braun

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Author name code: braun
ADS astronomy entries on 2022-09-14
author:"Braun, Douglas C."

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Title: Performance of the X-Calibur hard X-ray polarimetry mission
during its 2018/19 long-duration balloon flight
Authors: Abarr, Q.; Beheshtipour, B.; Beilicke, M.; Bose, R.;
Braun, D.; de Geronimo, G.; Dowkontt, P.; Errando, M.; Gadson, T.;
Guarino, V.; Heatwole, S.; Hossen, M.; Iyer, N.; Kislat, F.; Kiss,
M.; Kitaguchi, T.; Krawczynski, H.; Lanzi, J.; Li, S.; Lisalda, L.;
Okajima, T.; Pearce, M.; Peterson, Z.; Press, L.; Rauch, B.; Simburger,
G.; Stuchlik, D.; Takahashi, H.; Tang, J.; Uchida, N.; West, A.
2022APh...14302749A Altcode: 2022arXiv220409761A
X-Calibur is a balloon-borne telescope that measures the polarization of
high-energy X-rays in the 15-50 keV energy range. The instrument makes
use of the fact that X-rays scatter preferentially perpendicular to the
polarization direction. A beryllium scattering element surrounded by
pixellated CZT detectors is located at the focal point of the InFOCμS
hard X-ray mirror. The instrument was launched for a long-duration
balloon (LDB) flight from McMurdo (Antarctica) on December 29, 2018,
and obtained the first constraints of the hard X-ray polarization of
an accretion-powered pulsar. Here, we describe the characterization
and calibration of the instrument on the ground and its performance
during the flight, as well as simulations of particle backgrounds and
a comparison to measured rates. The pointing system and polarimeter
achieved the excellent projected performance. The energy detection
threshold for the anticoincidence system was found to be higher than
expected and it exhibited unanticipated dead time. Both issues will
be remedied for future flights. Overall, the mission performance was
nominal, and results will inform the design of the follow-up mission
XL-Calibur, which is scheduled to be launched in summer 2022.

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Title: SuperTIGER Abundances of Galactic Cosmic Rays for the Atomic
Number (Z) Interval 30 to 56
Authors: Walsh, N. E.; Akaike, Y.; Binns, W. R.; Bose, R. G.; Brandt,
T. J.; Braun, D.; Cannady, N.; Dowkontt, P. F.; Hams, T.; Israel,
M. H.; Krizmanic, J. F.; Labrador, A. W.; Link, J. T.; Mewaldt, R. A.;
Mitchell, J. W.; Murphy, R. P.; Rauch, B. F.; Sakai, K.; Sasaki, M.;
Simburger, G.; Stone, E. C.; Tatoli, T.; Ward, J. E.; Wiedenbeck,
M. E.; Zober, W. V.; deNolfo, G. A.
2022icrc.confE.118W Altcode: 2022PoS...395E.118W
No abstract at ADS

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Title: Erratum: "Probing the Solar Meridional Circulation Using
Fourier Legendre Decomposition" (2021, ApJ, 911, 54)
Authors: Braun, D. C.; Birch, A. C.; Fan, Y.
2022ApJ...924..140B Altcode:
No abstract at ADS

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

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Title: Probing the Solar Meridional Circulation Using Fourier
Legendre Decomposition
Authors: Braun, D. C.; Birch, A. C.; Fan, Y.
2021ApJ...911...54B Altcode: 2021arXiv210302499B
We apply the helioseismic methodology of Fourier Legendre decomposition
to 88 months of Dopplergrams obtained by the Helioseismic and Magnetic
Imager (HMI) as the basis of inferring the depth variation of the mean
meridional flow, as averaged between 20° and 60° latitude and in
time, in both the northern and southern hemispheres. We develop and
apply control procedures designed to assess and remove center-to-limb
artifacts using measurements obtained by performing the analysis with
respect to artificial poles at the east and west limbs. Forward modeling
is carried out using sensitivity functions proportional to the mode
kinetic energy density to evaluate the consistency of the corrected
frequency shifts with models of the depth variation of the meridional
circulation in the top half of the convection zone. The results, taken
at face value, imply substantial differences between the meridional
circulation in the northern and southern hemispheres. The inferred
presence of a return (equatorward propagating) flow at a depth of
approximately 40 Mm below the photosphere in the northern hemisphere is
surprising and appears to be inconsistent with many other helioseismic
analyses. This discrepancy may be the result of the inadequacy of our
methodology to remove systematic errors in HMI data. Our results appear
to be at least qualitatively similar to those by Gizon et al., which
point to an anomaly in HMI data that is not present in MDI or GONG data.

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

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Title: Submerged Sources of Transient Acoustic Emission from Solar
Flares
Authors: Lindsey, Charles; Buitrago-Casas, J. C.; Martínez Oliveros,
Juan Carlos; Braun, Douglas; Martínez, Angel D.; Quintero Ortega,
Valeria; Calvo-Mozo, Benjamín; Donea, Alina-Catalina
2020ApJ...901L...9L Altcode:
We report the discovery of ultra-impulsive acoustic emission from
a solar flare, emission with a seismic signature that indicates
submersion of its source approximately a Mm beneath the photosphere
of the active region that hosted the flare. Just over two decades ago
V. V. Zharkova and A. G. Kosovichev discovered the first acoustic
transient released into the Sun's interior by a solar flare. These
acoustic waves, refracted back upward to the solar surface after
their release, make conspicuous Doppler ripples spreading outward
from the flaring region that tell us a lot about their sources. The
mechanism by which these transients are driven has stubbornly eluded
our understanding. Some of the source regions, for example, are devoid
of secondary Doppler, magnetic, or thermal disturbances in the outer
atmosphere of the source regions that would signify the driving agent
of an intense seismic transient in the outer atmosphere. In this
study, we have applied helioseismic holography, a diagnostic based
upon standard wave optics, to reconstruct a 3D image of the sources
of acoustic waves emanating from the M9.3-class flare of 2011 July
30. These images contain a source component that is submerged a full
Mm beneath the active-region photosphere. The signature of acoustic
sources this deep in the solar interior opens new considerations into
the physics that must be involved in transient acoustic emission from
flares—and possibly of flare physics at large. We develop analogies
to seismicity remotely triggered by tremors from distant earthquakes,
and consider prospects of new insight into the architecture of magnetic
flux beneath flaring active regions.

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Title: Average motion of emerging solar active region
polarities. II. Joy's law
Authors: Schunker, H.; Baumgartner, C.; Birch, A. C.; Cameron, R. H.;
Braun, D. C.; Gizon, L.
2020A&A...640A.116S Altcode: 2020arXiv200605565S
Context. The tilt of solar active regions described by Joy's law
is essential for converting a toroidal field to a poloidal field in
Babcock-Leighton dynamo models. In thin flux tube models the Coriolis
force causes what we observe as Joy's law, acting on east-west flows
as they rise towards the surface. Aims: Our goal is to measure
the evolution of the average tilt angle of hundreds of active regions
as they emerge, so that we can constrain the origins of Joy's law. Methods: We measured the tilt angle of the primary bipoles in 153
emerging active regions (EARs) in the Solar Dynamics Observatory
Helioseismic Emerging Active Region survey. We used line-of-sight
magnetic field measurements averaged over 6 h to define the polarities
and measure the tilt angle up to four days after emergence. 
Results: We find that at the time of emergence the polarities are on
average aligned east-west, and that neither the separation nor the
tilt depends on latitude. We do find, however, that EARs at higher
latitudes have a faster north-south separation speed than those closer
to the equator at the emergence time. After emergence, the tilt
angle increases and Joy's law is evident about two days later. The
scatter in the tilt angle is independent of flux until about one day
after emergence, when we find that higher-flux regions have a smaller
scatter in tilt angle than lower-flux regions. Conclusions:
Our finding that active regions emerge with an east-west alignment
is consistent with earlier observations, but is still surprising
since thin flux tube models predict that tilt angles of rising flux
tubes are generated below the surface. Previously reported tilt angle
relaxation of deeply anchored flux tubes can be largely explained
by the change in east-west separation. We conclude that Joy's law is
caused by an inherent north-south separation speed present when the
flux first reaches the surface, and that the scatter in the tilt angle
is consistent with buffeting of the polarities by supergranulation.

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Title: Majorana representation for mixed states
Authors: Serrano-Ensástiga, E.; Braun, D.
2020PhRvA.101b2332S Altcode: 2019arXiv190907740S
We generalize the Majorana stellar representation of spin-s pure states
to mixed states, and in general to any Hermitian operator, defining
a bijective correspondence between three spaces: the spin-density
matrices, a projective space of homogeneous polynomials of four
variables, and a set of equivalence classes of points (constellations)
on spheres of different radii. The representation behaves well under
rotations by construction, and also under partial traces where the
reduced density matrices inherit their constellation classes from
the original state ρ . We express several concepts and operations
related to density matrices in terms of the corresponding polynomials,
such as the anticoherence criterion and the tensor representation of
spin-s states described in Giraud et al. [Phys. Rev. Lett. 114, 080401
(2015)]., 10.1103/PhysRevLett.114.080401

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Title: Probing the Variation with Depth of the Solar Meridional
Circulation Using Legendre Function Decomposition
Authors: Braun, D. C.; Birch, A.; Fan, Y.
2020ASSP...57..125B Altcode:
We apply the helioseismic methodology of Legendre Function Decomposition
to 7.5 years of Dopplergrams obtained by the Helioseismic and
Magnetic Imager (HMI) as the basis of inferring the depth variation
of the meridional flow between 20∘ and 60∘
latitude in both hemispheres. We assess and remove center-to-limb
artifacts using measurements obtained by applying the procedure to
pseudo poles at the east and west limbs. Forward modeling is carried
out to evaluate the consistency of the corrected frequency shifts
with models of the depth variation of the meridional circulation in
the top half of the convection zone. The observations are consistent
with a return flow in the northern hemisphere below about 40 Mm depth,
but no obvious return flow in the south.

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Title: Average surface flows before the formation of solar active
regions and their relationship to the supergranulation pattern
Authors: Birch, A. C.; Schunker, H.; Braun, D. C.; Gizon, L.
2019A&A...628A..37B Altcode:
Context. The emergence of solar active regions is an important but
poorly understood aspect of the solar dynamo. Aims: Knowledge
of the flows associated with the rise of active-region-forming
magnetic concentrations through the near-surface layers will help
determine the mechanisms of active region formation. Methods:
We used helioseismic holography and granulation tracking to measure
the horizontal flows at the surface that precede the emergence of
active regions. We then averaged these flows over about sixty emerging
active regions to reduce the noise, selecting active regions that
emerge into relatively quiet Sun. To help interpret the results,
we constructed a simple model flow field by generating synthetic
"emergence locations" that are probabilistically related to the
locations of supergranulation-scale convergence regions in the quiet
Sun. Results: The flow maps obtained from helioseismology and
granulation tracking are very similar (correlation coefficients for
single maps around 0.96). We find that active region emergence is,
on average, preceded by converging horizontal flows of amplitude
about 40 m s-1. The convergence region extends over about
40 Mm in the east-west direction and about 20 Mm in the north-south
direction and is centered in the retrograde direction relative to the
emergence location. This flow pattern is largely reproduced by a model
in which active region emergence occurs preferentially in the prograde
direction relative to supergranulation inflows. Conclusions:
Averaging over many active regions reveals a statistically significant
pattern of near-surface flows prior to emergence. The qualitative
success of our simple model suggests that rising flux concentrations
and supergranule-scale flows interact during the emergence process.

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Title: Probing the Variation with Depth of the Solar Meridional
Circulation using Legendre Function Decomposition
Authors: Braun, Douglas; Birch, Aaron C.; Fan, Yuhong
2019AAS...23431802B Altcode:
The solar meridional circulation is a crucial component of magnetic flux
transport and dynamo models. Despite decades of helioseismic study,
no consensus exists regarding the variation of its properties with
depth. It has become apparent that the main challenges consist of 1)
overcoming realization noise with multi-year long datasets, and 2)
the identification and robust removal of systematic center-to-limb
effects. Here we apply the helioseismic methodology of Legendre
Function Decomposition (LFD) to 7.5 years of Dopplergrams obtained by
the Helioseismic and Magnetic Imager (HMI) as the basis of inferring
the depth variation of the meridional flow between 20 and 60 degrees
latitude in both hemispheres. The LFD method, first developed by Braun
and Fan in 1998, probes subsurface flows through the Doppler-effect
induced distortion of power spectra. The procedure is optimized for
the detection of meridional flows and uses Legendre functions (of
the first and second kind) to characterize poleward and equatorward
wave propagation in spherical coordinates. For this study we have
developed control procedures which assess and remove center-to-limb
artifacts, using measurements obtained by applying the procedure to
pseudo poles at the east and west limbs. Forward modeling is carried
out to evaluate the consistency of the corrected LFD frequency shifts
with various assumed models of the depth variation of the meridional
circulation. DB is supported by the NASA Heliophysics Division
(awards 80NSSC18K0066 and 80NSSC18K0068) and by the Solar Terrestrial
program of the National Science Foundation (award AGS-1623844).

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Title: Active Region Flows and their Contribution to Varying Global
Dynamics
Authors: Braun, Douglas
2019AAS...23430210B Altcode:
We explore the general properties of the near-surface dynamics of
solar active regions (ARs) and show how AR flows may contribute
to longitudinally averaged measurements of global properties such
as meridional circulation and torsional oscillations. Helioseismic
holography is applied to HMI Dopplergrams yielding about 5000 flow
measurements of 336 ARs observed by SDO between 2010 and 2014. Ensemble
averages of the AR flows are presented, binned into subsets based on
total magnetic flux. These averages show converging flows, with speeds
about 10 m/s and spanning 10 degrees from the active region centers,
which are apparent for most ARs above the flux limit of our survey at
1021 Mx. Retrograde flows are also detected, with amplitudes
around 10 m/s, which predominantly, but not exclusively, flank the polar
side of the ARs. The high signal-to-noise levels of these averages makes
possible the assessment of individual AR contributions to time-varying
global flows. We demonstrate this for several solar rotations, showing
that individual active regions contribute substantially to these global
flows. This work is supported by the Solar Terrestrial program
of the National Science Foundation (award AGS-1623844) and by the NASA
Heliophysics Division (awards 80NSSC18K0066 and 80NSSC18K0068).

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Title: Average motion of emerging solar active region
polarities. I. Two phases of emergence
Authors: Schunker, H.; Birch, A. C.; Cameron, R. H.; Braun, D. C.;
Gizon, L.; Burston, R. B.
2019A&A...625A..53S Altcode: 2019arXiv190311839S
 Aims: Our goal is to constrain models of active region
formation by tracking the average motion of active region polarity
pairs as they emerge onto the surface. Methods: We measured
the motion of the two main opposite polarities in 153 emerging active
regions using line-of-sight magnetic field observations from the Solar
Dynamics Observatory Helioseismic Emerging Active Region (SDO/HEAR)
survey. We first measured the position of each of the polarities
eight hours after emergence, when they could be clearly identified,
using a feature recognition method. We then tracked their location
forwards and backwards in time. Results: We find that, on
average, the polarities emerge with an east-west orientation and the
separation speed between the polarities increases. At about 0.1 days
after emergence, the average separation speed reaches a peak value
of 229 ± 11 ms-1, and then starts to decrease. About
2.5 days after emergence the polarities stop separating. We also
find that the separation and the separation speed in the east-west
direction are systematically larger for active regions that have
higher flux. The scatter in the location of the polarities increases
from about 5 Mm at the time of emergence to about 15 Mm at two days
after emergence. Conclusions: Our results reveal two phases of
the emergence process defined by the rate of change of the separation
speed as the polarities move apart. Phase 1 begins when the opposite
polarity pairs first appear at the surface, with an east-west alignment
and an increasing separation speed. We define Phase 2 to begin when
the separation speed starts to decrease, and ends when the polarities
have stopped separating. This is consistent with a previous study: the
peak of a flux tube breaks through the surface during Phase 1. During
Phase 2 the magnetic field lines are straightened by magnetic tension,
so that the polarities continue to move apart, until they eventually
lie directly above their anchored subsurface footpoints. The scatter
in the location of the polarities is consistent with the length and
timescales of supergranulation, supporting the idea that convection
buffets the polarities as they separate.

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Title: Flows around Averaged Solar Active Regions
Authors: Braun, D. C.
2019ApJ...873...94B Altcode: 2019arXiv190202298B
We explore the general properties of near-surface flows around
solar active regions. Helioseismic holography is applied to HMI
Dopplergrams yielding nearly 5000 flow measurements of 336 unique
active regions observed by the Solar Dynamics Observatory between 2010
and 2014. Ensemble averages of the flows, over subsets of regions
sorted on the basis of magnetic flux, are performed. These averages
show that converging flows, with speeds of about 10 m s-1
and extending up to 10° from the active-region centers, are prevalent
and have similar properties for all regions with magnetic flux above
1021 Mx. Retrograde flows are also detected, with amplitudes
around 10 m s-1, which predominantly, but not exclusively,
flank the polar side of the active regions. We estimate the expected
contribution of these active-region flows to longitudinal averages
of zonal and meridional flows and demonstrate the plausibility that
they are responsible for at least some component of the time-varying
global-scale flows. The reliability of our flow determination is tested
using publicly available MHD simulations of both quiet-Sun convection
and of a sunspot. While validating the overall methodology in general,
the sunspot simulation demonstrates the presence of artifacts that
may compromise quantitative flow inferences from some helioseismic
measurements.

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Title: Validating Forward Modeling and Inversions of Helioseismic
Holography Measurements
Authors: DeGrave, K.; Braun, D. C.; Birch, A. C.; Crouch, A. D.;
Javornik, B.
2018ApJ...863...34D Altcode: 2018arXiv180703841D
Here, we use synthetic data to explore the performance of forward models
and inverse methods for helioseismic holography. Specifically, this work
presents the first comprehensive test of inverse modeling for flows
using lateral-vantage (deep-focus) holography. We derive sensitivity
functions in the Born approximation. We then use these sensitivity
functions in a series of forward models and inversions of flows from a
publicly available magnetohydrodynamic quiet-Sun simulation. The forward
travel times computed using the kernels generally compare favorably with
measurements obtained by applying holography, in a lateral-vantage
configuration, on a 15 hr time series of artificial Dopplergrams
extracted from the simulation. Inversions for the horizontal flow
components are able to reproduce the flows in the upper 3 Mm of the
domain, but are compromised by noise at greater depths.

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Title: Helioseismic Holography of Flows Around the Averaged Active
Region
Authors: Braun, Douglas C.
2018tess.conf10628B Altcode:
We apply helioseismic holography to HMI observations of several
hundred of the largest active regions and assess the inferred flows
averaged after spatially aligning active regions selected in several
ranges of magnetic flux. This ensemble averaging helps greatly reduce
the dominating effect of the supergranulation signal. We also report
progress on inferring the depth variation of these flows from modeling
the variation of the helioseismic signatures as a function of focus
depth. Some general features of the active-region flows among all flux
groups include 1) compact outflows centered on both magnetic polarities,
and 2) surrounding inflows with greater amplitudes in the trailing
polarities. This work is supported by the NSF Solar Terrestrial
Program through grant AGS-1623844.

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Title: Helioseismic Constraints on the Subsurface Flows of the
Averaged Supergranule
Authors: Braun, Douglas C.; Duvall, Thomas L., Jr.; Felipe, Tobias;
DeGrave, Kyle
2018tess.conf11506B Altcode:
We report progress on constraining the subsurface flow properties
of supergranulation from helioseismic holography applied to HMI/SDO
observations of over 63,000 individual supergranules. First, using
surface-focused measurements, we confirm the advantages of broader
phase-speed filters in reducing diffraction effects, noted by Duvall
and collaborators in prior time-distance analyses. Second, we expand
the type of measurements to include deep-focusing geometries. Third,
we compare all measurements with predictions made using numerical
wave-propagation simulations performed with the 3D MANCHA code using
a number of prescribed flow patterns. These model flows include those
inferred from prior time-distance analyses as well as a model based
on results of recent fully-convective MURaM-based computations. While
the model predictions are in general qualitative agreement with the
ensemble averaged measurements, no single model is fully consistent
with the complete set of measurements. This suggests there is room
for improvement in constraining the subsurface flows. This work
is supported by NASA grant 80NSSC18K0068 awarded to NWRA, as well as
by the NASA High-End Computing program at Ames Research Center.

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Title: EMIC wave events during the four QARBM challenge intervals
Authors: Engebretson, M. J.; Posch, J. L.; Braun, D.; Li, W.;
Angelopoulos, V.; Kellerman, A. C.; Kletzing, C.; Lessard, M.; Mann,
I. R.; Tero, R.; Shiokawa, K.; Wygant, J. R.
2017AGUFMSM51B2433E Altcode:
We present observations of EMIC waves from multiple data sources
during the four GEM challenge events in 2013 selected by the GEM
focus group on Quantitative Assessment of Radiation Belt Modeling:
March 17-18 (Stormtime Enhancement), May 31-June 2 (Stormtime Dropout),
September 19-20 (Non-storm Enhancement), and September 23-25 (Non-storm
Dropout). Observations include EMIC wave data from the Van Allen Probes
and THEMIS spacecraft in the inner magnetosphere and from several
arrays of ground-based search coil magnetometers worldwide, as well as
localized ring current proton precipitation data from the low-altitude
POES spacecraft. Each of these data sets provides only limited spatial
coverage, but their combination reveals consistent occurrence patterns,
which are then used to evaluate the effectiveness of EMIC waves in
causing dropouts of radiation belt electrons during these GEM events.

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Title: Nightside High Latitude Magnetic Impulse Events
Authors: Engebretson, M. J.; Connors, M. G.; Braun, D.; Posch, J. L.;
Kaur, M.; Guillon, S.; Hartinger, M.; Kim, H.; Behlke, R.; Reiter,
K.; Jackel, B. J.; Russell, C. T.
2017AGUFMSM31B2629E Altcode:
High latitude Magnetic Impulse Events (MIEs), isolated pulses with
periods 5-10 min, were first noted in ground-based magnetometer
data near local noon, and are now understood to be signatures of
transient pressure increases in the solar wind (sudden impulses -
SIs) and/or in the ion foreshock (traveling convection vortex events
- TCVs). However, solitary pulses with considerably larger amplitude
(ΔB up to 1500 nT) have often been observed in the night sector at
these same latitudes. These events are not directly associated with
transient external pressure increases, and are often large enough
to produce significant ground induced currents. Although many night
sector MIEs occur in association with substorm signatures, others
appear to be very isolated. We present here a survey of intense MIE
events identified in magnetometer data from the AUTUMNX and MACCS
arrays in eastern Arctic Canada at all local times between July 1,
2014 and June 30, 2017. We also show maps of horizontal and vertical
perturbations and maximum dB/dt values, as well as sample magnetograms,
for several example events using data from these and other arrays in
Arctic Canada, as well as in West Greenland and Antarctica, the latter
to show the conjugate nature of these events. A basic relation to GIC
data in the Hydro-Québec electrical transmission network in eastern
Canada has been determined and will be discussed.

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Title: Helioseismic holography of simulated sunspots: dependence of
the travel time on magnetic field strength and Wilson depression
Authors: Felipe, T.; Braun, D. C.; Birch, A. C.
2017A&A...604A.126F Altcode: 2017arXiv170509135F
Improving methods for determining the subsurface structure of sunspots
from their seismic signature requires a better understanding of the
interaction of waves with magnetic field concentrations. We aim to
quantify the impact of changes in the internal structure of sunspots
on local helioseismic signals. We have numerically simulated the
propagation of a stochastic wave field through sunspot models with
different properties, accounting for changes in the Wilson depression
between 250 and 550 km and in the photospheric umbral magnetic field
between 1500 and 3500 G. The results show that travel-time shifts at
frequencies above approximately 3.50 mHz (depending on the phase-speed
filter) are insensitive to the magnetic field strength. The travel
time of these waves is determined exclusively by the Wilson depression
and sound-speed perturbation. The travel time of waves with lower
frequencies is affected by the direct effect of the magnetic field,
although photospheric field strengths below 1500 G do not leave a
significant trace on the travel-time measurements. These results could
potentially be used to develop simplified travel-time inversion methods.

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Title: VizieR Online Data Catalog: Statistical analysis of solar
active regions (Barnes+, 2014)
Authors: Barnes, G.; Birch, A. C.; Leka, K. D.; Braun, D. C.
2017yCat..17860019B Altcode:
In brief, samples from two populations are considered: "pre-emergence"
targets (PE) that track a 32°x32° patch of the Sun prior to the
emergence of a NOAA-numbered AR and "non-emergence" targets (NE)
selected for lack of emergence and lack of strong fields in the
central portions of the tracked patch. The PE sample size comprises
107 targets obtained between 2001 and 2007, matched to 107 NE targets
drawn from an initially larger sample and selected further to match
the PE distributions in time and observing location on the disk. (2 data files).

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Title: Driving Early Biochemical Reactions by the Thermal Accumulation
of ATP over ADP/AMP?
Authors: Kühnlein, A.; Mast, C. B.; Benk, A.; Spatz, J. P.; Braun, D.
2017LPICo1967.4142K Altcode:
We propose a system which uses the prebiotically realistic thermal
trap to locally shift the equilibrium of ADP and ATP towards an ATP
bias and thereby allows biochemical reactions to take off.

---------------------------------------------------------
Title: Hosting Early Evolution in Heated Pores of Rock
Authors: Mast, C. B.; Möller, F.; Lanzmich, S.; Keil, L.; Braun, D.
2017LPICo1967.4037M Altcode:
Recent experiments with non-equilibrium microsystems suggest that
porous rock conditions drive early molecular evolution in many ways,
including accumulation, polymerization, replication, length selection
and gelation.

---------------------------------------------------------
Title: Thermally Driven Accumulation and Dry-Wet Cycles of Nucleotides
Authors: Morasch, M.; Liu, J.; Braun, D.
2017LPICo1967.4153M Altcode:
We show how a nonequilibrium system in form of a temperature gradient
across porous rock creates high local concentrations and dry-wet cycles
of nucleotides and other molecules.

