Author name code: labonte
ADS astronomy entries on 2022-09-14
author:"LaBonte, Barry J."
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Title: Survey of Magnetic Helicity Injection in Regions Producing
X-Class Flares
Authors: LaBonte, B. J.; Georgoulis, M. K.; Rust, D. M.
Bibcode: 2007ApJ...671..955L
Altcode:
Virtually all X-class flares produce a coronal mass ejection (CME),
and each CME carries magnetic helicity into the heliosphere. Using
magnetograms from the Michelson Doppler Imager on the Solar
and Heliospheric Observatory, we surveyed magnetic helicity
injection into 48 X-flare-producing active regions recorded by
the MDI between 1996 July and 2005 July. Magnetic helicity flux
was calculated according to the method of Chae for the 48 X-flaring
regions and for 345 non-X-flaring regions. Our survey revealed that a
necessary condition for the occurrence of an X-flare is that the peak
helicity flux has a magnitude >6×1036 Mx2
s-1. X-flaring regions also consistently had a higher net
helicity change during the ~6 day measurement intervals than nonflaring
regions. We find that the weak hemispherical preference of helicity
injection, positive in the south and negative in the north, is caused
by the solar differential rotation, but it tends to be obscured by the
intrinsic helicity injection, which is more disorganized and tends to be
of opposite sign. An empirical fit to the data shows that the injected
helicity over the range 1039-10 43 Mx2
s-1 is proportional to magnetic flux squared. Similarly,
over a range of 0.3-3000 days, the time required to generate the
helicity in a CME is inversely proportional to the magnetic flux
squared. Most of the X-flare regions generated the helicity needed
for a CME in a few days to a few hours.
Title: Magnetic Energy and Helicity Budgets in the Active Region
Solar Corona. I. Linear Force-Free Approximation
Authors: Georgoulis, Manolis K.; LaBonte, Barry J.
Bibcode: 2007ApJ...671.1034G
Altcode: 2007arXiv0706.4122G
We self-consistently derive the magnetic energy and relative magnetic
helicity budgets of a three-dimensional linear force-free magnetic
structure rooted in a lower boundary plane. For the potential magnetic
energy we derive a general expression that gives results practically
equivalent to those of the magnetic virial theorem. All magnetic energy
and helicity budgets are formulated in terms of surface integrals
applied to the lower boundary, thus avoiding computationally intensive
three-dimensional magnetic field extrapolations. We analytically and
numerically connect our derivations with classical expressions for the
magnetic energy and helicity, thus presenting a unified treatment of
the energy/helicity budgets in the constant-alpha approximation that
is lacking so far. Applying our derivations to photospheric vector
magnetograms of an eruptive and a noneruptive solar active region,
we find that the most profound quantitative difference between these
regions lies in the estimated free magnetic energy and relative magnetic
helicity budgets. If this result is verified with a large number of
active regions, it will advance our understanding of solar eruptive
phenomena. We also find that the constant-alpha approximation gives
rise to large uncertainties in the calculation of the free magnetic
energy and the relative magnetic helicity. Therefore, care must be
exercised when this approximation is applied to photospheric magnetic
field observations. Despite its shortcomings, the constant-alpha
approximation is adopted here because this study will form the basis
of a comprehensive nonlinear force-free description of the energetics
and helicity in the active region solar corona, which is our ultimate
objective.
Title: Photon Spectroscopy with Imaging X-Ray Instruments
Authors: Labonte, B. J.; Reardon, K. P.
Bibcode: 2007SoPh..240..387L
Altcode:
Individual X-ray photons in the keV energy range produce hundreds of
photoelectrons in a single pixel of a CCD array detector. The number
of photoelectrons produced is a linear function of the photon energy,
allowing the measurement of spectral information with an imaging
detector system. Most solar X-ray telescopes, such as Yohkoh/SXT and
Hinode/XRT, use CCD detectors in an integrating mode and are designed to
make temperature estimates from multiband filter photometry. We show how
such instruments can be used in a new way to perform a limited type of
this photon spectroscopy. By measuring the variance in intensity of a
series of repeated images through a single filter of an X-ray source,
the mean energy per detected photon can be determined. This energy
is related to the underlying coronal spectrum, and hence it can be
used to deduce the mean plasma temperature. We apply this technique to
data from the Yohkoh Soft X-Ray Telescope and compare the temperatures
obtained with this technique with the temperatures derived using the
standard filter ratio method for a postflare loop system. Given the
large dynamic range of the soft X-ray flux observed from the Sun,
we describe the requirements for a future instrument that would be
better suited to performing photon spectroscopy.
Title: Reconstruction of an Inductive Velocity Field Vector from
Doppler Motions and a Pair of Solar Vector Magnetograms
Authors: Georgoulis, Manolis K.; LaBonte, Barry J.
Bibcode: 2006ApJ...636..475G
Altcode: 2005astro.ph.11447G
We outline a general methodology to infer the inductive velocity
field vector in solar active regions. For the first time, both
the field-aligned and the cross-field velocity components are
reconstructed. The cross-field velocity solution accounts for the
changes of the vertical magnetic field seen between a pair of successive
active region vector magnetograms via the ideal induction equation. The
field-aligned velocity is obtained using the Doppler velocity and the
calculated cross-field velocity. Solving the ideal induction equation
in vector magnetograms measured at a given altitude in the solar
atmosphere is an underdetermined problem. In response, our general
formalism allows the use of any additional constraint for the inductive
cross-field velocity to enforce a unique solution in the induction
equation. As a result, our methodology can give rise to new velocity
solutions besides the one presented here. To constrain the induction
equation, we use a special case of the minimum structure approximation
that was introduced in previous studies and is already employed here
to resolve the 180° ambiguity in the input vector magnetograms. We
reconstruct the inductive velocity for three active regions, including
NOAA AR 8210, for which previous results exist. Our solution believably
reproduces the horizontal flow patterns in the studied active regions
but breaks down in cases of localized rapid magnetic flux emergence or
submergence. Alternative approximations and constraints are possible
and can be accommodated into our general formalism.
Title: Solar Probe Engineering Concept
Authors: Potocki, K. A.; Eng, D. A.; McComas, D. J.; Maldonado,
H. M.; Conde, R. F.; Dewry, D. G.; Guo, Y.; Hartka, T. J.; King,
D. E.; Labonte, B. J.; Mehoke, D. S.; Santo, A. G.; Sequiera, H. B.;
Vaughan, R. M.; Wirzburger, M. J.; Carrasco, C. J.
Bibcode: 2005ESASP.592..697P
Altcode: 2005ESASP.592E.140P; 2005soho...16E.140P
No abstract at ADS
Title: Distinguishing Between Eruptive and Quiescent Solar Active
Regions
Authors: Georgoulis, M. K.; Labonte, B. J.
Bibcode: 2005AGUSMSH53B..05G
Altcode:
We present a method to fully evaluate the energy-helicity formula in
solar active regions by using only photospheric vector magnetograms of
these active regions. At the moment, the method relies on the linear
force-free approximation and provides the total magnetic energy,
the magnetic energy of the vacuum (potential) magnetic field, and the
non-potential (free) magnetic energy relating to the total magnetic
helicity in an active region. The formulation of the technique allows
an upgrade to a nonlinear force-free evaluation of the energy-helicity
formula, which will be a more realistic approach especially when
chromospheric vector magnetograms of solar active regions become
available. Even with the linear force-free approximation, however,
we find that the magnitudes of the total helicity, as well as the
ratios of the free magnetic energy to the total magnetic energy are
distinctly higher for eruptive active regions as compared to quiescent
active regions. Eruptive active regions produce flares and might trigger
CMEs, so the method presents a viable way to discriminate between these
two types of active regions even in case a single vector magnetogram
of these active regions is available.
Title: Boundary Flows in Solar Active Regions
Authors: Georgoulis, M. K.; Labonte, B. J.
Bibcode: 2005AGUSMSH51C..10G
Altcode:
We present a general technique to calculate the flow field at the
altitude where vector magnetic field measurements of solar active
regions have been obtained. The velocity field vector is reconstructed
fully by solving the ideal induction equation of magnetohydrodynamics
for the cross-field velocity component and by utilizing the
Doppler velocity information to calculate the field-aligned velocity
component. Because solving the induction equation is an under-determined
problem, we have formulated our technique in such a way as to provide a
unique solution of the induction equation when the vertical (normal to
the boundary) component of the cross-field velocity is prescribed. We
provide examples of various possible choices for the cross-field
vertical velocity and we discuss the respective results. Moreover, we
showcase the validity of our technique by predicting the particular area
of NOAA active region 8210 from which a flare and a CME were triggered,
using the reconstructed velocity field vector.
Title: Observational Evidence of the Kink Instability in Solar
Filament Eruptions and Sigmoids
Authors: Rust, D. M.; LaBonte, B. J.
Bibcode: 2005ApJ...622L..69R
Altcode:
Two lines of observational evidence are used to infer that the MHD
helical kink instability is associated with solar eruptions. The
senses of twist and writhe are determined in images of seven erupting
filaments obtained at 10830, 1600, 195, and 171 Å. In every case the
sense of twist is the same as the sense of writhe, as required for
a kink. From images in the soft X-ray and EUV spectrum, measurements
of the height/width ratio of 623 sigmoids show a mean value of 5.47,
which is the ratio expected for kinked flux ropes.
Title: The X3 Flare of 2002 July 15
Authors: Li, Jing; Mickey, D. L.; LaBonte, B. J.
Bibcode: 2005ApJ...620.1092L
Altcode:
An X3-class flare occurred on 2002 July 15 with white-light emission
and a complex filament eruption. Observations were made in the optical
continuum, Hα, UV continuum, microwave, and soft X-rays, as well
as with high-cadence longitudinal magnetograms. Within the preflare
phase, intense heating is observed accompanying upward motion of
the filament. At the onset of the impulsive phase, filament Doppler
acceleration is increased from -1.5 to -7.0 km s-2. Flare
impulsive emission is double-peaked, possibly corresponding to two
magnetic reconnection events: the first occurs above the active
region in the corona, while the second takes place in a thin current
sheet underneath the eruptive filament. It is probable that a twisted
helical flux rope, seen in C IV TRACE images, is formed during the
second reconnection. The energy released by the white-light flare is
~1033 ergs and dominates the flare emission spectra. Within
the flare impulsive phase, the emission profiles show both abrupt and
gradual components in white light, UV, and Hα. These variations are
independently reflected in the transverse motions of flare kernels:
the abrupt emission phase corresponds to a rapid kernel motion, while
the gradual phase corresponds to a more modest kernel motion.
Title: Finding the sources of irradiance variation at sunspot
minimum .
Authors: Bernasconi, P. N.; Foukal, P.; Rust, D. M.; LaBonte, B. J.
Bibcode: 2005MmSAI..76..907B
Altcode:
In 2006-2007 the Solar Bolometric Imager (SBI) will operate in the polar
stratosphere where near-space conditions can be attained for 10 to 30
days. The instrument will provide bolometric (wavelength-integrated
light) and color temperature images of the Sun. At the upcoming sunspot
minimum, SBI observations will be able to detect subtle sources
of solar irradiance variation with the least confusion by signals
from the magnetic fields. This is the best observational approach
to characterizing potential causes of the long-term irradiance
variations. Possible predicted sources of secular variability
include torsional waves and meridional flow variations. SBI uses a
30-cm diameter F/12 Dall-Kirkham telescope with uncoated mirrors, and
neutral density filters to provide broadband (bolometric) sensitivity
that varies only by ±7% over the wavelengths from 0.31 mu m to 2.6
mu m. Inferred solar irradiance variations will be compared with space
based full-disk radiometric measurements.
Title: Transport of Magnetic Helicity and Dynamics of Solar Active
Regions
Authors: Georgoulis, M. K.; Labonte, B. J.; Rust, D. M.
Bibcode: 2005HiA....13..117G
Altcode:
We outline a simple method to monitor variations of the magnetic
helicity the current helicity and the non-potential (free) magnetic
energy on the photospheric boundary of solar active regions. Explicit
manifestations of dynamical activity in the solar atmosphere such as
flares coronal mass ejections and filament eruptions may be related to
these variations. While similar methods require knowledge of the vector
potential and the velocity field vector on the photosphere our method
requires only the photospheric potential magnetic field corresponding
to the observed magnetograms. The calculation of the potential field
for any given magnetogram is straightforward. Moreover our method
relies on the constant-alpha force-free approximation assumed to hold
in the active region. Whether the above is a realistic assumption
can be tested using an array of well-documented methods. Therefore
our technique may prove quite useful to at least a subset of active
regions in which the linear force-free approximation is justifiable.
Title: Finding the Sources of Irradiance Variation at Sunspot Minimum
Authors: Rust, D. M.; Bernasconi, P. N.; Foukal, P. V.; Labonte, B. J.
Bibcode: 2004AGUFMSH51E..02R
Altcode:
In 2006-2007 the Solar Bolometric Imager (SBI) and the Multi-Spectral
Imager (MSI) will operate in the polar stratosphere where near-space
conditions can be attained for 10 to 20 days. The instruments will
provide bolometric (wavelength-integrated light) and color temperature
images of the Sun. At the upcoming sunspot minimum, SBI observations
will be able to detect subtle sources of solar irradiance variation
with the least confusion by signals from the magnetic fields. This is
the best observational approach to characterizing potential causes
of the long-term irradiance variations. Possible predicted sources
of secular variability include torsional waves and meridional flow
variations. SBI uses a 30-cm diameter F/12 Dall-Kirkham telescope with
uncoated mirrors, and neutral density filters to provide broadband
(bolometric) sensitivity that varies only by ±7 percent over the
wavelengths from 0.28 microns to 2.6 microns. The MSI is a CCD-based
imager that will provide diagnostics of solar magnetic and thermal
structures while SBI assesses their radiance. Sunspots, faculae
and magnetic network will be identified from the MSI images. Sonic
filtering of the MSI images will isolate the oscillatory signal. That
signal will be used to remove oscillations from SBI averages to reduce
the solar noise. Inferred solar irradiance variations will be compared
with SORCE/TIM and ACRIMSAT measurements. The images and data products
will be openly available via the Web.
Title: Forecasting and Real-Time Diagnostics of Solar Coronal Mass
Ejections
Authors: Georgoulis, M. K.; Labonte, B. J.
Bibcode: 2004AGUFMSA43B..02G
Altcode:
We discuss an operational, fully automated, algorithm to follow
the dynamical evolution and the buildup of magnetic instabilities
that give rise to coronal mass ejections (CMEs) in solar active
regions. The tool relies on vector magnetic field measurements
of the active region photosphere / chromosphere and performs the
following tasks: (1) resolution of the 180-degree ambiguity in
the magnetic field measurements and preparation for further use,
(2) calculation of the magnetic forces and electric currents in
the active region photosphere/chromosphere, (3) reconstruction of
a magnetohydrodynamic velocity field corresponding to the measured
magnetic field to calculate the buildup rate of the magnetic helicity
in the active region atmosphere, and (4) estimation of the total
magnetic helicity in the active region corona. We present examples
showing that (I) flare- and CME-prolific active regions have much
higher magnetic helicity, stronger magnetic forces and more intense
cross-field electric currents than quiescent active regions, and
(II) the magnetic helicity, chirality, magnetic flux, and magnetic
energy of a CME can be calculated in real time from the results of the
algorithm before and after the CME. As a result, we can both identify
potentially eruptive areas on the visible solar disk and provide
detailed quantitative diagnostics of the resulting CMEs. Additional
work is required to predict the geoeffectiveness of these CMEs. For
the algorithm to be useful we need full-disk, ideally uninterrupted,
coverage of the solar magnetic field vector. This information will
be available in a few years with the Helioseismic and Magnetic Imager
(HMI) on board the Solar Dynamics Observatory (SDO; launch 2008). At
the moment, full-disk vector magnetograms will be provided by the
ground-based Vector Spectro-Magnetograph (VSM) of the Synoptic Optical
Long-Term Investigation of the Sun (SOLIS) telescope. We will utilize
the SOLIS vector magnetograms as soon as they become available.
Title: An Integrated Program to Forecast Geostorms
Authors: Labonte, B. J.; Rust, D.; Bernasconi, P.; Georgoulis, M.
