wilhelm

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Author name code: wilhelm
ADS astronomy entries on 2022-09-14
author:"Wilhelm, Klaus"

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Title: Anomalous Sun Flyby of 1I/2017 U1 (`Oumuamua)
Authors: Wilhelm, Klaus; Dwivedi, Bhola
2020Galax...8...83W Altcode:
The findings of Micheli et al. (Nature 2018, 559, 223-226) that
1I/2017 U1 (`Oumuamua) showed anomalous orbital accelerations have
motivated us to apply an impact model of gravity in search for an
explanation. A small deviation from the 1/r potential, where r is the
heliocentric distance, is expected for the gravitational interaction of
extended bodies as a consequence of this model. This modification of the
potential results from an offset of the effective gravitational centre
from the geometric centre of a spherically symmetric body. Applied to
anomalous Earth flybys, the model accounts for energy gains relative to
an exact Kepler orbit and an increased speed of several spacecraft. In
addition, the flat rotation profiles of eight disk galaxies could
be explained, as well as the anomalous perihelion advances of the
inner planets and the asteroid Icarus. The solution in the case of
`Oumuamua is also based on the proposal that the offset leads to an
approach and flyby trajectory different from a Kepler orbit without
postulating cometary activity. As a consequence, an adjustment of the
potential and centrifugal orbital energies can be envisaged outside
the narrow uncertainty ranges of the published post-perihelion data
without a need to re-analyse the original data. The observed anomalous
acceleration has been modelled with respect to the orbit solutions
JPL 16 and “Pseudo-MPEC” for 1I/`Oumuamua.

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Title: On the radial acceleration of disc galaxies
Authors: Wilhelm, Klaus; Dwivedi, Bhola N.
2020MNRAS.494.4015W Altcode: 2020MNRAS.tmp.1103W; 2020arXiv200511316W
The physical processes defining the dynamics of disc galaxies are
still poorly understood. Hundreds of articles have appeared in the
literature over the last decades without arriving at an understanding
within a consistent gravitational theory. Dark matter (DM) scenarios
or a modification of Newtonian dynamics (MOND) are employed to model
the non-Keplerian rotation curves in most of the studies, but the
nature of DM and its interaction with baryonic matter remains an open
question and MOND formulates a mathematical concept without a physical
process. We have continued our attempts to use the impact theory of
gravitation for a description of the peculiar acceleration and velocity
curves and have considered five more galaxies. Using published data
of the galaxies NGC 3198, NGC 2403, NGC 1090, UGC 3205, and NGC 1705,
it has been possible to find good fits without DM for the observed disc
velocities and, as example, also for the extraplanar matter of NGC 3198.

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Title: Impact Models of Gravitational and Electrostatic Forces
Authors: Wilhelm, Klaus; Dwivedi, Bhola N.
2020ptgy.book....5W Altcode:
No abstract at ADS

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Title: Plasma Flows in the Cool Loop Systems
Authors: Rao, Yamini K.; Srivastava, Abhishek K.; Kayshap, Pradeep;
Wilhelm, Klaus; Dwivedi, Bhola N.
2019ApJ...874...56R Altcode: 2019arXiv190205237R
We study the dynamics of low-lying cool loop systems for three data sets
as observed by the Interface Region Imaging Spectrograph. Radiances,
Doppler shifts, and line widths are investigated in and around
observed cool loop systems using various spectral lines formed between
the photosphere and transition region (TR). Footpoints of the loop
threads are either dominated by blueshifts or redshifts. The cospatial
variation of velocity above the blueshifted footpoints of various
loop threads shows a transition from very small upflow velocities
ranging from (-1 to +1) {km} {{s}} -1 in the Mg II k line
(2796.20 Å formation temperature: {log}(T/{{K}})=4.0) to the high
upflow velocities from (-10 to -20) {km} {{s}} -1 in Si
IV. Thus, the transition of the plasma flows from redshift (downflows)
to blueshift (upflows) is observed above the footpoints of these loop
systems in the spectral line C II (1334.53 Å log(T/{{K}}) = 4.3)
lying between Mg II k and Si IV (1402.77 Å {log}(T/{{K}})=4.8). This
flow inversion is consistently observed in all three sets of the
observational data. The other footpoint of the loop system always
remains redshifted, indicating downflowing plasma. The multispectral
line analysis in the present paper provides a detailed scenario of
the plasma flow’s inversions in cool loop systems leading to the
mass transport and their formation. The impulsive energy release due
to small-scale reconnection above the loop footpoint seems to be the
most likely cause for sudden initiation of the plasma flows evident
at TR temperatures.

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Title: Gravitational redshift and the vacuum index of refraction
Authors: Wilhelm, Klaus; Dwivedi, Bhola N.
2019Ap&SS.364...26W Altcode:
A physical process of the gravitational redshift was described in
an earlier paper (Wilhelm and Dwivedi, New Astron. 31:8, 2014). This
process did not require any information for the emitting atom neither
on the local gravitational potential U nor on the speed of light
c. Although it could be shown that the correct energy shift of the
emitted photon resulted from energy and momentum conservation principles
and the speed of light at the emission site, it was not obvious how
this speed is controlled by the gravitational potential. The aim of
this paper is to describe a physical process that can accomplish
this control. We determine the local speed of light c by deducing
a gravitational index of refraction nG as a function of
the potential U assuming a specific aether model, in which photons
propagate as solitons. Even though an atom cannot locally sense the
gravitational potential U (cf. Müller et al., Nature 467:E2, 2010) the
gravitational redshift will nevertheless be determined by U (cf. Wolf
et al., Nature 467:E1, 2010)—mediated by the local speed of light c.

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Title: A physical process of the radial acceleration of disc galaxies
Authors: Wilhelm, Klaus; Dwivedi, Bhola N.
2018MNRAS.474.4723W Altcode:
An impact model of gravity designed to emulate Newton's law
of gravitation is applied to the radial acceleration of disc
galaxies. Based on this model (Wilhelm et al. 2013), the rotation
velocity curves can be understood without the need to postulate any
dark matter contribution. The increased acceleration in the plane
of the disc is a consequence of multiple interactions of gravitons
(called `quadrupoles' in the original paper) and the subsequent
propagation in this plane and not in three-dimensional space. The
concept provides a physical process that relates the fit parameter
of the acceleration scale defined by McGaugh et al. (2016) to the
mean free path length of gravitons in the discs of galaxies. It may
also explain the gravitational interaction at low acceleration levels
in MOdification of the Newtonian Dynamics (MOND, Milgrom 1983, 1994,
2015, 2016). Three examples are discussed in some detail: the spiral
galaxies NGC 7814, NGC 6503 and M 33.

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Title: Understanding disk galaxy rotation velocities without dark
matter contribution--a physical process for MOND?
Authors: Wilhelm, K.; Dwivedi, B. N.
2017arXiv170902387W Altcode:
An impact model of gravity designed to emulate Newton's law
of gravitation is applied to the radial acceleration of disk
galaxies. Based on this model (Wilhelm et al. 2013), the rotation
velocity curves can be understood without the need to postulate any
dark matter contribution. The increased acceleration in the plane of
the disk is a consequence of multiple interactions of gravitons (called
"quadrupoles" in the original paper) and the subsequent propagation
in this plane and not in three-dimensional space. The concept provides
a physical process that relates the fit parameter of the acceleration
scale defined by McGaugh et al. (2016) to the mean free path length of
gravitons in the disks of galaxies. It may also explain the modification
of the gravitational interaction at low acceleration levels in MOND
(Milgrom 1983, 1994, 2015, 2016). Three examples are discussed in some
detail: The spiral galaxies NGC 7814, NGC 6503 and M 33.

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Title: Hydrogen Ly-α and Ly-β full Sun line profiles observed with
SUMER/SOHO (1996-2009)
Authors: Lemaire, P.; Vial, J. -C.; Curdt, W.; Schühle, U.;
Wilhelm, K.
2015A&A...581A..26L Altcode:
Context. Accurate hydrogen spectra emitted by the entire solar disc in
the Ly-α and Ly-βlines are valuable for deriving the distribution and
the behaviour of atomic hydrogen in the heliosphere, for understanding
the UV emissions of solar type stars better, and finally for estimating
the solar energy input that mainly initiates the chemical processes
occurring in the planetary and cometary outer atmospheres. Aims:
In this paper we want to accurately determine the irradiance solar
spectral profiles of Ly-α and Ly-β and their evolution through the
solar activity cycle 23. Methods: The SUMER/SOHO spectrometer is
a slit spectrometer that is only able to analyse a small part of the
solar image. Consequently, we used the scattered light properties of
the telescope to obtain average spectra over the solar disc. Then the
profile is calibrated using the SOLSTICE/UARS and TIMED/SEE irradiance
spectra. Results: We obtained a set of irradiance Ly-α and
Ly-β solar spectra with a 0.002 nm resolution through the solar
activity cycle 23. In each line a relation between the integrated
profile and the line centre intensity was obtained.Knowing the line
irradiance, it is possible to deduce the central line profile intensity,
a critical input into the interplanetary and planetary oxygen and
hydrogen fluorescent processes. Conclusions: The observation
of H i Ly-α and Ly-β line profiles by SUMER/SOHO during the cycle
23 allows analysis of the evolution of their characteristics and
accurate determination of UV radiation input into the solar system. Profiles are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/581/A26">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/581/A26</A>

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Title: VizieR Online Data Catalog: Sun hydrogen Lyman irradiance
lines profiles (Lemaire+, 2015)
Authors: Lemaire, P.; Vial, J. -C.; Curdt, W.; Schuhle, U.; Wilhelm, K.
2015yCat..35810026L Altcode:
Set of irradiance Ly-α and Ly-β solar spectra with a 0.002nm
resolution through the solar activity cycle 23. The wavelength distance
from line center is given every 0.001nm. (2 data files).

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Title: Anomalous Earth flybys of spacecraft
Authors: Wilhelm, Klaus; Dwivedi, Bhola N.
2015Ap&SS.358...18W Altcode:
A small deviation from the potential is expected for the gravitational
interaction of extended bodies. It is explained as a consequence
of a recently proposed gravitational impact model (Wilhelm et
al. in Astrophys. Space Sci. 343:135-144, 2013) and has been
applied to anomalous perihelion advances by Wilhelm and Dwivedi
(New Astron. 31:51-55, 2014). The effect—an offset of the effective
gravitational centre from the geometric centre of a spherical symmetric
body—might also be responsible for the observed anomalous orbital
energy gains and speed increases during Earth flybys of several
spacecraft. However, close flybys would require detailed considerations
of the orbit geometry. In this study, an attempt is made to explain
the anomalous Earth flybys of the Galileo, NEAR Shoemaker and Rosetta
spacecraft.

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Title: Solar Coronal Plumes and the Fast Solar Wind
Authors: Dwivedi, Bhola N.; Wilhelm, Klaus
2015JApA...36..185D Altcode: 2015JApA..tmp...14D; 2015arXiv150601700D
The spectral profiles of the coronal Ne viii line at 77 nm have
different shapes in quiet-Sun regions and Coronal Holes (CHs). A single
Gaussian fit of the line profile provides an adequate approximation in
quiet-Sun areas, whereas, a strong shoulder on the long-wavelength side
is a systematic feature in CHs. Although this has been noticed since
1999, no physical reason for the peculiar shape could be given. In an
attempt to identify the cause of this peculiarity, we address three
problems that could not be conclusively resolved, in a review article
by a study team of the International Space Science Institute (ISSI)
(Wilhelm et al. 2011): (1) The physical processes operating at the
base and inside of plumes, as well as their interaction with the
Solar Wind (SW). (2) The possible contribution of plume plasma to the
fast SW streams. (3) The signature of the First-Ionization Potential
(FIP) effect between plumes and inter-plume regions (IPRs). Before
the spectroscopic peculiarities in IPRs and plumes in Polar Coronal
Holes (PCHs) can be further investigated with the instrument Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) aboard the Solar
and Heliospheric Observatory (SOHO), it is mandatory to summarize
the results of the review to place the spectroscopic observations
into context. Finally, a plume model is proposed that satisfactorily
explains the plasma flows up and down the plume field lines and leads
to the shape of the neon line in PCHs.

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Title: On the potential energy in a gravitationally bound two-body
system
Authors: Wilhelm, Klaus; Dwivedi, Bhola N.
2015NewA...34..250W Altcode:
The potential energy problem in a gravitationally bound two-body system
is studied in the framework of a recently proposed impact model of
gravity (Wilhelm et al., 2013). The concept of a closed system has been
modified, before the physical processes resulting in the liberation
of the potential energy can be described. The energy is extracted from
the background flux of hypothetical interaction entities.

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Title: Photon in a cavity - a Gedankenexperiment
Authors: Wilhelm, Klaus; Dwivedi, Bhola N.
2015NewA...34..211W Altcode:
The inertial and gravitational mass of electromagnetic radiation
(i.e., a photon distribution) in a cavity with reflecting walls has
been treated by many authors for over a century. After many contending
discussions, a consensus has emerged that the mass of such a photon
distribution is equal to its total energy divided by the square of
the speed of light. Nevertheless, questions remain unsettled on the
interaction of the photons with the walls of the box. In order to
understand some of the details of this interaction, a simple case of
a single photon with an energy Eν=h ν bouncing up and
down in a static cavity with perfectly reflecting walls in a constant
gravitational field g, constant in space and time, is studied and
its contribution to the weight of the box is determined as a temporal
average.

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Title: Secular perihelion advances of the inner planets and asteroid
Icarus
Authors: Wilhelm, Klaus; Dwivedi, Bhola N.
2014NewA...31...51W Altcode:
A small effect expected from a recently proposed gravitational
impact model (Wilhelm et al., 2013) is used to explain the remaining
secular perihelion advance rates of the planets Mercury, Venus, Earth,
Mars, and the asteroid (1566) Icarus-after taking into account the
disturbances related to Newton’s Theory of Gravity. Such a rate was
discovered by Le Verrier (1859) for Mercury and calculated by Einstein
(1915, 1916) in the framework of his General Theory of Relativity
(GTR). Accurate observations are now available for the inner Solar
System objects with different orbital parameters. This is important,
because it allowed us to demonstrate that the quantitative amount of
the deviation from an 1/r potential is-under certain conditions-only
dependent on the specific mass distribution of the Sun and not on the
characteristics of the orbiting objects and their orbits. A displacement
of the effective gravitational from the geometric centre of the Sun by
about 4400 m towards each object is consistent with the observations
and explains the secular perihelion advance rates.

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Title: On the gravitational redshift
Authors: Wilhelm, Klaus; Dwivedi, Bhola N.
2014NewA...31....8W Altcode: 2013arXiv1307.0274W
The study of the gravitational redshift-a relative wavelength increase
of ≈2×10-6 was predicted for solar radiation by Einstein
in 1908-is still an important subject in modern physics. In a dispute
whether or not atom interferometry experiments can be employed for
gravitational redshift measurements, two research teams have recently
disagreed on the physical cause of the shift. Regardless of any
discussion on the interferometer aspect-we find that both groups of
authors miss the important point that the ratio of gravitational to
the electrostatic forces is generally very small. For instance, the
ratio of the gravitational force acting on an electron in a hydrogen
atom situated in the Sun’s photosphere to the electrostatic force
between the proton and the electron in such an atom is approximately
3×10-21. A comparison of this ratio with the predicted
and observed solar redshift indicates a discrepancy of many orders of
magnitude. With Einstein’s early assumption that the frequencies
of spectral lines depend only on the generating ions themselves as
starting point, we show that a solution can be formulated based on a
two-step process in analogy with Fermi’s treatment of the Doppler
effect. It provides a sequence of physical processes in line with the
conservation of energy and momentum resulting in the observed shift
and does not employ a geometric description. The gravitational field
affects the release of the photon and not the atomic transition. The
control parameter is the speed of light. The atomic emission is
then contrasted with the gravitational redshift of matter-antimatter
annihilation events.

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Title: The SUMER Data in the SOHO Archive
Authors: Curdt, W.; Germerott, D.; Wilhelm, K.; Schühle, U.; Teriaca,
L.; Innes, D.; Bocchialini, K.; Lemaire, P.
2014SoPh..289.2345C Altcode: 2013arXiv1309.1314C
We have released an archive of all observational data of the VUV
spectrometer Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) on SOHO that have been acquired until now. The operational
phase started with `first light' observations on 27 January 1996 and
will end in 2014. Future data will be added to the archive when they
become available. The archive consists of a set of raw data (Level
0) and a set of data that are processed and calibrated to the best
knowledge we have today (Level 1). This communication describes step
by step the data acquisition and processing that has been applied in an
automated manner to build the archive. It summarizes the expertise and
insights into the scientific use of SUMER spectra that has accumulated
over the years. It also indicates possibilities for further enhancement
of the data quality. With this article we intend to convey our own
understanding of the instrument performance to the scientific community
and to introduce the new, standard FITS-format database.

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Title: Increase of the mean Sun-Earth distance caused by a secular
mass accumulation
Authors: Wilhelm, Klaus; Dwivedi, Bhola N.
2013Ap&SS.347...41W Altcode: 2013Ap&SS.tmp..211W
Based on many planetary observations between the years 1971 and 2003,
Krasinsky and Brumberg (Celest. Mech. Dyn. Astron. 90:267-288, 2004)
have estimated a rate of increase in the mean Sun-Earth distance of
(15±4) m per century. Together with other anomalous observations in
the solar system, this increase appears to be unexplained (Lämmerzahl
et al. in Astrophys. Space Sci. Lib., vol. 349, pp. 75-101, 2008). We
explain these findings by invoking a recently proposed gravitational
impact model (Wilhelm et al. in Astrophys. Space Sci. 343:135-144, 2013)
that implies a secular mass increase of all massive bodies. This allows
us to formulate a quantitative understanding of the effect within the
parameter range of the model with a mass accumulation rate of the Sun of
(6.4±1.7)×1010 kg s-1.

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Title: Observing Photons in Space: A Guide to Experimental Astronomy
Authors: Huber, M. C. E.; Pauluhn, A.; Culhane, J. L.; Timothy, J. G.;
Wilhelm, K.; Zehnder, A.
2013opsg.book.....H Altcode:
No abstract at ADS

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Title: Observing Photons in Space: A Guide to Experimental Spae
Astronomy
Authors: Huber, M. C. E.; Pauluhn, A.; Culhane, J. L.; Timothy, J. G.;
Wilhelm, K.; Zehnder, A.
2013ops..book.....H Altcode:
No abstract at ADS

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Title: An impact model of Newton's law of gravitation
Authors: Wilhelm, Klaus; Wilhelm, Horst; Dwivedi, Bhola N.
2013Ap&SS.343..135W Altcode: 2012Ap&SS.tmp..315W
The far-reaching gravitational force—in the approximation of Newton's
law of gravitation—is described by a heuristic model with hypothetical
massless particles propagating at the speed of light in vacuum and
transferring momentum and energy between physical entities through
interactions on a local basis. The model has some similarities with
the impact theory presented by Nicolas Fatio de Duillier to the Royal
Society in 1690. Objections raised against this idea are dispelled
by invoking the Special Theory of Relativity, considering non-local
interactions, and replacing the shielding concept by a secular mass
increase of massive bodies. Some consequences and applications of the
model are discussed.

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Title: Gravity, massive particles, photons and Shapiro delay
Authors: Wilhelm, Klaus; Dwivedi, Bhola N.
2013Ap&SS.343..145W Altcode: 2012Ap&SS.tmp..347W
An impact model of gravity designed to emulate Newton's law of
gravitation is applied to particles with relative motions at slow and
relativistic speeds. Based on this model, a gravitational interaction
mode is then conceived between photons and massive particles. This
implies a deflection perpendicular to the propagation direction of
a photon twice as large as expected from the mass-energy relation of
photons—in accordance with observations and the General Theory of
Relativity. The longitudinal interaction is compatible with the energy
and momentum conservation principles applied to massless entities,
and the results are consistent with the observed Shapiro delay.

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Title: SUMER Observations of Coronal-Hole Temperatures
Authors: Wilhelm, Klaus
2013mspc.book...57W Altcode:
No abstract at ADS

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Title: SUMER Observations of Coronal-Hole Temperatures
Authors: Wilhelm, Klaus
2012SSRv..172...57W Altcode: 2010SSRv..tmp..181W
Observations of emission lines in the vacuum-ultraviolet spectral range
with calibrated instrumentation provide crucial information on the
prevailing plasma temperatures in the solar atmosphere. Coronal-hole
temperatures measured by the SUMER spectrometer on SOHO will
be presented in this contribution. Electron temperatures can be
estimated from the formation temperatures of the observed emission
lines. Line-ratio and emission-measure analyses, however, offer
higher accuracies. Typical electron temperatures at altitudes of
H&lt;200 Mm in coronal holes are below 1 MK in bright structures—the
coronal plumes—with higher values in darker areas—the inter-plume
regions. Line-width measurements yield effective ion temperatures,
which are much higher than the electron temperatures. Observations
of line profiles emitted from species with different masses allow a
separation of the effective temperatures into ion temperatures and
unresolved non-thermal motions along the line of sight.

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Title: An explanation of the Pioneer anomaly involving accelerated
atomic clocks
Authors: Wilhelm, K.; Dwivedi, B. N.
2011ASTRA...7..487W Altcode:
The Pioneer anomaly stands for unexplained frequency shifts of the
Doppler radio-tracking signals received at the ground stations from
the Pioneer 10 and 11 spacecraft in disagreement with expectations
based on model calculations. We consider here observations of Pioneer
10 at heliocentric distances between 40 ua and 70.5 ua over a time
interval of 11.55 years from 1987 to 1998. The anomaly has been
interpreted in the literature either as a Doppler shift caused by an
apparent spacecraft deceleration not accounted for by known effects,
or as an unexpected clock acceleration of the frequency standards
at the ground stations. The reasons for the anomalous behaviour are
not understood in both cases. Based on a gravitational impact model -
requiring a secular mass increase of all massive bodies - a solution
is proposed that implies a clock acceleration with a value close to
that of the Hubble constant.

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Title: Morphology, dynamics and plasma parameters of plumes and
inter-plume regions in solar coronal holes
Authors: Wilhelm, K.; Abbo, L.; Auchère, F.; Barbey, N.; Feng, L.;
Gabriel, A. H.; Giordano, S.; Imada, S.; Llebaria, A.; Matthaeus,
W. H.; Poletto, G.; Raouafi, N. -E.; Suess, S. T.; Teriaca, L.; Wang,
Y. -M.
2011A&ARv..19...35W Altcode: 2011arXiv1103.4481W
Coronal plumes, which extend from solar coronal holes (CH) into the high
corona and—possibly—into the solar wind (SW), can now continuously
be studied with modern telescopes and spectrometers on spacecraft,
in addition to investigations from the ground, in particular, during
total eclipses. Despite the large amount of data available on these
prominent features and related phenomena, many questions remained
unanswered as to their generation and relative contributions to
the high-speed streams emanating from CHs. An understanding of the
processes of plume formation and evolution requires a better knowledge
of the physical conditions at the base of CHs, in plumes and in the
surrounding inter-plume regions. More specifically, information is
needed on the magnetic field configuration, the electron densities
and temperatures, effective ion temperatures, non-thermal motions,
plume cross sections relative to the size of a CH, the plasma bulk
speeds, as well as any plume signatures in the SW. In spring 2007, the
authors proposed a study on `Structure and dynamics of coronal plumes
and inter-plume regions in solar coronal holes' to the International
Space Science Institute (ISSI) in Bern to clarify some of these aspects
by considering relevant observations and the extensive literature. This
review summarizes the results and conclusions of the study. Stereoscopic
observations allowed us to include three-dimensional reconstructions
of plumes. Multi-instrument investigations carried out during several
campaigns led to progress in some areas, such as plasma densities,
temperatures, plume structure and the relation to other solar phenomena,
but not all questions could be answered concerning the details of
plume generation process(es) and interaction with the SW.

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Title: Quantitative solar spectroscopy
Authors: Wilhelm, K.
2010AN....331..502W Altcode:
Quantitative solar spectroscopy must be based on calibrated
instrumentation. The basic requirement of a calibration, i.e.,
a comparison between the instrument under test and a primary
laboratory standard through appropriate procedures, will be briefly
reviewed, and the application to modern space instruments will be
illustrated. Quantitative measurements of spectral radiances with
high spectral and spatial resolutions as well as spectral irradiances
yield detailed information on temperatures, electron densities,
bulk and turbulent motions, element abundances of plasma structures
in various regions of the solar atmosphere - from the photosphere to
the outer corona and the solar wind. The particular requirements for
helioseismology and magnetic-field observations will not be covered
in any depth in this review. Calibration by a laboratory standard
is necessary, but not sufficient, because an adequate radiometric
stability can only be achieved together with a stringent cleanliness
concept that rules out a contamination of the optical system and
the detectors as much as possible. In addition, there is a need for
calibration monitoring through inter-calibration and other means.

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Title: Study of the structures of the explosive events in the UV
Authors: Niembro-Hernandez, R. T.; Mendoza-Torres, J. E.; Wilhelm, K.
2010IAUS..264..276N Altcode:
We analyze Si iv 139.37 nm emission line during solar Explosive Events
(EE) near the center of the solar disk with the aim to study the
structure of the sources of EEs observed at the VUV. The observations
were made by SUMER, on board SoHO, with a raster regime of six EW
positions that allowed us to identify the times and EW, NS positions
of the maximum amplitude of each EE. Based on one dimensional NS
distributions at three different wavelengths (blue, central and red)
for times around each maximum we have identified three different shapes
of the sources. Also, It was found that the maximum at the blue wing
is attained after the maxima at red and central wavelengths.

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Title: Spectroscopic Diagnostics of Polar Coronal Plumes
Authors: Wilhelm, K.; Dwivedi, B. N.; Curdt, W.
2010ASSP...19..454W Altcode: 2010mcia.conf..454W; 2009arXiv0902.4167W
Polar coronal plumes seen during solar eclipses can now be studied
with space-borne telescopes and spectrometers. We briefly discuss
such observations from space with a view to understanding their plasma
characteristics. Using these observations, especially from SUMER/SOHO,
but also from EUVI/STEREO, we deduce densities, temperatures, and
abundance anomalies in plumes and inter-plume regions, and discuss
their implications for better understanding of these structures in
the Sun's atmosphere.

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Title: Photons - from source to detector
Authors: Wilhelm, Klaus; Frohlich, Claus
2010ISSIR...9...23W Altcode:
The central theme of the book "Observing Photons in Space" is the
detection and characterization of photons with instruments aboard
spacecraft. This chapter presents a global overview of the fundamental
processes that accompany photons all the way from their origin in the
source region to their detection in our instruments. The radiation of
the Sun is taken as example in some cases and is treated in more detail.

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Title: Postscript
Authors: Huber, Martin C. E.; Pauluhn, Anuschka; Culhane, J. Len;
Timothy, J. Gethyn; Wilhelm, Klaus; Zehnder, Alex
2010ISSIR...9..647H Altcode:
We summarise the aim and content of the book "Observing Photons in
Space" (ISSI SR-009), comment on emerging national space activities
around the globe, and point out the trends toward global collaborations
in space astronomy.

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Title: Quantitative Solar Spectroscopy
Authors: Wilhelm, Klaus
2010RvMA...22...81W Altcode:
No abstract at ADS

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Title: 2.3 Solar short-wavelength telescopes and spectrometers on
space missions
Authors: Wilhelm, Klaus
2010LanB...4A..226W Altcode:
This document is part of Subvolume A 'Instruments and Methods' of Volume
4 'Astronomy, Astrophysics, and Cosmology' of Landolt-Börnstein -
Group VI 'Astronomy and Astrophysics'.

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Title: The extra-terrestrial vacuum-ultraviolet wavelength range
Authors: Timothy, J. Gethyn; Wilhelm, Klaus; Xia, Lidong
2010ISSIR...9...89T Altcode:
Electromagnetic radiation in the vacuum-ultraviolet (VUV) and
extra-terrestrial range at wavelengths from 10 nm to 300 nm is absorbed
in the upper atmosphere by ozone, molecular and atomic oxygen, and
molecular nitrogen. Observations at wavelengths down to ≈ 200 nm
can be carried out from stratospheric balloons, and observations
below 200 nm require space platforms operating at altitudes above
250 km. The VUV spectral region contains emission lines and continua
arising from plasma at formation temperatures ranging from about 104
K to more than 107 K. This chapter describes the wide range of plasma
diagnostic techniques available at VUV wavelengths, and the development
of instrumentation for studies of the high-temperature solar outer
atmosphere and astrophysical plasmas. Finally, the prospects for future
studies are briefly discussed.

---------------------------------------------------------
Title: Temporal Behavior of Explosive Events Seen in UV by SUMER
Authors: Mendoza Torres, J. E.; Niembro, T.; Wilhelm, K.
2009AGUFMSH23B1544M Altcode:
We study the source of (EE) at a the Si IV 139.37 nm emission line
observed by SUMER onboard SoHO. The North-South (NS) profiles
are studied at the different channels of the line with the aim
to identify plasma displacement at the source of EE. Differences
between the channels are observed in the extension and shape of the
source. In some cases expansion and displacement of the source are
observed. In this work such cases and others where there are clear
differences between the behavior of the red and the blue channels of
the emission line are shown. Data obtained in the raster regime were
used in order to identify the position (at both NS and EW direction)
and time of the maximum radiance of each EE.

---------------------------------------------------------
Title: The Structure and Origin of Solar Plumes: Network Plumes
Authors: Gabriel, A.; Bely-Dubau, F.; Tison, E.; Wilhelm, K.
2009ApJ...700..551G Altcode:
This study is based upon plumes seen close to the solar limb within
coronal holes in the emission from ions formed in the temperature region
of 1 MK, in particular, the band of Fe IX 171 Å from EIT on the Solar
and Heliospheric Observatory. It is shown, using geometric arguments,
that two distinct classes of structure contribute to apparently
similar plume observations. Quasi-cylindrical structures are anchored
in discrete regions of the solar surface (beam plumes), and faint
extended structures require integration along the line of sight (LOS)
in order to reproduce the observed brightness. This second category,
sometimes called "curtains," are ubiquitous within the polar holes and
are usually more abundant than the beam plumes, which depend more on
the enhanced magnetic structures detected at their footpoints. It is
here proposed that both phenomena are based on plasma structures in
which emerging magnetic loops interact with ambient monopolar fields,
involving reconnection. The important difference is in terms of physical
scale. It is proposed that curtains are composed of a large number
of microplumes, distributed along the LOS. The supergranule network
provides the required spatial structure. It is shown by modeling that
the observations can be reproduced if microplumes are concentrated
within some 5 Mm of the cell boundaries. For this reason, we propose to
call this second population "network plumes." The processes involved
could represent a major contribution to the heating mechanism of the
solar corona.

