Author name code: fludra
ADS astronomy entries on 2022-09-14
author:"Fludra, Andrzej"
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Title: Abundance diagnostics in active regions with Solar
Orbiter/SPICE
Authors: Giunta, Alessandra; Peter, Hardi; Parenti, Susanna; Buchlin,
Eric; Thompson, William; Auchere, Frederic; Kucera, Therese; Carlsson,
Mats; Janvier, Miho; Fludra, Andrzej; Hassler, Donald M.; Grundy,
Timothy; Sidher, Sunil; Guest, Steve; Leeks, Sarah; Fredvik, Terje;
Young, Peter
Bibcode: 2022cosp...44.2583G
Altcode:
With the launch of Solar Orbiter in February 2020, we are now able to
fully explore the link between the solar activity on the Sun and the
inner heliosphere. Elemental abundance measurements provide a key tracer
to probe the source regions of the solar wind and to track it from the
solar surface and corona to the heliosphere. Abundances of elements
with low first ionisation potential (FIP) are enhanced in the corona
relative to high-FIP elements, with respect to the photosphere. This is
known as the FIP effect, which is measured as abundance bias (FIP bias)
of low and high FIP elements. This effect is vital for understanding the
flow of mass and energy through the solar atmosphere. The comparison
between in-situ and remote sensing composition data, coupled with
modelling, will allow us to trace back the source of heliospheric
plasma. Solar Orbiter has a unique combination of in-situ and remote
sensing instruments that will help to make such a comparison. In
particular, the SPICE (Spectral Imaging of the Coronal Environment)
EUV spectrometer records spectra in two wavelength bands, 70.4-79.0
nm and 97.3-104.9 nm. SPICE is designed to provide spectroheliograms
using a core set of emission lines arising from ions of both low-FIP
and high-FIP elements such as C, N, O, Ne, Mg, S and Fe. These lines
are formed over a wide range of temperatures from 20,000 K to over 1
million K, enabling the analysis of the different layers of the solar
atmosphere. SPICE spectroheliograms can be processed to produce FIP
bias maps, which can be compared to in-situ measurements of the solar
wind composition of the same elements. During the Solar Orbiter Cruise
Phase, SPICE observed several active regions. We will present some of
these observations and discuss the SPICE diagnostic potential to derive
relative abundances (e.g., Mg/Ne) and the FIP bias in those regions.
Title: The SPICE spectrograph on Solar Orbiter: an introduction and
results from the first Orbits
Authors: Auchère, Frédéric; Peter, Hardi; Parenti, Susanna; Buchlin,
Eric; Thompson, William; Auchere, Frederic; Teriaca, Luca; Kucera,
Therese; Carlsson, Mats; Janvier, Miho; Fludra, Andrzej; Giunta,
Alessandra; Schuehle, Udo; Hassler, Donald M.; Grundy, Timothy;
Sidher, Sunil; Fredvik, Terje; Plowman, Joseph; Aznar Cuadrado, Regina
Bibcode: 2022cosp...44.1338A
Altcode:
The Spectral Imaging of the Coronal Environment (SPICE) instrument is
the EUV imaging spectrometer on board the Solar Orbiter mission. With
its ability to derive physical properties of the coronal plasma,
SPICE is a key component of the payload to establish the connection
between the source regions and the in-situ measurements of the solar
wind. The spacecraft was successfully launched in February 2020 and
completed its cruise phase in December 2021. During this period,
the remote sensing instruments were mostly operated during limited
periods of time for 'checkout' engineering activities and synoptic
observations. Nonetheless, several of these periods provided enough
opportunities already to obtain new insights on coronal physics. During
the march 2022 perihelion - close to 0.3 AU - SPICE will provide
its highest spatial resolution data so far. Coordinated observations
between the remote sensing and in-situ instruments will provide the
first opportunity to use the full potential of the Solar Orbiter
mission. We will review the instrument characteristics and present
initial results from the cruise phase and first close encounter.
Title: HiRISE - High-Resolution Imaging and Spectroscopy Explorer
- Ultrahigh resolution, interferometric and external occulting
coronagraphic science
Authors: Erdélyi, Robertus; Damé, Luc; Fludra, Andrzej; Mathioudakis,
Mihalis; Amari, T.; Belucz, B.; Berrilli, F.; Bogachev, S.; Bolsée,
D.; Bothmer, V.; Brun, S.; Dewitte, S.; de Wit, T. Dudok; Faurobert,
M.; Gizon, L.; Gyenge, N.; Korsós, M. B.; Labrosse, N.; Matthews,
S.; Meftah, M.; Morgan, H.; Pallé, P.; Rochus, P.; Rozanov, E.;
Schmieder, B.; Tsinganos, K.; Verwichte, E.; Zharkov, S.; Zuccarello,
F.; Wimmer-Schweingruber, R.
Bibcode: 2022ExA...tmp...21E
Altcode:
Recent solar physics missions have shown the definite role of waves and
magnetic fields deep in the inner corona, at the chromosphere-corona
interface, where dramatic and physically dominant changes occur. HiRISE
(High Resolution Imaging and Spectroscopy Explorer), the ambitious new
generation ultra-high resolution, interferometric, and coronagraphic,
solar physics mission, proposed in response to the ESA Voyage 2050
Call, would address these issues and provide the best-ever and most
complete solar observatory, capable of ultra-high spatial, spectral,
and temporal resolution observations of the solar atmosphere, from the
photosphere to the corona, and of new insights of the solar interior
from the core to the photosphere. HiRISE, at the L1 Lagrangian
point, would provide meter class FUV imaging and spectro-imaging,
EUV and XUV imaging and spectroscopy, magnetic fields measurements,
and ambitious and comprehensive coronagraphy by a remote external
occulter (two satellites formation flying 375 m apart, with a
coronagraph on a chaser satellite). This major and state-of-the-art
payload would allow us to characterize temperatures, densities, and
velocities in the solar upper chromosphere, transition zone, and inner
corona with, in particular, 2D very high resolution multi-spectral
imaging-spectroscopy, and, direct coronal magnetic field measurement,
thus providing a unique set of tools to understand the structure and
onset of coronal heating. HiRISE's objectives are natural complements
to the Parker Solar Probe and Solar Orbiter-type missions. We present
the science case for HiRISE which will address: i) the fine structure
of the chromosphere-corona interface by 2D spectroscopy in FUV at
very high resolution; ii) coronal heating roots in the inner corona by
ambitious externally-occulted coronagraphy; iii) resolved and global
helioseismology thanks to continuity and stability of observing at the
L1 Lagrange point; and iv) solar variability and space climate with,
in addition, a global comprehensive view of UV variability.
Title: First observations from the SPICE EUV spectrometer on Solar
Orbiter
Authors: Fludra, A.; Caldwell, M.; Giunta, A.; Grundy, T.; Guest,
S.; Leeks, S.; Sidher, S.; Auchère, F.; Carlsson, M.; Hassler, D.;
Peter, H.; Aznar Cuadrado, R.; Buchlin, É.; Caminade, S.; DeForest,
C.; Fredvik, T.; Haberreiter, M.; Harra, L.; Janvier, M.; Kucera, T.;
Müller, D.; Parenti, S.; Schmutz, W.; Schühle, U.; Solanki, S. K.;
Teriaca, L.; Thompson, W. T.; Tustain, S.; Williams, D.; Young, P. R.;
Chitta, L. P.
Bibcode: 2021A&A...656A..38F
Altcode: 2021arXiv211011252F
Aims: We present first science observations taken during the
commissioning activities of the Spectral Imaging of the Coronal
Environment (SPICE) instrument on the ESA/NASA Solar Orbiter
mission. SPICE is a high-resolution imaging spectrometer operating at
extreme ultraviolet (EUV) wavelengths. In this paper we illustrate
the possible types of observations to give prospective users a
better understanding of the science capabilities of SPICE.
Methods: We have reviewed the data obtained by SPICE between April
and June 2020 and selected representative results obtained with
different slits and a range of exposure times between 5 s and 180
s. Standard instrumental corrections have been applied to the raw
data.
Results: The paper discusses the first observations
of the Sun on different targets and presents an example of the full
spectra from the quiet Sun, identifying over 40 spectral lines from
neutral hydrogen and ions of carbon, oxygen, nitrogen, neon, sulphur,
magnesium, and iron. These lines cover the temperature range between
20 000 K and 1 million K (10 MK in flares), providing slices of the
Sun's atmosphere in narrow temperature intervals. We provide a list
of count rates for the 23 brightest spectral lines. We show examples
of raster images of the quiet Sun in several strong transition region
lines, where we have found unusually bright, compact structures in the
quiet Sun network, with extreme intensities up to 25 times greater
than the average intensity across the image. The lifetimes of these
structures can exceed 2.5 hours. We identify them as a transition
region signature of coronal bright points and compare their areas and
intensity enhancements. We also show the first above-limb measurements
with SPICE above the polar limb in C III, O VI, and Ne VIII lines, and
far off limb measurements in the equatorial plane in Mg IX, Ne VIII,
and O VI lines. We discuss the potential to use abundance diagnostics
methods to study the variability of the elemental composition that can
be compared with in situ measurements to help confirm the magnetic
connection between the spacecraft location and the Sun's surface,
and locate the sources of the solar wind.
Conclusions: The
SPICE instrument successfully performs measurements of EUV spectra
and raster images that will make vital contributions to the scientific
success of the Solar Orbiter mission.
Title: First Results From SPICE EUV Spectrometer on Solar Orbiter
Authors: Fludra, Andrzej
Bibcode: 2021EGUGA..23.5577F
Altcode:
SPICE (Spectral Imaging of Coronal Environment) is an EUV imaging
spectrometer onboard Solar Orbiter. SPICE observes the Sun in two
wavelength bands: 69.6-79.4 nm and 96.6-105.1 nm and is capable
of recording full spectra in these bands with exposures as short as
1s. SPICE can measure spectra from the disk and low corona, and records
all spectral lines simultaneously, using one of three narrow slits:
2"x11", 4""x11", 6""x11", or a wide slit 30""x14". The primary mirror
can be scanned in a direction perpendicular to the slit, allowing raster
images of up to 16" in size.The first SPICE data were taken during the
instrument commissioning carried out by the RAL Space team between 2020
April 21 and 2020 June 14, and at the first Solar Orbiter perihelion at
0.52AU between June 16-21. We give examples of full spectra from the
quiet Sun near disk centre and provide a list of key spectral lines
from neutral hydrogen and ions of carbon, oxygen, nitrogen, neon,
sulphur and magnesium. These lines cover the temperature range between
10,000 K and 1 million K (10MK in flares), providing slices of the
Sun"s atmosphere in narrow temperature intervals. We show examples of
raster images in several strong lines, obtained with different slits
and a range of exposure times between 5s and 180s.We have found several
unusually bright, compact structures (named "beacons") in the quiet
Sun network, with extreme intensities up to 22 times greater than the
average intensity across the image. The lifetimes of these sources are
longer than 1 hour. We will derive plasma velocities in the beacon area,
and co-align the SPICE rasters with the SDO/AIA 304 and 171 images and
the HMI magnetic field to better understand the origin and properties
of beacons.We also show the first above-limb measurements with SPICE in
Mg IX, Ne VIII and O VI lines, as obtained when the spacecraft pointed
at the limb. Maps of Mg/Ne abundance ratios on disk can be derived
and compared with in situ measurements to help confirm the magnetic
connection between the spacecraft location and the Sun"s surface,
and locate the sources of the solar wind.
Title: Relative coronal abundance diagnostics with Solar Orbiter/SPICE
Authors: Zambrana Prado, N.; Buchlin, E.; Peter, H.; Young, P. R.;
Auchere, F.; Carlsson, M.; Fludra, A.; Hassler, D.; Aznar Cuadrado,
R.; Caminade, S.; Caldwell, M.; DeForest, C.; Fredvik, T.; Harra,
L.; Janvier, M.; Kucera, T. A.; Giunta, A. S.; Grundy, T.; Müller,
D.; Parenti, S.; Schmutz, W. K.; Schühle, U.; Sidher, S.; Teriaca,
L.; Thompson, W. T.; Williams, D.
Bibcode: 2020AGUFMSH038..09Z
Altcode:
Linking solar activity on the surface and in the corona to the inner
heliosphere is one of Solar Orbiter's main goals. Its UV spectrometer
SPICE (SPectral Imaging of the Coronal Environment) will provide
relative abundance measurements which will be key in this quest
as different structures on the Sun have different abundances as a
consequence of the FIP (First Ionization Potential) effect. Solar
Orbiter's unique combination of remote sensing and in-situ instruments
coupled with observation from other missions such as Parker Solar
Probe will allow us to compare in-situ and remote sensing composition
data. With the addition of modeling, these new results will allow us
to trace back the source of heliospheric plasma. As high telemetry
will not always be available with SPICE, we have developed a method
for measuring relative abundances that is both telemetry efficient
and reliable. Unlike methods based on Differential Emission Measure
(DEM) inversion, the Linear Combination Ratio (LCR) method does not
require a large number of spectral lines. This new method is based
on linear combinations of UV spectral lines. The coefficients of
the combinations are optimized such that the ratio of two linear
combinations of radiances would yield the relative abundance of two
elements. We present some abundance diagnostics tested on different
combinations of spectral lines observable by SPICE.
Title: Dynamics and thermal structure in the quiet Sun seen by SPICE
Authors: Peter, H.; Aznar Cuadrado, R.; Schühle, U.; Teriaca, L.;
Auchere, F.; Carlsson, M.; Fludra, A.; Hassler, D.; Buchlin, E.;
Caminade, S.; Caldwell, M.; DeForest, C.; Fredvik, T.; Harra, L. K.;
Janvier, M.; Kucera, T. A.; Giunta, A. S.; Grundy, T.; Müller, D.;
Parenti, S.; Schmutz, W. K.; Sidher, S.; Thompson, W. T.; Williams,
D.; Young, P. R.
Bibcode: 2020AGUFMSH038..03P
Altcode:
We will present some of the early data of the Spectral Imaging of the
Coronal Environment (SPICE) instrument on Solar Orbiter. One of the
unique features of SPICE is its capability to record a wide range of
wavelengths in the extreme UV with the possibility to record spectral
lines giving access to a continuous plasma temperature range from 10.000
K to well above 1 MK. The data taken so far were for commissioning
purposes and they can be used for a preliminary evaluation of the
science performance of the instrument. Here we will concentrate on
sample spectra covering the whole wavelength region and on the early
raster maps acquired in bright lines in the quiet Sun close to disk
center. Looking at different quiet Sun features we investigate the
thermal structure of the atmosphere and flow structures. For this
we apply fits to the spectral profiles and check the performance in
terms of Doppler shifts and line widths to retrieve the structure of
the network in terms of dynamics. While the amount of data available
so far is limited, we will have a first look on how quiet Sun plasma
responds to heating events. For this, we will compare spectral lines
forming at different temperatures recorded at strictly the same time.
Title: First Results From SPICE EUV Spectrometer on Solar Orbiter
Authors: Fludra, A.; Caldwell, M.; Giunta, A. S.; Grundy, T.; Guest,
S.; Sidher, S.; Auchere, F.; Carlsson, M.; Hassler, D.; Peter, H.;
Aznar Cuadrado, R.; Buchlin, E.; Caminade, S.; DeForest, C.; Fredvik,
T.; Harra, L. K.; Janvier, M.; Kucera, T. A.; Leeks, S.; Mueller,
D.; Parenti, S.; Schmutz, W. K.; Schühle, U.; Teriaca, L.; Thompson,
W. T.; Tustain, S.; Williams, D.; Young, P. R.
Bibcode: 2020AGUFMSH038..02F
Altcode:
SPICE (Spectral Imaging of Coronal Environment) is one of the remote
sensing instruments onboard Solar Orbiter. It is an EUV imaging
spectrometer observing the Sun in two wavelength bands: 69.6-79.4 nm
and 96.6-105.1 nm. SPICE is capable of recording full spectra in these
bands with exposures as short as 1s. SPICE is the only Solar Orbiter
instrument that can measure EUV spectra from the disk and low corona
of the Sun and record all spectral lines simultaneously. SPICE uses
one of three narrow slits, 2"x11', 4''x11', 6''x11', or a wide slit
30''x14'. The primary mirror can be scanned in a direction perpendicular
to the slit, allowing raster images of up to 16' in size. We
present an overview of the first SPICE data taken on several days
during the instrument commissioning carried out by the RAL Space team
between 2020 April 21 and 2020 June 14. We also include results from
SPICE observations at the first Solar Orbiter perihelion at 0.52AU,
taken between June 16-21st. We give examples of full spectra
from the quiet Sun near disk centre and provide a list of key spectral
lines emitted in a range of temperatures between 10,000 K and over 1
million K, from neutral hydrogen and ions of carbon, oxygen, nitrogen,
neon, sulphur and magnesium. We show examples of first raster images
in several strong lines, obtained with different slits and a range
of exposure times between 5s and 180s. We describe the temperature
coverage and density diagnostics, determination of plasma flows, and
discuss possible applications to studies of the elemental abundances
in the corona. We also show the first off-limb measurements with SPICE,
as obtained when the spacecraft pointed at the limb.
Title: The Solar-C (EUVST) mission: the latest status
Authors: Shimizu, Toshifumi; Imada, Shinsuke; Kawate, Tomoko; Suematsu,
Yoshinori; Hara, Hirohisa; Tsuzuki, Toshihiro; Katsukawa, Yukio; Kubo,
Masahito; Ishikawa, Ryoko; Watanabe, Tetsuya; Toriumi, Shin; Ichimoto,
Kiyoshi; Nagata, Shin'ichi; Hasegawa, Takahiro; Yokoyama, Takaaki;
Watanabe, Kyoko; Tsuno, Katsuhiko; Korendyke, Clarence M.; Warren,
Harry; De Pontieu, Bart; Boerner, Paul; Solanki, Sami K.; Teriaca,
Luca; Schuehle, Udo; Matthews, Sarah; Long, David; Thomas, William;
Hancock, Barry; Reid, Hamish; Fludra, Andrzej; Auchère, Frederic;
Andretta, Vincenzo; Naletto, Giampiero; Poletto, Luca; Harra, Louise
Bibcode: 2020SPIE11444E..0NS
Altcode:
Solar-C (EUVST) is the next Japanese solar physics mission to
be developed with significant contributions from US and European
countries. The mission carries an EUV imaging spectrometer with
slit-jaw imaging system called EUVST (EUV High-Throughput Spectroscopic
Telescope) as the mission payload, to take a fundamental step towards
answering how the plasma universe is created and evolves and how the
Sun influences the Earth and other planets in our solar system. In
April 2020, ISAS (Institute of Space and Astronautical Science) of JAXA
(Japan Aerospace Exploration Agency) has made the final down-selection
for this mission as the 4th in the series of competitively chosen
M-class mission to be launched with an Epsilon launch vehicle in mid
2020s. NASA (National Aeronautics and Space Administration) has selected
this mission concept for Phase A concept study in September 2019 and
is in the process leading to final selection. For European countries,
the team has (or is in the process of confirming) confirmed endorsement
for hardware contributions to the EUVST from the national agencies. A
recent update to the mission instrumentation is to add a UV spectral
irradiance monitor capability for EUVST calibration and scientific
purpose. This presentation provides the latest status of the mission
with an overall description of the mission concept emphasizing on key
roles of the mission in heliophysics research from mid 2020s.
Title: Calibrating optical distortions in the Solar Orbiter SPICE
spectrograph
Authors: Thompson, W. T.; Schühle, U.; Young, P. R.; Auchere, F.;
Carlsson, M.; Fludra, A.; Hassler, D.; Peter, H.; Aznar Cuadrado, R.;
Buchlin, E.; Caldwell, M.; DeForest, C.; Fredvik, T.; Harra, L. K.;
Janvier, M.; Kucera, T. A.; Giunta, A. S.; Grundy, T.; Müller, D.;
Parenti, S.; Caminade, S.; Schmutz, W. K.; Teriaca, L.; Williams,
D.; Sidher, S.
Bibcode: 2020AGUFMSH0360029T
Altcode:
The Spectral Imaging of the Coronal Environment (SPICE) instrument on
Solar Orbiter is a high-resolution imaging spectrometer operating
at extreme ultraviolet (EUV) wavelengths from 70.4-79.0 nm and
97.3-104.9 nm. A single-mirror off-axis paraboloid focuses the solar
image onto the entrance slit of the spectrometer section. A Toroidal
Variable Line Space (TVLS) grating images the entrance slit onto a
pair of MCP-intensified APS detectors. Ray-tracing analysis prior
to launch showed that the instrument was subject to a number of
small image distortions which need to be corrected in the final data
product. We compare the ray tracing results with measurements made in
flight. Co-alignment with other telescopes on Solar Orbiter will also
be examined.
Title: First results from the EUI and SPICE observations of Alpha
Leo near Solar Orbiter first perihelion
Authors: Buchlin, E.; Teriaca, L.; Giunta, A. S.; Grundy, T.; Andretta,
V.; Auchere, F.; Peter, H.; Berghmans, D.; Carlsson, M.; Fludra, A.;
Harra, L.; Hassler, D.; Long, D.; Rochus, P. L.; Schühle, U.; Aznar
Cuadrado, R.; Caldwell, M.; Caminade, S.; DeForest, C.; Fredvik, T.;
Gissot, S.; Heerlein, K.; Janvier, M.; Kraaikamp, E.; Kucera, T. A.;
Müller, D.; Parenti, S.; Schmutz, W. K.; Sidher, S.; Smith, P.;
Stegen, K.; Thompson, W. T.; Verbeeck, C.; Williams, D.; Young, P. R.
Bibcode: 2020AGUFMSH0360024B
Altcode:
On June 16th 2020 Solar Orbiter made a dedicated observing campaign
where the spacecraft pointed to the solar limb to allow some of the
high resolution instruments to observe the ingress (at the east limb)
and later the egress (west limb) of the occultation of the star Alpha
Leonis by the solar disk. The star was chosen because its luminosity and
early spectral type ensure high and stable flux at wavelengths between
100 and 122 nanometers, a range observed by the High Resolution EUI
Lyman alpha telescope (HRI-LYA) and by the long wavelength channel
of the SPICE spectrograph. Star observations, when feasible, allow
to gather a great deal of information on the instrument performances,
such as the radiometric performance and the instrument optical point
spread function (PSF). We report here the first results from the
above campaign for the two instruments.
Title: Solar Orbiter: connecting remote sensing and in situ
measurements
Authors: Horbury, T. S.; Auchere, F.; Antonucci, E.; Berghmans, D.;
Bruno, R.; Carlsson, M.; del Toro Iniesta, J. C.; Fludra, A.; Harra,
L.; Hassler, D.; Heinzel, P.; Howard, R. A.; Krucker, S.; Livi, S. A.;
Long, D.; Louarn, P.; Maksimovic, M.; Mueller, D.; Owen, C. J.; Peter,
H.; Rochus, P. L.; Rodriguez-Pacheco, J.; Romoli, M.; Schühle, U.;
Solanki, S. K.; Teriaca, L.; Wimmer-Schweingruber, R. F.; Zouganelis,
Y.; Laker, R.
Bibcode: 2020AGUFMSH038..10H
Altcode:
A key science goal of the Solar Orbiter mission is to make connections
between phenomena on the Sun and their manifestations in interplanetary
space. To that end, the spacecraft carries a carefully tailored
payload of six remote sensing instruments and four making in situ
measurements. During June 2020, while the spacecraft was around 0.5
AU from the Sun, the remote sensing instruments operated for several
days. While this was primarily an engineering activity, the resulting
observations provided outstanding measurements and represent the ideal
first opportunity to investigate the potential for making connections
between the remote sensing and in situ payloads on Solar Orbiter. We present a preliminary analysis of the available remote sensing and
in situ observations, showing how connections can be made, and discuss
the potential for further, more precise mapping to be performed as
the mission progresses.
Title: First results from combined EUI and SPICE observations of
Lyman lines of Hydrogen and He II
Authors: Teriaca, L.; Aznar Cuadrado, R.; Giunta, A. S.; Grundy, T.;
Parenti, S.; Auchere, F.; Vial, J. C.; Fludra, A.; Berghmans, D.;
Carlsson, M.; Harra, L.; Hassler, D.; Long, D.; Peter, H.; Rochus,
P. L.; Schühle, U.; Buchlin, E.; Caldwell, M.; Caminade, S.; DeForest,
C.; Fredvik, T.; Gissot, S.; Heerlein, K.; Janvier, M.; Kraaikamp,
E.; Kucera, T. A.; Mueller, D.; Schmutz, W. K.; Sidher, S.; Smith, P.;
Stegen, K.; Thompson, W. T.; Verbeeck, C.; Williams, D.; Young, P. R.
Bibcode: 2020AGUFMSH0360003T
Altcode:
The Solar Orbiter spacecraft carries a powerful set of remote
sensing instruments that allow studying the solar atmosphere with
unprecedented diagnostic capabilities. Many such diagnostics require
the simultaneous usage of more than one instrument. One example of that
is the capability, for the first time, to obtain (near) simultaneous
spatially resolved observations of the emission from the first three
lines of the Lyman series of hydrogen and of He II Lyman alpha. In fact,
the SPectral Imaging of the Coronal Environment (SPICE) spectrometer
can observe the Lyman beta and gamma lines in its long wavelength
(SPICE-LW) channel, the High Resolution Lyman Alpha (HRI-LYA) telescope
of the Extreme Ultraviolet Imager (EUI) acquires narrow band images in
the Lyman alpha line while the Full Disk Imager (FSI) of EUI can take
images dominated by the Lyman alpha line of ionized Helium at 30.4 nm
(FSI-304). Being hydrogen and helium the main components of our star,
these very bright transitions play an important role in the energy
budget of the outer atmosphere via radiative losses and the measurement
of their profiles and radiance ratios is a fundamental constraint to
any comprehensive modelization effort of the upper solar chromosphere
and transition region. Additionally, monitoring their average ratios
can serve as a check out for the relative radiometric performance of
the two instruments throughout the mission. Although the engineering
data acquired so far are far from ideal in terms of time simultaneity
(often only within about 1 h) and line coverage (often only Lyman beta
was acquired by SPICE and not always near simultaneous images from all
three telescopes are available) the analysis we present here still
offers a great opportunity to have a first look at the potential of
this diagnostic from the two instruments. In fact, we have identified
a series of datasets obtained at disk center and at various positions
at the solar limb that allow studying the Lyman alpha to beta radiance
ratio and their relation to He II 30.4 as a function of the position
on the Sun (disk center versus limb and quiet Sun versus coronal holes).
