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Author name code: dere
ADS astronomy entries on 2022-09-14
author:"Dere, K."
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Title: The Temperature and Emission Measure Distribution in the
Quiet and Active Solar Corona: A Bayesian Approach
Authors: Dere, Kenneth P.
2022ApJ...930...86D Altcode: 2022arXiv220317086D
The reconstruction of the differential emission measure (DEM) from
observations of spectral line intensities provides information on
the temperature distribution of the emission measure in the region
observed. The inversion process is known to be highly unstable,
and it has been necessary to provide additional constraints, such as
requiring that the DEM should be smooth. However, this is a nonphysical
constraint. The goal of this analysis is to make an empirical
determination of the ability of a set of emission-line intensities to
constrain the reconstruction. Here, a simple model is used, by means
of a Markov Chain Monte Carlo process, to arrive at solutions that
reproduce the observed intensities in a region of the quiet Sun and
a solar active region. These solutions are compared by means of the
reduced chi-squared. The conclusion from this analysis is that the
observations are only capable of constraining a model consisting of
four temperature-emission measure pairs plus a determination of the
standard deviation of the model from the observed line intensities. A
more complex model with five temperature-emission measure pairs does
not improve the fit and leads to parameters that are irrelevant. A
more general conclusion is that the information content of a set of
observed emission lines is limited with respect to the determination
of the emission measure distribution.
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Title: CHIANTI—An Atomic Database for Emission Lines. XVI. Version
10, Further Extensions
Authors: Del Zanna, G.; Dere, K. P.; Young, P. R.; Landi, E.
2021ApJ...909...38D Altcode: 2020arXiv201105211D
We present version 10 of the CHIANTI package. In this release, we
provide updated atomic models for several helium-like ions and for
all the ions of the beryllium, carbon, and magnesium isoelectronic
sequences that are abundant in astrophysical plasmas. We include rates
from large-scale atomic structure and scattering calculations that
are in many cases a significant improvement over the previous version,
especially for the Be-like sequence, which has useful line diagnostics
to measure the electron density and temperature. We have also added
new ions and updated several of them with new atomic rates and line
identifications. Also, we have added several improvements to the IDL
software, to speed up the calculations and to estimate the suppression
of dielectronic recombination.
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Title: Quiet Sun electron densities and their uncertainties derived
from spectral emission line intensities
Authors: Dere, Kenneth P.
2020MNRAS.496.2334D Altcode: 2020arXiv200604184D; 2020MNRAS.tmp.1785D
The goal of this paper is to apply statistical methods to
determine electrons densities and their errors from measurements of
density-sensitive line intensities in the quiet Sun. Three methods are
employed. The first is the use of L-function plots to provide a quick
visual assessment of the likelihood that a set of line intensities
can provide a robust estimate of these quantities. A second methods
involves a χ<SUP>2</SUP> minimization together with a prescription
for determining the regions of statistical confidence in addition
to the best-fitting value. A third method uses a Bayesian inference
technique that employs a Monte Carlo Markov Chain (MCMC) calculation
from which an analysis of the posterior distributions provide estimates
of the mean and regions of high probability density. Using these three
methods, observations of extreme-ultraviolet spectral lines originating
from regions of the quiet Sun have been analysed. The quantitative
χ<SUP>2</SUP> minimization and MCMC sampling provide results that
are generally in good agreement, especially for sets of lines of ions
that have L-function plots that suggest that a robust analysis might
be possible.
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Title: Latest updates to the CHIANTI atomic database
Authors: Young, Peter R.; Dere, Kenneth P.; Del Zanna, Giulio; Landi,
Enrico; Sutherland, Ralph
2019AAS...23431402Y Altcode:
CHIANTI is a database of atomic data parameters and a software
package for computing the radiative emissions from optically-thin
astrophysical plasmas. CHIANTI is freely available to the community
(<A href="http://chiantidatabase.org">http://chiantidatabase.org</A>),
and is very widely used in the Heliophysics and Astrophysics
communities. The papers describing CHIANTI have been cited over
3500 times in the 22-year lifetime of the project. <P />Version 9 of
CHIANTI was released in March 2019, and this presentation summarizes
the new updates and highlights important applications. The key change
for CHIANTI 9 was the implementation of a new method to account for
recombination and dielectronic capture in the level balance equations
through new, two-ion models that fully capture the state-to-state
transitions between ions. The models are needed for the calculation
of X-ray satellite lines and, for the first time, enable density
sensitivity to be modeled. <P />A number of the standard atomic
data-sets have been updated, including recombination rates for several
important coronal iron ions. New software routines have been written
for computing the differential emission measure of a plasma, and for
computing the response functions of the Atmospheric Imaging Assembly
on board NASA's Solar Dynamics Observatory .
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Title: CHIANTI—An Atomic Database for Emission Lines. XV. Version 9,
Improvements for the X-Ray Satellite Lines
Authors: Dere, K. P.; Del Zanna, G.; Young, P. R.; Landi, E.;
Sutherland, R. S.
2019ApJS..241...22D Altcode: 2019arXiv190205019D
CHIANTI contains a large quantity of atomic data for the analysis
of astrophysical spectra. Programs are available in IDL and
Python to perform calculation of the expected emergent spectrum
from these sources. The database includes atomic energy levels,
wavelengths, radiative transition probabilities, rate coefficients
for collisional excitation, ionization, and recombination, as well
as data to calculate free-free, free-bound, and two-photon continuum
emission. In Version 9, we improve the modeling of the satellite
lines at X-ray wavelengths by explicitly including autoionization
and dielectronic recombination processes in the calculation of level
populations for select members of the lithium isoelectronic sequence
and Fe XVIII-XXIII. In addition, existing data sets are updated,
new ions are added, and new total recombination rates for several Fe
ions are included. All data and IDL programs are freely available at <A
href="http://www.chiantidatabase.org">http://www.chiantidatabase.org</A>
or through SolarSoft, and the Python code
ChiantiPy is also freely available at <A
href="https://github.com/chianti-atomic/ChiantiPy">https://github.com/chianti-atomic/ChiantiPy</A>.
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Title: The CHIANTI atomic database
Authors: Young, P. R.; Dere, K. P.; Landi, E.; Del Zanna, G.; Mason,
H. E.
2016JPhB...49g4009Y Altcode: 2015arXiv151205620Y
The freely available CHIANTI atomic database was first released
in 1996 and has had a huge impact on the analysis and modeling of
emissions from astrophysical plasmas. It contains data and software
for modeling optically thin atom and positive ion emission from low
density (≲10<SUP>13</SUP> cm<SUP>-3</SUP>) plasmas from x-ray to
infrared wavelengths. A key feature is that the data are assessed
and regularly updated, with version 8 released in 2015. Atomic data
for modeling the emissivities of 246 ions and neutrals are contained
in CHIANTI, together with data for deriving the ionization fractions
of all elements up to zinc. The different types of atomic data are
summarized here and their formats discussed. Statistics on the impact
of CHIANTI to the astrophysical community are given and examples of
the diverse range of applications are presented.
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Title: CHIANTI - An atomic database for emission lines. Version 8
Authors: Del Zanna, G.; Dere, K. P.; Young, P. R.; Landi, E.; Mason,
H. E.
2015A&A...582A..56D Altcode: 2015arXiv150807631D
We present version 8 of the CHIANTI database. This version includes
a large amount of new data and ions, which represent a significant
improvement in the soft X-ray, extreme UV (EUV) and UV spectral
regions, which several space missions currently cover. New data for
neutrals and low charge states are also added. The data are assessed,
but to improve the modelling of low-temperature plasma the effective
collision strengths for most of the new datasets are not spline-fitted
as previously, but are retained as calculated. This required a change
of the format of the CHIANTI electron excitation files. The format
of the energy files has also been changed. Excitation rates between
all the levels are retained for most of the new datasets, so the data
can in principle be used to model high-density plasma. In addition,
the method for computing the differential emission measure used in
the CHIANTI software has been changed.
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Title: ChiantiPy: Python package for the CHIANTI atomic database
Authors: Dere, Ken
2013ascl.soft08017D Altcode:
ChiantiPy is an object-orient Python package for calculating
astrophysical spectra using the CHIANTI atomic database for
astrophysical spectroscopy. It provides access to the database and the
ability to calculate various physical quantities for the interpretation
of astrophysical spectra.
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Title: CHIANTI 7.1: a new database release for SDO data analysis
Authors: Young, P. R.; Landi, E.; Del Zanna, G.; Dere, K. P.; Mason,
H. E.
2013enss.confE..58Y Altcode:
Version 7.1 of the CHIANTI atomic database was released in October 2012
and contains a number of improvements to better model data returned by
the AIA and EVE instruments on board SDO. Specifically the models for
the important iron ions Fe VIII to Fe XIV have been greatly expanded,
yielding many thousands of new transitions in the 50-170 angstrom
range that enable the irradiance spectra obtained by EVE to be modeled
more accurately. A lack of available atomic data meant that the AIA 94
angstrom channel was not well modeled at low temperatures in earlier
versions of CHIANTI. New data for Fe VIII, Fe X and Fe XIV added to
CHIANTI 7.1 give important contributions to the channel and greatly
improve comparisons with theory.
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Title: CHIANTI—An Atomic Database for Emission Lines. XIII. Soft
X-Ray Improvements and Other Changes
Authors: Landi, E.; Young, P. R.; Dere, K. P.; Del Zanna, G.; Mason,
H. E.
2013ApJ...763...86L Altcode:
The CHIANTI spectral code consists of two parts: an atomic database
and a suite of computer programs in Python and IDL. Together, they
allow the calculation of the optically thin spectrum of astrophysical
objects and provide spectroscopic plasma diagnostics for the analysis
of astrophysical spectra. The database includes atomic energy levels,
wavelengths, radiative transition probabilities, collision excitation
rate coefficients, ionization, and recombination rate coefficients,
as well as data to calculate free-free, free-bound, and two-photon
continuum emission. Version 7.1 has been released, which includes
improved data for several ions, recombination rates, and element
abundances. In particular, it provides a large expansion of the
CHIANTI models for key Fe ions from Fe VIII to Fe XIV to improve the
predicted emission in the 50-170 Å wavelength range. All data and
programs are freely available at http://www.chiantidatabase.org and
in SolarSoft, while the Python interface to CHIANTI can be found at
http://chiantipy.sourceforge.net.
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Title: Recent Developments with the CHIANTI Atomic Database for
Astrophysical Spectroscopy
Authors: Dere, Kenneth P.
2012AAS...22020802D Altcode:
The CHIANTI atomic database for astrophysical spectroscopy maintains
an assessed set of atomic data that are necessary to calculate emission
from ionized plasmas that exist throughout the universe. As new atomic
data becomes available, it is added to the CHIANTI database in order
to improve the accuracy of data already in the database, to extend the
range of spectral lines that can be reproduced or to develop new ions
that are not already in the database. <P />Version 7 of the database
was recently released (Landi et al., 2012). This included several new
ions and a wide range of updated ions. A Python interface to CHIANTI,
ChiantiPy, was developed to complement the existing IDL interface. A
web application, based on ChiantiPy, was also developed that allows the
user to make spectral calculations using the Chianti database directly
from a web browser. <P />Version 7.1 is expected to be released in
2012 and is expected to include updated atomic data for existing ions
and the develop of new ions. Ionization equilibria will be updated
based on new calculations of dielectronic recombination for some
isoelectronic sequences.
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Title: CHIANTI—An Atomic Database for Emission Lines. XII. Version
7 of the Database
Authors: Landi, E.; Del Zanna, G.; Young, P. R.; Dere, K. P.; Mason,
H. E.
2012ApJ...744...99L Altcode:
The CHIANTI spectral code consists of an atomic database and
a suite of computer programs to calculate the optically thin
spectrum of astrophysical objects and carry out spectroscopic plasma
diagnostics. The database includes atomic energy levels, wavelengths,
radiative transition probabilities, collision excitation rate
coefficients, and ionization and recombination rate coefficients,
as well as data to calculate free-free, free-bound, and two-photon
continuum emission. Version 7 has been released, which includes
several new ions, significant updates to existing ions, as well as
Chianti-Py, the implementation of CHIANTI software in the Python
programming language. All data and programs are freely available at
http://www.chiantidatabase.org, while the Python interface to CHIANTI
can be found at http://chiantipy.sourceforge.net.
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Title: Recent Progress with the CHIANTI Atomic Database for
Astrophysical Spectroscopy
Authors: Dere, Kenneth P.
2011AAS...21813402D Altcode: 2011BAAS..43G13402D
The first version of the CHIANTI atomic database for astrophysical
spectroscopy was released in 1997 and the most recent version in
2009. Recent progress with CHIANTI will be described. <P />Based on
the ionization rates developed by Dere (2007) and the radiative and
dielectronic recombination rates of Badnell and colleagues, a new set
of ionization balance calculations has been calculated. These show
some substantial difference from previous calculations. <P />A suite
of Python programs, ChiantiPy, has been developed to allow users to
use the CHIANTI database to calculate spectral line and continuum
intensities in an object-oriented manner. This package is also the
basis for a developmental web server that can show the results of
specifically requested calculations through a user web browser. <P
/>The direction of future work with CHIANTI will be outlined.
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Title: CHIANTI - an atomic database for emission lines. IX. Ionization
rates, recombination rates, ionization equilibria for the elements
hydrogen through zinc and updated atomic data
Authors: Dere, K. P.; Landi, E.; Young, P. R.; Del Zanna, G.; Landini,
M.; Mason, H. E.
2009A&A...498..915D Altcode:
Aims: The goal of the CHIANTI atomic database is to provide a set of
atomic data for the interpretation of astrophysical spectra emitted by
collisionally dominated, high temperature, optically thin sources. <BR
/>Methods: A complete set of ground level ionization and recombination
rate coefficients has been assembled for all atoms and ions of the
elements of H through Zn and inserted into the latest version of the
CHIANTI database, CHIANTI 6. Ionization rate coefficients are taken from
the recent work of Dere (2007, A&A, 466, 771) and recombination
rates from a variety of sources in the literature. These new rate
coefficients have allowed the calculation of a new set of ionization
equilibria and radiative loss rate coefficients. For some ions, such
as Fe VIII and Fe IX, there are significant differences from previous
calculations. In addition, existing atomic parameters have been revised
and new atomic parameters inserted into the database. <BR />Results:
For each ion in the CHIANTI database, elemental abundances, ionization
potentials, atomic energy levels, radiative rates, electron and proton
collisional rate coefficients, ionization and recombination rate
coefficients, and collisional ionization equilibrium populations are
provided. In addition, parameters for the calculation of the continuum
due to bremsstrahlung, radiative recombination and two-photon decay are
provided. A suite of programs written in the Interactive Data Language
(IDL) are available to calculate line and continuum emissivities
and other properties. All data and programs are freely available at
http://wwwsolar.nrl.navy.mil/chianti
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Title: The Coronal Mass of Solar Active Regions
Authors: Dere, Kenneth P.
2009SPD....40.3702D Altcode:
The material contained in coronal mass ejections (CMEs) that originate
from active regions is believed to be provided by the mass in the
active region itself. This loss of mass is exhibited by coronal
dimmings. Previous estimates of the lost mass have depended on
assumptions about the volume or density of the ejected material. The
Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode has the ability
to measure both emission measures and electron densities and provide
a better measure of the coronal mass in active regions. <P />The
technique for determining the coronal mass from EIS measurements is
described and applied to several active regions. The mass lost during
a CME eruption is calculated and compared to measurements of the mass
of a typical range of CMEs. One of the questions that can be addressed
is whether a CME accumulates or loses mass during its passage through
the heliosphere.
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Title: CHIANTI Version 6.0 - Inclusion of Ionization and Recombination
Rates
Authors: Dere, Kenneth P.; Landi, E.; Young, P.; Del Zanna, G.; Mason,
H.; Landini, M.
2009SPD....40.1504D Altcode:
A new version of the CHIANTI atomic database for astrophysical
spectroscopy is being prepared for imminent release. This will
constitute Version 6.0. The main focus of this release is the inclusion
of ionization cross-sections and rate coefficients from Dere (2007)
and recombination rate coefficients from the literature, in particular,
the calculations of Badnell and colleagues. A new set of ionization
equilibria have been calculated from these rate coefficients. These
show some significant differences from previous calculations. Atomic
data for many ions have been revised and new calculations are included
that enable the calculation of spectra of ions new to the CHIANTI
database. The radiative loss function has been calculated based on
the CHIANTI Version 6 database for both coronal and photospheric
abundances. <P />A paper describing CHIANTI Version 6.0 in detail has
been accepted for publication in Astronomy and Astrophysics.
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Title: Chiantipy - The Python Interface To Chianti
Authors: Dere, Kenneth P.
2009SPD....40.1505D Altcode:
Python is a free, modern, object-oriented programming language that
is well suited to scientific data analysis. A command line version
for use within the IPython shell is under development and significant
progress has already been made. Programmatically, each ion in the
CHIANTI database is treated as an object, providing a good match to
the structure of the CHIANTI database. Currently, ChiantiPy is able
to calculate and plot level populations, spectral line emissivities,
contribution functions, G(n,T), and line intensity ratios as functions
of temperature and electron and proton density. A GUI version is
also planned. <P />The current capabilities of ChiantiPy will be
demonstrated.
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Title: The plasma filling factor of coronal bright
points. II. Combined EIS and TRACE results
Authors: Dere, K. P.
2009A&A...497..287D Altcode:
Aims: In a previous paper, the volumetric plasma filling factor of
coronal bright points was determined from spectra obtained with the
Extreme ultraviolet Imaging Spectrometer (EIS). The analysis of these
data showed that the median plasma filling factor was 0.015. One
interpretation of this result was that the small filling factor was
consistent with a single coronal loop with a width of 1-2´´, somewhat
below the apparent width. In this paper, higher spatial resolution
observations with the Transition Region and Corona Explorer (TRACE)
are used to test this interpretation. <BR />Methods: Rastered spectra
of regions of the quiet Sun were recorded by the EIS during operations
with the Hinode satellite. Many of these regions were simultaneously
observed with TRACE. Calibrated intensities of Fe xii lines were
obtained and images of the quiet corona were constructed from the EIS
measurements. Emission measures were determined from the EIS spectra
and geometrical widths of coronal bright points were obtained from the
TRACE images. Electron densities were determined from density-sensitive
line ratios measured with EIS. A comparison of the emission measure
and bright point widths with the electron densities yielded the plasma
filling factor. <BR />Results: The median electron density of coronal
bright points is 3 × 10<SUP>9</SUP> cm<SUP>-3</SUP> at a temperature
of 1.6 × 10<SUP>6</SUP> K. The volumetric plasma filling factor of
coronal bright points was found to vary from 3 × 10<SUP>-3</SUP>
to 0.3 with a median value of 0.04. <BR />Conclusions: The current
set of EIS and TRACE coronal bright-point observations indicate the
median value of their plasma filling factor is 0.04. This can be
interpreted as evidence of a considerable subresolution structure in
coronal bright points or as the result of a single completely filled
plasma loop with widths on the order of 0.2-1.5´´ that has not been
spatially resolved in these measurements.
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Title: The plasma filling factor of coronal bright points. Coronal
bright points
Authors: Dere, K. P.
2008A&A...491..561D Altcode:
Aims: We determine the volumetric plasma filling factor of coronal
bright points. <BR />Methods: Rastered spectra of the regions of the
quiet Sun were recorded by the Extreme ultraviolet Imaging Spectrometer
(EIS) during operations with the Hinode satellite. Calibrated
intensities of Fe XII lines were obtained and images of the quiet corona
were constructed. From the imaged spectra, the emission measures and
geometrical widths of coronal bright points were obtained. Electron
densities were determined from density-sensitive line ratios. A
comparison of the emission measure and bright point widths with the
electron densities yielded the plasma-filling factor. <BR />Results:
The median electron density of coronal bright points is 4 ×
10<SUP>9</SUP> cm<SUP>-3</SUP> at a temperature of 1.6×10<SUP>6</SUP>
K. The volumetric plasma-filling factor of coronal bright points was
found to vary from 4 × 10<SUP>-5</SUP> to 0.2 with a median value
of 0.015. <BR />Conclusions: The current set of EIS coronal bright
point observations indicates that the median value of their plasma
filling-factor is 0.015. This can be interpreted as evidence of a
considerable subresolution structure in coronal bright points or as
the result of a single completely-filled plasma loop with a width on
the order of 1-2 arcsec that has not been spatially resolved in these
measurements. <P />Full Table 2 is only available in electronic form
at http://www.aanda.org
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Title: VizieR Online Data Catalog: Plasma filling factor of coronal
bright points (Dere+, 2008)
Authors: Dere, K. P.
2008yCat..34910561D Altcode:
The data describe the observed and derived properties of a set of corona
l bright points. The labeling allows the reader to correlate the data
in Table 2 with their images in Figures 2 and 3. <P />(1 data file).
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Title: The Plasma Filling Factor of Coronal Bright Points
Authors: Dere, K. P.
2008AGUSMSP31D..04D Altcode:
Rastered spectra of regions of the quiet Sun were recorded by the
Extreme ultraviolet Imaging Spectrometer (EIS) during operations with
the Hinode satellite. Calibrated intensities of Fe XII lines were
obtained and images of the quiet corona were constructed. From the
imaged spectra, the emission measures and geometrical widths of coronal
bright points were obtained. From density-sensitive line ratios,
electron densities were determined. A comparison of the emission
measure and bright point widths with the electron densities yielded
the plasma-filling factor. The median electron density of coronal
bright points is 2.5 × 109 cm-3 at a temperature of 1.4 × 106K. The
volumetric plasma filling factor of coronal bright points was found
to vary from 3 × 10-3 to unity with a median value of 0.02. The small
filling factors lends support to theories, such as the nanoflare theory
of Parker, that suggest coronal heating occurs on small spatial scales.
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Title: The Structure and Dynamics of the Quiet Corona from
Observations with the Extreme ultraviolet Imaging Spectrometer
Authors: Dere, K. P.; Doschek, G. A.; Mariska, J. T.; Harra, L. K.;
Matsuzaki, K.; Hansteen, V.; Thomas, R. J.
2007AGUFMSH53A1046D Altcode:
The goal of the Extreme-ultraviolet Imaging Spectrometer (EIS) on the
Hinode satellite is to measure such physical parameters as the velocity
and density of the solar corona in order to provide an observational
basis to understand how coronal plasmas are heated and accelerated. On
2007 January 20, EIS performed a raster of a 128 x 512 arc-sec. area
of a quiet region near Sun center. The observing program recorded
spectra of He II λ256, formed at 9 × 104 K, and lines of Fe VIII-XV,
formed at temperatures spanning the range from 5 × 105 through 2 × 106
K. Maps of intensities, velocities and electron densities derived from
these observations are presented and discussed. Intensity maps in He II
λ256 show the chromospheric network. Line intensities of Fe X-XIV show
small-scale bright points and more extended structures. The intensity
map of Fe VIII shows a transition between the two temperatures. The
coronal lines reveal regions of high outflow velocities on the
order of 100 km s-1 in a compact region and 12 km s-1 in an extended
region. The presence of these high velocities in the quiet corona
is an entirely new and unexpected result. Electron densities derived
from density sensitive line ratios of Fe XII and XIII are typically
about 3 - 20×108 cm-3. The highest densities are found in bright,
compact areas. For the first time, explosive events in the quiet sun
have been observed in the extreme-ultraviolet in He II λ256 profiles
and have properties similar to those previously reported.
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Title: The Structure and Dynamics of the Quiet Corona from
Observations with the Extreme Ultraviolet Imaging Spectrometer
on Hinode
Authors: Dere, Kenneth P.; Doschek, George A.; Mariska, John T.;
Hansteen, Viggo H.; Harra, Louise K.; Matsuzaki, Keiichi; Thomas,
Roger J.
2007PASJ...59S.721D Altcode:
The goal of the Hinode mission is to provide an observational basis for
understanding the heating and acceleration of coronal plasmas. On 2007
January 20, the Extreme ultraviolet Imaging Spectrometer performed
a raster of a quiet region near Sun center. Maps of intensities,
velocities, and electron densities derived from these observations are
presented and discussed. Intensity maps in HeII λ 256, formed at 9
× 10<SUP>4</SUP> K, show the chromospheric network. Line intensities
of FeX-XIV, formed at temperatures from 1-2 × 10<SUP>6</SUP> K, show
small-scale bright points and more extended structures. The intensity
map of FeVIII shows a transition between the two temperatures. The
coronal lines reveal regions of high outflow velocities on the order
of 100kms<SUP>-1</SUP> in a compact region and 12kms<SUP>-1</SUP> in
an extended region. The presence of such high velocities in the quiet
corona is an entirely new and unexpected result. Electron densities
derived from density sensitive line ratios of FeXII and XIII are
typically 3-20 × 10<SUP>8</SUP>cm<SUP>-3</SUP>. The highest densities
are found in bright, compact areas. For the first time, explosive
events in the quiet sun have been observed in the extreme-ultraviolet
in HeII λ 256 profiles.
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Title: Hot and Cool Loops Composing the Corona of the Quiet Sun
Authors: Matsuzaki, Keiichi; Hara, Hirohisa; Watanabe, Tetsuya; Dere,
Kenneth P.; Brown, Charles M.; Culhane, Len
2007PASJ...59S.683M Altcode:
We performed a raster scan observation of the quiet Sun with the EUV
Imaging Spectrometer (EIS) aboard Hinode and simultaneously analyzed
observed emission lines of Fe VIII to XV. From a combined analysis,
radiance maps from the observed emission lines were deconvolved into
plasma components at five representative temperatures between 0.40MK and
2.63MK. While the lowest temperature component shows network structures
on spatial scales of between 10" and 20", the higher temperature
components show thread-like patterns on larger scales. A comparison of
emission measures at the different temperatures suggests that the lowest
temperature component is mainly composed of bodies of small loops,
rather than a collection of foot points of the higher temperature
loops. The difference in morphologies is interpreted as being due to
different magnetic field configurations, loops within super-granule
cells and fields extending beyond the boundaries of super-granule cells,
with distinct peak temperatures following a loop scaling law.
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Title: The Temperature and Density Structure of an Active Region
Observed with the Extreme-Ultraviolet Imaging Spectrometer on Hinode
Authors: Doschek, George A.; Mariska, John T.; Warren, Harry P.;
Culhane, Len; Watanabe, Tetsuya; Young, Peter R.; Mason, Helen E.;
Dere, Kenneth P.
2007PASJ...59S.707D Altcode:
The Extreme-Ultraviolet Imaging Spectrometer (EIS) on Hinode
produces high resolution spectra that can be combined via rasters
into monochromatic images of solar structures, such as active
regions. Electron temperature and density maps of the structures can
be obtained by imaging the structures in different spectral lines with
ratios sensitive to either temperature or density. Doppler maps and
ion temperature maps can be made from spectral line wavelengths and
profiles, respectively. In this paper we discuss coronal temperature
and density distributions within an active region, illustrating the
power of EIS for solar plasma diagnostics.
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Title: EUV Emission Lines and Diagnostics Observed with Hinode/EIS
Authors: Young, Peter R.; Del Zanna, Giulio; Mason, Helen E.; Dere,
Ken P.; Landi, Enrico; Landini, Massimo; Doschek, George A.; Brown,
Charles M.; Culhane, Len; Harra, Louise K.; Watanabe, Tetsuya; Hara,
Hirohisa
2007PASJ...59S.857Y Altcode: 2007arXiv0706.1857Y
Quiet Sun and active region spectra from the Hinode/EIS instrument are
presented, and the strongest lines from different temperature regions
discussed. A list of emission lines recommended to be included in EIS
observation studies is presented based on analysis of blending and
diagnostic potential using the CHIANTI atomic database. In addition
we identify the most useful density diagnostics from the ions covered
by EIS.
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Title: Wavelength Determination for Solar Features Observed by the
EUV Imaging Spectrometer on Hinode
Authors: Brown, Charles M.; Hara, Hirohisa; Kamio, Suguru; Feldman,
Uri; Seely, John F.; Doschek, George A.; Mariska, John T.; Korendyke,
Clarence M.; Lang, James; Dere, Kenneth P.; Culhane, Len; Thomas,
Roger J.; Davila, Joseph M.
2007PASJ...59S.865B Altcode:
A wavelength calibration of solar lines observed by the high
resolution EUV Imaging Spectrometer (EIS) on the Hinode satellite
is reported. Spectral features of the quiet sun and of two mildly
active areas were measured and calibrated. A listing of the stronger
observed lines with identification of the leading contributor ions
is presented. 41 lines are reported, with 90% identified. Wavelength
precisions (2σ) of ±0.0031Å for the EIS short band and ±0.0029Å
for the EIS long band are obtained. These lines, typical of 1-2
×10<SUP>6</SUP> K plasmas, are recommended as standards for the
establishment of EIS wavelength scales. The temperature of EIS varies
by about 1D.5 C around the orbit and also with spacecraft pointing. The
correlation of these temperature changes with wavelength versus pixel
number scale changes is reported.
---------------------------------------------------------
Title: Application of CHIANTI to Solar-B
Authors: Dere, K.; Landi, E.; Del Zanna, G.; Young, P.; Mason, H.;
Landini, M.
2007ASPC..369...35D Altcode:
CHIANTI (http://wwwsolar.nrl.navy.mil/chianti.html) has been developed
to support the interpretation of solar and astrophysical spectroscopic
measurements. The most recent release, version 5.0 (Landi et al. 2005)
presents an improvement over previous versions by including new
large scale datasets for Fe ions from Fe XVII to Fe XXIV for X-ray
emission and improved atomic data for EUV line emission. We will
demonstrate how this can be applied to the analysis of XRT and EIS
data, in particular. For example, new excitation rates for Fe XII have
resolved a long standing problem in the use of Fe XII line ratios as
accurate density diagnostics. Current work involves improvements to
ionization and recombination rates which will also be useful in the
interpretation of Solar-B data
---------------------------------------------------------
Title: VizieR Online Data Catalog: Ionization rate coefficients for
elements H to Zn (Dere+, 2007)
Authors: Dere, K. P.
2007yCat..34660771D Altcode:
This table contains spline fits to scaled ionization rate coefficient
that will allow the computation of ionization rate coefficients of
all ions of the elements hydrogen through zinc over a wide range of
temperatures. <P />This file has been modified from the original to
correct the values for the calcium-like sequence on September 12,
2007. <P />(1 data file).
---------------------------------------------------------
Title: The EUV Imaging Spectrometer for Hinode
Authors: Culhane, J. L.; Harra, L. K.; James, A. M.; Al-Janabi, K.;
Bradley, L. J.; Chaudry, R. A.; Rees, K.; Tandy, J. A.; Thomas, P.;
Whillock, M. C. R.; Winter, B.; Doschek, G. A.; Korendyke, C. M.;
Brown, C. M.; Myers, S.; Mariska, J.; Seely, J.; Lang, J.; Kent,
B. J.; Shaughnessy, B. M.; Young, P. R.; Simnett, G. M.; Castelli,
C. M.; Mahmoud, S.; Mapson-Menard, H.; Probyn, B. J.; Thomas, R. J.;
Davila, J.; Dere, K.; Windt, D.; Shea, J.; Hagood, R.; Moye, R.; Hara,
H.; Watanabe, T.; Matsuzaki, K.; Kosugi, T.; Hansteen, V.; Wikstol, Ø.
2007SoPh..243...19C Altcode:
The EUV Imaging Spectrometer (EIS) on Hinode will observe solar corona
and upper transition region emission lines in the wavelength ranges
170 - 210 Å and 250 - 290 Å. The line centroid positions and profile
widths will allow plasma velocities and turbulent or non-thermal line
broadenings to be measured. We will derive local plasma temperatures and
densities from the line intensities. The spectra will allow accurate
determination of differential emission measure and element abundances
within a variety of corona and transition region structures. These
powerful spectroscopic diagnostics will allow identification
and characterization of magnetic reconnection and wave propagation
processes in the upper solar atmosphere. We will also directly study
the detailed evolution and heating of coronal loops. The EIS instrument
incorporates a unique two element, normal incidence design. The optics
are coated with optimized multilayer coatings. We have selected highly
efficient, backside-illuminated, thinned CCDs. These design features
result in an instrument that has significantly greater effective area
than previous orbiting EUV spectrographs with typical active region
2 - 5 s exposure times in the brightest lines. EIS can scan a field
of 6×8.5 arc min with spatial and velocity scales of 1 arc sec and
25 km s<SUP>−1</SUP> per pixel. The instrument design, its absolute
calibration, and performance are described in detail in this paper. EIS
will be used along with the Solar Optical Telescope (SOT) and the X-ray
Telescope (XRT) for a wide range of studies of the solar atmosphere.
---------------------------------------------------------
Title: Ionization rate coefficients for the elements hydrogen
through zinc
Authors: Dere, K. P.
2007A&A...466..771D Altcode:
Aims:The interpretation of astrophysical spectra depends directly on
a knowledge of the ionization state of the emitting plasma. This is
determined, in part, from collisional ionization rate coefficients. The
most recent assessments of these were performed by Arnaud &
Rothenflug (1985, A&AS, 60, 425) and Arnaud & Raymond
(1992, ApJ, 398, 394). Since their work, new laboratory measurements
of ionization cross sections have become available as well as the
Flexible Atomic Code (FAC) which enables theoretical calculations of
these rates. Our goal is to provide a complete set of ionization rate
coefficients for the elements hydrogen through zinc. <BR />Methods: A
scaling law, which assists the analysis of ionization cross sections
and rate coefficients, has been developed following the approach
of Burgess & Tully (1992, A&A, 254, 436). Essentially all
available measured cross sections along each isoelectronic sequence
have been examined and compared to cross sections calculated with
the Flexible Atomic Code (FAC) and with other calculations. Two
approaches has been taken to provide a complete set of ionization
cross sections. In the first, fits to scaled measured ionization cross
sections, particularly for neutral and singly ionized species, are
performed. In the second, fits to scaled calculated direct ionization
and excitation-autoionization cross sections are performed to provide
the remainder of the set. The fits to the cross sections are then
integrated over a Maxwellian velocity distribution to derive ionization
rate coefficients. <BR />Results: A complete set of ground level
ionization cross sections and rate coefficients has been developed
through the combination of these two approaches. A tabulation of
parameter fits to ground level ionization rate coefficients for all
atoms and ions of the elements of H through Zn is provided. <P />Full
Table [see full text] is only available in electronic form at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/466/771
---------------------------------------------------------
Title: Transition Region Explosive Events and their Relation to the
Solar Magnetic Field
Authors: Muglach, Karin; Dere, K.
2007AAS...210.9118M Altcode: 2007BAAS...39..207M
Magnetic field restructuring by reconnection is pervasive in solar
physics. It can potentially provide the energy to heat and accelerate
the plasma in the solar atmosphere. We will investigate the role
of small-scale magnetic reconnection in the formation of transition
region explosive events. These events are defined by strong transient
enhancements of the wings of spectral lines that form at transition
region temperatures (between 20 000 - 200 000 K).Using SUMER data
we are able to identify EEs by their spectral signature. With MDI we
can continuously map the photospheric magnetic field and search for a
manifestation of the reconnection in the lower solar atmosphere. We
have analysed several dozens of explosive events and will show how
the underlying magnetic field evolves during these events.
---------------------------------------------------------
Title: Two Successive Coronal Mass Ejections Driven by the Kink and
Drainage Instabilities of an Eruptive Prominence
Authors: Zhou, G. P.; Wang, J. X.; Zhang, J.; Chen, P. F.; Ji, H. S.;
Dere, K.
