Author name code: harvey-karen
ADS astronomy entries on 2022-09-14
author:"Harvey, Karen L." year:1970-2008
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Title: A Comparison of Feature Classification Methods for Modeling
Solar Irradiance Variation
Authors: Jones, H. P.; Chapman, G. A.; Harvey, K. L.; Pap, J. M.;
Preminger, D. G.; Turmon, M. J.; Walton, S. R.
Bibcode: 2008SoPh..248..323J
Altcode:
Physical understanding of total and spectral solar irradiance variation
depends upon establishing a connection between the temporal variability
of spatially resolved solar structures and spacecraft observations of
irradiance. One difficulty in comparing models derived from different
data sets is that the many ways for identifying solar features such as
faculae, sunspots, quiet Sun, and various types of "network" are not
necessarily consistent. To learn more about classification differences
and how they affect irradiance models, feature "masks" are compared as
derived from five current methods: multidimensional histogram analysis
of NASA/National Solar Observatory/Kitt Peak spectromagnetograph data,
statistical pattern recognition applied to SOHO/Michelson Doppler
Imager photograms and magnetograms, threshold masks allowing for
influence of spatial surroundings applied to NSO magnetograms, and
"one-trigger" and "three-trigger" algorithms applied to California
State University at Northridge Cartesian Full Disk Telescope intensity
observations. In general all of the methods point to the same areas of
the Sun for labeling sunspots and active-region faculae, and available
time series of area measurements from the methods correlate well with
each other and with solar irradiance. However, some methods include
larger label sets, and there are important differences in detail,
with measurements of sunspot area differing by as much as a factor
of two. The methods differ substantially regarding inclusion of fine
spatial scale in the feature definitions. The implications of these
differences for modeling solar irradiance variation are discussed.
Title: Narrow coronal holes in Yohkoh soft X-ray images and the slow
solar wind
Authors: Arge, C. N.; Harvey, K. L.; Hudson, H. S.; Kahler, S. W.
Bibcode: 2003AIPC..679..202A
Altcode:
Soft X-ray images of the solar corona sometimes show narrow dark
features not obviously present in HE I 10830Å images. We term
these ``narrow coronal holes'' (NCHs). A prototype for this type of
structure crossed solar central meridian on October 29, 2001. Standard
source-surface models showed open magnetic field lines in this
feature, tending to confirm its identification as a coronal hole. The
magnetic field in this example is relatively strong (above 100 G in
the low-resolution Kitt Peak magnetograms), and the boundaries of the
open-field domain fall within the unipolar area as expected. We have
surveyed the Yohkoh SXT data for other examples of this phenomenon,
and have found several candidates. From observations of the associated
solar wind, and from modeling, we find these regions to be sources of
slow solar wind.
Title: Observations of the Sun's magnetic field during the recent
solar maximum
Authors: Sanderson, T. R.; Appourchaux, T.; Hoeksema, J. T.; Harvey,
K. L.
Bibcode: 2003JGRA..108.1035S
Altcode:
We present new observations and analyses of the Sun's magnetic field and
coronal holes. Using magnetic field observations from the Wilcox Solar
Observatory, we present a simple means whereby the tilt angle of the
current sheet can be calculated. We use a data set covering the last 26
years, which shows for the first time how the dipole component rotated
once during a full 22-year solar cycle. We show how this influenced
the current sheet. At solar minimum, the Sun's coronal magnetic field
was essentially dipolar and aligned parallel to the spin axis. As a
result, the heliospheric current sheet was flat and had very little
warp. Around solar maximum, the dipole was perpendicular to the spin
axis, and the ratio of quadrupole to dipole strength was high for much
of the time. This meant that the current sheet was tilted and highly
warped, and reached up to high latitudes. Surprisingly, there were
also times close to solar maximum when the quadrupole/dipole ratio
was low, and the current sheet was relatively flat, but still highly
inclined. We apply for the first time to solar magnetic data a method,
which quantitatively analyses the quadrupole component of the magnetic
field. From the terms of the expansion of the observed photospheric
magnetic field, we compute the position of the poles of the magnetic
field. We combine for the first time over an extended period of time
magnetic field data from the Wilcox Solar Observatory with coronal
hole positions taken from the National Solar Observatory/Kitt Peak. We
find that the position of the coronal holes followed the motion of the
poles of the magnetic field as the poles moved over the surface of the
Sun and that the polar coronal holes broke up into groups of smaller
like-polarity holes as the poles approached the midlatitude regions
and the quadrupole became more important. We discuss the implications
for energetic particle observations at Ulysses.
Title: Polar Coronal Holes During Cycles 22 and 23
Authors: Harvey, Karen L.; Recely, Frank
Bibcode: 2002SoPh..211...31H
Altcode:
The National Solar Observatory/Kitt Peak synoptic rotation maps of the
magnetic field and of the equivalent width of the He i 1083 nm line are
used to identify and measure polar coronal holes from September 1989 to
the present. This period covers the entire lifetime of the northern and
southern polar holes present during cycles 22 and 23 and includes the
disappearance of the previous southern polar coronal hole in 1990 and
and formation of the new northern polar hole in 2001. From this sample
of polar hole observations, we found that polar coronal holes evolve
from high-latitude (∼ 60° ) isolated holes. The isolated pre-polar
holes form in the follower of the remnants of old active region fields
just before the polar magnetic fields complete their reversal during
the maximum phase of a cycle, and expand to cover the poles within
3 solar rotations after the reversal of the polar fields. During the
initial 1.2-1.4 years, the polar holes are asymmetric about the pole and
frequently have lobes extending into the active region latitudes. During
this period, the area and magnetic flux of the polar holes increase
rapidly. The surface areas, and in one case the net magnetic flux,
reach an initial brief maximum within a few months. Following this
initial phase, the areas (and in one case magnetic flux) decrease
and then increase more slowly reaching their maxima during the cycle
minimum. Over much of the lifetime of the measured polar holes, the
area of the southern polar hole was smaller than the northern hole
and had a significantly higher magnetic flux density. Both polar holes
had essentially the same amount of magnetic flux at the time of cycle
minimum. The decline in area and magnetic flux begins with the first
new cycle regions with the holes disappearing about 1.1-1.8 years
before the polar fields complete their reversal. The lifetime of the
two polar coronal holes observed in their entirety during cycles 22
and 23 was 8.7 years for the northern polar hole and 8.3 years for
the southern polar hole.
Title: Energetic Particle Observations During the Ulysses Fast
Latitude Scan
Authors: Sanderson, T. R.; Marsden, R. G.; Tranquille, C.; Hofer,
M. Y.; McKibben, R. B.; Forsyth, R. J.; Gosling, J. T.; Hoeksema,
J. T.; Harvey, K.
Bibcode: 2002AGUSMSH52B..05S
Altcode:
Peak/National Solar Observatory show that during the second Ulysses
fast latitude scan, the sun's magnetic dipole was oriented more or less
perpendicular to the spin axis (with at times a significant quadrupole
component) and that the current sheet was highly tilted. This
configuration is ideal for the formation of stream interaction
regions in the solar wind. Using particle intensity profiles and
anisotropy measurements over a wide range of energies from the COSPIN
instrument, and magnetic field and plasma observations, we identify the
magnetic structures in the heliosphere which are a consequence of the
magnetic field configuration on the Sun. We show that the heliosphere
contained many co-rotating interaction regions, stable only for a few
rotations. The many solar flares and CME's give rise to many injections
of highly energetic SEP particles. We identify CIR's and CME's which
locally accelerate the energetic particles. We show that during the
fast latitude scan, the heliosphere was filled by a complicated mix of
CME and CIR accelerated particles. When the solar activity was high,
the particle population was dominated by CME-accelerated particles,
but when activity was low, CIR accelerated particles Magnetic field
observations from the Wilcox Solar Observatory and coronal hole
observations from the Kitt dominated.
Title: Solar Irradiance Observations during Solar Cycles 22 and 23
Authors: White, O. R.; de Toma, G.; Chapman, G. A.; Walton, S. R.;
Preminger, D. G.; Cookson, A. M.; Harvey, K. L.; Livingston, W. C.
Bibcode: 2002AAS...200.5707W
Altcode: 2002BAAS...34..737W
We present a study of Total Solar Irradiance (TSI) variations during
solar cycles 22 and 23 from 1986 to the present. We will review the
recent measurements of solar magnetism, solar activity, and radiative
variability from both ground-based and space observatories and compare
TSI observations with empirical models of solar irradiance variability
based on facular and sunspot observations. To estimate facular/plage and
sunspot contribution to TSI we use the photometric indices derived from
the SFO full-disk solar images from 1988 to the present in the CaIIK
line at 393.4nm and in the red continuum at 672.3 nm. In these indices,
each solar structure is included with its measured contrast and area. We
also use the MgII core-to-wing index from space observatories as an
alternative index for plages and network. Comparison of the rising
and maximum phases of the two solar cycles, shows that cycle 23 is
magnetically weaker with sunspot and facular area almost a factor of
two lower than in solar cycle 22. However, analysis of multi-wavelength
observations indicate that different wavelengths respond differently
to the decreased magnetic activity during solar cycle 23.
Title: Transient Coronal Holes as seen in the HeI 1083nm Observations
Authors: de Toma, G.; Holzer, T. E.; Gilbert, H. R.; Burkepile, J. T.;
Harvey, K. L.
Bibcode: 2002AAS...200.3813D
Altcode: 2002BAAS...34R.700D
Observations from Yohkoh/SXT and SOHO/EIT have shown that dimming
regions often appear on the solar disk near the location of a Coronal
Mass Ejection (CME). We can now see in HeI observations made at Mauna
Loa Solar Observatory (MLSO) brightenings that form at the time of a
CME and are co-spatial with the ultraviolet and X-ray dimmings. Both
dimmings and brightenings can be interpreted as different manifestations
of the decreased density of the overlying corona caused by the ejection
of coronal material during the eruption, i.e. as transient coronal
holes. Because of the 3-minute cadence of the HeI 1083nm observations
at MLSO, we can now determine the appearance and evolution of transient
coronal holes with high accuracy. In this paper, we present examples
of transient coronal holes as seen in HeI data and compare them with
simultaneous observations in the H alpha line and in the ultraviolet.
Title: Signatures of CMEs in HeI 1083 nm Images and Estimation of
ICME Bz Direction
Authors: Harvey, J. W.; Harvey, K. L.; Henney, C. J.
Bibcode: 2002AAS...200.3706H
Altcode: 2002BAAS...34..695H
Coronal Mass Ejections (CMEs) are expulsions from the corona of material
at coronal and chromospheric temperatures. Since the strength of the
HeI absorption line multiplet at 1083 nm partly depends on the amount of
mass in the chromosphere and overlying corona, CME signatures appear in
1083 nm observations. We examined daily time-difference images for such
signatures in comparison with direct CME observations. We found that by
using good spatial resolution, the time-difference images readily show
disappearing filaments and sudden expansions of coronal holes which are
known to be frequently associated with CMEs. The images also show the
enhanced footpoints of arcades of post-flare loops as increases of line
strength, and plage intensity changes. The 1083 nm changes are often
spread widely over a large fraction of the solar disk, consistent with
direct coronal disk observations of CMEs. These difference images will
be available on NSO's web site, along with other data, as part of a
transition to new a new suite of synoptic instruments called SOLIS. As
an example of the utility of comparing different data, we examined
contemporaneous photospheric and chromospheric magnetograms to see if
the magnetic field Bz direction (north-south GSE coordinate) of the
interplanetary CME (ICME) could be predicted. A southward directed Bz is
associated with severe geomagnetic storms. Several predictive schemes
are promising but their reliability needs improvement. A significant
observational difficulty is that the detectable mass loss occurs where
the magnetic field is relatively weak. This work was supported in part
by ONR grant N00014-91-J-1040 and NSF grant ATM-9819842.
Title: A comparison of feature classification methods for modeling
solar irradiancevariation
Authors: Jones, H.; Harvey, K.; Pap, J.; Preminger, D.; Turmon, M.;
Walton, S.
Bibcode: 2002cosp...34E.641J
Altcode: 2002cosp.meetE.641J
A physical understanding of both total (bolometric) and spectral solar
irradiance variations depends upon establishing a connection between
the temporal variability of spatially resolved solar structures and
spacecraft observations of irradiance. One difficulty in comparing
models derived from different data sets is that the many ways for
identifying solar features such as faculae, sunspots, quiet sun, and
various flavors of "network" are not necessarily consistent. To learn
more about classification differences and how they affect irradiance
models, we compare feature "masks" on selected days together with
the temporal variation of feature areas derived from four current
methods: multidimensional histogram analysis of NASA/NSO Kitt Peak
spectromagnetograph data (Jones et al., 2000, ApJ 529, 1070);
statistical pattern recognition applied to SOHO/MDI photograms
and magnetograms (Turmon et al., 2002, ApJ 568, 396); threshhold
masks allowing for influence of spatial surroundings applied to
NSO magnetograms (Harvey and White, 1999, ApJ 515, 541); and the
"three-trigger" algorithm applied to CSUN CFDT images (Preminger et al.,
2001, Sol. Phys. 202, 53.). Developing a more uniform classification
system of features contributing to irradiance variations will help
to improve irradiance models used for climate studies. A practical
benefit of understanding the relationships between various methods is
the possibility of constructing a more continuous and extensive time
series from several incomplete sources.
Title: Observations of The Sun's Coronal Magnetic Field and Coronal
Holes During The Ulysess Fast Latitude Scan
Authors: Sanderson, T. R.; Appourchaux, T.; Hoeksema, J. T.; Harvey,
K. L.
Bibcode: 2002EGSGA..27..595S
Altcode:
We have combined magnetic field observations from the Wilcox
Solar Observatory and coronal holes observations from the Kitt Peak
Observatory to investigate how the Sun's magnetic field behaved during
the Ulysses fast latitude scan. Using the dipole and quadrupole
terms in the expansion of the coronal magnetic field, we show that the
dipole rotated once every 22-year solar cycle and that the quadrupole
term reached a maximum at the time of solar maximum. At solar minimum,
the current sheet was flat and had very little warp, but around solar
maximum, during the second Ulysses Southern Polar Pass, the ratio
of quadrupole to dipole strength was high for much of the time. The
current sheet was tilted and highly warped, and reached up to high
latitudes. Surprisingly, there were times when the quadrupole/dipole
ratio was low, and the current sheet was relatively flat, but still
highly inclined. The site of coronal holes follows the motion of
the poles of the magnetic field as the poles move over the surface
of the Sun. The polar coronal hole breaks up into groups of smaller
like-polarity holes as the poles approach the mid-latitude regions.
Title: The influence of the Sun's magnetic field on energetic
particles at high heliospheric latitudes
Authors: Sanderson, T. R.; Marsden, R. G.; Tranquille, C.; Balogh,
A.; Forsyth, R. J.; Goldstein, B. E.; Gosling, J. T.; Harvey, K. L.
Bibcode: 2001GeoRL..28.4525S
Altcode:
The first passage of the Ulysses spacecraft to high latitudes was during
the declining phase of solar cycle 22. The recent second passage to
high latitudes was close to the maximum of solar cycle 23. The axis
of the dipolar component of the Sun’s magnetic field was close
to 90° from the spin axis, and the coronal neutral line extended
up to high latitudes. A variable but generally slow solar wind was
observed all the way up to the highest latitudes reached by Ulysses,
as was the sector structure of the magnetic field. The high-latitude
heliosphere was populated with intensities of energetic particles with
energies around 1 MeV several orders of magnitude above background. We
show how the changes in the Sun’s magnetic field, the coronal holes,
and the configuration of the heliosphere could be responsible for the
differences between particle observations in the two orbits.
Title: Observations of the Sun's Coronal Magnetic Field and Coronal
Holes during the Recent Ulysess Second Polar Pass, and Implications
for Particle Observations
Authors: Sanderson, T. R.; Appourchaux, T.; Hoeksema, J. T.; Harvey,
K. L.
Bibcode: 2001AGUFMSH32A0723S
Altcode:
We combine magnetic field observations from the Wilcox Solar Observatory
and coronal hole observations from the National Solar Observatory/ Kitt
Peak. At solar minimum, the Sun's coronal magnetic field was dipolar and
aligned along the spin axis. The current sheet was flat and had very
little warp. Around solar maximum, during the second Ulysses southern
polar pass, the ratio of quadrupole to dipole strength was high for
much of the time. This meant that the current sheet was tilted and
highly warped, and reached up to high latitudes. Using the dipole and
quadrupole terms from the expansion of the coronal magnetic field,
we compute the position of the dipole and quadrupole poles. We find
that the location of coronal holes follows the motion of the poles
of the magnetic field as the poles move across the surface of the
Sun. The polar coronal holes break up into groups of smaller holes
all with the same polarity as the poles approach the mid-latitude
regions. Surprisingly, there were also times close to solar maximum
when the quadrupole/dipole ratio was low, and the current sheet was
relatively flat, but still highly inclined. We discuss the implications
for the observations of energetic particles at Ulysses.
Title: Evolution of Solar Filament Channels Observed during a Major
Poleward Surge of Photospheric Magnetic Flux
Authors: Gaizauskas, V.; Mackay, D. H.; Harvey, K. L.
Bibcode: 2001ApJ...558..888G
Altcode:
We describe the evolution of a solar filament channel marked by
extremes: a length near one solar radius, and a duration of a year. Its
genesis centers on an episode of flux emergence so powerful that it
launched a surge of photospheric magnetic flux almost to the northern
polar cap. This extraordinary injection of new flux at the solar
surface occurred in midterm of the longest lived activity complex
of cycle 21 (~20 rotations). The new flux emerged just north of the
equator as a pair of adjacent activity complexes-a ``supercluster''
of sunspots-remote from other active regions in a longitude band
spanning ~90°. Channels quickly formed along separate polarity
inversion lines in this large-scale quadrupolar configuration. None
of the initial channels survived more than two solar rotations; none
merged to form a greater whole. As individual bipoles within and
between the activity complexes expanded, fragmented, and cancelled,
only flux at the outermost edges of the adjacent complexes survived,
thanks to the remoteness of other strong concentrations of magnetic
flux. The result, after three solar rotations, was a simplified bipolar
pattern of poleward-streaming flux subject to global processes of flux
transport that sustained and extended it for up to a year. The long
and long-lived filament channel formed in the shape of a ``switchback''
along the polarity inversion between the converging streams of opposite
polarity flux, continuing along the polarity inversion between the
migrating flux and the flux in the polar cap. Our observations reveal
large-scale swirled patterns of chromospheric fibrils from which we
infer that substantial negative helicity was built up across both
adjacent activity complexes during their emergence. The patterns were
still detectable in the migrating flux after the source regions had
disappeared. Convergence of opposite polarity fluxes with negative
helicity leads naturally to dextral filaments and filament channels,
consistent with the chirality rule for the northern hemisphere found
by Martin, Bilimoria, & Tracadas. We measured the chiralities of
10 filament channels associated with the initial massive emergence
of magnetic flux and its subsequent surge poleward. Implications of
our findings on models for forming filaments and filament channels
are discussed.
