Author name code: mariska
ADS astronomy entries on 2022-09-14
author:"Mariska, John T."
------------------------------------------------------------------------
Title: Achievements of Hinode in the first eleven years
Authors: Hinode Review Team; Al-Janabi, Khalid; Antolin, Patrick;
Baker, Deborah; Bellot Rubio, Luis R.; Bradley, Louisa; Brooks,
David H.; Centeno, Rebecca; Culhane, J. Leonard; Del Zanna, Giulio;
Doschek, George A.; Fletcher, Lyndsay; Hara, Hirohisa; Harra,
Louise K.; Hillier, Andrew S.; Imada, Shinsuke; Klimchuk, James A.;
Mariska, John T.; Pereira, Tiago M. D.; Reeves, Katharine K.; Sakao,
Taro; Sakurai, Takashi; Shimizu, Toshifumi; Shimojo, Masumi; Shiota,
Daikou; Solanki, Sami K.; Sterling, Alphonse C.; Su, Yingna; Suematsu,
Yoshinori; Tarbell, Theodore D.; Tiwari, Sanjiv K.; Toriumi, Shin;
Ugarte-Urra, Ignacio; Warren, Harry P.; Watanabe, Tetsuya; Young,
Peter R.
Bibcode: 2019PASJ...71R...1H
Altcode:
Hinode is Japan's third solar mission following Hinotori (1981-1982)
and Yohkoh (1991-2001): it was launched on 2006 September 22 and is in
operation currently. Hinode carries three instruments: the Solar Optical
Telescope, the X-Ray Telescope, and the EUV Imaging Spectrometer. These
instruments were built under international collaboration with the
National Aeronautics and Space Administration and the UK Science and
Technology Facilities Council, and its operation has been contributed
to by the European Space Agency and the Norwegian Space Center. After
describing the satellite operations and giving a performance evaluation
of the three instruments, reviews are presented on major scientific
discoveries by Hinode in the first eleven years (one solar cycle long)
of its operation. This review article concludes with future prospects
for solar physics research based on the achievements of Hinode.
Title: Comprehensive Determination of the Hinode/EIS Roll Angle
Authors: Pelouze, Gabriel; Auchère, Frédéric; Bocchialini, Karine;
Harra, Louise; Baker, Deborah; Warren, Harry P.; Brooks, David H.;
Mariska, John T.
Bibcode: 2019SoPh..294...59P
Altcode: 2019arXiv190311923P
We present a new coalignment method for the EUV Imaging Spectrometer
(EIS) on board the Hinode spacecraft. In addition to the pointing
offset and spacecraft jitter, this method determines the roll angle
of the instrument, which has never been systematically measured, and
which is therefore usually not corrected. The optimal pointing for EIS
is computed by maximizing the cross-correlations of the Fe XII 195.119
Å line with images from the 193 Å band of the Atmospheric Imaging
Assembly (AIA) on board the Solar Dynamics Observatory (SDO). By
coaligning 3336 rasters with high signal-to-noise ratio, we estimate
the rotation angle between EIS and AIA and explore the distribution
of its values. We report an average value of (−0.387±0.007 )
∘. We also provide a software implementation of this method
that can be used to coalign any EIS raster.
Title: A Tale of Two Books
Authors: Mariska, John
Bibcode: 2016S&T...132c..86M
Altcode:
No abstract at ADS
Title: Progress toward high resolution EUV spectroscopy
Authors: Korendyke, C.; Doschek, G. A.; Warren, H.; Young, P. R.;
Chua, D.; Hassler, D. M.; Landi, E.; Davila, J. M.; Klimchuck, J.;
Tun, S.; DeForest, C.; Mariska, J. T.; Solar C Spectroscopy Working
Group; LEMUR; EUVST Development Team
Bibcode: 2013SPD....44..143K
Altcode:
HIgh resolution EUV spectroscopy is a critical instrumental technique
to understand fundamental physical processes in the high temperature
solar atmosphere. Spectroscopic observations are used to measure
differential emission measure, line of sight and turbulent flows,
plasma densities and emission measures. Spatially resolved, spectra of
these emission lines with adequate cadence will provide the necessary
clues linking small scale structures with large scale, energetic
solar phenomena. The necessary observations to determine underlying
physical processes and to provide comprehensive temperature coverage
of the solar atmosphere above the chromosphere will be obtained by the
proposed EUVST instrument for Solar C. This instrument and its design
will be discussed in this paper. Progress on the VEry high Resolution
Imaging Spectrograph (VERIS) sounding rocket instrument presently under
development at the Naval Research Laboratory will also be discussed.
Title: Observations of Thermal Flare Plasma with the EUV Variability
Experiment
Authors: Warren, Harry P.; Mariska, John T.; Doschek, George A.
Bibcode: 2013ApJ...770..116W
Altcode: 2012arXiv1211.1875W
One of the defining characteristics of a solar flare is the impulsive
formation of very high temperature plasma. The properties of the
thermal emission are not well understood, however, and the analysis of
solar flare observations is often predicated on the assumption that the
flare plasma is isothermal. The EUV Variability Experiment (EVE) on the
Solar Dynamics Observatory provides spectrally resolved observations of
emission lines that span a wide range of temperatures (e.g., Fe XV-Fe
XXIV) and allow for thermal flare plasma to be studied in detail. In
this paper we describe a method for computing the differential emission
measure distribution in a flare using EVE observations and apply it to
several representative events. We find that in all phases of the flare
the differential emission measure distribution is broad. Comparisons
of EVE spectra with calculations based on parameters derived from
the Geostationary Operational Environmental Satellites soft X-ray
fluxes indicate that the isothermal approximation is generally a poor
representation of the thermal structure of a flare.
Title: On-Orbit Sensitivity Evolution of the EUV Imaging Spectrometer
on Hinode
Authors: Mariska, J. T.
Bibcode: 2013SoPh..282..629M
Altcode: 2012arXiv1211.3694M
Since its launch on 22 September 2006, the EUV Imaging Spectrometer
onboard the Hinode satellite has exhibited a gradual decay in
sensitivity. Using spectroheliograms taken in the Fe VIII 185.21
Å and Si VII 275.35 Å emission lines in quiet regions near Sun
center we characterize that decay. For the period from December 2006
to March 2012, the decline in the sensitivity can be characterized
as an exponential decay with an average time constant of 7358±1030
days (20.2±2.8 years). Emission lines formed at temperatures ≳
106.1 K in the quiet Sun data exhibit solar-cycle effects.
Title: LEMUR: Large European module for solar Ultraviolet
Research. European contribution to JAXA's Solar-C mission
Authors: Teriaca, Luca; Andretta, Vincenzo; Auchère, Frédéric;
Brown, Charles M.; Buchlin, Eric; Cauzzi, Gianna; Culhane, J. Len;
Curdt, Werner; Davila, Joseph M.; Del Zanna, Giulio; Doschek, George
A.; Fineschi, Silvano; Fludra, Andrzej; Gallagher, Peter T.; Green,
Lucie; Harra, Louise K.; Imada, Shinsuke; Innes, Davina; Kliem,
Bernhard; Korendyke, Clarence; Mariska, John T.; Martínez-Pillet,
Valentin; Parenti, Susanna; Patsourakos, Spiros; Peter, Hardi; Poletto,
Luca; Rutten, Robert J.; Schühle, Udo; Siemer, Martin; Shimizu,
Toshifumi; Socas-Navarro, Hector; Solanki, Sami K.; Spadaro, Daniele;
Trujillo-Bueno, Javier; Tsuneta, Saku; Dominguez, Santiago Vargas;
Vial, Jean-Claude; Walsh, Robert; Warren, Harry P.; Wiegelmann,
Thomas; Winter, Berend; Young, Peter
Bibcode: 2012ExA....34..273T
Altcode: 2011ExA...tmp..135T; 2011arXiv1109.4301T
The solar outer atmosphere is an extremely dynamic environment
characterized by the continuous interplay between the plasma and the
magnetic field that generates and permeates it. Such interactions play a
fundamental role in hugely diverse astrophysical systems, but occur at
scales that cannot be studied outside the solar system. Understanding
this complex system requires concerted, simultaneous solar observations
from the visible to the vacuum ultraviolet (VUV) and soft X-rays, at
high spatial resolution (between 0.1'' and 0.3''), at high temporal
resolution (on the order of 10 s, i.e., the time scale of chromospheric
dynamics), with a wide temperature coverage (0.01 MK to 20 MK,
from the chromosphere to the flaring corona), and the capability of
measuring magnetic fields through spectropolarimetry at visible and
near-infrared wavelengths. Simultaneous spectroscopic measurements
sampling the entire temperature range are particularly important. These
requirements are fulfilled by the Japanese Solar-C mission (Plan B),
composed of a spacecraft in a geosynchronous orbit with a payload
providing a significant improvement of imaging and spectropolarimetric
capabilities in the UV, visible, and near-infrared with respect to
what is available today and foreseen in the near future. The Large
European Module for solar Ultraviolet Research (LEMUR), described
in this paper, is a large VUV telescope feeding a scientific payload
of high-resolution imaging spectrographs and cameras. LEMUR consists
of two major components: a VUV solar telescope with a 30 cm diameter
mirror and a focal length of 3.6 m, and a focal-plane package composed
of VUV spectrometers covering six carefully chosen wavelength ranges
between 170 Å and 1270 Å. The LEMUR slit covers 280'' on the Sun with
0.14'' per pixel sampling. In addition, LEMUR is capable of measuring
mass flows velocities (line shifts) down to 2 km s - 1 or
better. LEMUR has been proposed to ESA as the European contribution
to the Solar C mission.
Title: Long-Term Variation of the Corona in Quiet Regions
Authors: Kamio, S.; Mariska, J. T.
Bibcode: 2012SoPh..279..419K
Altcode: 2012arXiv1204.5575K
Using Hinode EUV Imaging Spectrometer (EIS) spectra recorded daily
at Sun center from the end of 2006 to early 2011, we studied the
long-term evolution of the quiet corona. The light curves of the
higher temperature emission lines exhibit larger variations in sync
with the solar activity cycle while the cooler lines show reduced
modulation. Our study shows that the high temperature component of
the corona changes in quiet regions, even though the coronal electron
density remains almost constant there. The results suggest that heat
input to the quiet corona varies with the solar activity cycle.
Title: Coupling of Particle Acceleration and Atmospheric Dynamic
Response to Impulsive Energy Release in Solar Flares
Authors: Liu, Wei; Petrosian, V.; Chen, Q.; Mariska, J.
Bibcode: 2012AAS...22020419L
Altcode:
In solar flares, acceleration and transport of high-energy particles
and fluid dynamics of the atmospheric plasma are interrelated
processes coupled in a circular chain. Chromospheric evaporation,
for example, can alter the density and temperature distribution
along the flare loop, in particular in the acceleration site near
the loop-top source. This produces a feedback on particle collisional
heating, and more importantly on the energy release and acceleration
process. This in turn will change the heating of the chromosphere and
mass flows in the corona. In recent years, there have been increasing
theoretical and observational motivations to investigate these coupled
processes together in a self-consistent manner. We present here combined
Fokker-Planck modeling of particles and hydrodynamic simulation of
flare plasma. We extended our earlier hybrid simulation (Liu, Petrosian,
Mariska 2009) by feeding the updated plasma density and temperature at
the loop-top source to the stochastic acceleration process. We find
that the density enhancement causes the ratio of the electron plasma
frequency to gyro-frequency to increase. This can lead to the reduction
of the efficiency of electron acceleration and thus the quenching
or spectral softening of nonthermal hard X-ray tails observed during
the late stages of flares. This also affects the relative production
of energetic electrons vs. protons (Petrosian and Liu 2004). We will
compare our results with recent observations from RHESSI, SDO, and
Hinode. We will also discuss their implications for cyclic spectral
hardening, quasi-periodic flare pulsations, and recently imaged
super-fast quasi-periodic coronal waves originating from flare kernels.
Title: Extreme Ultraviolet Variability Experiment (EVE) on the
Solar Dynamics Observatory (SDO): Overview of Science Objectives,
Instrument Design, Data Products, and Model Developments
Authors: Woods, T. N.; Eparvier, F. G.; Hock, R.; Jones, A. R.;
Woodraska, D.; Judge, D.; Didkovsky, L.; Lean, J.; Mariska, J.;
Warren, H.; McMullin, D.; Chamberlin, P.; Berthiaume, G.; Bailey,
S.; Fuller-Rowell, T.; Sojka, J.; Tobiska, W. K.; Viereck, R.
Bibcode: 2012SoPh..275..115W
Altcode:
The highly variable solar extreme ultraviolet (EUV) radiation is
the major energy input to the Earth's upper atmosphere, strongly
impacting the geospace environment, affecting satellite operations,
communications, and navigation. The Extreme ultraviolet Variability
Experiment (EVE) onboard the NASA Solar Dynamics Observatory (SDO) will
measure the solar EUV irradiance from 0.1 to 105 nm with unprecedented
spectral resolution (0.1 nm), temporal cadence (ten seconds), and
accuracy (20%). EVE includes several irradiance instruments: The
Multiple EUV Grating Spectrographs (MEGS)-A is a grazing-incidence
spectrograph that measures the solar EUV irradiance in the 5 to 37 nm
range with 0.1-nm resolution, and the MEGS-B is a normal-incidence,
dual-pass spectrograph that measures the solar EUV irradiance in the
35 to 105 nm range with 0.1-nm resolution. To provide MEGS in-flight
calibration, the EUV SpectroPhotometer (ESP) measures the solar EUV
irradiance in broadbands between 0.1 and 39 nm, and a MEGS-Photometer
measures the Sun's bright hydrogen emission at 121.6 nm. The EVE data
products include a near real-time space-weather product (Level 0C),
which provides the solar EUV irradiance in specific bands and also
spectra in 0.1-nm intervals with a cadence of one minute and with a
time delay of less than 15 minutes. The EVE higher-level products
are Level 2 with the solar EUV irradiance at higher time cadence
(0.25 seconds for photometers and ten seconds for spectrographs) and
Level 3 with averages of the solar irradiance over a day and over each
one-hour period. The EVE team also plans to advance existing models of
solar EUV irradiance and to operationally use the EVE measurements in
models of Earth's ionosphere and thermosphere. Improved understanding
of the evolution of solar flares and extending the various models to
incorporate solar flare events are high priorities for the EVE team.
Title: New Solar Extreme-ultraviolet Irradiance Observations during
Flares
Authors: Woods, Thomas N.; Hock, Rachel; Eparvier, Frank; Jones,
Andrew R.; Chamberlin, Phillip C.; Klimchuk, James A.; Didkovsky,
Leonid; Judge, Darrell; Mariska, John; Warren, Harry; Schrijver,
Carolus J.; Webb, David F.; Bailey, Scott; Tobiska, W. Kent
Bibcode: 2011ApJ...739...59W
Altcode:
New solar extreme-ultraviolet (EUV) irradiance observations from the
NASA Solar Dynamics Observatory (SDO) EUV Variability Experiment provide
full coverage in the EUV range from 0.1 to 106 nm and continuously at
a cadence of 10 s for spectra at 0.1 nm resolution and even faster,
0.25 s, for six EUV bands. These observations can be decomposed into
four distinct characteristics during flares. First, the emissions
that dominate during the flare's impulsive phase are the transition
region emissions, such as the He II 30.4 nm. Second, the hot coronal
emissions above 5 MK dominate during the gradual phase and are highly
correlated with the GOES X-ray. A third flare characteristic in the
EUV is coronal dimming, seen best in the cool corona, such as the
Fe IX 17.1 nm. As the post-flare loops reconnect and cool, many of
the EUV coronal emissions peak a few minutes after the GOES X-ray
peak. One interesting variation of the post-eruptive loop reconnection
is that warm coronal emissions (e.g., Fe XVI 33.5 nm) sometimes exhibit
a second large peak separated from the primary flare event by many
minutes to hours, with EUV emission originating not from the original
flare site and its immediate vicinity, but rather from a volume of
higher loops. We refer to this second peak as the EUV late phase. The
characterization of many flares during the SDO mission is provided,
including quantification of the spectral irradiance from the EUV late
phase that cannot be inferred from GOES X-ray diagnostics.
Title: Physical Properties of Solar Flares: New Results from EVE/SDO
Authors: Warren, H. P.; Mariska, J. T.; Doschek, G. A.; Eve Team
Bibcode: 2010AGUFMSH13A..06W
Altcode:
Much of our current understanding of the temperature and density
structure of solar flares has been derived from broad band X-ray
instruments, such as RHESSI, GOES, and SXT/Yohkoh, or the observation
of isolated emission lines, such as from BCS/Yohkoh. This has lead
to uncertainties in determining the distribution of temperatures and
densities in a flare. The EUV Variability Experiment (EVE) on the Solar
Dynamics Observatory (SDO) provides an unprecedented opportunity to
observe a very wide range of high-temperature emission lines at high
cadence (10 s) and relatively high spectral resolution (1 A). The
spectral range between 90 and 200 Angstroms is particularly rich in
emission lines from Fe that are formed at temperatures above 7 MK
(Fe XVIII - Fe XXIV). This range also includes one of the few density
diagnostics (Fe XXI 145.66/128.75) that is useful in solar flare
observations. Our initial calculations suggest very broad differential
emission measure distributions and indicate high densities (Log Ne as
high as 11.7), which implies a very rapid cooling of flare plasma. These
observations are broadly consistent with flare models that allow for
the release of energy on many independent threads and we will discuss
these results in the context of current theories of solar flares.
Title: Science Objectives for an X-Ray Microcalorimeter Observing
the Sun
Authors: Laming, J. Martin; Adams, J.; Alexander, D.; Aschwanden, M;
Bailey, C.; Bandler, S.; Bookbinder, J.; Bradshaw, S.; Brickhouse,
N.; Chervenak, J.; Christe, S.; Cirtain, J.; Cranmer, S.; Deiker, S.;
DeLuca, E.; Del Zanna, G.; Dennis, B.; Doschek, G.; Eckart, M.; Fludra,
A.; Finkbeiner, F.; Grigis, P.; Harrison, R.; Ji, L.; Kankelborg,
C.; Kashyap, V.; Kelly, D.; Kelley, R.; Kilbourne, C.; Klimchuk, J.;
Ko, Y. -K.; Landi, E.; Linton, M.; Longcope, D.; Lukin, V.; Mariska,
J.; Martinez-Galarce, D.; Mason, H.; McKenzie, D.; Osten, R.; Peres,
G.; Pevtsov, A.; Porter, K. Phillips F. S.; Rabin, D.; Rakowski, C.;
Raymond, J.; Reale, F.; Reeves, K.; Sadleir, J.; Savin, D.; Schmelz,
J.; Smith, R. K.; Smith, S.; Stern, R.; Sylwester, J.; Tripathi, D.;
Ugarte-Urra, I.; Young, P.; Warren, H.; Wood, B.
Bibcode: 2010arXiv1011.4052L
Altcode:
We present the science case for a broadband X-ray imager with
high-resolution spectroscopy, including simulations of X-ray spectral
diagnostics of both active regions and solar flares. This is part of
a trilogy of white papers discussing science, instrument (Bandler et
al. 2010), and missions (Bookbinder et al. 2010) to exploit major
advances recently made in transition-edge sensor (TES) detector
technology that enable resolution better than 2 eV in an array that
can handle high count rates. Combined with a modest X-ray mirror, this
instrument would combine arcsecondscale imaging with high-resolution
spectra over a field of view sufficiently large for the study of
active regions and flares, enabling a wide range of studies such as
the detection of microheating in active regions, ion-resolved velocity
flows, and the presence of non-thermal electrons in hot plasmas. It
would also enable more direct comparisons between solar and stellar
soft X-ray spectra, a waveband in which (unusually) we currently have
much better stellar data than we do of the Sun.
Title: SDO Extreme Ultraviolet Variability Experiment (EVE):
Instrument and First Light
Authors: Woods, Thomas N.; Eparvier, F.; Hock, R.; Jones, A.;
Didkovsky, L.; Judge, D.; Chamberlin, P.; Lean, J.; Warren, H.;
Mariska, J.
Bibcode: 2010AAS...21630802W
Altcode:
The Extreme ultraviolet Variability Experiment (EVE) aboard the
NASA Solar Dynamics Observatory (SDO) was launched on 11 February
2010. The EVE instruments measure the solar extreme ultraviolet
(EUV) irradiance from 0.1 to 105 nm with unprecedented spectral
resolution (0.1 nm), temporal cadence (10 sec minimum), and accuracy
(20% or better). The highly variable solar EUV irradiance is a key
measurement for the NASA Living With the Star (LWS) program as it is
the major energy input into the Earth's upper atmosphere and thus
impacts the geospace environment that affects satellite operations
and communication and navigation systems. The EVE measurements, along
with additional solar measurements from SDO and other satellite and
ground-based instruments, will be used to advance our understanding of
the solar EUV irradiance variability. For short time scales, EVE will
make detailed observations on the evolution of flare events that are
an important interest for space weather research and operations. For
longer time scales, EVE measurements will be compared to other solar
EUV irradiance measurements to help establish a composite time series
of the solar EUV irradiance. The EVE instrument will be described, and
first light results from EVE during the rise of solar cycle 24 will be
presented. The EVE instrument team is supported by the NASA SDO Project.
Title: Doppler-shift, Intensity, and Density Oscillations Observed
with the Extreme Ultraviolet Imaging Spectrometer on Hinode
Authors: Mariska, John T.; Muglach, K.
Bibcode: 2010ApJ...713..573M
Altcode: 2010arXiv1003.0420M
Low-amplitude Doppler-shift oscillations have been observed in
coronal emission lines in a number of active regions with the EUV
Imaging Spectrometer (EIS) on the Hinode satellite. Both standing
and propagating waves have been detected and many periods have been
observed, but a clear picture of all the wave modes that might be
associated with active regions has not yet emerged. In this study,
we examine additional observations obtained with EIS in plage near an
active region on 2007 August 22-23. We find Doppler-shift oscillations
with amplitudes between 1 and 2 km s-1 in emission lines
ranging from Fe XI 188.23 Å, which is formed at log T = 6.07, to Fe XV
284.16 Å, which is formed at log T = 6.32. Typical periods are near 10
minutes. We also observe intensity and density oscillations for some
of the detected Doppler-shift oscillations. In the better-observed
cases, the oscillations are consistent with upwardly propagating slow
magnetoacoustic waves. Simultaneous observations of the Ca II H line
with the Hinode Solar Optical Telescope Broadband Filter Imager show
some evidence for 10 minute oscillations as well.
Title: Doppler Shift Oscillations Observed with the EUV Imaging
Spectrometer on Hinode
Authors: Mariska, J. T.
Bibcode: 2009ASPC..415..283M
Altcode:
This contribution reports on the detection of Doppler-shift oscillations
in an active region observed on 2007 August 22-23. The oscillations,
which have a much lower amplitude than those observed with earlier
instruments, have periods of 7 to 10 min. These observations include
density-sensitive emission lines and oscillations are also present in
the derived densities. EIS is capable of detecting coronal velocity
fluctuations with amplitudes of less than 0.5 km s-1 with
short integration times in strong coronal lines, potentially allowing
access to a much richer range of coronal oscillatory phenomena than
has been available with earlier instruments.
Title: The Second Hinode Science Meeting: Beyond Discovery-Toward
Understanding
Authors: Lites, B.; Cheung, M.; Magara, T.; Mariska, J.; Reeves, K.
Bibcode: 2009ASPC..415.....L
Altcode:
No abstract at ADS
Title: Combined Fokker-Planck Modeling of Particle
Acceleration/Transport and Hydrodynamic Simulation of Atmospheric
Response in Solar Flares
Authors: Petrosian, V.; Liu, W.; Mariska, J. T.
Bibcode: 2009AGUFMSH21C..04P
Altcode:
Acceleration and transport of high-energy particles and fluid dynamics
of atmospheric plasma are interrelated aspects of solar flares, but for
simplicity they were artificially separated in the past. We present
here self-consistently combined Fokker-Planck modeling of particles
and hydrodynamic simulation of flare plasma. Energetic electrons are
modeled with the Stanford unified code of acceleration, transport,
and radiation, while plasma is modeled with the NRL flux tube code
(Mariska et al. 1989). We calculated the collisional heating rate
directly from the particle transport code, which is more accurate
than those in previous studies based on approximate analytical
solutions. We used a more realistic spectrum of injected electrons
provided by the stochastic acceleration model of Petrosian & Liu
(2004), which has a smooth transition from a quasi-thermal background
at low energies to a nonthermal tail at high energies. The inclusion of
low-energy electrons results in relatively more heating in the corona
(vs. chromosphere) and thus a larger downward heat conduction flux. The
interplay of electron heating, conduction, and radiative loss leads to
stronger chromospheric evaporation than obtained in previous studies,
which had a deficit in low-energy electrons due to an arbitrarily
assumed low-energy cutoff. The energy and spatial distributions of
energetic electrons and bremsstrahlung photons bear signatures of the
changing density distribution caused by chromospheric evaporation. In
particular, the density jump at the evaporation front gives rise to
enhanced X-ray emission, which could be responsible for the X-ray
sources moving along flare loops observed by RHESSI (Sui et al. 2006,
ApJL 645; Liu et al. 2006, ApJ 649). Various energy contents from the
simulations can be used to test the empirical Neupert effect. This
technique can also be applied to investigate a variety of high-energy
processes in solar, space, and astrophysical plasmas, such as planetary
auroras. Geometry of the model flare loop assumed in this study.
Title: Hinode/EIS observations of propagating low-frequency slow
magnetoacoustic waves in fan-like coronal loops
Authors: Wang, T. J.; Ofman, L.; Davila, J. M.; Mariska, J. T.
Bibcode: 2009A&A...503L..25W
Altcode: 2009arXiv0908.0310W
Aims: We report the first observation of multiple-periodic propagating
disturbances along a fan-like coronal structure simultaneously detected
in both intensity and Doppler shift in the Fe xii 195 Å line with the
EUV Imaging Spectrometer (EIS) onboard Hinode. A new application of
coronal seismology is provided based on this observation.
Methods:
We analyzed the EIS sit-and-stare mode observation of oscillations
using the running difference and wavelet techniques.
Results:
Two harmonics with periods of 12 and 25 min are detected. We measured
the Doppler shift amplitude of 1-2 km s-1, the relative
intensity amplitude of 3%-5% and the apparent propagation speed of
100-120 km s-1.
Conclusions: The amplitude relationship
between intensity and Doppler shift oscillations provides convincing
evidence that these propagating features are a manifestation of slow
magnetoacoustic waves. Detection lengths (over which the waves are
visible) of the 25 min wave are about 70-90 Mm, much longer than those
of the 5 min wave previously detected by TRACE. This difference may
be explained by the dependence of damping length on the wave period
for thermal conduction. Based on a linear wave theory, we derive an
inclination of the magnetic field to the line-of-sight about 59 ±
8°, a true propagation speed of 128 ± 25 km s-1 and
a temperature of 0.7 ± 0.3 MK near the loop's footpoint from our
measurements. Appendix is only available in electronic form at
http://www.aanda.org
Title: Combined Modeling of Acceleration, Transport, and Hydrodynamic
Response in Solar Flares. I. The Numerical Model
Authors: Liu, Wei; Petrosian, Vahé; Mariska, John T.
Bibcode: 2009ApJ...702.1553L
Altcode: 2009arXiv0906.2449L
Acceleration and transport of high-energy particles and fluid dynamics
of atmospheric plasma are interrelated aspects of solar flares, but
for convenience and simplicity they were artificially separated in the
past. We present here self-consistently combined Fokker-Planck modeling
of particles and hydrodynamic simulation of flare plasma. Energetic
electrons are modeled with the Stanford unified code of acceleration,
transport, and radiation, while plasma is modeled with the Naval
Research Laboratory flux tube code. We calculated the collisional
heating rate directly from the particle transport code, which is
more accurate than those in previous studies based on approximate
analytical solutions. We repeated the simulation of Mariska et
al. with an injection of power law, downward-beamed electrons using
the new heating rate. For this case, a ~10% difference was found from
their old result. We also used a more realistic spectrum of injected
electrons provided by the stochastic acceleration model, which has a
smooth transition from a quasi-thermal background at low energies to a
nonthermal tail at high energies. The inclusion of low-energy electrons
results in relatively more heating in the corona (versus chromosphere)
and thus a larger downward heat conduction flux. The interplay of
electron heating, conduction, and radiative loss leads to stronger
chromospheric evaporation than obtained in previous studies, which had a
deficit in low-energy electrons due to an arbitrarily assumed low-energy
cutoff. The energy and spatial distributions of energetic electrons
and bremsstrahlung photons bear signatures of the changing density
distribution caused by chromospheric evaporation. In particular, the
density jump at the evaporation front gives rise to enhanced emission,
which, in principle, can be imaged by X-ray telescopes. This model can
be applied to investigate a variety of high-energy processes in solar,
space, and astrophysical plasmas.
Title: Doppler Shift Oscillations Observed with the EUV Imaging
Spectrometer on Hinode
Authors: Mariska, John T.; Muglach, K.
Bibcode: 2009SPD....40.1301M
Altcode:
The EUV Imaging Spectrometer (EIS) on Hinode is capable of measuring
Doppler shift fluctuations with amplitudes of less than 0.5 km/s. This,
coupled with EIS's improved sensitivity over previous EUV spectrometers,
has expanded the range of coronal oscillatory phenomena available
for detailed study. For example, both kink mode and slow mode coronal
loop oscillations have already been detected with EIS. We report on
additional observations of Doppler shift and intensity oscillations
in an active region observed in 2007 August. An initial periodogram
analysis of portions of the data shows periods in the Doppler shift
data of 9 to 10 minutes in emission lines with temperatures of
formation from 1.2 to 2.1 MK. Periods of 8 to 12 minutes are seen
in the detrended intensity data over the same temperature range. The
EIS observations include density-sensitive emission lines from Fe XII
and Fe XIII, allowing us to quantify density fluctuations. The Solar
Optical Telescope on Hinode made simultaneous Ca II observations,
which we have co-aligned with the EIS data to understand better the
chromospheric environment in the oscillating region. This work
was supported by the NASA Hinode program.
Title: High-precision density measurements in the solar
corona. I. Analysis methods and results for Fe XII and Fe XIII
Authors: Young, P. R.; Watanabe, T.; Hara, H.; Mariska, J. T.
Bibcode: 2009A&A...495..587Y
Altcode: 2008arXiv0805.0958Y
Aims: The EUV Imaging Spectrometer (EIS) instrument on board the Hinode
satellite has access to some of the best coronal density diagnostics,
and the high sensitivity of the instrument now allows electron number
density, N_e, measurements to an unprecedented precision of up to
±5% in active regions. This paper gives a thorough overview of data
analysis issues for the best diagnostics of Fe XII and Fe XIII and
assesses the accuracy of the measurements.
Methods: Two density
diagnostics each from Fe XII (λ186.88/λ195.12 and λ196.64/λ195.12)
and Fe XIII (λ196.54/λ202.04 and λ203.82/λ202.04) are analysed in
two active region datasets from 2007 May 3 and 6 that yield densities
in the range 8.5≤ log (N_e/cm-3)≤ 11.0. The densities
are derived using v5.2 of the CHIANTI atomic database. Blending,
line fitting, and instrumental issues are discussed, and line fit
parameters presented.