Bibcode: 2004AGUFMSA51B0243L
Altcode:
We have developed several operational products and automated tools for
assessing the helicity content of solar regions and their probability of
launching a geoeffective coronal mass ejection. These include detection
of active region sigmoids, measurement of magnetic helicity injection
in active regions, measurement of the sense of helicity in solar
filaments, and the estimate of magnetic helicity content of active
regions from vector magnetogram observations. In this presentation
we discuss a new program to integrate the separate products and tools
into a single product that provides a quantitative mid-term forecast
of solar activity that results in geomagnetic storms.
Title: Vertical Lorentz Force and Cross-Field Currents in the
Photospheric Magnetic Fields of Solar Active Regions
Authors: Georgoulis, Manolis K.; LaBonte, Barry J.
Bibcode: 2004ApJ...615.1029G
Altcode:
We demonstrate that the vertical Lorentz force and a corresponding lower
limit of the cross-field electric current density can be calculated
from vector magnetograms of solar active regions obtained at a single
height in the solar atmosphere, provided that the vertical gradient
of the magnetic field strength is known at this height. We use a
predicted vertical magnetic field gradient derived from a previous
analysis. By testing various force-free solutions, we find that the
numerical accuracy of our method is satisfactory. Applying the method
to active region photospheric vector magnetograms, we find vertical
Lorentz forces ranging from several hundredths to a few tenths of
the typical photospheric gravitational force, and typical cross-field
current densities up to several times 10 mA m-2. The typical
vertical current density is found to be 2-3 times smaller, on the order
of 10-15 mA m-2. These differences are above the associated
uncertainties. The values of the cross-field currents decrease in an
averaged vector magnetogram, but the ratio of the cross-field to the
vertical current density increases, also above the uncertainties. We
conclude that the photospheric active region magnetic fields are not
force-free, contrary to the conjectures of some recent studies.
Title: The Imaging Vector Magnetograph at Haleakala : III. Effects
of Instrumental Scattered Light on Stokes Spectra
Authors: LaBonte, Barry
Bibcode: 2004SoPh..221..191L
Altcode:
The scattering of light over the field of view of a solar
spectropolarimeter affects all Stokes parameters. The magnetic
field vector inferred from the Stokes spectra then has systematic
error. The reason is that scattering affects polarized radiation as
well as unpolarized. Accurate correction of the Stokes spectra from
the Imaging Vector Magnetograph (IVM) of the Mees Solar Observatory
illustrates the problem and the solutions.
Title: On the Resolution of the Azimuthal Ambiguity in Vector
Magnetograms of Solar Active Regions
Authors: Georgoulis, Manolis K.; LaBonte, Barry J.; Metcalf, Thomas R.
Bibcode: 2004ApJ...602..446G
Altcode:
We introduce a ``structure minimization'' technique to resolve the
azimuthal ambiguity of 180°, intrinsic in solar vector magnetic
field measurements. We resolve the 180° ambiguity by minimizing the
inhomogeneities of the magnetic field strength perpendicular to the
magnetic field vector. This relates to a minimization of the sheath
currents that envelope the solar magnetic flux tubes, thus allowing
for more space-filling and less complex magnetic fields. Structure
minimization proceeds in two steps: First, it derives a local solution
analytically, by means of a structure minimization function. Second,
it reaches a global solution numerically, assuming smoothness of the
magnetic field vector. Structure minimization (i) is disentangled from
any use of potential or linear force-free extrapolations and (ii)
eliminates pixel-to-pixel dependencies, thus reducing exponentially
the required computations. We apply structure minimization to four
active regions, located at various distances from disk center. The
minimum structure solution for each case is compared with the
``minimum energy'' solution obtained by the slower simulated
annealing algorithm. We find correlation coefficients ranging from
significant to excellent. Moreover, structure minimization provides
an ambiguity-free vertical gradient of the magnetic field strength
that reveals the variation of the magnetic field with height. The
simplicity and speed of the method allow a near real-time processing
of solar vector magnetograms. This task was not possible in the past
and may be of interest to both existing and future solar missions and
ground-based magnetographs.
Title: Lorentz Forces and Helicity Diagnostics in Solar Active
Regions Based on a Fast Resolution of the Azimuthal Ambiguity in
Solar Vector Magnetograms
Authors: Georgoulis, Manolis K.; Labonte, Barry J.; Rust, David M.
Bibcode: 2004hell.conf...82G
Altcode:
No abstract at ADS
Title: Current Sheets in Stressed Coronal Magnetic Fields
Authors: Labonte, B. J.
Bibcode: 2003AGUFMSH42B0513L
Altcode:
The extrapolation of magnetic fields into the solar corona generally
assumes that the fields are fully relaxed - all possible reconnection
has occurred. This assumption is in conflict with the low magnetic
diffusivity in the corona. I will present initial results on
extrapolation based on stressed magnetic fields - those for which
no reconnection has occurred. As an opposite extreme to traditional
methods, stressed fields offer a different view of coronal fields. The
locations of current sheets between flux systems are directly
determined. Observational evidence of coronal reconnection can test
the completeness of the extrapolation, as the field lines spanning
flux systems must be in contact prior to reconnection. This work is
supported by NASA SEC GI grant NAG5-13020.
Title: Measuring Magnetic Helicity Transport in Solar Active Regions:
a Practical Implementation
Authors: Rust, D. M.; Labonte, B. J.
Bibcode: 2003AGUFMSH51A..02R
Altcode:
The causes of solar eruptions are not well understood, but it is clear
that the emergence of magnetic flux and the accumulation of twisted
(helical) magnetic fields in the solar atmosphere are preconditions
for eruption. It has been very difficult to study these indicators
because the magnetic data were unreliable due to varying `seeing'
conditions. However, SOHO produces reliable magnetograms every 95
minutes. Chae (Astrophys. J. 560, L95, 2001) showed how SOHO (Solar and
Heliospheric Observatory) data can yield reliable estimates of magnetic
flux and magnetic helicity accumulation in the solar atmosphere. Chae's
results suggest that regular time-series analyses of magnetograms could
provide a useful early indicator of the build up of energy in the
solar corona. Our objective has been to develop simple quantitative
indicators of pre-eruption build-up and thereby warn of potential
space weather related disturbances in space systems. We use the SOHO
data, but in the near future the Solar B and SDO missions will provide
much better magnetograms. So far, we have used Chae's method to map
helicity transport in several regions with solar flares. We will show
how advective helicity transport influences flare rate. We will also
compare our results with analyses of vector magnetograms, which show
both advective and convective helicity transport.
Title: Calculation of a Minimum Total Magnetic Helicity in Solar
Active Regions
Authors: Georgoulis, M. K.; Labonte, B. J.
Bibcode: 2003AGUFMSH51A..03G
Altcode:
Despite its extreme importance, the calculation of the total magnetic
helicity in solar active regions remains an unresolved problem in
solar physics. On the other hand, the helicity variations in an active
region can be calculated partially, for longitudinal magnetograms,
or in full, for vector magnetograms, but only by using coarse,
uncertain velocity field maps, calculated by means of correlation
tracking techniques. Whether one should apply correlation tracking
to magnetograms or white-light continuum images is also unclear,
as the two inputs do not yield identical outputs. We present a
technique that provides a lower limit of the total magnetic helicity
in active regions, without using any velocity fields. The temporal
variation of the total helicity can also be calculated in full if
a series of vector magnetograms is available. The method relies on
a comparison between the best linear force-free approximation and
the potential approximation for a given photospheric boundary and
begins by demonstrating that a commonly used formula for the magnetic
helicity density in the linear force-free approximation is, in fact,
erroneous. We have tested our method on vector magnetograms acquired by
the Imaging Vector Magnetograph (IVM) of the University of Hawaii. We
discuss the pros and cons of our approach and we compare our results for
the magnetic helicity variations with results obtained when classical
methods are employed.
Title: Sky Brightness Measurements at Haleakala, 1955-2002
Authors: LaBonte, Barry
Bibcode: 2003SoPh..217..367L
Altcode:
Measurements of the brightness of the clear daytime sky at Haleakala,
Maui are presented for the interval 1955 through 2002. The observations
are made near the direction of the Sun, where forward scattering off
aerosols dominates the sky brightness. The Haleakala summit at 3054
m is normally above the inversion layer. The Haleakala sky is dark;
the observed brightness per airmass has a median of 10 millionths of
the solar disk and a mode of 5 millionths, with Rayleigh scattering
contributing 1 millionth. There is no demonstrable long-term trend in
the data.
Title: An Automated System for Detecting Sigmoids in Solar X-ray
Images
Authors: LaBonte, B. J.; Rust, D. M.; Bernasconi, P. N.
Bibcode: 2003SPD....34.0504L
Altcode: 2003BAAS...35R.814L
The probability of a coronal mass ejection (CME) occurring is linked
to the appearance of structures, called sigmoids, in satellite X-ray
images of the sun. By examination of near real time images, we can
detect sigmoids visually and estimate the probability of a CME and
the probability that it will cause a major geomagnetic storm. We
have devised a pattern recognition system to detect the sigmoids in
Yohkoh SXT and GOES SXI X-ray images automatically. When implemented
in a near real time environment, this system should allow long term,
3 - 7 day, forecasts of CMEs and their potential for causing major
geomagnetic storms.
Title: Resolution of the Azimuthal Ambiguity in Photospheric Vector
Magnetograms of Solar Active Regions
Authors: Georgoulis, M. K.; LaBonte, B. J.
Bibcode: 2003SPD....34.1103G
Altcode: 2003BAAS...35Q.827G
We describe a simple technique to resolve the inherent azimuthal
ambiguity of 180o in vector magnetic field measurements of
solar active regions. The desired azimuth solution is the one that
minimizes an introduced function. This function includes a weighted
combination of the height derivative of the magnetic field strength,
calculated under conditions of minimum electric current density, and
the vertical component of a current density vector purely perpendicular
to the magnetic field lines. The above function reduces the number of
ambiguity states to two for each location on the heliographic plane. The
process is initially local, i.e., independent for each location on the
heliographic plane. Then, the initial azimuth solution is subjected
to a numerical analysis which yields the global azimuth solution
and ensures maximum continuity of the photospheric magnetic field
vector. This tactic reduces dramatically the required computing time to
only a small fraction of the time required by existing techniques. The
construction of the above-mentioned function is such that the method
works equally well for active regions located either near or far
from the center of the solar disk. The speed and simplicity of this
novel technique may lead to a near real-time processing of acquired
photospheric vector magnetograms. A reliable azimuth solution is a
prerequisite for further analysis of solar magnetic fields. Reaching
such a solution fast, is paramount for challenging modern problems,
such as space weather forecasting, for example.
Title: Observations of a Two Ribbon White Light Flare
Authors: Li, J.; Mickey, D.; LaBonte, B.
Bibcode: 2003SPD....34.1613L
Altcode: 2003BAAS...35Q.835L
On July 15 2002, an X3 flare occured within AR10030 and it was
accompanied with a white light flare (WLF). The Imaging Vector
Magnetograph (IVM) at Mees Solar Observatory recorded the entire event
including several hours of data before and after the flare. The IVM
continuum images are taken at time cadence as high as 1 seconds per
image. Such observations enabled us to resolve the WLF patches in time
and space. We will present (1). the initial WLF patch fell on a small
sunspot located at an area surrounded with single relatively weak
magnetic polarity between proceeding and following sunspot groups;
(2) the energy deposited during the WLF flare; (3) the light curves
of the optical continuum, the UV continuum (TRACE/1600) and microwaves
(1.2 - 18 GHz from Oven's Valley Solar Array). They demonstrate the same
profiles during flare impulsive phase. The observations suggest that the
origin of the WLF flare was caused by accelerated particles precipitate
into lower atmosphere along magnetic field lines. This work is
supported by NASA grant to Mess Solar Observatory and MURI program.
Title: Analysis of Vector Magnetic Fields in Solar Active Regions
by Huairou, Mees and Mitaka Vector Magnetographs
Authors: Zhang, H.; Labonte, B.; Li, J.; Sakurai, T.
Bibcode: 2003SoPh..213...87Z
Altcode:
We analyze the vector magnetograms in several well-developed active
regions obtained at Huairou Solar Observing Station, National
Astronomical Observatories of China, at Mees Solar Observatory,
University of Hawaii, and at National Astronomical Observatory
of Japan. It is found that there is a basic agreement on the
transversal fields among these magnetographs. The observational
error (mutual difference) for the transversal magnetic fields is
estimated. In addition to comparison of transversal fields among
different instruments, we used the morphological configurations of
sunspot penumbrae in white-light and EUV 171 Å images obtained by
the TRACE satellite as a reference of the orientation of transversal
magnetic fields.
Title: Near-infrared chromospheric observatory
Authors: Labonte, Barry; Rust, David M.; Bernasconi, Pietro N.;
Georgoulis, Manolis K.; Fox, Nicola J.; Kalkofen, Wolfgang; Lin,
Haosheng
Bibcode: 2003SPIE.4853..140L
Altcode:
NICO, the Near Infrared Chromosphere Observatory, is a platform for
determining the magnetic structure and fources of heating for the
solar chromosphere. NICO, a balloon-borne observatory, will use the
largest solar telescope flying to map the magnetic fields, velocities,
and heating events of the chromosphere and photosphere in detail. NICO
will introduce new technologies to solar flight missions, such as
wavefront sensing for monitoring telescope alignment, real-time
correlation tracking and high-speed image motion compensation, and
wide aperture Fabry-Perot etalons for extended spectral scanning.
Title: Transport of Helicity and Dynamics of Solar Active Regions
Authors: Georgoulis, Manolis K.; Rust, David M.; Labonte, Barry J.
Bibcode: 2003IAUJD...3E..29G
Altcode:
We outline a simple method to monitor variations of the magnetic
helicity the current helicity and the non-potential (free) magnetic
energy on the photospheric boundary of solar active regions. Explicit
manifestations of dynamical activity in the solar atmosphere such as
flares coronal mass ejections and filament eruptions may be related to
these variations. While similar methods require knowledge of the vector
potential and the velocity field vector on the photosphere our method
requires only the photospheric potential magnetic field corresponding
to the observed magnetograms. The calculation of the potential field
for any given magnetogram is straightforward. Moreover our method
relies on the constant-alpha force-free approximation assumed to hold
in the active region. Whether the above is a realistic assumption
can be tested using an array of well-documented methods. Therefore
our technique may prove quite useful to at least a subset of active
regions in which the linear force-free approximation is justifiable.
Title: Magnetic Fields in the Solar Photosphere are not Force-free
Authors: Labonte, B. J.
Bibcode: 2002AGUFMSH52A0483L
Altcode:
Coronal magnetic fields are often inferred from the extrapolation of
photospheric magnetic observations. The assumptions that the fields
are potential or force-free are not correct in the photosphere. The
magnitude of the forces and the sheet currents they drive are determined
from observations of the magnetic field vector made with the Imaging
Vector Magnetograph at Mees Solar Observatory.
Title: The Near-Infrared Chromosphere Observatory
Authors: Rust, David M.; Bernasconi, Pietro N.; Labonte, Barry J.;
Georgoulis, Manolis K.; Fox, Nicola J.; Kalkofen, Wolfgang; Lin,
Haoseng
Bibcode: 2002ESASP.505..561R
Altcode: 2002IAUCo.188..561R; 2002solm.conf..561R
The Near-Infrared Chromosphere Observatory (NICO) is a proposed
balloon-borne observatory aiming to investigate the magnetic structure
and the sources of heating in the solar chromosphere. NICO will be based
on the successful Flare Genesis Experiment (FGE), a pioneer in applying
novel technologies for the study of the Sun. NICO will map magnetic
fields, velocity fields, and heating events in the chromosphere with
unprecedented quality.
Title: Moving Dipolar Features in an Emerging Flux Region
Authors: Bernasconi, P. N.; Rust, D. M.; Georgoulis, M. K.; Labonte,
B. J.
Bibcode: 2002SoPh..209..119B
Altcode:
On 25 January, 2000, we observed active region NOAA 8844 with the
Flare Genesis Experiment (FGE), a balloon-borne observatory with an
80-cm solar telescope. FGE was equipped with a vector polarimeter and
a tunable Fabry-Pérot narrow-band filter. It recorded time series of
filtergrams, vector magnetograms and Dopplergrams at the Ca i 6122.2 Å
line, and Hα filtergrams with a cadence between 2.5 and 7.5 min. At
the time of the observations, NOAA 8844 was located at approximately
5° N 30° W. The region was growing rapidly; new magnetic flux was
constantly emerging in three supergranules near its center. We report on
the structure and behavior of peculiar moving dipolar features (MDFs)
in the emerging flux, and we describe in detail how the FGE data were
analyzed. In longitudinal magnetograms, the MDFs appeared to be small
dipoles flowing into sunspots and supergranule boundaries. Previously,
dipolar moving magnetic features (MMFs) have only been observed
flowing out from sunspots. The FGE vector magnetograms show that the
MDFs occurred in a region with nearly horizontal fields, the MDFs
being distinguished as undulations in these fields. We identify the
MDFs as stitches where the emerging flux ropes were still tied to the
photosphere by trapped mass. We present a U-loop model that accounts for
their unusual structure and behavior, as well as showing how emerging
flux sheds entrained mass.