Title: Helioseismic Holography and a Study of the Process of Magnetic
Flux Disappearance in Canceling Bipoles
Authors: Lindsey, Charles; Harvey, Karen L.; Braun, D.; Jones, H. P.;
Penn, M.; Hassler, D.
Bibcode: 2001STIN...0156300L
Altcode:
Project 1: We have developed and applied a technique of helioseismic
holography along the lines of originally set out in our proposal. The
result of the application of this diagnostic technique to solar activity
and the quiet Sun has produced a number of important discoveries:
(1) acoustic moats surrounding sunspots; (2) acoustic glories
surround large active regions; (3) acoustic condensations beneath
active regions; and (4) temporally-resolve acoustic images of a solar
flare. These results have been published in a series of papers in the
Astrophysical Journal. We think that helioseismic holography is now
established as the most powerful and discriminating diagnostic in local
helioseismology. Project 2: We conducted a collaborative observational
program to define the physical character and magnetic geometry of
canceling magnetic bipoles aimed at determining if the cancellation
process is the result of submergence of magnetic fields. This assessment
is based on ground-based observations combining photospheric and
chromospheric magnetograms from NSO/KP, BBSO, and SOHO-MDI, and EUV
and X-ray images from SOHO EIT/CDS, Yohkoh/SXT, and TRACE. Our study
involves the analysis of data taken during three observing campaigns to
define the height structure of canceling bipoles inferred from magnetic
field and intensity images, and how this varies with time. We find
that some canceling bipoles can be explained by the submerge of their
magnetic flux. A paper on the results of this analysis will be presented
at an upcoming scientific meeting and be written up for publication.
Title: The Evolution of the Polar Coronal Holes Over a Solar Cycle
Authors: Harvey, K. L.; Recely, F.
Bibcode: 2001AGUSM..SP51B02H
Altcode:
The polar coronal holes, areas of open magnetic field on the Sun,
persist for 10 years, first appearing shortly after the completion of
the polar magnetic field reversal and disappearing 1--2 years before
their next reversal. We present the results of a study of the polar
coronal holes observed during cycles 22 and 23 using the National
Solar Observatory/Kitt Peak photospheric magnetograms and He~I 10830
spectroheliograms. The locations and boundaries of coronal holes are
inferred from the He~I 10830 synoptic rotation maps. The magnetic field
properties are derived by superimposing the coronal hole boundaries
onto the corresponding synoptic rotation magnetograms. We find that
(1) the polar holes form from high-latitude, isolated, non-polar
holes that develop a few months before the completion of the polar
reversal; (2) The area and magnetic flux in the polar holes initially
increase rapidly, reaching their respective maxima within 1--2 years;
(3) In the decline of cycle 22, the southern polar hole was smaller
(3.7 x 1020 cm2) than the northern polar hole
(5.1 x 1020 cm2), while both holes had the same
absolute magnetic flux (3.1-3.2 x 1022 Mx); (4) The polar
holes decrease in area and magnetic flux with the onset of new cycle
activity, disappearing once the absolute magnetic flux in the more
extended polar regions decreased below about 5 x 1021
Mx. Results on the characteristics and behavior of polar holes and
their extension to lower latitude will be discussed. This work is
funded through NSF Grant ATM-9713576.
Title: Differences in the Sun's Radiative Output in Cycles 22 and 23
Authors: de Toma, Giuliana; White, Oran R.; Chapman, Gary A.; Walton,
Stephen R.; Preminger, Dora G.; Cookson, Angela M.; Harvey, Karen L.
Bibcode: 2001ApJ...549L.131D
Altcode:
Analysis of the current solar cycle 23 shows a greater increase
in total solar irradiance (TSI) for the early phase of this cycle
than expected from measurements of the total magnetic flux and
traditional solar activity indices, which indicate that cycle 23 is
weaker than cycle 22. In contrast, space observations of TSI from the
Solar and Heliospheric Observatory/VIRGO and the Upper Atmospheric
Research Satellite/ACRIMII show an increase in TSI of about 0.8-1.0
W m-2 from solar minimum in 1996 to the end of 1999. This
is comparable to the TSI increase measured by Nimbus 7/ERB from 1986
to 1989 during the previous cycle. Thus, solar radiative output near
the maximum of the 11 yr cycle has been relatively constant despite
a factor of 2 smaller amplitude increase for cycle 23 in sunspot and
facular areas determined from ground-based observations. As a result,
empirical models of TSI based on sunspot deficit and facular/network
excess in cycle 22 underestimate the TSI measurements in 1999. This
suggests either a problem in the observations or a change in the
sources of radiative variability on the Sun.
Title: Subject Index and Name Index (Volumes 191 - 197)
Authors: Harvey, Karen L.
Bibcode: 2001SoPh..197....1H
Altcode:
No abstract at ADS
Title: Coronal Cavities
Authors: Harvey, K.
Bibcode: 2000eaa..bookE2268H
Altcode:
Coronal cavities observed on the Sun are an important part of a complex
and larger coronal magnetic structure. They appear as regions of low
emission surrounding PROMINENCES and separate the prominence from an
overlying arcade of CORONAL LOOPS located in the lower portion of a
helmet streamer (see CORONAL STREAMERS). Observations show that the
density of material in a coronal cavity is lower tha...
Title: Solar Active Regions: Ephemeral
Authors: Harvey, K.
Bibcode: 2000eaa..bookE2275H
Altcode:
Magnetic flux emerges through the surface of the Sun as bipolar regions
with a wide range of sizes, such as shown in figure 1. Larger magnetic
bipoles develop SUNSPOTS and are identified as ACTIVE REGIONS. Small
bipolar regions, such as indicated in the lower panels of figure 1,
are called ephemeral regions, a name given by H Dodson in 1953 because
of their short lifetimes. Ephemeral regions have...
Title: Solar Coronal Structure Study
Authors: Nitta, Nariaki; Bruner, Marilyn E.; Saba, Julia; Strong,
Keith; Harvey, Karen
Bibcode: 2000STIN...0085876N
Altcode:
The subject of this investigation is to study the physics of the
solar corona through the analysis of the EUV and UV data produced
by two flights (12 May 1992 and 25 April 1994) of the Lockheed
Solar Plasma Diagnostics Experiment (SPDE) sounding rocket payload,
in combination with Yohkoh and ground-based data. Each rocket flight
produced both spectral and imaging data. These joint datasets are useful
for understanding the physical state of various features in the solar
atmosphere at different heights ranging from the photosphere to the
corona at the time of the, rocket flights, which took place during the
declining phase of a solar cycle, 2-4 years before the minimum. The
investigation is narrowly focused on comparing the physics of small-
and medium-scale strong-field structures with that of large-scale, weak
fields. As we close th is investigation, we have to recall that our
present position in the understanding of basic solar physics problems
(such as coronal heating) is much different from that in 1995 (when we
proposed this investigation), due largely to the great success of SOHO
and TRACE. In other words, several topics and techniques we proposed can
now be better realized with data from these missions. For this reason,
at some point of our work, we started concentrating on the 1992 data,
which are more unique and have more supporting data. As a result, we
discontinued the investigation on small-scale structures, i.e., bright
points, since high-resolution TRACE images have addressed more important
physics than SPDE EUV images could do. In the final year, we still spent
long time calibrating the 1992 data. The work was complicated because
of the old-fashioned film, which had problems not encountered with more
modern CCD detectors. After our considerable effort on calibration, we
were able to focus on several scientific topics, relying heavily on the
SPDE UV images. They include the relation between filaments and filament
channels, the identification of hot loops, and the physical conditions
of such loops especially at their foot-points. A total of four papers
were completed from this contract which are listed in the last section.
Title: Global Solar Variability: Cycle 23 Indicates a Change from
Recent Cycles
Authors: de Toma, G.; White, O. R.; Chapman, G. A.; Walton, S. R.;
Harvey, K. L.
Bibcode: 2000SPD....3102115D
Altcode: 2000BAAS...32..831D
This paper focuses on the rising phase of solar cycle 23 from the
time of solar minimum in 1996 to the present high activity level. A
number of observations indicate that cycle 23 maximum is now close, and
maybe is already in the maximum phase. They include the distribution
of coronal streamers, the presence of long--lived solar coronal holes
at low latitudes, the latitudinal distribution of sunspot regions,
and the unipolar magnetic fields in the polar regions. Most of the
activity indices, i.e. sunspot number, sunspot area, photospheric
magnetic flux, 10.7 cm radio flux, and UV irradiances, indicate this
cycle as a relatively weak cycle as compared to cycles 21 and 22. In
particular, observations at San Fernando Observatory of sunspot and
facular area are a factor of two or more lower than in solar cycle
22. This is consistent with the lower magnetic flux measured at NSO/KP
and UV irradiance measurements, but not with total solar irradiance
measurements. We analyze ground--based and space observations to give
a comprehensive picture of the evolution of the current cycle and
compare it to the solar cycle 22.
Title: Differences in the Sun's Radiative Output in Cycles 22 and 23
Authors: White, O. R.; de Toma, G.; Chapman, G. A.; Walton, S. R.;
Harvey, K. L.; Cookson, A. M.; Preminger, D. G.
Bibcode: 2000SPD....31.0127W
Altcode: 2000BAAS...32..806W
We study total solar irradiance (TSI) observations during the rising
phase of cycle 22 and 23 for the 5--year periods during 1986--1990
and 1996--2000. The increase in TSI in cycle 23 is greater than
expected from the observations of the photospheric magnetic flux, and
by traditional activity indices, like sunspot number, 10.7 cm radio
flux, MgII and HeI indices, all of which indicate that cycle 23 is
a relatively weak cycle. Space observations of TSI from SOHO/VIRGO
and UARS/ACRIMII show an increase in TSI of about 1 W/m2
from 1996 to 2000. This is comparable to the increase observed in
TSI during the previous cycle, from 1986 to 1990 as observed from
Nimbus7/ERB. To resolve the discrepancy between the variability in TSI
observed in the two last cycles, we used the San Fernando Observatory
(SFO) photometric data at 393.4 nm and 672.3 nm to evaluate sunspot
and facular contributions to TSI. The SFO image decomposition technique
has been tested against NSO/KP magnetograms decomposition for selected
days, and they are in good agreement. A 3--parameter fit to Nimbus--7
data for the years 1988--1993 based on SFO data and MgII index gives a
correlation coeff. r2 = 0.9. Extrapolation of the fit in time
largely underestimates the current SOHO/VIRGO TSI measurements. This
suggests there is either a problem in the observations or a change in
nature of radiative sources on the Sun.
Title: Properties and Time Variability of Solar Activity Structures
Authors: Harvey, K. L.; Barentine, J.
Bibcode: 2000SPD....31.0138H
Altcode: 2000BAAS...32Q.808H
We investigate the properties of active regions and the network
based on the results of an image decomposition of the NSO/Kitt Peak
magnetograms. Our decomposition technique uses the magnetic flux
density, the spatial distribution of magnetic flux, filling factor, and
the presence of sunspots to define six structures -- active regions,
decaying active regions, sunspots, enhanced network, quiet network,
and the quiet atmosphere (supergranular cell interiors). A total of
798 magnetograms were processed, providing 894 measurements of about
450 active regions and their associated sunspots. We will present the
results of a study of the characteristics of the six structure classes,
their total magnetic flux, area (surface and apparent), mean flux
densities, the partitioning of plage and sunspots in active regions,
and how these quantities vary with time during a three-year period from
1 January 1996 to 31 December 1998. This interval covers the minimum
period between cycles 22 and 23 and the rise of cycle 23 activity.
Title: A Picture of Solar Minimum and the Onset of Solar Cycle
23. I. Global Magnetic Field Evolution
Authors: de Toma, Giuliana; White, Oran R.; Harvey, Karen L.
Bibcode: 2000ApJ...529.1101D
Altcode:
NSO/Kitt Peak synoptic charts of magnetic flux in the period from 1996
to 1998 are analyzed together with time series for the 10.7 cm radio
flux, sunspot number, and Mg II chromospheric index to determine the
origin of the two times of minimum activity in 1996 and to study their
relationships in the ascending phase of solar cycle 23. The solar
activity minima in February-April and September-November of 1996
are found to correspond to periods of low magnetic activity in the
southern and northern solar hemispheres, respectively. The new solar
cycle becomes dominant in early 1997, but it is only in the summer
of 1997 that a significant increase can be detected in the magnetic
fields observations as well as in irradiance data, and by the end
of 1998, the activity level has increased to a value comparable to
the one observed in 1993. Using the magnetic synoptic charts,
we determine the number of persistent longitude bands of active nests
during this rising phase of solar cycle 23. We find an increase in the
number of active nests from zero in 1996 to three by 1998. We speculate
that these persistent bands of flux emergence correspond to a pattern
of low-order modes of instability of the type found in the theoretical
work of Gilman, Fox, and Dikpati on joint instability of latitudinal
differential rotation and toroidal magnetic fields at the base of the
convection zone. We argue that the observed increase in the number
of active nests is consistent with the increase in the longitudinal
wavenumber of magnetic instabilities in a concentrated toroidal field
in the tachocline discussed in 1999 by Gilman and Dikpati.
Title: Solar Activity and the Formation of Coronal Holes
Authors: Harvey, Karen L.; Hudson, Hugh S.
Bibcode: 2000AdSpR..25.1735H
Altcode:
We describe the evolution of a complex of active regions belonging
to cycle 22 and how its interaction with two new-cycle (23) regions
resulted in the formation of several isolated coronal holes, in the
development of the large coronal hole extending from the north polar
hole observed in late August 1996, and in significant changes in both
polar coronal holes
Title: Does Magnetic Flux Submerge at Flux Cancelation Sites?
Authors: Harvey, Karen L.; Jones, Harrison P.; Schrijver, Carolus J.;
Penn, Matthew J.
Bibcode: 1999SoPh..190...35H
Altcode:
Simultaneous measurements of the magnetic fields in the photosphere and
chromosphere were used to investigate if magnetic flux is submerging
at sites between adjacent opposite polarity magnetic network elements
in which the flux is observed to decrease or `cancel'. These data
were compared with chromospheric and coronal intensity images to
establish the timing of the emission structures associated with these
magnetic structures as a function of height. We found that most of
the cancelation sites show either that the bipole is observed longer
in the photosphere than in the chromosphere and corona (44%) or that
the timing difference of the disappearance of the bipole between these
levels of the atmosphere is unresolved. The magnetic axis lengths of the
structures associated with the cancelation sites are on average slightly
smaller in the chromosphere than the photosphere. These observations
suggest that magnetic flux is retracting below the surface for most,
if not all, of the cancelation sites studied.
Title: What is solar cycle minimum?
Authors: Harvey, Karen L.; White, Oran R.
Bibcode: 1999JGR...10419759H
Altcode:
Establishing the time of minimum between cycles 22 and 23 is complicated
because there are two periods of low solar activity during 1996. To
resolve this controversy, we studied the time of minimum in terms of
the historical basis for defining this fiducial point in the solar
cycle using several measures of solar activity, as well as the cycle
membership of active regions observed during the minimum phase between
these two cycles. Our conclusion is that cycle minimum is not defined
solely on the basis of the occurrence of the minimum in the smoothed
sunspot number, but rather by several additional parameters, including
the monthly (or rotationally) averaged sunspot number, the number
of regions (total, new- and old-cycle), and the number of spotless
days. Using these specific measures of solar activity, we recommend
that the minimum between cycles 22 and 23 occurred in September 1996
(1996.7) and not in May 1996 (1996.4).
Title: Studies of changing patterns of solar activity using the DRAO
Synthesis Radio Telescope.
Authors: Tapping, K.; Burke, I.; Cameron, H.; Harvey, K.; Zwaan, C.
Bibcode: 1999JRASC..93Q.186T
Altcode:
No abstract at ADS
Title: Evolution of Solar Magnetic Fields in 1996-1998
Authors: de Toma, G.; White, O. R.; Harvey, K. L.; Rottman, G. J.;
Woods, T. N.
Bibcode: 1999AAS...194.9202D
Altcode: 1999BAAS...31..986D
NSO/Kitt Peak synoptic charts of magnetic flux in the period from 1996
to 1998 are analyzed together with time series for the 10.7 cm radio
flux, sunspot number, and MgII chromospheric index to determine the
origin of two times of minimum activity in 1996 and to study the rising
phase of the current solar cycle 23 in 1997 and 1998. The two minima
between solar cycle 22 and 23 in the Spring and Fall of 1996 are found
to correspond to periods of low magnetic activity in the southern and
northern solar hemispheres, respectively. The new solar cycle becomes
dominant in early 1997, but it is only in the Summer of 1997 that
a significant increase in activity can be detected in the magnetic
fields observations as well as in irradiance data. By the end of 1998,
the activity level has increased to a value that suggests the current
cycle is about half way to solar maximum. The number of persistent
longitude bands of active nests increases from zero in 1996 to three
by 1998. This value seems consistent with numerical simulations which
study the dependence with longitudinal wavenumber, m, of magnetic
instabilities in concentrated toroidal fields at the tachocline.
Title: Solar Cycle Variation of He I 1083 NM Coronal Holes
Authors: Harvey, K. L.; Recely, F.