Results: The Fe XII and Fe XIII diagnostics
show broadly the same trend in density across the active region,
consistent with their similar temperatures of formation. However,
the high precision of the EIS measurements demonstrates significant
discrepancies of up to 0.5 dex in derived log Ne values, with
Fe XII always giving higher densities than Fe XIII. The discrepancies
may partly be due to real physical differences between the emitting
regions of the two plasmas, but the dominant factor lies in the
atomic models of the two ions. Two specific problems are identified
for Fe XII λ196.64 and Fe XIII λ203.82: the former is found to
be underestimated in strength by the CHIANTI atomic model, while
the high-density limit of the λ203.82/λ202.04 ratio appears to be
inaccurate in the CHIANTI atomic model. The small grating tilt of the
EIS instrument is found to be very significant when deriving densities
from emission lines separated by more than a few angstroms. Revised
wavelengths of 196.518± 0.003 Å and 196.647± 0.003 Å are suggested
for the Fe XIII λ196.54 and Fe XII λ196.64 lines, respectively.
Title: Commission 12: Solar Radiation and Structure
Authors: Martínez Pillet, Valentin; Kosovichev, Alexander;
Mariska, John T.; Bogdan, Thomas J.; Asplund, Martin; Cauzzi, Gianna;
Christensen-Dalsgaard, Jørgen; Cram, Lawrence E.; Gan, Weiqun; Gizon,
Laurent; Heinzl, Petr; Rovira, Marta G.; Venkatakrishnan, P.
Bibcode: 2009IAUTA..27..104M
Altcode:
Commission 12 encompasses investigations on the internal structure
and dynamics of the Sun, mostly accessible through the techniques of
local and global helioseismology, the quiet solar atmosphere, solar
radiation and its variability, and the nature of relatively stable
magnetic structures like sunspots, faculae and the magnetic network. A
revision of the progress made in these fields is presented. For some
specific topics, the review has counted with the help of experts
outside the Commission Organizing Committee that are leading and/or
have recently presented relevant works in the respective fields. In
this cases the contributor's name is given in parenthesis.
Title: Flows and Nonthermal Velocities in Solar Active Regions
Observed with the EUV Imaging Spectrometer on Hinode: A Tracer of
Active Region Sources of Heliospheric Magnetic Fields?
Authors: Doschek, G. A.; Warren, H. P.; Mariska, J. T.; Muglach, K.;
Culhane, J. L.; Hara, H.; Watanabe, T.
Bibcode: 2008ApJ...686.1362D
Altcode: 2008arXiv0807.2860D
From Doppler velocity maps of active regions constructed from spectra
obtained by the EUV Imaging Spectrometer (EIS) on the Hinode spacecraft
we observe large areas of outflow (20-50 km s-1) that can
persist for at least a day. These outflows occur in areas of active
regions that are faint in coronal spectral lines formed at typical
quiet-Sun and active region temperatures. The outflows are positively
correlated with nonthermal velocities in coronal plasmas. The bulk
mass motions and nonthermal velocities are derived from spectral line
centroids and line widths, mostly from a strong line of Fe XII at
195.12 Å. The electron temperature of the outflow regions estimated
from an Fe XIII to Fe XII line intensity ratio is about (1.2-1.4) ×
106 K. The electron density of the outflow regions derived
from a density-sensitive intensity ratio of Fe XII lines is rather low
for an active region. Most regions average around 7 × 108
cm-3, but there are variations on pixel spatial scales
of about a factor of 4. We discuss results in detail for two active
regions observed by EIS. Images of active regions in line intensity,
line width, and line centroid are obtained by rastering the regions. We
also discuss data from the active regions obtained from other orbiting
spacecraft that support the conclusions obtained from analysis of the
EIS spectra. The locations of the flows in the active regions with
respect to the longitudinal photospheric magnetic fields suggest that
these regions might be tracers of long loops and/or open magnetic
fields that extend into the heliosphere, and thus the flows could
possibly contribute significantly to the solar wind.
Title: Long Duration Flare Observed with Hinode EIS
Authors: Culhane, J. L.; Hara, H.; Watanabe, T.; Matsuzaki, K.; Harra,
L. K.; Cargill, P.; Mariska, J. T.; Doschek, G. A.
Bibcode: 2008ASPC..397..121C
Altcode:
The first Long Duration Event (LDE) observed with Hinode EIS using
a high spectral resolution raster scan is described. The hot plasma
features include a cusp-shaped arcade associated with a thermal RHESSI
source, cooling post-flare loops, complex plasma flows and an EIT
observation that shows expanding loops and inflows characteristic of
the standard magnetic reconnection model for solar flares. A Coronal
Mass Ejection (CME) is also seen by LASCO. The cusp is well observed
in the Ca XVII line and we find enhanced line broadening above this
region. Doppler velocity observations for the post-flare loops show both
up-flows and down-flows that are interpreted as due to siphon flows.
Title: Doppler Shifts in the Boundary of the Dimming Region
Authors: Imada, S.; Hara, H.; Watanabe, T.; Asai, A.; Kamio, S.;
Matsuzaki, K.; Harra, L. K.; Mariska, J. T.
Bibcode: 2008ASPC..397..102I
Altcode:
We present Hinode/EIS raster scan observations of the GOES X3.2
flare that occurred on 2006 December 13. There was a small transient
coronal hole which was located 200 arcsec east of the flare arcade. The
transient coronal hole was strongly affected by the X-class flare, and
the strong upflows were observed in Fe XV line 284.2 Å (log{T/{K}}
= 6.3) at the boundary of dimming region. In this paper, we discuss
how to obtain the velocity map by correcting the instrumental effects.
Title: Observations of Doppler Shift Oscillations with the EUV
Imaging Spectrometer on Hinode
Authors: Mariska, John T.; Warren, Harry P.; Williams, David R.;
Watanabe, Tetsuya
Bibcode: 2008ApJ...681L..41M
Altcode: 2008arXiv0806.0265M
Damped Doppler shift oscillations have been observed in emission lines
from ions formed at flare temperatures with the Solar Ultraviolet
Measurements of Emitted Radiation spectrometer on the Solar and
Heliospheric Observatory and with the Bragg Crystal Spectrometer
on Yohkoh. This Letter reports the detection of low-amplitude damped
oscillations in coronal emission lines formed at much lower temperatures
observed with the EUV Imaging Spectrometer on the Hinode satellite. The
oscillations have an amplitude of about 2 km s-1 and a
period of around 35 minutes. The decay times show some evidence for
a temperature dependence with the lowest temperature of formation
emission line (Fe XII 195.12 Å) exhibiting a decay time of about 43
minutes, while the highest temperature of formation emission line (Fe XV
284.16 Å) shows no evidence for decay over more than two periods of the
oscillation. The data appear to be consistent with slow magnetoacoustic
standing waves, but may be inconsistent with conductive damping.
Title: Non-Gaussian Line Profiles in a Large Solar Flare Observed
on 2006 December 13
Authors: Imada, S.; Hara, H.; Watanabe, T.; Asai, A.; Minoshima, T.;
Harra, L. K.; Mariska, J. T.
Bibcode: 2008ApJ...679L.155I
Altcode:
We have studied the characteristics of the non-Gaussian line profile
of the Fe XIV 274.20 Å line in and around a flare arcade. We found
that broad non-Gaussian line profiles associated with redshifts
are observed in the flare arcade. There were two typical types
of broad line profiles. One was a distorted line profile caused by
multiple flows, and the other was a symmetric line profile without any
additional component. We successfully distinguished those two types
using higher order statistical moments or M—the additional component
contribution—defined in this Letter. The distorted/symmetric broad
line profiles were preferentially observed in new/old flare loops,
respectively.
Title: Observations of Doppler Shift Oscillations With the EUV
Imaging Spectrometer on Hinode
Authors: Mariska, J. T.; Warren, H. P.; Williams, D. R.; Watanabe, T.
Bibcode: 2008AGUSMSP31A..04M
Altcode:
Damped Doppler shift oscillations have been observed in emission lines
from ions formed at flare temperatures with the Solar Ultraviolet
Measurements of Emitted Radiation spectrometer on SOHO and the Bragg
Crystal Spectrometer on Yohkoh. We report the detection of similar
oscillations in coronal emission lines observed with the EUV Imaging
Spectrometer on the Hinode satellite. The oscillations, which are
present in emission lines formed at lower temperatures than seen with
the instruments listed above, have an amplitude of about 2 km s- 1,
and a period of around 35 min. The decay times show some evidence
for a temperature dependence with the lowest temperature of formation
emission line (Fe~XII 195.12 Å) exhibiting a decay time of about 43
min, while the highest temperature of formation emission line (Fe~XV
284.16 Å) shows no evidence for decay over more than two periods of the
oscillation. The data appear to be consistent with slow magnetoacoustic
standing waves.
Title: Coronal Plasma Motions near Footpoints of Active Region Loops
Revealed from Spectroscopic Observations with Hinode EIS
Authors: Hara, Hirohisa; Watanabe, Tetsuya; Harra, Louise K.; Culhane,
J. Leonard; Young, Peter R.; Mariska, John T.; Doschek, George A.
Bibcode: 2008ApJ...678L..67H
Altcode:
The solar active region 10938 has been observed from the disk center
to the west limb with the Hinode EUV Imaging Spectrometer. In the
disk-center observation, subsonic upflow motions of tens of km
s-1 and enhanced nonthermal velocities have been found
near the footpoints of the active region loops assuming a single
Gaussian approximation for the emission-line profiles. When the same
part of the active region is observed near the limb, both upflows
and enhanced nonthermal velocities essentially decrease. There
is a strong correlation between Doppler velocity and nonthermal
velocity. Significant deviations from a single Gaussian profile are
found in the blue wing of the line profiles for the upflows. These
suggest that there are unresolved high-speed upflows. We discuss the
implications for coronal heating mechanisms.
Title: Observation and Modeling of Coronal "Moss" With the EUV
Imaging Spectrometer on Hinode
Authors: Warren, Harry P.; Winebarger, Amy R.; Mariska, John T.;
Doschek, George A.; Hara, Hirohisa
Bibcode: 2008ApJ...677.1395W
Altcode: 2007arXiv0709.0396W
Observations of transition region emission in solar active regions
represent a powerful tool for determining the properties of hot coronal
loops. We present the analysis of new observations of active region
moss taken with the Extreme Ultraviolet Imaging Spectrometer (EIS)
on the Hinode satellite. EIS observations of a density sensitive Fe
XII line ratio suggest moss densities of approximately 1010
cm-3 and pressures of 3 × 1016 cm-3
K. We find that the moss intensities predicted by steady, uniformly
heated loop models are too intense relative to the observations,
consistent with previous work. To bring the steady heating model into
agreement with the observations a filling factor is required. Our
analysis indicates that the filling factor in the moss is nonuniform
and varies inversely with the loop pressure. The intensities predicted
by steady uniform heating are generally consistent with the EIS moss
observations. There are, however, significant discrepancies for the
coolest emission line available in the data we analyze.
Title: 2006 December 17 Long Duration Flare Observed with the Hinode
EUV Imaging Spectrometer
Authors: Hara, Hirohisa; Watanabe, Tetsuya; Matsuzaki, Keiichi; Harra,
Louise K.; Culhane, J. Leonard; Cargill, Peter; Mariska, John T.;
Doschek, George A.
Bibcode: 2008PASJ...60..275H
Altcode:
A GOES C-class long-duration flare that occurred near the west limb on
2006 December 17 was observed with the Hinode EUV Imaging Spectrometer
(EIS) in raster-scan observations. Cusp-shaped arcades are prominent in
the spectroheliogram of the CaXVII emission line at 192.86Å. Spatial
relationships between hot flare loops with a cusp apex and cool post
flare loops with various temperatures are clearly shown in the EIS
observations. We find an enhanced line broadening above the bright
loop-top region in the CaXVII observation. The Doppler observations of
cooling post flare loops with coronal temperatures show both downflows
and upflows along the loops, and these are interpreted as a part of
siphon flows. Enhanced nonthermal line broadenings are identified at
the top of the post flare loops.
Title: Coronal Plasma Motions near Footpoints of Active Region Loops
Revealed from Spectroscopic Observations with {it Hinode} EIS
Authors: Hara, Hirohisa; Watanabe, Tetsuya; Harra, Louise K.; Culhane,
J. Leonard; Young, Peter R.; Doschek, G. A.; Mariska, John
Bibcode: 2008cosp...37.1175H
Altcode: 2008cosp.meet.1175H
We have observed the solar active region 10938 from the disk center
to the west limb with the Hinode EUV Imaging Spectrometer. In the
disk center observation subsonic upflow motions of tens of km s-1 and
enhanced nonthermal velocities have been found near the footpoints of
the active-region loops assuming a single Gaussian approximation for
the emission-line profiles. When the same part of the active region
is observed near the limb, both upflows and enhanced nonthermal
velocities essentially decrease, clearly showing that the enhanced
nonthermal velocities in the disk center observation are mainly due to
line-of-sight motions, which are likely parallel to magnetic field lines
of the coronal loops. There is a strong correlation between Doppler
velocity and nonthermal velocity in the upflow regions. The enhancement
in the blue wing of the line profiles is found for the upflows as a
significant deviation from a single Gaussian profile. These suggest
that there are unresolved high-speed upflows near the footpoints of
active region loops. We discuss the implications for coronal heating
mechanisms.
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.
Bibcode: 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.
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.
Bibcode: 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
× 104 K, show the chromospheric network. Line intensities
of FeX-XIV, formed at temperatures from 1-2 × 106 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-1 in a compact region and 12kms-1 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 × 108cm-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 HeII λ 256 profiles.
Title: Temperature and Density Structures of Solar Corona, A Test
of Iron Line Diagnostic Capability of EIS Instrument on Board Hinode
Authors: Watanabe, Tetsuya; Hara, Hirohisa; Culhane, Len; Harra,
Louise K.; Doschek, George A.; Mariska, John T.; Young, Peter R.
Bibcode: 2007PASJ...59S.669W
Altcode:
Increased diagnostic capability of the EUV Imaging Spectrometer
(EIS) aboard Hinode (former Solar-B) has been demonstrated with
a set of iron emission lines emerging in the two EIS observing
wavelength bands (170-210Å and 250-290Å) and their line-intensity
ratios. ``Abundance-uncertainty'' free relative emission measure
distributions as a function of temperature were deduced using only iron
emission lines of various ionization stages. First-light spectra of a
small active region show iron lines ranging from FeVIII (185.2Å and
186.6Å) through FeXVII (204.7Å, 254.9Å, and 269.4Å). Spectra of a
C-class flare confirms the presence of one of these higher temperature
lines (FeXVII at 254.9Å) more clearly, as well showing FeXXIV (192.0Å
and 255.1Å) and FeXXIII (263.8Å), which are normally only seen at
flare temperatures.
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.
Bibcode: 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.
Title: Hinode EUV Imaging Spectrometer Observations of Solar Active
Region Dynamics
Authors: Mariska, John T.; Warren, Harry P.; Ugarte-Urra, Ignacio;
Brooks, David H.; Williams, David R.; Hara, Hirohisa
Bibcode: 2007PASJ...59S.713M
Altcode: 2007arXiv0708.4309M
The EUV Imaging Spectrometer (EIS) on the Hinode satellite is capable of
measuring emission line center positions for Gaussian line profiles to a
fraction of a spectral pixel, resulting in relative solar Doppler-shift
measurements with an accuracy of a less than a km s-1 for
strong lines. We show an example of the application of that capability
to an active region sit-and-stare observation in which the EIS slit
is placed at one location on the Sun and many exposures are taken
while the spacecraft tracking keeps the same solar location within
the slit. For the active region examined (NOAA10930), we find that
significant intensity and Doppler-shift fluctuations as a function of
time are present at a number of locations. These fluctuations appear
to be similar to those observed in high-temperature emission lines
with other space-borne spectroscopic instruments. With its increased
sensitivity over earlier spectrometers and its ability to image many
emission lines simultaneously, EIS should provide significant new
constraints on Doppler-shift oscillations in the corona.
Title: Discovery of a Temperature-Dependent Upflow in the Plage
Region During a Gradual Phase of the X-Class Flare
Authors: Imada, Shinsuke; Hara, Hirohisa; Watanabe, Tetsuya; Kamio,
Suguru; Asai, Ayumi; Matsuzaki, Keiichi; Harra, Louise K.; Mariska,
John T.
Bibcode: 2007PASJ...59S.793I
Altcode:
We present Hinode/EIS raster scan observations of the plage region
taken during the gradual phase of the GOES X3.2 flare that occurred on
2006 December 13. The plage region is located 200" east of the flare
arcade. The plage region has a small transient coronal hole. The
transient coronal hole is strongly affected by an X-class flare,
and upflows are observed at its boundary. Multi-wavelength spectral
observations allow us to determine velocities from the Doppler shifts
at different temperatures. Strong upflows along with stationary plasma
have been observed in the FeXV line 284.2Å (log T / K = 6.3) in the
plage region. The strong upflows reach almost 150kms-1, which
was estimated by a two-component Gaussian fitting. On the other hand,
at a lower corona/transition region temperature (HeII, 256.3Å, log T /
K = 4.9), very weak upflows, almost stationary, have been observed. We
find that these upflow velocities clearly depend on the temperature
with the hottest line, FeXV, showing the fastest upflow velocity and the
second-highest line, FeXIV, showing the second-highest upflow velocity
(130kms-1). All velocities are below the sound speed. The
trend of the upflow dependence on temperature dramatically changes
at 1MK. These results suggest that heating may have an important role
for strong upflow.
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.
Bibcode: 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
×106 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: Nonthermal Velocities in Solar Active Regions Observed with
the Extreme-Ultraviolet Imaging Spectrometer on Hinode
Authors: Doschek, G. A.; Mariska, J. T.; Warren, H. P.; Brown, C. M.;
Culhane, J. L.; Hara, H.; Watanabe, T.; Young, P. R.; Mason, H. E.
Bibcode: 2007ApJ...667L.109D
Altcode:
We discuss nonthermal velocities in an active region as revealed
by the Extreme-Ultraviolet Imaging Spectrometer (EIS) on the Hinode
spacecraft. The velocities are derived from spectral line profiles in
the extreme-ultraviolet (EUV) from a strong line of Fe XII at 195.12 Å
by fitting each line profile to a Gaussian function. We compare maps
of the full width at half-maximum values, the Fe XII spectral line
intensity, the Fe XII Doppler shift, the electron temperature, and
electron density. We find that the largest widths in the active region
do not occur in the most intense regions, but seem to concentrate in
less intense regions, some of which are directly adjacent to coronal
loops, and some of which concentrate in regions which also exhibit
relative Doppler outflows. The increased widths can also occur over
extended parts of the active region.
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.
Bibcode: 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−1 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: A Long-duration Flare Observed With Hinode EIS
Authors: Hara, Hirohisa; Watanabe, T.; Harra, L.; Culhane, L.; Cargill,
P.; Doschek, G.; Mariska, J.
Bibcode: 2007AAS...210.6802H
Altcode: 2007BAAS...39..175H
Long-duration solar flares generally have a cusp apex at the loop
top. The cusp shape reflects the topology of magnetic fields near
the flare-loop top and it is one of the indirect pieces of evidence
supporting the occurrence of the magnetic reconnection process above
flare loops. The Hinode EUV Imaging Spectrometer (EIS) observed a
long-duration flare that occurred on 2006 Dec 17. We present the first
EIS spectroscopic observation of cusp-shaped flare loops. We also
report velocity fields around the cusp structures and post-flare loops.
Title: Hinode EIS Observations of Solar Active Regions
Authors: Mariska, John T.; Doschek, G. A.; Warren, H. P.; Brooks,
D. H.; Young, P. R.; Watanabe, T.; Culhane, J. L.
Bibcode: 2007AAS...210.7202M
Altcode: 2007BAAS...39R.178M
The EUV Imaging Spectrometer (EIS) on the Hinode satellite provides
high spatial and spectral resolution data along a 512 arcsec slit in
two wavelength ranges, 170--210 Angstroms and 250--290 Angstroms. These
wavelengths mostly contain emission lines from upper transition region
and coronal plasmas. Emission from these wavelengths is routinely
imaged using instruments such as the EIT on SOHO and TRACE, but there
are few high-resolution spectra to aid in more deeply understanding
the physical conditions and dynamics associated with the intensity
variations seen in the images. In this presentation, we show some
initial results from EIS active region studies aimed at mapping the
density, temperature, nonthermal broadening, and Doppler shifts in
active regions. This presentation focusses on spectroheliograms of
active regions in diagnostically interesting spectral lines. These
show the overall active region morphology and the behavior of Doppler
shifts, nonthermal velocities, and densities as a function of position,
but at the expense of high time resolution. Other presentations will
focus on how the observed physical parameters vary with time.
Title: Iron Line Ratio Analysis in an Active Region
Authors: Watanabe, Tetsuya; Hara, H.; Culhane, J. L.; Harra, L. K.;
Doschek, G. A.; Mariska, J. T.; Young, P. R.; Hinode EIS Team
Bibcode: 2007AAS...210.7204W
Altcode: 2007BAAS...39..179W
Increased diagnostic capability of the EIS instrument on board Hinode
(Solar-B) is demonstrated with a set of iron emission lines appearing
in the two EIS observing wavelengths (170 - 210 A & 250 - 290
A) and their line intensity ratios. First-light spectra of a small
active region show iron lines at the ionization stages of FeVIII
(185.2 A & 186.6 A) through FeXVII (204.7 A, 254.9 A, & 269.4
A). Decay phase spectra of a C-class flare confirms the presence of
this higher temperature line; FeXVII at 254.9 A more clearly, as well
as those lines of flare temperatures; FeXXIV (192.0 A & 255.1 A)
and FeXXIII (263.8 A).
Title: Commission 12: Solar Radiation & Structure
Authors: Bogdan, Thomas. J.; Martínez Pillet, Valentin; Asplund,
M.; Christensen-Dalsgaard, J.; Cauzzi, G.; Cram, L. E.; Dravins, D.;
Gan, W.; Henzl, P.; Kosovichev, A.; Mariska, J. T.; Rovira, M. G.;
Venkatakrishnan, P.
Bibcode: 2007IAUTA..26...89B
Altcode:
Commission 12 covers research on the internal structure and dynamics
of the Sun, the "quiet" solar atmosphere, solar radiation and its
variability, and the nature of relatively stable magnetic structures
like sunspots, faculae and the magnetic network. There is considerable
productive overlap with the other Commissions of Division II as
investigations move progressively toward the fertile intellectual
boundaries between traditional research disciplines. In large part,
the solar magnetic field provides the linkage that connects these
diverse themes. The same magnetic field that produces the more subtle
variations of solar structure and radiative output over the 11 yr
activity cycle is also implicated in rapid and often violent phenomena
such as flares, coronal mass ejections, prominence eruptions, and
episodes of sporadic magnetic reconnection.The last three years have
again brought significant progress in nearly all the research endeavors
touched upon by the interests of Commission 12. The underlying causes
for this success remain the same: sustained advances in computing
capabilities coupled with diverse observations with increasing levels
of spatial, temporal and spectral resolution. It is all but impossible
to deal with these many advances here in anything except a cursory and
selective fashion. Thankfully, the Living Reviews in Solar Physics; has
published several extensive reviews over the last two years that deal
explicitly with issues relevant to the purview of Commission 12. The
reader who is eager for a deeper and more complete understanding of
some of these advances is directed to http://www.livingreviews.org
for access to these articles.
Title: Optics and mechanisms for the Extreme-Ultraviolet Imaging
Spectrometer on the Solar-B satellite
Authors: Korendyke, Clarence M.; Brown, Charles M.; Thomas, Roger J.;
Keyser, Christian; Davila, Joseph; Hagood, Robert; Hara, Hirohisa;
Heidemann, Klaus; James, Adrian M.; Lang, James; Mariska, John T.;
Moser, John; Moye, Robert; Myers, Steven; Probyn, Brian J.; Seely,
John F.; Shea, John; Shepler, Ed; Tandy, Jason
Bibcode: 2006ApOpt..45.8674K
Altcode:
The Extreme-Ultraviolet Imaging Spectrometer (EIS) is the first of a
new generation of normal-incidence, two-optical-element spectroscopic
instruments developed for space solar extreme-ultraviolet astronomy. The
instrument is currently mounted on the Solar-B satellite for a planned
launch in late 2006. The instrument observes in two spectral bands,
170-210 Å and 250-290 Å. The spectrograph geometry and grating
prescription were optimized to obtain excellent imaging while still
maintaining readily achievable physical and fabrication tolerances. A
refined technique using low ruling density surrogate gratings and
optical metrology was developed to align the instrument with visible
light. Slit rasters of the solar surface are obtained by mechanically
tilting the mirror. A slit exchange mechanism allows selection among
four slits at the telescope focal plane. Each slit is precisely located
at the focal plane. The spectrograph imaging performance was optically
characterized in the laboratory. The resolution was measured using
the Mg iii and Ne iii lines in the range of 171-200 Å. The He ii line
at 256 Å and Ne iii lines were used in the range of 251-284 Å. The
measurements demonstrate an equivalent resolution of ∼2 arc sec on
the solar surface, in good agreement with the predicted performance. We
describe the EIS optics, mechanisms, and measured performance.
Title: The extreme UV imaging spectrometer for the JAXA Solar-B
mission
Authors: Culhane, J. L.; Doschek, G. A.; Watanabe, T.; Smith, A.;
Brown, C.; Hara, H.; Harra, L. K.; James, A. M.; al Janabi, K.;
Kent, B.; Korendyke, C.; Lang, J.; Mariska, J.; Myers, S.; Seely,
J.; Simnett, G.; Tandy, J.; Thomas, R.; Windt, D. L.
Bibcode: 2006SPIE.6266E..0TC
Altcode: 2006SPIE.6266E..22C
The ISAS/JAXA Solar-B mission includes an Extreme-UV Imaging
Spectrometer (EIS). It detects photons in the wavelength ranges 17 -
21 nm and 25 - 29 nm which include emission lines from several highly
ionised species that exist at temperatures log T = 4.7, 5.6, 5.8,
5.9 and 6.0 - 7.3 K. Instrument throughput is increased substantially
by the use of multilayer coatings optimized for maximum reflectance
in the two selected wavelength bands. The use of back-illuminated
CCDs provides significantly enhanced quantum efficiency over that
previously available from microchannel plate systems. In this paper we
will describe the design and operation of the instrument and present
its performance parameters e.g. spectral and spatial resolution and
sensitivity. Preliminary results of recent calibration measurements
will be described. The role of EIS in the Solar-B mission will be
illustrated with reference to the anticipated observing strategy for
the first three months of the mission which will be outlined.
Title: X-ray Emission from Flaring Loops: Comparison Between RHESSI
Observations and Hydrodynamic Simulations
Authors: Liu, Wei; Jiang, Y. W.; Petrosian, V.; Liu, S.; Mariska, J. T.
Bibcode: 2006SPD....37.2705L
Altcode: 2006BAAS...38..254L
RHESSI with its high temporal, spatial, and spectral resolution
has revealed many interesting results on the X-ray emission from
solar flares, some of which can shed light on the processes of
energy release, particle acceleration, heating, and evaporation of
chromospheric plasmas. During the impulsive phase of a limb flare,
Liu et al. (2006) reported hard X-ray (HXR) emission dominated by the
legs of the loop, as opposed to the commonly observed loop top (LT)
and footpoint (FP) emissions. The HXR emission tends to rise above
the FPs and eventually merge into a single LT source, suggestive of a
gradual density increase in the loop possibly caused by chromospheric
evaporation. During the decay phase of six limb flares, Jiang et
al. (2006) found that the thermal LT source is confined in a small
region near the top of the loop rather than spreading throughout the
whole loop. The total energy of the source decays much slower than
expected from the classical Spitzer conductive cooling alone. A
quasi-steady loop model that includes significant suppression of
thermal conductivity and/or continuous heating of the LT plasma,
presumably by plasma wave turbulence, was proposed to account for
this observation. A more thorough understanding of these phenomena
requires a solution of the time-dependent hydrodynamics of the flaring
plasma. We have embarked on combining our particle acceleration and
transport code with a one-dimensional hydrodynamics code (Mariska et
al. 1989) to simulate the response of the atmosphere to the energy
input during the impulsive and decay phases, and investigate the
effects of such response on the energy transport, X-ray radiation,
and even particle acceleration and plasma heating processes. Current
results from this work in progress will be presented. We will also
compare the results with RHESSI observations and thus put important
constraints on theoretical models.
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.
Bibcode: 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: Observations and Modeling of Solar Flare Doppler-Shift and
Intensity Oscillations
Authors: Mariska, John T.
Bibcode: 2006SPD....37.1307M
Altcode: 2006BAAS...38..241M
Doppler-shift and associated intensity oscillations have been observed
in high-temperature flare emission lines with both the SUMER experiment
on SOHO and the Bragg Crystal Spectrometer (BCS) on Yohkoh. These have
been identified as standing slow-mode waves, leading to the possibility
that modeling of the wave evolution can lead to improved understanding
of the conditions in the flaring structures. In this presentation,
I show some examples of the BCS data and initial results from loop
heating numerical simulations aimed at studying the initiation and
evolution of the oscillations. Many impulsive heating schemes easily
excite oscillations in the loop plasma. A key issue for investigation,
however, is whether detailed geometric information on the flaring
loop or loops coupled with the oscillation observations can critically
constrain the characteristics of the heating.
Title: Characteristics of Solar Flare Doppler-Shift Oscillations
Observed with the Bragg Crystal Spectrometer on Yohkoh
Authors: Mariska, John T.
Bibcode: 2006ApJ...639..484M
Altcode: 2005astro.ph.11070M
This paper reports the results of a survey of Doppler-shift oscillations
measured during solar flares in emission lines of S XV and Ca XIX with
the Bragg Crystal Spectrometer (BCS) on Yohkoh. Data from 20 flares
that show oscillatory behavior in the measured Doppler shifts have
been fitted to determine the properties of the oscillations. Results
from both BCS channels show average oscillation periods of 5.5+/-2.7
minutes, decay times of 5.0+/-2.5 minutes, amplitudes of 17.1+/-17.0
km s-1, and inferred displacements of 1070+/-1710 km, where
the listed errors are the standard deviations of the sample means. For
some of the flares, intensity fluctuations are also observed. These
lag the Doppler-shift oscillations by 1/4 period, strongly suggesting
that the oscillations are standing slow-mode waves. The relationship
between the oscillation period and the decay time is consistent with
conductive damping of the oscillations.
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.
Bibcode: 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: A new method for in-flight intensity calibration of
high-resolution EUV and FUV spectrometers
Authors: Feldman, U.; Landi, E.; Doschek, G. A.; Mariska, J. T.
Bibcode: 2005A&A...441.1211F
Altcode:
We introduce a new technique for the measurement of the in-flight
relative intensity calibration of high resolution spectrometers. This
technique makes use of the free-free radiation in hot, dense active
regions and flares, and combines it with spectral line intensities
in an iterative procedure. After a few iterations, the relative
intensity calibration and the temperature of the emitting plasma are
determined. The application of this technique to the EIS instrument
on board the Solar-B satellite (launch in 2006) is discussed.