Title: Coordination within the remote sensing payload on the Solar
Orbiter mission
Authors: Auchère, F.; Andretta, V.; Antonucci, E.; Bach, N.;
Battaglia, M.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Caminade,
S.; Carlsson, M.; Carlyle, J.; Cerullo, J. J.; Chamberlin, P. C.;
Colaninno, R. C.; Davila, J. M.; De Groof, A.; Etesi, L.; Fahmy,
S.; Fineschi, S.; Fludra, A.; Gilbert, H. R.; Giunta, A.; Grundy,
T.; Haberreiter, M.; Harra, L. K.; Hassler, D. M.; Hirzberger, J.;
Howard, R. A.; Hurford, G.; Kleint, L.; Kolleck, M.; Krucker, S.;
Lagg, A.; Landini, F.; Long, D. M.; Lefort, J.; Lodiot, S.; Mampaey,
B.; Maloney, S.; Marliani, F.; Martinez-Pillet, V.; McMullin, D. R.;
Müller, D.; Nicolini, G.; Orozco Suarez, D.; Pacros, A.; Pancrazzi,
M.; Parenti, S.; Peter, H.; Philippon, A.; Plunkett, S.; Rich, N.;
Rochus, P.; Rouillard, A.; Romoli, M.; Sanchez, L.; Schühle, U.;
Sidher, S.; Solanki, S. K.; Spadaro, D.; St Cyr, O. C.; Straus, T.;
Tanco, I.; Teriaca, L.; Thompson, W. T.; del Toro Iniesta, J. C.;
Verbeeck, C.; Vourlidas, A.; Watson, C.; Wiegelmann, T.; Williams,
D.; Woch, J.; Zhukov, A. N.; Zouganelis, I.
Bibcode: 2020A&A...642A...6A
Altcode:
Context. To meet the scientific objectives of the mission, the Solar
Orbiter spacecraft carries a suite of in-situ (IS) and remote sensing
(RS) instruments designed for joint operations with inter-instrument
communication capabilities. Indeed, previous missions have shown that
the Sun (imaged by the RS instruments) and the heliosphere (mainly
sampled by the IS instruments) should be considered as an integrated
system rather than separate entities. Many of the advances expected
from Solar Orbiter rely on this synergistic approach between IS and
RS measurements.
Aims: Many aspects of hardware development,
integration, testing, and operations are common to two or more
RS instruments. In this paper, we describe the coordination effort
initiated from the early mission phases by the Remote Sensing Working
Group. We review the scientific goals and challenges, and give an
overview of the technical solutions devised to successfully operate
these instruments together.
Methods: A major constraint for the
RS instruments is the limited telemetry (TM) bandwidth of the Solar
Orbiter deep-space mission compared to missions in Earth orbit. Hence,
many of the strategies developed to maximise the scientific return from
these instruments revolve around the optimisation of TM usage, relying
for example on onboard autonomy for data processing, compression,
and selection for downlink. The planning process itself has been
optimised to alleviate the dynamic nature of the targets, and an
inter-instrument communication scheme has been implemented which can
be used to autonomously alter the observing modes. We also outline the
plans for in-flight cross-calibration, which will be essential to the
joint data reduction and analysis.
Results: The RS instrument
package on Solar Orbiter will carry out comprehensive measurements
from the solar interior to the inner heliosphere. Thanks to the close
coordination between the instrument teams and the European Space
Agency, several challenges specific to the RS suite were identified
and addressed in a timely manner.
Title: Models and data analysis tools for the Solar Orbiter mission
Authors: Rouillard, A. P.; Pinto, R. F.; Vourlidas, A.; De Groof, A.;
Thompson, W. T.; Bemporad, A.; Dolei, S.; Indurain, M.; Buchlin, E.;
Sasso, C.; Spadaro, D.; Dalmasse, K.; Hirzberger, J.; Zouganelis, I.;
Strugarek, A.; Brun, A. S.; Alexandre, M.; Berghmans, D.; Raouafi,
N. E.; Wiegelmann, T.; Pagano, P.; Arge, C. N.; Nieves-Chinchilla,
T.; Lavarra, M.; Poirier, N.; Amari, T.; Aran, A.; Andretta, V.;
Antonucci, E.; Anastasiadis, A.; Auchère, F.; Bellot Rubio, L.;
Nicula, B.; Bonnin, X.; Bouchemit, M.; Budnik, E.; Caminade, S.;
Cecconi, B.; Carlyle, J.; Cernuda, I.; Davila, J. M.; Etesi, L.;
Espinosa Lara, F.; Fedorov, A.; Fineschi, S.; Fludra, A.; Génot,
V.; Georgoulis, M. K.; Gilbert, H. R.; Giunta, A.; Gomez-Herrero, R.;
Guest, S.; Haberreiter, M.; Hassler, D.; Henney, C. J.; Howard, R. A.;
Horbury, T. S.; Janvier, M.; Jones, S. I.; Kozarev, K.; Kraaikamp,
E.; Kouloumvakos, A.; Krucker, S.; Lagg, A.; Linker, J.; Lavraud,
B.; Louarn, P.; Maksimovic, M.; Maloney, S.; Mann, G.; Masson, A.;
Müller, D.; Önel, H.; Osuna, P.; Orozco Suarez, D.; Owen, C. J.;
Papaioannou, A.; Pérez-Suárez, D.; Rodriguez-Pacheco, J.; Parenti,
S.; Pariat, E.; Peter, H.; Plunkett, S.; Pomoell, J.; Raines, J. M.;
Riethmüller, T. L.; Rich, N.; Rodriguez, L.; Romoli, M.; Sanchez,
L.; Solanki, S. K.; St Cyr, O. C.; Straus, T.; Susino, R.; Teriaca,
L.; del Toro Iniesta, J. C.; Ventura, R.; Verbeeck, C.; Vilmer, N.;
Warmuth, A.; Walsh, A. P.; Watson, C.; Williams, D.; Wu, Y.; Zhukov,
A. N.
Bibcode: 2020A&A...642A...2R
Altcode:
Context. The Solar Orbiter spacecraft will be equipped with a wide
range of remote-sensing (RS) and in situ (IS) instruments to record
novel and unprecedented measurements of the solar atmosphere and
the inner heliosphere. To take full advantage of these new datasets,
tools and techniques must be developed to ease multi-instrument and
multi-spacecraft studies. In particular the currently inaccessible
low solar corona below two solar radii can only be observed
remotely. Furthermore techniques must be used to retrieve coronal
plasma properties in time and in three dimensional (3D) space. Solar
Orbiter will run complex observation campaigns that provide interesting
opportunities to maximise the likelihood of linking IS data to their
source region near the Sun. Several RS instruments can be directed
to specific targets situated on the solar disk just days before
data acquisition. To compare IS and RS, data we must improve our
understanding of how heliospheric probes magnetically connect to the
solar disk.
Aims: The aim of the present paper is to briefly
review how the current modelling of the Sun and its atmosphere
can support Solar Orbiter science. We describe the results of a
community-led effort by European Space Agency's Modelling and Data
Analysis Working Group (MADAWG) to develop different models, tools,
and techniques deemed necessary to test different theories for the
physical processes that may occur in the solar plasma. The focus here
is on the large scales and little is described with regards to kinetic
processes. To exploit future IS and RS data fully, many techniques have
been adapted to model the evolving 3D solar magneto-plasma from the
solar interior to the solar wind. A particular focus in the paper is
placed on techniques that can estimate how Solar Orbiter will connect
magnetically through the complex coronal magnetic fields to various
photospheric and coronal features in support of spacecraft operations
and future scientific studies.
Methods: Recent missions such as
STEREO, provided great opportunities for RS, IS, and multi-spacecraft
studies. We summarise the achievements and highlight the challenges
faced during these investigations, many of which motivated the Solar
Orbiter mission. We present the new tools and techniques developed
by the MADAWG to support the science operations and the analysis of
the data from the many instruments on Solar Orbiter.
Results:
This article reviews current modelling and tool developments that ease
the comparison of model results with RS and IS data made available
by current and upcoming missions. It also describes the modelling
strategy to support the science operations and subsequent exploitation
of Solar Orbiter data in order to maximise the scientific output
of the mission.
Conclusions: The on-going community effort
presented in this paper has provided new models and tools necessary
to support mission operations as well as the science exploitation of
the Solar Orbiter data. The tools and techniques will no doubt evolve
significantly as we refine our procedure and methodology during the
first year of operations of this highly promising mission.
Title: The Solar Orbiter Science Activity Plan. Translating solar
and heliospheric physics questions into action
Authors: Zouganelis, I.; De Groof, A.; Walsh, A. P.; Williams, D. R.;
Müller, D.; St Cyr, O. C.; Auchère, F.; Berghmans, D.; Fludra,
A.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.;
Owen, C. J.; Rodríguez-Pacheco, J.; Romoli, M.; Solanki, S. K.;
Watson, C.; Sanchez, L.; Lefort, J.; Osuna, P.; Gilbert, H. R.;
Nieves-Chinchilla, T.; Abbo, L.; Alexandrova, O.; Anastasiadis, A.;
Andretta, V.; Antonucci, E.; Appourchaux, T.; Aran, A.; Arge, C. N.;
Aulanier, G.; Baker, D.; Bale, S. D.; Battaglia, M.; Bellot Rubio,
L.; Bemporad, A.; Berthomier, M.; Bocchialini, K.; Bonnin, X.; Brun,
A. S.; Bruno, R.; Buchlin, E.; Büchner, J.; Bucik, R.; Carcaboso,
F.; Carr, R.; Carrasco-Blázquez, I.; Cecconi, B.; Cernuda Cangas, I.;
Chen, C. H. K.; Chitta, L. P.; Chust, T.; Dalmasse, K.; D'Amicis, R.;
Da Deppo, V.; De Marco, R.; Dolei, S.; Dolla, L.; Dudok de Wit, T.;
van Driel-Gesztelyi, L.; Eastwood, J. P.; Espinosa Lara, F.; Etesi,
L.; Fedorov, A.; Félix-Redondo, F.; Fineschi, S.; Fleck, B.; Fontaine,
D.; Fox, N. J.; Gandorfer, A.; Génot, V.; Georgoulis, M. K.; Gissot,
S.; Giunta, A.; Gizon, L.; Gómez-Herrero, R.; Gontikakis, C.; Graham,
G.; Green, L.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler,
D. M.; Hirzberger, J.; Ho, G. C.; Hurford, G.; Innes, D.; Issautier,
K.; James, A. W.; Janitzek, N.; Janvier, M.; Jeffrey, N.; Jenkins,
J.; Khotyaintsev, Y.; Klein, K. -L.; Kontar, E. P.; Kontogiannis,
I.; Krafft, C.; Krasnoselskikh, V.; Kretzschmar, M.; Labrosse, N.;
Lagg, A.; Landini, F.; Lavraud, B.; Leon, I.; Lepri, S. T.; Lewis,
G. R.; Liewer, P.; Linker, J.; Livi, S.; Long, D. M.; Louarn, P.;
Malandraki, O.; Maloney, S.; Martinez-Pillet, V.; Martinovic, M.;
Masson, A.; Matthews, S.; Matteini, L.; Meyer-Vernet, N.; Moraitis,
K.; Morton, R. J.; Musset, S.; Nicolaou, G.; Nindos, A.; O'Brien,
H.; Orozco Suarez, D.; Owens, M.; Pancrazzi, M.; Papaioannou, A.;
Parenti, S.; Pariat, E.; Patsourakos, S.; Perrone, D.; Peter, H.;
Pinto, R. F.; Plainaki, C.; Plettemeier, D.; Plunkett, S. P.; Raines,
J. M.; Raouafi, N.; Reid, H.; Retino, A.; Rezeau, L.; Rochus, P.;
Rodriguez, L.; Rodriguez-Garcia, L.; Roth, M.; Rouillard, A. P.;
Sahraoui, F.; Sasso, C.; Schou, J.; Schühle, U.; Sorriso-Valvo, L.;
Soucek, J.; Spadaro, D.; Stangalini, M.; Stansby, D.; Steller, M.;
Strugarek, A.; Štverák, Š.; Susino, R.; Telloni, D.; Terasa, C.;
Teriaca, L.; Toledo-Redondo, S.; del Toro Iniesta, J. C.; Tsiropoula,
G.; Tsounis, A.; Tziotziou, K.; Valentini, F.; Vaivads, A.; Vecchio,
A.; Velli, M.; Verbeeck, C.; Verdini, A.; Verscharen, D.; Vilmer, N.;
Vourlidas, A.; Wicks, R.; Wimmer-Schweingruber, R. F.; Wiegelmann,
T.; Young, P. R.; Zhukov, A. N.
Bibcode: 2020A&A...642A...3Z
Altcode: 2020arXiv200910772Z
Solar Orbiter is the first space mission observing the solar plasma
both in situ and remotely, from a close distance, in and out of the
ecliptic. The ultimate goal is to understand how the Sun produces
and controls the heliosphere, filling the Solar System and driving
the planetary environments. With six remote-sensing and four in-situ
instrument suites, the coordination and planning of the operations are
essential to address the following four top-level science questions:
(1) What drives the solar wind and where does the coronal magnetic field
originate?; (2) How do solar transients drive heliospheric variability?;
(3) How do solar eruptions produce energetic particle radiation that
fills the heliosphere?; (4) How does the solar dynamo work and drive
connections between the Sun and the heliosphere? Maximising the
mission's science return requires considering the characteristics
of each orbit, including the relative position of the spacecraft
to Earth (affecting downlink rates), trajectory events (such
as gravitational assist manoeuvres), and the phase of the solar
activity cycle. Furthermore, since each orbit's science telemetry
will be downloaded over the course of the following orbit, science
operations must be planned at mission level, rather than at the level
of individual orbits. It is important to explore the way in which those
science questions are translated into an actual plan of observations
that fits into the mission, thus ensuring that no opportunities are
missed. First, the overarching goals are broken down into specific,
answerable questions along with the required observations and the
so-called Science Activity Plan (SAP) is developed to achieve this. The
SAP groups objectives that require similar observations into Solar
Orbiter Observing Plans, resulting in a strategic, top-level view of
the optimal opportunities for science observations during the mission
lifetime. This allows for all four mission goals to be addressed. In
this paper, we introduce Solar Orbiter's SAP through a series of
examples and the strategy being followed.
Title: The Solar Orbiter SPICE instrument. An extreme UV imaging
spectrometer
Authors: SPICE Consortium; Anderson, M.; Appourchaux, T.; Auchère, F.;
Aznar Cuadrado, R.; Barbay, J.; Baudin, F.; Beardsley, S.; Bocchialini,
K.; Borgo, B.; Bruzzi, D.; Buchlin, E.; Burton, G.; Büchel, V.;
Caldwell, M.; Caminade, S.; Carlsson, M.; Curdt, W.; Davenne, J.;
Davila, J.; Deforest, C. E.; Del Zanna, G.; Drummond, D.; Dubau,
J.; Dumesnil, C.; Dunn, G.; Eccleston, P.; Fludra, A.; Fredvik, T.;
Gabriel, A.; Giunta, A.; Gottwald, A.; Griffin, D.; Grundy, T.; Guest,
S.; Gyo, M.; Haberreiter, M.; Hansteen, V.; Harrison, R.; Hassler,
D. M.; Haugan, S. V. H.; Howe, C.; Janvier, M.; Klein, R.; Koller,
S.; Kucera, T. A.; Kouliche, D.; Marsch, E.; Marshall, A.; Marshall,
G.; Matthews, S. A.; McQuirk, C.; Meining, S.; Mercier, C.; Morris,
N.; Morse, T.; Munro, G.; Parenti, S.; Pastor-Santos, C.; Peter, H.;
Pfiffner, D.; Phelan, P.; Philippon, A.; Richards, A.; Rogers, K.;
Sawyer, C.; Schlatter, P.; Schmutz, W.; Schühle, U.; Shaughnessy,
B.; Sidher, S.; Solanki, S. K.; Speight, R.; Spescha, M.; Szwec, N.;
Tamiatto, C.; Teriaca, L.; Thompson, W.; Tosh, I.; Tustain, S.; Vial,
J. -C.; Walls, B.; Waltham, N.; Wimmer-Schweingruber, R.; Woodward,
S.; Young, P.; de Groof, A.; Pacros, A.; Williams, D.; Müller, D.
Bibcode: 2020A&A...642A..14S
Altcode: 2019arXiv190901183A; 2019arXiv190901183S
Aims: The Spectral Imaging of the Coronal Environment (SPICE)
instrument is a high-resolution imaging spectrometer operating at
extreme ultraviolet wavelengths. In this paper, we present the concept,
design, and pre-launch performance of this facility instrument on the
ESA/NASA Solar Orbiter mission.
Methods: The goal of this paper
is to give prospective users a better understanding of the possible
types of observations, the data acquisition, and the sources that
contribute to the instrument's signal.
Results: The paper
discusses the science objectives, with a focus on the SPICE-specific
aspects, before presenting the instrument's design, including optical,
mechanical, thermal, and electronics aspects. This is followed by a
characterisation and calibration of the instrument's performance. The
paper concludes with descriptions of the operations concept and data
processing.
Conclusions: The performance measurements of the
various instrument parameters meet the requirements derived from the
mission's science objectives. The SPICE instrument is ready to perform
measurements that will provide vital contributions to the scientific
success of the Solar Orbiter mission.
Title: Understanding the origins of the heliosphere: integrating
observations and measurements from Parker Solar Probe, Solar Orbiter,
and other space- and ground-based observatories
Authors: Velli, M.; Harra, L. K.; Vourlidas, A.; Schwadron,
N.; Panasenco, O.; Liewer, P. C.; Müller, D.; Zouganelis, I.;
St Cyr, O. C.; Gilbert, H.; Nieves-Chinchilla, T.; Auchère, F.;
Berghmans, D.; Fludra, A.; Horbury, T. S.; Howard, R. A.; Krucker,
S.; Maksimovic, M.; Owen, C. J.; Rodríguez-Pacheco, J.; Romoli,
M.; Solanki, S. K.; Wimmer-Schweingruber, R. F.; Bale, S.; Kasper,
J.; McComas, D. J.; Raouafi, N.; Martinez-Pillet, V.; Walsh, A. P.;
De Groof, A.; Williams, D.
Bibcode: 2020A&A...642A...4V
Altcode:
Context. The launch of Parker Solar Probe (PSP) in 2018, followed
by Solar Orbiter (SO) in February 2020, has opened a new window in
the exploration of solar magnetic activity and the origin of the
heliosphere. These missions, together with other space observatories
dedicated to solar observations, such as the Solar Dynamics Observatory,
Hinode, IRIS, STEREO, and SOHO, with complementary in situ observations
from WIND and ACE, and ground based multi-wavelength observations
including the DKIST observatory that has just seen first light,
promise to revolutionize our understanding of the solar atmosphere
and of solar activity, from the generation and emergence of the Sun's
magnetic field to the creation of the solar wind and the acceleration of
solar energetic particles.
Aims: Here we describe the scientific
objectives of the PSP and SO missions, and highlight the potential for
discovery arising from synergistic observations. Here we put particular
emphasis on how the combined remote sensing and in situ observations of
SO, that bracket the outer coronal and inner heliospheric observations
by PSP, may provide a reconstruction of the solar wind and magnetic
field expansion from the Sun out to beyond the orbit of Mercury in the
first phases of the mission. In the later, out-of-ecliptic portions of
the SO mission, the solar surface magnetic field measurements from SO
and the multi-point white-light observations from both PSP and SO will
shed light on the dynamic, intermittent solar wind escaping from helmet
streamers, pseudo-streamers, and the confined coronal plasma, and on
solar energetic particle transport.
Methods: Joint measurements
during PSP-SO alignments, and magnetic connections along the same
flux tube complemented by alignments with Earth, dual PSP-Earth,
and SO-Earth, as well as with STEREO-A, SOHO, and BepiColumbo will
allow a better understanding of the in situ evolution of solar-wind
plasma flows and the full three-dimensional distribution of the
solar wind from a purely observational point of view. Spectroscopic
observations of the corona, and optical and radio observations,
combined with direct in situ observations of the accelerating solar
wind will provide a new foundation for understanding the fundamental
physical processes leading to the energy transformations from solar
photospheric flows and magnetic fields into the hot coronal plasma
and magnetic fields and finally into the bulk kinetic energy of the
solar wind and solar energetic particles.
Results: We discuss
the initial PSP observations, which already provide a compelling
rationale for new measurement campaigns by SO, along with ground-
and space-based assets within the synergistic context described above.
Title: The Solar Orbiter mission. Science overview
Authors: Müller, D.; St. Cyr, O. C.; Zouganelis, I.; Gilbert, H. R.;
Marsden, R.; Nieves-Chinchilla, T.; Antonucci, E.; Auchère, F.;
Berghmans, D.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic,
M.; Owen, C. J.; Rochus, P.; Rodriguez-Pacheco, J.; Romoli, M.;
Solanki, S. K.; Bruno, R.; Carlsson, M.; Fludra, A.; Harra, L.;
Hassler, D. M.; Livi, S.; Louarn, P.; Peter, H.; Schühle, U.;
Teriaca, L.; del Toro Iniesta, J. C.; Wimmer-Schweingruber, R. F.;
Marsch, E.; Velli, M.; De Groof, A.; Walsh, A.; Williams, D.
Bibcode: 2020A&A...642A...1M
Altcode: 2020arXiv200900861M
Aims: Solar Orbiter, the first mission of ESA's Cosmic Vision
2015-2025 programme and a mission of international collaboration between
ESA and NASA, will explore the Sun and heliosphere from close up and
out of the ecliptic plane. It was launched on 10 February 2020 04:03
UTC from Cape Canaveral and aims to address key questions of solar and
heliospheric physics pertaining to how the Sun creates and controls
the Heliosphere, and why solar activity changes with time. To answer
these, the mission carries six remote-sensing instruments to observe
the Sun and the solar corona, and four in-situ instruments to measure
the solar wind, energetic particles, and electromagnetic fields. In
this paper, we describe the science objectives of the mission, and how
these will be addressed by the joint observations of the instruments
onboard.
Methods: The paper first summarises the mission-level
science objectives, followed by an overview of the spacecraft and
payload. We report the observables and performance figures of each
instrument, as well as the trajectory design. This is followed by a
summary of the science operations concept. The paper concludes with a
more detailed description of the science objectives.
Results:
Solar Orbiter will combine in-situ measurements in the heliosphere
with high-resolution remote-sensing observations of the Sun to address
fundamental questions of solar and heliospheric physics. The performance
of the Solar Orbiter payload meets the requirements derived from the
mission's science objectives. Its science return will be augmented
further by coordinated observations with other space missions and
ground-based observatories. ARRAY(0x207ce98)
Title: The SPICE (Spectral Imaging of the Coronal Environment)
Ultraviolet Imaging Spectrograph Investigation
Authors: Hassler, D.; Auchere, F.; Carlsson, M.; Fludra, A.; Giunta,
A. S.; Mueller, D.; Peter, H.; Parenti, S.; Teriaca, L.; Fredvik, T.
Bibcode: 2019AGUFMSH24A..02H
Altcode:
One of the primary objectives of the Solar Orbiter mission is to link
remote sensing observations of the solar surface structures with in-situ
observations of solar wind streams. The SPICE (Spectral Imaging of the
Coronal Environment) instrument will characterize the plasma properties
of regions near the Sun to directly compare with in-situ measurements
from both Solar Orbiter & Parker Solar Probe. Specifically, SPICE
will map outflow velocities of surface features to solar wind structures
with similar composition (FIP, M/q) measured in-situ by the SWA/HIS
instrument on Solar Orbiter. These observations will help discriminate
models of solar wind origin by matching composition signatures in
solar wind streams to surface feature composition, and discriminate
physical processes that inject material from closed structures into
solar wind streams. This presentation will provide an overview of
the SPICE investigation, including science & measurement objective,
instrument design, capabilities and performance as measured during
calibration prior to delivery to the Solar Orbiter spacecraft. The
presentation will also provide a description of the operations concept
and data processing during the mission.
Title: The Solar-C_EUVST mission
Authors: Shimizu, Toshifumi; Imada, Shinsuke; Kawate, Tomoko;
Ichimoto, Kiyoshi; Suematsu, Yoshinori; Hara, Hirohisa; Katsukawa,
Yukio; Kubo, Masahito; Toriumi, Shin; Watanabe, Tetsuya; Yokoyama,
Takaaki; Korendyke, Clarence M.; Warren, Harry P.; Tarbell, Ted; De
Pontieu, Bart; Teriaca, Luca; Schühle, Udo H.; Solanki, Sami; Harra,
Louise K.; Matthews, Sarah; Fludra, A.; Auchère, F.; Andretta, V.;
Naletto, G.; Zhukov, A.