Bibcode: 1999AAS...194.9207H
Altcode: 1999BAAS...31..987H
Coronal holes are studied to investigate their variation over a
solar cycle. We use the NSO/Kitt Peak synoptic Carrington rotation
maps of He I 10830 nm and magnetic fields to identify coronal holes
and measure their position, area, boundaries, and magnetic flux as a
function of time. Our study covers a period from February 1975 to the
present (March 1999). This 25-year interval includes three minima, at
the onset of cycles 21, 22, and 23, and two maxima, that of cycles 21
and 22. We will present results on the temporal variation in area and
magnetic flux separating the identified coronal holes into two types,
polar and lower-latitude, isolated holes, and how these parameters
relate temporally and spatially to solar activity. We will also
consider differences in the variation of coronal holes between the
northern and southern hemispheres. This research is funded through
NSF Grant ATM-9713576.
Title: Magnetic and Radiative Variability of Solar Surface
Structures. I. Image Decomposition and Magnetic-Intensity Mapping
Authors: Harvey, Karen L.; White, Oran R.
Bibcode: 1999ApJ...515..812H
Altcode:
In order to specify quantitatively the contributions to irradiance
variability by specific types of solar surface structure, we analyzed
full-disk magnetograms and Ca II K images from the National Solar
Observatory and Big Bear Solar Observatory for two sets of several
days in early 1992 and mid-1993. These test days were chosen at
maxima and minima of the rotational modulation in the Lyα irradiance
from the Upper Atmosphere Research Satellite Solar-Stellar Irradiance
Comparison Experiment (UARS/SOLSTICE) spectrometer. For the eight days,
we isolated active regions, decaying active regions, the enhanced
network, the network, and the quiet atmosphere based on their magnetic
flux strength and distribution, filling factor, and association with
sunspots. Transfer of these image decompositions to Ca II K images
gives magnetic flux versus intensity (|B| vs. δK) relationships for
four structures with measurable magnetic flux. In the range 30-400 Mx
cm-2, these log-log curves are linear with a slope of 0.5,
which suggests that the Ca II K residual intensity is proportional
to the half-power of the magnetic flux density. The separation into
quiet and active Sun structures gives a prediction of the variation
of the |B| versus δK relation for the ensemble of our four principal
structures from minimum to maximum in the activity cycle of the Sun
viewed as a star.
Title: A Stable Filament Cavity with a Hot Core
Authors: Hudson, H. S.; Acton, L. W.; Harvey, K. L.; McKenzie, D. E.
Bibcode: 1999ApJ...513L..83H
Altcode:
We present observations of a long-lived solar filament cavity with
soft X-ray sources along its axis. This structure appeared above the
southern polar crown polarity-inversion line for approximately three
rotations during 1997 June-August, centered at a west-limb passage on
approximately July 3. At the limb, the Yohkoh soft X-ray data showed
a bright region situated above and around the projected filament
location but near the axis of the cavity. We describe measurements
of the geometry of the cavity, which we interpret as a flux rope that
is partially embedded in the photosphere, and use the Yohkoh data to
describe the physical parameters of the structure. We find that the
core consists of an unresolved mass of filamentary substructures, with a
volume filling factor significantly less than unity for the soft X-ray
telescope (SXT) resolution. The core has a higher temperature than the
cavity surrounding it, ruling out explanations in terms of a transition
region supported by thermal conduction. Transient activity occurred in
the polar crown region, but no detectable destabilization or eruption
of the cavity structure resulted from it. We suggest that the bright
structure at the core of the cavity corresponds to higher altitude
coronal segments of the field lines that support the filament material.
Title: Spatial structure of the solar wind and comparisons with
solar data and models
Authors: Neugebauer, M.; Forsyth, R. J.; Galvin, A. B.; Harvey,
K. L.; Hoeksema, J. T.; Lazarus, A. J.; Lepping, R. P.; Linker,
J. A.; Mikic, Z.; Steinberg, J. T.; von Steiger, R.; Wang, Y. -M.;
Wimmer-Schweingruber, R. F.
Bibcode: 1998JGR...10314587N
Altcode:
Data obtained by instruments on the Ulysses spacecraft during its rapid
sweep through >90° of solar latitude, crossing the solar equator
in early 1995, were combined with data obtained near Earth by the
Wind spacecraft to study the spatial structure of the solar wind and
to compare to different models of the interplanetary magnetic field
derived from solar observations. Several different source-surface
models matched the double sinusoidal structure of the heliospheric
current sheet (HCS) but with differences in latitude as great as
21°. The source-surface model that included an interplanetary
current sheet gave poorer agreement with observed current-sheet
crossings during this period than did the other source-surface models
or an MHD model. The differences between the calculated and observed
locations of the HCS were minimized when 22° of solar rotation was
added to the constant-velocity travel time from the source surface to
the spacecraft. The photospheric footpoints of the open field lines
calculated from the models generally agreed with observations in the
He 10,830 Å line of the locations of coronal holes with the exceptions
that (1) in some places, open field lines originated outside the coronal
hole boundaries and (2) the models show apparently closed-field regions
just inside some coronal hole boundaries. The patterns of mismatches
between coronal hole boundaries and the envelopes of open field lines
persisted over at least three solar rotations. The highest-speed wind
came from the polar coronal holes, with the wind originating deeper
within the hole being faster than the wind coming from near the
hole boundary. Intermediate and slow streams originated in smaller
coronal holes at low latitudes and from open field regions just
outside coronal hole boundaries. Although the HCS threaded regions
of low speed, low helium abundance, high ionization temperature,
and a high ratio of magnesium to oxygen densities (a surplus of an
element with low first-ionization potential), there was a great deal
of variation in these parameters from one place to another along
the HCS. The gradient of speed with latitude varied from 14 to 28
kms-1deg-1.
Title: Large-scale coronal heating by the small-scale magnetic field
of the Sun
Authors: Schrijver, C. J.; Title, A. M.; Harvey, K. L.; Sheeley,
N. R.; Wang, Y. -M.; van den Oord, G. H. J.; Shine, R. A.; Tarbell,
T. D.; Hurlburt, N. E.
Bibcode: 1998Natur.394..152S
Altcode:
Magnetic fields play a crucial role in heating the outer atmospheres
of the Sun and Sun-like stars, but the mechanisms by which magnetic
energy in the photosphere is converted to thermal energy in the corona
remain unclear. Observations show that magnetic fields emerge onto
the solar surface as bipolar regions with a broad range of length
scales. On large scales, the bipolar regions survive for months before
dispersing diffusively. On the smaller scales, individual bipolar
regions disappear within days but are continuously replenished by new
small flux concentrations, resulting in a sustained state of mixed
polarity. Here we determine the rate of emergence of these small
bipolar regions and we argue that the frequent magnetic reconnections
associated with these regions (an unavoidable consequence of continued
flux replacement) will heat the solar atmosphere. The model that
describes the details of these mixed-polarity regions is complementary
to the traditional diffusion model for large-scale flux dispersal and
a combination of the two should lead to a more complete understanding
of the role of magnetic fields in stellar atmospheres.
Title: Magnetic Field Properties of Solar X-Ray Jets
Authors: Shimojo, Masumi; Shibata, Kazunari; Harvey, Karen L.
Bibcode: 1998SoPh..178..379S
Altcode:
From a list of X-ray jets made by Shimojo et al. (1996), we selected
events for which there were magnetic field data from NSO/Kitt
Peak. Using co-aligned SXT and magnetograms, we examined the magnetic
field properties of X-ray jets. We found that 8% of the jets studied
occurred at a single pole (SP), 12% at a bipole (BP), 24% in a mixed
polarity (MP) and 48% in a satellite polarity (ST). If the satellite
polarity region is the same as the mixed polarity region, 72% of the
jets occurred at the (general) mixed polarity region.
Title: Spectral Irradiance and Magnetic Structures
Authors: Harvey, Karen L.; White, Oran R.
Bibcode: 1998ASPC..140..247H
Altcode: 1998ssp..conf..247H
No abstract at ADS
Title: Working Group 1: Total, Near-UV (λ > 300 nm), Visible
and Infrared Spectral Irradiance
Authors: Harvey, Karen L.; Wehrli, Christoph
Bibcode: 1998sers.conf..481H
Altcode:
No abstract at ADS
Title: The Formation and Evolution of the Coronal Holes Associated
with NOAA Region 7978
Authors: Harvey, K. L.; Hudson, H. S.
Bibcode: 1998ASSL..229..315H
Altcode: 1998opaf.conf..315H
No abstract at ADS
Title: The Solar Activity Cycle and Sun-As Variability in the Visible
and Infrared
Authors: Harvey, Karen L.
Bibcode: 1998saco.conf....7H
Altcode:
No abstract at ADS
Title: Filament Channels: Contrasting Their Structure in H-alpha
and H epsilon I 1083 NM
Authors: Harvey, K. L.; Gaizauskas, V.
Bibcode: 1998ASPC..150..269H
Altcode: 1998IAUCo.167..269H; 1998npsp.conf..269H
No abstract at ADS
Title: Enhanced Synoptic Observations: A Spacecraft on the Other
Side of the Sun
Authors: Ruzmaikin, A.; Feynman, J.; Harvey, J.; Harvey, K.;
Magsonas Team
Bibcode: 1998ASPC..140..553R
Altcode: 1998ssp..conf..553R
No abstract at ADS
Title: Global Magnetic Patterns of Chirality
Authors: Zirker, J. B.; Martin, S. F.; Harvey, K.; Gaizauskas, V.
Bibcode: 1997SoPh..175...27Z
Altcode:
During the past five years at least six manifestations of a global
organization of solar magnetic fields have been recognized. The magnetic
chirality (handedness) of the following features shows a hemispheric
preference: filament channels, quiescent filaments, sunspot whorls,
superpenumbral fibrils, coronal arcades, and interplanetary clouds
associated with CMEs. Although the patterns are clear in the data,
their interpretation and their possible connection to the dynamo is
open to question. This paper reviews the observations of the patterns,
corrects some misinterpretations, and offers a scenario for the origin
of the most marked pattern, the chirality of filaments. We suggest
the pattern arises from the reconnection of coronal loops, under
the influence of supergranulation and differential rotation. Unlike
alternative scenarios, ours relies only on observable surface motions
and fields.
Title: The Height and Temporal Structure of X-Ray Bright Points
Authors: Harvey, K. L.; Penn, M.; Tarbell, T.; Saba, J.; Hassler,
D.; Moses, J. D.; Fludra, A.
Bibcode: 1997SPD....28.0124H
Altcode: 1997BAAS...29..883H
On April 12, 1996, several ground-based observatories, the Yohkoh/SXT
and the SOHO/MDI, EIT, SUMER, and CDS instruments participated in a
collaborative study of X-Ray Bright Points (XBPs). During a several
hour period, simultaneous images were obtained of an area centered
at N10E00. At NSO/KP, observations were made of the HeI 1083 nm line
profile from which we have derived the intensity at line center,
equivalent width, and the velocity at every 1 pixel (1.15 arc-seconds)
within an 8 x 8 arc-minute area. Our paper will present the results
of a comparison, spatially and temporally, of these data with changes
in the magnetic field observed by the MDI, intensities and velocities
observed with SUMER and CDS, and the intensity images observed by
the SXT and EIT. We will use this ensemble of intensity, magnetic
and velocity field images to derive the height structure of XBPS,
its variation as a function of time and relation to the associated
magnetic field configuration.
Title: Panel achieves consensus prediction of solar cycle 23
Authors: Joselyn, J. A.; Anderson, J. B.; Coffey, H.; Harvey, K.;
Hathaway, D.; Heckman, G.; Hildner, E.; Mende, W.; Schatten, K.;
Thompson, R.; Thomson, A. W. P.; White, O. R.
Bibcode: 1997EOSTr..78..205J
Altcode:
In September 1996, a panel of experts on solar cycle prediction
techniques met in Boulder, Colorado, to survey forecasts of solar
and geomagnetic activity and to arrive at a consensus on how the
solar cycle will develop. After two weeks of deliberation, the panel
of 12 scientists (from Australia, Germany, the United Kingdom, and
the United States) agreed that a large amplitude solar cycle with
a smoothed sunspot maximum of approximately 160 is probable near the
turn of the century. The amplitude of the predicted cycle is comparable
to that of the previous two solar cycles (see Figure 1).Our ability to
predict solar and geomagnetic activity is crucial to many technologies,
including the operation of low-Earth orbiting satellites, electric power
transmission grids, geophysical exploration, and highfrequency radio
communications and radars. Because the scale height of Earth's upper
atmosphere (and thus the drag on satellites in low Earth orbit) depends
on the levels of short-wavelength solar radiation and geomagnetic
activity, we need to know the profile and magnitude of the next solar
and geomagnetic cycle in order to plan for reboosting the Hubble Space
Telescope and assembling the International Space Station.
Title: A Spacecraft Going Behind the Sun Will Support SOHO
Authors: Ruzmaikin, A.; Anderson, J. D.; Asmar, S.; Bird, M.; Cassiani,
A.; Coles, W.; Feynman, J.; Harvey, J.; Harvey, K.; Hollweg, J.;
Linker, K.; Mikic, Z.; Pätzold, M.; Smith, E. J.
Bibcode: 1997ESASP.404..653R
Altcode: 1997cswn.conf..653R
No abstract at ADS
Title: Solar identification of solar-wind disturbances observed
at Ulysses
Authors: Lemen, J. R.; Acton, L. W.; Alexander, D.; Galvin, A. B.;
Harvey, K. L.; Hoeksema, J. T.; Zhao, X.; Hudson, H. S.
Bibcode: 1996AIPC..382...92L
Altcode:
The Ulysses polar passages are producing a unique set of observations of
solar-wind disturbances at high heliographic latitudes. In this paper
we use the Yohkoh soft X-ray telescope (SXT) to locate some of these
events, as defined by the Ulysses/SWICS data, in the solar corona. Of 8
events, we identify two with flares, three with front-side large arcade
events, two with far-side events, and one was not seen in the Ulysses
data. The arcade events generally resemble long-duration flares seen
in active regions, but are larger, slower, and cooler. We present
Yohkoh images of each of these events. In the large arcade events
(see Alexander et al., 1996, for a detailed look at one of them) the
magnetic morphology at the location of the Yohkoh arcade is generally
consistent with the development of a large system of loops. Some of
the identifications are ambiguous, and we summarize the reasons for
this. From the SWICS data we have obtained ionization temperatures for
several events, and find that they have no obvious pattern in relation
to the X-ray temperatures; this may be expected on the basis that the
interplanetary plasma cloud is physically distinct from the plasma
trapped in the corona. Soft X-ray observations of the solar corona
show occasional occurrences of large-scale brightenings in the form
of arcades of loops. Such structures have been known since Skylab
(e.g., Sturrock, 1980), and have a clear relationship with coronal
mass ejections (e.g., Kahler, 1977). We now may study this phenomenon
statistically with the much more comprehensive Yohkoh observations;
with Yohkoh movies we can also begin to extend our knowledge to the
three-dimensional development of the structures. At the same time
Ulysses has sampled the latitude dependence of the interplanetary
effects. With this paper we introduce this subject and provide a
preliminary listing of events from the passage of Ulysses through
high heliographic latitudes. The starting point of the present
survey is a list of interplanetary plasma clouds (IPC's) derived
from Ulysses/SWICS data. These are essentially the same as the events
termed CMEs by Gosling et al. (1994a, 1994b). For this identification
the presence of bidirectional streaming in the suprathermal electron
distribution is one of the main criteria. We note that there are no
direct coronagraph observations, however. The Yohkoh observations
were examined at the apparent time of origin of each Ulysses event,
resulting in some clear and some less-certain identifications. We
also studied the ionization temperatures of the IPC material as a
beginning step to give the identifications a physical basis. There
has been little study thus far of the Yohkoh soft X-ray observations
in relationship to CMEs, which we believe to be closely related to
the interplanetary disturbances. Hiei et al. (1993) reported the only
Yohkoh event yet studied in conjunction with white-light coronagraph
observations. However Klimchuk et al. (1994) showed that X-ray eruptive
phenomena with parameters similar to those of CMEs occur frequently at
the limb, and there have been several studies of individual eruptive
events (e.g., Watanabe et al., 1992). Presently there is no systematic
knowledge of the X-ray coronal counterparts of CMEs, and the survey
represented here is part of the effort to rectify this situation.
Title: Yohkoh/SXT soft x-ray observations of sudden mass loss from
the solar corona
Authors: Hudson, H. S.; Acton, L. W.; Alexander, D.; Freeland, S. L.;
Lemen, J. R.; Harvey, K. L.
Bibcode: 1996AIPC..382...88H
Altcode:
With soft X-ray imaging we can study the entire coronal volume, except
for cold inclusions such as prominences, as a function of time. This
should allow us to observe the origins of coronal mass ejections. We
report here an initial survey of the Yohkoh/SXT observations at the
times of reported or apparent mass ejections: three LDE flare events
and two large-scale arcade formations. For each of the events we
can easily detect sudden coronal dimming, which we interpret as the
launch interval of a CME. In one of the flare events we have found
a well-defined plasma cloud, apparently formed from a set of loop
structures, which rises and disappears during the growth phase of the
flare emission. Its mass amounted to some 4×1014 g with
a density of 3×108 cm-3 and a temperature of
2.8 MK before its disappearance.
Title: The large scale eruptive event of 1994 April 14
Authors: Alexander, David; Harvey, K. L.; Hudson, H. S.; Hoeksema,
J. T.; Zhao, X.
Bibcode: 1996AIPC..382...80A
Altcode:
The polar crown event of 1994 April 14 is one of the largest scale
eruptive events observed by the Yohkoh/SXT. Associated with the
formation of an arcade of soft X-ray loops at the Sun was the
detection of an interplanetary forward/reverse shock event by the
Ulysses spacecraft some 7 days later. The relationship between the
coronal and interplanetary signatures of these events is important if
we are to address fully the initialisation and consequent development of
interplanetary phenomena, such as CMEs and counter-streaming electrons,
originating at the Sun. We investigate the development of the energetics
of the 1994 April 14 event and their relationship to the dynamics of
the eruption are investigated. The arcade formation, together with the
eruption of material into interplanetary space, suggests a large-scale
temporary reconfiguration of the coronal magnetic field. We examine
the effects of the formation of such a coronal arcade structure on
the HCS and discuss the dynamics involved with the passage of a large
scale disturbance through the interplanetary magnetic field.