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.
Bibcode: 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: Stochastic Particle Acceleration in a Self-Consistent Solar
Flare Atmosphere
Authors: Miller, J. A.; Mariska, J. T.
Bibcode: 2005AGUSMSP41C..02M
Altcode:
We present results from a unified and self-consistent model of particle
acceleration and atmospheric response in impulsive solar flares. In
our model, electrons and ions are stochastically energized from
thermal to relativistic energies on short timescales by cascading
MHD turbulence, which is assumed to have been excited initially
in the coronal region of a flare loop during the primary energy
release phase. The accelerated particles then propagate to the denser
transition region and chromosphere, where they can deposit a large
fraction of their energy and drive the formation of a hydrodynamic
shock that propagates back into the corona. The density enhancements
that accompany this shock in turn modify the particle acceleration
processes in the corona by altering (in a spatially-dependent manner)
the density and Alfvén speed, and hence the acceleration rates and
threshold energies. The two main components of this simulation are
the NRL Dynamic Solar Flux Tube Model code and a spatially-dependent
quasilinear particle acceleration/wave evolution code. As such, it
provides a comprehensive treatment of both macroscopic (chromospheric
evaporation) and microscopic (wave-particle interactions) processes. We
demonstrate the coupling between acceleration and atmospheric response
by presenting simulation results for realistic flare parameters,
and show the importance of including the later process in particle
acceleration studies. We also show that acceleration by cascading
MHD turbulence is able to account for all the major features of flare
energetic particles. This work was supported by NASA grant NAG5-12794.
Title: Nonthermal Velocities in Different Temperature Regions of
the Solar Lower Transition Region
Authors: Akiyama, S.; Doschek, G. A.; Mariska, J. T.
Bibcode: 2005ApJ...623..540A
Altcode:
We analyze the relationship between nonthermal velocities derived from
spectral lines of ions formed at different temperatures in the solar
lower transition region, using spectra from the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) spectrometer on board the
Solar and Heliospheric Observatory (SOHO). We find a high degree of
correlation among nonthermal motions arising at temperatures ranging
from 3×104 to 2.5×105 K over 1" spatial scales
in quiet-Sun regions. We discuss the implications of these results in
terms of the physical nature of the transition region.
Title: Observations of Solar Flare Doppler Shift Oscillations with
the Bragg Crystal Spectrometer on Yohkoh
Authors: Mariska, John T.
Bibcode: 2005ApJ...620L..67M
Altcode: 2005astro.ph..1093M
Oscillations in solar coronal loops appear to be a common
phenomenon. Transverse and longitudinal oscillations have been observed
with both the Transition Region and Coronal Explorer and Extreme
ultraviolet Imaging Telescope imaging experiments. Damped Doppler
shift oscillations have been observed in emission lines from ions
formed at flare temperatures with the Solar Ultraviolet Measurements
of Emitted Radiation spectrometer. These observations provide valuable
diagnostic information on coronal conditions and may help refine our
understanding of coronal heating mechanisms. I have initiated a study
of the time dependence of Doppler shifts measured during flares with
the Bragg Crystal Spectrometer (BCS) on Yohkoh. This Letter reports
the detection of oscillatory behavior in Doppler shifts measured as
a function of time in the emission lines of S XV and Ca XIX. For
some flares, both lines exhibit damped Doppler shift oscillations
with amplitudes of a few kilometers per second and periods and decay
times of a few minutes. The observations appear to be consistent with
transverse oscillations. Because the BCS observed continuously for
almost an entire solar cycle, it provides numerous flare data sets,
which should permit an excellent characterization of the average
properties of the oscillations.
Title: The Solar-B EUV imaging spectrometer and its science goals
Authors: Culhane, J. L.; Harra, L. K.; Doschek, G. A.; Mariska, J. T.;
Watanabe, T.; Hara, H.
Bibcode: 2005AdSpR..36.1494C
Altcode:
The Solar-B mission includes an Extreme-UV Imaging Spectrometer
(EIS). It detects photons in the ranges 170-210 and 250-290 Å which
include emission lines from several highly ionised species that exist
at temperatures log T = 4.7, 5.6, 5.8, 5.9 and 6.0-7.3 K. In this
paper, we will describe the design and operation of the instrument
and present its performance parameters, e.g., spectral and spatial
resolution and sensitivity. Preliminary results of recent calibration
measurements will be described. Its role in the Solar-B mission will
be illustrated with reference to several key science topics that the
EIS is expected to address. The anticipated observing strategy for
the first three months of the mission will be outlined.
Title: A Unified Model of Particle Acceleration and Atmospheric
Response in Solar Flares
Authors: Miller, J. A.; Mariska, J. T.
Bibcode: 2004AGUFMSH13A1149M
Altcode:
We present initial results from a unified and self-consistent model
of particle acceleration and atmospheric response in impulsive
solar flares. In our model, electrons and ions are stochastically
energized from thermal to relativistic energies on short timescales
by cascading MHD turbulence, which is assumed to have been excited
initially in the coronal region of a flare loop during the primary
energy release phase. The accelerated particles then propagate to the
denser transition region and chromosphere, where they can deposit a
large fraction of their energy and drive the formation of a hydrodynamic
shock that propagates back into the corona. The density enhancements
that accompany this shock in turn modify the particle acceleration
process in the corona. The two main components of the simulation are
the NRL Dynamic Solar Flux Tube Model code and a spatially-dependent
quasilinear particle acceleration/wave evolution code. We demonstrate
through these realistic simulations that stochastic acceleration by MHD
turbulence is able to account for all the major features of solar flare
energetic particles. This work was supported by NASA grant NAG5-12794.
Title: The Relationship of the Chromosphere to the Lower Solar
Transition Region
Authors: Doschek, G. A.; Mariska, J. T.; Akiyama, S.
Bibcode: 2004ApJ...609.1153D
Altcode:
We examine the intensity correlations among lower transition region
emission lines of N III, N IV, N V, O II, O III, O IV, O V, S IV, and S
V. We find strong intensity correlations, with 1 σ deviations in line
intensity ratios less than about 35% on spatial scales of 1". For strong
lines the percent deviations are significantly less than this. The line
intensities were obtained from the Solar Ultraviolet Measurement of
Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric
Observatory (SOHO). We find a dependence of the O II/O III and O V/N V
ratios with intensity. The degree of correlation we obtain on arcsecond
spatial scales is consistent with size scales for the basic transition
region structures that are significantly less than 1" (730 km).
Title: Observations of Doppler Shift Oscillations with the Bragg
Crystal Spectrometer on Yohkoh
Authors: Mariska, J. T.
Bibcode: 2004AAS...204.5410M
Altcode: 2004BAAS...36..759M
Oscillations in solar coronal loops appear to be a common
phenomenon. Transverse and longitudinal oscillations have been observed
with both the TRACE and EIT imaging experiments. Damped Doppler shift
oscillations have been observed in emission lines from ions formed at
flare temperatures with the SUMER experiment on SOHO. These observations
provide valuable diagnostic information on coronal conditions and may
help refine our understanding of coronal heating mechanisms. We have
initiated a study of the time dependence of Doppler shifts measured
during flares with the Bragg Crystal Spectrometer on Yohkoh. In this
presentation, we report some initial results on Doppler shifts as a
function of time measured in the emission lines of \ion{S}{15} and
\ion{Ca}{19}. For some flares, both lines exhibit damped Doppler shift
oscillations with amplitudes of a few km s-1 and periods
and decay times of a few minutes.
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
Bibcode: 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: Solar Extreme Ultraviolet and X-ray Irradiance Variations
Authors: Woods, Tom; Acton, Loren W.; Bailey, Scott; Eparvier, Frank;
Garcia, Howard; Judge, Darrell; Lean, Judith; Mariska, John T.;
McMullin, Don; Schmidtke, Gerhard; Solomon, Stanley C.; Tobiska,
W. Kent; Warren, Harry P.; Viereck, Rodney
Bibcode: 2004GMS...141..127W
Altcode:
The solar extreme ultraviolet (EUV) radiation at wavelengths shortward
of 120 nm is a primary energy source for planetary atmospheres and
is also a tool for remote sensing of the planets. For such aeronomic
studies, accurate values of the solar EUV irradiance are needed over
time periods of minutes to decades. There has been a variety of solar
EUV irradiance measurements since the 1960s, but most of the recent
observations have been broadband measurements in the X-ray ultraviolet
(XUV) at wavelengths shortward of 35 nm. A summary of the solar EUV
irradiance measurements and their variability during the last decade is
presented. One of the most significant new solar irradiance results is
the possibility that the irradiance below 20 nm is as much as a factor
of 4 higher than the reference Atmospheric Explorer E (AE-E) spectra
established in the 1970s and 1980s. The primary short-term irradiance
variability is caused by the solar rotation, which has a mean period
of 27 days. The primary long-term variability is related to the solar
dynamo and is known best by the 11-year sunspot cycle. The solar cycle
variability as a function of wavelength can be characterized as 20% to
70% between 120 and 65 nm and as a factor of 1.5 to 10 between 65 and 1
nm. The variability of the total solar EUV irradiance, integrated from
0 to 120 nm, is estimated to be 30-40% for a large 27-day rotational
period and a factor of about 2 for the 11-year solar cycle during the
recent, rather active, solar cycles.
Title: NRLEUV 2: A New Model of Solar EUV Irradiance Variability
Authors: Warren, H.; Mariska, J.
Bibcode: 2004cosp...35.1109W
Altcode: 2004cosp.meet.1109W
NRLEUV represents an independent approach to modeling the Sun's
EUV irradiance and its variability. Our model utilizes differential
emission measure distributions derived from spatially and spectrally
resolved solar observations, full-disk solar images, and an a database
of atomic physics parameters to calculate the solar EUV irradiance. Our
initial version of the model made use of Skylab spectra and a crude
partitioning of solar features into quiet Sun, coronal hole, and active
region components. Despite the simplicity of our initial effort, our
model was able to reproduce the observed EUV irradiance variability
at many wavelengths as well as most existing models based directly on
observations. In this presentation we will discuss a revised version of
the model that is based on extensive observations with the spectrometers
on SOHO, utilizes a continuous distribution of emission measures, and
includes the most comprehensive database of atomic physics parameters
available. Comparisons between our model, other empirical irradiance
models, and recent irradiance observations will also be discussed.
Title: The spatial correlation of the non-thermal velocities for O
IV and Si IV in the lower transition region
Authors: Akiyama, S.; Doschek, G. A.; Mariska, J. T.
Bibcode: 2003AdSpR..32.1137A
Altcode:
We analyze the spatial relationship between non-thermal velocities
derived from spectral lines of O IV. λ1401.16 (1.6×105 K) and Si
IV λ1402.77 (6.3x10 4 K) in the solar lower transition
region. The lines formed at different temperatures are observed
simultaneously and at the same locations on the solar disk by the Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer
on board the Solar and Heliospheric Observatory (S OHO). In order to
improve the accuracy of the non-thermal velocities determined from the
full width at half maximum (FVJHM) intensities of the lines, we select
data with sufficient counting statistics such that the uncertainty
of the non-thermal velocity is less than 10 % of its value derived
from the FWHMs. The spatial relationship between lines of O IV and
Si IV shows a strong correlation. The correlation coefficient of the
turbulent velocity is 0.856 for bright quiet Sun regions.
Title: Evolving Active Region Loops Observed with the Transition
Region and Coronal explorer. II. Time-dependent Hydrodynamic
Simulations
Authors: Warren, Harry P.; Winebarger, Amy R.; Mariska, John T.
Bibcode: 2003ApJ...593.1174W
Altcode:
Observations with the Transition Region and Coronal Explorer (TRACE)
have revealed a new class of active region loops. These loops have
relatively flat filter ratios, suggesting approximately constant
temperatures near 1 MK along much of the loop length. The observed
apex intensities are also higher than static, uniformly heated loop
models predict. These loops appear to persist for much longer than
a characteristic cooling time. Recent analysis has indicated that
these loops first appear in the hotter Fe XV 284 Å or Fe XII 195
Å filters before they appear in the Fe IX/Fe X 171 Å filter. The
delay between the appearance of the loops in the different filters
suggests that the loops are impulsively heated and are cooling when
they are imaged with TRACE. In this paper we present time-dependent
hydrodynamic modeling of an evolving active region loop observed with
TRACE. We find that by modeling the loop as a set of small-scale,
impulsively heated filaments we can generally reproduce the spatial
and temporal properties of the observed loop. These results suggest
that both dynamics and filamentation are crucial to understanding the
observed properties of active region loops observed with TRACE.
Title: Evolving Active Region Loops Observed With TRACE
Authors: Warren, H. P.; Winebarger, A. R.; Mariska, J. T.
Bibcode: 2003SPD....34.1007W
Altcode: 2003BAAS...35Q.826W
Recent observations with TRACE have revealed a new class of active
region loops with very interesting properties. These loops have
relatively flat filter ratios, suggesting approximately constant
temperatures along much of the loop length, and large densities relative
to the predictions of static loop models. Recent analysis has indicated
that these loops first appear in the hotter filters before they appear
in the cooler filters. The delay between the appearance of the loops in
the different filters suggests that the loops are impulsively heated and
are cooling when they are imaged with TRACE. In this paper we present
time-dependent hydrodynamic modeling of evolving active region loops
observed with TRACE. We find that by modeling the loops as small-scale,
impulsively heated filaments we can generally reproduce the spatial
and temporal properties of the observations. These results suggest
that both dynamics and filamentation are crucial to understanding the
observed properties of active region loops observed with TRACE. This research has been funded by the NASA SR&T and Sun-Earth
Connection Guest Investigator programs.
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.
Bibcode: 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. 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: Observing the Dynamic Corona: Diagnostics to Determine
Coronal Heating
Authors: Winebarger, A. R.; Warren, H. P.; Mariska, J. T.
Bibcode: 2003SPD....34.1008W
Altcode: 2003BAAS...35R.826W
High resolution observations made with TRACE have uncovered a dynamic
solar corona. Many of these observations indicate that TRACE is
imaging cooling loops (i.e., the loop appears in the TRACE filter
sensitive to hotter plasma before it appears in the cooler TRACE
filters.) Significant information can be garnered from the TRACE
observations. For instance, the delay between the appearance of loop
in different filters provides information on the cooling time of the
plasma and, hence, the total energy deposited in the loop. The cooling
time also indicates a density and hence can be used to determine the
degree of filamentation within a loop. TRACE observations of cooling
loops, however, tell us little about the spatial and temporal scales
for energy deposition. In this talk, we will discuss other diagnostics
necessary to pinpoint the magnitude, duration, and location of the
heating. The purpose of this talk is to establish the criteria of the
necessary spatial, spectral, and temperature resolution necessary to
discriminate between the coronal heating theories.
Title: Magnetic Modulation of Solar 304 Å Irradiance
Authors: Lean, J. L.; Mariska, J. T.; Warren, H. P.; Woods, T. N.;
Eparvier, F. G.; McMullin, D. R.; Judge, D. L.; Newmark, J. S.;
Viereck, R. A.
Bibcode: 2003SPD....34.1902L
Altcode: 2003BAAS...35..842L
Solar 304 Å irradiance is an important source of heating and ionization
in the Earth's upper atmosphere. Because only intermittent observations
exist prior to solar cycle 23, the absolute levels and solar cycle
variability of 304 Å irradiance are uncertain by a factor of two,
based on the range of estimates from four current EUV irradiance
variability models. Large active regions are a significant source of
304 Å radiation but their characteristics are not well specified,
with contrasts reported in the range of two to ten. Statistical
quantification of the role of small scale active regions and network
is also lacking. During solar cycle 23, three different instruments
are observing the Sun's 304 Å radiation concurrently. The EIT on SOHO
records the brightness distribution on the solar disk in a 20 Å band,
SEM on SOHO monitors the disk-integrated emission in an 80 Å band,
and the SEE grating spectrometer on the TIMED spacecraft recently began
observing EUV irradiance spectra with 4 Å resolution. We calculate
daily histograms of the brightness distributions of EIT images after
adjustments for various instrumental effects. Deconstructions of the
histograms permit statistical characterizations of magnetic sources
of 304 Å irradiance variability during solar cycle 23, in terms
of fractional disk areas and contrasts. We also study center-to-limb
variations. The calculations provide independent irradiance variability
estimates for comparison with the SEM and SEE direct irradiance
observations, and the models. We utilize the source characterizations
to revise the NRLEUV model, the present version of which estimates 304
Å emission by assuming that a bright active region has a contrast of
ten, and that source region evolution is temporally similar to the Mg
chromospheric irradiance index. Funded by NASA SEC GI Program.
Title: Transition Region and Coronal Explorer and Soft X-Ray Telescope
Active Region Loop Observations: Comparisons with Static Solutions
of the Hydrodynamic Equations
Authors: Winebarger, Amy R.; Warren, Harry P.; Mariska, John T.
Bibcode: 2003ApJ...587..439W
Altcode:
Active region coronal loop observations with broadband X-ray instruments
have often been found to be consistent with the predictions of static
loop models. Recent observations in the EUV, however, have discovered
a class of active region loops that are difficult to reconcile with
static loop models. In this paper, we take a comprehensive look at
how coronal loops compare with static models. We select 67 loops with
a large range of apex temperatures and half-lengths observed with
either the Transition Region and Coronal Explorer or the Soft X-Ray
Telescope. We compare these observations to static loop models using
both uniform and nonuniform heating. We find that only 2 of the 67
loops are fully consistent with static solutions with uniform heating
and a filling factor of unity. We further find that long, cool (<3
MK) loops are as much as 2500 times ``overdense,'' while short, hot
(>3 MK) loops are as much as 63 times ``underdense'' when compared
to the static solutions with uniform heating. We then consider the
possibility that the disparity in the density could be due to steady,
nonuniform heating along the loop and find that footpoint heating can
increase densities only by a factor of 3 over density solutions with
uniform heating while loop-top heating results in density solutions
that are, at most, a factor of 2.5 smaller than the density solutions
with uniform heating. Only 19 of the 67 loops in this data set could be
fully consistent with hydrodynamic solutions with steady heating. Hence,
we conclude that static loop models are poor representations of most
active region loops.
Title: A new model of solar EUV irradiance variability 2. Comparisons
with empirical models and observations and implications for space
weather
Authors: Lean, J. L.; Warren, H. P.; Mariska, J. T.; Bishop, J.
Bibcode: 2003JGRA..108.1059L
Altcode:
Motivated by the need for reliable specification of the Sun's
electromagnetic radiation in the extreme ultraviolet (EUV)
spectrum, we have developed a new model of solar EUV irradiance
variability at wavelengths from 50 to 1200 Å. Solar images are
used to quantify changes in the sources of EUV irradiance during the
solar cycle. Optically thin EUV emission line fluxes are estimated
from differential emission measures (DEMs) that characterize the
properties of the solar atmosphere in the source regions, while fluxes
for optically thick lines are modeled directly by specifying the source
region contrasts. We compare the new model, NRLEUV, with three different
empirical models of solar EUV irradiance since 1975. For solar cycles
21 and 22, NRLEUV predicts overall lower EUV irradiances and smaller
solar cycle variability than the empirical models. The average total
EUV energy at wavelengths from 50 to 1050 Å is 2.9 mW m-2,
smaller than the HFG, EUVAC, and SOLAR2000 models for which average
energies are 3.7, 4.3, and 5.6 mW m-2, respectively. These
differences have distinct wavelength dependencies. The solar cycle
variation in total EUV energy is 1.9 for NRLEUV compared with 2.7, 2.9,
and 2.3 for HFG, EUVAC, and SOLAR2000. Here, too, the differences are
wavelength dependent. We compare both the NRLEUV and the empirically
modeled EUV irradiances with selected wavelength bands and emission
lines measured during 4 years in cycle 21 by Atmospheric Explorer-E
(AE-E) and two broad bands at 170-200 and 260-340 Å measured in
cycle 23 by the Solar X-Ray Photometer (SXP) on the Student Nitric
Oxide Experiment (SNOE) and the Solar EUV Monitor (SEM) on the Solar
and Heliospheric Observatory (SOHO), respectively. The NRLEUV model
reproduces the variations observed during solar rotation better than, or
as well as, the empirical models. Comparisons of solar cycle variations
are more ambiguous because undetected instrumental drifts can cause
spurious trends in the observations over these longer timescales. Drifts
in the AE-E instruments may explain why the HFG and EUVAC models, which
are based on parameterizations of these data, have larger solar cycle
variations than NRLEUV. We assess the implications for space weather
of the significant differences among the modeled EUV irradiances by
using the Atmospheric Ultraviolet Radiance Integrated Code (AURIC)
to quantify corresponding differences in upper atmosphere energy
deposition and photoionization rates.
Title: Overview of the SDO Extreme ultraviolet Variability Experiment
(EVE)
Authors: Woods, T. N.; Eparvier, F. G.; Rottman, G. J.; Judge,
D. L.; McMullin, D. R.; Lean, J. L.; Mariska, J. T.; Warren, H. P.;
Berthiaume, G. D.; Bailey, S. M.; Viereck, R. A.; Tobiska, W. K.;
Fuller-Rowell, T. J.; Sojka, J. J.
Bibcode: 2002AGUFMSH21C..02W
Altcode:
The NASA Solar Dynamics Observatory (SDO), with its launch in 2007, is
the first mission for the NASA Living With a Star (LWS) program. The
SDO mission will provide measurements and modeling of the solar
radiation and dynamics that can disturb Earth's environment. The
Extreme ultraviolet Variability Experiment (EVE) is one of the
three instrument suites on SDO. The EVE measures the solar extreme
ultraviolet (EUV) irradiance with unprecedented spectral resolution,
temporal cadence, accuracy, and precision. Furthermore, the EVE program
will incorporate physics-based modeling to advance the understanding
of the solar EUV irradiance variations based on the activity of solar
magnetic features. The EVE instrument consists of three subsystems. The
Multiple EUV Grating Spectrograph (MEGS) measures the 4-120 nm spectral
irradiance with 0.1 nm spectral resolution. The Optics Free Spectrometer
(OFS), being ionization cells, provides daily, in-flight calibrations
for the MEGS channels. The EUV Spectrophotometer (ESP) completes the
spectral coverage at 0.1-5 nm and 119-125 nm and provides additional
MEGS calibrations. Collectively, the EVE instrument measures the
solar EUV irradiance from 0.1 to 125 nm with 7% accuracy and 4%
long-term precision.
Title: Ionospheric and dayglow responses to the radiative phase of
the Bastille Day flare
Authors: Meier, R. R.; Warren, H. P.; Nicholas, A. C.; Bishop, J.;
Huba, J. D.; Drob, D. P.; Lean, J. L.; Picone, J. M.; Mariska, J. T.;
Joyce, G.; Judge, D. L.; Thonnard, S. E.; Dymond, K. F.; Budzien, S. A.
Bibcode: 2002GeoRL..29.1461M
Altcode: 2002GeoRL..29j..99M
The Sun's Bastille Day flare on July 14, 2000 produced a variety of
geoeffective events. This solar eruption consisted of an X-class flare
followed by a coronal mass ejection that produced a major geomagnetic
storm. We have undertaken a study of this event beginning with an
analysis of the effects of the radiative phase of the flare on the
dayglow and the ionosphere. The key new enabling work is a novel
method of evaluating the X-ray and extreme ultraviolet (EUV) solar
spectral irradiance changes associated with the flare. We find that
the solar radiative output enhancements modeled during the flare are
consistent with measurements of both solar EUV irradiance and far UV
Earth thermospheric dayglow. We use the SAMI2 model to predict global
ionospheric changes along a magnetic meridian that show significantly
different northern and southern effects, suggesting that flares can
be used to study ionospheric dynamics.
Title: The Relationship between SiIV and OIV for Non-thermal
Turbulenc Velocity
Authors: Akiyama, S.; Doschek, G. A.; Mariska, J. T.
Bibcode: 2002AAS...200.3810A
Altcode: 2002BAAS...34..700A
We report nonthermal turbulence velocities of spectral lines of O IV
λ 1401.16 and Si IV λ 1402.77 observed with SUMER spectrometer abord
SOHO spacecraft. In ionization equilibrium, the electron temperatures
of these ions are 1.6X105 and 6.3X104 K,
respectively. Although their spectral line intensities and ratio are
vely similar at the quiet area in the lower solar transition region
in spite of differential emission measures (Doschek & Mariska
2001). Since these observations help to understand the physical
property and the morphology of the transition region, we take note of
nonthermal turbulence velocities in this study and compare O IV with
Si IV lines using by the observational data of Doschek & Mariska
(2001). In order to improve in accuracy, we select the points which
error of turbulence velocity are less then 10 % of turbulence velocity
both O IV and Si IV line. In the result, the correlation of turbulence
velocity between O IV and Si IV is 0.846, we can see strong correlation
at the bright points in the quiet region. We discuss the implications
of these results for the physical conditions of the transition region.
Title: The Structure of the Lower Solar Transition Region
Authors: Doschek, G. A.; Mariska, J. T.; Akiyama, S.
Bibcode: 2002AAS...200.3811D
Altcode: 2002BAAS...34Q.700D
Recent high-spatial resolution monochromatic images obtained from
the SUMER spectrometer on SOHO have shown that the lower transition
region ( 2 x 104 - 2 x 105 K) is composed of
small loops and knots of emission (seen on the disk), and thread-like
structures (seen above the limb) (Feldman, Widing, & Warren, ApJ,
522, 1133 (1999)). The structures seen in images of different spectral
lines formed at significantly different electron temperatures look
quite similar. However, because the temperatures are different, the
emitting plasma cannot be the same for the different images. What is
the physical relationship between lower transition region structures
that appear in lines formed at different temperatures? The answer to
this question can begin to be addressed by examining SUMER spectra of
lower transition region lines formed at different temperatures that
appear on the same SUMER exposures. In this case the spatial region on
the Sun viewed in both spectral lines is precisely the same, and both
lines are recorded simultaneously. The intensity relationship between
lines of Si IV (6.3 x 104 K) and O IV (1.3 x 105
K) for such spectra has already been discussed by Doschek & Mariska
(ApJ, 560, 420 (2001)), and a strong correlation between Si IV and O IV
intensities was found. We will discuss an extension of this work to line
groups of, (1) O II, O III (3 x 104, 9.0 x 104
K), (2) C IV, S V, O IV (1 x 105, 1.6 x 105,
1.6 x 105 K), and (3) N IV, O V (1.4 x 105,
2.5 x 105 K). The O II, O III comparison does not show
the strong correlation found for higher temperature lines, indicating
that chromospheric structures are significantly different from lower
transition region structures. The S V and O IV temperature regions
strongly overlap but are not identical. Nevertheless, the intensity
correlation is quite high. This work was supported by NASA solar
physics Guest Investigator Grant S137816.
Title: New Determinations of Solar EUV Irradiance Variability for
use in the NRLMSIS Atmospheric Density Specification Model
Authors: Lean, J. L.; Mariska, J. T.; Warren, H. P.; Bishop, J.;
Picone, J. M.
Bibcode: 2002AGUSMSH51B..03L
Altcode:
A variety of space weather models require knowledge of the Sun' s EUV
spectral irradiance because this radiation is the predominant source of
upper atmosphere heating and ionization. Lacking reliable observations
to specify the considerable variability of the EUV spectrum during the
solar activity cycle, space weather research and operational models
continue to use the 10.7 cm radio flux as a proxy for variations in EUV
radiation, even though its shortcomings have been recognized for some
time. For example, the largest source of error in special perturbations
propagation of spacecraft orbits is the parameterization of solar
EUV irradiance in the density models that the codes use to estimate
drag. The strongest lines in the EUV spectrum are formed in the Sun'
s upper chromosphere whereas the 10.7 cm flux is formed primarily in the
hotter corona. We have recently developed a composite chromospheric EUV
irradiance index by combining multiple space and ground-based datasets,
and are reformulating NRL' s upper atmosphere neutral density model
(NRLMSISE-00) to accommodate this new index. In a parallel effort
we have developed a new physics-based irradiance variability model
(NRLEUV) that calculates the EUV spectrum independently of direct
spectral irradiance observations. The model utilizes solar images
to extract information about the fraction of the solar atmosphere
occupied by different active, network and quiet regions, and coronal
holes. Representative differential emission measures are constructed
for each of the features and the EUV disk-integrated spectrum is
calculated by combining the emission measures with theoretically
determined values of plasma emissivity. We use a parameterized
version of the NRLEUV model that includes both chromospheric and
coronal indices to calculate variations during past solar cycles in
the total EUV energy incident at the top of the earth' s atmosphere,
and at selected altitude in the range 100 to 1000 km, for use in future
reformulations of NRLMSIS. We compare the new chromospheric index
and the physics-based EUV irradiance model products with existing EUV
model estimates derived from parameterizations of direct observations,
and describe how NRLMSIS will incorporate these new determinations of
the EUV irradiance to provide an improved density specification for
space weather applications.
Title: Spectral observations of quiescent EUV loops
Authors: Winebarger, A. R.; Mariska, J. T.; Warren, H. P.
Bibcode: 2002AAS...200.1603W
Altcode: 2002BAAS...34R.667W
Recent TRACE observations have detected a class of cool, quiescent
loops that are inconsistent with hydrostatic loop models. These loops
appear static, isothermal (1 MK), and overdense. In this talk, we
present co-aligned TRACE, SUMER and CDS observations of several EUV
loops. Every loop observed shows evidence of significant downflows
along the loop. We confirm that the temperature along some of the
observed loops is sharply peaked around 1 MK. In other loops, however,
we find evidence for emission at hotter (2 MK) and cooler (0.2 MK)
temperatures; this emission may be co-spatial with the loops observed
in TRACE. These observations suggest that non-hydrostatic models are
necessary to describe the loops.
Title: Energetics of Explosive Events Observed with SUMER
Authors: Winebarger, Amy R.; Emslie, A. Gordon; Mariska, John T.;
Warren, Harry P.
Bibcode: 2002ApJ...565.1298W
Altcode:
Observations of solar chromosphere-corona transition region plasma show
evidence of small-scale, short-lived dynamic phenomena characterized
by significant nonthermal broadening and asymmetry in the wings
of spectral line profiles. These impulsive mass motions (explosive
events) are thought to be the product of magnetic reconnection and to
be similar in driving mechanism (though larger in size) to nanoflares,
the small-scale events proposed to heat the corona. In this paper,
we present a statistical analysis of the energetics of explosive
events to address the viability of the nanoflare heating theory. We
consider high spectral, spatial, and temporal resolution spectra of the
C III λ977, N IV λ765, O VI λ1032, and Ne VIII λ770 lines observed
with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
telescope and spectrometer. Each line profile exhibiting explosive event
characteristics was analyzed using the velocity differential emission
measure (VDEM) technique. A VDEM is a measure of the emitting power
of the plasma as a function of its line-of-sight velocity and hence
provides a method of accurately measuring the energy flux associated
with an explosive event. We find that these events globally release
~4×104 ergs cm-2 s-1 toward both the
corona and chromosphere. This implies that explosive events themselves
are not energetically significant to the solar atmosphere. However, the
distribution of these explosive events as a function of their energy
has a power-law spectral index of α=2.9+/-0.1 for the energy range
1022.7-1025.1 ergs. Since α is greater than 2,
the energy content is dominated by the smallest events. Hence, if this
distribution is representative of the size distribution down to lower
energy ranges (~1022 ergs), such small and (currently)
undetectable events would release enough energy to heat the solar
atmosphere.