---------------------------------------------------------
Title: Stereoscopic Polar Plume Reconstructions from STEREO/SECCHI
Images
Authors: Feng, L.; Inhester, B.; Solanki, S. K.; Wilhelm, K.;
Wiegelmann, T.; Podlipnik, B.; Howard, R. A.; Plunkett, S. P.; Wuelser,
J. P.; Gan, W. Q.
2009ApJ...700..292F Altcode: 2009arXiv0908.2365F
We present stereoscopic reconstructions of the location and
inclination of polar plumes of two data sets based on the two
simultaneously recorded images taken by the EUVI telescopes in the
SECCHI instrument package onboard the Solar TErrestrial RElations
Observatory spacecraft. The 10 plumes investigated show a superradial
expansion in the coronal hole in three dimensions (3D) which is
consistent with the two-dimensional results. Their deviations from the
local meridian planes are rather small with an average of 6fdg47. By
comparing the reconstructed plumes with a dipole field with its axis
along the solar rotation axis, it is found that plumes are inclined
more horizontally than the dipole field. The lower the latitude is, the
larger is the deviation from the dipole field. The relationship between
plumes and bright points has been investigated and they are not always
associated. For the first data set, based on the 3D height of plumes
and the electron density derived from SUMER/SOHO Si VIII line pair,
we found that electron densities along the plumes decrease with height
above the solar surface. The temperature obtained from the density
scale height is 1.6-1.8 times larger than the temperature obtained
from Mg IX line ratios. We attribute this discrepancy to a deviation
of the electron and the ion temperatures. Finally, we have found that
the outflow speeds studied in the O VI line in the plumes corrected
by the angle between the line of sight and the plume orientation are
quite small with a maximum of 10 km s-1. It is unlikely
that plumes are a dominant contributor to the fast solar wind.

---------------------------------------------------------
Title: The solar plasma conditions in the source regions of two
explosive events
Authors: Mendoza-Torres, J. E.; Wilhelm, K.; Lara, A.
2009A&A...495..613M Altcode:
We analyze the ultraviolet emission during two explosive events
(EEI and EEII) recorded by SUMER aboard SOHO in the wavelength range
from 749 Å to 789 Å. The events occurred near the centre of the
solar disk on 17 November 1996. An attempt is made to separate the
emission of the primary energy release from that of the accelerated
plasma. We want to establish the characteristics of the sources, in
particular, how large they are and how they are spatially distributed
with respect to each other. Gaussian fits were calculated to estimate
the radiances of the brightest emissions in our wavelength range for
the core of the lines and their blue and red wings. The maximum of each
Gaussian approximation was used to define the spatial distributions
of the components. The electron densities were obtained with the
help of the O v line ratio. The relationship between the densities
and the spatial distribution of the radiances is then analyzed. The
distributions of EEI are more extended than those of EEII, probably
due to the different geometries of the observations. In both events,
there is an offset in the locations of red and blue components but
the offset is greater at EEI than at EEII. The Doppler velocities of
the components of EEI were smaller than those of EEII. Also, in both
events the density of the red component attained the highest values
(≥4 × 1010 cm-3). In EEI the electron density
distributions of the three components were considerably narrower
than the radiance distributions. The peak densities were observed
centred with respect to the radiance distributions, suggesting that
the sources of the first energy release of this event were near these
locations. Both the electron density and the radiance distributions
of EEI suggest a jet direction close to the line of sight.

---------------------------------------------------------
Title: The Solar Energy Spectrum
Authors: Wilhelm, Klaus
2009LanB...4B...14W Altcode: 2009LanB...4B.4113W
No abstract at ADS

---------------------------------------------------------
Title: Coronal Active Regions
Authors: Wilhelm, Klaus
2009LanB...4B..175W Altcode: 2009LanB...4B.4126W
No abstract at ADS

---------------------------------------------------------
Title: Solar Transition Region and Quiet Corona
Authors: Wilhelm, Klaus
2009LanB...4B...87W Altcode: 2009LanB...4B.4115W
No abstract at ADS

---------------------------------------------------------
Title: Prominences and Ejecta
Authors: Wilhelm, Klaus
2009LanB...4B..165W Altcode: 2009LanB...4B.4125W
No abstract at ADS

---------------------------------------------------------
Title: Flares
Authors: Wilhelm, Klaus
2009LanB...4B..180W Altcode: 2009LanB...4B.4127W
No abstract at ADS

---------------------------------------------------------
Title: Active Regions
Authors: Wilhelm, Klaus
2009LanB...4B..116W Altcode: 2009LanB...4B.4121W
No abstract at ADS

---------------------------------------------------------
Title: “Energy levels and spectral lines of Ne viii”
[Eur. Phys. J. D 39, 173 188 (2006)]
Authors: Wilhelm, K.; Curdt, W.; Dammasch, I. E.; Hassler, D. M.
2008EPJD...47..325W Altcode: 2008EPJD..tmp...78W
Kramida and Buchet-Poulizac [Eur. Phys. J. D 39, 173 (2006)] provide
a comprehensive compilation of Ne VIII energy levels and spectral
lines. We are concerned about the data of one line treated in the second
paragraph of Section 2, the line at 77.0 nm. This line is very important
for solar physics investigations as it is a bright line emitted in the
lower corona of the Sun, where mass flux and energy transport determine
the properties of the nascent solar wind. Consequently, it has been
studied in a number of investigations, of which we want to mention
two. The results are published by Peter and Judge [Astrophys. J. 522,
1148 (1999)] and Dammasch et al. [Astron. Astrophys. 346, 285
(1999)]. Both these studies concluded that the rest wavelength of the
Ne VIII line in question is 77.0428 nm with standard uncertainties
of 0.7 pm and 0.3 pm, respectively. Dammasch et al. discussed, in
particular, the uncertainty level of 0.5 pm stated by Bockasten et
al. [Proc. Phys. Soc. 81, 522 (1963)]. The conclusion was that it
is far too optimistic and not reliable. So, we take issue with the
statement of the authors that the Bockasten et al. measurements of
this line are the most accurate in the literature. If the Bockasten et
al. value (77.0409 nm ± 0.0005 nm) [Proc. Phys. Soc. 81, 522 (1963)]
for the rest wavelength of this line were true, it would imply downward
movements in the solar corona that are in conflict with the measurements
in other lines.

---------------------------------------------------------
Title: Multi-spacecraft observations of polar coronal plumes
Authors: Curdt, W.; Wilhelm, K.; Feng, L.; Kamio, S.
2008A&A...481L..61C Altcode:
Aims:Coronal plumes, along with their structure and rôle in the
acceleration of the fast solar wind, are of considerable importance
in understanding the physics of the solar atmosphere, in particular,
when contrasted with the adjacent plasma, the so-called interplume
regions. Methods: Observations of coronal plumes in a coronal hole
were obtained with the help of spectrographs and imagers on Hinode,
SOHO, STEREO, TRACE, and with ground-based instrumentation. The
measurements were performed by a large international team in April
2007. Results: First results of this study from Hinode, SOHO,
and STEREO are presented here, at the level of observational facts,
leaving the task of detailed analysis to the future.

---------------------------------------------------------
Title: Observations of the Sun at Vacuum-Ultraviolet Wavelengths
from Space. Part II: Results and Interpretations
Authors: Wilhelm, Klaus; Marsch, Eckart; Dwivedi, Bhola N.; Feldman,
Uri
2007SSRv..133..103W Altcode:
In Part I of this review, the concepts of solar vacuum-ultraviolet
(VUV) observations were outlined together with a discussion of
the space instrumentation used for the investigations. A section on
spectroradiometry provided some quantitative results on the solar VUV
radiation without considering any details of the solar phenomena leading
to the radiation. Here, in Part II, we present solar VUV observations
over the last decades and their interpretations in terms of the plasma
processes and the parameters of the solar atmosphere, with emphasis
on the spatial and thermal structures of the chromosphere, transition
region and corona of the quiet Sun. In addition, observations of
active regions, solar flares and prominences are included as well as
of small-scale events. Special sections are devoted to the elemental
composition of the solar atmosphere and theoretical considerations on
the heating of the corona and the generation of the solar wind.

---------------------------------------------------------
Title: Observations Supporting the Role of Magnetoconvection in
Energy Supply to the Quiescent Solar Atmosphere
Authors: McIntosh, Scott W.; Davey, Alisdair R.; Hassler, Donald M.;
Armstrong, James D.; Curdt, Werner; Wilhelm, Klaus; Lin, Gang
2007ApJ...654..650M Altcode: 2006astro.ph..9503M
Identifying the two physical mechanisms behind the production and
sustenance of the quiescent solar corona and solar wind poses two of
the outstanding problems in solar physics today. We present analysis of
spectroscopic observations from the Solar and Heliospheric Observatory
that are consistent with a single physical mechanism being responsible
for a significant portion of the heat supplied to the lower solar corona
and the initial acceleration of the solar wind; the ubiquitous action
of magnetoconvection-driven reprocessing and exchange reconnection of
the Sun's magnetic field on the supergranular scale. We deduce that
while the net magnetic flux on the scale of a supergranule controls the
injection rate of mass and energy into the transition region plasma,
it is the global magnetic topology of the plasma that dictates whether
the released ejecta provides thermal input to the quiet solar corona
or becomes a tributary that feeds the solar wind.

---------------------------------------------------------
Title: Lessons from SUMMER/SOHO Solar Ultraviolet Spectrograph
Authors: Wilhelm, K.
2006ihy..workE..30W Altcode:
Our understanding of the high-temperature solar atmosphere is to a
large extent based on spectroscopic observations of emission lines
and continuum radiation in the vacuum-ultraviolet (VUV) wavelength
range of the electromagnetic spectrum. The VUV radiation is produced
by transitions of atoms and ions, or to some extent, of molecules. The
atomic and ionic emission lines have formation temperatures between
10,000 K and several million Kelvin, representative of the chromosphere,
the transition region and the corona. The molecular lines and the
continua originate in cooler regions of the Sun. Radiation at VUV
wavelengths is strongly absorbed by the Earth's atmosphere and can only
be detected with instruments on sounding rockets and spacecraft above
the atmosphere. Detailed studies of the spectral radiances together
with atomic physics data furnish information on the electron density
and temperature of the solar atmosphere, as well as on elemental
abundances, whereas Doppler line-shift measurements show bulk plasma
motions, turbulence, and ion temperatures. Research in this field will
be presented using measurements of the Solar Ultraviolet Measurements
of Emitted Radiation (SUMER) instrument on the ESA/NASA Solar and
Heliospheric Observatory (SOHO). In addition, the instrumental technique
will be briefly introduced as well as the scientific use of the data
obtained over a period of ten years.

---------------------------------------------------------
Title: Solar coronal-hole plasma densities and temperatures
Authors: Wilhelm, K.
2006A&A...455..697W Altcode:
Polar plumes extending from the Sun into the solar corona have long been
seen during eclipses, and can now be studied without this restriction
with telescopes and spectrometers on board of spacecraft. Despite
the large amount of observational data available on this prominent
phenomenon, it is not clear whether plumes contribute substantially
to the fast solar-wind streams emanating from coronal holes. An
understanding of the processes leading to the formation of bright
plumes and the surrounding darker inter-plume regions in coronal holes
requires a good knowledge of the physical conditions in plumes and
their environment. This investigation aims at measuring the electron
densities and temperatures in these regions with the help of radiance
ratios of ultraviolet emission lines obtained by SUMER on SOHO. It
finds densities of about 7 × 107 cm-3 in bright
plumes and 1.3 × 107 cm-3 in inter-plume
lanes at ≈45 Mm above the limb. At this height, the total plume
cross-section relative to the size of the coronal hole was found to be
less than 8%. The densities drop by a factor of roughly two over the
next 80 Mm in height, in lanes a little less than seen in plumes. In
this height range, the electron temperatures in plumes are ≈7.5
× 105 K and ≈1.13 × 106 K in inter-plume
regions. The effective ion temperatures, deduced from the line widths,
are higher and nearly independent of the altitude in plumes, whereas
they increase in inter-plume regions, starting from an even higher
level. No systematic dependence of the line-of-sight bulk velocities
on the brightness could be found in the coronal-hole plasma.

---------------------------------------------------------
Title: Solar VUV measurements obtained by SOHO instruments and their
radiometric calibration
Authors: Wilhelm, Klaus
2006AdSpR..37..225W Altcode:
The Solar and Heliospheric Observatory (SOHO) of ESA and NASA is
equipped with a suite of instruments capable of observing the Sun
from the core to the outer corona. Several of these instruments detect
radiation in the vacuum-ultraviolet (VUV) wavelength range (shortwards
of 200 nm), where precise and accurate radiometric measurements are of
extreme significance for solar and terrestrial investigations, but, at
the same time, are very difficult to obtain due to degradation effects
of most optical systems under solar ultraviolet irradiation. The SOHO
instruments (built under strict particulate and chemical cleanliness
conditions) have been carefully calibrated before launch (traceable
to primary source standards) and cross-calibrated during the mission
operations. The solar observations obtained since the solar sunspot
minimum in 1996 to the present time allowed us to make a major step
forward in solar XUV radiometry, both as far as spectral radiance and
irradiance measurements are concerned.

---------------------------------------------------------
Title: Hydrogen Lyman α Profiles of AN Active Region Filament
Obtained with SUMER on SOHO
Authors: Vial, J. -C.; Boutry, C.; Wilhelm, K.
2005ESASP.600E.102V Altcode: 2005ESPM...11..102V; 2005dysu.confE.102V
No abstract at ADS

---------------------------------------------------------
Title: A new relation between the central spectral solar H I Lyman
α irradiance and the line irradiance measured by SUMER/SOHO during
the cycle 23
Authors: Emerich, Claude; Lemaire, Philippe; Vial, Jean-Claude; Curdt,
Werner; Schühle, Udo; Wilhelm, Klaus
2005Icar..178..429E Altcode:
The spectral irradiance at the center of the solar H I Lyman α
( λ=121.5664nm, referred to as Lyα in this paper) line profile
is the main excitation source responsible for the atomic hydrogen
resonant scattering of cool material in our Solar System. It has
therefore to be known with the best possible accuracy in order to
model the various Lyα emissions taking place in planetary, cometary,
and interplanetary environments. Since the only permanently monitored
solar irradiance is the total one (i.e. integrated over the whole
Lyα line profile), Vidal-Madjar [1975. Evolution of the solar Lyman
alpha flux during four consecutive years. Solar Phys. 40, 69-86] using
Orbiting Solar Observatory 5 (OSO-5) satellite Lyα data, established
a semi-empirical formula allowing him to deduce the central spectral
Lyα irradiance from the total one. This relation has been extensively
used for three decades. But, at the low altitude of the OSO-5 orbit,
the central part of the solar line profile was deeply absorbed by a
large column of exospheric atomic hydrogen. Consequently, the spectral
irradiance at the center of the line was obtained by a complex procedure
confronting the observations with simulations of both the geocoronal
absorption and the self-reversed shape of the solar Lyα profile. The
SUMER spectrometer onboard SOHO positioned well outside the hydrogen
geocorona, provided full-Sun Lyα profiles, not affected by such an
absorption [Lemaire et al., 1998. Solar H I Lyman α full disk profile
obtained with the SUMER/SOHO spectrometer. Astron. Astrophys. 334,
1095-1098; 2002. Variation of the full Sun Hydrogen Lyman α and β
profiles with the activity cycle. Proc. SOHO 11 Symposium, ESA SP-508,
219-222; 2004. Variation of the full Sun Hydrogen Lyman profiles
through solar cycle 23. COSPAR 2004 Meeting], making it—for the first
time—possible to measure the spectral and total Lyα solar irradiances
directly and simultaneously. A new relation between these two quantities
is derived in an expression that is formally similar to the previous
one, but with significantly different parameters. After having discussed
the potential causes for such differences, it is suggested that the
new relation should replace the old one for any future modeling of the
numerous Lyα absorptions and emissions observed in the Solar System.

---------------------------------------------------------
Title: The Height of Solar Wind Origin in Coronal Funnels and a 3-D
Scenario for Solar Wind Formation
Authors: Tu, C. -Y.; Zhou, C.; Marsch, E.; Wilhelm, Klaus; Xia,
Li-Dong; Zhao, Liang; Wang, Jing-Xia
2005ESASP.592..131T Altcode: 2005ESASP.592E..19T; 2005soho...16E..19T
No abstract at ADS

---------------------------------------------------------
Title: On the nature of the unidentified solar emission near 117 nm
Authors: Wilhelm, K.; Schühle, U.; Curdt, W.; Hilchenbach, M.;
Marsch, E.; Lemaire, P.; Bertaux, J. -L.; Jordan, S. D.; Feldman, U.
2005A&A...439..701W Altcode:
Spectral observations of the Sun in the vacuum-ultraviolet wavelength
range by SUMER on SOHO led to the discovery of unusual emission
features - called humps here - at 116.70 nm and 117.05 nm on either
side of the He i 58.43 nm line. This resonance line is seen in the
second order of diffraction, whereas the humps are recorded in the
first order with the SUMER spectrometer. In its spectra both orders
are superimposed. Two less pronounced humps can be detected at 117.27
nm and near 117.85 nm. After rejecting various possibilities of an
instrumental cause of the humps, they are studied in different solar
regions. Most of the measurements, in particular those related to the
limb-brightening characteristics, indicate that the humps are not part
of the background continuum. An assembly of spectrally-unresolved atomic
or ionic emission lines might be contributing to the hump at 117.05
nm, but no such lines are known near 116.7 nm. It is concluded that we
detect genuine radiation, the generation of which is not understood. A
two-photon emission process, parametric frequency down conversion,
and molecular emissions are briefly considered as causes of the humps,
but a final conclusion could not be reached.

---------------------------------------------------------
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.
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: Spicules, mass transfer, oscillations, and the heating of
the corona
Authors: Pasachoff, J. M.; Kozarev, K. A.; Butts, D. L.; Gangestad,
J. W.; Seaton, D. B.; de Pontieu, B.; Golub, L.; Deluca, E.; Wilhelm,
K.; Dammasch, I.
2005AGUSMSH13C..02P Altcode:
The mass moving in chromospheric spicules is enough to replace the
corona in a brief time, so understanding the dynamics of spicules
is important for understanding the support and heating of the
solar corona. We have undertaken a program involving simultaneous
high-resolution observations in various chromospheric visible lines
(H-alpha, Ca II H, and G-band, as well as Dopplergrams) using the
Swedish Solar Telescope on La Palma, ultraviolet chromospheric,
transition-region, and coronal lines (Fe IX/X 171 A, Lyman-alpha
1216 A, and continuum/C I/C IV 1600 A) using NASA's TRACE, and
ultraviolet chromospheric and transition-region lines (Si II 1533,
C IV 1548, and Ne VIII 770) using SUMER on SOHO. Our first coordinated
observing run, in May 2004, yielded a variety of images that are under
study, especially for the morphological statistics and dynamics of
spicules. The energy transfer through the chromosphere is relevant to
the overlapping investigation of coronal heating through rapid (1Hz
range) oscillations of coronal loops as observed at total eclipses
by Williams College expeditions. This research is supported by NASA
grant number NNG04GK44G to Williams College. TRACE analysis at SAO
is supported by a contract from Lockheed Martin. SOHO is a project of
international cooperation between ESA and NASA.

---------------------------------------------------------
Title: Correlation Heights of the Sources of Solar Ultraviolet
Emission Lines in a Quiet-Sun Region
Authors: Tu, Chuan-Yi; Zhou, Cheng; Marsch, Eckart; Wilhelm, Klaus;
Zhao, Liang; Xia, Li-Dong; Wang, Jing-Xiu
2005ApJ...624L.133T Altcode:
The radiance and Doppler-velocity maps of the emission lines of Si
II, C IV, and Ne VIII obtained in a quiet region of the Sun by SUMER
(Solar Ultraviolet Measurements of Emitted Radiation) are correlated
with the vertical component, Bz, of the magnetic field
vector as extrapolated, by means of a force-free field model, from
the photospheric magnetic field measured by MDI (Michelson Doppler
Imager). It is found that, with increasing vertical height, each of the
correlation coefficients initially increases to a maximum value before
it decreases again. The height corresponding to this maximum is called
the correlation height. For the data sets selected from a quiet-Sun
region, the correlation heights of Si II and C IV are near 2 Mm,
and for Ne VIII near 4 Mm. At their correlation heights, the averaged
square root of the radiance of the emission lines of Si II and C IV,
considered as a proxy of the plasma density, has a linear relationship
with Bz. This result supports the empirical concept that the
solar transition region is very thin and still affected by frozen-in
convection. A way for improvement of such studies is also outlined.

---------------------------------------------------------
Title: Solar Wind Origin in Coronal Funnels
Authors: Tu, Chuan-Yi; Zhou, Cheng; Marsch, Eckart; Xia, Li-Dong;
Zhao, Liang; Wang, Jing-Xiu; Wilhelm, Klaus
2005Sci...308..519T Altcode:
The origin of the solar wind in solar coronal holes has long been
unclear. We establish that the solar wind starts flowing out of the
corona at heights above the photosphere between 5 megameters and 20
megameters in magnetic funnels. This result is obtained by a correlation
of the Doppler-velocity and radiance maps of spectral lines emitted
by various ions with the force-free magnetic field as extrapolated
from photospheric magnetograms to different altitudes. Specifically,
we find that Ne7+ ions mostly radiate around 20 megameters,
where they have outflow speeds of about 10 kilometers per second,
whereas C3+ ions with no average flow speed mainly radiate
around 5 megameters. Based on these results, a model for understanding
the solar wind origin is suggested.

---------------------------------------------------------
Title: Explosive events in the solar atmosphere seen in
extreme-ultraviolet emission lines
Authors: Mendoza-Torres, J. E.; Torres-Papaqui, J. P.; Wilhelm, K.
2005A&A...431..339M Altcode:
We present observations of explosive events (EEs) in the solar
atmosphere obtained with the Solar Ultraviolet Measurements of Emitted
Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory
(SOHO) in the wavelength range from about 750 Å to 790 Å. Prominent
spectral lines in this range are emitted by ions which have temperatures
of maximum ionic abundances between 1.0×105 K and 6.3×
105 K in ionization equilibrium, and are therefore expected
to be formed in the transition region (TR) and in the low corona. The
aim of this work is to investigate whether the EEs originate in a
limited range of temperatures or in a wide interval. We analyzed the
behaviour of several emission lines during 114 EEs. In many events,
the radiance increased first in lines with formation temperatures near
1.5×105 K. A number of events produced profiles that clearly
revealed blue and red components, in addition to the central line. In
general, both the radiance and the line-of-sight (LOS) velocity of the
blue component are larger than those of the red one. From an inspection
of the profiles that did not show all three spectral components,
we found, in all the cases, that the lowest temperature line showed
a red shift whereas the highest temperature was characterized by a
blue shift. The inverse situation was not observed. We interpret these
results as an indication that most of the EEs originate at intermediate
temperatures of the TR as fast reconnection jets.

---------------------------------------------------------
Title: Variation of the full Sun hydrogen Lyman profiles through
solar cycle 23
Authors: Lemaire, P.; Emerich, C.; Vial, J. -C.; Curdt, W.; Schühle,
U.; Wilhelm, K.
2005AdSpR..35..384L Altcode:
The hydrogen Lyman (Lyα, 121.267 nm and Lyβ, 102.572 nm) lines are
important contributors to the solar extreme ultra violet (EUV) flux
which illuminates the upper Earth’s atmosphere. From high resolution
spectral observations performed with the solar ultraviolet measurement
of emitted radiations (SUMER) spectrometer on the Solar and Heliospheric
Observatory (SOHO), the detailed profiles of these two lines have been
obtained. Some insights into the variation of the shape of the profiles,
sampled throughout the present solar cycle 23, are given and discussed.

---------------------------------------------------------
Title: On the network structures in solar equatorial coronal
holes. Observations of SUMER and MDI on SOHO
Authors: Xia, L. D.; Marsch, E.; Wilhelm, K.
2004A&A...424.1025X Altcode:
By combining observations of the Sun made by SUMER and MDI aboard
SOHO, the network structures in equatorial coronal holes have been
studied, in particular the relationship between the ultraviolet
emission-line parameters (line radiance, Doppler shift and line width)
and the underlying magnetic field. The bases of coronal holes seen in
chromospheric spectral lines with relatively low formation temperatures
generally have similar properties as normal quiet-Sun regions, i.e.,
small bright patches with a size of about 2 arcsec to 10 arcsec are
the dominant features in the network as well as in cell interiors. With
the increase of the formation temperature, these features become more
diffuse, and have an enlarged size. Loop-like structures are the most
prominent features in the transition region. In coronal holes, we
found that many of such structures seem to have one footpoint rooted
in the intra-network and to extend into the cell interiors. Some of
them appear as star-shape clusters. In Dopplergrams of the O VI line
at 1032 Å, there are also fine structures with apparent blue shifts,
although, on average, they are red shifted. Structures with blue shifts
have usually also broader line widths. They seem to represent plasma
above large concentrations of unipolar magnetic field, without obvious
bipolar photospheric magnetic features nearby. Table 1 is only
available in electronic form at http://www.edpsciences.org

---------------------------------------------------------
Title: Dual Flows with Supersonic Velocities in the Sunspot Transition
Region
Authors: Brynildsen, N.; Maltby, P.; Kjeldseth-Moe, O.; Wilhelm, K.
2004ApJ...612.1193B Altcode:
Observations of sunspot transition region lines that deviate
significantly from a Gaussian shape are presented. Attention is given
to “dual flows,” a line profile phenomenon in which two distinct
velocities are observed within the same spatial resolution element. In
5 out of 12 sunspots we observe dual flows. Several emission line
profiles are well represented by two Gaussian line components, one
with a subsonic and one with a supersonic line-of-sight velocity.

---------------------------------------------------------
Title: A New Relation between Central and Total Solar H I Lyman-α
Irradiances, as measured by SOHO during Solar Cycle 23 (1996-2003)
Authors: Emerich, C.; Lemaire, P.; Vial, J. -C.; Curdt, W.; Schüle,
U.; Wilhelm, K.
2004AAS...204.9802E Altcode: 2004BAAS...36..984E
The spectral irradiance at the center of the solar H Ly-α line profile
is the main excitation source responsible for the atomic hydrogen
resonant scattering in cool material. It has therefore to be known
with the best possible accuracy to model the H Ly-α emissions taking
place in planetary, cometary and interplanetary environments. On
the other hand, the only permanently monitored solar irradiance is
the total one - either measured by near-Earth satellites, or deduced
from its correlation with solar activity indexes. It is the reason why
Vidal-Madjar (1975) using OSO-5 satellite H Ly-α data, established a
semi-empirical formula allowing to deduce the central H Ly-α irradiance
from the integrated one. This relation has been extensively used for
three decades. In fact, at the low altitude of the OSO-5 orbit, the
observed central part of the solar line profiles was deeply absorbed by
a large column of exospheric atomic hydrogen. Consequently, the solar
line center irradiances were not measured directly, but obtained by
confronting the measurements with simulations of both the geocoronal
absorption and the self-reversed shape of the central solar profile
itself. On the contrary, the SOHO/SUMER spectrometer orbiting well
outside the H geocoronal envelope (at the L1 Sun-Earth Lagrange point),
provided full Sun H Ly-α profiles, exempt from any central geocoronal
absorption (Lemaire et al. (1998, 2002, 2004)). This has made it
possible to directly measure the central H Ly-α solar irradiances
as a function of the integrated ones, during eight years of Solar
Cycle 23. The newly obtained relation confirms the general trend of
the previous one, but it is characterized by significantly different
coefficients. It will therefore provide new and more accurate inputs
for the future modeling of the various Ly-α emissions occurring inside
the Solar System.

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Title: Flare observation of the Sun as a star by SUMER/SOHO in the
hydrogen Lyman continuum
Authors: Lemaire, P.; Gouttebroze, P.; Vial, J. -C.; Curdt, W.;
Schühle, U.; Wilhelm, K.
2004A&A...418..737L Altcode:
During the execution of the programme “Sun as a star”, while the
SUMER (Solar Ultraviolet Emission of Emitted Radiation)/SOHO (SOlar and
Heliospheric Observatory) slit was collecting the scattered radiation
from the telescope mirror far away from the solar disk image, a class
X5.3/3b flare erupted on the solar disk, on 25 August 2001. During
the first phase of the flare a relative increase of a few percent was
detected at the head of the hydrogen Lyman continuum. After correction
from the instrumental parameters, the relative signal increase is 70%
at the head of the Lyman continuum (910 Å), and 190% in the C II 904
Å multiplet. Accounting for the area of the flare region, the local
increase of the radiance of the Lyman continuum and of the C II lines
is estimated to be a factor of several thousands. We compare this
result with other solar observations and models. Appendix A is
only available in electronic form at http://www.edpsciences.org

---------------------------------------------------------
Title: Observations of the Sun at Vacuum- Ultraviolet Wavelengths
from Space. Part I: Concepts and Instrumentation
Authors: Wilhelm, Klaus; Dwivedi, Bhola N.; Marsch, Eckart; Feldman,
Uri
2004SSRv..111..415W Altcode:
Studies of the high-temperature solar atmosphere are to a large extent
based on spectroscopic observations of emission lines and continuum
radiation in the vacuum-ultraviolet (VUV) wavelength range of the
electromagnetic spectrum. In addition, important contributions stem
from soft X-ray measurements. Most of the VUV radiation is produced
by transitions of atoms and ions. The resulting atomic and ionic
spectral lines have formation temperatures between 10 000 K and 20 MK,
representative of the chromosphere, transition region, corona, and
solar flares. Some molecular lines and the continua originate in cooler
regions of the Sun, around and below the temperature minimum between
the photosphere and the chromosphere. Radiation at VUV wavelengths
is strongly absorbed by the Earth's atmosphere. Consequently, it can
only be detected with instruments on sounding rockets and spacecraft
operating above the atmosphere. The progress in this field of research,
in particular over the last 25 years, will be presented in the first
part of this review by describing the concepts and instrumentation
of modern spectrographs and imaging telescopes. This presentation
is accompanied by some examples of high-resolution solar images
and a discussion of radiometric-calibration aspects and wavelength
measurements. A second part will follow in the near future, summarizing
important results obtained on the plasma conditions in the solar
atmosphere.