Title: The solar origins of two high-latitude interplanetary
disturbances
Authors: Hudson, H. S.; Acton, L. W.; Alexander, D.; Harvey, K. L.;
Kahler, S. W.; Kurokawa, H.; Lemen, J. R.
Bibcode: 1996AIPC..382...84H
Altcode:
Two extremely similar interplanetary forward/reverse shock events,
with bidirectional electron streaming, were detected by Ulysses in
1994 [Gosling et al., 1994]. Both events resulted in geomagnetic
storms and presumably were associated with coronal mass ejections. In
this paper we use the Yohkoh soft X-ray observations to characterize
the conditions in the lower corona at the times appropriate for the
launching of these two events. We find two strikingly different solar
events to be the likeliest candidates: an LDE flare on 20 Feb. 1994,
and a extremely large-scale arcade event on 14 April 1994.
Title: Coronal structures deduced from photospheric magnetic field
and He I λ10830 observations
Authors: Harvey, Karen L.
Bibcode: 1996AIPC..382....9H
Altcode:
The intensity of chromospheric structures observed in He I λ1083
nm is strongly modulated by overlying coronal radiation. For this
reason, observations in He I λ1083 nm and their detailed comparison
with photospheric magnetic fields and the X-ray corona allows us to
deduce some aspects of coronal structures and of the topology of
the coronal magnetic fields, particularly important at times when
there are no direct coronal disk observations available. This paper
discusses what He I λ1083 nm spectroheliograms can tell us about
the short- and long-term evolution of the coronal magnetic fields,
focusing on coronal holes, the large-scale, long-lived two `ribbon'
flare that follow the filament eruptions, and small-scale, short-lived
dark points. The National Solar Observatory/Kitt Peak He I λ1083 nm
and magnetic field data are compared with direct observations of the
coronal structure from the Yohkoh Soft X-ray Telescope.
Title: Simultaneous UV and X-ray Observations of Coronal Bright Points
Authors: Bruner, M. E.; Nitta, N.; Wuelser, J. P.; Harvey, K.; Handy,
B.; Dame, L.
Bibcode: 1996AAS...188.8607B
Altcode: 1996BAAS...28..964B
High resolution ultraviolet filtergrams recorded during the 1992 and
1994 flights of the Solar Plasma Diagnostics Experiment (SPDE) sounding
rocket payload revealed a number of coronal bright points that were
simultaneously observed with the Yohkoh soft x-ray telescope. UV images
made at 1550 Angstroms/, which include substantial contributions from
the C IV resonance lines, reveal pairs of sources under the x-ray bright
points; consistent with the conventional interpretation of the latter
as un-resolved loops. The 1994 flight also recorded high resolution
EUV images at 171 and 195 Angstroms/, corresponding to strong lines
of Fe IX and Fe XII, respectively. Excellent correspondence was found
between coronal bright points seen in these lines, which are formed at
relatively low coronal temperatures (1 -- 2 x 10(6) k), and the 2 --
5 x 10(6) k that typifies the Yohkoh SXT images. In this study, we
use the Yohkoh database to study the temporal development of several
coronal bright points both before and after each rocket flight in order
to determine the stage of evolution of the sources at the epoch of the
flight. The relationship between the plasma properties of the sources
and their stages of evolution will be discussed.
Title: Microflaring in Sheared Core Magnetic Fields and Episodic
Heating in Large Coronal Loops
Authors: Porter, J. G.; Falconer, D. A.; Moore, R. L.; Harvey, K. L.;
Rabin, D. M.; Shimizu, T.
Bibcode: 1996AAS...188.7018P
Altcode: 1996BAAS...28..941P
We have previously reported that large, outstandingly-bright coronal
loops within an active region or stemming from an active region have
one end rooted around a magnetic island of included polarity that is
itself a site of locally enhanced coronal heating (X-ray bright point)
[Porter et al 1996, in Proceedings of the Yohkoh Solar/Stellar IAU
Symposium, ed. Y. Uchida, T. Kosugi, H.S. Hudson (Kluwer: Dordrecht), in
press]. This suggests that exceptional magnetic structure in and around
the magnetic island fosters magnetic activity, such as microflaring,
that results in the enhanced coronal heating in both the compact core
field around the island and in the body of large loops that extend
from this site. We have also reported that enhanced coronal heating
in active regions goes hand-in-hand with strong magnetic shear in
the core magnetic fields along polarity neutral lines (Falconer et al
1995, BAAS, 27(2), 976). Here, by combining MSFC vector magnetograms
with an NSO full-disk magnetogram and Yohkoh SXT coronal images, we
examine the incidence of sheared core fields, enhanced coronal heating,
and microflaring in two active regions having several good examples
of enhanced extended coronal loops. It appears that the localized
microflaring activity in sheared core fields is basically similar
whether the core field is on the neutral line around an island of
included polarity or on the main neutral line of an entire bipolar
active region. This suggests that the enhanced coronal heating in an
extended loop stemming from near a polarity inversion line requires a
special field configuration at its foot to plug it into the activity at
the neutral line, rather than a different kind of activity in the core
field on the neutral line. We also examine whether the waxing and waning
of the coronal brightness of extended loops shows any correlation with
the vigor or frequency of microflaring at the feet. This research was
supported by the Solar Physics Branch of NASA's Office of Space Science.
Title: Observations of X-Ray Bright Points
Authors: Harvey, K. L.
Bibcode: 1996AAS...188.3605H
Altcode: 1996BAAS...28..873H
Since the launch of Yohkoh in 1991, a number of collaborative observing
campaigns have been conducted to determine the association of X-Ray
Bright Points (XBPs) with the underlying photospheric magnetic
fields and chromospheric structures. Simultaneous, high-time and
spatial observations were obtained by the Yohkoh Soft X-Ray Telescope
and several ground-based observatories (NSO/KP, BBSO, MSO, NSO/SP,
HAO, SOONSPOT). In this paper, the results of the analysis of these
data will be presented, focusing on and quantifying the XBP time and
spatial variability, the association of XBPs with the evolution of the
photospheric magnetic fields and of chromospheric structures observed
in HeI 1083 nm and Hα . The interpretation of the XBP phenomena in
terms of magnetic field reconnection will be considered.
Title: Large Scale Patterns of Magnetic Activity and the Solar Cycle
Authors: Harvey, K. L.
Bibcode: 1996AAS...188.3302H
Altcode: 1996BAAS...28..867H
Observations demonstrate that the large-scale magnetic fields vary in
a systematic and consistent way during a solar cycle. This paper will
discuss the evolution and development of the magnetic field patterns
based on 23 years of full-disk, high-resolution NSO/KP magnetograms. An
analysis of the properties of active regions and the variation of the
magnetic field distribution with time, the global pattern of magnetic
flux over the cycle can be described as follows: During the minimum
phase of a cycle, most of the surface magnetic fields form a pattern
of mixed polarities, i.e., the distribution of the magnetic network
elements that, on a spatial scale of at least a supergranule, is a
mixture of both polarities. The polar regions, however, are covered by
predominately unipolar fields that are of opposite polarity in each
hemisphere and extend to latitudes of around 50°. With increasing
activity levels, the mixed-polarity fields at lower latitudes are
replaced by active regions and at higher latitude by the large-scale
patterns of unipolar magnetic flux that develop as the active region
magnetic fields decay and disperse. These large scale magnetic flux
patterns appear to be transported systematically toward the poles by
a random-walk dispersal mechanism, merdidional motions, differential
rotation. The net effect of this process in the rise of the cycle
and into the maximum phase is a succession of large-scale patterns of
magnetic flux of both polarities extending from the activity belts to
higher latitudes. Those of the same polarity augment the polar fields,
while those of opposite polarity cancel with and eventually reverse
the polar fields during the sunspot cycle maximum. As cycle activity
declines, the unipolar fields in the polar regions increase in area
and strength, while the large-scale unipolar fields are replaced by
the time of sunspot minimum with patterns of mixed-polarity fields.
Title: Comparison and Relation of HeI 1083 NM Two-Ribbon Flares and
Large-Scale Coronal Arcades Observed by YOHKOH
Authors: Harvey, Karen L.; McAllister, Alan; Hudson, Hugh; Alexander,
David; Lemen, James R.; Jones, Harrison P.
Bibcode: 1996ASPC...95..100H
Altcode: 1996sdit.conf..100H
No abstract at ADS
Title: Observations of X-Ray Bright Points (Invited)
Authors: Harvey, K. L.
Bibcode: 1996ASPC..111....9H
Altcode: 1997ASPC..111....9H
The relation of X-ray bright points (XBPs) with the underlying
photospheric magnetic fields and chromospheric structures is studied
using simultaneous, high-time and spatial resolution observations
obtained from several campaigns by the Yohkoh SXT and several
ground-based observatories, NSO/KP, BBSO, MSO, NSO/SP, and HAO. The
initial results of the analysis of a total of 239 XBPs observed on 23
days during these campaigns are discussed. This paper focuses on the
variability of XBPs, the association of XBPs with the configuration and
evolution of the photospheric magnetic fields and structures observed
in He I line at 1083 nm.
Title: Magnetic Roots of Enhanced High Coronal Loops
Authors: Porter, J. C.; Falconer, D. A.; Moore, R. L.; Harvey, K. L.;
Rabin, D. M.; Shimizu, T.
Bibcode: 1996mpsa.conf..429P
Altcode: 1996IAUCo.153..429P
No abstract at ADS
Title: Statistical Study of Solar X-ray Jets Observed with the YOHKOH
Soft X-ray Telescope
Authors: Shimojo, M.; Hashimoto, T.; Shibata, K.; Hirayama, T.;
Harvey, K. L.
Bibcode: 1996mpsa.conf..449S
Altcode: 1996IAUCo.153..449S
No abstract at ADS
Title: Solar Magnetic Fields: The Key to Understanding Solar
Irradiance Variations
Authors: Harvey, Karen L.; White, Oran R.
Bibcode: 1996sprc.rept.....H
Altcode:
The objective of this research is the development of a scheme
for analyzing the properties of full-disk solar magnetograms to
determine the variability of different types of solar magnetic
structure and its effect on the variation of the radiation emitted
by these structures. This approach has operational applications
since we consider the analysis of daily synoptic measurements of the
line-of-sight magnetic field on the solar hemisphere visible from the
Earth with the view to using the results to estimate the variability
of solar irradiances at the Earth. However, the study is also one of
fundamental importance in solar physics: the relationship of solar
magnetism to the radiative losses in the solar atmosphere.
Title: The solar/interplanetary event of 14 April 1994 observed
by Yohkoh/SXT
Authors: Alexander, D.; Harvey, K. L.; Hudson, H. S.; Hoeksema, J. T.;
Zhao, X.
Bibcode: 1995sowi.conf...57A
Altcode:
The polar crown event of April 14 1994 is one of the largest
scale eruptive events observed by the Yohkoh/SXT. Associated with
the formation of an arcade of soft X-ray loops at the Sun was the
detection of an interplanetary forward/reverse shock event by the
Ulysses spacecraft some 4-7 days later. The relationship between the
coronal and interplanetary signatures of these events is important if we
are to address fully the initialization and consequent acceleration of
interplanetary phenomena, such as CMEs and counter-streaming electrons,
originating at the Sun. From detailed analysis of the energetics
of the arcade formed during the eruption of April 14 1994, we find
peak temperatures and emission measures of approximately 5MK and
approximately 1048cm-3 respectively. The total
thermal content of the arcade loop structure observed in soft X-rays
is calculated to be some 5 x 1029 ergs. The development
of these parameters as the event proceeds and their relationship to
the dynamics of the eruption are investigated. Although spanning a
longitudinal range of some 150 degrees the April 14 event displayed
the typical helmet streamer structure normally associated with coronal
mass ejections These helmet streamers are thought to be related to the
global solar magnetic field through the heliospheric current sheet
(HCS). The arcade formation, together with the eruption of material
into interplanetary space, signifies a large-scale reconfiguration of
the coronal magnetic field. We examine the effects of the formation of
such a coronal arcade structure on the HCS and discuss the dynamics
involved with the passage of a large scale disturbance through the
interplanetary magnetic field.
Title: Comparison of YOHKOH x-ray coronal events with ULYSSES
interplanetary events
Authors: Lemen, J. R.; Acton, L. W.; Alexander, D.; Galvin, A. B.;
Harvey, K. L.; Hoecksema, J. T.; Zhao, X.; Hudson, H.
Bibcode: 1995sowi.conf...58L
Altcode:
The Yohkoh soft X-ray telescope (SXT) has observed several
largescale eruptive events per year for the first three years
of observations (Aug. 1991 - Nov. 1994) Such events are most
prominent at high latitudes, but resemble long-duration flare
events seen in active regions. Some of the high-latitude events
have now been identified in the Ulysses/SWICS data base during the
Ulysses south polar passage. There are puzzling examples of solar
events with no interplanetary counterparts. A comparison of coronal
and interplanetary events can lead to better models for mapping
interplanetary disturbances back to their source location, especially
by combining Yohkoh morphology with three-dimensional representations
of the coronal magnetic field. In this paper we describe the parameters
of the hot plasma seen by SXT. There is clear evidence for non radial
motion in specific events. We present comparisons between the ionization
temperature of the interplanetary plasma with that observed at the
Sun in cases where this is possible.
Title: Yohkoh/SXT soft x-ray observations of sudden mass loss from
the solar corona
Authors: Hudson, H. S.; Acton, L. W.; Alexander, D.; Freeland, S. L.;
Lemen, J. R.; Harvey, K. L.
Bibcode: 1995sowi.confR..58H
Altcode:
Direct X-ray observations allow us to estimate the hot coronal mass
before and after a flare or other disturbance of the type leading to
a coronal mass ejection. The sudden disappearance of a large coronal
structure (scale greater than 105 km) gives evidence that an ejection
has occurred, if the time scales are much shorter than the conductive
or radiative cooling times for such structures. A flare also typically
adds large amounts of new material to the corona via evaporation
resulting from the coronal energy release. This provides a competing
mechanism that makes the estimation of the total mass loss somewhat
difficult. We note that the X-ray observations have the advantage of
covering the entire corona rather than the limb regions unlike the
coronagraph observations. We have identified two examples of coronal
mass disappearances. before and during long duration flare events on
21 Feb. 1992 (on the E limb) and 13 Nov. 1994 (near disk center). In
latter case the total mass amounted to some 4 x 1014 g with a
density of 3 x 108cm-3 and a temperature of 2.8 MK
before its disappearance. This corresponds to a radiative cooling time
of some 104 S. much longer than the observed time of disappearance. We
therefore suggest that these sudden mass disappearances correspond with
coronal mass ejections (CMEs), and suggest that further data analysis
will be able to confirm this by comparison with optical observations
of specific CMEs.
Title: Coronal structures deduced from photospheric magnetic field
and He I lambda 10830 observations
Authors: Harvey, Karen L.
Bibcode: 1995sowi.conf...27H
Altcode:
The National Solar Observatory synoptic program provides an extensive
and unique data base of high-resolution full-disk observations of the
line-of-sight photospheric magnetic fields and of the He I lambda 10830
equivalent width. These data have been taken nearly daily for more
than 21 years since 1974 and provide the opportunity to investigate
the behavior of the magnetic fields in the photosphere and those
inferred for the corona spanning on the time scales of a day to that
of a solar cycle. The intensity of structures observed in He I lambda
10830 are strongly modulated by overlying coronal radiation; areas
with low coronal emission are generally brighter in He I lambda 10830,
while areas with high coronal emission are darker. For this reason,
He I lambda 10830 was selected in the mid-1970's as way to identify
and monitor coronal holes, magnetic fields with an open configuration,
and the sources of high-speed solar wind streams. The He I lambda 10830
spectroheliograms also show a wide variety of other structures from
small-scale, short-lived dark points (less than 30 arc-sec, hours) to
the large-scale, long-lived two 'ribbon' flare events that follow the
filament eruptions (1000 arc-sec, days). Such structures provide clues
about the connections and changes in the large-scale coronal magnetic
fields that are rooted in concentrations of magnetic network and active
regions in the photosphere. In this paper, what observations of the
photospheric magnetic field and He I lambda 10830 can tell us about
the short- and long-term evolution of the coronal magnetic fields will
be discussed, focussing on the quiet Sun and coronal holes. These data
and what we infer from them will be compared with direct observations
of the coronal structure from the Yohkoh Soft X-ray Telescope.
Title: The solar origins of two high-latitude interplanetary
disturbances
Authors: Hudson, H. S.; Acton, L. W.; Alexander, D.; Harvey, K. L.;
Kurokawa, H.; Kahler, S.; Lemen, J. R.
Bibcode: 1995sowi.confS..58H
Altcode:
Two extremely similar interplanetary forward/reverse shock events,
with bidirectional electron streaming were detected by Ulysses in
1994. Ground-based and Yohkoh/SXT observations show two strikingly
different solar events that could be associated with them: an LDE flare
on 20 Feb. 1994, and a extremely large-scale eruptive event on 14 April
1994. Both events resulted in geomagnetic storms and presumably were
associated with coronal mass ejections. The sharply contrasting nature
of these solar events argues against an energetic causal relationship
between them and the bidirectional streaming events observed by Ulysses
during its S polar passage. We suggest instead that for each pair of
events. a common solar trigger may have caused independent instabilities
leading to the solar and interplanetary phenomena.
Title: Ephemeral Regions and the Diffusion of Photospheric Magnetic
Fields
Authors: Harvey, K. L.; Fan, Y.
Bibcode: 1995SPD....26.1009H
Altcode: 1995BAAS...27..978H
No abstract at ADS
Title: Calculation of Absolute Solar Irradiances and Their Variation
with Solar Activity
Authors: White, O. R.; Fontenla, J.; Fox, P.; Avrett, E. H.; Harvey, K.
Bibcode: 1995SPD....26..308W
Altcode: 1995BAAS...27..954W
No abstract at ADS
Title: Contrasting the Solar Cycle Effects in - and Small-Scale
Magnetic Structures
Authors: Strong, Keith; Harvey, Karen
Bibcode: 1995SPD....26..613S
Altcode: 1995BAAS...27R.963S
No abstract at ADS
Title: Photospheric Origins of Enhanced High Coronal Loops
Authors: Porter, J. G.; Falconer, D. A.; Moore, R. L.; Harvey, K. L.;
Rabin, D. M.