Bibcode: 2019SPIE11118E..07S
Altcode:
Solar-C EUVST (EUV High-Throughput Spectroscopic Telescope) is a
solar physics mission concept that was selected as a candidate for
JAXA competitive M-class missions in July 2018. The onboard science
instrument, EUVST, is an EUV spectrometer with slit-jaw imaging
system that will simultaneously observe the solar atmosphere from the
photosphere/chromosphere up to the corona with seamless temperature
coverage, high spatial resolution, and high throughput for the first
time. The mission is designed to provide a conclusive answer to the
most fundamental questions in solar physics: how fundamental processes
lead to the formation of the solar atmosphere and the solar wind, and
how the solar atmosphere becomes unstable, releasing the energy that
drives solar flares and eruptions. The entire instrument structure
and the primary mirror assembly with scanning and tip-tilt fine
pointing capability for the EUVST are being developed in Japan, with
spectrograph and slit-jaw imaging hardware and science contributions
from US and European countries. The mission will be launched and
installed in a sun-synchronous polar orbit by a JAXA Epsilon vehicle in
2025. ISAS/JAXA coordinates the conceptual study activities during the
current mission definition phase in collaboration with NAOJ and other
universities. The team is currently working towards the JAXA final
down-selection expected at the end of 2019, with strong support from
US and European colleagues. The paper provides an overall description
of the mission concept, key technologies, and the latest status.
Title: Spectroscopic EUV observations of impulsive solar energetic
particle event sources
Authors: Bučík, R.; Fludra, A.; Gómez-Herrero, R.; Innes, D. E.;
Kellett, B.; Kumar, R.; Mackovjak, Š.
Bibcode: 2018A&A...617A..40B
Altcode: 2018arXiv180700861B
Context. Remote observations of solar flare ion acceleration are rather
limited. Theoretical predictions for signatures of ion acceleration
in extreme ultraviolet (EUV) line profiles have been made. Previous
tests involve observations of flares with no evidence for energetic
ions.
Aims: We aim to examine a source flare of impulsive (or
3He-rich) solar energetic particle events with EUV line
spectroscopy.
Methods: We inspected all (more than 90) reported
3He-rich flares of the previous solar cycle 23 and found
only 4 (recurrent) jets in the field of view of the Coronal Diagnostic
Spectrometer (CDS) on board the Solar and Heliospheric Observatory
(SOHO). The jet with the most suitable spatial and temporal coverage
was analyzed in detail.
Results: Two enhanced (nonthermal)
line broadenings are observed in the cooler chromospheric and
transition-region lines, and they are localized near the site where the
closed magnetic loops reconnect with the open magnetic field lines. The
enhanced broadenings are both found at the sites with redshifts in
the lines, surrounded by the region with blueshifts. One enhanced line
broadening is associated with a small flare without energetic particle
signatures, while another occurs just after the particle acceleration
signatures of the main flare terminated.
Conclusions: The
observed excess broadening does not appear to be directly related to
the energetic ion production and motions. Further investigations are
required that cover the critical impulsive phase of the flare, ideally
with high-resolution spectrometers that are specifically pointed to
the 3He-rich solar energetic particle source.
Title: Testing Models of the Fast Solar Wind using Spectroscopic
and In Situ Observations
Authors: Fludra, Andrzej; Landi, Enrico
Bibcode: 2018IAUS..335...87F
Altcode:
We present a new technique to study joint observations of EUV spectral
line intensities and in situ charge states of the fast solar wind. We
solve the time-dependent equation for ionization and recombination
for a chosen element and calculate the charge state evolution along
the open magnetic fields for elements such as C, O, Ne, Mg, Si and
Fe. Comparing predicted spectral lines intensities above the limb and in
situ charge states to observations from SOHO/SUMER and Ulysses/SWICS,
we test how well the modelled thermodynamic parameters of the solar
wind reproduce observations. We outline the application of this method
to Solar Orbiter data.
Title: Charge States of Krypton and Xenon in the Solar Wind
Authors: Bochsler, Peter; Fludra, Andrzej; Giunta, Alessandra
Bibcode: 2017SoPh..292..128B
Altcode:
We calculate charge state distributions of Kr and Xe in a model for
two different types of solar wind using the effective ionization and
recombination rates provided from the OPEN_ADAS data base. The charge
states of heavy elements in the solar wind are essential for estimating
the efficiency of Coulomb drag in the inner corona. We find that xenon
ions experience particularly low Coulomb drag from protons in the inner
corona, comparable to the notoriously weak drag of protons on helium
ions. It has been found long ago that helium in the solar wind can be
strongly depleted near interplanetary current sheets, whereas coronal
mass ejecta are sometimes strongly enriched in helium. We argue that
if the extraordinary variability of the helium abundance in the solar
wind is due to inefficient Coulomb drag, the xenon abundance must
vary strongly. In fact, a secular decrease of the solar wind xenon
abundance relative to the other heavier noble gases (Ne, Ar, Kr)
has been postulated based on a comparison of noble gases in recently
irradiated and ancient samples of ilmenite in the lunar regolith. We
conclude that decreasing solar activity and decreasing frequency of
coronal mass ejections over the solar lifetime might be responsible
for a secularly decreasing abundance of xenon in the solar wind.
Title: The VUV instrument SPICE for Solar Orbiter: performance
ground testing
Authors: Caldwell, Martin E.; Morris, Nigel; Griffin, Douglas K.;
Eccleston, Paul; Anderson, Mark; Pastor Santos, Carmen; Bruzzi,
Davide; Tustain, Samuel; Howe, Chris; Davenne, Jenny; Grundy, Timothy;
Speight, Roisin; Sidher, Sunil D.; Giunta, Alessandra; Fludra, Andrzej;
Philippon, Anne; Auchere, Frederic; Hassler, Don; Davila, Joseph M.;
Thompson, William T.; Schuehle, Udo H.; Meining, Stefan; Walls, Buddy;
Phelan, P.; Dunn, Greg; Klein, Roman M.; Reichel, Thomas; Gyo, Manfred;
Munro, Grant J.; Holmes, William; Doyle, Peter
Bibcode: 2017SPIE10397E..08C
Altcode:
SPICE is an imaging spectrometer operating at vacuum ultraviolet
(VUV) wavelengths, 70.4 - 79.0 nm and 97.3 - 104.9 nm. It is a
facility instrument on the Solar Orbiter mission, which carries
10 science instruments in all, to make observations of the Sun's
atmosphere and heliosphere, at close proximity to the Sun, i.e to
0.28 A.U. at perihelion. SPICE's role is to make VUV measurements
of plasma in the solar atmosphere. SPICE is designed to achieve
spectral imaging at spectral resolution >1500, spatial resolution
of several arcsec, and two-dimensional FOV of 11 x16arcmins. The many
strong constraints on the instrument design imposed by the mission
requirements prevent the imaging performance from exceeding those of
previous instruments, but by being closer to the sun there is a gain in
spatial resolution. The price which is paid is the harsher environment,
particularly thermal. This leads to some novel features in the design,
which needed to be proven by ground test programs. These include a
dichroic solar-transmitting primary mirror to dump the solar heat, a
high in-flight temperature (60deg.C) and gradients in the optics box,
and a bespoke variable-line-spacing grating to minimise the number of
reflective components used. The tests culminate in the systemlevel test
of VUV imaging performance and pointing stability. We will describe how
our dedicated facility with heritage from previous solar instruments,
is used to make these tests, and show the results, firstly on the
Engineering Model of the optics unit, and more recently on the Flight
Model. For the keywords, select up to 8 key terms for a search on your
manuscript's subject.
Title: Diagnostics of Coronal Heating in Active-region Loops
Authors: Fludra, A.; Hornsey, C.; Nakariakov, V. M.
Bibcode: 2017ApJ...834..100F
Altcode:
Understanding coronal heating remains a central problem in solar
physics. Many mechanisms have been proposed to explain how energy
is transferred to and deposited in the corona. We summarize past
observational studies that attempted to identify the heating mechanism
and point out the difficulties in reproducing the observations of
the solar corona from the heating models. The aim of this paper is
to study whether the observed extreme ultraviolet (EUV) emission in
individual coronal loops in solar active regions can provide constraints
on the volumetric heating function, and to develop a diagnostic for
the heating function for a subset of loops that are found close to
static thermal equilibrium. We reconstruct the coronal magnetic field
from Solar Dynamics Observatory/HMI data using a nonlinear force-free
magnetic field model. We model selected loops using a one-dimensional
stationary model, with a heating rate dependent locally on the magnetic
field strength along the loop, and we calculate the emission from
these loops in various EUV wavelengths for different heating rates. We
present a method to measure a power index β defining the dependence
of the volumetric heating rate EH on the magnetic field,
{E}H\propto {B}β , and controlling also
the shape of the heating function: concentrated near the loop top,
uniform and concentrated near the footpoints. The diagnostic is based
on the dependence of the electron density on the index β. This method
is free from the assumptions of the loop filling factor but requires
spectroscopic measurements of the density-sensitive lines. The range of
applicability for loops of different length and heating distributions
is discussed, and the steps to solving the coronal heating problem
are outlined.
Title: The SPICE Spectral Imager on Solar Orbiter: Linking the Sun
to the Heliosphere
Authors: Fludra, Andrzej; Haberreiter, Margit; Peter, Hardi; Vial,
Jean-Claude; Harrison, Richard; Parenti, Susanna; Innes, Davina;
Schmutz, Werner; Buchlin, Eric; Chamberlin, Phillip; Thompson,
William; Gabriel, Alan; Morris, Nigel; Caldwell, Martin; Auchere,
Frederic; Curdt, Werner; Teriaca, Luca; Hassler, Donald M.; DeForest,
Craig; Hansteen, Viggo; Carlsson, Mats; Philippon, Anne; Janvier, Miho;
Wimmer-Schweingruber, Robert; Griffin, Douglas; Davila, Joseph; Giunta,
Alessandra; Waltham, Nick; Eccleston, Paul; Gottwald, Alexander;
Klein, Roman; Hanley, John; Walls, Buddy; Howe, Chris; Schuehle, Udo
Bibcode: 2016cosp...41E.607F
Altcode:
The SPICE (Spectral Imaging of the Coronal Environment) instrument is
one of the key remote sensing instruments onboard the upcoming Solar
Orbiter Mission. SPICE has been designed to contribute to the science
goals of the mission by investigating the source regions of outflows
and ejection processes which link the solar surface and corona to the
heliosphere. In particular, SPICE will provide quantitative information
on the physical state and composition of the solar atmosphere
plasma. For example, SPICE will access relative abundances of ions to
study the origin and the spatial/temporal variations of the 'First
Ionization Potential effect', which are key signatures to trace the
solar wind and plasma ejections paths within the heliosphere. Here we
will present the instrument and its performance capability to attain the
scientific requirements. We will also discuss how different observation
modes can be chosen to obtain the best science results during the
different orbits of the mission. To maximize the scientific return of
the instrument, the SPICE team is working to optimize the instrument
operations, and to facilitate the data access and their exploitation.
Title: Solar abundances with the SPICE spectral imager on Solar
Orbiter
Authors: Giunta, Alessandra; Haberreiter, Margit; Peter, Hardi;
Vial, Jean-Claude; Harrison, Richard; Parenti, Susanna; Innes, Davina;
Schmutz, Werner; Buchlin, Eric; Chamberlin, Phillip; Thompson, William;
Bocchialini, Karine; Gabriel, Alan; Morris, Nigel; Caldwell, Martin;
Auchere, Frederic; Curdt, Werner; Teriaca, Luca; Hassler, Donald M.;
DeForest, Craig; Hansteen, Viggo; Carlsson, Mats; Philippon, Anne;
Janvier, Miho; Wimmer-Schweingruber, Robert; Griffin, Douglas; Baudin,
Frederic; Davila, Joseph; Fludra, Andrzej; Waltham, Nick; Eccleston,
Paul; Gottwald, Alexander; Klein, Roman; Hanley, John; Walls, Buddy;
Howe, Chris; Schuehle, Udo; Gyo, Manfred; Pfiffner, Dany
Bibcode: 2016cosp...41E.681G
Altcode:
Elemental composition of the solar atmosphere and in particular
abundance bias of low and high First Ionization Potential (FIP)
elements are a key tracer of the source regions of the solar wind. These
abundances and their spatio-temporal variations, as well as the other
plasma parameters , will be derived by the SPICE (Spectral Imaging
of the Coronal Environment) EUV spectral imager on the upcoming
Solar Orbiter mission. SPICE is designed to provide spectroheliograms
(spectral images) using a core set of emission lines arising from ions
of both low-FIP and high-FIP elements. These lines are formed over
a wide range of temperatures, enabling the analysis of the different
layers of the solar atmosphere. SPICE will use these spectroheliograms
to produce dynamic composition maps of the solar atmosphere to be
compared to in-situ measurements of the solar wind composition of
the same elements (i.e. O, Ne, Mg, Fe). This will provide a tool to
study the connectivity between the spacecraft (the Heliosphere) and
the Sun. We will discuss the SPICE capabilities for such composition
measurements.
Title: Diagnostics of Coronal Heating in Solar Active Regions
Authors: Fludra, Andrzej; Hornsey, Christopher; Nakariakov, Valery
Bibcode: 2015TESS....120305F
Altcode:
We aim to develop a diagnostic method for the coronal heating mechanism
in active region loops. Observational constraints on coronal heating
models have been sought using measurements in the X-ray and EUV
wavelengths. Statistical analysis, using EUV emission from many active
regions, was done by Fludra and Ireland (2008) who studied power-law
relationships between active region integrated magnetic flux and
emission line intensities. A subsequent study by Fludra and Warren
(2010) for the first time compared fully resolved images in an EUV
spectral line of OV 63.0 nm with the photospheric magnetic field,
leading to the identification of a dominant, ubiquitous variable
component of the transition region EUV emission and a discovery
of a steady basal heating, and deriving the dependence of the basal
heating rate on the photospheric magnetic flux density. In this study,
we compare models of single coronal loops with EUV observations. We
assess to what degree observations of individual coronal loops made
in the EUV range are capable of providing constraints on the heating
mechanism. We model the coronal magnetic field in an active region using
an NLFF extrapolation code applied to a photospheric vector magnetogram
from SDO/HMI and select several loops that match an SDO/AIA 171 image of
the same active region. We then model the plasma in these loops using
a 1D hydrostatic code capable of applying an arbitrary heating rate as
a function of magnetic field strength along the loop. From the plasma
parameters derived from this model, we calculate the EUV emission along
the loop in AIA 171 and 335 bands, and in pure spectral lines of Fe
IX 17.1 nm and Fe XVI 33.5 nm. We use different spatial distributions
of the heating function: concentrated near the loop top, uniform and
concentrated near the footpoints, and investigate their effect on the
modelled EUV intensities. We find a diagnostics based on the dependence
of the total loop intensity on the shape of the heating function and
discuss its range of applicability for loops of different length.
Title: On Extreme-ultraviolet Helium Line Intensity Enhancement
Factors on the Sun
Authors: Giunta, A. S.; Fludra, A.; Lanzafame, A. C.; O'Mullane,
M. G.; Summers, H. P.; Curdt, W.
Bibcode: 2015ApJ...803...66G
Altcode:
Helium lines in the solar EUV spectrum provide useful diagnostics of
the solar atmosphere plasma. Helium is one of the few elements that
exhibits strong emission lines formed in the lower transition region,
and it is the second most abundant element in the Sun. However, the
analysis of helium lines is complicated by their optical thickness
and the unusual behavior of their intensities, with enhancements by a
factor of up to 15 reported in the literature. Detailed study requires
spatially and spectrally resolved observations in the EUV range, as
well as sophisticated atomic modeling. The present work focuses on
the application of the differential emission measure distribution to
reproduce the observed fluxes of the He i and He ii lines observed
by the Solar and Heliospheric Observatory (SOHO)/Coronal Diagnostic
Spectrometer and Hinode/EIS spectrometers, using the latest atomic
data. It is found that the comparison between observed and reconstructed
intensities for He i resonance lines λλ537.03, 522.21, and 515.62 and
the intercombination line λ591.41 does not show a real enhancement. By
contrast, He i λ584.33, the first line of the 1{{s}2}{{
}1}S-1s np{{ }1}P resonance series, shows a
depletion of a factor ∼2, due to the opacity effect, as supported
by non-LTE radiative transfer calculations. For single ionized helium
lines 303.78 and 256.32 Å, the enhancement factors obtained are higher
and agree with those of previous work. The different behavior of He
i and He ii lines suggests a mechanism that affects ionized helium only.
Title: Modulation of Galactic Cosmic Rays Observed at L1 in Solar
Cycle 23
Authors: Fludra, A.
Bibcode: 2015ApJ...799...31F
Altcode:
We analyze a unique 15 yr record of galactic cosmic-ray (GCR)
measurements made by the SOHO Coronal Diagnostic Spectrometer NIS
detectors, recording integrated GCR numbers with energies above 1.0
GeV between 1996 July and 2011 June. We are able to closely reproduce
the main features of the SOHO/CDS GCR record using the modulation
potential calculated from neutron monitor data by Usoskin et al. The
GCR numbers show a clear solar cycle modulation: they decrease by
50% from the 1997 minimum to the 2000 maximum of the solar cycle,
then return to the 1997 level in 2007 and continue to rise, in 2009
December reaching a level 25% higher than in 1997. This 25% increase is
in contrast with the behavior of Ulysses/KET GCR protons extrapolated
to 1 AU in the ecliptic plane, showing the same level in 2008-2009
as in 1997. The GCR numbers are inversely correlated with the tilt
angle of the heliospheric current sheet. In particular, the continued
increase of SOHO/CDS GCRs from 2007 until 2009 is correlated with the
decrease of the minimum tilt angle from 30° in mid-2008 to 5° in
late 2009. The GCR level then drops sharply from 2010 January, again
consistent with a rapid increase of the tilt angle to over 35°. This
shows that the extended 2008 solar minimum was different from the 1997
minimum in terms of the structure of the heliospheric current sheet.
Title: Sausage oscillations of coronal plasma slabs
Authors: Hornsey, C.; Nakariakov, V. M.; Fludra, A.
Bibcode: 2014A&A...567A..24H
Altcode:
Context. Sausage oscillations are observed in plasma non-uniformities
of the solar corona as axisymmetric perturbations of the
non-uniformity. Often, these non-uniformities can be modelled as
field-aligned slabs of the density enhancement.
Aims: We
perform parametric studies of sausage oscillations of plasma slabs,
aiming to determine the dependence of the oscillation period on
its parameters, and the onset of leaky and trapped regimes of the
oscillations.
Methods: Slabs with smooth transverse profiles
of the density of a zero-beta plasma are perturbed by an impulsive
localised perturbation of the sausage symmetry. In particular, the
slab can contain an infinitely thin current sheet in its centre. The
initial value problem is then solved numerically. The numerical
results are subject to spectral analysis. The results are compared
with analytical solutions for a slab with a step-function profile and
also with sausage oscillations of a plasma cylinder.
Results: We
established that sausage oscillations in slabs generally have the same
properties as in plasma cylinders. In the trapped regime, the sausage
oscillation period increases with the increase in the longitudinal
wavelength. In the leaky regime, the dependence of the period on the
wavelength experiences saturation, and the period becomes independent
of the wavelength in the long-wavelength limit. In the leaky regime
the period is always longer than in the trapped regime. The sausage
oscillation period in a slab is always longer than in a cylinder with
the same transverse profile. In slabs with steeper transverse profiles,
sausage oscillations have longer periods. The leaky regime occurs at
shorter wavelengths in slabs with smoother profiles.
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: Solar magnetism eXplorer (SolmeX). Exploring the magnetic
field in the upper atmosphere of our closest star
Authors: Peter, Hardi; Abbo, L.; Andretta, V.; Auchère, F.; Bemporad,
A.; Berrilli, F.; Bommier, V.; Braukhane, A.; Casini, R.; Curdt,
W.; Davila, J.; Dittus, H.; Fineschi, S.; Fludra, A.; Gandorfer, A.;
Griffin, D.; Inhester, B.; Lagg, A.; Landi Degl'Innocenti, E.; Maiwald,
V.; Sainz, R. Manso; Martínez Pillet, V; Matthews, S.; Moses, D.;
Parenti, S.; Pietarila, A.; Quantius, D.; Raouafi, N. -E.; Raymond, J.;
Rochus, P.; Romberg, O.; Schlotterer, M.; Schühle, U.; Solanki, S.;
Spadaro, D.; Teriaca, L.; Tomczyk, S.; Trujillo Bueno, J.; Vial, J. -C.
Bibcode: 2012ExA....33..271P
Altcode: 2011arXiv1108.5304P; 2011ExA...tmp..134P
The magnetic field plays a pivotal role in many fields of
Astrophysics. This is especially true for the physics of the solar
atmosphere. Measuring the magnetic field in the upper solar atmosphere
is crucial to understand the nature of the underlying physical
processes that drive the violent dynamics of the solar corona—that
can also affect life on Earth. SolmeX, a fully equipped solar space
observatory for remote-sensing observations, will provide the first
comprehensive measurements of the strength and direction of the
magnetic field in the upper solar atmosphere. The mission consists
of two spacecraft, one carrying the instruments, and another one in
formation flight at a distance of about 200 m carrying the occulter to
provide an artificial total solar eclipse. This will ensure high-quality
coronagraphic observations above the solar limb. SolmeX integrates two
spectro-polarimetric coronagraphs for off-limb observations, one in
the EUV and one in the IR, and three instruments for observations on
the disk. The latter comprises one imaging polarimeter in the EUV for
coronal studies, a spectro-polarimeter in the EUV to investigate the low
corona, and an imaging spectro-polarimeter in the UV for chromospheric
studies. SOHO and other existing missions have investigated the emission
of the upper atmosphere in detail (not considering polarization),
and as this will be the case also for missions planned for the near
future. Therefore it is timely that SolmeX provides the final piece of
the observational quest by measuring the magnetic field in the upper
atmosphere through polarimetric observations.
Title: Comparison between observed and theoretical O IV line ratios
in the UV/EUV solar spectrum as derived by SUMER, CDS and EIS
Authors: Giunta, A. S.; Fludra, A.; O'Mullane, M. G.; Summers, H. P.
Bibcode: 2012A&A...538A..88G
Altcode:
Aims: The joint use of SoHO Solar Ultraviolet Measurement of
Emitted Radiation (SUMER), Coronal Diagnostic Spectrometer (CDS)
and Hinode Extreme-ultraviolet Imaging Spectrometer (EIS) allow
observation of several O iv line ratios, useful for temperature plasma
diagnostics. Accurate atomic data are required to avoid interpretation
errors in deriving the electron temperature from these ratios. Muglach
et al. (2010) found that the measured ratio I(787.72 Å)/I(279.93 Å) is
lower than the predicted value by a factor 2-5. Here the predicted value
for this ratio is revised using updated atomic data. A comparison with
other observed O iv line ratios is shown and the electron temperature is
derived.
Methods: The analysis is based on new observations made
during the observational campaign of April 2009 and including three O iv
multiplets. The theoretical ratios have been derived using the Atomic
Data and Analysis Structure (ADAS) database and include comparison
with the most recent calculations available in the literature.
Results: The discrepancy for the O iv I(787.72 Å)/I(279.93 Å) ratio
has been solved by adding transitions involving higher excited levels,
which have been omitted in previous atomic models. This results in a
decrease of the theoretical line ratio, providing electron temperatures
in the range of log T = 5.17-5.39, close to the temperature expected
from a plasma in ionisation equilibrium.
Title: Heliospheric Modulation of Galactic Cosmic Rays Observed at
the L1 Lagrange Point in Solar Cycle 23
Authors: Fludra, A.
Bibcode: 2010AGUFMSH51B1670F
Altcode:
We analyze a unique 14-year record of Galactic Cosmic Ray measurements
made by the SOHO Coronal Diagnostic Spectrometer NIS detectors,
recording integrated GCR numbers with energies above 1.0 GeV between
July 1996 and June 2010. The GCR numbers decrease by 50 percent from the
1997 minimum to the 2000 maximum of the solar cycle, then increase back
to the 1997 level in 2007 and continue to rise, reaching in December
2009 a level 22% higher than in 1997. This 22% increase is in contrast
with the behaviour of Ulysses/KET GCR protons extrapolated to 1 AU
in the ecliptic plane, showing the same level in 2008-2010 as in 1997
(Heber et al. 2009). The increase of SOHO/CDS GCR numbers, continuing
until 2009, is correlated with the decrease of the tilt angle of the
heliospheric current sheet from 30 degrees in mid-2008 to 5 degrees
in late 2009. The GCR level then drops sharply from January 2010,
again consistent with a rapid increase of the tilt angle to over 35
degrees. We discuss the effect of the structure of the heliospheric
current sheet on cosmic ray transport. The CDS/NIS on SOHO currently
remains the only space instrument monitoring daily the GCR protons
with energies above 1.0 GeV. Unfortunately, CDS operations are to be
terminated in 2011.
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: Radiative and magnetic properties of solar active
regions. II. Spatially resolved analysis of O V 62.97 nm transition
region emission
Authors: Fludra, A.; Warren, H.
Bibcode: 2010A&A...523A..47F
Altcode:
Context. Global relationships between the photospheric magnetic flux
and the extreme ultraviolet emission integrated over active region
area have been studied in a previous paper by Fludra & Ireland
(2008, A&A, 483, 609). Spatially integrated EUV line intensities
are tightly correlated with the total unsigned magnetic flux, and
yet these global power laws have been shown to be insufficient for
accurately determining the coronal heating mechanism owing to the
mathematical ill-conditioning of the inverse problem.
Aims:
Our aim is to establish a relationship between the EUV line intensities
and the photospheric magnetic flux density on small spatial scales in
active regions and investigate whether it provides a way of identifying
the process that heats the coronal loops.