---------------------------------------------------------
Title: On the widths of the Mg X lines near 60 nm in the corona
Authors: Wilhelm, K.; Dwivedi, B. N.; Teriaca, L.
2004A&A...415.1133W Altcode:
We examine the line widths of both components of the Mg X 2s
2S1/2-2p 2P1/2,3/2
doublet at 60.98 nm and 62.50 nm in the low corona of the quiet Sun,
and find that the Doppler width (i.e. half 1/e width) broadens from
Δ λD ≈ 8.2 pm to ≈9.5 pm (with an estimated relative
standard uncertainty of 4%) between the limb and 220 Mm above the
limb in the equatorial corona. In a polar coronal hole, the Doppler
width increases from 10.8 pm near 30 Mm to 11.4 pm at around 80
Mm. The analysis does not provide any evidence for a narrowing of
the emission-line profiles as a function of the distance from the
solar limb.

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Title: Solar VUV Measurements obtained by SOHO Instruments and their
radiometric Calibration (Invited)
Authors: Wilhelm, K.
2004cosp...35..431W Altcode: 2004cosp.meet..431W
The SOlar and Heliospheric Observatory (SOHO) of ESA and NASA is
equipped with a suite of instruments capable of observing the Sun from
the core to the outer corona. Several of these instruments observe
radiation in the vacuum-ultraviolet (VUV) wavelength range (shortwards
of 200 nm), where precise and accurate radiometric measurements are of
extreme significance for solar and terrestrial investigations, but, at
the same time, are very difficult to obtain due to degradation effects
of most optical systems under solar ultraviolet irradiation. The SOHO
instruments have been carefully calibrated before launch (traceable
to primary source standards) and cross-calibrated during the mission
operations. The solar observations obtained since the solar sunspot
minimum in 1996 to the present time allowed us to make a major step
forward in solar radiometry, both as far as spectral radiance and
irradiance measurements are concerned.

---------------------------------------------------------
Title: Topological Changes of the Magnetic Network as Seen in
Different UV/EUV Emission Lines
Authors: Xia, L. D.; Marsch, E.; Wilhelm, K.
2004ESASP.547..169X Altcode: 2004soho...13..169X
By combining observations made by SUMER and MDI aboard SOHO, fine
structures in equatorial coronal holes have been studied, in particular
the relationship between the ultraviolet emission line parameters (line
radiance, Doppler shift and line width) and the underlying magnetic
field. The bases of coronal holes seen in chromospheric lines generally
have similar properties as normal QS regions, i.e., small bright points
are the predominant features. An obvious difference has been found in
the shape of the H I L line, which has very asymmetric profiles (skewed
towards the blue side) in coronal holes. Loop-like structures are the
most prominent features in the transition region. In coronal holes, we
found that many of such structures seem to have one footpoint rooted
in the intra-network and to extend into the cell interiors. Some of
them appear as star-shape clusters. In Dopplergrams of the O VI line,
there are also fine structures with apparent blue shifts, although on
average they are red shifted. Structures with blue shifts have usually
also broader line widths. They seem to represent plasma above large
concentrations of unipolar magnetic field, without obvious bipolar
photospheric magnetic features nearby.

---------------------------------------------------------
Title: Variation of the full Sun hydrogen Lyman profiles through
solar cycle 23
Authors: Lemaire, P.; Emerich, C.; Vial, J. -C.; Curdt, W.; Schühle,
U.; Wilhelm, K.
2004cosp...35..510L Altcode: 2004cosp.meet..510L
The hydrogen Lyman (121.267 nm and 102.572 nm) lines are important
contributors to the solar EUV flux which illuminates the upper Earth's
atmosphere. From high resolution spectral observations performed with
the SUMER FUV-EUV spectrometer on SoHO, the detailed profiles of these
two lines have been obtained. Some insights into the variation of the
shape of the profiles, sampled throughout the present solar cycle 23,
are shown and discussed.

---------------------------------------------------------
Title: Observations of the upper solar chromosphere with SUMER
Authors: Wilhelm, K.; Kalkofen, W.
2003A&A...408.1137W Altcode:
The structure and dynamics of the solar chromosphere are still matters
of debate. The chromospheric network reflecting the supergranulation
of the outer convection zone of the Sun is a prominent feature of the
lower solar atmosphere that extends into the transition zone between
chromosphere and corona. In particular, the physics of the so-called
“nonmagnetic” chromosphere in internetwork regions as well as the
physics of the magnetic network are not yet fully understood. Here
we present observations of the H I Lyman continuum obtained in areas
of the undisturbed Sun by the Solar Ultraviolet Measurements of
Emitted Radiation (SUMER) instrument on the Solar and Heliospheric
Observatory (SOHO). The observing sequences are unique in the sense
that they cover the spectral range from 67 nm to 93 nm with the
highest cadence the SUMER spectrometer can achieve operating near the
limit of its mechanism performance, telemetry allocation, and memory
capabilities. In this wavelength range not only the Lyman continuum
but also many extreme-ultraviolet emission lines (N II, N III, S IV,
O II, O III, O IV, O V, Ne VIII, and Mg IX) are prominent, allowing
the investigation of radiation formed at temperatures representative
of regions from the chromosphere to the corona. Brightenings have
been identified that are presumed to be related to the well-known
3 min oscillations as seen, for instance, in Ca II H2v
and K2v observations. The relative temporal variations of
the continuum radiance near 77 nm were typically 20% to 40%, whereas
simultaneously recorded transition-region lines varied by about 40%
of their lowest values in phase with the continuum. In the corona,
the Ne VIII and Mg IX lines with formation temperatures of 620 000
K and 950 000 K, respectively, experienced relative changes of ~ 10%
and displayed no phase relationship with the transition-region lines
or the continuum. Radiance variations in the spatial regime across
the solar disk show a higher correlation between the chromosphere
and the corona than between the transition region and the corona. The
observations will be discussed with a view towards providing constraints
for modelling chromospheric structure and dynamics. Part of this
work was carried out while KW was visiting the Harvard-Smithsonian
Center for Astrophysics, Cambridge, MA, USA.

---------------------------------------------------------
Title: Topological Changes of the Magnetic Network as Seen in
different UV/EUV Emission Lines
Authors: Xia, Lidong D.; Marsch, Eckart; Wilhelm, K.
2003ANS...324Q.100X Altcode: 2003ANS...324..P04X
No abstract at ADS

---------------------------------------------------------
Title: Images of the solar upper atmosphere from SUMER on SOHO
Authors: Feldman, Uri; Dammasch, Ingolf E.; Wilhelm, Klaus; Lemaire,
Philippe; Hassler, Donald M.; Battrick, Bruce
2003ESASP1274.....F Altcode: 2003isua.book.....F
During the first year of SOHO operations and later in 1999, SUMER
acquired several thousand images of the solar upper atmosphere. This
atlas includes most of the full-Sun images that SUMER recorded
and the majority of its images acquired during the Whole-Sun Month
campaign. One of our main tasks while selecting the atlas format has
been the implementation of our desire to maintain the high spatial
resolution that SUMER achieved. In particular we hope that people
with average vision will be able to see the finest details of the
plasma structures that SUMER can resolve. Thus the page size has
been chosen such that the finest resolution element in the images
corresponds to approximately 250 μm in this atlas. The images in
the atlas were recorded in spectral lines or in continuum radiation
emitted by plasmas spanning the electron temperature domain from
1×104K to 1.4×106K. Some of the images were
recorded simultaneously in radiation emitted by plasmas of different
temperatures. Due to substantial differences of the plasma properties
from which the radiation originated, the atlas provides a unique source
for studying many aspects of the solar upper atmosphere.

---------------------------------------------------------
Title: Oscillations in the wings of sunspot transition region lines
Authors: Brynildsen, N.; Maltby, P.; Kjeldseth-Moe, O.; Wilhelm, K.
2003A&A...398L..15B Altcode:
We explore a new approach to the investigation of optically thin
emission lines by comparing the intensity variations in opposite
wings of the spectral lines and apply the method to investigate the
oscillations above sunspots. The observations show that it is easier to
detect the 3 min oscillations above sunspots in the short wavelength
(“blue”) wing than in the long wavelength (“red”) wing of the
lines. The observed oscillations are compatible with the spectral line
signatures of upwardly propagating acoustic waves.

---------------------------------------------------------
Title: Past and recent observations of the solar upper atmosphere
at vacuum-ultraviolet wavelengths
Authors: Wilhelm, Klaus
2003JASTP..65..167W Altcode: 2003JATP...65..167W
Our understanding of the high-temperature solar atmosphere is to a
large extent based on spectroscopic observations of emission lines and
continuum radiation in the vacuum-ultraviolet (VUV) wavelength range
of the electromagnetic spectrum. In addition, important contributions
stem from soft X-ray measurements. The VUV radiation is produced by
transitions of atoms and ions, or to some extent, of molecules. The
atomic and ionic emission lines have formation temperatures between
10000K and several million kelvin, representative of the chromosphere,
the transition region and the corona. The molecular lines and the
continua originate in cooler regions of the Sun. Radiation at VUV
wavelengths is strongly absorbed by the Earth's atmosphere leading
to important geophysical processes at high altitudes. In our context
it means that this radiation can only be detected with instruments
on sounding rockets and spacecraft above the atmosphere. Detailed
studies of the spectral radiances together with atomic physics data
furnish information on the electron density and temperature of the
solar atmosphere, as well as on elemental abundances, whereas Doppler
line-shift measurements show bulk plasma motions, turbulence, and ion
temperatures. Highlights of the research in this field will be presented
from the first solar ultraviolet spectra to Skylab observations and the
modern measurements in the SOHO and TRACE era, and their relevance to
solar physics investigations will be outlined. Special emphasis will be
put on imaging telescopes and spectrographs, which provide insight both
into the morphology and the dynamics of the solar plasma structures.

---------------------------------------------------------
Title: Vacuum-ultraviolet emission line diagnostics for solar plasmas
Authors: Dwivedi, B. N.; Mohan, A.; Wilhelm, K.
2003dysu.book..353D Altcode:
Observations of the solar vacuum-ultraviolet emission lines obtained by
SUMER/SOHO and their interpretation in terms of atomic physics concepts
are given. Electron temperature and density diagnostics of the low
corona are described. Doppler line-of-sight measurements demonstrate
an outflow at the base of the corona in the dark areas of coronal
holes, which are seen as the source of the solar wind. Some aspects
of the dynamics of the upper solar atmosphere, such as explosive
events and sunspot oscillations, are mentioned as examples of the
quiet-Sun activity, but spectral observations during solar flare are
also shown with indications of plasmas with temperatures of several
million Kelvins.

---------------------------------------------------------
Title: Quiet-Sun chromospheric network evolution
Authors: Lemaire, Philippe; Vial, J. -C.; Curdt, W.; Schühle, U.;
Wilhelm, K.
2002ESASP.505..477L Altcode: 2002solm.conf..477L; 2002IAUCo.188..477L
Using the SUMER/SOHO spectrometer we have observed the same quiet-Sun
area during several days in a set of eight spectral lines of the
transition region. Line intensity maps of the rastered areas are used to
separate the interior of the supergranular cells from the network. Then,
following the evolution of the supergranular pattern, we measure the
variations of intensity and the Doppler shifts at several temperatures
of formation of the transition region. We find that the overall flow
velocity of the cell interior and the network generally decays within
ten hours, which represents a significant part of the supergranular
lifetime.

---------------------------------------------------------
Title: Transition region and coronal plasmas: instrumentation and
spectral analysis
Authors: Wilhelm, Klaus; Dammasch, Ingolf E.; Hassler, Donald M.
2002Ap&SS.282..189W Altcode:
The plasma conditions in the solar atmosphere and, in particular,
in coronal holes are summarized, before space-borne instrumentation
for observing these regions in vacuum-ultraviolet light is briefly
introduced with the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) spectrometer on the Solar and Heliospheric Observatory
(SOHO) as example. Spectroscopic measurements of small plasma jets
are then analyzed in detail. Magnetic reconnection is thought to be
responsible for heating the corona of the Sun as well as accelerating
the solar wind by converting magnetic energy into thermal and kinetic
energies. The continuous outflow of the fast solar wind from coronal
holes on ‘open’ field lines, which reach out into interplanetary
space, then requires many reconnection events of very small scale
sizes - most of them probably below the resolution capabilities of
present-day instruments. Our observations of such an event have been
obtained with the Solar and Heliospheric Observatory (SOHO) providing
both high-resolution imaging and spectral information for structural
and dynamical studies. We find whirling or rotating motions as well as
jets with acceleration along their propagation paths in close spatial
and temporal vicinity to the coronal jet.

---------------------------------------------------------
Title: Intercalibration of CDS and SUMER
Authors: Pauluhn, A.; Lang, J.; Schühle, U.; Solanki, S. K.; Wilhelm,
K.; Pike, C. D.; Thompson, W. T.; Rüedi, I.; Hollandt, J.; Huber,
M. C. E.
2002ESASP.508..223P Altcode: 2002soho...11..223P
The outcome of the Joint Observing Programme (JOP) Intercal-01, which
is the intercalibration of the SUMER (Solar Ultraviolet Measurements
of Emitted Radiation) instrument (detectors A and B) and the two CDS
(Coronal Diagnostic Spectrometer) instruments, the Normal Incidence
Spectrometer (NIS) and the Grazing Incidence Spectrometer (GIS),
is presented. Recent calibration updates of both instruments have
been employed, and the results indicate a very good correlation and
agreement of the measured radiances within the individual uncertainties.

---------------------------------------------------------
Title: Variation of the full Sun hydrogen Lyman α and β profiles
with the activity cycle
Authors: Lemaire, Philippe; Emerich, C.; Vial, J. -C.; Curdt, W.;
Schühle, U.; Wilhelm, K.
2002ESASP.508..219L Altcode: 2002soho...11..219L
Full Sun hydrogen Lyman α and β profiles obtained through the
activity cycle are needed to compare with stars, to understand the
hydrogen distribution in the heliosphere and to evaluate the processes
in the upper planetary atmospheres. Using the SUMER/SOHO telesocope
scattered light properties, we have measured the Lyman α and β
profiles at different epochs of the solar activity cycle. Here we
report modifications in the intensity and the shape of the profiles.

---------------------------------------------------------
Title: Observations of the Solar Chromosphere with SUMER on SOHO
Authors: Wilhelm, K.
2002AAS...200.5304W Altcode: 2002BAAS...34..730W
The structure and the dynamics of the solar chromosphere are still a
matter of scientific debate. In particular, the physics of the so-called
nonmagnetic chromosphere in cell regions of the network structure is
not yet fully understood. Here we present SUMER observations of the H
i Lyman continuum obtained in areas of the undisturbed Sun in November
1996. The sequences are unique in the sense that the spectral range from
75 nm to 79 nm is sampled several times with a cadence of 30 s for 390
s, which is near the limit of the telemetry and memory capabilities of
the instrument. In this wavelength range not only the Lyman continuum,
but also many EUV emission lines (N ii, N iii, S iv, O iv, O v, and Ne
viii) are prominent, allowing us to investigate radiation formed at
temperatures representative of regions from the chromosphere to the
corona. Several brightenings can be identified which are assumed to
be related to the well-known three-minute brightenings observed, for
instance, in the Ca ii line. The fractional variation of the continuum
radiance was up to 40 %, whereas simultaneously recorded transition
region lines varied by about 60 %. The Ne viii lines with a formation
temperature of 620 000 K showed relative changes of less than 14 %
and displayed no phase relationship with the transition region lines or
the continuum. We will discuss SUMER observations with a view towards
providing constraints for modeling chromospheric dynamics and structure.

---------------------------------------------------------
Title: Correlated Dynamics of Hot and Cool Plasmas in the Main Phase
of a Solar Flare
Authors: Kliem, B.; Dammasch, I. E.; Curdt, W.; Wilhelm, K.
2002ApJ...568L..61K Altcode:
We report far-ultraviolet observations of a solar limb flare obtained
by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
spectrometer. At a fixed pointing of the slit above the limb, spectra
were simultaneously obtained in several emission lines that covered
a wide temperature range from ~104 to ~107
K. The temporal evolution of the spectra revealed, for the first
time, a high degree of correlation between the dynamical behavior
of hot (T~107 K) and cool (T~104 K) coronal
material during the main phase of a flare. We note that the data
did not show any indication of the presence of a prominence. Hot and
cool plasmas brightened at nearly the same location. Their Doppler
shifts, which were opposite to each other, reached peak values
simultaneously. Thereafter, the two components showed anticorrelated,
rapidly damped, and oscillatory Doppler shifts and a very similar
decay of the line widths, but with the cool plasma reaching maximum
brightness before the hot plasma. This behavior points to an active
role for cool plasma in the dynamics of this flare, different from
the usual picture of passive cooling after the impulsive phase. We
suggest a model in which the localized cooling of coronal plasma by the
thermal instability triggers magnetic reconnection through the resulting
enhanced resistivity, the combined processes leading to the correlated
dynamics of hot and cool plasmas in a loop-loop interaction geometry.

---------------------------------------------------------
Title: Variability and dynamic state of active region loops
Authors: Fredvik, T.; Kjeldseth-Moe, O.; Haugan, S. V. H.; Brekke,
P.; Gurman, J. B.; Wilhelm, K.
2002AdSpR..30..635F Altcode:
A set of 218 consecutive CDS rasters taken at the solar limb on October
26-28 1999 has been used to investigate the variability and plasma
dynamics of active region loops. Each raster contains simultaneous
images in 6 different lines, covering the full temperature range of
CDS, 10 000 K (He I) to 2.7 MK (Fe XVI). Activity is seen to go on
without breaks at temperatures below 1 MK for the full 39 hours of the
series. Transition region loops or extended sections of loops, 50-200
Mm long, appear and disappear in intervals as short as 11 minutes,
the observing cadence. In the corona the emission is less variable,
but significant changes are seen. Measured Doppler shifts correspond
to typical plasma velocities of 20 km s -1 to 100 km
s -1, at temperatures 10 000 K to 450 000 K, and siphon
flows may occur in some of the loops. High velocities are frequently
seen where the emitted intensities are weak, often on the outer edges
of loops as defined in that particular spectral line. At coronal
temperatures, 1 MK and higher, systematic loop velocities occur only
occasionally. Simultaneous observations with EIT and SUMER were made
during part of the raster series and are compared with the CDS result.

---------------------------------------------------------
Title: Spectroradiometry of Spatially-resolved Solar Plasma Structures
Authors: Wilhelm, K.
2002ISSIR...2...37W Altcode: 2002ESASR...2...37W; 2002rcs..conf...37W
The investigation of spatially-resolved solar plasma features in terms
of radiometric measurements requires concepts different from those
useful for full-Sun observations. After a definition of the relevant
physical quantities, formulae are derived for studies of optically-thick
and optically-thin plasmas observed with both spectral and spatial
resolution. Simple examples of their applications to the determination
of electron densities and electron temperatures as well as to studies
of emission measures and elemental abundances are discussed.

---------------------------------------------------------
Title: Transition region quiet sun velocity field evolution
Authors: Lemaire, P.; Artzner, G.; Vial, J. -C.; Curdt, W.; Schühle,
U.; Wilhelm, K.
2002AdSpR..30..487L Altcode:
The UV/EUV SUMER spectrometer aboard SOHO can record profiles of lines
emitted by elements at different stages of ionization corresponding
to several temperatures within the transition region temperature
range. During the solar cycle minimum in July 1996, we were able to
observe the quiet Sun during five consecutive days. From the line
positions we have determined the velocity fields and follow their time
variations at different temperatures in the transition region. The line
intensity maps are used to separate supergranular cells and network and
they allow to compare the behaviors of the velocity fields evolution in
the two structures. The results are critically analyzed and discussed.

---------------------------------------------------------
Title: Observations of ultraviolet emission lines in solar coronal
holes on the disk with SUMER on SOHO
Authors: Wilhelm, Klaus; Dammasch, Ingolf E.; Xia, Lidong
2002AdSpR..30..517W Altcode:
The Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
spectrograph and other instruments on the Solar and Heliospheric
Observatory (SOHO) have observed many solar polar coronal holes (PCHs)
during the minimum of the sunspot cycle in 1996 and 1997. Based on the
results obtained for PCHs, investigations of near-equatorial coronal
holes (ECHs) have been planned and carried out at the beginning of
the new sunspot cycle, when ECHs regularly occurred on the solar
disk. These studies have been performed using ultraviolet emission
lines with formation temperatures ranging from 20 000 K to one million
kelvin as well as continuum radiation. The spectroscopic evaluation
provides information on line shifts and widths, and on the dynamics
of the low corona in coronal holes (CHs). The characteristics of ECHs
found are very similar to those of PCHs observed during the sunspot
minimum. Specifically, we find outflow speeds of Ne 7+
ions of about 5 km s -1 and of Mg 8+ ions of
15 km s -1 with respect to quiet-Sun (QS) regions. The
Doppler widths of the Mg IX (λ706) line inside ECHs and in the QS
are not significantly different and correspond to v1/ e
≈ 60 km s -1.

---------------------------------------------------------
Title: Solar Vacuum-ultraviolet Radiometry with SUMER
Authors: Wilhelm, K.; Schuhle, U.; Curdt, W.; Dammasch, I. E.;
Hollandt, J.; Lemaire, P.; Huber, M. C. E.
2002ISSIR...2..145W Altcode: 2002ESASR...2..145W; 2002rcs..conf..145W
Since the beginning of 1996, the space-based telescope and
spectrograph SUMER (Solar Ultraviolet Measurements of Emitted
Radiation) on the SOlar and Heliospheric Observatory (SOHO) of ESA
and NASA has obtained spectra of many features of the quiescent and
active Sun with high spectral and spatial resolution. In addition,
irradiance and radiance measurements of line and continuum emission
have been performed in the wavelength range 46.5 nm to 161.0 nm. The
instrument was radiometrically calibrated against the Berlin Electron
Storage ring for SYnchrotron radiation (BESSY I), a primary source
standard, with the help of a transfer source standard based on a
hollow-cathode discharge lamp. A thorough cleanliness programme,
specifically aimed at chemical contamination control, resulted in an
excellent radiometric stability of the normal-incidence optical system
as well as of the detectors. This has been verified under operational
conditions by various techniques employed during the SOHO mission,
such as line-ratio studies, observations of stars, and comparisons with
other instruments. The observations provide vacuum-ultraviolet (VUV)
radiometry of the Sun in many emission lines and continua of atoms
and ions with relative standard uncertainties of 15 % (detector A)
and 20 % (detector B) for the wavelength range 53 nm to 124 nm, with
larger uncertainties outside this interval and after the SOHO recovery
in 1998. We report on the present state of the SUMER radiometric
calibration and provide a full bibliography related to this topic.

---------------------------------------------------------
Title: Calibration and Intercalibration of SOHO's Vacuum-ultraviolet
Instrumentation
Authors: Wilhelm, K.
2002ISSIR...2...69W Altcode: 2002rcs..conf...69W; 2002ESASR...2...69W
The SOlar and Heliospheric Observatory (SOHO) is equipped with a
suite of instruments capable of observing the Sun from the core to the
outer corona. Several of these instruments observe radiation in the
vacuum-ultraviolet (VUV) wavelength range, where precise and accurate
radiometric measurements are of extreme significance for solar and
terrestrial investigations, but, at the same time, are very difficult to
obtain due to degradation effects of most optical systems under solar
ultraviolet irradiation. Radiometriccalibration and cross-calibration
matters have consequently been important topics from the initial
planning phase of the mission to the operational implementation. An
attempt will be made here to summarize the early requirements and
goals as well as the achievements of SOHO in this context. Although
not all plans could be carried out, the general picture is very
encouraging. SOHO allowed us to make a major step forward in solar
radiometry, in particular of spatially-resolved structures.

---------------------------------------------------------
Title: Sumer observations of solar transition region structures
and dynamics
Authors: Dammasch, Ingolf E.; Wilhelm, Klaus
2002AdSpR..30..495D Altcode:
Several raster scans of the UV/EUV spectrometer SUMER (Solar
Ultraviolet Measurements of Emitted Radiation) on SOHO (the Solar and
Heliospheric Observatory of ESA and NASA) in quiet-Sun regions were
used to study the region between the chromosphere and the corona,
i.e., the transition region with a temperature range between ≈
30 000 K and 400 000 K. A typical SUMER scan of 100 raster steps
with the 300″-long slit leads to 30 000 pixels containing spectral
information and it is, therefore, a good statistical base. The aim was
to calculate probability distributions of line intensities and shifts,
and to study the relationship between intensities and shifts. These
signatures were determined for emission lines with various formation
temperatures across the transition region. Results show that intensity
contrasts as well as Doppler shifts depend on the formation temperature
and peak around 100 000 K, which is also the region with the strongest
relation between line intensities and shifts.

---------------------------------------------------------
Title: Correlated Dynamics of Hot and Cool Plasmas in Two Solar Flares
Authors: Kliem, B.; Dammasch, I. E.; Curdt, W.; Wilhelm, K.
2002mwoc.conf..271K Altcode:
We report far-ultraviolet observations of a solar limb flare by
the Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
spectrometer. At a fixed pointing of the slit above the limb, spectra
were simultaneously obtained in several emission lines that covered a
wide temperature range of ≅ 104 -- 107 K. The
temporal evolution of the spectra revealed a high degree of correlation
between the dynamical behavior of hot (T ~107 K) and cool (T
~104 K) material during the main flare phase. Hot and cool
plasma brightened at nearly the same place, with cool plasma reaching
maximum brightness before the hot plasma. The opposite line-of-sight
velocities reached their peak values simultaneously. A correlated,
rapidly damped oscillatory motion followed, while the excess (turbulent)
line widths decayed in a similar manner. This behavior points to an
active role of cool plasma in the dynamics of this flare, different
from the usual picture of passive cooling after the impulsive phase. An
interpretation is suggested in terms of magnetic reconnection which
is triggered by rapid localized cooling due to the thermal instability
in a loop-loop interaction geometry.

---------------------------------------------------------
Title: The inner solar corona seen by SUMER, LASCO/C1, and EIT:
Electron densities and temperatures during the rise of the new
solar cycle
Authors: Wilhelm, K.; Inhester, B.; Newmark, J. S.
2002A&A...382..328W Altcode:
Detailed investigations of the corona and the source regions of
the solar wind have become possible with spectroscopic and imaging
instruments on the Solar and Heliospheric Observatory (SOHO). We
present observations in the extreme ultraviolet (EUV), pertinent to
the generation of the slow solar wind, which were obtained by the Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) spectrograph and
by the Extreme-ultraviolet Imaging Telescope (EIT) in early 1998 under
relatively quiet solar conditions, but with several active regions
of the new solar cycle present. At the same time, forbidden iron
lines in the visible were observed by the Large-Angle Spectroscopic
Coronagraph (LASCO/C1). We study, in particular, the plasma parameters
and the spatial structures of the low-altitude streamer regions,
and find an electron density of ne ~ 2x 108
cm-3 at 5 Mm above the equatorial limb for the coronal
plasma, and ne = (2 to 6)x 109 cm-3
for the plasma at transition-region temperatures. High-temperature
regions have been found at mid-latitudes with electron temperatures
of Te ~ 1.4x 106 K at heights of about 80 Mm
and lower temperatures near the equator.

---------------------------------------------------------
Title: Intercalibration of CDS and SUMER
Authors: Pauluhn, A.; Lang, J.; Schuhle, U.; Solanki, S. K.; Wilhelm,
K.; Thompson, W. T.; Pike, C. D.; Ruedi, I.; Hollandt, J.; Huber,
M. C. E.
2002ISSIR...2..235P Altcode: 2002rcs..conf..235P; 2002ESASR...2..235P
Simultaneous observations of the same solar features with different
instruments provide a way to compare radiometric calibrations and
detect changes in responsivity with time of EUV instruments in space
within the combined uncertainties of the individual instruments. Here
we present the intercalibration of the SUMER (Solar Ultraviolet
Measurements of Emitted Radiation) instrument (detectors A and B) and
the two CDS (Coronal Diagnostic Spectrometer) instruments, the Normal
Incidence Spectrometer (NIS) and the Grazing Incidence Spectrometer
(GIS) on the Solar and Heliospheric Observatory (SOHO). This work
describes the results of the Joint Observing Programme Intercal 01
and presents quiet-Sun comparisons from March 1996 up to February
2001, which represents the complete set of all available Intercal
01 measurements. Recent calibration updates of both instruments are
employed, and the results indicate a very good correlation and agreement
of the measured radiances within the combined uncertainties.

---------------------------------------------------------
Title: Intercalibration of SUMER and CDS on SOHO. II. SUMER detectors
A and B and CDS NIS
Authors: Pauluhn, Anuschka; Rüedi, Isabelle; Solanki, Sami K.;
Schühle, Udo; Wilhelm, Klaus; Lang, Jim; Thompson, William T.;
Hollandt, Jörg
2001ApOpt..40.6292P Altcode:
Results of an intercalibration between the extreme-ultraviolet
spectrometers Coronal Diagnostic Spectrometer (CDS) and Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) on board the Solar
and Heliospheric Observatory (SOHO) are reported. The results of the
joint observing program Intercal_01 are described, and intercalibration
results up to July 2000 of both SUMER detectors A and B and of the
CDS Normal Incidence Spectrometer (NIS) are presented. The instruments
simultaneously observed radiance of emission lines at the center of the
Sun, and three lines have been chosen for intercomparison: He I 584 Å,
Mg X 609 Å, and Mg X 624 Å. Initially the same area was observed by
both instruments, but, after restrictions were imposed by the scanning
mechanism of SUMER in November 1996, the instruments viewed areas of
different sizes. Nevertheless, the temporal correlation between the
two instruments remained good through June 1998, when contact with
the SOHO spacecraft was lost. Until then the CDS instrument measured
(33+/-5)% and (38+/-7)% (+/-1σ) higher intensity than SUMER in the
Hz I 584-Å line on average for detectors A and B, respectively. Data
from SUMER detector B agreed well for Mg X 609 Å and Mg X 624 Å
with the CDS intensities, showing offsets of (2+/-10)% and (9+/-15)%,
much less than the data of detector A with offsets of (7+/-8)% and
(16+/-7)% for the two lines, respectively, relative to CDS. Finally,
the intercalibration measurements after the loss and recovery of the
SOHO spacecraft are analyzed. The data for observations from November
1998 to July 2000 are compared, and it is shown that, although the
responses of the instruments have changed, the CDS and the SUMER still
perform well, and their temporal correlation is good.