Bibcode: 1995SPD....26..704P
Altcode: 1995BAAS...27..966P
No abstract at ADS
Title: Magnetic Field Topology at the Location of an X1/1B Solar Flare
Authors: Gaizauskas, V.; Démoulin, P.; Mandrini, C. H.; Rovira,
M. G.; Harvey, K. L.
Bibcode: 1995SPD....26.1319G
Altcode: 1995BAAS...27R.991G
No abstract at ADS
Title: The large scale coronal eruptive event of April 14 1994
Authors: Alexander, D.; Slater, Greg L.; Hudson, Hugh S.; McAllister,
Alan H.; Harvey, Karen L.
Bibcode: 1994ESASP.373..187A
Altcode: 1994soho....3..187A
No abstract at ADS
Title: The Contribution of Components of Magnetic Activity to
Variations in Solar Irradiance
Authors: Harvey, Karen L.; White, Oran R.
Bibcode: 1994AAS...18512309H
Altcode: 1994BAAS...26R1523H
The evolution of magnetic fields on the solar surface is the principal
underlying cause of variations observed in the radiative output of
the Sun. These magnetic fields are manifested in a wide range of
structures from large active regions with sunspots to small-scale
network elements. In this paper, we address the identification and
separation of the different components of solar magnetic surface
activity in digitally-recorded full-disk magnetograms. Such quantitative
identification provides a tool in learning how the magnetic field
distribution on the visible solar hemisphere effects variability of
the solar radiation received at the earth. Full-disk, high-resolution
magnetograms from the National Solar Observatory are the input to a
logic chain that defines several classes of magnetic structures: active
regions (plage, sunspots), decaying active regions (active network),
and weak and quiet network. The analysis technique employs several
criteria based on size of the region, its polarity, its maximum and
mean field strength, the magnetic filling factor, and association with
sunspots to differentiate and categorize these magnetic structures
and to create image masks that isolate these structure classes in
both magnetograms or spectral intensity images, such as Ca II K and
He I 10830 spectroheliograms. The final products are the image masks
defining the detailed geometrical shape on the visible solar hemisphere
plus a table of numerical parameters summarizing the properties of
each individual magnetic region. This physical classification is then
used to investigate the pixel-by-pixel relation between the observed
longitudinal component of the magnetic field in the different magnetic
structures and the strength of emission lines showing chromospheric
variability. We will show our progress in defining how each type of
solar magnetic structure contributes the variability of the Sun's
radiative output at two epochs in Solar Cycle 22, Jan-Feb 1992 and
Jun-Jul 1993. Our analysis addresses variability on solar rotation
time scales as well as the slower change from maximum conditions in
1992 to moderate levels of activity in 1993.
Title: X-ray bright points and high-speed wind streams: a preliminary
analysis from Yohkoh and Ulysses data
Authors: Poletto, G.; Suess, S. T.; Khan, J. I.; Uchida, Y.; Hiei,
E.; Neugebauer, M.; Goldstein, B. E.; Strong, K. T.; Harvey, K. L.
Bibcode: 1994ESASP.373..143P
Altcode: 1994soho....3..143P
No abstract at ADS
Title: Nonthermal Processes in Flaring X-Ray--bright Points
Authors: Kundu, M. R.; Strong, K. T.; Pick, M.; White, S. M.; Hudson,
H. S.; Harvey, K. L.; Kane, S. R.
Bibcode: 1994ApJ...427L..59K
Altcode:
X-ray-bright point (XBPs) are known to show variability on a number of
timescales, including impulsive X-ray brightenings. The relationship
between these XBP 'flares' and normal solar flares is poorly known. A
fundamental question is whether nonthermal acceleration of particles
takes place in XBP flares. We address this issue by searching for
nonthermal radio emission at metric wavelengths from flaring XBPs
identified in Yohkoh soft x-ray telescope (SXT) data. Unequivocal
evidence for type III-like radio bursts, usually attributed to beams
of nonthermal electrons on open field lines, is found. This suggests
that XBP flares are similar to normal flares and can indeed accelerate
nonthermal populations of energetic particles.
Title: The Photospheric Magnetic Flux Budget
Authors: Schrijver, C. J.; Harvey, K. L.
Bibcode: 1994SoPh..150....1S
Altcode:
The ensemble of bipolar regions and the magnetic network both contain
a substantial and strongly variable part of the photospheric magnetic
flux at any phase in the solar cycle. The time-dependent distribution
of the magnetic flux over and within these components reflects the
action of the dynamo operating in the solar interior. We perform a
quantitative comparison of the flux emerging in the ensemble of magnetic
bipoles with the observed flux content of the solar photosphere. We
discuss the photospheric flux budget in terms of flux appearance and
disappearance, and argue that a nonlinear dependence exists between
the flux present in the photosphere and the rate of flux appearance
and disappearance. In this context, we discuss the problem of making
quantitative statements about dynamos in cool stars other than the Sun.
Title: Large-scale velocity fields and small-scale magnetic fields
during the maximum of solar cycle 22
Authors: Martin, Sara F.; Harvey, K. L.
Bibcode: 1994cait.reptQ....M
Altcode:
Studies of the solar cycle have revealed that the size distribution
of active regions does not vary with the solar cycle. Size, rate of
rise, and lifetime of active regions are roughly proportional although
a wide range of variation exists among these parameters. The polar
field typically reverses about 2 years after solar maximum. The new
solar cycle does not seem to start until after the reversal of the
sign of the magnetic poles. However, the new solar cycle does overlap
appreciably with the previous cycle and begins 3 or more years prior
to the minimum in sunspot producing active regions. The solar cycle
begins with ephemeral regions at high latitudes. From the analysis of
active region and ephemeral region data over more than a whole solar
cycle it is concluded that ephemeral regions are in all respects the
small-scale end of the distribution of active regions. No rationale
was found for excluding ephemeral regions as one of the effects of the
solar dynamo. The search for the early ephemeral regions associated
with solar cycle 23 at high latitudes yielded the tentative conclusion
that it was detected during our observing runs during the spring of
1993 although confirming data is needed.
Title: Interactions between Nested Sunspots. I. The Formation and
Breakup of a Delta-Type Sunspot
Authors: Gaizauskas, V.; Harvey, K. L.; Proulx, M.
Bibcode: 1994ApJ...422..883G
Altcode:
We investigate a nest of sunspots in which three ordinary bipolar
pairs of sunspots are aligned collinearly. The usual spreading action
of the growing regions brings two spots of leading polarity together
(p-p collision) and forces the leading and trailing spots of the two
interior regions to overlap into a single penumbra (p-f collision),
thus forming a delta-spot. We examine digitally processed images
from the Ottawa River Solar Observatory of two related events inside
the delta-spot 5 days after the p-f collision begins: the violent
disruption of the f-umbra, and the formation in less than a day of
an hydrogen-alpha filament. The evolutionary changes in shape, area,
relative motions, and brightness that we measure for each spot in the
elongated nest are more compatible with Parker's (1979a) hypothesis
of a sunspot as a cluster of flux tubes held together by downdrafts
than with the notion of a sunspot as a monolithic plug of magnetic
flux. From chromospheric developments over the delta-spot, we show
that a shearing motion along a polarity inversion is more effective
than convergence for creating a chromospheric filament. We invoke
the release of an instability, triggered by a sequence of processes
lasting 1 day or more, to explain the disruption of the f-umbra in this
delta-spot. We show that the sequence is initiated when the colliding
p-f umbrae reach a critical separation around 3200 +/- 200 km. We
present a descriptive model in which the reconnected magnetic fields
block vertical transport of convective heat flux just beneath the
photosphere. We observe the formation of an unusual type of penumbra
adjacent to the f-polarity portion of this delta-spot just before
its disruption. A tangential penumbral band grows out of disordered
matter connected to the f-umbra. We present this as evidence for the
extrusion of umbral magnetic flux by thermal plumes rising through a
loosely bound umbra.
Title: Irradiance Models Based on Solar Magnetic Fields
Authors: Harvey, K. L.
Bibcode: 1994svsp.coll..217H
Altcode: 1994IAUCo.143P.217H
No abstract at ADS
Title: Slowly-Varying Microwave Emissions from the Solar Corona
Authors: Tapping, K. F.; Harvey, K. L.
Bibcode: 1994svsp.coll..181T
Altcode: 1994IAUCo.143P.181T
No abstract at ADS
Title: Non-Uniform Spatial Distribution of X-Ray Bright Points
Authors: Takami, M.; Tsuneta, S.; Takahashi, Te.; Strong, K. T.;
Slater, G. L.; Harvey, K. L.
Bibcode: 1994xspy.conf..237T
Altcode:
No abstract at ADS
Title: Coronal Eruptions Observed by YOHKOH
Authors: Klimchuk, J. A.; Acton, L. W.; Harvey, K. L.; Hudson, H. S.;
Kluge, K. L.; Sime, D. G.; Strong, K. T.; Watanabe, Ta.
Bibcode: 1994xspy.conf..181K
Altcode:
No abstract at ADS
Title: Patterns in the solar magnetic field (Invited Review)
Authors: Zwaan, C.; Harvey, K. L.
Bibcode: 1994smf..conf...27Z
Altcode:
No abstract at ADS
Title: Are X-Ray Bright Points the Signature of Magnetic Field
Reconnection?
Authors: Harvey, Karen L.; Strong, Keith S.; Nitta, Nariaki; Tsuneta,
Saku
Bibcode: 1994ASPC...68..377H
Altcode: 1994sare.conf..377H
No abstract at ADS
Title: Eruptive-Prominence Related Coronal Disturbances Observed
with YOHKOH SXT
Authors: Watanabe, T.; Kozuka, Y.; Ohyama, M.; Kojima, M.; Yamaguchi,
K.; Watari, S.; Tsuneta, S.; Joselyn, J. A.; Harvey, K. L.; Acton,
L. W.; Klimchuk, J. A.
Bibcode: 1994step.conf...85W
Altcode:
No abstract at ADS
Title: The solar magnetic cycle
Authors: Harvey, K. L.
Bibcode: 1994ASIC..433..347H
Altcode:
No abstract at ADS
Title: Observations of Dynamic Events in He I lambda 10830
Authors: Harvey, K. L.
Bibcode: 1994IAUS..154...71H
Altcode:
No abstract at ADS
Title: The Relationship of X-Ray Bright Points to the Photospheric
Magnetic Fields
Authors: Harvey, K. L.; Nitta, N.; Strong, K. T.; Tsuneta, S.
Bibcode: 1994xspy.conf...21H
Altcode:
No abstract at ADS
Title: Coronal/Interplanetary Disturbances Associated with a Solar
Filament Disappearance on September 28, 1991
Authors: Watanabe, T.; Kozuka, Y.; Ohyama, M.; Kojima, M.; Yamaguchi,
K.; Watari, S.; Tsuneta, S.; Joselyn, J. A.; Harvey, K. L.; Acton,
L. W.; Klimchuk, J. A.
Bibcode: 1994step.conf...89W
Altcode:
No abstract at ADS
Title: Properties and Emergence Patterns of Bipolar Active Regions -
Part One
Authors: Harvey, Karen L.; Zwaan, Cornelis
Bibcode: 1993SoPh..148...85H
Altcode:
Patterns in the properties of bipolar active regions are determined
throughout Cycle 21. Active regions that emerged on the visible
hemisphere were identified on NSO/KP full-disk magnetograms during 29
solar rotations selected from 1975 through 1986. The bipolar active
regions are included only once in this sampling; their properties
are derived at the time of maximum development. In order to study
an unbiased sample over the entire range of areas larger than 2.5
square degrees (or 373 Mm2), their counts are corrected for
size-dependent effects that reduce the chance of their identifications.
Title: Lifetimes and distribution of coronal bright points observed
with Yohkoh
Authors: Harvey, K. L.; Strong, K. T.; Nitta, N.; Tsuneta, S.
Bibcode: 1993AdSpR..13i..27H
Altcode: 1993AdSpR..13...27H
X-ray imaging from Skylab and various sounding rockets has established
the existence of and begun the characterization of coronal X-ray bright
points (XBPs). With the launch of Yohkoh, the Soft X-ray Telescope (SXT)
provides a new opportunity to observe these small-scale structures
with higher temporal resolution, improved dynamic range, and greater
sensitivity. We present the results from the analysis of SXT full-disk
images showing the location and detailed evolution of XBPs. We derive
correlations of XBPs with magnetic bipoles, He I 10830-Å dark points,
and other coronal features. From the evolution of 518 XBPs presented in
this initial study, we derive a mean lifetime of about 12 hours, with
some XBPs lasting as long as 5 days and others less than 10 minutes. A
comprehensive study of the relationship between XBP lifetime, X-ray
output, size, location, and variability may well lead to a re-evaluation
of the nature and definition of XBPs.
Title: Meter-Wave Radio Emission from Flaring X-ray Bright Points
Authors: Kundu, M. R.; Strong, K. T.; Pick, M.; Kane, S. R.; Harvey,
K.; White, S. M.
Bibcode: 1993BAAS...25.1180K
Altcode:
No abstract at ADS
Title: The Relationship of X-ray Bright Points to the Photospheric
Magnetic Fields
Authors: Harvey, K. L.; Strong, K.; Nitta, N.; Tsuneta, S.
Bibcode: 1993BAAS...25.1179H
Altcode:
No abstract at ADS
Title: The Dynamics of Coronal Holes as Determined From X-ray Synoptic
Maps Derived From SXT Imagery
Authors: Slater, G. L.; Linford, G. A.; Strong, K. T.; Acton, L. W.;
Tsuneta, S.; Hara, H.; Takahashi, T.; Hiei, H.; Kubo, M.; Harvey,
K.; Bornmann, P.; McIntosh, P. S.; Sime, D.; Watari, S.
Bibcode: 1993BAAS...25.1179S
Altcode:
No abstract at ADS
Title: The Formation and Break-up of a Simple Delta-type Sunspot
Authors: Gaizauskas, V.; Harvey, K. L.; Proulx, M.
Bibcode: 1993BAAS...25.1220G
Altcode:
No abstract at ADS
Title: Properties of Emerging Bipolar Active Regions
Authors: Harvey, K. L.
Bibcode: 1993ASPC...46..488H
Altcode: 1993mvfs.conf..488H; 1993IAUCo.141..488H
No abstract at ADS
Title: Magnetic bipoles on the Sun
Authors: Harvey, Karen Lorraine
Bibcode: 1993PhDT.......241H
Altcode:
No abstract at ADS
Title: Pre-Flare Conditions in Delta-Type Sunspots
Authors: Gaizauskas, V.; Harvey, K.; Proulx, M.
Bibcode: 1993stp2.conf..147G
Altcode:
No abstract at ADS
Title: Magnetic Bipoles on the Sun
Authors: Harvey, K. L.
Bibcode: 1993PhDT.......225H
Altcode:
No abstract at ADS
Title: Solar magnetic cycle
Authors: Harvey, Karen L.
Bibcode: 1993STIN...9425275H
Altcode:
Using NSO/KP magnetograms, the pattern and rate of the emergence
of magnetic flux and the development of the large-scale patterns
of unipolar fields are considered in terms of the solar magnetic
cycle. Magnetic flux emerges in active regions at an average rate of 2
x 1021 Mx/day, approximately 10 times the estimated rate in
ephemeral regions. Observations are presented that demonstrate that the
large-scale unipolar fields originate in active regions and activity
nests. For cycle 21, the net contribution of ephemeral regions to the
axial dipole moment of the Sun is positive, and is of opposite sign
to that of active regions. Its amplitude is smaller by a factor of 6,
assuming an average lifetime of ephemeral regions of 8 hours. Active
regions larger than 4500 Mm2 are the primary contributor
to the cycle variation of Sun's axial dipole moment.
Title: SOURCE: The Solar Ultraviolet Radiation and Correlative
Emissions Mission
Authors: Smith, P. L.; Lean, J. L.; Christensen, A. B.; Harvey, K. L.;
Judge, D. L.; Moore, R. L.; Torr, M. R.; Woods, T. N.
Bibcode: 1993Metro..30..275S
Altcode:
The Solar Ultraviolet Radiation and Correlative Emissions (SOURCE)
mission is intended to advance our ability to specify the spectral
irradiance of the Sun in the extreme ultraviolet (EUV) wavelength
range through simultaneous, radiometrically accurate measurements of
the solar EUV spectral irradiance and measurements, including EUV and
visible images, of solar parameters that are correlated with the EUV
flux. The data will be used in combination with empirical modelling
to develop and validate a more accurate system of proxy, or surrogate,
indices for the solar EUV flux.
Title: Correlation between X-ray Temporal Variability and Magnetic
Environment in Solar Flares
Authors: Nitta, N.; Harvey, K.; Hudson, H.; Ichimoto, K.; Metcalf,
T.; Mickey, D.; Sakai, J. -I.; Sakao, T.; Sakurai, T.; Takahashi, M.
Bibcode: 1992AAS...181.5503N
Altcode: 1992BAAS...24.1211N
The X-ray time history of a solar flare can reflect basic processes of
heating and/or acceleration, which in turn may depend on the magnetic
environment of the site. Some flares show a simple rise and fall
temporal behavior, whereas others show more than one peak. Comparisons
of images taken by the Soft X-ray Telescope (SXT) aboard the Yohkoh
spacecraft with ground-based magnetic data (Hawaii, Kitt Peak and
Mitaka) reveal that, at least for a flare-productive active region
(NOAA 7260), flares with double-peaked and single-peaked time profiles
occurred at systematically different locations within the region. We
discuss this result in terms of theoretical models, especially those
of coalescence of two current loops.
Title: Large-scale velocity fields and small-scale magnetic fields
during the maximum of solar cycle 22
Authors: Martin, Sara F.; Harvey, K. L.