---------------------------------------------------------
Title: Elucidating Signatures of the Genetic Code with Binding Assays
Authors: Edeleva, E. V.; Schwintek, P. J.; Braun, D.
2017LPICo1967.4036E Altcode:
What defined specific assignment of amino acids to their cognate
codons during the emergence of the genetic code? In this project,
we develop experimental strategies to test the stereochemical theory
of the genetic code origin.

---------------------------------------------------------
Title: A Fixed-point Scheme for the Numerical Construction of
Magnetohydrostatic Atmospheres in Three Dimensions
Authors: Gilchrist, S. A.; Braun, D. C.; Barnes, G.
2016SoPh..291.3583G Altcode: 2016arXiv160900733G; 2016SoPh..tmp..182G
Magnetohydrostatic models of the solar atmosphere are often based on
idealized analytic solutions because the underlying equations are too
difficult to solve in full generality. Numerical approaches, too, are
often limited in scope and have tended to focus on the two-dimensional
problem. In this article we develop a numerical method for solving the
nonlinear magnetohydrostatic equations in three dimensions. Our method
is a fixed-point iteration scheme that extends the method of Grad and
Rubin (Proc. 2nd Int. Conf. on Peaceful Uses of Atomic Energy31, 190,
1958) to include a finite gravity force. We apply the method to a test
case to demonstrate the method in general and our implementation in
code in particular.

---------------------------------------------------------
Title: SDO/HMI survey of emerging active regions for helioseismology
Authors: Schunker, H.; Braun, D. C.; Birch, A. C.; Burston, R. B.;
Gizon, L.
2016A&A...595A.107S Altcode: 2016arXiv160808005S
Context. Observations from the Solar Dynamics Observatory (SDO) have
the potential for allowing the helioseismic study of the formation of
hundreds of active regions, which would enable us to perform statistical
analyses. Aims: Our goal is to collate a uniform data set of
emerging active regions observed by the SDO/HMI instrument suitable for
helioseismic analysis, where each active region is centred on a 60° ×
60° area and can be observed up to seven days before emergence. 
Methods: We restricted the sample to active regions that were visible in
the continuum and emerged into quiet Sun largely avoiding pre-existing
magnetic regions. As a reference data set we paired a control region
(CR), with the same latitude and distance from central meridian, with
each emerging active region (EAR). The control regions do not have
any strong emerging flux within 10° of the centre of the map. Each
region was tracked at the Carrington rotation rate as it crossed
the solar disk, within approximately 65° from the central meridian
and up to seven days before, and seven days after, emergence. The
mapped and tracked data, consisting of line-of-sight velocity,
line-of-sight magnetic field, and intensity as observed by SDO/HMI,
are stored in datacubes that are 410 min in duration and spaced 320
min apart. We call this data set, which is currently comprised of 105
emerging active regions observed between May 2010 and November 2012,
the SDO Helioseismic Emerging Active Region (SDO/HEAR) survey. 
Results: To demonstrate the utility of a data set of a large number of
emerging active regions, we measure the relative east-west velocity of
the leading and trailing polarities from the line-of-sight magnetogram
maps during the first day after emergence. The latitudinally averaged
line-of-sight magnetic field of all the EARs shows that, on average,
the leading (trailing) polarity moves in a prograde (retrograde)
direction with a speed of 121 ± 22 m s-1 (-70 ± 13 m
s-1) relative to the Carrington rotation rate in the first
day. However, relative to the differential rotation of the surface
plasma, the east-west velocity is symmetric, with a mean of 95 ± 13
m s-1. Conclusions: The SDO/HEAR data set will not
only be useful for helioseismic studies, but will also be useful to
study other features such as the surface magnetic field evolution of
a large sample of EARs. We intend to extend this survey forwards in
time to include more EARs observed by SDO/HMI.

---------------------------------------------------------
Title: Helioseismic Holography of Simulated Sunspots: Magnetic and
Thermal Contributions to Travel Times
Authors: Felipe, T.; Braun, D. C.; Crouch, A. D.; Birch, A. C.
2016ApJ...829...67F Altcode: 2016arXiv160804893F
Wave propagation through sunspots involves conversion between waves of
acoustic and magnetic character. In addition, the thermal structure
of sunspots is very different than that of the quiet Sun. As a
consequence, the interpretation of local helioseismic measurements of
sunspots has long been a challenge. With the aim of understanding these
measurements, we carry out numerical simulations of wave propagation
through sunspots. Helioseismic holography measurements made from
the resulting simulated wavefields show qualitative agreement with
observations of real sunspots. We use additional numerical experiments
to determine, separately, the influence of the thermal structure of the
sunspot and the direct effect of the sunspot magnetic field. We use the
ray approximation to show that the travel-time shifts in the thermal
(non-magnetic) sunspot model are primarily produced by changes in the
wave path due to the Wilson depression rather than variations in the
wave speed. This shows that inversions for the subsurface structure
of sunspots must account for local changes in the density. In some
ranges of horizontal phase speed and frequency there is agreement
(within the noise level in the simulations) between the travel times
measured in the full magnetic sunspot model and the thermal model. If
this conclusion proves to be robust for a wide range of models, it
would suggest a path toward inversions for sunspot structure.

---------------------------------------------------------
Title: Constraining the common properties of active region formation
using the SDO/HEAR dataset
Authors: Schunker, H.; Braun, D. C.; Birch, A. C.
2016usc..confE...2S Altcode:
Observations from the Solar Dynamics Observatory (SDO) have the
potential for allowing the helioseismic study of the formation of
hundreds of active regions, which enable us to perform statistical
analyses. We collated a uniform data set of emerging active regions
(EARs) observed by the SDO/HMI instrument suitable for helioseismic
analysis, where each active region can be observed up to 7 days before
emergence. We call this dataset the SDO Helioseismic Emerging Active
Region (SDO/HEAR) survey. We have used this dataset to to understand
the nature of active region emergence. The latitudinally averaged
line-of-sight magnetic field of all the EARs shows that the leading
(trailing) polarity moves in a prograde (retrograde) direction with
a speed of 110 ± 15 m/s (-60 ± 10 m/s) relative to the Carrington
rotation rate in the first day after emergence. However, relative
to the differential rotation of the surface plasma the East-West
velocity is symmetric, with a mean of 90 ± 10 m/s. We have also
compared the surface flows associated with the EARs at the time
of emergence with surface flows from numerical simulations of flux
emergence with different rise speeds. We found that the surface flows
in simulations of emerging flux with a low rise speed of 70 m/s best
match the observations.

---------------------------------------------------------
Title: A low upper limit on the subsurface rise speed of solar
active regions
Authors: Birch, A. C.; Schunker, H.; Braun, D. C.; Cameron, R.; Gizon,
L.; Lo ptien, B.; Rempel, M.
2016SciA....2E0557B Altcode: 2016arXiv160705250B
Magnetic field emerges at the surface of the Sun as sunspots and active
regions. This process generates a poloidal magnetic field from a rising
toroidal flux tube, it is a crucial but poorly understood aspect of
the solar dynamo. The emergence of magnetic field is also important
because it is a key driver of solar activity. We show that measurements
of horizontal flows at the solar surface around emerging active regions,
in combination with numerical simulations of solar magnetoconvection,
can constrain the subsurface rise speed of emerging magnetic flux. The
observed flows imply that the rise speed of the magnetic field is
no larger than 150 m/s at a depth of 20 Mm, that is, well below the
prediction of the (standard) thin flux tube model but in the range
expected for convective velocities at this depth. We conclude that
convective flows control the dynamics of rising flux tubes in the upper
layers of the Sun and cannot be neglected in models of flux emergence.

---------------------------------------------------------
Title: Helioseismic Survey of the Near-surface Flows Around the
Largest Active Regions with SDO-HMI Observations
Authors: Braun, Douglas; DeGrave, Kyle
2016SPD....47.0702B Altcode:
We report on the properties of the near-surface flows, determined from
helioseismic holography applied to HMI Dopplergrams, of approximately
250 of the largest active regions observed during the first five
years of SDO observations. A recent study which examined the potential
association of flows with the production of solar flares in this survey
has recently been published (Braun 2016, ApJ 819, 106). We discuss here
additional findings on general flow properties of the regions in our
survey derived from ensemble averages of the flows. This averaging
eliminates the dominating effect of the supergranulation signal,
and shows outflows from sunspots surrounded by compact inflows. The
properties of these flows are described. The potential use of these
measurements for determining the contribution of active-region related
flows to global dynamics (including differential rotation and meridional
circulation) and flux-transport models is discussed. This work is
supported by the NSF Solar Terrestrial Program through grant AGS-1127327
and by the NASA Heliophysics Division through NNH12CF68C and NNX16AG88G.

---------------------------------------------------------
Title: Forward and Inverse Modeling of Helioseismic Holography
Measurements of MHD Simulations of Convection and Sunspot Flows
Authors: DeGrave, Kyle; Braun, Douglas; Birch, Aaron; Crouch, Ashley
D.; Javornik, Brenda; Rempel, Matthias D.
2016SPD....4720303D Altcode:
We test and validate newly-developed, empirically-derived sensitivity
kernels for use in helioseismic analysis. These kernels are based on
the Born approximation and derived from applying direct measurements to
artificial realizations of incoming and scattered wavefields. These
kernels are employed in a series of forward and inverse modeling
of flows from the near-surface layers of two publicly available
magnetohydrodynamic (MURaM-based) solar simulations - a quiet-Sun
simulation, and one containing a sunspot. Forward travel times
computed using the kernels generally compare favorably in non-magnetic
regions. One finding of note is the presence of flow-like artifacts in
the sunspot measurements which appear when the spot umbra or penumbra
falls within the measurement pupils. Inversions for the horizontal flow
components are able to reproduce the large-scale supergranule-sized
flows in the upper 3Mm of both domains, but are compromised by noise
at greater depths. In spite of the magnetic artifact, the moat flow
surrounding the spot is at least qualitatively recovered. This work
is supported by the NASA Heliophysics Division through NNH12CF68C,
NNH12CF23C, and NNX16AG88G, and by the NSF Solar-Terrestrial Program
through grant AGS-1127327.

---------------------------------------------------------
Title: Numerical construction of magneto-hydrostatic atmospheres in
three dimensions
Authors: Gilchrist, Stuart; Braun, Douglas; Barnes, Graham
2016SPD....47.0706G Altcode:
There is a general interest in constructing magneto-hydrostatic
models of the solar atmosphere. These models describe large-scale,
long-lived magnetic structures like sunspots, prominences, coronal
loops, and the corona itself on global scales. The nonlinearity
of the magneto-hydrostatic equations prohibits direct analytic
solution except when idealized approximations like self-similarity
are made. Numerical approaches, too, are limited in scope, and
primarily focus on the two-dimensional problem --- the general
three-dimensional magneto-hydrostatic problem is not treated. In
this presentation we present a new numerical scheme for solving the
magneto-hydrostatic equations in three dimensions. We are presently
using this method to construct sunspot models for helioseismic MHD
wave-propagation simulations with the goal of comparing the simulations
to local-helioseismic measurements. We will present the details of
the method and its application to test cases.This work is supported
by NASA Heliophysics Division through grant NNX14AD42G and by the NSF
Solar-Terrestrial program through grant AGS-1127327.

---------------------------------------------------------
Title: Magnetic and Thermal Contributions to Helioseismic Travel
times in Simulated Sunspots
Authors: Braun, Douglas; Felipe, Tobias; Birch, Aaron; Crouch,
Ashley D.
2016SPD....47.0701B Altcode:
The interpretation of local helioseismic measurements of sunspots
has long been a challenge, since waves propagating through sunspots
are potentially affected by both mode conversion and changes in the
thermal structure of the spots. We carry out numerical simulations of
wave propagation through a variety of models which alternately isolate
either the thermal or magnetic structure of the sunspot or include
both of these. We find that helioseismic holography measurements made
from the resulting simulated wavefields show qualitative agreement
with observations of real sunspots. Using insight from ray theory,
we find that travel-time shifts in the thermal (non-magnetic) sunspot
model are primarily produced by changes in the wave path due to the
Wilson depression rather than variations in the wave speed. This shows
that inversions for the subsurface structure of sunspots must account
for local changes in the density. In some ranges of horizontal phase
speed and frequency there is agreement (within the noise level of the
measurements) between the travel times measured in the full magnetic
sunspot model and the thermal model. If this conclusion proves to
be robust for a wide range of models, it suggests a path towards
inversions for sunspot structure. This research has been funded
by the Spanish MINECO through grant AYA2014-55078-P, by the NASA
Heliophysics Division through NNX14AD42G and NNH12CF23C, and the NSF
Solar Terrestrial program through AGS-1127327.

---------------------------------------------------------
Title: A Helioseismic Survey of Near-surface Flows Around Active
Regions and their Association with Flares
Authors: Braun, D. C.
2016ApJ...819..106B Altcode: 2016arXiv160200038B
We use helioseismic holography to study the association of shallow
flows with solar flare activity in about 250 large sunspot groups
observed between 2010 and 2014 with the Helioseismic and Magnetic
Imager on the Solar Dynamics Observatory. Four basic flow parameters:
horizontal speed, horizontal component of divergence, vertical component
of vorticity, and a vertical kinetic helicity proxy, are mapped for
each active region (AR) during its passage across the solar disk. Flow
indices are derived representing the mean and standard deviation of
these parameters over magnetic masks and compared with contemporary
measures of flare X-ray flux. A correlation exists for several of the
flow indices, especially those based on the speed and the standard
deviation of all flow parameters. However, their correlation with
X-ray flux is similar to that observed with the mean unsigned magnetic
flux density over the same masks. The temporal variation of the flow
indices are studied, and a superposed epoch analysis with respect to the
occurrence to 70 M and X-class flares is made. While flows evolve with
the passage of the ARs across the disk, no discernible precursors or
other temporal changes specifically associated with flares are detected.

---------------------------------------------------------
Title: Measurements with local helioseismology
Authors: Braun, D. C.
2015exse.book...77B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Influence of Magnetic and Thermal Effects on Helioseismic
Travel-time Shifts in Sunspot Models
Authors: Felipe, Tobias; Braun, Douglas; Crouch, Ashley D.; Birch,
Aaron
2014AAS...22420206F Altcode:
Sunspots are one of the most prominent manifestations of solar
magnetic activity and have been studied using local helioseismology for
decades. Recent modeling and observational studies indicate that the
interpretation of travel-time shifts is still subject to uncertainties
regarding the physical causes of the wave perturbations. Numerical wave
propagation has proved useful in addressing this problem. In this work,
we have analyzed travel-time shifts obtained from three dimensional
numerical simulations of wave propagation in a magnetohydrostatic
sunspot-like atmosphere. In particular, we isolate the individual
effects of the magnetic field and thermal perturbations on the
measurements by means of simulations where only one kind of perturbation
(magnetic or thermal) is included. The resulting travel-time shift maps,
obtained by applying helioseismic holography to the photospheric Doppler
signals in the simulated domain, will be compared and discussed. We
plan to make the artificial data available to the community for the
development and validation of other helioseismic methods. This work
is supported by the NASA SDO Science Center program (through contract
NNH09CE41C) and by the NASA Living With a Star Program (through grant
NNX14AD42G).

---------------------------------------------------------
Title: A Helioseismic Survey of Emerging Active Regions Using
HMI-SDO Data
Authors: Braun, Douglas; Schunker, Hannah; Birch, Aaron
2014AAS...22420201B Altcode:
A survey of the subsurface properties of approximately 100 emerging
active regions, determined from the application of helioseismic
holography to Dopplergrams obtained with the HMI instrument onboard
the Solar Dynamics Observatory, is being carried out. The goal of
this research is to use helioseismology and numerical simulations to
identify and understand possible signatures, in the form of acoustic
travel time shifts, due to rising magnetic flux concentrations
prior to their emergence at the solar photosphere. The status of
the project and current results will be discussed. We make use of
ensemble averages of travel-time shift measurements as proxies for
near-surface depth-integrated wave-speed changes and flows. The latter
include horizontal components of the flows as well as their horizontal
divergence and the vertical component of the flow vorticity. A control
sample of a similar number of quiet-Sun regions is used for comparison
and for identifying potential systematic effects. Preliminary results
confirm previous suggestions (obtained from a prior survey using GONG
data) that emergence sites are associated with converging photospheric
flows, such as the boundaries of supergranulation.This work is supported
by the NASA Heliophysics Supporting Research program through contract
NNH12CF23C.

---------------------------------------------------------
Title: A Helioseismic Survey to Investigate Relationships between
Subsurface Flows beneath Large Active Regions and Solar Flares
Authors: Braun, Douglas; Leka, K D.; Barnes, Graham
2014AAS...22421815B Altcode:
A survey of the subsurface flow properties of about 120 of the largest
active regions, determined from the application of helioseismic
holography to Dopplergrams obtained with the HMI instrument onboard
the Solar Dynamics Observatory, is being carried out. The overriding
goal is to characterize differences in the subsurface flows between
active regions associated with eruptive flares and the flows observed in
relatively quiescent regions. Applications to flare forecasting comprise
only one part of this investigation, since the potential response of
the subsurface environment to eruptive events during and after their
occurrence is also of scientific interest. Other priorities include
understanding the limitations of the helioseismic methods, identifying
and correcting systematic effects, and validating the reliability of
the measurements using artificial data. While inversions to determine
the variation with depth of subsurface flows are planned, preliminary
results will be discussed which make use of proxies for near-surface
depth-integrated properties, including the horizontal component of the
flow divergence and the vertical component of the flow vorticity.This
work is supported by the Solar Terrestrial Program of the National
Science Foundation, through grant AGS-1127327, and by the National
Oceanic and Atmospheric Administration SBIR program.

---------------------------------------------------------
Title: Studies on Forecasting Solar Flares
Authors: Leka, K. D.; Barnes, G.; Braun, D. C.; Wagner, E. L.
2014shin.confE.171L Altcode:
Forecasting solar flares is a challenge from various scientific
perspectives; major solar flares are inherently rare events, and all
observations available with which to evaluate the flare-readiness of the
Sun are remote, with inferences about the physical state rather than
direct measurements. We report on efforts to improve forecasts, using
data from the Helioseismic and Magnetic Imager on the Solar Dynamics
Observatory using magnetic field and helioseismic parametrization,
magnetic charge topology and Discriminant Analysis. We report on
preliminary results of the performance, including the temporal
variations of the parametrizations. This work is supported by
NASA contract NNH12CG10C and NOAA Contract WC-133R-13-CN-0079

---------------------------------------------------------
Title: Using Synthetic Data From Convection Simulations To Test
Helioseismic Holography Inversions For Three-Dimensional Vector Flows
Authors: Crouch, Ashley D.; Birch, Aaron; Braun, Douglas; Javornik,
Brenda; Rempel, Matthias D.
2014AAS...22421807C Altcode:
We investigate the efficacy of helioseismic holography for inferring
the three-dimensional vector flows in the near-surface layers of the
solar interior. Synthetic helioseismic data are taken from compressible
convection simulations. Travel times are measured from the synthetic
data using helioseismic holography. Kernels for the sensitivity
of travel times to subsurface flows are calculated using the Born
approximation. Inversions for subsurface flows are then performed
using subtractive optimally localized averaging. This provides an
opportunity to evaluate the accuracy of the inversion technique. We
compare the actual flows present in the convection simulations to the
flows retrieved by the inversion. We discuss the influence of the
regularization used by the inversion, and the effects of noise and
spatial resolution. This work is supported by the NASA SDO Science
Center program (NNH09CE41C), the NASA Heliophysics Guest Investigator
program (NNH12CF68C), and the NASA LWS TR&amp;T tools and methods
program (NNH09CF68C). The National Center for Atmospheric Research is
sponsored by the National Science Foundation.

---------------------------------------------------------
Title: Helioseismology of Pre-emerging Active
Regions. III. Statistical Analysis
Authors: Barnes, G.; Birch, A. C.; Leka, K. D.; Braun, D. C.
2014ApJ...786...19B Altcode: 2013arXiv1307.1938B
The subsurface properties of active regions (ARs) prior to their
appearance at the solar surface may shed light on the process of
AR formation. Helioseismic holography has been applied to samples
taken from two populations of regions on the Sun (pre-emergence and
without emergence), each sample having over 100 members, that were
selected to minimize systematic bias, as described in Paper I. Paper
II showed that there are statistically significant signatures in
the average helioseismic properties that precede the formation of
an AR. This paper describes a more detailed analysis of the samples
of pre-emergence regions and regions without emergence based on
discriminant analysis. The property that is best able to distinguish
the populations is found to be the surface magnetic field, even
a day before the emergence time. However, after accounting for the
correlations between the surface field and the quantities derived from
helioseismology, there is still evidence of a helioseismic precursor
to AR emergence that is present for at least a day prior to emergence,
although the analysis presented cannot definitively determine the
subsurface properties prior to emergence due to the small sample sizes.

---------------------------------------------------------
Title: Helioseismic Holography of an Artificial Submerged Sound Speed
Perturbation and Implications for the Detection of Pre-emergence
Signatures of Active Regions
Authors: Braun, D. C.
2014SoPh..289..459B Altcode: 2012SoPh..tmp..306B; 2012arXiv1210.7504B
We use a publicly available numerical wave-propagation simulation
of Hartlep et al. (Solar Phys.268, 321, 2011) to test the ability
of helioseismic holography to detect signatures of a compact,
fully submerged, 5 % sound-speed perturbation placed at a depth of
50 Mm within a solar model. We find that helioseismic holography
employed in a nominal "lateral-vantage" or "deep-focus" geometry
employing quadrants of an annular pupil can detect and characterize
the perturbation. A number of tests of the methodology, including the
use of a plane-parallel approximation, the definition of travel-time
shifts, the use of different phase-speed filters, and changes to
the pupils, are also performed. It is found that travel-time shifts
made using Gabor-wavelet fitting are essentially identical to those
derived from the phase of the Fourier transform of the cross-covariance
functions. The errors in travel-time shifts caused by the plane-parallel
approximation can be minimized to less than a second for the depths and
fields of view considered here. Based on the measured strength of the
mean travel-time signal of the perturbation, no substantial improvement
in sensitivity is produced by varying the analysis procedure from the
nominal methodology in conformance with expectations. The measured
travel-time shifts are essentially unchanged by varying the profile
of the phase-speed filter or omitting the filter entirely. The method
remains maximally sensitive when applied with pupils that are wide
quadrants, as opposed to narrower quadrants or with pupils composed
of smaller arcs. We discuss the significance of these results for the
recent controversy regarding suspected pre-emergence signatures of
active regions.

---------------------------------------------------------
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.
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: The Relativistic Electron-Proton Telescope (REPT) Instrument
on Board the Radiation Belt Storm Probes (RBSP) Spacecraft:
Characterization of Earth's Radiation Belt High-Energy Particle
Populations
Authors: Baker, D. N.; Kanekal, S. G.; Hoxie, V. C.; Batiste, S.;
Bolton, M.; Li, X.; Elkington, S. R.; Monk, S.; Reukauf, R.; Steg,
S.; Westfall, J.; Belting, C.; Bolton, B.; Braun, D.; Cervelli, B.;
Hubbell, K.; Kien, M.; Knappmiller, S.; Wade, S.; Lamprecht, B.;
Stevens, K.; Wallace, J.; Yehle, A.; Spence, H. E.; Friedel, R.
2013SSRv..179..337B Altcode: 2012SSRv..tmp..101B
Particle acceleration and loss in the million electron Volt (MeV)
energy range (and above) is the least understood aspect of radiation
belt science. In order to measure cleanly and separately both the
energetic electron and energetic proton components, there is a need for
a carefully designed detector system. The Relativistic Electron-Proton
Telescope (REPT) on board the Radiation Belt Storm Probe (RBSP)
pair of spacecraft consists of a stack of high-performance silicon
solid-state detectors in a telescope configuration, a collimation
aperture, and a thick case surrounding the detector stack to shield the
sensors from penetrating radiation and bremsstrahlung. The instrument
points perpendicular to the spin axis of the spacecraft and measures
high-energy electrons (up to ∼20 MeV) with excellent sensitivity
and also measures magnetospheric and solar protons to energies well
above E=100 MeV. The instrument has a large geometric factor ( g=0.2
cm2 sr) to get reasonable count rates (above background)
at the higher energies and yet will not saturate at the lower energy
ranges. There must be fast enough electronics to avert undue dead-time
limitations and chance coincidence effects. The key goal for the REPT
design is to measure the directional electron intensities (in the range
10-2-106 particles/cm2 s sr MeV)
and energy spectra (Δ E/ E∼25 %) throughout the slot and outer
radiation belt region. Present simulations and detailed laboratory
calibrations show that an excellent design has been attained for the
RBSP needs. We describe the engineering design, operational approaches,
science objectives, and planned data products for REPT.

---------------------------------------------------------
Title: A Search for Pre-Emergence Helioseismic Signatures of Active
Regions: Study Design and some Average Results
Authors: Leka, K. D.; Birch, A.; Barnes, G.; Braun, D.; Javornik,
B.; Gonzalez-Hernandez, I.; Dunn, T.
2013SPD....44...91L Altcode:
Helioseismology can be an important tool for understanding the
formation of active regions. This poster describes the design of a
recently completed study, testing whether pre-appearance signatures
of solar magnetic active regions were detectable using various tools
of local helioseismology. We provide details of the data selection
and preparation of samples, each containing over 100 members, of
two populations: regions on the Sun which produced a numbered NOAA
active region, and a "control" sample of areas which did not. The
seismology is performed on data from the GONG network; accompanying
magnetic data from the Michelson Doppler Imager aboard SoHO are used
for co-temporal analysis of the surface magnetic field. Samples are
drawn from 2001--2007, and each target is analyzed for 27.7hr prior
to an objectively determined time of emergence. We describe known
sources of bias and the approaches used to mitigate them. Examining the
average ensemble differences between the two populations, we describe
significant and surprising differences between our samples in both
quantities determined from helioseismology and from surface magnetic
fields. This work was supported by NASA contract NNH07CD25C.