Methods: We compare
spatially resolved EUV transition region emission and the photospheric
magnetic flux density. This analysis is based on the O V 62.97 nm line
recorded by the SOHO Coronal Diagnostic Spectrometer (CDS) and SOHO MDI
magnetograms for six solar active regions. The magnetic flux density
ϕ is converted to a simulated O V intensity using a model relationship
I(ϕ, L) = Cϕδ Lλ, where the loop length L is
obtained from potential magnetic field extrapolations. This simulated
spatial distribution of O V intensities is convolved with the CDS
instrument's point spread function and compared pixel by pixel with the
observed O V line intensity. Parameters δ and λ are derived to give
the best fit for the observed and simulated intensities.
Results:
Spatially-resolved analysis of the transition region emission reveals
the complex nature of the heating processes in active regions. In some
active regions, particularly large, local intensity enhancements up to
a factor of five are present. When areas with O V intensities above
3000 erg cm-2 s-1 sr-1 are ignored,
a power law has been fitted to the relationship between the local O
V line intensity and the photospheric magnetic flux density in each
active region. The average power index δ from all regions is 0.4±0.1
and λ = -0.15±0.07. However, the scatter of intensities in all
regions is significantly greater than ±3σ from the fitted model. We
therefore determine for the first time an empirical lower boundary for
the IOV-ϕ relationship that is the same for five active
regions. We postulate that it represents a basal heating. Because this
boundary is present in the spatially-resolved data, this is compelling
proof that the magnetic field is one of the major factors contributing
to the basal component of the heating of the coronal plasma. We discuss
the implications for the diagnostics of the coronal heating mechanism.
Title: Radiative and magnetic properties of solar active
regions. I. Global magnetic field and EUV line intensities
Authors: Fludra, A.; Ireland, J.
Bibcode: 2008A&A...483..609F
Altcode:
Context: The relationships between the photospheric magnetic flux
and either the X-ray or extreme ultraviolet emission from the solar
atmosphere have been studied by several authors. Power-law relations
have been found between the total magnetic flux and X-ray flux or
intensities of the chromospheric, transition region, and coronal
emission lines in solar active regions. These relations were then
used to infer the mechanism of the coronal heating.
Aims: We
derive accurate power laws between EUV line intensities and the total
magnetic flux in solar active regions and discuss their applications. We
examine whether these global power laws are capable of providing
the diagnostics of the coronal heating mechanism.
Methods:
This analysis is based on EUV lines recorded by the Coronal Diagnostic
Spectrometer (CDS) on SOHO for 48 solar active regions, as they crossed
the central meridian in years 1996-1998. Four spectral lines are used:
He I 584.3 Å (3×104 K), O V 629.7 Å (2.2×105
K), Mg IX 368.06 Å (9.5×105 K), and Fe XVI 360.76 Å
(2.0×106 K). In particular, the Fe XVI 360.76 Å line, seen
only in areas of enhanced heating in active regions or bright points,
has not been used before for this analysis.
Results: Empirical
power laws are established between the total active region intensity
in the lines listed above and the total magnetic flux. We demonstrate
the usefulness of some spatially integrated EUV line intensities, I_T,
as a proxy for the total magnetic flux, Φ, in active regions. We point
out the approximate, empirical nature of the I_T-Φ relationships and
discuss the interpretation of the global power index. Different power
index values for transition region and coronal lines are explained
by their different dependence on pressure under the assumption of
hydrostatic loop models. However, the global power laws are dominated by
the size of the active regions, and we demonstrate for the first time
the difficulties in uniquely relating the power index in the global
IT - Φ relationship to the power index for individual loops
and comment on results obtained by other authors. We caution against
using global power laws to infer the coronal heating mechanism without a
detailed knowledge of the distributions of the magnetic flux densities
and instrumental response as a function of temperature. Despite these
uncertainties, we show that the intensities of the transition region
lines in individual loops depend on the photospheric magnetic flux
density, φ, through I_tr ∝ φδ_t, δt < 1,
and the coronal line Fe XVI, I_Fe ∝ φδ_c, δc
> 1, and under the assumption of hydrostatic loops we can place a
constraint on the coronal heating models, obtaining the volumetric
heating rate, EH (erg cm-3 s-1),
EH ∝ φ^γ , where 0.6 < γ < 1.1.
Title: SOHO Observations of Polar Coronal Jets over the Last Solar
Cycle
Authors: Dobrzycka, Danuta; Raymond, J.; DeLuca, E.; Guman, J.;
Fludra, A.; Biesecker, D.
Bibcode: 2006ESASP.617E..87D
Altcode: 2006soho...17E..87D
No abstract at ADS
Title: The widths of vacuum-ultraviolet spectral lines in the
equatorial solar corona observed with CDS and SUMER
Authors: Wilhelm, K.; Fludra, A.; Teriaca, L.; Harrison, R. A.;
Dwivedi, B. N.; Pike, C. D.
Bibcode: 2005A&A...435..733W
Altcode:
Observations of the solar equatorial corona between heights of 36 Mm and
184 Mm above the limb obtained by the SOHO spectrometers CDS and SUMER
in December 2003 are presented and discussed with special emphasis on
the widths of the spectral lines Mg x at 62.50 nm, Al xi at 55.00 nm
and 56.82 nm, Ca x at 55.78 nm, and Si xi at 58.09 nm. SUMER observed,
in addition, the lines Mg x 60.98 nm, Ca x 57.40 nm, Fe xii 124.20 nm,
Fe xvii 115.31 nm, and Ca xiii 113.37 nm. The Si xii 52.11 nm line
was only observed by CDS. A different behaviour of the line width
of Mg x 62.50 nm as a function of height above the limb had been
found in studies carried out independently with both instruments at
different times. It is the aim of this joint investigation to (a)
study instrumental effects on line-width results; and (b) provide a
thorough analysis of line profiles with altitude for the new campaign.
Title: Evidence for Coexisting Hot and Cool Polar Coronal Jets -
Coordinated Observations of SOHO and TRACE
Authors: Dobrzycka, D.; Raymond, J. C.; Deluca, E. E.; Gurman, J.;
Biesecker, D.; Fludra, A.
Bibcode: 2004AGUSMSH52A..05D
Altcode:
The polar coronal jets were first observed by SOHO instruments
(EIT, LASCO, UVCS) during the last solar minimum. They were small,
fast ejections originating from flaring UV bright points within large
polar coronal holes. The polar holes disappeared at solar maximum and
the jets were not visible anymore. Currently, however, as the Sun's
activity declines, the polar holes again became permanent structures
and new polar coronal jets were observed by specially designed SOHO
Joint Observing Program (JOP 155). Their frequency of several events per
day appear comparable to the frequency from last solar minimum. Also,
the speed of ∼ 400~km~s-1 at 1.6~R⊙ is consistent
with typical velocities of polar jets in 1996-1998. The ejections are
believed to be triggered by the field line reconnection between the
emerging magnetic dipole and pre-existing unipolar field. Existing
models predict that the hot jet is ejected together with another jet
made of cool material. The coordinated SOHO and TRACE observations
within JOP 155 provide unique opportunity to test this prediction. We
will present observations and discuss evidence supporting the model.
Title: Short-Duration Active Region Brightenings Observed in the
Extreme Ultraviolet and Hα by the Solar and Heliospheric Observatory
Coronal Diagnostic Spectrometer and Hida Domeless Solar Telescope
Authors: Brooks, D. H.; Kurokawa, H.; Kamio, S.; Fludra, A.; Ishii,
T. T.; Kitai, R.; Kozu, H.; Ueno, S.; Yoshimura, K.
Bibcode: 2004ApJ...602.1051B
Altcode:
We present the first detection of an Hα counterpart to the EUV
blinker. The observations come from a coordinated campaign between
the Hida Observatory Domeless Solar Telescope (DST) and the Solar
and Heliospheric Observatory Coronal Diagnostic Spectrometer (CDS)
conducted in 2002 July and August. Utilizing studies designed for
high-cadence observations, many short-duration brightenings (<3
minutes) were identified in the He I λ584.334 and O V λ629.732
spectral lines in CDS data of active region NOAA 10039/10044. These
brightenings show similar characteristics (increases in intensity,
size) to longer duration EUV blinkers previously reported in active
regions and the quiet Sun. Focusing on two events that show pronounced
emission in the upper chromosphere (He I), we have been able to identify
cospatial bright points in the lower chromosphere (Hα center, +/-0.5
Å) that show enhanced emission during the EUV blinker. These bright
features have lifetimes similar to those of their EUV counterparts,
and their peak intensities occur nearly simultaneously with the peak
blinker intensities in the He I and O V lines. In both cases the He
I and O V lines show excess line broadening at the peak of the event
(>15 km s-1). Our high-cadence observations also enabled
us to examine the dimensions and lifetimes of short-duration active
region blinkers in detail. We find that the instrumental spatial and
temporal resolution can combine to distort their characteristics:
even short-duration blinkers appear to be composed of elementary
brightening events. The optical brightenings also appear to closely
follow the behavior of the elementary brightenings. The spatial and
temporal relationships between the brightenings indicate a causal link
between the EUV and Hα blinkers.
Title: Short Duration Active Region Brightenings Observed in the
EUV and Ha by SOHO/CDS and HIDA/DST
Authors: Brooks, D. H.; Kurokawa, H.; Kamio, S.; Fludra, A.; Ishii,
T. T.; Kitai, R.; Kosu, H.; Ueno, S.; Yoshimura, K.
Bibcode: 2004ESASP.547..273B
Altcode: 2004soho...13..273B
We present the 1st detection of an H counterpart to the EUV blinker,
using observations from a coordinated campaign between the SOHO Coronal
Diagnostic Spectrometer and the Kyoto University Hida Observatory,
Domeless Solar Telescope (DST). The observations were performed during
July and August 2002. By designing the CDS observing sequences for
high cadence and long duration observations, we were able to identify
many short duration (<3 mins.) brightenings simultaneously in the
He I 584.334A and O V 629.732A spectral lines. These brightenings
show similar characteristics (intensity increases, sizes) to longer
duration EUV blinkers previously reported in active regions and the
'quiet' Sun. Focusing on two events which show pronounced emission
in the upper chromosphere (He I), we have been able to identify
cospatial bright points in the lower chromosphere (H line centre,
60.5A) which show enhanced emission during the EUV blinkers. These
bright features have similar lifetimes to their EUV counterparts and
their peak intensities occur close to simultaneously with the peak
blinker intensities in the He I and O V lines. In both cases the He
I and O V lines show excess line broadening at the peak of the event
(>15 km s01) and in one event evidence of downward (red-shifted)
motion is observed. A statistical study is being performed to provide
a complete picture of the line width and velocity characteristics of
these events and to determine whether the H counterparts are common, or
confined to specific blinkers with pronounced He I emission. The high
cadence of our observations also allowed us to examine the eects of
spatial and temporal averaging on the determination of the properties
of blinkers. We find that both short and long duration blinkers are
composed of elementary brightening events and that such events can
be undetectable in observations with low temporal cadence. Finally,
the H brightenings appear to correlate well with the elementary EUV
brightening events.
Title: Spatially-Resolved Diagnostics of Coronal Heating in Solar
Active Regions
Authors: Fludra, A.; Ireland, J.
Bibcode: 2004ESASP.547..341F
Altcode: 2004soho...13..341F
We study the relationship between EUV spectral line intensities and the
photospheric magnetic field in solar active regions, using magnetograms
from SOHO-MDI and EUV spectra of the Fe XVI 360.8 Å line ( K) and the O
V 629.7 A line (220,000 K) from the Coronal Diagnostic Spectrometer on
SOHO, recorded for several active regions. Two complementary analysis
methods are compared - a global analysis applied to the coronal line
emission (Fe XVI), and a spatially-resolved analysis of the transition
region emission (O V). We overlay and compare spatial patterns of
the O V emission and the magnetic flux concentrations, with a spatial
resolution, and search for a relationship between the local O V line
intensity and the photospheric magnetic flux density in each active
region. While this dependence exhibits a certain amount of scatter,
it can be represented by a power law fit. The average power index from
all regions is . Applying static loop models, we derive the dependence
of the volumetric heating rate on the magnetic flux density, , and
compare it to the dependence predicted by the coronal heating models.
Title: Diagnostics of Coronal Heating in Solar Active Regions
Authors: Fludra, A.; Ireland, J.
Bibcode: 2004IAUS..219..478F
Altcode: 2003IAUS..219E.244F
We study the relationship between EUV spectral line intensities emitted
at transition region temperatures and the photospheric magnetic
field in solar active regions. We use magnetograms from SOHO/MDI
and EUV spectra of the O V 629.7 A line (220000 K) from the Coronal
Diagnostic Spectrometer on SOHO recorded for 25 active regions. We
overlay and compare spatial patterns of the OV emission and the
magnetic flux concentrations with a 2''x2'' spatial resolution and
search for a relationship between the local OV line intensity and the
photospheric magnetic flux density in each active region. While this
dependence exhibits a certain amount of scatter it can be represented
by a power law fit. We find that the power indeces are similar in
all regions. Applying static loop models we derive the dependence of
the heating rate on the magnetic flux density and compare it to the
dependence predicted by the coronal heating models. This spatially
resolved analysis extends the previous work of Fludra and Ireland
(2002 2003) who studied the relationship between area-integrated
coronal line intensities and the total magnetic flux.
Title: Variability of the solar EUV emission in cycle 23
Authors: Fludra, A.
Bibcode: 2004cosp...35.2954F
Altcode: 2004cosp.meet.2954F
We study the response of the solar atmosphere to the solar activity
cycle, using EUV spectra from the Coronal Diagnostic Spectrometer
(CDS) on SOHO. CDS has been monitoring time variability of EUV line
intensities since April 1996. The eight-year data set includes daily
synoptic observations recorded along the central meridian, in five EUV
lines: He I 584.3 Å , O V 629.7 Å , Mg IX 368 Å , Mg X 625 Å , and
Fe XVI 360.8 Å . These lines represent emission from the transition
region and corona. We present long-term variability of line intensities
along the central meridian and compare its quiet sun component to the
variability of the photospheric magnetic flux. Variation of intensities
and the coronal temperature with latitude is also discussed. We seek
for EUV signatures of the magnetic polarity reversal by comparing
intensities summed over several latitude bands and the magnetic flux
in these bands.
Title: Origins of the Solar Polar Jets - Coordinated SOHO and TRACE
Observations
Authors: Dobrzycka, D.; Raymond, J. C.; Deluca, E. E.; Gurman, J. B.;
Biesecker, D.; Fludra, A.
Bibcode: 2003AGUFMSH22A0187D
Altcode:
The polar jets are dynamic coronal eruptions originating in the low
solar atmosphere, in flaring UV bright points within polar coronal
holes. They were first observed by SOHO instruments (EIT, LASCO)
during last solar minimum in 1996 when the polar holes were dominating
coronal structures. UVCS/SOHO obtained ultraviolet spectroscopy of
the jet providing us with estimates of the jet plasma conditions,
evolution of the electron temperature and heating rate required to
reproduce the observed ionization state. As the Sun is currently at
the declining phase of its activity, the polar holes again became
permanent structures. The SOHO Joint Observing Program (JOP 155)
was designed to identify and study the jet phenomena that would be
counterparts of the solar minimum polar jets. The jets are believed
to be triggered by field line reconnection between emerging magnetic
dipole and pre-existing unipolar field. Existing models predict that the
hot jet is ejected together with another jet of a cool material. The
particular goal of the coordinated SOHO and TRACE observations was to
look for possible association of the hot and cool plasma ejections. We
present first results of the campaign and discuss their implications.
Title: The Magnetic Field and EUV Line Intensities in Solar Active
Regions
Authors: Fludra, A.; Ireland, J.
Bibcode: 2003csss...12..220F
Altcode:
Relationships between the photospheric magnetic flux and intensities of
spectral lines emitted from the solar atmosphere have been extensively
studied by several authors. Power-law relations have been found between
the total magnetic flux and total intensities of the chromospheric,
transition region and coronal emission lines in active regions. This
approach is applied to extreme ultraviolet lines recorded by the
Coronal Diagnostic Spectrometer (CDS) on SOHO for 50 solar active
regions, as they crossed the central meridian in years 1996-1998. Four
spectral lines are examined: ion{He}{1} 584.3 Å (2× 104 K),
ion{O}{5} 629.7 Å (2.2 × 105 K), ion{Mg}{9} 368.06 Å (9.5
× 105 K), and ion{Fe}{16} 360.76 Å (2.0 × 106
K). In particular, the ion{Fe}{16} 360.76 Å line, seen only in areas
of enhanced heating in active regions or bright points, has not been
used before for this analysis. Empirical relations are established
between the total active region intensity in ion{Fe}{16} and ion{O}{5}
lines, and the total magnetic flux and between the spatially-averaged
intensities and the magnetic flux density. The dependence of the
coronal loop heating rate on the magnetic flux density is derived and
its implications for the coronal heating models are discussed.
Title: Dynamical and Physical Properties of a Post-Coronal Mass
Ejection Current Sheet
Authors: Ko, Yuan-Kuen; Raymond, John C.; Lin, Jun; Lawrence, Gareth;
Li, Jing; Fludra, Andrzej
Bibcode: 2003ApJ...594.1068K
Altcode:
In the eruptive process of the Kopp-Pneuman type, the closed magnetic
field is stretched by the eruption so much that it is usually believed
to be ``open'' to infinity. Formation of the current sheet in such a
configuration makes it possible for the energy in the coronal magnetic
field to quickly convert into thermal and kinetic energies and cause
significant observational consequences, such as growing postflare/CME
loop system in the corona, separating bright flare ribbons in the
chromosphere, and fast ejections of the plasma and the magnetic flux. An
eruption on 2002 January 8 provides us a good opportunity to look into
these observational signatures of and place constraints on the theories
of eruptions. The event started with the expansion of a magnetic
arcade over an active region, developed into a coronal mass ejection
(CME), and left some thin streamer-like structures with successively
growing loop systems beneath them. The plasma outflow and the highly
ionized states of the plasma inside these streamer-like structures,
as well as the growing loops beneath them, lead us to conclude that
these structures are associated with a magnetic reconnection site,
namely, the current sheet, of this eruptive process. We combine the
data from the Ultraviolet Coronagraph Spectrometer, Large Angle and
Spectrometric Coronagraph Experiment, EUV Imaging Telescope, and Coronal
Diagnostic Spectrometer on board the Solar and Heliospheric Observatory,
as well as from the Mauna Loa Solar Observatory Mark IV K-coronameter,
to investigate the morphological and dynamical properties of this event,
as well as the physical properties of the current sheet. The velocity
and acceleration of the CME reached up to 1800 km s-1 and
1 km s-2, respectively. The acceleration is found to occur
mainly at the lower corona (<2.76 Rsolar). The post-CME
loop systems showed behaviors of both postflare loops (upward motion
with decreasing speed) and soft X-ray giant arches (upward motion
with constant speed, or acceleration) according to the definition of
Švestka. In the current sheet, the presence of highly ionized ions,
such as Fe+17 and Ca+13, suggests temperature as
high as (3-4)×106 K, and the plasma outflows have speeds
ranging from 300 to 650 km s-1. Absolute elemental abundances
in the current sheet show a strong first ionization potential effect and
have values similar to those found in the active region streamers. The
magnetic field strength in the vicinity of the current sheet is found
to be of the order of 1 G.
Title: Development of Multidimensional MHD Model for the Solar Corona
and Solar Wind
Authors: Sittler, E. C.; Ofman, L.; Gibson, S.; Guhathakurta, M.;
Davila, J.; Skoug, R.; Fludra, A.; Holzer, T.
Bibcode: 2003AIPC..679..113S
Altcode:
We are developing a time stationary self-consistent 2D MHD model of
the solar corona and solar wind that explicitly solves the energy
equation, using a semi-empirical 2D MHD model of the corona to provide
an empirically determined effective heat flux qeff (i.e., the term
effective means the possible presence of wave contributions). But,
as our preliminary results indicate, in order to achieve high
speed winds over the poles we also need to include the empirically
determined effective pressure Peff as a constraint in the momentum
equation, which means that momentum addition by waves above 2 RS are
required to produce high speed winds. At present our calculations do
not include the Peff constraint. The estimates of Peff and qeff come
from the semi-empirical 2D MHD model of the solar corona by Sittler
and Guhathakurta (1999a,2002) which is based on Mk-III, Skylab and
Ulysses observations. For future model development we plan to use SOHO
LASCO, CDS, EIT, UVCS and Ulysses data as constraints for our model
calculations. The model by Sittler and Guhathakurta (1999a, 2002) is
not a self-consistent calculation. The calculations presented here is
the first attempt at providing a self-consistent calculation based on
empirical constraints.
Title: Dynamical and Physical Properties of a Post-CME Current Sheet
Authors: Ko, Y. -K.; Raymond, J. C.; Lin, J.; Lawrence, G.; Li, J.;
Fludra, A.
Bibcode: 2003SPD....34.0510K
Altcode: 2003BAAS...35..815K
In the eruptive process of the Kopp-Pneuman type, the closed magnetic
field is stretched by the eruption so much that it is usually believed
to be ``open'' to infinity. Formation of the current sheet in such a
configuration makes it possible for the energy in the coronal magnetic
field to quickly convert into thermal and kinetic energies, and cause
significant observational consequences. A CME eruption on January 8,
2002 provides us a good opportunity to look into these observational
signatures of and place constraints on the theories of eruptions. This
event started with the expansion of a magnetic arcade, developed into
a CME, and left some thin streamer-like structures with successively
growing loop systems beneath them. The plasma outflow and the highly
ionized states of the plasma inside these streamer-like structures, as
well as the growing loops beneath them lead us to conclude that these
structures are associated with a magnetic reconnection site, namely the
current sheet, of this eruptive process. We combine the data from UVCS,
LASCO, EIT, and CDS on board SOHO, as well as data from MLSO MK4, to
investigate the morphological and dynamical properties of this event, as
well as the physical properties of the current sheet. The velocity and
acceleration of the CME reached up to 1800 km s-1 and 1 km
s-2, respectively. The acceleration are found to mainly occur
at the lower corona. The post-CME loop systems showed both behaviors
of post-flare loops and soft X-ray giant arches. In the current sheet,
UVCS spectra suggest temperature as high as 3-4 million degrees, and the
plasma outflows have speeds ranging from 300 km/s to 650 km/s. Absolute
elemental abundances in the current sheet show a strong FIP effect,
and have values similar to those found in the active region streamers.
Title: Inversion of the intensity-magnetic field relationship in
solar active regions
Authors: Fludra, A.; Ireland, J.
Bibcode: 2003A&A...398..297F
Altcode:
We discuss the relationship between the EUV spectral line intensities
and the photospheric magnetic flux in solar active regions. Since the
histograms of the magnetic flux density in active region plages can
be approximated by an exponential function, the equation describing
how the observed total line intensity integrated over an active region
area arises from the magnetic field, can be approximated by a Laplace
integral. We use this property to solve an inverse problem and derive
a function relating the line intensity from individual loops to the
photospheric magnetic flux density at their footpoints. We propose a
simple model in which the intensity of a coronal line Fe XVI 360.8 Å
in an individual coronal loop is proportional to the footpoint magnetic
flux density to the power of delta and explore how well the value of
delta is constrained by the observations. Using EUV spectra from the
Coronal Diagnostic Spectrometer (CDS) on SOHO and magnetograms from
SOHO Michelson Doppler Imager for 26 active regions without sunspots,
we find that the value of delta depends on the magnetic flux density
threshold used to define active region magnetic area. When even the
weakest fields are included, we obtain delta =1.3, where 1.0 <
delta < 1.6 with 90% confidence. This result can be used to provide
constraints on coronal heating models.
Title: Empirically Constrained Multidimensional MHD Model for the
Solar Corona and Solar Wind
Authors: Sittler, E. C.; Ofman, L.; Gibson, S.; Guthathakurta, M.;
Skoug, R.; Fludra, A.; Davila, J.; Holzer, T.
Bibcode: 2002AGUFMSH21A0502S
Altcode:
We are developing a time stationary self-consistent 2D MHD model of
the solar corona and solar wind that explicitly solves the energy
equation, using a semi-empirical 2D MHD model of the corona to provide
an empirically determined effective heat flux qeff (i.e.,
the term effective means the possible presence of wave contributions)
for the energy equation and effective pressure Peff
for the momentum equation. Preliminary results indicated that in
order to achieve high speed winds over the poles we not only needed
to use qeff in the energy equation, but also needed to
include the empirically determined effective pressure Peff
as a constraint in the momentum equation, which means that momentum
addition by waves above 2 RS are required to produce high
speed winds. A solution which only included qeff showed high
acceleration over the poles below 2 RS, but then drooped
above that radial distance indicating we needed momentum addition above
that height to get high speed flows over the poles. We will show new
results which include the added constraint of Peff in the
momentum equation. This method will allows us to estimate the momentum
addition term due to waves as a function of height and latitude within
the corona. The estimates of Peff and qeff come
from the semi-empirical 2D MHD model of the solar corona by Sittler and
Guhathakurta (1999, 2002) which is based on Mk-III, Skylab and Ulysses
observations. For future model development we plan to use SOHO LASCO,
CDS, EIT, UVCS, Spartan 201-05 and Ulysses data as constraints for
our model calculations. The model by Sittler and Guhathakurta (1999,
2002) is not a self-consistent calculation. The calculations presented
here are a continuing effort to provide a self-consistent calculation
based on empirical constraints.
Title: Temperature and Abundance Variations of an Active Region in
Three Solar Rotations
Authors: Ko, Y.; Fludra, A.; Raymond, J. C.
