity component that reverses at depths between ~2 and 5 Mm. A
measure of this pattern shows the same kind of relation with total
flare intensity as the vorticity components. The vertical vorticity
component shows no clear relation to flare activity.
Title: MDI and GONG Inferences of the Changing Sun
Authors: Burtseva, O.; González Hernández, I.; Hill, F.; Howe, R.;
Jain, K.; Kholikov, S.; Komm, R.; Leibacher, J.; Toner, C.; Tripathy,
S.; Haber, D.; Hindman, B.; Ladenkov, O.; Chou, D. -Y.
Bibcode: 2006ESASP.617E..41B
Altcode: 2006soho...17E..41B
No abstract at ADS
Title: Frequency Shifts on Time Scales of Nine Days
Authors: Tripathy, Sushanta C.; Hill, F.; Jain, K.; Leibacher, J. W.
Bibcode: 2006SPD....37.0501T
Altcode: 2006BAAS...38R.223T
Since the p-mode frequency changes are thought to be associated
with individual active regions that come and go continuously, one
would anticipate that the frequencies alsochange continuously on
any time scale. However, due to the finite life time of the mode,
the correlation between the frequency and activity may depend on the
length of the observing run. To test this hypothesis, we calculate and
analyze frequency variations on time scales as short as nine-days. Using
10 years of GONG data, we establish that the global p-mode frequencies
can be measured with sufficient precision on this timescale to exhibit
temporal variations. We also find that these modes are significantly
correlated with the strength of solar activity but the correlation
coefficients are smaller as compared to long-term measurements from
the GONG and SOHO/MDI.
Title: Anomalous variations in low-degree helioseismic mode
frequencies
Authors: Howe, R.; Chaplin, W. J.; Elsworth, Y.; Hill, F.; Komm,
R. W.; Isaak, G. R.; New, R.
Bibcode: 2006MNRAS.369..933H
Altcode: 2006MNRAS.tmp..504H
We compare changes in the frequencies of solar acoustic modes with
degree between 0 and 2, as derived from Global Oscillation Network Group
(GONG), Birmingham Solar Oscillations Network (BiSON) and Michelson
Doppler Imager (MDI) spectra obtained between 1995 and 2003. We find
that, after the solar-activity dependence has been removed from the
frequencies, there remain variations that appear to be significant,
and are often well correlated between the different data sets. We
consider possible explanations for these fluctuations, and conclude
that they are likely to be related to the stochastic excitation of the
modes. The existence of such fluctuations has possible relevance to
the analysis of other low-degree acoustic mode spectra such as those
from solar-type stars.
Title: Farside Helioseismic Holography: Recent Advances
Authors: Gonzalez-Hernandez, Irene; Braun, D. C.; Hanasoge, S. M.;
Hill, F.; Lindsey, C. A.; Scherrer, P. H.
Bibcode: 2006SPD....37.0502G
Altcode: 2006BAAS...38Q.223G
Both MDI and GONG have been calculating partial farside maps for some
time, showing a high degree of agreement in detecting large active
regions within approximately 45 degrees around the antipode of disk
center.Recently, the full-hemisphere capability has been added to the
farside pipelines of both instruments. We show here the capability of
detecting large active regions and tracking them through out the full
farside hemisphere by applying the technique to active region 10808.We
also report on efforts underway to calibrate the farside signal in
terms of equivalent magnetic field, including some preliminary maps
obtained from artificial helioseismic data.
Title: Solar Flares, Magnetic Fields, And Subsurface Vorticity. A
Survey Of Gong And Mdi Data
Authors: Mason, Douglas J.; Komm, R.; Howe, R.; Hill, F.; Haber, D.;
Hindman, B.
Bibcode: 2006SPD....37.0506M
Altcode: 2006BAAS...38..224M
We search for a relation between flare events and magnetic fields
in active regions and the subsurface flows associated with these
regions. For this purpose, we determine the solar subsurface flows
from high-resolution Global Oscillation Network Group (GONG) and and
Michelson Doppler Imager (MDI) Dynamics Program data using ring-diagram
analysis (a local helioseismology technique). For the first time,
we have been able to search out these connections with a statistical
analysis of consecutive data that encompass many years. We have
found that the vorticity of the flow field below the solar surface,
specifically the maximum flow vorticity within each active region,
correlates well with the total X-ray flare intensity data for the
region (provided by GOES, the Geostationary Operation Environmental
Satellite). Above a certain threshold of flare activity, vorticity
values exhibit a linear relationship with total flare activity
that is dependent on the magnetic flux of the active region.This
work is carried out through the National Solar Observatory Research
Experiences for Undergraduate (REU) site program, which is co-funded
by the Department of Defense in partnership with the National Science
Foundation REU Program.
Title: Advanced Technology Solar Telescope: a progress report
Authors: Wagner, J.; Rimmele, T. R.; Keil, S.; Barr, J.; Dalrymple,
N.; Ditsler, J.; Goodrich, B.; Hansen, E.; Hegwer, S.; Hill, F.;
Hubbard, R.; Phelps, L.; Price, R.; Richards, K.; Warner, M.
Bibcode: 2006SPIE.6267E..09W
Altcode: 2006SPIE.6267E...9W
The four-meter Advanced Technology Solar Telescope (ATST) will be
the most powerful solar telescope and the world's leading resource
for studying solar magnetism that controls the solar wind, flares,
coronal mass ejections and variability in the Sun's output. Development
of a four-meter solar telescope presents many technical challenges
(e.g., thermal control of the enclosure, telescope structure and
optics). We give a status report of the ATST project (e.g., system
design reviews, instrument PDR, Haleakala site environmental impact
statement progress) and summarize the design of the major subsystems,
including the telescope mount assembly, enclosure, mirror assemblies,
wavefront correction, and instrumentation.
Title: The Virtual Solar Observatory and the Heliophysics Meta-Virtual
Observatory
Authors: Gurman, Joseph B.; Bogart, R.; Tian, K.; Hill, F.;
Suárez-Sola, I.; Martens, P. C.; Yoshimura, K.; Davey, A.; Dimitoglou,
G.; Hourclé, J.
Bibcode: 2006SPD....37.0305G
Altcode: 2006BAAS...38..222G
The Virtual Solar Observatory (VSO) is now able to search for solar
data ranging from the radio to gamma rays, obtained from space and
groundbased observatories, from 26 sources at 12 data providers, and
from 1915 to the present. The solar physics community can use a Web
interface or an Application Programming Interface (API) that allows
integrating VSO searches into other software, including other Web
services. Over the next few years, this integration will be especially
obvious as the NASA Heliophysics division sponsors the development of
a heliophysics-wide virtual observatory (VO), based on existing VO's
in heliospheric, magnetospheric, and ionospheric physics as well as
the VSO. We examine some of the challenges and potential of such a
"meta-VO."
Title: How Sensitive are Helioseismic Mode Parameters and Subsurface
Flows to Choice of the Spectral Line?
Authors: Hill, Frank; Jain, K.; Gonzalez-Hernandez, I.; Toner, C. G.;
Tripathy, S. C.; Armstrong, J. D.; Jefferies, S.; Rhodes, E. J., Jr.;
Rose, P. J.
Bibcode: 2006SPD....37.0511H
Altcode: 2006BAAS...38Q.225H
We analyze simultaneous multi-spectral line observations to investigate
how the results of helioseismology are affected by the spectral
line used to observe the solar oscillations. The data sets include
observations obtained with the Ni I 676.8 nm (from Global Oscillation
Network Group - GONG), K I 769.9 nm (from Magneto Optical Filters
at Two Heights - MOTH experiment) and Na I D2 589.0 nm
(from MOTH experiment and Mount Wilson Observatory) lines during the
Austral summer of 2002-03. The depth formation of these lines occurs
about 200 km, 420 km and 780 km above the base of the photosphere,
respectively. The simultaneous observations in several atmospheric
layers allow us to determine the propagation behavior of acoustic
waves between these layers. We carry out ring-diagram analysis,
a local helioseismology technique, to study the relative changes in
local mode parameters and subsurface velocity fields inferred from
the different data sets. Preliminary analysis of the mode parameters
obtained from the Ni I 676.8 nm and K I 769.9 nm spectral lines clearly
show a significant increase in mode amplitude with increasing observing
height but with no apparent change in the mode width.
Title: GONG Magnetograms
Authors: Petrie, Gordon; Clark, R.; Donaldson-Hanna, K.; Harvey, J.;
Hill, F.; Toner, C.; Wentzel, T.
Bibcode: 2006SPD....37.0708P
Altcode: 2006BAAS...38..229P
Line-of-sight photospheric magnetograms are produced every minute
at GONG's six sites. Information on the solar atmospheric field can
most reliably be derived from photospheric data, from which the model
coronal field is then extrapolated. Limitations of incomplete temporal
coverage, poor sensitivity and poor knowledge of the zero point of
the measurements often limit the usefulness of such data. Recent
efforts to improve the quality of GONG magnetograms have yielded
encouraging results. All modulators and driving circuitry have
been replaced, improving the sensitivity, accuracy and zero point
by orders of magnitude. Improvements to the existing data include a
zero-point correction and histogram equating of magnetograms. These
improvements ensure that past and future data from GONG will provide
unique continuous, high-cadence, sensitive coverage of the photospheric
magnetic field. GONG is the official provider of magnetograms for
NASA's STEREO mission.
Title: Site testing for the Advanced Technology Solar Telescope
Authors: Hill, F.; Beckers, J.; Brandt, P.; Briggs, J.; Brown, T.;
Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Horst,
T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn,
M.; Radick, R.; Rimmele, T.; Socas-Navarro, H.; Streander, K.
Bibcode: 2006SPIE.6267E..1TH
Altcode: 2006SPIE.6267E..59H
The Advanced Solar Technology Telescope (ATST) is a 4-m solar telescope
being designed for high spatial, spectral and temporal resolution,
as well as IR and low-scattered light observations. The overall
limit of performance of the telescope is strongly influenced by the
qualities of the site at which it is located. Six sites were tested
with a seeing monitor and a sky brightness instrument for 1.5 to 2
years. The sites were Big Bear (California), Haleakala (Hawaii), La
Palma (Canary Islands, Spain), Panguitch Lake (Utah), Sacramento Peak
(New Mexico), and San Pedro Martir (Baja California, Mexico). In this
paper we will describe the methods and results of the site survey,
which chose Haleakala as the location of the ATST.
Title: Large-Scale Zonal Flows Near the Solar Surface
Authors: Howe, R.; Komm, R.; Hill, F.; Ulrich, R.; Haber, D. A.;
Hindman, B. W.; Schou, J.; Thompson, M. J.
Bibcode: 2006SoPh..235....1H
Altcode:
Migrating bands of weak, zonal flow, associated with the activity
bands in the solar cycle, have been observed at the solar surface for
some time. More recently, these flows have been probed deep within the
convection zone using global helioseismology and examined in more detail
close to the surface with the techniques of local helioseismology. We
compare the near-surface results from global and local helioseismology
using data from the Michelson Doppler Imager and the Global Oscillation
Network Group with surface Doppler velocity measurements from the Mount
Wilson 150-foot tower and find that the results are in reasonable
agreement, with some explicable differences in detail. All of the
data sets show zones of faster rotation approaching the equator from
mid-latitudes during the solar cycle, with a variation at any given
location that can be approximately, but not completely, described by a
single sinusoid and an amplitude that does not drop off steeply below
the surface.
Title: The VSO at Two and a Half
Authors: Gurman, J. B.; Hourclé, J. A.; Bogart, R. S.; Tian, K.;
Hill, F.; Suarez-Sola, I.; Wampler, S.; Davey, A. R.; Martens, P. C.;
Yoshimura, K.; Zarro, D. M.
Bibcode: 2006AGUSMSM31B..03G
Altcode:
The Virtual Solar Observatory (VSO) has survived its infancy and
provides metadata search and data identification for 26 data sets
held at 12 online archives, as well as flare and coronal mass ejection
(CME) event lists. Like any toddler, the VSO is good at getting into
anything and everything, and is now extending its grasp to more data
sets and providers, new missions, and new access methods using its
application programming interface (API). We discuss recent changes,
including developments for STEREO and SDO, and an IDL-callable interface
for the VSO API. We urge the heliophysics community to help civilize
this obstreperous youngster by providing input on ways to make the
VSO even more useful for system science research.
Title: Meridional Circulation Variability from Large-Aperture
Ring-Diagram Analysis of Global Oscillation Network Group and
Michelson Doppler Imager Data
Authors: González Hernández, I.; Komm, R.; Hill, F.; Howe, R.;
Corbard, T.; Haber, D. A.
Bibcode: 2006ApJ...638..576G
Altcode:
Ring-diagram analysis, a local helioseismology technique, has proven to
be very useful for studying solar subsurface velocity flows down to a
depth of about 0.97 Rsolar. The depth range is determined by
the modes used in this type of analysis, and thus depends on the size
of the area analyzed. Extending the area allows us to detect lower
spherical harmonic degree (l) modes which, at a constant frequency,
penetrate deeper in the Sun. However, there is a compromise between
the size of the area and the validity of the plane-wave approximation
used by the technique. We present the results of applying the ring
diagrams to 30° diameter areas over the solar surface in an attempt
to reach deeper into the solar interior. Meridional flows for 25
consecutive Carrington rotations (1985-2009) are derived by applying
this technique to Global Oscillation Network Group (GONG) and Michelson
Doppler Imager (MDI) data. This covers a time span of almost 2 yr,
starting at the beginning of 2002. The amplitude of the meridional
flow shows a variation of the order of 5 m s-1 during this
period. Our results indicate that the flows increase toward the interior
of the Sun for the depth range studied. We find a 1 yr periodicity in
the appearance of an equatorward meridional cell at high latitudes that
coincides with maximum values of the solar inclination toward the Earth
(B0 angle).
Title: Recent advances in helioseismic predictors of space weather
Authors: Hill, F.
Bibcode: 2006ilws.conf...15H
Altcode:
Helioseismology probes the solar interior using acoustic
oscillations. With current and future experiments providing continuous
data that can be analyzed via local helioseismology techniques, there
is now the potential of using subsurface observations to predict space
weather. Several relevant developments in helioseismology are reviewed
here. These include holographic imaging of the farside of the sun;
time-distance studies of rising active regions; and ring diagram
analysis of twisting flows underneath strongly-flaring active regions.
Title: The virtual solar observatory
Authors: Young, C. A.; Gurman, J. B.; Dimitoglou, G.; Hourcle, J.;
Bogart, R. S.; Tian, K.; Hill, F.; Suarz-Sola, I.; Wampler, S.;
Martens, P.; Yoshimura, S.; Davey, A.
Bibcode: 2006ilws.conf..226Y
Altcode:
The recent explosion of data quantity and complexity has lead to the
need for a new way to make data available, the virtual observatory. The
Virtual Solar Observatory (VSO) provides a versatile means for solar
physicists to discover and share the growing sources of data. We present
the development of the VSO, show the system in action and discuss how
data users and data providers can benefit from it.
Title: Helioseismic sensing of the solar cycle
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 2006AdSpR..38..845K
Altcode:
All quantities observed with helioseismic methods, such as
frequencies, width, and amplitudes of acoustic waves, vary with the
solar cycle. However, they relate to the dynamics and structure in
different parts of the solar convection zone. The rotation rate varies
with the solar cycle, showing the so-called torsional oscillation
pattern, from the surface throughout most of the convection zone. Near
the tachocline, the current observations do not show this solar-cycle
variation, but there is some evidence that there is a 1.3-year variation
of the rotation rate. The meridional flow, observed in the outer 2% of
the solar radius, varies with the solar cycle showing flows converging
toward the mean latitude of magnetic activity at depths less than about
10 Mm and flows diverging at greater depth. There is some evidence
for a counter-cell in the northern hemisphere during epochs of high
activity. Structure inversions show variations in asphericity near
the surface where the sound speed varies with the distribution of
surface activity. There are hints but no conclusive evidence that such
variations exist in the convection zone. The damping of acoustic modes
increases and the mode energy decreases with increasing activity. Their
variation with time and latitude shows that even global modes sense
the local distribution of the surface magnetic activity.
Title: Large-scale Flows in Subsurface Layers
Authors: Komm, R.; Howe, R.; González Hernández, I.; Hill, F.;
Toner, C.
Bibcode: 2005ASPC..346...33K
Altcode:
We analyze Global Oscillation Network Group (GONG) observations obtained
during 14 consecutive Carrington rotations CR 1979--1992. We use a
ring-diagram technique in order to measure the zonal and meridional flow
components in the upper solar convection zone from the near-surface
layers to 16 Mm in depth and derive the vertical velocity component
assuming mass conservation. The average flows show the patterns that
are expected as solar-cycle related variations. For example, the
vertical flow shows downflows near the mean latitude of activity and
upflows near the equator. This long-term pattern seems to be the net
effect of flows at locations that do not coincide with strong active
regions. Locations of strong active regions show downflows at depths
less than about 12 Mm on average and strong upflows at greater depths
independent of latitude. At these locations, the zonal flow is faster on
average than the average flow over regions with less magnetic activity.
Title: Solar Convection-Zone Dynamics, 1995-2004
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
Schou, J.; Thompson, M. J.
Bibcode: 2005ApJ...634.1405H
Altcode:
The nine-year span of medium-degree helioseismic data from the Global
Oscillation Network Group (GONG) and the Michelson Doppler Imager (MDI)
allows us to study the evolving zonal flows in the solar convection
zone over the rising phase, maximum, and early declining phase
of solar cycle 23. Using two independent two-dimensional rotation
inversion techniques, we investigate the depth profile of the flow
pattern known as the torsional oscillation. The observations suggest
that the flows penetrate deep within the convection zone-perhaps to
its base-even at low latitudes, and that the phase of the pattern is
approximately constant along lines of constant rotation rather than
lines of constant latitude.
Title: How Sensitive are Rotation Inversions to Subtle Features of
the Dynamo?
Authors: Howe, R.; Rempel, M.; Christensen-Dalsgaard, J.; Schou, J.;
Thompson, M. J.; Komm, R.; Hill, F.
Bibcode: 2005ASPC..346...99H
Altcode:
Global rotation inversions can probe the pattern of zonal flows
well into the convection zone. In this paper, we test the ability
of the inversions to constrain the predictions of dynamo models. A
flux-transport dynamo model, including a mean-field theory of
differential rotation and allowing for feedback of the Lorentz force
on differential rotation and meridional flow, was used to produce a
22-year cycle of simulated rotation profiles. These were then subjected
to simulated inversions with realistic mode sets and errors, in order
to test how well the subtle subsurface features of the input profile
could be recovered. The preliminary results are quite encouraging.
Title: My Teacher got a Trip to Kitt Peak Observatory, but all I
got was This Lousy Data CD: Lessons Learned in Optimizing a Teacher
Professional Development Program for Solar Research
Authors: Walker, C. E.; Hill, F.; Plymate, C.
Bibcode: 2005AGUFMED23A1239W
Altcode:
The solar project in "Teacher Leaders in Research-Based Science
Education" program provides the opportunity for teachers to study the
Sun with the world's largest solar telescope. This exciting program is
designed for middle and high school science teachers with more than
5 years experience teaching science. Funded by a National Science
Foundation (NSF) Teacher Retention and Renewal grant, teachers
learn how to acquire astronomy data and support their students
in conducting authentic astronomy research projects. In addition,
the program enhances their skills as leaders and mentors for those
science teachers new to the profession. The TLRBSE program includes:
1) A 14-week online distance learning program with an emphasis on
spectroscopy and data imaging; 2) A 2-week in-residence workshop
at the National Optical Astronomy Observatory in Tucson, including
several nights of research observing at a world-class observatory; 3)
A program of ongoing mentoring support for beginning teachers; and 4)
Partial funding to attend a national NSTA meeting with the mentees;
5) A journal to publish student and teacher research results and 6)
Access to ongoing research, via further observing runs or archival
data. Various factors have played a part in the evolution of the solar
project. It began as an activity that used sunspots to measure the solar
rotation rate. Then it progressed to a comparison of active regions
(e.g., the areas of sunspots) at various wavelengths, to measuring
the splitting of infrared spectral lines due to strong magnetic fields
in active regions, and to measuring the amount of polarization due to
weak magnetic fields. Challenges were presented as the project evolved
from an activity to a hands-on observing experience fully reflecting
the scientific research process. Some of the issues and trade-offs we
will discuss are hands-on observing experience vs. remote observing,
archival data retrieval vs. talking data, and more vs. less scientific
assistance in the project. Group dynamics among the teachers also played
a significant role in determining the cohort's success in research. The
move to accommodate a minimum in the solar cycle dictated a change in
the scientific program. Cross-platform issues arose as the software
reduction and analysis became more sophisticated. Future instrumentation
and telescopes offered further changes in scientific goals. Factors
beyond the preparation of the course and observing material, training
of the teachers, maintaining the program and on-going support of the
teachers will also be discussed. These aspects of the solar project will
be highlighted as we continue to morph into an improved version of the
project. The TLRBSE Program is funded by the National Science Foundation
under ESI 0101982, funded through the AURA/NSF Cooperative Agreement
AST-9613615. NOAO is operated by the Association of Universities for
Research in Astronomy (AURA), Inc. under cooperative agreement with
the National Science Foundation.
Title: Solar Flares, Magnetic Fields, and Subsurface Vorticity. A
survey of GONG data
Authors: Mason, D.; Komm, R.; Hill, F.; Howe, R.
Bibcode: 2005AAS...20711103M
Altcode: 2005BAAS...37.1341M
We search for a relation between flows below active regions on the Sun
and flare events in those active regions. For this purpose, we determine
the solar subsurface flows from high-resolution Global Oscillation
Network Group (GONG) data using the ring-diagram technique. We then
calculate the vorticity of the flows associated with active regions
and compare it with the X-ray flare intensity of these regions from
the Geostationary Operation Environmental Satellite (GOES). The maximum
unsigned vorticity of an active region is correlated with its maximum
magnetic flux and the maximum unsigned zonal and meridional vorticity
component are also correlated with flare intensity greater than 3.2 ×
10-5 W/m2. Above this threshold, large vorticity
values will accompany large magnetic flux for a given flare intensity
and larger flare activity will accompany lower magnetic field for a
given vorticity value. Active regions with strong flare intensity
additionally show a dipolar pattern in the zonal and meridional
vorticity component. We define a structure component as a measure of
this dipolar pattern and find that it can be represented as a linear
function of the logarithm of flare intensity where the slope is linearly
dependent on the unsigned flux. This work is carried out through
the National Solar Observatory Research Experiences for Undergraduate
(REU) site program, which is co-funded by the Department of Defense in
partnership with the National Science Foundation REU Program. Travel
is funded by the University of Southern California.
Title: Solar Site Survey for the Advanced Technology Solar
Telescope. I. Analysis of the Seeing Data
Authors: Socas-Navarro, H.; Beckers, J.; Brandt, P.; Briggs, J.;
Brown, T.; Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer,
S.; Hill, F.; Horst, T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.;
Oncley, S.; Penn, M.; Rimmele, T.; Streander, K.
Bibcode: 2005PASP..117.1296S
Altcode: 2005astro.ph..8690S
The site survey for the Advanced Technology Solar Telescope concluded
recently after more than 2 years of data gathering and analysis. Six
locations, including lake, island, and continental sites, were
thoroughly probed for image quality and sky brightness. The present
paper describes the analysis methodology employed to determine the
height stratification of the atmospheric turbulence. This information
is crucial, because daytime seeing is often very different between the
actual telescope aperture (~30 m) and the ground. Two independent
inversion codes have been developed to simultaneously analyze
data from a scintillometer array and a solar differential image
monitor. We show here the results of applying them to a sample subset
of data from 2003 May that was used for testing. Both codes retrieve a
similar seeing stratification through the height range of interest. A
quantitative comparison between our analysis procedure and actual in
situ measurements confirms the validity of the inversions. The sample
data presented in this paper reveal a qualitatively different behavior
for the lake sites (dominated by high-altitude seeing) and the rest
(dominated by near-ground turbulence).
Title: Ring Analysis of Solar Subsurface Flows and Their Relation
to Surface Magnetic Activity
Authors: Komm, R.; Howe, R.; Hill, F.; González-Hernández, I.;
Toner, C.; Corbard, T.
Bibcode: 2005ApJ...631..636K
Altcode:
We measure the horizontal flows in the outer 2% of the Sun by analyzing
14 consecutive Carrington rotations of Global Oscillation Network Group
(GONG) Doppler images and two of Michelson Doppler Imager (MDI) Dynamics
Program data with the ring-diagram technique. The zonal and meridional
flows show no variation with activity at low to medium activity levels
(below 71 G). At active region locations, the zonal flow increases
with increasing activity; active regions rotate faster than their
quieter surroundings. The meridional flow at active region locations
is more equatorward than on average at depths less than about 10 Mm;
the flow converges toward the mean latitude of activity. At depths
greater than about 10 Mm, some active region locations show poleward
and others equatorward motions indicating strong outflows from active
regions. The estimated vertical flow decreases with increasing activity
levels except at active region locations at depths greater than about
10 Mm; active regions show downflows near the surface and upflows at
depths greater than about 10 Mm. The velocity errors increase somewhat
with increasing activity at flux levels below 71 G, but they increase
rapidly up to about 2 times the median error at higher flux values. This
increase occurs at all depths. The flows averaged over all longitudes
show the patterns expected from solar cycle variations. The quiet and
the intermediate activity subsets show the same flow pattern, while
the active region subset shows a mixture of solar cycle flow pattern
and local flow behavior.
Title: Kinetic Helicity Density in Solar Subsurface Layers and Flare
Activity of Active Regions
Authors: Komm, R.; Howe, R.; Hill, F.; González Hernández, I.;
Toner, C.
Bibcode: 2005ApJ...630.1184K
Altcode:
We search for a relation between subsurface flows below active regions
and flare events occurring in those regions. For this purpose,
we use a ring-diagram analysis to determine the subsurface flows
from high-resolution Global Oscillation Network Group (GONG) and
Michelson Doppler Imager (MDI) data and derive the kinetic helicity
as a measure of the topology of the subsurface flows. We compare it
with X-ray flare data from the Geostationary Operational Environmental
Satellite (GOES). We study active regions in three Carrington rotations
(CR 1982, 1988, and 2009), which represent different levels of flare
activity. The maximum value of the unsigned kinetic helicity density
associated with each active region correlates remarkably well with the
total flare X-ray intensity of the active regions; active regions with
strong flare activity show large values of kinetic helicity density
in subsurface flows.
Title: Advanced Technology Solar Telescope: a progress report
Authors: Rimmele, T. R.; Keil, S.; Wagner, J.; Dalrymple, N.; Goodrich,
B.; Hansen, E.; Hill, F.; Hubbard, R.; Phelps, L.; Richards, K.;
Warner, M.
Bibcode: 2005SPIE.5901...41R
Altcode:
The four-meter Advanced Technology Solar Telescope (ATST) will be
the most powerful solar telescope and the world's leading resource
for studying solar magnetism that controls the solar wind, flares,
coronal mass ejections and variability in the Sun's output. Development
of a four-meter solar telescope presents many technical challenges,
which include: thermal control of optics and telescope structure;
contamination control of the primary mirror to achieve low scattered
light levels for coronal observations; control of instrumental
polarization to allow accurate and precise polarimetric observations of
solar magnetic fields; and high-order solar adaptive optics that uses
solar granulation as the wavefront sensing target in order to achieve
diffraction limited imaging and spectroscopy. We give a status report
of the ATST project focusing on the substantial progress that has been
made with the design of the ATST. We summarize the design of the major
subsystems, including the enclosure, the primary and secondary mirror
assemblies, the coude and Nasmyth focal stations, adaptive optics and
instrumentation. The site selection has been successfully concluded
and we discuss areas where the site selection impacts the design.
Title: Kinetic Helicity in Solar Subsurface Layers and Flare Activity
of Active Regions
Authors: Komm, R.; Howe, R.; Hill, F.; González Hernández, I.;
Toner, C. G.
Bibcode: 2005AGUSMSP43B..03K
Altcode:
We search for a relation between subsurface flows below active
regions and flare events occuring in those regions. For this purpose,
we use a ring-diagram analysis to determine the subsurface flows from
high-resolution Global Oscillation Network Group (GONG) and Michelson
Doppler Imager (MDI) data and derive the kinetic helicity as a measure
of the topology of the subsurface flows. We compare it with X-ray flare
data from Geostationary Operational Environmental Satellite (GOES). We
study active regions in three Carrington rotations (CR~1982, 1988, and
2009), which represent different levels of flare activity. The maximum
value of the unsigned kinetic helicity density associated with each
active region correlates remarkably well with the total flare X-ray
intensity of the active regions; active regions with strong flare
activity show large values of kinetic helicity density in subsurface
flows. This work has ben supported by NASA grant NAG 5-11703.
Title: The ATST Site Survey
Authors: Hill, F.; Beckers, J.; Brandt, P.; Briggs, J. W.; Brown, T.;
Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Horst,
T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn, M.;
Radick, R.; Rimmele, T.; Socas-Navarro, H.; Soltau, D.; Streander, K.
Bibcode: 2005AGUSMSP34A..04H
Altcode:
The Advanced Technology Solar Telescope (ATST) will be the world's
largest aperture solar telescope, and is being designed for high
resolution, IR, and coronal research. It must be located at a site that
maximizes the scientific return of this substantial investment. We
present the instrumentation, analysis and results of the ATST site
survey. Two instrumentation sets were deployed at each of six sites to
measure seeing as a function of height, and sky brightness as a function
of wavelength and off-limb position. Analysis software was developed
to estimate the structure function Cn2 as a function of height near
the ground, and the results were verified by comparison with in-situ
measurements. Additional software was developed to estimate the sky
brightness. The statistics of the conditions at the sites were corrected
for observing habits and the annualized hours of specific observing
conditions were estimated. These results were used to identify three
excellent sites suitable to host the ATST: Haleakala, Big Bear and La
Palma. Among them, Haleakala is proposed as the optimal location of
the ATST, La Palma and Big Bear being viable alternative sites.
Title: EGSO - A maturing VO for Solar Physics
Authors: Bentley, R. D.; Scholl, I.; Csillaghy, A.; Aboudarham, J.;
Antonucci, E.; Gurman, J.; Hill, F.; Pike, D.; Vial, J.; Zharkova, V.
Bibcode: 2005AGUSMSH43B..01B
Altcode:
The European Grid of Solar Observations, EGSO, is a Grid test-bed
funded under the Information Societies Thematic Priority of the European
Commission's Fifth Framework Programme (FP5). In the case of EGSO, the
application chosen was the use of Grid technology to establish a virtual
observatory for solar physics, and the project addresses the generic
problem of how to provide access to a distributed, heterogeneous data
set for a scattered user community. In order to identify observations
that match a user's search criteria, EGSO has been building an
environment that will support complex searches. Because of the absence
of the metadata needed to tie the heterogeneous data together, EGSO has
placed emphasis on the provision of databases that can be accessed from
the Internet through special providers. The provision of appropriate
metadata is of extreme importance in establishing a virtual observatory,
and the approach used can be adapted to facilitate the inclusion of
any data, including non-solar data. We report on the capabilities of
EGSO and discuss experience gained in creating the facility. We also
discuss how EGSO has been working with other virtual observatories that
support the solar, heliospheric and space plasma communities in order
to try to achieve interoperability between the numerous data sets. We
highlight what we consider are the most profitable ways of doing this.
Title: CME Population Distributions: Science Facilitated by the VSO
Authors: Davey, A.; Wills-Davey, M.; Gurman, J.; Bogart, R.;
Dimitoglou, G.; Hill, F.; Hourcle, J.; Martens, P.; Suarez Sola, I.;
Tian, K.; Wampler, S.; Yoshimura, K.
Bibcode: 2005AGUSMSP23A..09D
Altcode:
The Virtual Solar Observatory (VSO) exists to simplify and unify
access to Solar Physics data. It provides a single interface to
a broad spectrum of data types and sources which previously would
have required considerable effort to collect. Using this ability to
combine data sources, we access the entire SOHO/LASCO CME catalog and
compare it with GOES observations of X-ray flares. Because we consider
these data in their entirety, we find several instances where the
results of less extensive studies may show unintentional selection
effects. As a subpopulation, we specifically consider LASCO-observed
halo CMEs. In agreement with previous studies, we find halo CMEs are
the bulk of the fastest events. This selection effect is consistent
with randomly-distributed CMEs extending over wide angles (>120
degrees). We also examine the lack of slower halo CMEs; otherwise
randomly-distributed events are rarely Earth-directed. While geometric
and Thomson scattering issues make less-energetic halo CMEs hard to
detect, this dearth of slow observations may represent an additional
seeing threshold. The lack of low-energy detections may account for the
disparity in LASCO.s prediction of Kp ≥ 6 vs. Kp ≥ 5 geomagnetic
storms.
Title: The Virtual Solar Observatory: Still a Small Box
Authors: Gurman, J. B.; Bogart, R. S.; Davey, A. R.; Dimitoglou, G.;
Hill, F.; Hourclé, J. A.; Martens, P. C.; Suárez-Sola, I.; Tian,
K. Q.; Wampler, S.; Yoshimura, K.
Bibcode: 2005AGUSMSH43B..03G
Altcode:
Two and a half years after a design study began, and a year and a
half after development commenced, version 1.0 of the Virtual Solar
Observatory (VSO) was released at the 2004 Fall AGU meeting. Although
internal elements of the VSO have changed, the basic design has
remained the same, reflecting the team's belief in the importance of
a simple, robust mechanism for registering data provider holdings,
initiating queries at the appropriate provider sites, aggregating the
responses, allowing the user to iterate before making a final selection,
and enabling the delivery of data directly from the providers. In
order to make the VSO transparent, lightweight, and portable, the
developers employed XML for the registry, SOAP for communication
between a VSO instance and data services, and HTML for the graphic
user interface (GUI's). We discuss the internal data model, the API,
and user responses to various trial GUI's as typical design issues for
any virtual observatory. We also discuss the role of the "small box"
of data search, identification, and delivery services provided by the
VSO in the larger, Sun-Solar System Connection virtual observatory
(VxO) scheme.
Title: Global, Local and Surface Measurements of Large-Scale Zonal
Flows Near the Solar Surface
Authors: Howe, R.; Komm, R. W.; Haber, D. A.; Hindman, B. W.; Ulrich,
R. K.; Schou, J.; Thompson, M. J.; Hill, F.
Bibcode: 2005AGUSMSP32A..03H
Altcode:
Migrating bands of weak zonal flow, associated with the activity
bands in the solar cycle, have been observed at the solar surface
for some time. More recently, these flows have been probed deep
within the convection zone using global helioseismology, and
examined in more detail close to the surface with the techniques of
local helioseismology. We compare the results from global and local
helioseismology using data from the Michelson Doppler Imager and the
GONG network and also Doppler measurements from Mount Wilson, and find
that the results are in reasonable agreement, with some explicable
differences in detail. This was work was supported by the National
Science Foundation and NASA.
Title: Are You Being Served? - Solar Data Management at the National
Solar Observatory
Authors: Hill, F.; Suarez-Sola, I.; Harvey, J. W.; Henney, C. J.;
Keller, C.; Wampler, S.
Bibcode: 2005AGUSMSH43B..04H
Altcode:
Solar physics is a data driven field, where no progress can be made
without multi-wavelength and multi-cadence information about the
sun's behavior. The National Solar Observatory (NSO) has provided
data to the research community for over 30 years and thus has
considerable experience in the areas of data processing, archiving,
and distribution. This presentation will describe the development of
NSO's data services, outline what lessons have been learned along the
way, and attempt to forecast the future of data management at NSO.
Title: 2 Years of Meridional Circulation from GONG Ring Diagrams
Authors: Gonzalez Hernandez, I.; Komm, R.; Corbard, T.; Hill, F.;
Howe, R.; Haber, D. A.