Title: The Near-Infrared Chromosphere Observatory (NICO)
Authors: Rust, D. M.; Bernasconi, P. N.; LaBonte, B. J.; Georgoulis,
M. K.; Kalkofen, W.; Fox, N. J.; Lin, H.
Bibcode: 2002AAS...200.3902R
Altcode: 2002BAAS...34..701R
NICO is a proposed cost-effective platform for determining the magnetic
structure and sources of heating for the solar chromosphere. It is a
balloon-borne observatory that will use the largest solar telescope
flying and very high data rates to map the magnetic fields, velocities,
and heating events of the chromosphere and photosphere in unprecedented
detail. NICO is based on the Flare Genesis Experiment (FGE), which
has pioneered in the application of technologies important to NASA's
flight program. NICO will also introduce new technologies, such
as wavefront sensing for monitoring telescope alignment; real-time
correlation tracking and high-speed image motion compensation for
smear-free imaging; and wide aperture Fabry-Perot filters for extended
spectral scanning. The telescope is a classic Cassegrain design with
an 80-cm diameter F/1.5 primary mirror made of Ultra-Low-Expansion
glass. The telescope structure is graphite-epoxy for lightweight,
temperature-insensitive support. The primary and secondary mirror
surfaces are coated with silver to reflect more than 97% of the incident
solar energy. The secondary is made of single-crystal silicon, which
provides excellent thermal conduction from the mirror surface to its
mount, with negligible thermal distortion. A third mirror acts as a
heat dump. It passes the light from a 15-mm diameter aperture in its
center, corresponding to a 322"-diameter circle on the solar surface,
while the rest of the solar radiation is reflected back out of the
front of the telescope. The telescope supplies the selected segment
of the solar image to a polarization and spectral analysis package
that operates with an image cadence 1 filtergram/sec. On-board data
storage is 3.2 Terabytes. Quick-look images will be sent in near real
time to the ground via the TDRSS communications link.
Title: Investigation of the Sources of Irradiance Variation on the
Sun (ISIS)
Authors: LaBonte, B. J.; Bernasconi, P. N.; Rust, D.; Foukal, P.;
Hudson, H.; Spruit, H.
Bibcode: 2002AAS...200.5608L
Altcode: 2002BAAS...34..736L
There is a persistent correlation of the longterm climate change and
solar irradiance. ISIS is designed to understand the physical basis of
this correlation. ISIS combines an innovative bolometric imager and a
multiband CCD imager. The bolometric imager has uniform response from
200 nm to 3000 nm, spatial resolution < 5 arcseconds, and precision
of < 0.1% in a one minute integration. The multiband imager records
ultraviolet irradiance variation in the band from 200 to 350 nm,
measures photospheric temperature structure, and provides chromospheric
structure in Ca II K and H-alpha, with spatial resolution <1.0
arcsecond. Designed for flight on the Solar Dynamics Observatory,
ISIS will provide the comprehensive photometric measurements needed
to characterize the irradiance variation from identifiable structures
and challenge theoretical models of convection and the solar dynamo.
Title: An Automated System for Detecting Sigmoids in Solar X-ray
Images
Authors: LaBonte, B. J.; Rust, D. M.; Bernasconi, P. N.
Bibcode: 2002AGUSMSH52A..02L
Altcode:
The probability of a coronal mass ejection (CME) occurring is linked
to the appearance of structures, called sigmoids, in satellite X-ray
images of the sun. By examination of near real time images, we can
detect sigmoids visually and estimate the probability of a CME and
the probability that it will cause a major geomagnetic storm. We have
devised a pattern recognition system to detect the sigmoids in Yohkoh
and GOES (when available) X-ray images automatically. When implemented
in a near real time environment, this system should allow long term,
3 - 7 day, forecasts of CMEs and their potential for causing major
geomagnetic storms.
Title: Persistent Coronal Streamers and the Identification of
Sunspot Clusters
Authors: Li, Jing; LaBonte, Barry; Acton, Loren; Slater, Greg
Bibcode: 2002ApJ...565.1289L
Altcode:
We use limb synoptic plots to study long-lived features of the lower
solar corona. The most persistent features are the polar sinusoids,
which are generated by streamers associated with active regions. We
find that the lifetimes of these structures (up to about 10 solar
rotations) are much longer than the lifetimes of individual sunspots
(typically less than one solar rotation). The long lifetimes of
the polar sinusoids are due to clusters of spatially related but
noncontemporaneous spots. The continuous emergence of sunspots and
magnetic flux from spot clusters in the photosphere provides the
long life spans of the coronal streamers. Two-thirds of the ~180
sunspots recorded in the southern hemisphere in a 1-year period
near the 1996-1997 solar minimum were members of noncontemporaneous
clusters. The clusters suggest large-scale, long-lived structures in
the subphotospheric magnetic field from which sunspots emerge.
Title: Large-Scale and Long-Lived Coronal Structures Detected in
Limb Synoptic Maps
Authors: Li, J.; Labonte, B.; Acton, L.; Slater, G.
Bibcode: 2002mwoc.conf..333L
Altcode:
The presentation will summarize our recent work on the large-scale,
long-lived coronal streamers based on limb synoptic maps made from
Yohkoh/SXT and SOHO/EIT images. The number of properties of such
coronal streamers have been revealed on the limb synoptic maps: 1. They
originate from active regions and have large extent in both latitude
and altitude. 2. Because they are large in 3-dimension, they largely
control the visibility of polar hole regions. When the active region
is in close side of the sun, then may cover the polar holes. When
the active region is at far side of the sun, they can be seen above
the solar limb by projections; 3. The life time of such large-scaled
coronal streamers can be up to 10 solar rotations; 4. These structures
are associated with underlying, non-contemporaneous spot clusters;
5. Individual spots in the clusters are short-lived, but contribute
magnetic flux collectively to form the long-lived coronal features.
Title: Magnetic Fields in the Photosphere are not Force-Free
Authors: Labonte, B. J.
Bibcode: 2002mwoc.conf...87L
Altcode:
No abstract at ADS
Title: The Magnetic Free Energy and a CME in Active Region 8299
Authors: Metcalf, T. R.; Mickey, D. L.; Labonte, B. J.; Ryder, L. A.
Bibcode: 2002mwoc.conf..249M
Altcode:
We calculate the magnetic free energy as a function of time for
NOAA active region 8299 on 1998 August 11 using vector magnetic
field measurements in the ion Na 1 5896Å sepctral line observed
with the Imaging Vector Magnetograph at Mees Solar Observatory. The
free energy in this active region is significant with a magnitude
of about 1033 ergs, though the active region was not
flare productive. This amount of free energy is more than enough to
explain the enhanced heating of the active region corona. The free
energy dipped to a value consistent with zero for one hour during
the observation. Yohkoh/SXT images reveal that during this dip in the
free energy, the coronal structure of AR 8299 and the nearby AR8297
changed significantly. SXT observed the brightening of a coronal loop
connecting AR 8299 and AR 8297 and observed coronal dimming and the
formation of a cusp structure in AR 8297, suggesting that a gradual CME
was launched as the magnetic energy dipped. Unfortunately, LASCO data
were not available to confirm the existence of a halo CME. However,
the circumstantial evidence points to the magnetic free energy as the
energy source for the postulated CME.
Title: Sunspot Formation from Emerging Flux Ropes - Observations
from Flare Genesis
Authors: Rust, D. M.; Bernasconi, P. N.; Georgoulis, M. K.; LaBonte,
B. J.; Schmieder, B.
Bibcode: 2001AGUSM..SP42A09R
Altcode:
From January 10 to 27, 2000, the Flare Genesis payload observed
the Sun while suspended from a balloon in the stratosphere above
Antarctica. The goal of the mission was to acquire a long time series of
high-resolution images and vector magnetograms of the solar photosphere
and chromosphere. We obtained images, magnetograms and Dopplergrams
in the magnetically sensitive Ca I line at 6122 Angstroms. Additional
simultaneous images were obtained in the wing of H-alpha. On January
25, 2000, we observed in NOAA region 8844 at N05 W30. The rapid
development of a sunspot group that apparently included a delta spot
(two polarities within one umbra). We considered a variety of models
for interpreting these observations, including a twisted flux tube,
a bipole that annihilates, a bipole that submerges, and a field
distorted by mass loading. From the vector magnetograms and Doppler
measurements, we conclude that nearly horizontal flux ropes are swept
into the developing spot where they tilt upward to contribute to the
familiar nearly vertical sunspot fields. The largest flux rope exhibited
a twisted structure, and its angle with respect to the vertical was so
great that it could be mistaken for a positive magnetic field merging
into a negative sunspot. Flare Genesis was supported by NASA grant
NAG5-8331 and by NSF grant OPP-9909167.
Title: Peculiar Moving Magnetic Features Observed With the Flare
Genesis Experiment
Authors: Bernasconi, P. N.; Rust, D. M.; Georgoulis, M. K.; LaBonte,
B. J.; Schmieder, B.
Bibcode: 2001AGUSM..SP51A02B
Altcode:
With the Flare Genesis Experiment (FGE), a balloon-borne 80-cm solar
telescope, we observed the active region NOAA 8844 on January 25,
2000 for several hours. FGE was equipped with a vector polarimeter
and a lithium-niobate Fabry-Perot narrow-band filter. It recorded
time series of filtergrams, vector magnetograms, and dopplergrams
at the CaI 6122.2 Angstroms line, as well as Hα filtergrams, with a
cadence between 2.5 and 7.5 minutes. At the time of the observations
NOAA 8844 was located at approximately 5 deg N, 30 deg W. It was a new
flux emergence that first appeared on the solar disk two days before
and was still showing a very dynamic behavior. Its two main polarity
parts were rapidly moving away from each other and new magnetic flux
was constantly emerging from its center. Here we describe the structure
and behavior of peculiar small moving magnetic dipoles (called moving
magnetic features MMF's) that we observed near the trailing negative
polarity sunspot of NOAA 8844. Presentations by D. M. Rust, and by
M. K. Georgoulis at this meeting will focus on other aspects of the
same active region. The MMF's took the form of small dipoles that first
emerged into the photosphere near the center of a supergranular cell
located next to the main trailing flux concentration. They rapidly
migrated towards the spot, following the supergranular flow. The two
polarities of the little dipoles did not separate; they moved together
with same speed and in the same direction. The dipoles were oriented
parallel to their motion toward the negative spot, with the positive
polarity always leading. MMF's usually move away from sunspots, and
their orientation is the reverse of what we see here. In addition,
we noted that the dipole structure was not symmetric. The field lines
of the trailing part of the MMF's (negative polarity) were always
much more perpendicular to the local horizontal than the ones of the
leading part. The trailing part looked more compact and circular, while
the leading part was more elongated in the direction of the motion. We
conclude that we observed a new type of MMF's with a totally different
magnetic structure than previously seen. We present a possible model
that could explain their unusual structure and behavior. This work
was supported by NASA grant NAG5-8331 and NSF grant OPP-9909167.
Title: The global solar corona defined by newly emerged flux at
low latitudes
Authors: Li, J.; LaBonte, B.; Acton, L. W.; Slater, G. L.
Bibcode: 2001AGUSM..SH41B05L
Altcode:
The global structure of the solar corona changes greatly from solar
minimum to maximum. To understand the details of this restructuring,
we analyzed the full disk Yohkoh/SXT images taken during the years
1996 to 1998. We found that the global coronal structures are largely
defined by a handful of active regions which emerged at low latitudes
in the first year of the new solar cycle following solar minimum. The
rotation rates of the structures agree with photospheric differential
rotation rate of their associated active region. Following the first
year of the solar cycle, newly emerged flux tends to appear near the
old flux, which may give the impression of the existence of an active
longitude; however, the coronal structure is clearly associated in
space and time with the new flux, not some average location.
Title: Untwisting Sunspots
Authors: LaBonte, B. J.
Bibcode: 2001AGUSM..SH31D09L
Altcode:
Sunspots may display twisted structure, as observed in the
photospheric penumbra, the chromospheric superpenumbra, or in the
azimuths of the vector magnetic field. The twist is inferred to
be caused by field-aligned electric currents, and thus represents
free energy. Attempts to determine whether the free energy changes
discontinuously, in synchronism with flare energy release, have been
unconvincing. Beginning in 1999, observations with the Imaging Vector
Magnetograph at Mees Solar Observatory, Haleakala have finally used the
full spatial (1 arcsec) and temporal resolution (2 minutes). We have
found numerous cases in which isolated twisted sunspots, of a variety
of sizes, display continuous rotary motion. We will show a sample of
these spots, distinguishing those for which the rotary motion is a bulk
rotation of the spot from those for which it is an actual untwisting of
the fields. Estimates of the rate of untwisting and of the consequent
steady free energy decrease can then be made. This work is supported
by NASA grant NAG5-4941.
Title: Solar Polar Rays Are Not Polar
Authors: Li, J.; Jewitt, D.; Labonte, B.; Acton, L.
Bibcode: 2001IAUS..203..404L
Altcode:
In this poster we discuss the nature of polar rays, based on limb
synoptic images constructed from Yohkoh/SXT and SOHO/EIT data. In
the literature, polar rays and polar plumes are often mentioned
interchangably. We find that polar rays are projection effects caused
by hot plasma from equatorial active areas and are not physically
associated with the coronal polar holes. Instead, the rise in number
and strength of polar rays toward solar activity maximum is responsible
for hiding the polar holes and polar plumes. We will present the limb
synoptic maps and simple physical models to lead to this result.
Title: The Nature of Solar Polar Rays
Authors: Li, Jing; Jewitt, David; LaBonte, Barry
Bibcode: 2000ApJ...539L..67L
Altcode: 2000astro.ph..6377L
We use time series observations from the Solar and Heliospheric
Observatory and Yohkoh spacecraft to study solar polar rays. Contrary
to our expectations, we find that the rays are associated with active
regions on the Sun and are not features of the polar coronal holes. They
are extended, hot plasma structures formed in the active regions and
projected onto the plane of the sky above the polar coronal holes. We
present new observations and simple projection models that match
long-lived polar ray structures seen in limb synoptic maps. Individual
projection patterns last for at least five solar rotations.
Title: Global Solar Corona Revealed by Time Series Observations
Authors: Li, Jing; Kuhn, J.; LaBonte, B.; Raymond, J. C.; Acton, L. W.
Bibcode: 2000ApJ...538..415L
Altcode:
Time series observations at UV (Extreme Ultraviolet Imaging
Telescope/Solar and Heliospheric Observatory) and X-ray (Soft
X-Ray Telescope/Yohkoh) wavelengths reveal properties of the global
solar corona that are not easily identified in a single image. A
median-filtering technique that rejects features varying with time
is used to isolate background corona. The coronal hole boundaries,
polar plumes, and polar rays in the inner corona are clearly seen in
Extreme Ultraviolet Imaging Telescope data over 5 months during the
last solar minimum (1996 January through May). For the first time,
we provide physical evidence for coronal hole boundaries in the
inner corona. The observations show clearly that the polar coronal
holes expand divergently with height. A simple latitudinal and radial
electron density distribution for the inner corona is found.
Title: Physical properties of solar inner corona revealed by time
series observations made by EIT and SXT.
Authors: Li, J.; Labonte, B. J.; Acton, L. W.
Bibcode: 2000BAAS...32R.815L
Altcode:
No abstract at ADS
Title: Electric Current Systems in Solar Active Regions
Authors: LaBonte, B. J.; Mickey, D. L.