Title: The spatial correlation between the non-thermal velocities
of different lines in the solar lower transition region
Authors: Akiyama, S.; Doschek, G.; Mariska, J.
Bibcode: 2002cosp...34E2769A
Altcode: 2002cosp.meetE2769A
The physical relationship between different temperature regions of
the solar transition region is unclear. In an attempt to understand
this relationship, we analyze SUMER/SOHO spectra of lines formed at
different temperatures that are observed simultaneously at the same
locations on the solar disk. The present work concerns the relationship
in quiet Sun regions among non-thermal turbulent velocities measured in
several spectral lines. For each line, the velocity is determined from
the full width at half maximum intensity. To improve the accuracy of
the line width measurements, we select data with counting statistics
such that the uncertainty in the turbulent velocity is less than 10%
of the turbulent velocity. The spatial relationship between lines of
O IV1401.16 (1.6 ×105 K) and Si IV1402.77 (6.3 × 104 K) for such
spectra shows a strong correlation. The correlation coefficient of
the turbulent velocity between O IV and Si IV is 0.784 for bright
quiet Sun regions. In this poster we will discuss an extension of this
work to line groups of (1) O II, O III (3.2 × 104 , 1.0 × 105 K),
(2) N IV, S V, O IV (1.3 × 105 , 1.4 × 105 1.6 × 105 K). The N IV,
S V, O IV comparisons also show the correlation. We present these and
other results, and discuss the implications for the physical nature
of the transition region.
Title: Publicly Available Numerical Codes for Modeling the X-ray
and Microwave Emissions from Solar and Stellar Activity
Authors: Holman, G. D.; Mariska, J. T.; McTiernan, J. M.; Ofman, L.;
Petrosian, V.; Ramaty, R.
Bibcode: 2001AAS...199.9302H
Altcode: 2001BAAS...33.1444H
We have posted numerical codes on the Web for modeling the
bremsstrahlung x-ray emission and the gyrosynchrotron radio emission
from solar and stellar activity. In addition to radiation codes,
steady-state and time-dependent Fokker-Planck codes are provided for
computing the distribution and evolution of accelerated electrons. A
1-D hydrodynamics code computes the response of the stellar atmosphere
(chromospheric evaporation). A code for modeling gamma-ray line
spectra is also available. On-line documentation is provided for each
code. These codes have been developed for modeling results from the
High Energy Solar Spectroscopic Imager (HESSI) along with related
microwave observations of solar flares. Comprehensive codes for
modeling images and spectra of solar flares are under development. The
posted codes can be obtained on NASA/Goddard's HESSI Web Site at
http://hesperia.gsfc.nasa.gov/hessi/modelware.htm This work is supported
in part by the NASA Sun-Earth Connection Program.
Title: The Physics of the Solar Lower Transition Region
Authors: Doschek, G. A.; Mariska, J. T.
Bibcode: 2001ApJ...560..420D
Altcode:
We discuss quiet-Sun intensities of spectral lines of O IV λ1401.16
and Si IV λ1402.77, their ratio, and their relation to expected
properties of the lower solar transition region. The data consist
of simultaneous measurements of the two line intensities for
16,988 pixels with spatial dimensions of 1" square obtained by the
Solar Ultraviolet Measurement of Emitted Radiation spectrometer on
the Solar and Heliospheric Observatory spacecraft. In ionization
equilibrium, the electron temperatures of maximum concentration
of the two ions are 1.6×105 and 6.3×104 K,
respectively. Assuming ionization equilibrium, the line intensity
ratio is directly proportional to the emission measure ratio between
plasma at these temperatures. Thus, the observations represent 16,988
snapshots of two temperature regions of the differential emission
measure at arcsecond spatial scales in the quiet Sun. We derive an
average quiet-Sun λ1401.16/λ1402.77 ratio, acquired from observations
over 3 hr and a 30''×290'' spatial region,
of 0.267+/-0.050. The 1 σ deviation of this ratio is only 20%,
but it is about 2.4 times greater than expected purely from counting
statistics. We also find that the ratio is about 20% smaller for the
most intense features in the spectra. From analysis of another ratio,
i.e., O IV λ1399.77/O IV λ1401.16, we argue that this decrease could
be due to a higher electron density in the intense features relative
to the lower intensity features. We discuss the implications of these
observations for understanding the morphology of the transition region.
Title: A new model of solar EUV irradiance variability: 1. Model
formulation
Authors: Warren, H. P.; Mariska, J. T.; Lean, J.
Bibcode: 2001JGR...10615745W
Altcode:
We present a new model of solar irradiance variability at extreme
ultraviolet wavelengths (EUV, 50-1200 Å). In this model, quiet Sun,
coronal hole, and active region intensities for optically thin emission
lines are computed from emission measure distributions determined
from spectrally and spatially resolved observations. For optically
thick emission lines and continua, empirical values are used. The
contribution of various solar features to the spectral irradiance
variability is determined from a simple model of limb-brightening
and full-disk solar images taken at the Big Bear Solar Observatory
and by the Soft X-Ray Telescope on Yohkoh. To extend our irradiance
model beyond the time period covered by the available images, we
use correlations with proxies for solar activity. Comparisons with
the available irradiance data from the Atmospheric Explorer E (AE-E)
spacecraft show that our model is capable of reproducing the rotational
modulation of the EUV irradiance near solar maximum. The AE-E data,
however, show systematically more solar cycle variability than our
model estimates.
Title: Solar Flare Particle Acceleration and Atmospheric Response
Authors: Miller, J. A.; Mariska, J. T.
Bibcode: 2001AGUSM..SH31A09M
Altcode:
We present initial results from a self-consistent simulation of particle
acceleration and atmospheric heating during impulsive solar flares. The
simulation code consists of two main components, the UAH SDSPAC
(Spatially-Dependent Stochastic Particle Acceleration Code) and the NRL
DSFTM (Dynamic Solar Flux Tube Model) code, together with an interface
that allows these two components to communicate. Particle acceleration
occurs via cascading MHD turbulence. MHD turbulence (consisting of an
admixture of fast mode and Alfvén waves) is generated at large scales
in the corona and subsequently cascades through the inertial range and
into the dissipation range, where it stochastically accelerates both
ambient electrons and protons via transit-time and cyclotron resonance,
respectively. Both species are energized from thermal to relativistic
energies on subsecond timescales. Some of the energetic particles
then escape from the corona and enter the chromosphere, where they
thermalize through Coulomb collisions. The heated chromosphere then
expands into the corona, where the increased density and temperature
greatly affect the efficiency of the acceleration process. The
highly nonlinear interaction between the acceleration process and
the atmospheric response is described by a combined quasilinear and
hydrodynamic simulation, based upon the two previously-employed codes
above. This is, to our knowledge, the first simulation that acurately
takes into account both the micro- and macro-physics of particle
acceleration. We present preliminary results such as spatially-dependent
energetic particle distributions, coronal temperatures, and densities,
and also discuss their application to the spatially-resolved hard and
soft X-ray spectra to be obtained from HESSI. This work is supported
by NASA Solar Physics SR&T grant NAG5-8480.
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.
Bibcode: 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: Ionospheric and Thermospheric Response to Solar Activity on
July 14, 2000.
Authors: Nicholas, A. C.; Meier, R. R.; Thonnard, S. E.; Dymond,
K. F.; Budzien, S. A.; Mariska, J. T.; McCoy, R. P.
Bibcode: 2001AGUSM..SA51A07N
Altcode:
With the launch of the LORAAS sensor aboard the STP/P91-1 ARGOS mission
and the follow-on UV sensors on DMSP missions covering the next decade,
the scientific and operational communities will be able to assess
quantitatively the response of the upper atmosphere to solar and
geomagnetic forcing. Coincident observations of solar activity by the
LASCO/EIT, CELIAS and SEM instruments aboard SOHO and of the resulting
disturbances near Earth by WIND and ACE are analyzed. We report our
continuing investigation of the relationships among these sets of
observations to determine experimentally the timing and intensity of
the thermospheric and ionospheric response to solar-induced geomagnetic
forcing. We will focus on the sequence of events beginning with the
July 14, 2000 solar flare and ensuing coronal mass ejection.
Title: Ionospheric and Thermospheric Effects During the Initial
Radiative Phase of the Bastille Day Event
Authors: Meier, R. R.; Drob, D. P.; Nicholas, A. C.; Bishop, J.;
Picone, J. M.; Thonnard, S. E.; Dymond, K. F.; Budzien, S. A.; Lean,
J.; Mariska, J. T.; Huba, J. D.; Joyce, G.; Warren, H. P.; Judge, D. L.
Bibcode: 2001AGUSM..SA51A08M
Altcode:
Increases in the solar EUV and X-ray irradiance during a solar flare
can produce enhanced ionization and heating in the terrestrial
ionosphere. The resulting energetic photoelectrons in turn
cause increases in the far ultraviolet (FUV) dayglow (100 - 150
nm). Enhancements of some 50 per cent had previously been detected
in OGO-4 nadir-viewing data [C B Opal, Space Research XIII, 797,
1973]. Similar enhancements have now been seen in the FUV limb-viewing
dayglow observations from the ARGOS satellite during the Bastille Day
flare (July 14, 2000). Because extinction of the FUV dayglow by O2
prevents seeing below 140 km tangent altitude on the limb, increases
in the dayglow above that altitude must be caused by the component
of the flare spectral irradiance which is deposited there, namely at
wavelengths greater than 20 nm. This conclusion is corroborated by
the observation of the flare at 30.3 nm made by the SEM instrument on
the SOHO satellite. We study this solar-ionospheric connection using
a modified version of the NRL solar spectrum as input to the SAMI2
ionospheric model, and also calculate thermospheric heating rates for
this event.
Title: Spatially-Dependent Stochastic Acceleration in Solar Flares
Authors: Miller, J. A.; Newton, E. K.; Mariska, J.
Bibcode: 2000SPD....31.0248M
Altcode: 2000BAAS...32Q1291M
We present a unified spatially-dependent model for simultaneous ion and
electron acceleration in impulsive solar flares. In this model, both
particle species are stochastically accelerated out of the thermal
distribution and then to relativistic energies via resonance with
cascading low-amplitude MHD Alfven and fast mode waves. The coupled and
nonlinear wave and particle evolution are treated with a quasilinear
simulation, which takes into account additional relevant physical
processes such as Coulomb collisions, particle transport and escape,
wave transport, and the replenishment of the solar flare acceleration
region by a cospatial return current. We demonstrate how electron
and ion fluxes consistent with those from a large impulsive event are
readily obtained in this acceleration scenario, and consider the spatial
dependence of the electron and ion energy-differential distributions. We
conclude with the implications for the spatial dependence of the hard
X-ray emission. Funded by NASA SEC Solar Physics grant NAG5-8480.
Title: Commission 12: Solar Radiation and Structure (Radiation et
Structure Solaires)
Authors: Foukal, Peter; Solanki, Sami; Mariska, J.; Baliunas, S.;
Dravins, D.; Duvall, T.; Fang, C.; Gaizauskas, V.; Heinzel, P.;
Kononovich, E.; Koutchmy, S.; Melrose, D.; Stix, M.; Suematsu, Y.;
Deubner, F.
Bibcode: 2000IAUTA..24...73F
Altcode:
No abstract at ADS
Title: Analyzing the Energetics of Explosive Events Observed by
SUMER on SOHO
Authors: Winebarger, Amy R.; Emslie, A. Gordon; Mariska, John T.;
Warren, Harry P.
Bibcode: 1999ApJ...526..471W
Altcode:
The SUMER spectrometer on SOHO has obtained numerous observations of
optically thin chromosphere-corona transition-region line profiles
with high spatial, spectral, and temporal resolution. Many of these
profiles exhibit asymmetries and broadenings associated with impulsive
mass motions (explosive events) in the solar atmosphere. We present
here a new method of analyzing non-Gaussian line profiles to calculate
the distribution of fluid velocities and hence the associated energy
flux. We illustrate this method through a preliminary analysis
of explosive event line profiles observed by SUMER. We derive the
magnitudes of the energy fluxes directed both toward and away from the
observer, and their (``net flux'') differences. We also identify and
quantify the various components of each (i.e., kinetic, thermal and
nonthermal enthalpy, and the high-energy component associated with
the skewed tail of the distribution). The global energy contribution
of explosive events to the solar atmosphere is then estimated under
two different ``grouping'' assumptions. This preliminary analysis
reveals an average net upward energy flux over the entire Sun of
104-105 ergs cm-2 s-1,
up to an order of magnitude larger than previous estimates based
on characteristic velocities of the fluid. Furthermore, the global
estimate for the separate upward- and downward-directed energy fluxes
is 105-106 ergs cm-2 s-1,
which is comparable to the energy flux required for heating of the quiet
corona and indicates that explosive events may indeed have significant
implications for the energy balance of the chromosphere and corona.
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.
Bibcode: 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: Potential Field Source Surface Simulations of Soft X-ray
Corona Variability During the Solar Cycle
Authors: Lean, J. L.; Wang, Y. -M.; Mariska, J. T.; Acton, L. W.
Bibcode: 1999AAS...194.9208L
Altcode: 1999BAAS...31..987L
Magnetic fields that emerge in the solar photosphere and extend upwards
into the corona are associated with coronal heating. Some studies have
determined empirically that coronal brightness depends directly on
photospheric field strength, whereas others relate the brightness to the
length of the loops or to the sheering of opposite polarity fields. We
use the potential field source surface (PFSS) model of Wang and Sheeley
(ApJ, 392, 310, 1992) to investigate the applicability of a range of
quantitative associations between photospheric magnetic fields and the
global brightness of the non-flaring soft X-ray corona, recorded in full
disk X-rays images made by the SXT on Yohkoh. The model extrapolates all
photospheric magnetic field lines, in both active regions and smaller
scale features, into the corona. For an assigned coronal temperature of
1.5E6 K, the model determines coronal density by assuming hydrostatic
equilibrium along each closed field line and using adopted scaling
laws to relate the footpoint density to the magnetic field and/or
loop length. Integrating the brightness along the line of sight then
permits direct simulation of the independently measured SXT full disk
coronal images. With the NSO Carrington magnetic field maps as input,
the PFSS simulations can account for 85 global X-ray corona during
the six years from 1992 to 1997. This agreement is achieved using
a constant coronal temperature and a function that depends on both
the absolute strength of the photospheric magnetic field footprints,
and on the inverse loop length. Despite the overall good agreement
of the simulations and observations, significant differences occur
during some Carrington rotations. Simulations that utilize inputs
from three independent ground-based observatories (NSO, WSO and MWO)
can also at times differ significantly from each other. NASA Office
of Space Science has funded this work.
Title: A Numerical Package for Modeling Solar Flares and Interpreting
HESSI Data
Authors: Holman, G. D.; Mariska, J. T.; McTiernan, J. M.; Ofman, L.;
Petrosian, V.; Ramaty, R. R.
Bibcode: 1999AAS...194.8008H
Altcode: 1999BAAS...31..966H
HESSI, the High Energy Solar Spectroscopic Imager, will observe the
x-ray and gamma-ray emission from solar flares with an unprecedented
combination of spectral, spatial, and temporal resolution. The
quantitative interpretation of the HESSI data will require a level of
numerical modeling not generally demanded by previous observations. In
view of this, we are developing an integrated package of modular
numeric codes and models for the analysis and interpretation
of these data. The package will focus on the energetic electrons
produced during the impulsive phase of flares. It will compute both
the bremsstrahlung x-ray/gamma-ray emission and the gyrosynchrotron
radio emission from model flare configurations and initial electron
distributions. Steady-state and time-dependent Fokker-Planck codes
will compute the transport of suprathermal electrons. A hydrodynamic
code will compute the response of the flare plasma in the model
configurations. The proposed computational package will allow for
comprehensive modeling of energized electrons in different flare
scenarios. The predicted emissions can be compared directly with
HESSI and radio images and spectra. The package will provide the
necessary framework for comparing electron acceleration models with
HESSI data. This work is supported in part by the NASA Sun-Earth
Connection Program.
Title: Hard and Soft X-Ray Observations of Occulted and Nonocculted
Solar Limb Flares
Authors: Mariska, John T.; McTiernan, James M.
Bibcode: 1999ApJ...514..484M
Altcode:
Using observations from the Yohkoh Bragg Crystal Spectrometer (BCS),
the Soft X-Ray Telescope, and the Hard X-Ray Telescope, we have examined
the properties of 45 limb flares. Twenty-eight of the flares appear
to have most or all of their footpoints occulted by the solar limb,
leaving only soft X-ray emission from a looptop source visible. The
remaining 17 flares have exposed footpoints. In most observational
characteristics, occulted limb flares are indistinguishable from
nonocculted limb flares. There does appear to be some evidence that the
peak temperature observed in the BCS Ca XIX channel is lower by 2-3 MK
in the occulted flares. We also see some tendency for the hard X-ray
spectra averaged over the entire event to exhibit a softer spectral
index in the occulted limb flares. Most of the flares for which it is
possible to measure a peak in the Ca XIX nonthermal broadening velocity
as a function of time show that the peak in the nonthermal broadening
velocity occurs after the first significant hard X-ray peak.
Title: High-Resolution Observations of the Solar Hydrogen Lyman
Lines in the Quiet Sun with the SUMER Instrument on SOHO
Authors: Warren, H. P.; Mariska, J. T.; Wilhelm, K.
Bibcode: 1998ApJS..119..105W
Altcode:
We present high-resolution observations of the higher H Lyman series
lines taken with the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) experiment flown on the Solar and Heliospheric Observatory
(SOHO) spacecraft. We have used systematic observations extending
from disk center to the solar limb to compute average profiles for
representative solar features of the quiet Sun, limb-brightening curves,
and full-disk, quiet-Sun profiles for Lyβ through Lyλ(11) and the
Lyman continuum. The effects of radiative transfer are apparent in
all of the line profiles we studied. The average quiet-Sun profiles
for Lyβ through Lyɛ are self-reversed, and the remaining lines are
flat-topped. The characteristics of the line profiles vary markedly
with intensity. We observe strong enhancements in the red wings of
network profiles, while the faint cell-center profiles are nearly
symmetric. We also find that the intensities of the H Lyman lines
increase at the limb, although the limb brightening is weak compared
to optically thin transition region emission lines and largely obscured
by the intensity variations observed in the quiet Sun.
Title: A new reference spectrum for the EUV irradiance of the quiet
Sun 2. Comparisons with observations and previous models
Authors: Warren, H. P.; Mariska, J. T.; Lean, J.
Bibcode: 1998JGR...10312091W
Altcode:
In a companion paper we presented a new reference spectrum for the EUV
irradiance of the quiet Sun based primarily on intensities calculated
from a quiet Sun emission measure distribution and recent compilations
of atomic data. The contributions of optically thick emission lines
and continua were included empirically. In this paper we present
comparisons between this reference spectrum and independently measured
irradiance observations, previous quiet Sun reference spectra, and
the predictions of empirical EUV irradiance models. These comparisons
indicate relatively good agreement among fluxes of emission lines
formed in the solar chromosphere and transition region. The fluxes for
coronal emission lines in previous quiet Sun reference spectra, however,
do not agree with our calculated fluxes or with a recent irradiance
observation taken at a low level of solar activity. Coronal emission
lines in the Atmospheric Explorer E (AE-E) quiet Sun reference spectrum
SC21REFW have fluxes that are typically smaller than our calculated
fluxes by factors of 2 or more. We also identify inconsistencies in the
earlier reference spectrum of Heroux and Hinteregger [1978] (F74113),
where the fluxes of many coronal emission lines with wavelengths below
250 Å are inconsistent with the fluxes of coronal emission lines at
longer wavelengths. The fluxes of EUV continua in the various reference
spectra and irradiance observations also differ significantly.
Title: A new reference spectrum for the EUV irradiance of the quiet
Sun 1. Emission measure formulation
Authors: Warren, H. P.; Mariska, J. T.; Lean, J.
Bibcode: 1998JGR...10312077W
Altcode:
We present a quiet Sun irradiance spectrum from 50-1200 Å based
primarily on intensities computed from a newly constructed quiet Sun
emission measure distribution. We derive the emission measure from a
spectrum of a portion of the quiet solar disk measured with the Harvard
instrument on Skylab and recent compilations of atomic data. For
some specific emission lines and continua which are not optically
thin and cannot be computed using an emission measure, we either use
intensities from the Harvard spectrum directly or infer them from
other observations. Application of a simple center-to-limb variation
converts the intensities to equivalent full-disk quiet Sun fluxes.
Title: Hydrodynamic Modeling of the Response of the Solar Atmosphere
to Bombardment by a Beam of Nonthermal Protons
Authors: Emslie, A. Gordon; Mariska, John T.; Montgomery, Michele M.;
Newton, Elizabeth K.
Bibcode: 1998ApJ...498..441E
Altcode:
Using a one-dimensional time-dependent numerical hydrodynamic model,
we examine the response of the solar atmosphere to heating by a beam
of energetic protons with a characteristic energy near 1 MeV. At these
energies, the coronal portion of the flaring loop must be treated as a
``warm'' target, while the chromospheric portion behaves as a ``cold''
target. This results in a more uniform heating in the coronal portions
of the loop than is the case with energetic electrons, leading to
smaller pressure gradients and lower plasma upflow velocities. Such
lower velocities would appear at first to be more consistent with
observed soft X-ray line profiles. However, velocity differential
emission measures computed at various times in the calculation show
that heating by energetic protons does not satisfactorily reproduce
the atmospheric response as inferred from such observations.
Title: The Magnetic Reconnection Explorer (MAGREX)
Authors: Schühle, U.; Antionchos, S. K.; Barbee, T. W., Jr.; Bixler,
J. V.; Brown, C. M.; Carter, P. H., II; Curdt, W.; Davila, J. M.;
Doschek, G.; Feldman, U.; Goldstein, W. H.; Kordas, J.; Lemaire, P.;
Mariska, J. T.; Marsch, E.; Moses, J. D.; Seely, J. F.; Wilhelm, K.;
Woods, T. N.
Bibcode: 1998ESASP.417..289S
Altcode: 1998cesh.conf..289S
No abstract at ADS
Title: VDEM Analysis of Transition Region Line Profiles Observed
with the SUMER Instrument on SoHO
Authors: Winebarger, A. R.; Warren, H. P.; Emslie, A. G.; Mariska,
J. T.
Bibcode: 1997AAS...191.7302W
Altcode: 1997BAAS...29.1320W
The SUMER spectrometer has obtained numerous high spatial and spectral
resolution observations of optically-thin transition region line
profiles in various solar features (quiet Sun, active region, coronal
hole, etc.). Frequently, these line profiles show evidence for both
steady and impulsive mass motions, which can have profound implications
for the mass and energy balance of the transition region and
corona. These motions can be quantified using the Velocity Differential
Emission Measure (VDEM) technique to derive the distribution of emission
with respect to the line-of-sight velocity. This VDEM distribution
can then be used to infer mean plasma velocities, momenta, and energy
fluxes. We have found that representations of the energy flux by
either the ``mean flow approximation'' {1 / 2}n m{bar v}(3) or by the
``enthalpy approximation''(whether in a purely thermal form nkT {bar v}
or incorporating nonthermal turbulence {1 / 2}n m /line {v(2}) {bar
v}) all underestimate the true energy flux {1 / 2} n m /line{v(3})
by up to an order of magnitude. In cases where lines formed at
different temperatures have been observed in the SUMER spectral range
simultaneously, we have estimated the divergence of the energy flux
and so the energy deposition rate within the region bounded by the
formation heights of the two spectral lines; implications for coronal
heating are discussed. This work was supported by grants from the SoHO
Guest Investigator Program and by the Office of Naval Research.
Title: YOHKOH Bragg Crystal Spectrometer Light Curves for S XV
(5.0163 - 5.1143 Angstroms)
Authors: Mariska, John T.; Bentley, R. D.; Pike, C. D.
Bibcode: 1997STIN...9838248M
Altcode:
This memorandum report summarizes the data produced during the sixth
year of operation by the Bragg Crystal Spectrometer (BCS) on the Yohkoh
spacecraft. Each page shows the total count rate in the S XV channel
of the BCS for a single day. This channel nominally observes the Sun
in the wavelength range from 5.0163 - 5.1143 Angstroms. These plots
are useful for identifying flare data for further analysis and for
determining the data file name and tape number that contains the data.
Title: Observations of Doppler Shifts in a Solar Polar Coronal Hole
Authors: Warren, H. P.; Mariska, J. T.; Wilhelm, K.
Bibcode: 1997ApJ...490L.187W
Altcode:
Using observations from the Solar Ultraviolet Measurements of Emitted
Radiation experiment flown on the Solar and Heliospheric Observatory
spacecraft, we have measured Doppler wavelength shifts in the north
polar coronal hole in the 1032 and 1038 Å emission lines of O VI and
the 1036 and 1037 Å emission lines of C II relative to chromospheric
emission lines. These observations were obtained on 1996 November 2
when the north polar coronal hole boundary extended southward to about
750'' (cosθ=0.65). Our measurements indicate the presence
of average net redshifts in coronal holes at temperatures of less than
2.9×105 K. Measurements of systematic wavelength shifts
in the Ne VIII resonance lines relative to the quiet Sun suggest a
transition to average net outflows near 6.3×105 K in the
coronal hole.
Title: Observations of Thermal Plasma in a Solar Limb Flare
Authors: Mariska, John T.; Doschek, G. A.
Bibcode: 1997ApJ...485..904M
Altcode:
All but a small portion of the top of the 1991 October 21 flare was
occulted by the solar limb. Thus, both the Bragg crystal spectrometer
(BCS) and the soft X-ray telescope (SXT) on Yohkoh observed only a small
region of flaring plasma. Using observations from those instruments,
we have determined the temporal behavior of the emission measure,
temperature, and nonthermal broadening in the loop-top source. We find
that for a portion of the decay phase of this flare, the temperatures
determined using the Fe XXV, Ca XIX, and S XV BCS channels and SXT
filter ratios all agree. Assuming that the plasma is isothermal, we
determine the abundances of Fe XXII, Fe XXIII, and Fe XXIV relative
to Fe XXV. Comparing the results with recent ionization equilibrium
calculations, we find that there are discrepancies between the
Fe XXII-to-Fe XXV ratio, the Fe XXIII-to-Fe XXV ratio, and the Fe
XXIV-to-Fe XXV ratio and ionization equilibrium calculations, which
we attribute to uncertainties in the ionization balance calculations.
Title: Doppler Shifts and Nonthermal Broadening in the Quiet Solar
Transition Region: O VI
Authors: Warren, H. P.; Mariska, J. T.; Wilhelm, K.; Lemaire, P.
Bibcode: 1997ApJ...484L..91W
Altcode:
Using observations from the Solar Ultraviolet Measurements of Emitted
Radiation (SUMER) experiment flown on the Solar and Heliospheric
Observatory (SOHO) spacecraft, we have measured Doppler wavelength
shifts and nonthermal broadening in the 1032 and 1038 Å emission lines
of O VI and the 1036 and 1037 Å emission lines of C II. Near Sun center
the C II lines exhibit an average redshift of 2 +/- 3 km s-1,
consistent with earlier observations in this temperature range. The
O VI emission lines exhibit average Doppler velocities of 5 +/- 3
km s-1, suggesting the presence of redshifted material at
2.9 × 105 K. For the O VI lines, the average nonthermal
component of the observed line width is 34 +/- 3 km s-1.
Title: Electron Densities in the Solar Polar Coronal Holes from
Density-Sensitive Line Ratios of Si VIII and S X
Authors: Doschek, G. A.; Warren, H. P.; Laming, J. M.; Mariska, J. T.;
Wilhelm, K.; Lemaire, P.; Schühle, U.; Moran, T. G.
Bibcode: 1997ApJ...482L.109D
Altcode:
We derive electron densities as a function of height in the north and
south polar coronal holes from a forbidden spectral line ratio of Si
VIII. Si VIII is produced at about 8 × 105 K in ionization
equilibrium. We also derive densities from a similar line ratio of S X
(1.3 × 106 K). The spectra were obtained with the Solar
Ultraviolet Measurements of Emitted Radiation spectrometer flown on
the Solar and Heliospheric Observatory spacecraft. In addition to the
primary mechanism of electron impact excitation, the derivation of
theoretical level populations for Si VIII and S X includes both proton
and resonance capture excitation. We compare the coronal hole results
to quiet-Sun coronal measurements obtained outside the east and west
limbs. We find for distances of a few arcseconds outside the solar
limb that the average line-of-sight electron densities in the coronal
holes are about a factor of 2 lower than in quiet-Sun regions. The
decrease of density with height is exponential in the polar holes. We
also confirm the result known from a variety of earlier observations
that the temperature of most of the plasma in coronal holes does not
exceed about 106 K.
Title: The Solar Flare Dynamics Imager: A Low-Cost Mission for This
Solar Maximum
Authors: Wulser, J. -P.; Bruner, M. E.; Strong, K. T.; Canfield,
R. C.; Culhane, J. L.; Mariska, J. T.; Polidan, R.
Bibcode: 1997SPD....28.0232W
Altcode: 1997BAAS...29R.898W
The Solar Flare Dynamics Imager (SolFDI) is a very low-cost flare
mission proposed for this upcoming solar maximum. It is based on a small
solar EUV telescope/spectrograph for Spartan Lite, NASA's new ejectable
hitchhiker spacecraft. The experiment's main scientific objective is
to investigate the spatial, temporal, and velocity structure of the
upflowing hot plasma frequently observed in soft X-ray lines during
solar flares. Past observations were spatially unresolved, and the
nature of these plasma flows, and their relationship with the impulsive
phase flare energy release are not well understood. The second objective
is to image the spatial and velocity structure of eruptive flares. Such
observations can ultimately reveal the true three-dimensional geometry
of the eruptive component of the flare. The Solar Flare Dynamics
Imager will observe flares in a few selected extreme ultraviolet lines,
including a high temperature Fe XXIV line. The instrument uses normal
incidence multilayer coated optics to provide simultaneous imaging and
spectroscopy in these lines with good spatial, spectral, and temporal
resolution. The instrument is designed to fit within the envelope
of the Spartan Lite ejectable hitchhiker spacecraft. Spartan Lite is
smaller, and costs a fraction of a SMEX spacecraft. But if launched
into the upcoming solar maximum, its 6-12 month mission duration would
be sufficient to achieve SolFDI's scientific objectives.
Title: Observations of Doppler Shifts and Nonthermal Broadening in
the North Polar Coronal Hole and Adjacent Quiet Sun
Authors: Mariska, J. T.; Warren, H. P.; Wilhelm, K.; Lemaire, P.