Bibcode: 2005AGUSMSP32A..01G
Altcode:
Large Aperture Ring Diagram analysis has been used to search
for meridional circulation variability using a 2-year GONG data
series. This technique uses patches that are four times the size
of the typically studied sections of 15 degrees in diameter, so we
are able to recover information about lower l modes that penetrate
deeper into the Sun. Although extending the working area allow us
to reach further into the solar interior, there is a compromise
between the size of the patch and the validity of the plane wave
approximation used by the technique. In this particular study, we
search for variability of the meridional flows as a function of depth
for 25 consecutive Carrington rotations. We have studied patches of
30-degree diameter over the solar surface as they crossed the solar
central meridian. The range of modes recovered with these larger
regions goes down to l~100 and reach a maximum depth of approximately
0.96Rsun. A set of 15 overlapping sections, centered at latitudes
0,+/-7.5,+/-15,+/-22.5,+/-30.0,+/-37.5,+/-45.0 and +/-52.5, has been
analyzed for 24 intervals of 1664 minutes covering each Carrington
rotation from CR1985 to CR2009 (Jan-2002 to Dec-2003). Meridional
circulation results from standard ring diagram analysis and this
large-aperture technique are compared, as well as results obtained
from two different instruments GONG and MDI. This work was supported
in part by NASA grant NAG5-11703. SOHO is a project of international
cooperation between ESA and NASA. This work utilizes data obtained by
the Global Oscillation Network Group (GONG) Program, managed by the
National Solar Observatory, which is operated by AURA, Inc. under a
cooperative agreement with the National Science Foundation. The data
were acquired by instruments operated by the Big Bear Solar Observatory,
High Altitude Observatory, Learmonth Solar Observatory, Udaipur Solar
Observatory, Instituto de Astrofisico de Canarias, and Cerro Tololo
Interamerican Observatory.
Title: Local Helioseismic Mode Frequency Shifts With Magnetic
Activity, From GONG and MDI
Authors: Howe, R.; Komm, R. W.; Gonzalez Hernandez, I.; Hill, F.;
Haber, D. A.; Hindman, B. W.
Bibcode: 2005AGUSMSP11B..06H
Altcode:
We use the ring-diagram technique of local helioseismology to study the
frequency shifts of high-degree solar acoustic modes from over 600 days
of data from the Global Oscillations Network Group (GONG), covering
the period 2001-2004. The data are compared with contemporaneous
data from the Michelson Doppler Imager (MDI) dynamics program, where
available. We examine both synoptic charts and the day-to-day variations
in selected active regions. The results, once instrumental effects have
been removed, show strong dependence of the mode frequency on the local
magnetic flux, with the frequencies generally increasing with magnetic
index. We relate these findings to results from global modes. This
work was supported by the National Science Foundation and NASA
Title: Building a Virtual Solar Observatory: Lessons Learned
Authors: Bogart, R. S.; Tian, K. Q.; Davey, A.; Dimitoglou, G.;
Gurman, J. B.; Hill, F.; Hourclé, J.; Martens, P. C.; Suárez-Sola,
I.; Wampler, S.; Yoshimura, K.
Bibcode: 2005AGUSMSH51B..05B
Altcode:
Two years into its development, the VSO has emerged from a drawing board
concept into a full-fledged data query and data delivery system serving
the Solar Physics community. Throughout its development, the VSO has
lived up to its `small box' motto and has built light-weight servers
that can easily run on a desktop or laptop. The two basic functions
of the VSO are data query and data delivery. For these functions, the
VSO servers act like switchboards, dispatching query/data requests
to relevant data providers. More important, these servers present
an abstraction that integrates diverse data archives, thus reducing
complexity. The design of the VSO has evolved during its implementation
in response to difficulties and user feedback. We discuss the changes
in areas such as the data model, user interface, and performance. These
lessons should be of interest to people designing and building other
virtual observatories. We also discuss challenges and opportunities
we foresee as the VSO becomes a significant and enabling research tool.
Title: Comparison of Mode Parameters Between Velocity and Intensity
Acoustic Spectra via Ring Diagrams
Authors: Tripathy, S. C.; Hill, F.; González Hernández, I.; Howe,
R.; Komm, R. W.; Toner, C. G.
Bibcode: 2005AGUSMSP24A..03T
Altcode:
We analyse the local acoustic spectra at different locations over the
solar disk using both velocity and intensity images from MDI. These
spectra were fitted to obtain different mode parameters: e.g., acoustic
frequencies, mode amplitudes and life time using symmetric fits. We
find differences between frequencies derived from velocity and intensity
filtergrams, and it appears that the mode frequencies vary as a function
of location on the disk. Since the apparent frequency shift between an
oscillation observed in velocity and intensity can not be a property
of the mode, the analysis is expected to provide important information
about the driving and damping of local acoustic oscillations.
Title: Five-Minute Power Maps From GONG and MDI.
Authors: Howe, R.; Komm, R. W.; Hill, F.; Haber, D. A.; Hindman, B. W.
Bibcode: 2005AGUSMSP13A..01H
Altcode:
The presence of magnetic active regions on the solar surface is well
known to influence the detected power of the oscillation signal. We
consider maps of the five-minute power in the velocity signal from
Global Oscillations Network Group (GONG) observations covering much
of the disk over multiple Carrington Rotations, and compare these in
detail with magnetic and continuum intensity images, with estimates of
the velocity power from ring diagram helioseismic analysis, and also
with a small sample of contemporaneous MDI (Michelson Doppler Imager)
data. The comparison of power maps with magnetograms is carried out at
a pixel-by-pixel level, for averages over patches of 16× 16 degrees
in heliographic latitude and longitude, and at some intermediate
scales. This research was supported by the National Science Foundation
and NASA.
Title: Using the Collaborative Sun-Earth Connector for integrating
data systems
Authors: Hurlburt, N.; Freeland, S.; Slater, G.; Bentley, R.; Hill,
F.; Bose, P.
Bibcode: 2005AGUSMSH43B..05H
Altcode:
We demonstrate the coupling of disjoint data systems into virtual
collaborative operations using the Collaborative Sun-Earth Connector
(CoSEC). In addition to demonstrating possible interactions between
Virtual observatories, we will present how individual missions and
researchers can integrate their systems with space science services
already incorporated into CoSEC. We present more advanced concepts of
how to create collaborative data environments using upcoming solar
missions as examples. This research has been supported through NASA
contract NNH04CC00C.
Title: Vorticity and Kinetic Helicity in Solar Subsurface Layers
from GONG and MDI data
Authors: Komm, R.; Howe, R.; Hill, F.; Haber, D. A.; González
Hernández, I.
Bibcode: 2005AGUSMSP43B..04K
Altcode:
We use a ring-diagram analysis to determine the subsurface flows from
high-resolution Global Oscillation Network Group (GONG) and Michelson
Doppler Imager (MDI) data and derive the vorticity and the kinetic
helicity of the subsurface flows in the upper 16~Mm of the convection
zone. We separate the contributions of large-scale horizontal flows,
such as differential rotation, from those of small-scale variations,
such as the ones due to active regions, and analyze the large-scale and
the residual component independently. We study the relation between
magnetic activity and subsurface flows by comparing synoptic maps of
the derived residual quantities with maps of photospheric magnetic
activity. By comparing synoptic maps derived from GONG and MDI data,
we are able to cross-validate the results. We will present the latest
findings. This work has been supported by NASA and NSF.
Title: Solar Subsurface Flows of Active Region AR~0696
Authors: Komm, R.; Howe, R.; Donaldson Hanna, K.; Hill, F.; Sheeley, N.
Bibcode: 2005AGUSMSP24A..02K
Altcode:
We use a ring-diagram analysis to determine the subsurface flows in
the upper 16~Mm of the convection zone from high-resolution Global
Oscillation Network Group (GONG) data obtained during the first two
weeks of November 2004. The active region AR~0696 emerges near the
eastern limb and moves across the disk during this time period. The
region produced several terrestrially effective flares and halo
CMEs during its transit across the disk. During its disk passage,
AR~0696 is the only large active region in the northern hemisphere
and almost the only flare producing region on the sun. This makes it a
good candidate for investigating the relation between active regions,
their flare activity, and associated subsurface flows. We will present
the latest results. This work was supported by NASA grant NAG 5-11703.
Title: The Effects of Magnetically-Induced Spectral Line Profile
Changes on Helioseismic and Flare Observations
Authors: Edelman, F.; Hill, F.; Howe, R.; Komm, R.
Bibcode: 2005AGUSMSP13A..03E
Altcode:
We have modeled the effect of changes in the shape of the spectral
line used for the GONG and MDI observations, and we investigate
the consequences for measurements of properties of oscillations and
flares. We find that magnetic field measurements are not very sensitive
to line shape changes, but velocity estimates do strongly depend on
line variations. Using simulated observations of a flare we find that
recently observed associated magnetic field changes are not due to
line shape changes. On the other hand, a simulation of an oscillation
indicates that at least part of the observed amplitude suppression in
an active region is due to variations in the line shape. We also report
preliminary results of the effect of vertical phase variations across
the line profile on the helioseismic observations. This work is carried
out through the National Solar Observatory Research Experiences for
Undergraduate (REU) site program, which is co-funded by the Department
of Defense in partnership with the National Science Foundation REU
Program. This work utilizes data obtained by the Global Oscillation
Network Group (GONG) project, managed by the National Solar Observatory,
which is operated by AURA, Inc. under a cooperative agreement with
the National Science Foundation. The data were acquired by instruments
operated by the Big Bear Solar Observatory, High Altitude Observatory,
Learmonth Solar Observatory, Udaipur Solar Observatory, Instituto de
Astrofísica de Canarias, and Cerro Tololo Interamerican Observatory.
Title: Local helioseismology - what does it really tell us?
Authors: Hill, Frank
Bibcode: 2005HiA....13..428H
Altcode:
The subfield of local helioseismology is now 15 years old. In its
brief history it has yielded maps of flows beneath the solar surface
images of active regions on the far side of the sun and inferences
about the sound speed below sunspots. However there has not yet been
a systematic study of the consistency among results obtained with the
three major local methods of time-distance acoustic holography and ring
diagrams. In addition realistic numerical simulations of data suitible
for testing the methods have proven difficult to construct. In this
talk I will give an overview of the methods comparing them from a
heuristic point of view. I will also discuss the types of tests that
would be desirable and present the latest results from a data-based
comparison exercise now underway.
Title: Doing Science with the VSO: Signatures of CME Initiation
Authors: Davey, A. R.; Wills-Davey, M.; Gurman, J. B.; Bogart, R.;
Tian, K. Q.; Martens, P.; Yoshimura, K.; Hill, F.; Suarez-Sola, I.;
Hourclé, J.; Dimitoglou, G.; Wampler, S.
Bibcode: 2004AGUFMSH21B0414D
Altcode:
The Virtual Solar Observatory (VSO) was designed to simplify and unify
access to solar physics data. It provides a single interface to a broad
range of data types and sources which previously would have required
considerable effort to collect one by one. By combining access to online
data sources with published scientific catalogs, the VSO can facilitate
new science. This study seeks to investigate whether signatures of
coronal mass ejection (CME) initiation can be used to constrain CME
initiation models. We selected events from the SOHO/LASCO CME catalog,
generated a time window between the calculated CME ``start time" and
the first observation of the CME in LASCO C2, and examined EIT ``CME
Watch" and H-alpha observations identified by a VSO query as falling in
the specified time windows. We prioritized the EUV data by selecting
those events for which GOES data indicated a flare, and identified
flare sites and dimming regions in the EUV data, with the aim of more
precisely determining CME initiation locations and times. In addition,
we used H-alpha data to investigate CME's associated with by filament
eruptions. The results allow us to calculate minimum acceleration rates,
and determine correlations between coronal structures, ejection events,
and acceleration rates. We use these correlations in turn to identify
viable CME initiation mechanisms.
Title: Solving Science Use Cases that relate to the Sun and
Heliosphere with EGSO
Authors: Bentley, R. D.; Scholl, I.; Csillaghy, A.; Aboudarham,
J.; Antonucci, E.; Gurman, J. B.; Hill, F.; Pike, D.; Vial, J.;
Zharkova, V.
Bibcode: 2004AGUFMSH21B0415B
Altcode:
The European Grid of Solar Observations (EGSO) is a grid testbed
funded by the European Commission's Fifth Framework Programme under
its Information Society Technologies (IST) thematic priority. The
project started in 2002 and is designed to provide enhanced access to
solar and related data around the world. The EGSO grid is composed
of two main components, Roles to set up the grid and, catalogs and
registries to allow roles to answer users queries. Catalogs are made
of lists of observations, events and features (a new service provided
by EGSO). Registries are built from these catalogs and organized in
order to enhance search capabilities. EGSO is working closely with
other virtual observatory (VO) projects in the solar physics and
related domains. This includes the US Virtual Solar Observatory (VSO)
and the Collaborative Sun-Earth Connector (CoSEC). More recently we
have been working with the Virtual Space Plasma Observatory (VSPO) and
have contact with the Virtual Heliospheric Observatory (VHO). Through
discussions with future missions, and within the new IAU Working
Group on ``International Data Access'' (Solar and Heliospheric),
the VOs are studying ways of ensuring interoperability from the
``sun to dirt''. This type of integrated access will be particularly
important to missions such as STEREO and Living Witha Star. In this
paper we will report the current status of EGSO, demonstrate how the
catalogs and registries model serves within the user interface, and
show how the user can retrieve solar and heliospheric data to match
a scientific query. EGSO Release 4 is now being Beta-tested by users
and anyone interested should view the Web page detailing all the EGSO
capabilities under http://www.egso.org/demo
Title: STEREO in the Virtual Solar Observatory Context
Authors: Hourcle, J. A.; Bogart, R.; Davey, A.; Gurman, J. B.; Hill,
F.; Martens, P.; Suarez-Sola, I.; Tian, K.; Yoshimura, K.
Bibcode: 2004AGUFMSH21B0413H
Altcode:
The Virtual Solar Observatory (VSO) was designed with the goal that it
handle heterogeneous data sets from multiple observatories. With its
two spacecraft and multiple instruments, the STEREO mission provides
an excellent example of solar physics research based on multiple data
sets, and a good test of the abilities of the VSO. Here we will discuss
how the VSO will meet the key challenges that STEREO presents. In
particular, the wide range of data classes and the non-stationary
viewpoints of the two spacecraft demand a flexible underlying data
model of the VSO.
Title: The Status of the GONG Program
Authors: Hill, F.; GONG Team
Bibcode: 2004ESASP.559..128H
Altcode: 2004soho...14..128H
No abstract at ADS
Title: How Sensitive are Rotation Inversions to Subtle Features of
the Dynamo?
Authors: Howe, R.; Rempel, M.; Christensen-Dalsgaard, J.; Hill, F.;
Komm, R. W.; Schou, J.; Thompson, M. J.
Bibcode: 2004ESASP.559..468H
Altcode: 2004soho...14..468H
No abstract at ADS
Title: Searching for Subsurface Signatures of X-Class Flares
Authors: Komm, R.; Howe, R.; González Hernández, I.; Hill, F.;
Sudol, J.; Toner, C.
Bibcode: 2004ESASP.559..158K
Altcode: 2004soho...14..158K
No abstract at ADS
Title: Solar Subsurface Flows and Vorticity
Authors: Komm, R.; Howe, R.; González Hernández, I.; Hill, F.;
Haber, D.; Hindman, B.; Corbard, T.
Bibcode: 2004ESASP.559..520K
Altcode: 2004soho...14..520K
No abstract at ADS
Title: Local Frequency Shifts from GONG and MDI
Authors: Howe, R.; Komm, R. W.; González Hernández, I.; Hill, F.;
Haber, D. A.; Hindman, B. W.
Bibcode: 2004ESASP.559..484H
Altcode: 2004soho...14..484H
No abstract at ADS
Title: The Phase of the Torsional Oscillation Pattern
Authors: Howe, R.; Komm, R. W.; Hill, F.; Christensen-Dalsgaard, J.;
Schou, J.; Thompson, M. J.
Bibcode: 2004ESASP.559..476H
Altcode: 2004soho...14..476H
No abstract at ADS
Title: Meridional Variability from Large-Aperture Ring Diagrams
Authors: González Hernández, I.; Komm, R.; Hill, F.; Howe, R.;
Corbard, T.
Bibcode: 2004ESASP.559..444G
Altcode: 2004soho...14..444G
No abstract at ADS
Title: Medium-L Spherical Harmonic Rings
Authors: González Hernández, I.; Hill, F.; Kholikov, Sh. S.;
Gressett, K.; Jiménez-Reyes, S. J.
Bibcode: 2004ESASP.559..448G
Altcode: 2004soho...14..448G
No abstract at ADS
Title: A tale of Two Regions: Acoustic Power Maps and Magnetic
Activity in AR 10486 and AR 10488
Authors: Howe, R.; Komm, R. W.; González Hernández, I.; Hill, F.;
Haber, D. A.; Hindman, B. W.
Bibcode: 2004ESASP.559..480H
Altcode: 2004soho...14..480H
No abstract at ADS
Title: Flowmaps Covering Six Consecutive Carrington Rotations
Authors: Komm, R.; Howe, R.; Bolding, J.; Donaldson Hanna, K.;
González Hernández, I.; Hill, F.; Toner, C.
Bibcode: 2004ESASP.559..516K
Altcode: 2004soho...14..516K
No abstract at ADS
Title: The Effect of Spectral Line Shape Changes on GONG Observations
of Oscillations and Flares
Authors: Edelman, F.; Hill, F.; Howe, R.; Komm, R.
Bibcode: 2004ESASP.559..416E
Altcode: 2004soho...14..416E
No abstract at ADS
Title: An Automated Image Rejection System for GONG
Authors: Clark, R.; Toner, C.; Hill, F.; Hanna, K.; Ladd, G.; Komm,
R.; Howe, R.; Gonzalez-Hernandez, I.; Kholikov, S.
Bibcode: 2004ESASP.559..381C
Altcode: 2004soho...14..381C
No abstract at ADS
Title: Advanced Technology Solar Telescope: conceptual design
and status
Authors: Keil, Stephen; Oschmann, Jacobus M., Jr.; Rimmele, Thomas R.;
Hubbard, Rob; Warner, Mark; Price, Ron; Dalrymple, Nathan; Goodrich,
Bret; Hegwer, Steven; Hill, Frank; Wagner, Jeremy
Bibcode: 2004SPIE.5489..625K
Altcode:
The Advance Technology Solar Telescope (ATST) has finished its
conceptual design stage, submitted a proposal for construction funding
and is working towards a system level preliminary design review later
this year. The current concept (including integrated adaptive optics
and instrumentation) will be reviewed with concentration on solutions
to the unique engineering challenges for a four meter solar telescope
that have been previously presented. The overall status will be given
with a concentration on near term milestones and impact on final
completion targeted in 2012.
Title: Solar site testing for the Advanced Technology Solar Telescope
Authors: Hill, Frank; Beckers, Jacques; Brandt, Peter; Briggs, John;
Brown, Timothy; Brown, W.; Collados, Manuel; Denker, Carsten; Fletcher,
Steven; Hegwer, Steven; Horst, T.; Komsa, Mark; Kuhn, Jeff; Lecinski,
Alice; Lin, Haosheng; Oncley, Steve; Penn, Matthew; Rimmele, Thomas
R.; Socas-Navarro, Hector; Streander, Kim
Bibcode: 2004SPIE.5489..122H
Altcode:
The location of the Advanced Technology Solar Telescope (ATST) is a
critical factor in the overall performance of the telescope. We have
developed a set of instrumentation to measure daytime seeing, sky
brightness, cloud cover, water vapor, dust levels, and weather. The
instruments have been located at six sites for periods of one to two
years. Here we describe the sites and instrumentation, discuss the
data reduction, and present some preliminary results. We demonstrate
that it is possible to estimate seeing as a function of height near the
ground with an array of scintillometers, and that there is a distinct
qualitative difference in daytime seeing between sites with or without
a nearby lake.
Title: Convection-Zone Dynamics from GONG and MDI, 1995-2004
Authors: Howe, R.; Komm, R. W.; Hill, F.; Christensen-Dalsgaard, J.;
Haber, D. A.; Schou, J.; Thompson, M. J.
Bibcode: 2004ESASP.559..472H
Altcode: 2004soho...14..472H
No abstract at ADS
Title: The Virtual Solar Observatory: status and initial operational
experience
Authors: Hill, Frank; Bogart, Richard S.; Davey, Alisdair; Dimitoglou,
George; Gurman, Joseph B.; Hourcle, Joseph A.; Martens, Petrus C.;
Suarez-Sola, Igor; Tian, Karen; Wampler, Steven; Yoshimura, Keiji
Bibcode: 2004SPIE.5493..163H
Altcode:
The Virtual Solar Observatory (VSO) is a bottom-up grassroots approach
to the development of a distributed data system for use by the solar
physics community. The beta testing version of the VSO was released in
December 2003. Since then it has been tested by approximately 50 solar
physicists. In this paper we will present the status of the project,
a summary of the community's experience with the tool, and an overview
of the lessons learned.
Title: Virtual Solar Inc.
Authors: Bentley, R. D.; Hill, F.; Hurlburt, N.
Bibcode: 2004ASPC..314..311B
Altcode: 2004adass..13..311B
The need to develop new ways of accessing solar observations, coupled
with rapidly increasing volumes of data and the desire to share
data with other communities, has led to several projects intended
to create virtual solar observatories. We outline the three main
initiatives, EGSO, VSO and CoSEC, and describe how the the combined
effort will result in a facility that will better match the needs of the
community. Interaction with related communities are discussed, including
similarities and differences with the IVOA and interoperability.
Title: Activity-related Changes in Local Solar Acoustic Mode
Parameters from Michelson Doppler Imager and Global Oscillations
Network Group
Authors: Howe, R.; Komm, R. W.; Hill, F.; Haber, D. A.; Hindman, B. W.
Bibcode: 2004ApJ...608..562H
Altcode:
We use the ring-diagram technique of local helioseismology to study
the amplitude and line width of high-degree solar acoustic modes
from 474 days of data from the Michelson Doppler Imager Dynamics
program, covering the period 1996-2002. The 2002 data are compared
with contemporaneous data from the Global Oscillations Network Group
network. The results, once instrumental effects have been removed,
show a strong dependence of the amplitude and lifetime of the modes on
the local magnetic flux, with the amplitude and lifetime decreasing in
the 5 minute band and a reversed trend at high frequencies. We relate
these findings to results from global modes and from other approaches
for analyzing high-degree local oscillations.
Title: Latest Results from the ATST Site Survey
Authors: Hill, F.; Collados, M.; Navarro, H.; Beckers, J.; Brandt,
P.; Briggs, J.; Brown, T.; Denker, C.; Hegwer, S.; Horst, T.; Komsa,
M.; Kuhn, J.; Lin, H.; Oncley, S.; Penn, M.; Rimmele, T.; Soltau,
D.; Streander, K.
Bibcode: 2004AAS...204.6909H
Altcode: 2004BAAS...36..795H
We present the latest results and current status of the site survey
portion of the Advanced Technology Solar Telescope (ATST) project. The
ATST will provide high resolution solar data in the visible and IR. The
site is a major factor determining the performance of the telescope. The
most critical site characteristics are the statistics of daytime seeing
quality and sky clarity. These conditions are being measured by a suite
of instruments at three sites (Big Bear, Haleakala, La Palma). These
sites were chosen from a set of six that have been tested starting in
November 2001. The instrumentation includes a solar differential image
motion monitor, an array of scintillometers, a miniature coronagraph,
a dust monitor, and a weather station. The analysis of the data provides
an estimate of the seeing as a function of height near the ground. We
will present the latest results of the analysis of the survey data set.
Title: Two White Light Flares in AR10486 observed by the GONG
instruments
Authors: Howe, R.; Gonzalez-Hernandez, I.; Harvey, J. W.; Hill, F.
Bibcode: 2004AAS...204.0212H
Altcode: 2004BAAS...36R.669H
The GONG (Global Oscillation Network Group) program operates a worldwide
network of six instruments, primarily intended to give continuous
Doppler velocity images of the full solar disk for helioseismology. The
instruments also produce images in magnetic field strength, total
intensity and line depth for a 1Å band centered on the Ni I (6768 Å)
line, all at 60 second cadence with a spatial resolution of around 2
arcsecond. The X10 flare of 2003 October 29 and the X8.3 flare of 2003
November 2 both produced clear signatures in the GONG images, with
local 20 to 30 per cent enhancements in the total intensity and a 50
per cent drop in the line strength, indicating the presence of white
light emission. There are also both transient and persistent changes
in the magnetic field. This work was supported by NASA and NSF.
Title: Vorticity of Solar Subsurface Flows and Torsional Oscillations
Authors: Komm, R.; Howe, R.; Gonzalez-Hernandez, I.; Hill, F.; Haber,
D.; Hindman, B.; Corbard, T.
Bibcode: 2004AAS...204.5308K
Altcode: 2004BAAS...36Q.757K
We study horizontal flows in the upper solar convection zone
derived from GONG and MDI Dynamics Program data using ring-diagram
analysis. We start exploring the dynamics of the near surface layers
and the interaction between flows and magnetic flux by deriving the
vorticity of the horizontal flow components. A preliminary analysis of
synoptic flow maps shows that the vorticity is enhanced near locations
of active regions. In this study, we focus on the question of how
these flows with vorticity near active regions are related to the
so-called torsional oscillation pattern shown by zonal flows. During
a solar cycle, alternating bands of faster- and slower-than-average
rotation move from high latitudes toward the solar equator with the
faster-than-average band being equatorward of active regions. The
solar-cycle variation of the zonal flows thus contributes to the
vorticity measured in daily or synoptic flow maps. We plan to determine
the size of this contribution and will present our latest results. This work was supported by grants from NASA and NSF.
Title: Meridional Circulation Variability from Large-Aperture Ring
Diagrams
Authors: Gonzalez-Hernandez, I.; Komm, R.; Corbard, T.; Hill, F.;
Howe, R.
Bibcode: 2004AAS...204.5307G
Altcode: 2004BAAS...36..756G
Ring Diagram analysis, a local helioseismology technique, has proven
very useful in the study of solar subsurface velocity flows to a
depth of about 0.97Rsun. The depth range is determined by the modes
recovered with this method and thus depends on the size of the area
analyzed. Extending the working area allows us to detect lower l modes
that penetrate deeper into the Sun. However, there is a compromise
between the size of the patch and the validity of the plane wave
approximation used by the technique. Here we search for variability
of the meridional flows as a function of depth for three consecutive
Carrington rotations. We have studied patches of 30-degree diameter over
the solar surface as they crossed the solar central meridian. These
patches are twice the size of the typically studied sections of 15
degrees in diameter. The range of modes recovered with these larger
regions goes down to l 100. A set of 15 overlapping sections, centered
at latitudes 0 +/-7.5,+/-15,+/-22.5,+/-30.0,+/-37.5,+/-45.0 and +/-52.5,
has been analyzed for 25 intervals of 1664 minutes in each Carrington
rotation: CR1987, CR1988 and CR1989. Both GONG and MDI full disk
Dopplergrams have been used for the work. This work was supported
in part by NASA grant NAG5-11703. SOHO is a project of international
cooperation between ESA and NASA. This work utilizes data obtained by
the Global Oscillation Network Group (GONG) Program, managed by the
National Solar Observatory, which is operated by AURA, Inc. under a
cooperative agreement with the National Science Foundation. The data
were acquired by instruments operated by the Big Bear Solar Observatory,
High Altitude Observatory, Learmonth Solar Observatory, Udaipur Solar
Observatory, Instituto de Astrofisica de Canarias, and Cerro Tololo
Interamerican Observatory.
Title: Implementation of the Virtual Solar Observatory
Authors: Davey, A. R.; Bogart, R. S.; Gurman, J. B.; Hill, F.; Hourcle,
J.; Martens, P. C.; Suarez-Sola, I.; Tian, K. Q.; Yoshimura, K.
Bibcode: 2004AAS...204.7002D
Altcode: 2004BAAS...36..796D
The Virtual Solar Observatory (VSO) integrates diverse solar data
archives into a virtual collection providing common search and delivery
services. Having developed from a prototype installation involving
four major archives, it is now in the process of expanding to include
a larger variety of archives and data types. We are also refining and
expanding its services and user interfaces and defining an API. We
have defined a working extensible data model enabling us to provide
more detailed and comprehensive search capabilities and to incorporate
additional data products. The API will allow people to construct their
own interfaces to the core VSO functionality and integrate with other
web services and other virtual observatories. Here we describe the
structure of VSO as currently implemented and what is required to
incorporate additional archives.
Title: IAU Working Group on International Data Access for Solar and
Heliospheric data
Authors: Bentley, R. D.; Hill, F.; Hurlburt, N.; Roberts, A.
Bibcode: 2004AAS...204.5207B
Altcode: 2004BAAS...36S.754B
Division II (Sun and Heliosphere) of the IAU has initiated a Working
Group to study the archiving, retrieval and distribution of solar and
heliospheric data. The goal of the Working Group is to facilitate the
use of available solar and heliospheric data that are archived in
a large number of computers scattered all over the world. The
intent of the Working Group is to help coordinate the existing and
growing data exchange through the Internet and work with the virtual
observatory initiatives to propose guidelines for exchange at an
international level and encourage participation in the projects. The Working Group is working with the virtual observatory initiatives
to ensure that they develop standards and employ techniques that are
acceptable to the worldwide solar and heliospheric communities and
to encourage interoperability between the projects. The EGSO, VSO,
CoSEC and VSPO projects are all part of the Working Group and would
also like to encourage the communities to help develop standards and
participate in the virtual observatory projects. The aims of and
objectives the Working Group will be discussed and feedback from the
audience is encouraged.
Title: DASL--Data and Activities for Solar Learning
Authors: Hill, F.; Gearen, M.; Henney, C.; Jones, H.; Stagg, T.
Bibcode: 2004AAS...204.7703H
Altcode: 2004BAAS...36..808H
Data and Activities for Solar Learning (DASL) provides a classroom
learning environment based on a twenty-five year record of solar
magnetograms from the National Solar Observatory (NSO) at Kitt Peak,
AZ. The data, together with image processing software for Macs or PCs,
can be used to learn basic facts about the Sun and astronomy at the
middle school level. At the high school level, students can study
properties of the Sun's magenetic cycle with classroom excercises
emphasizing data and error analysis and can participate in a new
scientific study, Research in Active Solar Longitudes (RASL), in
collaboration with classrooms throughout the country and scientists
at NSO and NASA. We will have available a compact disc with the data
and software, and a web site for uploading the RASL results.
Title: Comparison of GONG and MDI solar p-mode background
Authors: Barban, C.; Hill, F.
Bibcode: 2004SoPh..220..399B
Altcode:
Using Severino's model, we estimate the amount of coherent correlated
and uncorrelated background and incoherent noise components needed to
reproduce the following four helioseismic spectra: V power, I power,
V-I phase difference and V-I coherence, using GONG and MDI data. We
confirm that a coherent correlated component of 10-15% of the total
background and noise is needed in both V and I and that a larger amount
of coherent uncorrelated background is needed for MDI data compared
to GONG data to compensate for a smaller incoherent noise.
Title: Solar Subsurface Fluid Dynamics Descriptors Derived from
Global Oscillation Network Group and Michelson Doppler Imager Data
Authors: Komm, R.; Corbard, T.; Durney, B. R.; González Hernández,
I.; Hill, F.; Howe, R.; Toner, C.
Bibcode: 2004ApJ...605..554K
Altcode:
We analyze Global Oscillation Network Group (GONG) and Michelson Doppler
Imager (MDI) observations obtained during Carrington rotation 1988
(2002 March 30-April 26) with a ring-diagram technique in order to
measure the zonal and meridional flow components in the upper solar
convection zone. We derive daily flow maps over a range of depths up
to 16 Mm on a spatial grid of 7.5d in latitude and longitude covering
+/-60° in latitude and central meridian distance and combine them
to make synoptic flow maps. We begin exploring the dynamics of the
near-surface layers and the interaction between flows and magnetic flux
by deriving fluid dynamics descriptors such as divergence and vorticity
from these flow maps. Using these descriptors, we derive the vertical
velocity component and the kinetic helicity density. For this particular
Carrington rotation, we find that the vertical velocity component is
anticorrelated with the unsigned magnetic flux. Strong downflows are
more likely associated with locations of strong magnetic activity. The
vertical vorticity is positive in the northern hemisphere and negative
in the southern hemisphere. At locations of magnetic activity,
we find an excess vorticity of the same sign as that introduced by
differential rotation. The vertical gradient of the zonal flow is
mainly negative except within 2 Mm of the surface at latitudes poleward
of about 20°. The zonal-flow gradient appears to be related to the
unsigned magnetic flux in the sense that locations of strong activity
are also locations of large negative gradients. The vertical gradient
of the meridional flow changes sign near about 7 Mm, marking a clear
distinction between near-surface and deeper layers. GONG and MDI data
show very similar results. Differences occur mainly at high latitudes,
especially in the northern hemisphere, where MDI data show a counter
cell in the meridional flow that is not present in the corresponding
GONG data.
Title: Extinction and Sky Brightness at Two Solar Observatories
Authors: Penn, M. J.; Lin, H.; Schmidt, A. M.; Gerke, J.; Hill, F.
Bibcode: 2004SoPh..220..107P
Altcode:
The Advanced Technology Solar Telescope site survey Sky Brightness
Monitor simultaneously images the solar disk and the sky to about
8 solar radii in four wavelengths at 450, 530, 890 and 940 nm. One
day of data from Mees Solar Observatory on Haleakala and from the
National Solar Observatory at Sacramento Peak (Sunspot, New Mexico)
are analyzed. Both sites show strong Rayleigh extinction, but while
Haleakala shows a larger aerosol component, Sunspot shows a large
variation in the aerosol component. Overall the Haleakala extinction
varies as λ−2 whereas the Sunspot extinction changes
from about λ−3.5 to about λ−2, suggesting
an increasing aerosol component during the day. Water vapor absorption
measurements from both sites are similar, though Sunspot shows larger
time variations than Haleakala. The instrument-corrected sky brightness
from both sites show comparable values, and again the Sunspot data show
more variations. The sky brightness values show a radial dependence
of sky brightness of r−0.1 at Haleakala, but a dependence
of r−1.0 at Sunspot. The wavelength variation of the sky
brightness at Haleakala is relatively constant at λ−1.5
but varies at Sunspot from λ−1.5 to λ−0.1
again suggesting an increasing aerosol contribution during the day
at Sunspot. Finally, dust measurements near the ground are compared
with the extinction wavelength exponent for data taken at Haleakala
on 24 Feb. 2003. The measurements suggest more large dust particles
are present near the ground than averaged over the whole air column.
Title: Advanced Technology Solar Telescope: a progress report
Authors: Oschmann, Jim; Dalrymple, Nathan; Warner, Mark; Price, Ron;
Hill, Frank; Hubbard, Rob; Rimmele, Thomas R.; Keller, Christoph U.;
Keil, Stephen
Bibcode: 2004SPIE.5171..160O
Altcode:
The 4m ATST will be the most powerful solar telescope in the world,
providing a unique scientific tool to study the Sun and other
astronomical objects. The design and development phase for the Advance
Technology Solar Telescope (ATST) is progressing. The conceptual design
review (CoDR) for the ATST is scheduled for August 2003. We present a
brief description of the science requirements of ATST, and remind the
reader of some of the technical challenges of building a 4-m solar
telescope. We will discuss some of the design strategies that will
allow us to achieve the required performance specifications, present
conceptual designs for the ATST, and summarize the results of trades
we have made on our path to the CoDR. The thermal impacts to local,
self-induced seeing with respect to some of our system level trades
that have been completed will be discussed.
Title: Simultaneous Velocity-Intensity Spectral and Cross-Spectral
Fitting of Helioseismic Data
Authors: Barban, C.; Hill, F.; Kras, S.