Bibcode: 2002AGUFMSH52A0472K
Altcode:
Active region 9718 (AR 9718) appeared at the east limb on November
26, 2001 which was newly formed when it was at the backside of the
Sun. It survives through three solar rotations -- AR 9755 and AR 9798
for subsequent rotations. AR 9798 decayed to no visible sunspot before
it reached the west limb. SOHO/UVCS observed this region four times,
as part of SOHO JOP 151, when it was at the limbs (AR 9718 at the
west limb, AR 9755 at both the east and west limbs, and AR 9798 at
the west limb). SOHO/CDS made observations when AR 9718 and AR 9755
were at the west limb. We investigate the temperature and abundance
variations of this active region during its lifetime, and look for
possible correlations between these physical parameters and its
magnetic characteristics.
Title: The magnetic fields and the heating of active regions
Authors: Fludra, A.; Ireland, J.
Bibcode: 2002ESASP.505..405F
Altcode: 2002IAUCo.188..405F; 2002solm.conf..405F
Fludra and Ireland (2002) established empirical power-laws between
the EUV line intensity averaged over the active region area and
the magnetic flux density, using SOHO/MDI magnetograms and two EUV
spectral lines, O V 629.7 Å (2.2×105K) and Fe XVI 360.76
Å (2.0×106K), recorded by the SOHO Coronal Diagnostic
Spectrometer for 45 active regions. These relationships were used to
derive the heating rate as a function of the magnetic flux density. In
this paper we examine a subset of 26 active regions without sunspots, to
investigate the change in these relationships in the absence of strong
sunspot magnetic fields. We find a reduced power index in the power-law
dependence between the average line intensities and the magnetic flux
density. This translates as a reduced power index in the dependence
of the heating rate on the magnetic flux density, EH ∝
B0.9, and affirms that most of the DC models of coronal
heating, predicting an EH ∝ B2 dependence,
are incompatible with our observations.
Title: Coronal heating in active regions
Authors: Fludra, A.; Ireland, J.
Bibcode: 2002ESASP.508..267F
Altcode: 2002soho...11..267F
Many theoretical models of coronal heating predict a different
dependence of the heating rate on the magnetic field strength. This
property can be used to test these models by studying relationships
between the photospheric magnetic flux and intensities of spectral
lines emitted from the solar atmosphere. We use SOHO/MDI magnetograms
and Extreme Ultraviolet lines recorded by the SOHO Coronal Diagnostic
Spectrometer for 50 solar active regions, as they crossed the central
meridian in years 1996-1998. We use two spectral lines: O V 629.7 Å
(2.2×105K) and Fe XVI 360.76 Å (2.0×106K). We
establish empirical power-laws between the total line intensity
integrated over the active region area and the total magnetic flux,
and derive the dependence of line intensities on the magnetic flux
density for an average individual coronal loop. The heating rate is
then derived as a function of the magnetic flux density and a comparison
is made with the coronal heating models.
Title: Physical and Dynamical Properties of a Post-CME Current Sheet
Authors: Ko, Y.; Raymond, J. C.; Lin, J.; Lawrence, G.; Li, J.;
Fludra, A.
Bibcode: 2002AGUSMSH21B..07K
Altcode:
On January 8, 2002 following a CME at the east limb, thin threads of
materials are formed, as seen in the white light corona, with continuous
outflow that lasted more than two days as it gradually moved toward the
north. We interprete it as a current sheet left behind the CME. UV/EUV
spectra were taken on January 10 by SOHO/UVCS and SOHO/CDS as part
of the SOHO JOP 151. The UV spectra at 1.6 Ro show a small region
(< 70 arcsec) of depleted low temperature emission and a high
temperature region where lines from highly ionized ions such as Fe+17
and Ca+13 are observed. We combine the data from UVCS, LASCO, EIT and
CDS on SOHO to derive the physical properties (electron temperature,
electron density and elemental abundances) and dynamical properties
(outflow speed and acceleration) of these regions which is likely to
be associated with this current sheet. Implications on its formation
and magnetic properties are discussed.
Title: The solar corona in cycle 23
Authors: Fludra, A.; Ireland, J.; Del Zanna, G.; Thompson, W. T.
Bibcode: 2002AdSpR..29..361F
Altcode:
The Coronal Diagnostic Spectrometer (CDS) on SOHO has been recording
EUV spectra and monitoring time variability of EUV line intensities,
electron temperature and density in the low solar corona during the
rising part of Cycle 23. The four-year data set includes daily synoptic
observations in four EUV lines along the central meridian since April
1996 and weekly diagnostic observations above the polar coronal holes
since July 1997. The history of line intensities along the central
meridian, and radial profiles of electron temperature and density above
the polar regions at heights up to 1.15 R⊙ are derived. EUV
line intensities and photospheric magnetic flux are also calculated
for 50 active regions observed from 1996 to June 1998. Variability of
temperature, density, and EUV spectral line intensities in the polar
coronal holes, quiet sun and active regions with the solar cycle is
discussed. Power-law relationships among the EUV line intensities from
the CDS synoptic data, and also between the EUV line intensities and
magnetic field flux in active regions are presented.
Title: Active Region EUV Intensities, Magnetic Flux and Coronal
Heating
Authors: Ireland, J.; Fludra, A.
Bibcode: 2001AGUFMSH11A0692I
Altcode:
Several authors have previously noted the existence of power law
relationships between the total unsigned photospheric magnetic
flux and the intensities of a variety of spectral lines emitted by
active regions. Applying this approach to more recent datasets, it
is shown that power law relationships exist for extreme ultraviolet
(EUV) emission data observed by the Coronal Diagnostic Spectrometer
(CDS) and photospheric flux as measured by the Michelson Doppler
Imager (MDI), both on-board the Solar and Heliospheric Observatory
(SOHO). Four spectral lines are examined, covering a wide range of
temperatures: He I 584.3 Å (2x 104~K), O V 629.7 Å (2.2
x 105~K), Mg IX 368.06 Å (9.5 x 105~K), and
Fe XVI 360.76 Å (2.0 x 106~K). Relations are established
between total EUV intensities and photospheric magnetic flux as well
as average EUV intensity and magnetic flux density. Comments are also
made on the viability of various coronal heating models in the light
of these results.
Title: Transition region oscillations above sunspots
Authors: Fludra, A.
Bibcode: 2001A&A...368..639F
Altcode:
We present observations of three sunspots made in the EUV wavelength
range with the Coronal Diagnostic Spectrometer (CDS) on SOHO. We
examine time series of line intensities obtained with a 15-s cadence and
calculate their Fourier power spectra and the wavelet transforms. We
find oscillations in the chromosphere and transition region above
sunspots in the temperature range 2 104-4 105
K. Most of the spectral power is contained in the 5-8 mHz frequency
range, and the dominant frequency is 5.9 mHz (170 s period). We find
a relationship between the oscillations and sunspot plumes which are
compact features located above sunspots and bright in the transition
region lines emitted between 1.7 105 and 4 105
K. When the CDS slit crosses a sunspot plume, the bright O IV
554.5 Å and O V 629.7 Å lines show clear 3 min oscillations. An
extreme alternative interpretation that excludes the presence of
oscillations in sunspot plumes carries the requirement that the
adjacent low-intensity plasma oscillate with high relative amplitudes
greater than 50 percent. We also observe oscillations in a fainter
area above a sunspot, outside the sunspot plume. The oscillations seen
at different temperatures are compared. Using the wavelet transform,
we find variability of the oscillation period in the range 120-200 s.
Title: What are the bright loop-top kernels in soft X-ray flares?
Authors: Phillips, K. J. H.; Jakimiec, J.; Tomczak, M.; Falewicz,
R.; Fludra, A.
Bibcode: 2001AdSpR..26.1773P
Altcode:
A major puzzle in the study of solar X-ray flares is the presence of
a bright, persistent 'kernel' at or near the tops of flaring loops in
soft X-ray images from Yohkoh. Here we argue that they can be explained
by a tangled magnetic field geometry with unresolved current sheets
continually being formed. Hot (20 MK) plasma is formed near the current
sheets and is surrounded by plasma which has cooled to ∼ 10 MK plasma
so that the two temperatures appear to co-exist.
Title: EUV Line Intensities and the Magnetic Field in Solar Active
Regions
Authors: Ireland, J.; Fludra, A.
Bibcode: 2001IAUS..203..276I
Altcode:
The Coronal Diagnostic Spectrometer on SOHO carries out daily synoptic
observations of the Sun, recording four EUV spectra : He I 584 Å, O
V 630 Å, Mg IX 368 Å and Fe XVI 360 Å, over a 4 arcmin-wide strip
along the solar central meridian. A study has been made of 55 active
regions and bright points appearing in the CDS synoptic dataset in years
1996-1998. Using the CDS dataset and the MDI full disk magnetograms
we study the correlation of the chromospheric, transition region and
coronal emission with the photospheric magnetic field for meridional
active regions, probing the relation between the radiative output and
magnetic observables. We establish empirical, quantitative relations
among intensities of different lines, and between intensities and the
magnetic field flux. This work extends the study of Schrijver (1985,
1987) to a larger sample of active regions and different EUV lines. We
discuss the implications of this study for coronal heating models.
Title: An Observational Test for Solar Atmospheric Heating
Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Ireland, J.; Thompson,
B.; Fludra, A.; Oláh, K.; Kövári, Zs.; Harra, L. K.; Mandrini,
C. H.; Bocchialini, K.; Orlando, S.
Bibcode: 2001IAUS..203..514V
Altcode:
We study the evolution of the emissivity and heating correlated with
magnetic observables of an active region from its birth throughout
its decay during seven solar rotations (July-Dec. 1996). Taking one
"snapshot" per g:wq: Command not found. time of flares, we analyse
multi-wavelength and multi-instrument data obtained from SOHO (MDI,
EIT, CDS and SUMER), Yohkoh (SXT), GOES, SOLSTICE and 10.7 cm radio
data from DRAO, Canada. We utilise our results to test the validity
of coronal heating models. We find that models which are based on
the dissipation of stressed, current-carrying magnetic fields are in
better agreement with the observations than the models which attribute
coronal heating to the dissipation of MHD waves.
Title: A study of opacity in SOHO-SUMER and SOHO-CDS spectral
observations. I. Opacity deduction at the limb
Authors: Brooks, D. H.; Fischbacher, G. A.; Fludra, A.; Harrison,
R. A.; Innes, D. E.; Landi, E.; Landini, M.; Lang, J.; Lanzafame,
A. C.; Loch, S. D.; McWhirter, R. W. P.; Summers, H. P.
Bibcode: 2000A&A...357..697B
Altcode:
A study is presented of the optical thickness of spectral lines of
carbon, nitrogen and oxygen ions in the quiet sun. The observations
consist of cross limb scans by the SUMER and CDS spectrometers on
the SOHO spacecraft. A maximum likelihood spectral line fitting code
has been adapted to analyse the multiplet profiles and to provide an
assessment of errors in the count rates, especially of close lying
components. Branching multiplet component ratios are presented as a
function of position across the limb and contrasted with theoretical
ratios in the optically thin case. The emergent fluxes are analysed
in an escape probability model to deduce the optical thicknesses in
the various spectral lines. Different specifications of the escape
probability are examined. These are used to compare the observations
with a geometric model of the emitting layer thickness across the limb
and the thinning of the emitting layer above the limb. Classification
of the deviations of quiet sun spectral line intensities from the
optically thin case is given to assist in the critical selection of
lines for differential emission measure analysis. This is linked to
a general purpose code for the calculation of the influence of the
line radiation fields on the local excited state population structure
of the selected ions so that the fluxes in any spectral lines can be
predicted. The Atomic Data and Analysis Structure (ADAS) was used for
the atomic calculations and data of the paper.
Title: Coordinated UVCS, CDS, TRACE Observations of a High Latitude
Streamer
Authors: Dobrzycka, D.; Fludra, A.; Strachan, L.; Uzzo, M.
Bibcode: 2000EOSTr..81..353D
Altcode:
We obtained coordinated UVCS/SOHO, CDS/SOHO and TRACE observations
of a high latitude NE streamer during the first week of the Whole Sun
Month III campaign (18-24 August 1999). The data cover the streamer,
the streamer boundary and adjacent region at heights from 1 to 3.5
Rs. The streamer remained stable for five days but showed gradual shift
towards lower latitudes. It originated above an active region with
prominent magnetic loop structures recorded by TRACE. The active region
was originally seen from behind the NE limb and then rotated onto the
disk. We present our analysis of the UVCS/SOHO observations. We describe
the distribution of the HI Lyman alpha, OVI(1032,1037 A) and MgX (625
A) emission as a function of both latitude and radius, and discuss the
complex structure of the streamer. We apply our diagnostic techniques to
characterize plasma properties like velocities along the line of sight
or kinetic temperatures in the streamer and the adjacent region. Our
results are further compared with CDS observations at the base of the
streamer. This work was supported by NASA under Grant NAG5-3192 to the
Smithsonian Astrophysical Observatory, by the Italian Space Agency,
and by Swiss Funding Agencies.
Title: The Third Whole Sun Month Campaign - Coronal Synoptic Maps
Authors: Biesecker, D. A.; Gibson, S. E.; Alexander, D.; Fludra, A.;
Hoeksema, J. T.; Panasyuk, A. V.; Thompson, B. J.
Bibcode: 2000SPD....31.0239B
Altcode: 2000BAAS...32..817B
Observations for the Third Whole Sun Month Campaign were made throughout
Carrington Rotation 1953 (August 18-September 14, 1999). As in the
first campaign; the primary focus is on understanding the large scale
solar corona and the connections to interplanetary space over a full
solar rotation. The fundamental notion of these campaigns is that the
observations are available for anyone to work with. In this poster,
we use synoptic maps to show the morphology of the solar corona during
CR1953 at a variety of wavelengths, heights, and temperatures. Data
are shown from YOHKOH SXT, MLSO Mk4, and SOHO MDI, CDS, UVCS, EIT,
and LASCO. The current campaign differs from the first campaign in that
near solar maximum conditions prevailed. We held one workshop in order
to get organized and begin collaborations. The planned studies will
include determining the plasma parameters in various coronal structures
and in modeling the structure of the coronal magnetic fields. In
addition, we had the opportunity to study how a "sigmoidal" active
region evolved as it crossed the solar disk and affected the global
corona through a series of flares and eruptive events, and to obtain
detailed observations of its structure over a wide range of heights
and temperatures. We will be holding future workshops to analyze the
data and work on models. We invite you to participate in this campaign
or at least see our current plans for data analysis and modeling.
Title: Decaying post-flare loops system observed by SOHO/CDS and
Yohkoh/SXT
Authors: Varady, M.; Fludra, A.; Heinzel, P.
Bibcode: 2000A&A...355..769V
Altcode:
The results of an analysis of joint SOHO/CDS and Yohkoh/SXT observations
of a decaying post-flare loops system with a rapid time evolution are
presented. The loop system was a remnant of a small single loop flare
(GOES class C2.9). Using the CDS raster taken in several EUV lines with
different formation temperatures and a temperature sensitive line pair
Fe XVI 360.8/Si XII 520.7 we confirmed the existence of the vertical
stratification in the loop system according to the line formation
temperature. The analysis of the SXT data showed a strong decay of the
system with time. While the temperature of the hot part of the system
(T =~ 2.5 MK) decreased only slightly, the total emission measure
dropped by more than a factor of four in approximately 103
s. This could be explained by a plasma outflow from the loops with
velocity approximately 10 km/s. On the other hand, signs of rapid,
probably radiative cooling can be identified in the images obtained
from the CDS raster taken in cool lines of O V and O III. Using the
density sensitive line pair of Fe XIV 334.2/353.8 and the integrated
intensity of Fe XIV 334.2 line we determined the electron densities
and emission measures across the top of the loop system. From the
results of these measurements, taking all known uncertainties into
account, we obtained that the geometrical filling factor at the top of
the system in the regions with maximum electron density in the Fe XIV
line lies in the interval from =~ 0.01 to =~ 0.2. A simple theoretical
approximation of the energy balance in the post-flare plasma gives a
total cooling time =~ 750 s.
Title: Large-Scale Evolution of the Active Region NOAA 7978, 7981,
7986 Observed by Goes, Soho, and Yohkoh
Authors: Orlando, S.; Khan, J.; van Driel-Gesztelyi, L.; Thompson,
B.; Fludra, A.; Foing, B.
Bibcode: 2000AdSpR..25.1913O
Altcode:
We took part in a joint project aimed to study the large-scale
evolution of an active region from its emergence throughout its decay
for several solar rotations. Our interest focuses on the understanding
of how energy is generated, released, deposited, and transformed in
active regions. To this end, we determined physical parameters like
intensity, temperature, and emission measure of the whole active region
as a function of time for the entire period selected. We present the
preliminary results of the analysis of GOES (Geosynchronous Operational
Environmental Satellite), SOHO (Solar and Heliospheric Observatory)
and Yohkoh data of the active region named NOAA 7978, 7981, and 7986
observed between July and October 1996
Title: Comparison of Transient Network Brightenings and Explosive
Events in the Solar Transition Region
Authors: Chae, Jongchul; Wang, Haimin; Goode, Philip R.; Fludra,
Andrzej; Schühle, Udo
Bibcode: 2000ApJ...528L.119C
Altcode:
The relation between transient network brightenings, known as blinkers,
and explosive events is examined based on coordinated quiet Sun
observations in the transition region line O V λ630 recorded by
the Coronal Diagnostic Spectrometer (CDS), in the transition region
line Si IV λ1402 recorded by the Solar Ultraviolet Measurements of
Emitted Radiation (SUMER) instrument, and in photospheric magnetograms
taken by the Big Bear Solar Observatory videomagnetograph. From these
observations, we find that (1) explosive events, which are traditionally
defined as features with very broad UV line profiles, tend to keep
away from the centers of network brightenings and are mostly located
at the edges of such brightenings, (2) CDS blinkers consist of many
small-scale, short-lived SUMER ``unit brightening events'' with a
size of a few arcseconds and a lifetime of a few minutes, and most
importantly (3) each SUMER unit brightening event is characterized by
a UV line profile that is not as broad as those of explosive events,
but still has significantly enhanced wings. Our results imply that,
like explosive events, individual unit brightening events involve high
velocities, and, hence, blinkers may have the same physical origin
as explosive events. It is likely that transient network brightenings
and explosive events are both due to magnetic reconnection--but with
different magnetic geometries.
Title: EUV brightness variations in the quiet Sun
Authors: Brković, A.; Rüedi, I.; Solanki, S. K.; Fludra, A.;
Harrison, R. A.; Huber, M. C. E.; Stenflo, J. O.; Stucki, K.
Bibcode: 2000A&A...353.1083B
Altcode:
The Coronal Diagnostic Spectrometer (CDS) onboard the SOHO satellite has
been used to obtain movies of quiet Sun regions at disc centre. These
movies were used to study brightness variations of solar features at
three different temperatures sampled simultaneously in the chromospheric
He I 584.3 Ä (2 * 104 K), the transition region O V 629.7
Ä (2.5 * 105 K) and coronal Mg IX 368.1 Ä (106
K) lines. In all parts of the quiet Sun, from darkest intranetwork to
brightest network, we find significant variability in the He I and O
V line, while the variability in the Mg IX line is more marginal. The
relative variability, defined by rms of intensity normalised to the
local intensity, is independent of brightness and strongest in the
transition region line. Thus the relative variability is the same
in the network and the intranetwork. More than half of the points
on the solar surface show a relative variability, determined over a
period of 4 hours, greater than 15.5% for the O V line, but only 5%
of the points exhibit a variability above 25%. Most of the variability
appears to take place on time-scales between 5 and 80 minutes for the
He I and O V lines. Clear signs of ``high variability'' events are
found. For these events the variability as a function of time seen
in the different lines shows a good correlation. The correlation is
higher for more variable events. These events coincide with the (time
averaged) brightest points on the solar surface, i.e. they occur in
the network. The spatial positions of the most variable points are
identical in all the lines.
Title: Comparison Between Euv And Radio Observations : A Powerful
Diagnostic For The Upper Solar Atmosphere
Authors: Chiuderi Drago, F.; Landi, E.; Fludra, A.; Delouis, J. M.;
Kerdraon, A.
Bibcode: 1999ESASP.446..287C
Altcode: 1999soho....8..287C
In the present work we show that EUV and radio observation can provide a
very powerful plasma diagnostics when combined together. The intensity
of EUV lines formed in the range of temperature corresponding to
the Chromosphere-Corona Transition Region, supplies the DEM function
defined as DEM(T)=Ne2 dh/dT. Above the temperature where no
more lines are detected, the DEM can be either truncated or arbitrarily
extrapolated to a very low value at a very high temperature. The DEM
derived with both assumptions reproduce of course very well the observed
line intensities, being derived from a best fit of these lines. We have
used the DEM, derived from a set of EUV lines observed by CDS in an
equatorial Coronal Hole using both assumptions, to compute the radio
brightness temperature. The comparison of the computed Tb
with the values observed by the Nancay Radiheliograph in the same hole,
shows that both DEM assumptions are unable to reproduce the observations
and that it is necessary to add the contribution of an isothermal
Corona above the region where the DEM is defined. From the fit of
the radio observations at four frequencies between 164 and 410 MHz,
the coronal hole Emission Measure and an upper limit of the coronal
electron temperature (T < 9. 105) are derived. Using this coronal
model, together with the DEM up to T < 9.105, we have computed the
theoretical EUV line intensities, obtaining a very good agreement with
the observations for T > 8x105 K, thus providing also a lower limit
to the hole temperature.
Title: Decaying Post-Flare Loops System Observed By SOHO/CDS And
Yohkoh/SXT
Authors: Varady, M.; Fludra, A.; Heinzel, P.
Bibcode: 1999ESASP.446..669V
Altcode: 1999soho....8..669V
The results of an analysis of joint CDS of SOHO and SXT of Yohkoh
observations of a decaying post-flare loop system are presented. The SXT
images were used to explain some peculiar structural features visible
in the examined CDS raster, resulting from the rapid evolution of the
observed system and from the way the CDS rasters are built. The SXT
data was also used to determine the time evolution of the temperature
and the emission measure of the hot part of the system during its
decay. The CDS data, with a very good temperature coverage, contains
a density sensitive line pair of Fe XIV which was used for electron
density analysis and a temperature sensitive line pair of Fe XVI and
Si XII which was used to study the temperature structure of the loop
system. From the integrated intensities of selected lines the emission
measures were calculated. From these measurements we estimated the
filling factor of the loop system in Fe XIV line.
Title: Long-Term Evolution Of Emissivity And Heating In A Solar
Active Region
Authors: van Driel-Gesztelyi, L.; Thompson, B.; Démoulin, P.; Orlando,
S.; Bocchialini, K.; Oláh, K.; Kövári, Z.; Deforest, C.; Khan,
J.; Fludra, A.; Mandrini, C.
Bibcode: 1999ESASP.446..663V
Altcode: 1999soho....8..663V
We study the evolution of the heating and emissivity of an active
region from its birth throughout its decay during six solar rotations
(July-Nov. 1996). We analyse multi-wavelength and multi-instrument
data obtained from SOHO (EIT, SUMER, CDS, MDI), Yohkoh (SXT), GOES
and 10.7cm radio data from DRAO, Canada. We take one "snapshot" per
rotation at the time of the central meridian passage (CMP) of the
AR, outside of time of flares, which appears to be representative
enough to allow us to make some general conclusions about the
long-term evolution. Deriving physical parameters like intensity
(flux), temperature and emission measure of the entire AR vs. time,
we formulate mathematically the change in radiation emitted by the
decaying AR at several wavelengths. Combining the emissivity data with
the evolution of magnetic flux density as the flux is being dispersed
by small- and larger-scale convective motions, we make an attempt to
understand the physics behind the emission and heating. We also analyse
the effects of flaring on the heating of the AR, and study whether and
how the flare properties evolve during the life of the active region.
Title: Transition Region Oscillations in Sunspot Plumes
Authors: Fludra, A.
Bibcode: 1999ESASP.446..327F
Altcode: 1999soho....8..327F
Sunspot plumes are compact features, located close to sunspots and
bright in the transition region lines emitted between 1.7x105 K and
4x105 K. Intensity oscillations of the transition region lines in
a sunspot plume in the active region AR8249 were reported by Fludra
(1999, Astron. Astrophys., 344, L75), based on the data recorded by
the Coronal Diagnostic Spectrometer (CDS). In this paper we examine
high-cadence CDS observations of five sunspot plumes, and present
the time series of line intensities and their power spectra. We find
that the OV 630 A line oscillates in all sunspot plumes with periods
between 150 and 200 seconds. The oscillation periods and amplitudes
seen at different temperatures are compared.
Title: Coronal Hole Diagnostics out to 8 solar radii
Authors: Doyle, J. G.; Teriaca, L.; Banerjee, D.; Fludra, A.
Bibcode: 1999ESASP.446..281D
Altcode: 1999soho....8..281D
The line width measurements (from Si VIII) and Ne estimates
(from Si VIII and Si IX) based on SUMER and CDS observations are
combined with LASCO and UVCS output to provide an overview of its
variations with height above a polar coronal hole. From the combined
dataset we find a radial dependence of the electron density, in the
range 1-2 solar radii as r-8, from 2 to 4 solar radii as r-4 and then
as r-2. Combining the Si VIII half width at 1/e of the peak intensity
with the UVCS O VI half width, we find a small increase of the half
width from 1 to 1.2 solar radii, then a plateau until 1.5 solar radii,
thereafter a sharp increase until 2 solar radii, finally a more gradual
increase reaching 550 km/s at 3.5 solar radii. Our data suggests that
the MHD waves responsible for the excess line broadening tends to
become non-linear as it reaches 1.2 solar radii.
Title: EUV and radio observations of an equatorial coronal hole
Authors: Chiuderi Drago, F.; Landi, E.; Fludra, A.; Kerdraon, A.