2006ApJ...651.1238Z Altcode:
We describe a clear case of the initiation of a propagating bright arc
and a CME on 2002 December 28, which were associated with an eruptive
prominence. In EIT 304 and 195 Å images, a very long filament showed
evidence of severe twisting in one of its fragments, which appeared as a
prominence on December 26; then, the prominence showed the conversion of
its twist into writhe. Two days later, the prominence displayed a slow
rising motion for hours. Internal twisting and mass motion took place
before the rapid acceleration and final eruption. The propagating bright
arc and the following CME corresponded to the early rising and the
subsequently eruptive phases of the prominence, respectively. Signatures
of magnetic reconnection, i.e., a cusp structure and postflare loops
in EUV wave bands and hard X-ray sources in the corona, were observed
after the prominence eruption. It appears that the kink instability
and the mass drainage in the prominence played key roles in triggering
the initiation of the CME. However, the rather impulsive acceleration
of the CME resulted from magnetic reconnection beneath the filament.
---------------------------------------------------------
Title: A Statistical Study of Main and Residual Accelerations of
Coronal Mass Ejections
Authors: Zhang, J.; Dere, K. P.
2006ApJ...649.1100Z Altcode:
In this paper we present the results of a statistical study of the
accelerations of coronal mass ejections (CMEs). A CME usually undergoes
a multiphased kinematic evolution, with a main acceleration phase
characterized by a rapid increase of CME velocity in the inner corona,
followed by a relatively smooth propagation phase characterized by a
constant speed or a small residual acceleration in the outer corona. We
study both the main acceleration and the residual acceleration for
50 CME events based on Large Angle Spectrometric Coronagraph (LASCO)
observations. We find that the magnitude of the main acceleration
has a wide distribution, from 2.8 to 4464.0 m s<SUP>-2</SUP>,
with a median (average) value of 170.1 (330.9 m s<SUP>-2</SUP>),
and a standard deviation of 644.8 m s<SUP>-2</SUP>, whereas the
magnitude of the residual acceleration ranges only from -131.0 to
52.0 m s<SUP>-2</SUP>, with a median (average) value of 3.1 (0.9 m
s<SUP>-2</SUP>) and a standard deviation of 25.3 m s<SUP>-2</SUP>. The
duration of the main acceleration is also widely distributed, from 6
to 1200 minutes, with a median (average) value of 54 (180 minutes) and
a standard deviation of 286 minutes.We find an intriguing scaling law
between the acceleration magnitude (A) and the acceleration duration
(T) over the entire parameter range of almost 3 orders of magnitude,
which can be expressed as A (m s<SUP>-2</SUP>)=10,000T<SUP>-1</SUP>
(minutes). The implications of these observational results on the
issues of CME classification and CME modelings are discussed.
---------------------------------------------------------
Title: The Extreme Ultraviolet Imaging Spectrometer (EIS) on Solar-B
Authors: Doschek, George A.; Brown, C. M.; Korendyke, C. M.; Mariska,
J. T.; Myers, S. H.; Seely, J. F.; Dere, K. P.; Lang, J.; Culhane,
J. L.; Watanabe, T.
2006SPD....37.3604D Altcode: 2006BAAS...38S.260D
The Extreme Ultraviolet Imaging Spectrometer (EIS) for Solar-B is a
high throughput state-of-the-art instrument designed to obtain solar
spectra and images in two wavelength bands centered near 195 and 270
Angstroms. Traditional spectra can be obtained using narrow slits or
images of solar structures can be obtained in individual spectral
lines using wide slots. Essentially, the instrument obtains images
in wavebands similar to TRACE but in each spectral line within the
waveband. This removes electron temperature ambiguities inherent in
broadband imagers and allows dynamic effects to be detected via Doppler
shifts and densities and other plasma parameters to be measured via
spectroscopic plasma diagnostics. After a brief description of how
the instrument works and a comparison with previous instrumentation
(sensitivity, etc.), the presentation will focus on the science that
can be accomplished with EIS, presented in the form of sample observing
sequences. The focus will be on active regions and solar flares with a
consideration of topics such as temperature and density distributions
in active region loops and their evolution, dynamical motions in active
region loops, the reconnection site in solar flares, and temperature
evolution of multimillion degree flare loops.
---------------------------------------------------------
Title: CMEs driven by an eruptive prominence
Authors: Zhou, G. P.; Wang, J. X.; Zhang, J.; Chen, P. F.; Ji, H. S.;
Dere, K.
2006IAUS..233..405Z Altcode:
A clear case on Dec. 28 2002 is presented. It is about the initiation of
two successive CMEs, which were related to an eruptive prominence. In
EIT 304 Å and 195 Å observations, we found a long filament severely
twisting in a piece of its fragments, which appeared as a prominence on
Dec. 26. Then, the prominence converted its twist into writhe. Two days
later, the prominence displayed a slow rising motion for hours. There
happened internal twisting and mass motion before the prominence rapid
acceleration and final eruption. Two successive CMEs recorded by LASCO
C2 coronagraph corresponded to the early rising and the subsequently
eruptive phases of the prominence, respectively. Evidence of magnetic
reconnection, i.e., a cusp structure and post-flare loops in EUV
wavebands, and hard X-ray sources in the corona, were observed after
the prominence disruption. It appears that the kink instability and the
mass drainage in the prominence played important roles in triggering two
CMEs' initiation. We suspected that the rather impulsive acceleration
of the second CME resulted from magnetic reconnection beneath the
prominence.
---------------------------------------------------------
Title: CHIANTI-An Atomic Database for Emission Lines. VII. New Data
for X-Rays and Other Improvements
Authors: Landi, E.; Del Zanna, G.; Young, P. R.; Dere, K. P.; Mason,
H. E.; Landini, M.
2006ApJS..162..261L Altcode:
The CHIANTI atomic database contains atomic energy levels, wavelengths,
radiative transition probabilities, and collisional excitation data for
a large number of ions of astrophysical interest. CHIANTI also includes
a suite of IDL routines to calculate synthetic spectra and carry out
plasma diagnostics. Version 5 has been released, which includes several
new features, as well as new data for many ions. The new features in
CHIANTI are as follows: the inclusion of ionization and recombination
rates to individual excited levels as a means to populate atomic
levels; data for Kα and Kβ emission from Fe II to Fe XXIV; new data
for high-energy configurations in Fe XVII to Fe XXIII; and a complete
reassessment of level energies and line identifications in the X-ray
range, multitemperature particle distributions, and photoexcitation
from any user-defined radiation field. New data for ions already in
the database, as well as data for ions not present in earlier versions
of the database, are also included. Version 5 of CHIANTI represents a
major improvement in the calculation of line emissivities and synthetic
spectra in the X-ray range and expands and improves theoretical spectra
calculations in all other wavelength ranges.
---------------------------------------------------------
Title: Observing the Solar atmosphere with the Extreme Ultraviolet
Imaging Spectrometer on Solar B
Authors: Korendyke, C. M.; Brown, C.; Dere, K.; Doschek, G.; Klimchuk,
J.; Landi, E.; Mariska, J.; Warren, H.; Lang, J.
2005AGUFMSH41B1124K Altcode:
The Extreme Ultraviolet Imaging Spectrometer (EIS) is part of the
instrument complement on the Solar B satellite, scheduled for launch
in the summer of 2006. The instrument has been calibrated and is
presently mounted on the spacecraft. EIS is the most sensitive EUV
solar spectrometer to be flown. The instrument is the first of a new
generation of two optical element, solar spectrographs. Preliminary
results from the laboratory focussing and calibration of the
instrument will be shown. The instrument wavelength coverage includes
reasonably bright spectral lines emitted by plasmas from 0.1 to 20 MK
in temperature. The wavelength range also provides coronal density
diagnostics. Temperature, density and velocity diagnostics will be
discussed. An example observing program for exploring active region
evolution and dynamics will be discussed.
---------------------------------------------------------
Title: Application of CHIANTI to High Resolution Solar Spectra
Authors: Dere, K. P.; Landi, E.
2005AGUFMSH44A..02D Altcode:
CHIANTI has been developed to support the interpretation of solar and
astrophysical spectroscopic measurements. The most recent release,
version 5.0 (Landi et al., 2005) presents an improvement over previous
versions by including new large scale datasets for Fe ions from Fe XVII
to Fe XXIV for X-ray emission and improved atomic data for EUV line
emission. We will show examples of its use in the analysis of X-ray
spectra from SMM, ultraviolet spectra from SOHO and the interpretation
of broadband instruments such as EIT and TRACE. Current work involves
the analysis of ionization and recombination rates based on recent
laboratory measurements and calculations with the Flexible Atomic
Code. The incorporation of ionization and recombination rates into
CHIANTI will allow us to explore such effects as the effect of finite
densities on ionization balance and transient and nonthermal ionization
populations.
---------------------------------------------------------
Title: Coronal and Stellar Mass Ejections, IAU Symposium Proceedings
of the International Astronomical Union 226,
Authors: Dere, Kenneth; Wang, Jingxiu; Yan, Yihua
2005IAUS..226.....D Altcode:
The Sun and other stars eject large clouds of plasma and magnetic
fields on a continual basis. They are accelerated to high speeds and
then become capable of producing highly energetic charged particles
and disrupting the magnetospheres of planets such as the Earth. This
proceeding reflects recent attempts to understand these processes as
well as how the magnetic evolution at the base of the corona can cause
these events, and how stars are capable of rapidly releasing energy
in the form of mass ejections. Contributions by leading scientists
make it a valuable astronomical resource.
---------------------------------------------------------
Title: Coronal and Stellar Mass Ejections (IAU S226)
Authors: Dere, Kenneth; Wang, Jingxiu; Yan, Yihua
2005csme.book.....D Altcode:
1. Historical introduction; 2. Observation of CMES; 3. CME source
regions; 4. Theoretical models of CMEs; 5. Comparisons of CME models
and observations; 6. CMES and energetic particles; 7. ICMEs in the
heliosphere; 8. CMES and geomagnetic storms; 9. Stellar ejections.
---------------------------------------------------------
Title: Recent developments of the CHIANTI database in the X-ray
wavelength range
Authors: Landi, E.; Dere, K. P.; Young, P. R.; del Zanna, G.; Mason,
H. E.; Landini, M.
2005AIPC..774..409L Altcode:
CHIANTI is a database of atomic data and transition probabilities that
allows the calculation of synthetic spectra and plasma diagnostics of
optically thin plasmas. It is primarily suited for wavelengths shorter
than 2000 Å but in principle can also be used at longer wavelengths. In
the present paper we illustrate the latest development of the CHIANTI
database, that include a huge expansion of the database in the X-ray
wavelength range, the renewal of several data in the EUV range, and
the inclusion of ionization and recombination in the level population
calculation. This enhanced database will constitute the Version 5
of CHIANTI.
---------------------------------------------------------
Title: The correlation between features in the solar spectrum near
Mg II and photospheric magnetic fields
Authors: Morrill, J.; Korendyke, C.; Dere, K.
2005AGUSMSP41B..06M Altcode:
During the HRTS-9 flight, spectrograms and spectroheliograms where
obtained of the quiet sun, quiet limb, plage, and sunspots. Previous
analysis of these observations required the correction of a small set
of spectra for instrumental distortions and the absolute intensity
calibration. We have applied these corrections to a larger portion
of the HRTS-9 observations where the spectrograph slit was rastered
across a small region of the sun along the solar equator. This set
of corrected spectrograms has allowed us to generate high spatial and
spectral resolution spectroheliograms of the observed quiet and active
portions of the sun. In addition, with use of a magnetogram taken while
the flight was in progress we have examined the relationship between
the photospheric magnetic field and both Mg II emission at 280 nm and
absorption features in the nearby solar spectrum due to both neutral and
singly ionized species. In this presentation we will present our high
resolution spectroheliograms as well as results showing the relationship
between the magnetic field and several specific spectral features.
---------------------------------------------------------
Title: The Extreme Ultraviolet Imaging Spectrometer on Solar-B
Authors: Mariska, J. T.; Brown, C. M.; Doschek, G. A.; Korendyke,
C. M.; Myers, S. H.; Seely, J. F.; Dere, K. P.; Lang, J.; Culhane,
J. L.; Watanabe, T.
2005AGUSMSP43A..02M Altcode:
The Extreme Ultraviolet Imaging Spectrometer (EIS) is currently under
development for flight on the Japanese Solar-B satellite. EIS uses a
multilayer-coated off-axis telescope mirror and a multilayer-coated
toroidal grating spectrometer to produce stigmatic spectra of solar
regions isolated by a 1024 arcsec high slit. The instrument produces
monochromatic images either by rastering the solar image across a
narrow entrance slit or by using a very wide slit. Half of each optic
is coated to optimize reflectance at 19.5 nm, and the other half to
optimize reflectance at 27.0 nm, with each wavelength range imaged
onto a separate CCD detector. EIS can provide key dynamical and density
diagnostic information. Combining EIS data with observations from the
other instruments on Solar-B should provide a detailed picture of solar
atmospheric processes from the visible surface into the corona. In
this presentation, we provide details of the instrument's expected
performance based on calibration of the individual flight optics and
end-to-end testing at the Rutherford Appleton Laboratory in the UK.
---------------------------------------------------------
Title: Three-dimensional Structure of Coronal Mass Ejections from
LASCO Polarization Measurements
Authors: Dere, Kenneth P.; Wang, Dennis; Howard, Russell
2005ApJ...620L.119D Altcode:
The three-dimensional structure of a coronal mass ejection (CME)
is essential information for understanding the process by which they
are ejected from the Sun. Coronagraphic measurements readily provide
information on the structure of CMEs in the plane of the sky. It has
been known for some time that polarization measurements can provide
information on the position of coronal plasmas out of the plane of
the sky. Recently, T. G. Moran & J. M. Davila have shown that
polarimetric measurements with the Large Angle and Spectrometric
Coronagraph (LASCO) can be used to determine the three-dimensional
structure of a CME with considerable definition. We have examined a
series of high-cadence (1 hr) LASCO polarization measurements obtained
during 2002 and discuss the analysis of two particularly well observed
events. One event indicates that the CME structure is that of a rising
arcade of loops, while the other appears to consist of a flux-rope
type of structure. Because we have examined a large, relatively high
cadence set of LASCO observations, we have been able to select events
that provide significantly greater definition of CME structure than
previously possible.
---------------------------------------------------------
Title: The Three Dimensional Structure of CMEs from LASCO Polarization
Measurements
Authors: Dere, Kenneth; Wang, Dennis
2005IAUS..226..114D Altcode:
The degree of polarization of Compton-scattered photospheric light
observed in a coronagraph is dependent on the distance of the scattering
electrons from the plane of the sky. Measurements of the polarization
of light scattered by CME structures have been observed by LASCO C2. We
have reduced and analyzed a month long sequence of such measurements
which were taken at a cadence of 1 hour. The CME brightness has been
distributed throughout a 3 dimensional cube and visualized at a variety
of angles. Several CMEs are found to have considerable fine-structure
consistent with expanding loop arcades. The analysis is subject to a
variety of assumptions such as a lack of knowledge of whether a source
is before or behind the plane of the sky. Nevertheless, the results
obtained to date are intriguing.
---------------------------------------------------------
Title: The CHIANTI database
Authors: Landi, E.; Dere, K. P.; Young, P. R.; Landini, M.; Mason,
H. E.; Del Zanna, G.
2005HiA....13..653L Altcode:
CHIANTI is a database of atomic data and transition rates necessary for
calculating synthetic spectra and carrying out plasma diagnostics of
astrophysical sources in the X-ray EUV and UV wavelength ranges. CHIANTI
includes both line and continuum emission from all astrophysically
abundant elements in the universe. All data are taken from refereed
literature and are critically assessed. CHIANTI also includes a suite
of IDL programs that allow spectroscopic analysis to be carried
out. CHIANTI data and software are freely distributed over the
internet. <P />In the present talk I will describe the contents of
the CHIANTI database its current status and the areas where CHIANTI
is being developed and I will also present a comparison of CHIANTI
predictions with the X-ray emission from astrophysical sources.
---------------------------------------------------------
Title: The Evolution of Photospheric Source Regions of CMEs
Authors: Muglach, K.; Dere, K.
2005IAUS..226..179M Altcode:
In this presentation we determine the source regions of CMEs that
were observed with SoHO/LASCO during times of solar activity maximum
(Feb./Mar. 2000) and during the declining phase of the solar cycle
(Nov./Dec. 2002). The CMEs were traced back onto the disk and EIT
EUV images were used for identifying the sources. With the help of
MDI synoptic magnetograms we follow the evolution of the photospheric
magnetic flux about 24h before and 12h after the event. We find that
about 87% of the identified CME source regions show small-scale
flux changes before the event, usually flux emergence and/or flux
disappearance. In 13% of the cases we find no signature of photospheric
flux changes.
---------------------------------------------------------
Title: The 3D structure of CMEs from LASCO polarization measurements
Authors: Dere, K. P.; Wang, D.; Howard, R.
2004AGUFMSH22A..03D Altcode:
The polarization of Compton scattered light from a coronal plasma
is a function of the distance of that plasma from the plane of the
sky. From an image of the polarization of the corona it is possible
to construct a 3D cube of intensity which can be visualized at any
angle to study it's three dimensional distribution. For a one month
period during July and August 2002, the LASCO C2 coronagraph performed
polarization measurements with a one hour cadence. During this period,
several CMEs were well observed. Two CMEs give the appearance of an
ejecting loop arcade. Another CME is not as easily described but may
indicate the presence of a flux tube. There are two main ambiguities in
the analysis. First, a given polarization can be produced by scattering
from in front of or behind the plane of the sky. This ambiguity can
be overcome by selecting CMEs that are completely out of the plane of
the sky. Second, in reconstructing the 3D distribution of intensity,
it is assumed that the intensity can be visualized as coming from a
single point in 3D space. The filamentary structures commonly seen in
the 3D visualizations suggest that this is not a significant problem.
---------------------------------------------------------
Title: Solar UV Spectral Radiance from SKYLAB
Authors: Morrill, J.; Korendyke, C.; Dere, K.
2004AGUFMSH53A0305M Altcode:
As part of an ongoing NASA-LWS sponsored research program, solar UV
spectral radiance has been determined for the quiet sun at a variety
of center-to-limb positions observed by the SO82B UV spectrograph
on SKYLAB. This has been done using a high quality flatbed scanner
to digitize the SKYLAB film data. The goal of the present program
is to develop a spectral irradiance model that utilizes the full
resolution of the SKYLAB spectra (~ 0.010 nm at 300 nm). The model
requires detailed knowledge of the center-to-limb variation (CLV) at
full resolution over the 200 - 400nm wavelength range. This information
is also required to determine the absolute intensity calibration which
uses full-disk irradiance measurements from UARS (SOLSTICE and SUSIM)
in addition to the CLV. This calibration is then used to derive the disk
center radiance. In addition to the quiet sun, spectra of sunspots and
active regions are also being digitized and an attempt is underway to
derive the CLV for these surface morphologies as well. Further, spectra
at shorter wavelength (~120 - 200nm) are being examined in order to
extend the wavelength coverage of these radiance and CLV results. In
this presentation we will present the details of the analysis methods
and results for the quiet sun. Ongoing work on sunspots and active
regions will be presented as will results involving work on shorter
wavelength spectra.
---------------------------------------------------------
Title: The Evolution of Photospheric Source Regions of CMEs
Authors: Muglach, K.; Dere, K.
2004AAS...204.3808M Altcode: 2004BAAS...36..713M
In this presentation we determine the source regions of CMEs that
were observed with SOHO/LASCO during times of solar activity maximum
(Feb./Mar. 2000) and during the declining phase of the solar cycle
(Nov./Dec. 2002). The CMEs were traced back onto the disk and EIT EUV
images were used for identifying the sources. With the help of MDI
synoptic and high cadence magnetograms we follow the evolution of the
photospheric magnetic flux about 12 h before and after the event. We
find that 80% of the identified CMEs (29 out of a total of 36 events)
show small--scale flux changes before the event, usually flux emergence
or flux disappearance. In 20% of the cases we find no signature of
photospheric flux changes.
---------------------------------------------------------
Title: A Comparison of the Mg II Index Derived from Estimated and
Observed Solar Spectra
Authors: Morrill, J.; Korendyke, C.; Dere, K.
2004AAS...204.7207M Altcode: 2004BAAS...36..799M
We have estimated values of the Mg II index using a model of solar
spectral irradiance developed at the Naval Research Laboratory. This
model uses Ca II K images and spatially resolved sun spot, quiet sun,
and active sun spectra measured by the HRTS-9 rocket to generate the
estimated spectra. These spectra are compared to observed spectra such
as the UARS-SUSIM and UARS-SOLSTICE data sets. In order to further
compare the observed and estimated spectra, a Mg II index is derived
from these two sets of spectra. In this presentation we will review
the details of the model, discuss the methods of deriving the Mg II
index, and compare the Mg II variability resulting from the observed
and estimated spectra.
---------------------------------------------------------
Title: Recent development of the CHIANTI database in the X-ray
wavelength range
Authors: Landi, E.; Dere, K. P.; Mason, H. E.; Del Zanna, G.; Landini,
M.; Young, P. R.
2004AAS...204.7310L Altcode: 2004BAAS...36R.801L
CHIANTI consists of a database of critically assessed atomic data
and transition rates to calculate line and continuum emission
from astrophysical plasmas. <P />During the last year the CHIANTI
database has been substantially expanded in the X-ray wavelength
region by including a large number of new configurations and lines,
and by including ionization and recombination processes in the level
population calculations. <P />We will describe these improvements,
the data we used, and illustrate examples of 1) their effects on
predicted emissivities and on plasma diagnostics 2) applications to
the study of flares in solar active regions
---------------------------------------------------------
Title: A Study of the Kinematic Evolution of Coronal Mass Ejections
Authors: Zhang, J.; Dere, K. P.; Howard, R. A.; Vourlidas, A.
2004ApJ...604..420Z Altcode:
We report the kinematic properties of a set of three coronal
mass ejections (CMEs) observed with the LASCO (Large Angle and
Spectrometric Coronagraph) on the Solar and Heliospheric Observatory
(SOHO) spacecraft, which showed characteristics of impulsive,
intermediate, and gradual acceleration, respectively. The first CME
had a 30 minute long fast acceleration phase during which the average
acceleration was about 308 m s<SUP>-2</SUP> this acceleration took
place over a distance of about 3.3 R<SUB>solar</SUB> (from 1.3 to
4.6 R<SUB>solar</SUB>, height measured from disk center). The CME
characterized by intermediate acceleration had a long acceleration
phase of about 160 minutes during which the average acceleration was
about 131 m s<SUP>-2</SUP> the CME traveled a distance of at least
4.3 R<SUB>solar</SUB>, reaching a height of 7.0 R<SUB>solar</SUB> at
the end of the acceleration phase. The CME characterized by gradual
acceleration had no fast acceleration phase. Instead, it displayed a
persistent weak acceleration lasting more than 24 hr with an average
acceleration of only 4.0 m s<SUP>-2</SUP> throughout the LASCO field
of view (from 1.1 to 30 R<SUB>solar</SUB>). This study demonstrates
that the final velocity of a CME is determined by a combination of
acceleration magnitude and acceleration duration, both of which can
vary significantly from event to event. The first two CME events were
associated with soft X-ray flares. We found that in the acceleration
phase there was close temporal correlation both between the CME velocity
and the soft X-ray flux of the flare and between the CME acceleration
and derivative of the X-ray flux. These correlations indicate that
the CME large-scale acceleration and the flare particle acceleration
are strongly coupled physical phenomena occurring in the corona.
---------------------------------------------------------
Title: Performance of multilayer-coated gratings for the
extreme-ultraviolet imaging spectrometer (EIS) for the Solar-B mission
Authors: Seely, John F.; Windt, David L.; Donguy, Soizik; Brown,
Charles; Holland, Glenn; Hunter, William R.; Kowalski, Michael
P.; Kjornrattanawanich, Benjawan; Doschek, George; Mariska, John;
Korendyke, Clarence; Dere, Ken
2004SPIE.5168...12S Altcode:
The measured efficiencies of two flight gratings and the reflectances
of two flight mirrors developed for the Extreme-Ultraviolet Imaging
Spectrometer (EIS) for the Japanese Solar-B mission are presented. Each
optic has two sectors with Mo/Si multilayers that refelct the 17 -
21 nm and 25 - 29 nm wavebands at normal incidence. The efficiencies
that were measured using monochromatic synchrotron radiation are in
good agreement with the calculated efficiencies.
---------------------------------------------------------
Title: CHIANTI -- An Atomic Database for UV and X-ray Cool star
spectroscopy
Authors: Young, P. R.; Landi, E.; Bromage, G. E.; del Zanna, G.;
Dere, K. P.; Landini, M.; Mason, H. E.
2003csss...12.1119Y Altcode:
The CHIANTI atomic database was first released in 1996 and has since
become the standard resource for the interpretation of UV spectra
from the transition regions and coronae of the Sun and other cool
stars. We describe the contents of the most recent release (v.3)
and some of the uses that have been found for the database.
---------------------------------------------------------
Title: Expected Performance of the Extreme Ultraviolet Imaging
Spectrometer on Solar-B
Authors: Mariska, J. T.; Brown, C. M.; Dere, K. P.; Doschek, G. A.;
Korendyke, C. M.; Myers, S. H.; Seely, J. F.; Culhane, J. L.;
Watanabe, T.
2003SPD....34.2006M Altcode: 2003BAAS...35..845M
The Extreme Ultraviolet Imaging Spectrometer (EIS) is currently under
development for flight on the Japanese Solar-B satellite. EIS uses a
multilayer-coated off-axis telescope mirror and a multilayer-coated
toroidal grating spectrometer to produce stigmatic spectra of solar
regions isolated by a 1024 arcsec high slit. The instrument produces
monochromatic images either by rastering the solar image across a
narrow entrance slit or by using a very wide slit. Half of each optic
is coated to optimize reflectance at 19.5 nm, and the other half to
optimize reflectance at 27.0 nm, with each wavelength range imaged
onto a separate CCD detector. <P />In this presentation we provide an
update on the EIS hardware development and show details of the expected
performance of the instrument in solar quiet regions, active regions,
and flares.
---------------------------------------------------------
Title: Normal-incidence EXtreme-Ultraviolet imaging Spectrometer
- NEXUS
Authors: Dere, K. P.
2003SPD....34.2405D Altcode: 2003BAAS...35..853D
NEXUS is the result of a breakthrough optical design that incorporates
new technologies to achieve high optical throughput at high spatial
(1 arcsec) and spectral (1-2 km s<SUP>-1</SUP>) resolution over
a wide field of view in an optimal extreme-ultraviolet spectral
band. This achievement was made possible primarily by two technical
developments. First, a coating of boron-carbide deposited onto a layer
of iridium provided a greatly enhanced reflectivity at EUV wavelengths
that would enable NEXUS to observe the Sun over a wide temperature
range at high cadence. The reflectivity of these coatings have been
measured and demonstrated in the laboratory. <P />The second key
development was the use of a variable-line-spaced toroidal grating
spectrometer. The spectrometer design allowed the Sun to be imaged
at high spatial and spectral resolution along a 1 solar radius-long
slit and over a wavelength range from 450 to 800 Å, nearly an entire
spectral order. Because the spectrograph provided a magnification of
about a factor of 6, only 2 optical elements are required to achieved
the desired imaging performance. Throughput was enhanced by the use
of only 2 reflections. The could all be accomodated within a total
instrument length of 1.5m. <P />We would like to acknowledge support
from ONR
---------------------------------------------------------
Title: Association between CME/Flare Events and Enhanced Oxygen
Charge States
Authors: Reinard, A. A.; Dere, K.; Howard, R.
2003SPD....34.0608R Altcode: 2003BAAS...35..818R
We present results from a study of coronal mass ejection (CME) data
obtained both optically (from SOHO/LASCO and SOHO/EIT) and in situ
(from ACE). Phenomena associated with optical CMEs, such as flares
and radio bursts, are compared with heliospheric CME signatures,
such as enhanced charge states and elevated helium densities, to
determine if there is any correspondence between them. A casual
relationship has been seen between CMEs with large flares and ICMEs
with enhanced oxygen charge state ratios. This relationship will be
further investigated. An understanding of how CME observations at the
Sun relate to CME observations in the heliosphere will increase our
understanding of CME dynamics and may provide insight into CME origins.
---------------------------------------------------------
Title: High Resolution Limb Darkening Function Near 2800 /AA/
Measured by HRTS
Authors: Morrill, J. S.; Dere, K. P.; Korendyke, C. M.
2003SPD....34.1909M Altcode: 2003BAAS...35..843M
We are currently developing an empirical model of solar spectral
irradiance varaibility. This model will combine ground based
observations of the areas and locations of plage and sunspots with
measured wavelength dependent contrast factors in order to estimate
the solar spectrum. One important component of this model is the
wavelength dependent limb darking function that must be determined
at high resolution. Using quiet sun spectra near Mg II at about 2800
/AA/ measured by the NRL HRTS instrument, we have recently determined
this function for the quiet sun. This function shows many features
similar to those seen in the active region contast that we have
reported earlier. In this presentation we will discuss the method of
determining the limb darkening function in the 2765 -2885 /AA/ region
and it's impact on the irradiance model.
---------------------------------------------------------
Title: CHIANTI-An Atomic Database for Emission Lines. VI. Proton
Rates and Other Improvements
Authors: Young, P. R.; Del Zanna, G.; Landi, E.; Dere, K. P.; Mason,
H. E.; Landini, M.
2003ApJS..144..135Y Altcode: 2002astro.ph..9493Y
The CHIANTI atomic database contains atomic energy levels, wavelengths,
radiative transition probabilities, and electron excitation data for
a large number of ions of astrophysical interest. Version 4 has been
released, and proton excitation data are now included, principally
for ground configuration levels that are close in energy. The fitting
procedure for excitation data, both electrons and protons, has been
extended to allow nine-point spline fits in addition to the previous
five-point spline fits. This allows higher quality fits to data from
close-coupling calculations where resonances can lead to significant
structure in the Maxwellian-averaged collision strengths. The effects
of photoexcitation and stimulated emission by a blackbody radiation
field in a spherical geometry on the level balance equations of
the CHIANTI ions can now be studied following modifications to the
CHIANTI software. With the addition of H I, He I, and N I, the first
neutral species have been added to CHIANTI. Many updates to existing
ion data sets are described, while several new ions have been added
to the database, including Ar IV, Fe VI, and Ni XXI. The two-photon
continuum is now included in the spectral synthesis routines, and a
new code for calculating the relativistic free-free continuum has been
added. The treatment of the free-bound continuum has also been updated.
---------------------------------------------------------
Title: Identification of Solar Sources of Major Geomagnetic Storms
between 1996 and 2000
Authors: Zhang, J.; Dere, K. P.; Howard, R. A.; Bothmer, V.
2003ApJ...582..520Z Altcode:
This paper presents identification of solar coronal mass ejection (CME)
sources for 27 major geomagnetic storms (defined by disturbance storm
timeindex<=-100 nT) occurring between 1996 and 2000. Observations of
CMEs and their solar surface origins are obtained from the Large Angle
and Spectrometric Coronagraph (LASCO) and the EUV Imaging Telescope
(EIT) instruments on the SOHO spacecraft. Our identification has
two steps. The first step is to select candidate front-side halo
(FSH) CMEs using a fixed 120 hr time window. The second step is
to use solar wind data to provide further constraints, e.g., an
adaptive time window defined based on the solar wind speed of the
corresponding interplanetary CMEs. We finally find that 16 of the
27 (59%) major geomagnetic storms are identified with unique FSH
CMEs. Six of the 27 events (22%) are associated with multiple FSH
CMEs. These six events show complex solar wind flows and complex
geomagnetic activity, which are probably the result of multiple halo
CMEs interacting in interplanetary space. A complex event occurs when
multiple FSH CMEs are produced within a short period. Four of the 27
(15%) events are associated with partial-halo gradual CMEs emerging
from the east limb. The surface origin of these events is not known
because of a lack of any EIT signature. We believe that they are
longitudinally extended CMEs having a component moving along the
Sun-Earth connection line. One of the 27 major geomagnetic storms is
caused by a corotating interaction region. We find an asymmetry in
the longitudinal distribution of solar source region for the CMEs
responsible for major geomagnetic storms. They are more likely
to originate from the western hemisphere than from the eastern
hemisphere. In terms of latitude, most geoeffective CMEs originate
within a latitude strip of +/-30°. The average transit time for a
solar CME to arrive at the near-Earth space is found to be 64 hr,
while it takes 78 hr on average to reach the peak of the geomagnetic
storm. There is a correlation between CME transit time from the Sun
to the near-Earth space (T, in hours) and the CME initial velocity
(V, in unit of kilometers per second) at the Sun, which can be simply
described as T=96-(V/21). We also find that while these geoeffective
CMEs are either full-halo CMEs (67%) or partial-halo CMEs (30%),
there is no preference for them to be fast CMEs or to be associated
with major flares and erupting filaments.
---------------------------------------------------------
Title: In Situ and Heliospheric CME Signature Relations
Authors: Reinard, Alysha; Dere, K.; Howard, R.; Zurbuchen, T.
2003IAUJD...7E..31R Altcode:
We present results from a study of coronal mass ejection (CME) data
obtained both optically (from SOHO/LASCO and SOHO/EIT) and in situ (from
ACE). Phenomena associated with optical CMEs such as flares and radio
bursts are compared with heliospheric CME signatures such as enhanced
charge states and elevated helium densities to determine if there is
any correspondence between them. A casual relationship has been seen
between CMEs with large flares and ICMEs with enhanced oxygen charge
state ratios. This relationship will be further investigated. An
understanding of how CME observations at the Sun relate to CME
observations in the heliosphere will increase our understanding of
CME dynamics and may provide insight into CME origins.
---------------------------------------------------------
Title: Chianti: Inclusion of Ionization and Recombination Rates
Authors: Dere, Kenneth P.
2003IAUJD..17E..17D Altcode:
The spectrum produced by an astrophysical plasma is directly dependent
on the ionization state of the plasma. In order to understand
the ionization balance it is necessary to know the ionization and
recombination rates of the various ions whether the plasma is in a
steady-state ionization state or a transient ionization state. <P
/>New and improved measurements and calculations of ionization and
recombination rate continue to become available. We have collected the
various measurements and calculations for inclusion into the CHIANTI
database. We have developed a scaling law for the ionization rates
similar to that of Burgess and Tully (1992) for electron excitation
rates. We will discuss our progress the adjustments needed for the
new rates and the need for more measurements and calculations.
---------------------------------------------------------
Title: CHIANTI - An Atomic Database for XUV Emission Lines
Authors: Landi, Enrico; Dere, Ken P.; Landini, Massimo; Young, Peter
R.; Mason, Helen E.; del Zanna, Giulio
2003IAUJD..17E..10L Altcode:
CHIANTI is a database of atomic data and transition rates necessary for
calculating synthetic spectra and carrying out plasma diagnostics of
astrophysical sources in the X-ray EUV and UV wavelength ranges. CHIANTI
includes both line and continuum emission from all astrophysically
abundant elements in the universe. All data are taken from refereed
literature and are critically assessed. CHIANTI also includes a suite
of IDL programs that allow spectroscopic analysis to be carried
out. CHIANTI data and software are freely distributed over the
internet. <P />In the present talk I will describe the contents of
the CHIANTI database its current status and the areas where CHIANTI
is being developed and I will also present a comparison of CHIANTI
predictions with the X-ray emission from astrophysical sources.