Bibcode: 2004ApJ...602..516B
Altcode:
Solar oscillation parameters, such as the frequency, are usually
estimated by fitting the mode profile in the velocity (V) power
spectrum. In this paper, the solar oscillation parameters are derived by
simultaneously fitting four observational spectra: V and I (intensity)
power, I-V phase difference, and I-V coherence using the model of
Severino et al. that contains several background components. We show
that this model reproduces the observed spectra for l=15-50 using
Global Oscillation Network Group (GONG) data. A study of the model
parameters as a function of frequency shows the well-known behavior
of the mode amplitude and width. Comparing the oscillation parameters
using the multispectral fitting and the V power spectrum alone with
an asymmetric profile shows that the oscillation frequency differs by
at most 0.2 μHz below 3 mHz but that the background components are
needed to adequately describe the spectrum at higher frequencies. The
background amplitudes and phases provide information about the solar
oscillation excitation mechanism. For example, the coherent correlated
background might be associated with the darkening observed in the
intergranular lane at the beginning of the seismic event, while the
coherent uncorrelated component might be related to seismic events
unable to excite the 5 minute oscillations.
Title: Helioseismic sensing of the solar cycle
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 2004cosp...35.1397K
Altcode: 2004cosp.meet.1397K
In the last decade, great progress has been made in understanding
the activity-cycle variation of the dynamics and structure of
the solar interior. Observations from SoHO/MDI, GONG, BiSON,
and Mt. Wilson have now provided detailed helioseismic information
over two decades. Parameters such as frequency, width, and amplitude
describing global acoustic modes sense the varying local distribution
of the surface magnetic activity with the solar cycle. Mode width
and amplitude contain information about the damping and excitation of
acoustic modes and hence have implications for the understanding of
the near-surface layers where the acoustic modes are generated. The
frequency variation of the global modes provides information about
the solar structure and interior rotation rate. The rotation rate
in the upper convection zone varies with the solar cycle: the zonal
flows are detectable in at least the upper third of the convection
zone. At the base of the convection zone, the rotation rate varies
with a period of about 1.3 yr which might indicate an exchange of
angular momentum between the radiative interior and the convection
zone. With local helioseismology techniques such as ring-diagram or
time-distance analysis, it is possible to measure the flow component
in the meridional direction. Its variation with depth and solar cycle
can provide insights into the operation of the solar dynamo.
Title: The Virtual Solar Observatory -- the Why, What, How and Where
Authors: Hill, F.; Bogart, R. S.; Davey, A.; Dimitoglou, G.; Gurman,
J. B.; Martens, P. C.; Tian, K.; Wampler, S.
Bibcode: 2003AGUFM.U22A0012H
Altcode:
Observational solar physics almost always involves the comparison of
several data sets obtained by different instruments and stored in a
variety of archives. Currently a researcher must laboriously locate
the relevant archives, search them with idiosyncratic interfaces,
and retrieve the data by a number of methods. The VSO is a tool to
streamline this process by providing a single unified interface and
search tool for solar archives. Eventually this will be supplemented
by distributed computing tools which will enable queries based on
data itself, in addition to standard queries on metadata. The VSO
will enable a new class of solar research -- large-scale correlative
statistical studies on many data sets, thereby facilitating space
weather studies. An example of a use case is a helioseismic study of the
subsurface structure of cornal hole boundaries and possible predictive
links between the solar interior and the solar wind. An intital
prototype has been built linking archives at GSFC, Stanford, MSU, and
NSO. This prototype has been constructed using a combination of XML,
SOAP, and Perl technologies, and a beta release is available now. The
initial set of archives will soon be expanded to include archives at
HAO, NGDC, and selected NOAA feature and event catalogues. In the
next 2 years, additonal service providers will be added, the user
interface will be fully developed, and distributed computing tools
will be initiated.
Title: Data Integration in the Virtual Solar Observatory
Authors: Bogart, R. S.; Davey, A.; Dimitoglou, G.; Gurman, J. B.;
Hill, F.; Martens, P. C.; Tian, K. Q.; Wampler, S.
Bibcode: 2003AGUFMSH42A0503B
Altcode:
The aim of the Virtual Solar Observatory (VSO) is the integration of
diverse data archives relevant to the study of Solar Physics into a
virtual collection providing common search and delivery services. The
back-end query services are implemented as Web Services and accessible
via the Simple Object Access Protocol (SOAP). SOAP defines a remote
procedure call mechanism that employs HTTP as its transport and
encodes the client-server interactions in XML documents. In addition
to its core function in identifying relevant datasets locally, a SOAP
server at each data provider acts as a wrapper that maps descriptions
in an abstract data model to those in the provider's specific model,
and vice versa. Heterogeneous data search services can thereby be
integrated with a common interface. This allows scientists to access
multiple archives with differing data organizations at once, enhancing
their ability to discover and and analyze correlative data from multiple
sources. We have chosen two SOAP implementations for the VSO: SOAP::Lite
and OpenSOAP. The former, written in Perl, is suitable for fast and
flexible prototyping in data search applications. SOAP::Lite servers
have been set up at each of the VSO archives, and can be readily
installed at other servers. OpenSOAP, written in C with built-in
support for service description and dispatch, may prove useful in
transforming current computing utilities into Web Services. We report
on initial experiments using OpenSOAP to provide additional services
to the basic query functionality of VSO.
Title: DASL--Data and Activities for Solar Learning
Authors: Hill, F.; Gearen, M. V.; Henney, C. J.; Jones, H. P.;
Stagg, T.
Bibcode: 2003AGUFMED41D1189H
Altcode:
Data and Activities for Solar Learning (DASL) provides a classroom
learning environment based on a twenty-five year record of solar
magnetograms from the National Solar Observatory (NSO) at Kitt Peak,
AZ. The data, together with image processing software for Macs or PCs,
can be used to learn basic facts about the Sun and astronomy at the
middle school level. At the high school level, students can study
properties of the Sun's magnetic cycle with classroom excercises
emphasizing data and error analysis and can participate in a new
scientific study, Research in Active Solar Longitudes (RASL), in
collaboration with classrooms throughout the country and scientists
at NSO and NASA. We will demonstrate a compact disc with the data and
software, and a web site for uploading the RASL results.
Title: A Comparison of Solar p-Mode Parameters from MDI and GONG:
Mode Frequencies and Structure Inversions
Authors: Basu, S.; Christensen-Dalsgaard, J.; Howe, R.; Schou, J.;
Thompson, M. J.; Hill, F.; Komm, R.
Bibcode: 2003ApJ...591..432B
Altcode:
Helioseismic analysis of solar global oscillations allows investigation
of the internal structure of the Sun. One important test of the
reliability of the inferences from helioseismology is that the
results from independent sets of contemporaneous data are consistent
with one another. Here we compare mode frequencies from the Global
Oscillation Network Group and Michelson Doppler Imager on board SOHO
and resulting inversion results on the Sun's internal structure. The
average relative differences between the data sets are typically less
than 1×10-5, substantially smaller than the formal errors in
the differences; however, in some cases the frequency differences show
a systematic behavior that might nonetheless influence the inversion
results. We find that the differences in frequencies are not a result
of instrumental effects but are almost entirely related to the data
pipeline software. Inversion of the frequencies shows that their
differences do not result in any significant effects on the resulting
inferences on solar structure. We have also experimented with fitting
asymmetric profiles to the oscillation power spectra and find that,
compared with the symmetric fits, this causes no significant change
in the inversion results.
Title: Flow maps from GONG+ ring diagrams
Authors: Komm, R.; Bolding, J.; Corbard, T.; Hill, F.; Howe, R.;
Toner, C.
Bibcode: 2003SPD....34.0811K
Altcode: 2003BAAS...35..823K
We show first results derived from one month or more of GONG++
data analyzed with a ring-diagram technique as part of the GONG++
local helioseimology analysis pipeline. We focus on observations
obtained during spring 2002 and especially on Carrington rotation 1988
(2002/3/30 - 2002/4/26) and measure horizontal flow components over a
range of depths up to 16 Mm on a spatial grid of 7.5 degree in latitude
and longitude. We calculate zonal and meridional flow components and
compare the average zonal flows with corresponding results of a global
rotation inversion. We create and analyze synoptic maps of large-scale
flows and compare them with corresponding synoptic maps of magnetic
activity. We will present the latest results. RH and RK are
partially supported by NASA Grant S-92698-F. NSO is operated by AURA,
Inc under a co-operative agreement with the National Science Foundation.
Title: A Comparison of Low-Degree Solar p-Mode Parameters from BiSON
and GONG: Underlying Values and Temporal Variations
Authors: Howe, R.; Chaplin, W. J.; Elsworth, Y. P.; Hill, F.; Komm,
R.; Isaak, G. R.; New, R.
Bibcode: 2003ApJ...588.1204H
Altcode:
Approximately 5 years of the l=0 time series from the GONG project
have been analyzed using the algorithm developed for the BiSON
zero-dimensional data. The data cover the period 1995-2000. The results
are compared with those from a parallel analysis of contemporaneous
BiSON data and also with the results of the traditional GONG analysis
of the low-degree time series. The spectra analyzed were prepared
using the multitaper spectral analysis technique used in the recent
reanalysis of the GONG data. We consider both solar cycle trends
and temporally averaged values for mode frequencies, line widths,
amplitudes, and asymmetry parameters.
Title: Estimates of helioseismic oscillation excitation parameters
from multi-spectral fitting.
Authors: Barban, C.; Hill, F.
Bibcode: 2003SPD....34.2610B
Altcode: 2003BAAS...35..855B
The solar oscillation parameters, as the frequency, are usually
determined by fitting a theoretical profile to the observed Doppler
velocity (V) power spectrum. We present here the solar oscillation
parameters determined using GONG V data as well as Intensity (I)
data. To do that, we used Severino et al. (2001, ApJ 561,444) model to
reproduce the following 4 helioseismic spectra: V and I power spectrum,
I-V phase difference and coherence spectra. This model is based on a
coherent resonant p-mode signal; two coherent background components, one
correlated and one uncorrelated to the oscillation modes; and, finally,
the uncoherent noise. Using this model, we have fitted simultaneously
the 4 helioseismic spectra mentioned above for several hundreds modes
between l=15 and 50 and for 9 GONG months rotation corrected m-average
data around the solar minimum. The solar oscillation parameters
(frequency, amplitude and width) obtained by this way will be presented
as well as a comparison with the results obtained using only V data. The
study of the background components used in the model with the aim of
better understanding the solar oscillation excitation mechanism will
be addressed. This work is supported by NASA grant NAG5-11703.
Title: The LoHCo Project. 1 -- Comparison of Ring-Diagram Local
Helioseismology on GONG++, MDI and Mt. Wilson Data Sets
Authors: Bogart, R. S.; Schou, J.; Basu, S.; Bolding, J.; Hill, F.;
Howe, R.; Komm, R. W.; Leibacher, J. W.; Toner, C. G.; Corbard, T.;
Haber, D. A.; Hindman, B. W.; Toomre, J.; Rhodes, E. J.; Rose, P. J.;
LoHCo Project Team
Bibcode: 2003SPD....34.0804B
Altcode: 2003BAAS...35..822B
Full deployment of the GONG+ enhanced observing network in October
2001 and implementation of ring-diagram helioseismology in the
GONG++ analysis pipeline this year has enabled us to make a detailed
intercomparison of results obtained through multiple paths, from
observation through each of the analysis steps. Such comparisons
can provide a certain degree of validation of the implementations
of the analysis procedures, hints of systematic errors, and better
characterization of the observations, possibly leading to improved
calibrations. The Local Helioseismology Comparison (LoHCo) Project
has been established to provide standards for intercomparison of
results obtained with different local helioseismic analysis techniques
applied to the available observational data sources. We present here
a detailed comparison of ring-diagram determinations of localized
sub-surface flows and frequency shifts obtained from both MDI and
GONG in common observing intervals during Carrington Rotation 1988
(2002/3/30 -- 2002/4/26), using both the MDI and the GONG analysis
pipelines. We also present preliminary results of similar analyses of
data obtained by the Mt. Wilson MOF during the same times. This
work is partially supported by grants from NASA and NSF.
Title: The Virtual Solar Observatory: The Best-Laid Schema
Authors: Gurman, J. B.; Dimitoglou, G.; Hill, F.; Wampler, S.; Bogart,
R. S.; Tian, K.; Martens, P.; Davey, A.
Bibcode: 2003SPD....34.0203G
Altcode: 2003BAAS...35..807G
Work on a protoype Virtual Solar Observatory (VSO) is now under way. The
prototype will offer access to data from online solar archives at
Stanford, NSO, Montana State, and the SDAC. We discuss some of the
features of the VSO for users, as well as the basic design and some
of the technical aspects, including the use of XML schemas and SOAP
to allow users a single access method for disparate data services.
Title: Inverting Scintillometer Array Data to Estimate
Cn2(h) for the ATST Site Survey
Authors: Hill, F.; Collados, M.
Bibcode: 2003SPD....34.2020H
Altcode: 2003BAAS...35..848H
One of the instruments developed for the Advanced Technology
Solar Telescope (ATST) site survey is a non-redundant array
of six scintillometers known as a ShaBaR (SHAdow BAnd Ranging)
system, developed by J. Beckers. The ShaBaR provides an estimate
of Cn2(h), the turbulence structure
function, in the Earth's atmosphere. We can use the estimate of
Cn2(h) to infer the value of r0, the
Fried parameter, at any height above the ground up to the maximum range
of the ShaBaR. In this poster, we present two methods of extracting
the estimates by 1) inverting the data via a kernel function derived
from the theory of atmospheric turbulence, and 2) assuming a modified
Hufnagel-Valley model of Cn2(h). We also show
a series of simulations that has been produced and used to test the
accuracy and precision of the methods.
Title: First Steps Towards a VSO
Authors: Davey, A. R.; Bogart, R. S.; Dimitoglou, G.; Gurman, J. B.;
Hill, F.; Martens, P. C.; Tian, K. Q.; Wampler, S.
Bibcode: 2003SPD....34.0311D
Altcode: 2003BAAS...35..810D
Work has started on constructing the Virtual Solar Observatory. This
poster describes some of the components of the VSO and the first steps
that have been taken to implement these components. A description of
the overall VSO structure is given, along with descriptions of data
and meta-data models, methods by which these data model are used by
the VSO, details of how VSO nodes are interconnected *
and ideas on the likely format of the VSO API. As an example, the
inclusion of Yohkoh-SXT data at MSU and the future inclusion of the
Yohkoh-Galileo project data will be discussed. *
See also ``Data Integration Using SOAP in the VSO" by Tian et al.
Title: Localized Frequency Shifts from GONG+
Authors: Howe, R.; Komm, R. W.; Hill, F.; Bolding, John; Toner, Cliff;
Corbard, Thierry
Bibcode: 2003SPD....34.0802H
Altcode: 2003BAAS...35Q.822H
Ring Diagram analysis uses 3-dimensional power spectra from small
areas of the solar disk to measure the local frequency of high-degree
modes and follow local flows below the surface. The pipeline for
processing ring diagrams from the 1024x 1024 pixel data generated
by the GONG+ network has now been implemented and the first data
has been analyzed. We will present our latest initial results on the
local variations in the mode frequency and their correlation with the
local magnetic index over a month or more of observations. RK,
CT, and RH in part, are supported by NASA contract S-92698-F. NSO is
operated by AURA, Inc under a co-operative agreement with the National
Science Foundation.
Title: Data Integration Using SOAP in the VSO
Authors: Tian, K. Q.; Bogart, R. S.; Davey, A.; Dimitoglou, G.;
Gurman, J. B.; Hill, F.; Martens, P. C.; Wampler, S.
Bibcode: 2003SPD....34.0312T
Altcode: 2003BAAS...35..810T
The Virtual Solar Observatory (VSO) project has implemented a time
interval search for all four participating data archives. The back-end
query services are implemented as web services, and are accessible
via SOAP. SOAP (Simple Object Access Protocol) defines an RPC (Remote
Procedure Call) mechanism that employs HTTP as its transport and encodes
the client-server interactions (request and response messages) in XML
(eXtensible Markup Language) documents. In addition to its core
function of identifying relevant datasets in the local archive, the SOAP
server at each data provider acts as a "wrapper" that maps descriptions
in an abstract data model to those in the provider-specific data model,
and vice versa. It is in this way that VSO integrates heterogeneous
data services and allows access to them using a common interface. Our
experience with SOAP has been fruitful. It has proven to be a better
alternative to traditional web access methods, namely POST and GET,
because of its flexibility and interoperability.
Title: GONG Magnetogram Zero-Point Correction Status
Authors: Clark, R.; Harvey, J.; Hill, F.; Toner, C.
Bibcode: 2003SPD....34.0803C
Altcode: 2003BAAS...35..822C
Line-of-sight component magnetograms from GONG+ are produced every
minute at every site. The noise level is about 3 G per pixel but the
zero point is incorrect by as much as 10 G. This zero point error varies
across the solar image and with time. This error precludes using the
magnetograms for meaningful extrapolations of weak photospheric fields
into the corona. Experiments show the cause is slow, asymmetric,
locally varying switching of the LCD modulator from one retardation
state to the other, generating a false magnetic field pattern (zero
error). The mirrors directing sunlight into the instrument produce
slight ( 1 varying during the day which interacts with modulator
imperfections to make a complicated correction problem. Atmospheric
variations during the one-minute integration period can also cause
trouble. The zero point error should affect the daily calibration
in virtually the same way as a regular magnetogram taken at the same
time. The daily calibration is used to create a 'magnetic flat field'
to correct a nearly simultaneous regular magnetogram. The result should
be a nearly rror-free magnetogram that can then be used to determine
the zero point error during the rest of the day by subtracting suitably
rotated and masked versions of the data. This error is then fit with a
suitable function (e.g. Zernike polynomials) and the coefficients used
to synthesize a correction at any time. The coefficients are smoothed
and averaged over several days to reduce instrumental and atmospheric
noise, and real solar changes that might leak through the masks. Present performance, determined by comparison among different sites,
is good to about 1 G. A limitation appears to be seeing effects causing
rapidly changing, small fluctuations of the zero point error. This is
being investigated.
Title: Temporal Variation of Angular Momentum in the Solar Convection
Zone
Authors: Komm, R.; Howe, R.; Durney, B. R.; Hill, F.
Bibcode: 2003ApJ...586..650K
Altcode:
We derive the angular momentum as a function of radius and time with the
help of the rotation rates resulting from inversions of helioseismic
data obtained from the Global Oscillation Network Group (GONG) and
the Michelson Doppler Imager (MDI) and the density distribution from
a model of the Sun. The base of the convection zone can be identified
as a local maximum in the relative angular momentum after subtracting
the contribution of the solid-body rotation. The angular momentum as
a function of radius shows the strongest temporal variation near the
tachocline. This variation extends into the lower convection zone and
into the radiative interior and is related to the 1.3 yr periodicity
found in the equatorial rotation rate of the tachocline. In the upper
convection zone, we find a small systematic variation of the angular
momentum that is related to torsional oscillations. The angular momentum
integrated from the surface to a lower limit in the upper convection
zone provides a hint that the torsional oscillation pattern extends
deep into the convection zone. This is supported by other quantities
such as the coefficients of a fit of Legendre polynomials to the
rotation rates as a function of latitude. The temporal variation of the
coefficient of P4, indicative of torsional oscillations,
suggests that the signature of these flows in the inversion results
extend to about r~0.83Rsolar. With the lower limit of
integration placed in the middle or lower convection zone, the angular
momentum fluctuates about the mean without apparent trend, i.e., the
angular momentum is conserved within the measurement errors. However,
when integrated over the layers slightly below the convection zone
(0.60-0.71Rsolar), the angular momentum shows the 1.3 yr
period and hints at a long-term trend that might be related to the
solar activity cycle.
Title: On the p-mode Asymmetry between Velocity and Intensity from
the GONG+ Data
Authors: Tripathy, S. C.; Jain, Kiran; Hill, Frank; Toner, C. G.
Bibcode: 2003BASI...31..321T
Altcode: 2003astro.ph..6027T
We have analyzed the local acoustic spectra of small regions over the
solar surface at different locations from disk center to limb via the
technique of ring diagrams. The analysis suggest that the frequency
shifts between velocity and intensity is a function of location on
the disk and is higher near the disk center than those near the limb.
Title: Temporal variation of angular momentum in the convection zone
Authors: Komm, R.; Howe, R.; Durney, B. R.; Hill, F.
Bibcode: 2003ESASP.517...97K
Altcode: 2003soho...12...97K
We derive the angular momentum as a function of radius and time with the
help of the rotation rates resulting from inversions of helioseismic
data obtained from the Global Oscillation Network Group (GONG)
and the Michelson Doppler Imager (MDI) and the density distribution
from a model of the Sun. The angular momentum as a function of radius
shows the strongest temporal variation near the base of the convection
zone. This variation extends into the lower convection zone and into
the radiative interior and is related to the 1.3-yr periodicity found in
the equatorial rotation rate of the tachocline. In the upper convection
zone, we find a small systematic variation of the angular momentum that
is related to torsional oscillations. The angular momentum integrated
from the surface to a lower limit in the upper convection zone provides
a hint that the torsional oscillation pattern extends deep into the
convection zone. With the lower limit of integration placed in the
lower half of the convection zone, the angular momentum fluctuates
about the mean without apparent trend, i.e. the angular momentum is
conserved within the measurement errors. However, when integrated over
the layers slightly below the convection zone, the angular momentum
shows the 1.3-yr period and hints at a long-term trend which might be
related to the solar activity cycle.
Title: Environmental factors affecting solar seeing
Authors: Hill, Frank; Briggs, John W.; Hegwer, Steven L.; Radick,
Richard R.
Bibcode: 2003SPIE.4853..285H
Altcode:
We investigate a number of ideas about the effect of various
topographical and climtatological factors on daytime seeing. Using the
results of the CalTech site survey in southern California, we confirm
that the presence of lakes and wind channels are beneficial for solar
observing conditions. We do not find that proximity to the ocean is
of benefit but is instead detrimental to seeing in the CalTech sample
possibly due to the influence of the Los Angeles metropolitan area. We
also study the effect of tree removal on the seeing at Sacramento
Peak Observatory, and find that removing trees improved the average
seeing by 25%. The effects of these and other factors will be further
investigated with the ATST site survey.
Title: Activity related variation of width and energy of global
p-modes
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 2003ESASP.517..325K
Altcode: 2003soho...12..325K
We derived mode width, energy, and energy supply rate from 66 108-day
GONG time series currently processed with multitapers. We show the
temporal variation of these mode parameters from the previous minimum
to the maximum of the current solar cycle localized in latitude. Mode
width and energy of global modes clearly sense the local distribution
of surface magnetic activity. The relation between magnetic activity
and localized mode energy and width is linear within the measurement
uncertainties. The energy supply rate however does not show such
a relation with the latitudinal distribution of surface magnetic
activity. The results presented here are consistent with previously
published results, where we analyzed periodograms instead of
multitapered spectra.
Title: Correcting GONG+ magnetograms for instrumental non-uniformities
Authors: Clark, R.; Harvey, J.; Hill, F.; Toner, C.
Bibcode: 2003ESASP.517..251C
Altcode: 2003soho...12..251C
No abstract at ADS
Title: Design and development of the Advanced Technology Solar
Telescope (ATST)
Authors: Keil, Stephen L.; Rimmele, Thomas; Keller, Christoph U.;
Hill, Frank; Radick, Richard R.; Oschmann, Jacobus M.; Warner, Mark;
Dalrymple, Nathan E.; Briggs, John; Hegwer, Steven L.; Ren, Dauxing
Bibcode: 2003SPIE.4853..240K
Altcode:
High-resolution studies of the Sun's magnetic fields are needed for
a better understanding of solar magnetic fields and the fundamental
processes responsible for solar variability. The generation of magnetic
fields through dynamo processes, the amplification of fields through
the interaction with plasma flows, and the destruction of fields
are still poorly understood. There is still incomplete insight as
to what physical mechanisms are responsible for heating the corona,
what causes variations in the radiative output of the Sun, and what
mechanisms trigger flares and coronal mass ejections. Progress in
answering these critical questions requires study of the interaction
of the magnetic field and convection with a resolution sufficient to
observe scales fundamental to these processes. The 4m aperture Advanced
Technology Solar Telescope (ATST) will be a unique scientific tool,
with excellent angular resolution, a large wavelength range, and low
scattered light. With its integrated adaptive optics, the ATST will
achieve a spatial resolution nearly 10 times better than any existing
solar telescope. Building a large aperture telescope for viewing the
sun presents many challenges, some of the more difficult being: · Heat
control and rejection · Contamination and scattered light control ·
Control of telescope and instrument polarization · Site selection
This talk will present a short summary of the scientific questions
driving the ATST design, the design challenges faced by the ATST, and
the current status of the developing design and siting considerations
Title: Transient oscillations near the solar tachocline
Authors: Toomre, Juri; Christensen-Dalsgaard, Jorgen; Hill, Frank;
Howe, Rachel; Komm, Rudolf W.; Schou, Jesper; Thompson, Michael J.
Bibcode: 2003ESASP.517..409T
Altcode: 2003soho...12..409T
We report on further developments in the 1.3-yr quasi-periodic
oscillations reported by Howe et al. (2000). These are small (6 to 8
nHz peak-to-peak) oscillations in the inferred rotation rate near the
bottom of the convection zone and in the outer part of the radiative
interior. The oscillations are strongest and most coherent at about a
fractional radius of 0.72 in the equatorial region. Further monitoring
of the oscillations near the equator shows that they continued for a
period after the end of the data analyzed by Howe et al., but appear to
have now diminished in amplitude. This is reminiscent of the transient
behavior of similar (1.3 to 1.4 yr) periodicities in solar-wind and
geomagnetic datasets previously reported. We speculate that the near
tachocline oscillation is associated with the rising phase of the
solar cycle. We discuss tests performed to eliminate various possible
explanations of the oscillations due to systematic errors in the data
and in their analyses.
Title: The GONG++ data processing pipeline
Authors: Hill, Frank; Bolding, John; Toner, Clifford; Corbard, Thierry;
Wampler, Steve; Goodrich, Bret; Goodrich, Jean; Eliason, Patricia;
Hanna, Kerri Donaldson
Bibcode: 2003ESASP.517..295H
Altcode: 2003soho...12..295H
We describe the hardware and software for the new GONG++ data processing
system, and discuss our current experience in developing a pipeline
for local helioseismology.
Title: Ring-diagram analysis with GONG++
Authors: Corbard, T.; Toner, C.; Hill, F.; Hanna, K. D.; Haber, D. A.;
Hindman, B. W.; Bogart, R. S.
Bibcode: 2003ESASP.517..255C
Altcode: 2003soho...12..255C
Images from the updated GONG network (GONG+) have been produced since
July 2001. In order to treat individual site images and the merged
images (Toner et al., 2003) for local helioseismology studies, we have
developed an enhanced tracking/remapping code that is now part of the
new GONG pipeline (GONG ++) (Hill et al., 2003). We present here the
data-cube, 3D power spectra and sub-surface flow maps that will become
part of the new GONG++ products and comapare the preliminary results
with the ring diagram analysis of MDI images for the same days.
Title: Technical challenges of the Advanced Technology Solar Telescope
Authors: Rimmele, Thomas R.; Keil, Stephen L.; Keller, Christoph
U.; Hill, Frank; Briggs, John; Dalrymple, Nathan E.; Goodrich, Bret
D.; Hegwer, Steven L.; Hubbard, Rob; Oschmann, Jacobus M.; Radick,
Richard R.; Ren, Deqing; Wagner, Jeremy; Wampler, Stephen; Warner, Mark
Bibcode: 2003SPIE.4837...94R
Altcode:
The 4m Advance Technology Solar Telescope (ATST) will be the most
powerful solar telescope in the world, providing a unique scientific
tool to study the Sun and possibly other astronomical objects, such
as solar system planets. We briefly summarize the science drivers and
observational requirements of ATST. The main focus of this paper is on
the many technical challenges involved in designing a large aperture
solar telescope. The ATST project has entered the design and development
phase. Development of a 4-m solar telescope presents many technical
challenges. Most existing high-resolution solar telescopes are designed
as vacuum telescopes to avoid internal seeing caused by the solar heat
load. The large aperture drives the ATST to an open-air design, similar
to night-time telescope designs, and makes thermal control of optics
and telescope structure a paramount consideration. A heat stop must
reject most of the energy (13 kW) at prime focus without introducing
internal seeing. To achieve diffraction-limited observations at visible
and infrared wavelengths, ATST will have a high order (order 1000
DoF) adaptive optics system using solar granulation as the wavefront
sensing target. Coronal observations require occulting in prime focus,
a Lyot stop and contamination control of the primary. An initial set of
instruments will be designed as integral part of the telescope. First
telescope design and instrument concepts will be presented.
Title: Solar oscillation parameters: simultaneous velocity-intensity
spectral & cross-spectral fitting
Authors: Barban, Caroline; Hill, Frank
Bibcode: 2003ESASP.517..223B
Altcode: 2003soho...12..223B
We use the Severino et al. (2001) model for simultaneously fitting four
spectra: V (velocity) and I (intensity) power, I-V phase difference
and I-V coherence to observational data. We show that this model allows
us to reproduce well the observed spectra for l = 15, 20, 25, 30, 35,
40, 45, 50 at low and intermediate frequencies. At high frequencies,
the contamination of the spectrum by leaks may prevent fitting the
data with the model. A study of the fit parameters as a function of
frequency shows the well-known behavior of the mode amplitude and
width, but additional modes are needed for a physical interpretation
of all fit parameters. Comparing the oscillation parameters from the
multi-spectral fitting and from using only the V spectra shows that
the oscillation frequency differs by at most 0.1 μHz.
Title: Science Objectives and Technical Challenges of the Advanced
Technology Solar Telescope (Invited review)
Authors: Rimmele, T.; Keil, S. L.; Keller, C.; Hill, F.; Penn, M.;
Goodrich, B.; Hegwer, S.; Hubbard, R.; Oschmann, J.; Warner, M.;
Dalrymple, N.; Radick, R.; Atst Team
Bibcode: 2003ASPC..286....3R
Altcode: 2003ctmf.conf....3R
No abstract at ADS
Title: Local Helioseismology -- what does it Really Tell Us?
Authors: Hill, Frank
Bibcode: 2003IAUJD..12E..15H
Altcode:
The subfield of local helioseismology is now 15 years old. In its
brief history it has yielded maps of flows beneath the solar surface
images of active regions on the far side of the sun and inferences
about the sound speed below sunspots. However there has not yet been
a systematic study of the consistency among results obtained with the
three major local methods of time-distance acoustic holography and ring
diagrams. In addition realistic numerical simulations of data suitible
for testing the methods have proven difficult to construct. In this
talk I will give an overview of the methods comparing them from a
heuristic point of view. I will also discuss the types of tests that
would be desirable and present the latest results from a data-based
comparison exercise now underway.
Title: Localizing the Solar Cycle Frequency Shifts in Global p-Modes
Authors: Howe, R.; Komm, R. W.; Hill, F.
Bibcode: 2002ApJ...580.1172H
Altcode:
The 6.5 yr span of observations from the Global Oscillation
Network Group and the Michelson Doppler Imager aboard the Solar
and Heliospheric Observatory allows a detailed study of the solar
cycle-related frequency shifts at the level of central frequencies
and a-coefficients from individual multiplets and even of individual
modes within a multiplet. We analyze such data and show that the
shifts at all levels of averaging are consistent with the hypothesis
that the global p-mode frequency shifts are closely related to the
surface magnetic field distribution. Furthermore, the evolution of the
surface magnetic flux distribution can be reconstructed by an inversion
technique operating on the shifts within individual (n, l) multiplets.
Title: Strawman Concept for A Virtual Solar Observatory
Authors: Martens, P. C. H.; Gurman, J. B.; Hill, F.; Bogart, R. S.;
Davey, A.; Dimitoglou, G.; Tian, K.; Wampler, S.
Bibcode: 2002AAS...20114103M
Altcode: 2003BAAS...35..567M
We propose here an architecture and feature set for a prototype Virtual
Solar Observatory (VSO). The prototype will not include all the features
that might eventually become part of the VSO, nor even all the features
that are concurrently under development elsewhere that should become
parts of the VSO's functionality. It is possible to approach the design
of such a system in at least two different ways. In one (top-down),
all possible features and uses of a system are studied, and the best
solution for as many as possible is proposed. This is the approach
taken by the European Grid of Solar Observations (EGSO). Alternately,
one can approach a system design from the bottom up, and ask what the
essential element or elements of the design have to be in order to have
a functioning and useful system. The VSO study group decided, after
examining different approaches to abstracting the procedures for solar
data identification and access, to build the “smallest box” possible
around that problem, rather than attempting to draw a box around all
possible aspects of a VSO. This design will be presented in the poster.
Title: The Right Amount of Glue: Technologies and Standards Relevant
to a Future Solar-Terrestrial Data Environment
Authors: Gurman, J. B.; Dimitoglou, G.; Bogart, R. S.; Tian, K. Q.;
Hill, F.; Wampler, S.; Martens, P. C.; Davey, A.
Bibcode: 2002AGUFMSH52C..03G
Altcode:
In order to meet the challenge of developing a new system science, we
will need to employ technology that enables researchers to access data
from fields with which they are at least initially unfamiliar as well as
from sources they use more regularly. At the same time, the quantity of
data to be obtained by missions such as the Solar Dynamics Observatory
demands ease and simplicity of data access. These competing demands
must in turn fit within severely constrained funding for data analysis
in such projects. \p Based on experience in only a single discipline
but with a diversity of data types and sources, we will give examples
of technology that have made a significant difference in the way people
do science. Similarly, we will show how adoption of a well-dcoumented
data format has made it easier for one community to search, reduce,
and analyze data. We will also describe a community-supported data
reduction and analysis software tree with useful features.\p We will
attempt to generalize the lessons learned in these instances to features
the broader, solar-terrestrial community might find compelling, while
avoiding overdesign of a common data environment.\p
Title: EGSO in need for a global schema
Authors: Hill, Frank; Csillaghy, Andre; Bentley, Robert D.; Aboudarham,
Jean; Antonucci, Ester; Finkelstein, Anthony; Ciminiera, Luigi;
Gurman, Joseph B.; Scholl, Isabelle; Pike, Dave; Zharkova, Valentin
Bibcode: 2002SPIE.4846...35H
Altcode:
The European Grid of Solar Observations (EGSO) is a project to develop
a virtual observatory for the solar physics community. Like in all
such projects, a vital component is a schema that adequately describes
the data in the distributed data sets. Here, we discuss the schema in
general terms, and present a draft example of a portion of a possible
XML schema.
Title: Data analysis for the SOLIS Vector Spectromagnetograph
Authors: Jones, Harrison P.; Harvey, John W.; Henney, Carl J.; Hill,
Frank; Keller, Christoph U.
Bibcode: 2002ESASP.505...15J
Altcode: 2002solm.conf...15J; 2002IAUCo.188...15J
The National Solar Observatory's SOLIS Vector Spectromagnetograph, which
will produce three or more full-disk maps of the Sun's photospheric
vector magnetic field every day for at least one solar magnetic cycle,
is in the final stages of assembly. Initial observations, including
cross-calibration with the current NASA/NSO spectromagnetograph (SPM),
will soon be carried out at a test site in Tucson. This paper discusses
data analysis techniques for reducing the raw data, calculation of
line-of-sight magnetograms, and both quick-look and high-precision
inference of vector fields from Stokes spectral profiles. Existing
SPM algorithms, suitably modified to accommodate the cameras, scanning
pattern, and polarization calibration optics for the VSM, will be used
to "clean" the raw data and to process line-of-sight magnetograms. A
recent version of the High Altitude Observatory Milne-Eddington (HAO-ME)
inversion code will be used for high-precision vector fields.