Bibcode: 1997SPD....28.0118M
Altcode: 1997BAAS...29..882M
Coronal holes are thought to be the source of high-speed solar
wind streams. It is, however, unclear at what height the outflow
of material first becomes apparent. Using the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) experiment on the Solar and
Heliospheric Observatory (SOHO), we have obtained observations in the
north polar coronal hole, its boundary region, and the adjacent quiet
Sun at wavelengths that cover emission lines of O VI at 1032 and 1038
Angstroms, Ne VIII at 770 Angstroms, and Mg X at 625 Angstroms. These
lines are formed at temperatures of 0.3, 0.8, and 1.25 MK, respectively,
and should thus help to determine the temperature at which outflows
are first detected. For O VI and Mg X, we will report on Doppler shift
measurements made relative to cooler chromospheric lines. Since there
are no suitable emission lines from ions formed in the chromosphere
for the Ne VIII line, we are only able to measure relative differences
between the coronal hole and the adjacent quiet Sun. We will also
report on the magnitude of the nonthermal broadening in these lines
in the different solar regions. This work was supported by a NASA SOHO
Guest Investigator Program grant.
Title: Co-Temporal Evolution of Magnetic Sources of Coronal and
Chromospheric/Photospheric Irradiance Variability
Authors: Lean, J. L.; Mariska, J. T.; Acton, L. W.
Bibcode: 1997SPD....28.1401L
Altcode: 1997BAAS...29R.917L
Magnetic features emergent from the Sun's convection zone modulate the
global radiative output throughout the solar atmosphere. Space-based
radiometric monitoring by instruments onboard Yohkoh and UARS have
tracked the decline in coronal soft X-rays concurrent with chromospheric
and photospheric UV global fluxes from high activity in 1991 to the
present solar minimum. Although these different global emissions can
at times vary in quite different ways they each exhibit components of
variability traceable to common magnetic variability sources, primarily
sunspots, bright plages and active network. Comparisons of the SXT
soft X-ray images of the corona with groundbased Ca K images of the
chromosphere/ photosphere permit the establishment of relationships
between these common magnetic sources in solar atmosphere regimes
with quite different temperatures and densities. While the impact
of large active regions seen in both the coronal and chromospheric
images provides the dominant modulation of the emissions (although with
different spectral signatures traceable to different spatial scales),
more diffuse, extended magnetic sources also contribute to solar cycle
changes in the overall background global emission of the corona as
well as the chromosphere/photosphere.
Title: Doppler Shifts and Nonthermal Broadening in the Quiet Solar
Transition Region: O VI
Authors: Warren, H. P.; Mariska, J. T.; Wilhelm, K.; Lemaire, P.
Bibcode: 1997SPD....28.0117W
Altcode: 1997BAAS...29..882W
Using observations from the Solar Ultraviolet Measurements of Emitted
Radiation (SUMER) experiment flown on the Solar and Heliospheric
Observatory (SOHO ) spacecraft, we have measured Doppler wavelength
shifts and nonthermal broadening in the 1032 and 1038 Angstroms emission
lines of Ovi and the 1036 and 1037 Angstroms emission lines of Cii. Near
Sun center the Cii lines exhibit an average redshift of 2+/-3km s(-1)
, consistent with earlier observations in this temperature range. The
Ovi emission lines exhibit average Doppler velocities of 5+/-3km s(-1)
suggesting the presence of redshifted material at 2.9*E(5) K. For the
Ovi lines, the average nonthermal component of the observed line width
is 34+/-3km s(-1) . These observations indicate a tendency for brighter
regions to have larger average redshifts and line widths than faint
features although the relationship is very weak. Preliminary analysis of
observations at the limb suggests that the Doppler velocities for Ovi do
not approach zero as would be expected for predominately radial motions.
Title: Determination of the Formation Temperature of Si IV in the
Solar Transition Region
Authors: Doschek, G. A.; Mariska, J. T.; Warren, H. P.; Wilhelm, K.;
Lemaire, P.; Kucera, T.; Schühle, U.
Bibcode: 1997ApJ...477L.119D
Altcode:
Using spectra obtained with the Solar Ultraviolet Measurements
of Emitted Radiation (SUMER) spectrometer flown on the Solar and
Heliospheric Observatory spacecraft, we deduce the temperature
of formation of the Si IV ion in the solar transition region
from the Si IV ultraviolet spectral line intensity ratio, 3p
2P3/2-3d 2D3/2,5/2/3s
2S1/2-3p 2P1/2,
and compare the result to the temperature predicted under the
assumption of ionization equilibrium. The wavelengths are as
follows: 2D3/2,5/2, 1128.325, 1128.340 Å
2P1/2, 1402.770 Å. Ratios are derived for
typical features of the quiet Sun, such as cell center and network,
and are systematically higher than those predicted at the 6.3 ×
104 K ionization equilibrium temperature of formation
of Si IV. For most solar features the ratios imply a temperature
of formation of about 8.5 × 104 K. The ratios for the
faintest features imply a temperature of formation of up to 1.6 ×
105 K. It is not clear, however, that all the discrepancies
between the measured and theoretical ratios are due to a temperature
effect. Accurate temperature measurements are important since a large
discrepancy from ionization equilibrium has significant implications
for the physics of the transition region, such as the possible presence
of nonthermal electrons.
Title: A Once and Future Stargazer
Authors: Mariska, John
Bibcode: 1997S&T....93a...6M
Altcode:
No abstract at ADS
Title: The Viability of Energetic Protons as an Agent for Atmospheric
Heating during the Impulsive Phase of Solar Flares
Authors: Emslie, A. Gordon; Henoux, Jean-Claude; Mariska, John T.;
Newton, Elizabeth K.
Bibcode: 1996ApJ...470L.131E
Altcode:
Recent observations of gamma -ray line intensities in solar flares
results have led to the suggestion that the energy content in
accelerated protons may rival that of accelerated electrons. However,
simply having a large energy content in accelerated protons is not
sufficient to ensure an important role for protons in driving the
response of the atmosphere to flare energy input: a viable model
must also deposit a large fraction of the particle energy at the top
of the chromosphere to account for the large increase in soft X-ray
emission measure that characterizes the main phase of a flare. While
hard X-ray producing electrons indeed deposit a sufficient amount of
energy at the appropriate depths in the atmosphere, only protons with
a characteristic energy of order 1 MeV do likewise. It is intriguing
that a characteristic energy of just this value has been obtained
through independent analysis of gamma -ray line intensities. However,
it must be noted that protons of this energy do not have a signature
in hard X-rays, leading us to conclude that a substantial fraction of
the flare energy budget must still reside in deka-keV electrons. In
order to complete the global energetic picture, further corroborating
observational diagnostics for MeV protons are desirable. In this Letter,
we discuss such suitable observations.
Title: Modeling solar extreme ultraviolet irradiance variability
using emission measure distributions
Authors: Warren, H. P.; Mariska, J. T.; Lean, J.; Marquette, W.;
Johannesson, A.
Bibcode: 1996GeoRL..23.2207W
Altcode:
We introduce a new model of solar irradiance variability at extreme
ultraviolet (EUV) wavelengths. The model combines a spectral emission
line database, solar emission measure distributions, and estimates
from ground-based solar images of the fraction of the Sun covered by
the various types of activity to synthesize the irradiance. Using Call
K-line images, the model can be used to estimate the irradiance from
EUV line emission formed in the upper chromosphere and lower transition
region. Comparisons of this new model with existing empirical models
reveal both similarities and disagreements in the absolute magnitude,
the amplitude of the rotational modulation, and the intermediate-term
solar cycle variability of the predicted fluxes.
Title: A New Model of Solar EUV Irradiance Variability
Authors: Warren, H. P.; Mariska, J. T.; Lean, J.
Bibcode: 1996AAS...188.3617W
Altcode: 1996BAAS...28R.875W
Solar soft X-ray (SXR, 1-100 Angstroms) and extreme ultraviolet (EUV,
100--1200 Angstroms) radiation plays a central role in the energetics
and dynamics of the Earth's upper atmosphere. Solar radiation at
these wavelengths is strongly affected by solar magnetic activity
and varies significantly during the solar activity cycle. Empirical
models of solar irradiance variability essentially parameterize
existing full-disk irradiance observations with proxies for solar
activity. However, the limitations of existing EUV observations and
absence of any current irradiance measurements at these wavelengths
limits the utility of empirical irradiance modeling. Motivated by solar
physics experiments on Yohkoh, SOHO, and TRACE we have developed a
new, physics-based approach to modeling solar SXR and EUV irradiance
variability. In this new model, the intensities of optically thin
spectral lines are calculated using theoretically determined values
of plasma emissivity coupled with emission measure distributions for
features of the solar atmosphere: coronal holes, quiet Sun, and active
regions. For emission lines with very complicated formation processes,
such as the Lyman lines of hydrogen and helium, spatially and spectrally
resolved solar observations are used in place of emission measure
calculations. Information about the distribution of emitting regions
on the Sun is inferred from full-disk images of the Sun, such as BBSO
CaII k-line and Yohkoh SXT images, rather than from proxies for solar
activity. Comparison of the model with existing empirical irradiance
models based on F_{10.7} and other proxies for solar activity reveals
disagreements in the absolute magnitude, the amplitude of the rotational
modulation, and the solar cycle variability of the predicted fluxes at
many wavelengths. This research was supported by the NASA SEE program.
Title: Energetic Protons as a Form of Energy Transport During The
Impulsive Phase of Solar Flares?
Authors: Emslie, A. G.; Henoux, J. -C.; Mariska, J. T.; Newton, E. K.
Bibcode: 1996AAS...188.2601E
Altcode: 1996BAAS...28..857E
Recent results based on hard X-ray and gamma-ray observations of solar
flares have suggested that the energy content in accelerated protons
may rival that of accelerated electrons. However, simply having a large
energy content in accelerated protons is not sufficient to ensure an
important role for protons in driving the response of the atmosphere to
flare energy input: a viable model must also deposit a large fraction
of the particle energy at the top of the chromosphere, to account for
the large increase in soft X-ray emission measure that characterizes
the main phase of a flare. While hard X-ray-producing electrons indeed
deposit a sufficient amount of energy at the appropriate depths in the
atmosphere, we show that only protons with a characteristic energy of
order 1 MeV do likewise. Since protons of this energy do not have a
signature in hard X-rays, we conclude that a substantial fraction of the
flare energy budget must indeed reside in deka-keV electrons. In order
to complete the global energetic picture, observational diagnostics
for MeV protons are required; suitable observations are discussed. This
work was supported by the NASA Office of Space Science and by the NSF
International Programs Division.
Title: Observations of Thermal Plasma in a Solar Limb Flare
Authors: Mariska, J. T.; Doschek, G. A.
Bibcode: 1996AAS...188.7004M
Altcode: 1996BAAS...28R.938M
While the earliest phases of a solar flare are characterized mainly by
nonthermal emissions, such as hard X-rays, the remainder of the event
manifests itself primarily as thermal emissions at wavelengths ranging
from X-rays through optical. This radiation comes from flare plasma
covering a wide range of temperatures. Yohkoh Soft X-Ray Telescope
(SXT) observations show that in soft X-rays this emission often
comes from complex emitting structures, with temperatures that vary
from feature to feature. These temperatures, however, are based on
filter ratios and are thus difficult to interpret for a multithermal
plasma. Yohkoh Bragg Crystal Spectrometer (BCS) observations also
provide a temperature diagnostic for the soft X-ray emitting flare
plasma. These temperatures often differ from those obtained using
filter ratios, again demonstrating that flare plasma is multithermal. We
report on observations of a limb flare observed on 1991 October 21 in
which the temperatures measured using emission lines of CaXIX and FeXXV
agreed, suggesting that this flare contained substantial amounts of
isothermal plasma. We use SXT and BCS data from this flare to verify
SXT filter ratio temperatures and to determine relative ion fractions
of FeXXII, FeXXIII, FeXIV, and FeXXV for comparison with ionization
balance calculations. This work was supported by the NASA Office of
Space Science and the Naval Research Laboratory.
Title: Hard and Soft X-Ray Observations of Solar Limb Flares
Authors: Mariska, John T.; Sakao, T.; Bentley, R. D.
Bibcode: 1996ApJ...459..815M
Altcode:
Using observations from the Yohkoh Bragg Crystal Spectrometer, hard
X-ray telescope, and soft X-ray telescope, we have examined eight limb
flares. Four of the flares have the footpoints occulted by the solar
limb. We find that the occulted flares generally have softer hard
X-ray spectra and smaller peak values of the nonthermal broadening
velocity than nonocculted flares. All other physical parameters show
no differences between occulted flares and nonocculted flares. The
hard X-ray spectra support a model in which the footpoint emission
is due to thick-target sources, while the looptop emission is due to
thin-target sources. High spectral resolution hard X-ray observations
should thus show a break in the hard X-ray spectrum of the looptop
source. We can find no obvious explanation for the differences in
nonthermal broadening velocity.
Title: Soft X-Ray Flare Dynamics
Authors: Doschek, G. A.; Mariska, John T.; Sakao, T.
Bibcode: 1996ApJ...459..823D
Altcode:
We discuss the dynamics of four soft X-ray flares as revealed by the
X-ray resonance line profiles of the He-like ions, Fe xxv, Ca xix,
and S xv. The flares chosen for analysis belong to a subclass of
events that have intense Doppler blueshifted spectral signatures
during the rise phase. The spectra were obtained froin the Bragg
crystal spectrometer (BC S) experiment flown on the Japanese Yohkoh
spacecraft. We deconvolve the line profiles into a flare decay phase
component (stationary component) produced by nonmoving plasma with
little or no turbulent motions, and a flare rise phase component
(dynamic component) produced by bulk plasma motion and turbulence. The
dynamic component is further deconvolved into a high-speed component
(greater than 400 km s 1) and a lower speed, more turbulent
component. We find that the dynamic and stationary components have
approximately the same electron temperature. The dynamic and stationary
component fluxes are compared with hard X-ray fluxes obtained from the
hard X-ray telescope (HXT) on Yohkoh We find that the onset time of
the high-speed dynamic component corresponds closely to the onset of
hard X-rays. We discuss the X-ray morphology of the flares as revealed
by the soft X-ray telescope (SXT) and hard X-ray telescope (HXT) on
Yohkoh. From analysis of the X-ray light curves of individual pixels in
the SXT images, we believe we have been able to determine at least some
of the locations of the dynamic component in the images. Although the
observations support many aspects of chromospheric evaporation models,
there are significant problems. No obvious rising fronts of plasma
are observed for any of the flares. There are apparent footpoint hard
X-ray sources that cannot be physically related in an obvious manner
with the main sources of soft X-ray emission. The flares are complex,
and therefore there are some ambiguities in interpretation of the
morphology.
Title: Timing of the soft X-ray blue-wing and the hard X-ray burst
from observations by YOHKOH
Authors: Bentley, R. D.; Doschek, G. A.; Mariska, J. T.
Bibcode: 1996AdSpR..17d..55B
Altcode: 1996AdSpR..17...55B
A knowledge of the relative timing of the hard X-ray burst and emission
in soft X-rays is helpful in deciding between a number of theoretical
models that describe the mechanism of a solar flare. Here we continue
a study of this relationship using observations from the Yohkoh Bragg
Crystal Spectrometer and Hard X-ray Telescope, together with supporting
observations from the CGRO Batse experiment. The enhanced capabilities
of the instruments onboard Yohkoh have made it possible to study the
problem in a way that was not previously possible. A study of the
timing, intensity and evolution of the soft X-ray blue-wing shows that
there is no simple relationship between hard and soft X-ray emissions;
strong blue-wings sometimes result from relatively weak hard X-ray
bursts; the burst responsible for the blue wing need not be the first
or most intense burst associated with the flare; the blue-wing is found
to follow very closely after the hard X-ray burst. We also discuss
timing issues and why other researchers may have reached different
conclusions on this matter.
Title: Testing the Impulsiveness of Solar Flare Heating through
Analysis of Dynamic Atmospheric Response
Authors: Newton, E. K.; Emslie, A. G.; Mariska, J. T.
Bibcode: 1996ApJ...459..804N
Altcode:
One crucial test of a solar flare energy transport model is its ability
to reproduce the characteristics of the atmospheric motions inferred
from soft X-ray line spectra. Using a recently developed diagnostic,
the velocity differential emission measure (VDEM), we can obtain from
observations a physical measure of the amount of soft X-ray mitting
plasma flowing at each velocity, v, and hence the total momentum of
the upflowing plasma, without approximation or parametric fitting. We
have correlated solar hard X-ray emission profiles by the Yohkoh
Hard X-ray telescope with the mass and momentum histories inferred
from soft X-ray line profiles observed by the Yohkoh Bragg crystal
spectrometers. For suitably impulsive hard X-ray emission, an analysis
of the hydrodynamic equations predicts a proportionality between the
hard X-ray intensity and the second time derivative of the soft X-ray
mitting plasma's momentum. This relationship is borne out by an analysis
of 18 disk-center impulsive flares of varying durations, thereby lending
support to the hypothesis that a prompt energy deposition mechanism,
such as an energetic electron flux, is indeed responsible for the soft
X-ray response observed in the rise phase of sufficiently impulsive
solar flares.
Title: YOHKOH Bragg Crystal Spectrometer Light Curves for S XV
(5.0163 - 5.1143 A)
Authors: Mariska, John T.; Bently, R. D.; Pike, C. D.
Bibcode: 1996nrl..rept.....M
Altcode:
This memorandum report summarizes the data produced during the third
year of operation by the Bragg Crystal Spectrometer (BCS) on the Yohkoh
spacecraft. Each page shows the total count rate in the S XV channel
of the BCS for a single day. This channel nominally observes the Sun
in the wavelength range from 5.0163 - 5.1143 A. These plots are useful
for identifying flare data for further analysis and for determining
the data file name and tape name that contains the data.
Title: Magnetic Reconnection in the Solar Atmosphere
Authors: Bentley, R. D.; Mariska, J. T.
Bibcode: 1996ASPC..111.....B
Altcode: 1997ASPC..111.....B
The following topics were dealt with: bright points, jets, emerging
flux, coronal heating, flare observations, flare theory, larger
structures and coronal ejections.
Title: YOHKOH observations of solar limb flares
Authors: Bentley, R. D.; Mariska, J. T.; Sakao, T.
Bibcode: 1996ASPC..109..107B
Altcode: 1996csss....9..107B
No abstract at ADS
Title: Radiative Influences
Authors: Mariska, John T.; Lean, Judith
Bibcode: 1996ASPC...95..555M
Altcode: 1996sdit.conf..555M
No abstract at ADS
Title: Dynamical Response of the Solar Atmosphere to Flare Heating
Authors: Newton, E. K.; Emslie, A. G.; Mariska, J. T.
Bibcode: 1996mpsa.conf..559N
Altcode: 1996IAUCo.153..559N
No abstract at ADS
Title: Hard and Soft X-ray Observations of Solar Limb Flares
Authors: Mariska, J. T.; Sakao, T.; Bentley, R. D.
Bibcode: 1996mpsa.conf..523M
Altcode: 1996IAUCo.153..523M
No abstract at ADS
Title: Relationships between Temperature and Emission Measure in
Solar Flares Determined from Highly Ionized Iron Spectra and from
Broadband X-Ray Detectors
Authors: Feldman, U.; Doschek, G. A.; Mariska, J. T.; Brown, C. M.
Bibcode: 1995ApJ...450..441F
Altcode:
We compare the electron temperature and emission measure of flares at
the time of maximum soft X-ray intensity derived using two different
techniques: (1) from the ratio of a dielectronic Fe XXIV line to
the resonance line of Fe XXV, combined with the absolute intensity
of the Fe XXV line, and (2) from the ratio of the 0.5-4.0 Å and 1-8
Å broadband X-ray fluxes, combined with the absolute flux in one of
the broadband spectral regions. The high-resolution Fe spectra are
obtained with the Bragg Crystal Spectrometer experiment flown on
the Japanese Yohkoh spacecraft. The broadband fluxes are obtained
from Geostationary Operational Environmental Satellites (GOES). A
data set of 540 X-ray magnitude C2 or brighter flares, observed by
both spacecraft, is used for the analysis. Both techniques assume an
isothermal plasma. The broadband temperatures are substantially lower
than the Fe xxv temperatures. We find that the maximum temperature
of flares brighter than MS exceeds 2 × 107 K and that the
maximum temperature of flares fainter than C4 is substantially lower
than 2 × 107 K. We find that the Fe XXV emission measure
is linearly proportional to the GOES flux in the 0.5-4.0 Å detector.
Title: The Velocity Differential Emission Measure: Diagnostic of
Bulk Plasma Motion in Solar Flares
Authors: Newton, E. K.; Emslie, A. G.; Mariska, J. T.
Bibcode: 1995ApJ...447..915N
Altcode:
Mass motions are a ubiquitous product of solar flare energy release. A
better understanding of the flare plasma's distribution how much is
moving and how fast permits insight into the mechanisms of energy
transport (and release) which lead to those motions. Observationally,
mass motions during flares are often manifested in the shape and
location of soft X-ray emission lines. Observed line profiles generally
exhibit a width greater than the thermal Doppler width and a blue-wing
asymmetry which has been cited as evidence for plasma motions along
the line of sight. Past efforts to characterize this excess width
and asymmetry have primarily involved the parametric fitting of a
double-Gaussian form. In this paper we show, however, that simple
two-component models are inconsistent with the observed evolution
of spectral lines and hence serve as a poor diagnostic of plasma
motions. We therefore generalize the synthesis of line profiles to the
case of a continuum of Gaussian components, by introducing a quantity
which we term the velocity differential emission measure (VDEM). The
VDEM measures the distribution of emission from a volume of plasma as
a function of its line-of-sight velocity. It can either be computed
from theoretical model atmospheres, or recovered from observed line
profiles using an inversion technique. We present the VDEMs of two
model flare atmospheres and discuss the differences between them. We
also deconvolve a VDEM from a representative Ca XIX flare spectrum
observed by the Bragg Crystal Spectrometer instrument aboard Yohkoh
Title: Temperature Structure of Active Regions Deduced from the
Helium-Like Sulphur Lines
Authors: Watanabe, Tetsuya; Haka, Hirohisa; Shimizu, Toshifumi; Hiei,
Eijiro; Bentley, Robert D.; Lang, James; Phillips, Kenneth J. H.; David
Pike, C.; Fludra, Andrzej; Bromage, Barbara J. I.; Mariska, John T.
Bibcode: 1995SoPh..157..169W
Altcode:
Solar active-region temperatures have been determined from the full-Sun
spectra of helium-like sulphur (SXV) observed by the Bragg Crystal
Spectrometer on board theYohkoh satellite. The average temperature
deduced from SXV is demonstrated to vary with the solar activity level:
A temperature of 2.5 × 106 K is derived from the spectra
taken during low solar activity, similar to the general corona, while
4 × 106 K is obtained during a higher activity phase. For
the latter, the high-temperature tail of the differential emission
measure of active regions is found most likely due to the superposition
of numerous flare-like events (micro/nano-flares).
Title: Hard and Soft X-Ray Observations of Solar Limb Flares
Authors: Mariska, J. T.; Sakao, T.; Bentley, R. D.
Bibcode: 1995SPD....26.1312M
Altcode: 1995BAAS...27..989M
No abstract at ADS
Title: The Velocity Differential Emission Measure - A Diagnostic of
Mass Motions in the Impulsive Phase of Solar Flares
Authors: Newton, E. K.; Emslie, A. G.; Mariska, J. T.
Bibcode: 1995SPD....26.1206N
Altcode: 1995BAAS...27..983N
No abstract at ADS
Title: Correlated brightness variations in solar radiative output
from the photosphere to the corona
Authors: Lean, J. L.; Mariska, J. T.; Strong, K. T.; Hudson, H. S.;
Acton, L. W.; Rottman, G. J.; Woods, T. N.; Willson, R. C.
Bibcode: 1995GeoRL..22..655L
Altcode:
Correlated brightness variations are shown to occur in time series of
coronal soft X-rays exclusive of prominent active regions, chromospheric
ultraviolet radiation, and the photospheric total solar irradiance
corrected for sunspot effects. These temporal correlations suggest that
upwardly extending magnetic fields may have a large scale impact on the
solar atmosphere in addition to their demonstrable role of generating
localized active regions. The correlations have implications for
improving and extending solar spectrum variability models.
Title: Cooling of Solar Flare Plasmas. I. Theoretical Considerations
Authors: Cargill, Peter J.; Mariska, John T.; Antiochos, Spiro K.
Bibcode: 1995ApJ...439.1034C
Altcode:
Theoretical models of the cooling of flare plasma are reexamined. By
assuming that the cooling occurs in two separate phase where conduction
and radiation, respectively, dominate, a simple analytic formula
for the cooling time of a flare plasma is derived. Unlike earlier
order-of-magnitude scalings, this result accounts for the effect of
the evolution of the loop plasma parameters on the cooling time. When
the conductive cooling leads to an 'evaporation' of chromospheric
material, the cooling time scales L5/6/p1/6, where
the coronal phase (defined as the time maximum temperature). When
the conductive cooling is static, the cooling time scales as
L3/4n1/4. In deriving these results, use was made
of an important scaling law (T proportional to n2) during
the radiative cooling phase that was forst noted in one-dimensional
hydrodynamic numerical simulations (Serio et al. 1991; Jakimiec et
al. 1992). Our own simulations show that this result is restricted
to approximately the radiative loss function of Rosner, Tucker, &
Vaiana (1978). for different radiative loss functions, other scaling
result, with T and n scaling almost linearly when the radiative loss
falls off as T-2. It is shown that these scaling laws are
part of a class of analytic solutions developed by Antiocos (1980).
Title: Testing the DC-Electric Field Model in a Solar Flare Observed
by YOHKOH and the Compton Gamma-Ray Observatory
Authors: Zarro, D. M.; Mariska, J. T.; Dennis, B. R.
Bibcode: 1995ApJ...440..888Z
Altcode:
We apply a DC-electric field model to the analysis of soft and hard
X-ray observations of a solar flare observed by Yohkoh and the Compton
Gamma-Ray Observatory CGRO on 1992 September 6. The flare was observed
simultaneously in the soft X-ray Ca XIX line by the Yokhoh Bragg Crystal
Spectrometer (BCS) and in hard X-rays (>50 keV) by the CGRO Burst
and Transient Spectrometer Experiment (BATSE). A strong stationary
component of Ca XIX emission was present at the start of impulsive hard
X-ray emission indicating an extended phase of heating prior to the
production of energetic nonthermal electrons. We interpret the preflare
Ca XIX emission as a signature of Joule heating by field-aligned
currents. We relate the temporal variation of impulsive hard X-ray
emission to the rate of runaway electron acceleration by the DC-electric
field associated with the current. We find that the initial rise in hard
X-ray emission is consistent with electron acceleration by a DC-electric
field that increased from a preflare value of ≲ 10-5 V
cm-1 to (9±1) × 10-5 V cm-1 at the
time of the first hard X-ray peak and then remained constant during
the rest of the impulsive phase. We attribute the increase in electric
field strength to the formation of a current sheet at the reconnection
point of two loop structures. The decrease in hard X-ray emission
after flare maximum is consistent with a reduction in the number of
runaway electrons due to an increase in coronal density produced by
chromospheric evaporation. The increased density quenches the runaway
process by enhancing collisional thermalization of electrons. To
avoid the generation of an unrealistically large magnetic field,
the flaring region must be highly filamented into ≳106
oppositely directed current channels of ∼30 cm width with an initial
preflare current of ≃3 × 1010 A per channel.
Title: YOHKOH Bragg Crystal Spectrometer light curves for CA 29(3.1633
- 3.1933 A): 1 October 1993 - 30 September 1994
Authors: Mariska, John T.; Bentley, R. D.; Pike, C. D.
Bibcode: 1994YBCSCrept.....M
Altcode:
This memorandum report summarizes the data produced during the third
year of operation by the Bragg Crystal Spectrometer (BCS) on the Yohkoh
spacecraft. Each page shows the total count rate in the Ca XIX channel
of the BCS for a single day. This channel nominally observes the Sun in
the wavelength range from 3.1633 to 3.1933 A. These plots are useful
for identifying flare data for further analysis and for determining
the data file name and tape name that contains the data.
Title: Jets and brightenings generated by energy deposition in the
middle and upper solar chromosphere
Authors: Sterling, Alphonse C.; Shibata, Kazunari; Mariska, John T.
Bibcode: 1994SSRv...70...77S
Altcode:
Numerical simulations of energy depositions in the middle and upper
solar chromosphere result in ejection of chromospheric material into
the corona and heating of the chromospheric gas. These simulations may
be capable of describing some of the features seen by the soft X-ray
telescope on board theYohkoh satellite.
Title: Flare Plasma Dynamics Observed with the YOHKOH Bragg Crystal
Spectrometer. II. Properties of the Fe xxv, CA xix, and S XV
Resonance Lines
Authors: Mariska, John T.
Bibcode: 1994ApJ...434..756M
Altcode:
Using data from the Bragg Crystal Spectrometer (BCS) on the Yohkoh
spacecraft, we have computed measures of the total intensity,
centroid position, and line widths for the resonance lines of Fe XXV,
Ca XIX, and S XV during the rise phase and after maximum for 190 solar
flares. The difference between centroid positions early and late in
each flare yields a measure of the line-of-sight velocity shift of the
line centroids. Roughly 25% of the flares show evidence for spatial
shifts of the emitting plasma during the flare. For all three resonance
lines in those flares that show only Doppler shifts, we find a trend in
the average value of the centroid shift with distance from Sun center
suggesting radial mass motions with characteristic velocities of 76,
63, and 58 km/s in the resonance lines of Fe XXV, Ca XIX, and S XV,
respectively. For each resonance line there is also a correlation
between the rise-phase line widths and the centroid shift. For each
resonance line we find no correlation between the centroid shift
and the peak intensity, rise time, and total flare duration; and no
correlation between the line width and the distance from Sun center,
peak intensity, rise time, and total flare duration. Comparing data
from the different BCS wavelength channels, we find that the centroid
shift in each channel is correlated with the centroid shifts in the
other channels. Similarly, the line width in each channel is correlated
with the line width in the other channels.
Title: The 1991 November 9 Flare at 03.2 UT: Observations from YOHKOH
Authors: Doschek, G. A.; Mariska, J. T.; Strong, K. T.; Bentley, R. D.;
Brown, C. M.; Culhane, J. L.; Lang, J.; Sterling, A. C.; Watanabe, T.
Bibcode: 1994ApJ...431..888D
Altcode:
We discuss X-ray spectra and soft X-ray images of an M1.9 flare that
occurred on 1991 November 9 near 03.2 UT. These data were obtained with
instrumentation on the Japanese Yohkoh spacecraft. They cover the entire
rise phase and peak flare emission, and the beginning of the decay
phase. We determine the dynamics, temperature, and emission measure
of the flare as inferred from the X-ray line profiles of resonance
lines of Fe XXV, Ca XIX, and S XV. We discuss the morphology of the
flare as inferred from the soft X-ray images. The November 9 flare is
atypical in that a stronger than usual blueshifted emission component
(relative to the stationary component) is observed for the resonance
lines at flare onset. We discuss several methods for deconvolving the
blueshifted component from the stationary component. The X-ray line
profiles are consistent with predictions of numerical simulations
of chromospheric evaporation. The X-ray images reveal a flare with a
complicated loop geometry that is not fully understood. Many of the
features in the images are moving upwards at speeds ranging from a
few km/s to about 800 km/s. The blueshifted emission begins near the
onset of hard X-ray emission, implying that particle acceleration and
upflowing plasma have a common energy source.