Bibcode: 1999A&A...348..261C
Altcode:
EUV and radio data of an equatorial coronal hole, observed in October
1996 at its central meridian transit, are compared. EUV lines were
observed by the CDS instrument onboard SOHO and the radio emission
by the Nancay Radioheliograph (France) in the frequency range 164-410
MHz. Using the Differential Emission Measure (DEM), derived from EUV
line intensities, we have computed the radio brightness temperature T_b,
leaving the coronal temperature (upper limit of the DEM definition)
and pressure as free parameters, to be determined from the comparison
with the observations. This analysis has shown that radio data,
contrarily to EUV line intensities, cannot be fitted without the
presence of isothermal plasma above the region where the DEM is
defined, independently of the choice of parameters. A model, nicely
fitting both sets of data, is derived, in which the coronal temperature
and density are T_c <= 9 x 10(5) K and N_e(0) =~ 3x 10(8 cm(-3))
respectively. The assumption of hydrostatic equilibrium with a scale
height derived from the electron temperature is discussed.
Title: Electron densities above a polar coronal hole based on improved
SI IX density diagnostics
Authors: Doyle, J. G.; Keenan, F. P.; Ryans, R. S. I.; Aggarwal,
K. M.; Fludra, A.
Bibcode: 1999SoPh..188...73D
Altcode:
Using new close-coupling excitation rates for the C-like ion Si ix,
density-diagnostic ratios based on Si ix lines have been re-evaluated
and applied to a sequence of CDS observations taken above a polar
coronal hole. The derived electron densities are in excellent agreement
with previous values of Neestimated from the N-like ion Si
viii for another coronal hole. The confirmed trend is for a fall-off
of one order of magnitude within the first 0.3 R⊙above the
limb. These densities are well fitted with an analytic formula for the
density profile out to at least 8 R⊙, by which stage the
electron density has fallen to ∼4×103 cm−3,
from 1.5×108 cm−3at 1.0 R⊙.
Title: The absolute coronal abundances of sulfur, calcium, and iron
from Yohkoh-BCS flare spectra
Authors: Fludra, A.; Schmelz, J. T.
Bibcode: 1999A&A...348..286F
Altcode:
Using X-ray spectra from the Bragg Crystal Spectrometer on Yohkoh,
we have derived the absolute coronal abundances of sulfur, calcium,
and iron using the ratio of the flux in the S XV, Ca XIX and Fe XXV
resonance lines to the continuum near the Ca XIX and S XV resonance
lines. For the 57 flares analyzed here, multi-thermal effects have been
taken into account using a differential emission measure analysis. We
compare these abundances of S, Ca, and Fe with their photospheric values
and with values derived for coronal plasma from both spectral and solar
energetic particle data. The mean Yohkoh abundance of sulfur relative
to hydrogen is 7.9 x 10(-6) , smaller than the photospheric value by
over a factor of two. The mean abundance of calcium is 3.4 x 10(-6)
, about 50% greater than the photospheric value. The mean abundance
of iron shows greater scatter around its mean value of 4.5 x 10(-5) ,
but is still higher than the accepted photospheric value. Comparison of
these results with others already in the literature, suggests that the
coronal abundance-normalization problem does not have a simple solution.
Title: The quiet Sun extreme ultraviolet spectrum observed in normal
incidence by the SOHO coronal diagnostic spectrometer
Authors: Brooks, D. H.; Fischbacher, G. A.; Fludra, A.; Harrison,
R. A.; Innes, D. E.; Landi, E.; Landini, M.; Lang, J.; Lanzafame,
A. C.; Loch, S. D.; McWhirter, R. W. P.; Summers, H. P.; Thompson,
W. T.
Bibcode: 1999A&A...347..277B
Altcode:
The extreme ultraviolet quiet Sun spectrum, observed at normal incidence
by the Coronal Diagnostic Spectrometer on the SOHO spacecraft, is
presented. The spectrum covers the wavelength ranges 308-381 Ä and
513-633 Ä and is based on data recorded at various positions on the
solar disk between October 1996 and February 1997. Datasets at twelve
of these `positions' were judged to be free from active regions and
data faults and selected for detailed study. A constrained maximum
likelihood spectral line fitting code was used to analyse the spectral
features. In all over 200 spectrum lines have been measured and about
50% identified. The line identification process consisted of a number
of steps. Firstly assignment of well known lines was made and used to
obtain the primary wavelength calibration. Variations of wavelengths
with position were used to assess the precision of calibration
achievable. Then, an analysis method first used in studies with the
CHASE experiment, was applied to the new observations. The behaviour
of the intensities of lines from like ions over the twelve positions,
called `position patterns', were used to distinguish probable emitters
of weaker lines and extend the identifications. Spectral line widths
and expected multiplet intensities were examined to identify lines and
probable blends. The product of the study is a table which includes all
clearly observed emission lines, their measured wavelengths, widths
and count rates. Adopted laboratory wavelengths, ion and transition
designations are also presented for identified lines. The table has an
estimate of the uncertainty of the count rates based on a statistical
analysis of the variability of each line. A marked spectrum is also
provided.
Title: Heating and jet formation by colliding shocks in solar
atmosphere
Authors: Tarbell, T.; Ryutova, M. P.; Covington, J.; Fludra, A.
Bibcode: 1999AIPC..471..419T
Altcode: 1999sowi.conf..419T
We show that ubiquitous small-scale magnetic flux ``tubes''
constantly emerging from subsurface layers, may cause the formation
of plasma jets and a sporadic excess of temperature near the solar
surface. Photospheric network magnetic elements collide and reconnect,
creating a sling-shot effect which generates complex 3D shock waves
with the curved surface. Self-focusing of these shocks occurs as they
propagate upward in the rarefied atmosphere. Depending on the geometry
of the shock collision, highly concentrated energy may be either
converted entirely into heat or into strong jets, or be distributed
between the two.
Title: Solar minimum streamer densities and temperatures using Whole
Sun Month coordinated data sets
Authors: Gibson, S. E.; Fludra, A.; Bagenal, F.; Biesecker, D.;
del Zanna, G.; Bromage, B.
Bibcode: 1999JGR...104.9691G
Altcode:
We model electron densities of the simplest, most symmetric solar
minimum streamer structure observed during the Whole Sun Month (WSM)
campaign, using coronal observations of both visible white light and
extreme ultraviolet (EUV) emission. Using white light data from the
SOHO/LASCO/C2 and HAO/Mauna Loa Mark 3 coronagraphs, we determine
electron densities by way of a Van de Hulst inversion. We compare the
white light densities to those determined from the density sensitive
EUV line ratios of Si IX 350/342 Å observed by the SOHO/coronal
diagnostic spectrometer (CDS). Moreover, from the white light density
profiles we calculate hydrostatic temperature profiles and compare
to temperatures derived from the Si XII/Mg X line ratio. We find
the white light and spectral analysis produce consistent density and
temperature information.
Title: Physical properties of a coronal hole from a coronal diagnostic
spectrometer, Mauna Loa Coronagraph, and LASCO observations during
the Whole Sun Month
Authors: Guhathakurta, M.; Fludra, A.; Gibson, S. E.; Biesecker, D.;
Fisher, R.
Bibcode: 1999JGR...104.9801G
Altcode:
Until recently [Guhathakurta and Fisher, 1998], inference of
electron density distribution in the solar corona was limited by
the field of view of white-light coronagraphs (typically out to 6
Rs). Now, for the first time we have a series of white-light
coronagraphs (SOHO/LASCO) whose combined field of view extends from
1.1-30 Rs. Quantitative information on electron density
distribution of coronal hole and coronal plumes/rays are estimated
by using white-light, polarized brightness (pB) observations from the
SOHO/LASCO/C2 and C3 and HAO/Mauna Loa Mark III coronagraphs from 1.15
to 8.0 Rs. Morphological information on the boundary of
the polar coronal hole and streamer interface is determined from the
white-light observations in a manner similar to the Skylab polar coronal
hole boundary estimate [Guhathakurta and Holzer, 1994]. The average
coronal hole electron density in the region 1-1.15 Rs is
estimated from the density-sensitive EUV line ratios of Si IX 350/342 Å
observed by the SOHO/coronal diagnostic spectrometer (CDS). We combine
these numbers with the estimate from white-light (WL) observations to
obtain a density profile from 1 to 8 Rs for the plumes and
the polar coronal hole. We find that white light and spectral analysis
produce consistent density information. Extrapolated densities inferred
from SOHO observations are compared to Ulysses in situ observations of
density. Like the density inferred from the Spartan 201-03 coronagraph,
the current SOHO density profiles suggest that the acceleration of
the fast solar wind takes place very close to the Sun, within 10-15
Rs. The density information is used to put constraints on
solar wind flow velocities and effective temperatures. Finally, these
results are compared to the recent analysis of the Spartan 201-03
white-light observations.
Title: Synoptic Sun during the first Whole Sun Month Campaign:
August 10 to September 8, 1996
Authors: Biesecker, D. A.; Thompson, B. J.; Gibson, S. E.; Alexander,
D.; Fludra, A.; Gopalswamy, N.; Hoeksema, J. T.; Lecinski, A.;
Strachan, L.
Bibcode: 1999JGR...104.9679B
Altcode:
A large number of synoptic maps from a variety of instruments are used
to show the general morphology of the Sun at the time of the First
Whole Sun Month Campaign. The campaign was conducted from August 10 to
September 8, 1996. The synoptic maps cover the period from Carrington
rotation 1912/253° to Carrington rotation 1913/45°. The synoptic maps
encompass both on-disk data and limb data from several heights in the
solar atmosphere. The maps are used to illustrate which wavelengths and
data sets show particular features, such as active regions and coronal
holes. Of particular interest is the equatorial coronal hole known as
the ``elephant's trunk,'' which is clearly evident in the synoptic
maps of on-disk data. The elephant's trunk is similar in appearance
to the Skylab-era, ``Boot of Italy,'' equatorial coronal hole. The
general appearance of the limb maps is explained as well. The limb
maps also show evidence for equatorial coronal holes.
Title: Electron density and temperature of the lower solar corona
Authors: Fludra, A.; Del Zanna, G.; Alexander, D.; Bromage, B. J. I.
Bibcode: 1999JGR...104.9709F
Altcode:
Off limb observations of the quiet Sun corona were made with the
Coronal Diagnostic Spectrometer (CDS) on SOHO during the Whole Sun
Month campaign in August 1996. Selected spectral lines in the Normal
Incidence range were recorded up to 1.2 solar radii above the east
and west limb and above the polar coronal holes. Intensities of the
coronal lines covering the temperature range from 9×105
to 2×106K have been measured and used to derive
electron temperature and electron density as a function of the
radial distance above the solar limb. Results from the east and
west equatorial regions and polar coronal holes are compared. The
temperature and density in the coronal holes is found to be lower
than in the closed field regions. A density-sensitive line ratio
of Si IX 350/342 Å is used to derive an average electron density
which is found to decrease from 5×108cm-3 near
the limb to 1×108cm-3 at 1.15RS,
in the equatorial region. Over the polar coronal holes, where
polar plumes dominate the emission close to the limb, the density
varies from 2×108cm-3 at the limb to
6×107cm-3 at 1.1RS. The
lowest density found inside the coronal hole on the disk is
9.9×107cm-3. An increase in the quiet Sun
temperature with the radial distance is found from the Si XII/Mg
X and Si XII/Mg IX line ratios, and an increase in the coronal
hole temperature is seen from the Mg X/Mg IX ratio. The Si XII/Mg
X temperature varies from 1.1×106K at r=RS
to 1.4×106K at r=1.2RS in the equatorial
regions. The EUV emission is compared with that of the soft X rays as
measured by the Yohkoh SXT. The densities and temperatures determined
from the SXT show a similar behavior to that determined from the
CDS. Density and temperature, averaged over a position angle range of
20-54°, show very little variation over a period of 20 days.
Title: The Hybrid Set of Absolute Coronal Abundances
Authors: Schmelz, J. T.; Fludra, A.
Bibcode: 1999AAS...19410001S
Altcode: 1999BAAS...31..996S
Knowledge of the abundances of trace elements relative to hydrogen
-- absolute abundances -- in the solar corona is essential for the
understanding of plasma conditions. Both spectroscopic and solar
energetic particle data agree that the coronal-to-photospheric abundance
ratios of elements with low First Ionization Potential (FIP <10
eV) seem to be enhanced by about a factor of four relative to those
with high FIP (>11 eV). The observations, however, do not agree
on the normalization of the trace elements with respect to hydrogen,
a result which is problematic in both the spectroscopic and particle
data analysis. Two different empirical models have been suggested
in the literature: (1) low-FIP elements may be enhanced by about
a factor of four with respect to their photospheric values while
high-FIP elements are the same in the corona and the photosphere; or
(2) low-FIP elements may be the same in the corona and the photosphere
while high-FIP elements are depleted by about a factor of four with
respect to their photospheric values. Unfortunately, however, neither of
these two empirical models accurately represents the data. We have used
the absolute coronal abundance results from several groups using both
spectroscopic and energetic particle data to show that a much better
representation is achieved with a 'hybrid' set of abundances. In this
empirical model, there is both low-FIP enhancement as well as high-FIP
depletion, each by about a factor of two. The data clearly show that
it is impossible for one model to explain all observations. It is
also vital to account for the possibility of abundance variability
when analyzing any data set. However, it is often useful to begin
the analysis with an assumed set of coronal abundances. The hybrid
abundances represent the best average values for all available data.
Title: Intensity Oscillations in Sunspot Plumes
Authors: Fludra, A.
Bibcode: 1999AAS...194.9314F
Altcode: 1999BAAS...31..990F
Sunspot plumes are compact features, located close to sunspots and
bright in the transition region lines emitted between 1.7 x 10(5) and
4x 10(5) K. Observations of a sunspot plume in the active region AR8249
have been made with the Coronal Diagnostic Spectrometer (CDS) on SOHO
with a 15-second time resolution. We report the finding of intensity
oscillations of the O V 629.7 Angstroms line in the sunspot plume,
with an amplitude up to 10 percent. Fourier analysis gives two periods
of 167 and 182 seconds. Oscillations are also seen in the Ne IV 543.9
Angstroms , Ne V 572.4 Angstroms and Ne VI 562.8 Angstroms lines (1.7-4x
10(5) K). Inspection of CDS data for several other sunspots shows that
all sunspot plumes show the intensity oscillations of the O V 629.7
Angstroms line and other transition region lines in the 1.7-4x 10(5) K
temperature range. This work was supported by the United Kingdom PPARC.
Title: Intensity oscillations in a sunspot plume
Authors: Fludra, A.
Bibcode: 1999A&A...344L..75F
Altcode:
Observations of a sunspot plume (a compact feature, bright in the
transition region line of O V 629.7 Angstroms at 2.2 x 10(5) K), seen
above a sunspot in the active region AR8249, have been made with a
15-second time resolution with the Coronal Diagnostic Spectrometer on
SOHO. Intensity of the O V 629.7 Angstroms line in the sunspot plume
oscillates with an amplitude of up to ten percent and periods of 167
and 182 seconds. The same oscillations are also seen in the Ne IV
543.9 Angstroms, Ne V 572.4 Angstroms and Ne VI 562.8 Angstroms lines
(1.7-4x 10(5) K) but with a lower signal-to-noise ratio. Inspection
of data for several other sunspots shows that all sunspot plumes show
the intensity oscillations of the O V 629.7 Angstroms line and other
transition region lines in the 1.7-4x 10(5) K temperature range.
Title: Heating and Jet Formation by Hydrodynamic Cumulation in the
Solar Atmosphere
Authors: Tarbell, T.; Ryutova, M.; Covington, J.; Fludra, A.
Bibcode: 1999ApJ...514L..47T
Altcode:
The solar transition region is the site of supersonic plasma jets and
sporadic radiative events, whose origin and physical nature have not
been understood. Here we show that ubiquitous small-scale magnetic flux
``tubes,'' constantly emerging from subsurface layers, may cause the
formation of plasma jets and a sporadic excess of temperature near
the solar surface. These flux tubes collide and reconnect, creating
a sling-shot effect that generates complex three-dimensional shock
waves with the curved surface. Self-focusing of these shocks occurs
as they propagate upward in the rarefied atmosphere. Depending on the
geometry of the shock collision, highly concentrated energy may be
converted entirely into either heat or strong jets, or distributed
between the two.
Title: SOHO JOP 078 - variability and properties of the quiet sun
supergranular network and internetwork.
Authors: Kučera, A.; Curdt, W.; Fludra, A.; Rybák, J.; Wöhl, H.
Bibcode: 1999joso.proc..149K
Altcode:
Study of the variability of the quiet solar atmosphere covering as
large as possible range of the temperatures using both the 2D imaging
and 1D spectra was the aim of SOHO JOP 78 observations. Supergranular
cells were the objects of the authors' main interest. This programme is
based on the cooperation of several SOHO instruments (SUMER, CDS, MDI,
EIT) and TRACE. Justification of the JOP, cooperation of instruments
and specially arranged measurements for the post-facto coalignment of
data from different instruments are described in this paper.
Title: EUV and Radio Observations of an Equatorial Coronal Hole
Authors: Chiuderi-Drago, F.; Kerdraon, A.; Landi, E.; Fludra, A.
Bibcode: 1999SSRv...87..141C
Altcode:
An equatorial coronal hole has been observed on 18 and 19 October 1996
with SOHO-CDS and with the Nancąy Radioheliograph (RH). The CDS EUV
line intensities are used to determine the coronal hole Differential
Emission Measure (DEM); in turn this is used to compute the radio
brightness temperature Tb at the observed frequencies,
leaving the coronal electron temperature and density as free
parameters. EUV line intensities, calculated from the derived models,
show a good agreement with EUV observations.
Title: EUV Observations Above Polar Coronal Holes
Authors: Fludra, A.; Del Zanna, G.; Bromage, B. J. I.
Bibcode: 1999SSRv...87..185F
Altcode:
We derive electron temperature and density as a function of height
up to 0.2 R⊙ above the limb in polar coronal holes,
using five EUV data sets recorded by the SOHO Coronal Diagnostic
Spectrometer between July 1997 and February 1998. Radial T and N
distributions, averaged in a 2° to 10° range of position angles,
are the same above the North and South coronal holes. They do not show
any time variability over a period of seven months. Polar plumes are
found to have lower electron temperature and higher density than the
interplume lanes. The electron density slope suggests that the proton
temperatures are twice as high as the electron temperatures.
Title: Brightness Variations in the Solar Atmosphere as Seen by SOHO
Authors: Brkovic, A.; Rüedi, I.; Solanki, S. K.; Huber, M. C. E.;
Stenflo, J. O.; Stucki, K.; Harrison, R.; Fludra, A.
Bibcode: 1999ASSL..239..231B
Altcode: 1999msa..proc..231B
We present preliminary results of a statistical analysis of the
brightness variations of solar features at different levels in
the solar atmosphere. We observed quiet Sun regions at disc centre
using the Coronal Diagnostic Spectrometer (CDS) onboard the Solar and
Heliospheric Observatory (SOHO). We find significant variability at all
time scales in all parts of the quiet Sun, from darkest intranetwork
to brightest network. Such variations are observed simultaneously in
the chromospheric He I 584.33 Angstroms (2 \cdot 10^4 K) line, the
transition region O V 629.74 Angstroms (2.5 \cdot 10^5 K) and coronal
Mg IX 368.06 Angstroms (10^6 K) line. The relative variability is
independent of brightness and most of the variability appears to take
place on time scales longer than 5 minutes for all 3 spectral lines. No
significant differences are observed between the different data sets.
Title: Coronal Abundances
Authors: Fludra, A.; Saba, J. L. R.; Henoux, J. -C.; Murphy, R. J.;
Reames, D. V.; Lemen, J. R.; Strong, K. T.; Sylwester, J.; Widing,
K. G.
Bibcode: 1999mfs..conf...89F
Altcode:
Flare X-Ray Measurements from BCS Calcium Abundance Fe/H and Fe/Ca
Abundance Relative Abundances of Ar. Ca. and Fe in Flares Factors
Affecting Abundance Determinations from X-Ray Spectra FCS Abundances
FCS Active-Region Abundances Abundance Variability in Active Regions
Impact of Resonance Scattering Assessment of FCS Active-Region Abundance
Results FCS Flare Abundance Studies Coronal CI/S and Ar/S Measurements
Dem Studies of Flare Abuncances Determination of Solar Abundances
by Solar Flare γ-Ray Spectrometry γ-Ray Spectral Analysis γ-Ray
Results Solar Energetic Particles Major Proton Events CIR Events from
Coronal Holes Impulsive Flare Events Theory of Abundance Fractionation
Gravitational Settling Pressure Gradient and Stationary Diffusion
Ion-Neutral Separation Due to Currents Ion-Neutral Separation Due to
Electromagnetic Forces Discussion Summary
Title: Measurement of the electron temperature gradient in a solar
coronal hole
Authors: David, C.; Gabriel, A. H.; Bely-Dubau, F.; Fludra, A.;
Lemaire, P.; Wilhelm, K.
Bibcode: 1998A&A...336L..90D
Altcode:
It has long been established that the high speed solar wind streams
observed at 1 A.U. originate from the coronal hole regions of the
Sun. Theoretical modelling of the acceleration mechanism depends
critically on the value of the maximum of temperature existing close
to the Sun. Measurements of the temperature in coronal holes prior
to SOHO are unreliable. The very low luminosity leads to extreme
observational difficulties, in particular due to light scattering in
the instrument telescopes. Using the two SOHO spectrometers CDS and
SUMER, electron temperatures have now been measured as a function of
height above the limb in a polar coronal hole. Temperatures of around
0.8 MK are found close to the limb, rising to a maximum of less than
1 MK at 1.15 R_sun, then falling to around 0.4 MK at 1.3 R_sun. With
these low temperatures, the classical Parker mechanism cannot alone
explain the high wind velocities, which must therefore be due to the
direct transfer of momentum from MHD waves to the ambient plasma.
Title: Detailed Evidence for Flare-to-Flare Variations of the Coronal
Calcium Abundance
Authors: Sylwester, J.; Lemen, J. R.; Bentley, R. D.; Fludra, A.;
Zolcinski, M. -C.
Bibcode: 1998ApJ...501..397S
Altcode:
The analysis of X-ray solar flare spectra obtained by the Bent
Crystal Spectrometer on board the Solar Maximum Mission satellite is
presented. The ratio of the Ca XIX resonance line intensity to the
nearby continuum is used to measure the calcium abundance relative to
hydrogen (ACa). A description of the spectroscopic method
of determining the absolute calcium abundance is given. Possible
instrumental and solar effects that might influence the abundance
estimates are evaluated. Over 5000 spectra from more than 100 flares are
analyzed. We find a flare-to-flare variation for ACa that is
not correlated with flare size, Hα importance, or with several other
flare characteristics. For flares observed from two active regions, the
observed value of ACa increases as a function of time. The
average for all flares is <ACa> = (5.77 +/- 1.41) ×
10-6. A discussion of investigated correlations of derived
ACa values with several flare characteristics is presented.
Title: The bright loop-top kernels in YOHKOH X-ray flares
Authors: Jakimiec, J.; Tomczak, M.; Falewicz, R.; Phillips, K. J. H.;
Fludra, A.
Bibcode: 1998A&A...334.1112J
Altcode:
We have investigated loop-top kernels of the soft X-ray emission seen
in the Yohkoh Soft X-ray Telescope (SXT) images. Detailed comparison
of the observations from various Yohkoh instruments shows that these
kernels contain two kinds of flare plasma: a cooler ( ~ 10 MK) and a
hotter ( ~ 20 MK) one. The cooler plasma plays a dominant role in the
emission recorded by the SXT and the hotter plasma is responsible for
the Fe xxv emission and the emission recorded by Hard X-ray Telescope
14-23 keV band during the post-impulsive phase of a flare. We argue
that the best model, which is in agreement with the above observational
results, is a turbulent model of a flare loop-top kernel. The magnetic
field is tangled in the kernel and a number of transient current sheets
occur there. The hotter ( ~ 20 MK) plasma is contained in the current
sheets and they are surrounded by the cooler ( ~ 10 MK) plasma. The
turbulent model of the flare loop-top kernel also allows us to explain
why the kernels are brighter than the ``legs'' connecting them with
the chromosphere.
Title: Empirical Models of Temperature, Densities, and Velocities
in the Solar Corona
Authors: Fludra, A.; Strachan, L.; Alexander, D.; Bagenal, F.;
Biesecker, D. A.; Dobrzycka, D.; Galvin, A. B.; Gibson, S.; Hassler,
D.; Yo, Y. -K.; Panasyuk, A. V.; Thompson, B.; Warren, H.; del Zanna,
G.; Zidowitz, S.; Antonucci, E.; Bromage, B. J. I.; Giordano, S.
Bibcode: 1998EOSTr..79..278F
Altcode:
We present empirical results for temperatures, densities, and outflow
velocities of constituents of the solar corona from 1 to 3 Ro in
polar coronal holes and an equatorial streamer. Data were obtained
from a variety of space and ground-based instruments during August
1996 as part of the SOHO Whole Sun Month Campaign. From white light
data obtained with the SOHO/LASCO/C2 and HAO/Mauna Loa coronagraphs,
we determine electron densities and compare them to those determined
from the density-sensitive EUV line ratio of Si IX 350/342 Angstroms
observed by the SOHO/Coronal Diagnostic Spectrometer (CDS). Moreover,
from the white light density profiles we calculate temperature profiles
and compare to temperature diagnostic information from EUV lines and
soft X-ray images from Yohkoh. H I Ly alpha and O VI 1032/1037 Angstrom
intensities from the SOHO Ultraviolet Coronagraph Spectrometer (UVCS)
are used to estimate both the direction and magnitude of plasma outflow
velocities in coronal holes and streamers above 1.5 Ro. The velocities
are derived using densities from white light coronagraph data and
coronal electron temperature estimates derived from Ulysses/SWICS
ion composition data. Near the base of the corona we find the white
light and spectral analysis produce consistent density and temperature
information. In the extended corona we find results consistent with
high outflow velocities and a superradial outflow geometry in polar
coronal holes.