Title: The Advanced Technology Solar Telescope
Authors: Keller, C. U.; Rimmele, T. R.; Hill, F.; Keil, S. L.;
Oschmann, J. M.; ATST Team
Bibcode: 2002AN....323..294K
Altcode:
The Advanced Technology Solar Telescope is the largest solar optical
facility currently under development. The National Solar Observatory
and its partners have just started the design and development phase
with first light being planned for late this decade. The 4-m telescope
will provide an angular resolution down to 0.025 arcsec, a large photon
flux for precise magnetic and velocity field measurements, and access
to a broad set of diagnostics from 0.3 to 28 mu m. We summarize the
currently envisioned scientific capabilities of the telescope and its
suite of instruments along with a glimpse at some of the early concepts.
Title: MDI and GONG inferences of the changing solar interior
Authors: Barban, C.; Howe, R.; Hill, F.; Komm, R. W.; Leibacher, J.;
Toner, C.; Bogart, R.; Braun, D.; Haber, D.; Hindman, B.; Lindsey, C.
Bibcode: 2002ESASP.508...55B
Altcode: 2002soho...11...55B
The Global Oscillation Network Group (GONG) and the Solar Oscillations
Investigation (SOI) using the Michelson Doppler Imager (MDI) instrument
aboard the SOHO spacecraft provide combined data sets that now cover
more than six years and allow us to probe the changing dynamics of the
convection zone in unprecedented detail. Here we present the latest
combined results from both projects, showing the evolution of the
migrating zonal flows close to the surface and also changes close to
and below the base of the convection zone, as well as changes in the
mode parameters related to surface magnetic activity variation in time
and latitude.
Title: Localizing Width and Energy of Solar Global p-Modes
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 2002ApJ...572..663K
Altcode:
We present the first attempt at localizing in latitude the temporal
variation of mode energy, energy supply rate, and lifetime of global
acoustic modes. We use Global Oscillation Network Group (GONG) and
Michelson Doppler Imager data analyzed with the GONG peak-fitting
algorithm to measure mode width and amplitude of individual (l, n, m)
modes. While measured amplitude and width values are inherently noisier
than frequency measurements, it is possible to use the (m/l) dependence
of these mode parameters to extract their variation in latitude. With
the currently analyzed data sets, we construct maps in time and latitude
of acoustic mode energy, lifetime (inverse of mode width), and energy
supply rate covering the rising phase of the current solar cycle from
the previous minimum to the current maximum. We find that the energy
and width of global modes vary in latitude as well as in time and
that the variation is clearly related to the distribution of magnetic
flux. After removing the average quantity, the residual mode width
shows a linear correlation with magnetic activity with a correlation
coefficient of 0.88, while the corresponding residual mode energy is
anticorrelated with magnetic activity with a correlation coefficient
of -0.90. These mode parameters derived from global p-modes respond to
the local distribution of surface magnetic activity. The energy supply
rate shows no correlation with the latitudinal distribution of magnetic
activity within the limits of the current measurements. We estimate the
variation of global mode energy in response to an individual magnetic
feature, such as a plage, and find that the global mode energy and the
mode lifetime are reduced by about 40% by an active region compared
to the quiet Sun.
Title: Using Velocity and Intensity helioseismic data for improving
our knowledge of the Solar interior.
Authors: Barban, C.; Hill, F.
Bibcode: 2002sf2a.conf..501B
Altcode:
Helioseismology, the study of the solar global oscillations, seeks
to infer the properties of the solar interior from the oscillation
mode parameters, primarily the frequency. The parameters are typically
determined by using the observed Doppler velocity (V) data, neglecting
the information contained in the total intensity (I) data. This
information content is demonstrated by qualitative differences
(frequency shifts, reverse mode line asymmetry) which are likely to
arise from the excitation mechanism. We present here our current work
about the use of both I and V data for improving the mode parameter
estimation and then our knowledge of the solar interior and also for
providing new measures of the excitation.
Title: Acoustic Power Mapping for Active Regions from MDI, HLH,
and TON Data
Authors: Ladenkov, O. V.; Hill, F.; Egamberdiev, Sh. A.; Chou, D. Y.
Bibcode: 2002AstL...28..411L
Altcode:
No abstract at ADS
Title: Solar Subsurface Weather and Possible Giant Cell Signatures
Authors: Haber, D. A.; Hindman, B. W.; Toomre, J.; Bogart, R. S.;
Hill, F.
Bibcode: 2002AAS...200.0414H
Altcode: 2002BAAS...34Q.645H
Helioseismic observations taken with SOI-MDI aboard SOHO have led to
a new era of discovery about complex and evolving dynamics within the
upper solar convection zone. The data now span nearly six years. Using
the technique of ring-diagram analysis applied to MDI Dynamics Program
Doppler data over a large number of regions on the solar disk, we have
generated synoptic maps of horizontal flows at a variety of depths
below the photosphere. These maps have been assembled for all of the
years for which the SOI-MDI Dynamics Program data are available, with
the latest data coming from March 2002. Flows associated with Solar
Subsurface Weather (SSW) are observed to vary from month to month and
year to year, with the largest flows occurring in and around regions
of intense magnetic activity. Longitudinal averages of the flows reveal
that the fast banded zonal flows seen in previous years have now merged
at the equator while the multiple cell structure found in the meridional
circulation within the northern hemisphere over the last four years is
still present at a reduced level in 2002. When the average flows are
removed, it is possible to see areas of cyclonic flow in regions of
quiet sun as well as divergent cells on the order of 30 to 40 degrees
in diameter that might be signatures of giant convection cells. This
research was supported by NAG5-7996.
Title: New Results from GONG `classic' data
Authors: Kras, S.; Howe, R.; Komm, R.; Hill, F.
Bibcode: 2002AAS...200.0408K
Altcode: 2002BAAS...34R.644K
We reprocessed all 59 108-day time series obtained during the operation
of GONG in `classic' mode (mid-1995--mid-2001) using multitapers. The
multitaper method helps to improve the fitting of mode parameters by
producing smoothed power spectra. The main benefit is an increase
in the number of modes that are fitted well, which leads to an
increase of the order of 10%\ in the number of multiplets for each
time sample. We will compare multitapered with previous untapered
results to show the improvement gained, for example, in the rotation
rates of the solar interior by this reprocessing step. In addition,
we analyzed 1-year and 3-year GONG classic time series in order to
improve the number of well-fitted modes at low frequencies (below 1.5
mHz). Preliminary results show an improvement in the number of modes at
low frequencies is gained by increasing the length of the time series
from 108 days to three years. We will present our latest results. The
Global Oscillation Network Group (GONG) project is managed by the
National Solar Observatory, which is operated by AURA, Inc. under a
cooperative agreement with the National Science Foundation.
Title: Temporal Variation of Angular Momentum in the Solar Convection
Zone
Authors: Komm, R.; Howe, R.; Durney, B.; Hill, F.
Bibcode: 2002AAS...200.0404K
Altcode: 2002BAAS...34Q.644K
We present the temporal variation of the solar angular momentum
derived from helioseismic observations. In the absence of `true'
angular momentum inversions, we use the rotation rates resulting from
rotation inversions of GONG data and the density distribution from a
model of the Sun. We focus especially on the layers near the base of
the convection zone and the layers near the solar surface. We derive
the angular momentum as a function of depth and the corresponding
solid-body rotation. The angular momentum decreases with increasing
radius following essentially the product of density times the fourth
power of radius. The tachocline can be identified as a local maximum
in the radial gradient of the angular momentum and as a local maximum
in the relative angular momentum after subtracting the contribution
of the solid-body rotation. The angular momentum shows the strongest
temporal variation near the tachocline. This variation is reminiscent
of the 1.3-yr periodicity found in the equatorial rotation rate of the
tachocline, which is not too surprising since the angular momentum of
a spherical shell is heavily weighted toward the equator. We discuss
the extension of this variation into the convection zone and into
the radiative interior. In addition, we fit the rotation rates as
functions of latitude with Legendre polynomials to cross-validate
the numerical results and to draw conclusions about the zonal flows
(`torsional oscillations') in the upper convection zone. This work
was supported by NASA Grant S-92698-F.
Title: Correcting GONG+ magnetograms for instrumental nonuniformities
Authors: Clark, R.; Hill, F.; Toner, C.
Bibcode: 2002AAS...200.0402C
Altcode: 2002BAAS...34..643C
GONG+ is now taking magnetograms every minute. It also takes daily
calibration observations that include east and west limb measurements
recorded in a non imaging mode, but with the magnetogram modulator
still active. There are large-scale spatial artifacts due to modulator
inhomogenieties, and we need to remove them. East and west limb
calibration observations are subjected to the normal calibration
procedures using known 60 day averaged calibration data. These
observations are taken with calibration lenses inserted in the
optical path to switch conjugal planes in the optical system, so
that the magnetogram modulator and optical elements at other pupil
planes in the instrument are imaged onto the CCD. Spatial features
in the resulting pupil plane magnetogram images are dominated by
instrumental nonuniformities. Averaging these over a long period allows
the determination of a modulator non uniformity correction which can
be aplied to normal GONG observations to give a zero point corrected
magnetogram.
Title: Building a Virtual Solar Observatory: I Look Around and
There's a Petabyte Following Me
Authors: Gurman, J. B.; Bogart, R.; Hill, F.; Martens, P.
Bibcode: 2002AAS...200.5805G
Altcode: 2002BAAS...34..740G
The 2001 July NASA Senior Review of Sun-Earth Connections missions
and data centers directed the Solar Data Analysis Center (SDAC) to
proceed in studying and implementing a Virtual Solar Observatory (VSO)
to ease the identification of and access to distributed archives of
solar data. Any such design (cf. the National Virtual Observatory
and NASA's Planetary Data System) consists of three elements: the
distributed archives, a "broker" facility that translates metadata
from all partner archives into a single standard for searches,
and a user interface to allow searching, browsing, and download of
data. Three groups are now engaged in a six-month study that will
produce a candidate design and implementation roadmap for the VSO. We
hope to proceed with the construction of a prototype VSO in US fiscal
year 2003, with fuller deployment dependent on community reaction to
and use of the capability. We therefore invite as broad as possible
public comment and involvement, and invite interested parties to a
`birds of a feather' session at this meeting. VSO is partnered with
the European Grid of Solar Observations (EGSO), and if successful, we
hope to be able to offer the VSO as the basis for the solar component
of a Living With a Star data system.
Title: The Advanced Technology Solar Telescope (ATST) Site Survey
Authors: Hill, F.; Briggs, J.; Radick, R.; Hegwer, S.
Bibcode: 2002AAS...200.5601H
Altcode: 2002BAAS...34R.734H
The performance of the ATST will be strongly influenced by the
atmospheric conditions of the site. In order to select the site,
we are testing six candidate locations: Big Bear Solar Observatory,
California; Observatorio del Roque de los Muchachos, La Palma,
Canary Islands, Spain; Mees Solar Observatory, Haleakala, Hawaii;
NSO/Sacramento Peak Observatory, New Mexico; Observatorio Astronomico
Nacional, San Pedro Martir, Baja California, Mexico; and Panguitch Lake,
Utah. The statistics of seeing, scattering, and cloud cover are being
measured with a suite of instruments including a solar differential
image motion monitor (S-DIMM), an array of six scintillometers, a
small externally occulted coronagraph, a water vapor meter, a dust
monitor, and a weather station. At the time of the meeting, we expect
to have four operational sites, and we will present a first look at
the relationship bewteen solar observing conditions and site geography,
topology, and meteorology. The National Solar Observatory is operated
by the Association of Universities for Research in Astronomy, under
a cooperative agreement with the National Science Foundation, for the
benefit of the astronomical community.
Title: Evolving Submerged Meridional Circulation Cells within the
Upper Convection Zone Revealed by Ring-Diagram Analysis
Authors: Haber, Deborah A.; Hindman, Bradley W.; Toomre, Juri; Bogart,
Richard S.; Larsen, Rasmus M.; Hill, Frank
Bibcode: 2002ApJ...570..855H
Altcode:
Using the local helioseismic technique of ring-diagram analysis
applied to Michelson Doppler Imager (MDI) Dynamics Program data from
the Solar and Heliospheric Observatory, we have discovered that the
meridional flow within the upper convection zone can develop additional
circulation cells whose boundaries wander in latitude and depth as
the solar cycle progresses. We report on the large-scale meridional
and zonal flows that we observe from 1996 to 2001. In particular, we
discuss the appearance and evolution of a submerged meridional cell
during the years 1998-2001, which arose in the northern hemisphere
and disrupted the orderly poleward flow and symmetry about the equator
that is typically observed. The meridional flows in the southern and
northern hemispheres exhibit striking asymmetry during the past four
years of the advancing solar cycle. Such asymmetry and additional
circulation cells should have profound impact on the transport of
angular momentum and magnetic field within the surface layers. These
flows may have a significant role in the establishment and maintenance
of the near-surface rotational shear layer.
Title: Enhanced facilities for local helioseismology with GONG+ images
Authors: Corbard, T.; Toner, C.; Hill, F.
Bibcode: 2002AAS...200.0407C
Altcode: 2002BAAS...34..644C
Images with the updated GONG network (GONG+) have been produced since
July 2001. In order to treat the individual site images and the merged
images for local helioseismology studies(ring diagram, time-distance,
back side imaging), we have developed an enhanced tracking/remapping
code that will be part of the new GONG+ pipeline accessible to all
GONG users. We present the features of this code and some comparisons
with ring diagram analysis made previously with GONG and MDI data.
Title: Simultaneous Velocity-Intensity Spectral and Cross-Spectral
Fitting for Helioseismology
Authors: Barban, C.; Hill, F.
Bibcode: 2002AAS...200.0410B
Altcode: 2002BAAS...34..644B
Helioseismology seeks to infer the properties of the solar interior
from the oscillation mode parameters, primarily the frequency. Thus,
increasing the precision and accuracy of the mode parameter estimates
correspondingly improves our knowledge of the solar interior. The
parameters are typically determined by fitting a theoretical profile
to the observed Doppler velocity (V) power spectrum, neglecting the
information contained in the spectrum of total intensity (I). This
information content is demonstrated by the qualitative differences, such
as substantial frequency shifts and the sense of the line asymmetry,
that are unmistakable in simultaneous V and I spectra. Clearly the
physics of the oscillation determining the mode parameters cannot
depend on the observed quantity, thus the differences are likely to
arise from the excitation mechanism. Further, these differences can
be used to derive a more complete and accurate model of the solar
oscillations improving the mode parameter estimation and providing
new measures of the excitation. Following Severino et al. (2001,ApJ
561,444), we present preliminary results from simultaneously fitting 4
spectra (V and I power, I-V phase difference and I-V coherence spectra)
to constrain the theoretical mode profile. This work is supported by
NASA grant NAG5-11703.
Title: Calculating the GONG and GONG+ leakage matrices -- latest
improvements
Authors: Howe, R.; Hill, F.
Bibcode: 2002AAS...200.0409H
Altcode: 2002BAAS...34..644H
In helioseismology, time series for each spherical harmonic are
calculated by convolving the imaged data with spherical harmonic
masks. Because we image only a part of the solar surface, each
time series is contaminated by power from neighbouring spherical
harmonics. This contamination can be quantified by calculating the
so-called `leakage matrix'. Many data analysis techniques depend on
a good estimate of this matrix. Motivated by the new GONG+ data, we
have improved the calculation of the leakage matrices for both GONG+
and GONG Classic images. Specifically, we have improved the grids used
for calculating the apodization; incorporated an empirical projection
function; and allowed for the different pixel aspect ratios and image
apodization functions of GONG+ and GONG Classic data. The effect of
these improvements will be shown through several comparisons between
the calculated matrices and the observed power spectra. NSO is operated
by AURA, Inc. under a co-operative agreement with NSF.
Title: The Advanced Technology Solar Telescope
Authors: Rimmele, T. R.; Keil, S. L.; Keller, C. U.; Hill, F.;
Oschmann, J. M.; Warner, M.; Dalrymple, N. E.; ATST Team
Bibcode: 2002AAS...200.3408R
Altcode: 2002BAAS...34..691R
The 4m aperture Advance Technology Solar Telescope (ATST) will be the
most powerful solar telescope in the world and a unique scientific tool
to study the Sun and other astronomical objects, such as planets. The
ATST will replace major existing national solar facilities at the end
of this decade. The ATST project has entered the design and development
phase. We present an overview of the ATST science drivers and discuss
preliminary design concepts and technical challenges. The ATST science
goals lead to the following general requirements for the ATST facility:
- Diffraction limited angular resolution in the visible and infrared
to study fundamental astrophysical processes with unprecedented
resolution enabling verification of model predictions. - A high photon
flux for accurate measurements of physical parameters throughout
the solar atmosphere, such as magnetic strength and direction,
temperature and velocity. - Access to a new diagnostics at relatively
unexplored infrared wavelength. - Low scattered light to enable
coronal observations. - Low instrumental polarization for accurate
measurements of magnetic fields. Development of a 4m solar telescope
presents many technical challenges. The large aperture drives the ATST
to an open-air design and makes thermal control of optics and telescope
structure a paramount consideration. To achieve diffraction-limited
observations at visible and infrared wavelength ATST will have a high
order solar adaptive optics system. Coronal observations require,
occulting in prime focus, a Lyot stop and contamination control of the
primary. An initial set of instruments will be designed as integral
part of the telescope. Preliminary telescope and instrument concepts
will be discussed.
Title: A Comparison of Solar p-Mode Parameters from the Michelson
Doppler Imager and the Global Oscillation Network Group: Splitting
Coefficients and Rotation Inversions
Authors: Schou, J.; Howe, R.; Basu, S.; Christensen-Dalsgaard, J.;
Corbard, T.; Hill, F.; Komm, R.; Larsen, R. M.; Rabello-Soares, M. C.;
Thompson, M. J.
Bibcode: 2002ApJ...567.1234S
Altcode:
Using contemporaneous helioseismic data from the Global Oscillation
Network Group (GONG) and Michelson Doppler Imager (MDI) onboard SOHO,
we compare frequency-splitting data and resulting inversions about the
Sun's internal rotation. Helioseismology has been very successful in
making detailed and subtle inferences about the solar interior. But
there are some significant differences between inversion results
obtained from the MDI and GONG projects. It is important for making
robust inferences about the solar interior that these differences are
located and their causes eliminated. By applying the different analysis
pipelines developed by the projects not only to their own data but
also to the data from the other project, we conclude that the most
significant differences arise not from the observations themselves
but from the different frequency estimation analyses used by the
projects. We find that the GONG pipeline results in substantially fewer
fitted modes in certain regions. The most serious systematic differences
in the results, with regard to rotation, appear to be an anomaly in
the MDI odd-order splitting coefficients around a frequency of 3.5 mHz
and an underestimation of the low-degree rotational splittings in the
GONG algorithm.
Title: Solar-cycle variation of the sound-speed asphericity from
GONG and MDI data 1995-2000
Authors: Antia, H. M.; Basu, S.; Hill, F.; Howe, R.; Komm, R. W.;
Schou, J.
Bibcode: 2001MNRAS.327.1029A
Altcode: 2001astro.ph..9326A
We study the variation of the frequency splitting coefficients
describing the solar asphericity in both GONG and MDI data, and
use these data to investigate temporal sound-speed variations as a
function of both depth and latitude during the period 1995-2000 and a
little beyond. The temporal variations in even splitting coefficients
are found to be correlated to the corresponding component of magnetic
flux at the solar surface. We confirm that the sound-speed variations
associated with the surface magnetic field are superficial. Temporally
averaged results show a significant excess in sound speed around
r=0.92Rsolar and latitude of 60°.
Title: Empirical Mode Decomposition and Hilbert Analysis Applied to
Rotation Residuals of the Solar Convection Zone
Authors: Komm, R. W.; Hill, F.; Howe, R.
Bibcode: 2001ApJ...558..428K
Altcode:
We apply empirical mode decomposition (EMD) and Hilbert analysis
to time series of rotation residuals at all latitudes and at all
depths in the convection zone derived from 49 Global Oscillation
Network Group data sets covering the period 1995 May 7 to 2000
May 15. Hilbert analysis combined with EMD is a tool to analyze
nonlinear and nonstationary signals and is used to localize events
in time-frequency space. We calculate Hilbert power spectra, power
as a function of time and frequency, for each time series in order to
determine whether the rotation rate in the convection zone shows any
other systematic temporal variation besides the so-called torsional
oscillation pattern in the upper convection zone and the periodicity
of 1.3 yr near the base of the convection zone. In other regions of the
convection zone, the temporal variations of the rotation residuals are
compatible with a noise signal except near about 0.86 Rsolar
in radius, where we find indications of a long-term period of about 6
yr. However, it is uncertain whether this signal is of solar origin,
since the available data set is too short to rule out the possibility
of an artifact. In addition, we calculate the amount of power contained
in the torsional oscillation signal as a function of time, latitude, and
radius to study the variation of the torsional oscillation pattern. The
depth to which the pattern extends apparently changes with time. For
example, at midlatitudes the pattern extends to deeper layers with
increasing time. The degree of stationarity doubles from the surface
to about 0.92 Rsolar in radius, which indicates that the
torsional oscillation pattern disappears with increasing depth in
agreement with previous results.
Title: A Comparison of GONG Intensity and Velocity Helioseismic Data
Authors: Barban, Caroline; Hill, F.
Bibcode: 2001sf2a.conf..197B
Altcode:
Helioseismology seeks to infer the properties of the solar interior
from global oscillation modes parameters (frequency,power,line
width). Qualitive difference have been observed in spectra obtained
simultane- ously in Doppler velocity (V) and total intensity
(I). These differen- ces are probably related to the damping and
excitation processes of the oscillation modes which are not completely
understood. A comparison of V and I data is explored both in GONG and
MDI data. The first goal is to obtain the central frequency of the real
solar oscillation modes simultaneously from I and V data. An additional
objective is to test models of the damping and excitation processes.
Title: Asymmetric Line Profiles Applied to Gong Helioseismic Data
Authors: Landy, D.; Howe, R.; Komm, R.; Hill, F.
Bibcode: 2001AGUSM..SP21C04L
Altcode:
P-mode frequencies have traditionally been fit using a symmetric
Lorentzian profile. Due to clear asymmetries in the peaks, researchers
have begun moving toward asymmetric near-Lorentzian profiles; amongst
the most popular is the Nigam profile. In this paper, results are
presented from a fit of the Nigam profile to two datasets, both
taken from GONG data, using a new peak fitting engine (PEAKFIND
Mark II). Details of PEAKFIND Mark II are presented. Results of the
Nigam model fits are compared with those achieved using a symmetric
Lorentzian line profile (those reported by the GONG network). Results
are also shown to be largely consistent with other published fits in
the low frequency region.
Title: Hilbert Spectral Analysis Applied to Helioseismic Time Series
Authors: Komm, R.; Hill, F.; Howe, R.
Bibcode: 2001AGUSM..SP31A07K
Altcode:
We apply Empirical Mode Decomposition and Hilbert spectral analysis
to helioseismic time series to study excitation and damping of solar
p-modes. We use time series from the Solar Oscillations Investigation
(SOI) project using the Michelson Doppler Imager (MDI) aboard the Solar
and Heliospheric Observatory (SOHO) spacecraft. The Hilbert spectral
analysis is a tool to analyze nonlinear and nonstationary signals and
is used to localize events in time-frequency space. The solar acoustic
oscillations are thought to be stochastically excited by the release of
acoustic energy from sources near the top of the turbulent convection
zone of the Sun. Individual modes are present during some time periods
and absent during others. We analyze time series of different l and m
values in order to detect individual excitation or damping events. In
addition, we compare data sets obtained during different levels of
solar magnetic activity to study the influence of magnetic activity on
solar p-modes. We will present the latest results of this investigation.
Title: Comparing Global Solar Rotation Results from MDI and GONG
Authors: Howe, R.; Komm, R. W.; Hill, F.; Christensen-Dalsgaard, J.;
Schou, J.; Thompson, M. J.; Corbard, T.
Bibcode: 2001AGUSM..SP31A14H
Altcode:
The GONG (Global Oscillations Network Group) project and the Solar
Oscillations Investigation (SOI) using the Michelson Doppler Imager
(MDI) instrument aboard the SOHO spacecraft have jointly accumulated
more than five years of data on medium-degree solar p-modes, including
nearly four years of contemporaneous observations. The inferences of
interior solar rotation from the two projects are broadly consistent
and show similar temporal variations, but there are also significant
systematic differences. We report here on the results of an ongoing
attempt to cross-compare the results and analysis techniques of the
two projects. Three 108-day periods, at low, medium and high solar
activity epochs, have been analysed, with both MDI and GONG analysis
being applied to each data set, and the results are compared.
Title: The Virtual Solar Observatory - Status and Plans
Authors: Hill, F.
Bibcode: 2001AGUSM..SP21B02H
Altcode:
The Virtual Solar Observatory (VSO) is a software environment for
searching, obtaining and analyzing data from archives of solar data that
are distributed at many different observatories around the world. This
"observatory" is virtual since it exists only on the Internet, not as
a physical structure. As a research tool, the VSO would enable a new
field of correlative statistical solar physics in which large-scale
comparative studies spanning many dimensions and data sources could
be carried out. Several groups with solar archives have indicated
their willingness to particpate as a VSO component. These include NSO
(KPVT GONG, and SOLIS); NASA/GSFC SDAC; SOHO; Stanford (SOI/MDI, TON,
WSO); Lockheed (TRACE); MSU (Yohkoh); UCLA (Mt. Wilson 150-ft Tower);
USC (Mt. Wilson 60-ft Tower); BBSO/NJIT; Arcetri (ARTHEMIS); Meudon;
HAO; and CSUN/SFO. The VSO will be implemented so that additional
systems can be easily incorporated. The VSO technical concept includes
the federation of distributed solar archives, an adaptive metadata
thesaurus, a single unified intuitive GUI, context-based searches,
and distributed computing. The underlying structure would most
likely be constructed using platform-independent tools such as XML
and JavaScript. There are several technical challenges facing the
VSO development. Issues of security, bandwidth, metadata, and load
balancing must be faced. While the VSO is currently in the concept
phase, a number of funding opportunities are bing pursued. The status of
these proposals and plans for the future will be updated at the meeting.
Title: Solar Seeing Seven Ways From Sunday
Authors: Hill, F.; Balasubramaniam, K. S.; Beckers, J. M.; Briggs,
J. W.; Hegwer, S.; Radick, R. R.; Rimmele, T. R.; Richards, K.;
Denker, C.
Bibcode: 2001AGUSM..SP21B03H
Altcode:
The Advanced Technology Solar Telescope (ATST) site survey will be
carried out with a Solar Differential Image Motion Monitor (S-DIMM)
and a six-scintillometer SHAdow BAnd Ranging (SHABAR) array. This
device will provide estimates of the Fried parameter, R0,
derived from the differential motion measurements of two images of the
same cut across the solar limb formed by two 45 mm diameter telescope
apertures 225 mm apart, and an estimate of the height dependence of the
index of refraction structure parameter, Cn2, from
the co-variance of the signals from an array of 6 scintillometers with
15 baseline separations. It will also provide a cloud cover measurement
and RMS scintillation signal. In preparation for the survey, we compare
estimates of daytime solar seeing obtained simultaneously from seven
different instruments. The observations were made at NSO/Sacramento
Peak during the period January 26 - February 5, 2001 under a variety of
seeing and transparency conditions ranging from poor to excellent. The
seven instruments were: 1. a S-DIMM/SHABAR mounted at the top of
the Dunn Solar Tower (DST) 2. an identical S-DIMM/SHABAR mounted at
ground level 3. the NSO/SP Adaptive Optics wavefront sensor providing
subaperature image motion measurements 4. a Dalsa camera providing
bursts of high-speed images for spectral ratio seeing estimates 5. a
Xedar camera obtaining granulation images for contrast and differential
stretching measurements 6. a Seykora scintillometer mounted in the
DST 7. a video camera recording a movie of the visual quality of the
image The analysis of this data set will provide the first direct
comparison of this many simultaneous solar seeing measurements, test
the ATST site survey system, and verify the SHABAR measurement of the
seeing height profile.
Title: Evolving Large-Scale Flows With Advancing Solar Cycle Using
Helioseismic Dense-Pack Ring-Diagram Analyses
Authors: Haber, D. A.; Hindman, B. W.; Toomre, J.; Bogart, R. S.;
Hill, F.
Bibcode: 2001AGUSM..SP22A02H
Altcode:
We have recently completed the first local helioseismic ring-diagram
analysis of the entire SOI-MDI Dynamics Program data. These data sets
include up to three months of continuous Doppler velocity data from
each of the years 1996 through 2000. A single ring-diagram analysis
over a 15o region of the sun, followed by an inversion
of the frequency shifts thus obtained, yields measurements of the
horizontal velocity field as a function of depth within the upper 14 Mm
of the convection zone beneath that region. By performing the analysis
over a Dense-Pack mosaic of 189 overlapping tiles and repeating the
procedure for each day of data, we have mapped the velocity field as
a function of time over a substantial fraction of the solar disk for
a number of full Carrington rotations. Our studies of the dynamics
of the upper convection zone have revealed the presence of striking
north-south asymmetries in both the zonal and meridional flows as a
function of depth. For example, a small second meridional flow cell
appeared at depths below 10 Mm at latitudes north of 45oN
in 1998, expanded upwards to 3 Mm in depth at all latitudes above
22oN in 1999, and then receded again in 2000. Synoptic maps,
formed from nearly 4500 ring-diagram analyses per Carrington rotation,
show that active regions are sites of convergent flow and appear at
the boundaries of the northern meridional cells in 1999. Even finer
sampling grids show that there are steep gradients in the flows within
active regions. Our work has also revealed a relationship between the
fast zonal "torsional oscillation" bands that migrate towards the
equator and the meridional flow as the solar cycle progresses. The
dominantly poleward meridional flow reaches maxima in both hemispheres
at the latitudes at which the zonal fast belts occur. As the zonal fast
belts drift towards the equator, the latitudes of maximal meridional
flow also drift equatorward.
Title: A Comparison of Global Intensity and Velocity Helioseismic
Data From SOI/MDI and GONG
Authors: BARBAN, C.; Hill, F.
Bibcode: 2001AGUSM..SP31A12B
Altcode:
Helioseismology seeks to infer the properties of the solar interior
from global oscillation mode parameters (frequency, power, line
width). Qualitative differences, such as substantial frequency shifts,
have been observed in data obtained simultaneously in Doppler velocity
(V) and total intensity (I). Clearly, the physics of the oscillation
determining the mode parameters cannot depend on the quantity we
observe from the Earth. These differences are thus probably related
to the damping and excitation processes of the oscillation modes,
which are not completely understood. A comparison of intensity and
velocity data is explored both in GONG and MDI data. We first derive
the relative phase and coherence between V and I, with the ultimate
goals of obtaining the central frequency of the real solar oscillation
modes simultaneously from V and I data, and testing models of the
damping and excitation processes.
Title: Solar Cycle Changes in p-Mode Frequencies and Asphericity
1995-2000
Authors: Howe, R.; Hill, F.; Komm, R. W.
Bibcode: 2001AGUSM..SP21C03H
Altcode:
With 5 years of analysed data from the GONG (Global Oscillation Network
Group) project and the Solar Oscillations Investigation (SOI) using
the Michelson Doppler Imager (MDI) aboard the SOHO spacecraft, we can
investigate the solar-cycle changes in the medium-degree solar p-mode
frequencies in much more detail than has previously been possible. The
quality of the data allows us to study the variations in the central
frequencies of individual (l,n) multiplets, and also to demonstrate
that the latitudinal variation of the frequency changes within a
multiplet correlates closely with the latitudinal distribution of
surface magnetic activity. We report here on the latest results of
such an investigation, and the implications for our understanding of
the relationship between p-mode frequencies and solar activity.
Title: Variations in Rotation Rate Within the Solar Convection Zone
From GONG and MDI 1995-2000
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
Schou, J.; Thompson, M. J.; Toomre, J.
Bibcode: 2001AGUSM..SP31A15H
Altcode:
Helioseismic measurements with the Michelson Doppler Imager (MDI)
instrument aboard SOHO, and complementary measurements from the Global
Oscillation Network Group (GONG) project, are revealing changes deep
within the Sun as the solar cycle progresses. We will present the
latest results based on recent data from both experiments, including
flows in the upper part of the convection zone and variations in the
rotation rate near its base.
Title: Comparison of GONG+ Velocity and Intensity Local Acoustic
Spectra via Ring Diagrams
Authors: Jain, K.; Toner, C. G.; Hill, F.
Bibcode: 2001AGUSM..SP31A13J
Altcode:
The local acoustic spectra of small regions over the solar surface
have been studied by using the ring diagram technique. The data
used here consist of velocity and intensity images obtained by GONG+
instrument at Tucson for the period from 2000 June 10-15. By studying
the local regions on the solar surface, we construct a three-dimensional
power spectrum (ω , kx, ky) of high degree
solar acoustic modes. A suitable normalization is applied to both
the spectra in order to investigate any observable difference in the
size and power of the rings. This will be compared to the differences
observed in global acoustic spectra obtained in velocity and intensity
to provide information about the driving and damping of local acoustic
oscillations.
Title: Hilbert Spectral Analysis Applied to Rotation Residuals of
the Solar Convection Zone
Authors: Komm, R.; Hill, F.; Howe, R.
Bibcode: 2001AGUSM..SP31A06K
Altcode:
We apply Empirical Mode Decomposition and Hilbert spectral analysis to
time series of rotation residuals at all latitudes and at all depths
in the solar convection zone derived from 49 data sets obtained by
the Global Oscillation Network Group (GONG) project covering the
period 1995 May 7 to 2000 May 15. The Hilbert spectral analysis is
a tool to analyze nonlinear and nonstationary signals and is used
to localize events in time-frequency space. We calculate Hilbert
power spectra, power as a function of time and frequency, for each
time series in order to determine whether the rotation rate in the
solar convection zone shows any other systematic temporal variation
besides the torsional oscillation pattern in the upper convection zone
and the 1.3-yr periodicity near the base of the convection zone. In
addition, we calculate the amount of power contained in the torsional
oscillation signal as a function of time, latitude, and radius to study
the variation of the torsional oscillation pattern. For example, the
degree of stationarity of the torsional oscillation doubles between
surface layers and a depth of about 8%\ of the solar radius. This
indicates that the torsional oscillation pattern disappears with
increasing depth in agreement with previous studies. We will present
the latest results of this investigation.
Title: The Advanced Technology Solar Telescope -- Science Goals and
Instrument Description.
Authors: Rimmele, T. R.; Keil, S. L.; Keller, C. U.; Hill, F.
Bibcode: 2001AGUSM..SH31D08R
Altcode:
High-resolution studies of the Sun's magnetic fields are needed for
a better understanding of solar magnetic fields and the fundamental
processes responsible for solar variability. The generation of magnetic
fields through dynamo processes, the amplification of fields through
the interaction with plasma flows, and the destruction of fields are
still poorly understood. There is still incomplete insight as to what
physical mechanisms are responsible for heating the corona, what causes
variations in the radiative output of the Sun, and what mechanisms
trigger flares and coronal mass ejections. Progress in answering
these critical questions requires study of the interaction of the
magnetic field and convection with a resolution sufficient to observe
physical scales fundamental to these processes. The 4m aperture ATST
will be a unique scientific tool, with excellent angular resolution,
a large wavelength range, and low scattered light. With its integrated
adaptive optics, the ATST will achieve a spatial resolution nearly 10
times better than any existing solar telescope. The ATST will provide:
Unprecedented angular resolution of 0.03 arcsec in the visible and
0.08 arcsec at 1.6 microns to enable us to clearly resolve and study the
fundamental astrophysical processes on their intrinsic scales and to
verify model predictions. A high photon flux for accurate and precise
measurements of physical parameters, such as magnetic field strength
and direction, temperature and velocity, on the short time scales
involved. Access to a broad set of diagnostics, from visible to thermal
infrared wavelengths. Low scattered light observations and coronagraphic
capabilities in the infrared, allowing measurements of coronal magnetic
fields. The ATST has been highly ranked by the latest Decadal Survey
of Astronomy and Astrophysics and the NAS/NRC study of ground-based
solar astronomy. A large part of the solar community will participate
in the design and development of the ATST. A strawman telescope design,
design challenges and instrument concepts will be discussed. Examples
of recent high resolution observations with adaptive optics, that
demonstrate the potential of this new technology will be shown.