Title: Energy Transport and Dynamics
Authors: Schmieder, B.; Peres, G.; Enome, S.; Falciani, R.; Heinzel,
P.; Hénoux, J. C.; Mariska, J.; Reale, F.; Rilee, M. L.; Rompolt, B.;
Shibasaki, K.; Stepanov, A. V.; Wülser, J. P.; Zarro, D.; Zharkova, V.
Bibcode: 1994SoPh..153...55S
Altcode:
We report findings concerning energy transport and dynamics in flares
during the impulsive and gradual phases based on new ground-based and
space observations (notably fromYohkoh). A preheating sometimes occurs
during the impulsive phase. CaXIX line shifts are confirmed to be
good tracers of bulk plasma motions, although strong blue shifts are
not as frequent as previously claimed. They often appear correlated
with hard X-rays but, forsome events, the concept that electron beams
provide the whole energy input to the thermal component seems not
to apply. Theory now yields: new diagnostics of low-energy proton
and electron beams; accurate hydrodynamical modeling of pulse beam
heating of the atmosphere; possible diagnostics of microflares (based
on X-ray line ratio or on loop variability); and simulated images of
chromospheric evaporation fronts. For the gradual phase, the continual
reorganization of magnetic field lines over active regions determines
where and when magnetic reconnection, the mechanism favoured for energy
release, will occur. Spatial and temporal fragmentation of the energy
release, observed at different wavelengths, is considered to be a
factor as well in energy transport and plasma dynamics.
Title: Studying Solar Flares with YOHKOH and the Compton Gamma-Ray
Observatory
Authors: Zarro, D.; Mariska, J. T.; Dennis, B. R.
Bibcode: 1994kofu.symp..221Z
Altcode:
We apply a DC-electric field model to the analysis of soft and hard
X-ray observations of a solar flare observed by Yohkoh and the Compton
Gamma-Ray Observatory on 1992 September 6. The flare was observed in Ca
XIX by the Yohkoh Bragg Crystal Spectrometer (BCS) and simultaneously
in hard X-rays by the CGRO Burst and Transient Spectrometer Experiment
(BATSE). A strong stationary component of Ca XIX emission was observed
at the start of impulsive hard X-ray emission indicating an extended
phase of heating prior to the production of energetic nonthermal
electrons. We interpret the preflare Ca XIX emission as a signature
of Joule heating by field-aligned currents. We relate the temporal
variation of impulsive hard X-ray emission to the rate of runaway
electron acceleration in the same DC-electric field.
Title: Book-Review - the Solar Transition Region
Authors: Mariska, J. T.; Harper, G.; Jordan, C.
Bibcode: 1994Obs...114...58M
Altcode:
No abstract at ADS
Title: A Resonance Line Rations Method for Determining Flare
Temperatures Using YOHKOH BCS Spectra
Authors: Sterling, A. C.; Doschek, G.; Mariska, J. T.; Hiei, E.;
Watanabe, T.
Bibcode: 1994xspy.conf..127S
Altcode:
No abstract at ADS
Title: The Correlation of Solar Flare Hard X-Ray Bursts with Doppler
Blueshifted Soft X-Ray Flare Emission
Authors: Bentley, R. D.; Doschek, G. A.; Simnett, G. M.; Rilee, M. L.;
Mariska, J. T.; Culhane, J. L.; Kosugi, T.; Watanabe, T.
Bibcode: 1994ApJ...421L..55B
Altcode:
We have investigated the temporal correlation between hard X-ray
bursts and the intensity of Doppler blueshifted soft X-ray spectral
line emission. We find a strong correlation for many events that have
intense blueshifted spectral signatures and some correlation in events
with modest blueshifts. The onset of hard X-rays frequently coincides to
within a few seconds with the onset of blueshifted emission. The peak
intensity of blueshifted emission is frequently close in time to the
peak of the hard X-ray emission. Decay rates of the blueshifted and hard
X-ray emission are similar, with the decay of the blueshifted emission
tending to lag behind the hard X-ray emission in some cases. There
are, however, exceptions to these conclusions, and, therefore, the
results should not be generalized to all flares. Most of the data for
this work were obtained from instruments flown on the Japanese Yohkoh
solar spacecraft.
Title: Temperature Structure of Active Regions Deduced from the
Helium-Like Sulphur Lines
Authors: Watanabe, T.; Hara, H.; Shimizu, T.; Hiei, E.; Mariska,
J. T.; Bentley, R. D.; Fludra, A.; Lang, J.; Phillips, K. J. H.;
Pike, C. D.; Bromage, B. J. I.
Bibcode: 1994xspy.conf...55W
Altcode:
No abstract at ADS
Title: Flare Plasma Dynamics Observed with the YOHKOH Bragg Crystal
Spectrometer. I. Properties of the CA XIX Resonance Line
Authors: Mariska, John T.; Doschek, G. A.; Bentley, R. D.
Bibcode: 1993ApJ...419..418M
Altcode:
Using data from the Bragg crystal spectrometer on the Yohkoh spacecraft
we have computed measures of the total intensity, centroid position,
and line width for the resonance line of Ca xix during the rise phase
and after maximum for 219 solar flares. The difference between the
centroid positions early and late in each flare yields a measure
of the line-of-sight velocity shift of the line centroid. We find
a trend in the average value of the centroid shift with distance
from Sun center suggesting radial mass motions with a characteristic
velocity of 58 km s-1. There is a correlation between the
rise-phase line widths and the centroid shift. We find no correlation
between the centroid shift and the peak intensity, rise time, and
total flare duration; and no correlation between the line width and
the distance from Sun center, the peak intensity, rise time, and total
flare duration. These results do not conclusively support or refute
the simple electron-beam-driven model or the thermal model for the
rise phase of a solar flare.
Title: Testing the Electric Field Model in Solar Flares
Authors: Zarro, D. M.; Mariska, J. T.; Dennis, B. R.
Bibcode: 1993AAS...183.6803Z
Altcode: 1993BAAS...25.1396Z
We are analyzing solar flares that show evidence for strong stationary
Ca XIX emission at the start of impulsive hard X-rays. An example
is an M3.3 event that occurred at 0857 UT on 1992 September 6 in
active region AR 7270. The flare was observed in Ca XIX by Yohkoh
BCS and simultaneously in hard X-rays by CGRO BATSE. A strong
stationary component of Ca XIX emission was already present at the
start of impulsive hard X-ray emission, indicating a temperature
T ~ 10 times 10(6) K and an emission measure EM ~ 7 times 10(47)
cm(-3) . Simultaneous Yohkoh SXT Be-filter images imply a simple
loop structure for the main soft X-ray source, with a characteristic
cross-sectional area of A ~ 10(17) cm(2) and a half-length L ~ 10(9)
cm. The detection of strong stationary soft X-ray emission before the
peak of hard X-rays cannot be explained easily by the thick-target
driven chromospheric evaporation model. To explain these observations,
we adopt a DC-electric field model in which preflare thermal Ca XIX
emission is produced by current heating dominating early in the flare,
and nonthermal HXR emission is produced by electron runaway acceleration
dominating during the impulsive phase. We present a novel method for
deriving the strength and temporal variation of the electric field. This
work was supported by NASA contracts NAS5-31235 and NAS-32064.
Title: The Moments of Ca-XIX Flare Spectra as Model Discriminators
Authors: Newton, E.; Emslie, A. G.; Mariska, J.
Bibcode: 1993AAS...183.0704N
Altcode: 1993BAAS...25.1300N
We have measured the moments of Ca-XIX solar flare spectral
profiles as observed by the Bragg Crystal Spectrometer aboard the
YOHKOH spacecraft. The moments are compared to those calculated for
spectra generated from numerical electron-heated model simulations,
two-component Gaussian fits, and heat flux models. The comparison
permits a test of various theories concerning the dynamics of the
solar atmosphere during flares.}
Title: YOHKOH Bragg Crystal Spectrometer Observations of Flare
Plasma Dynamics
Authors: Mariska, J. T.
Bibcode: 1993AAS...183.0703M
Altcode: 1993BAAS...25.1299M
Using data from the Bragg Crystal Spectrometer (BCS) on the Yohkoh
spacecraft, I have computed measures of the total intensity, centroid
position, and line width for the resonance lines of Fe XXV, Ca XIX,
and S XV during the rise phase and after maximum for 190 solar
flares. The difference between centroid positions early and late
in each flare yields a measure of the line-of-sight velocity shift
of the line centroids. Roughly 25% of the flares show evidence for
spatial shifts of the emitting plasma during the flare. For all three
resonance lines in those flares that show only Doppler shifts, I find
a trend in the average value of the centroid shift with distance
from Sun center suggesting radial mass motions with characteristic
velocities of 76, 63, and 58 km s(-1) in the resonance lines of Fe
XXV, Ca XIX, and S XV, respectively. For each resonance line, I find
no correlation between the centroid shift and the peak intensity,
rise time, and total flare duration; and no correlation between the
line width and the distance from Sun center, peak intensity, rise time,
and total flare duration. Comparing data from different BCS wavelength
channels, I find that the centroid shift in each channel is correlated
with the centroid shifts in the other channels. Similarly, the line
width in each channel is correlated with the line widths in the other
channels. Exploratory model atmosphere calculations suggest that many
of these properties can be explained by an electron-beam-heated flare
model. This work was supported by the Office of Naval Research.
Title: Implications of the Soft X-Ray versus Hard X-Ray Temporal
Relationship in Solar Flares
Authors: Li, Peng; Emslie, A. Gordon; Mariska, John T.
Bibcode: 1993ApJ...417..313L
Altcode:
We have calculated the time profiles of spatially integrated hard X-ray
(30-500 keV) and soft X-ray (1-8 Å) emission in both thick-target
electron-heated models, and bulk heated thermal models, of the impulsive
phase of solar flares. For the thermal model, we find a serious
difficulty: the time profiles of the 30-500 keV hard X-ray emission
do not peak at the same time as those for the higher energy component
(40-500 keV) of this emission, a result that manifestly disagrees with
the observations. In the thick-target model, however, the hard X-ray
light curves at all energies >30 keV peak at the same time, lending
considerable support to this model. Observations also suggest that
the relationship between the hard X-ray and soft X-ray emission is that
of "derivativity," that is, the hard X-ray time profile corresponds not
so much to the instantaneous soft X-ray flux, but rather its temporal
derivative. We have explored the relationship between the hard X-ray
(30-500 keV) and soft X-ray (1-8 Å) time profiles in the thick-target
model. Typically we find that the temporal derivative of the soft X-ray
emission does indeed correspond well to the instantaneous soft X-ray
emission, particularly during the rise phase of the event. The cause
of this behavior is a combination of heating and density enhancement
processes, and we assess the relative roles of each process for
a variety of simple hard X-ray time profiles, ranging from short
(5 s rise time) to long (60 s rise-time). As expected, temperature
enhancements dominate the behavior for the shortest bursts, with density
enhancements becoming important for bursts of greater than approximately
15 s duration. It also appears that some other form of gradual heating
(e.g., slow reconnection) persists through the decay phase of the event.
Title: The 1992 January 5 Flare at 13.3 UT: Observations from YOHKOH
Authors: Doschek, G. A.; Strong, K. T.; Bentley, R. D.; Brown, C. M.;
Culhane, J. L.; Fludra, A.; Hiei, E.; Lang, J.; Mariska, J. T.;
Phillips, K. J. H.; Pike, C. D.; Sterling, A. C.; Watanabe, T.; Acton,
L. W.; Bruner, M. E.; Hirayama, T.; Tsuneta, S.; Rolli, E.; Kosugi,
T.; Yoshimori, M.; Hudson, H. S.; Metcalf, T. R.; Wuelser, J. -P.;
Uchida, Y.; Ogawara, Y.
Bibcode: 1993ApJ...416..845D
Altcode:
We discuss X-ray spectra and soft X-ray images of an M1.9 flare that
occurred on 1992 January 5 near 13.3 UT. These data were obtained
with instrumentation on the Japanese Yohkoh spacecraft. They cover
the entire rise phase of the flare. To supplement these data we have
ground-based magnetograms and Hα spectroheliograms. We calculate
the electron temperature and emission measure of the flare as a
function of time during the early rise phase using X-ray spectral
line intensities and line ratios. Using spectral line widths, line
profile asymmetries, and wavelength shifts due to the Doppler effect,
we calculate the dynamical properties of the flare. The time development
of the morphology of the flare, as revealed by the soft X-ray images
and the Hα spectroheliograms, and the physical quantities inferred
from the X-ray spectra, are compared with chromospheric evaporation
models. There is an enhancement of blueshifted emission that is closely
correlated with the hard X-ray bursts. Heating of one loop in the flare
is consistent with a conduction-evaporation model, but heating is found
in several structures that do not appear to be physically associated
with each other. No standard evaporation model can adequately explain
all of the observations.
Title: Yohkoh observations of plasma upflows during solar flares
Authors: Culhane, J. L.; Phillips, A. T.; Pike, C. D.; Fludra, A.;
Bentley, R. D.; Bromage, B.; Doschek, G. A.; Hiei, E.; Inda, M.;
Mariska, J. T.; Phillips, K. J. H.; Sterling, A. C.; Watanabe, T.
Bibcode: 1993AdSpR..13i.303C
Altcode: 1993AdSpR..13..303C
Observations of two flares, an M 2.2 event on 16 December, 1991 and the
precursor to an X1 flare on 15 November, 1991 are presented. Spectra
obtained with the Bragg Crystal Spectrometer (BCS) are compared with
data from the Hard and Soft X-ray Telescopes (HXT, SXT) and the Wide
Band Spectrometer (WBS) on the satellite. For both events the creation
of upflowing plasma is detected. While the first event seems to conform
well to the chromospheric evaporation model for high temperature plasma
production, the behaviour for the second event is more complex.
Title: Books-Received - the Solar Transition Region
Authors: Mariska, J. T.
Bibcode: 1993Sci...261..239M
Altcode:
No abstract at ADS
Title: Upflowing Multimillion Degree Plasma During Solar Flares
Authors: Doschek, G. A.; Mariska, J. T.; Rilee, M.
Bibcode: 1993BAAS...25R1177D
Altcode:
No abstract at ADS
Title: Flare Plasma Dynamics Observed with the Yohkoh Bragg Crystal
Spectrometer
Authors: Mariska, J. T.; Doschek, G. A.; Bentley, R. D.
Bibcode: 1993BAAS...25Q1178M
Altcode:
No abstract at ADS
Title: A Comparison of Solar Flare Hard X-Ray Bursts with Doppler
Blue-Shifted Soft X-Ray Emission
Authors: Rilee, M. L.; Bentley, R. D.; Culhane, J. L.; Doschek, G. A.;
Mariska, J. T.; Simnett, G. M.; Watanabe, T.
Bibcode: 1993BAAS...25.1189R
Altcode:
No abstract at ADS
Title: Studying Flare Models with Yohkoh and GRO/BATSE
Authors: Zarro, D.; Mariska, J. T.; Dennis, B. R.
Bibcode: 1993BAAS...25.1186Z
Altcode:
No abstract at ADS
Title: Implications of the Soft X-Ray versus Hard X-Ray Temporal
Relationship in Solar Flares
Authors: Emslie, A. G.; Li, P.; Mariska, J. T.
Bibcode: 1993BAAS...25.1196E
Altcode:
No abstract at ADS
Title: Solar Chromospheric and Transition Region Response to Energy
Deposition in the Middle and Upper Chromosphere
Authors: Sterling, Alphonse C.; Shibata, Kazunari; Mariska, John T.
Bibcode: 1993ApJ...407..778S
Altcode:
A series of numerical simulations modeling the chromosphere and
transition region response to deposition of thermal energy ranging
from about 5 x 10 exp 24 to 5 x 10 exp 28 ergs in the middle or upper
chromosphere is reported. The dissipative effects of heat conduction,
optically thin radiation losses in the corona, and an approximate
expression for the radiation losses of lower temperature plasma are
calculated. In response to the energy deposition, chromospheric material
is ejected into the corona in the form of pressure gradient generated
jets, jets with pressure-gradient, and shock-generated components,
or high-speed gas plugs. Category of ejection depends on the spatial
and temporal distribution and the magnitude of the input energy source.
Title: YOHKOH Bragg Crystal Spectrometer light curves for CA XIX
(3.1631-3.1912A): 1 October 1991 - 30 September 1992
Authors: Mariska, John T.; Bentley, R. D.; Pike, C. D.
Bibcode: 1993YBCSCrept.....M
Altcode:
This Memo Report summarizes the data produced during the first year
of operation by the Bragg Crystal Spectrometer (BCS) on the Yohkoh
spacecraft. Each page shows the total count rate in the Ca XIX channel
of the BCS for a single day. This channel nominally observes the Sun in
the wavelength range from 3.1631 to 3.1912 A. These plots are useful
for identifying flare data for further analysis and for determining
the data file name and tape name that contain the data.
Title: Solar Doppler-Shift Measurements in the NE VII 465 Angstrom
Emission Line
Authors: Mariska, John T.; Dowdy, James F., Jr.
Bibcode: 1992ApJ...401..754M
Altcode:
Using a Dopplergram obtained with the Naval Research Laboratory extreme
ultraviolet spectrograph on Skylab, we have searched for Doppler shifts
in the Ne VII 465 A emission line, which is formed at a temperature of
about 500,000 K. In the quiet sun we find no measurable average Doppler
shift to a measurement accuracy of +/- 18 km/s. Small regions of the
quiet sun do, however, display measurable Doppler shifts. In active
regions, we measure Doppler shifts indicating downflow velocities of
up to 70 km/s.
Title: Diagnostics of Electron-heated Solar Flare Models. III. Effects
of Tapered Loop Geometry and Preheating
Authors: Emslie, A. G.; Li, Peng; Mariska, John T.
Bibcode: 1992ApJ...399..714E
Altcode:
A series of hydrodynamic numerical simulations of nonthermal
electron-heated solar flare atmospheres and their corresponding soft
X-ray Ca XIX emission-line profiles, under the conditions of tapered
flare loop geometry and/or a preheated atmosphere, is presented. The
degree of tapering is parameterized by the magnetic mirror ratio,
while the preheated atmosphere is parameterized by the initial upper
chromospheric pressure. In a tapered flare loop, it is found that
the upward motion of evaporated material is faster compared with the
case where the flare loop is uniform. This is due to the diverging
nozzle seen by the upflowing material. In the case where the flare
atmosphere is preheated and the flare geometry is uniform, the response
of the atmosphere to the electron collisional heating is slow. The
upward velocity of the hydrodynamic gas is reduced due not only to
the large coronal column depth, but also to the increased inertia
of the overlying material. It is concluded that the only possible
electron-heated scenario in which the predicted Ca XIX line profiles
agree with the BCS observations is when the impulsive flare starts in
a preheated dense corona.
Title: Observations of Several Small Flares with the Bragg Crystal
Spectrometer on YOHKOH
Authors: Culhane, J. Leonard; Fludra, Andrzej; Bentley, Robert D.;
Doschek, George A.; Watanabe, Tetsuya; Hiei, Eijiro; Lang, James;
Carter, Martin K.; Mariska, John T.; Phillips, Andrew T.; Phillips,
Kenneth J. H.; Pike, C. David; Sterling, Alphonse C.
Bibcode: 1992PASJ...44L.101C
Altcode:
We have analysed data from two flares of GOES class C7.1 and C8.5
observed by the Yohkoh Bragg Crystal Spectrometer. The high sensitivity
of the Yohkoh instrument allows us to observe the very early stages of
flare development and to study small events with a high signal-to-noise
ratio. Spectral fitting programs have been used to derive plasma
temperatures, emission measures and velocities from spectra of S XV,
Ca XIX and Fe XXV. Large plasma motions indicative of chromospheric
evaporation have been found. A more detailed analysis of a flare which
occurred on 1991 October 30 is presented.
Title: YOHKOH Bragg Crystal Spectrometer Observations of the Dynamics
and Temperature Behavior of a Soft X-Ray Flare
Authors: Doschek, George A.; Mariska, John T.; Watanabe, Tetsuya;
Hiei, Eijiro; Lang, James; Culhane, J. Leonard; Bentley, Robert D.;
Brown, Charles M.; Feldman, Uri; Phillips, Andrew T.; Phillips,
Kenneth J. H.; Sterling, Alphonse C.
Bibcode: 1992PASJ...44L..95D
Altcode:
We describe X-ray spectra of an M1.5 flare that occurred on 1991
November 9, starting at about 0313 UT. This flare is unusual in that
very intense blueshifted components are observed in the resonance
lines of Fe XXV, Ca XIX, and S XV. During the onset of the flare,
the resonance lines of Ca XIX and Fe XXV are primarily due to
this blueshifted component, which from the Doppler effect indicates
line-of-sight speeds and turbulent motions that in combination extend
up to 800 km s(-1) .
Title: Yohkoh BCS Observations of Doppler Shifts Early in Solar Flares
Authors: Mariska, J. T.; Doschek, G. A.; Sterling, A. C.; Culhane,
J. L.; Hiei, E.; Watanabe, T.; Lang, J.
Bibcode: 1992AAS...180.2308M
Altcode: 1992BAAS...24..761M
No abstract at ADS
Title: Time Variation of Solar Flare Temperatures Determined from
YOHKOH BCS Spectra
Authors: Sterling, A. C.; Doschek, G. A.; Mariska, J. T.; Pike, C. D.;
Culhane, J. L.; Hiei, E.; Watanabe, T.; YOHKOH BCS Team
Bibcode: 1992AAS...180.3001S
Altcode: 1992BAAS...24..775S
Bragg Crystal Spectrometer (BCS) X-ray spectra analysis from past
satellite missions indicate that it is possible to estimate temperatures
in highly ionized flare plasmas to within about 12\ resonance lines
in different He-like ions. This procedure is particularly valuable
in cases where other temperature measuring methods are insufficient,
such as during the rise phase of flares with strong X-ray spectra
blue shifts. Here we examine this ratio variation in several flares
using data from the Fe XXV, Ca XIX, and S XV channels of the BCS
experiment onboard the Yohkoh satellite. We select flares for
which we have good rise phase data, and calibrate the ratios using
dielectronic-to-resonance line ratios in selected Fe XXV spectra
assuming constant elemental abundances in each event. The Yohkoh BCS is
about an order of magnitude more sensitive than previous X-ray flare
spectrometers, and is therefore able to examine the early stages of
flare development in greater detail than previously possible. For this
study we select events for which we have good rise phase data, but data
well into the decay phase is available for a number of the selected
events. This allows us, for the first time, to follow the evolution
of flare spectra from relatively cool temperatures (~ 12 MK in Fe XXV)
to previously quoted ``typical" flare temperatures (~ 17 MK in Fe XXV).
Title: The solar transition region.
Authors: Mariska, J. T.
Bibcode: 1992CAS....23.....M
Altcode:
The solar transition region, which spans the temperature range from
20,000 to 1,000,000K, separates the chromosphere from the corona. All
the energy that heats the corona and powers the solar wind must pass
through this part of the solar atmosphere. All the mass that goes
into the solar wind must flow through it. This book summarizes recent
ultraviolet and extreme ultraviolet observations of the transition
region, the empirical models derived from them, and the physical
models that try to explain both the observations and the empirical
models. The observational focus is on quiet solar transition region
observations made with Skylab and subsequent rocket and satellite
experiments. In addition, the book presents a unified discussion of
the analysis of ultraviolet and extreme ultraviolet spectroscopic
data, including determination of the emission measure, and density
and temperature diagnostics.
Title: The Solar Transition Region
Authors: Mariska, John T.
Bibcode: 1992str..book.....M
Altcode: 1993str..book.....M; 1992QB528.M33......
The solar transition region that spans the temperature range from
about 20,000 to 1,000,000 K separates the solar chromosphere from
the corona. All energy that heats the corona and powers the solar
wind must pass through this part of the solar atmosphere. This book
summarizes recent ultraviolet and extreme ultraviolet observations
of the transition region, the empirical models derived from them,
and the physical models that try to explain both the observations
and the empirical models. The observational focus is on quiet solar
transition region observations made with Skylab and subsequent rocket
and satellite experiments. The book also presents a unified discussion
of the analysis of ultraviolet and extreme ultraviolet spectroscopic
data including the determination of the emission measure and density
and temperature diagnostics. This will be useful to astrophysicists
who are confronting high-resolution ultraviolet and extreme ultraviolet
data from astrophysical plasmas for the first time.
Title: The Bragg Crystal Spectrometer for SOLAR-A
Authors: Culhane, J. L.; Hiei, E.; Doschek, G. A.; Cruise, A. M.;
Ogawara, Y.; Uchida, Y.; Bentley, R. D.; Brown, C. M.; Lang, J.;
Watanabe, T.; Bowles, J. A.; Deslattes, R. D.; Feldman, U.; Fludra,
A.; Guttridge, P.; Henins, A.; Lapington, J.; Magraw, J.; Mariska,
J. T.; Payne, J.; Phillips, K. J. H.; Sheather, P.; Slater, K.;
Tanaka, K.; Towndrow, E.; Trow, M. W.; Yamaguchi, A.
Bibcode: 1991SoPh..136...89C
Altcode:
The Bragg Crystal Spectrometer (BCS) is one of the instruments which
makes up the scientific payload of the SOLAR-A mission. The spectrometer
employs four bent germanium crystals, views the whole Sun and observes
the resonance line complexes of H-like FeXXVI and He-like FeXXV,
CaXIX, and SXV in four narrow wavelength ranges with a resolving power
(λ/Δλ) of between 3000 and 6000. The spectrometer has approaching
ten times better sensitivity than that of previous instruments thus
permitting a time resolution of better than 1 s to be achieved. The
principal aim is the measurement of the properties of the 10 to 50
million K plasma created in solar flares with special emphasis on the
heating and dynamics of the plasma during the impulsive phase. This
paper summarizes the scientific objectives of the BCS and describes
the design, characteristics, and performance of the spectrometers.
Title: Numerical Simulations of Microflare Evolution in the Solar
Transition Region and Corona
Authors: Sterling, Alphonse C.; Mariska, John T.; Shibata, Kazunari;
Suematsu, Yoshinori
Bibcode: 1991ApJ...381..313S
Altcode:
Several observers report transient ultraviolet brightenings, often
referred to as microflares, in the solar atmosphere. In this paper,
the results are presented of a series of one-dimensional numerical
simulations examining possible relationships between microflares
and the generation of dynamical chromospheric and transition region
features. Low-energy and medium-energy microflares eject long-lived
cool, dense gas plugs into the corona, with the gas plug traversing
the loop apex in the medium energy case. In the case of high-energy
microflares, the gas plug is rapidly heated to the temperature of the
surrounding corona, and the results resemble the dynamics occurring
in standard solar flare thick-target electron beam models.
Title: Soft X-Ray Emission from Electron-Beam--heated Solar Flares
Authors: Mariska, John T.; Zarro, Dominic M.
Bibcode: 1991ApJ...381..572M
Altcode:
Using time-dependent numerical simulations and Solar Maximum Mission
observations of a solar flare on 1985 January 23, a study is conducted
of the ability of an electron-beam-heating model to reproduce the
rise phase of a flare as observed in soft X-ray lines of Ca XIX. The
electron beam is parameterized by a peak flux, a low-energy cutoff, and
a spectral index, and has a time dependence similar to the observed hard
X-ray burst. For a spectral index of 6, only models with a low-energy
cutoff of 20 keV reproduce the observed peak emission in the Ca XIX
line complex. All models with a low-energy cutoff of 15 keV produce
too much emission, while all models with a 25-keV cutoff too little
emission. None of the models reproduces the temporal behavior of the
soft X-ray emission. The electron-beam-heated component is theorized to
only represent a small fraction of the energy released in the impulsive
phase of this flare.
Title: Nonequilibrium Ionization Effects in Asymmetrically Heated
Loops
Authors: Spadaro, D.; Antiochos, Spiro K.; Mariska, J. T.
Bibcode: 1991ApJ...382..338S
Altcode:
The effects of nonequilibrium ionization on magnetic loop models with
a steady siphon flow that is driven by a nonuniform heating rate are
investigated. The model developed by Mariska (1988) to explain the
observed redshifts of transition region emission lines is examined,
and the number densities of the ions of carbon and oxygen along the
loop are computed, with and without the approximation of ionization
equilibrium. Considerable deviations from equilibrium were found. In
order to determine the consequences of these nonequilibrium effects
on the characteristics of the EUV emission from the loop plasma, the
profiles and wavelength positions of all the important emission lines
due to carbon and oxygen were calculated. The calculations are in broad
agreement with Mariska's conclusions, although they show a significant
diminution of the Doppler shifts, as well as modifications to the line
widths. It is concluded that the inclusion of nonequilibrium effects
make it more difficult to reproduce the observed characteristics of
the solar transition region by means of the asymmetric-heating models.
Title: Solar Doppler Shift Measurements in the Ne VII 465 Å
Emission Line
Authors: Mariska, J. T.; Dowdy, J. F., Jr.
Bibcode: 1991BAAS...23.1060M
Altcode:
No abstract at ADS
Title: Numerical Studies of Atmospheric Dynamics Driven by Energy
Deposition in the Chromosphere
Authors: Sterling, A. C.; Mariska, J. T.; Shibata, K.
Bibcode: 1991BAAS...23.1029S
Altcode:
No abstract at ADS
Title: Numerical Simulations of Electron-Beam-Heated Solar Flares
Authors: Mariska, John T.
Bibcode: 1991LNP...387..153M
Altcode: 1991fpsa.conf..153M
Using time-dependent numerical simulations and Solar Maximum Mission
(SMM) observations of a solar flare on 1985 January 23, we examine the
ability of an electron-beam-heated model to reproduce the rise phase
of a flare as observed in soft X-ray lines of CaXIX. For a spectral
index of 6, only models with a low-energy cutoff of 20 keV reproduce
the observed peak emission in the CaXIX line complex. None of the
models reproduces the temporal behavior of the soft X-ray emission.
Title: Numerical Simulations of Ultraviolet and X-ray Microflares
Authors: Sterling, A. C.; Shibata, K.; Mariska, J. T.
Bibcode: 1991LNP...387...71S
Altcode: 1991fpsa.conf...71S
A series of numerical simulations indicates that thermal energy
releases of 1025 - 1027 ergs in the middle chromosphere can produce
ejections into the corona in the form of pressure gradient generated
jets, jets with pressure gradient and shock generated components, or
high speed gas plugs. Heating of the chromosphere to X-ray emitting
temperatures occurs in association with gas plugs, perhaps generating
X-ray microflares observable by Solar-A. Chromospheric UV-microflares
can occur in association with some jets, but do not generally occur
with spicules.
Title: Numerical Simulation of Microflare Evolution in the Solar
Transition Region and Corona (With 4 Figures)
Authors: Sterling, A. C.; Mariska, J. T.