---------------------------------------------------------
Title: A Comparison between Coronal Emission Lines from an Isothermal
Spectrum Observed with the Coronal Diagnostic Spectrometer and
CHIANTI Emissivities
Authors: Landi, E.; Feldman, U.; Dere, K. P.
2002ApJ...574..495L Altcode:
The present paper compares off-disk spectral observations of the
solar corona in the ranges 307-379 and 513-633 Å with theoretical
emissivities calculated using the CHIANTI database. The observed spectra
were recorded by the Coronal Diagnostic Spectrometer instrument on
board the Solar and Heliospheric Observatory using the normal-incidence
portion of the instrument. Using line-ratio techniques, we first measure
the electron temperature and density in the emitting region, verifying
that it is nearly isothermal. Next, we use an emission-measure analysis
to compare measured spectral line intensities with predictions from the
CHIANTI database. This comparison allows us to assess the quality of
the CHIANTI data for the brightest coronal lines in the 307-379 and
513-633 Å spectral ranges. As a result, we are able to (1) select
lines and ions for which the agreement between theory and observation
is good, (2) identify a few lines that are blended, and (3) stress
inconsistencies between a few lines and theory, thus showing where
improvements to atomic data and transition probabilities are necessary.
---------------------------------------------------------
Title: Identifying Solar Sources of Major Geomagnetic Storms
Authors: Zhang, J.; Dere, K. P.; Howard, R. A.
2002AAS...200.2805Z Altcode: 2002BAAS...34..680Z
We identify solar coronal mass ejection (CME) sources for 27 (out
of 38) major geomagnetic storm events occurred between 1996 and 2000
based on complete solar and interplanetary observations from SOHO, ACE
and WIND spacecrafts. Our search begins with selecting all front-side
halo CMEs (FSH CMEs) based on a fixed transition window of 30--120
hours before the Dst peak time. Valid transition window is reduced
by using solar wind speed of corresponding ICME (Interplanetary CME)
for solar CMEs that are ejected at a speed higher than background
solar wind. We find that 15 of the 27 (60%) major geomagnetic storms
can be uniquely identified with a single FSH CME. However, 6 of the
27 events (20%) have multiple FSH CME sources. The complex solar wind
flow of these events indicate interaction of CMEs in their path toward
the Earth. The left 6 events (20%) have no FSH CME in the transition
window. It appears that 4 out of the 6 events are caused by partial
halo gradual CMEs originated from east limb, which are believed to
be longitudinal extended gradual CMEs with intrinsic wide-angle. One
event is caused by an impulsive CME from west limb, and another event
is caused by corotating interaction region (CIR) associated with a low
latitude coronal hole. The average transition time from the Sun to the
Earth is 64 hours while it is 78 hours to reach peak of geomagnetic
storms. There is a coarse correlation between CME speed (V in km/s)
and transition time (to ICME, T in hr.), simply as T=96-V/21. We
find that geo-effective CMEs are more likely originated from western
hemisphere than from eastern hemisphere. Almost all geo-effective CMEs
from western hemisphere are full halo CMEs, while most geo-effective
CMEs from eastern hemisphere are partial halo CMEs.
---------------------------------------------------------
Title: CHIANTI-An Atomic Database for Emission Lines. V. Comparison
with an Isothermal Spectrum Observed with SUMER
Authors: Landi, E.; Feldman, U.; Dere, K. P.
2002ApJS..139..281L Altcode:
CHIANTI is a database consisting of critically evaluated atomic data and
transition probabilities necessary to analyze spectral observations
of optically thin plasmas. Previous papers described the content
of the database and compared it to a solar active region spectrum
between 170 and 450 Å. The aim of the present paper is to compare
CHIANTI predictions to off-disk spectral observations of the solar
corona between 500 and 1500 Å. The observed spectra were recorded by
the SUMER instrument on board the Solar and Heliospheric Observatory
using the full spectral range allowed by the instrument. Earlier works
have demonstrated that the particular emitting plasma is isothermal
at a temperature of 1.35×10<SUP>6</SUP> K, making it ideal for the
assessment of the accuracy of the CHIANTI database. This assessment of
the CHIANTI database allowed us (1) to select lines and ions for which
the agreement between theory and observation is good, (2) to identify
several lines which are blended, and (3) to stress inconsistencies
between a few lines and theory, thus showing where improvements to
atomic data and transition probabilities are necessary.
---------------------------------------------------------
Title: Sun earth connection coronal and heliospheric investigation
(SECCHI)
Authors: Howard, R. A.; Moses, J. D.; Socker, D. G.; Dere, K. P.;
Cook, J. W.; Secchi Consortium
2002AdSpR..29.2017H Altcode:
The Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI)
on the NASA Solar Terrestrial Relations Observatory ( STEREO) mission
is a suite of remote sensing instruments consisting of an extreme
ultraviolet imager, two white light coronagraphs, and a heliospheric
imager. Two spacecraft with identical instrumentation will obtain
simultaneous observations from viewpoints of increasing separation
in the ecliptic plane. In support of the STEREO mission objectives,
SECCHI will observe coronal mass ejections from their birth at the Sun,
through the outer corona, to their impact at Earth. The SECCHI program
includes a coordinated effort to develope magneto-hydrodynamic models
and visualization tools to interpret the images that will be obtained
from the two spacecraft viewpoints. The resulting three-dimensional
analysis of CMEs will help to resolve some of the fundamental
outstanding questions in solar physics.
---------------------------------------------------------
Title: The CHIANTI Atomic Database and Instrument Calibration:
a Symbiosis
Authors: Mason, H. E.; Del Zanna, G.; Dere, K. P.; Landi, E.; Landini,
M.; Young, P. R.
2002ISSIR...2..271M Altcode: 2002ESASR...2..271M; 2002rcs..conf..271M
The CHIANTI atomic database comprises a comprehensive, accurate and
up-to-date database of atomic parameters, necessary for emission-line
spectroscopy. The suite of user-friendly software allows plasma
diagnostics to be carried out. Since its release in 1996, CHIANTI has
become a standard resource for the analysis of solar spectra. Accurate
atomic data can provide the foundation for in-flight instrument
calibrations. Conversely, an accurate instrument calibration can provide
a check on atomic parameters. The internal consistency of spectral-line
intensities can be used to highlight specific anomalies. In this paper,
we illustrate how CHIANTI has been used to validate the calibration of
solar EUV instruments: SOHO-CDS, -SUMER, -EIT and SERTS. In addition,
we show how anomalous spectral-line intensities indicate the need for
more accurate atomic calculations.
---------------------------------------------------------
Title: Relationship Between Coronal Mass Ejections and Flares
Authors: Zhang, J.; Dere, K.; Howard, R. A.
2001AGUFMSH31C..05Z Altcode:
We present the results of our observational study about the relationship
between CMEs (Coronal Mass Ejections) and flares. We make use of
CME events well observed by the LASCO instrument (Large Angle and
Spectrometric Coronagraph), which are suitable for studying their
detailed kinematic evolution throughout the lower corona (1.1--3
Rsun, the LASCO C1 field of view) and the upper corona (2--30 Rsun,
the LASCO C2/C3 field of view). We make height-time and velocity-time
plots for these events, giving special attention to the height range
of the lower corona where CME acceleration takes place. We find that
the evolution of impulsive CMEs can be divided into three phases:
initiation phase characterized by slow ascension (less than 80 km/s),
impulsive acceleration phase, and subsequent propagation phase. The
initiation phase starts earlier than the onset time of the associated
flare. However, the onset time of the impulsive acceleration phase
coincides with the onset time of the flare, and the acceleration
period of the impulsive acceleration phase coincides with the rise
phase of the flare. Gradual CMEs, which are not associated with flares,
do not show an impulsive acceleration phase. On the other hand, there
exists another class of CMEs, which we call explosive CMEs. Explosive
CMEs are accelerated extremely fast to reach a great velocity;
the acceleration takes place very low in the corona (less than 0.5
Rsun above the surface). They do not show an initiation phase and
are associated with major flares. The Nov. 6, 1997 CME/flare event,
which is a great particle event, is a typical explosive one and will
be discussed in detail in the presentation
---------------------------------------------------------
Title: Solar Irradiance Variability Modeled Near Mg II Using Plage
and Sunspot Contrast Factors Measured by HRTS
Authors: Morrill, J. S.; Dere, K. P.; Korendyke, C. M.; Floyd, L. E.
2001AGUFMSH11C0733M Altcode:
Empirical models of solar spectral irradiance varaibility combine areas
and locations of plage and sunspots with wavelength dependent contrast
factors in order to estimate the solar spectrum. At UV wavelengths,
these models have relied on estimated or calculated contrast factors
that are often at low resolution. Using quiet sun, plage, and sunspot
spectra near Mg II at ~ 2800Å measured by the NRL HRTS instrument,
we have recently determined the wavelength dependent contrast factors
for plage and sunspots. In this presentation we will discuss the use of
measured contrast factors in a spectral irradiance model of the 2765 -
2885Å region and the preliminary comparisons of model results with
SUSIM observations. These comparisons will examine spectral irradiance
variations on solar rotational and solar cycle time scales.
---------------------------------------------------------
Title: Source Regions of Coronal Mass Ejections
Authors: Subramanian, Prasad; Dere, K. P.
2001ApJ...561..372S Altcode: 2001astro.ph..7138S
Observations of the solar corona with the Large Angle and
Spectrometric Coronagraph Experiment (LASCO) and EUV Imaging
Telescope (EIT) instruments on the Solar and Heliospheric Observatory
(SOHO) provide an unprecedented opportunity to study coronal mass
ejections (CMEs) from their initiation through their evolution out
to 30 R<SUB>solar</SUB>. The objective of this study is to gain an
understanding of the source regions from which the CMEs emanate. To
this end, we have developed a list of 32 CMEs whose source regions
are located on the solar disk and are well observed in EIT 195 Å data
during the period from solar minimum in 1996 January through the rising
part of the cycle in 1998 May. We compare the EIT source regions with
photospheric magnetograms from the Michelson Doppler Imager (MDI)
instrument on SOHO and the National Solar Observatory at Kitt Peak
and also with Hα data from various sources. The overall results of
our study show that 41% of the CME-related transients observed are
associated with active regions and have no prominence eruptions, 44%
are associated with eruptions of prominences embedded in active regions,
and 15% are associated with eruptions of prominences outside active
regions. Those CMEs that do not involve prominence eruptions originate
in active regions both with and without prominences. We describe six
especially well observed events. These case studies suggest that active
region CMEs (without eruptive prominences) are associated with active
regions with lifetimes between 11 and 80 days. They are also often
associated with small-scale emerging or canceling flux over timescales
of 6-7 hr. CMEs associated with active region prominence eruptions,
on the other hand, are typically associated with old active regions
with lifetimes ~6-7 months.
---------------------------------------------------------
Title: Reconciling Extreme-Ultraviolet and Radio Observations of
the Sun's Corona
Authors: Zhang, J.; Kundu, M. R.; White, S. M.; Dere, K. P.; Newmark,
J. S.
2001ApJ...561..396Z Altcode:
The Sun's corona, which is composed of plasma at a temperature of a few
millions of degrees, can be best viewed in two electromagnetic domains,
one from wavelengths of a few angstroms to hundreds of angstroms
(in the soft X-ray and EUV domain), the other from wavelengths
of a few centimeters to several tens of centimeters (in the radio
domain). In this paper, we present a quantitative comparison of coronal
observations made in these two domains with high spatial resolution
over the full disk of the Sun. The EUV observations were taken with the
EIT (Extreme-Ultraviolet Imaging Telescope) on board SOHO (Solar and
Heliospheric Observatory), and the radio observations were taken with
the VLA (Very Large Array). The two sets of images show very similar
morphologies, indicating that the different wavelengths originate from
common solar features. We predict radio fluxes using the temperature
and emission measure of the corona calculated from EIT observations,
adopting Meyer's table of coronal abundances for the calculations. In
each of the seven observations investigated, there always exists a
good linear correlation in the pixel-by-pixel correlation plot between
the predicted and the observed radio flux for coronal features over a
wide range of flux variation. Nevertheless, the predicted radio flux
is systematically larger than that observed by a factor of 2.0+/-0.2,
on average. We attribute the difference to the underestimation of the
abundance of Fe relative to H in the abundances adopted by Meyer. On
this basis, we place the absolute Fe abundance in the corona at
7.8×10<SUP>-5</SUP>, which has an enrichment factor of 2.4 relative
to the accepted photospheric Fe abundance.
---------------------------------------------------------
Title: CHIANTI - An atomic database for X-EUV spectral lines
Authors: Dere, K. P.; Landi, E.
2001tysc.confE..64D Altcode:
CHIANTI provides a database of atomic energy levels, wavelengths,
radiative transition probabilities and electron excitation data for
a large number of ions of astrophysical interest. It also includes
a suite of Interactive Data Language (IDL) programs to calculate
optically thin synthetic spectra and to perform spectral analysis
and plasma diagnostics. This database allows the calculation of
theoretical line emissivities necessary for the analysis of optically
thin emission line spectra. The first version (1.01) of the CHIANTI
database was released in 1996 h paper1. The second version, released
in 1999, included continuum emission and data for additional ions
(Landi et al. 1999). Both versions of the CHIANTI database have been
used extensively by the astrophysical and solar communities to analyze
emission line spectra from astrophysical sources. Now the CHIANTI
database has been extended to wavelengths shorter than 50Å by including
atomic data for the hydrogen and helium isoelectronic sequences,
inner-shell transitions and satellite lines and several other ions. In
addition, some of the ions already present in the database have been
updated and extended with new atomic data from published calculations.
---------------------------------------------------------
Title: On the Temporal Relationship between Coronal Mass Ejections
and Flares
Authors: Zhang, J.; Dere, K. P.; Howard, R. A.; Kundu, M. R.; White,
S. M.
2001ApJ...559..452Z Altcode:
The temporal relationship between coronal mass ejections (CMEs) and
associated solar flares is of great importance to understanding the
origin of CMEs, but it has been difficult to study owing to the nature
of CME detection. In this paper, we investigate this issue using the
Large Angle and Spectrometric Coronagraph and the EUV Imaging Telescope
observations combined with GOES soft X-ray observations. We present
four well-observed events whose source regions are close to the limb
such that we are able to directly measure the CMEs' initial evolution
in the low corona (~1-3 R<SUB>solar</SUB>) without any extrapolation;
this height range was not available in previous space-based coronagraph
observations. The velocity-time profiles show that kinematic evolution
of three of the four CMEs can be described in a three-phase scenario:
the initiation phase, impulsive acceleration phase, and propagation
phase. The initiation phase is characterized by a slow ascension
with a speed less than 80 km s<SUP>-1</SUP> for a period of tens of
minutes. The initiation phase always occurs before the onset of the
associated flare. Following the initiation phase, the CMEs display an
impulsive acceleration phase that coincides very well with the flares'
rise phase lasting for a few to tens of minutes. The acceleration of
CMEs ceases near the peak time of the soft X-ray flares. The CMEs then
undergo a propagation phase, which is characterized by a constant speed
or slowly decreasing in speed. The acceleration rates in the impulsive
acceleration phase are in the range of 100-500 m s<SUP>-2</SUP>. One CME
(on 1997 November 6, associated with an X9.4 flare) does not show an
initiation phase. It has an extremely large acceleration rate of 7300 m
s<SUP>-2</SUP>. The possible causes of CME initiation and acceleration
in connection with flares are explored.
---------------------------------------------------------
Title: The Sources of Solar Ultraviolet Variability between 2765
and 2885 Å: Mg I, Mg II, Si I, and Continuum
Authors: Morrill, J. S.; Dere, K. P.; Korendyke, C. M.
2001ApJ...557..854M Altcode:
The variation of the solar spectrum between 2000 and 4000 Å is a
major component of the total irradiance variability of the Sun. Recent
analyses suggest that variations in the solar ultraviolet flux at
these wavelengths account for about 30% of the total solar irradiance
variability. Most estimates of solar spectral irradiance variability in
the ultraviolet are based on the ratio of the intensity of features such
as solar plages and sunspots to the intensity of the quiet Sun. These
ratios are referred to as contrast factors. To a large degree, contrast
factors at ultraviolet wavelengths have not been measured. We present
measurements of the average intensities of plage, sunspot, and quiet-Sun
regions in the spectral range between 2765 and 2885 Å, derived from
high spatial and spectral resolution spectra obtained during the ninth
rocket flight of the High Resolution Telescope and Spectrograph in
1995. From these average spectra, plage and sunspot contrast factors
are determined. To our knowledge, these are the first contrast factors
at these wavelengths derived from measured solar intensities. These
spectra show a large contrast in the Mg I, Mg II, and Si I Fraunhofer
lines and a much smaller contrast (1.01+/-0.015 to 1.04+/-0.04) in
the line-blanketed continuum. Contrast factors are also determined
for three intensity levels of the quiet Sun as well as for a single
sunspot. Many fine spectral features in the contrast factors can be
attributed to weak Fraunhofer lines of Cr II, Fe I, Fe II, and Mg I.
---------------------------------------------------------
Title: CHIANTI-An Atomic Database for Emission Lines. IV. Extension
to X-Ray Wavelengths
Authors: Dere, K. P.; Landi, E.; Young, P. R.; Del Zanna, G.
2001ApJS..134..331D Altcode:
CHIANTI provides a database of atomic energy levels, wavelengths,
radiative transition probabilities, and electron excitation data for
a large number of ions of astrophysical interest. It also includes a
suite of Interactive Data Language programs to calculate optically
thin synthetic spectra and to perform spectral analysis and plasma
diagnostics. This database allows the calculation of theoretical line
emissivities necessary for the analysis of optically thin emission-line
spectra. The first version (1.01) of the CHIANTI database was released
in 1996 and published by Dere et al. in 1997 as Paper I in this
series. The second version, released in 1999 by Landi et al., included
continuum emission and data for additional ions. Both versions of the
CHIANTI database have been used extensively by the astrophysical and
solar communities to analyze emission-line spectra from astrophysical
sources. Now the CHIANTI database has been extended to wavelengths
shorter than 50 Å by including atomic data for the hydrogen and helium
isoelectronic sequences, inner-shell transitions and satellite lines,
and several other ions. In addition, some of the ions already present
in the database have been updated and extended with new atomic data
from published calculations.
---------------------------------------------------------
Title: High-resolution Imaging of the Upper Solar Chromosphere:
First Light Performance of the Very-high-Resolution Advanced
ULtraviolet Telescope
Authors: Korendyke, C. M.; Vourlidas, A.; Cook, J. W.; Dere, K. P.;
Howard, R. A.; Morrill, J. S.; Moses, J. D.; Moulton, N. E.; Socker,
D. G.
2001SoPh..200...63K Altcode:
The Very-high-resolution Advanced ULtraviolet Telescope (VAULT)
experiment was successfully launched on 7 May 1999 on a Black Brant
sounding rocket vehicle from White Sands Missile Range. The instrument
consists of a 30 cm UV diffraction limited telescope followed by a
two-grating, zero-dispersion spectroheliograph tuned to isolate the
solar Lα emission line. During the flight, the instrument successfully
obtained a series of images of the upper chromosphere with a limiting
resolution of ∼ 0.33 arc sec. The resulting observations are the
highest-resolution images of the solar atmosphere obtained from space
to date. The flight demonstrated that sub-arc second ultraviolet
images of the solar atmosphere are achievable with a high-quality,
moderate-aperture space telescope and associated optics. Herein,
we describe the payload and its in-flight performance.
---------------------------------------------------------
Title: Solar Origin of Major Geo-magnetic Storms Between 1996 and 2000
Authors: Zhang, J.; Dere, K. P.; Howard, R. A.
2001AGUSM..SH62A11Z Altcode:
We investigate the solar origin of major geo-magnetic storms which
occurred between 1996 and 2000. Based on the hourly DST index, we
identify 39 major geo-magnetic storms (defined as peak DST less
than -100) in this period. The solar observations are primarily
based on LASCO (Large-Angle and Spectrometric Coronagraph) and EIT
(Extreme-ultraviolet Imaging Telescope) instruments on board SOHO
spacecraft. Using a six-day time window, we search through all
halo/partial-halo CMEs (Coronal Mass Ejections) seen in LASCO and
coronal dimmings seen in EIT for each storm to try to identify its
solar source. 30 of the 39 storms are in the LASCO/EIT duty cycle
(most of the other 9 events occurred during 1998-1999 SOHO failure). We
associate these storms to solar sources with three different confidence
levels. For 18 of the 30 events, we have reliably determined their solar
sources, all of which show both strong halo CME signature and almost
simultaneous strong coronal dimming signature; these signatures are
usually unique in the time window. For 5 of the 30 events, there are
multiple halo CMEs and dimmings found in the time window, and we can
not make unambiguous association with a particular solar source. For
the other 7 of the 30 events, we find it is difficult to identify
solar sources, due to lack of strong signature in either LASCO or
EIT observations or both. We investigate various characteristics of
solar sources for those 18 major storms with unambiguous association,
including CME morphology and kinematics, pre-eruption coronal structure
and evolution, coronal dimmings and waves, coronal post-eruption loops,
X-ray and optical flares, filaments, photospheric magnetic field
structure and distribution of heliocentric position. The purpose is
to understand the characteristics of CMEs observed near the Sun which
causes major geo-magnetic storms.
---------------------------------------------------------
Title: Ultra-High Resolution Observations of the Upper Chromosphere:
First Results From the NRL VAULT Sounding Rocket Payload
Authors: Vourlidas, A.; Korendyke, C. M.; Dere, K. P.; Klimchuk, J. A.
2001AGUSM..SP61A03V Altcode:
The Very high resolution Advanced ULtraviolet Telescope (VAULT) is
a new spectroscopic imaging instrument. The instrument was launched
on May 7, 1999 as a sounding rocket payload. The goal of the first
VAULT flight was to obtain sub-arcsecond images of the Sun in the
light of Lya (1216 Å). VAULT directly imaged an active region plage,
fliaments and the fine structures in the supergranule boundaries and
network with the unprecented spatial resolution of 0.33 arcseconds. We
present the VAULT images and the first results from the comparison of
the Lya data to observations from other instruments and in particular
with a sequence of TRACE 171 Å images taken during the VAULT flight.
---------------------------------------------------------
Title: CHIANTI - an atomic database for emission lines, Paper 4:
Extension to X-ray Wavelengths
Authors: Dere, K. P.; Landi, E.; Young, P. R.; Del Zanna, G.
2001AGUSM..SP21B08D Altcode:
CHIANTI provides a database of atomic energy levels, wavelengths,
radiative transition probabilities and electron excitation data for
a large number of ions of astrophysical interest. It also includes
a suite of Interactive Data Language (IDL) programs to calculate
optically thin synthetic spectra and to perform spectral analysis and
plasma diagnostics. This database allows the calculation of theoretical
line emissivities necessary for the analysis of optically thin emission
line spectra. The first version of the CHIANTI database was released
in 1996 (Dere et al., 1996). The second version, released in 1999,
included continuum emission and data for additional ions (Landi
et al. 1999). Both versions of the CHIANTI database have been used
extensively by the astrophysical and solar communities to analyze
emission line spectra from astrophysical sources. Now the CHIANTI
database has been extended to wavelengths shorter than 50Å by including
atomic data for the hydrogen and helium isoelectronic sequences,
inner-shell transitions and satellite lines and several other ions. In
addition, some of the ions already present in the database have been
updated and extended with new atomic data from published calculations.
---------------------------------------------------------
Title: The Extreme Ultraviolet Imaging Spectrometer on Solar-B
Authors: Mariska, J. T.; Brown, C. M.; Dere, K. P.; Doschek, G. A.;
Korendyke, C. M.; Culhane, J. L.; Watanabe, T.
2001AGUSM..SH41A12M Altcode:
Emission lines in the extreme ultraviolet spectral region provide a
sensitive probe of the high-temperature plasma in the solar transition
region and corona. Simultaneously achieving high spatial, spectral, and
temporal resolution in this wavelength region has been challenging. We
describe the design and capabilities of the Extreme Ultraviolet
Imaging Spectrometer (EIS) planned for flight on the Japanese Solar-B
satellite. EIS consists of a multilayer-coated off-axis telescope
mirror and a multilayer-coated toroidal grating spectrometer. The
telescope mirror forms a solar image on the spectrometer entrance slit
assembly and the spectrometer forms stigmatic spectra of the solar
region isolated by the 1024 arcsec high slit. The instrument includes
thin-film aluminum filters to reject longer wavelength radiation and
CCD detectors at the focal plane. Articulation of the primary mirror
provides roughly 1600 arcsec of east-west coarse pointing freedom
and 360 arcsec of fine east-west motion for rastering. Monochromatic
images are formed either by rastering the solar image across a narrow
entrance slit or by using a very wide slit. Half of each optic is
coated to optimize reflectance at 19.5 nm, and the other half to
optimize reflectance at 27.0 nm. Each wavelength range is imaged onto
a separate CCD detector. The EIS spectral range contains emission lines
formed over a temperature range from roughly 0.1 to 20 MK. Bright lines
in the selected wavelength bands will yield precision measurements of
line-of-sight velocities and nonthermal plasma motions. This spectral
range also includes several pairs of density-sensitive lines.
---------------------------------------------------------
Title: High Resolution Observations of Solar Spectral Variability
Near Mg II Measured by HRTS
Authors: Morrill, J. S.; Dere, K. P.; Korendyke, C. M.
2001AGUSM..SP32B03M Altcode:
The HRTS-9 rocket flight occurred on April 18, 1995 and made
measurements of solar spectral variability near the Mg II h and k
lines. These observations include high spatial and spectral resolution
spectrograms as well as spectroheliograms in four FUV passbands and
H-alpha. The spectrograms cover the wavelength range 2665 to 2885Å
with a spectral resolution of .2Å and a spatial resolution of 1
arc-second along a 900 arc-second slit. The most prominent features
in this spectral range include the strong Mg II h and k lines near
2800 Å, the Mg I and Si I Fraunhofer lines near 2850 and 2880Å,
respectively, and the line-blanketed quasi-continuum region. During
the HRTS-9 flight, spectrograms and spectroheliograms where obtained
of the quiet sun, quiet limb, plage, and sunspots. In addition to
instrumental corrections, we have recently applied an absolute intensity
calibration to the HRTS-9 data derived from SUSIM/ATLAS-3 and SUSIM/UARS
observations. The analysis of these calibrated data has focused on
the spectral variability of the above surface features and how these
observations impact solar irradiance variability. Specifically, we
examine the contrast variation of the plage and sunspot compared to the
quiet sun as well as contrast variation within the quiet sun. In this
presentation we will discuss the details of the observed spectra and
wavelength dependent contrast factors. This will include a comparison
of our present results with earlier estimates of plage contrast in this
wavelength region and a discussion of the fine structures observed at
high spectral resolution.
---------------------------------------------------------
Title: Source Regions of Coronal Mass Ejections
Authors: Dere, K. P.; Subramanian, P.
2001IAUS..203..362D Altcode:
A set of 32 coronal mass ejections observed with the LASCO and EIT
instruments on SOHO have been examined. These events have been selected
from the period between May 1997 through May 1998 and includes the
period of solar minimum and the rise of solar cycle 23. The criteria
for including these events were that they were observed as a CME
in LASCO, they were well observed with EIT and they were located
near disk center. The sources of these 32 events were active regions
without filaments (26 cases),active regions with filaments (7 cases)
and quiescent filaments (6 cases). In the EIT, the signature of the
initiation of the coronal mass ejection includes flares, EIT waves,
coronal dimmings and mass ejections. The characteristics of the
photospheric magnetic activity associated with these events, observed
with NSO/Kitt Peak and MDI/SOHO magnetograms, indicate that CMEs are
associated with a wide range of activity that includes small scale
flux emergence and cancellation, large scale flux emergence, and large
scale flux decay. During this period of the solar cycle, the solar disk
contains few active regions which are generally generally short lives
so that there may be a solar cycle dependence to these conclusions.
---------------------------------------------------------
Title: BEPPOSAX Observation of EQ Pegasi (CD-ROM Directory:
contribs/landi)
Authors: Landi, E.; Landini, M.; Dere, K.; Risaliti, G.
2001ASPC..223..991L Altcode: 2001csss...11..991L
No abstract at ADS
---------------------------------------------------------
Title: In-flight performance of the Very high Angular resolution
ULtraviolet Telescope sounding rocket payload
Authors: Korendyke, Clarence M.; Vourlidas, A.; Cook, John W.; Dere,
Kenneth P.; Feldman, R.; Howard, Russell A.; Lilley, D. N.; Morrill,
Jeff S.; Moses, J. Daniel; Moulton, Norman E.; Moye, Robert W.;
Roberts, D. E.; Shepler, E. L.; Smith, J. K.; Socker, Dennis G.;
Spears, T. R.; Waymire, R. S.; Brown, Wayne E.; Tarbell, Theodore D.;
Berger, Tom; Handy, Brian N.
2000SPIE.4139..340K Altcode:
The Very high Angular Resolution ULtraviolet Telescope experiment was
successfully launched on May 7, 1999 on a Black Brant sounding rocket
vehicle from White Sands Missile Range. The instrument consists of a
30 cm UV diffraction limited telescope followed by a double grating
spectroheliograph tuned to isolate the solar Lyman (alpha) emission
line. During the flight, the instrument successfully obtained a series
of images of the upper chromosphere with a limiting resolution of
approximately 0.33 arc-seconds. The resulting observations are the
highest resolution images of the solar atmosphere obtained from space
to date. The flight demonstrated that subarc-second ultraviolet images
of the solar atmosphere are achievable with a high quality, moderate
aperture space telescope and associated optics. Herein, we describe
the payload and its in- flight performance.
---------------------------------------------------------
Title: Solar Transition Region
Authors: Dere, K.
2000eaa..bookE2021D Altcode:
The solar transition region can generally be defined as those
plasmas at temperatures between 2×104 and 1×106 K, a temperature
regime bridging the CHROMOSPHERE and CORONA. Prior to the space age,
the transition region was unobserved although the existence of the
higher-temperature corona was known. Spectral lines formed at transition
region temperatures are found primarily below 2000 Å where they...
---------------------------------------------------------
Title: The Preflight Photometric Calibration of the
Extreme-Ultraviolet Imaging Telescope EIT
Authors: Dere, K. P.; Moses, J. D.; Delaboudinière, J. -P.; Brunaud,
J.; Carabetian, C.; Hochedez, J. -F.; Song, X. Y.; Catura, R. C.;
Clette, F.; Defise, J. -M.
2000SoPh..195...13D Altcode:
This paper presents the preflight photometric calibration of the
Extreme-ultraviolet Imaging Telescope (EIT) aboard the Solar and
Heliospheric Observatory (SOHO). The EIT consists of a Ritchey-Chrétien
telescope with multilayer coatings applied to four quadrants of the
primary and secondary mirrors, several filters and a backside-thinned
CCD detector. The quadrants of the EIT optics were used to observe
the Sun in 4 wavelength bands that peak near 171, 195, 284, and 304
Å. Before the launch of SOHO, the EIT mirror reflectivities, the filter
transmissivities and the CCD quantum efficiency were measured and these
values are described here. The instrumental throughput in terms of an
effective area is presented for each of the various mirror quadrant
and filter wheel combinations. The response to a coronal plasma as
a function of temperature is also determined and the expected count
rates are compared to the count rates observed in a coronal hole,
the quiet Sun and an active region.
---------------------------------------------------------
Title: Solar UV Irradiance Variability Observed at High Spatial and
Spectral Resolution by HRTS
Authors: Morrill, J. S.; Dere, K. P.; Korendyke, C. M.
2000SPD....31.0128M Altcode: 2000BAAS...32..806M
The HRTS-9 rocket flight occured on April 18, 1995 and was configured
to study the sources of solar variablity by observing ultraviolet
emission patterns near the Mg II h and k lines. These observations
include high spatial and spectral resolution spectrograms as
well as spectroheliograms in four FUV passbands and H-alpha. The
spectrograms cover the wavelength range 2665 to 2885 Angstroms \ with
a spectral resolution of .2 Angstroms \ and a spatial resolution of 1
arc-second along a 900 arc-second slit. Prominent spectral features
in this wavelength range include the Mg II h and k lines near 2800
Angstroms, the strong Mg I and Si I Fraunhofer lines near 2850 and
2880 Angstroms, respectively, and the line-blanketed quasi-continuum
region. HRTS-9 observations included the quiet sun, quiet limb,
plage, and sunspots. The analysis of this data set has focused on
the spatial intensity variability of the features as a function of
wavelength with particular regard for how these will affect solar
variability. Specifically, we examine the contrast variation of
the plage and sunspot compared to the quiet sun as well as contrast
variation within the quiet sun. The observed sunspot spectrum shows
the characteristic decrease in the quasi-continuum, the non-reversed
Mg II h and k line shapes as well as the enhancement in the Mg II
h and k core emissions over that observed in the quiet sun. In this
presentation we will discuss the wavelength dependent contrasts of
the plage and quiet sun regions, the characteristics of the observed
sunspot spectrum, and the implications on solar variability.
---------------------------------------------------------
Title: Large-Angle Spectrometric Coronagraph Measurements of the
Energetics of Coronal Mass Ejections
Authors: Vourlidas, A.; Subramanian, P.; Dere, K. P.; Howard, R. A.
2000ApJ...534..456V Altcode:
We examine the energetics of coronal mass ejections (CMEs) with data
from the large-angle spectrometric coronagraphs (LASCO) on SOHO. The
LASCO observations provide fairly direct measurements of the mass,
velocity, and dimensions of CMEs. Using these basic measurements,
we determine the potential and kinetic energies and their evolution
for several CMEs that exhibit flux-rope morphologies. Assuming flux
conservation, we use observations of the magnetic flux in a variety
of magnetic clouds near the Earth to determine the magnetic flux and
magnetic energy in CMEs near the Sun. We find that the potential and
kinetic energies increase at the expense of the magnetic energy as
the CME moves out, keeping the total energy roughly constant. This
demonstrates that flux-rope CMEs are magnetically driven. Furthermore,
since their total energy is constant, the flux-rope parts of the CMEs
can be considered a closed system above ~2 R<SUB>solar</SUB>.
---------------------------------------------------------
Title: LASCO and EIT observations of CMEs associated with flares
Authors: Zhang, J.; Dere, K. P.; Howard, R. A.; Kundu, M. R.; White,
S. M.
2000SPD....31.0906Z Altcode: 2000BAAS...32..841Z
Coronal mass ejections (CME) and flares are two primary causes
of adverse space weather. These two solar eruptive phenomenon are
often observed to be associated with each other. Yet the relationship
between them is not well known. With unprecedented LASCO (Large-Angle
and Spectrometric Coronagraph) and EIT (Extreme-ultraviolet Imaging
Telescope) observations combined with simultaneous HXT (Hard X-ray
Telescope), GOES and other flare observations, we pursue to make a
comprehensive study on the spatial, temporal and energetic relationship
between CMEs and flares. In order to make accurate measurement of the
onset time of CMEs, we primarily select CME events whose source regions
are close to the limb and which are well observed by LASCO/C1 from
1.1 to 3 solar radii. Although a flare occurs in a rather small area
of active region, the CME's source region often covers much larger
longitudinal and latitudinal extension. Some CMEs occur simultaneously
with flare (within only a few minutes), however, some CMEs occur
well before the flares (more than 30 minutes earlier). Fast CMEs are
associated with strong flares. These studies are aimed to understand
the initiation process of solar eruptive phenomenon, and to fit a
variety of observational aspects into a consistent picture.