Title: The Virtual Solar Observatory
Authors: Hill, F.
Bibcode: 2001ASPC..225..184H
Altcode: 2001vof..conf..184H
No abstract at ADS
Title: Studying asphericity in the solar sound speed from MDI and
GONG data
Authors: Antia, H. M.; Basu, S.; Hill, F.; Howe, R.; Komm, R. W.;
Schou, J.
Bibcode: 2001ESASP.464...45A
Altcode: 2001soho...10...45A
We study the variation of the frequency splitting coefficients
describing the solar asphericity in both GONG and MDI data, and
use these data to investigate temporal sound-speed variations as a
function of both depth and latitude during the period 1995-2000. The
temporal variations in even splitting coefficients are found to
be correlated with the corresponding component of magnetic flux at
the solar surface. The sound-speed variations associated with the
surface magnetic field appear to be superficial. Temporally averaged
results show a significant excess in sound speed around r = 0.92
Rsolar and latitude of 60°.
Title: Comparing mode frequencies from MDI and GONG
Authors: Howe, R.; Hill, F.; Basu, S.; Christensen-Dalsgaard, J.;
Komm, R. W.; Munk Larsen, R.; Roth, M.; Schou, J.; Thompson, M. J.;
Toomre, J.
Bibcode: 2001ESASP.464..137H
Altcode: 2001soho...10..137H
We present results of analyses of MDI and GONG time series covering
the same time intervals, and using both the MDI and GONG peakbagging
algorithms. We discuss some of the likely causes of differences between
the inferred frequencies and frequency splittings. In addition, we
consider the effect of these differences on the results of inversions
for the solar internal rotation and sound speed.
Title: Daily variations of large-scale subsurface flows and global
synoptic flow maps from dense-pack ring-diagram analyses
Authors: Haber, Deborah A.; Hindman, Bradley W.; Toomre, Juri; Bogart,
Richard S.; Hill, Frank
Bibcode: 2001ESASP.464..209H
Altcode: 2001soho...10..209H
Ring-diagram analyses carried out daily on a mosaic of sites spanning
much of the solar disk have allowed the mapping of large-scale flows in
the upper portion of the solar convection zone. Inversion of frequency
splittings from such local helioseismic analyses reveal large-scale
flows, in addition to the mean zonal and meridional flows, that vary
from day-to-day and with depth. We contrast such flow behavior in
regions of active and quiet sun. We also provide synoptic maps based
on dense-pack studies covering three full solar rotations in 1999.
Title: Solar cycle changes in convection zone dynamics from MDI and
GONG 1995 - 2000
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
Munk Larsen, R.; Schou, J.; Thompson, M. J.; Toomre, J.
Bibcode: 2001ESASP.464...19H
Altcode: 2001soho...10...19H
The combined GONG and MDI medium-degree helioseismic data sets now cover
just over 5 years and allow us to probe the changing dynamics of the
convection zone in unprecedented detail. Here we present the latest
results from both projects, showing the evolution of the migrating
zonal flows close to the surface and also changes close to and below
the base of the convection zone.
Title: Development of multiple cells in meridional flows and evolution
of mean zonal flows from ring-diagram analyses
Authors: Haber, Deborah A.; Hindman, Bradley W.; Toomre, Juri; Bogart,
Richard S.; Hill, Frank
Bibcode: 2001ESASP.464..213H
Altcode: 2001soho...10..213H
Meridional flows within the solar convection zone have been observed
with both direct Doppler measurements and with local helioseismic
techniques based on ring-diagram analyses and time-distance
methods. Typically these mean flows are poleward with speeds of
roughly 20 m s-1. Using ring-diagram analyses on a subset
of the MDI Dynamics Program data, called the dense-pack data set, we
find that a deviation from this general behavior occurs in 1999. A
second meridional cell appears below the surface in the northern
hemisphere. At the same time, the mean zonal flows do not reveal any
evidence of this cell. The zonal bands or "torsional oscillations"
continue their steady migration toward the equator.
Title: High-frequency multi-wavelength acoustic power maps
Authors: Hill, Frank; Ladenkov, Oleg; Ehgamberdiev, Shuhrat; Chou,
Dean-Yi
Bibcode: 2001ESASP.464..219H
Altcode: 2001soho...10..219H
Acoustic power maps have been constructed using SOHO/MDI velocity
and intensity data in Ni I 6768; NSO High-L Helioseismometer (HLH)
Ca K intensity; and Taiwan Oscillation Network (TON) intensity in
Ca K. The HLH data provides maps up to a frequency of 11.9 mHz,
substantially higher than the usual 8.33 mHz. The Ca K observations
show a surprising strong enhancement of power within a sunspot at
all temporal frequencies, while the Ni I data show the well-known
suppression of power. Tests suggest that this apparent acoustic
enhancement is the result of strong intensity gradients observed
through terrestrial seeing.
Title: Spatially-resolved Analysis of the the Upper Covnection Zone
Authors: Bogart, R. S.; Schou, J.; Basu, S.; Haber, D. A.; Hill, F.;
Antia, H. M.
Bibcode: 2001IAUS..203..183B
Altcode:
Plane-wave (ring-diagram) analysis of high-degree modes in data from the
SOI/MDI instrument on SOHO permits us to determine spatial and temporal
variations of the structure and dynamics of the upper convection zone,
to a depth of about 0.1 solar radius below the photosphere. The spatial
resolution achieved with full-disc data is at least 15 heliographic
degrees (180 Mm), and the temporal resolution is of order 1 day. Data
useful for such analysis cover at least two full Carrington rotations
in each year since 1996. Additional data with three times the spatial
resolution over a small portion of the disc are available for shorter
durations at various times. Analyses of the full-disc data from the
earlier years have already revealed systematic patterns in the global
meridional flow and flows associated with active regions during the
early phase of the solar cycle. Here we report on variations and trends
seen in the flows as the activity level of the cycle approaches maximum.
Title: Background amplitudes of solar p-modes observed by GONG
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 2001ESASP.464..645K
Altcode: 2001soho...10..645K
We analyzed the mode background amplitudes, derived from the 45
currently processed 108-day GONG time series. We found that the
background amplitudes and their solar-cycle variation qualitatively
resembles more the mode amplitude, A, than the quantity mode
amplitude times width squared, AΓ2. If the measured
background consists only of the tails of p-modes and leaks, then
the background amplitude should qualitatively follow the behavior of
AΓ2. This unexpected behavior might be a subtle artifact
of the temporal window correction or it might indicate that the tails
of leaks and modes are not the only contributors to the measured
background.
Title: Interior Solar-Cycle Changes Detected by Helioseismology
Authors: Howe, R.; Hill, F.; Komm, R. W.; Christensen-Dalsgaard, J.;
Munk Larsen, R.; Schou, J.; Thompson, M. J.; Toomre, J.
Bibcode: 2001IAUS..203...40H
Altcode:
Helioseismic measurements with the MDI instrument aboard SOHO,
and complementary measurements from the GONG network, are revealing
changes deep within the Sun as the solar cycle progresses. We will
present results based on recent data from both experiments, including
variations in the rotation rate deep inside the convection zone.
Title: The effect of magnetic flux distribution on individual-m
frequencies
Authors: Howe, R.; Landy, D. H.; Komm, R. W.; Hill, F.
Bibcode: 2001ESASP.464...91H
Altcode: 2001soho...10...91H
The GONG PEAKFIND algorithm generates a frequency for each m in an l,n
multiplet. For most purposes, we then fit orthogonal polynomials to the
frequencies to derive α-coefficients. The even-order coefficients are
strongly correlated with the distribution of the magnetic flux. With
over 4 years of GONG data, we can now demonstrate that the frequencies
of individual n, l, m components experience shifts correlated with
the surface flux distribution in the region sampled by that mode. At
high activity levels, this can give rise to visible distortion of
the "S-curve" shape within a multiplet, which in turn means that
higher-order α coefficients are needed to correctly represent the
shape and estimate the central frequency of the multiplet.
Title: Width and energy of solar p-modes observed by GONG 1995 - 1999
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 2001ESASP.464...33K
Altcode: 2001soho...10...33K
We present measurements of mode width, mean-square velocity power, the
energy per mode, and the energy supply rate, derived from all currently
processed 108-day GONG time series and discuss their implications
for p-mode excitation and damping. The mode width shows the familiar
"plateau" between 2.5 and 3.1 mHz with a "dip" near 2.9 mHz. This
dip is most prominent during solar-cycle minimum and disappears with
increasing magnetic activity. The mode energy, which reaches a maximum
value of about 2.2×1028 erg near 3.15 mHz, decreases with
increasing activity. The decrease is frequency dependent and shows
a maximum near 3 mHz with a change of about -13% from the previous
activity minimum to the currently highest level of activity. The energy
supply rate, reaching a maximum value of about 2.5×1023
erg s-1 near 3.6 mHz, decreases on average by about 3%
and its solar-cycle variation shows no frequency dependenc which
is in marked contrast to the other mode parameters. Therefore, the
variation in the energy supply rate might be compatible with a zero
change. We speculate that the excess of the supplied energy might be
transferred to the increasing number of flux tubes and might, in this
way, contribute to the irradiance variation.
Title: Subsurface Flows with Advancing Solar Cycle Using Dense-Pack
Ring-Diagram Analyses
Authors: Haber, D. A.; Hindman, B. W.; Toomre, J.; Bogart, R. S.;
Hill, F.
Bibcode: 2001IAUS..203..211H
Altcode:
Large-scale horizontal flows within the upper convection zone of
the sun are analyzed using the helioseismic technique of ring-diagram
analysis applied to data from SOI-MDI. We map the velocity field over a
substantial fraction of the solar disk by carrying out local inversion
analyses over a Dense-Pack mosaic of many overlapping sites. There
are substantial changes in subsurface flows at any given site from
one day to the next that appear to be of solar origin. Such mosaics
are processed almost daily for at least two solar rotations during
each of the MDI Dynamics Campaigns from 1996 through 1999. We find
that longitudinally-averaged zonal velocity possess bands of fast and
slow flow. As the solar cycle progresses, the latitudes at which the
fast bands occur migrate towards the equator and vary in their flow
amplitudes. These bands are not symmetric about the solar equator, and
their asymmetry changes with time. The average meridional flow for the
years 1996 to 1998 is primarily poleward, reaching maxima in the two
hemispheres at the latitudes at which the zonal fast belts occur. The
latitudes of maximal meridional flow drift equatorward in time much as
the zonal fast belts. However, in 1999, the meridional circulation in
the northern hemisphere develops a two-celled structure with latitude,
whereas in the southern hemisphere it remains single celled.
Title: Exploring time series analysis techniques
Authors: Komm, R.; Hill, F.; Howe, R.; Toner, C.
Bibcode: 2001ESASP.464..351K
Altcode: 2001soho...10..351K
Multitaper power spectra show greatly reduced noise compared
to single taper spectra, such as periodograms. We performed a
random-restart test to show that multitaper spectra do not bias the
fitted mode parameters. Then, we show a different way to increase the
signal-to-noise ratio of spectra by calculating interleaved shifted
cross-spectra. Finally, we start exploring the Hilbert spectral analysis
which is a tool to localize events in time-frequency space.
Title: The Advanced Technology Solar Telescope: Science Goals and
Instrument Description
Authors: Rimmele, T.; Keller, C.; Keil, S.; Hill, F.; Atst Team
Bibcode: 2001AGM....18S1006R
Altcode:
High-resolution studies of the Sun's magnetic fields are needed for
a better understanding of solar magnetic fields and the fundamental
processes responsible for solar variability. For example, the
generation of magnetic fields through dynamo processes is still poorly
understood. There is still incomplete insight as to what physical
mechanisms are responsible for heating the corona, what causes
variations in the radiative output of the Sun. Progress in answering
these critical questions requires study of the interaction of the
magnetic field and convection with a resolution sufficient to observe
scales fundamental to these processes. The 4m aperture ATST will be
a unique scientific tool, which will provide unprecedented angular
resolution, high photon flux, access to a broad set of diagnostics,
from visible to thermal infrared wavelengths, and low scattered light
observations and coronagraphic capabilities in the infrared. Development
of a 4-m solar telescope presents several technical challenges. The
large heat flux makes thermal control of optics and telescope structure
a paramount consideration. To achieve diffraction-limited performance,
a powerful solar adaptive optics system is required. Low scattered
light is essential for observing the corona but also to accurately
measure the physical properties of small structures in, for example,
sunspots. Contamination control of the primary and secondary mirrors
must therefore be addressed. An initial set of instruments will be
designed as integral part of the telescope during the upcoming design
and development phase. A strawman telescope design and instrument
concepts will be discussed.
Title: The Advanced Solar Telescope
Authors: Keil, S. L.; Rimmele, T. R.; Keller, C.; Hill, F.
Bibcode: 2000AAS...197.1710K
Altcode: 2000BAAS...32.1433K
The planned Advanced Technology Solar Telescope (ATST) will be a 4-m
aperture general-purpose solar telescope with integrated adaptive
optics and versatile post focus instrumentation. The ATST will achieve
an angular resolution of 0.03 arcsec (20 km on the solar surface)
in the visible, which is almost an order of magnitude better than
what is achieved with current solar telescopes. This will make it
possible to resolve the fundamental astrophysical hydrodynamic and
magnetohydrodynamic processes and structures in the solar atmosphere
such as the building blocks of solar magnetic fields that are believed
to be responsible for solar irradiance variations and the heating of the
outer solar atmosphere. The ATST will cover the wavelength range from
0.35 to 35 ?m and minimize scattered light. The initial set of post
focus instruments will exploit the unique capabilities of the ATST to
study magnetic fields at the highest spatial resolution in the visible
and near-infrared parts of the spectrum. The ATST was highly recommended
by the recent Decadal Study. A proposal for a four-year Design and
Development phase has just been submitted to the NSF. Construction is
expected to start in FY2005. The National Solar Observatory is operated
by the Associated Universities for Research in Astronomy and is funded
by the National Science Foundation under a cooperative agreement.
Title: Real Research In The Classroom - Solar Active Longitudes
Authors: Stagg, T.; Gearen, M.; Jacoby, S. H.; Jones, H. P.; Henney,
C. J.; Hill, F.
Bibcode: 2000AAS...197.8709S
Altcode: 2000BAAS...32.1556S
We present a high-school level educational/research module for a
project that improves computer and analytical skills and contributes
new scientific results to the field of solar astronomy and physics. The
module has been developed within the RET (Research Experience for
Teachers) program as a new application of a cooperative project
between the RBSE (Research-Based Science Education) initiative of
the NSF and the NASA Education/Public Outreach program. The research
goal is to improve our knowledge of the characteristics of solar
active longitudes, where sunspots tend to cluster. In particular,
the rotation rate of these regions is poorly known. It is suspected
that the active longitude rotation rate (ALRR) is different from the
rotation rate of the solar surface. If this is true, the ALRR can be
compared with the internal rotation rate deduced by helioseismology
providing an estimate of the active region depth. A good determination
of the ALRR requires the measurement of the position of thousands of
individual active regions, a step best done by interactive examination
of images, selection of regions, and determination of heliographic
position. These tasks are well-suited for high school students,
who are thus provided with a motivation to improve their computer
and scientific thinking skills. ScionImage (PC)/NIH Image (Macs)
macros for this purpose have been developed which access a CD-ROM of
25 years of NSO/Kitt Peak magnetogram data and laboratory exercises
developed previously for classroom use. In the future, a web site
will be created for collecting the data from classrooms across the US,
and for status reports on the results.
Title: Width and Energy of Solar p-Modes Observed by Global
Oscillation Network Group
Authors: Komm, R. W.; Howe, R.; Hill, F.
Bibcode: 2000ApJ...543..472K
Altcode:
We present measurements of mode width, Γ, and mean square
velocity power, 2>, derived from all currently processed 108 day
Global Oscillation Network Group (GONG) time series and discuss
their implications for p-mode excitation and damping. Assuming
stochastic excitation, we estimate the energy per mode, E, and the
energy supply rate, dE/dt. For modes with l=9-150, the mean square
velocity power and the mode energy peak at about 3.15 mHz reaching
values of 2>~1.4×103 cm2 s-2
and E~2.2×1028 ergs. The energy supply rate reaches
a maximum value of dE/dt~2.5×1023 ergs s-1
near 3.6 mHz. The mode width shows the familiar ``plateau'' between
2.5 and 3.1 mHz with a ``dip'' near 2.9 mHz, which is strongest
for l~40. This dip is most prominent during solar cycle minimum and
disappears with increasing magnetic activity. The energy supply rate
decreases on average by about 2.7% from the previous activity minimum
to the currently highest level of activity. The solar cycle variation
of dE/dt shows no frequency dependence, which is in marked contrast
to the other mode parameters. The mode parameters are adequately
represented by power laws in several frequency ranges, for example,
dE/dt~ν6.89+/-0.07 for 2.4 mHz<=ν<3.0 mHz and
dE/dt~ν-5.62+/-0.27 for 3.75 mHz<=ν<4.5 mHz. The
solar cycle variation of these parameters can then be expressed as
changes of a few percent in the power-law exponents and multipliers. Our
results agree reasonably well with previous studies of Birmingham
Solar-Oscillations Network and Big Bear Solar Observatory data.
Title: The National Solar Observatory Digital Library - a resource
for space weather studies
Authors: Hill, F.; Erdwurm, W.; Branston, D.; McGraw, R.
Bibcode: 2000JASTP..62.1257H
Altcode: 2000JATP...62.1257H
We describe the National Solar Observatory Digital Library (NSODL),
consisting of 200GB of on-line archived solar data, a RDBMS search
engine, and an Internet HTML-form user interface. The NSODL is
open to all users and provides simple access to solar physics data
of basic importance for space weather research and forecasting,
heliospheric research, and education. The NSODL can be accessed at
the URL www.nso.noao.edu/diglib.
Title: Studying Asphericity in the Solar Sound Speed from MDI and
GONG Data 1995-1999
Authors: Schou, J.; Antia, H. M.; Basu, S.; Howe, R.; Hill, F.; Komm,
R. W.
Bibcode: 2000SPD....31.0111S
Altcode: 2000BAAS...32..803S
We study the variation of the frequency splitting coefficients
describing the solar asphericity in both GONG and MDI data, and use
these data to investigate temporal sound-speed variations as a function
of both depth and latitude during the period 1995--99. We confirm that
the sound-speed variations associated with the surface magnetic field
are superficial.
Title: Solar-Cycle Changes in Convection-Zone Dynamics from SOI and
GONG Data
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J.
Bibcode: 2000SPD....31.0113H
Altcode: 2000BAAS...32..803H
The combined GONG and MDI medium-degree helioseismic data sets now cover
more than 4.5 years and allow us to probe the changing dynamics of the
convection zone in unprecedented detail. Here we present the latest
results from both projects, showing the evolution of the migrating zonal
flows close to the surface and also changes close to and below the base
of the convection zone. This work utilizes data obtained by the Global
Oscillation Network Group (GONG) project, managed by the National Solar
Observatory, a Division of the National Optical Astronomy Observatories,
which is operated by AURA, Inc. under a cooperative agreement with the
National Science Foundation. SOHO is a joint project of ESA and NASA.
Title: A Synoptic View of the Subphotospheric Horizontal Velocity
Flows in the Sun
Authors: González Hernández, I.; Patrón, J.; Roca Cortés, T.;
Bogart, R. S.; Hill, F.; Rhodes, E. J., Jr.
Bibcode: 2000ApJ...535..454G
Altcode: 2000ApJ...535..454H
Ring diagram analysis, a technique of local helioseismology, has
been applied to 120 regions of 15deg×15deg
over the solar surface in order to study the mass motions in the
upper layers of the convection zone. The horizontal flows from ~0.95
Rsolar up to the surface have been investigated in a region
spanning 360deg in longitude and about 75deg
in latitude. The regions were tracked in groups of five centered at
0, +/-15°, and +/-30° in latitude over a timespan of +/-768 minutes
from central meridian crossing. More than 30,000 full-disk Dopplergrams
taken by the Solar Oscillation Investigation/Michelson Doppler Imager
(SOI/MDI) on the Solar and Heliospheric Observatory (SOHO) spacecraft
have been analyzed to create a synoptic map. The images were taken
during the first SOI Dynamics Program in 1996 May and June and have
a pixel size of ~2" allowing coverage in l up to 1200. The p-modes
analyzed cover a range of 0<=n<=7 and 183<=l<=999. The
estimated velocity vectors provide information on the size and structure
of large-scale flows. The flows exhibit markedly meridional behavior
between 0.975 and 0.997 Rsolar. The zonal component is
mainly ruled by the differential rotation.
Title: A National Solar Digital Observatory
Authors: Hill, F.
Bibcode: 2000SPD....3102106H
Altcode: 2000BAAS...32..830H
The continuing development of the Internet as a research tool,
combined with an improving funding climate, has sparked new interest
in the development of Internet-linked astronomical data bases
and analysis tools. Here I outline a concept for a National Solar
Digital Observatory (NSDO), a set of data archives and analysis tools
distributed in physical location at sites which already host such
systems. A central web site would be implemented from which a user
could search all of the component archives, select and download data,
and perform analyses. Example components include NSO's Digital Library
containing its synoptic and GONG data, and the forthcoming SOLIS
archive. Several other archives, in various stages of development,
also exist. Potential analysis tools include content-based searches,
visualized programming tools, and graphics routines. The existence
of an NSDO would greatly facilitate solar physics research, as a user
would no longer need to have detailed knowledge of all solar archive
sites. It would also improve public outreach efforts. The National Solar
Observatory is operated by AURA, Inc. under a cooperative agreement
with the National Science Foundation.
Title: Helioseismic Dense-Pack Ring Diagram Analyses to Study
Evolution of Subsurface Flows With Advancing Solar Cycle
Authors: Haber, D. A.; Hindman, B. W.; Toomre, J.; Bogart, R. S.;
Larsen, R. M.; Hill, F.
Bibcode: 2000SPD....31.0103H
Altcode: 2000BAAS...32..801H
We analyze data obtained from the Michelson Doppler Imager (MDI) on
SOHO in 1996-1999 using the helioseismic ring-diagram technique to
infer large-scale horizontal flows within the upper solar convection
zone. Each separate ring analysis deduces the average flow components
below a 16 degree square region on the solar surface. We map the
velocity field over a substantial fraction of the solar disk by
repeating the analysis over a Dense-Pack mosaic of 189 overlapping
tiles, with each sampling interval spanning 1664 minutes. We process
such a mosaic on a nearly daily schedule and have analyzed two
Carrington rotations (48 days) in 1996 and one or two rotations each
in 1997, 1998, and 1999. There are substantial changes in subsurface
flows at any given site from one day to the next that appear to be of
solar origin. The mean zonal and meridional flows display gradual and
systematic changes. We find that the longitudinally-averaged zonal
velocity, after removing a smooth differential rotation component,
possesses bands of fast and slow flow, much like `torsional
oscillations' first reported from surface Doppler measurements and
recently from global helioseismic assessments. As the solar cycle
progresses, the latitudes at which the fast bands occur migrate towards
the equator. The amplitudes of these banded zonal flows increase with
magnetic activity. Our local-area analyses reveal that these belts
of fast and slow flow are not symmetric about the solar equator, and
their asymmetry changes with time. The average meridional flow (of
typical amplitudes 10-20 m/s) deduced from our samplings for 1996,
1997 and 1998 is primarily poleward and reaches maxima in the two
hemispheres at the latitudes at which the zonal fast belts occur. As
these zonal fast belts drift towards the equator, the latitudes of
maximal meridional flow also drift equatorward. We further find that
in 1999 the meridional circulation in the northern hemisphere has
developed a two-celled structure with latitude, whereas that in the
southern hemisphere is still single celled. This research was supported
by NASA through grants NAG 5-8133 and NAG 5-7996, and by NSF through
grant ATM-9731676.
Title: Width and Energy of Solar P-Modes Observed by GONG
Authors: Komm, R. W.; Howe, R.; Hill, F.
Bibcode: 2000SPD....31.0114K
Altcode: 2000BAAS...32..803K
We present mode width, Γ , and mean-square velocity power, <
v2 >, derived from all currently processed 108-day GONG
time series and discuss their implications for p-mode excitation and
damping. Assuming stochastic excitation, we estimate the energy per
mode, E, and the energy supply rate, dE / dt. For modes with l =
9 - 150, the mean-square velocity power and the mode energy peak
at about 3.15 mHz reaching values of < v2 > ≈
1.4 ; 103 cm2 s-2 and E ≈ 2.2 ;
1028 ergs. The energy supply rate reaches a maximum value of
dE / dt ≈ 2.5 ; 1023 ergs s-1 near 3.6 mHz. The
mode width shows the familiar `plateau' between 2.5 and 3.1 mHz with a
`dip' near 2.9 mHz, which is strongest for l ≈ 40. This dip is most
prominent during solar-cycle minimum and disappears with increasing
magnetic activity. The energy supply rate decreases on average
by about 2.7%\ from the previous activity minimum to the currently
highest level of activity. The solar-cycle variation of dE / dt shows
no frequency dependence, which is in marked contrast to the other mode
parameters. The mode parameters are adequately represented by power laws
in several frequency ranges, for example, dE / dt ~ ν 6.89
+/- 0.07 for 2.4 <= ν < 3.0 mHz and dE / dt ~ ν -5.62
+/- 0.27 for 3.75 <= ν < 4.5 mHz. The solar-cycle variation of
these parameters can then be expressed as changes of a few percent in
the power-law exponents and multipliers. Our results agree reasonably
well with previous studies of BiSON and BBSO data.
Title: Deeply Penetrating Banded Zonal Flows in the Solar Convection
Zone
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J.
Bibcode: 2000ApJ...533L.163H
Altcode: 2000astro.ph..3121H
Helioseismic observations have detected small temporal variations
of the rotation rate below the solar surface that correspond to the
so-called ``torsional oscillations'' known from Doppler measurements of
the surface. These appear as bands of slower- and faster-than-average
rotation moving equatorward. Here we establish, using complementary
helioseismic observations over 4 yr from the GONG network and from
the MDI instrument on board SOHO, that the banded flows are not
merely a near-surface phenomenon: rather, they extend downward at
least 60 Mm (some 8% of the total solar radius) and thus are evident
over a significant fraction of the nearly 200 Mm depth of the solar
convection zone.
Title: Variations in solar sub-surface rotation from GONG data
1995-1998
Authors: Howe, R.; Komm, R.; Hill, F.
Bibcode: 2000SoPh..192..427H
Altcode:
We have completed an analysis of the first 35 GONG Months (1 GM = 36
days) covering the last solar minimum and the rising phase of cycle
23. The mode parameters have been estimated from 33 time series,
each of 3-GM duration, with centers spaced by 1 GM. We report on the
temporal evolution of the rotational splitting coefficients up to 15th
order. The coefficients do not correlate well with any surface magnetic
flux measure yet considered, but we find small but significant trends in
their temporal evolution. Inverting the coefficients for two-dimensional
rotation information and looking at deviations from the mean produces
a picture of a systematic zonal flow migrating towards lower latitudes
during the rising phase of the cycle. This flow is probably associated
with the torsional oscillation. Similar trends are seen in the 1986
-1990 BBSO data.
Title: Solar shear flows deduced from helioseismic dense-pack
samplings of ring diagrams
Authors: Haber, D. A.; Hindman, B. W.; Toomre, J.; Bogart, R. S.;
Thompson, M. J.; Hill, F.
Bibcode: 2000SoPh..192..335H
Altcode:
We report on large-scale horizontal flows in the solar convection zone
and their variability in time and space using a local-helioseismology
technique known as ring-diagram analysis. By performing this analysis
on a dense mosaic of individual regions on the solar disk, i.e.,
a `Dense-Pack' sampling, and repeating the analysis periodically on
several time scales, we are able to assess the variation of horizontal
flows from day-to-day, week-to-week, and year-to-year. We find that
although there are changes in the flows on all these time scales,
there are also basic patterns that persist. On a daily time scale we
observe that the flow is reduced in those areas which are occupied
by large active regions. On somewhat longer time-scales we see bands
of persistent fast and slow zonal flow that are identifiable as
torsional oscillations. As we examine these bands during a series of
years, we find that these bands migrate toward the equator as solar
activity increases. Similarly, the latitudes at which the meridional
flow reaches maximum follow these regions of fast zonal flow as they
migrate equatorwards. These Dense-Pack samplings also reveal substantial
differences in the zonal and meridional flow patterns in the northern
and southern hemispheres.
Title: Dynamic Variations at the Base of the Solar Convection Zone
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J.
Bibcode: 2000Sci...287.2456H
Altcode:
We have detected changes in the rotation of the sun near the base of
its convective envelope, including a prominent variation with a period
of 1.3 years at low latitudes. Such helioseismic probing of the deep
solar interior has been enabled by nearly continuous observation of
its oscillation modes with two complementary experiments. Inversion of
the global-mode frequency splittings reveals that the largest temporal
changes in the angular velocity Ω are of the order of 6 nanohertz
and occur above and below the tachocline that separates the sun's
differentially rotating convection zone (outer 30% by radius) from
the nearly uniformly rotating deeper radiative interior beneath. Such
changes are most pronounced near the equator and at high latitudes and
are a substantial fraction of the average 30-nanohertz difference in Ω
with radius across the tachocline at the equator. The results indicate
variations of rotation close to the presumed site of the solar dynamo,
which may generate the 22-year cycles of magnetic activity.
Title: Solar-Cycle Changes in Gong P-Mode Widths and Amplitudes
1995-1998
Authors: Komm, R. W.; Howe, R.; Hill, F.
Bibcode: 2000ApJ...531.1094K
Altcode:
We search for a solar-cycle variation in mode widths and amplitudes
derived from 3 month GONG time series. The variation of mode width
and amplitude observed in GONG data are the combined effects of
fill factor, temporal variation, and measurement uncertainties. The
largest variation is caused by the fill factor resulting in modes with
increased width and reduced amplitude when fill is lower. We assume
that the solar-cycle variation is the only other systematic variation
beside the temporal window function effect. We correct all currently
available data sets for the fill factor and simultaneously derive the
solar-cycle variation. We find an increase of about 3% on average in
mode width from the previous minimum to October 1998 and a decrease of
about 7% and 6% in mode amplitude and mode area (widthxamplitude). We
find no l dependence of the solar-cycle changes. As a function of
frequency, these changes show a maximum between 2.7 and 3.3 mHz with
about 47% higher than average values for mode width and about 29%
and 36% higher ones for mode amplitude and area. We estimate the
significance of these rather small changes by a prewhitening method
and find that the results are significant at or above the 99.9% level,
with mode area showing the highest level of significance and mode width
the lowest. The variation in background amplitude is most likely not
significant and is consistent with a zero change.
Title: The Solar Cycle is More than Skin Deep!
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 2000ESASP.463...15K
Altcode: 2000sctc.proc...15K
No abstract at ADS
Title: The Virtual Solar Observatory Concept
Authors: Hill, F.
Bibcode: 2000ESASP.463..569H
Altcode: 2000sctc.proc..569H
No abstract at ADS
Title: Helioseismic detection of temporal variations of solar rotation
rate near the base of the convection zone
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J.
Bibcode: 1999AAS...19510702H
Altcode: 1999BAAS...31R1530H
The differential rotation of the Sun and its ability to generate
large-scale magnetic fields through cyclic dynamo action appear to be
intimately linked. It is now commonly thought that the global dynamo
behavior responsible for the emergence of active regions is derived
from strong organized toroidal magnetic fields generated by rotational
shear in a thin region (the tachocline) at the base of the convection
zone. The magnetic field could well have a feedback effect on the fluid
motions in the region. We are thus motivated to use helioseismology
to look for changes in rotation profiles near the tachocline as the
Sun's magnetic cycle progresses. This approach has become possible
using frequency-splitting data for p- and f-mode oscillations derived
over four years (from May 1995 to Sept 1999) of full-disk Doppler
observations from the ground-based Global Oscillation Network Group
(GONG) project and from the Michelson Doppler Imager (MDI) experiment
aboard the SOHO spacecraft. Inversions using two different methods of
the splittings from these two independent data sets reveal systematic
variations of the rotation rate close to the base of the convection
zone, with different behavior at low and high latitudes. Notable
are variations of order 6 nHz in rotation rates near the equator,
to be compared with the radial angular velocity contrast across the
tachocline of about 30 nHz. These exhibit several nearly repetitive
changes with a period of about 1.2-1.4 years and appear to be real
changes in the deep convection zone and tachocline rotation rates that
need to be followed as the solar cycle progresses. The GONG project is
managed by the National Solar Observatory, a Division of the National
Optical Astronomy Observatories, which is operated by AURA, Inc. under
a cooperative agreement with the National Science Foundation. SOHO is
a joint project of ESA and NASA.
Title: Evolution of Subsurface Zonal and Meridional Flows With
Advancing Solar Cycle Using Helioseismic Dense-Pack Samplings of
Ring Diagrams
Authors: Haber, D. A.; Hindman, B. W.; Toomre, J.; Bogart, R. S.;
Larsen, R. M.; Hill, F.
Bibcode: 1999AAS...19510701H
Altcode: 1999BAAS...31Q1530H
We report on the behavior of large-scale horizontal flows within the
upper convection zone of the sun, using the helioseismic technique of
ring-diagram analysis applied to data from the Michelson Doppler Imager
(MDI) on the SOHO spacecraft. Horizontal flows yield displacements in
the rings of power (at fixed frequency) associated with solar acoustic
waves propagating in different directions below a localized area being
studied. We pass these shifts through an inversion procedure and obtain
measurements of the zonal and meridional flows as a function of depth to
about 10 Mm below the surface. Each separate ring analysis deduces the
average flow below a 16 degree square region on the solar surface. We
map the velocity field over a substantial fraction of the solar disk by
repeating the analysis over a densely packed mosaic of 189 overlapping
tiles (called a Dense-Pack). We process such a mosaic on a nearly daily
schedule and have fully analyzed two Carrington rotations (48 days) in
1996 and one rotation each in 1997, 1998, and 1999 during MDI Dynamics
Campaigns. We find that the longitudinally-averaged zonal velocity,
after removing a smooth differential rotation component, possesses
bands of fast and slow flow, much like `torsional oscillations'
first reported from surface Doppler measurements and recently from
global helioseismic assessments. As the solar cycle progresses,
the latitudes at which the fast bands occur migrate towards the
equator. The amplitudes of these banded zonal flows increase with
magnetic activity. Our local-area analyses reveal that these belts of
fast and slow flow are not symmetric about the solar equator, and their
asymmetry changes with time. The average meridional flow is primarily
poleward and reaches maxima in the two hemispheres at the latitudes
at which the zonal fast belts occur. As these zonal fast belts drift
towards the equator, the latitudes of maximal meridional flow also drift
equatorward. This research was supported by NASA grants NAG 5--8133,
NAG 5--7996 and NAG 5--3077 and by NSF grant ATM-9731676.
Title: Solar Cycle Changes in GONG P-Mode Frequencies, 1995-1998
Authors: Howe, R.; Komm, R.; Hill, F.