Bibcode: 2000SPD....31.0145L
Altcode: 2000BAAS...32Q.809L
The first study to show the persistence of local field-aligned current
systems in active regions was reported by Pevtsov, Canfield, and Metcalf
(Astrophys. J., 425, L117, 1994). Their work was limited to a sample
of complex, flare-productive regions because of the sensitivity limit
of the data from the Haleakala Stokes Polarimeter. I report here on a
new survey of active regions with the Imaging Vector Magnetograph (IVM)
at Mees Solar Observatory. The IVM data permit a look at current systems
in simpler, more typical active regions, because of better sensitivity,
temporal sampling, spatial resolution and field-of-view. Small scale
current systems are commonly seen. Transport of current systems by
advective processes is commonly seen over times of hours. This work
was supported by NASA grant NAG5-4941 and by a subcontract with LMSAL
in support of NASA contract NAS8-40801 for YOHKOH SXT.
Title: Evolution of the Solar Corona From Cycle 22 to Cycle 23 As
Revealed by X-ray Limb Synoptic Maps
Authors: Slater, G. L.; Freeland, S. L.; LaBonte, B. J.; Li, J.;
Acton, L. W.
Bibcode: 2000SPD....31.0228S
Altcode: 2000BAAS...32..815S
How does the solar corona vary within a solar cycle? We present time
series observations assembled from the Yohkoh Soft X-ray Telescope
(SXT) full mission image database which reveal coronal structures in the
inner corona that are not easily identifiable in individual images. We
have generated limb synoptic maps prepared from SXT data taken over
8 years (1992 through 1999). This period covers the decay phase of
solar cycle 22 and the rise phase of solar cycle 23. The SXT images
have recently been re-calibrated using more precise techniques. We
will address such topics as the variation of the polar coronal holes,
the lifetimes of active regions and associated streamers, and the
nature of polar plumes in the two phases of the solar cycle.
Title: Physical Properties of Solar Inner Corona Revealed by Time
Series Observations made by EIT and SXT
Authors: Li, J.; LaBonte, B. J.; Acton, L. W.
Bibcode: 2000SPD....31.0227L
Altcode: 2000BAAS...32..815L
We present a useful way to study how the solar corona varies with
time. Observations by EIT and SXT are used to construct limb synoptic
maps. The maps show limb emissions as functions of polar angle and
time. We identify and interpret various persistent structures such as
coronal hole boundaries, polar rays, and polar plumes seen on these
maps. The physical properties of these structures are discussed.An
empirical 3-dimensional electron density model for the background
corona will be introduced. This model was obtained through the use of
a median-filtering technique on the EIT coronal images obtained during
solar minimum (January through May 1996). This work was supported by
NASA grant NAG5-4941 and by a subcontract with LMSAL in support of
NASA contract NAS8-40801 for YOHKOH SXT.
Title: Max Millennium/Whole Sun Month Observations of a Sigmoid Region
(AR 8668)
Authors: Zarro, D. M.; Canfield, R. C.; Nitta, N.; Myers, D. C.;
Gregory, S. E.; Qiu, J.; Alexander, D.; Hudson, H. S.; Thompson,
B. J.; LaBonte, B. J.
Bibcode: 2000SPD....31.0236Z
Altcode: 2000BAAS...32..817Z
We report on observations of a sigmoidal region AR 8668 obtained
during the Whole Sun Month #3 campaign and Max Millennium Coordinated
Observing Program #2. The observations pertain to the period 1999
August 16-17 during which several GOES B and C class flares occurred
in AR 8668. Near simultaneous observations were obtained by SOHO (EIT
195 Angstroms/ and MDI full-disk magnetograms), TRACE 171 Angstroms/,
Yohkoh SXT, Big Bear (Hα ), and Mees (IVM vector magnetograms). The
multi-wavelength nature of these data, combined with their overlapping
spatial and temporal coverages, provide a unique opportunity to study
the magnetic topology and flaring evolution of twisted flux structures
associated with sigmoids. An objective of this study is to co-align
images and magnetograms obtained before and during the observed flares,
and compare the results with inferences from the topological model of
Titov and Demoulin, A&A 351, 707 (1999). We will present examples
of these coalignments and identify sites of magnetic energy release
that are associated with topological features (e.g. separatrices)
predicted by this model.
Title: Observational Study of Sunspot Oscillations in Stokes I, Q,
U, and V
Authors: Kupke, Renate; Labonte, B. J.; Mickey, D. L.
Bibcode: 2000SoPh..191...97K
Altcode:
Time series of 2-dimensional spectro-polarmetric data were obtained
with the intent of studying the temporal behavior of velocity,
magnetic flux, and characteristics of the Stokes V profile in a
small region of a larger sunspot. Full Stokes profiles in I, Q, U,
and V were obtained. Velocity oscillations were found at frequencies
of 3.3 mHz in each of the profiles. Acoustic power maps indicate
that locations of highest power correspond to areas in which the
polarization signal was greatest, therefore no conclusion about the type
of wave mode participating in the oscillations can be made. Velocity
amplitudes were I: 71 m s−1, Q: 47 m s−1,
U: 65 m s−1 and V: 86 m s−1. Oscillatory
behavior was also detected in longitudinal field strength, with an
r.m.s. amplitude of 22 G, at 2.6 and 3.3 mHz. The power was localized
at the umbral/penumbral boundary. A phase analysis indicates a −130°
phase difference with Stokes V velocity oscillations at 3.3 mHz and a
75° difference at 2.6 mHz. Results are consistent with magnetic field
lines swaying in response to a p-mode driver. No oscillatory behavior
was seen in Stokes V asymmetry or amplitude splitting.
Title: The Imaging Vector Magnetograph at Haleakalā -
II. Reconstruction of Stokes Spectra
Authors: LaBonte, Barry J.; Mickey, Donald L.; Leka, K. D.
Bibcode: 1999SoPh..189....1L
Altcode:
The Imaging Vector Magnetograph (`IVM') at Mees Solar Observatory,
Haleakalā, Maui, Hawai`i, is designed to measure the magnetic field
vector over an entire solar active region on the Sun. The first step
in that process is to correct the raw data for all known systematic
effects introduced by the instrument and Earth's atmosphere. We define
a functional model of the atmosphere/instrument system and measure the
corrections for the degradation introduced by each component of the
model. We demonstrate the feasibility of this method and assess the
accuracy of the IVM spectra with a direct comparison of the resulting
Stokes spectra to a well-described spectropolarimeter.
Title: Magnetic evolution of NOAA Active Region 8210.
Authors: Labonte, B.
Bibcode: 1999BAAS...31.1237L
Altcode:
No abstract at ADS
Title: Magnetic Evolution of NOAA Active Region 8210
Authors: Labonte, B.
Bibcode: 1999AAS...194.5509L
Altcode: 1999BAAS...31Q.911L
NOAA Active Region 8210 produced a number of large flares in April -
May 1998. The Imaging Vector Magnetograph at the Mees Solar Observatory,
Haleakala made several day-long movies of this region. Large-scale
helicity in the active region magnetic structure was complicated by
continuing flux emergence. Much of the new flux appeared to emerge from
directly beneath the main sunspot cluster. Rapid, directed flow of the
new flux carried much of it far from the spots, to along locations
close the the sheared neutral line. We will report on quantitative
measures of the magentic properties of AR8210. This work was supported
by NASA grant NAG5-4914.
Title: Acoustic Imaging in Helioseismology
Authors: Chou, Dean-Yi; Chang, Hsiang-Kuang; Sun, Ming-Tsung; LaBonte,
Barry; Chen, Huei-Ru; Yeh, Sheng-Jen; TON Team; Tang, Heng-Tai; Shiu,
Wei-Cheng; Chen, Yi-Liang; Jimenez, Antonio; Rabello-Soares, Maria
Cristina; Ai, Guoxiang; Wang, Gwo-Ping; Goode, Philip; Marquette,
William; Ehgamberdiev, Shuhrat; Khalikov, Shukur
Bibcode: 1999ApJ...514..979C
Altcode:
The time-variant acoustic signal at a point in the solar interior can
be constructed from observations at the surface, based on the knowledge
of how acoustic waves travel in the Sun: the time-distance relation
of the p-modes. The basic principle and properties of this imaging
technique are discussed in detail. The helioseismic data used in
this study were taken with the Taiwan Oscillation Network (TON). The
time series of observed acoustic signals on the solar surface is
treated as a phased array. The time-distance relation provides the
phase information among the phased array elements. The signal at any
location at any time can be reconstructed by summing the observed
signal at array elements in phase and with a proper normalization. The
time series of the constructed acoustic signal contains information on
frequency, phase, and intensity. We use the constructed intensity to
obtain three-dimensional acoustic absorption images. The features in
the absorption images correlate with the magnetic field in the active
region. The vertical extension of absorption features in the active
region is smaller in images constructed with shorter wavelengths. This
indicates that the vertical resolution of the three-dimensional images
depends on the range of modes used in constructing the signal. The
actual depths of the absorption features in the active region may be
smaller than those shown in the three-dimensional images.
Title: Stokes profile reconstruction with the imaging vector
magnetograph
Authors: Leka, K. D.; Mickey, D. L.; Labonte, B. J.
Bibcode: 1999ASSL..243..305L
Altcode: 1999sopo.conf..305L
No abstract at ADS
Title: Probing the Subsurface Structure of Active Regions with the
Phase Information in Acoustic Imaging
Authors: Chen, Huei-Ru; Chou, Dean-Yi; Chang, Hsiang-Kuang; Sun,
Ming-Tsung; Yeh, Sheng-Jen; LaBonte, Barry; TON Team
Bibcode: 1998ApJ...501L.139C
Altcode:
We present the phase information of solar p-mode waves constructed with
an acoustic imaging technique in the solar interior. There exists a
phase shift between the time series constructed with ingoing waves and
outgoing waves. We find that this phase shift is different in an active
region and the quiet Sun. The p-mode travel time is shorter in the
magnetic regions than in the quiet Sun. We construct a three-dimensional
phase shift map of the solar interior. As with the acoustic absorption
images, the phase shift features of the active region in maps at
the surface correlate with magnetic fields. The vertical extension
of phase shift features in the active region is smaller in the phase
maps constructed with shorter wavelengths. This indicates the vertical
spatial resolution of these three-dimensional phase maps is sensitive to
the range of modes used in constructing the signal. The actual depths
of the phase shift features in the active region may be smaller than
those shown in the three-dimensional phase maps.
Title: Optical Proxies for High Energy Emissions from Solar Flares
Authors: Blais, K. A.; Labonte, B. J.
Bibcode: 1998AAS...192.1902B
Altcode: 1998BAAS...30R.845B
A comparison of solar and stellar flare models requires information
on the energy deposition into, and the energy partitioning of, flare
atmospheres. Most of the flare energy is deposited in the high energy
regime that corresponds to soft and hard X-ray emission. Optical
observations of stellar flares, taken in lieu of high energy
observations, suggest the existence of optical proxies for these
emissions. Since stellar flares are observed to occur on dMe stars,
it cannot be assumed that the same proxy relationship between optical
and high energy emissions will occur during solar flares. We present
the results of a study that investigates whether there are optical
proxies for high energy emissions in solar flares. The Ca II K and
H alpha emission of 31 solar flares is compared to the corresponding
soft and hard X-ray emission. We find evidence of both temporal and flux
proxies in solar flare emissions. The fractional Ca II K and hard X-ray
fluxes also portray a relationship analogous to the Neupert effect. An
examination of the energy budgeting demonstrates that the primary
source of heating for these flare atmospheres is non-thermal particles.
Title: Results of Acoustic Imaging with the TON Data
Authors: Chou, D. -Y.; Chang, H. -K.; Chen, H. -R.; LaBonte, B.; Sun,
M. -T.; Yeh, S. -J.; TON Team
Bibcode: 1998ESASP.418..597C
Altcode: 1998soho....6..597C
The acoustic signal in the solar interior can be constructed based
on the knowledge of how acoustic waves travel in the Sun, the
time-distance relation (Chang et al. 1997). We discuss the basic
principle and properties of the acoustic imaging and the update
results with the TON data. The acoustic signal can be reconstructed
with ingoing waves or outgiong waves. The time series of constructed
acoustic signal contains information of both phase and intensity
(Chou et al. 1998). The intensity information can be used to form the
three-dimensional intensity image and absorption image of the solar
interior. The absorption images show the absorption features in the
active region. There exists a phase shift between the time series
constructed with ingoing waves and outgoing waves. The phase shift
is different in the active region and the quiet Sun. We construct
a three-dimensional phase-shift map of the solar interior (Chen et
al. 1998). The phase-shift features of the active region in the maps at
the surface correlate well with magnetic fields. One can even identify
the correlation between the phase-shift feature and weak magnetic field
in the quiet Sun. The phase-shift maps show that travel time is shorter
in the magnetic regions than in the quiet Sun. The three-dimensional
intensity maps and phase maps can be used to study the subsurface
structure of magnetic field. We also present the theoretical foundation
of acoustic imaging.
Title: NOAA 7978: the Last best Old-Cycle Region
Authors: Hudson, H. S.; Labonte, B. J.; Sterling, A. C.; Watanabe, Te.
Bibcode: 1998ASSL..229..237H
Altcode: 1998opaf.conf..237H
No abstract at ADS
Title: Subsurface Acoustic Images of Solar Active Regions in Different
Frequencies with TON Data
Authors: Chang, H. -K.; Chou, D. -Y.; Chen, H. -R.; LaBonte, B.; Sun,
M. -T.; Yeh, S. -J.; TON Team
Bibcode: 1998ESASP.418..621C
Altcode: 1998soho....6..621C
We apply the method of `acoustic imaging' (Chang et al. 1997) to
construct subsurface acoustic images of solar active regions using
p-mode signals in different frequency ranges with TON data. Acoustic
imaging, based on a time-distance relationship, coherently collects
observed acoustic signals at the surface to reconstruct acoustic
signals in the solar interior. Earlier studies (Chang et al. 1997;
Chen et al. 1998; Chou et al. 1998) have shown that this method
successfully reveals acoustic signatures of solar magnetic regions,
both in the sense of intensity and phase shift. We now first separate
observed p-mode signals into frequency ranges centered at 3, 4, 5,
and 6 mHz with a band width of 1 mHz, and use them separately to
construct subsurface acoustic images. We will present results of this
study to discuss the wave-property effect on the depth resolution in
the method of acoustic imaging and to investigate the p-mode frequency
and wavelength dependence of acoustic absorption and phase-shift in
active regions.
Title: Dissipation and Emission of p-Mode in the Quiet Sun from
Acoustic Imaging with TON Data
Authors: Sun, M. -T.; Chou, D. -Y.; Chang, H. -K.; Chen, H. -R.; Yeh,
S. -J.; LaBonte, B.; TON Team
Bibcode: 1998ESASP.418..657S
Altcode: 1998soho....6..657S
The method of acoustic imaging (Chang et al. 1997) is a useful tool
in helioseismology. In the earlier studies (Chou et al. 1998; Chen
et al. 1998; Braun et al. 1998) it has been used to analyze active
regions. This technique is also applicable to the quiet Sun. Here
we present the result using acoustic imaging tecnique to study the
dissipation and emission of p-modes in quiet Sun. In acoustic imaging,
the acoustic signal at a target point and target time is reconstructed
by coherently summing the signals measured in an annular region centered
at the target point based on the time-distance relation. The signal can
be constructed with the inbound time-distance or outbound time-distance
curve. The difference between the signals constructed with inbound and
outbound time-distance relations provide information of dissipation
and emission of p-modes. The acoustic signal can be reconstructed
with multiple bounces time-distance curve. The variation of signals
constructed with the time-distance curve of successive bounces also
provide information of dissipation and emission of p-modes. We use
the helioseismic data observed with the Taiwan Oscillation Network
(TON). We select very quiet regions to minimize the intereferece of
active regions. The data is filtered through narrow band-pass filter
centered at 3, 4, 5, and 6 mHz to study the frequency dependency of
dissipation and emission of solar p-mode.
Title: Ambient acoustic imaging in helioseismology
Authors: Chang, Hsiang-Kuang; Chou, Dean-Yi; Labonte, Barry; TON Team
Bibcode: 1997Natur.389..825C
Altcode:
The increasing availability of high spatial resolution data of velocity
and intensity variations on the Sun has stimulated the development of
helioseismological techniques that probe the solar interior in localized
regions. The techniques developed so far have yielded information on
physical quantities (such as the flow velocity and magnetic field)
below the surface, but are still far from providing a detailed picture
of local subsurface inhomogeneities. Here we report the development and
application of a new method for constructing three-dimensional solar
images, utilizing acoustic noise (or stochastic P-mode oscillations)
in the Sun. We treat a region of the solar surface as a phased array of
acoustic sensors, which acts as a computational `lens' acoustic waves
`scattered' by local inhomogeneities, such as sunspots, are collected
and summed in phase, based on the knowledge of how (on average)
they travel within the Sun. In this way, we are able to construct a
three-dimensional image of a region of the solar interior.