Bibcode: 1992cait.rept.....M
Altcode:
One key accomplishment from the research during FY 1991 was the finding
by K. Harvey and P. Foukal that the photospheric network is the third
significant component that accounts for observed variations in the
total solar irradiance (the first previously recognized component is
the temporary decreases due to sunspots and the second is variation
due to plage brightness). Other key accomplishments were the K. Harvey
results from studying magnetic flux over the solar cycle: (1) increases
in the total magnetic flux by a factor of 4 to 5 from solar minimum to
solar maximum with the variation from active regions flux (greater than
25 Gauss) by more than a factor of 20 from cycle minimum to maximum
while the variation from quiet sun fields (less than 25 Gauss) was
no more than a factor of 2; (2) interpretation of (1) as meaning that
more than 70 percent of the magnetic flux in active regions disappears
without dispersing; (3) slower decreases of weak fields in phase with
the decrease in strong fields; and (4) irregular pulses of new flux
which appear to be primarily associated with active region complexes.
Title: Observations of the Variability of Coronal Bright Points by
the Soft X-Ray Telescope on YOHKOH
Authors: Strong, Keith T.; Harvey, Karen; Hirayama, Tadashi; Nitta,
Nariaki; Shimizu, Toshifumi; Tsuneta, Saku
Bibcode: 1992PASJ...44L.161S
Altcode:
We present the initial results of a study of X-ray bright points (XBPs)
made with data from the Yohkoh Soft X-ray Telescope. High temporal
and spatial resolution observations of several XBPs illustrate their
intensity variability over a wide variety of time scales from a few
minutes to hours as well as rapid changes in their morphology. Several
XBPs produced flares during their lifetime. These XBP flares often
involve magnetic loops, which are considerably larger than the XBP
itself, and which brighten along their lengths at speeds of up to 1100
km s(-1) . We speculate on the origin of the XBP variability and flares.
Title: Coronal/Interplanetary Disturbances Associated with
Disappearing Solar Filaments
Authors: Watanabe, Takashi; Kozuka, Yukio; Ohyama, Masamitsu; Kojima,
Masayoshi; Yamaguchi, Kisuke; Watari, Shin-Ichi; Tsuneta, Saku;
Joselyn, Jo A.; Harvey, Karen L.; Acton, Loren W.; Klimchuk, James. A.
Bibcode: 1992PASJ...44L.199W
Altcode:
We discuss two examples of coronal/interplanetary disturbances
associated with the disappearance of a 35(deg) long quiescent filament
occurring near the solar disk center on 1991 September 28 (McAllister
et al. 1992, Publ. Astron. Soc. Japan, 44, L205) and with a 25(deg)
long eruptive prominence at the eastern solar limb taking place on
1991 November 7. Bright soft X-ray arcades were observed for both
cases with the Yohkoh SXT, about 2--3 hr after the onset of each
Hα event. For the erupting prominence on November 7, the arcade
did not appear before the prominence reached a height of about 0.3
solar radii above the limb. This suggests that magnetic reconnection
occurred below the relevant Hα structures. A transient coronal hole
was formed in the immediate vicinity of the disappearing filament on
September 28. Formation of the new coronal hole is suggested to be a
cause of the filament disappearance. An interplanetary disturbance was
detected by radio scintillation (IPS) observations immediately after
the filament disappeared.
Title: Simultaneous Observations of Coronal Bright Points in X-Ray
and Radio Wavelengths
Authors: Nitta, Nariaki; Bastian, Timothy S.; Aschwanden, Markus J.;
Harvey, Karen L.; Strong, Keith T.
Bibcode: 1992PASJ...44L.167N
Altcode:
We present a first explicit comparison of coronal bright points in
soft X-ray and radio wavelengths, using the Soft X-ray Telescope
aboard the Yohkoh spacecraft and the Very Large Array. About half of
the 33 compact sources indentified in a 20-cm full-disk map appear
as X-ray bright points in the X-ray data. The other half apparently
corresponds to unipolar regions with enhanced magnetic fields. Thus,
the identification of radio bright points alone cannot reliably serve
as a proxy for X-ray bright points. A preliminary analysis reveals that
bright points commonly observed at 20 cm and in X-rays have temperatures
of (1.4--2.9) times 10(6) K and emission measures of (0.4--2.5) times
10(45) cm(-3) . The observed brightness temperatures at 20 cm [(1--2.5)
times 10(5) K] can be explained in terms of optically thin free-free
emission from a plasma with these parameters.
Title: Global Restructuring of the Coronal Magnetic Fields Observed
with the YOHKOH Soft X-Ray Telescope
Authors: Tsuneta, Saku; Takahashi, Tetsuo; Acton, Loren W.; Bruner,
Marilyn E.; Harvey, Karen L.; Ogawara, Yoshiaki
Bibcode: 1992PASJ...44L.211T
Altcode:
We present an example of the large-scale ``restructuring" of a polar
coronal magnetic structure taking place over a time period of 20
hr. A large-scale closed-loop arcade appears to be created from an
open field structure formed in association with the disappearance of a
polar crown filament. The loops increase their height with time. The
loop formation propagates westward, and a cusp structure, inside
of which is bright in X-rays, is seen on the west limb. This global
structural change of the coronal magnetic field appears to take place
only through a non-explosive, quasi-steady magnetic reconnection. The
Yohkoh soft X-ray images show that the solar corona is full of such
global restructuring, suggesting that magnetic reconnection is a
primary device for the general coronal magnetic evolution.
Title: Measurements of Solar Magnetic Fields as an Indicator of
Solar Activity Evolution
Authors: Harvey, K. L.
Bibcode: 1992sers.conf..113H
Altcode:
No abstract at ADS
Title: Study of Flare Productive Active Regions
Authors: Nitta, N.; Harvey, K. L.; Shibata, K.; Strong, K. T.
Bibcode: 1992AAS...180.1807N
Altcode: 1992BAAS...24..755N
The Soft X-ray Telescope (SXT) on the Yohkoh spacecraft has made it
possible for us for the first time to monitor the evolution of active
regions in soft X-rays with a good cadence and spatial resolution
over an extended period of time. One of our interests is what makes
an active region produce large flares. Since the SXT started its
operation, we have identified more than 40 active regions that have
produced flares whose GOES class are > M1. Although many such active
regions appear active when they first become visible on the eastern
limb, we have succeeded in observing some of them from their birth
through activation. We compare X-ray images taken from the SXT with
magnetograms and other groundbased data. We discuss similarities and
differences of such regions from other more quiet regions in terms of
morphology and physical parameters.
Title: X-ray Bright Point Flares Observed by YOHKOH
Authors: Harvey, K. L.; Strong, K.; Nitta, N.; Tsuneta, S.; Shimizu, T.
Bibcode: 1992AAS...180.1806H
Altcode: 1992BAAS...24..755H
X-ray images taken by the Soft X-Ray Telescope (SXT) on board the
Japanese Satellite Yohkoh are being used to study the characteristics
and variability of X-ray bright points and their relation to
the underlying photospheric magnetic field and chromospheric
structures. Though during this maximum phase of Cycle 22 there are few
X-ray bright points at any given time, more than a thousand have been
observed since Yohkoh began its observation in September 1991. Many of
these bright points flare; in many cases, these small-scale flares are
associated with with observed effects detected spanning substantial
distances away from the flaring bright point. This paper will report
on an investigation of the dynamics of the flares in these small-scale
coronal structures. Events will be discussed that show their complexity
and their relation to the large-scale coronal magnetic fields as
identified by coronal structures observed in X-rays.
Title: The Solar Cycle
Authors: Harvey, Karen L.
Bibcode: 1992ASPC...27.....H
Altcode: 1992socy.work.....H
In order to fully understand and model the solar cycle, several
fundamental questions needed to be resolved. The connection of the
surface manifestations of activity with the driving cycle mechanism
in the Sun's interior is not established until now.
Title: The Cyclic Behavior of Solar Activity
Authors: Harvey, Karen L.
Bibcode: 1992ASPC...27..335H
Altcode: 1992socy.work..335H
No abstract at ADS
Title: Do Changes in the Photospheric Magnetic Network Cause the 11
Year Variation of Total Solar Irradiance?
Authors: Foukal, P.; Harvey, K.; Hill, F.
Bibcode: 1991ApJ...383L..89F
Altcode:
Changes in the area of the photospheric magnetic network over the
sunspot cycle have been put forward as the 'missing component'
required to explain the 11-yr variation of total solar irradiance
observed by space-borne radiometers. It is shown that this explanation
is consistent with recent measurements of the photometric contrast of
magnetic faculae and with the present measurement of the network area
change during cycle 21.
Title: Filament disappearances and associated shocks of May 1979
Authors: Cane, H. V.; Richardson, I. G.; Harvey, K.
Bibcode: 1991JGR....9619525C
Altcode:
In late May 1979 a shock was seen at each of two locations separated by
about 90° in heliolongitude and at about the same time. A shock was
detected near the Earth, and a shock was detected at Helios 1 when it
was off the Sun's west limb. Some authors have considered that these
shocks were part of the same event, which originated with a filament
dispperance near 65°W. We discuss the observations which show that
a large complex filament, extending from 20°W to 70°W, disappeared
in several places, probably generated more than one shock. The shock
detected near Earth was probably associated with a filament section
which disappeared near the central meridian. If this is the case, then
the interplanetary scintillation observations of this time period can
be explained without invoking highly anisotropic shock propagation.
Title: Dark Points and Microflares Observed in the He I λ10830 Line
and Their Relation to the Quiet Sun Magnetic Fields
Authors: Harvey, K. L.
Bibcode: 1991BAAS...23Q1053H
Altcode:
No abstract at ADS
Title: On the Role of the Photospheric Magnetic Network in the
11-Year Variation of Total Solar Irradiance
Authors: Harvey, K. L.; Foukal, P. V.
Bibcode: 1991BAAS...23.1068H
Altcode:
No abstract at ADS
Title: The Scale Sizes of CMEs and Associated Surface Activity
Authors: Webb, D. F.; Harvey, K. L.; Cliver, E. W.; Kahler, S. W.
Bibcode: 1991BAAS...23.1062W
Altcode:
No abstract at ADS
Title: Microflares Observed in He I 10830 and Their Relation to the
Quiet Sun Magnetic Fields
Authors: Harvey, Karen L.
Bibcode: 1991LNP...387...62H
Altcode: 1991fpsa.conf...62H
The preliminary results of this study of three microflares are:
(1) The size scale of the He I 10830 microflares ranges from 8 to 25
arc-seconds and time scales of between 9 to 40 minutes; (2) He I 10830
microflares are accompanied by increased brightening in H and sometimes
20 cm emission; (3) Ejecta, such as filament eruptions or surges,
often occur in association with these events; (4) Microflares occur
at sites where opposite polarities are interacting, specifically at
the sites of magnetic flux cancellation; (5) Since microflares occur
only during a fraction of the time of the magnetic field interaction,
it is suggested that microflares (and dark points) result from local
magnetic field reconnection; (6) In all the events studied, H fibrils
or filaments connect the magnetic elements of opposite polarity that
are cancelling. In one instance, reconnection of the magnetic fields
of an ephemeral region with the nearby opposite polarity network begins
almost immediately after it has emerged.
Title: The solar activity cycle.
Authors: Rabin, Douglas M.; DeVore, C. R.; Sheeley, Neil R., Jr.;
Harvey, Karen L.; Hoeksema, J. T.
Bibcode: 1991sia..book..781R
Altcode:
Study of the solar cycle is entering a new era dominated by objective,
precise measurements of magnetic, velocity and radiation fields over the
surface of the Sun. This review emphasizes observations of photospheric
magnetic flux during cycle 21 (1976 - 1986) and how these measurements
have been used to model the cyclic variability of the heliospheric
magnetic field. Indices of solar activity are discussed in terms of
their potential to figure in theoretical or empirical models. Other
recent data, such as measurements of large-scale surface flows and
information on the Sun's internal rotation from helioseismology, as
well as the magnetic flux observations, are considered in the context
of Babcock's phenomenological model of the solar cycle: can this model
still serve? Is there anything better to replace it?
Title: Analysis of a 116 Year Record of Sunspot Positions and Sizes
Authors: Hathaway, D. H.; Harvey, K. L.
Bibcode: 1990BAAS...22..873H
Altcode:
No abstract at ADS
Title: Disintegration of Colliding Sunspots
Authors: Harvey, K. L.; Gaizauskas, V.
Bibcode: 1990BAAS...22Q.840H
Altcode:
No abstract at ADS
Title: The 10.7 cm flux and solar magnetic activity.
Authors: Harvey, K. L.; Trapping, K. F.
Bibcode: 1989JRASC..83Q.312H
Altcode:
No abstract at ADS
Title: X-ray bright points and He i λ 10830 dark points
Authors: Golub, L.; Harvey, K. L.; Herant, M.; Webb, D. F.
Bibcode: 1989SoPh..124..211G
Altcode:
Using near-simultaneous full disk solar X-ray images and HeI λ10830
spectroheliograms from three rocket flights, we compare dark points
identified on the HeI maps with X-ray bright points identified on the
X-ray images. We find that for the largest and most obvious features
there is a strong correlation: most HeI dark points correspond to
X-ray bright points. However, about two-thirds of the X-ray bright
points were not identified on the basis of the helium data alone. Once
an X-ray feature is identified it is almost always possible to find
an underlying dark patch of enhanced HeI absorption which, however,
would not a priori have been selected as a dark point. Therefore, the
HeI dark points, using current selection criteria, cannot be used as
a one-to-one proxy for the X-ray data. HeI dark points do, however,
identify the locations of the stronger X-ray bright points.
Title: The Distribution of Solar Magnetic Fluxes and the Nonlinearity
of Stellar Flux-Flux Relations
Authors: Schrijver, C. J.; Harvey, K. L.
Bibcode: 1989ApJ...343..481S
Altcode:
Synoptic maps for the 1975-1984 period are used to determine the
time-dependent distribution function of magnetic flux densities
in the solar atmosphere. The distribution function depends only
on the global level of magnetic activity, and it is used to study
how relations between magnetic flux densities and radiative flux
densities from different temperature regimes in the outer atmosphere
(derived from spatially resolved solar observations) transform into
relations between surface-averaged flux densities. It is found that
the transformation to surface-averaged fluxes preserves the power-law
character of relations between radiative and magnetic flux densities
for spatially resolved data.
Title: X-ray bright points and He I lambda 10830 dark points
Authors: Golub, L.; Harvey, K. L.; Herant, M.; Webb, D. F.
Bibcode: 1989sxsr.rept.....G
Altcode:
Using near-simultaneous full disk Solar X-ray images and He I 10830
lambda, spectroheliograms from three recent rocket flights, dark
points identified on the He I maps were compared with X-ray bright
points identified on the X-ray images. It was found that for the
largest and most obvious features there is a strong correlation:
most He I dark points correspond to X-ray bright points. However,
about 2/3 of the X-ray bright points were not identified on the basis
of the helium data alone. Once an X-ray feature is identified it is
almost always possible to find an underlying dark patch of enhanced He
I absorption which, however, would not a priori have been selected as
a dark point. Therefore, the He I dark points, using current selection
criteria, cannot be used as a one-to-one proxy for the X-ray data. He I
dark points do, however, identify the locations of the stronger X-ray
bright points.
Title: The Solar Cycle Behavior of Small Active Regions
Authors: Harvey, K. L.
Bibcode: 1989BAAS...21Q.839H
Altcode:
No abstract at ADS
Title: Granulation Bibliography
Authors: Harvey, K. L.
Bibcode: 1989ASIC..263..623H
Altcode: 1989ssg..conf..623H
No abstract at ADS
Title: SYSTEMATIC OBSERVATIONS OF THE SUN (In honour of Helen Dodson
Prince): Observations
Authors: McIntosh, P.; Snodgrass, H.; Mouradian, Z.; Harvey, K.;
Altrock, R.; Simon, P.; Legrand, J. -P.; Alissandrakis, G.; Neckel,
H.; Petropoulos, P.; Poulakis, X.; Gokhale, M. H.; Sivaraman, K. R.;
Pap, J.
Bibcode: 1989HiA.....8..672M
Altcode:
No abstract at ADS
Title: The extended solar activity cycle
Authors: Wilson, P. R.; Altrocki, R. C.; Harvey, K. L.; Martin, S. F.;
Snodgrass, H. B.
Bibcode: 1988Natur.333..748W
Altcode:
The solar cycle has been defined in terms of a sequential periodic
variation in sunspot numbers, the period being the interval between
successive minima, currently averaging 11.2 years. But a number of
observations have indicated that the activity cycle may begin at
higher latitudes before the emergence of the first sunspots of the
new cycle. Here we report results from sunspot cycle 21 concerning
the ephemeral active regions, the coronal green-line emission and the
torsional oscillation signal, which confirm the earlier suggestions. In
particular, we report the appearance of a high-latitude population of
ephemeral active regions in the declin-ing phase of sunspot cycle 21,
with orientations that tend to favour those for cycle 22 rather than
21. Taken together, these data indicate that sunspot activity is simply
the main phase of a more extended cycle that begins at high latitudes
before the maximum of a given sunspot cycle and progresses towards
the equator during the next 18-22 yr, merging with the conventional
'butterfly diagram' (the plot of the latitudes of emerging sunspots
against time) as it enters sunspot latitudes. We suggest that this
extended cycle may be understood in the perspective of a model of
giant convective rolls that generate dynamo waves propagating from
pole to equator.
Title: Simultaneous Observations of 20 Centimeter Bright Points and
He i 10830 Angstrom Dark Points in the Quiet Sun
Authors: Habbal, Shadia R.; Harvey, Karen L.
Bibcode: 1988ApJ...326..988H
Altcode:
The authors present the results of the first simultaneous observations
of the quiet Sun made at the 20 cm radio wavelength and in the He
I λ10830 line. Simultaneous magnetic field measurements were also
obtained with lower time resolution during the five consecutive
hours of observations. In the 512arcsec×512arcsec common observing
field of view the authors find that the 20 cm radio emisison, which
originates from the low corona-transition region, is always associated
with regions of enhances He I absorption; yet, it does not always
coincide with strong He I λ10830 absorption regions known as He I
"dark points". The temporal changes of the 20 cm emission and the
underlying He I absorption are also studied.
Title: Dynamic Nature of coronal heating
Authors: Habbal, S. R.; Harvey, K. L.