Title: The Nature of Loop-Top Sources in Solar X-ray Flares
Authors: Phillips, K. J. H.; Jakimiec, J.; Tomczak, M.; Falewicz,
R.; Fludra, A.
Bibcode: 1998ASPC..154..671P
Altcode: 1998csss...10..671P
Bright, compact loop-top sources or kernels are a conspicuous feature
of soft X-ray flares as imaged by the SXT instrument on the Japanese
solar mission Yohkoh, and their nature has been widely discussed. We
have done a detailed comparison of the observations from the hard
and soft X-ray imaging instruments (HXT and SXT) as well as the Bragg
Crystal Spectometer (BCS) on Yohkoh for some 36 flares. We find evidence
that the loop-top sources in these flares are highly non-isothermal,
with temperature ranging from ~10 MK (as seen by SXT) to ~20 MK or
more (as deduced from line ratios in the BCS range and the presence
of gradually varying emission in the HXT 14-23 keV energy band). The
SXT temperature maps (formed from the ratio of emission through two
different filters) show that the temperature distribution within the
loop-top source is uniform. We argue that the most plausible model to
explain this is one in which the loop-top source is made up of highly
tangled magnetic field lines, where current sheets continually form,
supplying energy to the region. Both freshly heated plasma (~20 MK)
and cooled plasma (~10 MK) co-exist in the same region. A calculation
of the energy balance of the loop-top region suggests that the heating
is not uniform within the region but rather is at a maximum near its
edge. This may be explained by the reconnection of the tangled field
with the field of the loop legs, which has a simple geometry.
Title: Iron and calcium abundances in solar flares from the
multitemperature analysis of X-ray spectra (abstract)
Authors: Fludra, A.; Bentley, R. D.; Culhane, J. L.; Lemen, J. R.;
Sylwester, J.
Bibcode: 1998PAICz..88...91F
Altcode:
No abstract at ADS
Title: Analysis of the flare evolution in the emission measure -
temperature diagrams for selected events observed by SMM (abstract)
Authors: Sylwester, B.; Sylwester, J.; Siarkowski, M.; Fludra, A.;
Serio, S.
Bibcode: 1998PAICz..88...94S
Altcode:
No abstract at ADS
Title: The Structure and Evolution of Solar Coronal Holes Observed
by SOHO During August and September 1996
Authors: Bromage, B. J. I.; del Zanna, G.; Fludra, A.; DeForest, C.;
Thompson, B.
Bibcode: 1997ESASP.415..307B
Altcode: 1997cpsh.conf..307B
No abstract at ADS
Title: Active Regions Observed in Extreme Ultraviolet Light by the
Coronal Diagnostic Spectrometer on SOHO
Authors: Fludra, A.; Brekke, P.; Harrison, R. A.; Mason, H. E.; Pike,
C. D.; Thompson, W. T.; Young, P. R.
Bibcode: 1997SoPh..175..487F
Altcode:
We present observations of five active regions made by the Coronal
Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory
(SOHO). CDS observes the Sun in the extreme ultraviolet range 150-780
Å. Examples of active region loops seen in spectral lines emitted at
various temperatures are shown. Several classes of loops are identified:
those that are seen in all temperatures up to 2 x 106 K;
loops seen at 106 K but not reaching 1.6 x 106
K; those at temperatures 2- 4 x 10-5 K and occasionally at
6 x 10-5 K but not reaching 106 K. An increasing
loop size with temperature and the relationship between the cool and
hot structures is discussed. CDS observations reveal the existence of
loops and other unresolved structures in active regions, at temperatures
between 1.5- 4 x 10-5 K, which do not have counterparts in
lines emitted above 8 x 10-5 K. Bright compact sources only
seen in the transition region lines are investigated. These sources can
have lifetimes of up to several days and are located in the vicinity
of sunspots. We study the variability of active region sources on time
scales from 30 sec to several days. We find oscillatory behaviour of Hei
and Ov line intensities in an active region on time scales of 5-10 min.
Title: Initial Comparison of MDI Photospheric Magnetic Movies and
CDS Transition Region Movies in Quiet Sun
Authors: Tarbell, T.; Brekke, P.; Fludra, A.; Deforest, C.; Saba,
J.; Covington, J.
Bibcode: 1997SPD....28.0111T
Altcode: 1997BAAS...29..881T
We present simultaneous, coaligned movies of photospheric magnetic
fields and transition region (TR) intensities in very quiet sun near
disk center obtained by SOHO in January, 1997. For example, the 22 Jan
1997 CDS movies show He I 584 (2x10(4) K) and O V 630 (2.4 x 10(5) K)
from 16:51 to 19:54 UT, with a 310 x 240 arcsecond field of view, 105
second cadence, and 1.7 arcsecond pixels. MDI photospheric longitudinal
magnetograms, with 60 second cadence and 0.6 arcsecond pixels, have been
coaligned with these. Bright TR emission correlates more strongly with
close bipoles in the photospheric magnetic field than with magnetic
flux alone. Some strong photospheric flux tubes are barely visible
in the TR emission, appearing only occasionally in connections with
nearby weak opposite polarity fields. Bright transient emissions in
the TR are located at places of cancelling opposite polarities in
photospheric magnetic fields. The flux cancellation continues for tens
of minutes or hours in the magnetic movies. Searches for more rapid
magnetic counterparts to these TR transients and for emerging magnetic
flux regions in the movies are under way. This work was supported by
NASA grant NAG5-3077 at Stanford and Lockheed Martin.
Title: The Height and Temporal Structure of X-Ray Bright Points
Authors: Harvey, K. L.; Penn, M.; Tarbell, T.; Saba, J.; Hassler,
D.; Moses, J. D.; Fludra, A.
Bibcode: 1997SPD....28.0124H
Altcode: 1997BAAS...29..883H
On April 12, 1996, several ground-based observatories, the Yohkoh/SXT
and the SOHO/MDI, EIT, SUMER, and CDS instruments participated in a
collaborative study of X-Ray Bright Points (XBPs). During a several
hour period, simultaneous images were obtained of an area centered
at N10E00. At NSO/KP, observations were made of the HeI 1083 nm line
profile from which we have derived the intensity at line center,
equivalent width, and the velocity at every 1 pixel (1.15 arc-seconds)
within an 8 x 8 arc-minute area. Our paper will present the results
of a comparison, spatially and temporally, of these data with changes
in the magnetic field observed by the MDI, intensities and velocities
observed with SUMER and CDS, and the intensity images observed by
the SXT and EIT. We will use this ensemble of intensity, magnetic
and velocity field images to derive the height structure of XBPS,
its variation as a function of time and relation to the associated
magnetic field configuration.
Title: Observations of the Quiet Sun Corona and Coronal Holes with
the Coronal Diagnostic Spectrometer on SOHO
Authors: Fludra, A.; del Zanna, G.; Bromage, B. J. I.
Bibcode: 1997SPD....28.0109F
Altcode: 1997BAAS...29..880F
Limb observations of the quiet sun corona were made with the
Coronal Diagnostic Spectrometer (CDS) on SOHO. A particularly large
data set was recorded in August 1996 during the Whole Sun Month
campaign. Representative examples of CDS images and spectra are
shown and their diagnostic capability is discussed. CDS spectra in
the wavelength range 150-780 Angstroms taken up to 1.3 solar radii
above the East and West limb, provide intensities of many spectral
lines as a function of the radial distance. Several density-sensitive
line ratios (e.g., Si IX, Fe XII, Fe XIII) are used to estimate an
average electron density. The temperature distribution above the limb
is inferred using lines from different ionization stages of iron,
magnesium and silicon: Fe IX-XVI, Mg IX-X, Si XI-XII. The relevance of
these measurements to the study of the structure of the lower corona is
discussed. CDS observations of polar coronal holes are also analyzed
to obtain estimates of electron density and temperature, and to study
the morphology and evolution of coronal hole boundaries.
Title: EUV Line Intensities Above the Limb Measured by CDS
Authors: Fludra, A.; Del Zanna, G.; Bromage, B. J. I.; Thomas, R. J.
Bibcode: 1997ESASP.404..385F
Altcode: 1997cswn.conf..385F
No abstract at ADS
Title: Properties of Brightenings Seen in CDS Movies
Authors: Rüedi, I.; Brkovic, A.; Solanki, S. K.; Harrison, R.;
Fludra, A.; Huber, M. C. E.; Stenflo, J. O.; Stucki, K.
Bibcode: 1997ESASP.404..641R
Altcode: 1997cswn.conf..641R
No abstract at ADS
Title: SOHO observations of the north polar solar wind
Authors: Peres, G.; Ciaravella, A.; Betta, R.; Orlando, S.; Reale,
F.; Kohl, J.; Noci, G.; Fineschi, S.; Romoli, M.; Brekke, P.; Fludra,
A.; Gurman, J. B.; Lemaire, P.; Schuhle, U.
Bibcode: 1997ESASP.404..587P
Altcode: 1997cswn.conf..587P
No abstract at ADS
Title: High-Resolution Observations of the Extreme Ultraviolet Sun
Authors: Harrison, R. A.; Fludra, A.; Pike, C. D.; Payne, J.;
Thompson, W. T.; Poland, A. I.; Breeveld, E. R.; Breeveld, A. A.;
Culhane, J. L.; Kjeldseth-Moe, O.; Huber, M. C. E.; Aschenbach, B.
Bibcode: 1997SoPh..170..123H
Altcode:
This paper presents first results of the Coronal Diagnostic Spectrometer
(CDS) recently launched aboard the Solar and Heliospheric Observatory
(SOHO). CDS is a twin spectrometer, operating in the extreme ultraviolet
range 151-785 Å. Thus, it can detect emission lines from trace
elements in the corona and transition region which will be used to
provide diagnostic information on the solar atmosphere. In this paper,
we present early spectra and images, to illustrate the performance of
the instrument and to pave the way for future studies.
Title: Application of Spectroscopic Diagnostics to Early Observations
with the SOHO Coronal Diagnostic Spectrometer
Authors: Mason, H. E.; Young, P. R.; Pike, C. D.; Harrison, R. A.;
Fludra, A.; Bromage, B. J. I.; Del Zanna, G.
Bibcode: 1997SoPh..170..143M
Altcode:
The Coronal Diagnostic Spectrometer (CDS) has as a scientific goal
the determination of the physical parameters of the solar plasma
using spectroscopic diagnostic techniques. Absolute intensities and
intensity ratios of the EUV spectral emission lines can be used to
obtain information on the electron density and temperature structure,
element abundances, and dynamic nature of different features in the
solar atmosphere. To ensure that these techniques are accurate it is
necessary to interface solar analysis programs with the best available
atomic data calculations. Progress is reported on this work in relation
to CDS observations.
Title: Extreme ultraviolet observations of the solar corona: first
results from the coronal diagnostic spectrometer on SOHO
Authors: Harrison, R. A.; Fludra, A.; Sawyer, E. C.; Culhane, J. L.;
Norman, K.; Poland, A. I.; Thompson, W. T.; Kjeldseth-Moe, O.;
Aschenbach, B.; Huber, M. C. E.; Gabriel, A. H.; Mason, H. E.
Bibcode: 1997AdSpR..20.2239H
Altcode:
We present first results from the Coronal Diagnostic Spectrometer (CDS)
aboard the ESA/NASA Solar and Heliospheric Observatory (SOHO). CDS is
a double spectrometer operating in the 151-785 A˚ range. This region
of the solar spectrum is rich in emission lines from trace elements
in the solar atmosphere, which can be used to derive diagnostic
information on coronal and transition region plasma. Early spectra are
presented and well identified lines are listed. In addition, examples
of images in selected wavelength ranges are shown, for a prominence,
a loop system and a bright point, demonstrating well the power of such
extreme ultraviolet observations.
Title: Energy release and transport in arcade flares
Authors: Jakimiec, J.; Tomczak, M.; Fludra, A.; Falewicz, R.
Bibcode: 1997AdSpR..20.2341J
Altcode:
This work is based on hard and soft X-ray observations from the
YOHKOH satellite. We investigate an example of an arcade flare,
for which the arcade channel is seen in soft X-rays as a long bright
filament. We have found that: (1) Energy can efficiently flow along
the arcade channel from the very beginning of a flare. (2) During flare
evolution a few kernels of hard X-ray emission develop along the arcade
channel. Clearly, they are new, additional sources of the flare energy
release. A probable scheme of formation of such hard X-ray kernels is
briefly discussed.
Title: Coordinated SOHO Observations of Polar Plumes
Authors: Deforest, C. E.; Scherrer, P. H.; Tarbell, T.; Harrison,
R. A.; Fludra, A.; Delaboudiniere, J. P.; Gurman, J. B.; Wilhelm,
K.; Lemaire, P.; Hassler, D. M.; Kohl, J. L.; Noci, G.; Fineschi,
S.; Brueckner, G. E.; Howard, R. A.; Cyr, O. C. St.
Bibcode: 1996AAS...188.4909D
Altcode: 1996BAAS...28R.898D
On 7 and 8 March 1996, SOHO instruments engaged in their first
joint science operation, a 12-hr observation of polar plumes
over the South polar coronal hole. The observing mini-campaign
included observations from SOHO, other spacecraft, and ground-based
observatories. Contributing SOHO instruments -- in order of altitude,
MDI, CDS, SUMER, EIT, UVCS, and LASCO -- made overlapping, simultaneous
observations of plume structures from the photosphere out to the
LASCO C3 limit of 32 solar radii. MDI provided line-of-sight surface
magnetograms with a one-min cadence and 0.6 arcsec resolution;
CDS, SUMER, and EIT supplied temperature-sensitive images of the
lower corona with varying cadences and resolutions; UVCS measured
fluctuations in Ly B intensity across the coronal hole with a one-min
cadence at 1.4 R0; and LASCO imaged the entire corona out to 30 R0 in
various visible passbands. Plume footpoints in the lower corona are
observed by EIT and CDS to vary by a factor of two in EUV brightness
with a timescale of tens of minutes, while the structures above are
(as as been previously observed) quiescent on at least a ten-hr time
scale. We present preliminary results of cross-instrument analysis
of the observed plumes, and suggest how this and similar future data
sets can be used to constrain quiet-sun wind acceleration and coronal
heating models for the coronal hole. This research is supported by
the SOI-MDI NASA contract NAG5-3077 at Stanford University. SOHO is
project of international cooperation between NASA and ESA.
Title: Helium like sulphur X-ray emission in solar flares and
laboratory plasmas.
Authors: Harra-Murnion, L. K.; Phillips, K. J. H.; Lemen, J. R.;
Zarro, D. M.; Greer, C. J.; Foster, V. J.; Barnsley, R.; Coffey,
I. H.; Dubau, J.; Keenan, F. P.; Fludra, A.; Rachlew-Kaellne, E.;
Watanabe, T.; Wilson, M.
Bibcode: 1996A&A...308..670H
Altcode:
Theoretical X-ray spectra of He-like sulphur (S xv) derived from the
General Relativistic Atomic Structure Package, the Dirac R-matrix code
and other calculations are compared to laboratory spectra obtained
from the Alcator C tokamak and JET, and solar flare spectra obtained
from the Yohkoh Bragg Crystal Spectrometer (BCS) and with the SMM Flat
Crystal Spectrometer. The spectra depend on electron temperature and
electron density for plasma densities greater than 10^14^ cm^-3^. The
fits of the derived synthetic spectra to the laboratory spectra at
measured density and temperature are in fair agreement. Very good
agreement can be achieved with the solar flare spectra, which are
in general consistent with the S xv low-density limit, by adjusting
temperature. Thus, S xv line spectra can be used to determine the
temperatures of relatively weak flares for which diagnostics from
higher-temperature ions are unavailable. Using the synthetic spectra,
a search for density effects in Yohkoh BCS data at the time of compact
flares was made. None was found, so that it can be deduced that for
such flares the electron density is less than 10^14^cm^-3^. Density
estimates are made from emission measures and image sizes using
Yohkoh Soft X-ray Telescope data. Research has been carried out with
the results of laboratory spectra which indicate a variation of the
I_x_/I_y_ line intensity ratio across the tokamak minor radius. We
have studied various flares which occur at different locations across
the solar disk to determine if the same effect exists on the Sun.
Title: Helium-like sulfur emission in solar flares and laboratory
plasmas.
Authors: Harra-Murnion, L. K.; Phillips, K. J. H.; Lemen, J. R.;
Zarro, D. M.; Greer, C. J.; Foster, V. J.; Barnsley, R.; Coffey,
I. H.; Dubau, J. D.; Keenan, F. P.; Fludra, A.; Rachlew-Källne, E.;
Watanabe, T.; Wilson, M.
Bibcode: 1996uxsa.conf..417H
Altcode: 1996uxsa.coll..417H
Theoretical X-ray spectra of S XV derived from the General Relativistic
Structure Package, the Dirac R-matrix code and other calculations are
compared to laboratory spectra obtained from the Alcator C tokamak and
JET, and solar flare spectra obtained from the Yohkoh Bragg Crystal
Spectrometer (BCS) and with the SMM Flat Crystal Spectrometer. The
spectra depend on electron temperature and, electron density for
plasma densities greater than 1014cm-3. The
fits of the derived synthetic spectra to the laboratory spectra at
measured density and temperature are in fair agreement. Very good
agreement can be achieved with the solar flare spectra, which are
in general consistent with the S XV low-density limit, by adjusting
temperature. Thus, S XV line spectra can be used to determine the
temperatures of relatively weak flares for which diagnostics from
higher-temperature ions are unavailable.
Title: The Coronal Diagnostic Spectrometer for the Solar and
Heliospheric Observatory
Authors: Harrison, R. A.; Sawyer, E. C.; Carter, M. K.; Cruise,
A. M.; Cutler, R. M.; Fludra, A.; Hayes, R. W.; Kent, B. J.; Lang,
J.; Parker, D. J.; Payne, J.; Pike, C. D.; Peskett, S. C.; Richards,
A. G.; Gulhane, J. L.; Norman, K.; Breeveld, A. A.; Breeveld, E. R.; Al
Janabi, K. F.; Mccalden, A. J.; Parkinson, J. H.; Self, D. G.; Thomas,
P. D.; Poland, A. I.; Thomas, R. J.; Thompson, W. T.; Kjeldseth-Moe,
O.; Brekke, P.; Karud, J.; Maltby, P.; Aschenbach, B.; Bräuninger,
H.; Kühne, M.; Hollandt, J.; Siegmund, O. H. W.; Huber, M. C. E.;
Gabriel, A. H.; Mason, H. E.; Bromage, B. J. I.
Bibcode: 1995SoPh..162..233H
Altcode:
The Coronal Diagnostic Spectrometer is designed to probe the solar
atmosphere through the detection of spectral emission lines in the
extreme ultraviolet wavelength range 150 - 800 å. By observing
the intensities of selected lines and line profiles, we may derive
temperature, density, flow and abundance information for the plasmas
in the solar atmosphere. Spatial and temporal resolutions of down to
a few arcseconds and seconds, respectively, allow such studies to be
made within the fine-scale structure of the solar corona. Futhermore,
coverage of large wavelength bands provides the capability for
simultaneously observing the properties of plasmas across the wide
temperature ranges of the solar atmosphere.
Title: Evolution of two small solar flares.
Authors: Fludra, A.; Doyle, J. G.; Metcalf, T.; Lemen, J. R.; Phillips,
K. J. H.; Culhane, J. L.; Kosugi, T.
Bibcode: 1995A&A...303..914F
Altcode:
Data from the YOHKOH satellite have been analysed for two small flares
(GOES class C) of total duration of 10 and 60 minutes. Upflows in S
XV, Ca XIX and Fe XXV lines were compared and the presence of a range
of upflow velocities was found. Emission from flare loop footpoints
corresponding to plasma moving with a typical velocity of 200-400km/s
is seen in soft X-ray images. In one of these events (23 June 1992),
which occurred in sheared loops being part of a sparse magnetic arcade,
with initial energy release taking place near one of the footpoints, a
large proportion of upflowing plasma was seen at least 1 minute before
the first peak in hard X-rays. In the second event (13 July 1992), the
increase of soft X-ray emission began more than 3 minutes before, and
weak mass upflows one minute before the rapid increase of temperature
and the onset of the detectable hard X-ray emission. This event was
probably triggered by emerging magnetic flux and accompanied by heating
and restructuring of two nearby magnetic loops. In both events the
emission measure of upflowing plasma is present simultaneously to,
and is very well correlated in time with the hard X-ray flux in the
14-23keV band. Differential emission measure in the temperature range
5-60x10^6^K was derived from S XV, Ca XIX and Fe XXV line and continuum
fluxes, and from images in two broad band soft X-ray filters, and
used to analyse the thermal contribution to the hard X-ray emission. A
non-thermal component of the hard X-ray emission is found at the peak
of the 23 June 1992 flare. The hard X-ray emission in the 13 July 1992
flare is primarily thermal, however, a possibility of an enhanced tail
of the electron energy distribution above 14keV is also indicated. The
chromospheric evaporation in these flares was driven both by electron
beams and thermal conduction, with conduction predominating during most
of the rise phase of the 13 July 1992 flare. In both events, the soft
X-ray emission measure at flare maximum was a few times 10^48^cm^-3^
with an electron temperature 19 and 24x10^6^K; the estimated lower
limit of the electron density is ~10^11^cm^-3^. The broadening of
Ca XIX spectral lines in the decay phase of these flares indicates
persisting random motions with a velocity of 60km/s, which is very
similar to the non-thermal broadening observed previously by SMM in
M and X class flares.
Title: Absolute Abundances of Flaring Coronal Plasma Derived from
SMM Spectral Observations
Authors: Fludra, A.; Schmelz, J. T.
Bibcode: 1995ApJ...447..936F
Altcode:
X-ray spectra simultaneously observed by the Flat Crystal Spectrometer
and Bent Crystal Spectrometer on Solar Maximum Mission have been
analyzed for two solar flares. Elemental abundances for O, Ne, Mg, Si,
S, Ca, and Fe with respect to hydrogen have been derived with the aid
of a differential emission measure analysis. Absolute abundances of
elements with a high first ionization potential (FIP) are depleted in
the corona relative to their photospheric values. An indication for
a gradual change in the coronal-to-photospheric abundance ratio as a
function of FIP is found, rather than the step-function distribution
associated with solar energetic particles. The coronal abundance of
low-FIP calcium is enhanced by a factor of 1.5-2.0, while the high-FIP
oxygen is depleted by a factor of 0.25, with respect to photospheric
abundances. Anomalous values of neon and argon abundances are discussed.
Title: Evidence for the equality of the solar photospheric and
coronal abundance of iron
Authors: Phillips, K. J. H.; Pike, C. D.; Lang, J.; Zarro, D. M.;
Fludra, A.; Watanabe, T.; Takahashi, M.
Bibcode: 1995AdSpR..15g..33P
Altcode: 1995AdSpR..15Q..33P
The Fe Kalpha and Kbeta X-ray lines (wavelengths 1.94 and 1.76
Angstroms) in the solar X-ray spectrum are formed by fluorescence of
photospheric iron atoms, and the ratio of the intensity of either to the
He-like iron (Fe xxv) resonance line at 1.85 Angstroms is a function
of the photospheric-to-coronal abundance of iron. The temperature
dependence of this ratio is weak as long as the flare temperature
T_e>^⋈ 15 x 10^6K. Comparison of the theoretical value of this
intensity ratio with observations from crystal spectrometers on Yohkoh,
SMM and P78-1 are consistent with the photospheric abundance of Fe
being equal to the coronal.
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: Yohkoh observations of the creation of high-temperature plasma
in the flare of 16 December 1991
Authors: Culhane, J. L.; Phillips, A. T.; Inda-Koide, M.; Kosugi,
T.; Fludra, A.; Kurokawa, H.; Makishima, K.; Pike, C. D.; Sakao, T.;
Sakurai, T.; Doschek, G. A.; Bentley, R. D.
Bibcode: 1994SoPh..153..307C
Altcode:
Yohkoh observations of an impulsive solar flare which occurred on 16
December, 1991 are presented. This flare was a GOES M2.7 class event
with a simple morphology indicative of a single flaring loop. X-ray
images were taken with the Hard X-ray Telescope (HXT) and soft X-ray
spectra were obtained with the Bragg Crystal Spectrometer (BCS)
on board the satellite. The spectrometer observations were made at
high sensivity from the earliest stages of the flare, are continued
throughout the rise and decay phases, and indicate extremely strong
blueshifts, which account for the majority of emission in CaXIX during
the initial phase of the flare. The data are compared with observations
from other space and ground-based instruments. A balance calculation
is performed which indicates that the energy contained in non-thermal
electrons is sufficient to explain the high temperature plasma which
fills the loop. The cooling of this plasma by thermal conduction
is independently verified in a manner which indicates that the loop
filling factor is close to 100%. The production of `superhot' plasma
in impulsive events is shown to differ in detail from the morphology
and mechanisms appropriate for more gradual events.
Title: Long Duration Events in Magnetic Arcades and Large Loops
Authors: Fludra, A.; Jakimiec, J.; Tomczak, M.; Culhane, J. L.; Acton,
L. W.
Bibcode: 1994kofu.symp..393F
Altcode:
A number of long duration flares, with decay time between 1 and
17 hours, have been analysed using the Yohkoh Soft X-ray Telescope
images and spectra from the Bragg Crystal Spectrometer. X-ray images
suggest that these events typically occur in the following magnetic
field configurations: magnetic arcade, expanding arch, or large loops
triggered and heated up by a low-lying, compact, impulsive flare
located below these high loops. A continued energy release is observed
during decay of these events. Single loop flare models should not be
indiscriminately applied to analysis of thermodynamics of these flares
due to their more complex structure and restructuring of the magnetic
field, and often increasing height.