Title: Image Reconstruction for Stokes Polarimetry
Authors: Mickey, D. L.; Labonte, B. J.
Bibcode: 1997SPD....28.0221M
Altcode: 1997BAAS...29R.896M
Trying to determine solar vector magnetic fields from Zeeman-effect
observations is a process made difficult by the realities of
observational science at every step. The source of the largest errors in
ground-based imaging spectropolarimetry is that the measurements span
four dimensions, only two of which can be observed simultaneously. In
the Imaging Vector Magnetograph at Haleakala, Hawaii, the polarization
and spectral dimensions are obtained from a temporal sequence of
images. Frame-to-frame distortion by atmospheric seeing causes spurious
polarization and spectral signatures. We describe here a method of
compensating, frame by frame, for not only rigid image translation
but also differential image motion and blur in small areas of the
image. The method relies on a second camera which records a broad-band
image simultaneously with the main camera. The auxiliary "geometry"
image is used to obtain a parametric model of the instantaneous seeing,
which can then be used to correct the main image. The technique results
in a factor of at least ten reduction in spurious polarization signal
at spot boundaries, as well as an overall improvement in image fidelity.
Title: X-ray photon spectroscopy with the YOHKOH Soft X-ray telescope
Authors: Labonte, B.; Reardon, K.
Bibcode: 1997SPD....28.0140L
Altcode: 1997BAAS...29..886L
Individual X-ray photons in the keV energy range produce hundreds of
photoelectrons in a single pixel of a CCD array detector. The number
of photoelectrons produced is a linear function of the photon energy,
allowing the measurement of spectral information with an imaging
detector system. The Yohkoh Soft X-ray Telescope uses a CCD in an
integrating mode and makes temperature estimates from multiband filter
photometry. We show how the SXT can be used in a new way to perform
a limited type of photon spectroscopy. By measuring the variance in
intensity through a single filter of an x-ray source on repeated SXT
images, the mean energy per detected photon can be determined. This
value is related to the underlying coronal spectrum, and hence can
be used to deduce the plasma temperature. We compare the results
of the temperatures derived using this new technique on a series of
SXT images of a post-flare loop system with the temperatures derived
using the standard flux-ratio method. We demonstrate that the bright
postflare loops really are cooler than the surrounding material, as
shown by Tsuneta et al. (1992). Given the large dynamic range of the
soft x-ray flux observed from the Sun, we describe the requirements for
a future instrument that would take advantage of photon spectroscopy.
Title: Erratum: "The imaging vector magnetograph at Haleakala"
[Sol. Phys., Vol. 168, No. 2, p. 229 - 250 (Oct 1996)].
Authors: Mickey, D. L.; Canfield, R. C.; Labonte, B. J.; Leka, K. D.;
Waterson, M. F.; Weber, H. M.
Bibcode: 1997SoPh..170..455M
Altcode:
No abstract at ADS
Title: High resolution coronal imaging. 11 July, 1991 total eclipse
with University of Hawaii 2.24 meter telescope on Mauna Kea.
Authors: Labonte, B.; Livingston, W.; Zirker, J.
Bibcode: 1997ASIC..494...35L
Altcode: 1997topr.conf...35L
The authors observed the corona with the potential for unprecedented
spatial resolution afforded by a large stellar instrument at a prime
site. An ambitious experiment involving the recording of 5 narrow-band
1024×1024 CCD images failed because of a last minute software
change. Eclipses are unforgiving in this regard. However, a simple
video camera was also fed by a beam-splitter pickoff with excellent
results. This video tape, shown at the workshop, indicates how the
field of interest was selected, concentrating on a large prominence
at the NW limb. The role of seeing is evident; the smallest features
detected were 0.6 arcsec in size.
Title: STEREO: a solar terrestrial event observer mission concept
Authors: Socker, Dennis G.; Antiochos, S. K.; Brueckner, Guenter E.;
Cook, John W.; Dere, Kenneth P.; Howard, Russell A.; Karpen, J. T.;
Klimchuk, J. A.; Korendyke, Clarence M.; Michels, Donald J.; Moses,
J. Daniel; Prinz, Dianne K.; Sheely, N. R.; Wu, Shi T.; Buffington,
Andrew; Jackson, Bernard V.; Labonte, Barry; Lamy, Philippe L.;
Rosenbauer, H.; Schwenn, Rainer; Burlaga, L.; Davila, Joseph M.; Davis,
John M.; Goldstein, Barry; Harris, H.; Liewer, Paulett C.; Neugebauer,
Marcia; Hildner, E.; Pizzo, Victor J.; Moulton, Norman E.; Linker,
J. A.; Mikic, Z.
Bibcode: 1996SPIE.2804...50S
Altcode:
A STEREO mission concept requiring only a single new spacecraft has been
proposed. The mission would place the new spacecraft in a heliocentric
orbit and well off the Sun- Earth line, where it can simultaneously view
both the solar source of heliospheric disturbances and their propagation
through the heliosphere all the way to the earth. Joint observations,
utilizing the new spacecraft and existing solar spacecraft in earth
orbit or L1 orbit would provide a stereographic data set. The new
and unique aspect of this mission lies in the vantage point of the
new spacecraft, which is far enough from Sun-Earth line to allow an
entirely new way of studying the structure of the solar corona, the
heliosphere and solar-terrestrial interactions. The mission science
objectives have been selected to take maximum advantage of this new
vantage point. They fall into two classes: those possible with the
new spacecraft alone and those possible with joint measurements using
the new and existing spacecraft. The instrument complement on the new
spacecraft supporting the mission science objectives includes a soft
x-ray imager, a coronagraph and a sun-earth imager. Telemetry rate
appears to be the main performance determinant. The spacecraft could
be launched with the new Med-Lite system.
Title: The Imaging Vector Magnetograph at Haleakala
Authors: Mickey, D. L.; Canfield, R. C.; LaBonte, B. J.; Leka, K. D.;
Waterson, M. F.; Weber, H. M.
Bibcode: 1996SoPh..168..229M
Altcode:
We describe an instrument we have built and installed at Mees Solar
Observatory on Haleakala, Maui, to measure polarization in narrow-band
solar images. Observations in Zeemansensitive photospheric lines have
been made for nearly all solar active regions since the instrument
began operations in 1992. The magnetograph includes a 28-cm aperture
telescope, a polarization modulator, a tunable Fabry-Pérot filter,
CCD cameras and control electronics. Stokes spectra of a photospheric
line are obtained with 7 pm spectral resolution, 1 arc sec spatial
resolution over a field 4.7 arc min square, and polarimetric precision
of 0.1%. A complete vector magnetogram observation can be made every
eight minutes. The flexibility of the instrument encourages diverse
observations: besides active region magnetograms we have made, for
example, composite vector magnetograms of the full solar disk, and
Hα polarization movies of flaring regions.
Title: The Prospects for Asteroseismology from Ground-based Sites
Authors: Heasley, J. N.; Janes, Kenneth; Labonte, Barry; Guenther,
David; Mickey, Donald; Demarque, Pierre
Bibcode: 1996PASP..108..385H
Altcode:
We reexamine the possibility of detecting p-mode oscillations in
Sun-like stars with ground-based telescopes. Previous attempts to
make such observations with photometric techniques have been limited
to subgiant stars in M67 and have illustrated the great difficulties
involved in performing ground-based asteroseismology. Substantial gains
in observing efficiency can be realized from new diagnostic techniques
and improvements in instrumentation, especially with newer CCD camera
systems. We show that for appropriately selected field stars observed
with a network of telescopes or at a high duty cycle site, it will be
possible to detect p-mode oscillations from the ground. An alternative
to a network of telescopes for asteroseismology would be to develop a
dedicated observatory for this purpose at a high duty cycle site, i.e.,
the South Pole. We estimate the scintillation, the main noise source
in asteroseismology, at the pole by modeling the index of refraction
structure parameter from meterological data. The model results show that
at the Pole the variance of the relative intensity fluctuations--i.e.,
the scintillation--should be a factor of 5 smaller than at at Mauna
Kea. Taking into account the improvements possible with target selection
and instrumentation, the South Pole would be an excellent site for
asteroseismological work on Sun-like stars. (SECTION: Stars)
Title: A search for optical proxies for high energy emissions from
solar flares
Authors: Blais, K. A.; Labonte, B. J.
Bibcode: 1996ASPC..109..109B
Altcode: 1996csss....9..109B
No abstract at ADS
Title: A Search for Optical Proxies for High Energy Emissions from
Solar Flares
Authors: Blais, K. A.; Labonte, B. J.
Bibcode: 1995AAS...18710109B
Altcode: 1995BAAS...27.1427B
Recent studies indicate that stellar flares produce Ca II K line
emission that is photometrically similar to the soft X-ray emission
which dominates the gradual phase of Solar flares. This result
suggests that Ca II K may be an optical proxy for soft X-ray emission
in flares. Solar flares provide a better chance of conclusively
testing this hypothesis than stellar flares due to the relative ease
of acquiring numerous and simultaneous observations of the sun in the
optical and high energy regimes. Despite the many Solar atmospheric
and helioseismology studies using Ca II K, this hypothesis has not
been thoroughly investigated for Solar flares because previous Ca II K
flare studies were unrelated to the question of proxies, or limited in
observed number, or had inadequate temporal resolution. We present the
results of a study designed to search for optical proxies by comparing
the flux calibrated Ca II K, Hα, and soft and hard X-ray emissions
of 30 Solar flares.
Title: Alaska as a Site for High Duty-Cycle Solar Observations
Authors: LaBonte, Barry J.; Kupke, Renate; Ronan, Robert
Bibcode: 1995SoPh..158....1L
Altcode:
The day/night cycle at a single observatory prevents definitive
observations of many aspects of solar activity, convection, and
oscillations with timescales near 1 day. Solutions to this problem
include multi-site networks, spacecraft observatories, and observations
from high-latitude sites during their summer season. We report here on
our experience in using Alaska as a high-latitude site for observations
of solar oscillations.
Title: Recent Progress of the Avalanche Model of Solar Flares
Authors: Labonte, Barry; Lu, Edward
Bibcode: 1995SPD....26.1316L
Altcode: 1995BAAS...27..990L
No abstract at ADS
Title: Near-Infrared Emission-Line and Continuum Observations from
the 1991 Eclipse
Authors: Penn, M. J.; Arnaud, J.; Mickey, D. L.; Labonte, B. J.
Bibcode: 1994ApJ...436..368P
Altcode:
We report observations made during the 1991 July 11 total solar eclipse
from the University of Hawaii 61 cm south telescope on the summit of
Mauna Kea, Hawaii. The eclipse observations entail CCD imaging of a
coronal region on the southeast limb of the Sun using four wavelength
channels isolated with narrowband interference filters. We obtain two
long exposure images in each channel including the continuum (lambda
= 10690 A), the two near-infrared (Fe XIII) emission lines (lambda =
10747, 10798 A), and the He I line (lambda = 10830 A). We calibrate the
images to the center-of-disk solar intensity. The (Fe XIII) images are
the first coronal images published from these emission lines. We find
significant structural differences between the line and continuum images
implying large temperature gradients in our small field of view. We
compute the line ratio of the two (Fe XIII) emission lines (R) and find
that the ratio is within the limits 1.2 greater than or = R greater
than or = 15.0. We examine the motion seen in the prominence structure
and find transverse velocities of up to about 30 km/s. Finally we see
no cold coronal emission to a limit of 2 x 10-7 solar BETA.
Title: Coronal electron density measurements using the near-ir
[Fe XIII] emission lines
Authors: Penn, M. J.; Kuhn, J. R.; Arnaud, J.; Mickey, D. L.; Labonte,
B. J.
Bibcode: 1994SSRv...70..185P
Altcode:
Observations made during the 1991 total solar eclipse and recent
observations from NSO/Sac Peak are discussed. The ground-based density
measurements will be complimentary to SOHO observations, particularly
SOHO electron density measurements.
Title: The Global Oscillation Network Group Site Survey - Part Two
Authors: Hill, Frank; Fischer, George; Forgach, Suzanne; Grier,
Jennifer; Leibacher, John W.; Jones, Harrison P.; Jones, Patricia
B.; Kupke, Renate; Stebbins, Robin T.; Clay, Donald W.; Ingram,
Robert E. L.; Libbrecht, Kenneth G.; Zirin, Harold; Ulrichi, Roger
K.; Websteri, Lawrence; Hieda, Lester S.; Labonte, Barry J.; Lu,
Wayne M. T.; Sousa, Edwin M.; Garcia, Charles J.; Yasukawa, Eric
A.; Kennewell, John A.; Cole, David G.; Zhen, Huang; Su-Min, Xiao;
Bhatnagar, Arvind; Ambastha, Aashok; Al-Khashlan, Abdulrahman Sa'ad;
Abdul-Samad, Muhammad-Saleh; Benkhaldoun, Zouhair; Kadiri, Samir;
Sánchez, Francisco; Pallé, Pere L.; Duhalde, Oscar; Solis, Hernan;
Saá, Oscar; González, Ricardo
Bibcode: 1994SoPh..152..351H
Altcode:
The Global Oscillation Network Group (GONG) Project will place a
network of instruments around the world to observe solar oscillations as
continuously as possible for three years. The Project has now chosen the
six network sites based on analysis of survey data from fifteen sites
around the world. The chosen sites are: Big Bear Solar Observatory,
California; Mauna Loa Solar Observatory, Hawaii; Learmonth Solar
Observatory, Australia; Udaipur Solar Observatory, India; Observatorio
del Teide, Tenerife; and Cerro Tololo Interamerican Observatory, Chile.
Title: Solar Cycle Changes in the High Frequency Spectrum
Authors: Ronan, R. S.; Cadora, K.; Labonte, B. J.
Bibcode: 1994SoPh..150..389R
Altcode:
We present observations of high frequency, intermediate degree, Ca-K
line solar intensity oscillations. We compare the peak frequencies
determined from these 1991.4 observations with the peak frequencies
from 1987.9 South Pole observations (Duvallet al., 1991) in that portion
of the spatio-temporal diagram where the two datasets overlap (degrees
between 30 and 150 and frequencies between 4 and 6.6 mHz). We find that
temporal changes are detectable in the high frequency spectrum and are
particularly large near 5.4 mHz. The m-averaged high frequency peaks
decreased in frequency in 1991.4 compared to the peak frequencies
measured in 1987.9. The magnitude of the frequency shift is of the
order of 10 μHz near 5.4 mHz, increases with degree, and decreases
to near zero both above and below 5.4 mHz. It is unlikely that these
temporal changes in the high frequency spectrum are due to a change
in the height of the subphotospheric acoustic source layer. A physical
mechanism for these frequency shifts has not yet been identified.
Title: Intermediate Degree P-Mode Frequency Splittings Near Solar
Maximum
Authors: Ronan, R. S.; Labonte, B. J.
Bibcode: 1994SoPh..149....1R
Altcode:
We report on observations of global solar Ca K-line intensity
oscillations taken in May 1991 from Mees Solar Observatory, Hawaii. We
measurep-mode frequency splittings for modes of spherical harmonic
degrees between 20 and 129 averaged over the radial order of the
modes. Our measurement of the antisymmetric component of the splittings
is comparable with previous measurements and thus indicates a decrease
in the latitudinal differential rotation with depth into the convection
zone and the upper radiative zone. We find evidence for a 1% variation
in the rotation rate of the upper convection zone roughly in phase with
the solar activity cycle. Our measurement of the symmetric component of
the splittings is of the same order as was reported from the previous
solar maximum and is an order of magnitude larger than has been measured
near solar minimum. From the degree dependence of the symmetric
component of the splittings, we find evidence for an aspherical
fractional sound speed perturbation located at a depth of 0.85 ±
0.05 solar radii. This perturbation has a magnitude ofδc/c ≈ +9 ×
10−4 at the equator relative to the poles. Additionally,
there is evidence for a near-surface aspherical sound speed perturbation
of smaller magnitudeδc/c ≈ +4 × 10−4 at the equator
relative to the poles. If an intense global magnetic field were the
dominant source of the observed symmetric component of the splittings,
instead of latitudinal gradients in the sound speed, then global fields
of order 105 G would be required in the convection zone.