---------------------------------------------------------
Title: LASCO and EIT Observations of Coronal Mass Ejections
Authors: Dere, K. P.; Vourlidas, A.; Subramanian, Prasad
2000astro.ph..2061D Altcode:
We present a brief overview of LASCO and EIT observations of CMEs. We
discuss CME energetics, the relation of CMEs to streamers and conclude
with some insights into the source regions of CMEs.
---------------------------------------------------------
Title: Non-Radial Unipolar Coronal Streamers in Magnetically High
Latitudes and Radial Bipolar Streamers at the Magnetic Equator of
the Sun
Authors: Saito, Takao; Shibata, K.; Dere, K. P.; Numazawa, S.
2000AdSpR..26..807S Altcode:
The complex structure of coronal streamers can be better understood by
their classification into two classes: non-radial unipolar streamers
emanating from magnetically high latitudes, and radial bipolar streamers
emanating from the magnetic equator. The coronal streamers observed
during the total solar eclipses of July 11,1991 and February 26, 1998
are classified into the two types. Various characteristics of the two
types are discussed and summarized. Important relations of the two to
solar, interplanetary, and terrestrial phenomena are discussed
---------------------------------------------------------
Title: Coronal Mass Ejections and the Solar Wind: New Results
from LASCO
Authors: Dere, K. P.; Howard, R. A.; Brueckner, G. E.
2000AdSpR..25.1837D Altcode:
The LASCO and EIT experiments on SOHO have provided a revolutionary
picture of coronal dynamics. In the past, the corona has largely been
thought to be a region where the evolution of the coronal structures
occurred on relatively large time scales, aside from the intermittent
coronal mass ejection. The outflows in the polar coronal holes were
largely considered to be time-independent. The picture now presented by
the LASCO and EIT observations are of a highly dynamic corona. Continual
small scale sporadic outflows are observed in quiet streamers and
in the polar coronal holes. The LASCO images of CMEs shows that many
appear to have circular structures that indicate that they consist of
helical magnetic flux ropes. In addition, a new class of CMEs has been
observed and are called `global' CMEs since they appear to involve
regions of the corona separated by as much as 180°
---------------------------------------------------------
Title: Commission 10: Solar Activity: (Activite Solaire)
Authors: Ai, G.; Benz, A.; Dere, K. P.; Engvold, O.; Gopalswamy, N.;
Hammer, R.; Hood, A.; Jackson, B. V.; Kim, I.; Marten, P. C.; Poletto,
G.; Rozelot, J. P.; Sanchez, A. J.; Shibata, K.; van Driel-Geztelyi, L.
2000IAUTA..24...67A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Microwave and Extreme Ultraviolet Observations of Solar
Polar Regions
Authors: Nindos, A.; Kundu, M. R.; White, S. M.; Gary, D. E.;
Shibasaki, K.; Dere, K. P.
1999ApJ...527..415N Altcode:
The poles of the Sun are brighter than the rest of the quiet Sun's
emission in a limited range of radio frequencies from 17 GHz to 87
GHz. We have studied microwave images of the quiet Sun made with
the Nobeyama radioheliograph at 17 GHz. They show that the so-called
polar-cap brightening consists of two components: a diffuse component
of 1500 K excess brightness and patchy compact sources with localized
excess brightness of about 3500 K. We test the reality of the compact
sources using the maximum entropy method deconvolution. The total flux
and the number of compact polar sources as well as the north-south
extent of the diffuse polar emission are larger in the pole that is
closest to the Earth. We compared the microwave polar emission with
nearly simultaneous SOHO EIT images taken in the lines of He II at 304
Å and Fe XII at 195 Å. No one-to-one correlation between the compact
radio sources and the bright EUV features was found: most of the radio
emission arises between the plumes visible to EIT. The boundaries of
the polar-cap brightenings did not match exactly the boundaries of the
coronal holes as seen in either the Fe XII 195 Å images or the He II
304 Å images. The temporal variations of the compact microwave sources
did not correspond to any significant changes in EUV emission. On the
other hand, most He II 304 Å changing features were associated with the
diffuse polar microwave emission, which was practically constant. Our
data suggest that the origin of the polar brightening is not coronal;
it seems that the bulk of the patchy radio emission comes from heights
below the 80,000 K layer.
---------------------------------------------------------
Title: LASCO Measurements of the Energetics of Coronal Mass Ejections
Authors: Vourlidas, Angelos; Subramanian, Prasad; Dere, K. P.; Howard,
R. A.
1999astro.ph.12069V Altcode:
We examine the energetics of Coronal Mass Ejections (CMEs) with data
from the LASCO coronagraphs on SOHO. The LASCO observations provide
fairly direct measurements of the mass, velocity and dimensions of
CMEs. Using these basic measurements, we determine the potential and
kinetic energies and their evolution for several CMEs that exhibit a
flux-rope morphology. Assuming flux conservation, we use observations
of the magnetic flux in a variety of magnetic clouds near the Earth
to determine the magnetic flux and magnetic energy in CMEs near the
Sun. We find that the potential and kinetic energies increase at the
expense of the magnetic energy as the CME moves out, keeping the total
energy roughly constant. This demonstrates that flux rope CMEs are
magnetically driven. Furthermore, since their total energy is constant,
the flux rope parts of the CMEs can be considered to be a closed system
above $\sim$ 2 $R_{\sun}$.
---------------------------------------------------------
Title: CHIANTI: A database for astrophysical emission line
spectroscopy
Authors: Del-Zanna, Giulio; Young, Peter; Dere, Ken; Landini, Massimo;
Landi, Enrico; Mason, Helen
1999ascl.soft11004D Altcode:
CHIANTI consists of a critically evaluated set of atomic data necessary
to calculate the emission line spectrum of astrophysical plasmas. The
data consists of atomic energy levels, atomic radiative data such as
wavelengths, weighted oscillator strengths and A values, and electron
collisional excitation rates. A set of programs that use these data to
calculate the spectrum in a desired wavelength range as a function of
temperature and density are also provided. These programs have been
written in Interactive Data Language (IDL) and descriptions of these
various programs are provided on the website.
---------------------------------------------------------
Title: Concept Study Report: Extreme-Ultraviolet Imaging Spectrometer
Solar-B
Authors: Doschek, George A.; Brown, Charles M.; Davila, Joseph M.;
Dere, Kenneth P.; Korendyke, Clarence M.; Mariska, John T.; Seely,
John F.
1999STIN...0011153D Altcode:
We propose a next generation Extreme-ultraviolet Imaging Spectrometer
(EIS) that for the first time combines high spectral, spatial, and
temporal resolution in a single solar spectroscopic instrument. The
instrument consists of a multilayer-coated off-axis telescope mirror
and a multilayer-coated grating spectrometer. The telescope mirror
forms solar images on the spectrometer entrance slit assembly. The
spectrometer forms stigmatic spectra of the solar region located
at the slit. This region is selected by the articulated telescope
mirror. Monochromatic images are obtained either by rastering the solar
region across a narrow entrance slit, or by using a very wide slit
(called a slot) in place of the slit. Monochromatic images of the
region centered on the slot are obtained in a single exposure. Half
of each optic is coated to maximize reflectance at 195 Angstroms; the
other half to maximize reflectance at 270 Angstroms. The two Extreme
Ultraviolet (EUV) wavelength bands have been selected to maximize
spectral and dynamical and plasma diagnostic capabilities. Spectral
lines are observed that are formed over a temperature range from about
0.1 MK to about 20 MK. The main EIS instrument characteristics are:
wavelength bands - 180 to 204 Angstroms; 250 to 290 Angstroms; spectral
resolution - 0.0223 Angstroms/pixel (34.3km/s at 195 Angstroms and
23.6 km/s at 284 Angstroms); slit dimensions - 4 slits, two currently
specified dimensions are 1" x 1024" and 50" x 1024" (the slot);
largest spatial field of view in a single exposure - 50" x 1024";
highest time resolution for active region velocity studies - 4.4 s.
---------------------------------------------------------
Title: The relationship of coronal mass ejections to streamers
Authors: Subramanian, Prasad; Dere, K. P.; Rich, N. B.; Howard, R. A.
1999JGR...10422321S Altcode: 1999astro.ph..6207S
We have examined images from the Large-Angle and Spectrometric
Coronagraph (LASCO) to study the relationship of coronal mass ejections
(CMEs) to coronal streamers. We wish to test the suggestion [Low,
1996] that CMEs arise from flux ropes embedded in a streamer erupting
and disrupting the streamer. The data span a period of 2 years near
Sunspot minimum through a period of increased activity as Sunspot
numbers increased. We have used LASCO data from the C2 coronagraph
which records Thomson scattered white light from coronal electrons at
heights between 1.5 and 6R<SUB>s</SUB>. Maps of the coronal streamers
have been constructed from LASCO C2 observations at a height of
2.5R<SUB>s</SUB> at the east and west limbs. We have superposed the
corresponding positions of CMEs observed with the C2 coronagraph onto
the synoptic maps. We identified the different kinds of signatures CMEs
leave on the streamer structure at this height (2.5R<SUB>s</SUB>). We
find four types of CMEs with respect to their effect on streamers:
1. CMEs that disrupt the streamer, 2. CMEs that have no effect on
the streamer, even though they are related to it, 3. CMEs that create
streamer-like structures and 4. CMEs that are latitudinally displaced
from the streamer. CMEs in categories 3 and 4 are not related to the
streamer structure. This is the most extensive observational study
of the relation between CMEs and streamers to date. Previous studies
using SMM data have made the general statement that CMEs are mostly
associated with streamers and that they frequently disrupt it. However,
we find that approximately 35% of the observed CMEs bear no relation
to the preexisting streamer, while 46% have no effect on the observed
streamer, even though they appear to be related to it. Our conclusions
thus differ considerably from those of previous studies.
---------------------------------------------------------
Title: SOHO/EIT Observations of the 1997 April 7 Coronal Transient:
Possible Evidence of Coronal Moreton Waves
Authors: Thompson, B. J.; Gurman, J. B.; Neupert, W. M.; Newmark,
J. S.; Delaboudinière, J. -P.; Cyr, O. C. St.; Stezelberger, S.;
Dere, K. P.; Howard, R. A.; Michels, D. J.
1999ApJ...517L.151T Altcode:
We report observations obtained with the Extreme ultraviolet
Imaging Telescope (EIT) on board SOHO of a large-scale coronal
transient propagating across the disk of the Sun at a speed of 250 km
s<SUP>-1</SUP>, in apparent association with a flare and coronal mass
ejection. The observations consist of a series of images taken in the
Fe XII 195 Å bandpass at an average cadence of 15 minutes. A visible
increase in coronal emission propagates away from the erupting region,
traveling across most of the solar disk in less than an hour. As the
wave propagates through the ambient corona, its path is not homogeneous,
and it is less observable near strong magnetic features such as
active regions and magnetic neutral lines. The characteristics of
this event appear to be representative of several other “EIT waves,”
which we identify as strong candidates for the coronal manifestation
of Moreton waves.
---------------------------------------------------------
Title: Microwave and Extreme Ultraviolet Observations of Solar
Polar Regions
Authors: Nindos, A.; Kundu, M. R.; White, S. M.; Gary, D. E.;
Shibasaki, K.; Dere, K. P.
1999AAS...194.3207N Altcode: 1999BAAS...31..871N
The radio emission of solar poles is brighter than the rest of the
quiet Sun's emission in a limited range of frequencies from 17 GHz to
87 GHz. We have studied microwave images of the quiet Sun made with
the Nobeyama Radioheliograph at 17 GHz. They show that the so-called
polar-cap brightening consists of two components: a diffuse component
of 1500 K excess brightness, and patchy compact sources with localized
excess brightness of about 3500 K. The total flux and the number of
compact polar sources as well as the North-South extent of the diffuse
polar emission are larger in the pole which is closest to the Earth. We
compared the microwave polar emission with nearly simultaneous SoHO EIT
images taken in the lines of He ii at 304 Angstroms and Fe xii at 195
Angstroms. No one-to-one correlation between the compact radio sources
and the bright EUV features was found: most of the radio emission arises
between the plumes visible to EIT. The boundaries of the polar-cap
brightenings did not match exactly the boundaries of the coronal holes
as seen in the Fe xii 195 Angstroms images. The temporal variations of
the compact microwave sources did not correspond to any significant
changes in EUV emission. On the other hand, most He ii 304 Angstroms
changing features were associated with the diffuse polar microwave
emission which was practically constant. Our data suggest that the
origin of the polar brightening is not coronal; it seems that the bulk
of the patchy radio emission comes from heights below the 80000 K layer.
---------------------------------------------------------
Title: LASCO Measurements of Erupting Flux Ropes
Authors: Vourlidas, A.; Subramanian, P.; Dere, K. P.; Howard, R. A.
1999AAS...19410103V Altcode: 1999BAAS...31..998V
It is commonly assumed that Coronal Mass Ejections from the Sun are
magnetically driven. We address this question with data from the LASCO
coronagraphs aboard the SOHO spacecraft. These observations provide
fairly direct measurements of the energetics of CMEs. We determine
the kinetic and gravitational energies and their evolution for several
helical CMEs. We estimate the evolution of the magnetic energy based on
the conservation of magnetic flux and observations of magnetic clouds
near the Earth. From the magnitude and variation of these three forms
of energy, we examine the energetics of CMEs from the perspective that
they are driven through their internal magnetic energy.
---------------------------------------------------------
Title: Global Coronal Mass Ejections observed with LASCO
Authors: Dere, K. P.; Howard, R. A.
1999AAS...19410101D Altcode: 1999BAAS...31..998D
The Large Angle Spectrometric Coronagraph (LASCO) on the Solar
and Heliospheric Observatory (SOHO) spacecraft has provide nearly
continuous observations of the solar corona from January 1996 until the
present. This covers periods near minimum solar activity through the
rise of the current sunspot cycle. Numerous coronal mass ejections
(CMEs) have been observed during this period. Many of these can
be characterized as arising from a spatially limited area of the
corona. However, there now appears to be a class of CMEs that involve
involve coronal structures spanning a hemisphere or more and we refer
to these CMEs as global CMEs. In some cases, simultaneous CME activity
are seen above the limb on opposite sides of the solar disk. Several
examples of global CMEs are presented. The fact that they can occur
during periods of relatively low solar activity supports the sugestion
that these large scale CMEs are not simply the chance occurence of 2
or more unrelated CMEs at about the same time.
---------------------------------------------------------
Title: HRTS Observations of Solar Fine Scale Structures in the Near-UV
Authors: Morrill, J. S.; Dere, K. P.; Korendyke, C. M.
1999AAS...194.9311M Altcode: 1999BAAS...31..990M
The NRL High Resolution Telescope and Spectrograph (HRTS) obtains
ultraviolet spectra, ultraviolet spectroheliograms and H alpha
spectroheliograms at a spatial resolution of about 1 arc-second along
a 900 arc-second slit. The HRTS-9 rocket flew on April 18, 1995 during
the declining phase of the solar cycle. The HRTS-9 instrument and
observing program were tailored to observe emission patterns inthe
ultraviolet for the purpose of studying solar variability. Observation
targets included the quiet sun, active regions and the quiet limb. The
wavelength range of HRTS-9 spectrograph was from 275 nm to 290 nm. Some
of the prominent spectral features in this wavelength range are the
Mg II h and k lines at 280 nm, the strong Mg I Fraunhofer line at 285
nm, and the continuum. The ultraviolet spectroheliograph obtained
images of a portion of the sun at wavelengths corresponding to a
range of temperatures: 1550 (C IV), 1540 (Si I), 1560 (C I), and 1600
(continuum). The primary goal of the HRTS-9 rocket program was to
examine the origin of the total solar variability in the intensity
variations of solar structures in the near ultraviolet on a variety
of spatial scales. The HRTS-9 data reveals the fine structure of the
quiet sun, plage, and sun spots in the near ultraviolet. In addition,
active region contrast factors are determined for comparison with
modes of full disk ultraviolet variability based on SUSIM and SOLTICE
observations from UARS.
---------------------------------------------------------
Title: The Increase in Mass of CMEs due to Propagation
Authors: Howard, R. A.; Dere, K. P.; Sheeley, N. R., Jr.; Subramanian,
P.; Vourlidas, A.; Wang, D.
1999AAS...19410102H Altcode: 1999BAAS...31..998H
The question we would like to address is whether coronal mass ejections
snowplow ambient material. Some of the CMEs observed by the LASCO
coronagraph on SOHO have a clearly defined loop-like front, meaning
that the trailing edge of the front can be clearly defined. We measure
the mass in the front of the CME in this subclass. We find that for
some of the events, the mass in the leading edge increases, implying
that the CME is indeed "snowplowing" ambient material. If there is a
significant increase in mass, then the CME frontal speed might decrease
to conserve momentum. We estimate the amount of ambient material,
using a model of coronal densities, and find that it is consistent
with the mass increase. We can also estimate the height in the corona,
below the occulting disk, from where the original material in the CME
is released. These concepts as well as conditions for when the mass
increases will be discussed.
---------------------------------------------------------
Title: Solar Polar Imager
Authors: Moses, D.; Dere, K. P.; Howard, R. A.; Korendyke, C. M.;
Socker, D. G.; Wang, Y. -M.; Goldstein, B. E.; Liewer, P. E.
1999AAS...194.7613M Altcode: 1999BAAS...31..958M
Observation of the global coronal and magnetic field structure of
the Sun requires coronal imaging and magnetograms from a perspective
out of the ecliptic. While the upcoming Solar Terrestrial Relations
Observatory (STEREO) mission will provide a great advance in the
understanding of the three-dimensional structure of the corona and
interplanetary medium, the orientation of the Sun's large scale magnetic
axis of symmetry with the STEREO spacecraft separation defines the
limits of this mission. The global structure of the streamer belts,
polar coronal holes and coronal plumes all reflect the symmetry of
the large scale solar magnetic field. Observations of Coronal Mass
Ejections (CMEs) from the LASCO and EIT instruments on the Solar and
Heliospheric Observatory (SOHO) indicate the need for synoptic coronal
imaging out of the ecliptic (Solar Polar Imager), as well as in stereo
pairs in the ecliptic (STEREO), for advancement in the understanding
of the origins and consequences of CMEs. The SOHO MDI has shown the
need for observations of the evolution of the polar magnetic fields
and convection patterns to understand the generation and transport
of the solar magnetic fields. Finally, the Ulysses mission has shown
the need for polar coronal imaging and magnetograms for understanding
the source of the solar wind. Ulysses has demonstrated the need for
on-board in situ particles and fields instruments as a link to the
remote sensing observations. Lightweight and compact instrumentation for
these observations has already been demonstrated technically. An orbital
mission involving a Jupiter assist such as Ulysses is also technically
demonstrated, although the duration of the polar observations is limited
to the point of degrading the studies of solar cycle evolution. An
orbital mission involving a circularized polar orbit is possible with
the use of solar-sail propulsion, but this involves technology that
has yet to be demonstrated.
---------------------------------------------------------
Title: LASCO and EIT Observations of Helical Structure in Coronal
Mass Ejections
Authors: Dere, K. P.; Brueckner, G. E.; Howard, R. A.; Michels, D. J.;
Delaboudiniere, J. P.
1999ApJ...516..465D Altcode:
Observations of coronal mass ejections (CMEs) by the Large Angle
Spectrometric Coronagraph (LASCO) on the Solar and Heliospheric
Observatory (SOHO) show a significant fraction with circular intensity
patterns. In the past, these would have been called “disconnection”
events, but we suggest that these are evidence of CMEs containing
helical magnetic flux ropes that are often central to many theoretical
models of CMEs and have been observed in magnetic clouds near
1 AU. Three examples are examined in detail with the LASCO and
Extreme-Ultraviolet Imaging Telescope (EIT) data sets, which provide
observations from their initiation through 30 R<SUB>solar</SUB>.
---------------------------------------------------------
Title: CHIANTI - an atomic database for emission lines. III. Continuum
radiation and extension of the ion database
Authors: Landi, E.; Landini, M.; Dere, K. P.; Young, P. R.; Mason,
H. E.
1999A&AS..135..339L Altcode:
CHIANTI provides a database of atomic energy levels, wavelengths,
radiative transition probabilities and electron excitation data for a
large number of ions of astrophysical interest. This database allows
the calculation of theoretical line emissivities necessary for the
analysis of optically thin emission line spectra, and includes also
a suite of IDL (Interactive Data Language) programs to calculate
optically thin synthetic spectra and to perform spectral analysis and
plasma diagnostics. The first version (1.0) of the CHIANTI database was
released in 1996 te[(Dere et al. 1997)]{Der97} and has been extensively
used for analysis of line spectra from astrophysical sources by the
scientific community. The present paper describes the first major update
to the CHIANTI database which will subsequently be labeled version
2.0. The update consists of the addition of a large number of new ions,
the revision of existing data for some ions and the inclusion of an
IDL procedure to calculate the continuum. The CHIANTI atomic database
and supporting IDL routines are freely available through the internet.
---------------------------------------------------------
Title: Observations of Coronal Structures Above an Active Region by
EIT and Implications for Coronal Energy Deposition
Authors: Neupert, W. M.; Newmark, J.; Delaboudinière, J. -P.;
Thompson, B. J.; Catura, R. C.; Moses, J. D.; Gurman, J. B.;
Portier-Fozzani, F.; Gabriel, A. H.; Artzner, G.; Clette, F.; Cugnon,
P.; Maucherat, A. J.; Defise, J. M.; Jamar, C.; Rochus, P.; Dere,
K. P.; Howard, R. A.; Michels, D. J.; Freeland, S.; Lemen, J. R.;
Stern, R. A.
1998SoPh..183..305N Altcode:
Solar EUV images recorded by the EUV Imaging Telescope (EIT) on SOHO
have been used to evaluate temperature and density as a function of
position in two largescale features in the corona observed in the
temperature range of 1.0-2.0 MK. Such observations permit estimates
of longitudinal temperature gradients (if present) in the corona and,
consequently, estimates of thermal conduction and radiative losses
as a function of position in the features. We examine two relatively
cool features as recorded in EIT's Fe ix/x (171 Å) and Fe xii (195 Å)
bands in a decaying active region. The first is a long-lived loop-like
feature with one leg, ending in the active region, much more prominent
than one or more distant footpoints assumed to be rooted in regions of
weakly enhanced field. The other is a near-radial feature, observed
at the West limb, which may be either the base of a very high loop
or the base of a helmet streamer. We evaluate energy requirements to
support a steady-state energy balance in these features and find in
both instances that downward thermal conductive losses (at heights
above the transition region) are inadequate to support local radiative
losses, which are the predominant loss mechanism. The requirement that a
coronal energy deposition rate proportional to the square of the ambient
electron density (or pressure) is present in these cool coronal features
provides an additional constraint on coronal heating mechanisms.
---------------------------------------------------------
Title: A new perspective on the sun from SOHO-challenges for atomic
physics
Authors: Dere, Kenneth; Mason, Helen
1998AIPC..434..213D Altcode: 1998amda.conf..213D
The Solar and Heliospheric Observatory (SOHO) carries several
ultraviolet spectrometers to diagnose the plasma conditions of
the solar atmosphere in order to address several outstanding
questions in solar research: why is the corona hot and how is the
solar wind accelerated. Diagnostic techniques for determining the
magnetohydrodynamic state (magnetic field, density, temperature,
velocity) are discussed. We describe the CHIANTI database which has been
designed to provide the necessary spectroscopic diagnostics for these
data as well as for other spectroscopic missions. The database is built
on 3 main files for each ion: atomic energy levels, radiative data,
and electron collisional data. The electron collision strengths are
assessed and scaled using the Burgess and Tully scaling laws. Analyses
of EUV line intensities often reveal discrepancies between observed
and predicted line intensities of about of 2 when considering lines of
the same ion. A more recent analysis has shown that it is possible to
arrive at a subset of EUV spectral lines where the line intensities
are reproducible to within about 25%. For X-ray lines, as will be
observed by AXAF, there is still considerable need for energy levels,
radiative data and collision strengths, particularly for the Δn>=1
transitions.
---------------------------------------------------------
Title: LASCO/EIT Observations of Coronal Mass Ejections from
Large-Scale Filament Channels
Authors: Plunkett, S. P.; Dere, K. P.; Howard, R. A.; Michels, D. J.;
Brueckner, G. E.; Thompson, B. J.; Delaboudiniere, J. -P.
1998ASPC..150..475P Altcode: 1998npsp.conf..475P; 1998IAUCo.167..475P
No abstract at ADS
---------------------------------------------------------
Title: CHIANTI - an Atomic Database For Emission Lines Paper I:
Wavelengths Greater than 50 Angstroms
Authors: Dere, K. P.; Landi, E.; Mason, H. E.; Fossi, B. C. M.; Young,
P. R.
1998ASPC..143..390D Altcode: 1998sigh.conf..390D
No abstract at ADS
---------------------------------------------------------
Title: LASCO and EIT Observations of the Dynamic Corona
Authors: Dere, K. P.; Brueckner, G. E.
1998HiA....11..861D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Important atomic processes in solar physics
Authors: Dere, K.
1998sese.conf..283D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: White-Light Coronal Mass Ejections: A New Perspective from
LASCO
Authors: St. Cyr, O. C.; Howard, R. A.; Simnett, G. M.; Gurman, J. B.;
Plunkett, S. P.; Sheeley, N. R.; Schwenn, R.; Koomen, M. J.; Brueckner,
G. E.; Michels, D. J.; Andrews, M.; Biesecker, D. A.; Cook, J.; Dere,
K. P.; Duffin, R.; Einfalt, E.; Korendyke, C. M.; Lamy, P. L.; Lewis,
D.; Llebaria, A.; Lyons, M.; Moses, J. D.; Moulton, N. E.; Newmark,
J.; Paswaters, S. E.; Podlipnik, B.; Rich, N.; Schenk, K. M.; Socker,
D. G.; Stezelberger, S. T.; Tappin, S. J.; Thompson, B.; Wang, D.
1997ESASP.415..103S Altcode: 1997cpsh.conf..103S
No abstract at ADS
---------------------------------------------------------
Title: The Structure of "halo" Coronal Mass Ejections
Authors: Vourlidas, A.; Howard, R. A.; Dere, K. P.; Passwaters, S. E.
1997AAS...191.7305V Altcode: 1997BAAS...29.1321V
We investigate the relation between the structure of "halo" coronal
mass ejections (CMEs) and the global coronal structure. In particular,
we compare two "halo" events which occured on October 21, 1997 and were
observed with the SoHO/LASCO coronographs at a high cadence. Although
the two CME occured at different locations on the solar disk, they
both exhibit similar morphology which appear to be influenced by the
global coronal structure. By comparing the data from the coronaraphs,
EIT and magnetograms, we will attempt to decipher the interplay between
the ejected material and the surrounding corona.
---------------------------------------------------------
Title: LASCO observations of CMEs with helical geometries
Authors: Dere, K.
1997AAS...19112005D Altcode: 1997BAAS...29R1402D
In the past, many observations of coronal mass ejections (CMEs) have
been obtained. Nevertheless, their structure and magnetic topology
remains an open question. Previous observations have often been found
consistent with simple loop, arcade or bubble geometries. More recently,
helical flux rope geometries have been suggested by Low, Chen, Rust and
Kumar, and Wu et al. Observations of CMEs with the LASCO coronagraphs
on SOHO include events which appear to be consistent with a toroidal
geometry. This topology is also that deduced for magnetic clouds
observed near the Earth. Examples of helical CMEs observed with LASCO
are presented and analyzed.
---------------------------------------------------------
Title: Analysis of Coronal Mass Ejections observed by LASCO
Authors: Subramanian, P.; Dere, K. P.; Howard, R. A.; St. Cyr, C.;
Brueckner, G. E.
1997AAS...191.7306S Altcode: 1997BAAS...29.1321S
The LASCO instrument on the SOHO spacecraft has been observing
coronal mass ejections from the sun from February 1996 to the present
time. This covers a range of solar activity ranging from near-minimum
activity to increasing activity. We present a database of coronal mass
ejection locations, times and velocities. These are then compared
with photospheric magnetic field patterns and large scale coronal
structures. We hope to gain an understanding of coronal mass ejection
initiation mechanisms through these observations. Preliminary results
from our analyses will be presented here.
---------------------------------------------------------
Title: LASCO Observations of Disconnected Magnetic Structures Out
to Beyond 28 Solar Radii During Coronal Mass Ejections
Authors: Simnett, G. M.; Tappin, S. J.; Plunkett, S. P.; Bedford,
D. K.; Eyles, C. J.; St. Cyr, O. C.; Howard, R. A.; Brueckner, G. E.;
Michels, D. J.; Moses, J. D.; Socker, D.; Dere, K. P.; Korendyke,
C. M.; Paswaters, S. E.; Wang, D.; Schwenn, R.; Lamy, P.; Llebaria,
A.; Bout, M. V.
1997SoPh..175..685S Altcode:
Two coronal mass ejections have been well observed by the LASCO
coronagraphs to move out into the interplanetary medium as disconnected
plasmoids. The first, on July 28, 1996, left the Sun above the west
limb around 18:00 UT. As it moved out, a bright V-shaped structure
was visible in the C2 coronagraph which moved into the field-of-view
of C3 and could be observed out to beyond 28 solar radii. The derived
average velocity in the plane of the sky was 110 ± 5 km s<SUP>-1</SUP>
out to 5 solar radii, and above 15 solar radii the velocity was 269
± 10 km s<SUP>-1</SUP>. Thus there is evidence of some acceleration
around 6 solar radii. The second event occurred on November 5, 1996
and left the west limb around 04:00 UT. The event had an average
velocity in the plane of the sky of ∼54 km s<SUP>-1</SUP> below
4 R⊙, and it accelerated rapidly around 5 R⊙ up to 310 ± 10 km
s<SUP>-1</SUP>. In both events the rising plasmoid is connected back
to the Sun by a straight, bright ray, which is probably a signature of
a neutral sheet. In the November event there is evidence for multiple
plasmoid ejections. The acceleration of the plasmoids around a projected
altitude of 5 solar radii is probably a manifestation of the source
surface of the solar wind.
---------------------------------------------------------
Title: First View of the Extended Green-Line Emission Corona At
Solar Activity Minimum Using the Lasco-C1 Coronagraph on SOHO
Authors: Schwenn, R.; Inhester, B.; Plunkett, S. P.; Epple, A.;
Podlipnik, B.; Bedford, D. K.; Eyles, C. J.; Simnett, G. M.; Tappin,
S. J.; Bout, M. V.; Lamy, P. L.; Llebaria, A.; Brueckner, G. E.;
Dere, K. P.; Howard, R. A.; Koomen, M. J.; Korendyke, C. M.; Michels,
D. J.; Moses, J. D.; Moulton, N. E.; Paswaters, S. E.; Socker, D. G.;
St. Cyr, O. C.; Wang, D.
1997SoPh..175..667S Altcode:
The newly developed C1 coronagraph as part of the Large-Angle
Spectroscopic Coronagraph (LASCO) on board the SOHO spacecraft has
been operating since January 29, 1996. We present observations
obtained in the first three months of operation. The green-line
emission corona can be made visible throughout the instrument's full
field of view, i.e., from 1.1 R⊙ out to 3.2 R⊙ (measured from Sun
center). Quantitative evaluations based on calibrations cannot yet be
performed, but some basic signatures show up even now: (1) There are
often bright and apparently closed loop systems centered at latitudes
of 30° to 45° in both hemispheres. Their helmet-like extensions
are bent towards the equatorial plane. Farther out, they merge into
one large equatorial `streamer sheet' clearly discernible out to 32
R⊙. (2) At mid latitudes a more diffuse pattern is usually visible,
well separated from the high-latitude loops and with very pronounced
variability. (3) All high-latitude structures remain stable on time
scales of several days, and no signature of transient disruption of
high-latitude streamers was observed in these early data. (4) Within
the first 4 months of observation, only one single `fast' feature was
observed moving outward at a speed of 70 km s<SUP>-1</SUP> close to
the equator. Faster events may have escaped attention because of data
gaps. (5) The centers of high-latitude loops are usually found at the
positions of magnetic neutral lines in photospheric magnetograms. The
large-scale streamer structure follows the magnetic pattern fairly
precisely. Based on our observations we conclude that the shape
and stability of the heliospheric current sheet at solar activity
minimum are probably due to high-latitude streamers rather than to
the near-equatorial activity belt.
---------------------------------------------------------
Title: EIT Observations of the Extreme Ultraviolet Sun
Authors: Moses, D.; Clette, F.; Delaboudinière, J. -P.; Artzner,
G. E.; Bougnet, M.; Brunaud, J.; Carabetian, C.; Gabriel, A. H.;
Hochedez, J. F.; Millier, F.; Song, X. Y.; Au, B.; Dere, K. P.; Howard,
R. A.; Kreplin, R.; Michels, D. J.; Defise, J. M.; Jamar, C.; Rochus,
P.; Chauvineau, J. P.; Marioge, J. P.; Catura, R. C.; Lemen, J. R.;
Shing, L.; Stern, R. A.; Gurman, J. B.; Neupert, W. M.; Newmark,
J.; Thompson, B.; Maucherat, A.; Portier-Fozzani, F.; Berghmans, D.;
Cugnon, P.; Van Dessel, E. L.; Gabryl, J. R.
1997SoPh..175..571M Altcode:
The Extreme Ultraviolet Imaging Telescope (EIT) on board the SOHO
spacecraft has been operational since 2 January 1996. EIT observes
the Sun over a 45 x 45 arc min field of view in four emission line
groups: Feix, x, Fexii, Fexv, and Heii. A post-launch determination
of the instrument flatfield, the instrument scattering function, and
the instrument aging were necessary for the reduction and analysis
of the data. The observed structures and their evolution in each
of the four EUV bandpasses are characteristic of the peak emission
temperature of the line(s) chosen for that bandpass. Reports on the
initial results of a variety of analysis projects demonstrate the range
of investigations now underway: EIT provides new observations of the
corona in the temperature range of 1 to 2 MK. Temperature studies of
the large-scale coronal features extend previous coronagraph work
with low-noise temperature maps. Temperatures of radial, extended,
plume-like structures in both the polar coronal hole and in a low
latitude decaying active region were found to be cooler than the
surrounding material. Active region loops were investigated in detail
and found to be isothermal for the low loops but hottest at the loop
tops for the large loops.
---------------------------------------------------------
Title: CHIANTI - an atomic database for emission lines
Authors: Dere, K. P.; Landi, E.; Mason, H. E.; Monsignori Fossi,
B. C.; Young, P. R.
1997A&AS..125..149D Altcode:
A comprehensive set of accurate atomic data is required for analyses of
astrophysical and solar spectra. CHIANTI provides a database of atomic
energy levels, wavelengths, radiative data and electron excitation
data for ions which are abundant in cosmic plasmas. The most recent
electron excitation data have been assessed and stored following
the method of \cite[Burgess \& Tully (1992)]{bur92}. The current
version is essentially complete for specifying the emission spectrum
at wavelengths greater than 50 Angstroms. A list of observed lines in
the spectral region between 50 and 1100 Angstroms has been compiled
and compared with the lines predicted by the CHIANTI database. The
CHIANTI database reproduces the vast majority of lines observed at
these wavelengths. CHIANTI includes IDL (Interactive Data Language)
routines to calculate optically thin synthetic spectra for equilibrium
conditions. IDL routines to calculate theoretical line intensities
required for electron density or temperature diagnostics and emission
measure studies are also included. The CHIANTI atomic database and
supporting IDL routines are available by anonymous FTP.