---------------------------------------------------------
Title: A multi-wavelength study of solar coronal-hole regions showing
radio enhancements
Authors: Moran, T.; Gopalswamy, N.; Dammasch, I. E.; Wilhelm, K.
2001A&A...378.1037M Altcode:
We observed 17 GHz microwave-enhanced regions in equatorial coronal
holes (ECH) together with extreme-ultraviolet (EUV), far-ultraviolet
(FUV) and visible emissions in a search for temperature increases which
might explain the bright spots in radio wavelengths. The ultraviolet
(UV) observations span a wide range of formation temperatures (8000 K
to 630 000 K). Increased UV emission was observed at the approximate
location of the radio enhancements, but unlike the radio brightening,
the UV emission did not exceed the mean quiet sun level. However,
there were two observations showing increased Hα brightness in radio
enhancements above mean quiet sun levels. No Hα bright spots were
detected in ECHs outside of radio enhancement regions. The ECH Hα
bright spots were caused by bright fibrils, bright points and a lack
of dark fibrils. Since the 17 GHz and Hα enhancements are co-spatial,
have equal integrated normalized enhanced emission and brightness
temperatures, the observations suggest that the radio enhancements
are caused by increased fibril radio emission. In addition, increased
Fe XII EUV emission was recorded at the location of some well-defined
radio enhancements, which were the bases of coronal plumes. Since the
radio brightness temperature is much lower than the Fe xii formation
temperature, the radio and EUV enhancements are likely both related
to the presence of concentrated magnetic flux, but do not arise from
the same physical layer.

---------------------------------------------------------
Title: Measuring Solar Abundances
Authors: von Steiger, R.; Vial, J. -C.; Bochsler, P.; Chaussidon, M.;
Cohen, C. M. S.; Fleck, B.; Heber, V. S.; Holweger, H.; Issautier, K.;
Lazarus, A. J.; Ogilvie, K. W.; Paquette, J. A.; Reisenfeld, D. B.;
Teriaca, L.; Wilhelm, K.; Yusainee, S.; Laming, J. M.; Wiens, R. C.
2001AIPC..598...13V Altcode: 2001sgc..conf...13V
This is the rapporteur paper of Working Group 2 on Measuring Solar
Abundances. The working group presented and discussed the different
observations and methods for obtaining the elemental and isotopic
composition of the Sun, and critically reviewed their results and
the accuracies thereof. Furthermore, a few important yet unanswered
questions were identified, and the potential of future missions to
provide answers was assessed. .

---------------------------------------------------------
Title: The SUMER spectral atlas of solar-disk features
Authors: Curdt, W.; Brekke, P.; Feldman, U.; Wilhelm, K.; Dwivedi,
B. N.; Schühle, U.; Lemaire, P.
2001AIPC..598...45C Altcode: 2001sgc..conf...45C
A far-ultraviolet and extreme-ultraviolet (FUV, EUV) spectral atlas
of the Sun between 670 Å and 1609 Å in first order of diffraction
has been derived from observations obtained with the SUMER (Solar
Ultraviolet Measurements of Emitted Radiation) spectrograph on
the spacecraft SOHO (Solar and Heliospheric Observatory) [1]. The
atlas contains spectra of the average quiet Sun, a coronal hole and
a sunspot on disk. Different physical parameters prevalent in the
bright network (BN) and in the cell interior (CI)-contributing in a
distinct manner to the average quiet-Sun emission-have their imprint
on the BN/CI ratio, which is also shown for the entire spectral
range. With a few exceptions, all major lines are given with their
identifications and wavelengths. Lines that appear in second order
are superimposed on the first order spectra, but below 500 Å the
responsivity of the normal-incidence optical system is very low. The
spectra include emissions from atoms and ions in the temperature range
6 103 K to 2 106 K, i.e., continua and mission
lines emitted from the lower chromosphere to the corona. This spectral
atlas, with its broad wavelength coverage, provides a rich source
of new diagnostic tools for studying the physical parameters in the
chromosphere, the transition region and the corona. In particular,
the wavelength range below 1100 Å as observed by SUMER represents
a significant improvement over the spectra produced in the past. In
view of the manifold appearance and temporal variation of the solar
atmosphere it is obvious that our atlas can only be a-hopefully
typical-snapshot. The spectral radiances are determined with a
relative uncertainty of 0.15 to 0.30 (1σ), and the wavelength scale
is accurate to typically 10 mÅ, which is the level achievable with
semi-automatic processing. The SUMER solar-disk spectral atlas will
be published in the near future by Curdt et al. [2]. It includes
profiles of the average quiet Sun, an equatorial coronal hole, and
a sunspot. As an example we show in Fig. 1 the spectral range from
1300 Å to 1342 Å with the prominent O I and C II lines. Resolved
emission lines are indicated by a mark, the measured wavelength in
angstrom, and the identification, if available. Marks point to line
lists available in the literature, where additional information about
a specific line can be found [3-7]. New lines or identifications
are indicated. Lines observed in first order and in second-order of
diffraction are distinguished. Only the three least-significant digits
of the wavelength values are given. If available, unidentified lines
are characterized by the temperature classification defined in [3] (a:
Te&lt;3 105 b: Te~3 105 c:
Te~4 105 d: 6 105&lt;Te
&lt;9 105 e: Te~1.4 106 f:
Te~1.8 106). The vertical axes are scaled
to spectral radiance in units of mW sr-1 m-2
Å-1 on the left the radiometric calibration for first
order lines is given, on the right for second order lines. Note,
that second order lines are always superimposed on a first order
background. We have taken care of the type of photocathode (bare or KBr)
when applying the radiometric calibration to different sections of the
spectrum. Also displayed in green is the BN/CI ratio in an attempt
to characterize the quiet-Sun chromospheric network structure. A
pre-print of the SUMER spectral atlas and a line list is available at
http://www.linmpi.mpg.de/~curdt. .

---------------------------------------------------------
Title: On the Unresolved Fine Structures of the Solar Upper
Atmosphere. IV. The Interface with the Chromosphere
Authors: Feldman, U.; Dammasch, I. E.; Wilhelm, K.
2001ApJ...558..423F Altcode:
An important objective of the solar physics community is the
unambiguous determination of the morphology of the fine structures of
the solar upper atmosphere in quiet-Sun and coronal hole regions and
the relationship of the cold chromosphere to the hot corona. Recently
the Solar Ultraviolet Measurements of Emitted Radiation spectrometer
on board the Solar and Heliospheric Observatory succeeded in obtaining
observations that can be used to achieve this goal. In this paper
we study the spatial relationship between previously unresolved fine
structures and the chromospheric emissions that underlie them. The main
result is that looplike structures seen in transition region lines
with length scales of 10"-20" straddle the chromospheric network and
have no chromospheric counterpart near their apparent footpoints.

---------------------------------------------------------
Title: Plumes and oscillations in the sunspot transition region
Authors: Maltby, P.; Brynildsen, N.; Kjeldseth-Moe, O.; Wilhelm, K.
2001A&A...373L...1M Altcode:
The suggestion that sunspot transition region oscillations are a typical
feature of the sunspot plumes is examined. The present observations show
3 min oscillations in the umbra that end at the umbral rim. We find
that sunspot plumes located above the umbra show these oscillations,
in contrast to plumes above the penumbra. These two findings suggest
that the oscillations may be a property of the umbral transition region.

---------------------------------------------------------
Title: A Study of Chromospheric Oscillations Using the SOHO and
TRACE Spacecraft
Authors: Judge, Philip G.; Tarbell, Theodore D.; Wilhelm, Klaus
2001ApJ...554..424J Altcode:
We analyze line and continuum time-series data of the solar atmosphere,
with between 10 and 60 s cadence, using the MDI and SUMER instruments
on the SOHO spacecraft and the UV bandpasses on the TRACE satellite. The
co-aligned data sets sample spectral features formed from photosphere to
the middle transition region, spanning five decades in pressure, under
quiet-Sun and plage conditions. We discuss power, phase difference,
and coherence spectra, and examine data in the time domain. The
observed photospheric and chromospheric oscillations are strongly
coupled for frequencies between 2 and 8 mHz. Phase coherences decrease
with increasing height, with only occasional periods and locations of
observable coherence up to heights where transition region emission
lines are formed. The middle chromosphere (in the SUMER continua)
oscillates in several megameter (Mm) diameter coherent patches
with power predominantly in the 5-7 mHz range. The TRACE data,
formed in the upper photosphere, show smaller patterns superimposed
on these large-scale oscillations, resulting (at least in part)
from granulation. At the observed spatial scales, all the observed
properties point to p-modes, especially the “pseudomodes” just above
the acoustic cutoff frequency, as the dominant mode of the chromospheric
dynamics. Smaller scale “acoustic event” drivers, associated
with granular dynamics, appear to be less important. The predominant
internetwork chromospheric oscillations arise from regions much larger
horizontally than vertically. If propagating largely vertically, this
can naturally explain why the one-dimensional simulations of Carlsson
&amp; Stein might be more successful than expected. The chromospheric
response to the p-mode driving is, however, intermittent in space and
time. Some of the intermittency appears to result from the interaction
of the upward-propagating waves with magnetic fields. Evidence for this
includes suppressed intensities and oscillations near quiet-Sun network
elements (which we dub “magnetic shadows”), absence of oscillations
in internetwork regions neighboring plage magnetic fields, and a change
in character of the quiet-Sun internetwork oscillations between the
119 and 104 nm continua formed at 1 and 1.2 Mm. The latter might be
caused by canopy fields that form between these heights under typical
quiet-Sun conditions. A SUMER-only data set reported by Wikstøl et
al. has a factor of 3 more oscillatory power in the 104 nm continuum
than the data analyzed here, with stronger coherences extending into
the solar transition region. Together, these data support the general
picture that the chromosphere oscillates primarily in response to
forcing by the p-modes, they are therefore large-scale (several Mm
across) waves, and they are often strongly influenced by magnetic
effects (internetwork fields, or the overlying canopy), before the
oscillations even reach the transition region.

---------------------------------------------------------
Title: VizieR Online Data Catalog: SUMER Spectral Atlas of Solar
Disk Features (Curdt+, 2001)
Authors: Curdt, W.; Brekke, P.; Feldman, U.; Wilhelm, K.; Dwivedi,
B. N.; Schuhle, U.; Lemaire, P.
2001yCat..33750591C Altcode:
List of spectral lines in the wavelength range from 668Å to 1611Å
identified in SUMER (Solar Ultraviolet Measurements of Emitted
Radiation, spectrograph on the spacecraft SOHO) spectra of the average
quiet Sun (QS), a coronal hole (CH) and a sunspot on disk (SS). Spectral
lines observed in second order of diffraction which are also given
here, extend the lower wavelength limit to below 500Å. For each entry
we give the observed wavelengths in angstrom, the identification,
the transition, the peak of spectral radiance, Lpeak, in
mW/(sr*m2*Å) (incl. background), and a cross-reference
to other line lists available in the literature (cf., Sect. 5.1). For
second-order lines radiance entries are generally not provided, since
the background separation in both orders of diffraction is a non-trivial
task, which can not be automated. Only a few radiance values of strong
second-order lines with negligible first-order contribution are given,
which are marked by an asterisk (*). (1 data file).

---------------------------------------------------------
Title: An Observational Study of Solar Coronal-hole Regions Showing
Radio Enhancements
Authors: Moran, T. G.; Gopalswamy, N.; Dammash, I.; Wilhelm, K.
2001AGUSM..SH41A13M Altcode:
We observed 17~GHz microwave-enhanced regions in equatorial coronal
holes (ECH) together with extreme-ultraviolet (EUV), far-ultraviolet
(FUV) and visible emissions in a search for temperature increases which
might explain the bright spots in radio wavelengths. The ultraviolet
(UV) observations span a wide range of formation temperatures (8000~K
to 630 000~K). Increased UV emission was observed at the approximate
location of the radio enhancements, but unlike the radio brightening,
the UV emission did not exceed the mean quiet sun level. However,
there were two observations showing increased Hα brightness in radio
enhancements above mean quiet sun levels. No Hα bright spots were
detected in ECHs outside of radio enhancement regions. The ECH Hα
bright spots were caused by bright fibrils, bright points and a lack
of dark fibrils. Since the 17~GHz and Hα enhancements are co-spatial,
have equal integrated normalized enhanced emission and brightness
temperatures, the observations suggest that the radio enhancements
are caused by increased fibril radio emission. In addition, increased
Fe xii EUV emission was recorded at the location of some well-defined
radio enhancements, which were the bases of coronal plumes. Since the
radio brightness temperature is much lower than the Fe xii formation
temperature, the radio and EUV enhancements are likely both related
to the presence of concentrated magnetic flux, but do not arise from
the same physical layer.

---------------------------------------------------------
Title: Dual Flows and Oscillations in the Sunspot Transition Region
Authors: Brynildsen, N.; Maltby, P.; Kjeldseth-Moe, O.; Wilhelm, K.
2001ApJ...552L..77B Altcode:
New knowledge about sunspot transition region lines that deviate
significantly from a Gaussian shape are presented. Attention is given
to “multiple flows,” a line profile phenomenon in which two or more
distinct velocities are observed within the same spatial resolution
element. We observe line profiles that are well represented by two
Gaussian line components in the N V λ1242 and O V λ629 lines and
introduce the notation “dual flow.” We have detected transition region
oscillations in one of the line components in the dual-flow events.

---------------------------------------------------------
Title: Comparison of quiet-Sun radiances measured by CDS and SUMER
on SOHO
Authors: Pauluhn, A.; Solanki, S. K.; Schühle, U.; Wilhelm, K.;
Lang, J.; Thompson, W. T.; Rüedi, I.; Hollandt, J.; Huber, M. C. E.
2001SSRv...97...63P Altcode:
Since the beginning of the SOHO (Solar and Heliospheric Observatory)
mission an intercalibration programme was carried out which included
simultaneous observations of the EUV instruments CDS (Coronal Diagnostic
Spectrometer) and SUMER (Solar Ultraviolet Measurements of Emitted
Radiation) of common targets on the quiet Sun. The observations in the
chromospheric line of He i (584 Å) and the two coronal lines of Mg x
(609 Å and 624 Å) thus cover the long period of 4 years and provide a
data set highly suitable not only for instrumental comparison but also
for studies of the quiet Sun's long term variability. Up to the SOHO
accident, both instruments show a very good temporal correlation and
stability. Even after the loss and recovery of the spacecraft, when
the instruments had been exposed to extreme temperature conditions,
the performance of the CDS and SUMER instruments is still good, as is
the temporal correlation. However, the ratio between the efficiencies
of the two instruments, which remained constant with time until the
SOHO accident seems to have changed afterwards. In the coronal lines
both instruments show an increase of average radiances towards the
solar maximum.

---------------------------------------------------------
Title: Sunspot transition region oscillations
Authors: Rendtel, J.; Staude, J.; Wilhelm, K.; Gurman, J. P.
2001ESASP.464..235R Altcode: 2001soho...10..235R
Intensity and velocity oscillations have been observed over a period
of 4.3 hours in lines of Ne VIII and C IV with the SUMER spectrograph
aboard SOHO. These lines are formed in the EUV plume above a
sunspot. Applying a wavelet analysis, we find oscillations mainly close
to 3 mHz. The temporal behaviour is strongly intermittent, particularly
for the velocity oscillations. This non-stationary behaviour may be
related with occurrence of blinkers in the umbral transition region.

---------------------------------------------------------
Title: Spectroscopic Signatures of a Flare Observed by SUMER
Onboard SOHO
Authors: Dammasch, I. E.; Curdt, W.; Kliem, B.; Dwivedi, B. N.;
Wilhelm, K.
2001IAUS..203..264D Altcode:
On 06 November 1999, SUMER (the Solar Ultraviolet Measurements of
Emitted Radiation spectrometer on SOHO) observed a post-flare site
above active region NOAA 8758 which was approaching the north-east
limb. SUMER recorded a time series taken with a constant slit position
and several spectral windows covering a wide temperature range (10 000 -
10 000 000 K), preceded and followed by contextual raster scans. During
this operation, a flare of size C4.6 occurred in the observed region,
also observed by the GOES 8 X-ray flux monitor, the SOHO/EIT imager
and the YOHKOH/SXT instrument. All data sets have been coaligned. The
temporal evolution seen in SUMER spectra is presented and compared
with the other observations.

---------------------------------------------------------
Title: Sunspot Plumes and Flow Channels
Authors: Brynildsen, N.; Maltby, P.; Fredvik, T.; Kjeldseth-Moe, O.;
Wilhelm, K.
2001SoPh..198...89B Altcode:
It is well known that sunspots are dark. This statement is not correct
in the sunspot atmosphere between the chromosphere and the corona,
where sunspots often are brighter than their surroundings. The brightest
feature in the sunspot transition region is called a sunspot plume. Not
all sunspots contain a plume. We find that 20 out of 21 sunspots show
a plume when one magnetic polarity dominates the sunspot region out
to a distance of 50 ” from the sunspot. Most sunspots show
downflows that exceed 25 km s−1 in the sunspot plumes at
temperatures close to 250 000 K. This downflow is not maintained by
inflow from the corona, but by gas at transition region temperatures,
streaming in flow channels from locations well outside the sunspot. We
suggest that this inflow is a necessary requirement for the sunspot
plume to occur and present a working hypothesis for the origin of
sunspot plumes. This paper is the first thorough spectral analysis of
sunspot plumes. It is based on simultaneous observations of ten or six
EUV emission lines in 42 sunspot regions with the Coronal Diagnostic
Spectrometer - CDS on the Solar and Heliospheric Observatory - SOHO. The
line profiles are studied in detail with another SOHO instrument,
the Solar Ultraviolet Measurements of Emitted Radiation - SUMER.

---------------------------------------------------------
Title: Spectroscopic features in the EUV emission of a M8 flare
observed by SUMER
Authors: Curdt, W.; Landi, E.; Feldman, U.; Innes, D.; Dwivedi, B.;
Wilhelm, K.
2001IAUS..203..260C Altcode:
On May 9, 1999 a flare of size M8 occurred while SUMER obtained a
spectral scan above the active region NOAA 8537 at the west limb. We
recorded spectra during the pre-flare phase, at flare onset, and during
the decay phase. More than 60 flare lines were observed during this
event, which include Fe XVIII - Fe XXIII lines that provide evidence
of 107 K plasmas. We also recorded lines from He-like ions,
such as Ne IX, Na X, Mg XI or Si XIII. Accurate wavelength measurements
of such lines are of interest in basic atomic physics studies. Using
plasma diagnostic techniques, we investigated the temporal evolution
of the electron densities and temperatures during the event. Since
the spectra contain lines from many different elements, we were able
to determine elemental abundances in the flaring plasma.

---------------------------------------------------------
Title: Properties of Solar Polar Coronal Hole Plasmas Observed above
the Limb
Authors: Doschek, G. A.; Feldman, U.; Laming, J. M.; Schühle, U.;
Wilhelm, K.
2001ApJ...546..559D Altcode:
We determine the line-of-sight emission measure distribution and
nonthermal motions as a function of height above the limb in the
north and south polar coronal holes. These quantities are derived from
extreme-ultraviolet (EUV) spectra obtained from the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) spectrometer on the Solar
and Heliospheric Observatory (SOHO) spacecraft. The SUMER slit was
oriented along the north-south direction for all the observations,
and the spatial resolution is about 1". The spectra were obtained
from a number of different types of observations in 1996. We select
a group of emission lines for analysis for which, under the usual
assumption of ionization equilibrium, the maximum emissivities span
the temperature range from about 3×105 K up to about
1.1×106 K. We compare our results with recently published
similar observations of a west limb quiet-Sun streamer region, with
other coronal hole results based on SUMER spectra, and with earlier
observations of the quiet Sun and coronal holes obtained from Skylab
and rocket spectra. We find that the electron temperature in the polar
holes increases with height above the limb, that the emission measure
distribution of plasma located at line-of-sight heights less than
about 60" peaks at a temperature of about 9×105 K, and that
nonthermal motions sometimes, but not always, increase slightly with
height above the limb. When observed, these increases level off above
the limb at about 120". We speculate that the increases with height
above the limb may be a manifestation of the fast solar wind. They
may also be due to the reduction in transition region structures with
increasing limb height. We also discuss wave heating as a cause of
the line width increases.

---------------------------------------------------------
Title: Comparison of far-ultraviolet emission lines formed in coronal
holes and the quiet Sun
Authors: Stucki, K.; Solanki, S. K.; Schühle, U.; Rüedi, I.; Wilhelm,
K.; Stenflo, J. O.; Brković, A.; Huber, M. C. E.
2000A&A...363.1145S Altcode:
We present an analysis of 26 far-ultraviolet emission lines belonging
to 19 atoms and ions observed on both sides of the boundary of polar
coronal holes as well as other quiet Sun areas along the limb. The
observations were made with the SUMER instrument (Solar Ultraviolet
Measurements of Emitted Radiation) onboard the Solar and Heliospheric
Observatory (SOHO). We compare line intensities, shifts and widths
in coronal holes with the corresponding values obtained in the quiet
Sun. We find that with increasing formation temperature, spectral
lines show on average an increasingly stronger blueshift in coronal
holes relative to the quiet Sun at equal heliospheric angle, with the
coolest lines in our sample (formation temperature ~ 104
K) indicating a small relative redshift. With respect to the rest
wavelength, however, only lines formed above 5 * 105 K
show blueshifts in coronal holes, which is not very different from
the quiet Sun. The width of the lines is generally larger (by a few
kilometers per second) inside the coronal hole. Intensity measurements
clearly show the presence of the coronal hole in Ne VIII lines as well
as in Fe XII, and provide evidence for a slightly enhanced emission
in polar coronal holes for lines formed below 105 K. This
last result is, however, less certain than the rest due to relatively
poor statistics. Intensity histograms also exhibit distinct differences
between coronal hole and quiet-Sun data. For cooler chromospheric lines,
such as Ni II, the coronal holes display a greater spread in intensities
than the quiet Sun. Transition-region lines, e.g. O IV, do not reveal
such differences, while Ne VIII shows characteristics of a coronal line
with lower average intensity and lower intensity spread inside holes.

---------------------------------------------------------
Title: Identification of Spectral Lines in the 500-1600 Å Wavelength
Range of Highly Ionized Ne, Na, Mg, Ar, K, Ca, Ti, Cr, Mn, Fe, Co,
and Ni Emitted by Flares (Te&gt;=3×106 K)
and Their Potential Use in Plasma Diagnostics
Authors: Feldman, U.; Curdt, W.; Landi, E.; Wilhelm, K.
2000ApJ...544..508F Altcode:
On 1999 May 9 the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) spectrometer on the Solar and Heliospheric Observatory
(SOHO) recorded spectra from a high-temperature region located
in the solar corona above the west limb. These spectra contain
lines from rather less-abundant elements in solar plasmas. In
this paper we present identifications of the high-temperature
(Te&gt;=3×106 K) Ne, Na, Mg, Ar, K, Ca, Ti,
Cr, Mn, Fe, Co, and Ni lines that were detected in the 500-1600 Å
spectral range of SUMER. In addition, accurate wavelength measurements
have been obtained with uncertainties varying between 0.015 and 0.040
Å (1 σ). Making use of the newly measured wavelengths, we derive
energy levels in the ground configuration of a number of highly
charged ions. We present intensity ratio calculations of lines in
the SUMER range that could be used to measure electron densities in
high-temperature solar plasmas. We also provide emissivities for Ca
XIII-Ca XV and Fe XVIII-Fe XXIII lines that could be used to determine
emission measures and electron temperatures of high-temperature
plasmas. We discuss a method for measuring elemental abundance
variations in high-temperature solar plasmas using lines presented
in the paper. A list of spectral lines spanning the 300-30000 Å
wavelength range and their branching ratios that are suitable for
efficiency calibration of space-borne spectrographs is provided.

---------------------------------------------------------
Title: The Morphology of the Solar Upper Atmosphere During the
Sunspot Minimum
Authors: Feldman, U.; Dammasch, I. E.; Wilhelm, K.
2000SSRv...93..411F Altcode:
The solar upper atmosphere (SUA) is defined as the volume above the
photosphere occupied by plasmas with electron temperatures, T_e,
above ~ 2×10^4 K. Until the Skylab era, only little was known about
the morphology of the SUA, while the quality of the spectroscopic
observations was continually improving. A spherically symmetric
atmosphere was assumed at that time, in which the temperature increased
with height. With advances in the observational techniques, it became
apparent that the morphology of the SUA was very complex even during the
minimum of the magnetic activity cycle. In particular, spectroscopic
measurements with high spectral and spatial resolution, which were
made in the light of ultraviolet emission lines representing a variety
of temperatures, led to the conclusion that most of the radiation
from the solar transition region could not be explained by assuming
a continuous chromosphere-corona interface, but rather by a region of
unresolved fine structures. Recent observational results obtained by
modern instruments, such as the Extreme-ultraviolet Imaging Telescope
(EIT), the Large Angle Spectroscopic Coronagraph (LASCO), and the
Solar Ultraviolet Measurements of (SUMER) spectrograph on the Solar and
Heliospheric Observatory (SOHO), as well as the Transition Region and
Coronal Explorer (TRACE), and their interpretations will be presented
in this review of our understanding of the morphology of the SUA.

---------------------------------------------------------
Title: Wavelength measurements of heliumlike 1s2s
3S1-1s2p 3P0,2
transitions in Ne8+, Na9+, Mg10+,
and Si12+ emitted by solar flare plasmas
Authors: Curdt, W.; Landi, E.; Wilhelm, K.; Feldman, U.
2000PhRvA..62b2502C Altcode:
With the Solar Ultraviolet Measurements of Emitted Radiation
instrument-a high-resolution normal-incidence telescope and spectrometer
on board the Solar and Heliospheric Observatory-heliumlike 1s2s
3S1-1s2p 3P0,2 transitions
in the highly ionized species Ne8+, Na9+,
Mg10+, and Si12+ were observed. The spectral
lines were emitted by high-temperature solar flare plasmas. In this
paper, we report on wavelength measurements of the He-like lines
identified in the recorded spectra. The wavelength uncertainties
we obtained from the solar measurements are &lt;=20 mÅ(1σ),
and in one case &lt;=30 mÅ. This is comparable to or better than
the best determinations so far achieved for these heliumlike 1s2s
3S1-1s2p 3P0,2 transitions
with instrumentation in the laboratory. For the Na9+
3S1-3P2 transition we
report what is to our knowledge the first wavelength measurement. The
knowledge of the accurate wavelengths can provide important checks on
atomic structure calculations.

---------------------------------------------------------
Title: Solar spicules and macrospicules observed by SUMER
Authors: Wilhelm, K.
2000A&A...360..351W Altcode:
Motivated by recent observations of spicules and macrospicules in
the far-ultraviolet (FUV) wavelength range with the Solar Ultraviolet
Measurements of Emitted Radiation spectrograph (SUMER) on the Solar and
Heliospheric Observatory (SOHO), a generation mechanism for spicules and
macrospicules is outlined which deviates significantly from most of the
previous concepts. The important aspect is that the spicule propagation
is not strictly aligned along the local magnetic field direction
and that there is a close association with explosive events. It is
suggested that the chromospheric material will be carried up by the
relaxing magnetic field following a field line reconnection. Some
of the consequences for spicules and other features of the quiet-
Sun (QS) atmosphere will be discussed, such as the average red shift
of FUV emission lines in the transition region (TR) and polar plume
formation in coronal holes (CHs).

---------------------------------------------------------
Title: Hydrogen temperature gradient in the transition region of a
solar coronal hole
Authors: Marsch, E.; Tu, C. -Y.; Wilhelm, K.
2000A&A...359..381M Altcode:
The Lyman series of hydrogen was observed by SUMER on SOHO on the
north polar limb of the Sun with a total exposure time of more than
ten hours. The resulting line profiles have been analysed using
the technique described by Marsch et al. (1999). The data analysis
corroborates earlier findings on the Lyman lines, but also yields
phenomena which cannot be fully understood at the present time. Firstly,
the line width of the Lyman lines increases with decreasing series or
quantum number. Secondly, the hydrogen temperature gradient in the
height range from 12 000 km to 18 000 km is unexpectedly small and
does not reveal a steep jump as might be expected from modelling of
the transition region. The average temperature increases only slightly
from 1;105 K to 2;105 K. Possible explanations
of these observations are given and models are briefly discussed.

---------------------------------------------------------
Title: Observed Variability and Dynamics of Active Region Loops
Authors: Haugan, S. V. H.; Brekke, P.; Fredvik, T.; Kjeldseth-Moe,
O.; Wilhelm, K.; Gurman, J. B.
2000SPD....31.0205H Altcode: 2000BAAS...32..811H
A series of 218 rasters taken with the Coronal Diagnostic Spectrometer
(CDS) on SOHO demonstrates the strong time variability and
dynamical state of the plasma in active region loops at transition
region temperatures, i.e. 10 000 K to 500 000 K, first reported
by Kjeldseth-Moe and Brekke (1998). The continuous raster series,
which covered 39 hours, show how transition region loops or sections
of loops, 50-200 Mm in length, appear and disappear in intervals as
short as 10 minutes, the observing cadence. At the same temperatures
plasma velocities of 20 km s-1 to 100 km s-1
are indicated from observed Doppler shifts. Siphon flows may occur in
some of the loops, but in other loops patterns are less obvious. High
velocities are frequently seen where the emitted intensities are weak,
often on the “outside” of the loops as defined by the emission in
that particular spectral line. At coronal temperatures the emission
is less time variable, but significant changes are seen. Systematic
loop velocities occur only occasionally in the corona. Simultaneous
observations with EIT and SUMER were made during part of the raster
series and is compared with the CDS result.