Title: A Possible Mechanism for Enhanced Absorption of p-Modes in
Sunspot and Plage Regions
Authors: Labonte, Barry J.; Ryutova, Margarita
Bibcode: 1993ApJ...419..388L
Altcode:
Magnetic regions on the Sun's surface are observed to absorb large
fractions of the p-mode (acoustic) wave power incident upon them. We
propose a mechanism to explain the absorption, based on the idea that
sunspots are assembled from many individual flux tubes with highly
variant physical conditions. Strong gradients in the (perturbed)
parameters of a wave propagating through such an inhomogeneous medium
result in enhanced absorption of the wave power. The gradients in the
wave parameters occur on the scale of the background flux tubes which
is smaller than the wavelength.
Title: Direct Mapping of Solar Acoustic Power
Authors: Toner, C. G.; Labonte, B. J.
Bibcode: 1993ApJ...415..847T
Altcode:
We investigate the spatial distribution of acoustic power on the Sun
as a function of both horizontal wavenumber, k, and temporal frequency,
ν. Using time series of full-disk Ca II K line observations, obtained
at the University of Hawaii's Mees Solar Observatory, we generated a set
of six synoptic maps which represent the total acoustic power integrated
over the three different frequency ranges; (a) 195.3 μHz ≤ ν ≤
1790.4 μHz, (b) 1790.4 μHz ≤ ν ≤ 5501.3 μHz, and (c) 5501.3 μHz
≤ ν ≤ 8333.3 μHz, for values of k ≲ 0.25 Mm-1 and k
≳ 0.25 Mm-1. At high temporal frequencies we find "halos"
of enhanced acoustic power surrounding active regions. The amount of
enhancement is ∼10%±5% relative to the quiet photosphere. Both the
high- and low-k maps exhibit the phenomenon. Our rather poor resolution
in k does not allow a complete study of the spatial dependence of the
halos, but there is some indication that their morphology may depend
weakly on k. The halos extend several tens of Mm beyond the boundary
of the plage as seen in the K line. These appear to be true solar
features, and not an artifact of variable seeing. We also looked for
evidence of subphotospheric magnetic structures, such as the "fingers"
reported by Braun et al. We find one very faint, diffuse feature
apparently connecting an active region in the southern hemisphere with
one in the north. We hesitate to say that this is a true signature
of a subphotospheric structure because of its very low signal level
relative to the background. The high-k, p-mode map was examined for any
evidence for an acoustic power deficit at the antipodal points of active
regions. We estimate that any power deficit at active region antipodal
points must be no more than ∼1%, and we therefore conclude that no
strong deficit exists at the antipodes of sunspots. At low frequencies,
both the high- and low-k maps show enhanced power at the locations of
the active regions. This represents active region evolution.
Title: The Source of 5 Minute Period Photospheric Umbral Oscillations
Authors: Penn, M. J.; Labonte, B. J.
Bibcode: 1993ApJ...415..383P
Altcode:
We observed the oscillations in the umbrae of two sunspots, using the
MCCD imaging spectrograph at the Mees Solar Observatory on Haleakala,
Maui. We perform four spatial analyses of the umbral velocity and find
that (1) there is more power traveling toward the center of the umbrae
than leaving the center of the umbrae (this provides a direct measure
of the absorption of p-modes by the sunspot umbrae); (2) the umbral
oscillations display power in the same spatial and temporal frequency
band as the quiet-sun oscillations; (3) Fourier-Bessel analysis of
one umbra shows no obvious resonant frequencies which might represent
natural oscillation modes; and (4) the centers of the umbrae have
less rms velocity at high spatial wavenumber than the edges of the
umbrae. We conclude: (1) the photospheric umbral oscillations are driven
by a source external to the sunspot, the global p-mode oscillations;
(2) there are no resonant frequencies in the oscillations; and (3)
the absorption of acoustic waves occurs inside the umbrae.
Title: Steps toward understanding the solar dynamo
Authors: Labonte, Barry
Bibcode: 1993huha.rept.....L
Altcode:
Progress has been made toward solving the problem of the solar
dynamo. The flux tube dynamo has been defined as a promising model for
future investigation. Surface solar magnetic fields have been observed
to determine whether electric currents carried by the fields can yield
information about the dynamo region. Observational tools have been
developed to probe the internal solar magnetic fields.
Title: Solar Cycle Variations in the Intermediate Degree, High
Frequency Spectrum
Authors: Ronan, R. S.; Cadora, K.; Labonte, B. J.
Bibcode: 1993BAAS...25.1194R
Altcode:
No abstract at ADS
Title: Coronal Electron Density Measurements from the Total Solar
Eclipse of 11 July 1991
Authors: Penn, M. J.; Arnaud, J.; Mickey, D. L.; Labonte, B. J.
Bibcode: 1993BAAS...25.1210P
Altcode:
No abstract at ADS
Title: Enhanced absorption of p-modes in sunspot and plage regions.
Authors: Labonte, Barry J.; Ryutova, Margarita
Bibcode: 1993ppcn.conf..275L
Altcode:
Magnetic regions on the Sun's surface are observed to absorb large
fractions of the p-mode (acoustic) wave power incident upon them. The
authors propose a mechanism to explain the absorption, based on the
idea that sunspots are assembled from many individual flux tubes with
highly variant physical conditions. Strong gradients in the (perturbed)
parameters of a wave propagating through such an inhomogeneous medium
results in enhanced absorption of the wave power. The gradients in
the wave parameters occur on the scale of the background flux tubes
which is smaller than the wavelength.
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.
Bibcode: 1993ASPC...42...77B
Altcode: 1993gong.conf...77B
No abstract at ADS
Title: Observations of High Frequency Solar Oscillations
Authors: Ronan, R. S.; Labonte, B. J.
Bibcode: 1993ASPC...42...93R
Altcode: 1993gong.conf...93R
No abstract at ADS
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.
Bibcode: 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: Properties of 5 Minute Period Oscillations in Sunspot Umbrae
Authors: Penn, M. J.; Labonte, B. J.
Bibcode: 1992AAS...180.0603P
Altcode: 1992BAAS...24..736P
No abstract at ADS
Title: The Haleakala Imaging Vector Magnetograph
Authors: Mickey, D. L.; Canfield, R. C.; Labonte, B. J.; Metcalf, T. R.
Bibcode: 1992AAS...180.4005M
Altcode: 1992BAAS...24..793M
The Imaging Vector Magnetograph, now in daily use at Mees Solar
Observatory, Haleakala, Hawaii, extends our capabilities in the
measurement of solar vector magnetic fields by providing high
spatial and temporal resolution, together with extended area
coverage. The instrument is based on a fast-readout CCD camera as
its primary detector, a tunable air-spaced Fabry-Perot filter for
spectral selection, and variable nematic liquid-crystal retarders
for polarization selection. A 28 cm aperture reflecting telescope
provides an image the size of a large active region; it is coupled
to the magnetograph in a configuration compact enough to mount on
the Observatory's 3.6 m equatorial spar. The assembly can be pointed
independently of the spar to select a region of interest, so the
telescope is always used on-axis. A tip-tilt image stabilizer corrects
for image displacement due to spar shake or large-scale atmospheric
turbulence. A workstation-based computer control system, incorporating
separate processors for user interface, process management and device
control, permits accurate process timing along with a flexible user
interface. The latter is implemented in an X-windows framework, so that
in fact we have found it quite reasonable to operate the instrument
from an X terminal at a remote location. The raw data images are
stored on 8mm tape for off-line processing, or can be reduced in a
few minutes using the instrument's built-in array processor to provide
near-real-time magnetograms. Instrument operational parameters can be
adjusted in several ways to favor spatial resolution, spatial field,
temporal resolution or magnetic sensitivity, but typically we have
a 4.5 x 4.5 arcminute field, 1 arcsecond spatial sampling, and an
observation interval of five minutes. Initial solar observations
showing current capabilities will be presented.
Title: Intermediate Degree p Mode Frequency Splittings Near Solar
Maximum
Authors: Ronan, R. S.; Labonte, B. J.
Bibcode: 1992AAS...180.1701R
Altcode: 1992BAAS...24..753R
No abstract at ADS
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.
Bibcode: 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.
Title: Surface Mapping of Slowly Rotating, Cool Stars Using Line
Bisector Variations
Authors: Toner, Clifford G.; Labonte, Barry J.
Bibcode: 1992LNP...397..192T
Altcode: 1992sils.conf..192T
No abstract at ADS
Title: The Solar Spatio-Temporal Spectrum at High Frequency
Authors: Ronan, R. S.; Labonte, B. J.; Kupke, R.
Bibcode: 1991BAAS...23.1442R
Altcode:
No abstract at ADS
Title: The Mees CCD imaging spectrograph
Authors: Penn, Matthew J.; Mickey, Donald L.; Canfield, Richard C.;
Labonte, Barry J.
Bibcode: 1991SoPh..135..163P
Altcode:
The Mees CCD (MCCD) instrument is an imaging spectroscopy device which
uses the 25 cm coronagraph telescope and the 3.0 m Coudé spectrograph
at Mees Solar Observatory (MSO) on Haleakala, Maui. The instrument works
with resolving power up to R ≈ 200 000 with significant throughput
from λ3934 Å (CaII K) to λ ≈ 10 000 Å. A fast guiding active
mirror stabilizes the image during observations. A rapidly writing
magnetic tape storage system allows observations to be recorded
at 256 kbytes s−1. Currently, the MCCD is used for
imaging spectroscopy of solar flares at λ6563 Å (Hα), and velocity
measurements of umbral oscillations; future plans include emission
line studies of active region coronae, and photospheric studies of
solar oscillations.
Title: Power Spectra of Solar Convection
Authors: Chou, D. -Y.; Labonte, B. J.; Braun, D. C.; Duvall, T. L., Jr.
Bibcode: 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: Analysis of p-modes in a Sunspot Umbra
Authors: Penn, M.; Labonte, B.
Bibcode: 1991BAAS...23.1049P
Altcode:
No abstract at ADS
Title: Can the Starpatch on XI Bootis A Be Explained by Using
Tangential Flows?
Authors: Toner, Clifford G.; Labonte, Barry J.
Bibcode: 1991ApJ...368..633T
Altcode:
It is demonstrated that a modification of the starpatch model of
Toner and Gray (1988), using tangential flows instead of an enhanced
granulation velocity dispersion within the patch, is very successful at
reproducing both the observed line asymmetry and the line broadening
variations observed in the G8 dwarf Xi Boo A. Areal coverage of
10 percent + or - 3 percent of the visible disk, latitude 30 deg +
or - 4 deg, mean brightness 0.85 + or - 0.05 relative to the 'quiet'
photosphere, mean tangential flow velocities of 8.0 + or - 1.5 km/s,
and dispersions about the mean of 8/0 + or - 2.0 km/s are inferred
for the patch. A feature at a latitude of about 30 deg is inferred
which covers about 10 percent of the visible disk and is 10-20 percent
fainter than the rest of the photosphere. It is inferred that 70-80
percent of the patch is penumbra.
Title: The Spatial Distribution of p-Mode Absorption in Active Regions
Authors: Braun, D. C.; Labonte, B. J.; Duvall, T. L., Jr.
Bibcode: 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.
Title: Xi-Bootis - Starpatch or Moat Flow
Authors: Toner, C. G.; Labonte, B. J.
Bibcode: 1990ASPC....9..161T
Altcode: 1990csss....6..161T
No abstract at ADS
Title: An imaging vector magnetograph for the next solar maximum
Authors: Mickey, D. L.; Labonte, B. J.; Canfield, R. C.
Bibcode: 1989dots.work..324M
Altcode:
Researchers describe the conceptual design of a new imaging vector
magnetograph currently being constructed at the University of
Hawaii. The instrument combines a modest solar telescope with a
rotating quarter-wave plate, an acousto-optical tunable prefilter
as a blocker for a servo-controlled Fabry-Perot etalon, CCD cameras,
and on-line digital image processing. Its high spatial resolution (1/2
arcsec pixel size) over a large field of view (5 by 5 arcmin) will be
sufficient to significantly measure, for the first time, the magnetic
energy dissipated in major solar flares. Its millisecond tunability
and wide spectral range (5000 to 7000 A) enable nearly simultaneous
vector magnetic field measurements in the gas-pressure-dominated
photosphere and magnetically-dominated chromosphere, as well as
effective co-alignment with Solar-A's X ray images. Researchers
expect to have the instrument in operation at Mees Solar Observatory
(Haleakala) in early 1991. They have chosen to use tunable filters
as wavelength-selection elements in order to emphasize the spatial
relationships between magnetic field elements, and to permit
construction of a compact, efficient instrument. This means that
spectral information must be obtained from sequences of images, which
can cause line profile distortions due to effects of atmospheric seeing.
Title: The GONG site survey.
Authors: Hill, F.; Ambastha, A.; Ball, W.; Duhalde, O.; Farris,
D.; Fischer, G.; Hieda, L.; Zhen, Huang; Ingram, B.; Jackson, P.;
Jones, H.; Jones, W.; Kennewell, J.; Kunkel, W.; Kupke, R.; Labonte,
B.; Leibacher, J.; Libbrecht, K.; Lu, W.; Morrison, L.; Odell, C.;
Pallé, P.; Saá, O.; Sousa, E.; Stebbins, T.; Xiao, Suming; GONG
Site Survey Team
Bibcode: 1988ESASP.286..209H
Altcode:
The Global Oscillation Network Group (GONG) project is planning to
place six observing stations around the world to observe the solar
oscillations as continuously as possible. This paper describes the
procedures that are being used to select the six sites. The latest
results of measurements of cloud cover obtained by networks of 6
(out of 10) radiometers show a duty cycle of over 93%, with the first
diurnal sidelobe in the window power spectrum suppressed by a factor
of 400. The results are in good agreement with the predictions of a
computer model of the expected cloud cover at individual sites.
Title: The Absorption of High-Degree p-Mode Oscillations in and
around Sunspots
Authors: Braun, D. C.; Duvall, T. L., Jr.; Labonte, B. J.
Bibcode: 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: The 3rd Joint Solar Dynamics Project data summary: Solar
magnetic field, chromospheric and coronal observations near the time
of the 18 March 1988 solar eclipse
Authors: Sime, D. G.; Garcia, C. J.; Lundin, W. E.; Yasukawa, E. A.;
Mickey, D. L.; Labonte, B.
Bibcode: 1988jsdp.rept.....S
Altcode:
The general goal of the HAO/University of Hawaii Joint Solar Dynamics
Project is to establish the relationships that exist between the solar
magnetic field which is detected in the photosphere and the structure
and evolution of the corona. The SOLDYN programs of 1982 and 1983
demonstrated the ability to use existing instruments to gather data
of value in the pursuit of that goal. The goals for the observations
in 1988 are as follows: (1) Document the state of the sun, from the
photosphere up through the chromosphere and out into the corona for the
approximately four-week interval around the total solar eclipse of 18
March 1988, and (2) Identify the relationship between the photospheric
magnetic fields and the temperature and density structure of the
corona. The reduced observations made during this SOLDYN 3 period
necessary to achieve these goals are provided. The observations are
presented both in the form of daily photographic and photo-electric
measurements, and in synoptic format for the period.
Title: Mass and Energy Flow Near Sunspots - Part Two
Authors: Nye, Alan; Bruning, David; Labonte, Barry J.
Bibcode: 1988SoPh..115..251N
Altcode:
Sunspots block the flow of energy to the solar surface. The blocked
energy heats the volume beneath the spot, producing a pressure excess
which drives an outflow of mass. Linear numerical models of the mass and
energy flow around spots were constructed to estimate the predictions
of this physical picture against the observed properties of sunspot
bright rings and moat flows. The width of the bright ring and moat
are predicted to be proportional to the depth of the spot penumbra,
in conflict with the observed proportionally of the moat width to the
spot diameter. Postulating that spot depths are proportional to spot
diameters would bury the moat flow too deeply to be observed, because
the radial velocity at the surface is found to be inversely proportional
to the depth of the spot penumbra. The radial velocity at the surface is
of order a few hundred meters per second after 1 day, in agreement with
the observed excess of moat velocities over supergranule velocities.