---------------------------------------------------------
Title: The Relationship of Green-Line Transients to White-Light
Coronal Mass Ejections
Authors: Plunkett, S. P.; Brueckner, G. E.; Dere, K. P.; Howard,
R. A.; Koomen, M. J.; Korendyke, C. M.; Michels, D. J.; Moses, J. D.;
Moulton, N. E.; Paswaters, S. E.; St. Cyr, O. C.; Socker, D. G.;
Wang, D.; Simnett, G. M.; Bedford, D. K.; Biesecker, D. A.; Eyles,
C. J.; Tappin, S. J.; Schwenn, R.; Lamy, P. L.; Llebaria, A.
1997SoPh..175..699P Altcode:
We report observations by the Large Angle Spectrometric Coronagraph
(LASCO) on the SOHO spacecraft of three coronal green-line transients
that could be clearly associated with coronal mass ejections (CMEs)
detected in Thomson-scattered white light. Two of these events, with
speeds >25 km s<SUP>-1</SUP>, may be classified as `whip-like'
transients. They are associated with the core of the white-light
CMEs, identified with erupting prominence material, rather than with
the leading edge of the CMEs. The third green-line transient has a
markedly different appearance and is more gradual than the other two,
with a projected outward speed <10 km s<SUP>-1</SUP>. This event
corresponds to the leading edge of a `streamer blowout' type of CME. A
dark void is left behind in the emission-line corona following each of
the fast eruptions. Both fast emission-line transients start off as a
loop structure rising up from close to the solar surface. We suggest
that the driving mechanism for these events may be the emergence of new
bipolar magnetic regions on the surface of the Sun, which destabilize
the ambient corona and cause an eruption. The possible relationship of
these events to recent X-ray observations of CMEs is briefly discussed.
---------------------------------------------------------
Title: MHD Interpretation of LASCO Observations of a Coronal Mass
Ejection as a Disconnected Magnetic Structure
Authors: Wu, S. T.; Guo, W. P.; Andrews, M. D.; Brueckner, G. E.;
Howard, R. A.; Koomen, M. J.; Korendyke, C. M.; Michels, D. J.; Moses,
J. D.; Socker, D. G.; Dere, K. P.; Lamy, P. L.; Llebaria, A.; Bout,
M. V.; Schwenn, R.; Simnett, G. M.; Bedford, D. K.; Eyles, C. J.
1997SoPh..175..719W Altcode:
We present a qualitative and quantitative comparison of a single
coronal mass ejection (CME) as observed by LASCO (July 28-29, 1996)
with the results of a three-dimensional axisymmetric time-dependent
magnetohydrodynamic model of a flux rope interacting with a helmet
streamer. The particular CME considered was selected based on the
appearance of a distinct `tear-drop' shape visible in animations
generated from both the data and the model.
---------------------------------------------------------
Title: EIT and LASCO Observations of the Initiation of a Coronal
Mass Ejection
Authors: Dere, K. P.; Brueckner, G. E.; Howard, R. A.; Koomen, M. J.;
Korendyke, C. M.; Kreplin, R. W.; Michels, D. J.; Moses, J. D.;
Moulton, N. E.; Socker, D. G.; St. Cyr, O. C.; Delaboudinière, J. P.;
Artzner, G. E.; Brunaud, J.; Gabriel, A. H.; Hochedez, J. F.; Millier,
F.; Song, X. Y.; Chauvineau, J. P.; Marioge, J. P.; Defise, J. M.;
Jamar, C.; Rochus, P.; Catura, R. C.; Lemen, J. R.; Gurman, J. B.;
Neupert, W.; Clette, F.; Cugnon, P.; Van Dessel, E. L.; Lamy, P. L.;
Llebaria, A.; Schwenn, R.; Simnett, G. M.
1997SoPh..175..601D Altcode:
We present the first observations of the initiation of a coronal mass
ejection (CME) seen on the disk of the Sun. Observations with the EIT
experiment on SOHO show that the CME began in a small volume and was
initially associated with slow motions of prominence material and a
small brightening at one end of the prominence. Shortly afterward,
the prominence was accelerated to about 100 km s<SUP>-1</SUP> and
was preceded by a bright loop-like structure, which surrounded an
emission void, that traveled out into the corona at a velocity of
200-400 km s<SUP>-1</SUP>. These three components, the prominence,
the dark void, and the bright loops are typical of CMEs when seen at
distance in the corona and here are shown to be present at the earliest
stages of the CME. The event was later observed to traverse the LASCO
coronagraphs fields of view from 1.1 to 30 R⊙. Of particular interest
is the fact that this large-scale event, spanning as much as 70 deg in
latitude, originated in a volume with dimensions of roughly 35" (2.5
x 10<SUP>4</SUP> km). Further, a disturbance that propagated across
the disk and a chain of activity near the limb may also be associated
with this event as well as a considerable degree of activity near the
west limb.
---------------------------------------------------------
Title: Origin and Evolution of Coronal Streamer Structure During
the 1996 Minimum Activity Phase
Authors: Wang, Y. -M.; Sheeley, N. R., Jr.; Howard, R. A.; Kraemer,
J. R.; Rich, N. B.; Andrews, M. D.; Brueckner, G. E.; Dere, K. P.;
Koomen, M. J.; Korendyke, C. M.; Michels, D. J.; Moses, J. D.;
Paswaters, S. E.; Socker, D. G.; Wang, D.; Lamy, P. L.; Llebaria,
A.; Vibert, D.; Schwenn, R.; Simnett, G. M.
1997ApJ...485..875W Altcode:
We employ coronal extrapolations of solar magnetograph data to interpret
observations of the white-light streamer structure made with the LASCO
coronagraph in 1996. The topological appearance of the streamer belt
during the present minimum activity phase is well described by a model
in which the Thomson-scattering electrons are concentrated around a
single, warped current sheet encircling the Sun. Projection effects
give rise to bright, jet-like structures or spikes whenever the current
sheet is viewed edge-on multiple spikes are seen if the current sheet is
sufficiently wavy. The extreme narrowness of these features in polarized
images indicates that the scattering layer is at most a few degrees
wide. We model the evolution of the streamer belt from 1996 April to
1996 September and show that the effect of photospheric activity on
the streamer belt topology depends not just on the strength of the
erupted magnetic flux, but also on its longitudinal phase relative
to the background field. Using flux transport simulations, we also
demonstrate how the streamer belt would evolve during a prolonged
absence of activity.
---------------------------------------------------------
Title: Nonthermal Velocities in the Solar Transition Zone and Corona
Authors: Doyle, J. G.; O'Shea, E.; Erdélyi, R.; Dere, K. P.; Socker,
D. G.; Keenan, F. P.
1997SoPh..173..243D Altcode:
Nonthermal velocities are presented for spectral lines covering the
temperature range 10 4-10 6 K, measured from high-spectral-resolution
data for several solar features observed at the limb by the high
resolution telescope and spectrograph (HRTS), including a coronal hole,
`quiescent regions' and several small-scale active regions. These
results are compared with predictions based on acoustic waves and
heating via Alfvén waves. It is likely that more than one mechanism is
operating simultaneously, in particular, resonant Alfvén wave heating,
which is very sensitive to background plasma motions.
---------------------------------------------------------
Title: Measurements of Flow Speeds in the Corona Between 2 and 30
R<SUB>⊙</SUB>
Authors: Sheeley, N. R.; Wang, Y. -M.; Hawley, S. H.; Brueckner,
G. E.; Dere, K. P.; Howard, R. A.; Koomen, M. J.; Korendyke, C. M.;
Michels, D. J.; Paswaters, S. E.; Socker, D. G.; St. Cyr, O. C.;
Wang, D.; Lamy, P. L.; Llebaria, A.; Schwenn, R.; Simnett, G. M.;
Plunkett, S.; Biesecker, D. A.
1997ApJ...484..472S Altcode:
Time-lapse sequences of white-light images, obtained during sunspot
minimum conditions in 1996 by the Large Angle Spectrometric Coronagraph
on the Solar and Heliospheric Observatory, give the impression of
a continuous outflow of material in the streamer belt, as if we
were observing Thomson scattering from inhomogeneities in the solar
wind. Pursuing this idea, we have tracked the birth and outflow of
50-100 of the most prominent moving coronal features and find that:
<P />1. They originate about 3-4 R<SUB>⊙</SUB> from Sun center as
radially elongated structures above the cusps of helmet streamers. Their
initial sizes are about 1 R<SUB>⊙</SUB> in the radial direction and
0.1 R<SUB>⊙</SUB> in the transverse direction. <P />2. They move
radially outward, maintaining constant angular spans and increasing
their lengths in rough accord with their speeds, which typically
double from 150 km s<SUP>-1</SUP> near 5 R<SUB>⊙</SUB> to 300 km
s<SUP>-1</SUP> near 25 R<SUB>⊙</SUB>. <P />3. Their individual speed
profiles v(r) cluster around a nearly parabolic path characterized
by a constant acceleration of about 4 m s<SUP>-2</SUP> through most
of the 30 R<SUB>⊙</SUB> field of view. This profile is consistent
with an isothermal solar wind expansion at a temperature of about
1.1 MK and a sonic point near 5 R<SUB>⊙</SUB>. <P />Based on their
relatively small initial sizes, low intensities, radial motions, slow
but increasing speeds, and location in the streamer belt, we conclude
that these moving features are passively tracing the outflow of the
slow solar wind.
---------------------------------------------------------
Title: Association of Extreme-Ultraviolet Imaging Telescope (EIT)
Polar Plumes with Mixed-Polarity Magnetic Network
Authors: Wang, Y. -M.; Sheeley, N. R.; Dere, K. P.; Duffin, R. T.;
Howard, R. A.; Michels, D. J.; Moses, J. D.; Harvey, J. W.; Branston,
D. D.; Delaboudinière, J. -P.; Artzner, G. E.; Hochedez, J. F.;
Defise, J. M.; Catura, R. C.; Lemen, J. R.; Gurman, J. B.; Neupert,
W. M.; Newmark, J.; Thompson, B.; Maucherat, A.; Clette, F.
1997ApJ...484L..75W Altcode:
SOHO EIT spectroheliograms showing the polar coronal holes during the
present sunspot minimum are compared with National Solar Observatory
(Kitt Peak) magnetograms taken in Fe I λ8688 and Ca II λ8542. The
chromospheric λ8542 magnetograms, obtained on a routine, near-daily
basis since 1996 June, reveal the Sun's strong polar fields with
remarkable clarity. We find that the Fe IX λ171 polar plumes occur
where minority-polarity flux is in contact with flux of the dominant
polarity inside each polar hole. Moreover, the locations of “plume
haze” coincide approximately with the patterns of brightened He
II λ304 network within the coronal hole. The observations appear
to be consistent with mechanisms of plume formation involving
magnetic reconnection between unipolar flux concentrations and nearby
bipoles. The fact that minority-polarity fields constitute only a small
fraction of the total magnetic flux within the polar holes suggests
that plumes are not the main source of the high-speed polar wind.
---------------------------------------------------------
Title: The Solar-B Mission
Authors: Antiochos, Spiro; Acton, Loren; Canfield, Richard; Davila,
Joseph; Davis, John; Dere, Kenneth; Doschek, George; Golub, Leon;
Harvey, John; Hathaway, David; Hudson, Hugh; Moore, Ronald; Lites,
Bruce; Rust, David; Strong, Keith; Title, Alan
1997STIN...9721329A Altcode:
Solar-B, the next ISAS mission (with major NASA participation), is
designed to address the fundamental question of how magnetic fields
interact with plasma to produce solar variability. The mission has
a number of unique capabilities that will enable it to answer the
outstanding questions of solar magnetism. First, by escaping atmospheric
seeing, it will deliver continuous observations of the solar surface
with unprecedented spatial resolution. Second, Solar-B will deliver the
first accurate measurements of all three components of the photospheric
magnetic field. Solar-B will measure both the magnetic energy driving
the photosphere and simultaneously its effects in the corona. Solar-B
offers unique programmatic opportunities to NASA. It will continue an
effective collaboration with our most reliable international partner. It
will deliver images and data that will have strong public outreach
potential. Finally, the science of Solar-B is clearly related to the
themes of origins and plasma astrophysics, and contributes directly
to the national space weather and global change programs.
---------------------------------------------------------
Title: Using LASCO Observations to Infer Solar Wind Flow Near the Sun
Authors: Sheeley, N. R., Jr.; Brueckner, G. E.; Dere, K. P.; Howard,
R. A.; Korendyke, C. M.; Michels, D. J.; Socker, D. G.; Koomen, M. J.;
Paswaters, S. E.; Wang, D.; Lamy, P. L.; Llebaria, A.; Schwenn, R.;
St Cyr, O. C.; Simnett, G. M.; Plunkett, S.; Biesecker, D. A.
1997SPD....28.0301S Altcode: 1997BAAS...29..907S
We have continued to track individual coronal features as they become
detached from helmet streamers and move outward from the Sun. The
composite speed profile for 50-100 features has a parabolic shape
with a constant acceleration of about 4 m/s(2) over the 2-30 R field
of view. This well-determined speed profile contrasts strongly with
the nearly uniform scatterplot obtained for about 50 nominal coronal
mass ejections (CMEs), and suggests that these detached bits of coronal
“debris” are passively tracing the speed of the slow solar wind. We
have also begun the more difficult task of tracking outflow along
polar plumes and will summarize these results as of June 1997.
---------------------------------------------------------
Title: EIT and LASCO observations of the initiation of a coronal
mass ejection
Authors: Dere, K.; Brueckner, G. E.; Delaboudiniere, J. -P.
1997SPD....28.0502D Altcode: 1997BAAS...29R.908D
We present the first observations of the initiation of a coronal mass
ejection (CME) seen on the disk of the Sun. Observations with the EIT
experiment on SOHO show that the CME began in a small volume and was
initially associated with slow motions of prominence material and a
small brightening at one end of the prominence. Shortly afterward,
the prominence was accelerated to about 200 kms and was preceded by
a bright loop-like structure, which surrounded an emission void,
that traveled out into the corona at a velocity of 400 kms. These
three components, the prominence, the dark void, and the bright loops
are typical of CMEs when seen at distance in the corona and here are
shown to be present at the earliest stages of the CME. The event was
later observed to traverse the LASCO coronagraphs fields of view from
1.1 to 30 R_⊙. Of particular interest is the fact that this large
scale event, spanning as much as 70 degrees in latitude, originated
in a volume with dimensions of roughly 35" (2.5 x 10(4) km). Further,
a disturbance that propagated across the disk and a chain of activity
near the limb may also be associated with this event as well as a
considerable degree of activity near the west limb.
---------------------------------------------------------
Title: Observations of Coronal Features by EIT above an Active Region
by EIT and Implications for Coronal Heating
Authors: Neupert, W. M.; Newmark, J.; Thompson, B. J.; Catura, R.;
Moses, J. D.; Portier-Fozzani, F.; Delaboudiniere, J. P.; Gabriel, A.;
Artzner, G.; Clette, F.; Cugnon, P.; Maucherat, A.; Defise, J. M.;
Jamar, C.; Rochus, P.; Howard, R.; Michels, D.; Dere, K.; Freeland,
S.; Lemen, J.; Stern, R.; Gurman, J.
1997SPD....28.0115N Altcode: 1997BAAS...29..881N
The EUV Imaging Telescope (EIT) on the SOHO provides the capability
for multi-wavelength imaging of the corona in four spectral bands,
centered at 171, 195, 284, and 304 Angstroms, using multilayer telescope
technology. These bands encompass coronal temperatures from 1 MK
to 2.5 MK as well as the upper chromosphere, at about 60,000 K. In
particular, nearly simultaneous imaging in the 171 and 195 Angstrom
bands, the former including major Fe IX and Fe X emission lines, the
latter including a strong Fe XII line, provides a capability to infer
the morphology and characteristics of the corona at temperatures of
1.0 - 1.7 MK. We have examined the corona in this temperature range
over an active region observed from SOHO from May - September, 1996 and
find that low-lying loops (below a density scale height of 75,000 km,
characteristic of Fe X) vary little in brightness and temperature along
their length. For features extending to greater heights, however, both
brightness gradients and temperature gradients are observed. Preliminary
analysis of the observations when the region was on the West limb
on September 30 indicates a small positive temperature gradient of
approximately 0.5 K/km in one loop system that extended above 100,000
km. On the other hand, a nearly radial feature extending to the edge of
the EIT FOV was isothermal or had at most a slight negative temperature
gradient. Such measurements may have application to the modeling of
coronal loops and streamers and the processes of coronal heating and
solar wind acceleration.
---------------------------------------------------------
Title: VizieR Online Data Catalog: CHIANTI - An Atomic Database For
Emission Lines I. (Dere+ 1997)
Authors: Dere, K. P.; Landi, E.; Mason, H. E.; Monsignori Fossi,
B. C.; Young, P. R.
1997yCat..41250149D Altcode:
A comprehensive set of accurate atomic data is required for analyses of
astrophysical and solar spectra. CHIANTI provides a database of atomic
energy levels, wavelengths, radiative data and electron excitation
data for ions which are abundant in cosmic plasmas. The most recent
electron excitation data have been assessed and stored following
the method of Burgess & Tully (1992A&A...254..436B). The
current version is essentially complete for specifying the emission
spectrum at wavelengths greater than 50Å. A list of observed lines
in the spectral region between 50 and 1100Å has been compiled
and compared with the lines predicted by the CHIANTI database. The
CHIANTI database reproduces the vast majority of lines observed at
these wavelengths. CHIANTI includes IDL (Interactive Data Language)
routines to calculate optically thin synthetic spectra for equilibrium
conditions. IDL routines to calculate theoretical line intensities
required for electron density or temperature diagnostics and emission
measure studies are also included. The CHIANTI atomic database and
supporting IDL routines are available by anonymous FTP. (1 data file).
---------------------------------------------------------
Title: Imaging the solar corona in the EUV
Authors: Delaboudiniere, J. -P.; Stern, R. A.; Maucherat, A.;
Portier-Fozzani, F.; Neupert, W. M.; Gurman, J. B.; Catura, R. C.;
Lemen, J. R.; Shing, L.; Artzner, G. E.; Brunaud, J.; Gabriel, A. H.;
Michels, D. J.; Moses, J. D.; Au, B.; Dere, K. P.; Howard, R. A.;
Kreplin, R.; Defise, J. M.; Jamar, C.; Rochus, P.; Chauvineau, J. P.;
Marioge, J. P.; Clette, F.; Cugnon, P.; van Dessel, E. L.
1997AdSpR..20.2231D Altcode:
The SOHO (SOlar and Heliospheric Observatory) satellite was launched on
December 2nd 1995. After arriving at the Earth-Sun (L1) Lagrangian point
on February 14th 1996, it began to continuously observe the Sun. As
one of the instruments onboard SOHO, the EIT (Extreme ultraviolet
Imaging Telescope) images the Sun's corona in 4 EUV wavelengths. The
He II filter at 304 A˚ images the chromosphere and the base of the
transition region at a temperature of 5 - 8 x 10^4 K; the Fe IX-X
filter at 171 A˚ images the corona at a temperature of ~ 1.3 x 10^6 K;
the Fe XII filter at 195 A˚ images the quiet corona outside coronal
holes at a temperature of ~ 1.6 x 10^6 K; and the Fe XV filter at 284
A˚ images active regions with a temperature of ~ 2.0 x 10^6 K. About
5000 images have been obtained up to the present. In this paper,
we describe also some aspects of the telescope and the detector
performance for application in the observations. Images and movies
of all the wavelengths allow a look at different phenomena present in
the Sun's corona, and in particular, magnetic field reconnection.
---------------------------------------------------------
Title: Dynamical Evolution of a Coronal Mass Ejection (CME) to
Magnetic Cloud: A Preliminary Analysis of the January 6-10, 1997
CME Observed by LASCO/SOHO
Authors: Wu, S. T.; Guo, W. P.; Michels, D. J.; Andrews, M. D.;
Brueckner, G. E.; Howard, R. A.; Koomen, M. J.; Korendyke, C. M.;
Moses, J. D.; Socker, D. G.; Dere, K. P.; Bougeret, Jean-Louis; Lamy,
P. L.; Schwenn, R.; Simnett, G. M.
1997ESASP.404..739W Altcode: 1997cswn.conf..739W
No abstract at ADS
---------------------------------------------------------
Title: EIT and LASCO Observations of the Initiation of a Coronal
Mass Ejection
Authors: Dere, K. P.; Brueckner, G. E.; Howard, R. A.; Koomen, M. J.;
Korendyke, C. M.; Michels, D. J.; Moses, J. D.; Moulton, N. E.; Socker,
D. G.; Delaboudiniere, J. P.; Hochedez, J. F.; Lamy, P. L.; Schwenn,
R.; Simnett, G. M.; Defise, J. M.; Catura, R. C.
1997IAUJD..19E..18D Altcode:
We present the first observations of the initiation of a corona mass
ejection (CME) seen on the disk of the Sun. Observations with the EIT
and LASCO experiments on SOHO show that the CME starts in a small volume
and is associated with slow motions of prominence material. At about
the same time, a shock wave is created that travels out into the corona
at a velocity of 400 km s^{-1} ahead of an eruptive prominence. This
shock wave is clearly the event that is later seen as a classical CME
when observed in the coronagraph above 1.5 solar radii. Although the
CME clearly starts in a small region, a chain of activity near the
limb may also be associated with this event.
---------------------------------------------------------
Title: First Results from EIT
Authors: Clette, F.; Delaboudiniere, J. -P.; Artzner, G. E.; Brunaud,
J.; Gabriel, A. H.; Hochedez, J. -F.; Millier, F.; Song, X. Y.; Au, B.;
Dere, K. P.; Howard, R. A.; Kreplin, R.; Michels, D. J.; Moses, J. D.;
Defise, J. -M.; Jamar, C.; Rochus, P.; Chauvineau, J. -P.; Marioge,
J. -P.; Catura, R. C.; Lemen, J. R.; Shing, L.; Stern, R. A.; Gurman,
J. B.; Neupert, W. M.; Maucherat, A.; Cugnon, P.; van Dessel, E. L.
1997ASPC..118..268C Altcode: 1997fasp.conf..268C
The Extreme-UV Imaging telescope has already produced more than 15000
wide-field images of the corona and transition region, on the disk
and up to 1.5R_⊙ above the limb, with a pixel size of 2.6\arcsec. By
using four different emission lines, it provides the global temperature
distribution in the quiet corona, in the range 0.5 to 3*E(6) K. Its
excellent sensitivity and wide dynamic range allow unprecedented views
of low emission features, even inside coronal holes. Those so-called
“quiet” regions actually display a wide range of dynamical phenomena,
in particular at small spatial scales and at time scales going down
to only a few seconds, as revealed by all EIT time sequences of
full- or partial-field images. The initial results presented here
demonstrate the importance of this wide-field imaging experiment for
a good coordination between SOHO and ground-based solar telescopes,
as well as for science planning.
---------------------------------------------------------
Title: The Rate of Magnetic Reconnection Observed in the Solar
Atmosphere
Authors: Dere, Kenneth P.
1996ApJ...472..864D Altcode:
The structure of the solar corona is often observed to evolve in a
manner that is generally attributed to the process of magnetic field
line reconnection. The spatial and temporal scales for a variety of
reconnection events have been examined on the basis of descriptions in
the scientific literature. These events tend to fall into two general
categories. In the first category, reconnection proceeds as the corona
adjusts itself to the emergence of new magnetic flux. In the second
category, the field lines have been explosively blown open by a flare or
mass ejection, and the field lines eventually return to a more potential
field configuration by means of reconnection. Estimates of the density,
temperature, and magnetic field strength in the reconnection volume
provide a basis on which to calculate the reconnection rate expected
for resistive diffusion, tearing mode reconnection, and reconnection
at the Alfvén speed. The observed temporal and spatial scales of the
reconnection events indicate that the rate of reconnection is on the
order of 0.001-0.1 of the Alfvén rate, the Alfvén speed divided by
the observed length scale. This indicates that the effective Reynolds
number for large-scale structures in the corona is of the order of 10-
1000. In none of the cases examined does the reconnection appear to be
driven by external flows, but the process is more properly described
as the relaxation of nonpotential magnetic field configurations toward
a potential configuration.
---------------------------------------------------------
Title: STEREO: a solar terrestrial event observer mission concept
Authors: Socker, Dennis G.; Antiochos, S. K.; Brueckner, Guenter E.;
Cook, John W.; Dere, Kenneth P.; Howard, Russell A.; Karpen, J. T.;
Klimchuk, J. A.; Korendyke, Clarence M.; Michels, Donald J.; Moses,
J. Daniel; Prinz, Dianne K.; Sheely, N. R.; Wu, Shi T.; Buffington,
Andrew; Jackson, Bernard V.; Labonte, Barry; Lamy, Philippe L.;
Rosenbauer, H.; Schwenn, Rainer; Burlaga, L.; Davila, Joseph M.; Davis,
John M.; Goldstein, Barry; Harris, H.; Liewer, Paulett C.; Neugebauer,
Marcia; Hildner, E.; Pizzo, Victor J.; Moulton, Norman E.; Linker,
J. A.; Mikic, Z.
1996SPIE.2804...50S Altcode:
A STEREO mission concept requiring only a single new spacecraft has been
proposed. The mission would place the new spacecraft in a heliocentric
orbit and well off the Sun- Earth line, where it can simultaneously view
both the solar source of heliospheric disturbances and their propagation
through the heliosphere all the way to the earth. Joint observations,
utilizing the new spacecraft and existing solar spacecraft in earth
orbit or L1 orbit would provide a stereographic data set. The new
and unique aspect of this mission lies in the vantage point of the
new spacecraft, which is far enough from Sun-Earth line to allow an
entirely new way of studying the structure of the solar corona, the
heliosphere and solar-terrestrial interactions. The mission science
objectives have been selected to take maximum advantage of this new
vantage point. They fall into two classes: those possible with the
new spacecraft alone and those possible with joint measurements using
the new and existing spacecraft. The instrument complement on the new
spacecraft supporting the mission science objectives includes a soft
x-ray imager, a coronagraph and a sun-earth imager. Telemetry rate
appears to be the main performance determinant. The spacecraft could
be launched with the new Med-Lite system.
---------------------------------------------------------
Title: Next-generation EUV imaging spectrometer for solar flare
observations
Authors: Moses, J. Daniel; Brueckner, Guenter E.; Dere, Kenneth P.;
Korendyke, Clarence M.; Moulton, Norman E.; Prinz, Dianne K.; Seely,
John F.; Socker, Dennis G.; Bruner, Marilyn E.; Lemen, James R.
1996SPIE.2804..260M Altcode:
The Naval Research Laboratory Skylab SO82A slitless spectrograph
provided solar flare observations that have never been equaled
in diagnostic capabilities for interpreting thermal flare
physics. Improvements in detector technology, optics and optical
coating technology, and almost two decades of analysis of SO82A data
can be combined with the basic concept of an EUV objective grating
spectrograph to build an instrument to address many of the remaining
mysteries of solar flares. This next generation instrument incorporates
two sets of two identical, orthogonally mounted slitless spectrographic
Cassegrain telescopes. Each telescope consists of a multilayer coated,
Wadsworth mount objective grating and multilayer coated spherical
secondary mirror; a backside illuminated CCD detector is installed
at the focal plane. The orthogonal mounting changes the dispersion
direction by 90 degrees on the disk image; processing on the two
resulting images allows recovery of the undispersed disk image and
spectral line profiles. The resulting instrument will obtain high time
cadence, spectrally-dispersed images with improved spatial resolution,
dynamic range, signal-to-noise ratio, and velocity discrimination.
---------------------------------------------------------
Title: A Model for Active Region Emission at Centimeter Wavelengths
Authors: Nindos, A.; Alissandrakis, C. E.; Gelfreikh, G. B.; Kundu,
M. R.; Dere, K. P.; Korzhavin, A. N.; Bogod, V. M.
1996SoPh..166...55N Altcode:
We present multi-frequency observations and model computations of the
microwave emission of a solar active region. The radio observations
were obtained with the RATAN-600 at several wavelengths between 0.8
and 31.6 cm and with the VLA at 6 and 20 cm. The active region was
also observed in the EUV O Iv lines by the HRTS instrument aboard
the Space Shuttle Spacelab-2 mission. These lines are formed in the
chromosphere-corona transition region and their intensity ratio is
sensitive to pressure. Photospheric magnetograms provided both the
longitudinal and the transverse component of the magnetic field. The
microwave observations were checked against model computations
taking into account both the free-free and the gyro-resonance emission
mechanisms and using the pressure data from the O IV lines. The magnetic
field was computed through constant-α force-free extrapolations of
the longitudinal photospheric field. We computed both the flux from
2 to 20 cm and the spatial structure of the microwave emission at 6
and 20 cm. The comparison of the computed and observed flux spectra
allowed us to estimate the magnetic field strength at the base of the
transition region and in the low corona, as well as the values of the
conductive flux and the height of the base of the transition region. The
model maps at 6 cm and 20 cm showed that α was not constant above the
active region; the same conclusion was reached on the basis of the
photospheric observations. The use of pressure measurements allowed
us to identify microwave structures which were determined by pressure
enhancements. At 6 cm the computations confirmed the fact that the
magnetic field is the principal factor that determines the structure
of sunspot-associated sources and showed that the effect of pressure
variations was small. Pressure variations were more important at 20 cm,
where the peak of the emission was associated with the sunspot and a
diffuse component was associated with the plage which had an average
pressure higher by a factor of 1.54 than the sunspot.
---------------------------------------------------------
Title: CHIANTI - an Atomic Database for Emission Line Spectroscopy:
Version 1 - Wavelengths greater than 50 Angstroms
Authors: Dere, K. P.; Monsignori-Fossi, B. C.; Landi, E.; Mason,
H. E.; Young, P. R.
1996AAS...188.8501D Altcode: 1996BAAS...28..961D
A comprehensive set of accurate atomic data is required for analyses of
astrophysical and solar spectra. CHIANTI provides an atomic database of
energy levels (wavelengths), radiative data and electron excitation data
for ions which are abundant in astrophysical plasmas. The most recent
electron excitation data have been assessed and stored following the
method of Burgess and Tully (1992). CHIANTI includes IDL (Interactive
Data Language) routines to produce optically thin synthetic spectra
for lambda > 50 Angstroms, assuming equilibrium conditions. It also
includes IDL routines to calculate theoretical line intensities required
for electron density or temperature diagnostics and emission measure
studies. The CHIANTI atomic database and supporting IDL routines are
available by anonymous FTP.
---------------------------------------------------------
Title: LASCO Observations of the 03Feb96 Streamer Blow-out
Authors: Andrews, M. D.; Korendyke, C. M.; Koomen, M. J.; Brueckner,
G. E.; Cook, J. W.; Dere, K. P.; Howard, R. A.; Michels, D. J.; Moses,
J. D.; Morrill, J. S.; Moulton, N. E.; Paswaters, S. E.; Socker, D. G.;
St. Cyr, O. C. St.; Wang, D.; Lamy, P. L.; Llebaria, A.; Bout, M. V.;
Schwenn, R.; Podlipnik, B.; Bedford, D. K.; Biesecker, D. A.; Eyles,
C. J.; Plunkett, S.; Simnett, G. M.
1996AAS...188.3716A Altcode: 1996BAAS...28..880A
The C2 and C3 telescopes on the Large Angle Spectrometric Coronograph
(LASCO) have recorded images of a Streamer Blow-out which occured
on 03Feb96. We will present a series of images produces by combining
data from the 2 coronographs. These images show a rapid evolution of
the coronal streamer belt over projected distances of 2 to 20 solar
radii. The streamer belt shows a dramatic brightening, which is seen to
propagate outward. A bubble-like structure is seen to move away from
the Sun and expand. At the end of this event, the equatorial corona
is significantly less bright than prior to the event.
---------------------------------------------------------
Title: LASCO Observations of the Solar Corona to 32 R<SUB>sun</SUB>
Authors: Cook, J. W.; Koomen, M. J.; Korendyke, C. M.; Brueckner,
G. E.; Dere, K. P.; Howard, R. A.; Michels, D. J.; Morrill, J. S.;
Moses, J. D.; Socker, D. G.; Paswaters, S. E.; Wang, D.; Moulton,
N. E.; Cyr, O. C. St.; Andrews, M. D.; Schwenn, R.; Podlipnik, B.;
Lamy, P. L.; Llebaria, A.; Bout, M. V.; Simnett, G. M.; Bedford,
D. K.; Eyles, C. J.; Plunkett, S.; Biesecker, D. A.
1996AAS...188.3717C Altcode: 1996BAAS...28..880C
The Large Angle Spectrometric Coronagraph (LASCO) was launched on
board the SOHO satellite on 2 December 1995. The C3 externally-occulted
coronagraph of LASCO observes the solar corona over a field from 3.7-32
R_ ⊙, using a 1024x1024 CCD detector with a pixel size corresponding
to 56 arc sec. Observations can be made using color filters ranging
from the blue (420-520 nm) to the near-IR (860-1050 nm), and through
polarizing filters. We report on early observations of the solar corona
out to 32 R<SUB>sun</SUB>.
---------------------------------------------------------
Title: Preliminary Photometric Calibration of LASCO C3 Coronagraph
Images using Pre-Flight Laboratory Images of Standard Sources and
In-Flight Images of Standard Stars
Authors: Korendyke, C. M.; Koomen, M. J.; Andrews, M. D.; Brueckner,
G. E.; Cook, J. W.; Dere, K. P.; Howard, R. A.; Michels, D. J.;
Moses, J. D.; Morrill, J. S.; Moulton, N. E.; Paswaters, S. E.;
Socker, D. G.; St. Cyr, O. C.; Wang, D.; Lamy, P. L.; Llebaria, A.;
Bout, M. V.; Schwenn, R.; Podlipnik, B.; Bedford, D. K.; Biesecker,
D. A.; Eyles, C. J.; Plunkett, S.; Simnett, G. M.
1996AAS...188.3621K Altcode: 1996BAAS...28..876K
The C3 coronagraph is a wide field (+/-8.0 degrees), externally
occulted, white light coronagraph. The instrument is one of three
coronagraphs comprising the Large Angle Spectrometric COronagraph
(LASCO) experiment mounted on the Solar Heliospheric Observatory
satellite. The satellite was launched on Dec. 2, 1996; C3 observations
began in early Jan. 1997. The coronagraph optical train includes a set
of five broadband color filters mounted in a wheel. Prior to flight,
an image was obtained through each color filter of a well characterized,
rear-illuminated, opal glass diffusing screen. The C3 in-flight images,
in addition to the coronal structures, also contain several hundred
bright stars. We present a comparison of the photometric calibration
derived from standard stars with the laboratory measurements. The
resulting calibration is then used to examine color variations in the
white light corona over the field of view. The LASCO experiment was
developed by a scientific consortium of members from NRL (USA), MPAe
(Germany), LAS (France) and U. Birmingham (United Kingdom).