Bibcode: 1999ApJ...524.1084H
Altcode:
We have analyzed 27 3 month sets of Global Oscillaiton Network Group
(GONG) data from the end of cycle 22 and the beginning of cycle
23 and here present evidence of significant shifts in the central
frequencies and the even a-coefficients of the frequency splittings of
the modes. The temporal behavior of the even a-coefficients is better
reproduced by the corresponding coefficients of a Legendre polynomial
decomposition of the surface magnetic field than by the total flux;
i.e., the temporal variation is strongly correlated with the latitudinal
distribution of the surface magnetic activity. These changes are
consistent with available data from previous solar cycles. The even
a-coefficients, which sense the asphericity of the solar structure,
appear to show similar temporal evolution at all depths. The odd
a-coefficients, which sense the internal differential rotation, show
no significant variation with time or depth. In particular they show
no significant correlation with either the magnetic flux or with the
corresponding odd Legendre components of the flux. This suggests that
the solar cycle related variation of the oscillation frequencies is
not due to contamination of observed Doppler shifts by the surface
magnetic fields.
Title: Multitaper Spectral Analysis and Wavelet Denoising Applied
to Helioseismic Data
Authors: Komm, R. W.; Gu, Y.; Hill, F.; Stark, P. B.; Fodor, I. K.
Bibcode: 1999ApJ...519..407K
Altcode:
Estimates of solar normal mode frequencies from helioseismic
observations can be improved by using multitaper spectral analysis
(MTSA) to estimate spectra from the time series, then using wavelet
denoising of the log spectra. MTSA leads to a power spectrum
estimate with reduced variance and better leakage properties than
the conventional periodogram. Under the assumption of stationarity
and mild regularity conditions, the log multitaper spectrum has a
statistical distribution that is approximately Gaussian, so wavelet
denoising is asymptotically an optimal method to reduce the noise in
the estimated spectra. We find that a single m-ν spectrum benefits
greatly from MTSA followed by wavelet denoising and that wavelet
denoising by itself can be used to improve m-averaged spectra. We
compare estimates using two different five-taper estimates (Slepian
and sine tapers) and the periodogram estimate for Global Oscillation
Network Group (GONG) time series at selected angular degrees l. We
compare those three spectra with and without wavelet denoising,
both visually and in terms of the mode parameters estimated from the
preprocessed spectra using the GONG peak-fitting algorithm. The two
multitaper estimates give equivalent results. The number of modes
fitted well by the GONG algorithm is 20%-60% larger (depending on l
and the temporal frequency) when applied to the multitaper estimates
than when applied to the periodogram. The estimated mode parameters
(frequency, amplitude, and width) are comparable for the three power
spectrum estimates, except for modes with very small mode widths (a
few frequency bins), where the multitaper spectra broaden the modes
compared with the periodogram. At frequencies below 3 mHz, wavelet
denoising of the log multitaper power spectra tends to increase the
number of modes for which the GONG peak-fitting algorithm converges
well. Close to 3 mHz, where all modes are resolved, wavelet denoising
makes little difference. At higher frequencies close to the acoustic
cutoff frequency, where modes are blended into ridges, wavelet denoising
the multitaper spectra reduces the number of good fits. We tested the
influence of the number of tapers used and found that narrow modes
at low n-values are broadened to the extent that they can no longer
be fitted if the number of tapers is too large. For helioseismic time
series of this length and temporal resolution, the optimal number of
tapers is less than 10.
Title: The SOLIS Data Handling and Archive System
Authors: Hill, F.; Goodrich, B.; Wampler, S.; SOLIS Team
Bibcode: 1999AAS...194.7609H
Altcode: 1999BAAS...31..957H
The Synoptic Optical Long-term Investigation of the Sun (SOLIS)
project at NSO will replace the Kitt Peak Vacuum Telescope with a
suite of state-of-the-art observing instruments. These instruments,
comprising a Vector Spectromagnetograph (VSM), a Full-Disk Patrol
(FDP), and an Integrated Sunlight Spectrometer (ISS), will provide
a 25-year record of synoptic solar observations. In this poster we
describe the systems that a typical user will be most concerned with --
the data handling and archiving systems. The current design separates
the reduction of the SOLIS data from the archiving. In this design,
the reduction will be performed at the observing site on Kitt Peak
using distributed work stations, RAIDs, and a storage area network. The
reduced data will be transmitted via a DS3 link to the archive located
in the NOAO headquarters in downtown Tucson. Quick-look calibrated data
will be available over the web within 10 minutes of acquisition. The
current archive design comprises two servers, a RAID, a high-capacity
tape jukebox, and several optical-disk jukeboxes. A portion of the
core synoptic science program will be permanently held on-line. Some
of the data products that will be available are 3-per-day photospheric
vector magnetograms, chromospheric line-of-sight magnetograms, and
He I 10830 quantities; 1-per-10-minute H-alpha, He I 10830, continuum
and Ca K images; and 60 disk-integrated solar spectra per day. Users
will be able to search and download this data in a manner similar
to the current NSO Digital Library. Additional core synoptic data
(e.g. 1-per-minute H-alpha and He I 10830 images) will be in near-line
tape storage, while PI data will be distributed via high-capacity tapes.
Title: Daily Variations and Average Structure of Solar Shear Flows
Deduced from Helioseismic Dense-Pack Samplings of Ring Diagrams
Authors: Haber, D. A.; Hindman, B. W.; Toomre, J.; Bogart, R. S.;
Schou, J.; Hill, F.
Bibcode: 1999AAS...194.5611H
Altcode: 1999BAAS...31..913H
We report on the daily variations and average behavior of large-scale
flows in the upper convection zone as determined by ring-diagram
helioseismic analysis applied to SOI-MDI full-disk velocity data from
the 1996 and 1998 Dynamics Campaigns. We have tracked many small regions
of 15 degrees diameter whose centers are spaced 7.5 degrees apart in
latitude and longitude, creating a mosaic of tiles that oversample
the spatial domain. The tiles cover the solar disk out to a distance
of 52.5 degrees from disk center. An individual dense-pack mosaic
is prepared by tracking each of 189 regions for 1664 minutes (27.7
hrs). Successive mosaics are prepared every 15 degrees in Carrington
longitude, roughly once every 1633 minutes. Such mosaics now cover
more than two full Carrington rotations in 1996 and one rotation in
1998. This is the best spatial and temporal coverage of any ring-diagram
study carried out to date. The longitudinally averaged meridional flow
varies with latitude but remains relatively constant with depth below
the upper shear layer at 2 Mm down to a depth of about 16 Mm. The
averaged zonal flow increases with depth within this same layer and
agrees well with the rotation rates found from global modes. However
with the high-degree wave field data from this analysis we are better
able to resolve that shear layer within the upper convection zone. We
see bands of faster averaged zonal flow near 30 degrees latitude both
in the northern and southern hemisphere that are present at all depths
studied. We also present movies of the daily variations in the flows
within this dense pack for given depths that show the evolution of
the complex velocity field. This research was supported by NASA grants
NAG5-3077 and NAG5-7996, and NSF grant AST-9417337.
Title: Solar Cycle Changes in GONG Data 1995-1998
Authors: Komm, R.; Howe, R.; Hill, F.
Bibcode: 1999AAS...194.5601K
Altcode: 1999BAAS...31..911K
The GONG project has now analysed 3-month velocity time series
covering the period late 1995 to mid-1998, covering the end of solar
cycle 22 and the beginning of cycle 23. We here present an analysis
of the highly significant shifts in the central frequencies and the
a_2 and a_4 coefficients of the modes, and relate them to magnetic
activity indices and to the corresponding coefficients of a Legendre
polynomial decomposition of the surface magnetic field. These changes
are confirmed by an analysis of the MDI-SOI time series for some of
the equivalent time periods using the GONG peakfinding algorithm,
and are consistent with available data from previous solar cycles. In
addition, we study mode widths and amplitudes derived from the GONG
data and search for a variation of these mode parameters with the solar
cycle. With increased activity from cycle minimum to mid-1998, we find
a small increase in mode width of about 2% on average and about 4% in
the frequency range from 2.9 to 3.3 mHz. We find a decrease of similar
size in mode amplitude and mode area (width times amplitude). The
change in background amplitude is not significant and is consistent
with a zero change.
Title: Estimation Of Seeing Quality Using Low-Resolution Solar
Image Data
Authors: Bell, Eric F.; Hill, Frank; Harvey, John W.
Bibcode: 1999SoPh..185...15B
Altcode:
Modulation transfer functions (MTFs), generated as a by-product of the
analysis of low-resolution solar images taken for the Global Oscillation
Network Group, were used to estimate the quality of seeing at its six
sites. These MTFs, after approximate correction for the effects of the
instrumental point spread function, were fitted with physically-motived
functional forms representing the effects of seeing and scattering. It
was found that the estimates of seeing quality were relatively robust
to the effects of scattering, but were severely biased by effects
caused by changes in instrumental focus. Relative trends in seeing
quality are preserved on time scales shorter than a few months and
it is found that local topography dominates the observed trends in
daytime seeing quality.
Title: Solar Cycle Changes in Oscillation Parameters From the First
35 Months of GONG
Authors: Hill, F.; Howe, R.; Komm, R.
Bibcode: 1999soho....9E..63H
Altcode:
We have completed an analysis of the first 35 GONG Months (1 GM = 36
days) covering the last solar minimum and the rising phase of Cycle
23. The mode parameters have been estimated from 33 time series,
each of 3-GM duration, with centers spaced by 1 GM. We report on
the temporal evolution of the frequency, splitting coefficients up
to 15th order, widths, and amplitudes. We clearly observe the bulk
frequency shift that is well-correlated with the surface magnetic
flux, and are able to discern fine details in this evolution. We find
that the even frequency splitting coefficients up to 14th order are
highly correlated not with the total magnetic surface flux, but instead
with the corresponding Legendre components of the average latitudinal
surface flux. On the other hand, the odd coefficients do not correlate
well with any surface magnetic flux measure yet considered. We find
small yet significant trends in the temporal evolution of the odd
coefficients up to 15th order. The widths and amplitudes also show
evidence of temporal evolution, with widths slightly increasing (up
to 10%) and amplitudes similarly decreasing as the activity level rises.
Title: Ring-Diagram Analysis: Status and Perspectives
Authors: Hill, F.
Bibcode: 1999soho....9E...2H
Altcode:
Ring diagram analysis is now more than a decade old. While the details
of the technique are still evolving, the application of the method
to MDI, TON, Mt. Wilson, HLH, and GONG data is providing intriguing
results. Thanks to the work of many people, it is now becoming possible
to observationally infer the complicated dynamics in the outer 15
Mm of the solar convection zone, investigate the depth dependence of
meridional flow, and get a closer look at zonal jet-stream structures
in the mid-latitudes. We may soon be able to similarly investigate the
spatio-temporal distribution of scalar fields. As ring diagrams and
other local helioseismology methods such as time-distance and acoustic
imaging continue to mature, the comparison of results from different
techniques on common data sets will provide a useful reality check.
Title: Changes in High-Degree Oscillation Frequencies from 1996 to
1999 Determined from Ring-Diagram Analysis
Authors: Bogart, R. S.; Schou, J.; Haber, D. A.; Hindman, B. W.;
Toomre, J.; Hill, F.
Bibcode: 1999soho....9E..45B
Altcode:
Ring-diagram analysis has traditionally been used primarily as a
diagnostic for large-scale flows in the upper convection zone. It
also yields values for the unperturbed (rest) frequencies of the
local high-degree p-mode oscillations. These frequencies, positioned
predominantly in a regime where ridge-fitting of traditional
global modes is difficult, possess information about the average
near-surface temperature profile in the region being analyzed. As
the solar magnetic activity level increased from 1996 through 1999,
we might expect these frequencies to have changed correspondingly. We
present spatially and temporally averaged rest frequencies determined
from ring-diagram analysis of full-disk Doppler data for selected
intervals from each of the four annual SOI Dynamics campaigns covering
the rise in solar activity from 1996 through 1999. These analyses are
performed on a `dense-pack' mosaic of tracked tiles that oversample
the spatial domain with a resolution of 15 heliographic degrees (180
Mm). Tiles are individually tracked over time spans of 1664 minutes
(27.7 hr), so a given physical region on the Sun is sampled from 7 to
15 times depending on its latitude as it rotates across the visible
hemisphere. We discuss the frequency changes seen for comparable areas
on the disc over the years analyzed. This research is supported by
NASA grant NAG5-3077 at Stanford University.
Title: Solar Shear Flows Deduced From Helioseismic Dense-Pack
Samplings of Ring Diagrams
Authors: Haber, D. A.; Hindman, B. W.; Toomre, J.; Bogart, R. S.;
Schou, J.; Hill, F.
Bibcode: 1999soho....9E..62H
Altcode:
Large-scale flows in the upper convection zone can be inferred
by ring-diagram helioseismic analysis, permitting the study of
both their daily variations and their longer temporal means. We use
selected full-disk SOI-MDI velocity data from the 1996, 1997, and 1998
Dynamics campaigns. We have tracked sets of regions (each 15 degrees
in diameter and spaced 7.5 degrees apart in latitude and longitude),
creating a `dense-pack' mosaic of such tiles that oversamples the
spatial domain. The tiles cover the solar disc to a distance of up to
52.5 degrees from center. A single dense-pack mosaic is prepared by
tracking each of 189 regions for 1664 minutes (27.7 hrs). Such mosaics
now cover more than two full Carrington rotations in 1996 and one-third
of a rotation each in both 1997 and 1998. This is the best spatial and
temporal coverage of any ring-diagram study carried out to date. We
are able to compare the mean flows determined over 9-day averages
for data from the different SOI-MDI Dynamics campaigns, as well as
examine the daily flow maps, allowing us to study possible changes
in the convection during the rising magnetic activity of the current
solar cycle. We also present movies of the daily variations in the
flows within this dense pack for given depths that show the evolution
of the complex velocity field. The longitudinally-averaged meridional
flow varies with latitude but remains relatively constant with depth
below the upper shear layer at 2 Mm down to a depth of about 16 Mm. The
averaged zonal flow increases with depth within this same layer and
agrees well with the rotation rates found from global modes. However,
with the high-degree wave-field data from this analysis we are better
able to resolve the shear layer within the upper convection zone. We
see bands of faster and slower average zonal flows in both hemispheres;
these are present at all depths studied.
Title: Power spectrum modelisation of helioseismic data: an
application to the measurement of solar p-mode uncertainties
Authors: Fierry Fraillon, D.; Gelly, B.; Schmider, F. X.; Hill, F.;
Fossat, E.; Pantel, A.
Bibcode: 1998A&A...333..362F
Altcode:
We estimate the statistical uncertainties of low-l solar p-modes
parameters based on a Monte Carlo approach. Random perturbations of
ideal Lorentz profiles L(a nu _i) can provide many estimations of the
set of p-modes parameters a and allow one to estimate statistical
error-bars sigma_ {a} by modelling the parameters' distribution
function. Unlike frequencies, which show symmetric distributions,
amplitudes and linewidths have asymmetric probability density function
similar to the distribution function for time-averaged energies of
stochastically excited solar p-modes (Kumar, 1988). A comparison between
sigma_ ν and uncertainties based on Hessian's computation (Libbrecht
1992, Toutain and Appourchaux 1994) shows a nice agreement. However,
our error-bars take into account more statistical effects, and rely
less on the initial parameters' estimation. Such a technique has
been used on the IRIS power spectra computed from gapped data, and
on one GONG power spectrum computed from almost continuous data. We
also present IRIS linewidths and error bars averaged over the years
1989-92 and computed with a fitting strategy using imposed frequency
which improves the value of both the parameter and its uncertainty.
Title: Subphotospheric Convective Flows Determined by Ring-Diagram
Analyses of SOI-MDI Observations
Authors: Haber, D.; Hindman, B.; Toomre, J.; Bogart, R.; Schou, J.;
Hill, F.
Bibcode: 1998ESASP.418..791H
Altcode: 1998soho....6..791H
The variation of large-scale velocity flows with depth and location
on the sun places important constraints on theoretical models of the
solar convection zone and dynamo. High-degree oscillations can be
viewed as nearly plane waves that are advected and distorted by the
underlying flows. By conducting observations over limited regions
of the solar surface to obtain `ring diagram' power spectra, we can
deduce spatially-averaged horizontal flows with depth below that
region. Previous analyses of ring diagrams have already suggested
the presence of strong shearing flows below the surface. We have
now implemented a highly efficient technique for determining these
horizontal flows with depth and report here on a systematic analysis of
full-disk Doppler velocity data taken continuously with a one-minute
cadence during portions of the two-month dynamics observing program
with SOI-MDI in 1996. The square regions examined span about 15-circ,
and are studied for time intervals each of about 1536 mins (~25 hrs). A
lattice of such squares is considered: their centers are spaced 15-circ
apart in longitude and there are seven such regions across the solar
disk at +20-circ, 0-circ, -20-circ latitude. Another set of regions
is placed along the central meridian at 10-circ and 15-circ intervals
in latitude. Properties of the underlying large-scale subphotospheric
flows and their temporal variations so revealed are presented in detail.
Title: Estimating Low-Degree Mode Parameters from GONG Data Using
the Leakage Matrix
Authors: Howe, R.; Hill, F.
Bibcode: 1998ESASP.418..237H
Altcode: 1998soho....6..237H
The estimation of mode frequencies from any solar oscillation data
is complicated by leakage between the spectra for different degrees,
which is unavoidable due to the limited area of the Sun's surface
used for observations. At low l and m, the leakage between modes of
the same l but different m (`m-leakage') is substantial, and ignoring
it can distort the frequency estimates. We outline a fitting method
under development in which the leakage matrix information is used to
fit simultaneously to several spectra which contain leaked power from
the mode of interest, and which themselves leak into the spectrum
associated with that mode. Some preliminary results are presented
which illustrate the effects of m-leakage on the low-degree rotational
splitting measurements.
Title: Comparison of SOHO-SOI/MDI and GONG Spectra
Authors: Komm, R. W.; Anderson, E.; Hill, F.; Howe, R.; Kosovichev,
A. G.; Scherrer, P. H.; Schou, J.; Fodor, I.; Stark, P.
Bibcode: 1998ESASP.418..253K
Altcode: 1998soho....6..253K
We compare solar p-mode parameters, such as central frequency, width,
and amplitude, derived from GONG and SOHO-SOI/MDI Medium-l Program
time series obtained during the same time period. With the excellent
data available now from GONG and SOHO-SOI/MDI, there exist data
sets long enough to make such a comparison useful. For this study,
we have chosen time series of three ell values (ell = 30, 65, and 100)
corresponding to GONG month 16 (Oct 28 -- Dec 2, 1996). For each time
series, we calculated multitaper power spectra using generalized
sine tapers to reduce the influence of the gap structure, which is
different for the two data sets. Then, we applied the GONG peakfitting
algorithm to the spectra to derive mode parameters and selected `good'
fits common to both MDI and GONG spectra, according to three selection
criteria. Preliminary results show that mode frequencies determined
from MDI spectra are essentially the same as the frequencies from
GONG spectra and that the difference is, in general, well within one
formal error bar. The background slope at frequencies above 5mHz is
different between MDI and GONG spectra depending on ell. At present,
we are analyzing 3-month time series of ell = 0 to ell = 150. We intend
to present the results of the on-going comparison.
Title: Multitaper Spectral Analysis and Wavelet Denoising Applied
to Helioseismic Data
Authors: Komm, Rudolf; Gu, Yeming; Hill, Frank; Stark, Phil; Fodor,
Imola
Bibcode: 1998ASPC..154..783K
Altcode: 1998csss...10..783K
Our goal is to improve the estimates of mode frequencies, amplitudes,
and widths derived from helioseismic observations. To this end, we
apply Multitaper Spectral Analysis (MTSA) to the observed time series
to derive power spectrum estimates, and then we apply wavelet denoising
to the log spectra to further improve the signal-to-noise ratio of the
modes. The rationale behind this approach is that MTSA leads to a power
spectrum estimate with reduced variance and better leakage properties
than the conventional periodogram and that since the log multitaper
spectrum is close to Gaussian, distributed wavelet denoising is the
optimum method to reduce the noise level in the calculated spectra. We
applied MTSA and wavelet denoising to GONG and SOHO-SOI/MDI time series
and found that a single m-nu spectrum benefits greatly from MTSA plus
wavelet denoising and that wavelet denoising by itself can be used to
improve m-averaged spectra.
Title: Multitaper Analysis Applied to a 3-month Time Series
Authors: Komm, R. W.; Anderson, E.; Hill, F.; Howe, R.; Fodor, I.;
Stark, P.
Bibcode: 1998ESASP.418..257K
Altcode: 1998soho....6..257K
We show the benefit of multitapering by applying this technique to
a 3-month helioseismic time series, then deriving p-mode parameters
using the GONG peakfitting algorithm. A multitaper spectrum is an
average over uncorrelated spectra derived from the same time series
by applying a set of orthogonal tapers. Thus, a multitaper spectrum
has less variance or noise than a single taper spectrum and has better
leakage properties than a periodogram. We use generalized sine tapers,
which are orthogonal tapers taking the gap structure of the time
series into account. We applied this technique with great success to
a variety of time series from SOHO-SOI/MDI and GONG. The benefit of
multitapering is that more modes can be fitted than in a periodogram
due to the reduced noise. The improvement depends on ell and other
details of the time series and is typically between 20% and 60% for
low to medium ell values for GONG as well as MDI data. For example,
for the 3-month GONG time series covering months 12--14, the number
of good fits increases by 10% on average for all modes from ell =
0--150, using 5 generalized sine tapers. The largest improvement is
at ell <= 70 where at low frequencies one extra ridge can be fitted
in the multitaper spectrum.
Title: Helioseismology and the Solar Cycle
Authors: Hill, F.
Bibcode: 1998ASPC..140...33H
Altcode: 1998ssp..conf...33H
No abstract at ADS
Title: Estimated Mode Parameters from the Fitting of GONG Spectra
Authors: Hill, F.; Anderson, E.; Howe, R.; Jefferies, S. M.; Komm,
R.; Toner, C.
Bibcode: 1998ESASP.418..231H
Altcode: 1998soho....6..231H
The estimation of mode parameters is a critical step in the helioseismic
data reduction process. Several estimation methods are currently in
use, and a comparison of the resulting frequencies from a common data
set shows small, yet significant, differences. This suggests that the
fitting procedures can introduce systematic errors. These errors will
affect subsequent inversions of the data. For example, the presence of
a high-latitude jet in the solar rotation rate appears to depend on the
type of spectral fitting used to estimate the splitting coefficients. In
addition, as the available helioseismic observations have improved,
it has become apparent that several effects have been neglected in the
peak fitting techniques. These effects include line profile asymmetry,
coupling between the background and the mode signal, fine details in
the leakage matrix, and the differences in the oscillation spectrum
when observed in Doppler velocity or total intensity. Here we report
on the latest GONG fitting methods and present the resulting mode
parameter estimates. The GONG fitting technique now includes improved
mode quality assurance checks and asymmetrical line profiles. Currently
under development are multi-dimensional fitting, multi-taper time
series analysis, background/mode coupling, simultaneous fitting
of velocity and intensity spectra, and the inclusion of a leakage
matrix. The improvements have resulted in higher-quality frequency
estimates that are now being computed for 108-day long time series
spaced by 36 days. After completion, each frequency table is made
freely available to the helioseismic community.
Title: Calculating the GONG Leakage Matrix
Authors: Hill, F.; Howe, R.
Bibcode: 1998ESASP.418..225H
Altcode: 1998soho....6..225H
Since spherical harmonics do not form a complete orthonormal basis
set over a portion of a sphere, helioseismic spectra computed for
a specific target mode with degree ellt and azimuthal
degree mt also contain modes with nearby ell''
and m''. These spatial leaks greatly increase the
complexity of the observed spectrum, complicating the spectral
fitting and degrading the resulting mode parameter estimates. This
is particularly true where the target mode and the leaks have
similar frequencies. Some strategies for fitting helioseismic
spectra explicitly include the leakage matrix which estimates the
relative strength of a mode (ell'' and m'')
in the spectrum at (ellt,mt). Since the fitting
methods assume that the matrix is correct and apply it as a constraint,
an inaccurate matrix introduces systematic errors in the estimated
mode parameters. It is thus important to have as accurate a matrix as
possible. Here we report on the calculation of the leakage matrix for
the GONG observations. The matrix elements are essentially the integrals
(over the observed portion of the solar surface) of the crossproducts of
the two spherical harmonics. However, several effects have been included
to increase the accuracy of the matrix. These include the projection
factor of the observable (velocity, intensity, modulation), the
spatial apodization applied to the data, the finite rectangular pixel
dimensions of the observations, and possible errors in the estimated
image geometry. Other factors to be incorporated are the observed MTF,
the merging of the GONG images, and the horizontal components of the
oscillatory velocity field. We will compare the latest calculation
with the observed spectrum and assess the relative importance of the
input factors. We will also compare the leakage matrices for velocity
and intensity to estimate their contribution to the large apparent
differences in the helioseismic spectra obtained from these observables.
Title: GONG Spectra in three observables: What is a p-mode frequency?
Authors: Harvey, J.; Hill, F.; Komm, R.; Leibacher, J.; Pohl, B.;
GONG Team
Bibcode: 1998IAUS..185...49H
Altcode:
No abstract at ADS
Title: The Procyon campaign: Observations from Kitt Peak
Authors: Pilachowski, C. A.; Barden, S.; Hill, F.; Harvey, J. W.;
Keller, C. U.; Giampapa, M. S.
Bibcode: 1998IAUS..185..319P
Altcode:
Time series spectra of the F5IV star Procyon (alpha CMi) were obtained
at the Kitt Peak National Observatory during a 35-night observing run
in January-February 1997. The observations were obtained as part of an
international collaboration to detect and study acoustic oscillations
in solar-type stars. Spectra covered the wavelength range from 4000
to 5300 AA , with a resolving power of approximately 3500 (1.3 AA
resolution). The sampling rate was one observation per minute, and
the typical S/N ratio per observation is in excess of 1000. At the
time of writing, we have obtained over 10,000 spectra. The spectra
will be analyzed to identify any periodic signals due to acoustic
oscillations in Procyon. In addition to measuring the equivalent widths
of the three Balmer lines (Kjeldsen et al. 1995) covered by our spectra
(Hβ, Hγ, and Hdelta) we will also examine the spectra for variations
in the average metal line strength. Preliminary power spectra will
be presented.
Title: Helioseismic Data Reduction
Authors: Hill, F.
Bibcode: 1998IAUS..185...13H
Altcode:
No abstract at ADS
Title: Asteroseismology from equivalent widths: a test of the sun
Authors: Keller, C. U.; Harvey, J. W.; Barden, S. C.; Giampapa, M. S.;
Hill, F.; Pilachowski, C. A.
Bibcode: 1998IAUS..185..375K
Altcode:
Kjeldsen et al. (1995) reported a probable detection of solar-like,
low-amplitude, p-mode oscillations of eta Bootes using equivalent
width measurements from low-resolution spectra of the hydrogen Balmer
lines. We tested the usefulness of this technique using observations of
the Sun in integrated light. Despite the very high signal-to-noise ratio
of the data stretching over six continuous days, no solar oscillation
signal was found so far in the equivalent width of Hβ. Spatially
resolved observations of the Hβ equivalent width at solar disk center
reveal that the oscillation signal is suppressed in the wings of Hβ
as compared to the continuum. Extrapolation of the oscillation signal
seen in the spatially resolved data suggests an amplitude of about
1ppm for integrated light measurements, which is about a factor of
5 lower than expected from simple theoretical arguments. We explore
other methods to deduce an oscillation signal from all spectral lines
simultaneously. cont has: Deng, L. et al.; auths fixed below
Title: Helioseismology and the Solar Cycle
Authors: Hill, F.
Bibcode: 1997sspn.work.....H
Altcode:
As with many other solar phenomena, the oscillations of the sun vary as
the activity cycle progresses. It has been known since 1984 that the
frequencies of the global modes in the 3-mHz band increase by about
0.5 micro Hz between minimum and maximum solar activity, and that
the frequency shift is highly correlated with the surface magnetic
field strength. We now have evidence that the lifetime of the modes,
the acoustic reflectivity of the solar atmosphere, and the detailed
shape of the oscillation spectral lines also vary with the activity
cycle. In addition, helioseismic inversions show signs of cycle
variations in the dynamics and structure of the solar interior, and in
the characteristics of the source of the oscillations. In this paper,
the observations of helioseismic solar cycle effects are reviewed,
and the results placed in the context of synoptic solar physics.
Title: Preliminary Results Towards a Synoptic Velocity Map of the
Solar Subsurface
Authors: Gonzalez Hernandez, I.; Patron, J.; Bogart, R. S.; Haber,
D. A.; Hill, F.; SOI Team
Bibcode: 1997BAAS...29Q1121G
Altcode:
No abstract at ADS
Title: Persistent Convective Structures on the Sun
Authors: Beck, J. G.; Ulrich, R. K.; Hill, F.; Bogart, R.; Bertello,
Luca
Bibcode: 1997BAAS...29R1121B
Altcode:
No abstract at ADS
Title: The National Solar Observatory Digital Library
Authors: Hill, F.; Branston, D.; Erdwurm, W.
Bibcode: 1997SPD....28.0272H
Altcode: 1997BAAS...29..906H
NSO provides several important data sets to the solar physics community,
such as full-disk daily magnetograms, He 10380 spectroheliograms,
and solar spectral atlases from Kitt Peak; as well as H-alpha and
Ca K spectroheliograms, and coronal scans from Sacramento Peak. The
usage of these data sets has rapidly increased over the last 3 years
as indicated in the logs of NSO/KP anonymous FTP activity which show
increases of 400% in the number of logins, and 100% in the number of
files transferred. In order to provide better access to these data for
the solar physics community, NSO is developing a digital library. A
robotic jukebox that holds 300 CD ROMs (about 210 GB) on-line has
been installed at NSO, and the migration of data into this system is
substantially underway. At the present time, the entire set of spectra
from the Fourier Transform Spectrometer is on-line, as well as about
15% of the Kitt Peak magnetograms and He 10830 images. The Sacramento
Peak H-alpha and Ca K spectroheliograms are now being digitized and
transferred to CDs. A web-based user interface and search tool is also
in development. Oracle has been selected and installed as the RDBMS
search engine. Software to populate the database tables using FITS
header parameters has been developed. Issues of file name conventions,
user request tracking, and download strategies are under study. We
expect to have a simple prototype interface and search tool for the
Kitt Peak magnetograms available for testing by the user community by
Summer 1997. This will provide a foundation that can be easily extended
to include additional data sets.
Title: Helioseismic frequency determination using homomorphic
deconvolution
Authors: Baudin, Frederic; Hill, Frank
Bibcode: 1997SPD....28.0203B
Altcode: 1997BAAS...29R.893B
Since the succesful launch of the SOHO mission and the completion of the
GONG network, data of high quality are available in great quantity and
must be analysed with the greatest care. When determining the spectral
characteristics of the p-modes, the classical Fourier Transform is in
general used. However, it has been shown to be inadequate because of
the non-stationarities of helioseismic signals (excitation process
of the p-modes). Alternative methods, which take this aspect into
account, can be used, for example the ``homomorphic deconvolution'',
which has shown promising results. In this work, the efficacy of this
method is tested using both simulated and real (MDI/SOHO) data. The
results will focus on the reliability of the frequency determination
and precision, as solar p-modes frequencies are an important tool for
sounding the solar interior, the more precise these frequencies are,
the more efficient this sounding is.
Title: Multitaper Spectral Analysis and Wavelet Denoising Applied
to Helioseismic Data
Authors: Komm, R.; Gu, Y.; Stark, P.; Hill, F.
Bibcode: 1997SPD....28.0215K
Altcode: 1997BAAS...29..895K
Our goal is to improve the estimates of mode frequencies, amplitudes,
and widths derived from helioseismic observations. To this end, we
apply Multitaper Spectral Analysis (MTSA) to the observed time series
to derive power spectrum estimates, and then we apply wavelet denoising
to the spectra to improve the signal-to-noise ratio of the modes. The
rationale behind this approach is that MTSA leads to a more accurate
and robust power spectrum estimate than the conventional periodogram and
that since the log multitaper spectrum is close to Gaussian distributed
wavelet denoising is the optimum method to reduce the noise level
in the calculated spectra. We have put together a `pipeline' to
calculate a multitaper spectral estimate from a given time series,
to apply wavelet denoising to the log spectra and then to derive
mode parameters using the GONG peak-fitting algorithm. This pipeline
was applied to a set of simple artificial data in order to check for
systematic errors and consistency. The wavelet denoising method was
already applied to m-averaged South Pole spectra and to some GONG
spectra of different L values reducing the noise level considerably
and improving the fit. At the moment, we apply the pipeline to GONG
and SOHO-SOI/MDI time series. We intend to present a comparison of
two multitaper estimates using Slepian and Sinusoidal tapers with a
conventional periodogram and a comparison of each of the three spectra
with the corresponding wavelet denoised spectrum. This comparison will
allow us to discuss the benefits of adding these methods to existing
helioseismic data analysis packages.
Title: Persistence of Large-Scale Flows Beneath Quiet Sun: Local-Area
Analysis Using MDI Doppler Data
Authors: Haber, D.; Toomre, J.; Bogart, R.; Schou, J.; Gonzalez, I.;
Hill, F.
Bibcode: 1997SPD....28.0201H
Altcode: 1997BAAS...29..893H
Knowing the large-scale flows that occur in the upper convection zone
is critical to our understanding of the processes that govern the
solar cycle. Here we apply solar oscillation ring-diagram analysis to
several small tracked regions on the sun, approximately 15(deg) on a
side, as they rotate across the solar disk, in order to determine the
persistence and depth variation of the large-scale flows beneath these
regions. We use the Doppler velocity images from the Michelson Doppler
Imager (MDI) instrument aboard the Solar Heliospheric Observatory
(SOHO) satellite using quiet-sun data taken during the MDI Dynamics
campaign of 1996. Three regions at different latitudes were extracted
from full-disk Doppler images of 1024 x 1024 pixels (pixel size ~
2'' square) with a one-minute temporal cadence. Eight sequential
1536-minute time intervals were tracked, remapped onto great-circle
grids, spatially and temporally filtered, and apodized in space and
time. They were then Fourier transformed in two spatial dimensions
and time. The resulting power spectra show characteristic rings at
each frequency slice. Shifts in the center positions of the rings are
caused by underlying flow fields and can be inverted to map these flows
with depth. We use several techniques to fit these shifts in order to
assess the stability of the results.
Title: Seismic investigation of the solar structure using GONG
frequencies
Authors: Tripathy, S. C.; Antia, H. M.; Hill, F.; Ambastha, A.
Bibcode: 1997astro.ph..3179T
Altcode:
Using the recently obtained GONG frequencies, we investigate the
properties of the solar interior by constructing solar models with
various input physics like opacities, equation of state, nuclear
reaction rates etc. The differential asymptotic inversion technique is
then used to infer the relative difference in sound speed between the
Sun and solar models. Here we apply these results to test equation of
state and different formulation for calculating the convective flux.
Title: Plane-wave analysis of 501 data
Authors: Bogart, R. S.; Discher de Sá, L. A.; González Hernández,
I.; Patrón Recio, J.; Haber, D. A.; Toomre, J.; Hill, F.; Rhodes,
E. J., Jr.; Xue, Y.; SOI Ring Diagrams Team
Bibcode: 1997IAUS..181..111B
Altcode:
No abstract at ADS
Title: The seismic structure of the Sun from GONG
Authors: Anderson, E.; Antia, H. M.; Basu, S.; Chaboyer, B.; Chitre,
S. M.; Christensen-Dalsgaard, J.; Eff-Darwich, A.; Elliott, J. R.;
Giles, P. M.; Gough, D. O.; Guzik, J. A.; Harvey, J. W.; Hill,
F.; Leibacher, J. W.; Kosovichev, A. G.; Monteiro, M. J. P. F. G.;
Richard, O.; Sekii, T.; Shibahashi, H.; Takata, M.; Thompson, M. J.;
Toomre, J.; Vauclair, S.; Vorontsov, S. V.
Bibcode: 1997IAUS..181..151A
Altcode:
No abstract at ADS
Title: Asteroseismology via equivalent widths - tests on Procyon,
Eta Bootis, and Alpha Trianguli.