Title: Direct Imager for Nonradial Global-Oscillations
Authors: Labonte, B.
Bibcode: 1988BAAS...20..701L
Altcode:
No abstract at ADS
Title: Mass and Energy Flow Near Sunspots - Part One
Authors: Brickhouse, Nancy S.; Labonte, Barry J.
Bibcode: 1988SoPh..115...43B
Altcode:
New measurements of the velocities of moving magnetic features (MMFs)
are made from spectroheliograms and filtergrams. The sample includes 200
MMFs found in the moats surrounding 7 different sunspots. Our data are
compiled with the data from other authors to uncover common properties
of moats. The moat radius is roughly twice the penumbral radius. No
significant correlation between the average moat velocity or angular
extent and any noted property of the spot or moat (size, age, stage of
development) is found. Individual MMFs move radially outward with a
constant speed, but nearby MMFs may have quite different speeds. The
average moat speed is twice the supergranule flow speed. The speed
of MMFs in moats is equal on average to the surface gas flow speed. A
large bias is found in much of the existing observations of moat speeds
from MMFs.
Title: The Structure of the White Light Corona at the Time of the
1988 March 18 Total Solar Eclipse
Authors: Sime, D. G.; Fisher, R. R.; Labonte, B. J.
Bibcode: 1988BAAS...20..703S
Altcode:
No abstract at ADS
Title: Moat Flows Using Magnetic Tracers
Authors: Penn, M. J.; Labonte, B. J.
Bibcode: 1988BAAS...20..680P
Altcode:
No abstract at ADS
Title: Tomography of Solar Active Regions
Authors: Braun, D. C.; Labonte, B. J.; Duvall, T. L., Jr.
Bibcode: 1988BAAS...20..701B
Altcode:
No abstract at ADS
Title: Ground-Based Photometric Measurements
Authors: Labonte, B.
Bibcode: 1988srov.proc..156L
Altcode:
No abstract at ADS
Title: Ground-based photometric measurements
Authors: Labonte, Barry J.
Bibcode: 1987STIA...8832826L
Altcode:
Resolution in space, time, magnetic field strength, intensity variance,
and wavelength all are used to isolate the signals from sunspots,
plage, network, and nonmagnetic areas. Ground data has demonstrated the
dominance of sunspots in causing irradiance variance on time scales
of hours to months, the near balance of spot deficit and facular
excess emission, and the low level of irradiance variation caused by
nonmagnetic regions. Present techniques limit the accuracy of comparison
with direct irradiance measures, and improvements should be made. Goals
for ground-based photometry for the next cycle are suggested.
Title: Acoustic Absorption by Sunspots
Authors: Braun, D. C.; Duvall, T. L., Jr.; Labonte, B. J.
Bibcode: 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: Flare-Induced Magnetic Field Changes in the Chromosphere
Authors: Labonte, Barry J.
Bibcode: 1987BAAS...19..921L
Altcode:
No abstract at ADS
Title: The Absorption of 5-Minute Oscillations by Sunspots
Authors: Braun, D. C.; Labonte, B. J.; Duvall, T. L., Jr.
Bibcode: 1987BAAS...19..936B
Altcode:
No abstract at ADS
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.
Bibcode: 1987BAAS...19R.934D
Altcode:
No abstract at ADS
Title: Flare-induced magnetic field changes in the chromosphere
Authors: LaBonte, Barry J.
Bibcode: 1987SoPh..113..285L
Altcode: 1982SoPh..113..285L
It is well known that flares cause changes in the azimuthal direction
of chromospheric magnetic field lines (e.g. Zirin, 1983). It is less
well known that flares also cause changes in the inclination angle
of chromospheric magnetic field lines (Bruzek, 1975). Inclination
angle changes are notable in that horizontal field lines take the
form of fibrils, while vertical field lines take the form of plages
(Marsh, 1976). This study examines a complete sample of large flares
to determine when the field inclination changes during the flare. The
Hard X-ray Burst Spectrometer Event Listing (Dennis et. al, 1985) was
searched for events with total counts > 105 and start
times > 14 UT but <24 UT. Big Bear Solar Observatory Hα films
were examined to identify which X-ray events show large horizontal
ribbon motion over regions of fibrils. Of the 7 events found, 6 contain
areas of the chromosphere that have the magnetic field direction turned
from horizontal to vertical. The change in field direction at a given
location occurs after the arrival of the ribbon, often 103
to 104 s after the flare start. No change in the chromosphere
is seen before the ribbon arrival.
Title: Spectra of Plages on the Sun and Stars. I. CA II H and K Lines
Authors: Labonte, B. J.
Bibcode: 1986ApJS...62..229L
Altcode:
Spectra of solar plages are used to define indices of plage properties
in the Ca II H and K line region. Chromospheric and photospheric
emission is examined and the details of height structure are noted. It
is found that: (1) all spectral lines are weakened in plages except
those of H I, He I, and some ionized metals; (2) the irradiation
contribution from a plage is roughly constant throughout its disk
passage; and (3) plage emission distorts spectral and photometric
measures of stellar gravity, metallicity, and temperature.
Title: Spectra of Plages on the Sun and Stars. II. The H i H
alpha Line
Authors: Labonte, B. J.
Bibcode: 1986ApJS...62..241L
Altcode:
Spectra of solar plages are used to define indices of plage emission
properties in the region of the H I Hα line. Results include the
following: (I) The range of Hα emission in solar plages matches the
range observed in solar-type stars. (2) Emission in the wings of Hα
causes a systematic error in stellar temperature measurements. (3)
Plage emission at disk center is dominated by photospheric radiation,
not chromospheric. (4) Integrated over the visible spectrum, the
emission from a plage is constant to within a factor of 2 as it
transits the disk. (5) A second parameter in addition to the average
magnetic field strength is needed to specify the plage atmosphere. (6)
The width and shift of the chromospheric core of the Hα line are
nonlinearly proportional to plage strength and can be used to infer
the area coverage of plage on an unresolved system like a star.
Title: The line spectrum of plages at disk center.
Authors: Labonte, B. J.
Bibcode: 1986BAAS...18R.852L
Altcode:
No abstract at ADS
Title: Sunspot Blocking and Energy Storage in the Convection Zone
Authors: Nye, A. H.; Labonte, B. J.; Bruning, D. H.
Bibcode: 1985BAAS...17..895N
Altcode:
No abstract at ADS
Title: Active-region plages and the Hyades anomaly ?
Authors: Labonte, B. J.; Rose, J. A.
Bibcode: 1985PASP...97..790L
Altcode:
The Hyades are known to differ in their photometric properties (Crawford
1969; Campbell 1984) and spectral properties (Rose 1984) from field
stars of similar metal abundance. Using spectra of solar plages,
it is demonstrated that the Hyades spectral anomalies are caused by
excess emission from magnetic regions (plages) on the surfaces of these
cluster stars. It is further speculated that the Hyades photometric
anomalies arise from the same cause, but photometric data on solar
plages necessary to resolve this issue are not available. The Pleiades
stars and a few extreme emission stars show similar spectral anomalies,
but of such magnitude to indicate that plages on Pleiades stars have
higher surface brightnesses than on the sun and do not merely cover
a larger fraction of the stars.
Title: The Solar Irradiance From January to February, 1981
Authors: Braun, D. C.; Labonte, B. J.
Bibcode: 1985BAAS...17..756B
Altcode:
No abstract at ADS
Title: Variations of the Asymmetry of Disk Integrated Solar Line
Profiles
Authors: Bruning, D. H.; Labonte, B.
Bibcode: 1985SoPh...97....1B
Altcode:
Mean line bisector positions were found for the neutral iron line at
γ 5250.2 using disk-integrated sunlight. After correction for the
apparent time variation of the instrumental profile, it was found
that the mean bisector position was constant during the period from
May 1982 to February 1983.
Title: Heat and Mass Flow Around Sunspots
Authors: Bruning, D. H.; Labonte, B. J.
Bibcode: 1985BAAS...17Q.611B
Altcode:
No abstract at ADS
Title: Measuring solar torsional oscillations using sunspot motions
Authors: Labonte, B. J.
Bibcode: 1984A&A...135..176L
Altcode:
In trying to measure the solar torsional oscillations by using sunspot
motions, it is necessary to use correct time-latitude averages.
Title: A Global Irradiance Program
Authors: Hudson, H. S.; Chapman, G. A.; LaBonte, B. J.
Bibcode: 1984NASCP2310..313H
Altcode: 1984siva.work..311H
Basic requirements for a long-term program of ground-based measurements
of the solar brightness are outlined.
Title: Recent ground-based observations of the global properties of
the Sun.
Authors: Labonte, B. J.
Bibcode: 1984NASCP2310..151L
Altcode: 1984siva.work..151L
Ground-based observations have achieved sufficient sensitivity and
duration to scrutinize many global properties of the Sun. Variations
in the properties of granular and supergranular convection have been
measured. The surface rotation measurements continue to present
contradictory results. A spectrum of torsional motions has been
detected. A variety of oscillation measurements now are available for
nearly direct probing of the solar interior.
Title: Solar Irradiance Variations on Active Region Time Scales
Authors: Labonte, B. J.; Chapman, G. A.; Hudson, H. S.; Willson, R. C.
Bibcode: 1984NASCP2310.....L
Altcode: 1984QB531.S576.....; 1984siva.work.....L
No abstract at ADS
Title: The Hyades Anomaly
Authors: Labonte, B. J.; Rose, J. A.
Bibcode: 1984BAAS...16Q.490L
Altcode: 1984BAAS...16Z.490L
No abstract at ADS
Title: Solar irradiance variations on active region time
scales. Proceedingsof a workshop held at the California Institute
of Technology, Pasadena, California, June 20 - 21, 1983.
Authors: Labonte, B. J.; Chapman, G. A.; Hudson, H. S.; Willson,
R. C.; Newkirk, G. A., Jr.; Bruning, D. H.
Bibcode: 1984sivo.book.....L
Altcode:
No abstract at ADS
Title: Integrated Light Observations of the Asymmetry of the
λ5250 Line
Authors: Bruning, D. H.; Labonte, B. J.
Bibcode: 1984ssdp.conf..338B
Altcode:
A search for temporal variations in the asymmetry of the Fe I λ5250
solar flux profile has been started at Mount Wilson Observatory. A
preliminary analysis has indicated that the mean line bisector
position has shifted towards the red by 0.2 mÅ from May to December
of 1982. This is aproximately the shift expected if one extrapolates
the shift seen by Livingston from May 1980 to September 1981.
Title: Is stellar differential rotation observable?
Authors: Labonte, B. J.
Bibcode: 1984ApJ...276..335L
Altcode:
Daily measures of the disk integral 2.8 GHz solar flux from the years
1947 through 1982 are analyzed to determine the detectability of stellar
differential rotation using the tracer method. Autocorrelation and
power spectral analyses of 1 yr data sets yield rotation periods whose
scatter about the mean period is too large to permit detection of the
expected differential rotation signal. The principal noise source is
the random appearance of tracer regions on the solar surface, in time
and longitude. Criteria are given for optimizing stellar observations
and analyses to detect differential rotation.
Title: H-alpha as a Diagnostic of Stellar Activity
Authors: Labonte, B. J.
Bibcode: 1983BAAS...15..947L
Altcode:
No abstract at ADS
Title: Interpretation of solar irradiance variations using
ground-based observations
Authors: Bruning, D. H.; LaBonte, B. J.
Bibcode: 1983ApJ...271..853B
Altcode:
Solar intensity observations made in the wings of the Fe I 5250.2-A
absorption line using the 46-m tower telescope at Mt. Wilson
during 1980 are analyzed and related to SMM-ACRIM measurements by
a least-squares fitting procedure. Positive (P) and negative (N)
relative flux parameters are derived and attributed to facular and
sunspot contributions to the solar irradiance, respectively. P is
found to remain almost constant over the year, so that N variations
are the cause of 85 percent of the changes in irradiance observed by
ACRIM. An upper amplitude limit of 0.12 percent is calculated for any
11-year cyclic variation in solar irradiance, and P and N effects are
shown to balance each other when averaged over the year. From this
it is inferred that poleward-directed solar flux and (hence) solar
luminosity are increased by the presence of magnetic activity, although
longer-term observations will be needed to confirm this hypothesis. The
implications of the present findings for proposed models of sunspots,
faculae, global brightness change, and brightness variation not caused
by magnetic regions are discussed.
Title: The Mount Wilson Magnetograph (Report from a Solar Institute)
Authors: Howard, R.; Boyden, J. E.; Bruning, D. H.; Clark, M. K.;
Crist, H. W.; Labonte, B. J.
Bibcode: 1983SoPh...87..195H
Altcode:
Alterations to the Mount Wilson Observatory solar magnetograph were
made during 1981. The present state of the instrument, including
the spectrograph, is described. The magnetic and Doppler velocity
signals and the setup procedure for the magnetogram observation are
discussed. The advantages of the new system are described.
Title: Solar Rotation Results at Mount-Wilson - Part Four - Results
Authors: Howard, R.; Adkins, J. M.; Boyden, J. E.; Cragg, T. A.;
Gregory, T. S.; Labonte, B. J.; Padilla, S. P.; Webster, L.
Bibcode: 1983SoPh...83..321H
Altcode:
We publish here rotation results from Doppler velocity measurements
made at Mount Wilson over a period of more than 14 years. Altogether
data from 188 rotations are presented. These results are displayed in
various tables and figures. Measurements of scattered light along with
its effect on the measured rotation rate are shown.
Title: Is Stellar Differential Rotation Detectable?
Authors: Labonte, B.
Bibcode: 1983BAAS...15..720L
Altcode:
No abstract at ADS
Title: The observed relationships between some solar rotation
parameters and the activity cycle
Authors: Howard, R.; Labonte, B. J.
Bibcode: 1983IAUS..102..101H
Altcode:
Several parameters of the solar rotation show variations which appear
to relate to the phase of the solar-activity cycle. The latitude
gradient of the differential rotation, as seen in the coefficients
of the sin2 and sin4 terms in the latitude expansion, shows marked
variations with the cycle. One of these variations may be described
as a one-cycle-per-hemisphere torsional oscillation with a period of
11 years, where the high latitudes rotate faster at solar-activity
maximum and slower at minimum, and the low latitudes rotate faster at
solar-activity minimum and slower at maximum. Another variation is a
periodic oscillation of the fractional difference in the low-latitude
rotation between north and south hemispheres. The possibility of a
variation in the absolute rotational velocity of the sun in phase with
the solar cycle remains an open question. The two-cycle-per-hemisphere
torsional waves in the solar rotation also represent an aspect of the
rotation which varies with the cycle. It is shown that the amplitude
of the fast flowing zone rises a year before the rise to activity
maximum. The fast zone seems to be physically the more significant of
the two zones.
Title: Solar Rotation Measurements at Mount-Wilson - Part Three -
Meridional Flow and Limbshift
Authors: Labonte, B. J.; Howard, R.
Bibcode: 1982SoPh...80..361L
Altcode:
The `ears' velocity pattern described in Paper I (Howard et al., 1980)
had no physical explanation. A reanalysis shows that the large scale
solar velocity patterns are better described by a nonmonotonic limbshift
and a meridional flow. The results of the new analysis imply that the
study of solar velocity pattern at the level of a few ms−1
required that magnetic regions be treated separately from nonmagnetic
regions.
Title: Are the high-latitude torsional oscillations of the sun real?
Authors: Labonte, B. J.; Howard, R.
Bibcode: 1982SoPh...80..373L
Altcode:
A numerical test is made to determine if the high-latitude torsional
wave is generated from the low-latitude torsional pattern as a result of
our reduction procedures. The results indicate that the high-latitude
motions are not an artifact of the analysis, but are true solar
features. We demonstrate also that the one-wave-per-hemisphere torsional
oscillation does not result from the reduction procedure. These results
place the observations in conflict with the predictions of α - (ω)
models of the solar cycle.
Title: Solar calibration of stellar rotation tracers
Authors: Labonte, B. J.