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

---------------------------------------------------------
Title: The Helioseismic Search for Emerging Flux
Authors: Braun, D. C.
2013enss.confE..64B Altcode:
Arguably considered the holy grail of local helioseismology
is the detection of emerging flux before its appearance as a
sunspot or magnetic region on the photosphere. After almost two
decades of searching, this goal remains elusive and, at best,
controversial. Helioseismic exploration is increasingly assisted
by numerical simulations of rising flux which offer predictions of
the magnitude and type of signatures, and also by computational wave
propagation models which can validate and help improve the methods. We
discuss some of these developments as well as results of a recent
survey, carried out at NWRA, of approximately one hundred emerging
active regions observed with the GONG network. A new survey, carried
out in collaboration with colleagues at the Max Planck Institute for
Solar System Research and made using the observations obtained by the
HMI instrument on SDO is under way. This talk reviews work at NWRA
which has been funded through the NASA Living with a Star program
and currently though the NASA Solar and Heliospheric SR&amp;T program
(contract NNH12CF23C) and Heliophysics GI program (contract NNH12CF68C).

---------------------------------------------------------
Title: Testing Helioseismic-Holography Inversions for Supergranular
Flows Using Synthetic Data
Authors: Dombroski, D. E.; Birch, A. C.; Braun, D. C.; Hanasoge, S. M.
2013SoPh..282..361D Altcode: 2012arXiv1211.6886D
Supergranulation is one of the most visible length scales of solar
convection and has been studied extensively by local helioseismology. We
use synthetic data computed with the Seismic Propagation through
Active Regions and Convection (SPARC) code to test regularized-least
squares (RLS) inversions of helioseismic-holography measurements
for a supergranulation-like flow. The code simulates the acoustic
wavefield by solving the linearized three-dimensional Euler equations
in Cartesian geometry. We model a single supergranulation cell with
a simple, axisymmetric, mass-conserving flow.

---------------------------------------------------------
Title: Helioseismology of Pre-emerging Active Regions. II. Average
Emergence Properties
Authors: Birch, A. C.; Braun, D. C.; Leka, K. D.; Barnes, G.;
Javornik, B.
2013ApJ...762..131B Altcode: 2013arXiv1303.1391B
We report on average subsurface properties of pre-emerging active
regions as compared to areas where no active region emergence was
detected. Helioseismic holography is applied to samples of the two
populations (pre-emergence and without emergence), each sample having
over 100 members, which were selected to minimize systematic bias,
as described in Leka et al. We find that there are statistically
significant signatures (i.e., difference in the means of more than a few
standard errors) in the average subsurface flows and the apparent wave
speed that precede the formation of an active region. The measurements
here rule out spatially extended flows of more than about 15 m
s-1 in the top 20 Mm below the photosphere over the course
of the day preceding the start of visible emergence. These measurements
place strong constraints on models of active region formation.

---------------------------------------------------------
Title: Helioseismology of Pre-emerging Active Regions. I. Overview,
Data, and Target Selection Criteria
Authors: Leka, K. D.; Barnes, G.; Birch, A. C.; Gonzalez-Hernandez,
I.; Dunn, T.; Javornik, B.; Braun, D. C.
2013ApJ...762..130L Altcode: 2013arXiv1303.1433L
This first paper in a series describes the design of a study testing
whether pre-appearance signatures of solar magnetic active regions
were detectable using various tools of local helioseismology. The
ultimate goal is to understand flux-emergence mechanisms by setting
observational constraints on pre-appearance subsurface changes, for
comparison with results from simulation efforts. This first paper
provides details of the data selection and preparation of the samples,
each containing over 100 members, of two populations: regions on
the Sun that produced a numbered NOAA active region, and a "control"
sample of areas that did not. The seismology is performed on data from
the GONG network; accompanying magnetic data from SOHO/MDI are used
for co-temporal analysis of the surface magnetic field. Samples are
drawn from 2001-2007, and each target is analyzed for 27.7 hr prior
to an objectively determined time of emergence. The results of two
analysis approaches are published separately: one based on averages of
the seismology- and magnetic-derived signals over the samples, another
based on Discriminant Analysis of these signals, for a statistical test
of detectable differences between the two populations. We include
here descriptions of a new potential-field calculation approach
and the algorithm for matching sample distributions over multiple
variables. We describe known sources of bias and the approaches used
to mitigate them. We also describe unexpected bias sources uncovered
during the course of the study and include a discussion of refinements
that should be included in future work on this topic.

---------------------------------------------------------
Title: X-Spec: A Multi-Object Wideband Survey Spectrograph for CCAT
Authors: Bradford, Charles; Hailey-Dunsheath, S.; Shirokoff, E.;
Hollister, M.; Kovacs, A.; Zmuidzinas, J.; Padin, S.; Seiffert, M. D.;
Braun, D.; Banales, G.; LeDuc, H.; Stacey, G. J.; Nikola, T.; Glenn,
J.; Chapman, S.
2013AAS...22115009B Altcode:
We are developing a multi-object dispersive survey spectrograph
for CCAT. X-Spec is optimized for rest-frame far-IR / submm atomic
and molecular transitions in high-z galaxies, and it will conduct
multi-galaxy spectral survey up to 10x faster than ALMA. Detected lines
will provide redshifts for and interstellar gas conditions in tens of
thousands of galaxies ranging from the early universe (z &gt; 6) to the
present day. X-Spec will be particularly sensitive to the 158-micron
ionized carbon fine-structure transition [CII], and the initial
instrument will target the 650-um, 850-um, and 1-mm atmospheric windows,
corresponding to 3.5 to 9 for [CII]. By following up high-z candidate
objects, X-Spec surveys of [CII] will reveal the early evolution of
galaxies' energy sources and interstellar gas conditions. CCAT/X-Spec
can also probe below individually-detected sources by using fluctuation
analyses; the spatial-spectral fluctuations mm and submm bands are
dominated by [CII], and can be used to measure the growth of large-scale
structure and the global properties of galaxies in the reionization
epoch. X-Spec will have at least 15 independent spectrometer backend
'pixels', each covering 195-520 GHz instantaneously at R=400-700,
in both polarizations with photon-background-limited sensitivity. It
will use lithographically-patterned filterbank chips formed with
superconducting transmission line. The detectors are titanium-nitride
kinetic inductance detectors (KIDs), and each spectrometer chip
will have ~500 KIDs integrated with the filterbank in a package a
few square cm in size. Each chip has a bandwidth of ~ 1:1.6 and is
single-polarization, so coverage of the full 195-520 GHz range in
dual-pol requires 4 chips and ~2000 detectors. With the compact size
and inexpensive mass production, much larger spectrometer formats
(100-300 pixels) will be possible as detector readout technology
progresses. To optimize on-source observation efficiency, a 2-axis
rotary positioning system for each pixel will steer to an arbitrary
position in a circular patch of sky; this system will steer to target
galaxies, compensate for field rotation, and enable beam modulation
(chopping) at ~1-2 Hz for sky subtraction.

---------------------------------------------------------
Title: Scattering of the f-mode by Small Magnetic Flux Elements from
Observations and Numerical Simulations
Authors: Felipe, T.; Braun, D.; Crouch, A.; Birch, A.
2012ApJ...757..148F Altcode: 2012arXiv1208.4024F
The scattering of f-modes by magnetic tubes is analyzed using
three-dimensional numerical simulations. An f-mode wave packet is
propagated through a solar atmosphere embedded with three different
flux tube models that differ in radius and total magnetic flux. A
quiet-Sun simulation without a tube present is also performed as a
reference. Waves are excited inside the flux tube and propagate along
the field lines, and jacket modes are generated in the surroundings
of the flux tube, carrying 40% as much energy as the tube modes. The
resulting scattered wave is mainly an f-mode composed of a mixture of m
= 0 and m = ±1 modes. The amplitude of the scattered wave approximately
scales with the magnetic flux. A small amount of power is scattered
into the p 1-mode. We have evaluated the absorption and
phase shift from a Fourier-Hankel decomposition of the photospheric
vertical velocities. They are compared with the results obtained
from the ensemble average of 3400 small magnetic elements observed in
high-resolution MDI Doppler datacubes. The comparison shows that the
observed dependence of the phase shift with wavenumber can be matched
reasonably well with the simulated flux tube model. The observed
variation of the phase shifts with the azimuthal order m appears to
depend on details of the ensemble averaging, including possible motions
of the magnetic elements and asymmetrically shaped elements.

---------------------------------------------------------
Title: A Search for Pre-Emergence Helioseismic Signatures of Active
Regions
Authors: Barnes, Graham; Birch, A.; Leka, K.; Braun, D.; Dunn, T.;
Javornik, B.; Gonzalez Hernandez, I.
2012AAS...22020510B Altcode:
Helioseismology can be an important tool for understanding the formation
of active regions. As a first step towards this goal, we have carried
out a search for statistically significant helioseismic precursors
of active region emergence. We used an automatic method to determine
the time of emergence based on the NOAA/NGDC active region catalog
and MDI/SOHO 96 minute magnetograms. Using GONG data, we applied
helioseismic holography to 107 pre-emergence active regions and a
control sample of 107 regions where no active region was present. We
found some significant and surprising differences between our samples
in both quantities determined from helioseismology and from surface
magnetic fields. However, we do not see a clear signature of emergence
when considering individual active regions. The results of this
investigation may shed some light on the mechanism responsible for
flux emergence, and certainly illustrate the care which must be taken
in conducting such an investigation. This work was supported by
NASA contract NNH07CD25C.

---------------------------------------------------------
Title: Comparison of Numerical and Observational Scattering of the
f-mode by Small Magnetic Elements
Authors: Felipe, Tobias; Braun, D. C.; Crouch, A. D.; Birch, A. C.
2012AAS...22010906F Altcode:
The observed scattering of the f-mode by small magnetic elements
is studied through Fourier-Hankel analysis and compared with
three-dimensional numerical simulations of the scattering produced by
magnetic flux tube models. The numerical setup consists of an f-mode
wave packet which is propagated through a realistic solar atmosphere
embedded with a flux tube model. A quiet Sun simulation without a
tube present is also performed as a reference. Sausage (m=0) and kink
(m=±1) modes are excited in the flux tube and propagate along the field
lines, and jacket modes are generated in the surroundings of the flux
tube, carrying 40% as much energy as the tube modes. The resulting
scattered wave is mainly an f-mode composed of a mixture of m=0 and
m=±1 modes. We find the observed dependence of the phase shift with
wavenumber for an ensemble average of about 3400 magnetic elements
can be matched reasonably well with the simulated flux tube model. The
observed variation with azimuthal order m of the phase-shifts appears
to depend on details of the ensemble averaging, including possible
motions of the magnetic elements and asymmetrically shaped elements. This research has been funded by NASA through projects NNH09CE43C,
NNH09CF68C, and NNH07CD25C.

---------------------------------------------------------
Title: Comment on “Detection of Emerging Sunspot Regions in the
Solar Interior”
Authors: Braun, Douglas C.
2012Sci...336..296B Altcode:
Ilonidis et al. (Reports, 19 August 2011, p. 993) report acoustic
travel-time decreases associated with emerging sunspot regions before
their appearance on the solar surface. An independent analysis using
helioseismic holography does not confirm these travel-time anomalies for
the four regions illustrated by Ilonidis et al. This negative finding
is consistent with expectations based on current emerging flux models.

---------------------------------------------------------
Title: Helioseismology of a Realistic Magnetoconvective Sunspot
Simulation
Authors: Braun, D. C.; Birch, A. C.; Rempel, M.; Duvall, T. L.
2012ApJ...744...77B Altcode:
We compare helioseismic travel-time shifts measured from a realistic
magnetoconvective sunspot simulation using both helioseismic holography
and time-distance helioseismology, and measured from real sunspots
observed with the Helioseismic and Magnetic Imager instrument on
board the Solar Dynamics Observatory and the Michelson Doppler Imager
instrument on board the Solar and Heliospheric Observatory. We
find remarkable similarities in the travel-time shifts measured
between the methodologies applied and between the simulated and real
sunspots. Forward modeling of the travel-time shifts using either Born
or ray approximation kernels and the sound-speed perturbations present
in the simulation indicates major disagreements with the measured
travel-time shifts. These findings do not substantially change with
the application of a correction for the reduction of wave amplitudes
in the simulated and real sunspots. Overall, our findings demonstrate
the need for new methods for inferring the subsurface structure of
sunspots through helioseismic inversions.

---------------------------------------------------------
Title: Numerical simulations of the subsurface structure of sunspots
Authors: Rempel, M.; Cheung, M.; Birch, A. C.; Braun, D. C.
2011AGUFMSH52B..02R Altcode:
Knowledge of the subsurface magnetic field and flow structure of
sunspots is essential for understanding the processes involved in their
formation, dynamic evolution and decay. Information on the subsurface
structure can be obtained by either direct numerical modeling or
helioseismic inversions. Numerical simulations have reached only
in recent years the point at which entire sunspots or even active
regions can be modeled including all relevant physical processes
such as 3D radiative transfer and a realistic equation of state. We
present in this talk results from a series of different models: from
simulations of individual sunspots (with and without penumbrae) in
differently sized computational domains to simulations of the active
region formation process (flux emergence). It is found in all models
that the subsurface magnetic field fragments on an intermediate scale
(larger than the scale of sunspot fine structure such as umbral dots);
most of these fragmentations become visible as light bridges or flux
separation events in the photosphere. The subsurface field strength is
found to be in the 5-10 kG range. The simulated sunspots are surrounded
by large scale flows, the most dominant and robust flow component is
a deep reaching outflow with an amplitude reaching about 50% of the
convective RMS velocity at the respective depth. The simulated sunspots
show helioseismic signatures (frequency dependent travel time shifts)
similar to those in observed sunspots. On the other hand it is clear
from the simulations that these signatures originate in the upper
most 2-3 Mm of the convection zone, since only there substantial
perturbations of the wave speed are present. The contributions from
deeper layers are insignificant, in particular a direct comparison
between an 8 Mm and 16 Mm deep simulation leads to indiscernible
helioseismic differences. The National Center for Atmospheric Research
is sponsored by the National Science Foundation. This work is in part
supported through the NASA SDO Science Center.

---------------------------------------------------------
Title: Numerical simulations of scattering of f-modes by magnetic
flux tubes
Authors: Felipe, Tobias; Birch, Aaron C.; Crouch, Ashley D.; Braun,
Douglas C.
2011sdmi.confE..80F Altcode:
The scattering of the f-mode by a magnetic flux tube is analyzed
using three-dimensional numerical simulations. An f-mode wave packet
is propagated through a realistic solar atmosphere embedded with a
flux tube of 200 km radius and 1600 G field strength. A quiet Sun
simulation without the tube being present is also performed as a
reference. Sausage (m=0) and kink (m=± 1) modes are excited in the
magnetic tube and propagate downward along the field lines, while the
resulting scattered wave is mainly an f-mode composed of a mixture
of m=0 and m=± 1 modes. Low power is also scattered into high-order
acoustic p-modes. We have evaluated the absorption and phase shift
from a Fourier-Hankel decomposition of the vertical velocities.

---------------------------------------------------------
Title: "Hare and Hounds" Tests of Helioseismic Holography
Authors: Birch, A. C.; Parchevsky, K. V.; Braun, D. C.; Kosovichev,
A. G.
2011SoPh..272...11B Altcode: 2011SoPh..tmp..315B; 2011SoPh..tmp..290B; 2011SoPh..tmp..257B;
2011SoPh..tmp..188B
We use the output of numerical wave-propagation simulations as synthetic
data for "hare and hounds" tests of helioseismic holography. In
the simple non-magnetic models examined here, we show that when the
inversion method includes a consistent treatment of the filtering
applied during the data analysis the inversions for the subsurface
sound speed are qualitatively correct.

---------------------------------------------------------
Title: Towards physics-based helioseismic inversions of subsurface
sunspot structure
Authors: Braun, D. C.; Birch, A. C.; Crouch, A. D.; Rempel, M.
2011IAUS..273..379B Altcode:
Numerical computations of wave propagation through sunspot-like magnetic
field structures are critical to developing and testing methods to
deduce the subsurface structure of sunspots and active regions. We
show that helioseismic analysis applied to the MHD sunspot simulations
of Rempel and collaborators, as well as to translation-invariant
models of umbral-like fields, yield wave travel-time measurements in
qualitative agreement with those obtained in real sunspots. However,
standard inversion methods applied to these data fail to reproduce the
true wave-speed structure beneath the surface of the model. Inversion
methods which incorporate direct effects of the magnetic field,
including mode conversion, may be required.

---------------------------------------------------------
Title: Helioseismic probing of the subsurface structure of sunspots
Authors: Crouch, A. D.; Birch, A. C.; Braun, D. C.; Clack, C. T. M.
2011IAUS..273..384C Altcode:
We discuss recent progress in the helioseismic probing of the subsurface
structure of solar magnetic regions. To simulate the interaction of
helioseismic waves with magnetic fields and thermal perturbations we
use a simple model that is translation invariant in the horizontal
directions, has a realistic stratification in the vertical direction,
and has physically consistent boundary conditions for the waves at
the upper and lower boundaries of the computational domain. Using
this model we generate synthetic helioseismic data and subsequently
measure time-distance travel times. We evaluate a model for the
wave-speed perturbation below sunspots that replaces the sound speed
in a non-magnetic model by the fast-mode speed from a magnetic model;
our results indicate that this approach is unlikely to be useful in
modeling wave-speed perturbations in sunspots. We develop and test
an inversion algorithm for inferring the sound-speed perturbation in
magnetic regions. We show that this algorithm retrieves the correct
sound-speed perturbation only when the sensitivity kernels employed
account for the effects of the magnetic field on the waves and the
subsurface structure.

---------------------------------------------------------
Title: Helioseismic Inversions For Magnetic Field And Sound-speed
Perturbations
Authors: Clack, Christopher; Crouch, A. D.; Birch, A. C.; Braun, D. C.
2011SPD....42.1602C Altcode: 2011BAAS..43S.1602C
In local helioseismology, inversion methods that can separate magnetic
and thermal perturbations are needed, especially for probing the
subsurface structure of sunspots. We present a method for performing
linear helioseismic inversions that can infer small-amplitude
perturbations to both the magnetic field strength and the sound-speed
profile in translation-invariant background models permeated by a 3
kG vertical magnetic field, consistent with expectations for sunspot
umbrae. We introduce a novel inversion routine that consists of
two parts: first; a traditional regularized least squares inversion
is utilized to search regularization-parameter space for inversion
coefficients and second; an analysis of these inversion coefficients
identifies the sets of coefficients that have the required attributes
for a pair of inferred sound-speed and magnetic fields models. We show a
case study in which this inversion method is able to accurately recover
a sound-speed perturbation and a perturbation in the magnetic field
strength simultaneously. We will discuss how these results relate to
the local helioseismology of sunspots. This work is supported by NASA
contracts NNH09CE41C and NNG07EI51C.

---------------------------------------------------------
Title: F-mode Seismology Of Solar Simulations
Authors: DeGrave, Kyle; Jackiewicz, J.; Braun, D.; Birch, A. C.;
Research Associates, NorthWest
2011SPD....42.1613D Altcode: 2011BAAS..43S.1613D
Time-distance helioseismology using f-mode travel times is used to
study near-surface regions of realistic numerical magnetohydrodynamic
simulations. A fully-consistent inversion procedure is used to analyze
the simulation flow field outside of a sunspot. This approach is carried
out to validate the time-distance technique, as well as the sensitivity
kernels and the inversion algorithm. This work is supported by NASA
under the SDO Science Center project (contract NNH09CE41C) as well as
well as a NASA EPSCoR award.

---------------------------------------------------------
Title: Local Helioseismology of Small-Scale Magnetic Elements
Authors: Crouch, Ashley D.; Braun, D. C.; Felipe, T.; Birch, A. C.;
Duvall, T. L.
2011SPD....42.1604C Altcode: 2011BAAS..43S.1604C
We will discuss recent progress in the measurement and modeling of the
interaction of helioseismic waves with small-scale magnetic elements. We
will present measurements of the Hankel analysis phase shifts
and absorption coefficients associated with an average small-scale
magnetic element, measured using ensemble-averaging techniques. We
will show results from theoretical calculations and the numerical
simulations of wave interactions with thin magnetic flux tubes. We
will compare the Hankel analysis measurements with the predictions
from these theoretical models, and discuss how these results pertain
to the local helioseismology of magnetic flux concentrations. This
work is supported by NASA contract NNH09CE43C.

---------------------------------------------------------
Title: Towards Reliable Physics-based Helioseismic Inversions of
Sunspot Structure
Authors: Braun, Douglas; Birch, A.; Crouch, A.; Clack, C.; Dombroski,
D.; Rempel, M.; Duvall, T., Jr.
2011SPD....42.1603B Altcode: 2011BAAS..43S.1603B
Inversion methods capable of reliably probing the subsurface structure
beneath regions of strong magnetic fields, such as sunspots,
remain elusive. We will review progress of a SDO Science Center
project, funded to (among other goals) develop and evaluate new
methods for this problem. Progress to date has included extensive
production of magneto-convective sunspot models for the testing and
validation of existing methods, for which a 27 hour run of artificial
photospheric Dopplergrams is available online to the community. We
will also summarize progress on the use of magnetostatic models for
the development and testing of novel inversion methods designed to
distinguish between magnetic field and thermal perturbations. This
work is supported by NASA contracts NNH09CE41C and NNG07EI51C.

---------------------------------------------------------
Title: Local Helioseismology of Magnetoconvective Sunspot Simulations
and the Reliability of Standard Inversion Methods
Authors: Braun, Douglas; Birch, A.; Rempel, M.; Duvall, T.; J.
2011SPD....42.1607B Altcode: 2011BAAS..43S.1607B
Controversy exists in the interpretation and modeling of helioseismic
signals in and around magnetic regions like sunspots. We show the
results of applying local helioseismic inversions to travel-time shift
measurements from realistic magnetoconvective sunspot simulations. We
compare travel-time maps made from several simulations, using
different measurements (helioseismic holography and center-annulus
time distance helioseismology), and made on real sunspots observed
with the HMI instrument onboard the Solar Dynamics Observatory. We
find remarkable similarities in the travel-time perturbations
measured between: 1) simulations extending both 8 and 16 Mm deep,
2) the methodology (holography or time-distance) applied, and 3)
the simulated and real sunspots. The application of RLS inversions,
using Born approximation kernels, to narrow frequency-band travel-time
shifts from the simulations demonstrates that standard methods fail
to reliably reproduce the true wave speed structure. These findings
emphasize the need for new methods for inferring the subsurface
structure of active regions. Artificial Dopplergrams from our
simulations are available to the community at www.hao.ucar.edu under
"Data" and "Sunspot Models." This work is supported by NASA under the
SDO Science Center project (contract NNH09CE41C).

---------------------------------------------------------
Title: Newly Identified Properties of Surface Acoustic Power
Authors: Schunker, H.; Braun, D. C.
2011SoPh..268..349S Altcode: 2010SoPh..tmp..146S; 2010SoPh..tmp...76S; 2009arXiv0911.3042S
The cause of enhanced acoustic power surrounding active regions,
known as the acoustic halo, is not as yet understood. We explore the
properties of the enhanced acoustic power observed near disk center
from 21 to 27 January 2002, including AR 9787. We find that i) there
exists a strong correlation of the enhanced high-frequency power with
magnetic-field inclination, with greater power in more horizontal
fields, ii) the frequency of the maximum enhancement increases along
with magnetic-field strength, and iii) the oscillations contributing
to the halos show modal ridges that are shifted to higher wavenumber
at constant frequency in comparison to the ridges of modes in the
quiet Sun.

---------------------------------------------------------
Title: The Need for Physics-based Inversions of Sunspot Structure
and Flows
Authors: Braun, D. C.; Birch, A. C.; Crouch, A. D.; Rempel, M.
2011JPhCS.271a2010B Altcode:
Current controversy exists in the interpretation and modeling
of helioseismic signals in and around magnetic regions like
sunspots. Unresolved issues include the dependence of the sign of
both the inferred flows and wave speed on the type of filtering used,
and the discrepancy between the relatively deep two-layer wave-speed
models derived from standard time-distance methods and shallow, positive
wave-speed models derived using forward models which include effects of
mode conversion To make full use of the year-round, almost limb-to-limb,
coverage provided by the Solar Dynamics Observatory, an efficient and
reliable inversion method incorporating possible magnetic effects and
the currently unexplained sensitivity to methodology is critical.

---------------------------------------------------------
Title: Properties of Near-surface Flows around Active Regions from
Helioseismic Holography
Authors: Braun, D. C.; Wan, K.
2011JPhCS.271a2007B Altcode:
A variety of local-helioseismic analyses have shown ~50 m/s flows
converging on active regions (ARs). We have examined the average
properties of both the 75 strongest converging and 75 strongest
diverging flows present in Carrington rotation CR1988 within the
uppermost 3 Mm of the Sun. The flows, averaged over 5 days, were deduced
from calibrated helioseismic holography measurements applied to MDI
observations of CR1988. Inflows associated with ARs typically have
maximum speed of between 20 and 60 m/s at about 3 heliocentric degrees
from their centers and fall to zero by a radius of 7 degrees. Similar
converging flows, however, are prevalent in the quiet Sun. Outflows
of similar spatial extent, but signficantly larger speeds, are present
diverging from sunspots (i.e. the moat flows). Many of the converging
flows in ARs appear to simply mark the boundaries of the moats while
others converge on plage regions. In general, large ARs containing
sunspots contain a complex mixture of both inflows and outflows which,
aside from sunspot moats, also appear similar in property to convective
components of the quiet Sun.