Bibcode: 1988ASSL..143..215H
Altcode: 1988acse.conf..215H
The authors present the results of the first simultaneous observations
of the quiet sun made at 20 cm with the VLA and in He I 10830 Å,
together with the line of sight component of the photospheric magnetic
field. The nature of the correlation found between changes in He I dark
points and the 20 cm radio sources, as well as with the underlying
magnetic field, suggest that topological changes in the underlying
magnetic field are playing an important role in the transient coronal
heating process.
Title: Microflares in the Solar Magnetic Network
Authors: Porter, J. G.; Moore, R. L.; Reichmann, E. J.; Engvold, O.;
Harvey, K. L.
Bibcode: 1987ApJ...323..380P
Altcode:
It is suggested that the events observed by HRTS are microflares
in tiny magnetic bipoles (some in cell interiors but most in the
magnetic network) and that these same events, when strong enough
and frequent enough in some of the larger bipoles, sustain X-ray
bright points. In this paper, the authors present new evidence in
favor of this hypothesis. Using C IV spectroheliograms in combination
with magnetograms and He I λ10,830 spectroheliograms they find that
impulsive heating events of the class observed by HRTS are common at
small bipoles in the network, both at bipoles corresponding to X-ray
bright points and at many weaker bipoles that show no sustained enhanced
coronal brightness.
Title: Magnetic Fields on the Sun, Variation of Solar Cycle 21
Authors: Harvey, K. L.
Bibcode: 1987BAAS...19..924H
Altcode:
No abstract at ADS
Title: Magnetogram and soft X-ray comparisons of XBP and ER.
Authors: Golub, Leon; Harvey, Karen L.; Webb, David F.
Bibcode: 1986NASCP2442..365G
Altcode: 1986copp.nasa..365G
The potential importance of the smallest emerging flux regions on the
sun was discussed in numerous publications. The association between the
objects seen in ground-based data, such as high resolution magnetrons
or H alpha and soft X-ray data has produced results which are often
contradictory. In the hope of resolving the present impasse, as much
simultaneous soft X-ray and magnetogram data as possible were assembled
in order to clarify the situation. It was found that separation of
magnetic features into chance encounters and emerging flux makes some
difference in overlapp with X-ray bright points (XBPs), although the
effect is not overwhelming. The difference in solar cycle dependence
between XBP and ephemeral regions is not explainable in terms of
the results.
Title: Magnetic location of C IV events in the quiet network.
Authors: Porter, Jason G.; Reichmann, Ed J.; Moore, Ronald L.; Harvey,
Karen L.
Bibcode: 1986NASCP2442..383P
Altcode: 1986copp.nasa..383P
Ultraviolet Spectrograph and Polarimeter (UVSP) observations
of C IV intensity in the quiet sun were examined and compared
to magnetograms and He I 10830 A spectroheliograms from Kitt Peak
National Laboratory. The observations were made between 3 and 9 April,
1985. Spatially rastered UVSP intensity measurements were obtained at 11
wavelength positions in the 1548 A line of C IV. It was concluded that
the stochastic process whereby convective shuffling of loop footprints
leads to many topically dissipative events in active regions and the
larger bipoles treated here continues to operate in regions of fewer,
weaker flux loops, but the resulting events above threshold are less
frequent.
Title: Simultaneous observations of changes in coronal bright point
emissionat the 20 cm radio and He I λ10830 wavelengths.
Authors: Habbal, Shadia R.; Harvey, Karen L.
Bibcode: 1986NASCP2442..343H
Altcode: 1986copp.nasa..343H
Preliminary results of observations of solar coronal bright points
acquired simultaneously from ground based observatories at the radio
wavelength of 20 cm and in the He I wavelength 10830 line on September
8, 1985, are reported. The impetus for obtaining simultaneous radio and
optical data is to identify correlations, if any, in changes of the low
transition-coronal signatures of bright points with the evolution of
the magnetic field, and to distinguish between intermittent heating
and changes in the magnetic field topology. Although simultaneous
observations of H alpha emission and the photospheric magnetic field
at Big Bear were also made, as well as radio observations from Owen
Valley Radio Interferometer and Solar Maximum Mission (SSM) (O VIII
line), only the comparison between He 10830 and the Very Large Array
(VLA) radio data are presented.
Title: The association of chromospheric and coronal phenomena with
the evolution of the quiet sun magnetic fields.
Authors: Harvey, Karen L.; Tang, Frances; Gaizauskas, Victor
Bibcode: 1986NASCP2442..359H
Altcode: 1986copp.nasa..359H
Using daily full-disk magnetograms and He I 10830 spectroheliograms to
study the count and surface distribution of ephemeral regions over the
solar cycle, Harvey (1985) concluded that the small dark structures
seen in 10830, thought to correspond to X-ray bright points, were
more often associated with magnetic bipoles that appeared to result
from an encounter of already existing opposite polarity magentic flux
than with emerging small magnetic bipoles (ephemeral regions). Such
encounters would be more likely to occur in areas of mixed polarity. The
fractional area of the sun covered by mixed polarity fields varies
anti-correlated with the solar cycle leading to a possible explanation
for the 180 degrees out of phase solar cycle variation of X-ray bright
points. To establish the validity of this suggestion, a detailed study
of time-sequence magnetic field, He I wavelength 10830, Ha, C IV, and
Si II observations of selected areas of the quiet sun was initiated
about 2 years ago. The preliminary results of this study are reported.
Title: Simultaneous Observations of Coronal Bright Point Emission
at 20 cm Radio and He 10830 Å Wavelengths
Authors: Harvey, K. L.; Habbal, S. R.
Bibcode: 1986BAAS...18R.901H
Altcode:
No abstract at ADS
Title: Simultaneous Observations of the Quiet Sun at 90 and 20 cm
Radio and He 10830 Å Wavelengths
Authors: Habbal, S. R.; Gonzalez, R.; Harvey, K. L.
Bibcode: 1986BAAS...18..932H
Altcode:
No abstract at ADS
Title: Ephemeral active regions and coronal bright points: A solar
maximum Mission 2 guest investigator study
Authors: Harvey, K. L.; Tang, F. Y. C.; Gaizauskas, V.; Poland, A. I.
Bibcode: 1986gsfc.rept.....H
Altcode:
A dominate association of coronal bright points (as seen in He
wavelength 10830) was confirmed with the approach and subsequent
disappearance of opposite polarity magnetic network. While coronal
bright points do occur with ephemeral regions, this association is a
factor of 2 to 4 less than with sites of disappearing magnetic flux. The
intensity variations seen in He I wavelength 10830 are intermittent
and often rapid, varying over the 3 minute time resolution of the
data; their bright point counterparts in the C IV wavelength 1548
and 20 cm wavelength show similar, though not always coincident time
variations. Ejecta are associated with about 1/3 of the dark points and
are evident in the C IV and H alpha data. These results support the
idea that the anti-correlation of X-ray bright points with the solar
cycle can be explained by the correlation of these coronal emission
structures with sites of cancelling flux, indicating that, in some
cases, the process of magnetic flux removal results in the release of
energy. That the intensity variations are rapid and variable suggests
that this process works intermittently.
Title: Erratum - Numerical Simulations of Largescale Solar Magnetic
Fields
Authors: DeVore, C. R.; Sheeley, N. R., Jr.; Boris, J. P.; Young,
T. R., Jr.; Harvey, K. L.
Bibcode: 1986AuJPh..39..115D
Altcode:
No abstract at ADS
Title: Magnetic shear produced by colliding sunspots
Authors: Gaizauskas, V.; Harvey, K. L.
Bibcode: 1986AdSpR...6f..17G
Altcode: 1986AdSpR...6Q..17G
The leading and trailing sunspots of two adjacent active regions are
observed to collide as the evolving regions expand along the same
direction. During approximately four days of this collinear motion,
fibrils linking the colliding sunspots form a pattern suggestive
of a potential magnetic field. No flares can be associated with the
collision at this stage. Within a single day, and without an apparent
change in the direction of the spots, the pattern of fibrils changes
to a non-potential configuration. This onset of shear occurs rapidly
in the absence of grazing motions. Thereafter, one spot splits,
grazing motions develop, and shear is greatly enhanced along the line
of polarity inversion. Sustained subflare activity begins after the
onset of shear; stronger flares erupt as shear is enhanced. These
circumstances are consistent with concepts based on shear as an
essential ingredient of flares and which require critical levels of
shear to be exceeded in order to trigger flares.
Title: HE I 10830 Observations of Flare Generated Coronal Holes
Authors: Recely, F.; Harvey, K.
Bibcode: 1986stp..conf..204R
Altcode: 1986STP.....2..204R
No abstract at ADS
Title: HE I 10830 A Observations of Two-Ribbon Flare-Like Events
Associated with Filament Disappearances
Authors: Harvey, K.; Sheeley, N., Jr.; Harvey, J.
Bibcode: 1986stp..conf..198H
Altcode: 1986STP.....2..198H
No abstract at ADS
Title: Simulations of Magnetic-Flux Transport in Solar Active Regions
Authors: DeVore, C. R.; Sheeley, N. R., Jr.; Boris, J. P.; Young,
T. R., Jr.; Harvey, K. L.
Bibcode: 1985SoPh..102...41D
Altcode:
We simulate the evolution of several observed solar active regions by
solving a transport equation for magnetic flux at the photosphere. The
rates of rotation, meridional flow, and diffusion of the flux are
determined self-consistently in the calculations. Our findings
are in good quantitative agreement with previous measures of the
rotation rate and diffusion constant associated with photospheric
magnetic fields. Although our meridional velocities are consistent
in direction and magnitude with recently reported poleward flows,
relatively large uncertainties in our velocity determinations make
this result inconclusive.
Title: Acknowledgment
Authors: Harvey, Karen L.
Bibcode: 1985SoPh..101D...5H
Altcode:
No abstract at ADS
Title: Associations of Compact C IV Events, He I 10830 A Dark Points,
and Magnetic Structures
Authors: Porter, J. G.; Reichmann, E. J.; Moore, R. L.; Harvey, K. L.
Bibcode: 1985BAAS...17..842P
Altcode:
No abstract at ADS
Title: The Association of He I λ10830 'Dark Points' and the Evolution
of the Quiet Sun Magnetic Fields
Authors: Harvey, K. L.; Tang, F.; Gaizauskas, V.
Bibcode: 1985BAAS...17..632H
Altcode:
No abstract at ADS
Title: Sunspots in Collision
Authors: Gaizauskas, V.; Harvey, K. L.
Bibcode: 1985BAAS...17..632G
Altcode:
No abstract at ADS
Title: The relationship between coronal bright points as seen in
He I Lambda 10830 and the evolution of the photospheric network
magnetic fields
Authors: Harvey, K. L.
Bibcode: 1985AuJPh..38..875H
Altcode:
Transient 'dark points' in He I λ10830 are found to be associated
with small magnetic bipoles. The number of these dark points varies
inversely with the sunspot number. Sampled over a solar cycle, about
one-third of the dark points are associated with erupting magnetic flux
(ephemeral regions) while the other two-thirds are associated with
chance encounters of opposite magnetic polarity features. Since coronal
bright points are associated with He I dark points, it is suggested
that the inverse correlation of both of these events with the sunspot
number results from the higher probability of chance encounters between
magnetic network of opposite polarity (larger areas of mixed magnetic
polarity) during low levels of solar activity.
Title: Numerical simulations of large-scale solar magnetic fields
Authors: DeVore, C. R.; Boris, J. P.; Young, T. R., Jr.; Sheeley,
N. R.; Harvey, K. L.
Bibcode: 1985AuJPh..38..999D
Altcode:
The authors have solved numerically a transport equation which describes
the evolution of the large-scale magnetic field of the Sun. Data
derived from solar magnetic observations are used to initialize the
computations and to account for the emergence of new magnetic flux
during the sunspot cycle. The authors' objective is to assess the
ability of the model to reproduce the observed evolution of the field
patterns. They discuss recent results from simulations of individual
active regions over a few solar rotations and of the magnetic field
of the Sun over sunspot cycle 21.
Title: Solar cycle variation of ephemeral regions
Authors: Harvey, K. L.
Bibcode: 1984noaa.rept.....H
Altcode:
Ephemeral active regions (ER) have been identified and counted for
selected periods from 1970 to mid-1984 using the daily, full-disk
photospheric magnetograms taken by the National Solar Observatory. The
number of ephemeral regions varies nearly in phase with the solar
cycle. At solar minimum, ER are distributed almost uniformly in
latitude; by solar maximum, peaks in the latitude distribution are
observed in the sunspot zones and in higher latitude bands. In the
quiet sun, 37% of the He I lambda 10830 dark points, used as a proxy
for X-ray bright points (XBP), are associated with ER; 63% overlie
bipoles that appear to be the chance encounter of opposite polarity
network. The percentages are somewhat different in coronal holes;
21% of the dark points in He I are associated with ephemeral regions
and 79% with bipoles that apparently result from chance encounters of
flux. The dark points observed in the quiet sun and in coronal holes,
vary anti-correlated with the solar cycle. Little relations was found
between the areal density of He I dark points and ephemeral regions
within the boundaries of coronal holes and parameters of the high
speed solar wind streams associated with coronal holes. This study
suggests that (1) ephemeral regions are not small active regions and
that they may be primarily a surface phenomena, possibly resulting
from convection interacting with sub-photospheric fields, and (2) He
I dark points, and therefore, XBP, are more often associated with the
encounter of existing opposite polarity network flux, the occurrence
of which is related to the amount of mixed polarity areas which varies
inversely with the solar cycle.
Title: Solar cycle variation of ephemeral active regions.
Authors: Harvey, K. L.
Bibcode: 1984ESASP.220..235H
Altcode: 1984ESPM....4..235H
Ephemeral active regions (ER) have been identified and counted for
selected periods from 1970 to mid-1984 using the daily, full-disk
photospheric magnetograms taken by the National Solar Observatory. The
number of ER varies in phase with the solar cycle.
Title: Sunspots in Collision
Authors: Gaizauskas, V.; Harvey, K. L.
Bibcode: 1984BAAS...16..928G
Altcode:
No abstract at ADS
Title: Coronal Mass Ejections and Sudden Filament Disappearances
Authors: Sheeley, N. R., Jr.; Howard, R. A.; Harvey, K. L.
Bibcode: 1984BAAS...16..930S
Altcode:
No abstract at ADS
Title: He I 10830 observations of the 3N/M4.0 flare of 4 September,
1982
Authors: Harvey, K. L.; Recely, F.
Bibcode: 1984SoPh...91..127H
Altcode:
HeI 10830 Å spectroheliograms of a major 3N two-ribbon flare occurring
in Boulder Region 3885/3886 early on 4 September, 1982 are discussed
and compared with Hα and soft X-ray observations of the event. This
flare, observed for more than 60 hr in HeI 10830, was associated
with the eruption of a large filament in the active region complex,
the formation of coronal holes, a long-duration soft X-ray event,
and was the probable source of a earthward coronal mass ejection and
the largest geomagnetic storm of this solar cycle. The results of this
study suggest the HeI flare is a chromospheric manifestation of the
X-ray coronal loop structures associated with flares.
Title: Ephemeral Active Regions and Coronal Bright Points
Authors: Harvey, K. L.; Tang, F.
Bibcode: 1984BAAS...16Q.534H
Altcode:
No abstract at ADS
Title: Relationships of a growing magnetic flux region to flares
Authors: Martin, S. F.; Bentley, R. D.; Schadee, A.; Antalova, A.;
Kucera, A.; Dezső, L.; Gesztelyi, L.; Harvey, K. L.; Jones, H.;
Livi, S. H. B.; Wang, J.
Bibcode: 1984AdSpR...4g..61M
Altcode: 1984AdSpR...4...61M
Some sites for solar flares are known to develop where new magnetic
flux emerges and becomes abutted against opposite polarity pre-existing
magnetic flux (review by Galzauskas/1/). We have identified and analyzed
the evolution of such flare sites at the boundaries of a major new and
growing magnetic flux region within a complex of active regions, Hale
No. 16918. This analysis was done as a part of a continuing study of the
circumstances associated with flares in Hale Region 16918, which was
designated as an FBS target during the interval 18 - 23 June 1980. We
studied the initiation and development of both major and minor flares in
Hα images in relation to the identified potential flare sites at the
boundaries of the growing flux region and to the general development
of the new flux. This study lead to our recognition of a spectrum of
possible relationships of growing flux regions to flares as follows:
(1) intimate interaction with adjacent old flux - flare sites centered
at new/old flux boundary, (2) forced or ``intimidated'' interaction
in which new flux pushes old field having lower flux density towards a
neighboring old polarity inversion line where a flare then takes place,
(3) ``influential'' interaction - magnetic lines of force over an old
polarity inversion line, typically containing a filament, reconnect to
the new emerging flux; a flare occurs with erupting filament when the
magnetic field overlying the filament becomes too weak to prevent its
eruption, (4) inconsequential interaction - new flux region is too small
or has wrong orientation for creating flare conditions, (5) incidental -
flare occurs without any significant relationship to new flux regions.
Title: Patterns of the Sun
Authors: Gaizauskas, V.; Harvey, K. L.; Harvey, J. W.; Zwaan, C.
Bibcode: 1983S&T....66..291G
Altcode:
No abstract at ADS
Title: Meridional Flows and Magnetic Flux Transport on the Sun
Authors: Boris, J. P.; Sheeley, N. R., Jr.; Young, T. R., Jr.; DeVore,
C. R.; Harvey, K. L.
Bibcode: 1983BAAS...15R.701B
Altcode:
No abstract at ADS
Title: Observations of Major Flares in He I 10830
Authors: Harvey, K. L.; Recely, F.; Sheeley, N. R., Jr.; Howard,
R. A.; Koomen, M. J.; Michels, D. J.
Bibcode: 1983BAAS...15..712H
Altcode:
No abstract at ADS
Title: Large-scale patterns formed by solar active regions during
the ascending phase of cycle 21
Authors: Gaizauskas, V.; Harvey, K. L.; Harvey, J. W.; Zwaan, C.