Title: Ejection of Heated Mass into a Helix-Like Structure from
Active Region NOAA 7172 on May 21-27, 1992
Authors: Uchida, Y.; Fludra, A.; Khan, J. I.
Bibcode: 1994kofu.symp...83U
Altcode:
Following an extended soft X-ray flare on May 19, 1992, the magnetic
structure related to the active region NOAA 7172 settled down into a
roundish agitated active region with a helix-like structure extending
in the south-west direction. Repeated ejections of heated mass into
the helix-like structure took place from a point of contact between
the helix-like structure and the agitated active region. We discuss two
of these mass ejection events occurred on May 21--22, and May 26. The
three-dimensional velocity in the event on May 26 could be examined
through a coordinated use of the relevant part of the brightening of
the images from the Soft X-ray Telescope (SXT) and the integrated
intensity of the blue-wing profile of the S XV resonance line from
the spatially non-resolving Bragg Crystal Spectrometer (BCS).
Title: Multispectral Observations of Chromospheric Evaporation in
the 1991 November 15 X-Class Solar Flare
Authors: Wuelser, Jean-Pierre; Canfield, Richard C.; Acton, Loren W.;
Culhane, J. Leonard; Phillips, Andrew; Fludra, Andrzej; Sakao, Taro;
Masuda, Satoshi; Kosugi, Takeo; Tsuneta, Saku
Bibcode: 1994ApJ...424..459W
Altcode:
We analyze simultaneous H(alpha) images and spectra (from Mees
Solar Observatory), and soft and hard X-ray images and spectra (from
YOHKOH) during the early phase of an X1.5/3B flare. We investigate
the morphological relationship between chromospheric downflows,
coronal upflows, and particle precipitation sites, and the energetic
relationship between conductive heating, nonthermal particle heating,
and the chromospheric response. We find that the observations
consistently fit the chromospheric evaporation model. In particular,
we demonstrate that the observed upflowing coronal and downflowing
chromospheric plasma components originate in the same locations,
and we show that our unique set of optical and X-ray observations
can clearly distinguish between conductively driven and electron beam
driven evaporation.
Title: Dynamics of a Low Energetic Solar Flare
Authors: Doyle, J. G.; Fludra, A.; Bentley, R. D.; Culhane, J. L.;
Metcalf, T.; Lemen, J. R.; Kosugi, T.
Bibcode: 1994ASPC...64..402D
Altcode: 1994csss....8..402D
No abstract at ADS
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: Hα and X-Ray Signatures of Chromospheric Evaporation Observed
during the Early Phase of the 15 November 1991 Flare
Authors: Wülser, J. -P.; Canfield, R. C.; Acton, L. W.; Culhane,
J. L.; Phillips, A.; Fludra, A.; Sakao, T.; Masuda, S.; Kosugi, T.
Bibcode: 1994xspy.conf...75W
Altcode:
No abstract at ADS
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: Unique SMM observations of an impulsive double solar flare:
Enhanced neon abundance
Authors: Schmelz, J. T.; Fludra, A.
Bibcode: 1993AdSpR..13i.325S
Altcode: 1993AdSpR..13..325S
The Solar Maximum Mission Flat Crystal Spectrometer observed a GOES
M5 double impulsive flare on 05 November 1980. Simultaneous spectra
of seven bright soft X-ray resonance lines provide information
over a broad temperature range (2-35 × 106 K) and are
available throughout the event. A differential emission measure
analysis reveals that the flux of the Ne IX resonance line is larger
than expected. Various sources of contamination, non-equilibrium and
multi-thermal effects, and possible errors in the atomic physics
calculations are investigated and eliminated as the source of the
unexpected flux, and it is suggested, rather, that the neon abundance
is enhanced in this flare.
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: Determination of coronal abundances of sulphur, calcium and
iron using the yohkoh bragg crystal spectrometer
Authors: Fludra, A.; Culhane, J. L.; Bentley, R. D.; Doschek, G. A.;
Hiei, E.; Phillips, K. J. H.; Sterling, A.; Watanabe, T.
Bibcode: 1993AdSpR..13i.395F
Altcode: 1993AdSpR..13..395F
Using spectra from the Bragg Crystal Spectrometer on Yohkoh we have
derived coronal abundances of sulphur, calcium and iron during several
flares from the ratio of the flux in the resonance line to the nearby
continuum. Multi-thermal effects have been taken into account using
differential emission measure analysis. We have also determined the
abundance of S in cool active regions during a period of very low solar
activity. We compare the coronal abundances of S, Ca and Fe with their
photospheric values.
Title: Dynamics of flaring loops. III - Interpretation of flare
evolution in the emission measure-temperature diagram
Authors: Sylwester, B.; Sylwester, J.; Serio, S.; Reale, F.; Bentley,
R. D.; Fludra, A.
Bibcode: 1993A&A...267..586S
Altcode:
The aim of the paper is to illustrate the application of the
density-temperature diagrams discussed by Jakimiec (1992) to
interpretation of soft X-ray measurements, namely, calcium spectra
recorded by the Solar Maximum Mission Bent Crystal Spectrometer. Using
the emission measure and the temperature values derived for a set
of hydrodynamic flare models discussed in previous papers, we have
obtained and analyzed the (sq rt epsilon-T) counterparts of the (N-T)
diagrams. Inspection of these diagrams reveals that they qualitatively
resemble the (N-T) diagrams. The inclinations of the decay trajectories
make the main difference. Next, we have performed a comparison of the
modeled and observed flare evolutionary trajectories. This comparison
allowed us to identify characteristic cases of evolution during the
decay phase. We have discussed time variations of the heating rate
for selected observed flares. The results of this paper illustrate
how to use the diagnostic diagrams in the interpretation of flare soft
X-ray measurements.
Title: Determination of element abundances using the Yohkoh Bragg
Crystal Spectrometer.
Authors: Fludra, A.; Culhane, J. L.; Bentley, R. D.; Doschek, G. A.;
Hiei, E.; Phillips, K. J. H.; Sterling, A.; Watanabe, T.
Bibcode: 1993uxrs.conf..542F
Altcode: 1993uxsa.conf..542F
No abstract at ADS
Title: Helium-Like Sulphur Emission Lines in Solar Active Regions
and Their Sub-C Class Variability
Authors: Watanabe, Tetsuya; Hiei, Eijiro; Lang, James; Culhane,
J. Leonard; Bentley, Robert D.; Doschek, George A.; Bromage, Barbara
J. I.; Brown, Charles M.; Feldman, Uri; Fludra, Andrzej; Kato, Takako;
Payne, Jeffrey
Bibcode: 1992PASJ...44L.141W
Altcode:
Helium-like sulphur spectra (formation temperature, T_m ~ 18times
10(6) K) from coronal active regions are being obtained by the Bragg
Crystal Spectrometer onboard the Yohkoh mission. The average electron
temperatures of the quiescent active regions deduced from the full-disk
integrated sulphur spectra are 3.5--4 times 10(6) K. The temporal
behavior of the emission lines in the sub-C level events shows that
hot plasmas (T > 10(7) K) can be produced in these weak events.
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: The X Flare of 1991 November 15: Coordinated Mees/Yohkoh
Observations
Authors: Canfield, Richard C.; Hudson, Hugh S.; Leka, K. D.; Mickey,
Donald L.; Metcalf, Thomas R.; Wuelser, Jean-Pierre; Acton, Loren W.;
Strong, Keith T.; Kosugi, Takeo; Sakao, Taro; Tsuneta, Saku; Culhane,
J. Leonard; Phillips, Andrew; Fludra, Andrzej
Bibcode: 1992PASJ...44L.111C
Altcode:
This is a preliminary report on two unique new results from coordinated
observations at Mees Solar Observatory and Yohkoh of the X1.5 flare
of 1991 November 15, using vector magnetograms, Hα imaging spectra,
X-ray images, and X-ray spectra. First, we find a close spatial
relationship between Hα redshifts and X-rays from a flare loop and
its footpoints at a time of large X-ray blueshifts. Second, we find
that impulsive-phase hard X-rays originate in regions that are near,
but not coincident with, the peaks of the vertical electrical current
density distribution in AR 6919.
Title: The Performance of the YOHKOH Bragg Crystal Spectrometer
Authors: Lang, James; Bentley, Robert D.; Brown, Charles M.; Culhane,
J. Leonard; Doschek, George A.; Watanabe, Tetsuya; Hiei, Eijiro;
Deslattes, Richard D.; Fludra, Andrzej; Guttridge, Philip R.; Magraw,
John E.; Payne, Jeffrey; Pike, C. David; Trow, Matthew W.
Bibcode: 1992PASJ...44L..55L
Altcode:
An overview of the Yohkoh Bragg Crystal Spectrometer is given,
complemented by details of the laboratory testing prior to launch. The
in-orbit performance of the instrument is described.
Title: Soft X-ray Blueshifts and Hα Redshifts in the November 15,
1991 X-Class Flare
Authors: Wulser, J. -P.; Acton, L.; Canfield, R.; Culhane, L.; Fludra,
A.; Masuda, S.; Phillips, A.; Sakao, T.
Bibcode: 1992AAS...180.1805W
Altcode: 1992BAAS...24..755W
We analyzed simultaneous Hα line profile observations (from Mees Solar
Observatory), CaXIX line profile observations (from the Bragg Crystal
Spectrometer aboard YOHKOH), and soft- and hard X-ray images (from SXT
and HXT on YOHKOH) of the November 15, 1991 X-class flare. The observed
CaXIX emission shows strong blueshifts very early in the flare. The soft
X-ray images suggest that this blueshifted emission originates from
one or more of three localized soft X-ray bright points. At the same
time, the Hα line profile shows redshifted and blueshifted emission
in several locations. Two Hα redshift kernels are associated with the
two brightest soft X-ray sources. On the basis of their relationship
to the magnetic neutral line and their subsequent development, we
conclude that these Hα redshift kernels are the footpoints of a
single loop, which initially exhibits two soft X-ray bright points
in the loop legs. The results suggest that chromospheric evaporation
is the responsible mechanism for the observed Hα redshifts and CaXIX
blueshifts in the early stage of the flare. The independent hard X-ray
(HXT) and Hα observations both indicate that this chromospheric
evaporation is not associated with strong non-thermal electron
precipitation. The third soft X-ray bright point, the faintest of the
three, is not associated with redshifted Hα emission. This bright spot
develops into a connection between the second Hα redshift kernel,
and another Hα kernel with strong blueshifts. The Hα blueshift is
associated with a mass ejection phenomenon.
Title: A Multi-Thermal Analysis of Two Solar Flares Observed with SMM
Authors: Schmelz, J. T.; Fludra, A.
Bibcode: 1992AAS...180.1804S
Altcode: 1992BAAS...24Q.755S
Two flares observed with the Solar Maximum Mission Flat Crystal
Spectrometer are compared and contrasted. The first (a GOES M1.5 flare)
had a gradual rise and a slow decay, while the second (a GOES M5 flare)
was much more impulsive. Spectra taken simultaneously of seven bright
resonance lines provide information over a broad temperature range
(2 - 35 MK) and are available throughout both flares. Simultaneous
data from the Bent Crystal Spectrometer are also available, making
these events unique in the Solar Maximum Mission database. Elemental
abundance variations, non-thermal line broadening, and Superhot
component existence are investigated with the aid of a differential
emission measure analysis. (*) NAS/NRC Resident Research Associate
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: Iron and calcium abundances in solar flares from the
multi-temperature analysis of X-ray spectra
Authors: Fludra, A.; Bentley, R. D.; Culhane, J. L.; Lemen, J. R.;
Sylwester, J.
Bibcode: 1991AdSpR..11a.155F
Altcode: 1991AdSpR..11Q.155F
A generalized method of calculating the distribution of the emission
measure with temperature (DEM) for optically thin plasma has been
developed. The method simultaneously uses line flux ratios in addition
to line fluxes. When a ratio of lines from the same element is used,
the resulting DEM is independent of this element's abundance. The method
has been applied to derive the absolute abundances of iron in solar
flares from X-ray spectra recorded by the Bent Crystal Spectrometer on
SMM. The iron abundances have been found to vary between flares. The
calcium abundances have also been calculated using the same method and
are found to be in close agreement with the values derived from the
line-to-continuum technique (Lemen et al., 1990 and Sylwester et al.,
1990). The variation of iron and calcium abundances is compared. A
correction to the ionization balance for iron is proposed.
Title: Investigation of turbulent kernels in solar flares
Authors: Jakimiec, J.; Fludra, A.
Bibcode: 1991AdSpR..11e..99J
Altcode: 1991AdSpR..11...99J
Observational evidence that the plasma in hot X-ray sources in solar
flares is highly turbulent is presented. The turbulent flare kernels are
considered to be the main source of the flare energy release. Properties
of kernels in big flares are discussed.
Title: On the Dependence of Solar Flare X-Ray Spectral Line Intensity
Ratios of Highly Ionized Sulfur, Calcium, and Iron on Electron
Temperature, Differential Emission Measure, and Atomic Physics
Authors: Doschek, G. A.; Fludra, A.; Bentley, R. D.; Lang, J.;
Phillips, K. J. H.; Watanabe, T.
Bibcode: 1990ApJ...358..665D
Altcode:
This paper focuses on what can be learned about the emission measure
distribution and certain atomic physics parameters from spectral lines
of highly ionized ions of sulfur, calcium, and iron that appear in
solar flare spectra. The particular lines chosen for analysis allow the
electron temperature to be determined independently of the assumption
of ionization equilibrium. An attempt is made to find emission measure
models based on selected functional dependences of emission measure
on temperature that reproduce the observed temperatures deduced from
spectral line ratios as well as the relative intensities of resonance
lines of different elements.
Title: Investigation of non-uniform heating during the decay phase
of solar flares
Authors: Sylwester, B.; Sylwester, J.; Bentley, R. D.; Fludra, A.
Bibcode: 1990SoPh..126..177S
Altcode:
We have analysed X-ray spectra of 13 solar flares as obtained
by the Bent Crystal Spectrometer (BCS) on the Solar Maximum
Mission. In particular, we have examined the observed ratio of
TFe/TCa where TFe and TCa
are the temperatures obtained from the FeXXV and CaXIX spectra,
respectively. In order to simplify the investigation we have analysed
only flares which reach quasi-steady-state during the decay. It
turned out that the observed ratios cannot be explained by a model
consisting of a single, uniformly heated loop, with a constant or
variable cross-sectional area. We propose that this problem may be
solved by introducing some distribution of the heating function across
the flaring loop. This model has been tested by detailed calculations.
Title: The Decay Phase of Three Large Solar Flares
Authors: Fludra, A.; Bentley, R. D.; Culhane, J. L.; Jakimiec, J.;
Lemen, J. R.; Sylwester, J.; Moorthy, S. T.
Bibcode: 1990PDHO....7..266F
Altcode: 1990ESPM....6..266F; 1990dysu.conf..266F
No abstract at ADS
Title: Study of Non-Uniform Heating in Solar Flares
Authors: Sylwester, B.; Sylwester, J.; Jakimiec, J.; Serio, S.; Reale,
F.; Bentley, R. D.; Fludra, A.
Bibcode: 1990PDHO....7..255S
Altcode: 1990ESPM....6..255S; 1990dysu.conf..255S
The authors have analyzed the ratios of the temperatures derived from Fe
and Ca spectra (TFe/TCa) for the rising phase of
11 solar flares. Corresponding hydrodynamic models have been calculated
and the obtained results are compared with the observational data for
selected flares.
Title: Turbulent and Directed Plasma Motions in Solar Flares
Authors: Fludra, A.; Lemen, J. R.; Jakimiec, J.; Bentley, R. D.;
Sylwester, J.
Bibcode: 1989ApJ...344..991F
Altcode:
An improved method for fitting asymmetric soft X-ray line profiles
from solar flares is presented. A two-component model is used where one
component represents the total emission from directed upflow plasma and
the other the emission from the plasma at rest. Unlike previous methods,
the width of the moving component is independent from that of the
stationary component. Time variations of flare plasma characteristics
(i.e., temperature, emission measure of moving and stationary plasma,
upflow and turbulent velocities) are derived from the Ca XIX and Fe XXV
spectra recorded by the Bent Crystal Spectrometer on the Solar Maximum
Mission. The fitting technique provides a statistical estimation
for the uncertainties in the fitting parameters. The relationship
between the directed and turbulent motions has been studied, and
a correlation of the random and directed motions has been found in
some flares with intensive plasma upflows. Mean temperatures of the
upflowing and stationary plasmas are compared for the first time from
ratios of calcium to iron X-ray line intensities. Finally, evidence
for turbulent motions and the possibility of plasma upflow late into
the decay phase is presented and discussed.
Title: Coronal Activity in F-, G-, and K-Type Stars. III. The
Coronal Differential Emission Measure Distribution of Capella,
sigma 2 Coronae Borealis, and Procyon
Authors: Lemen, J. R.; Mewe, R.; Schrijver, C. J.; Fludra, A.
Bibcode: 1989ApJ...341..474L
Altcode:
EXOSAT soft X-ray spectra of three binary systems of cool stars
are analyzed: Capella (G6 III + F9 III), Sigma-squared CrB (F8 V +
G1 V), and Procyon (F5 IV-V + DF). The EXOSAT transmission grating
spectrometer permits the study of individual spectral lines and line
complexes between 10 and 200 A with approximately 3 A resolution. First
it is demonstrated that the spectra can be described reasonably well
by a two-temperature model corona. Then the assumption that only two
temperatures exist in the stellar coronas is relaxed and differential
emission measure distributions are derived from the three spectra. The
results from the multithermal modeling are consistent with those of
the two-temperature models: emission from the coronas of each of the
three stars is dominated by plasma in two relative narrow temperature
intervals. These intervals are centered on 5 MK and 25 MK in the cases
of Capella and Sigma-squared CrB, and 0.6 MK and 3 MK in the case of
Procyon. The implications of the results for the structure of stellar
coronas are briefly discussed.
Title: Flare Dynamics
Authors: Zarro, D.; Alexander, D.; Fludra, A.; Emslie, G.; Gurman, J.;
Graeter, M.; Li, P.; Phillips, K.; Saba, J.; Schmieder, B.; Slater,
G.; Wulser, J. P.; Watanabe, T.; Dulk, G.; MacKinnon, A.; McClements,
K.; Spicer, D.
Bibcode: 1989tnti.conf....2Z
Altcode:
No abstract at ADS
Title: Investigations of turbulent and directed motions in solar
flares
Authors: Lemen, J. R.; Fludra, A.; Jakimiec, J.
Bibcode: 1988AdSpR...8k.161L
Altcode: 1988AdSpR...8..161L
During the past solar maximum, spectrally resolved observations
obtained with the P78-1, Hinotori, and Solar Maximum Mission (SMM)
satellites have revealed strongly asymmetric line profiles as well as
symmetrically broadened (in excess of thermal broadening) line profiles
during the impulsive phase of most solar flares. These line profiles
are the result of emissions from plasmas which have high upflow bulk
velocities in the flaring loop added to the emission from the plasma
which has a relatively low bulk velocity. The large observed symmetric
broadening is the result of random ionic or turbulent motions within
the flaring loop. Most observations have been made in soft X-rays
of the 107 K and hotter plasma, although, similar effects
have been noted in UV emissions. The importance of these observations
is clear: the soft X-ray emission represents the thermal response
of the rapidly heated flare plasma, and a proper understanding of
these emissions necessarily constraints the interpretation for the
heating source. For example, plasma heated by fast electrons or thermal
conduction fronts may produce different directed and turbulent motions
which could be detected in the observed X-ray spectra. We present a
new method for fitting these asymmetric spectra which we have applied
to over 40 flares observed with the Bent Crystal Spectrometer (BCS)
on board the SMM. Correlations between turbulent and directed motions
are discussed and we infer the temperature of the upflowing component
separately from the stationary component from ratios of Ca xix and Fe
xxv line intensities.
Title: Intercomparison of flare observations with two SMM
spectrometers: BCS and HXIS
Authors: Jakimiec, J.; Prés, P.; Fludra, A.; Bentley, R. D.; Lemen,
J. R.; Mewe, R.; Schrijver, J.; Sylwester, J.
Bibcode: 1988AdSpR...8k.231J
Altcode: 1988AdSpR...8..231J
The temperature diagnostics of hot flare plasma, obtained from two
Solar Maximum Mission instruments (HXIS and BCS), is compared. A good
general agreement between the HXIS and BCS-Fe temperature scales has
been found. However, for the growth phase of some flares a systematic
difference, THXIS>TFe, has been found,
which is not likely to be due to the typical non-thermal electron
beams. Possible explanation of this effect is briefly discussed.
Title: Investigations of Turbulent and Direct Motions in Solar Flares
Authors: Bentley, R. D.; Fludra, A.; Lemen, J. R.; Jakimiec, J.;
Sylwester, J.
Bibcode: 1987BAAS...19R.750B
Altcode:
No abstract at ADS
Title: Evidence for Expanding Loop Geometries in Stellar Coronae
Authors: Mewe, R.; Lemen, J. R.; Schrijver, C. J.; Fludra, A.
Bibcode: 1987LNP...291...60M
Altcode: 1987csss....5...60M; 1987LNP87.291...60M
No abstract at ADS
Title: LEBAN diagnostic for basic flaring loop parameters.
Authors: Sylwester, B.; Sylwester, J.; Jakimiec, J.; Fludra, A.;
Peres, G.; Serio, S.
Bibcode: 1987PAICz..66..229S
Altcode: 1987eram....1..229S
The authors describe the diagnostic procedure called LEBAN which may
be helpful in deriving basic geometrical loop parameters. "Palermo
Code" hydrodynamic flare model calculations have been used to test
reliability of the procedure.
Title: Comparison of Three Methods Used for Calculation of the
Differential Emission Measure
Authors: Fludra, A.; Sylwester, J.
Bibcode: 1986SoPh..105..323F
Altcode:
A comparison of three methods used for multi-temperature analysis of
solar X-ray spectra is presented. The modified method of conjugate
gradients appears to be very efficient for minimizing χ2
subject to regularizing (smoothing) constraints. The Withbroe-Sylwester
method also ensures good fits, particularly when computations are
carried out in wide temperature intervals. Both methods are much faster
than the Maximum Entropy method and yield models with an entropy close
to that of the Maximum Entropy models. The reliability of revealing
the shape of the differential emission measure is discussed. It is
shown that the total emission measure and the plasma thermal energy
content can be calculated to within a few percent.
Title: Density-temperature diagnostics of 31 August double flare
Authors: Sylwester, J.; Jakimiec, J.; Fludra, A.; Leman, J. R.
Bibcode: 1986CoSka..15..153S
Altcode:
No abstract at ADS
Title: Physical conditions in a large flare loop on Nov. 1980 derived
from SMM observations
Authors: Sylwester, B.; Sylwester, J.; Jakimiec, J.; Fludra, A.;
Bentley, R. D.; Schrijver, J.
Bibcode: 1986CoSka..15..145S
Altcode:
The authors present the study of a large X-ray loop related to the
H-alpha 2N flare close to the center of the solar disc. Data from Solar
Maximum Mission have been used in the analysis. The authors have derived
the temperatures, densities and the geometrical parameters (length,
diameter) for a hot core and for a cooler envelope of the flaring loop.
Title: Investigations of turbulent motions and particle acceleration
in solar flares
Authors: Jakimiec, J.; Fludra, A.; Lemen, J. R.; Dennis, B. R.;
Sylwester, J.
Bibcode: 1986AdSpR...6f.191J
Altcode: 1986AdSpR...6..191J
Investigations of X-ray spectra of solar flares show that intense
random (turbulent) motions are present in hot flare plasma. Here we
argue that the turbulent motions are of great importance for flare
development. They can efficiently enhance flare energy release and
accelerate particles to high energies.
Title: On the quasi-homologous limb flares observed on 3 August 1981
Authors: Dezsö, L.; Fludra, A.; Gerlei, O.; Jakimiec, J.; Kovács,
Á.; Pettauer, T.
Bibcode: 1986AdSpR...6f..65D
Altcode: 1986AdSpR...6...65D
Five limb flares and a large surge, triggered obviously by the second
flare, have been investigated on the basis of Hα on- and off-band
heliograms and X-ray data obtained during a 6-hour period on 3 August
1981. In addition, in the vicinity of the flare location the sunspots
and filaments were followed by observations over several of the former
days too. Emphasis was layed on the ascending motion in the course of
flare build-up and on the time evolution of the flare energy release
using GOES observations in the case of the first and second flares. It
was found that their ascending Hα flare kernels, which reached to a
height of 20-25×103 km, have been the main center both
the source and the starting points of flare loops and perhaps also
the main site of the soft X-ray emissions.
Title: Differential emission measure analysis of hot-flare plasma
from solar-maximum mission X-ray data
Authors: Jakimiec, J.; Sylwester, J.; Lemen, J. R.; Mewe, R.; Bentley,
R. D.; Fludra, A.; Schrijver, J.; Sylwester, B.
Bibcode: 1984AdSpR...4g.203J
Altcode: 1984AdSpR...4..203J
We have investigated differential emission measure (DEM) distribution
of hot flare plasma (T>10 MK) using SMM X-ray data from Bent Crystal
Spectrometer (BCS) and Hard X-ray Imaging Spectrometer (HXIS). We have
found that the analysis provide a very sensitive test of consistency
of observational data coming from different instruments or different
channels of the same instrument. This has allowed to eliminate some
systematic differences contained in the analysed data. Typical
examples of the DEM distribution are discussed. It is stressed that
these improvements in the multitemperature flare diagnostics are very
important for the discussion of flare energetics.