---------------------------------------------------------
Title: Sunspot Seismology with the Solar Dynamics Observatory
Helioseismic and Magnetic Imager
Authors: Braun, D. C.; Birch, A. C.; Crouch, A. D.; Clack, C.;
Dombroski, D.; Rempel, M.
2010AGUFMSH14A..05B Altcode:
The Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
Observatory (SDO) promises to yield detailed information about the
subsurface dynamics and structure of solar active regions. A SDO Science
Center was recently funded and initiated by NASA to (among other goals)
enable the reliable measurements of subsurface flow, magnetic field,
and sound speed in regions of strong magnetic fields. Using analyses
of sunspots observed with HMI/SDO, we illustrate the challenges of
this goal and suggest a plan for the development and implementation of
new physics-based modeling of the subsurface structure of sunspots. Key
components of this effort will be discussed, including numerical forward
modeling of the wave propagation through model sunspots. These efforts
incorporate both magnetostatic and magneto-convective models. This
work is supported by the NASA SDO Science Center and Heliophysics GI
programs through contracts NNH09CE41C and NNG07EI51C.

---------------------------------------------------------
Title: An Estimate of the Detectability of Rising Flux Tubes
Authors: Birch, A. C.; Braun, D. C.; Fan, Y.
2010ApJ...723L.190B Altcode:
The physics of the formation of magnetic active regions (ARs) is one
of the most important problems in solar physics. One main class of
theories suggests that ARs are the result of magnetic flux that rises
from the tachocline. Time-distance helioseismology, which is based on
measurements of wave propagation, promises to allow the study of the
subsurface behavior of this magnetic flux. Here, we use a model for a
buoyant magnetic flux concentration together with the ray approximation
to show that the dominant effect on the wave propagation is expected
to be from the roughly 100 m s-1 retrograde flow associated
with the rising flux. Using a B-spline-based method for carrying out
inversions of wave travel times for flows in spherical geometry, we
show that at 3 days before emergence the detection of this retrograde
flow at a depth of 30 Mm should be possible with a signal-to-noise
level of about 8 with a sample of 150 emerging ARs.

---------------------------------------------------------
Title: Modeling the Subsurface Structure of Sunspots
Authors: Moradi, H.; Baldner, C.; Birch, A. C.; Braun, D. C.; Cameron,
R. H.; Duvall, T. L.; Gizon, L.; Haber, D.; Hanasoge, S. M.; Hindman,
B. W.; Jackiewicz, J.; Khomenko, E.; Komm, R.; Rajaguru, P.; Rempel,
M.; Roth, M.; Schlichenmaier, R.; Schunker, H.; Spruit, H. C.;
Strassmeier, K. G.; Thompson, M. J.; Zharkov, S.
2010SoPh..267....1M Altcode: 2009arXiv0912.4982M; 2010SoPh..tmp..171M
While sunspots are easily observed at the solar surface, determining
their subsurface structure is not trivial. There are two main
hypotheses for the subsurface structure of sunspots: the monolithic
model and the cluster model. Local helioseismology is the only means
by which we can investigate subphotospheric structure. However, as
current linear inversion techniques do not yet allow helioseismology to
probe the internal structure with sufficient confidence to distinguish
between the monolith and cluster models, the development of physically
realistic sunspot models are a priority for helioseismologists. This
is because they are not only important indicators of the variety of
physical effects that may influence helioseismic inferences in active
regions, but they also enable detailed assessments of the validity of
helioseismic interpretations through numerical forward modeling. In
this article, we provide a critical review of the existing sunspot
models and an overview of numerical methods employed to model wave
propagation through model sunspots. We then carry out a helioseismic
analysis of the sunspot in Active Region 9787 and address the serious
inconsistencies uncovered by Gizon et al. (2009a, 2009b). We find that
this sunspot is most probably associated with a shallow, positive
wave-speed perturbation (unlike the traditional two-layer model)
and that travel-time measurements are consistent with a horizontal
outflow in the surrounding moat.

---------------------------------------------------------
Title: Erratum: Erratum to: Helioseismology of Sunspots: A Case
Study of NOAA Region 9787
Authors: Gizon, L.; Schunker, H.; Baldner, C. S.; Basu, S.; Birch,
A. C.; Bogart, R. S.; Braun, D. C.; Cameron, R.; Duvall, T. L.;
Hanasoge, S. M.; Jackiewicz, J.; Roth, M.; Stahn, T.; Thompson, M. J.;
Zharkov, S.
2010SSRv..156..257G Altcode: 2010SSRv..tmp...99G
No abstract at ADS

---------------------------------------------------------
Title: Modeling the Sensitivity of Helioseismic Measurements to
Magnetic Fields and Thermal Perturbations
Authors: Crouch, Ashley D.; Birch, A.; Braun, D.
2010AAS...21631906C Altcode: 2010BAAS...41Q.910C
We will discuss recent progress in modeling the interaction of
helioseismic waves with magnetic fields and thermal perturbations. We
employ a background model that is translation-invariant in the
horizontal directions, has a realistic stratification in the vertical
direction, and includes uniform, inclined magnetic fields. Physically
consistent boundary conditions for the waves are implemented at the
upper and lower boundaries of the model. Using this model we generate
synthetic data and subsequently measure time-distance travel times. We
will show the sensitivity of these travel times to magnetic fields and
changes in sound speed. We will show the effect of magnetic fields on
inversions for wave speed. We will discuss how these results relate
to the local heliseismology of sunspots. This work is supported by
NASA contracts NNH09CE41C and NNG07EI51C.

---------------------------------------------------------
Title: Developing Physics-Based Procedures for Local Helioseismic
Probing of Sunspots and Magnetic Regions
Authors: Birch, Aaron; Braun, D. C.; Crouch, A.; Rempel, M.; Fan,
Y.; Centeno, R.; Toomre, J.; Haber, D.; Hindman, B.; Featherstone,
N.; Duvall, T., Jr.; Jackiewicz, J.; Thompson, M.; Stein, R.; Gizon,
L.; Cameron, R.; Saidi, Y.; Hanasoge, S.; Burston, R.; Schunker, H.;
Moradi, H.
2010AAS...21630805B Altcode:
We have initiated a project to test and improve the local helioseismic
techniques of time-distance and ring-diagram analysis. Our goals are
to develop and implement physics-based methods that will (1) enable the
reliable determinations of subsurface flow, magnetic field, and thermal
structure in regions of strong magnetic fields and (2) be quantitatively
tested with realistic solar magnetoconvection simulations in the
presence of sunspot-like magnetic fields. We are proceeding through a
combination of improvements in local helioseismic measurements, forward
modeling of the helioseismic wavefield, kernel computations, inversions,
and validation through numerical simulations. As improvements over
existing techniques are made they will be applied to the SDO/HMI
observations. This work is funded through the the NASA Heliophysics
Science Division through the Solar Dynamics Observatory (SDO) Science
Center program.

---------------------------------------------------------
Title: Tests of Helioseismic Holography Sound-Speed Inversions Using
Synthetic Data
Authors: Birch, Aaron; Braun, D.; Crouch, A.; Parchevsky, K.;
Kosovichev, A.
2010AAS...21640006B Altcode: 2010BAAS...41..855B
Helioseismic holography is an important method for measuring physical
conditions in the solar interior. Synthetic data is a powerful tool
for validating the methods of local helioseismology. Here we show
some example inversions of surface-focusing holography measurements of
synthetic data sets. We show that Born-approximation based inversions
of phase-speed and ridge-filtered measurements yield models that
are consistent with the true sound-speed structure in some simple
test cases. This work is supported by NASA contracts NNH09CE41C and
NNG07EI51C.

---------------------------------------------------------
Title: How Much Data Do We Need to Detect the Deep Solar Meridional
Circulation?
Authors: Braun, D. C.; Birch, A. C.
2009ASPC..416..131B Altcode:
We assess the noise in p-mode travel-time shifts which would
form the basis of inferences of large-scale flows throughout the
solar convection zone. We derive the expected travel times from a
parameterized return flow component of the meridional circulation. We
show that a helioseismic detection of the return component may not be
possible using data spanning an interval less than a solar cycle.

---------------------------------------------------------
Title: The Internal Dynamics and Magnetism of the Sun -- the
Perspective from Local Helioseismology (Invited)
Authors: Braun, D. C.
2009AGUFMSH11B..03B Altcode:
The application of innovative local helioseismic methods to solar
observations made with GONG, MDI, and other instruments over the past
two decades has shed light on dynamical and magnetic processes in the
solar interior. The community now stands poised for the onslaught
of new data of unprecedented quality and quantity from the SDO
mission. However, we are already substantially benefiting from the
appearance of sophisticated numerical analyses and artificial data
products. I will touch upon three problems in local helioseismology
which are subject to substantive renewed efforts: the deep meridional
circulation, the detection of magnetic flux prior to its appearance
at the photosphere, and the subsurface nature of sunspots. All three
problems pose major challenges, but there is considerable hope for
breakthroughs within the next few years. DCB acknowledges support
from NSF grant AST-0406225; NASA contracts NNH09CE41C, NNG07EI51C,
and NNH07CD25C; and a subcontract from the NASA sponsored HMI project
at Stanford University.

---------------------------------------------------------
Title: Numerical sunspot models - subsurface structure and
helioseismic forward modeling (Invited)
Authors: Rempel, M.; Birch, A. C.; Braun, D. C.
2009AGUFMSH11B..02R Altcode:
The magnetic and thermal subsurface structure of sunspots has been
debated for decades. While local helioseismic inversions allow in
principle to constrain the subsurface structure of sunspots, a full
inversion is still not possible due to the complicated interaction
between waves and magnetic field. As an alternative it is possible to
address this problem through forward modeling. Over the past few years
numerical MHD models of entire sunspots including radiative transfer and
a realistic equation of state have become possible. These simulations
include p-modes excited by convection and the full interaction of these
modes with the magnetic and thermal structure of the sunspot. In this
talk I will present recent progress in MHD modeling of sunspots with
special emphasis on the thermal and magnetic structure of numerical
sunspot models. It turns out that modeled sunspots so far impose
rather shallow perturbations to sound and fast mode speeds in the
upper most 2 Mm. Nevertheless the seismic signatures are very similar
to observed sunspots.

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

---------------------------------------------------------
Title: Absorption of p Modes by Magnetic Plage
Authors: Jain, R.; Hindman, B. W.; Braun, D. C.; Birch, A. C.
2009ASPC..416...55J Altcode:
The Sun's magnetic active regions, composed of sunspots and plage,
are topologically complex. The magnetic field is highly structured,
forming a tangle of fibrils within the plage and more compact,
regimented bundles within sunspot umbrae. The fragmented nature
of the field makes helioseismic observations within active regions
rather difficult to interpret. We choose to study the propagation of
acoustic waves through regions of plage, modeling the magnetic field
therein as a collection of thin flux tubes. In this paper, we present
the first results of this research; the computation of the absorption
coefficient from an ensemble of many flux tubes. The incoming acoustic
waves interact with the magnetic flux tube, exciting sausage and kink
tube waves which propagate downward and upward carrying away energy,
thereby producing absorption. We calculate the resulting theoretical
absorption coefficients and compare with the most recent observations.

---------------------------------------------------------
Title: Detecting, Selecting, And Controlling For Emerging
ActiveRegions In The Search For Helioseismic Pre-emergence Signatures.
Authors: Leka, K. D.; Dunn, T.; Gonzalez-Hernandez, I.; Barnes, G.;
Braun, D.; Birch, A.
2009SPD....40.0708L Altcode:
Helioseismology is potentially capable of predicting the emergence of
solaractive regions. As part of a search for statistically significant
helioseismic predictors of active region emergence, we have developed
methods for the automatic determination of emergence times based on the
NOAA/NGDC active region catalog and MDI/SOHO 96 minute magnetograms. We
demonstrate the application of this method and its sister task of
selecting an appropriate control sample. We show first results from
a statistical study investigating the pre-emergence signatures of
Solar Active Regions using GONG data. This work was supported by NASA
contract NNH07CD25C.

---------------------------------------------------------
Title: A Search for Pre-Emergence Signatures of Active Regions
Authors: Birch, Aaron; Braun, D. C.; Leka, K. D.; Barnes, G.; Dunn,
T. L.; González Hernández, I.
2009SPD....40.0402B Altcode:
Prediction of solar active region emergence is an important goal
for helioseismology. As a first step towards developing prediction
methods, we are carrying out a search for helioseismic pre-emergence
signatures. Using GONG data, we have applied helioseismic holography
to about 150 pre-emergence active regions and a control sample of 450
quiet-Sun regions. We will show preliminary results of this study. This work was supported by NASA contract NNH07CD25C

---------------------------------------------------------
Title: Helioseismology of a Realistic MHD Sunspot Simulation
Authors: Braun, Douglas; Birch, A. C.; Rempel, M.
2009SPD....40.0303B Altcode:
We have recently measured travel times and absorption of p modes
propagating through a realistic numerical model of solar convection in
the presence of a sunspot-like structure. Both the mean travel-time
perturbations and the absorption in the simulation are remarkably
similar to those observed in typical sunspots. Therefore, simulations
of this type provide both the means to understand the physics behind
the helioseismic observations and the opportunity to validate existing
and future models of the subsurface structure of sunspots. We will
compare helioseismic measurements made with the simulation with
those of a typical sunspot observed with MDI. We will discuss the
implications of these comparisons for structural inversions of sunspots
and understanding the role of MHD mode conversion in interpreting
helioseismic observations. This work is supported by NASA contracts
NNH09CE41C and NNG07EI51C.

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

---------------------------------------------------------
Title: Helioseismic Inversions applied to a Realistic MHD Sunspot
Simulation
Authors: Birch, Aaron; Braun, D. C.; Rempel, M.
2009SPD....40.0713B Altcode:
Local helioseismology applied to the realistic magneto-convection
sunspot simulations of Rempel et al. produces solar-like wave travel
times. We apply standard ray-theory based inversions to infer subsurface
wave speed from these travel times. We find that the inferred wave-speed
perturbations are similar to the wave-speed perturbations found from
the analysis of typical sunspots observed with MDI. We show, however,
that the ray theory inversions fail to retrieve the true time-averaged
sound speed or fast-mode speed from the simulations. We propose some
alternative strategies for inferring the subsurface structure of
sunspots. This work is supported by NASA contracts NNH09CE41C
and NNG07EI51C.

---------------------------------------------------------
Title: Helioseismology of Sunspots: A Case Study of NOAA Region 9787
Authors: Gizon, L.; Schunker, H.; Baldner, C. S.; Basu, S.; Birch,
A. C.; Bogart, R. S.; Braun, D. C.; Cameron, R.; Duvall, T. L.;
Hanasoge, S. M.; Jackiewicz, J.; Roth, M.; Stahn, T.; Thompson, M. J.;
Zharkov, S.
2009SSRv..144..249G Altcode: 2008SSRv..tmp..188G; 2010arXiv1002.2369G
Various methods of helioseismology are used to study the subsurface
properties of the sunspot in NOAA Active Region 9787. This sunspot
was chosen because it is axisymmetric, shows little evolution during
20-28 January 2002, and was observed continuously by the MDI/SOHO
instrument. AR 9787 is visible on helioseismic maps of the farside
of the Sun from 15 January, i.e. days before it crossed the East
limb. Oscillations have reduced amplitudes in the sunspot at all
frequencies, whereas a region of enhanced acoustic power above 5.5 mHz
(above the quiet-Sun acoustic cutoff) is seen outside the sunspot and
the plage region. This enhanced acoustic power has been suggested to
be caused by the conversion of acoustic waves into magneto-acoustic
waves that are refracted back into the interior and re-emerge as
acoustic waves in the quiet Sun. Observations show that the sunspot
absorbs a significant fraction of the incoming p and f modes around 3
mHz. A numerical simulation of MHD wave propagation through a simple
model of AR 9787 confirmed that wave absorption is likely to be due
to the partial conversion of incoming waves into magneto-acoustic
waves that propagate down the sunspot. Wave travel times and mode
frequencies are affected by the sunspot. In most cases, wave packets
that propagate through the sunspot have reduced travel times. At
short travel distances, however, the sign of the travel-time shifts
appears to depend sensitively on how the data are processed and,
in particular, on filtering in frequency-wavenumber space. We carry
out two linear inversions for wave speed: one using travel-times
and phase-speed filters and the other one using mode frequencies
from ring analysis. These two inversions give subsurface wave-speed
profiles with opposite signs and different amplitudes. The travel-time
measurements also imply different subsurface flow patterns in the
surface layer depending on the filtering procedure that is used. Current
sensitivity kernels are unable to reconcile these measurements, perhaps
because they rely on imperfect models of the power spectrum of solar
oscillations. We present a linear inversion for flows of ridge-filtered
travel times. This inversion shows a horizontal outflow in the upper
4 Mm that is consistent with the moat flow deduced from the surface
motion of moving magnetic features. From this study of AR 9787, we
conclude that we are currently unable to provide a unified description
of the subsurface structure and dynamics of the sunspot.

---------------------------------------------------------
Title: Surface-Focused Seismic Holography of Sunspots:
II. Expectations from Numerical Simulations Using Sound-Speed
Perturbations
Authors: Birch, A. C.; Braun, D. C.; Hanasoge, S. M.; Cameron, R.
2009SoPh..254...17B Altcode: 2008SoPh..tmp..186B
Helioseismic observations of sunspots show that wave travel times, at
fixed horizontal phase speed, depend on the temporal frequency of the
waves employed in the data analysis. This frequency variation has been
suggested to be consistent with near-surface (vertical length scales
of order one Mm or smaller) changes in wave propagation properties
relative to the quiet Sun. We investigate this suggestion by employing
numerical simulations of acoustic-wave propagation through models
with horizontally and vertically inhomogeneous structure. Standard
methods of surface-focused helioseismic holography are applied to the
resulting simulated wave fields. We find that the travel-time shifts
measured using holography from the simulations with deep sound-speed
perturbations (relative to a plane-parallel quiet-Sun model) do not
show a systematic frequency dependence at phase speeds above about
20 km s−1. However, shallow sound-speed perturbations,
similar to those proposed to model the acoustic scattering properties
of sunspots observed with Hankel analysis, produce systematic frequency
dependence at these phase speeds. In both cases, positive travel-time
shifts can be caused by positive sound-speed perturbations. The details
of the travel-time shifts are, however, model dependent.

---------------------------------------------------------
Title: Magnetic flux emergence on the Sun and Sun-like stars
Authors: Rempel, Matthias; Fan, Yuhong; Birch, Aaron; Braun, Douglas
2009astro2010S..74R Altcode: 2009astro2010S..74F
No abstract at ADS

---------------------------------------------------------
Title: Prospects for the Detection of the Deep Solar Meridional
Circulation
Authors: Braun, Douglas; Birch, A. C.
2009AAS...21349202B Altcode: 2009BAAS...41..471B
We perform helioseismic holography to assess the noise in p-mode
travel-time shifts which would form the basis of inferences of
large-scale flows throughout the solar convection zone. We also
derive the expected travel times from a parameterized return
(equatorward) flow component of the meridional circulation at the
base of the convection zone from forward models under the assumption
of the Born approximation. From estimations of the signal-to-noise
ratio for measurements focused near the base of the convection zone,
we conclude that the helioseismic detection of the deep meridional
flow including the return component may not be possible using data
spanning an interval less than a solar cycle.

---------------------------------------------------------
Title: Prospects for the Detection of the Deep Solar Meridional
Circulation
Authors: Braun, D. C.; Birch, A. C.
2008ApJ...689L.161B Altcode: 2008arXiv0810.0284B
We perform helioseismic holography to assess the noise in p-mode
travel-time shifts which would form the basis of inferences of
large-scale flows throughout the solar convection zone. We also derive
the expected travel times from a parameterized return (equatorward)
flow component of the meridional circulation at the base of the
convection zone from forward models under the assumptions of the ray
and Born approximations. From estimates of the signal-to-noise ratio
for measurements focused near the base of the convection zone, we
conclude that the helioseismic detection of the deep meridional flow
including the return component may not be possible using travel-time
measurements spanning an interval less than a solar cycle. We speculate
that this conclusion may be generally true for other helioseismic
methods under the assumption that the underlying measurements are
equivalently limited by solar realization noise.

---------------------------------------------------------
Title: Physical Properties of Wave Motion in Inclined Magnetic Fields
within Sunspot Penumbrae
Authors: Schunker, H.; Braun, D. C.; Lindsey, C.; Cally, P. S.
2008SoPh..251..341S Altcode: 2008arXiv0801.4448S; 2008SoPh..tmp...41S
At the surface of the Sun, acoustic waves appear to be affected by the
presence of strong magnetic fields in active regions. We explore the
possibility that the inclined magnetic field in sunspot penumbrae may
convert primarily vertically-propagating acoustic waves into elliptical
motion. We use helioseismic holography to measure the modulus and phase
of the correlation between incoming acoustic waves and the local surface
motion within two sunspots. These correlations are modeled by assuming
the surface motion to be elliptical, and we explore the properties
of the elliptical motion on the magnetic-field inclination. We also
demonstrate that the phase shift of the outward-propagating waves is
opposite to the phase shift of the inward-propagating waves in stronger,
more vertical fields, but similar to the inward phase shifts in weaker,
more-inclined fields.

---------------------------------------------------------
Title: Surface-Focused Seismic Holography of Sunspots: I. Observations
Authors: Braun, D. C.; Birch, A. C.
2008SoPh..251..267B Altcode: 2008arXiv0802.2652B; 2008SoPh..tmp...46B
We present a comprehensive set of observations of the interaction
of p-mode oscillations with sunspots using surface-focused seismic
holography. Maps of travel-time shifts, relative to quiet-Sun travel
times, are shown for incoming and outgoing p modes as well as their
mean and difference. We compare results using phase-speed filters
with results obtained with filters that isolate single p-mode ridges,
and we further divide the data into multiple temporal frequency
bandpasses. The f mode is removed from the data. The variations of the
resulting travel-time shifts with magnetic-field strength and with the
filter parameters are explored. We find that spatial averages of these
shifts within sunspot umbrae, penumbrae, and surrounding plage often
show strong frequency variations at fixed phase speed. In addition, we
find that positive values of the mean and difference travel-time shifts
appear exclusively in waves observed with phase-speed filters that
are dominated by power in the low-frequency wing of the p1
ridge. We assess the ratio of incoming to outgoing p-mode power using
the ridge filters and compare surface-focused holography measurements
with the results of earlier published p-mode scattering measurements
using Fourier - Hankel decomposition.

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

---------------------------------------------------------
Title: Helioseismic Holography of Simulated Solar Convection and
Prospects for the Detection of Small-Scale Subsurface Flows
Authors: Braun, D. C.; Birch, A. C.; Benson, D.; Stein, R. F.;
Nordlund, Å.
2007ApJ...669.1395B Altcode: 2007arXiv0708.0214B
We perform helioseismic holography on realistic solar convection
simulations and compare the observed travel-time perturbations
with the expected travel times from the horizontal flows in the
simulations computed from forward models under the assumption of
the Born approximation. We demonstrate reasonable agreement between
the observed and model travel times, which reinforces the validity
of helioseismic holography in the detection of subsurface horizontal
flows. An assessment is made of the uncertainty of the measured p-mode
travel times from the rms of the residuals. From the variation of the
signal-to-noise ratio with depth we conclude that the helioseismic
detection of individual flow structures with spatial scales of
supergranulation or smaller is not possible for depths below about 5 Mm
below the surface over timescales of less than a day. The travel-time
noise estimated from these simulations appears to be similar to noise
in measurements made using solar observations. We therefore suggest
that similar limitations exist regarding the detection of analogous
subsurface flows in the Sun. A study of the depth dependence of
the contribution to the travel-time perturbations for focus depths
between 3 and 7 Mm is made, showing that approximately half of the
observed signal originates within the first 2 Mm below the surface. A
consequence of this is a rapid decrease (and reversal in some cases)
of the travel-time perturbations with depth due to the contribution to
the measurements of oppositely directed surface flows in neighboring
convective cells. This confirms an earlier interpretation of similar
effects reported from observations of supergranulation.

---------------------------------------------------------
Title: Helioseismic Holography of Simulated Solar Convection and
Prospects for the Detection of Small-Scale Subsurface Flows
Authors: Braun, Douglas; Birch, A. C.; Benson, D.; Stein, R. F.;
Nordlund, A.
2007AAS...210.2201B Altcode: 2007BAAS...39..124B
We perform helioseismic holography on the solar convection simulations
of Benson, Stein, and Nordlund and compare the observed acoustic
travel-time perturbations with the expected travel times from the
horizontal flows in the simulations computed from forward models under
the assumption of the Born approximation. The agreement between the
observed and model travel times reinforces the validity of helioseismic
holography in the detection of subsurface horizontal flows. However,
from the variation of the signal-to-noise ratio with depth, we conclude
that the local helioseismic detection of individual supergranule-size
(or smaller) flow patterns is not possible for depths below about
5 Mm below the surface over time scales less than a day. We suggest
that similar limitations exist regarding the detection of analogous
subsurface flows in the Sun. We also study the depth dependence of
the contribution to the travel-time perturbations for the simulated
flows. For holography measurements focused down to 7 Mm, we find
that approximately half of the observed signal originates within
the first 2 Mm below the surface. A consequence of this is a a rapid
decrease (and possible reversal) of the travel-time perturbations with
increasing focus depth due to the contribution to the measurements of
oppositely directed surface flows in neighboring convective cells. This
confirms an earlier interpretation of similar effects reported from
holographic analyses of observations of supergranulation. This
work is supported by NASA contracts NNH05CC76C and NNH04CC05C, NSF
grant AST-0406225 , and a subcontract through the HMI project at
Stanford University awarded to NWRA, and by NASA grant NNG04GB92G and
NSF grant AST-0605738 to MSU.