---------------------------------------------------------
Title: Observations of the South coronal hole from EIT and YOHKOH
Authors: Handy, B. N.; Catura, R.; Freeland, S.; Lemen, J.; Stern,
R.; Gurman, J. B.; Delaboudiniere, J. P.; Artzner, G.; Gabriel, A.;
Maucherat, A.; Defise, J. M.; Jamar, C.; Rochus, P.; Clette, F.;
Cugnon, P.; Howard, R.; Michels, D.; Moses, J. D.; Dere, K.; Cyr,
O. C. St.; Catura, R.; Freeland, S.; Lemen, J.; Stern, R.; Neupert,
W.; Einfalt, E.; Newmark, J.
1996AAS...188.0206H Altcode: 1996BAAS...28..821H
The Extreme ultraviolet Imaging Telescope (EIT) on board the
SOHO spacecraft is capable of studying solar transition region,
chomospheric and coronal plasmas over bandpasses optimized for He II
304 Angstroms (0.08 MK), Fe IX/X 171, 173 Angstroms (0.8 - 1.0 MK),
Fe XII 195 Angstroms (1.5 MK), and Fe XV 284 Angstroms (2.0 - 2.5
MK) with 2.5 arcsecond spatial resolution. This telescope in concert
with the Yohkoh/SXT instrument allows us to simultaneously observe
solar structures at temperatures ranging from less than 0.1MK in the
transition region to over 3MK in the solar corona. EIT has had several
opportunities to observe the South coronal hole with high spatial and
temporal resolution. We compare observations from EIT and SXT with
an eye towards correlating temporal variations over the range of
wavelengths, activity of polar crown filament systems and relating
large-scale morphology of the X-ray corona to the transition region
in He II.
---------------------------------------------------------
Title: There's No Such Thing as the Quiet Sun: EUV Movies from SOHO
Authors: Gurman, J. B.; Delaboudiniere, J. P.; Artzner, G.; Gabriel,
A.; Maucherat, A.; Defise, J. M.; Jamar, C.; Rochus, P.; Clette, F.;
Cugnon, P.; Howard, R.; Michels, D.; Moses, J. D.; Dere, K.; Cyr,
O. C. St.; Catura, R.; Freeland, S.; Lemen, J.; Stern, R.; Neupert,
W.; Einfalt, E.; Newmark, J.
1996AAS...188.3718G Altcode: 1996BAAS...28..880G
We present unique time series of high-resolution solar images from the
normal-incidence Extreme ultraviolet Imaging Telescope (EIT) on board
the SOHO spacecraft. With a pixel scale of 2.6 arc sec and a detector
dynamic range of > 10(4) , the EIT can be used to study the dynamics
of chromospheric and coronal features in multilayer bandpasses optimized
for He II 304 Angstroms (0.08 MK), Fe IX/X 171, 173 Angstroms (0.8 -
1.0 MK), Fe XII 195 Angstroms (1.5 MK), and Fe XV 284 Angstroms (2.0 -
2.5 MK). Among the most striking features of the digital movies we will
display are: the dynamic nature of small-scale loop features in the
polar coronal holes, the constant activity of the polar crown filament
systems, the locations of the bases of polar plumes, the presence
of dark (scattering) filament material in the coronal emission line
images, and the evolution of a unique, linear, dark feature in a young
active region. The latter feature is suggestive of the “coronal void”
observed in the electron scattering corona by Macqueen et al./ (1983).
---------------------------------------------------------
Title: Coronal structure and heating: comparison between SXT/Yohkoh
observations of an active region and magnetogram
Authors: Cheng, C. -C.; Dere, K. P.; Wu, S. T.; Hagyard, M. J.;
Hiei, E.
1996AdSpR..17d.205C Altcode: 1996AdSpR..17..205C
We have studied the magnetic structure in AR 7150 (S09E06) observed on
29 April 1992 by the Soft X-Ray Telescope (SXT) on Yohkoh. The observed
X-ray images are compared with force-free magnetic fields with different
values of alpha, extrapolated from the MSFC photospheric magnetogram
observed at the same time. The results show that the magnetic field
of the active region is not potential. Different groups of loops are
characterized by different values of alpha. Bright loops correspond to
field with large alpha, indicating twisting of the loop. However, there
is no obvious correlation between the brightness of individual loops
with the amount of twist. Further investigation of the magnetic state of
the loop structure requires accurate nonlinear force-free calculations.
---------------------------------------------------------
Title: Observations of the south coronal hole from EIT and Yohkoh.
Authors: Handy, B. N.; Catura, R.; Freeland, S.; Lemen, J.; Stern,
R.; Gurman, J. B.; Delaboudinière, J. P.; Artzner, G.; Gabriel,
A.; Maucherat, A.; Defise, J. M.; Jamar, C.; Rochus, P.; Clette, F.;
Cugnon, P.; Howard, R.; Michels, D.; Moses, J. D.; Dere, K.; St. Cyr,
O. C.; Neupert, W.; Einfalt, E.; Newmark, J.
1996BAAS...28Q.821H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Nonthermal velocities in the solar transition and coronal
region observed with the high-resolution telescope and spectrograph
Authors: O'Shea, E.; Doyle, J. G.; Dere, K. P.; Keenan, F. P.
1996ASPC..109..145O Altcode: 1996csss....9..145O
No abstract at ADS
---------------------------------------------------------
Title: Observations of the comet Hyakutake by the LASCO coronagraph
on the SOHO satellite.
Authors: Andrews, M. D.; Paswaters, S. E.; Brueckner, G. E.; Korendyke,
C. M.; Dere, K. P.; Howard, R. A.; Michels, D. J.; Moses, J. D.;
Morril, J. S.; Moulton, N. E.; Socker, D. G.; St. Cyr, O. C.; Wang,
D.; Lamy, P. L.; Llebaria, A.; Bout, M. V.; Schwenn, R.; Podlipnik,
B.; Bedford, D. K.; Biesecker, D. A.; Eyles, C. J.; Plunket, S.;
Simnet, G. M.
1996BAAS...28.1195A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: EIT: Extreme-Ultraviolet Imaging Telescope for the SOHO Mission
Authors: Delaboudinière, J. -P.; Artzner, G. E.; Brunaud, J.; Gabriel,
A. H.; Hochedez, J. F.; Millier, F.; Song, X. Y.; Au, B.; Dere, K. P.;
Howard, R. A.; Kreplin, R.; Michels, D. J.; Moses, J. D.; Defise,
J. M.; Jamar, C.; Rochus, P.; Chauvineau, J. P.; Marioge, J. P.;
Catura, R. C.; Lemen, J. R.; Shing, L.; Stern, R. A.; Gurman, J. B.;
Neupert, W. M.; Maucherat, A.; Clette, F.; Cugnon, P.; Van Dessel,
E. L.
1995SoPh..162..291D Altcode:
The Extreme-ultraviolet Imaging Telescope (EIT) will provide wide-field
images of the corona and transition region on the solar disc and up to
1.5 R⊙ above the solar limb. Its normal incidence multilayer-coated
optics will select spectral emission lines from Fe IX (171 å), Fe
XII (195 å), Fe XV (284 å), and He II (304 å) to provide sensitive
temperature diagnostics in the range from 6 × 10<SUP>4</SUP> K to 3
× 10<SUP>6</SUP> K. The telescope has a 45 x 45 arcmin field of view
and 2.6 arcsec pixels which will provide approximately 5-arcsec spatial
resolution. The EIT will probe the coronal plasma on a global scale,
as well as the underlying cooler and turbulent atmosphere, providing
the basis for comparative analyses with observations from both the
ground and other SOHO instruments. This paper presents details of the
EIT instrumentation, its performance and operating modes.
---------------------------------------------------------
Title: The Large Angle Spectroscopic Coronagraph (LASCO)
Authors: Brueckner, G. E.; Howard, R. A.; Koomen, M. J.; Korendyke,
C. M.; Michels, D. J.; Moses, J. D.; Socker, D. G.; Dere, K. P.;
Lamy, P. L.; Llebaria, A.; Bout, M. V.; Schwenn, R.; Simnett, G. M.;
Bedford, D. K.; Eyles, C. J.
1995SoPh..162..357B Altcode:
The Large Angle Spectroscopic Coronagraph (LASCO) is a three
coronagraph package which has been jointly developed for the Solar
and Heliospheric Observatory (SOHO) mission by the Naval Research
Laboratory (USA), the Laboratoire d'Astronomie Spatiale (France),
the Max-Planck-Institut für Aeronomie (Germany), and the University
of Birmingham (UK). LASCO comprises three coronagraphs, C1, C2, and C3,
that together image the solar corona from 1.1 to 30 R<SUB>⊙</SUB> (C1:
1.1 - 3 R<SUB>⊙</SUB>, C2: 1.5 - 6 R<SUB>⊙</SUB>, and C3: 3.7 - 30
R<SUB>⊙</SUB>). The C1 coronagraph is a newly developed mirror version
of the classic internally-occulted Lyot coronagraph, while the C2 and
C3 coronagraphs are externally occulted instruments. High-resolution
imaging spectroscopy of the corona from 1.1 to 3 R<SUB>⊙</SUB> can
be performed with the Fabry-Perot interferometer in C1. High-volume
memories and a high-speed microprocessor enable extensive on-board image
processing. Image compression by a factor of about 10 will result in
the transmission of 10 full images per hour.
---------------------------------------------------------
Title: Ultraviolet Observations of the Structure and Dynamics of an
Active Region at the Limb
Authors: Korendyke, C. M.; Dere, K. P.; Socker, D. G.; Brueckner,
G. E.; Schmieder, B.
1995ApJ...443..869K Altcode:
The structure and dynamics of active region NOAA 7260 at the limb have
been studied using ultraviolet spectra and spectroheliograms obtained
during the eighth rocket flight of the Naval Research Laboratory's
High Resolution Telescope an Spectrograph (HRTS). The instrument
configuration included a narrow-bandpass spectroheliograph to observe
the Sun in the lines of C IV lambda 550 and a tandem-Wadsworth mount
spectrograph to record the profiles of chromospheric transition
region and coronal lines in the 1850-2670 A region. The combination
of high spatial resolution and high spectral purity C IV slit jaw
images with ultraviolet emission-line spectra corresponding allows
examination of a variety of active region phenomena. A time series
of spectroheliograms shows large-scale loop systems composed of
fine-scale threads with some extending up to 100 Mm above the
limb. The proper motion of several supersonic features, including
a surge were measured. The accelerated plasmas appear in several
different geometries and environments. Spectrograph exposures were
taken with the slit positioned at a range of altitudes above the limb
and provide a direct comparison between coronal, transition region
and chromospheric emission line profiles. The spectral profiles of
chromospheric and transition region emission lines show line-of-sight
velocities up to 70 km/s. These lower temperature, emission-line spectra
show small-scale spatial and velocity variations which are correlated
with the threadlike structures seen in C IV. Coronal lines of Fe XII
show much lower velocities and no fine structure.
---------------------------------------------------------
Title: The Rate of Magnetic Reconnection in the Solar Corona
Authors: Dere, K. P.
1995SPD....26..612D Altcode: 1995BAAS...27..963D
No abstract at ADS
---------------------------------------------------------
Title: EIT: The Extreme Ultraviolet Imaging Telescope. Synoptic
Observations of Small and Large-Scale Coronal Structures
Authors: Clette, F.; Delaboudinière, J. P.; Dere, K. P.; Cugnon,
P.; EIT Science Team
1995LNP...444..251C Altcode: 1995cmer.conf..251C
The EIT will provide wide-field images of the corona and transition
region, on the solar disc and up to 1 R<SUB>⊙</SUB> above the
limb. Its normal incidence multilayer-coated optics will select the
spectral emission lines of four ions (Fe IX, 171 Å; Fe XII, 195
Å; Fe XV, 284 Å; Hell, 304 Å), providing a sensitive temperature
diagnostic in the range 6.10<SUP>4</SUP> to 3.10<SUP>6</SUP>K. This
SOHO instrument will thus probe the coronal plasma on a global scale,
as well as the underlying cooler and turbulent atmosphere. The EIT's
characteristics and performances are presented, and prospects for
coordinated observations with ground-based radio observatories are
outlined.
---------------------------------------------------------
Title: Magnetic Structure and Heating of an Active Region: Comparison
Between SXT/Yohkoh Observations and Magnetogram
Authors: Cheng, C. -C.; Dere, K. P.; Wang, Jingxiu; Ai, Guoxiang
1994AAS...185.8604C Altcode: 1994BAAS...26.1464C
We have studied the magnetic structure of AR7420 observed on 9
February 1993 by the Soft X-Ray Telescope (SXT) on Yohkoh. The
observed X-ray images of the active region are compared with various
force-free magnetic fields, extrapolated from the photospheric
magnetograms obtained at the same time by the Huairou Station of the
Beijing Astronomical Observatory. The results show that the magnetic
configuration of the active region is not a potential field. Different
groups of loops are characterized by different values of alpha ,
indicating that the loops are twisted and that there are currents
flowing through them. Here alpha is given by nabla times B=alpha B
for a force free field, where B is the magnetic field. In particular,
we find that there are opposite current systems in the active region,
as specified by positive and negative values of alpha . In addition,
we find that there is no obvious correlation between the brightness of
individual loops with the amount of twist. Implications of the results
will be discussed.
---------------------------------------------------------
Title: Hierarchy of spatial scale sin UV prominences
Authors: Schmieder, B.; Wiik, J. E.; Dere, K. P.
1994SSRv...70..175S Altcode:
Ultraviolet spectra of a quiescent prominence observed with theHigh
Resolution Telescope and Spectrograph (HRTS) are analyzed. Different
techniques lead to greatly different spatial scales for the prominence
structures. The UV spectra show strong variations in intensity and
Doppler shift on scales larger than 1700 km. Spectroscopic diagnostics
employing line intensity ratios indicate the existence of scales
between 400 m to some hundred kilometers. We attempt to interpret
various aspects of the prominence intensities and velocities with a
multiple thread model.
---------------------------------------------------------
Title: Solar mass flow in fine-scale structures
Authors: Dere, K. P.
1994SSRv...70...21D Altcode:
Observations of transient and steady velocities at chromospheric,
transition region and coronal temperatures in the quiet Sun and coronal
holes are reviewed. The relevance of fine-scale structures in governing
the mass balance of the solar atmosphere is stressed. At present,
a coherent picture of these mass flows does not exist. However, the
current observational base of transition region and coronal velocity
information is limited but should greatly improve with measurements
from the SOHO satellite.
---------------------------------------------------------
Title: Solar Fine-Scale Structures in the Corona, Transition Region,
and Lower Atmosphere
Authors: Moses, Dan; Cook, J. W.; Bartoe, J. -D. F.; Brueckner, G. E.;
Dere, K. P.; Webb, D. F.; Davis, J. M.; Harvey, J. W.; Recely, F.;
Martin, S. F.; Zirin, H.
1994ApJ...430..913M Altcode:
The American Science and Engineering Soft X-ray Imaging Payload and the
Naval Research Laboratory High Resolution Telescope and Spectrograph
(HRTS) were launched from White Sands on 1987 December 11 in coordinated
sounding rocket flights. The goal was to investigate the correspondence
of fine-scale structures from different temperature regimes in the
solar atmosphere, and particularly the relationship between X-ray bright
points (XBPs) and transition region explosive events. We present results
of the analysis of co-aligned X-ray images, maps of sites of transition
region explosive events observed in C IV 10<SUP>5</SUP>, HRTS 1600
A spectroheliograms of the T<SUB>min</SUB> region, and ground-based
magnetogram and He I 10830 A images. We examined the relationship
of He I 10830 A dark features and evolving magnetic features which
correspond to XBPs. We note a frequent double ribbon pattern of the
He I dark feature counterparts to XBPs. We discuss an analysis of the
relationship of XBPs to evolving magnetic features by Webb et al.,
which shows that converging magnetic features of opposite polarity are
the most significant magnetic field counterparts to XBPs. The magnetic
bipolar features associated with XBPs appear as prominent network
elements in chromospheric and transition region images. The features
in C IV observations corresponding to XBP sites are in general bright,
larger scale (approximately 10 arcsec) regions of complex velocity
fields of order 40 km/s, which is typical of brighter C IV network
elements. These C IV features do not reach the approximately 100 km/s
velocities seen in the C IV explosive events. Also, there are many
similar C IV bright network features without a corresponding XBP in the
X-ray image. The transition region explosive events do not correspond
directly to XBPs. The explosive events appear to be concentrated in
the quiet Sun at the edges of strong network, or within weaker field
strength network regions. We find a greater number of C IV events than
expected from the results of a previous Spacelab 2 HRTS disk survey. We
attribute this at least partly to better spatial resolution with the
newer HRTS data. The full-disk X-ray image shows a pattern of dark
lanes in quiet Sun areas. The number density of C IV events is twice
as large inside as outside a dark lane (4.6 x 10<SUP>-3</SUP> vs. 2.3
x 10<SUP>-3</SUP> explosive events per arcsec <SUP>2</SUP>). The dark
lane corresponds to an old decaying magnetic neutral line. We suggest
that this provides an increased opportunity for small-scale convergence
and reconnection of opposite polarity magnetic field features, in
analogy with the results of Webb et al. for XBPs but at a reduced
scale of reconnection.
---------------------------------------------------------
Title: HRTS Observations of Explosive Events in a Flaring Active
Region
Authors: Dere, K. P.; Martin, S. F.
1994kofu.symp..289D Altcode:
Explosive events are a highly dynamic, small-scale phenomena that are
commonly observed on the Sun with the NRL High Resolution Telescope and
Spectrograph (HRTS). There is now considerable evidence which suggests
that they are signatures of magnetic reconnection during flux emergence
and cancellation. Data from the Big Bear Solar Observatory and the
HRTS instrument are used to demonstrate the direct correspondence
between explosive events and evolving magnetic structures.
---------------------------------------------------------
Title: Combined HRTS-8 Sounding Rocket Observations and YOHKOH Soft
X-ray Observations of NOAA Active Region 7260 at the Solar Limb
Authors: Korendyke, C. M.; Dere, K. P.; Brueckner, G. E.; Waljeski,
K.; Lemen, J. R.
1994kofu.symp..293K Altcode:
On 24 August 1992, the Naval Research Laboratory (NRL) High Resolution
Telescope and Spectrograph (HRTS) was launched aboard a Black Brant
sounding rocket from White Sands, New Mexico. During the flight, the
instrument recorded a unique set of near ultraviolet slit spectra and
1550 A spectroheliograms of an active region at the solar limb. An
extensive set of observations of this region were obtained with the
Yohkoh Soft X-ray Telescope (SXT) near the time of the flight. The C IV
spectroheliograms obtained during this flight are some of the highest
resolution images of the solar transition region ever obtained. The
spectra and spectroheliograms dramatically demonstrate the fundamental
difference between coronal and chromospheric/transition-region plasmas
at 700 km spatial scales. The cooler plasmas exhibit a great deal of
dynamic, fine scale structure with significant flows or proper motion
particularly in the transition zone loops. The coronal emission lines
in the spectra! are relatively uniform and quiescent. The Yohkoh data
during the period before and after the flight show a set of diffuse
high temperature coronal loops with only minimal correspondence to
the structures visible in the C IV spectroheliograms.
---------------------------------------------------------
Title: The Composition of a Coronal Active Region
Authors: Waljeski, K.; Moses, D.; Dere, K. P.; Saba, J. L. R.; Strong,
K. T.; Webb, D. F.; Zarro, D. M.
1994ApJ...429..909W Altcode:
The relative abundances of iron, oxygen, magnesium, and neon in a
coronal active region are determined from measurements of soft X-ray
line and broadband intensities. The emission measure, temperature,
and column density are derived from these measured intensities and are
used to place a constraint on the abundances of the heavier elements
relative to hydrogen in the corona. The intensity measurements were
made on 1987 December 11, when an active region was observed jointly by
the American Science and Engineering (AS&E) High Resolution Soft
X-Ray Imaging Sounding-Rocket Payload and the X-Ray Polychromator
Flat Crystal Spectrometer (FCS) onboard the Solar Maximum Mission
spacecraft. The coordinated observations include images through two
broadband filters (8 to 29 A and 8 to 39, 44 to 60 A) and profiles
of six emission lines: Fe XVII (15.01 A), FE VIII (15.26 A), O VIII
(18.97 A), Mg XI (9.17 A), Ne IX (13.44 A), and Fe XVIII (14.21 A). The
effects of resonance scattering are considered in the interpretation
of the FCS line intensities. We calculated the expected intensity
ratio of the two Fe XVII lines as a function of optical depth and
compared this ratio with the observed intensity ratio to obtain the
optical depths of each of the lines and the column density. The line
intensities and the broadband filtered images are consistent with
the emission from a thermal plasma where Fe, O, Mg, and Ne have
the 'adopted coronal' abundances of Meyer (1985b) relative to one
another, but are not consistent with the emission from a plasma having
photospheric abundances: The ratios of the abundances of the low first
ionization potential (FIP) elements (Fe and Mg) to the abundances of
the high-FIP elements (Ne and O) are higher than the ratios seen in the
photosphere by a factor of about 3.5. This conclusion is independent of
the assumption of either an isothermal or a multithermal plasma. The
column densities derived from the Fe XVII line ratio and the geometry
of the active region provide a diagnostic of the abundance of hydrogen
relative to the heavier elements. We find that the abundance of iron
with respect to hydrogen in the corona is higher than the value given
Meyer (1985b) by a factor of 8.2(-5.4, +5.1). This means that, for the
observed active region, the absolute abundances of the low-FIP elements
(Fe and Mg) are enhanced in the corona relative to the photosphere,
while the abundances of the high-FIP elements (Ne and O) are either
slightly enhanced in the corona or nearly the same in the photosphere
and the corona.
---------------------------------------------------------
Title: Explosive events, magnetic reconnection, and coronal heating
Authors: Dere, K. P.
1994AdSpR..14d..13D Altcode: 1994AdSpR..14...13D
Signatures of explosive events are prominent in transition region
spectra where they display exceptionally large velocities (>100 km
s<SUP>-1</SUP>) in small areas (1500 km). Their physical properties,
deduced from previous analyses of HRTS spectra and more recent work, are
summarized here. It now appears that the explosive events are associated
with the process of magnetic cancellation and HRTS data obtained during
the most recent rocket flight in 1990 provide direct evidence for this
assertion. Flux cancellation, which tends to proceed on time-scales
of hours, most likely involves magnetic reconnection in a very bursty
manner which explains the small, short-lived explosive events. These
reconnection events are part of a larger pattern where small flux
elements emerge in the supergranule centers and are transported to
the boundaries to continually regenerate the network fields on a
timescale of about 8 hours. These timescales are also sufficiently
short to account for the energetics of the quiet sun.
---------------------------------------------------------
Title: Observational characteristics of explosive events
Authors: Hénoux, J. -C.; Dere, K. P.
1994LNP...432..203H Altcode:
The characteristics of dynamic phenomena observed in the EUV with
the HRTS instruments, chromospheric jets and explosive events, are
reviewed here. Most of the review is devoted to explosive events that
are short duration explosions involving a plasma at 105 K. These
events are characterised by strong Doppler shifts rather than by
brightness enhancements, contrary to EUV impulsive brightenings
observed by SMM. They are presumably due to magnetic reconnection
involving unresolved fine structures of the magnetic field near the
network. The role of the density of concentrated magnetic fluxtubes
in a reconnection scenario has still to be understood.
---------------------------------------------------------
Title: Observational characteristics of explosive events.
Authors: Hénoux, J. C.; Dere, K. P.
1994LNP...432..205H Altcode: 1994LNPM...11..205H
The characteristics of dynamic phenomena observed in the EUV with
the HRTS instruments, chromospheric jets and explosive events, are
reviewed. Most of the review is devoted to explosive events that are
short duration explosions involving a plasma at 10<SUP>5</SUP>K. These
events are characterised by strong Doppler shifts rather than by
brightness enhancements, contrary to EUV impulsive brightenings
observed by SMM. They are presumably due to magnetic reconnection
involving unresolved fine structures of the magnetic field near the
network. The role of the density of concentrated magnetic fluxtubes
in a reconnection scenario has still to be understood.
---------------------------------------------------------
Title: A New Synthetic XUV Spectrum
Authors: Dere, K. P.; Mason, H. E.; Fossi, B. C. Monsignori; Waljeski,
K. H.
1993AAS...18311203D Altcode: 1993BAAS...25.1459D
We have begun a program to develop a synthetic XUV spectrum for the
70 - 2500 /AA wavelength region based on a critical analysis of the
most recent calculations of atomic parameters, in particular, atomic
collision strengths and their thermal averages. Ultraviolet spectra
returned by the EUVE and HST instruments demonstrate a continued need
for the most accurate atomic parameters in order to determine the
physical conditions in the emitting plasmas. Most previous synthetic
spectra has relied heavily on the gaunt factor approximation which can
predict excitation rates only for dipole transitions and only to within
a factor of 2 to 3. In many cases, direct calculations of the collision
strengths are now available. Burgess and Tully (1992) have developed
a technique for critically evaluating collision strength calculations
and scaling and compacting the data. Different scalings are available
for resonance, intercombination and forbidden excitations. This method
will be applied in the construction of our spectrum. In the end, we
intend to produce a set of critically evaluated atomic parameters
from which the nearly optically thin spectrum of a low density
astrophysical plasma can be calculated, together with the programs
necessary to perform these calculations. We will include the ability
to prescribe elemental abundances and to correct for optical depth
and populations of metastable levels as a function of density. The
data sets and programs will be made available by anonymous ftp.
---------------------------------------------------------
Title: A Description of the HRTS-8 Instrument Configuration
Authors: Korendyke, C. M.; Dere, K. P.; Brueckner, G. E.; Socker, D. G.
1993BAAS...25.1182K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: HRTS Untraviolet Observations of the Chromosphere Transition
Region and Corona of a Solar Active Region
Authors: Dere, K. P.; Korendyke, C. M.; Brueckner, G. E.
1993BAAS...25.1182D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: UV prominences observed with the HRTS: structure and physical
properties
Authors: Wiik, J. E.; Dere, K.; Schmieder, B.
1993A&A...273..267W Altcode:
Ultraviolet spectra of two quiescent prominences (PL1, PL2) observed
with the High Resolution Telescope and Spectrograph (HRTS) are described
and analyzed. Meudon synoptic maps and spectroheliograms indicate that
prominence PL 1 was extremely active during the flight and that material
ejections were likely. PL2 appeared to be a more stable prominence. The
significant differences between the spectra of the two prominences
can perhaps be explained by their levels of activity. The spectrum of
the more active prominence PL1 is dominated by transition zone lines
formed near 10<SUP>5</SUP> K whereas the second prominence PL2 shows
considerable emission of cooler chromospheric lines formed near 2
× 1O<SUP>4</SUP> K. PL 1 also exhibits larger bulk flow velocities
(up to ∼ 30 km s<SUP>-1</SUP>) and non-thermal velocities (∼20km
s<SUP>-1</SUP>). From line ratios (O IV, N V, N IV, Si IV) a relatively
large electron density (∼10<SUP>11</SUP> cm<SUP>-3</SUP>) is derived
for the PL1 prominence transition region (PTR). In comparison, PL2 is
a relatively quiet prominence with bulk flow velocities generally less
than ∼3 km s<SUP>-1</SUP>. <P />Different techniques yield greatly
different spatial scales for the prominence. The UV spectra show strong
variations in intensity and Doppler shift on scales of about 1700km. The
combined density and emission measures indicate path lengths of 400 m
or less. The optical depth in C IV requires path lengths of 40 km or
less. If, as suggested by these analyses, it is assumed that prominence
emission is due to a number of micro-structures with a Gaussian velocity
distribution, then spatial scales of the micro-structures of a few
hundred kilometers are found.
---------------------------------------------------------
Title: Transition Region Explosive Events in an X-Ray Dark Lane
Region of the Quiet Sun
Authors: Cook, J. W.; Moses, D.; Brueckner, G. E.; Dere, K. P.;
Bartoe, J. -D. F.; Webb, D.; Davis, J. M.; Harvey, J. W.; Recely,
F.; Martin, S. F.; Zirin, H.
1993BAAS...25.1181C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Scaling Laws for Coronal Heating: X-ray Loop Observations
Authors: Waljeski, K.; Dere, K. P.; Moses, D.
1993BAAS...25.1212W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Nonthermal Velocities in the Solar Transition Zone Observed
with the High-Resolution Telescope and Spectrograph
Authors: Dere, K. P.; Mason, H. E.
1993SoPh..144..217D Altcode:
Data obtained during the first rocket flight of the NRL High Resolution
Telescope and Spectrograph (HRTS) have been used to study nonthermal
velocities for spectral lines primarily covering the temperature
range 10<SUP>4</SUP> to 2 × 10<SUP>6</SUP> K. The high spectral and
spatial resolution, combined with an enhanced dynamic intensity range
of the reduced data, has enabled us to study the distribution of the
nonthermal velocities for quiet and active regions. Average values
of the nonthermal velocities peak at about 27 km s<SUP>−1</SUP>
at 10<SUP>5</SUP> K for the quiet regions, with a wide distribution
of nonthermal velocities for each line. The active region nonthermal
velocities have a narrower distribution which is weighted towards higher
values. The SiIV and C IV line profiles are not well described by a
single Gaussian, indicating that high-velocity components (above 30 km
s<SUP>−1</SUP>) are present in the quiet-Sun spectra. The radiative
losses for all plasma above l0<SUP>5</SUP> K have been calculated for
the quiet Sun, an active region and a coronal hole. These have been
compared with the acoustic wave flux inferred from the nonthermal line
widths. There appears to be a sufficient flux of waves to heat these
regions of the atmosphere.
---------------------------------------------------------
Title: Observational test of coronal heating models.
Authors: Waljeski, Katrina; Dere, Ken P.; Moses, Dan
1992ESASP.348..281W Altcode: 1992cscl.work..281W
The properties of coronal loops are measured and used to test the
predictions of coronal heating models. The coronal loop temperature,
emission measure, geometry, and magnetic field strength are measured
from broadband soft X-ray images obtained by the American Science
and Engineering High Resolution Soft X-Ray Imaging Sounding Rocket
Payload and from coordinated ground-based observations. The radiative
energy loss rates for these loops, calculated from the observed plasma
properties, are compared to the scalings with loop length or magnetic
field strength predicted by various models of coronal heating. The
loop scaling laws of Rosner, Tucker, and Vaiana and of Golub et al. are
also tested with these observations.
---------------------------------------------------------
Title: Solar corona synoptic observations from SOHO with an Extreme
Ultraviolet Imaging Telescope.
Authors: Delaboudinière, J. P.; Gabriel, A. H.; Artzner, G. E.;
Dere, K.; Howard, R.; Michels, D.; Catura, R.; Lemen, J.; Stern, R.;
Gurman, J.; Neupert, W.; Cugnon, P.; Koeckelenbergh, A.; van Dessel,
E. L.; Jamar, C.; Maucherat, A.
1992ESASP.348...21D Altcode: 1992cscl.work...21D
The major scientific objective of the EUV Imaging Telescope (EIT)
is to study the evolution of coronal structure over a wide range
of spatial and temporal scales and temperatures. A second strategic
objective is to provide full disk synoptic maps of the global corona
to aid in unifying SOHO (Solar and Heliospheric Observatory)/Cluster
investigations. EIT will also provide images to support the planning
of detailed spectroscopic investigations by the CDS (Coronal Diagnostic
Spectrometer) and SUMER spectrometers in SOHO. EIT observations will be
made in four narrow spectral bands, centered at 171 A (Fe 9), 195 A(Fe
12), 284 A (Fe 15), and 304 A (He 2) representing restricted temperature
domains within a wide temperature range from 40,000 to 3,000,000
K. The results will be images of the solar atmosphere from the upper
chromosphere and transition region to the active region corona. These
maps, made at appropriate time intervals, will be used to study the fine
structures in the solar corona and to relate their dynamic properties
to the underlying chromosphere and photosphere. Dynamic events in the
inner corona will be related to white light transients in the outer
corona, and observations of the internal structure of coronal holes
will be used to investigate origins of the solar wind.
---------------------------------------------------------
Title: Intensity, velocity and turbulence in prominences observed
with the HRTS instrument.
Authors: Schmieder, B.; Wiik, J. E.; Dere, K. P.
1992JAF....43...36S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Explosive events and magnetic reconnection in the solar
atmosphere
Authors: Dere, K. P.
1992AIPC..267...63D Altcode: 1992ecsa.work...63D
Explosive events are highly-dynamic, small-scale phenomena commonly
observed in spectra of transition zone lines. Their velocities are near
100 km s-1, sizes near 1500 km, and time scales near 60 s. They occur at
a height of 1000-2000 km, below typical transition zone structures. It
has been demonstrated that some explosive events are caused by
emerging magnetic flux and there is good evidence to indicate that
the great majority are related to magnetic flux cancellation. The most
probable mechanism for their generation is magnetic reconnection. The
characteristics of explosive events and flux cancellation taken together
show that magnetic reconnection in the quiet sun apparently proceeds
readily in rapid bursts along the neutral line separating opposite
flux elements that are convected together by photospheric flows.
---------------------------------------------------------
Title: Ultraviolet Explosive Events and Evolving Magnetic Fields
Authors: Dere, K. P.; Martin, S. F.
1992AAS...180.5604D Altcode: 1992BAAS...24..821D
No abstract at ADS
---------------------------------------------------------
Title: Intensity, velocity and turbulence in prominences observed
with the HRTS.
Authors: Wiik, J. E.; Dere, K.; Schmieder, B.
1992ESASP.344...65W Altcode: 1992spai.rept...65W
The moments of UV emission line profiles between 1206 and 1670 A
observed in two quiescent prominences with the High Resolution Telescope
and Spectrograph (HRTS) are analysed. Spectral lines in this region
of the solar spectrum provide information on plasmas in the 10000K
to 200000K range. In both prominences a good correlation is found
between the intensities of lines formed at different temperatures. A
good correlation is also found between the non-thermal velocities of
different lines.
---------------------------------------------------------
Title: LASCO - Large Angle Spectrometric Coronagraph for SOHO
Authors: Howard, R. A.; Brueckner, G. E.; Dere, K. P.; Korendyke,
C. M.; Koomen, M. J.; Michels, D. J.; Moses, D.; Socker, D. G.;
Schwenn, R.; Inhester, B.; Lamy, P.; Maucherat, A.; Simnett, G. M.;
Eyles, C.
1992AAS...180.3307H Altcode: 1992BAAS...24..781H
No abstract at ADS
---------------------------------------------------------
Title: Transition region dynamics.
Authors: Dere, K. P.
1992ESASP.344...43D Altcode: 1992spai.rept...43D
The solar transition region has qualities that make it an ideal testing
ground for theories of coronal heating and dynamics. Strong diagnostic
lines formed at transition region temperatures (2×10<SUP>5</SUP> to
10<SUP>6</SUP>K) are found at VUV wavelengths that are observable with
relatively straightforward optical techniques. The transition region
is highly dynamic; nonthermal velocities peak at 10<SUP>5</SUP>K and
high velocity explosive events, indicators of magnetic reconnection,
are commonly found throughout the quiet and active sun. The fine-scale
density and velocity structures indicate that important information
will be found at spatial scales below 1″
---------------------------------------------------------
Title: Dynamics in the Prominence - Corona Transition Region from
HRTS Spectra
Authors: Schmieder, B.; Dere, K. P.; Wiik, J. E.