---------------------------------------------------------
Title: Active Region Loops Observed with SUMER on Board the SOHO
Authors: Chae, Jongchul; Wang, Haimin; Qiu, Jiong; Goode, Philip R.;
Wilhelm, Klaus
2000ApJ...533..535C Altcode:
We study the emission and dynamical characteristics of transition region
temperature plasmas in magnetic loops by analyzing a high-resolution,
limb observation of the active region NOAA 7962. The observations were
performed by the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) instrument on board the Solar and Heliospheric Observatory
(SOHO). The SUMER observation produced a set of raster scans of the
region, in the four lines, H I Lyβ λ1025, O VI λλ1032, 1038,
and C II λ1037. The data are used to construct intensity, velocity,
and line width maps of the active region, from which more than 10
well-resolved loops are identified and classified into four different
groups. We determine several physical parameters of the loops in each
group such as diameter, length, temperature, line-of-sight plasma
velocity, and nonthermal line broadening. Our results indicate that
both kinds of temperature variations exist in active region loops:
variations from loop to loop and variations along each loop. It is
also found that there is a distinction between stationary loops and
dynamic loops. The dynamic loops have large bulk motions and large
nonthermal line broadenings. Some of the dynamic loops display large
velocity shears with the sign of line-of-sight velocities changing
across the loop axes. These velocity shears appear to represent
rotational motions around the loop axes with velocities of up to 50 km
s-1. There are indications that nonthermal line broadening
is the result of magnetohydrodynamic turbulence inside the loops. Based
on our observations, we postulate that when loops erupt, some of the
kinetic and magnetic energy cascades down to turbulent energy which
would be dissipated as heat.

---------------------------------------------------------
Title: Radiance variations of the quiet Sun at far-ultraviolet
wavelengths
Authors: Schühle, U.; Wilhelm, K.; Hollandt, J.; Lemaire, P.;
Pauluhn, A.
2000A&A...354L..71S Altcode:
We have measured the radiance of quiet-Sun areas at the centre of the
solar disk using the vacuum-ultraviolet telescope-spectrograph SUMER
(Solar Ultraviolet Measurements of Emitted Radiation) on the Solar and
Heliospheric Observatory (SOHO). The radiances of selected emission
lines have been measured from March 1996 to the present. The lines that
have been observed regularly since the beginning of the SOHO mission
are He i 584 Å, Mg x 609 Å and 624 Å, Ne viii 770 Å, N v 1238 Å,
and the H i Lyman continuum at 880 Å. We investigate the variability
of these emission lines during the solar minimum and the ascending
phase of the present solar activity cycle. The transition region and
coronal lines show an increasing trend of up to 100% since the sunspot
minimum. The results are important for models of solar VUV variability
on the basis of radiance contrast ratios of solar disk regions. Our
spatially resolved images allow a separation of the network and cell
areas of the quiet-Sun. Both regimes show similar variations.

---------------------------------------------------------
Title: Mid-term Radiance Variation of Far-Ultraviolet Emission Lines
from Quiet-Sun Areas
Authors: Schühle, U.; Hollandt, Jorg; Pauluhn, Anuschka; Wilhelm,
Klaus
2000ESASP.463..427S Altcode: 2000sctc.proc..427S
No abstract at ADS

---------------------------------------------------------
Title: Solar Irradiances of Ultraviolet Emission Lines Measured
During the Minimum of Sunspot Activity in 1996 and 1997
Authors: Wilhelm, K.; Lemaire, P.; Dammasch, I. E.; Hollandt, J.;
Schuhle, U.; Curdt, W.; Kucera, T.; Hassler, D. M.; Humbler, M. C. E.
2000PCEC...25..389W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Radiometric Calibration of the Vacuum-Ultraviolet Spectrograph
SUMER on the SOHO Spacecraft with the B Detector
Authors: Schühle, Udo; Curdt, Werner; Hollandt, Jörg; Feldman, Uri;
Lemaire, Philippe; Wilhelm, Klaus
2000ApOpt..39..418S Altcode:
The Solar Ultraviolet Measurement of Emitted Radiation (SUMER)
vacuum-ultraviolet spectrograph was calibrated in the laboratory
before the integration of the instrument on the Solar and Heliospheric
Observatory (SOHO) spacecraft in 1995. During the scientific operation
of the SOHO it has been possible to track the radiometric calibration
of the SUMER spectrograph since March 1996 by a strategy that employs
various methods to update the calibration status and improve the
coverage of the spectral calibration curve. The results for the A
Detector were published previously Appl. Opt. 36, 6416 (1997) . During
three years of operation in space, the B detector was used for two
and one-half years. We describe the characteristics of the B detector
and present results of the tracking and refinement of the spectral
calibration curves with it. Observations of the spectra of the stars and
Leonis permit an extrapolation of the calibration curves in the range
from 125 to 149.0 nm. Using a solar coronal spectrum observed above
the solar disk, we can extrapolate the calibration curves by measuring
emission line pairs with well-known intensity ratios. The sensitivity
ratio of the two photocathode areas can be obtained by registration of
many emission lines in the entire spectral range on both KBr-coated and
bare parts of the detector s active surface. The results are found to be
consistent with the published calibration performed in the laboratory
in the wavelength range from 53 to 124 nm. We can extrapolate the
calibration outside this range to 147 nm with a relative uncertainty
of 30% (1 ) for wavelengths longer than 125 nm and to 46.5 nm with 50%
uncertainty for the short-wavelength range below 53 nm.

---------------------------------------------------------
Title: Observations of sunspot transition region oscillations
Authors: Brynildsen, N.; Maltby, P.; Leifsen, T.; Kjeldseth-Moe, O.;
Wilhelm, K.
2000SoPh..191..129B Altcode:
Oscillations with a period of 3 minutes are observed in the transition
region of six sunspots with the Solar and Heliospheric Observatory
- SOHO joint observing programme for velocity fields in sunspot
regions. Observations of the transition region lines O v λ629
and N v λλ1238, 1242 with the SUMER instrument show significant
differences in the amplitude of the 3-minute oscillations from one
sunspot to another, both in intensity and line-of-sight velocity. In
four sunspots the central part of the umbra is observed. Two of these
sunspots show coincidence between the maxima in peak line intensity
and velocity directed towards the observer, as is expected for an
upward-propagating acoustic wave. The two other sunspots show large
oscillation amplitudes and a difference of 25° between maxima in
intensity and blue shift. The possible effect of partial wave reflection
on the observed phase relation is discussed. For one sunspot only a part
of the umbra, close to the penumbra, was observed and the observations
show a difference of 50° between maxima in intensity and blueshift. For
the smallest sunspot the observations are found to be contaminated by
contributions from an area without oscillations. Observed oscillations
in line width are small, but probably significant in two sunspots. The
observations of NOAA 8378 allow us to compare simultaneous recordings
of the oscillations in the chromospheric Si ii λ1260 line with the
oscillations in the transition region lines. We question the suggestion
by Fludra (1999) that the sunspot transition region oscillations are
a typical feature of the sunspot plumes.

---------------------------------------------------------
Title: Sumer Observations of the Quiet Sun: Transition Region and
Low Corona
Authors: Wilhelm, Klaus
2000AdSpR..25.1723W Altcode:
SUMER - the Solar Ultraviolet Measurements of Emitted Radiation
instrument on the Solar and Helio-spheric Observatory (SOHO) of ESA
and NASA - observed its first light on January 24, 1996 and covered
the minimum of the sunspot activty between the solar cycles 22 and 23
with nearly continuous observations. Consequently, in many studies
particular emphasis was put on quiet Sun investigations. We will
review in this presentation some of the observational results on the
transition region and the low corona obtained by UV and EUV emission
line measurements. The chromospheric network, including its small
scale activity, will be discussed, as well as polar coronal holes

---------------------------------------------------------
Title: Signatures of Magnetic Reconnection and Observed EUV Emission
Line Profiles in An Active Region
Authors: Brekke, P.; Brynildsen, N.; Kjeldseth-Moe, O.; Maltby, P.;
Wilhelm, K.
2000AdSpR..26..457B Altcode:
We report on observations with SUMER on SOHO of high-velocity events,
also called explosive events. The high spatial and spectral resolutions
of SUMER allow simultaneous observations of EUV emission lines formed
at different temperatures within the transition region. Complex
line profiles with three separate line components appear to be
a characteristic feature of many high-velocity events based on a
survey of Si IV λ1393 observations. The present study is based on
551 spectra of the active region NOAA 7995 obtained on 17 November
1996. We find that the complex line profiles of explosive events may be
represented by a composite line profile consisting of three Gaussian
line components. Both positive and negative line-of-sight velocities
are found to be significantly larger at 6.3 ×105 K than
at 1.5 - 1.7 ×105 K. We briefly confront the observations
with signatures predicted from magnetic reconnections, disturbances
originating in the corona and flows in an extremely structured
transition region

---------------------------------------------------------
Title: Radiance Variations of Vacuum-Ultraviolet Emission Lines of
the Quiet Sun Observed with SUMER on SOHO
Authors: Schuhle, U.; Pauluhn, A.; Hollandt, J.; Lemaire, P.;
Wilhelm, K.
2000PCEC...25..429S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On the source regions of the fast solar wind in polar
coronal holes
Authors: Wilhelm, K.; Dammasch, I. E.; Marsch, E.; Hassler, D. M.
2000A&A...353..749W Altcode:
Fast streams of the solar wind with speeds of up to ~ 800 km
s-1 at a distance of 1 AU (astronomical unit) from the Sun
are known to originate in solar coronal holes. With the Solar and
Heliospheric Observatory (SOHO) detailed studies of the solar wind
source regions have been made possible for the first time. We show
images of solar polar coronal holes in the extreme ultraviolet (EUV),
which were obtained by the Solar Ultraviolet Measurements of Emitted
Radiation (SUMER) spectrograph on the SOHO spacecraft. The light is
emitted in spectral lines of helium atoms and Ne7+ ions
formed at temperatures of about 20 000 K and 630 000 K, respectively,
in ionization equilibrium. The sources of the fast solar wind in polar
coronal holes can clearly be seen in the chromospheric He i line and
in the Ne viii line of the low corona, either as dark polar caps
in radiance diagrams or as regions of predominant blue shift. The
average blue shifts along the line of sight in coronal holes amount
to speeds of ~ 3 km s-1 for both He and Ne7+,
if the Doppler shift can be interpreted as an indication of bulk
motions. Bright points and polar plumes seen in Ne viii (lambda 770)
do, however, not show signatures of outflow.

---------------------------------------------------------
Title: Solar spectroradiometry with the telescope and spectrograph
SUMER on the Solar and Heliospheric Observatory SOHO
Authors: Wilhelm, K.; Schühle, U.; Curdt, W.; Dammasch, I. E.;
Hollandt, J.; Lemaire, P.; Huber, M. C. E.
2000Metro..37..393W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On the Electron Temperatures, Densities and Hot Ions in
Coronal Hole Plasma Observed by Sumer on SOHO
Authors: Dwivedi, B. N.; Mohan, A.; Wilhelm, K.
2000AdSpR..25.1751D Altcode:
Making use of high-resolution ultraviolet observations obtained
with SUMER (Solar Ultraviolet Measurements of Emitted Radiation)
on the spacecraft SOHO (Solar and Heliospheric Observatory), we
study plasma temperatures, densities and hot ions in polar coronal
holes (source region of the high-speed solar wind). In particular,
we present spectroscopic diagnostics for NeVIII, Mg VIII, Si VIII,
and Mg IX lines to infer these physical parameters and discuss the
constraints of their applications in the coronal hole plasma. We
also present the implications of this investigation in addressing
the acceleration mechanisms of the solar wind, one of the outstanding
problems in solar physics

---------------------------------------------------------
Title: Dynamics of Chromiospheric and Transition Region Lines Observed
with SOHO/SUMER and the GCT/Tenerife
Authors: Muglach, K.; Fleck, B.; Schühle, U.; Stolpe, F.; Foing,
B. H.; Wilhelm, K.
2000AdSpR..25.1731M Altcode:
High-resolution spectroscopic observations of the quiet Sun have been
carried out in September 1996 at the German Gregory Coudé Telescope
(GCT) in Tenerife and in May 1997 with the SUMER instrument onboard
SOHO. Time sequences of spectra in the visible and near infrared
as well as in the ultraviolet have been taken, covering a range of
heights from the solar photosphere up into the transition region. In
this contribution we present the dynamical behaviour observed at the
various heights in the solar atmosphere

---------------------------------------------------------
Title: SUMER Observations of the Source Regions of the Fast Solar Wind
Authors: Wilhelm, K.
1999ESASP.448.1083W Altcode: 1999ESPM....9.1083W; 1999mfsp.conf.1083W
No abstract at ADS

---------------------------------------------------------
Title: On the sunspot transition region
Authors: Maltby, P.; Brynildsen, N.; Fredvik, T.; Kjeldseth-Moe, O.;
Wilhelm, K.
1999SoPh..190..437M Altcode:
The EUV line emission and relative line-of-sight velocity in the
transition region between the chromosphere and corona of 36 sunspot
regions are investigated, based on observations with the Coronal
Diagnostic Spectrometer - CDS and the Solar Ultraviolet Measurements of
Emitted Radiation - SUMER on the Solar and Heliospheric Observatory -
SOHO. The most prominent features in the transition-region intensity
maps are the sunspot plumes. In the temperature range between log T=5.2
and log T=5.6 we find that 29 of the 36 sunspots contain one or two
sunspot plumes. The relative line-of-sight velocity in sunspot plumes
is high and directed into the Sun in the transition region, for 19 of
the sunspots the maximum velocity exceeds 25 km s−1. The
velocity increases with increasing temperature, reaches a maximum
close to log T=5.5 and then decreases abruptly.

---------------------------------------------------------
Title: Solar Ultraviolet Irradiance and Radiance Observations by
SUMER on SOHO
Authors: Dammasch, I. E.; Wilhelm, K.; Curdt, W.; Schühle, U.
1999ESASP.448.1165D Altcode: 1999ESPM....9.1165D; 1999mfsp.conf.1165D
No abstract at ADS

---------------------------------------------------------
Title: Evidence for Non-Maxwellian Electron Energy Distributions in
the Solar Transition Region: Si III Line Ratios from SUMER
Authors: Pinfield, D. J.; Keenan, F. P.; Mathioudakis, M.; Phillips,
K. J. H.; Curdt, W.; Wilhelm, K.
1999ApJ...527.1000P Altcode:
Recent calculations of Si III emission-line strengths are compared with
SUMER observations from a quiet solar region, a coronal hole, and an
active region. Diagnostic line ratios are used to derive Te
and Ne for the emitting plasma in each region, and good
agreement between theory and observations is found. A major enhancement
in the intensity of the 1313 Å emission line is observed, as well
as some evidence of a small decrease in the temperature of maximum
ionization fraction, as one moves from the coronal hole to the active
region. Possible explanations for these effects are discussed, and
it is concluded that they may be caused by the presence of nonthermal
electrons in the transition region.

---------------------------------------------------------
Title: The solar ultraviolet spectrum from 1200 Å to 1560 Å:
a radiometric comparison between SUMER/SOHO and SOLSTICE/UARS
Authors: Wilhelm, K.; Woods, T. N.; Schühle, U.; Curdt, W.; Lemaire,
P.; Rottman, G. J.
1999A&A...352..321W Altcode:
After short descriptions of the SUMER (Solar Ultraviolet Measurements
of Emitted Radiation) spectrometer onboard SOHO (the Solar and
Heliospheric Observatory) and the SOLSTICE (Solar-Stellar Irradiance
Comparison Experiment) spectrometer on UARS (the Upper Atmosphere
Research Satellite), a radiometric comparison is carried out of solar
irradiance spectra measured by SOLSTICE and spectra derived from
SUMER radiance observations of quiet-Sun regions in the wavelength
range from 1200 Å to 1560 Å. The emission lines N v (lambda 1238)
and C iv (lambda 1548) are considered in detail. For these lines,
irradiance data are also available from full-Sun raster scans of SUMER
and deviations of less than 15% are found between SOLSTICE and SUMER
results - well within the combined uncertainty margins.

---------------------------------------------------------
Title: A new Sun: Probing solar plasmas in the extreme-ultraviolet
light from SUMER on SOHO
Authors: Dwivedi, Bhola N.; Mohan, Anita; Wilhelm, Klaus
1999CSci...77.1521D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Plasma Flows In Coronal Hole Regions
Authors: Landi, E.; Mullan, D.; Poletto, G.; Wilhelm, K.
1999ESASP.446..417L Altcode: 1999soho....8..417L
More than two decades after coronal holes (CH) had been recognized
to be the source regions of solar wind, we still do not know which
structures, within CH, most contribute to the solar wind mass flux. In
a recent work, Hassler et al. (1999) obtained velocity maps of a
coronal hole region, in the Ne VIII 770 Angstrom line, which suggest
that localized areas within the network might be sources of the solar
wind. On the opposite, an earlier work of Dupree et al. (1996), from
an analysis of the He I 10830 Angstrom line, suggested cell regions
as sources of the solar wind. In the present work, we reinvestigate
this issue analysing SUMER data taken in an equatorial and in a polar
coronal hole, observed respectively on 29 August 1996 and 21 September
1996. We study the behavior of Si II, C IV, O V, N V, Ne VIII, Mg X and
Fe XII ions, whose temperatures of formation range from chromospheric
(around 2x104 K) to coronal values (around 1.5x105
K). In particular, we analysed intensity and velocity distributions
of these lines, and illustrate changes in the plasma velocity pattern
as a function of the temperature regime where lines form.

---------------------------------------------------------
Title: The Off-Limb Behaviour Of The FIP Effect In The Solar Plasma
observed by SUMER on SOHO
Authors: Dwivedi, B. N.; Curdt, W.; Wilhelm, K.
1999ESASP.446..293D Altcode: 1999soho....8..293D
We present results from a study of EUV off-limb spectra obtained
on 1996 August 8 and 9 with the SUMER spectrometer on spacecraft
SOHO. With the capabilities of SUMER, we rastered the emitting source
from 30” off the lim outwards, and secured a unique high quality set
of high-resolution EUV spectra. Using this observation, we investigate
the FIP-effect in the transition region emission in the corona and also
its variation as a function of height above the lim. We compare and
rediscuss our results with the similar observation taken with SUMER
on 1996 June 20 but beginning from 40” off the limb outwards. The
abstrat of this paper is already submitted by Dr W. Curdt : A quiet
Sun Spectral Atlas Between 660-1500 A Observed with SUMER on SOHO by
Curdt, Brekke, Schuhle, Wilhelm and Dwivedi.

---------------------------------------------------------
Title: Sunspot Transition Region Oscillations
Authors: Brynildsen, N.; Kjeldseth-Moe, O.; Maltby, P.; Wilhelm, K.
1999ESASP.446..207B Altcode: 1999soho....8..207B
Based on the SOHO joint observing programme for velocity fields in
sunspots, we have detected 3 min transition region umbral oscillations
in six sunspots. Simultaneous recordings of O V lambda 629, NV lambdas
1238, 1242 and Si I lambda 1260 with the SUMER instrument allow us to
compare the transition region oscillations with the 3 min chromospheric
oscillations above the sunspot. We investigate the amplitudes and phase
relations of the oscillations in peak line intensity, line-of-sight
velocity and line width. The spatial distributions of power in the
3 min oscillations, both in intensity and line-of-sight velocity,
are presented. The observations show that the maxima in peak line
intensity are nearly, but not exactly in phase with the maxima in
velocity directed towards the observer. The suggestion that the waves
are upward propagating acoustic waves is confronted with observations.

---------------------------------------------------------
Title: The SUMER EUV Atlas in the Spectral Range 670 A - 1498 A
Authors: Curdt, W.; Brekke, P.; Schühle, U.; Wilhelm, K.; Dwivedi,
B. N.
1999ESASP.446..251C Altcode: 1999soho....8..251C
An extreme ultraviolet spectral atlas between 660 and 1600 A (first
order) of a quiet Sun, a coronal hole, and a Sun spot region has
been derived from observations with the SUMER (Solar Ultraviolet
Measurements of Emitted Radiation) instrument on SOHO. More than 1000
emission lines are given with the best available identification. The
spectra are radiometrically calibrated. Lines in second order are
superimposed on this spectrum. The spectral scans include emissions
from atoms and ions in the temperature range from 6 000 to 2000 000 K,
i.e., continua and emission lines emitted from the lower chromosphere
to the corona. This broad wavelength coverage provides an important
new diagnostic tool for studying the essential physical parameters
throughout the upper solar atmosphere. In particular, the wavelength
range shortward of 1100 A as observed by SUMER represents a significant
improvement over the spectra produced in the past. A brief description
of the data reduction and calibration procedures is given. The absolute
intensities are determined with an uncertainty of better than +- 15%
in most of the range presented, and the wavelength scale is accurate
to better than 0.01 A. The atlas will also be available in machine
readable form.

---------------------------------------------------------
Title: Solar Mg X and Fe XII Wavelengths Measured By SUMER
Authors: Dammasch, I. E.; Hassler, D. M.; Wilhelm, K.; Curdt, W.
1999ESASP.446..263D Altcode: 1999soho....8..263D
Several SUMER studies will be presented that were performed in August/
September 1996 during the "Whole Sun Month" campaign "The large scale
structure of the solar minimum corona". The spatial scans with long
exposure times cover regions of quiet Sun, polar coronal holes and
corona. They are used to determine off-limb the rest wavelengths of
coronal lines (Mg X, Fe XII), which are found to differ from earlier
literature values. Additionally, we try to determine Doppler velocities
on different parts of the disk, which is more complicated, since here
the coronal lines are blended with colder lines.

---------------------------------------------------------
Title: SUMER Observations of Intensity Oscillations in the Transition
Region of a Sunspot
Authors: Rendtel, J.; Staude, J.; Innes, D. E.; Wilhelm, K.
1999ASPC..184..271R Altcode:
UV spectroscopic data obtained with the SUMER spectrograph aboard SOHO
have been analysed to detect oscillations in the chromosphere-corona
transition region (TR) above sunspots. We observed the active region
NOAA 7986 in the wavelength bands around the Ne VIII line at 770.4 Å
and the C IV line at 1548.1 Å on August 29, 1996, between 09:08 UT
and 13:31 UT. Simultaneous observations with the Normal Incidence
Spectrometer of CDS aboard SOHO have shown, that the spot had a
bright EUV plume at TR temperatures. A preliminary data analysis
indicates intensity oscillations in the 2-minute range (7.3...7.9
mHz) in both spectral lines. The temporal variation of oscillatory
power in the two spectral lines is generally in opposite directions,
i.e. during an increase of oscillatory power in the Ne VIII line we
find a decrease in the C IV line. A similar but smaller tendency is
observed in the average intensity of the line profiles. This hints at
a non-adiabatic behaviour of the oscillations and a slow cooling of
the emitting sunspot plume region.

---------------------------------------------------------
Title: Proton and hydrogen temperatures at the base of the solar
polar corona
Authors: Marsch, E.; Tu, C. -Y.; Heinzel, P.; Wilhelm, K.; Curdt, W.
1999A&A...347..676M Altcode:
The SUMER (Solar Ultraviolet Measurements of Emitted Radiation)
Spectrometer on SOHO (Solar and Heliospheric Observatory) has been
used to observe the lines of the Lyman series (up to quantum numbers
larger than 20) of hydrogen emitted in the solar atmosphere. The
line shapes and intensities versus height are obtained near the limb
from about -10\arcsec to 70\arcsec. The lines are broad and show the
typical self-absorption reversal near the limb, where the emission
comes from optically thick material, and change systematically with
increasing height. The H i Ly6, Ly7 and Ly9 lines attain a Gaussian
shape at heights above the visible limb between about 19\arcsec and
22\arcsec, where the emission comes from an optically thin plasma. The
line shapes and intensities can be fitted well by model profiles
obtained from multilevel NLTE (Non Local-Thermodynamic-Equilibrium)
radiative transfer calculations which allow us, assuming excitation
and ionization equilibrium, to derive consistently the temperatures and
densities of the hydrogen atoms and, with additional assumptions, of the
protons. Temperature values range between 1 10(5) K to 2 10(5) K. We
present the systematics of the line shapes as observed in different
emission regions and discuss briefly the relevance of these results
for the solar wind acceleration and coronal heating.

---------------------------------------------------------
Title: Multiple-Thread Model of a Prominence Observed by SUMER and
EIT on SOHO
Authors: Wiik, J. E.; Dammasch, I. E.; Schmieder, B.; Wilhelm, K.
1999SoPh..187..405W Altcode:
A quiescent polar crown prominence was observed at Meudon in Hα and
Ca ii lines, and by EIT and SUMER on board SOHO in UV lines from 9
to 10 March 1996. SUMER observed the prominence continuously in a
scanning mode between 21:40 UT on 9 March, and 18:13 UT on 10 March,
in the nitrogen line N v (λ1238) with a 1 arc sec2
resolution. Altogether 190 prominence images (121×108 pixels)
were obtained. These are presented in a movie. The prominence is
highly dynamic. Large-scale features, such as mixed loop systems and
dark cavities are changing on time scales of a few hours. Filamentary
structure is evident and is changing within a few frames of the movie. A
lifetime of 20-25 min for the fine structure has been found by the
autocorrelation method. We have statistically analysed the three
moments of the N v line in the prominence: line intensity, Doppler
shift and linewidth, in the context of a multiple-thread model. We
find that the data are consistent with a model where the prominence is
assumed to be an ensemble of small threads. In the brightest parts of
the prominence it is possible that there are many unresolved threads
(15-20) along the line of sight with diameters smaller than a few
hundred kilometers. The filling factor is probably very small and in
that case the structures occupy only a fraction of the volume.

---------------------------------------------------------
Title: SOHO, der ungetrübte Blick auf die Sonne.
Authors: Schwenn, R.; Wilhelm, K.
1999S&WSp...4...38S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Alfvén waves in the solar polar coronal holes
Authors: Banerjee, D.; Teriaca, L.; Doyle, J. G.; Wilhelm, K.
1999AIPC..471..289B Altcode: 1999sowi.conf..289B
We study the variation of the line width and electron density as a
function of height above two coronal holes from forbidden spectral
lines of Si VIII. The spectra were obtained with the Solar Ultraviolet
Measurements of Emitted Radiation spectrometer flown on the Solar and
Heliospheric Observatory spacecraft. The observations concentrate on the
dark regions outside the plumes, which are believed to be the location,
where the fast solar wind originates. The line width data show that
the non-thermal line-of-sight velocity increases from 20 km s-1 at
27 arc sec above the limb to 37 km s-1 some 370 arc sec (i.e. ~1.38
Rsolar) above the limb. The electron density shows a
decrease from 3.5 108 cm-3 to 1.6 107
cm-3 over the same distance. This data implies that the
non-thermal velocity is inversely proportional to the quadratic root of
the electron density in the range 1-1.2 Rsolar, in excellent
agreement with that predicted for undamped radially propagating Alfvén
waves. Beyond 1.2 Rsolar our data suggests an effective
breakdown of linear theory for the propagation of Alfvén waves.

---------------------------------------------------------
Title: The low-latitude inner corona of the sun observed by SUMER
on SOHO
Authors: Wilhelm, Klaus
1999AIPC..471..269W Altcode: 1999sowi.conf..269W
High-resolution spectra obtained by the Solar Ultraviolet Measurements
of Emitted Radiation (SUMER) spectrograph in both spectral and
spatial regimes provided the opportunity to study streamer plasmas
in detail at low and medium solar latitudes of the inner corona. An
analysis of EUV and UV emission lines shows that the lines exhibit
a fundamentally different behavior depending on their formation
temperatures. These observations have been supported by line ratio
plasma diagnostics. Electron densities have been deduced from the
Si VIII line ratio L(1440 Å)/L(1445 Å). The Mg IX ratio L(706
Å)/L(750 Å) has been used to determine the corresponding electron
temperatures. The neon-to-magnesium ratio is changing with latitude
both in the east and the west streamer in the same manner.

---------------------------------------------------------
Title: A Comparison of Measurements of Solar Extreme-Ultraviolet
Spectral Line Intensities Emitted by C, N, O, and S Ions with
Theoretical Calculations
Authors: Doschek, E. E.; Laming, J. M.; Doschek, G. A.; Feldman, U.;
Wilhelm, K.
1999ApJ...518..909D Altcode:
Atomic data for ionized atoms are important for many astrophysical
applications. The launch of the Solar Ultraviolet Measurements of
Emitted Radiation (SUMER) extreme-ultraviolet (EUV) spectrometer aboard
the Solar and Heliospheric Observatory (SOHO) allows us to test the
accuracy of certain computed relative excitation rate coefficients
and transition probabilities for a number of important astrophysical
ions. We use spectral line intensity ratios derived from SUMER spectra
to compare these quantities with the best available theoretical
calculations for transitions within the ions C II, N III, N IV, O III,
O IV, O V, S III, S IV, and S V. The results of this work are important
for many current and upcoming NASA astrophysics missions. In addition
to the published atomic data, we calculate some new atomic data using
the Hebrew University Lawrence Livermore Atomic Code (HULLAC). Our
comparison of measured intensity ratios with theoretical predictions
reveals significant discrepancies between the predicted and measured
intensity ratios for several ions, particularly for S III, S IV, and
S V. S III and S IV produce strong line emission in the Io torus. We
discuss the methods we used to ensure that our ratios are accurate,
the possible effects of Lyman continuum absorption on our data, and the
ramifications of ignoring dielectronic capture resonances in certain
transitions as a possible explanation for some of the discrepancies.

---------------------------------------------------------
Title: The NE BT VIII (lambda 770) resonance line: solar wavelengths
determined by SUMER on SOHO
Authors: Dammasch, I. E.; Wilhelm, K.; Curdt, W.; Hassler, D. M.
1999A&A...346..285D Altcode:
The investigation of the source and acceleration of the solar wind was
among the prime scientific goals of SOHO - ESA's and NASA's Solar and
Heliospheric Observatory. For the coronal regions closest to the Sun,
the bright extreme ultraviolet (EUV) resonance lines of the Ne viii
spectrum at 770 { Angstroms} and 780 { Angstroms} with a formation
temperature of 630 000 K are promising targets for detecting the
initial solar wind outflow. The investigations published up to now using
data obtained by SUMER - the Solar Ultraviolet Measurements of Emitted
Radiation spectrometer - on SOHO gave conflicting results. They accepted
a rest wavelength of 770.409 { Angstroms} for the brighter Ne viii line
as reported in the literature. We deduce the solar wavelength of this
line for several conditions on the Sun and derive a rest wavelength
of (770.428 +/- 0.003) { Angstroms} and outflow speeds in coronal
hole regions of ~ 9 km s(-1) . This is in agreement with other recent
studies using SUMER data. The rest wavelength determination is based
on the assumptions of no average Doppler shift above the solar limb
and a comparison with laboratory wavelengths of cool chromospheric
lines. Quiet Sun areas exhibit an average blue shift of (1 +/- 1)
km s(-1) in this line.