---------------------------------------------------------
Title: Sunspot Seismology: Testing Surface Effects with Numerical
Simulations
Authors: Braun, Douglas; Birch, A. C.; Hanasoge, S. M.
2007AAS...210.2206B Altcode: 2007BAAS...39..125B
The discovery that sunspots absorb acoustic waves was first announced
twenty years ago at a previous SPD meeting in Honolulu. A considerable
effort has been made to understand the physics of the interaction
between acoustic waves and sunspots. However, the implications of this
two-decade old discovery are still being explored in helioseismology. An
ongoing controversy involves the role of surface effects, including
absorption, in modeling the subsurface structure of sunspots. Braun
and Birch recently suggested that observed frequency variations,
at fixed phase speeds, of acoustic travel-time perturbations through
sunspots offers evidence for a strong contribution to travel times
from structures with vertical scales smaller than about one Mm
near the solar surface. We test this suggestion with the numerical
simulations of acoustic-wave propagation hrough specified sound-speed
perturbations of a background solar model. An important finding is that
travel times measured using helioseismic holography from simulations
employing sound-speed perturbations typical of recent time-distance
inversions do not predict the strong frequency variations observed in
with solar data. We are in the process of evaluating whether shallow
sound-speed perturbations, such as that proposed by Fan, Braun and
Chou to explain the acoustic scattering propertis of sunspots observed
with Hankel analysis, can reproduce the frequency variations observed
in sunspots. This work is supported by contracts NAS5-02139,
NNH05CC76C and NNH04CC05C from NASA, and grant AST-0406225 from the NSF.

---------------------------------------------------------
Title: Surface magnetic field effects in local helioseismology
Authors: Schunker, H.; Braun, D. C.; Cally, P. S.
2007AN....328..292S Altcode: 2010arXiv1002.2379S
Using helioseismic holography strong evidence is presented that
the phase (or equivalent travel-time) of helioseismic signatures in
Dopplergrams within sunspots depend upon the line-of-sight angle in
the plane containing the magnetic field and vertical directions. This
is shown for the velocity signal in the penumbrae of two sunspots
at 3, 4 and 5 mHz. Phase-sensitive holography demonstrates that they
are significantly affected in a strong, moderately inclined magnetic
field. This research indicates that the effects of the surface magnetic
field are potentially very significant for local helioseismic analysis
of active regions.

---------------------------------------------------------
Title: The Role of MHD Mode Conversion in Sunspot Seismology
Authors: Crouch, A. P.; Cally, P. S.; Charbonneau, P.; Braun, D. C.;
Desjardins, M.
2006ASPC..354..161C Altcode:
Sunspots absorb energy from and shift the phase of f and p modes
incident upon them. Understanding the mechanism causing each of these
effects is vital to the local helioseismology of sunspots (and magnetic
flux concentrations in general). Because the beta-equals-unity layer
typically lies in the near surface layers below the photospheres
of sunspot umbrae, MHD mode conversion can occur. Mode conversion
provides a promising absorption mechanism because the slow
magnetoacoustic-gravity waves and Alfvén waves guide energy along
the magnetic field away from the acoustic cavity. Our previous mode
conversion calculations have shown that simple sunspot models with
non-vertical magnetic fields can produce ample absorption to explain the
Hankel analysis measurements, along with phase shift predictions that
agree well with the observations. Those calculations only considered
the possibility of MHD waves propagating down the magnetic field into
the interior. In this contribution, we consider a second additional
possibility -- waves propagating up into the atmosphere overlying
sunspots.

---------------------------------------------------------
Title: Behaviour of Acoustic Waves in Sunspots
Authors: Schunker, H.; Braun, D. C.; Cally, P. S.; Lindsey, C.
2006ASPC..354..244S Altcode:
Because helioseismology uses surface signals to calculate subsurface
characteristics the behaviour of surface acoustic oscillations in
sunspots is important in interpreting helioseismic results. SOHO-MDI
Doppler velocity analysis of AR9026 and AR9033 at 3, 4, and 5 mHz,
using helioseismic holography, show that the amplitude and the phase
in the correlation of the acoustic ingression with the observed surface
velocity are found to be sensitive to the relative line-of-sight angle
in the penumbra of both sunspots. This is consistent with a conversion
of vertically propagating acoustic waves into magneto-acoustic waves
with motion described by ellipses.

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

---------------------------------------------------------
Title: The interaction between acoustic waves and inclined magnetic
fields near the β~1 layer
Authors: Schunker, H.; Braun, D. C.; Cally, P. S.; Lindsey, C.
2006IAUJD..17E..16S Altcode:
The acoustic showerglass effect may be hindering our helioseismic
renditions of the solar subsurface. We present the results of near
-surface wave conversion of acoustic waves in a model polytropic
atmosphere by a uniform, inclined magnetic field. The upcoming fast,
acoustic wave undergoes conversion to a slow, magnetic wave at the β
~ 1 layer where the sound speed and Alfven speed are comparable. The
conversion is dependent upon the " attack angle" between the ray path
and the magnetic field. The angle of the wave vectors at the polytropic
" surface" is compared to observations of surface velocity vectors in
sunspot penumbrae. AR9026 and AR9057 both have well- defined, static
penumbrae and their Doppler velocities are viewed from different
angles by SOHO-MDI as they cross the solar disk. The phase of the
correlation between the ingression and surface velocity, determined by
helioseismic holography, is used to assess the effect the penumbral
magnetic field has on incoming acoustic waves. The phase is found to
be dependent upon the line-of-sight of observation indicating that
this is a surface phenomenon, which could otherwise be interpreted as
subsurface travel-time perturbations of up to one minute. Furthermore,
using vector magnetograms from the IVM at the Mees Observatory, the
phase of the correlation is found to be dependent on the magnetic
field tilt from vertical, and the dependence is consistent across the
two sunspots. Comparing the results from the polytropic model with the
observations show strong support for the near-surface wave conversion
theory, although many questions still remain.

---------------------------------------------------------
Title: Observed Frequency Variations of Solar p-Mode Travel Times
as Evidence for Surface Effects in Sunspot Seismology
Authors: Braun, D. C.; Birch, A. C.
2006ApJ...647L.187B Altcode:
Using helioseismic holography, we measure acoustic (p-mode) travel-time
perturbations, observed within solar active regions, as functions of
frequency and phase speed. We find evidence for a frequency variation,
at fixed phase speed, of the travel times that has not previously been
reported. This variation is not expected from typical sound-speed models
of sunspots, which result from the inversion of travel times and may
indicate a significant contribution to the travel times from structures
with vertical scales smaller than about 1 Mm near the solar surface.

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

---------------------------------------------------------
Title: Genetic magnetohelioseismology with Hankel analysis data
Authors: Crouch, A. D.; Cally, P. S.; Charbonneau, P.; Braun, D. C.;
Desjardins, M.
2005MNRAS.363.1188C Altcode: 2005MNRAS.tmp..856C
Hankel analysis determined that sunspots absorb energy from and
shift the phase of f- and p-modes incident upon them. One promising
mechanism that can explain the absorption is partial conversion
to slow magnetoacoustic-gravity (MAG) waves and Alfvén waves,
which guide energy along the magnetic field away from the acoustic
cavity. Our recent mode conversion calculations demonstrated that
simple sunspot models, which roughly account for the radial variation
of the magnetic field strength and inclination, can produce ample
absorption to explain the observations, along with phase shifts that
agree remarkably well with the Hankel analysis data. In this paper,
we follow the same approach, but adopt a more realistic model for the
solar convection zone that includes the thermal perturbation associated
with a sunspot's magnetic field. Consistent with our earlier findings,
we show that a moderately inclined, uniform magnetic field exhibits
significantly enhanced absorption (mode conversion) in comparison
to a vertical field (depending on the frequency and radial order of
the mode). A genetic algorithm is employed to adjust the parameters
that control the radial structure of our sunspot models, in order
to minimize the discrepancy between the theoretical predictions and
the Hankel analysis measurements. For models that best fit the phase
shifts, the agreement with the Hankel analysis data is excellent, and
the corresponding absorption coefficients are generally in excess of the
observed levels. On the other hand, for models that best fit the phase
shift and absorption data simultaneously, the overall agreement is very
good but the phase shifts agree less well. This is most likely caused
by the different sizes of the regions responsible for the absorption and
phase shift. Typically, the field strengths required by such models lie
in the range 1-3kG, compatible with observations for sunspots and active
regions. While there remain some uncertainties, our results provide
further evidence that mode conversion is the predominant mechanism
responsible for the observed absorption in sunspots; and that field
inclination away from vertical is a necessary ingredient for any model
that aims to simultaneously explain the phase shift and absorption data.

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

---------------------------------------------------------
Title: Flow Inversions for Phase-Sensitive Helioseismic Holography
Authors: Birch, A. C.; Braun, D. C.
2005AGUSMSP24A..05B Altcode:
Phase-sensitive holography has been used extensively to study solar
subsurface mass flows. To date though, the ingression-egression
correlation phases measured using phase-sensitive holography data
have never been inverted. We present an inversion procedure, based
on Born-approximation sensitivity functions and the MCD algorithm,
for estimating subsurface flows from phase-sensitive holography
measurements. We present some simple validation tests and example flow
maps resulting from inversions of SOHO/MDI data.

---------------------------------------------------------
Title: Comparison of Solar Subsurface Velocities Using Small-Scale
Ring Analysis, Time-Distance and Holography
Authors: Haber, D. A.; Featherstone, N. A.; Braun, D. C.; Hindman,
B. W.; Bogart, R. S.
2005AGUSMSP24A..01H Altcode:
For the first time we compare subsurface horizontal velocity flows
determined by all three common local helioseismic analysis methods
on a very small scale (approximately 1-2 degrees). Holographic and
time-distance techniques have been compared on small scales, however,
ring analysis techniques have mainly been performed with 15 degree
size tiles spaced 7.5 degrees apart. Here we use tiles approximately
2 degrees in size with a spacing of 1 degree and compare the results
with those of time-distance and holography. All three techniques have
been applied to full-disc Doppler velocity data with 4" resolution (0.2
deg at disc center) taken with the Michelson Doppler Imager instrument
aboard SOHO during Carrington Rotation 1988 in March-April of 2002.

---------------------------------------------------------
Title: Towards Assessing, Understanding, and Correcting the Influence
of Surface Magnetism in Local Helioseismology
Authors: Braun, D. C.; Schunker, H.; Lindsey, C.; Cally, P. S.
2005AGUSMSP23C..03B Altcode:
Efforts to probe subsurface wave-speed variations and mass flows
near and under solar active regions are complicated and potentially
compromised by strong phase and amplitude perturbations introduced in
the photosphere by magnetic fields. Recently it has been shown that
the phase distortions correlate with surface magnetic field strength
and may be corrected to image wave-speed variations underlying active
regions. A strong phase asymmetry between waves arriving into and
departing from a magnetic region is also shown to produce spurious
signatures of horizontal outflows below active regions. Further
evidence of the photospheric origin of these phase distortions, as
well as a key to their physical origin, is also presented. Using MDI
observations, from the SOHO spacecraft, we perform ingression control
correlations in the inclined magnetic fields of sunspot penumbra and
demonstrate that incoming acoustic waves produce photospheric motion
that describes an ellipse tilted towards the inclination of the magnetic
field. A consequence is that the phase of the correlation varies with
the viewing angle with respect to the field direction. Observations
of the vector components of the photospheric fields could be used to
correct these phase perturbations analogous to the procedures already
developed using line-of-sight magnetograms. A physical understanding
of surface distortions will come through MHD modeling, including
simulations of the interaction of acoustic and magneto-acoustic-gravity
waves with prescribed magnetic and sound-speed perturbations and flows
(artificial data). The development of appropriate tools for assessing
and correcting the effects of the surface magnetism will be vital for
the interpretation of helioseismic data from the upcoming HMI mission
on SDO. DCB and CL gratefully acknowledge support from the NSF (SAA/AST)
and NASA (LWS, SR&amp;T).

---------------------------------------------------------
Title: The Local Helioseismology of Inclined Magnetic Fields and
the Showerglass Effect
Authors: Schunker, H.; Braun, D. C.; Cally, P. S.; Lindsey, C.
2005ApJ...621L.149S Altcode:
We present evidence for the dependence of helioseismic Doppler
signatures in active regions on the line-of-sight angle in inclined
magnetic fields. Using data from the Michelson Doppler Imager
(MDI) on board the Solar and Heliospheric Observatory, we performed
phase-sensitive holography in the penumbrae of sunspots over the
course of several days as the spots traversed the solar disk. Control
correlations, which comprise a correlation of the surface wave amplitude
with the incoming acoustic wave amplitude from a surrounding region,
were mapped. There is a direct dependence of control-correlation phase
signatures on the line-of-sight angle in the plane defined by the
vertical and magnetic field vectors. The phase shift of waves observed
along directions close to the orientation of the magnetic field is
smaller than the phase shift observed when the line of sight is at a
significant angle with respect to the field orientation. These findings
have important implications for local helioseismology. The variation
in phase shift (or the equivalent acoustic travel-time perturbations)
with line-of-sight direction suggests that a substantial portion of the
phase shift occurs in the photospheric magnetic field. Observations of
the vector components of the field may be used to develop a proxy to
correct these phase perturbations (known as the acoustic showerglass)
that introduce uncertainties in the signatures of acoustic perturbations
below the surface.

---------------------------------------------------------
Title: The Acoustic Showerglass. I. Seismic Diagnostics of
Photospheric Magnetic Fields
Authors: Lindsey, Charles; Braun, D. C.
2005ApJ...620.1107L Altcode:
A problem of major interest in the helioseismology of active
regions is the acoustics of magnetic photospheres and shallow
subphotospheres. Magnetic fields suppress the photospheric signatures
of acoustic waves impinging onto them from the underlying solar
interior and shift their phases. The phase shifts function as a
sort of acoustic showerglass that impairs the coherence of seismic
waves arriving from below, degrading images of subsurface anomalies
derived by mechanical reconstruction of phase-coherent waves. The
purpose of this study is to characterize the “acoustic showerglass”
in general optical terms and make a rough practical assessment of its
impact on local seismic diagnostics of the shallow subphotospheres of
active regions. We compile statistics comparing the acoustic field in
magnetic photospheres with holographic projections of waves arriving
from distant surrounding pupils. These “local control correlations”
are consistent with an acoustic anomaly in the shallow subphotosphere
of the active region that is strong but predominantly superficial;
we call this the “acoustic Wilson depression.” The local control
correlations also exhibit a phenomenon we call the “penumbral acoustic
anomaly,” characterized by a conspicuous phase shift in regions of
inclined magnetic field. This appears to be consistent with a fairly
straightforward hydromechanical interpretation of the interaction of
acoustic waves with photospheric magnetic forces. Detailed numerical
simulations of the interaction of acoustic waves with magnetic forces
can greatly facilitate our understanding of the acoustic showerglass
and the thermal structure of the top few hundred kilometers of active
region subphotospheres.

---------------------------------------------------------
Title: The Acoustic Showerglass. II. Imaging Active Region
Subphotospheres
Authors: Lindsey, Charles; Braun, D. C.
2005ApJ...620.1118L Altcode:
Seismic diagnostics of the shallow subphotospheres of strong active
regions are substantially impacted by large amplitude and phase
perturbations introduced by overlying surface magnetic fields. These
function as an “acoustic showerglass” that impairs the coherence
of acoustic waves impinging onto the solar surface from below,
degrading images of subsurface anomalies derived by phase-coherent
seismic reconstruction. In an independent study we have developed a
rough proxy to characterize showerglass phase errors based on maps of
the square magnitude of the vector magnetic field at the surface. In
this study we apply the proxy to correct helioseismic observations of
active region photospheres from the Michelson Doppler Imager aboard the
Solar and Heliospheric Observatory. We apply phase-correlation seismic
holography to the corrected observations to image the underlying 5-10
Mm subphotosphere. The corrected phase maps show no consistent evidence
for sound-speed anomalies more than 5 Mm beneath a moderately large,
isolated sunspot. Forward-modeling computations applied to simple
models suggest sound-speed anomalies limited to approximately +/-250 m
s-1 for depths from 5 to 10 Mm, averaged over the horizontal
extent of the sunspot. For complex active regions, uncertainties are
considerably greater. However, results of this study suggest that more
careful modeling of the acoustic showerglass will lead to substantially
improved seismic diagnostics of active region subphotospheres. Detailed
hydromechanical computations of acoustics models of active region
photospheres and subphotospheres are needed to facilitate the
interpretation of showerglass-corrected holographic signatures.

---------------------------------------------------------
Title: Principles of Seismic Holography for Diagnostics of the
Shallow Subphotosphere
Authors: Lindsey, Charles; Braun, D. C.
2004ApJS..155..209L Altcode:
We develop the wave-mechanical formalism for phase-correlation
computational seismic holography of the shallow subphotosphere under
the plane-parallel approximation and apply it to helioseismic Doppler
observations from the Michelson Doppler Imager on the SOHO spacecraft
of both the quiet Sun and active regions. We compare holographic
signatures computed wave-mechanically with similar signatures
computed under the widely used eikonal approximation. The major
difference between the hydromechanical and eikonal computations can
be expressed in terms of acoustic dispersion effects within a few
Mm of the solar surface. With an appropriate account for dispersion,
the eikonal computations are remarkably accurate over a broad range
of practical applications. A major imposition that confronts local
diagnostics of the shallow subphotosphere is a phenomenon we call
“ghost signatures,” artifacts introduced by a local ambiguity in
the origin of the waves that give rise to the helioseismic signatures
observed in the photosphere. Phase-correlation holographic signatures
of the shallow subphotospheres of active regions are predominated by
strong, stochastic phase shifts associated with magnetic fields at the
solar surface. These introduce effects similar to those of an optical
showerglass, significantly impairing the coherence of waves impinging
into the magnetic photosphere from beneath, smearing the holographic
signatures of possible subphotospheric anomalies.

---------------------------------------------------------
Title: Local Helioseismology of Inclined Magnetic Fields and the
Showerglass Effect
Authors: Schunker, H.; Braun, D. C.; Lindsey, C.; Cally, P. S.
2004ESASP.559..227S Altcode: 2004soho...14..227S
No abstract at ADS

---------------------------------------------------------
Title: Local Helioseismology of Near-Surface Flows
Authors: Braun, D. C.; Birch, A. C.; Lindsey, C.
2004ESASP.559..337B Altcode: 2004soho...14..337B
No abstract at ADS

---------------------------------------------------------
Title: The Penumbral Acoustic Anomaly
Authors: Lindsey, C.; Braun, D. C.
2004ESASP.559..552L Altcode: 2004soho...14..552L
No abstract at ADS

---------------------------------------------------------
Title: Local Helioseismology of Solar Dynamics
Authors: Braun, D. C.; Lindsey, C.; Birch, A. C.
2004AAS...204.5309B Altcode: 2004BAAS...36..757B
We have initiated a systematic exploration of the dynamics of the
solar interior, applying Doppler-sensitive seismic holography to data
from the MDI instrument onboard the SOHO spacecraft and the Global
Oscillations Network Group (GONG). Goals of this comprehensive project
include understanding the nature of supergranulation, monitoring the
subsurface variations of the meridional circulation, and understanding
other subsurface flows and their relation to solar activity. We
present initial results on our inference of subsurface flows due with
an emphasis on control work, including comparisons between MDI and GONG
datasets and other local seismic procedures such as ring diagrams. The
project will develop and test data analysis tools and a forward
(and inverse) modeling formalism based on the Born approximation,
in preparation for their routine application to the next generation
of helioseismic data from the Helioseismic and Magnetic Imager (HMI)
on the Solar Dynamics Observer. This work is supported by funding
from NASA SR&amp;T and Living With a Star programs and the NSF Stellar
Astronomy and Astrophysics program.

---------------------------------------------------------
Title: The Acoustic Showerglass and Diagnostics of Active Region
Subphotospheres
Authors: Lindsey, C.; Braun, D. C.
2004AAS...204.5310L Altcode: 2004BAAS...36..757L
Magnetic fields introduce large phase shifts into acoustic waves
passing through the upper 400 km of an active region subphotosphere,
impairing the phase coherence of time-distance correlation measurements,
including seismic images of the underlying subphotosphere. We call
this the "acoustic showerglass" effect. Reliable diagnostics of active
region subphotospheres require a careful account of the interaction of
acoustic waves with showerglass magnetic fields. A clear understanding
of the acoustics of shallow magnetic fields offers the facility for
detailed thermal modeling of the showerglass layer. It also opens the
possibility of a high-quality magnetic proxy to correct showerglass
phase errors, greatly improving our view of the underlying magnetic
subphotosphere. The research reported in this poster is supported by
grants from the National Aeronautics and Space Administration and the
National Science Foundation.

---------------------------------------------------------
Title: Acoustic Holographic Studies of Solar Active Regions
Authors: Malanushenko, A.; Braun, D.; Kholikov, S.; Leibacher, J.;
Lindsey, C.
2004IAUS..223..283M Altcode: 2005IAUS..223..283M
We present results of a study of the morphology and evolution of
active regions using solar acoustic holography. These include acoustic
signatures of large far-side active regions and their relationship to
near-side activity indices a half rotation before and after the farside
image, and the direct comparison of near-side acoustic signatures with
the standard activity indicators, not only in their own right but also
to calibrate the farside acoustic signature.

---------------------------------------------------------
Title: Microfluidic Experiments exploring Thermal Force approaches
to the Origin of Life
Authors: Braun, D.
2004cosp...35..781B Altcode: 2004cosp.meet..781B
Microfluidic experiments are discussed where temperature gradients
across mesoscopic pores provide essential boundary conditions for
autonomous molecular evolution: (1) Laminar thermal convection can
drive exponential DNA replication as the molecules are continuously
cycled between hot and cold regions of a chamber. (2) Thermophoresis
can induce strong accumulation of charged biopolymers such as DNA in the
same convection settings. Combined, the experiments demonstrate a robust
nonequilibrium boundary condition for the replication and accumulation
of evolving molecules. The experimental conditions are comparable to
conditions in porous rocks near submarine hydrothermal mounds. It is
expected that further studies of microscopic open systems can reveal
further unexpected connecting pieces in the fascinating puzzle on
the origins of life. 1. D. Braun, N.L. Goddard and A. Libchaber,
Exponential DNA Replication by Laminar Convection, Physical Review
Letters 91:158103 (2003) 2. D. Braun &amp; A. Libchaber, Trapping of
DNA by Thermophoretic Depletion and Convection, Physical Review Letters
89:188103 (2002) 3. D. Braun &amp; A. Libchaber, Thermal force approach
to molecular evolution, Physical Biology, accepted

---------------------------------------------------------
Title: Probing sunspot magnetic fields with p-mode absorption and
phase shift data
Authors: Cally, P. S.; Crouch, A. D.; Braun, D. C.
2003MNRAS.346..381C Altcode:
Long-standing observations of incoming and outgoing f- and p-modes
in annuli around sunspots reveal that the spots partially absorb
and substantially shift the phase of waves incident upon them. The
commonly favoured absorption mechanism is partial conversion to
slow magneto-acoustic waves that disappear into the solar interior
channelled by the magnetic field of the sunspot. However, up until
now, only f-mode absorption could be accounted for quantitatively by
this means. Based on vertical magnetic field models, the absorption of
p-modes was insufficient. In this paper, we use the new calculations
of Crouch &amp; Cally for inclined fields, and a simplified model of
the interaction between spot interior and exterior. We find excellent
agreement with phase shift data assuming field angles from the
vertical in excess of 30° and Alfvén/acoustic equipartition depths
of around 600-800 km. The absorption of f-modes produced by such
models is considerably larger than is observed, but consistent with
numerical simulations. On the other hand, p-mode absorption is generally
consistent with observed values, up to some moderate frequency dependent
on radial order. Thereafter, it is too large, assuming absorbing regions
comparable in size to the inferred phase-shifting region. The excess
absorption produced by the models is in stark contrast with previous
calculations based on a vertical magnetic field, and is probably due
to finite mode lifetimes and excess emission in acoustic glories. The
excellent agreement of phase shift predictions with observational
data allows some degree of probing of subsurface field strengths, and
opens up the possibility of more accurate inversions using improved
models. Most importantly, though, we have confirmed that slow mode
conversion is a viable, and indeed the likely, cause of the observed
absorption and phase shifts.

---------------------------------------------------------
Title: Computational Seismic Holography of Active Region
Subphotospheres
Authors: Lindsey, C.; Braun, D. C.
2003SPD....34.0808L Altcode: 2003BAAS...35Q.823L
We apply phase-correlation seismic holography to SOHO/MDI observations
of large sunspots to render signatures of local sound-speed anomalies
in their shallow subphotospheres. In the computations reported
here, a magnetic proxy we call the “showerglass correction” was
applied to correct large phase errors introduced by surface magnetic
fields. Preliminary results suggest a general sound speed enhancement
in the range 1--4% up to depths of 10 Mm over horizontally extended
regions surrounding large sunspots. These regions cover diameters
roughly in the range 30--50 Mm. Phase maps of large active region
complexes show signatures that tend to blanket most of the active
region. The correlation between the phase shift and the magnetic
field strength is generally high, but there are localized regions in
which the phase signature departs significantly from the magnetic. The
signature of the sunspot itself tends to be subtle with a maximum that
may be significantly displaced towards the periphery of the active
region. The research reported here is supported by funding from the
Supporting Research and Technology and the Living with a Star Programs
of the National Aeronautics and Space Administration, and from the
Astronomical Sciences Division of the National Science Foundation.

---------------------------------------------------------
Title: The showerglass effect in seismic diagnostics of active
region subphotospehres
Authors: Lindsey, Charles; Braun, D. C.
2003ESASP.517...23L Altcode: 2003soho...12...23L
A major obstacle that encumbers local seismic diagnostics of the shallow
subphotospheres of strong active regions is phase errors introduced by
overlying surface magnetic fields. These errors function as a sort of
"acoustic showerglass" that obscures subphotospheric acoustic anomalies,
scrambling computational images of these derived by phase-coherent
seismic reconstruction. We develop a proxy based on the surface magnetic
field to correct the showerglass phase errors and image acoustic
scatterers beneath it. Preliminary applications of this correction give
us signatures that appear to signify strong, sharply outlined acoustic
anomalies 3-9 Mm beneath large growing active regions. Correction of
the showerglass correction appears to be important, if not essential,
for diffraction-limited diagnostics of acoustic anomalies in the
shallow subphotospheres of strong active regions.