1992LNP...399..333S Altcode: 1992esf..coll..333S; 1992IAUCo.133..333S
Line profiles of UV emission lines between 1206Å and 1670Å observed
in two prominences with the High Resolution Telescope and Spectrograph
(HRTS) are analysed. Spectral lines in this region of the solar spectrum
such as C I, Fe II, Si IV and C IV, provide information on plasmas in
the 10 000 K to 200 000 K range. In the active prominence observed
with HRTS-1 a good correlation is found between the intensities and
velocities of different lines formed over a range of temperatures. On
the contrary, poor cross correlation between the velocities observed
in plasmas of cold temperatures indicates the presence of different
structures in the SL2 prominence. Microturbulent velocities from 0 to
25km s-1 are found in both prominences.
---------------------------------------------------------
Title: The chromospheric and transition region manifestations of an
Ellerman bomb.
Authors: Cook, J. W.; Brueckner, G. E.; Dere, K. P.; Martin, S. F.;
Gayley, K. G.
1992BAAS...24.1074C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Explosive events and magnetic reconnection in the solar
atmosphere
Authors: Dere, K. P.
1992sws..coll...11D Altcode:
Signatures of explosive events are prominent in transition region
spectra where they display large (100 km/s) in small areas (1500
km). Their physical properties, deduced from previous analyses of
HRTS spectra and more recent work, are summarized here. It now appears
that the explosive events are associated with the process of magnetic
cancellation and HRTS data obtained during the most recent rocket flight
in 1990 provide direct evidence for this assertion. Flux cancellation,
which tends to proceed with timescales of hours, most likely involved
magnetic reconnection in a very bursty manner which explains the small,
short-lived explosive events.
---------------------------------------------------------
Title: Relative Abundances in the Lower Solar Transition Region
Authors: Doschek, G. A.; Dere, K. P.; Lund, P. A.
1991ApJ...381..583D Altcode:
Properties of the lower solar transition region as determined from
UV spectral lines recorded by the Naval Research Laboratory HRTS
are investigated. The spectra were obtained from a rocket flight in
July 1975. Variations of intensity ratios of strong lines of C IV,
Si IV, C II, Si III, and O IV over the entire field of view of the
HRTS instrument, which extends from disk center to the solar limb are
discussed. The largest apparent abundance variations appear to be in
the active regions surrounding a sunspot. The C/Si ratio is lower in
the active regions than anywhere else in the instrument field of view,
implying a lower C/Si abundance ratio in the active regions. There
is a possible correlation of line intensity variation in the active
region with Doppler shift of the lines; the explanation for this is
unclear. The magnitude and reality of intensity ratio variations of
all observed solar features are discussed, and monotonic center-to-limb
intensity ratio variations due to the opacity of some of the spectral
lines are measured.
---------------------------------------------------------
Title: Velocity Gradients in the Chromosphere-Corona Transition Region
Authors: Athay, R. G.; Dere, K. P.
1991ApJ...381..323A Altcode:
Velocity data obtained from Doppler shifts of EUV spectral lines
observed with the High Resolution Telescope and Spectrograph flown
on Spacelab II are analyzed to determine the properties of the mean
velocities V-bar and its spatial variance V(sigma), for chromospheric
and transition region lines. The lines studied include the ions O I,
C I, Fe II, C II, Si III, Si IV, and C IV. The constancy of V(sigma)
from center to limb together with a systematic maximum redshift in
V-bar in central disk regions is interpreted to mean that the plasma
flow is divergent from the tops of closed field lines and that the
cool plasma more or less fills the magnetic loops from which most of
the radiation originates. The same is true of the hotter plasma. It
is suggested that the crossfield component of Delta T is large and
that the alternation from cool loops to hot loops occurs on spatial
scales much less than 1 arcsec.
---------------------------------------------------------
Title: Chromospheric and Transition Region Diagnostics Using
Emission-Line Intensities
Authors: Athay, R. G.; Dere, K. P.
1991ApJ...379..776A Altcode:
EUV emission-line intensities from the HRTS experiment on Spacelab 2 are
analyzed to determine the causes of intensity variations from point to
point on the solar surface. Chromospheric lines of O I and transition
region lines of C II, Si IV, and C IV exhibit saturation effects that
limit the line intensities in the brighter regions. No such effect
is found in lines of C I, Fe II, or Si III. The chromospheric lines
saturate because the optical thickness exceeds the thermalization depth,
whereas the transition region lines saturate because of the geometry
of the unresolved fine structure. The latter is assumed to consist
of elongated cylinder-like features oriented along magnetic lines of
force that are mainly vertical. Saturation occurs when the optical
thickness along the axis of the cylinders exceeds unity. Estimates
based on the observed saturation effects give fill factors for the fine
structure 0.005 and 0.4 at 100,000 K and 30,000 K, respectively. The
corresponding lengths of the cylinders are estimated at 1000 km and
40 km at the two temperatures.
---------------------------------------------------------
Title: Explosive events and magnetic reconnection in the solar
atmosphere
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.; Ewing,
J.; Lund, P.
1991JGR....96.9399D Altcode:
Explosive events are highly energetic, small-scale phenomena which are
frequently detected throughout the quiet and active Sun. They are seen
in profiles of spectral lines formed at transition zone temperatures
as exceptionally Doppler-shifted features, typically at 100 km
s<SUP>-1</SUP> to the red and/or blue of the rest wavelength. Sufficient
observational evidence has now been developed to demonstrate that some
explosive events are associated with the emergence of new magnetic
flux. In these cases it is likely that the acceleration of plasma is
caused by the magnetic reconnection resulting from flux emergence. We
take as a working hypothesis the proposal that all explosive events
are the result of magnetic reconnection. Since explosive events tend
to occur on the edges of high photospheric magnetic field regions,
we identify them with reconnection that occurs during the cancellation
of photospheric magnetic flux (Martin, 1984; Livi et al., 1985). The
combined observational characteristics of photospheric flux cancellation
and transition zone explosive events provide powerful diagnostic
information concerning the nature of magnetic reconnection. Reconnection
in the quiet solar atmosphere apparently proceeds in bursts at sites
much smaller than the boundary between opposite polarity flux elements
that are observed to cancel in magnetograph sequences. Equating the
velocity of the expelled transition zone plasma with the Alfvén speed
yields magnetic field strengths of 20 G at the site of reconnection. The
speed at which the reconnection proceeds is commensurate with the rapid
rates predicted by Petschek (1964). ©1991 American Geophysical Union
---------------------------------------------------------
Title: The Magnetic Network Location of Explosive Events Observed
in the Solar Transition Region
Authors: Porter, J. G.; Dere, K. P.
1991ApJ...370..775P Altcode:
Compact short-lived explosive events have been observed in solar
transition region lines with the High-Resolution Telescope and
Spectrograph (HRTS) flown by the Naval Research Laboratory on a series
of rockets and on Spacelab 2. Data from Spacelab 2 are coaligned
with a simultaneous magnetogram and near-simultaneous He I 10,380 -A
spectroheliogram obtained at the National Solar Observatory at Kitt
Peak. The comparison shows that the explosive events occur in the solar
magnetic network lanes at the boundaries of supergranular convective
cells. However, the events occur away from the larger concentrations
of magnetic flux in the network, in contradiction to the observed
tendency of the more energetic solar phenomena to be associated with
the stronger magnetic fields.
---------------------------------------------------------
Title: The Prime Energy Release of a Solar Flare
Authors: Brueckner, G. E.; Moses, D.; Cook, J. W.; Dere, K. P.;
Korendyke, C. M.; Socker, D. G.; Bartoe, J. -D. F.
1991BAAS...23.1026B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Nonthermal Velocities in the Solar Transition Region
Authors: Dere, K. P.; Mason, H. E.
1991BAAS...23Q1028D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Flaring Active Region Structures in the Corona, Transition
Region, and Lower Atmosphere Observed in the SAROC
Authors: Moses, D.; Brueckner, G. E.; Cook, J. W.; Dere, K. P.;
Korendyke, C. M.; Socker, D. G.; Bartoe, J. -D. F.
1991BAAS...23.1026M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coordinated observations with high resolution spectrographs
(HRTS, SERTS, MSDP)
Authors: Schmieder, B.; Thompson, W. T.; Neupert, W. M.; Thomas,
R. J.; Dere, K. P.
1991AdSpR..11e.255S Altcode: 1991AdSpR..11R.255S
Observations with the High Resolution Telescope Spectrograph
(HRTS) aboard Spacelab2 in 1985, and more recently with the Solar
Extreme-ultraviolet Rocket Telescope and Spectrometer (SERTS) during
the rocket flight of May 5, 1989 were well coordinated with the Meudon
instruments, principally with the Multichannel Subtractive Double Pass
(MSDP) spectrograph. These instruments allow the study of phenomena
in a large temperature range and the determination of the energy
budget. MSDP observations coordinated with the SERTS have permitted
the analysis of physical parameters of coronal plasma surrounding
dynamical chromospheric events, such as preflaring region and a
filament. By combining Hα spectrograms and HRTS data, C IV flow
(~50 km s<SUP>-1</SUP>) detected at the footpoints of a prominence
has been interpreted by horizontal velocities along the axis of the
arches of the prominence.
---------------------------------------------------------
Title: High resolution solar physics from rockets
Authors: Dere, K. P.
1991AdSpR..11e.191D Altcode: 1991AdSpR..11..191D
Explosive events are highly energetic phenomena that are frequently
seen throughout the quiet and active sun, particularly in spectral
lines formed at transition zone temperatures. Sufficient observational
evidence has now been developed to conclusively demonstrate that some
explosive events are caused by magnetic reconnection in emerging
magnetic flux regions. It is also consistent with observations of
photospheric magnetic flux cancellation to propose that all explosive
events are the result of magnetic reconnection. By combining the
observational facts concerning photospheric flux cancellation and
transition zone explosive events it can be shown that reconnection in
the quiet solar atmosphere proceeds in bursts at sites much smaller
than the boundary between opposite polarity flux elements that are
observed to cancel in magnetograph sequences.
---------------------------------------------------------
Title: Bifurcation in the Low Chromosphere
Authors: Athay, R. Grant; Dere, K. P.
1990ApJ...358..710A Altcode:
Bright chromospheric faculae of diameter d(c) covering an area of
the solar disk f(c) smaller than 1 yield a predictable level of limb
brightening. For a resolution diameter d(r), the combination of f(c) and
d(c) leads, also, to a prediction of the fraction, phi(0), of observing
pixels (resolution areas) that are free of facular emission. Data from
the first flight of the High Resolution Telescope and Spectrograph of
the U.S. Naval Research Laboratory with d(r) about 1 arcsec are used to
measure both the level of limb brightening and phi(0) in EUV emission
lines of O I, C I, and Fe II. The results favor f(c) about 0.9 and d(c)
greater than about 2.5 arcssec. It is concluded that the chromospheric
temperature rise is present over about 90 percent of the solar surface.
---------------------------------------------------------
Title: Flow patterns in a sunspot region observed in the photosphere,
chromosphere and transition region
Authors: Dere, K. P.; Schmieder, B.; Alissandrakis, C. E.
1990A&A...233..207D Altcode:
The flow patterns around a sunspot at photospheric, chromospheric, and
transition zone temperatures is examined. The spiral fibril pattern
observed in H-alpha is consistent with a constant alpha force-free
field extrapolation of the photospheric magnetic field. Evidence
is found for the first time that C IV fibrils near spots follow the
field lines parallel to the chromospheric H-alpha fibrils. The observed
large-scale pattern of redshifts and blueshifts in the vicinity of the
sunspot is stable and conforms to the typical Evershed flow patterns
of radial outflow at the photospheric levels and radial inflows at
the chromospheric and transition region levels. The three-dimensional
velocity vectors associated with this flow are derived assuming an
axially symmetric Evershed flow.
---------------------------------------------------------
Title: The High Resolution Telescope and Spectrograph (HRTS) on
Board the Orbiting Solar Laboratory (OSL)
Authors: Brueckner, G. E.; Bartoe, J. -D. F.; Dere, K. P.; Socker,
D. G.
1990BAAS...22..845B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal Dark Lanes and the Location of Transition Region
Explosive Events
Authors: Moses, D.; Cook, J. W.; Bartoe, J. -D. F.; Brueckner, G. E.;
Dere, K. P.; Davis, J. M.
1990BAAS...22..899M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The HRTS/OSL Vacuum Ultraviolet CCD Development Program
Authors: Socker, D. G.; Dere, K. P.; Korendyke, C. M.
1990BAAS...22..889S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ultraviolet Spectra of a Prominence
Authors: Dere, K.; Lund, P.; Schmieder, B.
1990BAAS...22R.815D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Relationship between a spot and a filament observed during
spacelab 2 mission
Authors: Schmieder, B.; Dere, K. P.; Raadu, M. A.; Démoulin, P.;
Alissandrakis, C. E.
1990AdSpR..10i.195S Altcode: 1990AdSpR..10..195S
During the Spacelab 2 Mission, an active region including a sunspot,
plages, fibrils and a filament which disappears during the observation
period, was observed in Hα and in the C IV lines. The analysis of the
observations leads to several conclusions. Shear in the active region
filament is observed before its disappearance. Hα and C IV upflows
in the filament are well correlated spatially, but the transition
zone (C IV) velocities are an order of magnitude larger than the Hα
chromospheric ones. Over the sunspot, the reverse-Evershed effect is
observed in Hα and in C IV Dopplershift images while strong downflows
are also detected in the C IV profiles. <P />Magnetograph data for
the whole region are used to calculate the linear force-free magnetic
field. A single value of the force-free parameter α is found to give a
good fit to both the sheared filament structure and the sunspot spiral
structures, indicating a causal relationship. <P />We propose a model
based on the inductive coupling between current systems associated with
the filament and the sunspot. Relaxation phenomena due to resistive
effects in the filament could lead to irreversible conversion of
magnetic energy into kinetic energy and heating.
---------------------------------------------------------
Title: Heating of the solar transition region in fine-scale structures
Authors: Dere, K. P.
1990AdSpR..10i.169D Altcode: 1990AdSpR..10..169D
Studies of the solar transition region with ultraviolet instruments
such as the NRL High Resolution Telescope and Spectrograph (HRTS)
point out the advantages of this region to understanding nonthermal
heating in the solar atmosphere. In contrast to the classical picture
where the transition zone is a thin region maintained simply by the
dissipation of heat conducted down from the corona, high resolution
spectroheliograms show that the transition zone consists of elongated
structures that must be heated locally because the field aligned
temperature gradients are insufficient to support the necessary
conductive flux. An analysis of the observationally determined
emission measures (n<SUB>e</SUB><SUP>2</SUP>Δ1) and pressures of
transition region structures reveals that they consist of fine-scale
subresolution structures with dimensions less than 100 km. Further
evidence for subresolution structure is found in spectral line widths
which are wider than expected from thermal broadening. The velocity
power spectrum, derived from both resolved motions evident in net
Doppler shifts of line profiles and unresolved motions seen in the
nonthermal widths, shows the need for significant power at scales of
10 km or less. The power, because it extends to such high wavenumbers,
can be dissipated by viscosity and joule heating at a rate sufficient
to maintain transition zone against its radiative losses.
---------------------------------------------------------
Title: A brief scientific history of the NRL HRTS program.
Authors: Dere, K. P.
1990ppst.conf...29D Altcode:
Since its first flight in 1975, the NRL High Resolution Telescope and
Spectrograph (HRTS) has now recorded high quality ultraviolet spectra
of the Sun on 6 rocket flights and during extended operations on the
Space Shuttle Spacelab 2 mission in 1985.
---------------------------------------------------------
Title: The Relationship of C IV Transition Region Structures to the
Photospheric Magnetic Field
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.
1990BAAS...22..744D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High Resolution Spectrography in Ultraviolet
Authors: Schmieder, B.; Thompson, W. T.; Neupert, W. M.; Thomas,
R. J.; Dere, K. P.
1990PDHO....7..250S Altcode: 1990ESPM....6..250S; 1990dysu.conf..250S
The authors point out some of the advantages of coordinated observations
with ground-based and space instrumentation. Results obtained during
the rocket flight of the Solar Extreme-ultraviolet Rocket Telescope
and Spectrograph (SERTS) for a preflaring region are presented and the
complementarity of observations is pointed out with the High Resolution
Telescope and Spectrograph (HRTS) which permits the detection of
dynamical structures in hot plasma surrounding cool structures such
as prominences and sunspots seen in visible light.
---------------------------------------------------------
Title: Temperature and Center-Limb Variations of Transition Region
Velocities
Authors: Athay, R. G.; Dere, K. P.
1989ApJ...346..514A Altcode:
HRTS data from the Spacelab 2 mission are used to derive the
center-limb and temperature variations of the mean velocity and the
velocity variance in the solar chromosphere and transition zone. The
mean velocity is found to vary much more rapidly from center to limb
and with temperature than does the velocity variance. Also, the mean
velocity shows a characteristic signature at some magnetic neutral
lines in accordance with the findings of Klimchuk (1987) from Solar
Maximum Mission (SMM) data. The velocity variance does not show a
characteristic signature at the neutral lines but shows an inverse
correlation with intensity. The latter is interpreted as reduced
velocity variance in strong field regions. The results are discussed
in terms of downflow along lines of force in magnetic arcades.
---------------------------------------------------------
Title: Transition Zone Flows Observed in a Coronal Hole on the
Solar Disk
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.; Recely, F.
1989ApJ...345L..95D Altcode:
A rocket flight of the NRL High Resolution Telescope and Spectrograph
(HRTS) was performed to obtain ultraviolet spectra of a well-defined
coronal hole on the solar system. Observed emission lines included
strong transition zone lines of C IV at 1548 and 1550 A, strong
chromospheric lines of C I near 1560 A, and chromospheric lines of Fe
(II) at 1563 A. Continuum radiation formed in the temperature minimum
was also recorded. The cumulative histogram of the C IV velocities in
the coronal hole shows an average Doppler shift of 2 km/sec to the red
(downflow) with 26 percent of the profiles having blueshifts (outflows)
compared to 7 percent in the quiet sun. The present observations have
the advantages of higher spatial resolution and a nearly absolute
wavelength scale determined from narrow chromospheric lines of Si I
with an accuracy of about 1 km/sec. The nonthermal velocities, derived
from the C IV line widths, are only marginally larger inside the coronal
hole than those in the quiet sun, thus indicating that the magnitude of
small-scale motions, which may represent energy available for coronal
heating and solar wind acceleration, is equal in the two regions.
---------------------------------------------------------
Title: Correspondence between solar fine-scale structures in the
corona, transition region, and lower atmosphere from collaborative
observations
Authors: Moses, J. Daniel; Cook, J. W.; Bartoe, J. -D. F.; Brueckner,
G. E.; Dere, K. P.; Webb, D. F.; Davis, John M.; Recely, F.; Martin,
S. F.; Zirin, H.
1989sxsr.reptR....M Altcode:
The Soft X-Ray Imaging Payload and the High Resolution Telescope and
Spectrograph (HRTS) instrument were launched from White Sands on 11
December 1987 in coordinated sounding rocket flights to investigate the
correspondence of coronal and transition region structures, especially
the relationship between X-ray bright points (XBPs) and transition
region small spatial scale energetic events. The coaligned data from
X-ray images are presented along with maps of sites of transition
region energetic events observed in C IV (100,000 K), HRTS 1600 A
spectroheliograms of the T<SUB>min</SUB> region and ground based
magnetogram and He I 10830 A images.
---------------------------------------------------------
Title: Extreme ultraviolet imaging telescope on board the Solar
Heliospheric Observatory
Authors: Delaboudiniere, Jean-Pierre; Gabriel, Alan H.; Artzner,
Guy E.; Millier, F.; Michels, Donald J.; Dere, Kenneth P.; Howard,
Russell A.; Kreplin, Robert W.; Catura, Richard C.; Stern, Robert A.;
Lemen, James R.; Neupert, Werner M.; Gurman, Joseph B.; Cugnon, P.;
Koeckelenbergh, A.; van Dessel, E. L.; Jamar, Claude A.; Maucherat,
Andre J.; Chauvineau, Jean-Pierre; Marioge, Jean-Paul
1989SPIE.1160..518D Altcode: 1989xeoa.conf..518D
The design of the multibandpass Extreme-Ultraviolet Imaging Telescope
designed for 1996 launch on board the Solar Heliospheric Observatory
is described. The telescope will observe simultaneously distinct
temperature ranges in the solar corona, defined by well chosen emission
lines. Images in four narrow bandpasses at wavelengths ranging from 17
to 31 nm will be obtained using normal-incidence multilayered optics
deposited on quadrants of a Ritchey-Chretien telescope. Results are
presented on the performances measured on a 2/3 scale mock-up. The
bandpasses could be adjusted to better than 1 percent in wavelength.
---------------------------------------------------------
Title: Turbulent Power and Dissipation in the Solar Transition Zone
Authors: Dere, Kenneth P.
1989ApJ...340..599D Altcode:
The power spectrum of the spatial velocity fluctuations of the solar
transition zone are determined from high-resolution telescope and
spectrograph solar spectra of C IV. It is found that virtually all of
the power resides at higher wavenumbers and that the spectrum is flatter
than predicted for the inertial range of a turbulent fluid. The results
suggest that the small-scale fluctuations are maintained by a driving
mechanism such as magnetic reconnection or wave motions produced in
the photosphere.
---------------------------------------------------------
Title: Dynamics of a filament at the boundary of a SPOT region with
magnetic shear
Authors: Schmiedler, B.; Demoulin, P.; Raadu, M. A.; Dere, K. P.
1989A&A...213..402S Altcode:
H-alpha (MSDP), magnetograph (Meudon), and C IV (HRTS) observations are
used to investigate the relationship between the dynamics of a solar
filament and a spot region with vortex structure. Comparisons are made
between the structures in H-alpha and C IV intensity and Doppler-shift
images. These show filament shearing and a good correlation between
H-alpha and C IV upflow, the C IV filament being very dynamic (+ or -
50 km/s). Magnetograph data for the whole region including the sunspot
are used to calculate linear force-free fields. The magnetic structure
at the filament is found to be favorable for support.
---------------------------------------------------------
Title: The HRTS Guest Investigator Program
Authors: Lund, P.; Ewing, J.; Cook, J.; Dere, K.; Brueckner, G.
1989BAAS...21..841L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Comparison of HRTS Sounding Rocket Observations at 1600 Å
and Hα with Groundbased Magnetograms and He I 10830 Å Images
Authors: Cook, J. W.; Bartoe, J. -D. F.; Brueckner, G. E.; Dere, K. P.
1989BAAS...21..840C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ultraviolet Observations of Macrospicules at the Solar Limb
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.; Cook,
J. W.; Socker, D. G.; Ewing, J. W.
1989SoPh..119...55D Altcode:
During the Spacelab 2 mission, the NRL High Resolution Telescope and
Spectrograph (HRTS) obtained a time-series of broad-band ultraviolet
images of macrospicules at the solar limb inside a polar coronal
hole with a temporal resolution of 20 and 60 s. The properties of the
macrospicules observed in the Spacelab data are measured and compared
with the properties reported for EUV macrospicules observed during
Skylab (Bohlin et al., 1975; Withbroe et al., 1976). There is a general
agreement between the data sets but several differences. Because of
the higher temporal resolution of the Spacelab data, it is possible
to see macrospicules with shorter lifetimes than seen during Skylab,
as well as variations on faster timescales. The largest (30-60') and
fastest (150 km s <SUP>-1</SUP>) macrospicules seen during Skylab were
not found in the Spacelab observations. The Spacelab data support the
conclusion that many macrospicules decay by simply fading away.
---------------------------------------------------------
Title: Explosive Events in the Solar Transition Zone
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.
1989SoPh..123...41D Altcode:
The properties of explosive events in the solar transition zone are
presented by means of detailed examples and statistical analyses. These
events are observed as regions of exceptionally high velocity (∼
100 km s<SUP>−1</SUP>) in profiles of CIV, formed at 10<SUP>5</SUP>
K, observed with the High Resolution Telescope and Spectrograph
(HRTS). The following average properties have been determined from
observations obtained during the third rocket flight of the HRTS: full
width at half maximum extent along the slit - 1.6 × 10<SUP>3</SUP> km;
maximum velocity - 110 km s<SUP>−1</SUP>; peak emission measure -
4 × 10<SUP>41</SUP> cm<SUP>−3</SUP>; lifetime - 60 s; birthrate -
4 × 10<SUP>−21</SUP> cm<SUP>−2</SUP> s<SUP>−1</SUP> in a coronal
hole and 1 × 10<SUP>−20</SUP> cm<SUP>−2</SUP> s<SUP>−1</SUP>
in the quiet Sun; mass - 6 × 10<SUP>8</SUP> g; and, kinetic energy - 6
× 10<SUP>22</SUP> erg. The 6 examples show that there are considerable
variations from these average parameters in individual events. Although
small, the events show considerable spatial structure and are not
point-like objects. A spatial separation is often detected between the
positions of the red and blue shifted components and consequently the
profile cannot be explained by turbulence alone. Mass motions in the
events appear to be isotropic because the maximum observed velocity
does not show any correlation with heliographic latitude. Apparent
motions of the 100 km s<SUP>−1</SUP> plasmas during their 60 s
lifetime should be detected but none are seen. The spatial frequency
of occurrence shows a maximum near latitudes of 40-50°, but otherwise
their sites seem to be randomly distributed. There is enough mass in
the explosive events that they could make a substantial contribution
to the solar wind. It is hard to explain the heating of typical quiet
structures by the release of energy in explosive events.
---------------------------------------------------------
Title: HRTS Transition Region Observations of a Coronal Hole on the
Solar Disk
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.
1989BAAS...21..841D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Model for the Heating of the Transition Region
Authors: Antiochos, S. K.; Dere, K. P.
1989BAAS...21..841A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Associations of Explosive Events
Authors: Porter, J. G.; Dere, K. P.
1989BAAS...21..852P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Plasma Motions in an Emerging Flux Region
Authors: Brueckner, G. E.; Bartoe, J. -D. F.; Cook, J. W.; Dere,
K. P.; Socker, D.; Kurokawa, H.; McCabe, M.
1988ApJ...335..986B Altcode:
Ultraviolet spectra of C IV show large nonthermal broadening in an
area of emerging flux. These nonthermal motions are observed at a very
early stage of reconnecting field lines. The spectra can be traced
to small, rapidly changing surge or filament-like features which
are seen in the center, blue, and red wing of H-alpha. They seem to
have the characteristics of macrospicules or explosive events. They
are precursors of the reconnection process. Plasma turbulence and/or
plasma waves in the reconnecting plasma may cause the broad C IV line
profiles. The activity in the transition zone precedes the formation
of a bright chromospheric loop system.
---------------------------------------------------------
Title: LASCO: A wide-field white light and spectrometric coronagraph
for SOHO
Authors: Michels, D. J.; Schwenn, R.; Howard, R. A.; Bartoe, J. -D. F.;
Antiochos, S. K.; Brueckner, G. E.; Cheng, C. -C.; Dere, K. P.;
Doschek, G. A.; Mariska, J. T.
1988sohi.rept...55M Altcode:
The scientific objectives of the LASCO (light and spectrometric
coronagraph) project in the SOHO (solar and heliospheric observatory)
mission are described. These include investigation of mechanisms
for heating of the corona and acceleration of the solar wind, causes
of coronal transients, and their role in development of large scale
coronal patterns and interplanetary disturbances. The distribution
and properties of dust particles, including those released from
sun-grazing comets are investigated. Interactions of coronal plasma
with the dust are studied. The corona is analyzed spectroscopically
by a high-resolution scanning, imaging interferometer. The spectral
profiles of three emission lines and one Fraunhofer line are measured
for each picture point, giving temperatures, velocities, turbulent
motions and volume densities. Polarization analysis yields the direction
of coronal magnetic fields.
---------------------------------------------------------
Title: Gas Flows in the Transition Region above Sunspots
Authors: Kjeldseth-Moe, O.; Brynildsen, N.; Brekke, P.; Engvold, O.;
Maltby, P.; Bartoe, J. -D. F.; Brueckner, G. E.; Cook, J. W.; Dere,
K. P.; Socker, D. G.
1988ApJ...334.1066K Altcode:
Strong downflows and moderate upflows in the transition region over
a sunspot have been observed with the HRTS on Spacelab 2 in 1985. The
flows are persistent in the sense that they are seen in the same spot
for 5 days. The downflows are prominent in regions of limited extent
(4arcsec - 6arcsec), and flow velocities are in the range 40 - 80 km
s<SUP>-1</SUP> and are thus supersonic. Upward flows have smaller
velocities, 5 - 20 km s<SUP>-1</SUP>, but may extend over a larger
area. In the downflowing regions there is always an appreciable amount
of gas at rest in the line of sight. Flow speeds derived from the
profiles of different lines formed in the transition region between
30,000 and 230,000K are very similar implying constant downflow in
this temperature range.
---------------------------------------------------------
Title: EIT: Solar corona synoptic observations from SOHO with an
Extreme-ultraviolet Imaging Telescope
Authors: Delaboudiniere, J. P.; Gabriel, A. H.; Artzner, G. E.;
Michels, D. J.; Dere, K. P.; Howard, R. A.; Catura, R.; Stern, R.;
Lemen, J.; Neupert, W.
1988sohi.rept...43D Altcode:
The Extreme-ultraviolet Imaging Telescope (EIT) of SOHO (solar and
heliospheric observatory) will provide full disk images in emission
lines formed at temperatures that map solar structures ranging from
the chromospheric network to the hot magnetically confined plasma in
the corona. Images in four narrow bandpasses will be obtained using
normal incidence multilayered optics deposited on quadrants of a
Ritchey-Chretien telescope. The EIT is capable of providing a uniform
one arc second resolution over its entire 50 by 50 arc min field of
view. Data from the EIT will be extremely valuable for identifying
and interpreting the spatial and temperature fine structures of the
solar atmosphere. Temporal analysis will provide information on the
stability of these structures and identify dynamical processes. EIT
images, issued daily, will provide the global corona context for aid
in unifying the investigations and in forming the observing plans for
SOHO coronal instruments.
---------------------------------------------------------
Title: The Correspondence Between Fine-Scale Structures in the Solar
Corona and Transition Region
Authors: Moses, J. D.; Bartoe, J. -D. F.; Brueckner, G. E.; Cook,
J. W.; Dere, K. P.; Davis, J. M.; Webb, D.
1988BAAS...20..722M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Correlation of Transition Region C IV High-Velocity Events
With Magnetogram and He I 10830 Å Data
Authors: Cook, J. W.; Bartoe, J. -D. F.; Brueckner, G. E.; Dere,
K. P.; Recely, F.; Martin, S.; Zirin, H.
1988BAAS...20..722C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Power Spectrum of Velocities in the Solar Transition Zone
Authors: Dere, K. P.
1988BAAS...20..722D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar physics from Spacelab 2.
Authors: Dere, K. P.
1988JPhys..49....3D Altcode: 1988IAUCo.102....3D
Four instruments were flown aboard the Spacelab 2 shuttle mission
to perform systematic observations of the solar atmosphere at high
resolution and to measure specific global properties of the sun. The
Solar Optical Universal Polarimeter recorded series of white light
images with which the evolution of the granulation and sunspot
phenomena have been studied. The Coronal Helium Abundace Shuttle
Experiment provided measurements of a number of EUV coronal lines, and,
in particular, the intensities of He II λ304 and H I λ1216 from which
the coronal helium abundance can be determined. The High Resolution
Telescope and Spectrograph obtained stigmatic spectra in the 1200 -
1700 Å wavelength range, as well as broad band UV spectroheliograms, to
provide diagnostic information on the solar chromosphere and transition
zone. The Solar Ultraviolet Spectral Irradiance Monitor measured the
total solar irradiance at a resolution of 1.5 and 50 Å in the 1200
to 4000 Å wavelength range to an accuracy of 3%.
---------------------------------------------------------
Title: Results from the High Resolution Telescope and Spectrograph
(HRTS) Experiment on Board Spacelab 2
Authors: Brueckner, G. E.; Bartoe, J. -D. F.; Cook, J. W.; Dere,
K. P.; Socker, D. G.
1988ApL&C..27..151B Altcode:
Several papers including reviews have been published during different
stages of the data analysis after the SL-2 flight. In order to avoid
repetition, this article lists all publications and briefly mentions
some of the highlights.
---------------------------------------------------------
Title: Ultraviolet Observations of Solar Fine Structure
Authors: Dere, Kenneth P.; Bartoe, John-David F.; Brueckner, Guenter
E.; Cook, John W.; Socker, Dennis G.
1987Sci...238.1267D Altcode:
The High Resolution Telescope and Spectrograph was flown on the
Spacelab-2 shuttle mission to perform extended observations of the
solar chromosphere and transition zone at high spatial and temporal
resolution. Ultraviolet spectroheliograms show the temporal development
of macrospicules at the solar limb. The C IV transition zone emission
is produced in discrete emission elements that must be composed of
exceedingly fine (less than 70 kilometers) subresolution structures.
---------------------------------------------------------
Title: Chromospheric and Transition Zone Flows in a Solar Active
Region
Authors: Dere, K. P.; Schmieder, B.
1987BAAS...19.1118D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Discrete Subresolution Structures in the Solar Transition Zone
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.; Cook,
J. W.; Socker, D. G.
1987SoPh..114..223D Altcode:
During operations on the Spacelab-2 Shuttle mission, the NRL High
Resolution Telescope and Spectrograph (HRTS) recorded spectra of a
variety of solar features in the 1200-1700 Å wavelength region which
contains spectral lines and continua well suited for investigating
the temperature minimum, the chromosphere and transition zone. These
data show that, at the highest spatial resolution, the transition zone
spectra are broken up from a continuous intensity distribution along
the slit into discrete emission elements. The average dimensions
of these discrete transition zone structures is 2400 km along the
slit, but an analysis of their emission measures and densities shows
that the dimensions of the actual emitting volume is conciderably
less. If these structures are modelled as an ensemble of subresolution
filaments, we find that these filaments have typical radii of from
3 to 30 km and that the cross-sectional fill factor is in the range
from 10<SUP>−5</SUP> to 10<SUP>−2</SUP>. The transport of mass
and energy through these transition zone structures is reduced by
this same factor of 10<SUP>−5</SUP> to 10<SUP>−2</SUP> which has
significant consequences for our understanding of the dynamics of the
solar atmosphere. Because the HRTS transition zone line profiles are
not broadened by resolved large-spatial-scale solar velocity fields,
the line widths of the CIV lines have been analyzed. The average line
width is 0.195 Å (FWHM) and requires an average nonthermal velocity
of 16 km s<SUP>−1</SUP> (most-probable) or 19 km s<SUP>−1</SUP>
(root-mean-square) which is lower than previously observed values.
---------------------------------------------------------
Title: Transition Zone Flow Patterns in Sunspots
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.; Cook,
J. W.; Socker, D. G.
1987BAAS...19..639D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Statistical Properties of Small High-Velocity Events in the
Solar Transition Region
Authors: Cook, J. W.; Lund, P. A.; Bartoe, J. -D. F.; Brueckner,
G. E.; Dere, K. P.; Socker, D. G.
1987LNP...291..150C Altcode: 1987csss....5..150C
We discuss the energy contribution of small high-velocity events
observed in the solar transition region to atmospheric heating. These
events do not directly provide enough energy to heat the atmosphere,
but are instead after-products of turbulent energy dissipation at the
sites of the actual primary nonthermal heating process.
---------------------------------------------------------
Title: Identification of [Fe III] in the solar ultraviolet spectrum
Authors: Jordan, C.; Bartoe, J. -D. F.; Brueckner, G. E.; Dere, K. P.