Bibcode: 1991mcch.conf..630S
Altcode:
No abstract at ADS
Title: Flare Loop Areas Inferred from Ca XIX Observations
Authors: Zarro, D. M.; Mariska, J. T.
Bibcode: 1990BAAS...22.1197Z
Altcode:
No abstract at ADS
Title: Dynamic modeling of the solar atmosphere
Authors: Mariska, J. T.; Dahlburg, R. B.; Karpen, J. T.; Picone, J. M.
Bibcode: 1990EOSTr..71..791M
Altcode:
A brief review is presented of work done over the last eight years
investigating the fundamental physics of plasmas and magnetic fields
under conditions similar to those that are thought to be present in the
outer layers of the solar atmosphere, including the transition region
and the corona. The models used to study the coronal structures and
the thermal instability in the solar atmosphere are discussed. The
results of studies of magnetic energy release in the corona and MHD
turbulence in the solar wind are examined.
Title: Numerical Simulations of the Rebound Shock Model for Solar
Spicules
Authors: Sterling, Alphonse C.; Mariska, John T.
Bibcode: 1990ApJ...349..647S
Altcode:
Using time-dependent numerical simulations, the proposed rebound shock
mechanism for spicules has been examined. At temperatures above a
critical value, T(c), the radiation is characteristic of the conditions
in the optically thin corona and near optically thin transition
region. When T less than T(c), the atmosphere has a radiative cooling
time, tau(rad) characteristic of chromosphere. The spicule is initiated
with a quasi-impulsive force in the low chromosphere, which drives a
train of upward propagating rebound shocks along the rigid magnetic flux
tube. These shocks then move the transition region upward. The material
below the displaced transition region has temperatures and densities
similar to those of spicules when T(c) = 20,000 K or more and tau(rad)
= 500 s or more, but not when T(c) = 10,000 K, and probably not when
tau(rad) = 100 s. For all the cases where the cross sectional area
diverges rapidly with height, the upward velocity of the transition
region is less than that of spicules. Moreover, the maximum height is
less than that of average spicules. Taller, higher velocity spicules
result when the magnetic field cross sectional area is constant. In
all cases, the rebound shock mechanism produces substantial motions
and temperature and density variations in chromospheric and transition
region material. It is suggested that this may be a partial explanation
for the continuous dynamic state of the lower solar atmosphere.
Title: Numerical Simulations of Impulsively Heated Solar Flares
Authors: Mariska, John T.; Emslie, A. Gordon; Li, Peng
Bibcode: 1989ApJ...341.1067M
Altcode:
The response of a model solar atmosphere to heating by an electron beam
has been studied for electron beam flux spectra which are power laws
with low-energy 'knees' (rising linearly with time to a peak at 30 s
and then falling linearly to 0 at 60 s) ranging from 10 to 20 keV. The
results indicate that high peak electron beam fluxes, low-energy knees,
and larger spectral indices all move the atmospheric response toward
greater enhancements of the parameters in the coronal regions of the
atmosphere. Coronal responses can thus be used as a diagnostic of the
parameters of the electron beam.
Title: Soft X-Ray Diagnostics of Electron-heated Solar Flare
Atmospheres
Authors: Li, Peng; Emslie, A. Gordon; Mariska, John T.
Bibcode: 1989ApJ...341.1075L
Altcode:
The dependence of the impulsive-phase Ca XIX w line profile on the
form of the flare energy input (assumed to be due to the collisional
degradation of a beam of high-energy electrons) is considered. The
injected flux spectrum has the form of a power law with a low-energy
'knee', and the effects of varying the total energy flux, spectral
index, and knee energy on the w line profile during the impulsive
phase have been evaluated. Early in the burst, blueshifts of order 400
km/s are noted, and the peak intensity of the blueshifted component
together with spatially unresolved hard X-ray burst spectra can be
used to determine the beam filling factor.
Title: Soft X-Ray Emission from Electron-Beam-Heated Solar Flares
Authors: Mariska, J. T.; Zarro, D. M.
Bibcode: 1989BAAS...21..850M
Altcode:
No abstract at ADS
Title: Soft X-Ray Profiles as a Diagnostic of Impulsive Flare Energy
Deposition
Authors: Emslie, A. G.; Li, P.; Mariska, J. T.
Bibcode: 1989BAAS...21..850E
Altcode:
No abstract at ADS
Title: Observational Signatures of Loop Flows Driven by Asymmetric
Heating
Authors: Mariska, John T.
Bibcode: 1988ApJ...334..489M
Altcode:
Using time-dependent numerical simulations, the author has investigated
the observational consequences of highly asymmetric heating in small
transition-region loops. The simulations show that, to an observer
looking down on the loop, the plasma at C IV - emitting temperatures
will appear to be redshifted, as is seen on the Sun. Because of the
highly asymmetric location, there will be some cutoff temperature above
which the redshifted emission will be replaced by only blueshifted
emission. These calculations show that the observation of a blueshifted
emission line in the upper transition region of the Sun or other
late-type stars may not be evidence for the initial acceleration of
the solar wind, but rather just part of a closed circulation 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.
Bibcode: 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: Numerical Simulations of the Rebound Shock Model for Spicules
Authors: Sterling, A. C.; Mariska, J. T.
Bibcode: 1988BAAS...20Q.989S
Altcode:
No abstract at ADS
Title: Ca XIX X-Ray Emission-Line Signatures of Impulsively Heated
Solar Flares
Authors: Mariska, J. T.
Bibcode: 1988BAAS...20..978M
Altcode:
No abstract at ADS
Title: Helical magnetohydrodynamic turbulence and the coronal
heating problem
Authors: Dahlburg, R. B.; Dahlburg, J. P.; Mariska, J. T.
Bibcode: 1988A&A...198..300D
Altcode:
Numerical simulations are used to investigate the relaxation of an
unconfined, helically turbulent, fully three-dimensional magnetofluid,
with conditions similar to those which are thought to result in
the heating of the solar corona. In these simulations, the system
evolves through a succession of force free states. After a relatively
quiescent period of Ohmic decay, a phase of accelerated magnetic
energy dissipation occurs. Some magnetic energy is transformed into
kinetic energy, and the magnitude of entrophy created is a nontrival
fraction of the mean square electric current. Concentrated vorticity
structures are seen to play almost as important a role as electric
current sheets in the heating process. Coincident with this accelerated
dissipation process, a reorganization of the magnetic fields occurs,
with transfer of magnetic energy to both shorter and longer wavelength
modes than are initially present. The ratio of the magnetic field to
the electric current density, alpha does not in general tend to assume
a constant value in the force free regions during the evolution of
the magnetofluid.
Title: Heating-related Flows in Cool Solar Loops
Authors: Klimchuk, J. A.; Mariska, J. T.
Bibcode: 1988ApJ...328..334K
Altcode:
The authors have investigated the effects of spatial and temporal
variations in the heating of cool loop models in an attempt
to explain the net redshifts that are observed on the Sun. In
none of the situations considered are the induced flows able to
satisfactorily reproduce the observations. In the case of asymmetric
heating, the end-to-end flows can be as fast as 20 km s-1,
but the downflowing leg is neither appreciably faster nor appreciably
brighter than the upflowing leg; no net redshift is produced. In the
case of symmetric heating, the downflows can also be large, but they are
restricted to temperatures that are well below 105K. Neither
situation would give rise to the ⪆7 km s-1 disk-averaged
redshifts seen in emission lines of species like C IV.
Title: Numerical Simulations of Impulsively Heated Solar Flares
Authors: Mariska, J. T.; Emslie, A. G.; Li, P.
Bibcode: 1988BAAS...20..715M
Altcode:
No abstract at ADS
Title: Soft X-Ray Diagnostics of Impulsively Heated Solar Flare
Atmosphere
Authors: Li, P.; Emslie, A. G.; Mariska, J. T.
Bibcode: 1988BAAS...20..715L
Altcode:
No abstract at ADS
Title: Influence of Heating Rate on the Condensational Instability
Authors: Dahlburg, R. B.; Mariska, J. T.
Bibcode: 1988SoPh..117...51D
Altcode:
We determine by analysis and numerical simulation the effect that
various heating rates have on the linear and nonlinear evolution of
a typical plasma within a solar magnetic flux tube subject to the
condensational instability. We first derive a dispersion relation
for infinitesimal disturbances to a condensationally unstable fluid
subject to heating rates which are functions of temperature and thermal
pressure. This relation leads to an algebraic model for predicting
solar flux tube stability in the longwavelength limit as a function
of temperature. We find that linear stability depends strongly on the
heating rate. We then present the results of numerical simulations of
the nonlinear evolution of the condensational instability in a solar
magnetic flux tube. Different heating rates lead to quite different
nonlinear evolution, as evidenced by the behaviour of the global
internal energy. Almost all of the heating rates that we consider
produce saturation in bifurcated states, but at somewhat different
temperatures and mass densities.
Title: A model for the structure and formation of prominences.
Authors: Poland, A. I.; Mariska, J. T.
Bibcode: 1988dssp.conf..133P
Altcode:
The authors present a geometric model for the magnetic structure of
a prominence inspired by recent high resolution images and magnetic
field measurements of filaments and prominences. In this model the
observed prominence structures are a mapping of locations in the
magnetic field structure where material can condense without falling
to the chromosphere. Vertical structures near the footpoints are a
series of near potential fields.
Title: Solar transition region and coronal response to heating rate
perturbations.
Authors: Mariska, John T.
Bibcode: 1987NASCP2483..117M
Altcode: 1987tphr.conf..117M
The solar transition region is in a dynamic state characterized by
impulsively upflowing plasma and continually downflowing plasma. Using
numerical simulations, the conjecture that the areas of downflowing
plasma are simply the base regions of coronal loops in which the
heating rate is gradually decreasing and the areas of upflowing
plasma are the base regions of coronal loops in which the heating
rate is gradually increasing is examined. The calculations suggest
that gradually reducing or increasing the heating in a magnetic flux
tube will not result in plasma motions that are similar to those that
are observed at high spatial resolution in the UV.
Title: Observational Consequences of Highly Asymmetric Heating in
Coronal Loops
Authors: Mariska, J. T.
Bibcode: 1987BAAS...19.1133M
Altcode:
No abstract at ADS
Title: Production of Heat Energy in a Potential Magnetic Field
Authors: Dahlburg, R. B.; Mariska, J. T.
Bibcode: 1987BAAS...19.1121D
Altcode:
No abstract at ADS
Title: A Numerical Study of the Nonlinear Thermal Stability of
Solar Loops
Authors: Klimchuk, J. A.; Antiochos, S. K.; Mariska, J. T.
Bibcode: 1987ApJ...320..409K
Altcode:
A time-dependent numerical model is used to investigate the nonlinear
thermal stability of static loops of various heights. Simulations show
that the instability of a hot state with loop heights of less than about
1000 km is physically significant, with an initially hot atmosphere
in low-lying compact loops evolving to an extended atmosphere with
temperatures far below 100,000 K. Results also show that high-lying
loops are stable to all reasonable perturbations, including those of
large initial amplitude and long wavelength. The simulation results
suggest that low-lying compact loops should not be common to the sun,
and that cool loops with temperatures near 100,000 K must be formed
in the cool state initially and cannot evolve from preexisiting loops.
Title: A numerical study of the thermal stability of solar loops.
Authors: Klimchuk, J. A.; Antiochos, S. K.; Mariska, J. T.
Bibcode: 1987NASCP2483..113K
Altcode: 1987tphr.conf..113K
An important property of all loops is their thermal stability. If low
lying hot loops were thermally unstable, for example, a great majority
of the low loops on the Sun might be expected to be cool. How small
perturbations evolve in low lying, linearly unstable hot loops was
determined and how high lying, linearly stable hot loops respond to
large amplitude disturbances such as might be expected on the Sun were
examined. Only general descriptions and results are given.
Title: Solar Transition Region and Coronal Response to Heating
Rate Perturbations
Authors: Mariska, John T.
Bibcode: 1987ApJ...319..465M
Altcode:
Observations of Doppler shifts in UV emission lines formed in the
solar transition region show continual plasma downflows and impulsive
plasma upflows. Using numerical simulations, the authors examine the
conjecture that areas of downflowing plasma are the base regions of
coronal loops in which the heating is gradually decreasing and that
areas of upflowing plasma are the base regions of coronal loops in which
the heating rate is gradually increasing. Beginning with a coronal loop
in equilibrium, the heating rate is reduced on time scales of 100,
1000, and 2000 s to 10 percent and 1 percent of the initial value,
and the loop is allowed to evolve to a new equilibrium. The heating
rate for the cooled models is then increased back to the initial value
on the same time scales. While significant mass motions do develop in
the simulations, both the emission measure and the velocity at 100,000
K do not show the characteristics present in UV observations.
Title: Heating Related Flows in Cool Loops
Authors: Klimchuk, J. A.; Mariska, J. T.
Bibcode: 1987BAAS...19..932K
Altcode:
No abstract at ADS
Title: Nonlinear Evolution of Radiation-driven Thermally Unstable
Fluids
Authors: Dahlburg, R. B.; DeVore, C. R.; Picone, J. M.; Mariska,
J. T.; Karpen, J. T.
Bibcode: 1987ApJ...315..385D
Altcode:
The nonlinear evolution of a radiation-driven thermally unstable planar
fluid is simulated numerically using a semiimplicit finite-difference
algorithm. When the equilibrium state of the fluid is perturbed
by random initial excitation of the velocity field, dense, cool,
two-dimensional structures are found to form in a rarer, warmer
surrounding medium. The nonlinear phase of evolution is characterized
by the turbulent contraction of the condensed region, accompanied by a
significant increase in the amount of energy radiated. It is found that,
if the random velocity perturbation has a sufficiently large amplitude,
the fluid will not form condensed structures. Finally, the relationship
of these results to observations of the solar chromosphere, transition
region, and corona is discussed.
Title: Nonlinear aspects of planar condensational instability
Authors: Dahlburg, R. B.; DeVore, C. R.; Picone, J. M.; Mariska,
J. T.; Karpen, J. T.
Bibcode: 1987STIN...8723565D
Altcode:
The numerical simulation of the nonlinear evolution of a radiation
driven thermally unstable planar fluid, using a semi-implicit finite
difference algorithm is discussed. When the equilibrium state of the
fluid is perturbed by random initial excitation of the velocity field,
dense, cool, two dimensional structures are observed forming in a
rarer, warmer, surrounding medium. The nonlinear phase of evolution
is characterized by the turbulent contraction of the condensed
region, accompanied by a significant increase in the amount of energy
radiated. If the random velocity perturbation has a sufficiently large
amplitude, the fluid will not form condensed structures. Finally, the
relationship of these results to observations of the solar chromosphere,
transition region and corona is discussed.
Title: A Model for the Structure and Formation of Prominences
Authors: Poland, A. I.; Mariska, J. T.
Bibcode: 1987dssp.work..133P
Altcode: 1987ASSL..150..133P
No abstract at ADS
Title: Flux Tube Dynamics and Solar/Stellar Redshift Measurements
(Invited review)
Authors: Mariska, John T.
Bibcode: 1987LNP...291...21M
Altcode: 1987csss....5...21M; 1987LNP87.291...21M
On the Sun and other late-type stars, UV observations show persistent
red-shifted profiles in emission lines formed near 105 K in
the transition region. These downflows could be the result either of
the cooling and downfall of material in coronal loops or of the steady
end-to-end flow of plasma in smaller loops. Time-dependent numerical
simulations suggest that the steady flow explanation is the most likely.
Title: Numerical simulations of a siphon mechanism for quiescent
prominence formation.
Authors: Poland, A. I.; Mariska, J. T.; Klimchuk, J. A.
Bibcode: 1986NASCP2442...57P
Altcode: 1986copp.nasa...57P
Quiescent prominences represent a significant challenge to our
understanding of the flow of mass and energy in the outer layers of
the solar atmosphere. A small number of quiescent prominences contain
as much mass as the entire corona (Athay, 1976). The problem then is
how to get that much material into the relatively small volume of
a prominence and maintain it at a temperature of 10,000 K in close
proximity to material at one million K. The thermal insulation to
conduction provided by the magnetic field explains the disparate
temperatures. The mass source problem is less well understood. One
method for supplying mass to the prominence is to siphon it from the
chromosphere. The siphon mechanism begins with a magnetic loop that
evolves into a configuration with a gravitational well, such as that
described by Kippenhahn and Schluter (1957). This could be formed, for
example, by a twist in the magnetic field. A gravitational well could
also be formed by a condensation induced sag in the field. This could
further enhance the condensation process. Once this well has formed,
or as it is forming, the material in the well area of the loop must
cool and condense to the point where radiative losses exceed any
heat input. Additional material must also flow into the well from
the underlying chromosphere to supply the mass required to form the
prominence. One example from a series of numerical simulations that were
performed to study the formation of quiescent prominences is presented.
Title: A numerical study of the thermal stability of low-lying
coronal loops.
Authors: Klimchuk, J. A.; Antiochos, S. K.; Mariska, J. T.
Bibcode: 1986NASCP2442..389K
Altcode: 1986copp.nasa..389K
The nonlinear evolution of loops that are subjected to a variety
of small but finite perturbations was studied. Only the low-lying
loops are considered. The analysis was performed numerically using a
one-dimensional hydrodynamical model developed at the Naval Research
Laboratory. The computer codes solve the time-dependent equations
for mass, momentum, and energy transport. The primary interest is
the active region filaments, hence a geometry appropriate to those
structures was considered. The static solutions were subjected to a
moderate sized perturbation and allowed to evolve. The results suggest
that both hot and cool loops of the geometry considered are thermally
stable against amplitude perturbations of all kinds.
Title: Numerical Simulation of Turbulent Coronal Self-Organization
Authors: Dahlburg, R. B.; Dahlburg, J. P.; Mariska, J. T.
Bibcode: 1986BAAS...18..901D
Altcode:
No abstract at ADS
Title: Solar Transition Region and Coronal Response to Heating
Rate Perturbation
Authors: Mariska, J. T.
Bibcode: 1986BAAS...18..901M
Altcode:
No abstract at ADS
Title: A Siphon Mechanism for Supplying Prominence Mass
Authors: Poland, A. I.; Mariska, J. T.
Bibcode: 1986SoPh..104..303P
Altcode:
We examine a siphon-like mechanism for moving mass from the chromosphere
to a gravitational well at the top of a magnetic loop to form a
prominence. The calculations assume no apriori flow velocity at the loop
base. Instead heating in the loop legs drives the flow. The prominence
formation process requires two steps. First, the background heating
rate must be reduced to on the order of 1 % of the initial heating
rate required to maintain the coronal loop. This forms an initial
condensation at the top of the loop. Second, the heating must take
place only in the loop legs in order to produce a pressure differential
which drives mass up into the well at the top of the loop. The heating
rate in the loop must be increased once the prominence has begun to
form or full prominence densities can not be achieved in a reasonable
time. We conclude that this heating driven siphon-like mechanism is
feasible for producing and maintaining prominences.
Title: Turbulent Condensation
Authors: Dahlburg, R. B.; Picone, J. M.; Mariska, J. T.
Bibcode: 1986BAAS...18..676D
Altcode:
No abstract at ADS
Title: A Numerical Study of the Stability of Low-Lying Solar Loops
Authors: Mariska, J. T.; Klimchuk, J. A.; Antiochos, S. K.
Bibcode: 1986BAAS...18Q.708M
Altcode:
No abstract at ADS
Title: The quiet solar transition region.
Authors: Mariska, John T.
Bibcode: 1986ARA&A..24...23M
Altcode:
The results of recent studies (in the UV) of the structure and dynamics
of the quiet solar transition region and its role in the mass and energy
balance of the outer layers of the solar atmosphere are summarized. The
region is one in which temperature increases from 25,000 K to about 1
million K and the matter density, fed by the outward flowing wind and
the inward streaming plasma, increases by a factor of 40. The morphology
of the region is described, along with the theoretical models being
applied to the observed nonthermal line broadening, Doppler wavelength
shifts, temporal fluctuations, and fine structure. Deficiencies in
existing simple models of the region are discussed.
Title: Magnetic energy storage and conversion in the solar atmosphere.
Authors: Spicer, D. S.; Mariska, J. T.; Boris, J. P.
Bibcode: 1986psun....2..181S
Altcode:
Contents: Fundamental concepts (magnetic energy generation, ideal MHD
theory, non-MHD properties, the concept of "anomalous" resistivity,
global electrodynamic coupling). Magnetically controlled energy
conversion (magnetic modifications of plasma transport, transition
region structure and flows, channeling and acceleration of plasma,
channeling and dissipation of MHD waves, anomalous dissipation
of field-aligned currents). Magnetohydrodynamic energy conversion
(magnetic flux tube emergence, geometric rearrangements, reconnection
and magnetic tearing, particle acceleration at a neutral sheet, flare
trigger mechanisms). Outstanding questions.
Title: On V and hard X-rays, observations and model calculations.
Authors: Poland, A. I.; Mariska, J. T.
Bibcode: 1986NASCP2449..279P
Altcode: 1986rfsf.nasa..279P
This paper is an amalgamation of two published works that discuss
the observation and theoretical calculations of O V (T ≡ 250,000K)
and hard X-rays (30 - 100 keV) emitted during flares. The papers are
by Poland et al. (1984, see Abstr. 37.073.132) and Mariska and Poland
(1985, see Abstr. 39.076.024). The observations of hard X-rays and
O V show that the excitation processes for each type of emission are
closely coupled. Except for small differences the two types of emission
rise and fall together during a flare. Model calculations are able
to reproduce this behavior to a large extent, only when conductive
processes do not dominate the energy transport processes.
Title: Nonlinear Numerical Simulation of Planar Thermal Instability
Authors: Dahlburg, R. B.; DeVore, C. R.; Picone, J. M.; Karpen, J. T.;
Mariska, J. T.
Bibcode: 1985BAAS...17..833D
Altcode:
No abstract at ADS
Title: Two-Dimensional Nonlinear Numerical Simulations of Thermal
Instability in the Solar Atmosphere
Authors: Picone, J. M.; Dahlburg, R. B.; DeVore, C. R.; Karpen, J. T.;
Mariska, J. T.
Bibcode: 1985BAAS...17..843P
Altcode:
No abstract at ADS
Title: Numerical Simulation of a Siphon Mechanism for Quiescent
Prominences
Authors: Mariska, J. T.; Poland, A. I.
Bibcode: 1985BAAS...17..842M
Altcode:
No abstract at ADS
Title: Alfvenic pulses in the solar atmosphere
Authors: Mariska, J. T.; Hollweg, J. V.
Bibcode: 1985ApJ...296..746M
Altcode:
Some nonlinear aspects of Alfvenic pulses propagating in coronal loops
and the underlying chromosphere are numerically investigated. Heat
conduction and radiation are included. The Alfvenic pulses
are modeled as axisymmetric twists on a vertical cylindrical
flux tube. They nonlinearly couple into acoustic-gravity waves
propagating along the flux tube. A single Alfvenic pulse is found
to leave two acoustic-gravity pulses in its wake. These pulses can
result in significant motions of the transition region and underlying
chromosphere. These motions do not resemble spicules, but they may
correspond to a variety of observations indicating that the solar
atmosphere is in a continual dynamic state. It is suggested that
a dynamic chromosphere and transition region may be the inevitable
consequence of the coronal heating process itself.
Title: The Relation Between Hard X-Ray and Transition Region Line
Emission in Solar Flares
Authors: Mariska, J. T.; Poland, A. I.
Bibcode: 1985SoPh...96..317M
Altcode:
Observational evidence suggests that both the hard X-ray and ultraviolet
emission from the impulsive phase of flares result from an electron
beam. We present the results of model calculations that are consistent
with this theory. The impulsive phase is envisioned as occurring
in many small magnetically confined loops, each of which maintains
an electron beam for only a few seconds. This model successfully
matches several observed aspects of the impulsive phase. The corona is
heated to less than 2 × 106 K, maximum enhanced emission
occurs in lines formed near 105 K, and there is only
slight enhancement between 105 and 2 × 106
K. The slope of the observed relationship between hard X-ray and
OV 1371 Å emission is also matched, but the relative emission is
not. The calculations indicate that UV emission lines formed below a
temperature of about 105 K will arise predominantly from
the chromospheric region heated by the electron beam to transition
region temperatures. Emission lines formed at higher temperatures will
be produced in the transition region. This should be detectable in
density-sensitive line ratios. To account successfully for the impulsive
UV emission, the peak temperature in the impulsively heated loops must
remain below about 2 × 106 K. Thus our model implies that
the impulsive heating takes place in different loops from the hotter
gradual phase emission.
Title: Alfvénic Pulses in the Solar Atmosphere
Authors: Mariska, J. T.; Hollweg, J. V.
Bibcode: 1985BAAS...17..643M
Altcode:
No abstract at ADS
Title: Effects of mass motions on solar emission measures inferred
from transition-region emission lines
Authors: Mariska, J. T.
Bibcode: 1984ApJ...281..435M
Altcode:
Extreme ultraviolet emission line intensities predicted by a numerical
model which includes nonequilibrium ionization balance are used as
input "observational" intensities to calculate volume emission measures
following a standard method which assumes ionization equilibrium. These
"observational" emission measures are then compared with the actual
emission measure distribution in the atmospheric model. For static
equilibrium models, the two sets of emission measures are in good
agreement. When mass motions are present, the emission measures
calculated from the line intensities differ significantly from the
actual values.
Title: The energy relation between hard X-ray and O V emission in
solar flares
Authors: Poland, A. I.; Orwig, L. E.; Mariska, J. T.; Auer, L. H.;
Nakatsuka, R.
Bibcode: 1984ApJ...280..457P
Altcode:
The relationship between energy emitted in hard X-rays and the
ultraviolet during the impulsive phase of solar flares provides
an important diagnostic for understanding the energy flow from
nonthermal to thermal. Many flares were observed from the Solar
Maximum Mission satellite simultaneously in hard X-rays and the O V
line at 1371 A formed at 250,000 K, providing information relevant to
this problem. Previous work has shown that short time scale peaks in
emission of these two types of radiation coincide in time to within 1
s. In this work the energy relation between the two types of emission
is investigated and it is found that for any given flare there is a
definite relation between hard X-ray and O V emissions throughout
the flare, but from one flare to the next this relation varies
markedly. These differences are attributed to the initial conditions in
the flaring loops and some exploratory model calculations are presented
to support this hypothesis.
Title: The Relation Between Hard X-Ray and Transition-Region Line
Emission in Solar Flares
Authors: Mariska, J. T.; Poland, A. I.
Bibcode: 1984BAAS...16R.543M
Altcode:
No abstract at ADS
Title: MHD waves and turbulence in the sun and interplanetary medium.
Authors: Barnes, A.; Goldstein, M.; Hollweg, J.; Mariska, J.;
Matthaeus, W.; Smith, C.; Smith, E.; Stein, R.; Withbroe, G.; Woo, R.
Bibcode: 1984NASRP1120....4B
Altcode:
Contents: Introduction. Global oscillations of the sun. Observations
related to waves or turbulence in the solar atmosphere. Local waves
in the solar atmosphere: theoretical considerations. Interplanetary
hydromagnetic fluctuations. Recent studies of the interplanetary plasma
based on turbulence theory. Effects of waves and turbulence of the
solar wind.
Title: Effects of Mass Motions on Solar Emission Measures Inferred
from Transition Region Emission Lines
Authors: Mariska, J. T.
Bibcode: 1983BAAS...15..918M
Altcode:
No abstract at ADS
Title: Dynamics and spectroscopy of asymmetrically heated coronal
loops
Authors: Mariska, J. T.; Boris, J. P.
Bibcode: 1983ApJ...267..409M
Altcode:
Numerical models of steady flows along coronal magnetic flux tubes of
varying cross sectional areas are investigated. The flows are induced
by altering the spatial symmetry of the heating. In two cases the flux
tube geometry is symmetric about the top of the loop, but the spatial
dependence of the heating rate is changed from a symmetric deposition
which supports a stationary equilibrium to a time-independent asymmetric
deposition. In a third case the volumetric heating rate is uniform, but
one half of the loop is larger in volume than the other. The resulting
velocity structure varies significantly with changes in the flux tube
geometry. Calculations of the ionization balance and line emission for
a number of ionization stages of oxygen suggest that heating induced
flows may be responsible for the redshifts seen in spectral lines
formed in the network at transition region temperatures.
Title: Relation Between Hard X-ray and OV Energy Emitted During
Solar Flares
Authors: Poland, A. I.; Orwing, L. E.; Mariska, J. T.; Auer, L. H.
Bibcode: 1983BAAS...15..713P
Altcode:
No abstract at ADS
Title: Numerical simulations of loops heated to solar flare
temperatures. I
Authors: Cheng, C. -C.; Oran, E. S.; Doschek, G. A.; Boris, J. P.;
Mariska, J. T.
Bibcode: 1983ApJ...265.1090C
Altcode:
The NRL's Dynamic Flux Tube Model is used to numerically simulate
the dynamic response of a coronal magnetic loop to an energy input of
the order encountered in solar flares. The coronal plasma is heated
by the deposition of flare energy at the top of the loop to more
than 10 million K, yielding a conduction front that moves toward
the chromosphere, where the plasma is heated by the large downward
conductive flux and ablates upward to the coronal part of the loop at
velocities of a few hundred km/sec. The conduction front simultaneously
produces chromospheric ablation and compresses the material ahead of
it. With the aid of compressional instabilities, the compressed plasma
grows throughout the flare heating phase, presenting a possible source
of the flare optical continuum emission which is correlated with soft
X-ray radiation. The observational consequences of rapidly heated
loop gas dynamic processes are discussed. In the second part of this
presentation, the dynamical calculation results previously obtained are
used to predict the spectral line intensities, profiles and wavelengths
of several X-ray lines and the UV line of Fe XXI at 1354.1 A. Three
different viewing orientations of the loop are considered.
Title: Numerical Simulations of Loops Heated to Solar Flare
Temperatures - Part Two - X-Ray and Ultraviolet Spectroscopy
Authors: Doschek, G. A.; Cheng, C. C.; Oran, E. S.; Boris, J. P.;
Mariska, J. T.
Bibcode: 1983ApJ...265.1103D
Altcode:
In the first paper in this series, numerical simulation techniques
were used to investigate the fluid dynamics of plasma that is confined
to a magnetic flux tube and is heated to solar flare temperatures of
about 2 × 107 K. The temperature, density, and velocity
of the plasma were derived as functions of position and time in the
flux tube or loop, after deposition of flare energy at the top of the
loop. In this paper the results of the dynamical calculations described
in the first paper in this series are used to predict the spectral
line intensities, profiles, and wavelengths of several X-ray lines
and the UV line of Fe XXI at 1354.1 Å. The distribution of emission
from these lines within the loop is computed, as well as the profiles
of the lines that would be recorded by a spectrometer that viewed
the entire loop. Three different viewing orientations of the loop are
considered. The computed spectra are compared with recent observations
obtained from orbiting spacecraft. The computed differential emission
measure is flatter than observed, and this result is similar to previous
analytical and numerical calculations. The computed X-ray profiles
of Fe xxv and Ca xix lines show a stationary component, i.e., no shift
in wavelength due to the Doppler effect, and shifted components produced
by ablated chromospheric plasma. These profiles qualitatively resemble
some of the X-ray observations. A large Doppler shift of about 0.7
Å is predicted for the Fe XXI line. Such a shift is unobserved in
spectra obtained from the Naval Research Laboratory spectrograph on
Skylab. Physically different flare models can apparently produce
markedly different spectroscopic results. Differences between computed
and observed spectra suggest modifications of the model that might
produce better agreement between these quantities and hence result in
a better understanding of flare morphology and heating mechanisms.