---------------------------------------------------------
Title: Helioseismic imaging of the farside and the interior
Authors: Braun, D. C.; Lindsey, C.
2003ESASP.517...15B Altcode: 2003soho...12...15B
Helioseismic holography is a highly efficient and flexible procedure
with a wide range of utility, from mapping sound wave travel times over
the entire far solar hemisphere to imaging small scale scatterers and
flows beneath solar active regions. Seismic images covering the entire
far hemisphere of the Sun have been constructed using data from the
recently upgraded Global Oscillation Network Group (GONG+) network
and compare favorably with those made using simultaneous data from
the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric
Observer (SOHO). We are also continuing our comprehensive exploration
of diffraction-limited seismic imaging of active regions. We have
recently extended our applications of helioseismic holography to include
Doppler diagnostics of active regions and quiet Sun. A major finding
presented here is that the horizontal velocity field in supergranules
and sunspot moats appears to be concentrated at the surface. Another
recent, but vital, contribution to local helioseismology has been a
study of what is termed the "showerglass effect". Magnetic fields in
the photosphere produce large, local amplitude and phase perturbations
to the observed acoustic wave field which may be quantified and removed
prior to the holographic computations. Removal of the showerglass from
local helioseismic images of active regions is proving to be a crucial
step in the detection of compact subsurface scatterers.

---------------------------------------------------------
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.
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: The First Seismic Images of the Solar Interior and Far Side
from the GONG+ Network
Authors: Braun, D. C.; Lindsey, C.
2002AAS...200.8906B Altcode: 2002BAAS...34..791B
Since mid-2001, the upgraded GONG+ network has been providing
high-resolution Doppler images of the Sun. We are now analyzing GONG+
data as part of our program in local helioseismology and acoustic
holography. The bulk of the results shown here are derived from data
obtained during a 24-hour period in 2001 September, when simultaneous
full-disk observations from the MDI instrument onboard the SOHO
spacecraft were available for comparison. Images showing the acoustic
travel-time perturbations over the entire far hemisphere obtained from
GONG+ and MDI data are essentially identical. This demonstrates that
the GONG+ network may be used as the basis of a synoptic far-side
imaging program of comparable quality to that now provided by
MDI. Holographic depth-diagnostics of travel-time perturbations below
several active regions on the solar front side are also presented. These
phase-sensitive holographic images from GONG+ and MDI have similar
noise characteristics when computed using acoustic modes with degree
(wavenumber) below about 300, which implies that the r.m.s. fluctuations
in these images are solar in nature. At higher wavenumbers, atmospheric
seeing introduces an excess r.m.s., which increases with mode degree,
to the images derived from GONG+ data. However, acceptable images are
possible using modes with degrees up to at least 700. We will discuss
how GONG+ data may be advantageously utilized in detailed, continuous,
and long-term local-helioseismic analyses of the far side and deep
interior of the Sun. This work is supported by awards AST-9987286 from
NSF, and awards NASW-01007 and NAG5-10984 from NASA.

---------------------------------------------------------
Title: Computational Seismic Holography of the Deep Interior and
Far Surface of the Sun
Authors: Lindsey, C.; Braun, D. C.
2002AAS...200.7903L Altcode: 2002BAAS...34..780L
Computational seismic holography has given us a remarkably flexible and
powerful new utility for local diagnostics of the solar interior. Major
results to date include the following: - Seismic signatures
surrounding sunspots up to 100 Mm in diameter, called “acoustic
moats.” - Enhancements of locally stochastic seismic emission, called
“acoustic glories,” surrounding complex active regions. - Chromatic
siesmic emission maps of a solar flare. - Signatures suggesting compact
thermal enhancements in the shallow subphotospheres of surface magnetic
regions. - Synoptic phase-correlation maps of active regions on the
far surface of the Sun. Prospects for deep interior diagnostics of the
solar interior are highly encouraging. Seismic holography applied to the
database we expect from the Solar Dynamics Observatory is nearly certain
to give us a synoptic view of the local structure of flows and torsional
oscillations down to the base of the convection zone. Cooperative
seismic observations of both near and far surfaces of the Sun offer
high quality holographic diagnostics of the solar core. Holographic
diagnostics promise deep insight into the operation of the solar dynamo,
and may give us indications of emerging magnetic fields significantly
in advance of their appearance at the solar surface. This research
has been supported by funding from the National Science Foundation
and the National Aeronautics and Space Administration.

---------------------------------------------------------
Title: Helioseismological observations of active regions
Authors: Braun, Douglas
2002ocnd.confE...3B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Seismic forecasting of solar activity
Authors: Braun, D. C.; Lindsey, C.
2002HiA....12..378B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Seismic Imaging of the Far Hemisphere of the Sun
Authors: Braun, D. C.; Lindsey, C.
2001ApJ...560L.189B Altcode:
We apply phase-sensitive helioseismic holography to Solar and
Heliospheric Observatory/Michelson Dopper Imager data to demonstrate
how acoustic travel-time perturbations may be mapped over the entire
portion of the Sun facing away from the Earth, including the polar
regions. In addition to offering significant improvements to ongoing
space weather forecasting efforts, the procedure offers the possibility
of local seismic monitoring of both the temporal and spatial variations
in the acoustic properties of the Sun over all of the far surface.

---------------------------------------------------------
Title: Helioseismic Holography and a Study of the Process of Magnetic
Flux Disappearance in Canceling Bipoles
Authors: Lindsey, Charles; Harvey, Karen L.; Braun, D.; Jones, H. P.;
Penn, M.; Hassler, D.
2001STIN...0156300L Altcode:
Project 1: We have developed and applied a technique of helioseismic
holography along the lines of originally set out in our proposal. The
result of the application of this diagnostic technique to solar activity
and the quiet Sun has produced a number of important discoveries:
(1) acoustic moats surrounding sunspots; (2) acoustic glories
surround large active regions; (3) acoustic condensations beneath
active regions; and (4) temporally-resolve acoustic images of a solar
flare. These results have been published in a series of papers in the
Astrophysical Journal. We think that helioseismic holography is now
established as the most powerful and discriminating diagnostic in local
helioseismology. Project 2: We conducted a collaborative observational
program to define the physical character and magnetic geometry of
canceling magnetic bipoles aimed at determining if the cancellation
process is the result of submergence of magnetic fields. This assessment
is based on ground-based observations combining photospheric and
chromospheric magnetograms from NSO/KP, BBSO, and SOHO-MDI, and EUV
and X-ray images from SOHO EIT/CDS, Yohkoh/SXT, and TRACE. Our study
involves the analysis of data taken during three observing campaigns to
define the height structure of canceling bipoles inferred from magnetic
field and intensity images, and how this varies with time. We find
that some canceling bipoles can be explained by the submerge of their
magnetic flux. A paper on the results of this analysis will be presented
at an upcoming scientific meeting and be written up for publication.

---------------------------------------------------------
Title: Progress in Helioseismic Holography
Authors: Braun, D. C.
2001AGUSM..SP21C07B Altcode:
Local Helioseismology uses acoustic waves to probe small-scale
structures in the solar interior down to a spatial resolution
imposed by wave diffraction. Although its practitioners, including
this author, may sometimes employ measurements of the acoustic wave
field made over a local area of the Sun's surface to examine its
shallow layers, local helioseismology generally has a much broader
utility. For example, some applications of helioseismic holography
(and other local diagnostics) require global acoustic modes, observed
over large portions of the surface, to produce diffraction-limited
images of the far side or deep interior of the Sun. In this review,
I will summarize recent progress achieved in seismic holography in
collaboration with C. Lindsey (SPRC). With P. Scherrer and the SOI-MDI
team at Stanford, we have helped to realize a daily synoptic monitor of
far-side activity using medium-resolution MDI images obtained within
24 hours of their acquisition by the SOHO spacecraft. In addition,
we have laid out the basic theoretical groundwork for the application
of computational seismic holography to the deep solar interior to
image the tachocline and underlying radiative core of the Sun. Taking
advantage of the substantial depth sensitivity of horizontal-flow
diagnostics, we have recently adapted our holographic software to
test the basic techniques on the shallow subphotospheres of active
regions. The utility of both ground- and space-based instruments is
usually enhanced by their combination and comparison. I will present
the results of holographic analyses of simultaneous GONG+ prototype
and SOI-MDI observations of a large flare-producing active region. The
general similarity of the helioseismic images from both instruments is
noteworthy. This demonstrates the feasibility of increasing the temporal
and spatial coverage available to local analyses by combining SOHO data
with that obtained from the GONG+ network. We gratefully acknowledge
recent support from the National Science Foundation (AST-9987286)
and a contract (PY-0184) from the NASA-funded SOI-MDI project at
Stanford University.

---------------------------------------------------------
Title: Prospects for Helioseismic Holography in the Deep Solar
Interior
Authors: Lindsey, C.; Braun, D. C.
2001AGUSM..SP21C08L Altcode:
Holographic seismic imaging of low-degree acoustic noise
opens new prospects for solar interior diagnostics that are most
encouraging. Seismic imaging of the near solar interior has given us the
discoveries of “acoustic moats,” surrounding sunspots, of anomalous
emission from “acoustic glories” surrounding large active regions,
acoustic images of solar flares, and the signatures of apparent acoustic
perturbations up to 20~Mm beneath active region photospheres. Low-degree
seismic holography is now giving us images of large magnetic regions
on the far surface of the Sun, a utility with valuable space-weather
forecasting and general synoptic applications. Extensions of the
foregoing applications promise insight into the deep solar interior,
to the base of the convection zone and into the Sun's nuclear-burning
core. Diffraction-limited imaging of low-degree noise over pupils
covering most of the near solar hemisphere offer the most discriminating
probe of the deep solar interior. Earth-based helioseismic observations
coordinated with seismic observations of the far side of the Sun at
frequencies in the range 6--7 mHz would allow us to resolve local
thermal and Doppler structure in the solar core with a resolution of
75~Mm. Coordinated seismic observations of both near and far sides
of the Sun are essential to take advantage of the superior spatial
resolution offered by high-frequency waves.

---------------------------------------------------------
Title: Seismic Holography of the Solar Interior and Far Side
Authors: Braun, D. C.; Lindsey, C.
2001IAUS..203..167B Altcode:
The development of solar acoustic holography has opened a major
new diagnostic avenue in local helioseismology. Its application to
SOI-MDI data from SOHO has revealed “acoustic moats” surrounding
sunspots, “acoustic glories” surrounding complex active-regions,
and “acoustic condensations” suggesting the existence of significant
seismic anomalies up to 20 Mm beneath active-region photospheres. It has
given us the first seismic images of a solar flare, and has uncovered a
remarkable anomaly in the statistical distribution of seismic emission
from acoustic glories. Phase-sensitive seismic holography is now
producing high-resolution maps of sound travel-time anomalies caused
by magnetic forces in the immediate subphotosphere, apparent thermal
enhancements in acoustic moats, and Doppler signatures of subsurface
flows. It has also produced the first seismic images of active regions
on the far-side of the Sun, giving us a powerful tool for forecasting
more than a week in advance their arrival at the east limb. This
diagnostic now promises a new insight into the hydromechanical and
thermal environments of the solar interior in the local perspective.

---------------------------------------------------------
Title: Seismic Holography of the Deep Solar Interior
Authors: Lindsey, C.; Braun, D. C.
2000SPD....31.0503L Altcode: 2000BAAS...32R.836L
The first images of magnetic regions on the far solar surface
were recently secured by applying seismic holography to five-minute
oscillations with spherical harmonic degrees roughly in the range 20 to
40 in SOHO-MDI observations. These waves penetrate up to half way to the
sun's center, and can therefore sample the base of the convection zone
with a resolution similar to that of the aforementioned far-side images,
approximately 10o in longitude at the solar equator. However,
by far the best seismic diagnostics are invariably offered by the
highest possible frequencies, 6 mHz and above, if possible. Because
these waves are efficiently absorbed by the solar surface, helioseismic
observations that can compare the far side of the sun with earth-based
observations of the near side are needed for coherent phase-sensitive
imaging of the deep solar interior. Coordinated near- and far-side
seismic observations of the sun at frequencies in the range 6--7
mHz would allow us to examine the thermal and Doppler profile of the
solar core with a resolution of 75 Mm. This presentation is based on
research supported by grants NAG5-7236 from NASA and AST-9528249 from
NSF, and by a contract, PY-0184, with Stanford University.

---------------------------------------------------------
Title: Seismic Imaging of the Far Side and Interior of the Sun
Authors: Braun, D. C.; Lindsey, C.
2000SPD....3102112B Altcode: 2000BAAS...32Q.831B
Images of active regions on the far side of the Sun were derived
by applying seismic holography to observations from the SOI-MDI
instrument on the SOHO spacecraft. Synoptic seismic imaging of
far-side solar activity will allow anticipation of the appearance of
large active regions more than a week ahead of their arrival on the
east limb. The technical requirements for a synoptic monitor appear
to be quite modest, given real time access to observations from the
Global Oscillations Network Group, for example. Currently, seismic
images of the solar far side are easily computed in less than a day
using a single-processor Pentium-based PC running Linux. In addition to
providing new applications for space weather prediction, the development
of solar acoustic holography is opening major new diagnostic avenues in
the study of the solar interior. Phase-sensitive seismic holography is
producing high-resolution maps of sound travel-time anomalies caused
by magnetic forces in the immediate subphotosphere, apparent thermal
enhancements in acoustic moats around sunspots, and Doppler signatures
of subsurface flows. Seismic holography applied to global modes, such
as those used to image the far side, has directly demonstrated the
influence of active regions on these modes. This reinforces a growing
consensus that reduced sound travel times in magnetic regions explain
the entirety of the frequency shifts of global modes with the solar
cycle. Phase-sensitive holography will also be used to probe thermal
and Doppler perturbations deep in the solar convection zone and the
tachocline. This work is supported by grants NAG5-7236 from NASA
and AST-9528249 from NSF, and by a contract, PY-0184, from Stanford
University.

---------------------------------------------------------
Title: Stochastic Seismic Emission from Acoustic Glories and the
Quiet Sun
Authors: Donea, A. -C.; Lindsey, C.; Braun, D. C.
2000SoPh..192..321D Altcode:
Helioseismic images of multipolar active regions show enhanced seismic
emission in 5-mHz oscillations in a halo surrounding the active region
called the `acoustic glory'. The acoustic glories contain elements
that sustain an average seismic emission 50% greater than similar
elements in the quiet Sun. The most intense seismic emitters tend to
form strings in non-magnetic regions, sometimes marking the borders of
weak magnetic regions and the separation between weak magnetic regions
of opposite polarity. This study compares the temporal character
of seismic emission from acoustic glories with that from the quiet
Sun. The power distribution of quiet-Sun seismic emission far from solar
activity is exponential, as for random Gaussian noise, and therefore
not perceivably episodic. The distribution of seismic power emanating
from the most intense elements that comprise the acoustic glories is
exponential out to approximately 4 times the average power emitted
by the quiet Sun. Above this threshold the latter distribution shows
significant saturation, suggesting the operation of a hydromechanical
non-linearity that sets limits on the acoustic power generated by
the convection zone. This could give us considerable insight into the
physical mechanism of seismic emission from the near subphotosphere.

---------------------------------------------------------
Title: Helioseismic Holography of Active-Region Subphotospheres -
(Invited Review)
Authors: Braun, D. C.; Lindsey, C.
2000SoPh..192..285B Altcode:
The development of solar acoustic holography has opened a major new
diagnostic avenue in local helioseismology. It has revealed `acoustic
moats' surrounding sunspots, `acoustic glories' surrounding complex
active regions, and `acoustic condensations' suggesting the existence
of significant seismic anomalies up to 20 Mm beneath active-region
photospheres. Phase-sensitive seismic holography is now yielding
high-resolution maps of sound travel-time anomalies caused by magnetic
forces in the immediate subphotosphere, apparent thermal enhancements
in acoustic moats, and Doppler signatures of subsurface flows. It has
given us the first seismic images of a solar flare, and has uncovered a
remarkable anomaly in the statistical distribution of seismic emission
from acoustic glories. Seismic holography will probably give us the
means for early detection of large active regions on the far-surface
of the Sun, and possibly of deep subsurface activity as well. This
powerful diagnostic now promises a new insight into the hydromechanical
and thermal environments of the solar interior in the local perspective.

---------------------------------------------------------
Title: Seismic Images of the Far Side of the Sun
Authors: Lindsey, C.; Braun, D. C.
2000Sci...287.1799L Altcode:
Images of an active region on the far side of the sun were derived by
applying seismic holography to recent helioseismic observations from
space. Active regions are the centers of energetic phenomena such as
solar flares and coronal mass ejections, whose resulting electromagnetic
and particle radiation interfere with telecommunications and power
transmissions on Earth and can pose significant hazards to astronauts
and spacecraft. Synoptic seismic imaging of far-side solar activity
will now allow anticipation of the appearance of large active regions
more than a week ahead of their arrival on the east solar limb.

---------------------------------------------------------
Title: Phase-sensitive Holography of Solar Activity
Authors: Braun, D. C.; Lindsey, C.
2000SoPh..192..307B Altcode:
Phase-correlation statistics comparing acoustic radiation coming
out of a particular point on the solar photosphere with acoustic
radiation going into it show considerably reduced sound travel times
through the subphotospheres of active regions. We have now applied
techniques in phase-sensitive seismic holography to data from the Solar
Oscillations Investigation - Michelson Doppler Imager (SOI-MDI) on the
Solar and Heliospheric Observatory (SOHO) spacecraft to obtain high
resolution phase-correlation maps of a large, complex active region
and the `acoustic moat' which surrounds it. We report the following
new results: First, the reduced sound travel-time perturbations in
sunspots, acoustic moats, and isolated plages increase approximately in
proportion to the logarithm of the surface magnetic flux density, for
flux densities above 10 G. This is consistent with an interpretation
of the travel-time anomalies, observed with holographic and other
local-helioseismic procedures, as caused by acoustic Wilson-like
depressions in photospheres of magnetic regions. Second, we find that,
compared with isolated plages, the acoustic moats have an additional
sound travel-time reduction on the order of 3-5 s which may be
explained by a thermal excess due to the blockage of convective
transport by the sunspot photosphere. Third, the combined effect of
the Wilson depression in plages, acoustic moats, and sunspots may
explain the observed variation of global p-mode frequencies with the
solar cycle. Fourth, we find that active regions, including sunspots,
acoustic moats, and plages, significantly reflect p modes above the
acoustic cut-off frequency, where the surface of the quiet Sun acts
as a nearly perfect absorber of incident acoustic radiation.

---------------------------------------------------------
Title: Basic Principles of Solar Acoustic Holography - (Invited
Review)
Authors: Lindsey, C.; Braun, D. C.
2000SoPh..192..261L Altcode:
We summarize the basic principles of holographic seismic imaging of
the solar interior, drawing on familiar principles in optics and
parallels with standard optical holography. Computational seismic
holography is accomplished by the phase-coherent wave-mechanical
reconstruction of the p-mode acoustic field into the solar interior
based on helioseismic observations at the solar surface. It treats the
acoustic field at the solar surface in a way broadly analogous to how
the eye treats electromagnetic radiation at the surface of the cornea,
wave-mechanically refocusing radiation from submerged sources to render
stigmatic images that can be sampled over focal surfaces at any desired
depth. Holographic diagnostics offer a straight-forward assessment of
the informational content of the observed p-mode spectrum independent
of prospective physical models of the local interior anomalies that
it represents. Computational holography was proposed as the optimum
approach whereby to address the severe diffraction effects that
confront standard tomography in the solar p-mode environment. It has
given us a number of remarkable discoveries in the last two years
and now promises a new insight into solar interior structure and
dynamics in the local perspective. We compare the diagnostic roles of
simple acoustic-power holography and phase-sensitive holography, and
anticipate approaches to solar interior modeling based on holographic
signatures. We identify simple computational principles that, applied to
high-quality helioseismic observations, make it easy for prospective
analysts to produce high-quality holographic images for practical
applications in local helioseismology.

---------------------------------------------------------
Title: Seismic Forecasting of Solar Activity
Authors: Lindsey, C.; Braun, D. C.
2000IAUJD...7E...4L Altcode:
from SOHO, has recently given us the first images of an active region on
the far side of the Sun. The advent of phase-coherent seismic imaging is
now allowing us quite literally to look into the solar interior from a
local perspective, indeed to see through the solar interior acoustically
to its far surface. Space and ground-based helioseismic observatories
will soon have the capability for “real-time helioseismology,” and
will be routinely monitoring the far surface of the Sun. This will
greatly facilitate medium-range forecasts important to space weather,
allowing us to anticipate more than a week in advance the arrival
of large far-side active regions at the Sun's east limb to within a
few hours.

---------------------------------------------------------
Title: The MVACS soil temperature probe.
Authors: Wood, S. E.; Paige, D. A.; Nguyen, A.; Crisp, D.; Alleruzzo,
R.; Labaw, C.; Mahoney, C.; Vargas, R.; Gunderson, H.; Braun, D.;
Slostad, J.; Manvi, R.; Brown, K.; Oakes, E.
1999BAAS...31.1146W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The MVACS Soil Temperature Probe
Authors: Wood, S. E.; Paige, D. A.; Nguyen, A.; Crisp, D.; Alleruzzo,
R.; Labaw, C.; Mahoney, C.; Vargas, R.; Gunderson, H.; Braun, D.;
Slostad, J.; Manvi, R.; Brown, K.; Oakes, E.
1999DPS....31.4711W Altcode:
As part of the Mars Volatiles and Climate Surveyor (MVACS) payload
on Mars Polar Lander, currently on its way to a Dec. 3, 1999 landing
on the south polar layered deposits, the Soil Temperature Probe (STP)
will make direct measurements of the temperatures and thermophysical
properties of soils and/or ices accessible by the Robotic Arm (RA). The
STP consists of a thin, rigid fiberglass tube 15 cm long containing 2
platinum resistance temperature sensors; one in the metal tip which can
be heated (PRT-1), and another inside the tube (PRT-2). It is mounted
on the side of the scoop at the end of the RA. To make measurements,
the RA places the STP in the desired location on or beneath the surface,
and Robotic Arm Camera (RAC) image(s) are taken to verify its position,
using ruler markings on the STP to measure its depth. The temperatures
of both PRT's are recorded every 3 seconds. Data and commanding
are handled through the meteorology instruments (MET) electronics
package. Measurement of thermophysical properties can be done actively
or passively. In active mode, PRT-1 is heated at a constant rate ( 10
mW). The thermal conductivity of the surrounding soil can be derived
from the asymptotic temperature rise. The thermal diffusivity (alpha )
can be derived from the transient response. In passive mode alpha can
also be determined by measuring the change in the amplitude and phase
of the diurnal thermal wave at different depths. The temperature and
thermophysical property measurements obtained with the STP will be
very useful for interpreting other MVACS observations including air
temperature and humidity, the presence or absence of subsurface ice,
the identity of any surface frosts (CO_2 or H_2O), and Thermal Evolved
Gas Analyzer soil sample analysis. These STP measurements will also
provide invaluable "ground truth" for comparison with data from orbiting
spacecraft such as Mars Global Surveyor and Mars Climate Orbiter.

---------------------------------------------------------
Title: New Results from Helioseismic Holography
Authors: Braun, D. C.
1999AAS...194.4202B Altcode: 1999BAAS...31..882B
The application of helioseismic holography (also called seismic
imaging) to solar data is among the latest developments in local
helioseismology. This procedure applies helioseismic observations at
the solar surface in time-reverse to a model of the solar interior,
coherently regressing the surface disturbances downward to render
acoustic images of subsurface structure. I will describe the basic
concept, first developed ten years ago by C. Lindsey and D. Braun
(1990 Solar Physics, 126, 101), and present new results from our
recent application of the method to SOHO/MDI data. Notable discoveries
include the “acoustic moat” (extended 3-mHz absorption surrounding
all active regions), “acoustic glories” (high frequency halos of
emission around complex active regions), acoustic condensations up to
20 Mm beneath active regions, and the 6-mHz acoustic reflectivity of
active regions. Recent results obtained with phase-sensitive seismic
holography demonstrate a wave-speed perturbation beneath acoustic moats,
which may be a manifestation of a localized convection cell predicted
by theoretical models of sunspot convection and energy transport. The
development of seismic-imaging procedures sensitive to Doppler and
thermal perturbations promises to provide considerable insight into
the physical conditions underlying active regions. This research is
supported by NSF Grants AST 9521637 and AST 9528249, and NASA Grants
NAGW-97029 and NAG5-7236.

---------------------------------------------------------
Title: Phase-Sensitive Holography of Acoustic Moats
Authors: Braun, D. C.; Lindsey, C.
1999AAS...194.5610B Altcode: 1999BAAS...31..913B
Phase-correlation statistics comparing acoustic radiation coming out
of a particular point on the solar photosphere with acoustic radiation
going into it show considerably reduced sound travel times through the
subphotospheres of active regions. This is already well established by
time-distance correlations measured by Duvall et al., and is consistent
with earlier measurements of scattering phase shifts of single sunspots
by Braun and Fan. We have now applied techniques in phase-sensitive
seismic holography to obtain high resolution phase-correlation maps
of active regions and the “acoustic moats” that surround them. The
important new result which the holographic correlation maps give us
is that the seismic perturbation manifested by the acoustic moats
is generally quite significant and in large active-region complexes
predominant. Indeed, the acoustic moat surrounding the large active
region complex NOAA AR 8179 (1998 March 16) manifests a one-way
travel-time reduction of ~ 30s over an area of some 10(4) Mm(2) ,
encompassing all of the significant sunspots in the region. Onto
this phase perturbation the major sunspots impose an additional
localized contribution of ~ 30s. These results strongly reinforce an
interpretation of the acoustic moat as a well integrated convection
cell driven by the thermal perturbation that results from the local
blockage of convective heat transport by the sunspot photosphere. The
remarkable lateral extent of the acoustic moat, some 100 Mm in latitude
and more than 150 Mm in longitude, suggests a convective flow that
undertakes to spread the thermal perturbation into a relatively thin
layer, such that the excess heat contained therein can access the
solar surface through normal supergranular and granular diffusion. We
expect holographic Doppler diagnostics, now under development, to shed
considerable light very soon on the flows that are needed to explain
the extended dimensions of the thermal perturbations that surround
large active regions. This research is supported by NSF Grants AST
9521637 and AST 9528249, and NASA Grants NAGW-97029 and NAG5-7236.