Authors: Harvey, J. W.; Pilachowski, C.; Barden, S.; Giampapa, M.;
Keller, C. U.; Hill, F.
Bibcode: 1996BAAS...28..917H
Altcode:
No abstract at ADS
Title: GONG Observations of Solar Surface Flows
Authors: Hathaway, D. H.; Gilman, P. A.; Harvey, J. W.; Hill, F.;
Howard, R. F.; Jones, H. P.; Kasher, J. C.; Leibacher, J. W.; Pintar,
J. A.; Simon, G. W.
Bibcode: 1996Sci...272.1306H
Altcode:
Doppler velocity observations obtained by the Global Oscillation Network
Group (GONG) instruments directly measure the nearly steady flows in
the solar photosphere. The sun's differential rotation is accurately
determined from single observations. The rotation profile with respect
to latitude agrees well with previous measures, but it also shows a
slight north-south asymmetry. Rotation profiles averaged over 27-day
rotations of the sun reveal the torsional oscillation signal-weak,
jetlike features, with amplitudes of 5 meters per second, that are
associated with the sunspot latitude activity belts. A meridional
circulation with a poleward flow of about 20 meters per second is
also evident. Several characteristics of the surface flows suggest
the presence of large convection cells.
Title: Simulations of Magnetic Field Effects on Solar Oscillation
Ring Diagrams
Authors: Hill, F.; Zweibel, E.; Haber, D.
Bibcode: 1996AAS...188.6905H
Altcode: 1996BAAS...28Q.936H
Solar oscillation ring diagrams are an effective technique for inferring
the horizontal velocity in the solar convection zone as a function of
heliographic position and depth. While the signature of the velocity in
the diagram is a shift in the central position of the rings, the shape
of the rings contains information on the subsurface temperature and
magnetic field. Direct detection of the velocity and magnetic fields
in the convection zone will provide important input to theories of
the solar activity cycle, convection, and the dynamo. We present here
the results of simulating ring shape variations arising from magnetic
effects. Simple polytropic models containing various magnetic field
profiles are used to construct artificial oscillation ring diagrams. We
then determine the altered ring shapes, invert for the magnetic field,
and compare the results of the inversion to the field of the model to
place limits on the sensitivity of the technique.
Title: The Current State of Solar Modeling
Authors: Christensen-Dalsgaard, J.; Dappen, W.; Ajukov, S. V.;
Anderson, E. R.; Antia, H. M.; Basu, S.; Baturin, V. A.; Berthomieu,
G.; Chaboyer, B.; Chitre, S. M.; Cox, A. N.; Demarque, P.; Donatowicz,
J.; Dziembowski, W. A.; Gabriel, M.; Gough, D. O.; Guenther, D. B.;
Guzik, J. A.; Harvey, J. W.; Hill, F.; Houdek, G.; Iglesias, C. A.;
Kosovichev, A. G.; Leibacher, J. W.; Morel, P.; Proffitt, C. R.;
Provost, J.; Reiter, J.; Rhodes, E. J., Jr.; Rogers, F. J.; Roxburgh,
I. W.; Thompson, M. J.; Ulrich, R. K.
Bibcode: 1996Sci...272.1286C
Altcode:
Data from the Global Oscillation Network Group (GONG) project and
other helioseismic experiments provide a test for models of stellar
interiors and for the thermodynamic and radiative properties, on which
the models depend, of matter under the extreme conditions found in the
sun. Current models are in agreement with the helioseismic inferences,
which suggests, for example, that the disagreement between the predicted
and observed fluxes of neutrinos from the sun is not caused by errors in
the models. However, the GONG data reveal subtle errors in the models,
such as an excess in sound speed just beneath the convection zone. These
discrepancies indicate effects that have so far not been correctly
accounted for; for example, it is plausible that the sound-speed
differences reflect weak mixing in stellar interiors, of potential
importance to the overall evolution of stars and ultimately to estimates
of the age of the galaxy based on stellar evolution calculations.
Title: Preliminary Ring-Diagram Analysis of Doppler Velocity Fields
Observed with MDI on SOHO
Authors: Haber, D. A.; Bogart, R. S.; Sa, L. A. D.; Hill, F.; Toomre,
J.; Duvall, T. L., Jr.
Bibcode: 1996AAS...188.3710H
Altcode: 1996BAAS...28Q.879H
We analyze properties of high-degree acoustic wave fields over small
patches of the sun using high-resolution Doppler velocity observations
with the Michelson Doppler Imager (MDI) on the Solar Heliospheric
Observatory (SOHO). By studying asymmetric frequency shifts in the
acoustic waves that propagate in different horizontal directions,
we can make inferences about the underlying large-scale flows which
contribute to these shifts. We here analyze two different sets of
data obtained from early observations with MDI. One is a continuous
80-hour sequence of full-disk Doppler images with a 60 s cadence and 4''
resolution, the other is an 8-hour sequence of high-resolution images
that have 1.2'' resolution. Both sets have 1024 x 1024 pixels but the
second set only covers about 36deg on the sun and is centered on the
central meridian and somewhat above disk center. In both cases we remap
a number of smaller areas of the data and compute three-dimensional
Fourier transforms (two in space, one in time) over each patch. The
resulting power diagrams have cross-sections in frequency that exhibit
power distributed along rings. The detailed shapes and displacements
of the rings depend upon the averaged velocities and their gradients,
which can be estimated by theory. We measure the displacements of the
rings using two different analysis techniques, thereby determining
the frequency splittings which are then used in inversion procedures
to deduce the underlying smoothed flow fields in each region. The
results from the various patches provide preliminary estimates of the
flow structures present in the upper convection zone.
Title: The Seismic Structure of the Sun
Authors: Gough, D. O.; Kosovichev, A. G.; Toomre, J.; Anderson,
E.; Antia, H. M.; Basu, S.; Chaboyer, B.; Chitre, S. M.;
Christensen-Dalsgaard, J.; Dziembowski, W. A.; Eff-Darwich, A.;
Elliott, J. R.; Giles, P. M.; Goode, P. R.; Guzik, J. A.; Harvey,
J. W.; Hill, F.; Leibacher, J. W.; Monteiro, M. J. P. F. G.; Richard,
O.; Sekii, T.; Shibahashi, H.; Takata, M.; Thompson, M. J.; Vauclair,
S.; Vorontsov, S. V.
Bibcode: 1996Sci...272.1296G
Altcode:
Global Oscillation Network Group data reveal that the internal
structure of the sun can be well represented by a calibrated standard
model. However, immediately beneath the convection zone and at the
edge of the energy-generating core, the sound-speed variation is
somewhat smoother in the sun than it is in the model. This could be a
consequence of chemical inhomogeneity that is too severe in the model,
perhaps owing to inaccurate modeling of gravitational settling or to
neglected macroscopic motion that may be present in the sun. Accurate
knowledge of the sun's structure enables inferences to be made about
the physics that controls the sun; for example, through the opacity,
the equation of state, or wave motion. Those inferences can then be
used elsewhere in astrophysics.
Title: The Global Oscillation Network Group (GONG) Project
Authors: Harvey, J. W.; Hill, F.; Hubbard, R. P.; Kennedy, J. R.;
Leibacher, J. W.; Pintar, J. A.; Gilman, P. A.; Noyes, R. W.; Title,
A. M.; Toomre, J.; Ulrich, R. K.; Bhatnagar, A.; Kennewell, J. A.;
Marquette, W.; Patron, J.; Saa, O.; Yasukawa, E.
Bibcode: 1996Sci...272.1284H
Altcode:
Helioseismology requires nearly continuous observations of the
oscillations of the solar surface for long periods of time in
order to obtain precise measurements of the sun's normal modes of
oscillation. The GONG project acquires velocity images from a network
of six identical instruments distributed around the world. The GONG
network began full operation in October 1995. It has achieved a duty
cycle of 89 percent and reduced the magnitude of spectral artifacts by
a factor of 280 in power, compared with single-site observations. The
instrumental noise is less than the observed solar background.
Title: Differential Rotation and Dynamics of the Solar Interior
Authors: Thompson, M. J.; Toomre, J.; Anderson, E. R.; Antia, H. M.;
Berthomieu, G.; Burtonclay, D.; Chitre, S. M.; Christensen-Dalsgaard,
J.; Corbard, T.; De Rosa, M.; Genovese, C. R.; Gough, D. O.; Haber,
D. A.; Harvey, J. W.; Hill, F.; Howe, R.; Korzennik, S. G.; Kosovichev,
A. G.; Leibacher, J. W.; Pijpers, F. P.; Provost, J.; Rhodes, E. J.,
Jr.; Schou, J.; Sekii, T.; Stark, P. B.; Wilson, P. R.
Bibcode: 1996Sci...272.1300T
Altcode:
Splitting of the sun's global oscillation frequencies by large-scale
flows can be used to investigate how rotation varies with radius
and latitude within the solar interior. The nearly uninterrupted
observations by the Global Oscillation Network Group (GONG) yield
oscillation power spectra with high duty cycles and high signal-to-noise
ratios. Frequency splittings derived from GONG observations confirm
that the variation of rotation rate with latitude seen at the surface
carries through much of the convection zone, at the base of which is
an adjustment layer leading to latitudinally independent rotation at
greater depths. A distinctive shear layer just below the surface is
discernible at low to mid-latitudes.
Title: Solar Oscillation Observations with the MDI Line Depth
Parameter
Authors: Henney, C. J.; Ulrich, R. K.; Bogart, R. S.; Sa, L. A. D.;
Haber, D. A.; Hill, F.
Bibcode: 1996AAS...188.3711H
Altcode: 1996BAAS...28R.879H
The line-depth parameter determined by the Michelson Doppler Imager
(MDI) on the Solar Heliospheric Observatory (SOHO) provides a measure of
magnetic field structures on the Sun. This parameter, along with the MDI
continuum parameter, will be used to estimate the change in the solar
brightness, due to active region effects, at the NaD working points of
the Global Oscillation Low Frequency (GOLF) instrument on SOHO to allow
correction of the GOLF signal. Preliminary comparison of simultaneous
full-disk observations of line-depth and Doppler images show a weak
correlation. We investigate the possible causes for this correlation. In
addition, we use ring-diagram analysis of high-resolution observations,
taken using the MDI line-depth parameter on March 7, 1996, to study
large-scale flows beneath the heliographic south pole.
Title: The Sun's Acoustic Spectrum and Normal Mode Parameters
Authors: Stebbins, R. T.; Hill, F.; Stark, P. B.; GONG Data Reduction
Team; GONG Analysis Team
Bibcode: 1996AAS...188.5306S
Altcode: 1996BAAS...28..904S
GONG seeks to measure the frequencies, amplitudes and line widths of
the Sun's acoustic normal modes. The Project estimates these parameters
for more than 250,000 acoustic modes of the Sun from every 36 day-long
set of data. Data from the network are archived, calibrated, reduced
to several science products and made available for distribution to
researchers at the pace of observations. GONG also produces magnetograms
and temporally filtered solar images for convective velocity and
magnetic field studies. The frequency resolution of a single data set
is 0.321 mu Hz. For m- averaged frequencies the median formal error
is 0.044 mu Hz, and the associated median fractional frequency error
is 1.6 x 10(-5) . Results from concatenated data sets are now becoming
available. For a three-year data set, the fractional error is expected
to be 3 x 10(-6) , providing the highest quality helioseismic frequency
measurements to date. Examples of power spectra and mode parameters
will be shown. To demonstrate the reliability of the initial GONG
frequencies, m-averaged frequency measurements will be compared with
other helioseismic data sets. The mean systematic variations among
the data sets are 0.03 to 0.08 mu Hz. The differences arise from a
combination of systematic errors, random errors, and possible changes
in solar structure and dynamics. Error sources will be discussed.
Title: Asteroseismology via Equivalent Widths -- Tests on Procyon,
Eta Bootes, and Alpha Triangulum
Authors: Harvey, J.; Pilachowski, C.; Barden, S.; Giampapa, M.;
Keller, C.; Hill, F.
Bibcode: 1996AAS...188.5903H
Altcode: 1996BAAS...28S.917H
Recently, Kjeldsen et al. reported a probable detection of solar-like
low-amplitude p-mode oscillations of Eta Bootes using equivalent
width measurements from low-resolution spectra of the H Balmer
lines. This technique has the potential to provide stellar oscillation
measurements good enough to allow the asteroseismic inference of stellar
structure. Here we report on the preliminary analysis of data from three
observing runs with the Kitt Peak Coude Feed and 2.1-m telescope in
November 1995 (Alpha Triangulum), February 1996 (Procyon), and March
1996 (Eta Bootes). These runs are being used to develop observing
and data reduction techniques, such as a synchronized timing system
to maintain evenly spaced temporal samples, a continuous unshuttered
CCD readout to increase the duty cycle of the observations, and a
simulation of the probability of a detection as a function of observing
run length. We observed the region around the H beta, gamma, and delta
lines with a spectral dispersion of about 0.4 Angstroms per pixel,
extracted equivalent widths, and performed time series analysis. The
temporal spectrum of Alpha Triangulum contains a significant peak near
the theoretical prediction, however, we do not yet know the origin of
this peak.
Title: The Global Oscillation Network Group Project
Authors: Leibacher, J. W.; Harvey, J. W.; Hill, F.; Hubbard, R.;
Kennedy, J. R.; Pintar, J. A.; Bhatnagar, A.; Kennewell, J. A.;
Marquette, W.; Patron, J.; Saa, O.; Yasukawa, E.; GONG Project Team
Bibcode: 1996AAS...188.5301L
Altcode: 1996BAAS...28..903L
The NSF-sponsored Global Oscillation Network Group (GONG) project
has developed and is operating a network of six velocity imaging
instruments around the world, and a data analysis system that can keep
up with the massive data flow, in support of a vigorous community that
shares in all aspects of this program to explore the structure and
dynamics of the solar interior. Data from the first three stations
were obtained starting in March 1995, and the full six-station
network became operational in early October 1995. The system noise
is below the solar background of incoherent surface motions, and the
overall data processing pipeline is maintaining cadence with the data
flood. The scientific objectives, design and performance of the network,
instrumentation, and data processing, and plans for the future will be
presented. The National Optical Astronomy Observatories are operated
by the Association of Universities for Research in Astronomy, Inc.,
under cooperative agreement with the National Science Foundation.
Title: The Solar Acoustic Spectrum and Eigenmode Parameters
Authors: Hill, F.; Stark, P. B.; Stebbins, R. T.; Anderson, E. R.;
Antia, H. M.; Brown, T. M.; Duvall, T. L., Jr.; Haber, D. A.;
Harvey, J. W.; Hathaway, D. H.; Howe, R.; Hubbard, R. P.; Jones,
H. P.; Kennedy, J. R.; Korzennik, S. G.; Kosovichev, A. G.; Leibacher,
J. W.; Libbrecht, K. G.; Pintar, J. A.; Rhodes, E. J., Jr.; Schou, J.;
Thompson, M. J.; Tomczyk, S.; Toner, C. G.; Toussaint, R.; Williams,
W. E.
Bibcode: 1996Sci...272.1292H
Altcode:
The Global Oscillation Network Group (GONG) project estimates
the frequencies, amplitudes, and linewidths of more than 250,000
acoustic resonances of the sun from data sets lasting 36 days. The
frequency resolution of a single data set is 0.321 microhertz. For
frequencies averaged over the azimuthal order m, the median formal
error is 0.044 microhertz, and the associated median fractional error
is 1.6 x 10-5. For a 3-year data set, the fractional error
is expected to be 3 x 10-6. The GONG m-averaged frequency
measurements differ from other helioseismic data sets by 0.03 to 0.08
microhertz. The differences arise from a combination of systematic
errors, random errors, and possible changes in solar structure.
Title: Velocity Fields within the Solar Convection Zone: Evidence
from Oscillation Ring Diagram Analysis of Mount Wilson Dopplergrams
Authors: Patron, J.; Hill, F.; Rhodes, E. J., Jr.; Korzennik, S. G.;
Cacciani, A.
Bibcode: 1995ApJ...455..746P
Altcode:
A ring-diagram analysis of solar oscillations has been applied to
a 3 day time series of full-disk Doppler images obtained at Mount
Wilson. A model of the three-dimensional power spectrum assuming a
Lorentzian profile in frequency and the advection of the wave front by
horizontal flows has been fitted to the observed spectrum. The model
provides estimates of the two horizontal components of subsurface
flows averaged over depth. These estimates are then input to a
least-squares smoothness-constrained inversion procedure to infer
the depth dependence of the horizontal velocity. The method has been
applied at nine different heliographic positions. The results indicate
the presence of three east-west shear layers at all longitudes and
latitudes, associated in depth with the ionization zones of hydrogen
and helium in the outermost 20 Mm. The direction of the shear with
respect to the average surface rotation rate alternates with depth, with
organized north-south flows apparent between the east-west flows. Thus,
the resultant vector velocity field appears to execute a spiral as
a function of depth. Below ∼30 Mm, the organized character of the
flow disappears, and a chaotic spatial distribution dominates. There
is also an indication of a convergent flow at ∼10° north latitude,
suggesting the presence of a toroidal convective roll. The magnitudes
of the flows are on the order of 100-200 ms-1 in the outer
20 Mm, rising to several hundred ms-1 at 50 Mm.
Title: Resolution and Error Trade-Offs in Velocity Fields Inferred
from Ring Diagrams
Authors: Hill, F.
Bibcode: 1995ESASP.376b.127H
Altcode: 1995soho....2..127H; 1995help.confP.127H
Ring diagrams are being developed as local helioseismic probes of the
internal solar velocity field. An important aspect of all helioseismic
methods is the trade-off between the spatial resolution of the solar
interior, and the errors in the inferred quantity. The computational
expense of the ring diagram method, particularly in the fitting of
the rings, has so far prevented a determination of the trade-off. A
further complication arises from the need to compute the trade-off
in several dimensions. This paper presents the first results of a
numerical simulation of the trade-off. The simulation uses a center
of gravity method to compute the estimated errors in the velocity
as a function of radial order, temporal frequency, spatial scale,
area coverage, temporal coverage, spectral signal-to-noise ratio,
and spatial scale precision. Both the magnitudes and the qualitative
functional behavior of the simulated errors as a function of frequency
agree well with errors estimated from actual data.
Title: Preliminary Results from Plane-Wave Analysis of Helioseismic
Data
Authors: Bogart, R. S.; Sá, L. A. D.; Haber, D. A.; Hill, F.
Bibcode: 1995ESASP.376b.151B
Altcode: 1995soho....2..151B; 1995help.confP.151B
The authors have analyzed the p-mode spectra in four consecutive
days of Ca II K-filtergram data from the High-l Helioseismometer,
at Kitt Peak. Although the mode frequencies have not been inverted,
the amplitude and phase of the frequency shifts analyzed this way
demonstrate consistent behaviour that appears to be tied to solar
features. These results are compared with results from a separate
plane-wave (ring-diagram) analysis of the same data.
Title: Implementation of an Mtf-Based Merging Algorithm for GONG
Image Data
Authors: Williams, W. E.; Toner, C.; Hill, F.
Bibcode: 1995ESASP.376b.185W
Altcode: 1995soho....2..185W; 1995help.confP.185W
The GONG project will use a weighted average based upon the modulation
transfer function (MTF) in order to combine image data from a six-site
network into a single time series of spherical harmonic coefficients
for helioseismic analysis. Tests with artificially generated data and
solar observations taken with the GONG instruments, including some
observations taken with a part of the GONG instrument network in place,
indicate that the MTF method for data merging can be successfully
applied to helioseismic data.
Title: A Study of the Background Solar Velocity Spectrum Using
GONG Data
Authors: Beck, J. G.; Hill, F.; Ulrich, R. K.
Bibcode: 1995ESASP.376b.401B
Altcode: 1995soho....2..401B; 1995help.confP.401B
No abstract at ADS
Title: Plane-Wave Analysis of Solar Acoustic-Gravity Waves: a
(slightly) New Approach
Authors: Bogart, R. S.; Sá, L. A. D.; Duvall, T. L.; Haber, D. A.;
Toomre, J.; Hill, F.
Bibcode: 1995ESASP.376b.147B
Altcode: 1995soho....2..147B; 1995help.confP.147B
Plane-wave decomposition of acoustic-gravity wave effects observed
in the photosphere provides a computationally efficient technique for
probing the structure of the upper convective zone and boundary, where
the flat-Sun approximation is reasonably accurate. The authors describe
the technique to be used for systematic plane-wave analysis of MDI
data as part of the SOI data analysis pipeline, and the SOI analysis
plan. The authors present estimates of sensitivity and discuss the
effects of using different planar mappings. The technique is compared
with previous approaches to the 3-dimensional plane-wave problem.
Title: Local-Area Analysis of High-Degree Solar Oscillations: New
Ring-Fitting Procedures
Authors: Haber, D. A.; Toomre, J.; Hill, F.; Gough, D. O.
Bibcode: 1995ESASP.376b.141H
Altcode: 1995help.confP.141H; 1995soho....2..141H
Local-area analysis of five-minute solar oscillations using ring
diagrams to determine subphotospheric velocity flows is on the brink
of becoming an important tool in understanding convective zone
dynamics. One of the main problems up to this point has been the
large computational burden of fitting the rings. The authors present a
faster method for carrying out the ring fits using data obtained with
the High-l Helioseismometer at Kitt Peak. The authors first eliminate
serious sources of noise, then use a perturbation approach to fit the
azimuthally averaged spectrum. The parameters so determined are held
constant while fitting the entire ring diagram.
Title: Measurement of High-Degree Solar Oscillation Frequencies
Authors: Bachmann, K. T.; Duvall, T. L., Jr.; Harvey, J. W.; Hill, F.
Bibcode: 1995ApJ...443..837B
Altcode:
We present m-averaged solar p- and f-mode oscillation frequencies over
the frequency range nu greater than 1.8 and less than 5.0 mHz and the
spherical harmonic degree range l greater than or equal to 100 and
less than or equal to 1200 from full-disk, 1000 x 1024 pixel, Ca II
intensity images collected 1993 June 22-25 with a temporal cadence
of 60 s. We itemize the sources and magnitudes of statistical and
systematic uncertainties and of small frequency corrections, and we
show that our frequencies represent an improvement in accuracy and
coverage over previous measurements. Our frequencies agree at the 2
micro Hz level with Mount Wilson frequencies determined for l less
than or equal to 600 from full-disk images, and we find systematic
offsets of 10-20 micro Hz with respect to frequencies measured from
Big Bear and La Palma observations. We give evidence that these latter
offsets are indicative of spatial scaling uncertainties associated with
the analysis of partial-disk images. In comparison with theory, our
p-mode frequencies agree within 10 micro Hz of frequencies predicted
by the Los Alamos model but are as much as 100 micro Hz smaller than
frequencies predicted by the Denmark and Yale models at degrees near
1000. We also find systematic differences between our n = 0 frequencies
and the frequencies closely agreed upon by all three models.
Title: Local Probes of the Solar Interior
Authors: Hill, F.
Bibcode: 1995ESASP.376a..63H
Altcode: 1995heli.conf...63H; 1995soho....1...63H
Interest in local helioseismology has been growing as techniques
have been developed to probe the solar interior in localized regions,
rather than as global averages over the entire Sun. Three techniques
have been developed so far - ring diagrams, time-distance, and Hilbert
transforms. Ring diagrams (or plane-wave analysis) use three-dimensional
Fourier transforms of remapped velocity data to infer properties
below the observing area. Time-distance methods are closely related to
terrestrial seismology techniques, and provide information about the
conditions along a ray path. Hilbert transforms attempt to measure the
instantaneous phase and amplitude of an acoustic wave across the solar
surface. The status of the development of these methods along with their
advantages, disadvantages, and application to solar data are reviewed.
Title: Frequencies of High Degree Solar Oscillations
Authors: Bachmann, K. T.; Duvall, T. L., Jr.; Harvey, J. W.; Hill, F.
Bibcode: 1995ASPC...76..156B
Altcode: 1995gong.conf..156B
No abstract at ADS
Title: Local Helioseismology via Ring Diagrams and Trumpet Surfaces
Authors: Hill, F.
Bibcode: 1995ASPC...76..484H
Altcode: 1995gong.conf..484H
No abstract at ADS
Title: Test of a Data Merging Algorithm Based on the Modulation
Transfer Function
Authors: Williams, W. E.; Toner, C.; Hill, F.
Bibcode: 1995ASPC...76..500W
Altcode: 1995gong.conf..500W
No abstract at ADS
Title: Detection of Chromospheric Oscillations in High-L Data
Authors: Tripathy, S. C.; Hill, F.
Bibcode: 1995ASPC...76..334T
Altcode: 1995gong.conf..334T
No abstract at ADS
Title: Ring Diagram Analysis of Mt. Wilson Data: Velocity Fields
within the Solar Convection Zone
Authors: Patron, J.; Hill, F.; Rhodes, E. J., Jr.; Korzennik, S. G.;
Cacciani, A.
Bibcode: 1995ASPC...76..208P
Altcode: 1995gong.conf..208P
No abstract at ADS
Title: A Study of the Magnetic-Darkening Velocity Using GONG
Modulation Images
Authors: Beck, J. G.; Ulrich, R. K.; Hill, F.
Bibcode: 1995ASPC...76..296B
Altcode: 1995gong.conf..296B
No abstract at ADS
Title: Solar Oscillation Ring Diagrams: Benefits of Great Circle
Remapping
Authors: Haber, D.; Toomre, J.; Hill, F.; Gough, D.
Bibcode: 1995ASPC...76..272H
Altcode: 1995gong.conf..272H
No abstract at ADS
Title: Implementation of an MTF Based Merging Algorithm for Image Data
Authors: Williams, W. E.; Toner, C.; Hill, F.
Bibcode: 1994AAS...185.4404W
Altcode: 1994BAAS...26.1377W
The GONG project will use a weighted average based upon the Modulation
Transfer Function (MTF) in order to combine image data from a six-site
network into a single time series of spherical harmonic coefficients for
helioseismic analysis. We present an overview of the MTF merge method,
including a capsule description of its theoretical basis, a summary of
the method, application to merging time series of images from different
sites in the network, and the limits of its applicability encountered
during testing. In order to test the method, an artificial data set
of selected helioseismic modes was computed. From this "perfect"
data, a degraded set of data including atmospheric, day length and
instrumental effects was created to model the anticipated data from
the six-site network. The results of tests comparing time series and
mode frequencies from 18 days of the "perfect" data set and the set
of site days merged into a single time series support the use of this
algorithm for the GONG project merge.
Title: Measurements of High-Degree Solar Oscillation Parameters
Authors: Bachmann, K. T.; Duvall, T. L., Jr.; Harvey, J. W.; Hill, F.
Bibcode: 1994AAS...185.4405B
Altcode: 1994BAAS...26R1377B
We present results obtained from full-disk, 1000times 1024 pixel, Ca II
intensity images of the Sun collected with the High-L Helioseismometer
(HLH). Our measurement of p- and f-mode oscillation frequencies over
the frequency range 1.8<=nu <=5.0 mHz and the spherical harmonic
degree range 100<=l<=1200 from 22-25 June 1993 data represents an
improvement over previous measurements. We are able to differentiate
among the predictions of several solar models, thus constraining
physical models of the solar convection zone. We also include recent
splitting and frequency results from data collected during the entire
month of June 1994. The purpose of the HLH research program is to
measure high-degree solar oscillation parameters for the remainder
of this decade in support of the Solar Oscillations Investigation -
Michelson Doppler Imager collaboration, which is part of the Solar
and Heliospheric Observatory, a joint ESA-NASA satellite mission.
Title: The Global Oscillation Network Group Site Survey - Part One
Authors: Hill, Frank; Fischer, George; Grier, Jennifer; Leibacher,
John W.; Jones, Harrison B.; Jones, Patricia P.; Kupke, Renate;
Stebbins, Robin T.
Bibcode: 1994SoPh..152..321H
Altcode:
The Global Oscillation Network Group (GONG) Project is planning to place
a set of instruments around the world to observe solar oscillations as
continuously as possible for at last three years. The Project has now
chosen the sites that will comprise the network. This paper describes
the methods of data collection and analysis that were used to make
this decision.
Title: The Global Oscillation Network Group Site Survey - Part Two
Authors: Hill, Frank; Fischer, George; Forgach, Suzanne; Grier,
Jennifer; Leibacher, John W.; Jones, Harrison P.; Jones, Patricia
B.; Kupke, Renate; Stebbins, Robin T.; Clay, Donald W.; Ingram,
Robert E. L.; Libbrecht, Kenneth G.; Zirin, Harold; Ulrichi, Roger
K.; Websteri, Lawrence; Hieda, Lester S.; Labonte, Barry J.; Lu,
Wayne M. T.; Sousa, Edwin M.; Garcia, Charles J.; Yasukawa, Eric
A.; Kennewell, John A.; Cole, David G.; Zhen, Huang; Su-Min, Xiao;
Bhatnagar, Arvind; Ambastha, Aashok; Al-Khashlan, Abdulrahman Sa'ad;
Abdul-Samad, Muhammad-Saleh; Benkhaldoun, Zouhair; Kadiri, Samir;
Sánchez, Francisco; Pallé, Pere L.; Duhalde, Oscar; Solis, Hernan;
Saá, Oscar; González, Ricardo
Bibcode: 1994SoPh..152..351H
Altcode:
The Global Oscillation Network Group (GONG) Project will place a
network of instruments around the world to observe solar oscillations as
continuously as possible for three years. The Project has now chosen the
six network sites based on analysis of survey data from fifteen sites
around the world. The chosen sites are: Big Bear Solar Observatory,
California; Mauna Loa Solar Observatory, Hawaii; Learmonth Solar
Observatory, Australia; Udaipur Solar Observatory, India; Observatorio
del Teide, Tenerife; and Cerro Tololo Interamerican Observatory, Chile.
Title: Temporal window effects and their deconvolution from solar
oscillation spectra
Authors: Lazrek, M.; Hill, F.
Bibcode: 1993A&A...280..704L
Altcode:
Long unbroken time series are a primary goal of observational
helioseismology, but it is impossible to completely eliminate
temporal gaps regardless of the adopted strategy. Here we report on
a study of the effects of the gaps on the measurement of oscillation
line parameters. We created observing windows described by a duty
cycle, a gap periodicity, and a randomness factor. We then used a
maximum-likelihood method to fit a simulated oscillation spectrum
containing a single spectral line convolved with the window function. We
find that frequent (less than 1.0 d apart) gaps have little or no
effect on the oscillation parameters. Infrequent gaps (2 d apart) have
more substantial effects on the measured oscillation line parameters,
with the largest systematic deviations occurring for nearly periodic
windows with low duty cycles. For these windows, the average gap length
is a substantial fraction of the lifetime of the simulated mode. In
this case, the deviations can be as high as 0.01 micro-Hz in central
frequency, 0.2 micro-Hz in line width, with relative deviations of 15%
in the energy and a factor of 5 in the background when compared to
simulations with a perfect ungapped window. As the randomness of the
window increases, we find that generally the systematic deviations
decrease while the random errors increase. These results may well
be different for a more realistic solar-like spectrum containing
may spectral lines. We have tested a simple deconvolution method to
remove the effects of the gaps from the oscillations spectrum. This
procedure computes the deconvoluted spectrum from the ratio of the
autocorrelation functions of the convolved signal and the window. The
deconvolution alters the statistical distribution of the observations,
and this effect must be accounted for in the fitting of the mode. We
find that, in spectra with infrequent gaps and low duty cycles, this
method can improve the estimate of the line width by as much as 40%
and the estimate of the energy by 70%. However, the background is
overestimated by as much as a factor of 30 in these cases.
Title: Ring Diagram Analysis of Mt. Wilson Data: Current Status
Authors: Hill, F.; Patron, J.; Rhodes, E. J., Jr.; Korzennik, S. G.;
Cacciani, A.
Bibcode: 1993BAAS...25R1193H
Altcode:
No abstract at ADS
Title: Invited Talk: (Convection Zone Flow Mapping Using Solar
Oscillations: Recent Progress and Future Prospects)
Authors: Hill, F.
Bibcode: 1993BAAS...25Q1219H
Altcode:
No abstract at ADS
Title: Ring Diagram Analysis of MT.WILSON Data
Authors: Patron, J.; Hill, F.; Rhodes, E. J., Jr.; Korzennik, S. G.;
Cacciani, A.; Brown, T. M.
Bibcode: 1993ASPC...42..437P
Altcode: 1993gong.conf..437P
No abstract at ADS
Title: Subsurface Transverse Flows Near an Active Region
Authors: Milford, P. N.; Hill, F.; Tarbell, T. D.
Bibcode: 1993ASPC...42...85M
Altcode: 1993gong.conf...85M
No abstract at ADS
Title: Tests of a Simple Data Merging Algorithm for the GONG Project
Authors: Williams, W.; Hill, F.; Toner, C.
Bibcode: 1993ASPC...52..494W
Altcode: 1993adass...2..494W
The GONG (Global Oscillation Network Group) project proposes to reduce
the impact of diurnal variations on helioseismic measurements by using
the data from six sites placed around the globe. The data from the sites
must be combined into a single time series in order to determine mode
frequencies, amplitudes and line widths. Here, we report on tests of
a simple (all weights = 1) average merging algorithm emphasizing the
results in the p-mode frequency band around 3 mHz. Astronomy
Observatories are operated by the Association of Universities for
Research in Astronomy, Inc. (AURA) under cooperative agreement with
the National Science Foundation.
Title: Solar G-Mode Signatures in P-Mode Signals
Authors: Kennedy, J. R.; Jefferies, S. M.; Hill, F.
Bibcode: 1993ASPC...42..273K
Altcode: 1993gong.conf..273K
No abstract at ADS
Title: Artificial Data for Testing Helioseismology Algorithms
Authors: Bogart, R. S.; Hill, F.; Toussaint, R.; Hathaway, D. H.;
Duvall, T. L., Jr.
Bibcode: 1993ASPC...42..429B
Altcode: 1993gong.conf..429B
No abstract at ADS
Title: Tests of a Simple GONG P-Mode Merging Algorithm
Authors: Williams, W.; Hill, F.; Toner, C.; Brown, T. M.
Bibcode: 1993ASPC...42..441W
Altcode: 1993gong.conf..441W
No abstract at ADS
Title: GONG Project Update
Authors: Harvey, J.; Hill, F.; Kennedy, J.; Leibacher, J.
Bibcode: 1993ASPC...42..397H
Altcode: 1993gong.conf..397H
No abstract at ADS
Title: The Deconvolution of Temporal Window Effects from Solar
Oscillation Spectra
Authors: Lazrek, M.; Hill, F.
Bibcode: 1993ASPC...42..449L
Altcode: 1993gong.conf..449L
No abstract at ADS
Title: Plans for MT.WILSON - Crimean Observatory High-Degree
Helioseismology Network
Authors: Rhodes, E. J., Jr.; Cacciani, A.; Dappen, W.; Didkovsky,
L. V.; Hill, F.; Korzennik, S. G.; Kosovichev, A. G.; Kotov, V. A.;
Scherrer, P. H.
Bibcode: 1993ASPC...42..477R
Altcode: 1993gong.conf..477R
No abstract at ADS
Title: Geometrical Correction of Solar Oscillation Ring Diagrams
Authors: Hill, F.; Patron, J.
Bibcode: 1992AAS...180.0602H
Altcode: 1992BAAS...24R.736H
No abstract at ADS
Title: On the Interpretation of Inversions of Helioseismic Rotational
Splltting Measurements
Authors: Hill, Frank
Bibcode: 1992ASPC...27..286H
Altcode: 1992socy.work..286H
No abstract at ADS
Title: Do Changes in the Photospheric Magnetic Network Cause the 11
Year Variation of Total Solar Irradiance?
Authors: Foukal, P.; Harvey, K.; Hill, F.