Title: The dynamics of accelerating coronal bullets
Authors: Karpen, J. T.; Oran, E. S.; Mariska, J. T.; Boris, J. P.;
Brueckner, G. E.
Bibcode: 1982ApJ...261..375K
Altcode:
Results are presented of computer simulations of the jets
that accelerate through the corona at velocities of 50 to 400
km/s. Particular emphasis is placed on the sensitivity of the induced
acceleration to the form in which energy is put into the system. A
comparison is made between the observed and predicted physical
characteristics of the high-velocity bullets; the potential contribution
of the bullets to the mass and energy balance of the solar corona is
considered. It is found that the velocity and temperature evolution
of the bullets can be modeled successfully by assuming energy input
in the form of an external force, pushing continuously on the ejected
material. From the physical characteristics of the model bullets and the
energy input required to reproduce the observations, it is concluded
that the bullets may constitute a significant fraction of the coronal
mass flux but only a negligible component of the coronal energy budget.
Title: An explanation for the systematic flow of plasma in the solar
transition region
Authors: Boris, J. P.; Mariska, J. T.
Bibcode: 1982ApJ...258L..49B
Altcode:
Using numerical simulations, it is shown that the systematic flow
of plasma along a coronal magnetic flux tube is easily produced by a
change in the spatial dependence of the heating rate from a symmetric
deposition which supports a stationary equilibrium to a time-independent
asymmetric deposition. The velocity of the flow is roughly proportional
to the heating symmetry and is directed to the side of the loop away
from the bulk of the energy deposition.
Title: A Numerical Simulation of Cooling Coronal Flare Plasma
Authors: Doschek, G. A.; Boris, J. P.; Cheng, C. C.; Mariska, J. T.;
Oran, E. S.
Bibcode: 1982ApJ...258..373D
Altcode:
We have simulated the cooling of coronal flare plasma (Te
> 107 K) using a numerical model of a vertical magnetic
flux tube containing an idealized flare chromosphere, transition region,
and corona. The model solves the set of one-dimensional, two-fluid
hydrodynamic equations. The cooling of the flux tube is calculated for
a specific case beginning with an initial atmosphere in hydrostatic
equilibrium and a maximum temperature of about 18 × 106
K. The behavior of temperature, density, and velocity is calculated as
a function of height as the system cools. Early in the cooling, energy
is transported by conduction into the transition region and chromosphere
where it is radiated away. Later, the transition region-corona interface
moves upward into the tube at velocities of about 20 km s-1,
while the chromosphere cools and the coronal component cools by both
conduction and radiation. Coronal downflow velocities of about 60 km
s-1 are evident during this phase. The expected spectral
line emission from the system in X-ray lines of Fe XXV, Fe XXIV,
Fe XXII, O VIII, and O VII is also calculated and compared to recent
observational results. Some observational results can be explained
as a consequence of simple cooling of flare flux tubes. The expected
spectral line emission from certain transition region lines is also
briefly considered. The dependence of our results on flare size is
discussed, and our results are compared with similar previous work.
Title: Solar transition region response to variations in the
heating rate
Authors: Mariska, J. T.; Doschek, G. A.; Boris, J. P.; Oran, E. S.;
Young, T. R., Jr.
Bibcode: 1982ApJ...255..783M
Altcode:
The response of a numerical model for the upper chromosphere,
transition region, and corona to variations in the energy input has
been examined. The numerical model solves the set of one-dimensional
two-fluid hydrodynamic equations in a simple vertical magnetic flux
tube. The atmosphere responds to both the increase and decrease in
energy deposition by smoothly readjusting the temperature gradient and
the amount of material in the region of peak radiating efficiency to
radiate away energy being deposited. At no time during this readjustment
is a departure from a thin laminar transition region structure seen. In
addition, a time-dependent description of the nonequilibrium ionization
of all of the ionization stages of oxygen has been included. This
calculation is coupled with the self-consistent calculations of the
dynamical variables. It is found that the nonequilibrium ionization
balance calculations for both heating and cooling small loops in the
quiet sun predict relative ionic abundances which differ substantially
from those which would be predicted by an equilibrium calculation
Title: The condensational instability in the solar transition region
and corona
Authors: Oran, E. S.; Mariska, J. T.; Boris, J. P.
Bibcode: 1982ApJ...254..349O
Altcode:
The stability of plasmas at temperatures and densities typical of the
solar transition region and corona is investigated using both a linear
analysis and nonlinear time-dependent numerical simulations. Growth
rates, decay rates, and oscillation frequencies of the perturbations
determined from the linear analysis are in excellent agreement with the
simulations. The nonlinear regime is characterized by a bifurcation of
the plasma into a cool dense condensation surrounded by a hot tenuous
corona. The condensation may then be accelerated by forces in the plasma
such as those arising from gravity or differential heating. Finally,
the results of the detailed simulation show that the transition region
is a dynamically stable structure which is the result of the nonlinear
evolution of the condensational instability.
Title: Detailed Structure and Energetics of Accelerating Coronal
Bullets
Authors: Karpen, J. T.; Oran, E. S.; Boris, J. P.; Mariska, J. T.
Bibcode: 1982BAAS...14..622K
Altcode:
No abstract at ADS
Title: Dynamic phenomena in coronal flux tubes.
Authors: Mariska, J. T.; Boris, J. P.
Bibcode: 1982SAOSR.392A..53M
Altcode: 1982csss....2...53M
The study of stellar atmospheres and the determination of specific
physical mechanisms, geometries, and magnetic structures by which
coronae are maintained is examined. Ultraviolet and soft X-ray
components observed in the radiative output of cool stars and the Sun
require counterentropic temperature gradients for their explanation. The
existence of a hot corona is recognized as a result of mechanical or
fluid dynamic effects and the importance of the magnetic field in the
heating is accepted. Magnetohydrodynamic energy release associated with
the emergence of magnetic flux through the chromosphere and its dynamic
readjustment in the corona are major counterentropic phenomena which are
considered as primary candidates for corona heating. Systematic plows
in coronal flux tubes result from asymmetric heating and systematic
flows can exist without substantial chromospheric pressure differences.
Title: The E and F region ionospheric response to solar flares:
1. Effect of approximations of solar flare EUV fluxes
Authors: Mariska, J. T.; Oran, E. S.
Bibcode: 1981JGR....86.5868M
Altcode:
SOLRAD and many other satellite systems have provided a large data base
showing the time-dependent behavior of broadband solar fluxes in the
X-ray and EUV spectral regions. These bands are broad in the sense
that one band may contain many ionospherically important spectral
lines. We present results of tests performed to determine how this
information can best be used to predict the effects of a solar flare
on the ionosphere. Our approach has been to first adopt a model of
the spectral line and continuum enhancements based on a synthesis
of many types of flare observations. This detailed spectral model is
used in a time-dependent ionosphere model to calculate the response
of the electron and ion density profiles. Then the spectral model
is mathematically filtered to show how it would appear to the SOLRAD
EUV detectors, and this degraded information is used in the ionosphere
model. Comparison of the two ionosphere calculations shows that the two
spectra produce changes in the total electron content in the ionosphere
that differ by only a few percent. Thus, given the present uncertainty
in our knowledge of solar flare EUV spectra, SOLRAD broadband EUV solar
flux measurements can be used to calculate the ionospheric effects
of EUV flare enhancements. Significant changes due to the flare which
occur in the individual species densities are described.
Title: Mass motions in optically thin solar transition zone lines
Authors: Doschek, G. A.; Mariska, John T.; Feldman, U.
Bibcode: 1981MNRAS.195..107D
Altcode:
The widths of optically thin EUV spectral lines formed at temperatures
between ≃ 3 × 104 and 2 × 105 K in the
solar transition zone are larger than expected assuming ionization
equilibrium. This result has been interpreted as due to non-thermal
mass motions, characterized by a parameter ξ(km s-1) In
this paper we discuss observations of spectral line recorded mostly at
+2 arcsec outside the limb of the north and south polar coronal holes,
and compare the derived values of ξ to values deduced from spectra of
quiet Sun regions. These spectra were recorded by the NRL spectrograph
on Skylab (1100-2000 Å). Systematic differences in line widths between
coronal holes and quiet Sun region spectra are probably no larger than
0.01 Å, for the optically thin lines used in the analysis. -sight
path lengths of the emitting plasma at 2 arc sec above the limb are
calculated from the intensity ratios of optically thick lines of C IV,
N V, Al III, and Si IV. These ratios should be 2:1 in the optically thin
limit, but they are around 1.5 at 2 arcsec above the solar limb. The
derived path lengths range from ≃1000 to 5000km.
Title: The Dynamics of Coronal Flare Loops: II. Comparison to
Observations
Authors: Doschek, G. A.; Cheng, C. -C.; Boris, J. P.; Mariska, J. T.;
Oran, E. S.
Bibcode: 1981BAAS...13..819D
Altcode:
No abstract at ADS
Title: The Dynamics of Accelerating Coronal Bullets
Authors: Karpen, J. T.; Oran, E. S.; Boris, J. P.; Mariska, J. T.;
Brueckner, G. E.
Bibcode: 1981BAAS...13..913K
Altcode:
No abstract at ADS
Title: The Dynamics of Coronal Flare Loops: I. Gasdynamics
Authors: Cheng, C. -C.; Doschek, G. A.; Boris, J. P.; Mariska, J. T.;
Oran, E. S.
Bibcode: 1981BAAS...13Q.819C
Altcode:
No abstract at ADS
Title: Solar Transition Region Response to Heating Rate Variations
Authors: Oran, E. S.; Mariska, J. T.; Boris, J. P.; Young, T. R.;
Doschek, G. A.
Bibcode: 1981BAAS...13..836O
Altcode:
No abstract at ADS
Title: Mass Flows in the Solar Corona as a Diagnostic of the Coronal
Heating Function
Authors: Mariska, J. T.; Boris, J. P.
Bibcode: 1981BAAS...13..836M
Altcode:
No abstract at ADS
Title: The detection of companion stars to the Cepheid variables
Eta Aquilae and T Monocerotis.
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1981NASCP2171..209M
Altcode: 1981NASCP3171..209M; 1980IUE80......209M; 1981uviu.nasa..209M
Ultraviolet spectra of the classical Cepheid variables eta Aq1
and T Mon at several phases in their periods were obtained with
IUE. For eta Aq1 significant ultraviolet emission is detected at
wavelengths less than 1600 A, where little flux is expected from
classical Cepheids. Furthermore, the emission at wavelengths less
than about 1600 A does not vary with phase. Comparison with model
atmosphere flux distributions shows that the nonvariable emission is
consistent with the flux expected from a main sequence companion star
with an effective temperature of about 9500 K (AO V - A1 V). For T Mon
a nonvarying component to the ultraviolet emission is observed for
wavelengths less than 2600 A. Comparison with model atmosphere flux
distributions suggests that the companion has an effective temperature
of around 10,000 K (AO) and is near the main sequence.
Title: The ionospheric response to solar flares. 1: Effects of
approximations of solar flare EUV fluxes
Authors: Oran, E. S.; Mariska, J. T.
Bibcode: 1981STIN...8117976O
Altcode:
SOLRAD and many other satellite systems have provided a large data
base showing the time-dependent behavior of broad and band solar
fluxes in the X-ray and EUV spectral regions. These bands are broad
in the sense that one band may contain many ionospherically important
spectral lines. We present results of tests performed to determine how
this information can be best be used to predict the effects of a solar
flare on the ionosphere. Our approach has been to first adopt a model
of the spectral line and continuum enhancements based on a synthesis
of many types of flare observations. This detailed spectral model is
used in a time-dependent ionosphere model to calculate the response
of the electron and ion density profiles. Then the spectral model is
mathematically filtered to show how it would appear to the SOLRAD EUV
detectors, and this degraded information is used in the ionosphere
model. Comparison of the two ionosphere shows that the two spectra
produces changes in the total electron content in the ionosphere that
differ by only a few percent. More significant changes which occur in
the individual species densities are described.
Title: The detection of a companion star to the Cepheid variable
T Monocerotis
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1980ApJ...242.1083M
Altcode:
We have obtained ultraviolet spectra with the International Ultraviolet
Explorer (IUE) spacecraft of the classical Cepheid T Mon at several
phases in the 27 day period. Significant ultraviolet emission is
detected at wavelengths less than 1600 A, where little flux is expected
from classical Cepheids. Furthermore, the emission at wavelengths
less than about 1900 A does not vary with phase. Comparison with model
atmosphere flux distributions shows that the emission is consistent with
the flux expected from a companion star with an effective temperature
of about 10,000 K (approximately A0) near the main sequence.
Title: High-resolution X-ray spectra of solar flares. IV - General
spectral properties of M type flares
Authors: Feldman, U.; Doschek, G. A.; Kreplin, R. W.; Mariska, J. T.
Bibcode: 1980ApJ...241.1175F
Altcode:
The spectral characteristics in selected narrow regions of the X-ray
spectrum of class M solar flares are analyzed. High-resolution spectra
in the ranges 1.82-1.97, 2.98-3.07, 3.14-3.24 and 8.26-8.53 A, which
contain lines important for the determination of electron temperature
and departure from ionization equilibrium, were recorded by spaceborne
Bragg crystal spectrometers. Temperatures of up to 20,000,000 K are
obtained from line ratios during flare rise phases in M as well as X
flares, while in the decay phase the calcium temperature can be as low
as 8,000,000 K, which is significantly lower than in X flares. Large
nonthermal motions (on the order of 130 km/sec at most) are also
observed in M as well as X flares, which are largest during the soft
X-ray rise phase. Finally, it is shown that the method proposed by
Gabriel and Phillips (1979) for detecting departures of electrons
from Maxwellian velocity distributions is not sufficiently sensitive
to give reliable results for the present data.
Title: Numerical Simulation of a Cooling Flare Loop for Application
to X-Ray Flare Spectra
Authors: Doschek, G. A.; Boris, J. P.; Mariska, J. T.; Oran, E. S.
Bibcode: 1980BAAS...12..912D
Altcode:
No abstract at ADS
Title: A Dynamic Flux-Tube Model for Compressible MHD Processes in
the Solar Atmosphere
Authors: Boris, J. P.; Mariska, J. T.; Book, D. L.; Oran, E. S.;
Young, T.; Doschek, G. A.
Bibcode: 1980BAAS...12..908B
Altcode:
No abstract at ADS
Title: Condensational Instability in Coronal Plasmas
Authors: Oran, E. S.; Boris, J. P.; Mariska, J. T.; Doschek, G. A.
Bibcode: 1980BAAS...12..910O
Altcode:
No abstract at ADS
Title: Some Aspects of Transition Zone Dynamics
Authors: Mariska, J. T.; Boris, J. P.; Oran, E. S.; Doschek, G. A.
Bibcode: 1980BAAS...12..908M
Altcode:
No abstract at ADS
Title: Physical conditions in the solar atmosphere above an active
region
Authors: Mariska, J. T.; Feldman, U.; Doschek, G. A.
Bibcode: 1980ApJ...240..300M
Altcode:
From a series of EUV spectra obtained at several heights above the
limb in a solar active region, the volume emission measure is derived
as a function of the electron temperature in the temperature range
70,000-1,500,000 K and the electron density at two locations. The
emission measure from the coronal material (temperature greater than
700,000 K) is nearly the same everywhere and represents most of the
material in the line of sight, while the emission measure from the
transition region material (temperature between 70,000 and 250,000
K) fluctuates by two orders of magnitude from position to position
above the active region. This is in agreement with the picture of
this active region as consisting of a number of well-defined loops
or lower portions of loops at transition region temperatures that
are inhomogeneously distributed in much larger and more diffuse loop
structures at coronal temperatures. The coronal data are in reasonable
agreement with simple coronal models. Emission measures near 1,000,000
K evaluated using different ions differ by a factor of 4, suggesting
difficulties with the atomic physics data.
Title: The detection of a companion star to the Cepheid variable
eta Aql.
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1980ApJ...238L..87M
Altcode:
Ultraviolet spectra have been obtained with IUE of the classical Cepheid
Eta Aquilae at several phases in the 7.18 day period. Significant
ultraviolet emission is detected at wavelengths less than 1600 A,
where little flux is expected from classical Cepheids. Furthermore,
the emission at wavelengths less than about 1600 A does not vary with
phase. Comparison with model atmosphere flux distributions shows that
the nonvariable emission is consistent with the flux expected from a
main-sequence companion star with an effective temperature of about
9500 K (A0 V). The observed ultraviolet flux and spectral type are
used to compute a distance of 300 pc to the system, in agreement with
the distance predicted using the period luminosity relation.
Title: The Companion of Eta-Aquilae
Authors: Mariska, J. T.
Bibcode: 1980S&T....59..295M
Altcode:
No abstract at ADS
Title: Mass Motions in the Transition Zone of Coronal Holes
Authors: Doschek, G. A.; Mariska, J. T.; Feldman, U.
Bibcode: 1980BAAS...12S.518D
Altcode:
No abstract at ADS
Title: The Detection of an Early Type Companion Star to the Classical
Cepheid T Mon
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1980BAAS...12Q.462M
Altcode:
No abstract at ADS
Title: Relative chemical abundances in different solar regions
Authors: Mariska, J. T.
Bibcode: 1980ApJ...235..268M
Altcode:
Intensities of extreme-ultraviolet emission lines formed in quiet
sun regions, a coronal hole, an active region, and a prominence are
used to derive chemical abundances of carbon, nitrogen, and oxygen
relative to silicon in each region. For each element the relative
abundance in each region agrees to within the estimated errors in the
analysis. This means that the relative abundances are constant over
a wide range of electron densities, emission measures, turbulent mass
motions, and heights above the limb. Uncertainties in the atomic data
appear to be the primary source of scatter in the derived abundances.
Title: The Detection of a Companion Star to the Cepheid Variable
Eta Aquilae
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1979BAAS...11..687M
Altcode:
No abstract at ADS
Title: Extreme-ultraviolet limb spectra of a prominence observed
from Skylab.
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1979ApJ...232..929M
Altcode:
Line profiles of extreme ultraviolet emission lines observed in a
solar prominence at positions above the white-light limb with the NRL
slit spectrograph on Skylab are discussed. Absolute line intensities
and full widths at half-maximum are presented, and emission measures,
electron densities, and mass motions are derived at several locations
within the prominence. For electron temperatures less than 40,000
K, the calculated mass motions are found to be near zero, while for
electron temperatures greater than 40,000 K, the nonthermal velocity
decreases with increasing height in the prominence. It is suggested
that falling material is responsible for the fact that the measured
electron density decreases with height less rapidly than the decrease
predicted for a hydrostatic gas. In addition, from the He II 1640 A
line profile, an average temperature of 27,000 K is derived for the
region in which He II is emitted.
Title: On the structure of the solar transition zone and lower corona.
Authors: Feldman, U.; Doschek, G. A.; Mariska, J. T.
Bibcode: 1979ApJ...229..369F
Altcode:
Recent observations of the solar transition zone and corona
obtained primarily from NRL spectrographs on Skylab are summarized
and used to examine the structure of the transition zone. The
transition zone is revealed to be more inhomogeneous than is
apparent from spectroheliograms with spatial resolution of about 3
arcsec. Transition-zone emission appears to arise in spicularlike
structures. The effective area covered by the emitting structures at
lower transition-zone temperatures (about 100,000 K) is only about 1%
of the total surface area of the sun. The transition zone is highly
inhomogeneous even over cell interior regions, where fluctuations in
brightness by factors of 25 can occur. It is shown that homogeneous
coronal models are not valid for the inner corona. Most of the
higher-density inner corona is concentrated into looplike structures
that extend down to the white-light limb. These structures are
unrelated to the spicular-type structures that produce most of the
transition-zone emission.
Title: Relative Chemical Abundances in Different Solar Regions
Authors: Mariska, J. T.
Bibcode: 1979BAAS...11Q.405M
Altcode:
No abstract at ADS
Title: Nonthermal broadening of extreme ultraviolet emission lines
near the solar limb.
Authors: Mariska, J. T.; Feldman, U.; Doschek, G. A.
Bibcode: 1979A&A....73..361M
Altcode:
Summary. Line profiles of optically thin extreme ultraviolet emission
lines observed in quiet-Sun regions at 8', 12', and 20' above the
white light limb with the NRL slit spectrograph (5082-B) on Skylab are
discussed. Random mass-motion velocities are calculated. The velocity
is found to increase with increasing height above the white light limb
for all the lines regardless of the temperature of formation between 4
l0 K and 2l0 K. At +12' a typical velocity is about 33km -1 Key words:
Sun - transition zone - EUV spectra
Title: Electron densities in the solar corona from density-sensitive
line ratios in the N I isoelectronic sequence.
Authors: Feldman, U.; Doschek, G. A.; Mariska, J. T.; Bhatia, A. K.;
Mason, H. E.
Bibcode: 1978ApJ...226..674F
Altcode:
Electron densities are derived in the solar inner corona from forbidden
lines of S x near 1100 A. The density-sensitive line ratio considered
is (4S0312-2D0312)/(4S0312-2D0612). The ratio is calculated as a
function of density for four ions of the N I isoelectronic sequence,
i.e., Mg VI, Si VIII, S x, and Ar XII. The variation of the ratio
(4S0312-2P0312)/(4S0312-2D0312) with density is also calculated. The
results are applied to off-limb spectra recorded by the NRL Skylab
spectrograph. Densities were found to be the same in five quiet Sun
regions and four active regions observed at heights > 8" outside
the white-light limb. The average density derived from the S x lines
for all regions considered is 1.0 x 10 cm -3. This result applies to
plasma at the temperature of formation of S x, i.e., 1.3 x 106 K. At
heights greater than 20" outside the limb the average density is 7.7 x
108 cm -3, and between 8" and 12" above the limb the average density is
1.0 x 10 cm 3, for both quiet Sun and active regions. Subject heading:
Sun: corona
Title: Measurements of extreme-ultraviolet emission-line profiles
near the solar limb.
Authors: Mariska, J. T.; Feldman, U.; Doschek, G. A.
Bibcode: 1978ApJ...226..698M
Altcode:
Line profiles of optically thin extreme-ultraviolet emission
lines observed in a quiet sun region at positions within and above
the white-light limb with the NRL slit spectrograph (S082-B) on
Skylab are discussed. Absolute line intensities and full widths at
half-maximum are presented for lines formed over the temperature range
from about 10,000 to 22,000 K. The line intensities are compared with
the predictions of simple atmospheric models consisting of a spicule
component and a thin spherically symmetric or network models, but can
be explained by assuming that the emission arises from spicule-like
inhomogeneities. Random mass-motion velocities are calculated. The
velocity increases with increasing temperature of line formation. Near
the limb and above about 4000 K the calculated velocity is consistent
with the predictions of a constant acoustic flux passing through the
transition zone. For the ions formed at temperatures not less than
about 63,000 K, the velocity is found to increase with increasing
height above the white-light limb.
Title: Electron densities in stellar atmospheres determined from
IUE spectra.
Authors: Doschek, G. A.; Feldman, U.; Mariska, J. T.; Linsky, J. L.
Bibcode: 1978ApJ...226L..35D
Altcode:
No abstract at ADS
Title: Temperature gradients in the inner corona.
Authors: Mariska, J. T.; Withbroe, G. L.
Bibcode: 1978SoPh...60...67M
Altcode:
Emission gradient curves for extreme ultraviolet (EUV) resonance lines
of O VI and Mg X have been constructed from spectroheliograms of quiet
limb regions observed with the Harvard experiment on Skylab. An analysis
of these data suggests that the coronal temperature rises throughout
the height range 1.03R⊙≤r≤1.3R⊙. This
result implies that in quiet regions there is significant coronal
heating beyond r = 1.3R⊙.
Title: Analysis of extreme-ultraviolet observations of a polar
coronal hole.
Authors: Mariska, J. T.
Bibcode: 1978ApJ...225..252M
Altcode:
Emission gradient curves for extreme-ultraviolet resonance lines
of lithiumlike ions have been constructed from spectroheliograms
of a northern polar coronal hole observed on August 14, 1973,
with the Harvard experiment on Skylab. An emission-measure analysis
indicates both reduced density and coronal temperature in the coronal
hole. The boundary geometry of the coronal hole is determined,
and a temperature-density model that is consistent with the observed
intensities is constructed. The model gives a conductive flux of 60,000
erg/sq cm per sec at 1.03 solar radii. The boundary geometry and density
distribution are combined with typical solar-wind parameters at the
earth to determine an outflow velocity of 15 km/s at 1.08 solar radii.
Title: A search for stellar oscillations.
Authors: Traub, W. A.; Mariska, J. T.; Carleton, N. P.
Bibcode: 1978ApJ...223..583T
Altcode:
A PEPSIOS spectrometer has been used to search for stellar photospheric
oscillations with periods in the range from about 10 to 5000 s, and
with velocity sensitivities down to about 1 m/s (rms) at the 1-sigma
level. In the nine stars observed, no evidence is found for ocillations
at the 3-sigma level. However, by using the same technique on the sun,
the well-known 300-s oscillation was detected with an rms amplitude
of 1.6 + or - 0.5 m/s for the integrated disk.
Title: Nonthermal Broadening of Extreme Ultraviolet Emission Lines
near the Solar Limb
Authors: Mariska, J. T.; Feldman, U.; Doschek, G. A.
Bibcode: 1978BAAS...10..432M
Altcode:
No abstract at ADS
Title: A Composite Coronal Hole Model.
Authors: Munro, R. H.; Mariska, J. T.
Bibcode: 1977BAAS....9..370M
Altcode:
No abstract at ADS
Title: The structure of the solar transition region and inner corona
Authors: Mariska, John Thomas
Bibcode: 1977PhDT.......265M
Altcode:
No abstract at ADS
Title: The Structure of the Solar Transition Region and Inner Corona.
Authors: Mariska, J. T.
Bibcode: 1977PhDT........14M
Altcode:
Emission gradient curves for extreme ultraviolet resonance lines of
lithium-like ions were constructed from spectroheliograms of quiet
limb regions and a north polar coronal hole observed with the Harvard
experiment on Skylab. The observations are interpreted with simple
coronal models. The coronal models are extended downward and the
calculated emission from them is compared with averaged, network and
cell line intensities to derive models in a quiet region and a coronal
hole. The energy balance implications of the models are examined. In
the transition region both conduction and radiation are important
in determining the energy balance in network regions in both quiet
areas and coronal holes. Additional energy sources are required in
the network in coronal holes. In the corona, the energy losses, and
hence the requirements for mechanical heating, are the same in quiet
regions and coronal holes.
Title: Analysis of EUV limb brightening observations from ATM. II:
Influence of spicules.
Authors: Withbroe, G. L.; Mariska, J. T.
Bibcode: 1976SoPh...48...21W
Altcode:
A comparison of limb brightening measurements with theoretical limb
brightening curves calculated for simple atmospheric models indicates
that a significant fraction of the EUV emission from lines formed
in the transition layer comes from spicules. We find that spicules
contribute about 20% of the total quiet Sun intensity for lines of the
C II, C III, N III, and O VI ions. The uncertainty in the magnitude of
the percentage is about a factor of 2. The EUV-emission scale heights
above the limb are consistent with the assumption that the variation
with height of the number of EUV-emitting spicules is the same as for
Hα-emitting spicules. Optical depths derived for the C II λ1335 and
C III λ977 lines yield estimates for the pressure P = neT
in the transition layer, log P = 14.7±0.5, that are in good agreement
with pressures derived under the assumption that the transition layer
is in pressure equilibrium with the chromosphere and corona.
Title: Extreme Ultraviolet Observations of a Polar Coronal Hole
Authors: Mariska, J. T.
Bibcode: 1976BAAS....8R.338M
Altcode:
No abstract at ADS
Title: Analysis of EUV Limb-Brightening Observations from ATM. I:
Model for the Transition Layer and the Corona
Authors: Mariska, J. T.; Withbroe, G. L.
Bibcode: 1975SoPh...44...55M
Altcode:
Limb-brightening curves for EUV resonance lines of O VI and Mg X
have been constructed from spectroheliograms (5″ resolution)
of quiet limb regions observed with the Harvard experiment on
Skylab. The observations are interpreted with a simple model for
the transition layer and the corona. A comparison of theoretical and
observed limb-brightening curves indicates that the lower boundary of
the corona, where Te= 106K, is at a height of
about 8000 km in typical quiet areas. For 1.01 R⊙≲r1.25
R⊙, the corona can be represented by a homogeneous model in
hydrostatic equilibrium with a temperature of 106K for 1.01
R⊙≲r<1.1 R⊙ and 1.1 × 106K
for r≳1.1 R⊙. The model for the transition layer is
inhomogeneous, with the temperature gradient a factor of 3 shallower
in the network than in the intranetwork regions. It appears that
spicules should be included in the model in order to account for the
penetration into the corona of cool (Te<106K)
EUV-emitting material to heights up to 20000 km above the limb.
Title: Extreme Ultraviolet Solar Limb Brighteness Observations
Authors: Mariska, J. T.; Withbroe, G. L.
Bibcode: 1975BAAS....7Q.460M
Altcode:
No abstract at ADS
Title: Extreme Ultraviolet Solar Limb Brightening Observations of
Lithium-Like Ions
Authors: Mariska, J. T.; Withbroe, G. L.
Bibcode: 1975BAAS....7..354M
Altcode:
No abstract at ADS
Title: Solar Activity and the Variations of the Geomagnetic
Kp-Index. I: Photospheric Activity
Authors: Mariska, John T.; Oster, Ludwig
Bibcode: 1972SoPh...26..241M
Altcode:
A careful correlation analysis is made between various types of solar
activity as observed at photospheric levels and the daily variations
of the geomagnetic Kp-index which, in turn, is a measure
of the solar wind speed. We find that in no case does a significant
enough correlation exist to pin-point a physical relation between
some aspect of photospheric activity and the solar wind speed. It is
concluded that the physical processes that do determine the wind speed
occur at coronal heights.
Title: Solar Activity and the Variation of the Geomagnetic
Kp-Index
Authors: Oster, Ludwig; Mariska, John T.; Altschuler, Martin D.;
Trotter, Dorothy E.
Bibcode: 1972BAAS....4R.389O
Altcode:
No abstract at ADS
Title: Equilibrium, Pulsational, and Secular Stability Properties
of the Lower Carbon-Burning Main Sequence
Authors: Mariska, John T.; Hansen, Carl J.
Bibcode: 1972ApJ...171..317M
Altcode:
Results are presented for stellar models composed of equal amounts of
12C and 100 in complete equilibrium within the mass range 0.82 <
M/M0 < 2.31. The character of the static models is analogous to
the lower helium main sequence in that they are double-valued with
respect to mass whereas the central density is monotonic along the
sequence. All the models are pulsationally unstable, but only one,
near the minimum mass, is secularly unstable.