---------------------------------------------------------
Title: Seismic Images of a Solar Flare
Authors: Donea, A. -C.; Braun, D. C.; Lindsey, C.
1999ApJ...513L.143D Altcode:
We have used helioseismic holography to render seismic images of
the solar flare of 1996 July 9, whose helioseismic signature was
recently reported by Kosovichev &amp; Zharkova. We computed time
series of “egression power maps” in 2 mHz bands centered at 3.5 and
6 mHz. These images suggest an oblong acoustic source associated with
the flare some 18 Mm in the north-south direction and approximately 15
Mm in the east-west direction. The considerable preponderance of the
flare acoustic power emanates in the 3.5 mHz band. However, because
the ambient noise in the 6 mHz band is much lower and the diffraction
limit for 6 mHz waves is much finer, the flare is rendered far more
clearly in the 6 mHz band. The 6 mHz flare signature lags the 3.5 mHz
by approximately 4 minutes.

---------------------------------------------------------
Title: Helioseismic Images of an Active Region Complex
Authors: Braun, D. C.; Lindsey, C.
1999ApJ...513L..79B Altcode:
Helioseismic images of a large active region complex at a frequency
of 5 mHz show a prominent halo of acoustic emission, which we
call the “acoustic glory,” surrounding the active region. This
feature is remarkably intense and contains small-scale elements of
concentrated seismic emission which cluster in strings in nonmagnetic
regions. Subsurface images show condensations of acoustic deficit
that appear to represent acoustic perturbations located in excess of
10 Mm beneath the photosphere. The analysis of this complex active
region suggests that these features are common in the neighborhoods of
large active regions and can appear tens of megameters horizontally
separated from sunspots. We propose that acoustic condensations are
the result of refraction or scattering by subsurface thermal or Doppler
perturbations below active regions. The appearance of acoustic glories
and condensations strongly suggests that complex active regions have
acoustic properties that are fundamentally different from those of
single isolated sunspots.

---------------------------------------------------------
Title: Chromatic Holography of the Sunspot Acoustic Environment
Authors: Lindsey, C.; Braun, D. C.
1999ApJ...510..494L Altcode:
We use helioseismic holography to obtain seismic images of a sunspot
and its local environment over the 3-8 mHz acoustic spectrum. We
are particularly interested in the acoustic deficit brought about by
strong acoustic absorption by the sunspot itself in the 3-4 mHz range
and in the helioseismic character of the “acoustic moat” recently
discovered by Braun et al. The holographic images computed here clearly
show that over a broad range in frequency the sunspot replaces the
acoustic radiation impinging into it from the ambient solar interior
with an outgoing acoustic flux that is only a fraction of that which
it receives. This acoustic deficit persists uniformly over the 3-7
mHz spectrum, even as the reflectivity of the quiet-Sun photosphere
goes from being an almost perfect, specular reflector at 4 mHz to an
almost perfect absorber at 5 mHz. As far as we can judge, the acoustic
moat surrounding the sunspot need not require a helioseismic absorption
mechanism of its own. Its signature in 3-4 mHz images could arise from
simple scattering of an acoustic deficit that originates in the nearby
sunspot. Such scattering may be the result of a thermal perturbation
resulting from the blockage of convective heat transport through the
sunspot photosphere. Alternatively, it could be the signature of a
Doppler perturbation attendant to the rapid convective outflow that
might be driven by such a thermal accumulation. While the results
presented here do not rule out the possibility that the acoustic moat
has its own absorption mechanism, they show little independent evidence
to indicate that the acoustic moat otherwise behaves very differently
from the quiet Sun where absorption and reemission of acoustic flux
are concerned. Helioseismic images of conspicuous halos that
appear in 6 mHz acoustic power maps show no significant enhancement of
acoustic emission from these regions. A fairly broad region surrounding
the sunspot appears to render a weak enhancement, ~2.5%, in the local
generation of 5 mHz acoustic power. This seems to explain peculiarities
in the spectrum of acoustic flux balance measurements based on Hankel
analysis. The distribution of the 5 mHz “acoustic egression” excess
is fairly diffuse and does not seem to be spatially correlated with
the strong acoustic power halos seen in 6 mHz acoustic power maps.

---------------------------------------------------------
Title: Erratum: Helioseismic Measurements of the Subsurface
Meridional Flow
Authors: Braun, D. C.; Fan, Y.
1999ApJ...510L..81B Altcode:
In the Letter “Helioseismic Measurements of the Subsurface Meridional
Flow” by D. C. Braun and Y. Fan (<A href="/abs/1998ApJ...508L.105">ApJ,
508, L105 [1998]</A>), equation (4) was misprinted and should appear as
follows:&lt;Uθ&gt;≡-(θmax-θmin)-1θminθmaxU\b.dot
θ̂dθ. (4)

---------------------------------------------------------
Title: Comparative Results from Seismic Imaging and Hankel Analysis
Authors: Braun, D. C.
1999soho....9E..27B Altcode:
Studies of solar active regions using Hankel-decomposition techniques
have clearly demonstrated over the past decade that sunspots and plage
are efficient absorbers of acoustic waves, and that the wave speeds
below sunspots are generally greater than that of the surrounding quiet
Sun. These results have been consistently confirmed by more recent
applications of both seismic-imaging and time-distance correlation
analyses. The development of seismic imaging (or helioseismic
holography), originally conceived ten years ago by C. Lindsey and
D. Braun, and recently applied to SOHO/MDI data, has additionally
provided important insights regarding the spatial (horizontal and
vertical) structure of the acoustic perturbations first detected
with Hankel analysis. Moreover, holography has enabled a number of
remarkable new discoveries including the "acoustic moat," "acoustic
glories," acoustic condensations up to 20 Mm beneath active regions,
and the reflectivity of active regions above the quiet-Sun acoustic
cut-off frequency. Recent application of phase-sensitive holographic
procedures have also revealed a subsurface wave-speed perturbation
extending tens of Mm beyond the sunspots, possibly associated with
a convection cell driven by the local blockage of heat transport
by the spots. A significant controversy still remains regarding the
depth of the primary acoustic perturbation below sunspots. Modeling of
scattering phase-shifts and seismic-imaging observations suggests that
the perturbations are strongly concentrated within depths of a few Mm
or less, in contrast to the deeper signatures implied by inversions of
time-distance correlation measurements. Simple, but straightforward
theoretical considerations, imply that the burden of proof rests
with proponents of the latter scenario. Complexities introduced by
the use of the photospheric signals within sunspots themselves also
contribute to uncertainties in the interpretations. Careful control
work and comparisons among diverse techniques, coupled with a continued
theory-based effort in understanding and modeling local-helioseismic
techniques and results, are crucial in providing a full understanding
of the physics of solar active regions and their interaction with
acoustic radiation.

---------------------------------------------------------
Title: Seismic images of the solar flare of July 9, 1996.
Authors: Donea, A. -C.; Braun, D. C.; Lindsey, C.
1999joso.proc..124D Altcode:
The helioseismic holography is a new method useful for rendering
seismic images of the solar flare of July 9, 1996. Time series of the
"egression power map" are computed in 2 mHz bands centered at 3.5
mHz and 6 mHz. The images show an acoustic source associated with the
flare some 18 mm in the N-S direction and approximately 15 mm in the
E-W. The flare is rendered far more clearly in the 6 mHz band. The 6
mHz flare signature lags the 3.5 mHz by approximately 6 minutes.

---------------------------------------------------------
Title: Phase-Sensitive Seismic Holography of the Photospheres and
Near Subphotospheres of Active Regions
Authors: Lindsey, C.; Braun, D. C.
1999soho....9E..71L Altcode:
The discovery of acoustic power halos surrounding active regions by
Braun, et al., Brown et al., and Toner and LaBonte, suggested that
surface regions with weak magnetic fields were enhanced emitters of
high-frequency seismic noise. Seismic holography of these regions
by Lindsey and Braun showed clearly that this was not generally the
case. Phase-sensitive holography of these features shows that these are
regions in which the Doppler signatures of seismic waves from distant
sources are locally enhanced, but the local seismic emission is not
enhanced. On the other hand, acoustic glories are regions of strongly
enhanced seismic emission from the quiet Sun just outside of magnetic
regions. Moreover, regions of strong magnetic field show suppressed
seismic emission. We examine the phase relation between the acoustic
ingressions, acoustic egressions, and local acoustic amplitudes of
these regions and consider how these can be treated as diagnostic of
the photospheres and near subphotospheres of active regions.

---------------------------------------------------------
Title: Helioseismic Holography - a Technique for Understanding
Solar Flares
Authors: Donea, A. C.; Lindsey, C.; Braun, D.
1999RoAJ....9S..71D Altcode:
The helioseismic holography is a technique which allows the analysis of
the photosphere of the Sun from the point of view of the acoustics. In
this paper we shall discuss mainly the seismic image of the flare of
July 9, 1996 which produced the largest sunquake observed by MDI-SOHO
instrument. We emphasize the fact that the kernel-like structure
observed in the seismic signature at both 3.5 mHz and 6 mHz egression
power maps are not side lobes effect. The seismic signature reveals
the presence of an extended acoustic source, much larger than the
Doppler redshift motion observed in the MDI-SOHO Dopplergrams.

---------------------------------------------------------
Title: Seismic Imaging of Acoustic Moats around Active Regions
Authors: Braun, D. C.; Lindsey, C.
1999soho....9E..46B Altcode:
Phase-correlation statistics comparing acoustic radiation coming out
of a particular point on the solar photosphere with acoustic radiation
going into it show considerably reduced sound travel times through the
subphotospheres of active regions. This is already well established
by scattering phase shifts of single sunspots by Braun and Fan, and
by time-distance correlations measured by Duvall et al. We have now
applied techniques in phase-sensitive seismic holography to obtain high
resolution phase-correlation maps of active regions and the "acoustic
moats" that surround them. Correlation maps obtained for several active
regions show that the seismic perturbation manifested by the acoustic
moats extends 30 Mm or so beyond the visible sunspots, and in large
active-region complexes is quite predominate. Indeed, the acoustic moat
surrounding the large active region complex NOAA AR 8179 (1998 March 15)
manifests a one-way travel-time reduction of approximately 30s over an
area of some 10,000 sq. Mm, encompassing all of the significant sunspots
in the region. Onto this phase perturbation the major sunspots impose an
additional localized contribution of about 30s. These results strongly
reinforce an interpretation of the acoustic moat as a well integrated
convection cell driven by the thermal perturbation that results from the
local blockage of convective heat transport by the sunspot photosphere.

---------------------------------------------------------
Title: Acoustic Signatures of Subphotospheric Structure Underlying
Sunspots
Authors: Lindsey, C.; Braun, D. C.
1998ApJ...509L.129L Altcode:
Helioseismic holography of active regions at frequencies in the
range of 5-6 mHz renders acoustic signatures that we think signify
acoustic perturbations several megameters beneath the photosphere. The
application of holographic diagnostics at 5-6 mHz gives us images
with considerably finer horizontal spatial resolution, and likewise
much finer depth resolution with respect to focus, than the 3 mHz
diagnostics we have recently published. This Letter reports comparative
results of standard focus-defocus diagnostics of a single sunspot at 3
and 6 mHz. Images of the “acoustic egression power” at 6 mHz show a
remarkable, compact acoustic deficit that persists in acoustic focal
planes submerged up to 11.2 Mm beneath the solar surface. We propose
that this and other similar features associated with other active
regions are the result of refraction or scattering by submerged thermal
or Doppler perturbations of an acoustic deficit that is caused by strong
wave absorption in the overlying photosphere of the active region.

---------------------------------------------------------
Title: Helioseismic Measurements of the Subsurface Meridional Flow
Authors: Braun, D. C.; Fan, Y.
1998ApJ...508L.105B Altcode:
We measure the mean frequencies of acoustic (p-mode) waves propagating
toward and away from the poles of the Sun from observations made with
the Solar Oscillations Investigation-Michelson Doppler Imager on board
the Solar and Heliospheric Observatory and the ground-based Global
Oscillations Network Group. We demonstrate that there is a significant
frequency shift between poleward- and equatorward-traveling waves
measured over solar latitudes 20°-60°, which is consistent with
the Doppler effect of a poleward meridional flow on the order of 10 m
s-1. From the variation of the frequency shifts of p-modes
with degree l between 72 and 882 as a function of the lower turning
point depth, we infer the speed of the meridional flow, averaged over
these latitudes, over a range in depth extending over the top half
of the solar convection zone. We find no evidence for a significant
equatorward return flow within this depth range.

---------------------------------------------------------
Title: Seismic Holography of Solar Activity
Authors: Braun, D. C.; Lindsey, C.; Fan, Y.; Fagan, M.
1998ApJ...502..968B Altcode:
Helioseismic images of sunspots show a remarkable acoustic anomaly
surrounding the sunspot. We applied the computational formalism of
“helioseismic holography” to SOHO-MDI observations to render
acoustic images of NOAA AR 7973, an active region containing a
moderately large sunspot. The results of this study are based on
simple “acoustic power holography,” to image the absorption of
p-mode waves by the sunspot. These images clearly show a strong,
compact acoustic deficit representing the sunspot, as well as plages
in the neighborhood of the sunspot, consistent with earlier results of
“Hankel analysis.” However, they also show surrounding the sunspot
a conspicuous acoustic halo extending out to a radius of approximately
35,000 km. We propose that this “acoustic moat” is the helioseismic
manifestation of a single convection eddy that is driven by the thermal
disturbance resulting from the local blockage of convective transport
in the sunspot subphotosphere. Depth diagnostics based on acoustic
focus show a rapidly defocusing sunspot image as the focal plane is
submerged. Acoustic noise models in which absorption by the sunspot
is entirely superficial yield images that defocus significantly more
slowly with increasing focal-plane depth than the SOHO-MDI images of
NOAA AR 7973. Extending the absorption significantly beneath the model
photosphere enhances the discrepancy. More recent tests tentatively
suggest that this “focus anomaly” is the result of neglect of image
smearing introduced into the MDI instrument to suppress aliasing,
and that a proper account of the instrumental MTF will render
defocus profiles roughly consistent with superficial absorption. Our
holographic images roughly indicate that the sunspot in NOAA AR 7973
absorbs low-l waves with approximately the same efficiency as it does
high-l waves. Contrary to widely held opinion, this result is entirely
consistent with that of the Hankel analysis, given that the absorption
of waves by magnetic regions is indeed superficial. We expect that the
efficient absorption of low-l waves will make it possible to image large
active regions on the far side of the Sun by the acoustic-absorption
signatures they render at their antipodes.

---------------------------------------------------------
Title: The Acoustic Moat and Thermal Transport in the Neighborhoods
of Sunspots
Authors: Lindsey, C.; Braun, D. C.
1998ApJ...499L..99L Altcode:
Helioseismic holography of sunspots shows a remarkable acoustic anomaly
surrounding the sunspot, which we call an “acoustic moat.” We used
Solar and Heliospheric Observatory (SOHO) Michelson Doppler Imager
observations of NOAA Active Region 7973 to render acoustic images
of a typical sunspot. These images show a conspicuous halo, 70,000
km in diameter, surrounding the sunspot, in which there appears a
predominant acoustic deficit. This “acoustic moat” may be terminated
by a sharp outer boundary, which appears to circumscribe the sunspot
completely in some instances. The outer boundary of the acoustic
moat coincides conspicuously with plages in the neighborhood of the
sunspot. Depth diagnostics based on acoustic focus suggest that the
acoustic perturbations characterizing both the sunspot and the acoustic
are predominantly superficial, within a few thousand kilometers of
the solar surface. Following work by Meyer et al., we propose that
the acoustic moat is the helioseismic manifestation of a single,
integrated convection eddy that is driven by heat accumulation
resulting from the local blockage of convective transport from the
solar interior into the sunspot subphotosphere. We propose that the
acoustic deficit predominantly characterizing the halo is the result
of thermal refraction or Doppler scattering by the eddy outflow of an
acoustic deficit originating in the helioseismic absorption by the
nearby sunspot and possibly neighboring plages. With the advent of
SOHO and the Global Oscillation Network Group, helioseismic holography
promises considerable insight into the general subject of convective
flows surrounding sunspots, an issue that is certain to be critical
to the long-standing problem of thermal transport in the neighborhoods
of sunspots.

---------------------------------------------------------
Title: The Seismology of Sunspots: A Comparison of Time-Distance
and Frequency-Wavenumber Methods
Authors: Bogdan, T. J.; Braun, D. C.; Lites, B. W.; Thomas, John H.
1998ApJ...492..379B Altcode:
A pair of formulae are developed that relate the absorption coefficient
and partial-wave phase shift concepts of frequency-wavenumber local
helioseismology to the center-annulus cross-correlation function
of time-distance helioseismology, under the general circumstances
that both induced and spontaneous sunspot oscillations may be
present. These formulae show that spontaneous emission of p-modes
by magnetic and Reynolds stresses within the spot and the mode
mixing between incoming and outgoing p-modes affect only the
outgoing center-annulus cross-correlation time τ+,
and they caution that real or spurious phase lags of the umbral
oscillation signal lead to differences in the incoming and outgoing
correlation times, resulting in τ- ≠ τ+. The
application of these methods to actual helioseismic data obtained
by the Global Oscillation Network Group (GONG) project is carried
out in order to provide a tangible illustration of how time-distance
and frequency-wavenumber ideas can profitably be combined to yield
deeper insight into the seismic probing of sunspots. By using the
helioseismic GONG data in conjunction with concurrent observations of
Doppler velocities and vector magnetic fields obtained by the High
Altitude Observatory/National Solar Observatory (HAO/NSO) Advanced
Stokes Polarimeter (ASP) for the 1995 October disk passage of active
region NOAA 7912, we demonstrate that the inferred GONG umbral
signal actually originates from the umbra-penumbra boundary about 6
Mm distant from the center of the spot. Further, the ASP observations
show that the 5 minute oscillations at the umbra-penumbra boundary lag
behind those in the center of the umbra by approximately 1 minute,
which is precisely the difference between the incoming and outgoing
correlation times for NOAA 7912 recently determined by Braun. This
remarkable result underscores the perils of using umbral oscillations
in time-distance helioseismology, and it calls into question previous
claims that correlation time differences constitute direct evidence
for the existence of a steady downflow in and around sunspots. Taken
together, the observational and theoretical evidence suggest that
the p-mode forcing of the spot leads to the generation of upwardly
propagating slow magnetoatmospheric waves. These waves are in turn
responsible for the decreased amplitudes of the outwardly propagating
p-modes in the surrounding quiet Sun, and the dispersion in their travel
times between the hidden subsurface layer where they are forced and
the overlying level where the Doppler signals originate leads to the
observed phase lag between the umbral and penumbral oscillations and
the corresponding correlation time differences. This work utilizes
data obtained by the Global Oscillations 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.

---------------------------------------------------------
Title: Helioseismic Signatures of Subphotospheric Structure Beneath
Active Regions
Authors: Lindsey, C.; Braun, D. C.
1998ESASP.418..641L Altcode: 1998soho....6..641L
No abstract at ADS

---------------------------------------------------------
Title: Time-Distance Sunspot Seismology with GONG Data
Authors: Braun, D. C.
1997ApJ...487..447B Altcode:
We present time-distance analyses of several active regions and a
region of quiet Sun observed with the Global Oscillation Network Group
(GONG). Analyzing temporal correlations between the p-mode oscillation
signal observed within the sunspots with the signals integrated within
surrounding annuli, we confirm the recent finding of Duvall and his
colleagues that travel times (τ+) for outward propagating
p-modes are smaller by approximately 1 minute than corresponding inward
travel times (τ-). We also analyze correlations of the
oscillation signal integrated within annuli of different radii. By
varying the radius of the inner annulus (that which is closer to the
target) we show that the radial extent of the region giving rise to
the travel time perturbations is coincident with the outer boundary
of the sunspot penumbrae. A comparison of independent methods
designed to determine the mean travel time perturbations of p-modes
passing through the sunspots is made. We find the surprising result that
time-distance correlations that do not utilize the signal within the
sunspot itself (employing “two-skip” trajectories) yield mean travel
times that differ substantially from the average of τ+
and τ- and that are significantly closer in agreement
with times predicted from scattering phase shifts measured by Hankel
decomposition techniques. These observations suggest that it unlikely
that Doppler shifts caused by subsurface flows are responsible for the
travel time differences determined from center-annuli correlations
targeted on sunspots. 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.

---------------------------------------------------------
Title: Helioseismic Holography
Authors: Lindsey, C.; Braun, D. C.
1997ApJ...485..895L Altcode:
We describe the basic principles of “helioseismic holography,” an
analytic technique intended for local helioseismology of subsurface
structure. The purpose of this technique is to provide depth
discrimination of subsurface structure that manifests a surface
signature in acoustic waves. It is based on the computational
application of spatially resolved helioseismic observations to the
surface of an acoustic model of the solar interior that contains no
local structure. The observed surface oscillations are applied to
the model in time reverse, and the model is then computationally
sampled at various depths in its interior. This technique takes
advantage of the coherence retained by waves in a smooth acoustic
medium following an interaction with subsurface structure, allowing
us to extrapolate the acoustic field with high accuracy to the depth
where the structure lies. Depth discrimination is then accomplished by
focus-defocus diagnostics. We describe computational approaches
to the technique from two different perspectives, the “spectral”
and the “spatial.” For rigorous models of the solar interior,
the computational demands of the spectral and spatial approaches are
approximately the same. For diagnostics of relatively shallow structure,
the plane-parallel approximation of the model is useful. In this case
the spectral approach reduces computational holography essentially to
Fourier transforms, which can be performed rapidly with very modest
hardware. We illustrate the technique in this case, using artificial
data characterizing waves in an idealized plane-parallel medium
with acoustic absorbers located at various depths. At present,
we prefer to maintain a secure distinction between holography and
modeling. While we do not discuss modeling in this paper, we think
that it is important to develop an approach to modeling that takes
advantage of holographic reconstruction. The prospect of viewing local
subsurface magnetic regions and flows opens an entirely new dimension
to helioseismology and to solar and stellar physics in general. It may
make it possible to anticipate solar activity far in advance of its
emergence to the surface. Local acoustic diagnostics could revolutionize
our understanding of the solar dynamo and the 22 yr activity cycle.

---------------------------------------------------------
Title: Doppler Acoustic Diagnostics of Subsurface Solar Magnetic
Structure
Authors: Lindsey, C.; Braun, D. C.; Jefferies, S. M.; Woodard, M. F.;
Fan, Y.; Gu, Y.; Redfield, S.
1996ApJ...470..636L Altcode:
We used the Bartol-NSO-NASA South Pole helioseismic observations of 1991
January to probe the subsurface structure of active regions to depths
of ∼15,000 km. The helioseismic signature we particularly examine is
intended to register acoustic Doppler effects caused by horizontal flows
associated with the active region. We propose to show that the Doppler
acoustic signature of horizontal flows is particularly well suited
for deep subsurface diagnostics in terms of vertical discrimination
of the structure. This study is based primarily on observations of
NOAA Active Regions 6431, 6432, 6440, and 6442 between 1991 January
1 and January 8. We interpret the acoustic signatures we find in
terms of a general outflow of the solar medium surrounding the active
region. The acoustic signatures are strongly dependent on wavenumber,
which suggests an outflow that is quite weak near the surface, the upper
4000 km of the subphotosphere, but which increases strongly with depth
to velocities of several hundred meters per second at 15,000 km. This
depth profile evolves rapidly as the active region matures. Young
active regions show a strong outflow signature for waves that explore
depths between 4000 and 8000 km. As the active region matures, the
outflow vacates these intermediate layers and submerges to depths
mostly below 8000 km. We examine the location of AR 6442 for a
possible preemergence signature. We also show evidence for extended,
relatively superficial flows in the quiet Sun between the active region
bands directed roughly into the active region bands.

---------------------------------------------------------
Title: Helioseismic Measurements of Subsurface Outflows From Sunspots
Authors: Braun, D. C.; Fan, Y.; Lindsey, C.; Jefferies, S. M.
1996AAS...188.6911B Altcode: 1996BAAS...28Q.937B
We measure the mean frequencies of acoustic waves propagating toward
and away from sunspots employing a spot-centered Fourier-Hankel
decomposition of p-mode amplitudes as measured from observations made at
the South Pole in 1988 and 1991. There is a significant frequency shift
between the inward and outward traveling waves which is consistent with
the Doppler effect of a radial outflow from the sunspots. For p-modes
of temporal frequencies of 3 mHz it is observed that the frequency
shift decreases slightly with spatial frequency, for modes with degree
l between 160 to 600. From the l dependence of the frequency shift, we
infer that the mean radial outflow within the observed annular region
(which extends between 30 and 137 Mm from the spots) increases nearly
linearly with depth, reaching a magnitude of about 200 m/s at a depth
of 20 Mm. This outflow exhibits properties similar to flows recently
reported by Lindsey, et al. (1996 ApJ submitted) using spatially
sensitive local helioseismic techniques. This work is supported by
NSF Grant AST 9496171 and NASA Grant NAGW-4143.

---------------------------------------------------------
Title: Doppler Acoustic Diagnostics of Subsurface Solar Magnetic
Structure
Authors: Lindsey, C.; Braun, D.; Jefferies, S.; Fan, Y.; Gu, Y.;
Redfield, S.
1996AAS...188.7903L Altcode: 1996BAAS...28R.955L
We used the Bartol-NSO-NASA South Pole helioseismic observations of 1991
January to study the subsurface structure of active regions to depths of
~ 15,000 km. The helioseismic signature we particularly examine is based
on acoustic Doppler effects caused by horizontal flows associated with
the active region. We demonstrate that the Doppler-acoustic signature
of horizontal flows is particularly well suited for deep subsurface
diagnostics in terms of vertical discrimination of the structure. This
study is based primarily on observations of NOAA active regions 6431,
6432, 6440 and 6442 between 1991 January 1 and January 8. We interpret
the Doppler signatures we find in terms of a general outflow of the
solar medium surrounding the active region. The existence of deep
subsurface structure is indicated by the strong dependence of the
Doppler signature on horizontal wavelength. The outflows in surface
layers, the upper 4,000 km of the subphotosphere, are quite weak but
increase strongly with depth to velocities of several hundred m/s at
15,000 km. This depth profile evolves rapidly as the active region
matures. Young active regions show strong outflows at depths between
4,000 and 8,000 km. As the active region matures, the outflow vacates
these intermediate layers and submerges to depths mostly below 8,000
km. We examine the location of Region 6442 for a possible pre-emergence
signature. We also show strong evidence for extended, relatively
superficial flows in the quiet Sun between the active-region bands
directed roughly into the active region bands.