---------------------------------------------------------
Title: Nonlinear Sunspot Transition Region Oscillations in NOAA 8378
Authors: Brynildsen, N.; Kjeldseth-Moe, O.; Maltby, P.; Wilhelm, K.
1999ApJ...517L.159B Altcode:
Observations obtained with the Solar and Heliospheric Observatory
joint observing program for velocity fields in sunspot regions are
used to study the 3 minute transition region oscillations above four
sunspots. Here we report mainly on the results obtained for NOAA 8378,
based on simultaneous recordings of the transition region lines O
V λ629 and N V λλ1238, 1242 and the chromospheric Si II λ1260
line with the Solar Ultraviolet Measurements of Emitted Radiation
instrument. The 3 minute transition region oscillations in NOAA 8378
occur mainly above the umbra and show (1) larger peak line intensity
amplitudes than reported before, (2) clear signs of nonlinearities,
(3) significant oscillations in line width, (4) maxima in peak line
intensity and maxima in velocity directed toward the observer that
are nearly, but not exactly in phase, and (5) a clear connection to
the oscillations in the sunspot chromosphere. The suggestion that the
waves are upward-propagating acoustic waves is confronted with the
observations by a simple test.

---------------------------------------------------------
Title: Properties of Quiet-Sun Coronal Plasmas at Distances of
1.03&lt;=Rsolar&lt;=1.50 along the Solar Equatorial Plane
Authors: Feldman, U.; Doschek, G. A.; Schühle, U.; Wilhelm, K.
1999ApJ...518..500F Altcode:
We determine the physical properties, i.e., electron temperature,
density, line-of-sight emission measure, and element-abundance variation
with height, in the Sun's equatorial west limb streamer region from
extreme-ultraviolet (EUV) spectra recorded by the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and
Heliospheric Observatory (SOHO) spacecraft. The spectra were recorded
on 1996 November 21-22 during a special “roll” maneuver in which
the SUMER slit was oriented in the east-west direction. Because the
SUMER spectrometer is stigmatic along the slit length, the spectra are
spatially resolved in the east-west direction. The spectra we discuss
cover an effective distance range outside the west limb from 1.03 to
1.50 solar radii (Rsolar) the maximum spatial resolution is
1”. We select a group of emission lines for analysis that
under the usual ionization equilibrium assumption span the temperature
range from 3×105 up to 2×106 K. However,
we note that above the limb a major fraction of a line intensity may
arise at a temperature that is far from the temperature of maximum
emitting efficiency in ionization equilibrium. In this paper we assume
ionization equilibrium in deriving plasma parameters. Readers can redo
our analysis without this assumption if desired, because the line
intensities we present in this paper are simply the measured photon
production rates in the lines. Assuming ionization equilibrium, we
determine the electron temperature, electron density, line-of-sight
emission measure, and abundance variation with height above the limb
from the line intensities and line intensity ratios. The spatial
resolution has allowed us to detect an apparent element-abundance
variation as a function of height above the west limb that is strong
evidence for gravitational settling of “heavy” elements.

---------------------------------------------------------
Title: Analysis of Extreme-Ultraviolet Off-Limb Spectra Obtained
with SUMER/SOHO: Ne VI-Mg VI Emission Lines
Authors: Dwivedi, Bhola N.; Curdt, Werner; Wilhelm, Klaus
1999ApJ...517..516D Altcode:
We present results from a study of extreme-ultraviolet (EUV) off-limb
spectra. These were obtained on 1996 June 20 with the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) instrument on the Solar
and Heliospheric Observatory (SOHO). With the capabilities of SUMER,
we rastered the emitting source from 40" off the limb outward, and
secured a unique, high-quality set of high-resolution EUV spectra. The
scientific objective of this observing sequence was to record Ne
VI and Mg VI intercombination/forbidden lines, which provide good
possibilities to study the relative element abundance of Ne (high FIP)
and Mg (low FIP) in transition-region emission in the corona, and the
electron density in the solar atmosphere. While this observing sequence
produced excellent spectra of the Ne VI and Mg VI lines, the occurrence
of a dynamic event in the corona is an added bonus of the program. We
also observed several other bright, as yet unidentified lines. Among
these are lines that have been observed for the first time. Using the
new data, we have been able to deduce the plasma density and relative
element abundance in the source. In addition, improved values of the
wavelengths of the Ne VI and Mg VI intercombination/forbidden lines
have been obtained. Possible identifications of the bright lines
not previously observed, along with their measured intensities,
are discussed. Paper presented at the JD-19/IAU, Kyoto, 1997
August 26-27.

---------------------------------------------------------
Title: Sunspot Transition Region Oscillations in NOAA 8156
Authors: Brynildsen, N.; Leifsen, T.; Kjeldseth-Moe, O.; Maltby, P.;
Wilhelm, K.
1999ApJ...511L.121B Altcode: 1998astro.ph.12012B
Based on observations obtained with the Solar and Heliospheric
Observatory joint observing program for velocity fields in sunspot
regions, we have detected 3 minute transition region umbral oscillations
in NOAA 8156. Simultaneous recordings of O V λ629 and N V λ1238,
λ1242 with the SUMER instrument give the spatial distribution of power
in the 3 minute oscillations, both in intensity and in line-of-sight
velocity. Comparing loci with the same phase, we find that the entire
umbral transition region oscillates. The observed maxima in peak line
intensity are nearly in phase with the maxima in velocity directed
toward the observer. We discuss the suggestion that the waves are
upward-propagating acoustic waves.

---------------------------------------------------------
Title: Solar Wind Outflow and the Chromospheric Magnetic Network
Authors: Hassler, Donald M.; Dammasch, Ingolf E.; Lemaire, Philippe;
Brekke, Pal; Curdt, Werner; Mason, Helen E.; Vial, Jean-Claude;
Wilhelm, Klaus
1999Sci...283..810H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Beobachtungen der ruhigen Sonne im ultravioletten Licht. Das
Spektrometer SUMER auf SOHO.
Authors: Wilhelm, K.
1999S&W....38..131W Altcode:
After describing the UV spectrometer SUMER on-board SOHO relevant
observations of the quiet Sun made in the years 1996 - 97 are presented.

---------------------------------------------------------
Title: Coronal Hole Properties Observed with SUMER
Authors: Stucki, K.; Solanki, S. K.; Rüedi, I.; Stenflo, J. O.;
Brković , A.; Schühle, U.; Wilhelm, K.; Huber, M. C. E.
1999SSRv...87..315S Altcode:
We analyze SUMER spectra of 14 lines belonging to 12 ions, obtained
on both sides of the boundary of polar coronal holes as well as at
other locations along the limb. We compare line intensities, shifts
and widths in coronal holes with values obtained in the quiet Sun. We
find that with increasing formation temperature, spectral lines show
an increasingly stronger blueshift in coronal holes relative to the
quiet Sun at an equal heliospheric angle. The width of the lines is
generally larger (by a few km/s) inside the coronal hole. Intensity
measurements show the presence of the coronal hole in Ne VIII lines
as well as in Fe XII, with evidence for a slightly enhanced emission
in polar coronal holes for lines formed below 105 K.

---------------------------------------------------------
Title: Coronal Holes Versus Normal Quiet Sun Observed with SUMER
Authors: Stucki, K.; Solanki, S. K.; Rüedi, I.; Stenflo, J. O.;
Brković, A.; Schühle, U.; Wilhelm, K.; Huber, M. C. E.
1999Ap&SS.264...53S Altcode: 1998Ap&SS.264...53S
We present a preliminary analysis of spectral lines obtained with the
SUMER instrument (Solar Ultraviolet Measurements of Emitted Radiation)
onboard the Solar and Heliospheric Observatory (SOHO), as observed
during three observing campaigns. From the 70 observed spectral lines,
we selected 12, representing 9 ions or atoms, in order to analyse line
intensities, shifts and widths in polar coronal holes as well as in the
normal quiet Sun. We find that coronal lines show a distinct blueshift
in coronal holes relative to the quiet Sun at equal heliospheric
angle, while there is no evidence for such a shift for lines formed at
temperatures below 10^5 K. The widths of lines formed at temperatures
above 3 - 10^4 K are slightly increased inside the coronal hole,
but unaffected for lower temperatures. Intensity measurements clearly
show the center-to-limb variation, as well as an intensity diminution
inside the coronal hole for lines formed above approximately 10^5 K.

---------------------------------------------------------
Title: The Darkest Regions of Solar Polar Coronal Holes Observed by
SUMER on SOHO
Authors: Wilhelm, Klaus
1999Ap&SS.264...43W Altcode: 1998Ap&SS.264...43W
No abstract at ADS

---------------------------------------------------------
Title: Observations of the Sun obtained by SUMER on SOHO
Authors: Wilhelm, K.
1999AGAb...15....9W Altcode: 1999AGM....15..A09W
Solar observations will be presented which make use of the high
spectral and spatial resolution capabilities of the Solar Ultraviolet
Measurements of Emitted Radiation spectrograph (SUMER) on the SOlar
and Heliospheric Observatory (SOHO) of ESA and NASA. The spatial
resolution of the instrument is limited by the pixel size along the
slit (1 pixel corresponds to ~1 ”) and is approximately 1”.2 in a
raster mode employing the narrowest slit (with a width of 0”.3). The
spectral resolution element is ~22 mÅ in the second order of the
diffraction grating (~400 Å to 800 Å) and ~44 mÅ in first order
(~800 Å to 1600 Å). Radiance spectra of structures and events will be
discussed including features of the chromospheric network, bright points
in coronal holes, active region loops, spicules, and macrospicules.

---------------------------------------------------------
Title: Statistical Analysis of EUV and UV Lines Inside and Outside
of Solar Coronal Holes
Authors: Dammasch, I. E.; Hassler, D. M.; Curdt, W.; Wilhelm, K.
1999SSRv...87..161D Altcode:
Two studies performed with SUMER (the Solar Ultraviolet Measurements
of Emitted Radiation spectrometer on SOHO) in September 1996 are
presented. Spatial scans, a long exposure time and a broad spectral
window provide reliable line profiles for various regions of the Sun
(off-limb corona, coronal hole, quiet Sun, bright and dark regions
on disk) and for different formation temperatures (Si II, 14 000 K;
C IV, 100 000 K; Ne VIII, 630 000 K). Line intensity, position and
width distributions are presented together with the line positions
relative to the wavelength seen above the limb.

---------------------------------------------------------
Title: Signatures of Coronal Hole Spectra Between 660 Å and 1460
Å Measured with SUMER on SOHO
Authors: Schühle, U.; Curdt, W.; Wilhelm, K.; Solanki, S. K.;
Stucki, K.
1999SSRv...87..299S Altcode:
Spectra of the northern polar coronal hole measured with the SUMER
spectrometer on SOHO on 25 October 1996 are analyzed. We present spectra
taken at locations on the solar disk where part of the spectrometer
slit intersects a polar coronal hole region and an area of brighter
emission from outside of the coronal hole area. By comparing the line
intensities between the parts of the spectrum taken inside the "dark"
area of the coronal holes and the brighter regions, we work out the
signatures of the specific coronal hole in the chromosphere, transition
region and lower corona. We find that emissions of neutral atom lines,
of which there are many in the spectrum of SUMER, show no difference
between the coronal hole and the bright boundary areas, whereas all
ionized species show strong intensity enhancements, including the
continuum emissions of carbon and hydrogen. These enhancements are
larger than in normal quiet Sun areas.

---------------------------------------------------------
Title: Solar irradiances of UV and EUV lines during the minimum of
the sunspot activity in 1996
Authors: Wilhelm, K.; Lemaire, P.; Dammasch, I. E.; Hollandt, J.;
Schühle, U.; Curdt, W.; Kucera, T.; Hassler, D. M.; Huber, M. C. E.
1999AdSpR..24..229W Altcode:
Full Sun observations in UV and EUV emission lines were performed
by SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on
SOHO (Solar and Heliospheric Observatory) in 1996. The radiometric
preflight calibration of SUMER is traceable to a primary radiometric
source standard - the electron storage ring BESSY. Based on this
calibration and on its inflight refinements, the irradiance values at
SOHO have been obtained for the lines He i (λ584.33), O v (λ629.74),
Ne viii (λ770.41), S v (λ786.47), O iv (λ787.72), S vi (λλ933.39,
944.52), H i Ly ɛ (λ937.80), C iii (λ977.04), N v (λ1238.81),
Si i (λ1256.52), and C iv (λ1548.20), and the continuum near 1549
Å. In this contribution, we compare our measurements with other recent
irradiance determinations and discuss, in particular, the observations
in the C iv line.

---------------------------------------------------------
Title: Multiple-thread model of a prominence observed by SUMER and
EIT on SOHO and by GBO's.
Authors: Wiik, J. E.; Dammasch, I. E.; Schmieder, B.; Wilhelm, K.
1999joso.proc..184W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Search for Signatures of a Coronal Hole in Transition Region
Lines Near Disk Center
Authors: Lemaire, P.; Bocchialini, K.; Aletti, V.; Hassler, D.;
Wilhelm, K.
1999SSRv...87..249L Altcode:
The analysis of data taken by SUMER near disk center, where a small
coronal hole is observed in EIT images, is performed. From the
measurements of Doppler non-thermal velocities and intensities, we
search for the diagnostics and the signature of small scale structures
in the coronal hole using transition region lines. Transition region
lines in the range of 7 × 104 K to 2.5 × 105
K have a non-thermal velocity excess of 4.0 to 5.5 km s-1
relative to the contiguous quiet Sun. While the average intensity is
lower in the coronal hole than in the quiet area, this result shows
an increase of turbulence at the base of the high speed solar wind.

---------------------------------------------------------
Title: Ion Temperatures as Observed in a Solar Coronal Hole
Authors: Tu, C. -Y.; Marsch, E.; Wilhelm, K.
1999SSRv...87..331T Altcode:
From the widths of the extreme ultraviolet (EUV) lines measured by
the SUMER instrument on SOHO, it was found previously (Tu et al. 1998)
that the average temperature of Ne+7, at heights (relative
to h0) above the southern solar limb from 17″ to 64″,
ranges between 1.3 and 5 × 106 K and of Ne+6
between 1 and 4 × 106 K. For mass-per-charge numbers
greater than 4 the temperatures of the ions increase slightly with
increasing mass-per-charge, while the thermal speed reveals no clear
trend. We present a new data set with exposure times much longer than
the ones in the previous study. The results obtained from line width
analysis of Fe XII (1242 Å), Mg X (1249 Å), Mg VIII (772 Å) Ne VIII
(770 Å), and Si VIII (1445 Å) support our previous study. In this
case, the trend of increasing temperature begins at a mass-per-charge
number of 3. A qualitative explanation based on ion-cyclotron-resonance
heating within linear kinetic theory is suggested.

---------------------------------------------------------
Title: The evolution of solar bipolar jets observed in the UV by
SUMER on SOHO.
Authors: Mendoza-Torres, J. E.; Wilhelm, K.; Innes, D. E.; Curd, W.;
Kliem, B.; Brekke, P.
1998larm.confE..17M Altcode:
Observations of bipolar jets made in the UV by SUMER onboard SOHO
are presented. The observations were carried out in the interval
74.9-79.0 nm which contains some chromospheric and transition region
lines. The theory predicts that under the conditions of the solar
chromosphere the reconnection of magnetic lines accelerates plasma
into two oppositely directed jets. In the chromosphere, as well as in
other solar layers, different phenomena, where plasma acceleration
take place, are observed. Of them the UV jets, observed by SUMER,
represent one of the most clear evidences of the link between magnetic
reconnection and plasma acceleration. The jets are clearly revealed
by a considerably intensity increase and large doppler shifts of the
line wings. It should be noted that the enhancement of only one wing
also occurs and that the central component of the line also undergoes
velocity shifts and amplitude enhancement. The behavior of the wings
found in this work is consistent with results obtained for other events
(Innes et al. 1997) namely: 1)The wings are observed during few minutes
2) The doppler velocities of the line wings (red and blue) are similar
to each other and typical values are of the order of 100 km/sec, 3) In
general, the blue component is more long-lived than the red one, 4)the
red component is, in general, more intense than the blue one. In this
work, an analysis of the velocities of the three spectral components
(the central and the wings) as a function of the location on the slit,
used for the observations, is also done. The ratios of two OV (density
sensitive) and two OIV (temperature sensitive) lines, whose wavelengths
are in the observed range, are also analyzed. An important result is
that these parameters show gradients along the slit. An analysis of
the spatial distributions and the correlations between them is done. A
discussion of these results, in relation with the appearance and the
evolution of the jets, will be done.

---------------------------------------------------------
Title: High-Resolution Observations of the Solar Hydrogen Lyman
Lines in the Quiet Sun with the SUMER Instrument on SOHO
Authors: Warren, H. P.; Mariska, J. T.; Wilhelm, K.
1998ApJS..119..105W Altcode:
We present high-resolution observations of the higher H Lyman series
lines taken with the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) experiment flown on the Solar and Heliospheric Observatory
(SOHO) spacecraft. We have used systematic observations extending
from disk center to the solar limb to compute average profiles for
representative solar features of the quiet Sun, limb-brightening curves,
and full-disk, quiet-Sun profiles for Lyβ through Lyλ(11) and the
Lyman continuum. The effects of radiative transfer are apparent in
all of the line profiles we studied. The average quiet-Sun profiles
for Lyβ through Lyɛ are self-reversed, and the remaining lines are
flat-topped. The characteristics of the line profiles vary markedly
with intensity. We observe strong enhancements in the red wings of
network profiles, while the faint cell-center profiles are nearly
symmetric. We also find that the intensities of the H Lyman lines
increase at the limb, although the limb brightening is weak compared
to optically thin transition region emission lines and largely obscured
by the intensity variations observed in the quiet Sun.

---------------------------------------------------------
Title: The Electron Pressure in the Solar Lower Transition Region
Determined from O V and Si III Density-sensitive Line Ratios
Authors: Doschek, G. A.; Feldman, U.; Laming, J. M.; Warren, H. P.;
Schüle, U.; Wilhelm, K.
1998ApJ...507..991D Altcode:
We determine the electron density at the temperatures of formation
of O+4 and Si+2 ions, which are about 2.5 ×
105 and 3.2 × 104 K in ionization equilibrium,
respectively. These temperatures occur in the lower transition
region of the Sun's atmosphere and allow a test of the often invoked
assumption of constant pressure in quiet-Sun models. The O+4
density is determined from a density-sensitive spectroscopic O V
line ratio involving 2s2p3P-2p23P
transitions that fall near 760 Å. The Si+2 density is
determined from a density-sensitive Si III line ratio within the
3s3p3P-3p23P multiplet near 1300
Å. There are few available line ratio techniques for determining
the density and hence electron pressure in the quiet-Sun and coronal
hole transition regions using lines emitted by the same ion, and
determining these quantities is the principal motivation for this
work. The spectra used in our analysis were obtained from the Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) experiment on the
Solar and Heliospheric Observatory (SOHO). We determine the electron
density and pressure in typical quiet-Sun/coronal hole regions, and
densities in active region brightenings and in an explosive event. Our
O V and Si III results indicate that constant pressure is valid or
nearly valid in quiet-Sun lower transition regions, although there
are complications arising from the weakness of a key Si III line in
the quiet-Sun disk spectra. We also discuss our results in light of
other density measurements and theories regarding the structure and
heating of the transition region.

---------------------------------------------------------
Title: Broadening of SI VIII lines observed in the solar polar
coronal holes
Authors: Banerjee, D.; Teriaca, L.; Doyle, J. G.; Wilhelm, K.
1998A&A...339..208B Altcode:
We study the variation of the line width and electron density as a
function of height above two coronal holes from forbidden spectral
lines of Si viii. The spectra were obtained with the Solar Ultraviolet
Measurements of Emitted Radiation spectrometer flown on the Solar and
Heliospheric Observatory spacecraft. The observations concentrate on the
dark regions outside the plumes, which are believed to be the locations,
where the fast solar wind originates. The line width data show that
the non-thermal line-of-sight velocity increases from 27 {km s}(-1) at
27 arc sec above the limb to 46 {km s}(-1) some 250 arc sec ({i.e. } ~
180,000 km) above the limb. The electron density shows a decrease from
1.1 10(8) {cm}(-3) to 1.6 10(7) {cm}(-3) over the same distance. This
data implies that the non-thermal velocity is inversely proportional
to the quadratic root of the electron density, in excellent agreement
with that predicted for undamped radially propagating Alfven waves. We
show that the energy flux associated with these hydromagnetic waves
is sufficient to drive the high speed solar wind streams.

---------------------------------------------------------
Title: Center-to-limb line width measurements of solar chromospheric,
transition region and coronal lines
Authors: Erdelyi, R.; Doyle, J. G.; Perez, M. E.; Wilhelm, K.
1998A&A...337..287E Altcode:
Line widths derived from observational data obtained by SUMER
onboard SOHO in August 1996 at disk center and at the limb are used
to confront those derived via assuming Alfven and/or magneto-acoustic
wave heating. The observational data clearly shows a center-to-limb
variation in the upper chromospheric and transition region lines,
with only a marginal difference in the coronal lines in the sense of
additional broadening further from disk center. Numerical estimations
based on linear MHD, favour the existence of Alfven wave heating
over magneto-acoustic heating, although further calculations are
required. For example, non-linear effects could change the wave
characteristics which in turn can have a major effect on the overall
line broadening.

---------------------------------------------------------
Title: The Si/Ne Abundance Ratio in Polar Coronal Hole and Quiet-Sun
Coronal Regions
Authors: Doschek, G. A.; Laming, J. M.; Feldman, U.; Wilhelm, K.;
Lemaire, P.; Schühle, U.; Hassler, D. M.
1998ApJ...504..573D Altcode:
Using spectra obtained from the Solar Ultraviolet Measurements
of Emitted Radiation (SUMER) spectrometer flown on the Solar and
Heliospheric Observatory (SOHO) spacecraft, we determine the Si/Ne
abundance ratio in diffuse, interplume polar coronal hole regions,
as well as the ratio relative to quiet-Sun coronal regions. Ne has
the second highest first ionization potential (FIP) of solar abundant
elements, and Si is a low-FIP element. Thus the Si/Ne ratio is a
sensitive indicator of abundance variations due to the FIP effect. We
develop new spectroscopic diagnostics for the determination of the
Si/Ne abundance ratio. Assuming ionization equilibrium, we find that
the Si/Ne abundance ratio in interplume polar coronal hole regions is
about a factor of 2 greater than the photospheric value and is close
to or the same as in coronal quiet-Sun regions. This result pertains
to the electron temperature range 5-8 × 105 K. However,
the combined atomic physics, instrumental, and statistical uncertainty
in this result is about a factor of 2, and therefore this observed
enhancement is consistent with no enhancement in the polar hole
abundances. Nevertheless, our results follow the same trend, i.e., a
greater than photospheric abundance ratio of low-FIP elements in the
corona relative to high-FIP elements, as found from other abundance
measurements in the corona that involve different atomic physics and
different instruments. Therefore we feel that our results reflect
an actual abundance enhancement, despite being within an uncertainty
level bar that encompasses photospheric abundances. We also examine
the Ne/Mg abundance ratio over a 24.5 hr observation and find no
significant abundance variations. (Mg is a low-FIP element.) Thus,
no large transient abundance variations appear to occur on timescales
shorter than about a day, although this result is based on only
one observation. From lines of Mg VII, Mg VIII, Mg IX, and Mg X we
find that the electron temperature along the line of sight increases
with height above the limb over the polar coronal holes, as has been
previously reported. We determine the emission measure distribution as
a function of height from Mg VII, Mg VIII, and Mg X lines. We determine
average temperatures along the line of sight over the polar holes from
Ne VIII/Ne VII, Mg VIII/Mg VII, and Si VIII/Si VII line ratios. We also
discuss the temperature properties of the coronal hole and quiet-Sun
regions using forbidden lines of Fe X and Fe XI. We comment on the
possibility that ionization equilibrium is not valid in polar coronal
hole regions, a possible scenario in light of recent observations that
show outflows in coronal holes beginning at about the temperature of
formation of Ne VIII.

---------------------------------------------------------
Title: High-Temperature Lines in SUMER Spectra Recorded Above a
Bright Solar Active Region
Authors: Feldman, U.; Curdt, W.; Doschek, G. A.; Schühle, U.; Wilhelm,
K.; Lemaire, P.
1998ApJ...503..467F Altcode:
We identify spectral lines emitted by solar abundant elements due
primarily to transitions within the 2s22pk and
3s23pk (where k = 1, 5) ground configurations
of ions that are formed in ionization equilibrium between 2 ×
106 and 8 × 106 K. The transitions were
identified in spectra of a bright active region recorded 1997
September 6, by the Solar Ultraviolet Measurements of Emitted Radiation
Spectrometer (SUMER) flown on the Solar and Heliospheric Observatory
(SOHO). Some of these lines provide useful plasma diagnostic tools
for measuring the physical conditions in the solar corona.

---------------------------------------------------------
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.
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: Ion Temperatures in a Solar Polar Coronal Hole Observed by
SUMER on SOHO
Authors: Tu, C. -Y.; Marsch, E.; Wilhelm, K.; Curdt, W.
1998ApJ...503..475T Altcode:
The temperatures of some highly charged ions in the southern solar polar
coronal hole are determined from the widths of the extreme ultraviolet
(EUV) lines measured by the SUMER (Solar Ultraviolet Measurements
of Emitted Radiation) instrument on SOHO (Solar and Heliospheric
Observatory). Radiation from both light ions, such as Ne6+,
Ne7+, Mg7+, Mg9+, Si6+,
and Si7+, and heavy ions, such as Fe9+,
Fe10+, and Fe11+, are recorded in off-limb
observations. We refer here to the limb as the height, h0,
where the limb brightening of the N IV 765 Å line maximizes. After
correction of the measured line widths for instrument contributions,
the intrinsic widths of these emission lines are derived. These are
produced by thermal motions of the ions and turbulent wave motions of
the background plasma. Since the turbulent line broadening should be the
same for all the different ions, its upper limit can be determined from
the widths of the iron lines, assuming zero iron temperatures. Thus,
the range of kinetic temperatures permitted for the light species can
be delimited. For example, the average temperature of Ne7+,
at heights above the southern limb relative to h0 from 17"
to 64", ranges between 1.3 and 5 × 106 K, and the average
temperature of Ne6+ ranges between 1 and 4 × 106
K. The interpretation of these measurements does not require knowledge
of the ion formation (or electron) temperature. It is also found that
the ion thermal speed decreases with increasing mass per charge, while
the ion temperature remains roughly constant. In another observation
at heights from 167" to 183" above h0, the temperature of
the ions increases slightly with increasing mass per charge, while
the thermal speed reveals no clear trend. The upper limits of the
turbulence amplitude, &lt;δv2&gt;1/2, derived
for these two altitude ranges are 33-37 and 44 km s-1,
respectively. The implications of these results for the heating of
the solar corona and the acceleration of the solar wind are discussed.

---------------------------------------------------------
Title: Evidence in Support of the “Nanoflare” Picture of Coronal
Heating from SUMER Data
Authors: Judge, P. G.; Hansteen, V.; Wikstøl, Ø.; Wilhelm, K.;
Schühle, U.; Moran, T.
1998ApJ...502..981J Altcode:
We study high signal-to-noise profiles of O IV emission lines obtained
using the SUMER instrument on SOHO. Data for the quiet Sun obtained
close to the disk center and at the solar limb were acquired. After
careful data processing in which disk data were analyzed differentially
against limb data, we find a systematic correlation between a
density-sensitive emission-line ratio and Doppler shift across the
same emission-line profiles. While unidentified blended lines cannot be
completely discounted, the data suggest that the effects of such blends
are small. Based on theoretical results in an earlier paper, we argue
that if wave motions are responsible for the observed behavior, then
the data reveal evidence for compressive waves propagating downward
from the corona to the chromosphere. This analysis naturally lends
support to the dominance of the “nanoflare” mechanism for coronal
heating over other theories that invoke upward wave propagation,
but other mechanisms capable of generating downward-propagating waves
cannot be discounted. If, instead, steady flows are the cause of the
observed behavior, such as return flows from spicules, then they must
be such that the density is higher in the downflowing plasma. While
these particular data do not allow us to discriminate between waves
or steady flows, additional data from SOHO should be able to address
this problem. This work required and achieved very accurate wavelength
calibrations (better than 1/5 of a pixel on the detectors), taking
SUMER close to its observational capabilities. We therefore present
the elements of the analysis and calibration of SUMER data that may
be of interest to other users.

---------------------------------------------------------
Title: Ultraviolet Observations of a Dynamic Event in the Solar Corona
Authors: Innes, D. E.; Curdt, W.; Dwivedi, B. N.; Wilhelm, K.
1998SoPh..181..103I Altcode:
The Solar Ultraviolet Measurements of Emitted Radiation instrument
(SUMER) observations show high Doppler shifts and temporal variations
in profiles of ultraviolet lines from low temperature gas in the
corona above the active region NOAA 7974. The profiles indicate ≈
100 km s-1 flows coming from an almost stationary source
that appears bright in the lines of N III and Si III. The variations
in line-of-sight velocities and intensities suggest small knots of
cooling plasma emanating from a small region high in the corona. A
few arc sec sunward of the region where the cool flows are seen is an
elongated region of enhanced higher temperature, low velocity Ne VI
and Mg VI line emission.