Bibcode: 1991ApJ...383L..89F
Altcode:
Changes in the area of the photospheric magnetic network over the
sunspot cycle have been put forward as the 'missing component'
required to explain the 11-yr variation of total solar irradiance
observed by space-borne radiometers. It is shown that this explanation
is consistent with recent measurements of the photometric contrast of
magnetic faculae and with the present measurement of the network area
change during cycle 21.
Title: GONG site evaluation program at Udaipur Solar Observatory
Authors: Ambastha, Ashok; Bhatnagar, Arvind; Jain, Rajmal; Srivastava,
Nandita; Gupta, Sudhir; Sharma, Richa; Agrawal, Gopal; Kumawat,
Vishnu; Hill, Frank; Fischer, George
Bibcode: 1991BASI...19..215A
Altcode:
The Global Oscillations Network Group (GONG) project to study the
internal structure and dynamic of the sun is discussed. The GONG project
will measure waves that penetrate throughout the sun's core. Power
spectra of the monthly average transparency for each calendar month were
obtained and analyzed. The resulting clear and dark time distributions
and monthly average extinction coefficients and transparency power
spectra are shown and discussed. The various possible networks from
the candidate sites participating in the GONG project are compared.
Title: The Bartol/NASA/NSO High-Degree Helioseismometer
Authors: Harvey, J.; Hill, F.; Duvall, T., Jr.; Jones, H.; Jefferies,
S.; Pomerantz, M.
Bibcode: 1991BAAS...23.1032H
Altcode:
No abstract at ADS
Title: The Solar Equatorial Internal Rotation Rate Estimated from
Combined South Pole and NSO/Sac Peak Helioseismic Data Sets
Authors: Hill, F.; Jefferies, S. M.; Pomerantz, M. A.; Duvall, T. L.,
Jr.; Harvey, J. W.
Bibcode: 1991BAAS...23.1050H
Altcode:
No abstract at ADS
Title: Simulation of Effects of Atmospheric Seeing on the Observation
of High-Degree Solar Oscillations
Authors: Hill, Frank; Gough, Douglas; Merryfield, William J.;
Toomre, Juri
Bibcode: 1991ApJ...369..237H
Altcode:
Numerical simulations of the effects of atmospheric seeing distortions
on observations of solar oscillations of intermediate and high degree
are performed. The simulations involve a representation of about 100
p-modes of oscillation, with degrees l = 50-150 (intermediate-degree)
and 150-450 (high-degree), formed from the complement of a sexated mode
set. These modes are superposed on a steady large-scale convective
background, and projected onto the plane of the sky. Image motion is
modeled by displacement maps generated from two-dimensional turbulence
power spectra; the maps are scaled so that the rms amplitude of the
displacements has values of 2-5 arcsec. The distorted velocity field is
then Fourier analyzed to produce simulated (l, nu) power diagrams, where
nu is the temporal cyclic frequency. The results show that power in the
mode ridges is diminished as atmospheric seeing worsens, particularly
at high degrees. Redistribution of power produces an apparent decrease
in the frequencies of the oscillations as measured by the centroids
of the ridges in the power spectra. It is found that time-averaging
the observations is quite effective in reducing the noise.
Title: On the Detection of g-mode Signatures in p-mode Signals
Authors: Kennedy, J.; Jefferies, S.; Hill, F.
Bibcode: 1991BAAS...23R1032K
Altcode:
No abstract at ADS
Title: Solar Oscillation Ring Diagrams from Mt. Wilson Full-Disk
Magneto-Optical Dopplergrams
Authors: Hill, Frank; Rhodes, Edward J.; Korzennik, Sylvain G.;
Cacciani, Alessandro; Brown, Timothy M.
Bibcode: 1991LNP...388..271H
Altcode: 1991ctsm.conf..271H
Three-dimensional power spectra of solar oscillations have been
computed from moderate-resolution full disk Doppler images obtained
with the Magneto-Optical Filter at Mt. Wilson. Slices of the spectra
at constant frequency reveal the ring structures that are analogous
to the ridges in two-dimensional spectra. Ring diagrams obtained
at different heliographic positions show large differences in the
structure of the rings. These variations can be attributed to the
changing effective spatial resolution of the observations across the
disk. After correction for this effect, and .for terrestrial seeing,
the rings will be used to map the horizontal flows in the convection
zone as a function of position and depth.
Title: Ground-based helioseismology networks
Authors: Hill, Frank; Leibacher, John
Bibcode: 1991AdSpR..11d.149H
Altcode: 1991AdSpR..11..149H
The diurnal rising and setting of the Sun severely compromises
helioseismology from a single ground-based observatory. This periodic
interruption creates sidelobes in power spectra at multiples of 1/day
(11.57 μHz) centered around each solar line, contaminating the spectra
and hampering mode identification and frequency measurement. So far,
three strategies have been used to overcome the difficulty - observing
from the Polar regions, observing with a network of stations placed
around the Earth, or observing from a fully sunlit orbit in space. This
paper reports on the status of the networks that are either currently in
operation or being planned. These include the Global Oscillation Network
Group (GONG) project, the Birmingham network, the IRIS network of the
University of Nice, the SCLERA network of the University of Arizona,
and the ESTEC network. The scientific objectives and instrumentation
of these networks are briefly described. The relationship between
networks and the helioseismology experiments on the SOHO mission
are described. Operated by the Association of Universities for
Research in Astronomy, Inc. under cooperative agreement with the
National Science Foundation.
Title: Simulation of the Effect of Active Regions on
Intermediate-Degree Solar Oscillations
Authors: Haber, Deborah A.; Hill, Frank
Bibcode: 1991LNP...388..253H
Altcode: 1991ctsm.conf..253H
The effect of active regions on the solar oscillations is simulated
by artificially suppressing the velocities in full-disk quiet-sun
Doppler images. An image of the active sun is used as a template to
mask the regions within which the velocities are reduced by as much as
35%. Two-dimensional - power spectra from both the quiet sun and the
masked data are compared. We find that the addition of one large active
region does not significantly alter the power in the oscillations,
but the presence of several simulated regions decreases the power in
the global modes by up to 25%, in agreement with observations. The
shapes of the oscillation spectral lines do not substantially change,
suggesting that frequencies measured from these spectra will not be
significantly altered.
Title: The role of f modes in the inversion of high-ℓ rotational
splittings
Authors: Haber, Deborah A.; Hill, Frank; Toomre, Juri
Bibcode: 1991LNP...388...87H
Altcode: 1991ctsm.conf...87H
The contribution of the solar f modes of oscillation to the inversion
of high-degree rotational splitting data is examined. We find that
the f modes play an important role in such inversions as revealed
by the magnitude of their weighting coefficients c i . This may be
attributed to the single-peaked structure of the f-mode kernels,
which is similar to that of the desired averaging kernels and in
contrast to the many-peaked shape of the higher-order kernels. The
high weight placed on the f modes in the inversions raises issues for
observational techniques since the f modes possess modest power levels
and their detection is influenced by the choice of spatial filtering.
Title: Oscillation observations.
Authors: Hill, Frank; Deubner, Franz-Ludwig; Isaak, George
Bibcode: 1991sia..book..329H
Altcode:
This chapter reviews recent observations of solar oscillations. The
oscillations discussed are global and local 5-min p-modes, the 160-min
oscillation and oscillations in the solar atmosphere. Experimental
and data reduction methods are described. Summaries of recent results
are provided, including measurements of frequencies, amplitudes, line
widths and splittings. Other topics include active-region tomography,
solar cycle changes, the chromospheric cavity and diameter measurements.
Title: Effects of spatial filtering on high-ℓ power spectra and
rotational splitting inversions
Authors: Haber, Deborah A.; Hill, Frank; Toomre, Juri
Bibcode: 1991LNP...388..259H
Altcode: 1991ctsm.conf..259H
The effects of the spatial filtering algorithm on the results of an
inversion of high-degree solar oscillation data are examined. In
attempting to isolate sectoral modes, the Fourier transforms in
longitude are accompanied by three different spatial filterings in
the orthogonal direction. The filters are: simple averaging in the
plane of the sky, averaging along lines of constant heliographic
longitude with uniform weighting, and another with weighting based
on appropriate Legendre functions. The choice of spatial filter
changes the distribution of power in the two-dimensional spectrum
of the oscillations, particularly in the f and p 1 ridges. These
variations in the power distribution affect the determination of the
rotational splittings, thereby influencing the results of inversions
which emphasize information contained in the low-order ridges.
Title: A Map of the Horizontal Flows in the Solar Convection Zone
Authors: Hill, Frank
Bibcode: 1990SoPh..128..321H
Altcode: 1990IAUCo.121P.321H
The first map of the horizontal flows as a function of depth and
heliocentric position in the solar convection zone is presented. The
map is inferred from a least-squares smoothness-constrained inversion
of velocities measured from ring diagrams of the solar p-mode
oscillations. The data provide information in four longitude regions
at a latitude just south of the solar equator. The presence of several
features is suggested by the results: A prograde directed longitudinal
jet between the hydrogen and first helium ionization zone, reversing
direction to retrograde below the second helium ionization zone.
Title: Do Active Regions Change the Frequencies Seen in Global
Five-Minute Oscillations of Intermediate Degree?
Authors: Haber, D.; Hill, F.
Bibcode: 1990BAAS...22..856H
Altcode:
No abstract at ADS
Title: The Effect of Large-Scale Flows on Oscillation Ring Diagrams
Authors: Hill, Frank
Bibcode: 1990LNP...367..173H
Altcode: 1990psss.conf..173H
The effect of different flow scenarios on the solar oscillation
ring diagrams is examined. Several combinations of longitudinal and
latitudinal flow components as a function of depth are used to predict
possible distributions of ring positions via the forward problem. The
predicted positions are combined with plausible unperturbed dispersion
relation parameters to produce sets of artificial rings. These rings
are then fitted with ellipses, and the measured ellipse parameters
are compared with observational results. The results indicate that
the data are more compatible with the presence of local maxima in
the depth dependence of both horizontal flow components, rather than
constant slope solutions.
Title: Networks for Helioseismic Observations
Authors: Hill, Frank
Bibcode: 1990ASSL..159..265H
Altcode: 1990insu.conf..265H; 1990IAUCo.121..265H
No abstract at ADS
Title: Solar Oscillation Ring Diagrams and Large-Scale Flows
Authors: Hill, Frank
Bibcode: 1989ApJ...343L..69H
Altcode:
A new analysis that results in the appearance of rings in the power
spectrum of solar oscillations has been used to detect horizontal
flows in two directions on the sun. An analysis of the rings obtained
over four different solar longitude ranges suggests the presence of
large-scale flows with longitudinal variations of about 20 m/s. The
position of these flows are correlated with the location of an active
region.
Title: A Test of a Modified Algorithm for Computing Spherical Harmonic
Coefficients Using an FFT
Authors: Elowitz, Mark; Hill, Frank; Duvall, Thomas L., Jr.
Bibcode: 1989JCoPh..80..506E
Altcode:
No abstract at ADS
Title: The GONG data reduction and analysis system.
Authors: Pintar, J. A.; Andersen, B.; Anderson, E. R.; Armet, D. B.;
Brown, T. M.; Hathaway, D. H.; Hill, F.; Jones, H. P.; GONG Data Team
Bibcode: 1988ESASP.286..217P
Altcode:
Each of the six GONG observing stations will produce three, 16-bit,
256×256 images of the Sun every 60 seconds of sunlight. These
data will be transferred from the observing sites to the GONG Data
Management and Analysis Center (DMAC), in Tucson, on high-density tapes
at a combined rate of over 1 gigabyte per day. The contemporaneous
processing of these data will produce several standard data products
and will require a sustained throughput in excess of 7 megaflops. Peak
rates may exceed 50 megaflops. Archives will accumulate at the rate
of approximately 1 terabyte per year, reaching nearly 3 terabytes in
three years of observing. Researchers will access the data products
with a machine-independent GONG Reduction and Analysis Software
Package (GRASP). Based on the Image Reduction and Analysis Facility
(IRAF), this package will include database facilities and helioseismic
analysis tools. Users may access the data as visitors in Tucson, or
may access DMAC remotely through networks, or may process subsets of
the data at their local institutions using GRASP or other systems of
their choice. Elements of the system will reach the prototype stage
by the end of 1988. Full operation is expected in 1992 when data
acquisition begins.
Title: Oscillation ring diagrams and the thermodynamics of the outer
solar convection zone.
Authors: Hill, Frank
Bibcode: 1988ESASP.286..103H
Altcode: 1988ssls.rept..103H
A recently developed three-dimensional Fourier analysis results in the
appearance of rings in the power spectrum of solar oscillations. These
rings are the cross-sections at constant temporal frequency ω of
trumpet surfaces, and are the analog of the familiar ridges. The shape
of the rings provides information on the local dispersion relationship
of the oscillations expressed in a simple power law. The exponent
and constant in the power law are related to the thermodynamics of
the region in the solar interior where the waves propagate. Asymptotic
expressions for high-degree modes, coupled with the assumption that the
upper part of the solar envelope is an adiabatic polytrope, predict
that the exponent should be 1/2. The constant should depend on the
polytropic index of the envelope, and on a phase factor resulting
from wave leakage. Analysis of over 5000 rings results in an observed
exponent ranging between 0.3 and 0.6, a polytropic index between 1
and 7, and a phase factor between -1.5 and 5.
Title: The GONG site survey.
Authors: Hill, F.; Ambastha, A.; Ball, W.; Duhalde, O.; Farris,
D.; Fischer, G.; Hieda, L.; Zhen, Huang; Ingram, B.; Jackson, P.;
Jones, H.; Jones, W.; Kennewell, J.; Kunkel, W.; Kupke, R.; Labonte,
B.; Leibacher, J.; Libbrecht, K.; Lu, W.; Morrison, L.; Odell, C.;
Pallé, P.; Saá, O.; Sousa, E.; Stebbins, T.; Xiao, Suming; GONG
Site Survey Team
Bibcode: 1988ESASP.286..209H
Altcode:
The Global Oscillation Network Group (GONG) project is planning to
place six observing stations around the world to observe the solar
oscillations as continuously as possible. This paper describes the
procedures that are being used to select the six sites. The latest
results of measurements of cloud cover obtained by networks of 6
(out of 10) radiometers show a duty cycle of over 93%, with the first
diurnal sidelobe in the window power spectrum suppressed by a factor
of 400. The results are in good agreement with the predictions of a
computer model of the expected cloud cover at individual sites.
Title: Local effects of a major flare on solar five-minute
oscillations.
Authors: Haber, D. A.; Toomre, J.; Hill, Frank; Gough, Douglas O.
Bibcode: 1988ESASP.286..301H
Altcode: 1988ssls.rept..301H
Doppler velocity images of the full Sun were obtained both during and
after a major white-light flare. These velocities were interpolated onto
a cylindrical coordinate system centered on the flare and decomposed
into radially propagating waves defined by Hankel functions. For
a similar analysis of quiet Sun regions the authors find fairly
comparable power in incoming and outgoing waves irrespective of the
presence of the flare. However, for the flaring region, there is 14%
greater power in incoming as opposed to outgoing waves when there
is no flare, but 5% greater power in outgoing than in incoming waves
during the flare. This result suggests that the flare may have excited
outgoing waves which counteracted the more usual absorption of incoming
acoustic waves by sunspots.
Title: Rings and Trumpets---Three-dimensional Power Spectra of
Solar Oscillations
Authors: Hill, Frank
Bibcode: 1988ApJ...333..996H
Altcode:
When slices of characteristic 'trumpet' surfaces visible in
three-dimensional power spectra of the Doppler shifts observed on
the solar surface are taken at constant temporal frequency, the
cross sections form 'rings'. Analysis of the shape and position of
these rings provides information on the horizontal flow field and
the thermodynamic structure below the photosphere. The relationship
between the parameters of an elliptical approximation to the rings
and the subphotospheric state is derived, and a numerical simulation
is presented. A preliminary application to real data suggests the
presence of a flow of 100 m/s directed from the equator toward the
south pole. A comparison of the velocities inferred from a single
ring obtained at different longitudes shows variations of 20-40 m/s,
suggesting that large-scale convection is not azimuthally symmetric.
Title: On the Expansion of the Rotational Eigenfrequencies in
Legendre Polynomials
Authors: Durney, Bernard R.; Hill, Frank; Goode, Philip R.
Bibcode: 1988ApJ...326..486D
Altcode:
In the context of helioseismology, it has become customary to fit
data using Δv(n, l, m) ≡ v(n, l, m) - v(n, l) = L ΣN
i=0 ai Pi(-m/L) (Duvall, Harvey,
and Pomerantz) where v is the frequency of the nth p-mode averaged
over m, the Pi are Legendre polynomials and L = [(l +
1)l]1/2. It is shown here that, instead, it is advantageous
to use the following expansion for v(n, l, m) - v(n, l): v(n, l, m) -
v(n, l) = m Σ N i=0 bi Pi
(m/L). In this case the bi's are simply related to the
coefficients which determine the angular velocity, leading to the
expectation that we can more accurately determine the internal rotation
of the Sun from the extant helioseismological data.
Title: The Global Oscillation Network Group (GONG)
Authors: Harvey, J. W.; Hill, F.; Kennedy, J. R.; Leibacher, J. W.;
Livingston, W. C.
Bibcode: 1988AdSpR...8k.117H
Altcode: 1988AdSpR...8..117H
As a community facility, the National Solar Observatory is establishing
a six-site ground-based solar observing network around the world. This
Global Oscillation Network Group (GONG) aims at essentially continuous
imaged observations of global solar oscillations for a minimum of three
years. Resulting data will be used to study the solar interior using
helioseismology. The heart of the observing instrument is a thermally
compensated, wide-field Fourier Techometer operated automatically by a
computer control system. Data from the six GONG stations is expected to
total over one gigabyte per day. Pipeline processing of these data will
proceed contemporaneously, reducing the raw data to several standard
product data sets at sustained throughput rates in excess of 6 megaflops
and peak rates that may exceed 50 megaflops. In support of widespread
scientific participation, software analysis tools based on the Image
Reduction and Analysis Facility (IRAF) and data distribution will be
provided. Science teams have been formed and are actively supporting
the project. The field instrument will reach the prototype stage in
early 1989 and full operation of the network is expected in 1992. Operated by the Association of Universities for Research in Astronomy,
Inc., under contract to the National Science Foundation.
Title: Solar Equatorial Rotation Rate Inferred from Inversion of
Frequency Splitting of High-Degree Modes
Authors: Hill, F.; Gough, D. O.; Toomre, J.; Haber, D. A.
Bibcode: 1988IAUS..123...45H
Altcode:
The equatorial rotation rate has been inferred as a function of depth
through the outer 16 Mm of the Sun from observations of high-degree
five-minute oscillations. The results imply that the solar rotation
rate increases with depth by 0.023 μHz reaching a maximum at about
2 Mm below the surface, then decreases by 0.037 μHz down to 16 Mm.
Title: Performance of a Stabilized Fabry-Perot Solar Analyzer
Authors: Rust, D. M.; Appourchaux, T.; Hill, F.
Bibcode: 1988IAUS..123..475R
Altcode:
A unique solar lineshift analyzer described by Rust, Burton and Leistner
(1986) has been used to study solar oscillations. Operation of this
"Stabilized Solar Analyzer" depends on the electro-optic effect in
crystalline lithium niobate, the substrate of the solid Fabry-Perot
etalon. For 10 days in February, 1986, at the Vacuum Tower Telescope
of the Sacramento Peak Observatory, the authors obtained full-disk
observations of the solar oscillations.
Title: Rotation in the Solar Convection Zone Inferred from Fabry-Perot
Observations of the 5-MIN Oscillations
Authors: Hill, F.; Rust, D. M.; Appourchaux, T.
Bibcode: 1988IAUS..123...49H
Altcode:
Full disk observations of the 5-min solar oscillations have been
obtained with a lithium niobate Fabry-Perot filter. The equatorial
solar rotation rate as a function of depth has been inferred from the
sectoral modes of oscillation using the Backus-Gilbert optimal averaging
inversion method. The results show a rotation rate that slowly decreases
over the depths of 15 to 56 Mm below the photosphere. The results are
in agreement with the previous Duvall-Harvey observations.
Title: Response of the Solar 5-MINUTE Oscillations to a Major Flare
Authors: Haber, D. A.; Toomre, J.; Hill, F.
Bibcode: 1988IAUS..123...59H
Altcode:
Solar five-minute oscillations of intermediate-degree l were observed
both before and after a very strong white-light flare. The data
were projected onto both equatorial and polar sectoral modes and
Fourier transformed in time. Comparing the resulting power spectra,
the authors find a substantial increase in power in the p5
ridge of the equatorial modes on the day after the flare. When data
from all the ridges are considered, there is an average increase in
power of only a few percent the day after the flare.
Title: Observations of Solar Oscillations with a Fabry-Perot Etalon
Authors: Rust, D. M.; Hill, F.; Appourchaux, T.
Bibcode: 1987BAAS...19R.933R
Altcode:
No abstract at ADS
Title: Subphotospheric Flows Inferred from Three-Dimensional
ky-k-ω Diagrams of High Degree Oscillations
Authors: Hill, Frank
Bibcode: 1987BAAS...19..934H
Altcode:
No abstract at ADS
Title: The Equatorial Rotation Rate in the Solar Convection Zone
Authors: Hill, Frank
Bibcode: 1987ASSL..137...45H
Altcode: 1987isav.symp...45H
The equatorial sidereal rotation rate is presented as a function of
depth Z in the outer solar convection zone, as inferred from five
different studies using helioseismology. Consideration is given to
the implications for dynamo and convection theories. It is believed
that the rise in the angular solar velocity in the very outer edge
of the convection zone represents a thin boundary layer within which
conservation of angular momentum is the dominant process.
Title: Local Response of the Five-Minute Oscillations to a Major
Solar Flare
Authors: Haber, D. A.; Toomre, J.; Hill, F.; Gough, D. O.
Bibcode: 1986BAAS...18Q1011H
Altcode:
No abstract at ADS
Title: Influence of spatial filtering on possible anisotropies in
solar oscillations.
Authors: Hill, Frank; Haber, Deborah A.; Toomre, Juri; November,
Laurence J.
Bibcode: 1986ASIC..169...85H
Altcode: 1986ssds.proc...85H
The authors have used full disk Doppler observations of solar
oscillations to compare the amplitudes of sectoral modes propagating
along the equator with those of similar modes propagating along a
great circle aligned with the poles. They find that the amplitudes are
generally not equal for the two classes of modes, but the results are
sensitive to analysis procedures attempting to isolate the different
modes of oscillation. Spatial filtering of the data using spherical
harmonics suggests that greater amplitudes are associated with "polar"
sectoral modes than with "equatorial" sectoral modes.
Title: A Simple Irradiance Monitor for Testing Solar Global
Oscillation Network Sites
Authors: Fischer, G.; Hill, F.; Jones, W.; Leibacher, J.; McCurnin,
W.; Stebbins, R.; Wagner, J.
Bibcode: 1986SoPh..103...33F
Altcode:
We describe a simple irradiance monitor intended for use in assessing
the suitability of candidate sites for a worldwide network of small
solar telescopes. The network will observe the Sun as continuously
as possible in order to provide high quality solar oscillation data
with low diurnal sidelobe contamination and high temporal frequency
resolution.
Title: Changes in Subsurface Horizontal Velocities Inferred from
Observations of High Degree 5-Minute Solar Oscillations
Authors: Hill, F.; Toomre, J.; Gough, D. O.
Bibcode: 1985BAAS...17..643H
Altcode:
No abstract at ADS
Title: On the Expected Performance of a Solar Oscillation Network
Authors: Hill, F.; Newkirk, G., Jr.
Bibcode: 1985SoPh...95..201H
Altcode:
We have estimated the performance of several hypothetical ground-based
networks intended to provide continuous observations of solar
oscillations for one year. These networks were composed of from 2 to
6 stations distributed both in longitude and between the northern and
southern hemispheres. Weather patterns at each site were simulated
using a 4 parameter climate model and the results analyzed to yield
the duty cycle of the representative networks.
Title: Sensitivity of inferred subphotospheric velocity field to
mode selection, analysis technique and noise.
Authors: Hill, F.; Gough, D.; Toomre, J.
Bibcode: 1984sses.nasa...95H
Altcode: 1984sss..conf...95H
The horizontal velocity immediately below the photosphere can be
inferred from observations of high-degree solar oscillations by an
optimal-averaging inversion technique. The authors investigate the
sensitivity of the results to various details of both the inversion
and the determination of the frequencies. The results are shown to be
quite stable to the choice of most parameters, suggesting that this
procedure produces reliable estimates of the subsurface velocity.
Title: The effects of a nearly 100% duty cycle on observations of
solar oscillations.
Authors: Hill, F.
Bibcode: 1984sses.nasa..271H
Altcode: 1984sss..conf..271H
Power spectra of window functions with duty cycles between 80% and
99% and with randomly spaced gaps are computed and their effect on
observations of solar oscillations are discussed. It is found that
for all the cases considered, observations of solar oscillations would
not be severely impacted as long as the gap structure is random rather
than periodic.
Title: The effects of image motion on the l-ν diagram.
Authors: Hill, F.
Bibcode: 1984sses.nasa..255H
Altcode: 1984sss..conf..255H
A simple two dimensional (x,t) model of the solar oscillatory velocity
field is subjected to a form of differential image motion. This image
motion is meant to approximately model the effect of the Earth's
atmosphere on observations of high degree solar oscillations. The
distorted velocity field is analyzed to provide the apparent frequencies
of the modes. It is shown that the image motion can produce a
discrepancy of as much as 12 micro Hz.
Title: Attempt to measure the solar subsurface velocity
Authors: Hill, F.; Gough, D.; Toomre, J.
Bibcode: 1984MmSAI..55..153H
Altcode:
Five-minute oscillation modes are advected by horizontal velocities
below the solar surface, and thus can be used as probes of rotation
and large-scale convective flows. Results of inverse theory applied
to observations of high-degree modes carried out on six separate days
reveal variations in horizontal velocities with depth from day to day
that may be the result of giant convection cells, through noise in
the data makes this interpretation somewhat tentative.
Title: Simulation of Effects of Atmospheric Seeing on Observations
of Solar Five-Minute Oscillations
Authors: Merryfield, W. J.; Toomre, J.; Hill, F.; Gough, D. O.
Bibcode: 1984BAAS...16..532M
Altcode:
No abstract at ADS
Title: Horizontal Velocities in the Solar Convection Zone Inferred
from High Degree 5-Minute Oscillations
Authors: Hill, F.; Toomre, J.; Gough, D. O.
Bibcode: 1984BAAS...16R.451H
Altcode: 1984BAAS...16..451H
No abstract at ADS
Title: Effects of Spherical Harmonic Filtering on Analysis of
Five-Minute Solar Oscillations of High-Degree
Authors: Haber, D.; Toomre, J.; Hill, F.
Bibcode: 1984BAAS...16Q.533H
Altcode:
No abstract at ADS
Title: On the Determination of the Lifetime of Vertical Velocity
Patterns in Mesogranulation and Supergranulation
Authors: Hill, F.; Toomri, J.; November, L. J.; Gebbie, K. B.
Bibcode: 1984ssdp.conf..160H
Altcode:
Observational studies of the vertical velocities of mesogranulation
and supergranulation provide conflicting results for the lifetimes
of these patterns when analyzed by two different methods. Visual
inspection of the velocity images suggests that mesogranulation has
a lifetime in excess of 2 hours, while cross-correlation methods
imply a lifetime of only about 40 min. For supergranulation, the
correlation technique yields a lifetime of 2.7 hours, far short of the
24 hours found by many other studies considering network structures
or horizontal velocities. The authors consider the possible reasons
for such discrepancies.
Title: Variability in the power spectrum of solar five-minute
oscillations
Authors: Hill, F.; Toomre, J.; November, L. J.
Bibcode: 1983SoPh...82..411H
Altcode: 1983IAUCo..66..411H
Two-dimensional power spectra of solar five-minute oscillations
display prominent ridge structures in (k, ω) space, where k is the
horizontal wavenumber and ω is the temporal frequency. The positions
of these ridges in k and ω can be used to probe temperature and
velocity structures in the subphotosphere. We have been carrying out a
continuing program of observations of five-minute oscillations with the
diode array instrument on the vacuum tower telescope at Sacramento Peak
Observatory (SPO). We have sought to establish whether power spectra
taken on separate days show shifts in ridge locations; these may arise
from different velocity and temperature patterns having been brought
into our sampling region by solar rotation. Power spectra have been
obtained for six days of observations of Doppler velocities using the
MgIλ5173 and FeIλ5434 spectral lines. Each data set covers 8 to 11
hr in time and samples a region 256″ × 1024″ in spatial extent,
with a spatial resolution of 2″ and temporal sampling of 65 s. We have
detected shifts in ridge locations between certain data sets which are
statistically significant. The character of these displacements when
analyzed in terms of eastward and westward propagating waves implies
that changes have occurred in both temperature and horizontal velocity
fields underlying our observing window. We estimate the magnitude of
the velocity changes to be on the order of 100 m s-1; we may
be detecting the effects of large-scale convection akin to giant cells.
Title: Relation of Ephemeral Magnetic Regions to the Low Amplitude
Branch of Persistent Vertical Velocities
Authors: Gebbie, K. B.; Toomre, J.; Haber, D. A.; Hill, F.; Simon,
G. W.; November, L. J.; Gurman, J. B.; Shine, R. A.
Bibcode: 1982BAAS...14R.939G
Altcode: 1982BAAS...14..939G
No abstract at ADS
Title: Solar Five-Minute Oscillations, Subsurface Velocities and
Inverse Theory
Authors: Gough, D. O.; Hill, F.; Toomre, J.
Bibcode: 1982BAAS...14..938G
Altcode:
No abstract at ADS
Title: Oscillatory probes and direct observations of solar convection
Authors: Hill, Frank
Bibcode: 1982PhDT.......131H
Altcode:
No abstract at ADS
Title: Oscillatory probes and direct observations of solar convection
Authors: Hill, Frank
Bibcode: 1982opdo.book.....H
Altcode:
No abstract at ADS
Title: Solar 5-MINUTE Oscillations as Probes of Structure in the
Subphotosphere
Authors: Hill, F.; Toomre, J.; November, L. J.
Bibcode: 1982pccv.conf..139H
Altcode:
No abstract at ADS
Title: Oscillatory Probes and Direct Observations of Solar Convection.
Authors: Hill, F.
Bibcode: 1982PhDT.........2H
Altcode:
Three different observational techniques are used to study solar
convection directly in the atmosphere and by inference below the
surface: variations in the spatial and temporal (k-(omega)) power
diagram for the five-minute oscillations are used to infer changes
in subsurface velocity and thermal fields; observations of vertical
velocities obtained at Sacramento Peak Observatory (SPO) are utilized
to estimate the lifetime of mesogranulation; and coordinated Solar
Maximum Mission (SMM) satellite and SPO ground-based observations
are used to study persistent flows over a range of heights in
the solar atmosphere. Comparison of power in k-(omega) diagrams
obtained on different days at SPO reveals shifts in the positions
of the ridges that may be due to different large-scale subsurface
temperature and velocity fields being brought beneath the observing
window by solar rotation. These shifts appear to be periodic in time,
recurring after 5 and 27 days, suggesting that they are caused by
a flow pattern with a horizontal scale of 800 Mm and a lifetime of
at least one month. Such patterns may be due to giant cells whose
vertical velocities may be deflected into strong horizontal flows
below the photosphere. Analysis of a series of suitably time-averaged
and spatially filtered observations of vertical velocities obtained
at SPO in the Mg I (lamda)5173 spectral line suggests that the
lifetime of mesogranulation is at least two hours, though correlation
estimates yield shorter lifetimes. Differences in the estimates may
be due to differential distortions of the velocity pattern caused
by magnetic field evolution. Comparison of simultaneous velocity
observations carried out with SMM and at SPO shows that steady flows
of supergranular scale are able to penetrate upward at least to the
transition region. The horizontal and vertical components of the flow
both have similar 4 km/s rms amplitudes at the height of formation of
the C IV (lamda)1548 line, implying that little braking of the flow
is occurring in this region. Correlations of intensity and steady
velocity in the transition region show a bimodal pattern which may be
due to a combination of convectively and magnetically controlled flows.
Title: Steady flows in the solar transition region observed with SMM
Authors: Gebbie, K. B.; Hill, F.; November, L. J.; Gurman, J. B.;
Shine, R. A.; Woodgate, B. E.; Athay, R. G.; Tandberg-Hanssen, E. A.;
Toomre, J.; Simon, G. W.
Bibcode: 1981ApJ...251L.115G
Altcode:
Steady flows in the quiet solar transition region have been observed
with the Ultraviolet Spectrometer and Polarimeter experiment on the
Solar Maximum Mission (SMM) satellite. The persistent vertical motions
seen at disk center have spatial rms amplitudes of 1.4 km/s in the C
II line, 3.9 km/s in Si IV, and 4.2 km/s in C IV. The amplitudes of
the more horizontal flows seen toward the limb tend to be somewhat
higher. Plots of steady vertical velocity versus intensity seen at
disk center in Si IV and C IV show two distinct branches.
Title: The use of climatological and synoptic data for forecasting
orographic enhancement of rainfall
Authors: Hill, F. F.; Browning, K. A.
Bibcode: 1981ESASP.165..207H
Altcode: 1981nmos.conf..207H
No abstract at ADS
Title: Solar Five-Minute Oscillations as Probes of Velocity and
Temperature Fields
Authors: Hill, F.; Toomre, J.; November, L. J.
Bibcode: 1981BAAS...13Q.860H
Altcode: 1981BAAS...13..860H
No abstract at ADS
Title: Height Dependence of Steady Flows Determined from Coordinated
SMM and SPO Observations
Authors: Gebbie, K. B.; Hill, F.; Toomre, J.; November, L. J.; Simon,
G. W.; Gurman, J. B.; Shine, R. A.; Woodgate, B. E.
Bibcode: 1981BAAS...13..914G
Altcode:
No abstract at ADS
Title: OSO 8 Observations of Coherent Chromospheric Oscillations
Authors: Hill, F.; Toomre, J.; November, L. J.
Bibcode: 1980BAAS...12R.894H
Altcode:
No abstract at ADS
Title: Steady Flows in the Solar Transition Region Observed with
the UVSP Experiment on SMM
Authors: Gebbie, K. B.; Hill, F.; Toomre, J.; November, L. J.; Simon,
G. W.; Athay, R. G.; Bruner, E. C.; Rehse, R.; Gurman, J. B.; Shine,
R. A.; Woodgate, B. E.; Tandberg-Hanssen, E. A.
Bibcode: 1980BAAS...12..907G
Altcode:
No abstract at ADS
Title: The Lifetime of Solar Mesogranulation
Authors: November, L. J.; Gebbie, K. B.; Hill, F.; Toomre, J.; Simon,
G. W.
Bibcode: 1980BAAS...12..895N
Altcode:
No abstract at ADS
Title: The circumstellar envelope of IRC +10216.
Authors: Kwan, J.; Hill, F.
Bibcode: 1977ApJ...215..781K
Altcode:
The circumstellar envelope of IRC +10216 is modeled by assuming
steady spherically symmetric mass loss from the star. The mass outflow
is presumed to be due to radiation pressure on grains formed in the
stellar atmosphere and momentum-coupled to the gas, and the temperature
of the expanding gas is determined by taking account of cooling due
to free expansion and molecular emission as well as heating resulting
from gas-dust collisions. The excitation of molecular emission from CO,
(C-13)O, HCN, and H(C-13)N is computed and compared with observations in
order to obtain information about the mass-loss rate and the molecular
abundances. For a distance of 200 pc, a mass-loss rate of 0.00002
solar mass per yr is derived along with a CO/H2 abundance ratio of
0.0008, a CO/(C-13)O isotope ratio of 35, and a momentum-transfer
efficiency factor (averaged over the continuum energy distribution)
of 0.013. Uncertainties in these results and their dependence on the
assumed distance are discussed.