Bibcode: 1982ApJ...260..647L
Altcode:
A study of the time variability of the disk-integrated solar magnetic
flux, with a view to the behavior of emission-line intensity variations
observed in lower main sequence stars, has determined that solar
rotation modulation of the integrated flux is present in 75% of all
rotations. For observing intervals of more than twice the lifetime
of the features causing rotational modulation, the correct rotation
period is identified in more than 90% of all cases. The optimum time
for measuring rotational modulation is the decay phase of the activity
cycle, and the solar rotation period is measured with an accuracy
of a few percent. The lifetime of a rotational modulation period is
approximately five rotations, and a sensitivity limit of Delta S=
0.005 is found for the Vaughan et al (1981) stellar rotation measures.
Title: The Magnetic Flux in the Quiet Sun Network
Authors: Labonte, B. J.; Howard, R.
Bibcode: 1982SoPh...80...15L
Altcode:
The Ca II K line emission from the quiet Sun network does not vary with
the 11-year cycle (White and Livinston, 1981). We confirm this result
from direct magnetic measurements. This effect is not simply explained
by present empirical models of the evolution of surface magnetic fields.
Title: Evidence for a Poleward Meridional Flow on the Sun
Authors: Topka, K.; Moore, R.; Labonte, B. J.; Howard, R.
Bibcode: 1982SoPh...79..231T
Altcode:
We define for observational study two subsets of all polar zone
filaments, which we call polemost filaments and polar filament
bands. The behavior of the mean latitude of both the polemost filaments
and the polar filament bands is examined and compared with the evolution
of the polar magnetic field over an activity cycle as recently distilled
by Howard and LaBonte (1981) from the past 13 years of Mt. Wilson
full-disk magnetograms. The magnetic data reveal that the polar
magnetic fields are built up and maintained by the episodic arrival of
discrete f-polarity regions that originate in active region latitudes
and subsequently drift to the poles. After leaving the active-region
latitudes, these unipolar f-polarity regions do not spread equatorward
even though there is less net flux equatorward; this indicates that
the f-polarity regions are carried poleward by a meridional flow,
rather than by diffusion. The polar zone filaments are an independent
tracer which confirms both the episodic polar field formation and the
meridional flow. We find: The mean latitude of the polemost filaments
tracks the boundary of the polar field cap and undergoes an equatorward
dip during each arrival of additional polar field.
Title: Torsional Waves on the Sun and the Activity Cycle
Authors: Labonte, B. J.; Howard, R.
Bibcode: 1982SoPh...75..161L
Altcode:
Some properties of the recently-discovered torsional oscillations of
the Sun are presented. The detailed relation of this velocity feature
to magnetic activity gives evidence that these motions represent a
fundamental oscillation within the Sun that is responsible for the
solar activity cycle and that they are not a natural consequence
of an α-ω dynamo. A new torsional oscillation with wave number 1
hemisphere−1 is demonstrated to exist on the Sun.
Title: Observations of large-scale motions of the Sun
Authors: LaBonte, B.
Bibcode: 1981NASCP2191..235L
Altcode: 1981vsc..conf..235L
Recent observations of large-scale mass motions on the Sun are
discussed. The principal large-scale velocity flows are convection,
rotation, meridional flow, and torsional and radial oscillations.
Title: Surface Magnetic Fields during the Solar Activity Cycle
Authors: Howard, R.; Labonte, B. J.
Bibcode: 1981SoPh...74..131H
Altcode:
We examine magnetic field measurements from Mount Wilson that cover the
solar surface over a 13 1/2 year interval, from 1967 to mid-1980. Seen
in long-term averages, the sunspot latitudes are characterized by
fields of preceding polarity, while the polar fields are built up by
a few discrete flows of following polarity fields. These drift speeds
average about 10 m s-1 in latitude - slower early in the
cycle and faster later in the cycle - and result from a large-scale
poleward displacement of field lines, not diffusion. Weak field
plots show essentially the same pattern as the stronger fields, and
both data indicate that the large-scale field patterns result only
from fields emerging at active region latitudes. The total magnetic
flux over the solar surface varies only by a factor of about 3 from
minimum to a very strong maximum (1979). Magnetic flux is highly
concentrated toward the solar equator; only about 1% of the flux is
at the poles. Magnetic flux appears at the solar surface at a rate
which is sufficient to create all the flux that is seen at the solar
surface within a period of only 10 days. Flux can spread relatively
rapidly over the solar surface from outbreaks of activity. This is
presumably caused by diffusion. In general, magnetic field lines at
the photospheric level are nearly radial.
Title: Measurement of Solar Radius Changes
Authors: Labonte, B. J.; Howard, R.
Bibcode: 1981Sci...214..907L
Altcode:
Photoelectric solar radius measurements since 1974 at Mount Wilson show
no change in the solar radius, with a limit of about 0.1 arc second
(1 standard deviation), over the interval. The limit is set by residual
systematic effects.
Title: An improved search for large-scale convection cells in the
solar atmosphere
Authors: Labonte, B. J.; Howard, R.; Gilman, P. A.
Bibcode: 1981ApJ...250..796L
Altcode:
A reanalysis of Mount Wilson solar velocity observations was made to
search for giant cellular patterns. The reanalysis avoids several errors
made in a previous search. No cells are detected with sensitivity of
3 to 12 m/s depending upon wavenumber. The observed amplitudes do not
conflict with recent model predictions.
Title: Solar measurements at Mount Wilson. II. Systematic instrumental
effects and the absolute rotation rate.
Authors: Labonte, B. J.; Howard, R.
Bibcode: 1981SoPh...73....3L
Altcode:
Possible sources of systematic error in solar Doppler rotational
velocities are examined. Scattered light is shown to affect the
Mount Wilson solar rotation results, but this effect is not enough
to bring the spectroscopic results in coincidence with the sunspot
rotation. Interference fringes at the spectrograph focus at Mount
Wilson have in two intervals affected the rotation results. It has been
possible to correlate this error with temperature and thus correct for
it. A misalignment between the entrance and exit slits is a possible
source of error, but for the Mount Wilson slit configuration the
amplitude of this effect is negligibly small. Rapid scanning of the
solar image also produces no measurable effect.
Title: Solar rotation.
Authors: Labonte, B. J.
Bibcode: 1981BAAS...13..548L
Altcode:
No abstract at ADS
Title: Solar Calibration of Stellar Rotation Tracers
Authors: Labonte, B.
Bibcode: 1981BAAS...13..889L
Altcode:
No abstract at ADS
Title: Horizontal Motions on the Solar Surface
Authors: Howard, R.; Labonte, B.
Bibcode: 1981siwn.conf...93H
Altcode:
No abstract at ADS
Title: Solar Brightness Variations as seen in λ5250
Authors: Bruning, D. H.; Labonte, B. J.
Bibcode: 1981BAAS...13R.876B
Altcode:
No abstract at ADS
Title: Solar Rotation
Authors: Labonte, B. J.
Bibcode: 1981BAAS...13Q.545L
Altcode:
No abstract at ADS
Title: Mount Wilson Solar Diameter Measurements
Authors: Labonte, B.; Howard, R.
Bibcode: 1981siwn.conf..362L
Altcode:
No abstract at ADS
Title: The Orientation of the Solar Rotation Axis from Doppler
Velocity Observations
Authors: Labonte, B. J.
Bibcode: 1981SoPh...69..177L
Altcode:
Mt. Wilson observations of solar velocity fields have been examined
for evidence that the rotation axis of the nonmagnetic gas at the solar
surface is oriented differently than the axis found by Carrington (1863)
from sunspot observations. No difference is found with an accuracy of
0°.15 in the angle of inclination of the axis to the ecliptic.
Title: Currents on the Sun
Authors: Howard, R.; LaBonte, B.
Bibcode: 1980S&T....60..485H
Altcode:
No abstract at ADS
Title: Large-Scale Solar Magnetic Fields Over the Last Cycle
Authors: Howard, Robert; Labonte, Barry J.
Bibcode: 1980BAAS...12..893H
Altcode:
No abstract at ADS
Title: Polar Crown Filaments and the Polar Magnetic Field
Authors: Topka, K.; Moore, R. L.; Labonte, B. J.; Howard, R.
Bibcode: 1980BAAS...12..893T
Altcode:
No abstract at ADS
Title: Observational Search for Variations in the Solar Convection
Authors: Labonte, B. J.; Howard, R.
Bibcode: 1980BAAS...12..914L
Altcode:
No abstract at ADS
Title: The sun is observed to be a torsional oscillator with a period
of 11 years
Authors: Howard, R.; Labonte, B. J.
Bibcode: 1980ApJ...239L..33H
Altcode:
Twelve years of full-disk Mount Wilson velocity data have been analyzed
to study horizontal east-west motions. A torsional wave pattern with
alternating latitude zones of slow and fast rotation is found, after
subtracting a differentially rotating frame. Amplitudes of the flow
pattern average about 3 m/s. It requires about 22 years for zones
to drift from the poles, where they originate, to the equator, where
they disappear. The pattern is symmetric about the equator. The zones
representing the next solar cycle (No. 22) are seen now at high solar
latitudes. Solar active regions are formed in a latitude strip centered
on the boundary of fast- and slow-velocity zones. This pattern evidently
represents a deep-seated circulation pattern and is the first evidence
of the association of mass motions with large-scale characteristics
of the solar activity cycle.
Title: A search for large-scale convection cells in the solar
atmosphere
Authors: Howard, R.; Labonte, B. J.
Bibcode: 1980ApJ...239..738H
Altcode:
Mount Wilson magnetograph velocity observations are used to search
for east-west motions resulting from hypothetical cellular patterns
extending over one or two hemispheres in the latitude direction. No
such solar patterns were found. Upper limits established by this
analysis depend on the cell lifetime and the pattern stability, but
in all cases they are no more than about 10 m/s.
Title: Solar Rotation Measurements at Mount-Wilson - Part One -
Analysis and Instrumental Effects
Authors: Howard, R.; Boyden, J. E.; Labonte, B. J.
Bibcode: 1980SoPh...66..167H
Altcode:
We examine the background velocity fields of the Sun as observed at
Mount Wilson. The method of velocity reduction of the full-disk Mount
Wilson data is outlined. We describe a number of tests that have been
carried out in order to find an instrumental origin for short-term
rotation variations and a large-scale background line-shift - the
ears. No instrumental cause can be found for this ear effect, although
such a cause cannot yet be ruled out.
Title: Torsional Oscillations of the Sun and Magnetic Flux Eruption
Authors: Labonte, B. J.; Howard, R.
Bibcode: 1980BAAS...12..473L
Altcode:
No abstract at ADS
Title: Solar Currents and the Magnetic Cycle
Authors: Howard, R.; Labonte, B.; Dicke, R. H.; Wilcox, J.
Bibcode: 1980SciN..117..245H
Altcode:
No abstract at ADS
Title: Search for giant cells in the solar convection zone
Authors: Labonte, B. J.; Howard, R.
Bibcode: 1980IAUS...91...21L
Altcode:
No abstract at ADS
Title: Unraveling Solar Magnetism
Authors: Wilcox, J. M.; Scherrer, P. H.; Hoeksema, J. T.; Howard,
R.; Labonte, B.
Bibcode: 1980SciN..117..374W
Altcode:
No abstract at ADS
Title: The filament eruption in the 3B flare of July 29, 1973 -
Onset and magnetic field configuration
Authors: Moore, R. L.; Labonte, B. J.
Bibcode: 1980IAUS...91..207M
Altcode:
The filament eruption in the large expanding two-ribbon solar flare
which occurred July 29, 1973 is discussed. Observational evidence is
presented for the preflare magnetic field configuration, the nature
of the filament destabilization and triggering of the flare, and
the magnetic field configuration after the filament eruption. The
observations show that the filament is under an arcade of closed
magnetic field lines prior to the eruption. The eruption of the filament
and the onset of the two-ribbon H-alpha flare are preceded by precursor
activity in the form of small H-alpha brightenings and mass motion along
the neutral line and well below the bottom edge of the filament. The
precursor H-alpha brightenings and the first brightenings in the flare
ribbons are in the vicinity of the steepest magnetic field gradient
in the flare region.
Title: Activity in the quiet sun. I. Observations of macrospicules
in Halpha and D3.
Authors: Labonte, B. J.
Bibcode: 1979SoPh...61..283L
Altcode:
Macrospicules have been observed in Hα and He I D3,
on the disk and above the limb. In 1975, a rate of 1400
(A⊙day)−1 is inferred, and the ratio of
equatorial to polar rates ≲ 2. D3 intensities are a
few × 10−3 of the disk center, and do not decrease in
coronal holes. The ratio of Hα to D3 intensities is ≈
10. The integral number of macrospicules with D3 intensity
≥I0 is proportional to I0−1.
Title: Physics of the Sun - Synoptic Observations at MT.WILSON
Rotation of the Sun - Large-Scale Velocity Fields - Active Regions
Regions - Solar Axis Elements - Big Bear Solar Observatory -
Instruments - Blue Continuum in Flares - Thermal X-Ray Plasma in
Solar Flares
Authors: Howard, R.; Goeden, R.; Eaton, S.; Labonte, B.; Patterson,
A.; Zirin, H.; Tanaka, H.; Moore, R.
Bibcode: 1979haob.rept..716H
Altcode:
No abstract at ADS
Title: Studies of chromospheric activity observes in H[alpha] and D3
Authors: Labonte, Barry James
Bibcode: 1979PhDT.......169L
Altcode: 1979PhDT........88L
Several studies of chromospheric activity as observed in H[alpha] and
D3 have been made. These are: H[alpha] Observations of the August 12,
1975 Type III-RS Bursts (Solar Physics, 50, 201, 1976); A Measurement
of the Helium D3 Profile with a Birefringent Filter (Solar Physics, 53,
369, 1977); The Properties of Macrospicules Observed in H[alpha] and
D3 (Big Bear Solar Observatory Preprint No. 0171); Polar Flares with
D3 Emission: November 15, 1974 (Big Bear Solar Observatory Preprint
No. 0170); and Thick Target Models of Impulsive Chromospheric Flares
(Big Bear Solar Observatory Preprint No. 0173).
Title: Studies of chromospheric activity observes in Hα and
D3
Authors: LaBonte, Barry James
Bibcode: 1979PhDT.......177L
Altcode:
No abstract at ADS
Title: A measurement of the helium D3 profile with a
birefringent filter.
Authors: Labonte, B. J.
Bibcode: 1977SoPh...53..369L
Altcode:
The D3 line profile in plages on the disk is measured using
a birefringent filter. The best fit Gaussian has a 1/e width of 0.4 Å,
with negligible instrumental contribution. The D3 opacity
is produced in regions with thermal linewidth -0.1 Å; the much larger
observed width indicates large non-thermal motions in the chromosphere.
Title: Halpha observations of the August 12, 1975 type III-RS
(reverse slope) bursts.
Authors: Labonte, B. J.
Bibcode: 1976SoPh...50..201L
Altcode: 1976STIN...7623138L
We present Hα filtergram observations of a number of the Type
III-RS (reverse slope) bursts that occurred on August 12, 1975. Solar
radio emission was peculiar on that date in that a large number, and
proportion, of the usually rare reverse slope bursts were observed
(Tarnstrom and Zehntner, 1975). We show that the radio bursts coincide
in time with a homologous set of Hα flares located at the limbward
edge of spot group Mt. Wilson 19598. We propose a model in which the
reverse slope bursts are the downward branches of U bursts, whose
upward branches are hidden behind the coronal density enhancement over
the spot group.
Title: Solar activity on August 12, 1975
Authors: Labonte, Barry J.
Bibcode: 1976Natur.261..525L
Altcode:
No abstract at ADS
Title: Polar Flares with He I D3 Emission
Authors: Labonte, B. J.
Bibcode: 1976BAAS....8..375L
Altcode:
No abstract at ADS
Title: A Phenomenological Study of High Resolution Granulation
Photography
Authors: Labonte, B. J.; Simon, G. W.; Dunn, R. B.
Bibcode: 1975BAAS....7..366L
Altcode:
No abstract at ADS
Title: A Phenomenological Study of High-Resolution Granulation
Photographs
Authors: LaBonte, Barry J.; Simon, George W.; Dunn, Richard B.
Bibcode: 1974BAAS....6..285L
Altcode:
No abstract at ADS
Title: H-alpha Bright Points
Authors: Labonte, B.
Bibcode: 1973BAAS....5..274L
Altcode:
No abstract at ADS
Title: Magnetic Outflow - A Stage in the Development of an Active
Region
Authors: Allen, R.; Edberg, S.; Labonte, B.; Sheeley, N. R.
Bibcode: 1973BAAS....5Q.268A
Altcode:
No abstract at ADS