---------------------------------------------------------
Title: SOHO Observations of the Connection Between Line Profile
Parameters in Active and Quiet Regions and the Net Red Shift in EUV
Emission Lines
Authors: Brynildsen, N.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.;
Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Wilhelm, K.
1998SoPh..181...23B Altcode:
We present high spatial and spectral resolution observations of
one active and one quiet-Sun region, obtained with CDS and SUMER on
SOHO. The connections between the line profile parameters are studied
and a systematic wavelength shift towards the red with increasing peak
line intensity (line broadening) is detected. The large scatter in
the data calls for another approach. We apply conditional probability
analysis to a series of EUV emission lines and find significant
correlations between line profile parameters. For a given interval in
wavelength shift we find that: (1) line profiles with large intensities
(line widths) and red shifts above the average constitute an increasing
fraction of the profiles as the relative wavelength shift increases,
(2) line profiles with large intensities (line widths) and blue
shifts compared to the average, on the other hand, constitute a
decreasing fraction of the profiles as the relative wavelength shift
increases. These results extend the findings of an earlier quiet-Sun
study from one to several emission lines and expand the validity to
include the active region. Interestingly, the active region observations
show correlations between peak line intensity and wavelength shift in
the coronal lines.

---------------------------------------------------------
Title: Solar irradiances and radiances of UV and EUV lines during
the minimum of sunspot activity in 1996
Authors: Wilhelm, K.; Lemaire, P.; Dammasch, I. E.; Hollandt, J.;
Schuehle, U.; Curdt, W.; Kucera, T.; Hassler, D. M.; Huber, M. C. E.
1998A&A...334..685W Altcode:
Full Sun observations in UV and EUV emission lines were performed
by SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on
SOHO (Solar and Heliospheric Observatory) in 1996. The radiometric
pre-flight calibration of SUMER is traceable to a primary radiometric
source standard - the electron storage ring BESSY. Based on this
calibration, the irradiance values at SOHO and at 1 AU have been
obtained for the lines He i (lambda 584.33 { Angstroms}), O v (lambda
629.74 { Angstroms}), Ne viii (lambda 770.41 { Angstroms}), S v (lambda
786.47 { Angstroms}), O iv (lambda 787.72 { Angstroms}), S vi (lambda
lambda 933.39, 944.52 { Angstroms}), H i Ly epsilon (lambda 937.80 {
Angstroms}), C iii (lambda 977.04 { Angstroms}), N v (lambda 1238.81
{ Angstroms}), Si i (lambda 1256.52 { Angstroms}), and C iv (lambda
1548.20 { Angstroms}). The spatially resolved measurements allowed
good estimates to be made of the active region contributions to the
irradiance of the quiet Sun. The centre-to-limb radiance variations of
these lines have also been obtained from these measurements. For quiet
solar conditions, a radiance spectrum was determined for wavelengths
from 800 { Angstroms} to 1500 { Angstroms} near the centre of the
solar disk.

---------------------------------------------------------
Title: The Solar Corona Above Polar Coronal Holes as Seen by SUMER
on SOHO
Authors: Wilhelm, Klaus; Marsch, Eckart; Dwivedi, Bhola N.; Hassler,
Donald M.; Lemaire, Philippe; Gabriel, Alan H.; Huber, Martin C. E.
1998ApJ...500.1023W Altcode:
In order to address two of the principal scientific objectives of the
Solar and Heliospheric Observatory (SOHO), studies of the heating
mechanisms of the solar corona and the acceleration processes of
the solar wind, we deduce electron temperatures, densities, and
ion velocities in plumes and interplume regions of polar coronal
holes using ultraviolet observations from SUMER (Solar Ultraviolet
Measurements of Emitted Radiation) on SOHO. SUMER allows us to study
the inner corona up to a distance of about 430,000 km above the
limb, or r = 1.6 R⊙ (solar radius) from the center
of the disk. We find the electron temperatures, Te,
to be less than 800,000 K in a plume in the range from r = 1.03 to
1.60 R⊙, decreasing with height to ~330,000 K. Near
an interplume lane, the electron temperature is also low, but stays
between 750,000 and 880,000 K in the same height interval. Doppler
widths of O VI lines in plumes are narrower (ΔλD ~
150 mÅ, v1/E ~ 43 km s-1) than in interplume
lanes (~190 mÅ, ~55 km s-1). The thermal and turbulent
ion speeds, v1/E, of Si7+ reach values up to
~80 km s-1 in the darkest regions outside plumes above the
coronal hole. This corresponds to a kinetic ion temperature of 1 ×
107 K. A limit of ~18 km s-1 for the bulk speed
in plumes below r = 1.2 R⊙ is deduced from O VI line shift
measurements and consideration of the three-dimensional plume geometry
(differential line-of-sight velocities &lt;=3 km s-1),
whereas differential line-of-sight velocities of Mg8+
ions up to 34 km s-1 can be seen in dark regions.

---------------------------------------------------------
Title: Solar H i Lyman alpha full disk profile obtained with the
SUMER/SOHO spectrometer
Authors: Lemaire, P.; Emerich, C.; Curdt, W.; Schuehle, U.; Wilhelm, K.
1998A&A...334.1095L Altcode:
An uncalibrated solar hydrogen Lyman alpha profile was obtained with
the use of the spectrometer on SOHO. The collection of the light
scattered by the telescope permitted to average the profile over
the full solar disk. The profile taken at the L1 Sun-Earth
Lagrangian position is free of the central geocoronal absorption. Then,
taking advantage of the absolute flux measured by the SOLSTICE/UARS
spectrometer, an absolute line profile intensity is derived, and is
compared with previous observations at minimum solar activity.

---------------------------------------------------------
Title: Observational evidence for coronal mass injection by
“evaporation" of spicular plasma
Authors: Budnik, F.; Schroeder, K. -P.; Wilhelm, K.; Glassmeier, K. -H.
1998A&A...334L..77B Altcode:
Despite being a common feature of the solar chromosphere, spicules
are still a poorly understood phenomenon. Not much is known about
their impact on the physics of the transition region and corona,
for which spicules are believed to be the dominant mechanism for
mass injection. We recently observed the spatial plasma structure of
polar spicules in a large temperature range with the EUV spectrometer
SUMER onboard the SOHO spacecraft. The spectrometer slit was placed
tangentially to the polar limb at various projected heights &lt;
22\arcsec. Our spectra in the wavelength range of 748-792 { Angstroms}
simultaneously record emission lines which are formed in a wide
temperature range between 30 000 and 600 000 K.We find that the typical
structure of spicular plasma grows, horizontally and vertically, with
increasing emission-line temperature, reaching ~ 20\arcsec at 1 - 2*
10(5) K. This suggests an “evaporation" of spicular plasma into the
transition region (TR) and corona, for which we find further evidence
from an emission measure analysis.

---------------------------------------------------------
Title: Solar EUV and UV Emission Line Observations Above a Polar
Coronal Hole
Authors: Wilhelm, K.; Bodmer, R.
1998SSRv...85..371W Altcode:
The roll manoeuvre of SOHO on September 3, 1997 provided the opportunity
to study the northern coronal hole with SUMER slits in east-west
orientation, so that polar plumes and inter-plume lanes could be
observed simultaneously. A preliminary analysis of the observations
shows that lines emitted by ions with the lowest formation temperatures
(with the exceptions of Ne7+ and Ar7+) have
the largest ratios of plume to lane radiances at heights between 35
000 km and 70 000 km above the photosphere. All lines have narrower
widths inside plumes than outside. Electron densities have been
deduced in plumes and lanes from Si VIII and Mg VIII line radiance
ratios. The Mg IX pair was used to determine the corresponding electron
temperatures. Neon (with a high first-ionization potential) is found
to be less abundant relative to magnesium (with low FIP) in a plume
compared to an inter-plume lane, but the variation is smaller than
previously determined Ne/Mg abundance ratios in a plume relative to
the photosphere.

---------------------------------------------------------
Title: EUV Spectroscopy of the Sunspot Region NOAA 7981 Using SOHO -
II. Velocities and Line Profiles
Authors: Brynildsen, N.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.;
Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Pike, C. D.; Rimmele,
T.; Thompson, W. T.; Wilhelm, K.
1998SoPh..179..279B Altcode:
We have studied the dynamics in the sunspot transition region between
the chromosphere and the corona and investigated the extension of
the flow field into the corona. Based on EUV spectra of a medium size
sunspot and its surroundings, NOAA 7981, observed with CDS and SUMER
on SOHO, we derive line-of-sight velocities and study the line profiles
for a series of emission lines.

---------------------------------------------------------
Title: EUV Spectroscopy of the Sunspot Region NOAA 7981 Using SOHO -
I. Line Emission and Time Dependence
Authors: Brynildsen, N.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.;
Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Pike, C. D.; Rimmele,
T.; Thompson, W. T.; Wilhelm, K.
1998SoPh..179...43B Altcode:
EUV spectra of a medium-size sunspot and its surroundings, NOAA 7981,
were obtained on 2 August 1996 with the Coronal Diagnostic Spectrometer
(CDS) and the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) on the Solar and Heliospheric Observatory (SOHO). The spectral
lines formed in the transition region and corona show considerable
structure and large deviations from a uniform spatial distribution over
the active region. Enhanced EUV emissions in transition region lines
are concentrated in small regions outside the umbra of the sunspot
throughout most of the observing sequence. Only during a short,
active period do we find an enhanced line emission that reaches into
the umbra. Preliminary values for the umbral intensity are given.

---------------------------------------------------------
Title: SUMER observations of bi-directional flows in coronal plasmas
Authors: Curdt, W.; Innes, D. E.; Wilhelm, K.
1998ESASP.421..123C Altcode: 1998sjcp.conf..123C
No abstract at ADS

---------------------------------------------------------
Title: First observational evidence for 'evaporating' spicules
Authors: Budnik, F.; Schröder, K. -P.; Glassmeier, K. -H.; Wilhelm, K.
1998ESASP.421..249B Altcode: 1998sjcp.conf..249B
No abstract at ADS

---------------------------------------------------------
Title: Sunspot Oscillations from SUMER Spectra
Authors: Rendtel, J.; Staude, J.; Innes, D.; Wilhelm, K.; Gurman, J. B.
1998ESASP.417..277R Altcode: 1998cesh.conf..277R
No abstract at ADS

---------------------------------------------------------
Title: Plasma jets in the solar atmosphere observed in EUV emission
lines by SUMER on SOHO
Authors: Wilhelm, K.; Innes, E. E.; Curdt, W.; Kliem, B.; Brekke, P.
1998ESASP.421..103W Altcode: 1998sjcp.conf..103W
No abstract at ADS

---------------------------------------------------------
Title: The Magnetic Reconnection Explorer (MAGREX)
Authors: Schühle, U.; Antionchos, S. K.; Barbee, T. W., Jr.; Bixler,
J. V.; Brown, C. M.; Carter, P. H., II; Curdt, W.; Davila, J. M.;
Doschek, G.; Feldman, U.; Goldstein, W. H.; Kordas, J.; Lemaire, P.;
Mariska, J. T.; Marsch, E.; Moses, J. D.; Seely, J. F.; Wilhelm, K.;
Woods, T. N.
1998ESASP.417..289S Altcode: 1998cesh.conf..289S
No abstract at ADS

---------------------------------------------------------
Title: Three Dimensional EUV Imaging of Sunspot Regions Observed
with SOHO
Authors: Brynildsen, N.; Brekke, P.; Haugan, S. V. H.; Kjeldseth-Moe,
O.; Maltby, P.; Harrison, R. A.; Rimmele, T.; Wilhelm, K.
1998ASPC..155..171B Altcode: 1998sasp.conf..171B
No abstract at ADS

---------------------------------------------------------
Title: Results from the SUMER Telescope and Spectrometer - Solar
Ultraviolet Measurements of Emitted Radiation - on SOHO
Authors: Wilhelm, Klaus
1998asct.conf...75W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Oscillations in a Sunspot Transition Region Observed with SOHO
Authors: Staude, J.; Rendtel, J.; Innes, D.; Wilhelm, K.; Gurman, J. B.
1998ESASP.418..651S Altcode: 1998soho....6..651S
Measurements of oscillations in the chromosphere-corona transition
region (TR) above sunspots are of fundamental importance for
investigating sunspot structure and dynamics; for instance, resonator
models of magneto-atmospheric waves and their non-adiabatic behavior
can be tested in this way (Staude et al., 1985). UV spectroscopic
data obtained with the SUMER spectrograph aboard SOHO have been
analyzed to detect such oscillations. The longest time series was
obtained on August 29, 1996, between 09:08 UT and 13:31 UT. During
this period, scans were made over the active region NOAA 7986 in the
wavelength bands around 770.4 AA (Ne VIII line, formed at T ~6 times
105 K) and 1548.1 AA (C IV line, T ~7 times 104
dots 1.3 times 105 K). The large dominating sunspot of this
active region was close to the disk centre. Simultaneous observations
with the Normal Incidence Spectrometer of CDS aboard SOHO have shown,
that the spot had a bright EUV plume at TR temperatures (Maltby et al.,
1998). For compensating possible instrumental and exposure effects,
we extract background information from each image. A preliminary
data analysis indicates intensity oscillations in the 2-minute range
(at 7.4 dots 7.7 mHz) in both spectral lines and a slow temporal
decrease of oscillatory power in the Ne VIII line, but an increase
in the C IV line. These results hint at a non-adiabatic behavior of
the oscillations and a slow cooling of the emitting sunspot plume
region. Further supplementary observations of the active region NOAA
7986 are from EIT aboard SOHO (in the Fe IX/X lines at 171 AA ---
T ~1.3 times 106 K --- a time series of 2 hours has been
obtained simultaneous to the first part of the SUMER series, moreover,
single high-resolution pictures in 4 UV lines exist) as well as from
the magnetograph of the Einsteinturm observatory at Potsdam showing
a rather complex polarity distribution. It is planned to extend the
study towards velocity variations and to correlations between the
oscillations in the two SUMER lines. Furthermore, correlations will
be investigated towards the EIT time series.

---------------------------------------------------------
Title: SUMER observations in transition region lines
Authors: Betta, R.; Hansteen, V.; Carlsson, M.; Wilhelm, K.
1998MmSAI..69..699B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: SUMER Observations of the Quiet Solar Atmosphere: The Network
Chromosphere and Lower Transition Region
Authors: Judge, Philip; Carlsson, Mats; Wilhelm, Klaus
1997ApJ...490L.195J Altcode:
We examine spectral properties of the network chromosphere and lower
transition region from the SUMER instrument on the SOHO spacecraft,
using time-series data sets discussed in an accompanying Letter by
Carlsson, Judge, &amp; Wilhelm. The data were obtained early in the
mission with no tracking of solar features and so cannot generally
be used to examine intrinsic variations in features on timescales
in excess of 383 s. Upon examination of the temporal variations and
some preliminary power spectrum analysis, we find the following:
(1) Transition region lines show more redshift in network regions
than in internetwork regions and also a correlation between line
intensity brightenings and increased redshift. (2) The internetwork
“Ca II grain” phenomenon is not seen in He I λ584 or in lines
of Si III and C III. (3) Very rapid changes are seen in the network
for transition region lines with no obvious correspondence with the
underlying chromosphere. (4) He I λ584 line profiles show very slow
time variations. (5) Small-amplitude (2-5 km s-1) coherent
oscillations of 5"-10" scale length and ~130 s period are seen in
Doppler shifts of Si III between regions of bright network elements. (6)
Essentially all blueshifts or redshifts are substantially less than line
widths. We conclude that upward-propagating acoustic shock waves do not
contribute significantly to the heating of the lower transition region,
and that ionization equilibrium is likely to fail for the interpretation
of certain emission lines. The spatial coherency of the Si III velocity
oscillations indicates that the quiet Sun's magnetic field topology
is more uniform than emission-line intensity data alone might suggest.

---------------------------------------------------------
Title: Observations of Doppler Shifts in a Solar Polar Coronal Hole
Authors: Warren, H. P.; Mariska, J. T.; Wilhelm, K.
1997ApJ...490L.187W Altcode:
Using observations from the Solar Ultraviolet Measurements of Emitted
Radiation experiment flown on the Solar and Heliospheric Observatory
spacecraft, we have measured Doppler wavelength shifts in the north
polar coronal hole in the 1032 and 1038 Å emission lines of O VI and
the 1036 and 1037 Å emission lines of C II relative to chromospheric
emission lines. These observations were obtained on 1996 November 2
when the north polar coronal hole boundary extended southward to about
750” (cosθ=0.65). Our measurements indicate the presence
of average net redshifts in coronal holes at temperatures of less than
2.9×105 K. Measurements of systematic wavelength shifts
in the Ne VIII resonance lines relative to the quiet Sun suggest a
transition to average net outflows near 6.3×105 K in the
coronal hole.

---------------------------------------------------------
Title: The solar disk spectrum between 660 and 1175 Anstroms (first
order) obtained by SUMER on SOHO
Authors: Curdt, W.; Feldman, U.; Laming, J. M.; Wilhelm, K.; Schuehle,
U.; Lemaire, P.
1997A&AS..126..281C Altcode:
SUMER -- Solar Ultraviolet Measurements of Emitted Radiation -- onboard
of SOHO -- Solar and Heliospheric Observatory -- obtained its first
spectrum on January 25, 1996 near the north polar limb. The range
from 660 Angstroms to 1175 Angstroms which has never before been
observed with such a good spectral resolution contains a wealth of
spectroscopic details. Identification of about 400 lines in this
spectral range is given. We list the wavelengths of identified
transitions and provide their absolute peak intensities. General
spectral features of the most abundant elements H, He, C, N, O,
Ne, Mg, Si, S, Ar, and Fe are described. In this spectral range
many density- and temperature-sensitive line pairs are found. It is
shown in examples how they can be used as diagnostic tools. Table
1 and Fig.nearlimb are also available in digital form at the CDS
via anonymous ftp to cdsarc.u-strasbg. fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/Abstract.html

---------------------------------------------------------
Title: The Off-Limb Behaviour of the Solar Transition Region FIP
Effect
Authors: Laming, J. M.; Feldman, U.; Drake, J. J.; Schuhle, U.; Curdt,
W.; Wilhelm, K.; Lemaire, P.
1997AAS...191.7301L Altcode: 1997BAAS...29.1320L
We investigate the behaviour of the solar FIP effect (the abundance
enhancement of elements with first ionization potential &lt; 10 eV by
factor of 3-4 in the corona with respect to photospheric values) with
height above the limb in a region of diffuse quiet corona observed
by the SUMER instrument on SOHO. Line ratios formed at log T &gt;
5.8 show coronal abundances for all heights. Line ratios formed at
lower temperatures are consistent with coronal abundances well off the
limb, with the apparent magnitude of the FIP enhancement decreasing
by a factor of 1.5 - 2 as one approaches the solar limb. Thus our
observations support a spatial variation in the quiet sun transition
region FIP effect inferred previously from studies of the full disk
solar spectrum (Laming, Drake, &amp; Widing 1995, ApJ, 443, 416
and references therein). This result adds to the probability that
emission from the solar disk transition region and corona originates
from qualitatively different structures for values of log T {&lt;atop
&gt;} 5.8, having different FIP effects.

---------------------------------------------------------
Title: Sonnenradiometrie mit SUMER auf SOHO.
Authors: Hollandt, J.; Curdt, W.; Schühle, U.; Wilhelm, K.
1997PhyBl..53.1101H Altcode: 1997PhB....53.1101H
No abstract at ADS

---------------------------------------------------------
Title: A Coronal Spectrum in the 500--1610 Angstrom Wavelength Range
Recorded at a Height of 21,000 Kilometers above the West Solar Limb
by the SUMER Instrument on Solar and Heliospheric Observatory
Authors: Feldman, U.; Behring, W. E.; Curdt, W.; Schühle, U.; Wilhelm,
K.; Lemaire, P.; Moran, T. M.
1997ApJS..113..195F Altcode:
We present a solar coronal spectrum recorded by the extreme UV
spectrometer SUMER on the Solar and Heliospheric Observatory. The
spectrum was taken between 21:28 UT on 1996 June 25 and 02:47 UT on
1996 June 26, at a height of 21,000 km above the west equatorial limb
with the slit oriented in the north-south direction. At the time of
the observations the Sun was rather quiet, and the west limb appeared
“devoid of any activity.” The spectrum, which covers the 500-1610
Å wavelength range, originates from plasmas with temperatures
ranging between 1.5 × 104 and 1.5 × 106
K. Identification of lines originating from different temperature
regimes is facilitated by the appearance of their intensity along the
300" long slit. Well over 800 lines have been found, many of which
were not previously observed. We present the entire spectrum and discuss
line identifications. A table of the wavelengths of lines observed,
with their identifications and peak intensities, is provided. Although
we have identified lines previously detected in laboratory plasmas and
a number of new lines not previously observed, over 40% of the SUMER
lines remain unidentified. Among the newly detected lines, some have
a potential as plasma density diagnostics.

---------------------------------------------------------
Title: Doppler Shifts in the Quiet-Sun Transition Region and Corona
Observed with SUMER on SOHO
Authors: Brekke, P.; Hassler, D. M.; Wilhelm, K.
1997SoPh..175..349B Altcode:
New observations of systematic red shifts of transition region and
coronal lines obtained with SUMER (Solar Ultraviolet Measurements of
Emitted Radiation) on SOHO (the Solar and Heliospheric Observatory)
are presented. With the extensive wavelength coverage of SUMER it is
possible to extend the measurements of the red shifts to much higher
temperatures compared to previous instruments. We find lines formed in
the upper transition region (e.g. Ov, Sv, and Svi) to be red-shifted
similar to lower temperature lines (T ≤ 1.8 x 10-5
K). Even hotter lines such as Ovi, Neviii and Mgx show systematic red
shifts on the order of 5 km s-1 in the quiet Sun. This is
a new and significant result since previous measurements of the red
shifts were less well constrained.

---------------------------------------------------------
Title: Bursts of Explosive Events in the Solar Network
Authors: Innes, D. E.; Brekke, P.; Germerott, D.; Wilhelm, K.
1997SoPh..175..341I Altcode:
Observations of the quiet-Sun network in the UV emission line Siiv 1393
Å over a time period of two hours are presented. Bursts of explosive
events, highly Doppler-shifted emission, seem to be sporadically emitted
from the brighter regions of the network lanes. Individual events have
typical lifetimes of ≈ 1-6 min and come in bursts of up to 30 min. The
most spectacular burst in this dataset, shown in the accompanying movie,
lasts ≈ 30 min and shows a wide variety of line profiles with both
red and blue shifts ≈180 km s1. There appears to be no
characteristic form or evolutionary pattern to the line profiles in
either the individual events or series of events. There are about
twice as many blue shifts as red shifts.

---------------------------------------------------------
Title: Observations of Polar Plumes with the SUMER Instrument on SOHO
Authors: Hassler, D. M.; Wilhelm, K.; Lemaire, P.; Schühle, U.
1997SoPh..175..375H Altcode:
We present new observations of O vi 1032 Å line profiles in polar
plumes, and inter-plume regions, on the disk and above the limb in
the north coronal hole obtained with the SUMER (Solar Ultraviolet
Measurements of Emitted Radiation) instrument on the SOHO (Solar and
Heliospheric Observatory) spacecraft. On 22 May 1996, a 5 x 5 arc min
spectroheliogram was scanned above the north polar coronal hole with
the entrance slit extending from 1.03 to 1.33 solar radii with 1.5 arc
sec spatial resolution and ≈ 0.044 Å per pixel spectral resolution
in the wavelength range 1020-1040 Å. Detailed plume structure in
O vi 1032 Å can be seen extending beyond 1.3 solar radii, with
intensities in the plume regions 10-50% brighter, but line widths
10-15% narrower, than the inter-plume regions. Possible explanations
for this observed anti-correlation between line width and intensity
in the plume and inter-plume regions are discussed. We conclude that
the source of the high-speed solar wind may not be polar plumes, but
the inter-plume lanes associated with open magnetic field regions of
the chromospheric network.

---------------------------------------------------------
Title: SUMER Observations Confirm the Dynamic Nature of the Quiet
Solar Outer Atmosphere: The Internetwork Chromosphere
Authors: Carlsson, Mats; Judge, P. G.; Wilhelm, K.
1997ApJ...486L..63C Altcode: 1997astro.ph..6226C
On 1996 March 12, during the commissioning phase of the SOHO mission, we
obtained observations of the quiet-Sun with the SUMER instrument. The
observations were sequences of 15-20 s exposures of ultraviolet
emission-line profiles and of the neighboring continua. These data
contain signatures of the dynamics of the solar chromosphere that are
uniquely useful because of wavelength coverage, moderate signal-to-noise
ratios, and image stability. We focus on data for the internetwork
chromosphere. The dominant observed phenomenon is an oscillatory
behavior that is analogous to the 3 minute oscillations seen in CaII
lines. The oscillations appear to be coherent over 3"-8" diameter
areas. At any time they occur over about 50% of the area studied,
and they appear as large perturbations in the intensities of lines
and continua. The oscillations are most clearly seen in intensity
variations in the ultraviolet (λ &gt; 912 Å) continua, and they are
also seen in the intensities and velocities of chromospheric lines of
CI, NI, and OI. Intensity brightenings are accompanied by blueshifts
of typically 5 km s-1. Phase differences between continuum
and line intensities also indicate the presence of upward propagating
waves. The detailed behavior is different between different lines,
sometimes showing phase lags. The 3 minute intensity oscillations
are occasionally seen in second spectra (CII λ1335) but never in
third spectra (CIII and SiIII). Third spectra and HeI λ584 show
oscillations in velocity that are not simply related to the 3 minute
oscillations. The continuum intensity variations are consistent with
recent simulations of chromospheric dynamics (Carlsson and Stein),
while the line observations indicate that important ingredients are
missing at higher layers in the simulations. The data show that
time variations are crucial for our understanding of the chromosphere
itself and for the spectral features formed there--the quiet-Sun's
chromosphere is very dynamic and not “quiet.” The implications of
these data should be considered when planning chromospheric work with
instruments such as those on SOHO.

---------------------------------------------------------
Title: Radiometric calibration of SUMER: refinement of the laboratory
results under operational conditions on SOHO
Authors: Wilhelm, Klaus; Lemaire, Philippe; Feldman, Uri; Hollandt,
Jörg; Schühle, Udo; Curdt, Werner
1997ApOpt..36.6416W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Electron Density Diagnostics for the Solar Upper Atmosphere
from Spectra Obtained by SUMER/SOHO
Authors: Laming, J. M.; Feldman, U.; Schühle, U.; Lemaire, P.; Curdt,
W.; Wilhelm, K.
1997ApJ...485..911L Altcode:
We evaluate the electron density in various solar regions above the
limb observed by the Solar Ultraviolet Measurement of Emitted Radiation
(SUMER) instrument on SOHO. We find in general good agreement among
line ratios from Be-, B-, N-, and Mg-like ions, giving densities of
order 108 cm-3.

---------------------------------------------------------
Title: Turbulent Velocities and Ion Temperatures in the Solar Corona
Obtained from SUMER Line Widths
Authors: Seely, J. F.; Feldman, U.; Schühle, U.; Wilhelm, K.; Curdt,
W.; Lemaire, P.
1997ApJ...484L..87S Altcode:
Turbulent plasma velocities and ion temperatures were determined from
the line widths recorded by the Solar Ultraviolet Measurements of
Emitted Radiation instrument on the Solar and Heliospheric Observatory
spacecraft. From the widths of the lines of five light elements
(Ne, Na, Mg, Si, and S) and a heavy element (Fe), it was possible
to determine the contributions of turbulent plasma motion and ion
thermal motion to the line widths. The results indicated that the
turbulent velocity was approximately 22 km s-1 at 30"
above the limb and decreased to less than 10 km s-1 at 109"
and 209" above the limb. At 30" above the limb, the ion temperatures
of the hotter lines were comparable to the electron temperatures for
ionization equilibrium. The ion temperatures of the cooler lines were
higher than the ionization equilibrium temperatures; at 109" and 209"
above the limb, the ion temperatures were at least a factor of 2.5
higher than the ionization equilibrium temperatures.

---------------------------------------------------------
Title: Doppler Shifts and Nonthermal Broadening in the Quiet Solar
Transition Region: O VI
Authors: Warren, H. P.; Mariska, J. T.; Wilhelm, K.; Lemaire, P.
1997ApJ...484L..91W Altcode:
Using observations from the Solar Ultraviolet Measurements of Emitted
Radiation (SUMER) experiment flown on the Solar and Heliospheric
Observatory (SOHO) spacecraft, we have measured Doppler wavelength
shifts and nonthermal broadening in the 1032 and 1038 Å emission lines
of O VI and the 1036 and 1037 Å emission lines of C II. Near Sun center
the C II lines exhibit an average redshift of 2 +/- 3 km s-1,
consistent with earlier observations in this temperature range. The
O VI emission lines exhibit average Doppler velocities of 5 +/- 3
km s-1, suggesting the presence of redshifted material at
2.9 × 105 K. For the O VI lines, the average nonthermal
component of the observed line width is 34 +/- 3 km s-1.

---------------------------------------------------------
Title: Electron Densities in the Solar Polar Coronal Holes from
Density-Sensitive Line Ratios of Si VIII and S X
Authors: Doschek, G. A.; Warren, H. P.; Laming, J. M.; Mariska, J. T.;
Wilhelm, K.; Lemaire, P.; Schühle, U.; Moran, T. G.
1997ApJ...482L.109D Altcode:
We derive electron densities as a function of height in the north and
south polar coronal holes from a forbidden spectral line ratio of Si
VIII. Si VIII is produced at about 8 × 105 K in ionization
equilibrium. We also derive densities from a similar line ratio of S X
(1.3 × 106 K). The spectra were obtained with the Solar
Ultraviolet Measurements of Emitted Radiation spectrometer flown on
the Solar and Heliospheric Observatory spacecraft. In addition to the
primary mechanism of electron impact excitation, the derivation of
theoretical level populations for Si VIII and S X includes both proton
and resonance capture excitation. We compare the coronal hole results
to quiet-Sun coronal measurements obtained outside the east and west
limbs. We find for distances of a few arcseconds outside the solar
limb that the average line-of-sight electron densities in the coronal
holes are about a factor of 2 lower than in quiet-Sun regions. The
decrease of density with height is exponential in the polar holes. We
also confirm the result known from a variety of earlier observations
that the temperature of most of the plasma in coronal holes does not
exceed about 106 K.