---------------------------------------------------------
Title: Diagnostics of a Subsurface Radial Outflow From a Sunspot
Authors: Braun, D. C.; Fan, Y.; Lindsey, C.; Jefferies, S. M.
1996astro.ph..3078B Altcode:
We measure the mean frequencies of acoustic waves propagating toward
and away from a sunspot employing a spot-centered Fourier-Hankel
decomposition of p-mode amplitudes as measured from a set of
observations made at the South Pole in 1991. We demonstrate that
there is a significant frequency shift between the inward and outward
traveling waves which is consistent with the Doppler effect of a radial
outflow from the sunspot. For p-modes of temporal frequencies of 3
mHz it is observed that the frequency shift decreases slightly with
spatial frequency, for modes with degree l between 160 to 600. From
the l dependence of the frequency shift, we infer that the mean radial
outflow within the observed annular region (which extends between 30 and
137 Mm from the spot) increases nearly linearly with depth, reaching a
magnitude of about 200 m/s at a depth of 20 Mm. This outflow exhibits
properties similar to flows recently reported by Lindsey, et al. (1996)
using spatially sensitive local helioseismic techniques.

---------------------------------------------------------
Title: Scattering of p-Modes by Sunspots. II. Calculations of Phase
Shifts from a Phenomenological Model
Authors: Fan, Y.; Braun, D. C.; Chou, D. -Y.
1995ApJ...451..877F Altcode:
We model the scattering of p-mode waves in a polytropic atmosphere
by localized inhomogeneities in wave speed, pressure, and density
of the medium. The effect of the inhomogeneities is attributed to
a source term in the pressure wave equation. The inhomogeneous wave
equation for the scattered waves is solved under the simplification
of the Born approximation. From the solution for the scattered waves,
we compute the phase shifts between the incoming and outgoing waves of
individual modes. We find that the variations of the computed
phase shifts with degree l and radial order n of the modes show
different behavior for inhomogeneities with different characteristic
depths. Depths significantly shallower than the depth of the modes
seem to show a phase shift dependence on l and n that is similar to
the qualitative behavior of the observed phase shifts produced by
sunspots. Direct quantitative comparison of the computed phase shifts
with observations is limited to modes with lower degree (l &lt; 200)
in which the observed phase shifts are reasonably small so that the
Born approximation is applicable. We find that for inhomogeneities
with a wave speed contrast reasonable for sunspots, occupying a volume
described by a characteristic depth D 108 cm and horizontal radius R ≍
2.5 × 109 cm, the computed phase shifts at lower l range
are in agreement with the observed phase shifts from sunspots in both
their magnitudes as well as their variation with l and frequency (or n).

---------------------------------------------------------
Title: Scattering of p-Modes by Sunspots. I. Observations
Authors: Braun, D. C.
1995ApJ...451..859B Altcode:
The acoustic scattering properties of two large sunspots and a plage are
determined from a Fourier-Hankel decomposition of p-mode amplitudes as
measured from 68 hr subsets of a larger set of observations made at the
South Pole in 1988. We present measurements of p-mode absorption and
scattering phase shifts as functions of the incident mode properties
(degree, radial order, and azimuthal order). In the two sunspots
we observe a distinct modulation of the absorption with temporal
frequency in a fashion that is very nearly independent of the degree
of the mode. In particular, the absorption exhibits a broad peak at 3
mHz, an absence of absorption at 5 mHz, and a rise in absorption at
higher temporal frequencies. This variation is in good qualitative
agreement with a prediction of a model of p-mode absorption by slow
mode conversion described recently by Spruit &amp; Bogdan (see also
the recent work of Cally &amp; Bogdan). The spotless plage also shows
significant p-mode absorption, at a level of 20% of the value seen in
the spots. Control tests made by repeating the analysis in a region of
quiet Sun have confirmed the recent observation by Bogdan et al. that
the quiet Sun shows an apparent acoustic emission. In particular, we
find a significant anticorrelation between the absorption coefficient
in the quiet Sun and the values measured in a nearby sunspot. The
scattering phase shifts are shown to increase with the degree of the
modes with an increase that is faster than a linear relation. At
constant degree the phase shifts increase with temporal frequency
(radial order) before leveling off at a roughly constant value. We
suggest that this behavior is consistent with a relatively shallow
sound-speed perturbation produced by the spots. The variation of
the phase shift and the absorption with azimuthal order suggest
that the phase shifts are largely produced within the area of the
sunspot, while significant absorption is occurring in a more extended
region. Related to this observation is the finding that the plage,
while absorbing p-modes, produces no measurable phase shifts. Upper
limits place any phase shifts caused by the plage to be less than
about 5 % of that observed in the spots. Finally, we find strong
evidence of mode mixing in the two sunspots, as demonstrated by a
significant correlation of the phases of incident p-modes of a given
radial order with the phases of outgoing modes of adjacent orders at
the same temporal frequency.

---------------------------------------------------------
Title: Observations and Models of p-Mode Scattering by Sunspots
Authors: Braun, D. C.; Fan, Y.
1995SPD....26..403B Altcode: 1995BAAS...27..954B
No abstract at ADS

---------------------------------------------------------
Title: Active Region Seismology
Authors: Bogdan, T. J.; Braun, D. C.
1995ESASP.376a..31B Altcode: 1995heli.conf...31B; 1995soho....1...31B
Active region seismology is concerned with the determination and
interpretation of the interaction of the solar acoustic oscillations
with near-surface target structures, such as magnetic flux
concentrations, sunspots, and plages. Observations with high spatial
resolution and long temporal duration have enabled the measurement
of the scattering matrix for sunspots and solar active regions as a
function of the mode properties (wavenumber, frequency and azimuthal
order). From this information one may determine the amount of p-mode
absorption, partial-wave phase shift, and mode mixing introduced by
the sunspot. In addition, the possibility of detecting the presence of
completely submerged magnetic fields has been raised and new procedures
for performing acoustic holography of the solar interior are being
developed. The accumulating evidence points to the mode conversion of
p-modes to various magneto-atmospheric waves within the magnetic flux
concentration as the unifying physical mechanism responsible for these
diverse phenomena.

---------------------------------------------------------
Title: Sunspot Seismology: New Observations and Prospects
Authors: Braun, D. C.
1995ASPC...76..250B Altcode: 1995gong.conf..250B
No abstract at ADS

---------------------------------------------------------
Title: A Model of P-mode Scattering by Sunspots
Authors: Fan, Y.; Braun, D. C.
1994AAS...185.4406F Altcode: 1994BAAS...26.1377F
It has recently been discovered that sunspots scatter intermediate and
high-degree p-modes. The scattering may be characterized by a shift
in phase between modes travelling toward and away from the spot. These
observations offer the hope that suitable models of the scattering may
yield important clues about the subsurface evolution and structure
of magnetic regions. We model the scattering of p-mode waves in a
polytropic atmosphere by localized inhomogeneities in compressibility
(the wave speed), density and pressure of the media. The effect of the
inhomogeneities is to introduce a source term in the pressure wave
equation. We solve this inhomogeneous equation for the scattered
wave amplitudes using standard Green's function techniques under
the simplification of the Born approximation. We found that with
reasonable strength (or contrast) of the inhomogeneities we can
obtain phase shifts between the outgoing and the in-going waves
similar to observations of p-modes in both the magnitude and degree
(l) dependence. We discuss how the strength of the scattered waves may
depend on the depth distribution of the inhomogeneities. This work is
supported by a NSF grant AST-9496171 and NASA grant NAGW-4143 awarded
to DCB. YF is supported by ONR grant N00014-91-J-1040.

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Title: An active solar prominence in 1.3 MM radiation
Authors: Harrison, R. A.; Carter, M. K.; Clark, T. A.; Lindsey, C.;
Jefferies, J. T.; Sime, D. G.; Watt, G.; Roellig, T. L.; Becklin,
E. E.; Naylor, D. A.; Tompkins, G. J.; Braun, D.
1993A&A...274L...9H Altcode:
We present new millimetre-wavelength observations of an active solar
prominence. Observations made over a two-day period with the James
Clerk Maxwell Telescope on Manna Kea, Hawaii, give a unique view in
1.3 mm radiation of the spectacular prominence that appeared on the
west solar limb in the total solar eclipse of 11 July 1991.

---------------------------------------------------------
Title: Prospects in Helioseismic Holography
Authors: Lindsey, C. A.; Braun, D. C.; Jefferies, S. M.
1993BAAS...25.1220L Altcode:
No abstract at ADS

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Title: The P-Mode Scattering Properties of a Sunspot
Authors: Braun, D. C.; Labonte, B. J.; Duvall, T. L., Jr.; Jefferies,
S. M.; Harvey, M. A.; Pomerantz, J. W.
1993ASPC...42...77B Altcode: 1993gong.conf...77B
No abstract at ADS

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Title: Local Helioseismology of Subsurface Structure
Authors: Lindsey, C.; Braun, D. C.; Jefferies, S. M.
1993ASPC...42...81L Altcode: 1993gong.conf...81L
No abstract at ADS

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Title: Measurement of the Height of the Solar CO Layer During the
11 July 1991 Eclipse
Authors: Clark, T. A.; Naylor, D. A.; Tompkins, G. J.; Lindsey, C. A.;
Becklin, E. E.; Jefferies, J. T.; Harrison, R. A.; Roellig, T. L.;
Carter, M.; Braun, D. C.; Watt, G.
1992AAS...181.8108C Altcode: 1992BAAS...24.1253C
No abstract at ADS

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Title: Extreme-infrared brightness profile of the solar chromosphere
obtained during the total eclipse of 1991
Authors: Lindsey, C.; Jefferies, J. T.; Clark, T. A.; Harrison, R. A.;
Carter, M. K.; Watt, G.; Becklin, E. E.; Roellig, T. L.; Braun, D. C.;
Naylor, D. A.
1992Natur.358..308L Altcode:
THE solar chromosphere is a thin layer of gas that is several thousand
degrees hotter than the underlying photosphere, and responsible for
most of the Sun's ultraviolet emission. The mechanism by which it is
heated to temperatures exceeding 10,000 K is not understood. Millimetre
and submillimetre radiometry can be used to obtain the chromospheric
temperature profile, but the diffraction-limited resolution for the
largest telescopes is at best 17 arcsec, or ~12,500 km at the Sun's
distance. This is greater than the thickness of the quiet chromosphere
itself. The total eclipse of July 1991, which passed over the Mauna
Kea Observatory in Hawaii, provided a rare opportunity to make limb
occultation observations with a large submillimetrewavelength telescope,
the 15-m James Clerk Maxwell Telescope, and in this way we obtained a
temperature profile in 1.3-mm radiation with ~300 km resolution at the
Sun. Our observations indicate that spicules (magnetically entrained
funnels of gas) reach a temperature of 8,000 K at 3,000-4,000 km above
the photosphere, a temperature lower than those of many spicule models.

---------------------------------------------------------
Title: Local Acoustic Diagnostics of the Solar Interior
Authors: Braun, D. C.; Lindsey, C.; Fan, Y.; Jefferies, S. M.
1992ApJ...392..739B Altcode:
Two diagnostic utilities, acoustic power maps, and surface acoustic
flux maps are used to explore the local diagnostics of magnetic field
structure in the solar interior. The acoustic power maps, constructed
from 50 hr of continuous K-line intensity images, show three general
features: acoustic power deficits at 3 mHz corresponding to surface
magnetic flux, acoustic power enhancements at 6 mHz surrounding the
exterior of magnetic regions, and occasional power deficits at 3 mHz
which extend beyond magnetic regions visible on the surface to regions
of quiet-sun. Surface acoustic flux vector maps of two active regions
were constructed for two 6-hr time-series of Dopplergrams. Both maps
show the divergence of 3-mHz acoustic flux into surface magnetic
structures and also sources and sinks of wave energy which are not
associated with surface features.

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Title: Scattering of p-Modes by a Sunspot
Authors: Braun, D. C.; Duvall, T. L., Jr.; Labonte, B. J.; Jefferies,
S. M.; Harvey, J. W.; Pomerantz, M. A.
1992ApJ...391L.113B Altcode:
The acoustic scattering properties of a large sunspot are determined
from a Fourier-Hankel decomposition of p-mode amplitudes as measured
from a 68-hr subset of a larger set of observations made at the
South Pole in 1988. It is shown that significant improvement in the
measurement of p-mode scattering amplitudes results from the increased
temporal frequency resolution provided by these data. Scattering
phase shifts are unambiguously determined for the first time, and the
dependence of the p-mode phase shift and absorption with wavenumber
and frequency is presented.

---------------------------------------------------------
Title: Prospects in Acoustic Holography of the Solar Interior
Authors: Lindsey, C.; Braun, D. C.; Fan, Y.; Jefferies, S. M.
1992AAS...180.1703L Altcode: 1992BAAS...24..753L
Acoustic power maps of the solar surface show strong evidence
of magnetic structure crossing the solar equator not far beneath
the photosphere to connect the active latitude bands. These maps,
generated using the Bartol-NSO-NASA South Pole Observations show long
finger-like acoustic shadows we think are caused by absorption of
acoustic energy by the submerged magnetic structure. These features
suggest a solar interior magnetic structure quite different from any
previously expected. These new results open the prospect of a new and
powerful solar interior diagnostic based on acoustic holography.

---------------------------------------------------------
Title: Scattering of p-Modes by a Sunspot
Authors: Braun, D. C.; Duvall, T. L., Jr.; Labonte, B. J.; Jefferies,
S. M.; Harvey, J. W.; Pomerantz, M. A.
1992AAS...180.0604B Altcode: 1992BAAS...24..737B
For the first time the scattering phase shifts of solar p-modes
from a sunspot have been unambiguously determined. This is made
possible by the recent availability of long duration, high duty
cycle observations. The results presented here are determined from a
Fourier-Hankel decomposition of p-mode amplitudes as measured from a
68 hr subset of a larger set of observations made at the South Pole in
1988. In addition to the detection of the phase shifts, the quality of
the data allows the dependence of the p-mode scattering and absorption
with azimuthal order, spatial wavenumber and temporal frequency to
be independently determined. Thus, unlike previous observations, our
measurements of absorption and phase shifts do not represent averages
over a range of p-modes. With this information we have for the first
time a complete description of the acoustic scattering amplitudes
from a large sunspot. Interpretation of these observations requires a
suitable theory of the interaction of p-modes and sunspots. However,
with the complete scattering amplitudes now available one may apply
inverse scattering algorithms, based on a few simplifying assumptions,
to deduce a 3-dimensional map of the scattering strength of the active
region. This offers the hope that general information about subsurface
morphology of active regions might be gained even without a detailed
understanding of the physical scattering processes involved. DCB is
supported by Air Force URI grant AFOSR-90-0116. The South Pole program
is supported in part by National Science Foundation grants DPP87-15791
and 89-17626, and by the Solar Physics Branch of the Space Physics
Division of NASA.

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Title: Power Spectra of Solar Convection
Authors: Chou, D. -Y.; Labonte, B. J.; Braun, D. C.; Duvall, T. L., Jr.
1991ApJ...372..314C Altcode:
The properties of convective motions on the sun are studied using
Kitt Peak Doppler images and power spectra of convection. The
power peaks at a scale of about 29,000 km and drops off smoothly
with wavenumber. There is no evidence of apparent energy excess at
the scale of the mesogranulation proposed by other authors. The
vertical and horizontal power for each wavenumber are obtained
and used to calculate the vertical and horizontal velocities of the
supergranulation. The amplitude of vertical and horizontal velocities
of the supergranulation are 0.034 (+ or - 0.002) km/s and 0.38 (+ or -
0.01) km/s, respectively. The corresponding rms values are 0.024 (+
or - 0.002) km/s and 0.27 (+ or - 0.01) km/s.

---------------------------------------------------------
Title: An Acoustic Poynting Vector for Solar p-mode Oscillations
Authors: Braun, D. C.; Lindsey, C.
1991BAAS...23.1049B Altcode:
No abstract at ADS

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Title: p-mode absorption in the giant active region of 10 March, 1989
Authors: Braun, D. C.; Duvall, T. L., Jr.
1990SoPh..129...83B Altcode:
A time series of velocity oscillations is observed in the vicinity of
NOAA region 5395 with the Kitt Peak vacuum telescope for 6.8 hours on
1989 March 10 as part of a program to study the interaction of solar
p-mode oscillations with solar active regions. The data is transformed
in a cylindrical coordinate system centered on the visible sunspot,
then Hankel- and Fourier-transformed to produce the power spectra of in-
and outgoing acoustic waves. It is observed that a maximum of nearly 70%
of the power of incident high-degree modes is absorbed by this unusually
large sunspot group. The absorptive properties of this active region
are compared with those of more typical regions studied previously.

---------------------------------------------------------
Title: The Spatial Distribution of p-Mode Absorption in Active Regions
Authors: Braun, D. C.; Labonte, B. J.; Duvall, T. L., Jr.
1990ApJ...354..372B Altcode:
The interaction of solar p-mode waves and active regions
has been the subject of recent observational and theoretical
investigations. Observations show that up to one-half of the power
of incident high-degree acoustic may be absorbed in and around
sunspots. In this paper the horizontal spatial distribution of
high-degree p-mode absorption in solar active regions is explored. An
appropriate Fourier-Hankel transform can be used to detect the mean
absorption of waves passing through any given point on the solar
surface. By repeating the analysis at multiple positions a map of the
absorption can be constructed. A technique for optimal computation of
absorption maps is developed and applied to observations of several
active regions and an area of quiet sun near disk center. By comparing
the distribution of p-mode absorption with magnetograms and line-wing
intensity images, it is directly observed that the absorption is not
limited to the location of the visible sunspots but is also associated
with magnetic fields in the surrounding plage. It is estimated that the
absorption efficiency scales roughly with the magnetic flux density,
although the absorption appears to saturate inside the strongest fields.

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Title: Helioseismic Imaging of Sunspots at Their Antipodes
Authors: Lindsey, Charles; Braun, Douglas C.
1990SoPh..126..101L Altcode:
Recent work by Braun, Duvall, and LaBonte has shown that sunspots absorb
helioseismic waves. We propose that sunspot absorption causes a seismic
deficit that should be imaged at the antipode of the sunspot. If these
images are observable, it should be possible to produce seismic maps
of magnetic regions on the far side of the Sun. This possibility opens
a broad range of synoptic and diagnostic applications. Diagnostic
applications would include lifetimes of higher-frequency modes, and
possibly rotation of the solar interior and detection of subsurface
magnetic structure. We outline elements of the theory of seismic
imaging and consider some applications. We propose the extention of
acoustic holography to solar interior diagnostics in the context of
antipodal imaging.

---------------------------------------------------------
Title: Far-Infrared Intensity Variations Caused by 5 Minute
Oscillations
Authors: Lindsey, C.; Kopp, G.; Becklin, E. E.; Roellig, T.; Werner,
M. W.; Jefferies, J. T.; Orrall, F. Q.; Braun, D.; Mickey, D. L.
1990ApJ...350..475L Altcode:
Observations of solar IR intensity variations at 50, 100, and
200 microns were made simultaneously and cospatially with Doppler
measurements in the sodium D1 line at 5896 A. Brightness temperature
variations of several K in amplitude are highly correlated with five
minute Doppler oscillations. The brightness variations are attributed
to work done on the chromospheric medium by compression, driven by the
five minute oscillations. The Doppler oscillations lead the brightness
variations by about 47 deg in phase at 50 and 100 microns and by about
72 deg in phase at 200 microns.

---------------------------------------------------------
Title: Observations of p-Mode Absorption in Active Regions
Authors: Braun, D. C.; Duvall, T. L., Jr.; Jefferies, S. M.
1990LNP...367..181B Altcode: 1990psss.conf..181B
We present here a summary of results on the interaction of p-modes with
solar active regions based on observations made at the Kitt Peak Solar
Vacuum Telescope and the geographic South Pole. A travelling wave
decomposition of p-modes is performed in a cylindrical coordinate
system centered on the active regions. Significant absorption of
p-mode wave power is observed to occur in all of the regions and
is a function of horizontal wavenumber () - increasing linearly
with k up to some maximum value and remaining constant for higher
wavenumbers. The maximum fractional absorption of incident power
is about 0.2 for small pores and 0.4 for typical isolated sunspots
(radius = 15 Mm). A maximum of 70% absorption is seen in the large
sunspot group of March 1989 (radius = 60 Mm). No convincing variation
of the absorption with temporal frequency (i.e. radial order) is seen,
although not entirely ruled out considering the relative errors involved
with the power measurements. No significant difference in the amount
of p-mode absorption is detected between equal 3-hour time intervals
before and after a class X4 flare in the March 1989 region. No excess
of outgoing waves following the time of the flare is detected. These
observations do not support the suggestion that large flares may excite
observable acoustic waves in the photosphere.

---------------------------------------------------------
Title: The interaction of high-degree p-mode oscillations with solar
active regions
Authors: Braun, Douglas C Doug
1988PhDT.......201B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Absorption of High-Degree p-Mode Oscillations in and
around Sunspots
Authors: Braun, D. C.; Duvall, T. L., Jr.; Labonte, B. J.
1988ApJ...335.1015B Altcode:
The direct interaction of p-modes and sunspots is investigated in
four observed active regions using a partial wave analysis in a
cylindrical coordinate system centered on the spots. Up to half the
power of incident p-modes is absorbed by the sunspots. By measuring
the magnitude of absorption as a function of horizontal wavenumber
and azimuthal order the authors have determined that the absorption is
not only from the umbrae of the spots but is also significant within
the penumbrae, and in some cases it appears to be associated with the
presence of extended magnetic fields surrounding the sunspots. The
amount of p-mode energy removed by magnetic fields is estimated for
each of the regions observed.

---------------------------------------------------------
Title: Tomography of Solar Active Regions
Authors: Braun, D. C.; Labonte, B. J.; Duvall, T. L., Jr.
1988BAAS...20..701B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Solar Chromosphere and Spicule Model Based on Far-Infrared
Limb Observations
Authors: Braun, D.; Lindsey, C.
1987ApJ...320..898B Altcode:
Techniques developed for LTE radiative transfer problems in a rough
atmosphere were used to compute a model chromosphere containing spicules
consistent with high-resolution solar limb observations from 100 microns
to 2.6 mm. The model consists of a smooth, plane-parallel temperature
minimum region extending from the photosphere to a height of 1000 km
and randomly distributed cylindrical spicules above this height. It
is found that the observed limb brightness profiles are well fitted
by spicules with electron temperatures on the order of 7000 K.

---------------------------------------------------------
Title: Acoustic Absorption by Sunspots
Authors: Braun, D. C.; Duvall, T. L., Jr.; Labonte, B. J.
1987ApJ...319L..27B Altcode:
The paper presents the initial results of a series of observations
designed to probe the nature of sunspots by detecting their influence
on high-degree p-mode oscillations in the surrounding photosphere. The
analysis decomposes the observed oscillations into radially propagating
waves described by Hankel functions in a cylindrical coordinate system
centered on the sunspot. From measurements of the differences in power
between waves traveling outward and inward, it is demonstrated that
sunspots appear to absorb as much as 50 percent of the incoming acoustic
waves. It is found that for all three sunspots observed, the amount of
absorption increases linearly with horizontal wavenumber. The effect
is present in p-mode oscillations with wavelengths both significantly
larger and smaller than the diameter of the sunspot umbrae. Actual
absorption of acoustic energy of the magnitude observed may produce
measurable decreases in the power and lifetimes of high-degree p-mode
oscillations during periods of high solar activity.

---------------------------------------------------------
Title: The Absorption of 5-Minute Oscillations by Sunspots
Authors: Braun, D. C.; Labonte, B. J.; Duvall, T. L., Jr.
1987BAAS...19..936B Altcode:
No abstract at ADS

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Title: Sunspots as Sinks of P-Mode Wave Energy
Authors: Duvall, T. L., Jr.; Harvey, J. W.; Braun, D. C.; Labonte,
B. J.; Pomerantz, M. A.
1987BAAS...19R.934D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Solar Irradiance From January to February, 1981
Authors: Braun, D. C.; Labonte, B. J.
1985BAAS...17..756B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observations of the Ca II K spectral line in He 10830 Å
dark points.
Authors: Holt, R.; Fortune, N.; Braun, D.; Mullan, D.
1985BAAS...17..760H Altcode:
No abstract at ADS

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Title: Planet Size Stars or Star Size Planets
Authors: McCarthy, D.; Low, F.; Kleinmann, S.; Lippincott, S. L.;
Braun, D.
1983S&T....66..114M Altcode:
No abstract at ADS

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Title: Astrometric and infrared speckle analysis of the visually
unresolved binary BD +41 328.
Authors: Lippincott, S. L.; Braun, D.; McCarthy, D. W., Jr.
1983PASP...95..271L Altcode:
BD +41°328 (PCC 372), a solar-type 5th magnitude star at a distance of
14 parsecs was discovered to have an unseen companion from proper-motion
analysis of astrometric plates taken with the Sproul 61-cm refractor,
thus excluding it as a candidate for a solar planetary-type system. The
combination of an improved photocentric orbit from recent astrometry and
measurement of the companion's separation and brightness by infrared
speckle interferometry at 2.2 microns indicates that the companion is
a red dwarf with a mass of 0.38 ± 0.07Msun. It revolves
around the primary with a period of 19.5 years and a semimajor axis
of 8.9 ± 0.5 AU.