Bibcode: 1983ApJ...265.1056G
Altcode:
Synoptic maps of photospheric magnetic fields prepared at the Kitt Peak
National Observatory are used in investigating large-scale patterns
in the spatial and temporal distribution of solar active regions
for 27 solar rotations between 1977 and 1979. The active regions are
found to be distributed in 'complexes of activity' (Bumba and Howard,
1965). With the working definition of a complex of activity based
on continuity and proximity of the constituent active regions, the
phenomenology of complexes is explored. It is found that complexes of
activity form within one month and that they are typically maintained
for 3 to 6 solar rotations by fresh injections of magnetic flux. During
the active lifetime of a complex of activity, the total magnetic flux
in the complex remains steady to within a factor of 2. The magnetic
polarities are closely balanced, and each complex rotates about the
sun at its own special, constant rate. In certain cases, the complexes
form two diverging branches.
Title: A quantitative study of magnetic flux transport on the Sun
Authors: Sheeley, N. R., Jr.; Boris, J. P.; Young, T. R., Jr.; DeVore,
C. R.; Harvey, K. L.
Bibcode: 1983IAUS..102....2S
Altcode:
A computational model, based on diffusion, differential rotation,
and meridional flow, has been developed to simulate the transport
of magnetic flux on the Sun. Using Kitt Peak magnetograms as input,
as have determined a best-fit diffusion constant by comparing the
computed and observed fields at later times. This paper presents
the initial results of a project to simulate the transport of solar
magnetic flux using diffusion, differential rotation, and meridional
flow. The study concerns the evolution of large-scale fields on a time
scale of weeks of years, and ignores the rapid changes that accompany
the emergence of new magnetic regions and the day-to-day changes of
the supergranular network itself.
Title: A Quantitative Study of Magnetic Flux Transport on the Sun
Authors: Sheeley, N. R., Jr.; Boris, J. P.; Young, T. R., Jr.; DeVore,
C. R.; Harvey, K. L.
Bibcode: 1983IAUS..102..273S
Altcode:
A computational model, based on diffusion, differential rotation, and
meridional circulation, has been developed to simulate the transport
of magnetic flux on the Sun. Using Kitt Peak magnetograms as input,
the authors have determined a best-fit diffusion constant by comparing
the computed and observed fields at later times. The results suggest
that diffusion may be fast enough to account for the observed polar
magnetic field reversal without requiring a significant assist from
meridional currents.
Title: A Model for the Evolution of Large-Scale Magnetic Fields in
the Solar Photosphere
Authors: DeVore, C. R.; Boris, J. P.; Young, T. R., Jr.; Sheeley,
N. R., Jr.; Harvey, K. L.
Bibcode: 1982BAAS...14..978D
Altcode:
No abstract at ADS
Title: Magnetic measurements of coronal holes during 1975 1980
Authors: Harvey, K. L.; Sheeley, N. R., Jr.; Harvey, J. W.
Bibcode: 1982SoPh...79..149H
Altcode:
Photospheric magnetic fluxes and average field strengths have been
measured beneath 33 coronal holes observed on 63 occasions during
1975-1980. The principal result is that low-latitude holes contained
3 times more flux near sunspot maximum than near minimum despite the
fact that their sizes were essentially the same. Average magnetic
field strengths ranged from 3-36 G near sunspot maximum compared to
1-7 G near minimum. Evidently the low-latitude coronal holes received
a proportion of the extra flux that was available at low latitudes
near sunspot maximum.
Title: Observations of coronal structure during sunspot maximum.
Authors: Sheeley, N. R., Jr.; Howard, R. A.; Koomen, M. J.; Michels,
D. J.; Harvey, K. L.; Harvey, J. W.
Bibcode: 1982SSRv...33..219S
Altcode:
This paper presents some of the results that have been obtained from
the Kitt Peak observations of coronal holes and the NRL observations
of coronal transients during the recent years near sunspot maximum
(1979 1981). On the average, low-latitude coronal holes of comparable
size contained 3 times more flux near sunspot maximum than near the
previous minimum. In the outer corona, transients occurred at the
observed rate of at least 2 per day, and quiet conditions persisted
during less than 15 % of the observed days. We describe a sample of
the more than 800 events that we have observed so far, including the
observation of a comet apparently colliding with the Sun.
Title: Bright point study
Authors: Tang, F.; Harvey, K.; Bruner, M.; Kent, B.; Antonucci, E.
Bibcode: 1982AdSpR...2k..65T
Altcode: 1982AdSpR...2...65T
Transition region and coronal observations of bright points by
instruments aboard the Solar Maximum Mission were accompanied
by high resolution photospheric magnetograph observations on
September 11, 1980. In the photosphere a total of 31 bipolar
ephemeral regions were observed from birth in 9.3 hours of combined
magnetograph observations from three observatories. The Ultraviolet
Spectrometer-Polarimeter observed 2 of the 3 ephemeral regions present
in its field of view in the C IV 1548Å line. The unobserved ephemeral
region was the shortest-lived (2.5 hr) and lowest in magnetic flux
density (13G) of the three. In the O VIII 18.969Å line, the
Flat Crystal Spectrometer detected only low level signals that are
not statistically significant to be positively identified with any
of the 16 ephemeral regions observed in the photosphere. The
SMM data shows that at any given time there lacked a one-to-one
correspondence between observable bright points and photospheric
ephemeral regions. More ephemeral regions were observed than their
counterparts in the transition region and the corona.
Title: Emerging magnetic flux, flares and filaments - FBS interval
16-23 June 1980
Authors: Martin, S. F.; Dezso, L.; Antalova, A.; Kucera, A.; Harvey,
K. L.
Bibcode: 1982AdSpR...2k..39M
Altcode: 1982AdSpR...2...39M
17 emerging magnetic flux regions with arch filaments related to
new sunspots were identified in Hale Active Region No. 16918 during
the 7 day interval from 16-22 June. Most of the new flux regions
were clustered around the filament channel between the old opposite
polarity fields as were most of the flares. The two largest regions of
new magnetic flux and a few of the smaller flux regions developed very
near the end points of filaments. This suggests that the emergence of
flux in existing active regions might be non-random in position along
a filament channel as well as in distance from a filament channel. We have analyzed the positions of 88 flares to date during about
half of each day. We find that slightly more than half (50%) of the
flares, irrespective of their size, are centered within the new flux
regions. About 1/5 (20%) were centered on the border between the new
flux and the adjacent older magnetic field. Less than 1/3 occurred
outside of the newly emerging flux regions but in many cases were very
close to the newly emerging flux. We conclude that at least 2/3 of
the flares are intimately related to the emerging flux regions while
the remaining 1/3 might be either indirectly related or unrelated to
the emerging flux.
Title: Large-Scale Patterns in Solar Activity During the Ascending
Phase of Cycle 21
Authors: Gaizauskas, V.; Harvey, K.; Harvey, J.; Zwaan, C.
Bibcode: 1981BAAS...13R.906G
Altcode:
No abstract at ADS
Title: The Pre-eruption Phase of Filaments Observed in HeI 10830
Authors: Harvey, K. L.
Bibcode: 1981BAAS...13..890H
Altcode:
No abstract at ADS
Title: Preface
Authors: Harvey, Karen L.
Bibcode: 1981SoPh...72D...5H
Altcode:
No abstract at ADS
Title: Coronal Holes and the Sun's Mean Magnetic Field
Authors: Harvey, K. L.; Sheeley, N. R., Jr.
Bibcode: 1980BAAS...12..918H
Altcode:
No abstract at ADS
Title: Double Ribbon Events Observed in He I 10830 Å Associated
with Filament Disappearances
Authors: Harvey, K.; Sheeley, N., Jr.; Harvey, J.
Bibcode: 1980BAAS...12..503H
Altcode:
No abstract at ADS
Title: Forecasting of Solar Flares based on Magnetic Field
Configurations
Authors: Harvey, K. L.; Martin, S. F.
Bibcode: 1980STP.....3...30H
Altcode:
No abstract at ADS
Title: Photospheric Velocity Fields as Indicators of Flare Activity
Authors: Harvey, K. L.; Harvey, J. W.
Bibcode: 1980STP.....3...41H
Altcode:
No abstract at ADS
Title: Photospheric Velocity Fields as Indicators of Flare Activity
Authors: Harvey, K.; Harvey, J.
Bibcode: 1979BAAS...11..440H
Altcode:
No abstract at ADS
Title: Ephemeral Active Regions during Solar Minimum.
Authors: Harvey, K. L.; Martin, S. F.
Bibcode: 1978BAAS...10..417H
Altcode:
No abstract at ADS
Title: Ephemeral active regions during the solar minimum. 1: General
properties and trends over the solar cycle. 2: Characteristics of
individual ephemeral regions
Authors: Martin, S. F.; Harvey, K. L.
Bibcode: 1976sosylrept.....M
Altcode:
General properties of ephemeral active regions were studied using Kitt
Peak daily magnetograms from Apr. - Nov. 1975. Although this interval
was prior to sunspot minimum, ephemeral regions related to incoming
cycle 21 were already more numerous than ephemeral regions related to
outgoing cycle 20. The transition between the old and new solar cycle
was identified by a reversal of the statistically dominant orientation
of regions and sometimes by a minimum in the latitude distribution
where adjacent cycles overlapped. During this interval the transition
between cycle 20 and 21 was at N18 deg and S24 deg. Comparing this 1975
data with previously studied data from 1970 and 1973, we find evidence
that incoming cycle 21 was already present on the sun at middle and high
latitudes in 1973 and 1970. Extrapolating backward and forward in time
from these three periods, we find that it is conceivable that two solar
cycles may be present on the sun at all times. It appears that further
statistical studies of ephemeral active regions may yield long-term
prognostic information on the future course of solar activity. The
birth of 90 ephemeral regions was recorded. Prior to the birth of
regions, existing network was found to disappear or show lateral
displacement. The growth and decay rates of regions were comparable. In
the decaying phase, some flux elements simply disappeared; some merged
with network or other elements of regions of similar polarity; some
collided and simultaneously disappeared with network or elements of
other regions of opposite polarity. All clearly identifiable ephemeral
regions dissipated by these processes while continuing to expand.
Title: A study of the magnetic and velocity fields in an active
region.
Authors: Harvey, K. L.; Harvey, J. W.
Bibcode: 1976SoPh...47..233H
Altcode:
A time sequence of magnetograms and velocity-grams in the Hα and
Fe I 6569 Å lines has been made at a rate of 12 h−1
of McMath Region 10385 from 26 to 29 October, 1969. The 14 flares
observed during this period have been studied in relation to the
configuration and changes in the magnetic and velocity fields. There
was little correlation between flare position and the evolutionary
changes in the photospheric magnetic and velocity field, except
at large central meridian distances where the velocity observations
suggested shearing taking place at flare locations. At central meridian
distances > 30° we found that flares are located in areas of low
line-of-sight photospheric velocity surrounded by higher velocity
hills. The one exception to this was the only flare which produced a
surge. Blue-shifted velocity changes in the photosphere of 0.3 to 1
km s−1 were observed in localized areas at the times of
8 of 14 flares studied.
Title: A Comparison of Flares in Hα and D3 (He I).
Authors: Ramsey, H. E.; Martin, S. F.; Harvey, K. L.
Bibcode: 1975BAAS....7..424R
Altcode:
No abstract at ADS
Title: Flares and Their Relation to the Photospheric Velocity Field.
Authors: Harvey, K. L.; Harvey, J. W.
Bibcode: 1975BAAS....7..438H
Altcode:
No abstract at ADS
Title: A comparison of flares and prominences in D3 and H(alpha)
Authors: Ramsey, H. E.; Martin, S. F.; Harvey, K. L.
Bibcode: 1975lock.rept.....R
Altcode:
During 1973, flares were photographed using a 0.4A filter on the D3
line of HeI and, in 1974, with an additional passband at 0.8A into
the red wing. During most of this period, time-lapse photographs also
were taken on either or both the H(alpha) multi-slit spectrograph
and the H(alpha) Doppler filter. On a separate telescope, limb events
were photographed in D3 and H(alpha) through similar 8A filters. Very
few flares displayed D3 in emission in part of the flare. For large
flares, some absorption parts of the D3 flare correspond closely to the
H(alpha) flare both spatially and temporally. However, the D3 flare
boundaries are more sharply defined. It seemed D3 absorption events
were correlated more frequently with surges and active filaments than
with flare elements. The relative brightness of D3 and H(alpha) were
examined for a number of solar phenomena observed at the limb. High
velocity portions of surges, erupting filaments and loops brightened
more in H(alpha) were examined for a number of solar phenomena observed
at the limb. High velocity portions of surges, erupting filaments
and loops brightened more in H(alpha) than in D3. In limb flares,
D3 brightened more than H(alpha).
Title: Ephemeral Active Regions in 1970 and 1973
Authors: Harvey, K. L.; Harvey, J. W.; Martin, S. F.
Bibcode: 1975SoPh...40...87H
Altcode:
A study of ephemeral active regions (ER) identified on good quality
full-disk magnetograms reveals: On the average 373 and 179 ER were
present on the Sun in 1970 and 1973 respectively. The number varies
with the solar cycle.
Title: A study of the magnetic and velocity fields in an active center
Authors: Harvey, K. L.; Harvey, J. W.
Bibcode: 1974lock.reptQ....H
Altcode:
The report compares in detail the magnetic fields and velocity fields
between the chromosphere and photosphere and investigates changes
occurring in association with flares. Three aspects of the analysis are
discussed: (1) flare location and development relative to the magnetic
and velocity field configuration, (2) slow or evolutionary changes
in the magnetic and velocity field in relation to flare occurrence,
(3) rapid changes (i.e., changes having time scales comparable to that
of flares) in the magnetic and velocity field occurring at the times
of flares.
Title: Ephemeral active regions in 1970 and 1973
Authors: Harvey, K. L.; Martin, S. F.; Harvey, J. W.
Bibcode: 1974lock.reptR....H
Altcode:
The work reported here was undertaken to learn more about the spatial
distribution of Ephemeral active regions (ER), lifetime, solar
cycle variation, and association with major active centers. Primary
consideration was given to the question of whether or not ER represent,
in part, a new class of solar activity or are simply small active
regions.
Title: Correlation of a Flare-Wave and Type II Burst
Authors: Harvey, Karen L.; Martin, Sara F.; Riddle, Anthony C.
Bibcode: 1974SoPh...36..151H
Altcode:
We have studied the relation of a flare-induced wave and the type II and
III radio bursts associated with the 26 April 1969, 2258 UT flare. Our
observations suggest the flare-wave and type II bursts were produced
by a common source.
Title: A Statistical Study of Ephemeral Active Regions in 1970
and 1973
Authors: Harvey, K.; Harvey, J.
Bibcode: 1974BAAS....6S.288H
Altcode:
No abstract at ADS
Title: Rare Observations of the Flare-Related Wave Effects
Authors: Martin, S. F.; Harvey, K. L.
Bibcode: 1974fpsw.conf...39M
Altcode:
No abstract at ADS
Title: Polar Magnetic Fields and the New Solar Cycle
Authors: Gillespie, B.; Harvey, J.; Livingston, W.; Harvey, K.
Bibcode: 1973ApJ...186L..85G
Altcode:
Recent magnetograph observations show evidence of the onset of the
new solar cycle (number 21). A small active region with the new-cycle
polarity configuration appeared at S45 on 1973 August 22 and persisted
until 1973 August 26. In addition, ephemeral active regions have
shown a predominance of new-cycle polarity configurations at high
latitudes, especially in the southern hemisphere. The polar magnetic
fields reversed polarity during 1971-1972. This reversal is a prelude
to the start of the new cycle according to the models of Babcock and
Leighton. Subject headings: solar activity - magnetic fields, solar -
rotation, solar
Title: Ephemeral Active Regions
Authors: Harvey, Karen L.; Martin, Sara F.
Bibcode: 1973SoPh...32..389H
Altcode:
Ephemeral active regions attain maximum development within 1 day or
less of their initial appearance and are typically observed for 1-2
days. They appear mostly as small bipolar regions having a typical
dimension of about 30000 km and a maximum total flux of the order of
1020 Mx. The ephemeral regions generally do not produce
sunspots and flares, though they are identified in Hα as small
active centers.
Title: Observations of Moving Magnetic Features near Sunspots
Authors: Harvey, K.; Harvey, J.
Bibcode: 1973SoPh...28...61H
Altcode:
The properties of small (< 2″) moving magnetic features near
certain sunspots are studied with several time series of longitudinal
magnetograms and Hα filtergrams. We find that the moving magnetic
features: Are associated only with decaying sunspots surrounded entirely
or in part by a zone without a permanent vertical magnetic field.
Title: Observations of Moving Magnetic Features Near Sunspots
Authors: Harvey, K.; Harvey, J.
Bibcode: 1972BAAS....4Q.384H
Altcode:
No abstract at ADS
Title: A Study of D_{3} Emission in a Solar Flare by Use of
Narrow-Band Filtergrams
Authors: Milkey, Robert W.; Harvey, Karen L.
Bibcode: 1972PASP...84..400M
Altcode:
We report observations of helium D3 emission in the solar flare
of 11 February 1970 made at the Lockheed Solar Observatory. The
morphological relationship between the D3 and Ha emission is explored,
and a photometric reduction technique is applied to the filtergrams
to determine peak intensity of the D3 emission relative to the local
quiet sun continuum. Key words: flare - filtergram - helium D3
Title: The Explosive Phase of Solar Flares
Authors: Harvey, Karen L.
Bibcode: 1971SoPh...16..423H
Altcode:
The explosive phase of a flare can be defined by a simple photometric
measurement of Hα film records of the flare development. Using the
quantitative definition, improved correlations are found between the
start of the explosive phase and the start of 10.7 cm radio bursts
and Sudden Frequency Deviations compared to earlier correlations of
the same data using visual estimates of the start of the explosive
phase. Explosive development may be confined to only part of a flare.
Title: Observations of Magnetic Field Changes in Active Regions
Authors: Harvey, K. L.; Livingston, W. C.; Harvey, J. W.; Slaughter,
C. D.
Bibcode: 1971IAUS...43..422H
Altcode:
No abstract at ADS
Title: Observational Effects of Flare-Associated Waves
Authors: Smith, S. F.; Harvey, K. L.
Bibcode: 1971ASSL...27..156S
Altcode: 1971psc..conf..156S
No abstract at ADS