1986Natur.324..444J Altcode:
Solar ultraviolet spectra have been obtained with high spectral and
spatial resolution using the Naval Research Laboratory's high-resolution
telescope and spectrograph<SUP>1</SUP> (HRTS) flown on rockets since
1975 and most recently on the Spacelab 2 Shuttle flight. Because the
solar spectrum between ~1,170 and 1,719 Å has been well observed for
some years, few lines of substantial intensity remain unidentified. (See
for example the recent compilation by Sandlin et al.<SUP>2</SUP>). The
longest exposures during the first rocket flight of the HRTS, which
obtained spectra with a spatial resolution of ~ 1 arc s along the slit,
of length ~ 1 solar radius, and a spectral resolution of ~0.05 Å,
showed a number of weak emission lines at the solar limb, in particular
between 1,570 and 1,600 Å (see Plates 16 and 17 in ref. 3), that could
not readily be identified. Improved observations of these lines were
obtained during the flight of HRTS on the Spacelab 2 Shuttle flight in
July-August 1985, by making longer exposures (60,100 and 250 s). The
scope of the data obtained has been described<SUP>4</SUP>. We have
now identified the emission lines concerned as forbidden (electric
quadrupole and magnetic dipole) transitions in Fe III, the first
detection of these particular transitions in any source. They must now
be considered potential candidates for previously unidentified lines in
other low-density (N<SUB>e</SUB> <~ 10<SUP>10</SUP> cm<SUP>-3</SUP>)
astrophysical sources.
---------------------------------------------------------
Title: Outflows and Ejections in the Solar Transition Zone
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.
1986ApJ...310..456D Altcode:
Time series images of C IV transition zone intensities and velocities
are analyzed to study the uncommon patterns of blueshifted emission. The
images are constructed from stigmatic spectra obtained during the third
flight of the NRL High Resolution Telescope and Spectrograph. A sample
of 11 blueshifted events with near-Gaussian profiles are analyzed. Of
these 11 cases, three are expulsions of material from the network, two
are spicular flows, one is a simple jet, another is associated with
a filament, and four are unexplained. It is not possible to identify
a simple mechanism whereby upflows return to form the predominant
downflows observed in the transition zone, and the upward mass flux
is three orders of magnitude lower than the downward mass flux.
---------------------------------------------------------
Title: Observation of the Density Sensitive Line Mg V 1324 Å in a
Solar Sunspot
Authors: Cook, J. W.; Socker, D. G.; Bartoe, J. -D. F.; Brueckner,
G. E.; Dere, K. P.
1986BAAS...18R.991C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Culgoora Radio and SKYLAB Extreme Ultraviolet Observations
of Emerging Magnetic Flux in the Lower Corona
Authors: Stewart, R. T.; Brueckner, G. E.; Dere, K. P.
1986SoPh..106..107S Altcode:
Detailed comparisons of Culgoora 160 MHz radioheliograms of solar noise
storms and Skylab EUV spectroheliograms of coronal loop structures
are presented. It is concluded that: (1) there is a close association
between changes in large-scale magnetic fields in the corona and
the onset or cessation of noise storms; (2) these coronal changes
result from the emergence of new magnetic flux at the photospheric
level; (3) although new magnetic flux at the photospheric level is
often accompanied by an increase in flare activity the latter is
not directly responsible for noise storm activity; rather the new
magnetic flux diffuses slowly outwards through the corona at rates
∼1-2 km s<SUP>−1</SUP> and produces noise storms at 160 MHz 1-2
days later; (4) the coronal density above or in large-scale EUV loop
systems is sufficiently dense to account for noise storm emission
at the fundamental plasma frequency; (5) the scatter in noise storm
positions can be accounted for by the appearance and disappearance of
individual loops in a system.
---------------------------------------------------------
Title: High-Resolution Telescope and Spectrograph Images of the
Solar Chromosphere and Transition Zone
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.
1986ApJ...305..947D Altcode:
Observations of a 10-arcsec-wide 800-arcsec-long region of the
southern solar hemisphere, obtained at 150-160 nm by the rocket-borne
High-Resolution Telescope and Spectrograph on March 1, 1979, are
reported and analyzed. Rastered stigmatic spectra are reduced to create
color images of intensity, Doppler shift, and line width providing
information on the UV structure of the solar atmosphere. Characteristics
discussed include temperature stratification in quiet-sun network
elements; chromospheric jets appearing at supergranular cell centers;
general redshift of 5 km/s in quiet-sun C IV; downflow patterns in C
IV, Fe II, and C I; plage structures with temperature stratification
and 6-km/s C IV downflow; and faint filament emission with blueshifts
near the top and redshifts at the sides in the C IV images.
---------------------------------------------------------
Title: Discrete Components of Solar Transition Zone Emission
Authors: Dere, K. P.; Brueckner, G. E.; Bartoe, J. -D. F.; Cook,
J. W.; Socker, D. G.
1986BAAS...18Q.662D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Statistical Properties of Small High-Velocity Transition
Region Events on the Sun Observed by HRTS on Spacelab 2
Authors: Cook, J. W.; Lund, P. A.; Brueckner, G. E.; Bartoe, J. -D. F.;
Dere, K. P.; Socker, D. G.
1986BAAS...18..662C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Results from the High Resolution Telescope and Spectrograph
(HRTS) Experiment
Authors: Brueckner, G. E.; Cook, J. W.; Dere, K. P.
1986BAAS...18..675B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: HRTS Spacelab 2 Observations of the Temporal Development of
the C IV Transition Zone
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.; Cook,
J. W.; Lund, P.; Socker, D. G.
1986BAAS...18..633D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: HRTS results from spacelab 2
Authors: Brueckner, G. E.; Bartoe, J. -D. F.; Cook, J. W.; Dere,
K. P.; Socker, D. G.
1986AdSpR...6h.263B Altcode: 1986AdSpR...6..263B
The HRTS instrument flew on the Spacelab 2 mission from 29 July -
6 August 1985. HRTS consisted of a 30 cm Gregorian telescope, a slit
spectrograph covering the 1190-1680 Å region with 0.05 Å spectral
resolution, a broadband (90 Å FWHM) spectroheliograph tuned to 1550
Å, and an H-alpha filter system. The spectrograph slit was 920 arc
sec, approximately 1 R<SUB>0</SUB>, in length. Sub arc second spatial
resolution along the slit is possible, but because of jitter in the
Spacelab Instrument Pointing System (IPS) good exposures actually
achieved 1-2 arc sec resolution. We describe the scientific results
from HRTS.
---------------------------------------------------------
Title: Results from the NRL instruments on Spacelab 2
Authors: Bartoe, J. -D. F.; Brueckner, G. E.; Cook, J. W.; Dere,
K. P.; Morrison, M. D.
1986aiaa.meetZ....B Altcode:
The instrumental features of the high resolution Telescope and
spectrograph (HRTS) and the solar UV spectral irradiance monitor
(SUSIM) used for solar observations on the Spacelab 1 mission are
described. The HRTS has three focal plane instruments receiving light
from a 30 cm aperture furnishing at 15 X 15 arcmin FOV which can
be modified for slit photography and raster scans. The focal plane
instruments are a spectrograph, spectroheliograph and a television
camera and photographic film fronted by a mica Fabry-Perot filter. About
13 hr of solar observations were made with the HRTS during the 8
day mission. Sample spectral and photographic data are provided and
discussed. SUSIM is an UV spectrometer with redundant optical paths for
in-flight calibration with a D2 lamp. It is sensitive in the 1200-4000
A range. Several wavelength ranges are evaluated. Particular attention
is given to multitemporal Ly-alpha recordings.
---------------------------------------------------------
Title: HRTS Spacelab 2 Observations of Spicular Emission at the
Solar Limb
Authors: Cook, J. W.; Bartoe, J. -D. F.; Brueckner, G. E.; Dere,
K. P.; Socker, D. G.
1985BAAS...17..834C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ultraviolet Observations of Fine Structure in the Solar
Chromosphere and Transition Zone
Authors: Dere, K.
1985tphr.conf..233D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Time Series Images of the UV Chromosphere and Transition Zone
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.
1985BAAS...17..630D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Report of the working group on future observations of the sun.
Authors: Dere, K.; Kneer, F.; Landman, D.
1985cdm..proc...14D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: HRTS observations of the solar chromosphere and transition
zone.
Authors: Dere, K. P.
1985cdm..proc...50D Altcode:
The NRL High Resolution Telescope and Spectrograph (HRTS) consists
of a 30 cm Cassegrain telescope which focuses an image of the sun
with 1 arcsec resolution, a stigmatic tandem-Wadsworth mount UV
spectrograph, a UV broadband spectroheliograph and H-alpha film
and video cameras. Images of the UV line and continuum intensities
show that they are all strongly associated with the chromospheric
network, with an almost one-to-one correspondence found between Fe II
intensity images and H-alpha -0.6 A spectroheliograms. The region of
C IV emission occurs above the chromospheric mottles at a height of
3900 km when the continuum height is placed at 500 km; significant C
IV transition-zone emission was also found at the base of the network
elements. C IV profiles are generally near Gaussian, with dimensions on
the order of 200 km. Time series and velocity field data are provided,
and it is concluded that a steady state heating mechanism is present
in the chromosphere.
---------------------------------------------------------
Title: UV observations of fine structure in the solar chromosphere
and transition zone.
Authors: Dere, K. P.
1985MPARp.212..233D Altcode:
The capabilities of the NRL High Resolution Telescope and Spectrograph
(HRTS) made it possible to obtain UV spectra at a spatial resolution
sufficient to resolve fine structures in the solar chromosphere and
transition zone. To date, it has made observations during 4 rocket
flights and recently obtained highly successful longer term observations
during the Spacelab-2 mission. Obviously, only the rocket spectra
have been analyzed in any detail. The author addresses three areas
where the understanding of the solar chromosphere and transition zone,
based on these HRTS observations, may need reassessment.
---------------------------------------------------------
Title: High-resolution telescope and spectrograph observations of
the quiet solar chromosphere and transition zone
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.
1984ApJ...281..870D Altcode:
A systematic program to observe the two-dimensional structure of the
solar atmosphere and its temporal variation was conducted in connection
with the third rocket flight of the High Resolution Telescope and
Spectrograph (HRTS). A description is presented of the manner in which
line intensities, Doppler shifts (velocities), and line widths are
obtained from HRTS spectra. These quantities are derived for a single
stigmatic slit spectra of the quiet sun. It is pointed out that an
accurate wavelength scale can be derived from narrow Si I lines in
the spectra. The intensity of chromospheric lines such as C I lambda
1560 is found to be largely the result of the structures forming the
chromospheric network. A number of conclusions are drawn about quiet
transition zone Doppler shifts (flows).
---------------------------------------------------------
Title: Ultraviolet spectroscopy of the chromosphere and transition
zone at high spatial and temporal resolution
Authors: Dere, K. P.
1984AdSpR...4h..55D Altcode: 1984AdSpR...4...55D
The third rocket flight of the NRL High Resolution Telescope and
Spectrograph (HRTS) recorded UV spectra of the quiet Sun in a 10”
× 800” region. By rastering the slit in 2” increments, a time
series with 20s resolution of two-dimensional spectra with 1” spatial
resolution was obtained. The spectrum includes strong chromospheric
diagnostic lines of C I, Si I, and Fe II, transition zone lines of C IV
and the continuum which is produced in the temperature minimum. Images
of the network show that Fe II emission is well-correlated with
dark Hα mottles, that the transition zone is produced in extended
structures which are apparently continuations of the mottles, and
that the strongest continuum emission is from near the base of the
mottles. Time series of C I profiles show little variation in most
features aside from the chromospheric jets which develop rapidly over
timescales of 30s. The C IV profiles also show only gradual variations
over most of the slit except for the numerous small explosive events.
---------------------------------------------------------
Title: HRTS Ultraviolet Images of the Solar Chromosphere and
Transition Zone
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.
1984LNP...193..180D Altcode: 1984csss....3..180D
No abstract at ADS
---------------------------------------------------------
Title: HRTS Ultraviolet Solar Spectroscopy (invited Paper)
Authors: Dere, K. P.
1984uxsa.coll...22D Altcode: 1984IAUCo..86...22D; 1984uxsa.conf...22D
No abstract at ADS
---------------------------------------------------------
Title: HRTS observations of the fine structure and dynamics of the
solar chromosphere and transition zone.
Authors: Dere, K. P.
1983NASCP.2280..33D Altcode: 1983sowi.conf...33D
Arc-second UV observations of the Sun by the NRL High Resolution
Telescope and Spectrograph (HRTS) have led to the discovery of
dynamic fine structures such as 400 km s<SUP>-1</SUP> coronal jets and
chromospheric jets (spicules) and have provided new information about
the structure and dynamics of the transition zone. These observations
are reviewed and their relevance to the origin of the solar wind
is discussed.
---------------------------------------------------------
Title: Mass and energy balance in the 1973 August 9 flare
Authors: Dere, K. P.; Cook, J. W.
1983A&A...124..181D Altcode:
The mass and energy balance of the thermal plasma during the decay
phase of the solar flare of August 9, 1973, are studied. The analysis
is based on observationally determined values for the differential
emission measure, density, turbulent and bulk velocities, and
physical dimensions. The total particle content and total thermal
energy content of the flare plasmas with temperatures above 100,000 K
and their variation with time are calculated. The particle loss and
the energy losses through radiation, conduction, and convection are
evaluated. The decrease in total particle content can be accounted
for by the convective losses through the loop footprints at 100,000
K. Radiation is the dominant energy loss mechanism although convective
losses at 100,000 K can be important. Conductive losses at 100,000
K into cooler chromospheric material appear to be negligible. The
decrease in the total energy content during the decay phase is equal
to the sum of the energy losses over the period of observation. No
requirement is found for continued heating during the decay phase.
---------------------------------------------------------
Title: Chromospheric jets - Possible extreme-ultraviolet observations
of spicules
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.
1983ApJ...267L..65D Altcode:
Stigmatic EUV spectra of chromospheric lines obtained by the Naval
Research Laboratory High Resolution Telescope and Spectrograph (HRTS)
show small arc second regions with strong (10-20 km/s) Doppler shifts
which are called 'chromospheric jets'. Because of the strong resemblance
of their physical and statistical properties, such as temperature,
density, velocity, size, and birthrate, to those of visible light
spicules, it is highly likely that they are different manifestations
of the same phenomena, although a one-to-one identification has not yet
been made. The main difference is the 40 s lifetime of the chromospheric
jets which is shorter than the 5 minute lifetime of visible light
spicules. The chromospheric jets are found in the supergranular cell
interiors where chromospheric and transition zone line intensities
are weak. Dark H-alpha mottles found in the cell boundaries are well
correlated with intense, symmetric chromospheric EUV line profiles
and are only weakly related to the chromospheric jets.
---------------------------------------------------------
Title: HRTS Images of the Quiet Solar Chromosphere and Transition Zone
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.
1983BAAS...15..702D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The NRL SOLRAD 11 Satellites (1976-023C, 1976-023D) description
of experiments
Authors: Horan, D. M.; Kreplin, R. W.; Dere, K. P.
1982nrl..reptY....H Altcode:
The Naval Research Laboratory's SOLRAD 11 satellites were successfully
launched on 15 March 1976. The two satellites each carried an identical
complement of 25 experiments to measure solar electromagnetic and
charged particle emissions, Earth auroral and stellar X-ray emission,
terrestrial and interplanetary extreme ultraviolet emission, X-ray and
charged particle emission from the anti-solar direction, and gamma
ray bursts. This report provides general descriptive information on
the satellites and their sensors.
---------------------------------------------------------
Title: Observations of Extreme Ultraviolet Spicules
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.
1982BAAS...14..939D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar transition zone pressures from EUV observations of O
IV and N IV
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.
1982ApJ...259..366D Altcode:
NRL High Resolution Telescope and Spectrograph observations of the O
IV and N IV EUV lines emitted from the Sun are examined. The instrument
provides stigmatic spectra with a spatial resolution of 1 arcsec and a
spectral resolution of 0.05 A in the range 1170-1710 A. Intensity ratios
of the intersystem lines of O IV near 1400 A are used as the primary
diagnostic to measure electron pressures in a sunspot and plage. These
ratios are strongly sensitive to electron pressure but are insensitive
to the temperature structure of the emitting plasma. Average electron
pressures of 9 x 10 to the 15th per cu cm K (1.2 dyn/sq cm) in a plage,
4 x 10 to the 15th per cu cm K (0.6 dyn/sq cm) in a sunspot and 2.2 x 10
to the 15th per cu cm K (0.3 dyn/sq cm) in high speed sunspot downflows
are found. The ratio of I(Nv) + I(C IV) to I(N IV 1486A) is shown to
be relatively insensitive to temperature and gives pressures consistent
with those obtained from the O IV ratio. It is demonstrated that ratios
of allowed lines such as C IV and Si IV to the O IV intersystem lines
are temperature sensitive and hence are unreliable pressure diagnostics.
---------------------------------------------------------
Title: Extreme Ultraviolet Spectra of Solar Active Regions and
Their Analysis
Authors: Dere, K. P.
1982SoPh...77...77D Altcode:
Extreme ultraviolet spectra of several active regions are presented
and analyzed. Spectral intensities of 3 active regions observed with
the NRL Skylab XUV spectroheliograph (170-630 Å) are derived. From
this data density sensitive line ratios of Mg VIII, Si X, S XII,
Fe IX, Fe X, Fe XI, Fe XII, Fe XIII, Fe XIV, and Fe XV are examined
and typically yield, to within a factor of 2, electron pressures
of 1 dyne cm<SUP>−2</SUP> (n<SUB>e</SUB>T = 6 × 10<SUP>15</SUP>
cm<SUP>−3</SUP> K). The differential emission measure of the brightest
35″ × 35″ portion of an active region is obtained between 1.4
× 10<SUP>4</SUP> K and 5 × 10<SUP>6</SUP> K from HCO OSO-VI XUV
(280-1370 Å) spectra published by Dupree et al. (1973). Stigmatic EUV
spectra (1170-1710 Å) obtained by the NRL High Resolution Telescope
and Spectrograph (HRTS) are also presented. Doppler velocities as a
function of position along the slit are derived in an active region
plage and sunspot. The velocities are based on an absolute wavelength
scale derived from neutral chromospheric lines and are accurate to ±2
km s<SUP>−1</SUP>. Downflows at 10<SUP>5</SUP> K are found throughout
the plage with typical velocities of 10 km s<SUP>−1</SUP>. In
the sunspot, downflows are typically 5 to 20 km s<SUP>−1</SUP>
over the umbra and zero over the penumbra. In addition localized 90
and 150 km s<SUP>−1</SUP> downflows are found in the umbra in the
same 1″ × 1″ resolution elements which contain the lower velocity
downflows. Spectral intensities and velocities in a typical plage 1″
resolution element are derived. The velocities are greatest (∼ 10 km
s<SUP>−1</SUP>) at 10<SUP>5</SUP> K with lower velocities at higher
and lower temperatures. The differential emission measure between 1.3
× 10<SUP>4</SUP> K and 2 × 10<SUP>6</SUP> K is derived and is found to
be comparable to that derived from the OSO-VI data. An electron pressure
of 1.4 dynes cm<SUP>−2</SUP> (n<SUB>e</SUB>T = 1.0 × 10<SUP>16</SUP>
cm<SUP>−3</SUP> K) is determined from pressure sensitive line ratios
of Si III, O IV, and N IV. From the data presented it is shown that
convection plays a major role in determining the structure and dynamics
of the active region transition zone and corona.
---------------------------------------------------------
Title: The XUV structure of solar active regions
Authors: Dere, K. P.
1982SoPh...75..189D Altcode:
XUV spectroheliograms of 2 active regions are studied. The images are
due to lines emitted at temperatures between 8 x 10<SUP>4</SUP> K and
2 x 10<SUP>6</SUP> K and thus are indicative of transition region and
coronal structures. The hot coronal lines are formed solely in loop
structures which connect regions of opposite photospheric magnetic
polarity but are not observed over sunspots. Transition region lines are
emitted in plages overlying regions of intense photospheric magnetic
field and in loops or loop-segments connecting such regions. The
hot coronal loops are supported hydrostatically while only some of
the transition zone loops are. The coronal and transition zone loops
are distinctly separated and are not coaxial. A comparison of direct
measurements of electron densities using density sensitive line ratios
with indirect measurements using emission measures and path lengths
shows the existence of fine structures of less than a second of arc
in transition region loops. From a similar analysis, hot coronal loops
do not have any fine structure below about 2 seconds of arc.
---------------------------------------------------------
Title: Transient plasmas in the solar transition zone
Authors: Dere, K. P.; Bartoe, J. -D.; Brueckner, G. E.; Vanhoosier,
M. E.; Dykton, M. D.
1981ApJ...249..333D Altcode:
Observations of C IV emission from the transition zone of the quiet
sun have been obtained with high spatial (1 arcsec), spectral (0.1
A), and temporal (20 s) resolution by a high resolution telescope
and spectrograph. Over spatial scales of several arc seconds, the C
IV profile often exhibits dramatic changes in either the red or blue
wing or in the overall profile at the 20 s temporal resolution of the
observations. It is suggested that some of the rapidly varying emission
may be produced by radiatively cooling plasmas that result from the
thermal instability of coronal plasma. It is shown that such plasmas,
which are in transient ionization, can emit 35 s pulses of C IV emission
for reasonable pressure values. It is also shown that, because of the
limited ability of coronal plasma to maintain ionization equilibrium,
the criteria for the thermal radiative instability must be evaluated
in a manner different from the standard treatment in the case of rapid
perturbations or growth times. From a consideration of length scales
it is determined that these instabilities are most likely to occur in
the upper transition zone.
---------------------------------------------------------
Title: HRTS Observations of the Solar Chromosphere and Transition Zone
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.
1981BAAS...13..845D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Extreme Ultraviolet Emission of O IV and N IV from the Sun
Authors: Dere, K. P.; Bartoe, J. -D. F.; Brueckner, G. E.
1981BAAS...13R.542D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Mass and Energy Balance in the 1973 August 9 Flare
Authors: Cook, J. W.; Dere, K. P.
1981BAAS...13..554C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Spectroscopic diagnostics of the active region: transition
zone and corona.
Authors: Dere, K. P.; Mason, H. E.
1981sars.work..129D Altcode:
Techniques currently used in the analysis of X-ray and UV spectroscopic
data on solar features are reviewed with particular emphasis on
those used for studies of active regions in the transition zone
and corona. Attention is given to temperature and emission measure
diagnostics by the use of line emission from a low-density plasma,
broadband X-ray diagnostics, and diagnostics specific to various
active region structures, and to electron density diagnostics based
on metastable levels and the ratio of emission measure to the volume
derived from spatially resolved images. Methods used for calculating
atomic structure, electron and proton scattering, the ionization
equilibrium and the effects on it of diffusion and flows, and the line
profiles and optical depths are also considered.
---------------------------------------------------------
Title: Analysis and Interpretation of EUV Emission from Solar
Active Regions
Authors: Dere, K. P.
1980BAAS...12..908D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Density and Temperature Measurements for Short Lived Transition
Zone Phenomena
Authors: Nicolas, K. R.; Dere, K. P.; Bartoe, J. -D. F.; Brueckner,
G. E.
1980BAAS...12R.530N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Transient Plasmas in the Solar Transition Zone
Authors: Dere, K. P.; Nicolas, K. R.; Brueckner, G. E.
1980BAAS...12R.518D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The thermal X-ray flare plasma
Authors: Moore, R.; McKenzie, D. L.; Svestka, Z.; Widing, K. G.; Dere,
K. P.; Antiochos, S. K.; Dodson-Prince, H. W.; Hiei, E.; Krall, K. R.;
Krieger, A. S.
1980sfsl.work..341M Altcode: 1980sofl.symp..341M
Following a review of current observational and theoretical knowledge
of the approximately 10 to the 7th K plasma emitting the thermal soft
X-ray bursts accompanying every H alpha solar flare, the fundamental
physical problem of the plasma, namely the formation and evolution of
the observed X-ray arches, is examined. Extensive Skylab observations
of the thermal X-ray plasmas in two large flares, a large subflare and
several compact subflares are analyzed to determine plasma physical
properties, deduce the dominant physical processes governing the plasma
and compare large and small flare characteristics. Results indicate
the density of the thermal X-ray plasma to be higher than previously
thought (from 10 to the 10th to 10 to the 12th/cu cm for large to
small flares), cooling to occur radiatively as much as conductively,
heating to continue into the decay phase of large flares, and the
mass of the thermal X-ray plasma to be supplied primarily through
chromospheric evaporation. Implications of the results for the basic
flare mechanism are indicated.
---------------------------------------------------------
Title: The Extreme Ultraviolet Structure of Solar Active Regions.
Authors: Dere, K. P.
1980PhDT.........2D Altcode:
The extreme ultraviolet emissions from solar active regions have
been analyzed to determine their temperatures, densities, pressures,
emission measures, flow velocities and structures. The accuracy and
limitations of the diagnostic techniques are discussed. It is found
that the active region structures are well correlated with the inferred
and observed magnetic fields and that the electron pressure of the
plasma is essentially constant over a wide range of temperatures. Cool
(10('5)K (LESSTHEQ) T (LESSTHEQ) 10('6)K) loop structures are shon to be
composed of unresolved filaments. Static and steady flow one dimensional
hydrodynamical models of active region loops have been constructed and
used to interpret the observations. Both models require a loop cross
section that diverges with height. This is found by comparing the
static model with the observed emission measures and the steady flow
model with the observed flow velocities. No local heating is found to
be needed in the transition zone. Transition zone downflows in active
regions indicate a mass loss from the overlying coronal structures
for which there is no know supply.
---------------------------------------------------------
Title: Radiative energy output of the 5 September 1973 flare
Authors: Canfield, R. C.; Cheng, C. -C.; Dere, K. P.; Dulk, G. A.;
McLean, D. J.; Schmahl, E. J.; Robinson, R. D., Jr.; Schoolman, S. A.
1980sfsl.work..451C Altcode: 1980sofl.symp..451C
Measurements of the radiative energy output of the solar flare of
Sept. 5, 1973, over a wavelength range of more than ten decades,
from below 1 A to above 1 m are presented. Observations of soft
X-rays (0.5-20 A), XUV and EUV lines (171-1863 A) and EUV continua
(1400-1960 A), H alpha radiation, visible lines and continua (3700-8700
A) and radio emission (centimeter to meter wavelengths) were obtained
concurrently by Skylab and ground-based instruments. Estimates of power
output at flare maximum are obtained for the observed wavelengths with
uncertainty of at least half an order of magnitude, due to corresponding
uncertainties in EUV and visible fluxes. Taking into account energy
radiated at unobserved wavelengths and the characteristic time of
the best-reduced data (the soft X-ray), calculations indicate a total
radiated flare energy of approximately 4 x 10 to the 29th erg.
---------------------------------------------------------
Title: Mass Flow and Energy Balance in a Solar Flare
Authors: Cook, J. W.; Dere, K. P.
1979BAAS...11..678C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: XUV electron density diagnostics for solar flares.
Authors: Dere, K. P.; Mason, H. E.; Widing, K. G.; Bhatia, A. K.
1979ApJS...40..341D Altcode:
Potential electron-density diagnostics for the high-temperature
component of solar flares are studied with reference to the wavelength
region from 171 to 630 A. The specific ions discussed include Fe
IX through Fe XV, Ni XI through Ni XVII, and ions in the beryllium,
boron, carbon, and nitrogen isoelectronic sequences. Line ratios that
could be useful as density indicators under solar-flare conditions
are indicated, available data for the ions considered are reviewed,
and several theoretical intensity ratios are plotted. The results are
employed to determine the electron-density distribution as a function
of electron temperature for several spectra from two flares. For these
flares it is found that the electron density increases from 10 billion
to 500 billion per cu cm for a temperature increase from 1 million to
10 million K.
---------------------------------------------------------
Title: The decay of the 1973 August 9 flare.
Authors: Dere, K. P.; Cook, J. W.
1979ApJ...229..772D Altcode:
The state and evolution of the decay-phase plasma from a compact solar
flare that occurred on August 9, 1973, are investigated on the basis of
XUV and X-ray observations from Skylab and Solrad 9. Density-sensitive
line ratios are used to determine the electron density over the
temperature range from 30,000 to 5 million K, and the differential
emission measure in the temperature interval from 30,000 to 20 million
K is derived for several times in the decay phase. The morphology of the
flare is discussed, including its relation to the observed photospheric
magnetic field. The sequential formation of new loops during the decay
phase is emphasized as an essential element for understanding the
decay phase of the flare. This idea is developed further by comparing
the observed differential emission measure with that predicted by
a semiempirical model which considers the sequential formation of
isothermal loops that cool by radiation and thermal conduction.
---------------------------------------------------------
Title: Errors in Differential Emission Measure Solutions
Authors: Dere, K. P.
1978A&A....70..439D Altcode:
Summary. The possible errors in differential emission measures
derived from spectral line intensities of limited accuracy have been
examined by direct numerical simulation. The results indicate that if a
functional form that is smooth and non-negative is used to approximate
the differential emission measure, it is possible to obtain solutions
which have errors that are not significantly greater than the errors
in the spectral data. Key words: X-ray - XUV - spectra-plasmas
---------------------------------------------------------
Title: Evolution of the coronal and transition-zone plasma in a
compact flare: the event of 1973 August 9.
Authors: Underwood, J. H.; Antiochos, S. K.; Feldman, U.; Dere, K. P.
1978ApJ...224.1017U Altcode:
X-ray and extreme ultraviolet observations of a compact flare were
analyzed to determine the relative importance of radiation, thermal
conduction, and 'evaporation' in the evolution of the temperature and
density structure of the plasma. In the event studied (1973 August 9),
the electron density was relatively high (5 x 10 to the eleventh to 1 x
10 to the twelfth) and radiation was evidently an important energy-loss
and cooling mechanism. The light curves of ultraviolet lines formed at
temperatures between 10 to the fifth to 10 to the seventh K indicate a
time-varying emission measure gradient, and hence temperature gradient,
during the flare. Radiative instability evidently played an important
role in determining the steepness of these gradients during the rise
and fall phases, and caused strong downward motions of material during
the cooling phase. Toward the end of the event, the coronal electron
density decreased and the temperature gradient relaxed toward that
expected from a conduction-dominated plasma. For this flare, evaporative
cooling did not appear to be a significant factor.
---------------------------------------------------------
Title: Spectral lines observed in solar flares between 171 and
630 Angstroms.
Authors: Dere, K. P.
1978ApJ...221.1062D Altcode:
Several hundred spectral lines emitted in solar flares between
171 and 630 A have been recorded by the Naval Research Laboratory
spectroheliograph aboard Skylab. The wavelengths, identifications, and
intensity estimates of these lines are presented, based on measurements
of all of the suitable flare plates. Nearly 100 new and unidentified
lines have been observed. Identifications of three Fe XXI and two Fe
XVII lines are suggested.
---------------------------------------------------------
Title: EUV Observations of a Solar Active Region
Authors: Dere, K. P.
1978BAAS...10..440D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Multiple loop activation and continuous energy release in
the solar flare of June 15, 1973.
Authors: Widing, K. G.; Dere, K. P.
1977SoPh...55..431W Altcode:
The spatial and temporal evolution of the high temperature plasma
in the flare of 1973 June 15 has been studied using the flare images
photographed by the NRL XUV spectroheliograph on Skylab.
---------------------------------------------------------
Title: Structure and dynamics of a solar flare: X-ray and XUV
observations.
Authors: Dere, K. P.; Horan, D. M.; Kreplin, R. W.
1977ApJ...217..976D Altcode:
Results are presented for an analysis of X-ray and XUV emission from
the solar flare that occurred on September 5, 1973. X-ray emission
was monitored by ionization chambers aboard the Solrad 9 satellite,
and the XUV emission in the wavelength range 170-345 A was recorded
by a slitless objective-grating spectroheliograph on Skylab. The
physical parameters of the flare plasma, including temperature, density,
volume, and magnetic-field configuration, are evaluated. A geometrical
loop model is used to determine the volumes of the various emitting
regions. The structure of the flare in the rise and decay phases
is examined in detail, and conclusions about the effect of various
dynamic processes in the flare plasma are made. A major finding is
that continued energy release is required well into the flare decay
phase. In the rise phase, energy is apparently released only along a
small portion of a loop, and in the decay phase apparently throughout
most of its length.
---------------------------------------------------------
Title: Electron densities in solar flares from line ratios of Ca XVII.
Authors: Doschek, G. A.; Feldman, U.; Dere, K. P.
1977A&A....60L..11D Altcode:
Summary. We show that the intensity ratios of certain extreme
ultraviolet spectral lines of Ca XVII are sensitive to electron density
in solar flares. Calculations of the line ratios as functions of
density are presented. These calculations are based on published atomic
data for Ca XVII and for other ions of the beryllium isoelectronic
sequence. For a flare that occurred on 9 August 1973, we derive a
density of about 5 x 101 from the Ca XVII line ratios. Key words:
solar flares - Be I sequence
---------------------------------------------------------
Title: The Solar Spectrum Below 10Å
Authors: Kreplin, R. W.; Dere, K. P.; Horan, D. M.; Meekins, J. F.
1977soiv.conf..287K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Forbidden lines of highly ionized iron in solar flare spectra.
Authors: Doschek, G. A.; Feldman, U.; Dere, K. P.; Sandlin, G. D.;
Vanhoosier, M. E.; Brueckner, G. E.; Purcell, J. D.; Tousey, R.
1975ApJ...196L..83D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Multi-Thremal Analysis of Solar X-Ray Emission
Authors: Dere, Kenneth P.; Horan, Donald M.; Kreplin, Robert W.
1974SoPh...36..459D Altcode:
The NRL SOLRAD 10 satellite carries six ionization chambers to measure
solar X-radiation in the 0.5 to 60 Å wavelength band. The X-ray
emission spectrum in this range is determined by the derivative of
the coronal emission measure (∫ N<SUB>e</SUB><SUP>2</SUP>dV) with
respect to temperature when the thermal processes of bremsstrahlung,
radiative recombination and line radiation are considered. If a simple
model for this differential emission measure is used and detector
responses to the calculated spectra are fitted to the SOLRAD data
by a least squares method, the differential emission measure can
be obtained for temperatures between 2 × 10<SUP>6</SUP>K and 64 ×
10<SUP>6</SUP>K. Data during quiet and flaring periods are analyzed and
the general behavior of the differential emission measure during flares
is presented. This analysis is based on experimental measurements of
the efficiencies of the SOLRAD detectors.
---------------------------------------------------------
Title: The spectral dependence of solar soft X-ray flux values
obtained by SOLRAD 9.
Authors: Dere, K. P.; Horan, D. M.; Kreplin, R. W.
1974JATP...36..989D Altcode:
The determination of solar energy flux values from ionization chamber
experiments is discussed. Procedures and calculations necessary
for the correction of SOLRAD 9 0.5-3 Å and 1-8 Å data and for the
determination of the flare plasma temperature and emission measure
are presented. These calculations are based on the continuum spectrum
of CULHANE (1969), the line spectrum of TUCKER and KOREN (1971),
and experimental values of the detector efficiencies.
---------------------------------------------------------
Title: Electron temperature and emission measure variations in the
solar corona.
Authors: Horan, D. M.; Dere, K. P.; Kreplin, R. W.
1974spre.conf..441H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Reduction of solar X-ray flux measurements for use in
ionospheric research.
Authors: Kreplin, R. W.; Horan, D. M.; Dere, K. P.
1973spre.conf..469K Altcode: 1973spre....1..469K
No abstract at ADS