---------------------------------------------------------
Title: Translimb Spectroscopy with SOHO/SUMER
Authors: Ayres, T. R.; Lemaire, P.; Schuhle, U.; Wilhelm, K.; Ruedi,
I.; Solanki, S.
1997SPD....28.0104A Altcode: 1997BAAS...29..879A
We have used SUMER to obtain deep exposures of the 1300--1400 Angstroms
spectrum, at the extreme limb and off-limb. Previous “translimb”
studies in the thermal infrared had revealed remarkable extensions
of cold material (T ~ 3000 K)---traced by carbon monoxide emission
lines---into the heart of the hot chromosphere. A main objective of
our program was to search for corresponding far-UV signatures of the
“thermally-bifurcated” low chromosphere; for example, radiatively
fluoresced emissions of the CO A--X 4th-positive system (collisional
excitation would be negligible in cold gas). We conducted two separate
observing programs with SUMER. Both made use of the 1(”) -diameter
circular aperture, translated across the limb in the minimum motor
step increments of 0.(”) 375, along the central meridian in the
Northern polar coronal hole. The first program executed for nine hours
beginning 19UT 25 Oct 1996. The full wavelength range was 1340--1400
Angstroms. It was recorded in two overlapping segments, placing key
regions of the spectrum alternately on the KBr and bare parts of
the detector, to help isolate 2nd-order features. Each segment was
integrated for 500 s, and 32 pairs were obtained to span a 12(”)
swath centered on the optical limb. The second program was conducted
00--09UT 01 Dec 1996. It consisted of a single wavelength setting
(1300--1340 Angstroms) with exposure time 500 s, but twice the spatial
coverage of the earlier series: 64 steps, for a total displacement
of 24(”) . The strong chromospheric resonance lines of atomic oxygen
(1302--1305 Angstroms) and ionized carbon (1334--1335 Angstroms) were
observed on the bare part of the MCP camera. We report our progress
in cataloging the rich, diverse translimb emission spectrum; and our
efforts to deduce fundamental properties of the thermally heterogeneous
chromosphere. [-3mm] SOHO is a project of international cooperation;
the participation of TRA was supported by NASA grant NAG5-3226.

---------------------------------------------------------
Title: The Electron Density, Temperature, and Si/Ne Abundance Ratio
in Polar Coronal Holes from SUMER
Authors: Doschek, G. A.; Laming, J. M.; Warren, H. P.; Lemaire, P.;
Wilhelm, K.
1997SPD....28.0404D Altcode: 1997BAAS...29Q.908D
The Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
spectrometer flown on the Solar and Heliospheric Observatory (SOHO)
covers a wavelength range with spectral and spatial resolution and
sensitivity not previously obtained by any other solar spectrometer
experiment. Consequently, new plasma diagnostic techniques have been
used and developed to measure plasma parameters such as electron
density. In this paper we discuss the electron density as a function
of height above the solar surface in the polar coronal holes as
determined from line ratios of Si VIII and S X. The densities vary
between about 3 x 10(6) cm(-3) and 10(8) cm(-3) . We determine the
emission measure at selected temperatures as a function of position
above the polar limbs from lines of Mg VII, Mg VIII, Mg IX, and Mg
X. The electron temperature is lower in the polar holes than in the
quiet Sun. This result is also based on intensities of lines of Fe X,
Fe XI, and Fe XII. We determine the Si/Ne abundance ratio (low/high
first ionization potential elements) using lines of Ne VII, Ne VIII,
Si VII, and Si VIII. The preliminary result is that the Si/Ne abundance
ratio in interplume regions is close to photospheric. We also compare
the coronal hole density and abundance results with similar results
obtained for the quiet Sun in the east and west coronal streamers. We
discuss our conclusions in light of results from previous missions.

---------------------------------------------------------
Title: New Insights into the Physical Mechanisms of Polar Plumes
with Observations from the SUMER Instrument on SOHO
Authors: Hassler, Donald M.; Wilhelm, Klaus; Lemaire, Philippe;
Schuehle, Udo
1997SPD....28.0802H Altcode: 1997BAAS...29..912H
SUMER (Solar Ultraviolet Measurements of Emitted Radiation)
line profiles above the limb in coronal holes are important for
constraining thermodynamic models governing the outflow of the solar
wind. Observational constraints in terms of thermal and nonthermal
velocities, and upper limits on wave velocity amplitudes can be directly
compared with in-situ observations. We present new observations of
line profiles in polar plumes, and inter-plume regions, above the
limb in coronal holes obtained with the SUMER instrument on the SOHO
spacecraft. Detailed structure can be seen extending beyond 1.5 solar
radii (out to the edge of the SUMER field-of-view), with intensities in
the plume regions roughly 10-50% brighter than the inter-plume regions,
but line widths in the plumes roughly 10% narrower than the inter-plume
regions. Possible explanations for this observed anti-correlation
between line width and intensity, and the correspondence with observed
in-situ solar wind signatures will be discussed.

---------------------------------------------------------
Title: Wave Propagation in the Chromosphere and Transition Region:
Where Have All the Shock Waves Gone?
Authors: Fleck, B.; Steffens, S.; Deubner, F. -L.; Wilhelm, K.;
Harrison, R.; Gurman, J.
1997SPD....28.0120F Altcode: 1997BAAS...29..882F
We present first results from a joint observing program (SOHO JOP 26)
involving SUMER, CDS and EIT on SOHO, coordinated with ground-based
observations at the Vacuum Tower Telescope at Iza{\ n}a, Tenerife. The
objective of this study is to characterize the wave propagation
properties in the solar atmosphere, from the photosphere through the
chromosphere up into the transition region. Particular emphasis is laid
on the 3-min shock waves observed in the Ca II K line. How do they
impact the transition region and what signature do they leave there
and in the lower corona? The ground-based measurements comprise high
resolution time series (both filtergrams and spectrograms) in Ca II K,
Hα and Mgb_2. With SUMER we ran four sequences covering different
temperature regimes: a) O I 1302, O I 1306, Si II 1309, C I 1311,
C II 1334, C II 1335, b) Si I 1256, N V 1242, O V 629 c) He I 584,
C III 1175, O I 1152, d) H I 1025, O VI 1031, O VI 1037. With CDS we
took spectral time series in O VI 554, He I 584, He II 607, Mg IX 368,
and O V 629 as well as wide-slit (90x240”) “movies” in He I 584,
Mg IX 368 and O V 629, while EIT ran sub-field high cadence sequences
in He II 304.

---------------------------------------------------------
Title: Observations of Doppler Shifts and Nonthermal Broadening in
the North Polar Coronal Hole and Adjacent Quiet Sun
Authors: Mariska, J. T.; Warren, H. P.; Wilhelm, K.; Lemaire, P.
1997SPD....28.0118M Altcode: 1997BAAS...29..882M
Coronal holes are thought to be the source of high-speed solar
wind streams. It is, however, unclear at what height the outflow
of material first becomes apparent. Using the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) experiment on the Solar and
Heliospheric Observatory (SOHO), we have obtained observations in the
north polar coronal hole, its boundary region, and the adjacent quiet
Sun at wavelengths that cover emission lines of O VI at 1032 and 1038
Angstroms, Ne VIII at 770 Angstroms, and Mg X at 625 Angstroms. These
lines are formed at temperatures of 0.3, 0.8, and 1.25 MK, respectively,
and should thus help to determine the temperature at which outflows
are first detected. For O VI and Mg X, we will report on Doppler shift
measurements made relative to cooler chromospheric lines. Since there
are no suitable emission lines from ions formed in the chromosphere
for the Ne VIII line, we are only able to measure relative differences
between the coronal hole and the adjacent quiet Sun. We will also
report on the magnitude of the nonthermal broadening in these lines
in the different solar regions. This work was supported by a NASA SOHO
Guest Investigator Program grant.

---------------------------------------------------------
Title: Doppler Shifts and Nonthermal Broadening in the Quiet Solar
Transition Region: O VI
Authors: Warren, H. P.; Mariska, J. T.; Wilhelm, K.; Lemaire, P.
1997SPD....28.0117W Altcode: 1997BAAS...29..882W
Using observations from the Solar Ultraviolet Measurements of Emitted
Radiation (SUMER) experiment flown on the Solar and Heliospheric
Observatory (SOHO ) spacecraft, we have measured Doppler wavelength
shifts and nonthermal broadening in the 1032 and 1038 Angstroms emission
lines of Ovi and the 1036 and 1037 Angstroms emission lines of Cii. Near
Sun center the Cii lines exhibit an average redshift of 2+/-3km s(-1)
, consistent with earlier observations in this temperature range. The
Ovi emission lines exhibit average Doppler velocities of 5+/-3km s(-1)
suggesting the presence of redshifted material at 2.9*E(5) K. For the
Ovi lines, the average nonthermal component of the observed line width
is 34+/-3km s(-1) . These observations indicate a tendency for brighter
regions to have larger average redshifts and line widths than faint
features although the relationship is very weak. Preliminary analysis of
observations at the limb suggests that the Doppler velocities for Ovi do
not approach zero as would be expected for predominately radial motions.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Solar disk spectrum (660-1175A)
(Curdt+ 1997)
Authors: Curdt, W.; Feldman, U.; Laming, J. M.; Wilhelm, K.; Schuehle,
U.; Lemaire, P.
1997yCat..41260281C Altcode:
The near-limb quiet-Sun spectrum recorded on January 25, 1996
near the solar North pole is presented in tabular form and in
graphical form. Table 1 - the line list - lists all lines found
in the spectrum providing absolute peak intensities, measured and
literature wavelengths, identification, and classification of the
transition. Fig. 4 is a display the composite spectrum. The most
prominent lines are labelled. In this figure intensities are given in
instrumental units and logarithmic scale. (1 data file).

---------------------------------------------------------
Title: Bi-directional plasma jets produced by magnetic reconnection
on the Sun
Authors: Innes, D. E.; Inhester, B.; Axford, W. I.; Wilhelm, K.
1997Natur.386..811I Altcode:
Magnetic reconnection, the process by which magnetic lines of force
break and rejoin into a lower-energy configuration, is considered to
be the fundamental process by which magnetic energy is converted into
plasma kinetic energy1. The Sun has a large reservoir of
magnetic energy, and the energy released by magnetic reconnection
has been invoked to explain both large-scale events, such as solar
flares2,3 and coronal mass ejections4, and
small-scale phenomena, such as the coronal and chromospheric microflares
that probably heat and accelerate the solar wind5,6. But the
observational evidence for reconnection is largely indirect, resting
on observations of variations in solar X-ray morphology and sudden
changes in the magnetic topology7,8, and on the apparent
association between some small-scale dynamic events and magnetic
bipoles9,10. Here we report ultraviolet observations of
explosive events in the solar chromosophere that reveal the presence
of bi-directional plasma jets ejected from small sites above the solar
surface. The structure of these jets evolves in the manner predicted by
theoretical models of magnetic reconnection11,12, thereby
lending strong support to the view that reconnection is the fundamental
process for accelerating plasma on the Sun.

---------------------------------------------------------
Title: Probing the Sun.
Authors: Dwivedi, B.; Wilhelm, K.
1997AsNow..11...53D Altcode: 1997AstNw..11...53D
On board SOHO is an instrument, SUMER, which is probing the Sun in EUV.

---------------------------------------------------------
Title: Determination of the Formation Temperature of Si IV in the
Solar Transition Region
Authors: Doschek, G. A.; Mariska, J. T.; Warren, H. P.; Wilhelm, K.;
Lemaire, P.; Kucera, T.; Schühle, U.
1997ApJ...477L.119D Altcode:
Using spectra obtained with the Solar Ultraviolet Measurements
of Emitted Radiation (SUMER) spectrometer flown on the Solar and
Heliospheric Observatory spacecraft, we deduce the temperature
of formation of the Si IV ion in the solar transition region
from the Si IV ultraviolet spectral line intensity ratio, 3p
2P3/2-3d 2D3/2,5/2/3s
2S1/2-3p 2P1/2,
and compare the result to the temperature predicted under the
assumption of ionization equilibrium. The wavelengths are as
follows: 2D3/2,5/2, 1128.325, 1128.340 Å
2P1/2, 1402.770 Å. Ratios are derived for
typical features of the quiet Sun, such as cell center and network,
and are systematically higher than those predicted at the 6.3 ×
104 K ionization equilibrium temperature of formation
of Si IV. For most solar features the ratios imply a temperature
of formation of about 8.5 × 104 K. The ratios for the
faintest features imply a temperature of formation of up to 1.6 ×
105 K. It is not clear, however, that all the discrepancies
between the measured and theoretical ratios are due to a temperature
effect. Accurate temperature measurements are important since a large
discrepancy from ionization equilibrium has significant implications
for the physics of the transition region, such as the possible presence
of nonthermal electrons.

---------------------------------------------------------
Title: The Non-Uniformity in the Sunspot Transition Region
Authors: Brynildsen, N.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.;
Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Rimmele, T.;
Wilhelm, K.
1997ESASP.404..257B Altcode: 1997cswn.conf..257B
No abstract at ADS

---------------------------------------------------------
Title: Transition Region Velocities and Line Profiles in the Sunspot
Region 7981
Authors: Brynildsen, N.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.;
Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Pike, C. D.; Rimmele,
T. Thompson, W. T.; Wilhelm, K.
1997ESASP.404..251B Altcode: 1997cswn.conf..251B
No abstract at ADS

---------------------------------------------------------
Title: First Results from SOHO on Waves Near the Solar Transition
Region
Authors: Steffens, S.; Deubner, F. -L.; Fleck, B.; Wilhelm, K.;
Schuhle, U.; Curdt, W.; Harrison, R.; Gurman, J.; Thompson, B. J.;
Brekke, P.; Delaboudiniere, J. -P.; Lemaire, P.; Hessel, B.; Rutten,
R. J.
1997ASPC..118..284S Altcode: 1997fasp.conf..284S
We present first results from simultaneous observations with the
CDS, EIT and SUMER instruments {please see Solar Physics 162 (1995)
for a description of the instruments} onboard SOHO and the VTT at
Tenerife. Our aim is to study the wave propagation, shock formation,
and transmission properties of the upper chromosphere and transition
region. The preliminary results presented here include the variation
of velocity power spectra with height, difference in power between
internetwork and network regions, and variations in mean flows displayed
by different spectral lines.

---------------------------------------------------------
Title: The Net Redshifts in EUV Emission Lines and the Connection
Between Intensity and Doppler Shift
Authors: Brynildsen, N.; Fredvik, T.; Maltby, P.; Kjeldseth-Moe, O.;
Brekke, P.; Haugan, S. V. H.; Harrison, R. A.; Wilhelm, K.
1997ESASP.404..263B Altcode: 1997cswn.conf..263B
No abstract at ADS

---------------------------------------------------------
Title: SUMER Observations Detecting Downward Propagating Waves in
the Solar Transition Region
Authors: Wiskstøl, Ø.; Judge, P. G.; Hansteen, V.; Wilhelm, K.;
Schühle, U.; Moran, T.
1997ESASP.404..731W Altcode: 1997cswn.conf..731W
No abstract at ADS

---------------------------------------------------------
Title: EUV Line Emission and Time Dependence in the Sunspot Region
NOAA 7981
Authors: Brynildsen, N.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.;
Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Pike, C. D.; Rimmele,
T.; Thompson, W. T.; Wilhelm, K.
1997ESASP.404..245B Altcode: 1997cswn.conf..245B
No abstract at ADS

---------------------------------------------------------
Title: Bright Plumes and Dark Lanes as Observed in MgX 625 Å and
NV 1239 Å in the Solar Polar Corona
Authors: Marsch, E.; Tu, C. -Y.; Wilhelm, K.; Curdt, W.; Schühle,
U.; Dammasch, I. E.
1997ESASP.404..555M Altcode: 1997cswn.conf..555M
No abstract at ADS

---------------------------------------------------------
Title: A New Look at the Quiet Sun Network in the Upper Atmosphere
During a Minimum of Activity Cycle
Authors: Lemaire, P.; Schuehle, U.; Curdt, W.; Wilhelm, K.; Poland,
A.; Falciani, R.
1997ESASP.404..517L Altcode: 1997cswn.conf..517L
No abstract at ADS

---------------------------------------------------------
Title: Temporal Variability in the Quiet Sun Transition Region
Authors: Wikstoøl, Ø.; Hansteen, V. H.; Brynildsen, N.; Maltby,
P.; Kyeldseth-Moe, O.; Harrison, R. A.; Wilhelm, K.; Tarbell, T. D.;
Scherrer, P. H.
1997ESASP.404..733W Altcode: 1997cswn.conf..733W
No abstract at ADS

---------------------------------------------------------
Title: First Results of the SUMER Telescope and Spectrometer on SOHO -
I. Spectra and Spectroradiometry
Authors: Wilhelm, K.; Lemaire, P.; Curdt, W.; Schühle, U.; Marsch, E.;
Poland, A. I.; Jordan, S. D.; Thomas, R. J.; Hassler, D. M.; Huber,
M. C. E.; Vial, J. -C.; Kühne, M.; Siegmund, O. H. W.; Gabriel, A.;
Timothy, J. G.; Grewing, M.; Feldman, U.; Hollandt, J.; Brekke, P.
1997SoPh..170...75W Altcode:
SUMER - the Solar Ultraviolet Measurements of the Emitted Radiation
instrument on the Solar and Heliospheric Observatory (SOHO) - observed
its first light on January 24, 1996, and subsequently obtained a
detailed spectrum with detector B in the wavelength range from 660
to 1490 Å (in first order) inside and above the limb in the north
polar coronal hole. Using detector A of the instrument, this range
was later extended to 1610 Å. The second-order spectra of detectors
A and B cover 330 to 805 Å and are superimposed on the first-order
spectra. Many more features and areas of the Sun and their spectra
have been observed since, including coronal holes, polar plumes and
active regions. The atoms and ions emitting this radiation exist at
temperatures below 2 × 106 K and are thus ideally suited
to investigate the solar transition region where the temperature
increases from chromospheric to coronal values. SUMER can also be
operated in a manner such that it makes images or spectroheliograms
of different sizes in selected spectral lines. A detailed line profile
with spectral resolution elements between 22 and 45 mÅ is produced for
each line at each spatial location along the slit. From the line width,
intensity and wavelength position we are able to deduce temperature,
density, and velocity of the emitting atoms and ions for each emission
line and spatial element in the spectroheliogram. Because of the high
spectral resolution and low noise of SUMER, we have been able to detect
faint lines not previously observed and, in addition, to determine
their spectral profiles. SUMER has already recorded over 2000 extreme
ultraviolet emission lines and many identifications have been made on
the disk and in the corona.

---------------------------------------------------------
Title: Observations of the Solar Atmosphere by the SUMER Spectrometer
on SOHO
Authors: Wilhelm, Klaus; Sumer Consortium
1997ASPC..118..259W Altcode: 1997fasp.conf..259W
SUMER -- the Solar Ultraviolet Measurements of Emitted Radiation
instrument on the Solar and Heliospheric Observatory (SOHO) -- observed
its first light on January 24, 1996. The instrument can measure in the
wavelength range from below 500 to 1610 { Angstroms}. Many features
and areas of the Sun and their spectra have been observed since,
including coronal holes, polar plumes and active regions. The atoms
and ions emitting this radiation exist at temperatures below 2 x 10(6)
K and are thus ideally suited to investigate the solar transition
region where the temperature increases from chromospheric to coronal
values. Detailed line profiles with spectral resolution elements
between 21 and 45 m{ Angstroms} are produced for each lin e at each
spatial location along the slit. From the line width, intensity and
wavelength position we are able to deduce temperature, density, and
velocity of the emitting atoms and ions for each emission line and
spatial element in the spectroheliogram.

---------------------------------------------------------
Title: High resolution solar ultraviolet measurements
Authors: Lemaire, P.; Wilhelm, K.; Schühle, U.; Curdt, W.; Poland,
A. I.; Jordan, S. D.; Thomas, R. J.; Hassler, D. M.; Vial, J. -C.
1997AdSpR..20.2249L Altcode:
The increase of our understanding of the processes acting in the solar
corona and maintaining it is strongly dependent on the quality of the
data that are obtained to check theories. The fine structure of the
solar atmosphere seen from the photosphere and extending to the hottest
parts of the corona requires data with high resolution in all parameter
space (angular, spectral and temporal). To constrain the hypotheses that
are proposed to describe the solar corona, it is necessary to establish
an accurate energy budget taking into account the processes which are
acting from the chromosphere to the corona. Some requirements can be
established and compared with the data collected so far (or about to
be collected) with the present SUMER (Solar Utraviolet Measurements
of Emitted Radiations) instrumentation.

---------------------------------------------------------
Title: Intensity and Velocity Variations in Transition Region Lines
Observed with SUMER
Authors: Betta, R.; Hansteen, V.; Carlsson, M.; Wilhelm, K.
1997ESASP.404..205B Altcode: 1997cswn.conf..205B
No abstract at ADS

---------------------------------------------------------
Title: Systematic Redshifts in the Quiet Sun Transition Region and
Corona Observed with SUMER on SOHO
Authors: Brekke, P.; Hassler, D. M.; Wilhelm, K.
1997ESASP.404..229B Altcode: 1997cswn.conf..229B
No abstract at ADS

---------------------------------------------------------
Title: Tracing CA K Grains Through the Chromosphere into the
Transition Region
Authors: Steffens, S.; Deubner, F. -L.; Fleck, B.; Wilhelm, K.
1997ESASP.404..685S Altcode: 1997cswn.conf..685S
No abstract at ADS

---------------------------------------------------------
Title: First Results of the SUMER Telescope and Spectrometer on SOHO -
II. Imagery and Data Management
Authors: Lemaire, P.; Wilhelm, K.; Curdt, W.; SchÜle, U.; Marsch,
E.; Poland, A. I.; Jordan, S. D.; Thomas, R. J.; Hassler, D. M.; Vial,
J. C.; KÜhne, M.; Huber, M. C. E.; Siegmund, O. H. W.; Gabriel, A.;
Timothy, J. G.; Grewing, M.
1997SoPh..170..105L Altcode:
SUMER - Solar Ultraviolet Measurements of Emitted Radiation - is not
only an extreme ultraviolet (EUV) spectrometer capable of obtaining
detailed spectra in the range from 500 to 1610 Å, but, using the
telescope mechanisms, it also provides monochromatic images over
the full solar disk and beyond, into the corona, with high spatial
resolution. We report on some aspects of the observation programmes
that have already led us to a new view of many aspects of the Sun,
including quiet Sun, chromospheric and transition region network,
coronal hole, polar plume, prominence and active region studies. After
an introduction, where we compare the SUMER imaging capabilities to
previous experiments in our wavelength range, we describe the results
of tests performed in order to characterize and optimize the telescope
under operational conditions. We find the spatial resolution to be
1.2 arc sec across the slit and 2 arc sec (2 detector pixels) along
the slit. Resolution and sensitivity are adequate to provide details
on the structure, physical properties, and evolution of several solar
features which we then present. Finally some information is given on
the data availability and the data management system.

---------------------------------------------------------
Title: Building the Spectrum of a G2V Star During a Minimum of
Activity Cycle
Authors: Lemaire, P.; Schuehle, U.; Curdt, W.; Wilhelm, K.; Hassler, D.
1997ESASP.404..513L Altcode: 1997cswn.conf..513L
No abstract at ADS

---------------------------------------------------------
Title: Analysis of the EUV Spectra Obtained with SUMER/SOHO; -
NE VI / MG IV
Authors: Dwivedi, B.; Curdt, W.; Wilhelm, K.
1997IAUJD..19E...3D Altcode:
The talk will discuss results from a study of EUV off-limb spectra. The
spectra were obtained on June 20, 1996, with the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) instrument on board SOHO. With
the capabilities of SUMER, we rastered the emitting source from 40^{”}
off the limb and outwards, and secured a unique, high quality set of
high resolution EUV spectra. The scientific objective of this observing
sequence was to record the Ne VI and Mg VI intercombination lines which
provide good possibilities to study the relative high-FIP/low-FIP
element abundance Ne/Mg, and electron density in the solar
atmosphere. While this observing sequence produced excellent spectra of
the Ne VI and Mg VI lines, the presence of several other bright lines,
yet unidentified, is an extra bonus of the program. Using the new data,
we have been able to deduce the plasma density, emission measure and
relative element abundance in the source. In addition, improved values
of the wavelengths of the Ne VI and Mg VI intercombination lines have
been obtained. Possible identifications of bright, lines which have
not previously been observed, will be discussed.

---------------------------------------------------------
Title: Wave Propagation in the Chromosphere and Transition Region
Authors: Steffens, S.; Deubner, F. -L.; Fleck, B.; Wilhelm, K.;
Harrison, R.; Gurman, J.
1997ESASP.404..679S Altcode: 1997cswn.conf..679S
No abstract at ADS

---------------------------------------------------------
Title: A New Sun from SUMER/SOHO
Authors: Dwivedi, B. N.; Wilhelm, K.
1997CSci...72..609D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Highlights of the SUMER Observations on SOHO
Authors: Wilhelm, K.; Sumer Consortium
1997ESASP.404...17W Altcode: 1997soho....5...17W; 1997cswn.conf...17W
No abstract at ADS

---------------------------------------------------------
Title: First Observations SUMER - VTT, SI IV - CA II K
Authors: Balthasar, H.; von Uexkull, M.; Innes, D.; Gigas, D.;
Wilhelm, K.
1997ASPC..118..315B Altcode: 1997fasp.conf..315B
We tried to do a comparison of Ca II K (393.3 nm) filtergrams obtained
at the Vacuum Tower Telescope on Tenerife with spectra in the line Si
IV 139.4 nm obtained simultaneously with the SUMER telescope on the
SOHO-spacecraft. Some bright features can be well identified in both
observations. We compare temporal changes of the brightness for these
common features.

---------------------------------------------------------
Title: Radiometric calibration of the telescope and ultraviolet
spectrometer SUMER on SOHO
Authors: Hollandt, Jörg; Schühle, Udo; Paustian, Wolfgang; Curdt,
Werner; Kühne, Michael; Wende, Burkhard; Wilhelm, Klaus
1996ApOpt..35.5125H Altcode:
The prelaunch spectral-sensitivity calibration of the solar spectrometer
SUMER (Solar Ultraviolet Measurements of Emitted Radiation) is
described. SUMER is part of the payload of the Solar and Heliospheric
Observatory (SOHO), which begins its scientific mission in 1996. The
instrument consists of a telescope and a spectrometer capable of taking
spatially and spectrally highly resolved images of the Sun in a spectral
range from 50 to 161 nm. The pointing capabilities, the dynamic range,
and the sensitivity of the instrument allow measurements both on
the solar disk and above the limb as great as two solar radii. To
determine plasma temperatures and densities in the solar atmosphere,
the instrument needs an absolute spectral-sensitivity calibration. Here
we describe the prelaunch calibration of the full instrument, which
utilizes a radiometric transfer-standard source. The transfer standard
was based on a high-current hollow-cathode discharge source. It
had been calibrated in the laboratory for vacuum UV radiometry of
the Physikalisch-Technische Bundesanstalt by use of the calculable
spectral photon flux of the Berlin electron storage ring for synchrotron
radiation (BESSY)-a primary radiometric source standard.

---------------------------------------------------------
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.
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: A Solar EUV Spectral Atlas Observed with SUMER
Authors: Brekke, P.; Wilhelm, K.; Lemaire, P.; Curdt, W.; Schuhle,
U.; Poland, A.; Kucera, T.; Hassler, D. M.; Siegmund, O. H. W.
1996AAS...188.3713B Altcode: 1996BAAS...28..879B
We present the first solar EUV spectral atlas in the wavelength range
500 -- 1600 { Angstroms}. The spectra were recorded with the Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) which is part
of the ESA/NASA Solar and Heliospheric Observatory (SOHO). The solar
spectrum below 1200 { Angstroms} is not very well known. Thus, the
present spectral atlas, and SUMER observations in general, represents
a new important diagnostic tool to study essential physical parameters
of the solar atmosphere. It includes emission from atoms and ions in
the temperature range 10(4) to 2 x 10(6) K. Thus, emission lines and
continua emitted from the lower chromosphere to the lower corona
can be studied. The atlas is also useful as a planning tool for
SUMER studies to determine useful dwell times, possible blends, and
to select proper data extraction windows. The angular resolution of
SUMER is close to 1 arcsec, but the atlas presented here represents an
average along part of the 1-arcsec wide slit, typically 30 arcsec. The
spectral resolving power of the instrument is lambda /Delta lambda =
17770-38300. For more details about the SUMER instrument we refer to
Wilhelm et al. (Solar Physics, 162, 189, 1995). The spectral data in
this atlas were obtained with the spectrometer slit positioned at the
center of the solar disk with a dwell time of 300 s to bring up weak
lines and continua. The full spectral range was put together from
a number of exposures each covering approximately 20 { Angstroms}
in 1st order on the coated, and therefore most sensitive, part (KrB)
of the detector. 1st and 2nd order spectra are superimposed. The
spectral atlas is available in a computer readable format together
with a IDL program to read and display the data using a widget
interface. The atlas and the programs can be obtained via the World
Wide Web (http://hydra.mpae.gwdg.de/mpae_projects/SUMER/sumer.html)
or by contacting one of the authors.

---------------------------------------------------------
Title: Intercalibration and Co-Registration of the LASCO, UVCS and
SUMER instruments on SOHO
Authors: Michels, J.; Kohl, J. L.; Noci, G.; Antonucci, E.; Tondello,
G.; Huber, M. C. E.; Curdt, W.; Hollandt, J.; Lemaire, P.; Schuhle,
U.; Wilhelm, K.; Korendyke, C.; Moran, T.; Raymond, J. C.; Romoli,
M.; Benna, C.; Ciaravella, A.; Fineschi, S.; Gardner, L. D.; Giordano,
S.; Naletto, G.; Nicolosi, P.; Siegmund, O. H. W.; Spadaro, D.; Smith,
P. L.; Strachan, L.
1996AAS...188.3706M Altcode: 1996BAAS...28..878M
Joint observations of equatorial streamers by three SOHO instruments
have been used for radiometric intercalibration, co-registration and
other spectroscopic comparisons. The results are used to track the
stability of the radiometric calibrations of the Ultraviolet Coronagraph
Spectrometer (UVCS) and the Solar Ultraviolet Measurements of Emitted
Radiation (SUMER) experiment at overlapping wavelenghs. Observations
of equatorial streamers at heliocentric heights from 1.25 to 1.5
R_⊙ are used for the intercalibrations. The results are compared to
pre-launch laboratory calibrations and to observations of stars. The
first stellar observation was for 38 AQI. These UV observations are
compared to coronal green line (Fe XIV) observations obtained with the
Large Angle Spectrometric Coronagraph (LASCO) C1 coronagraph obtained
in the same time frame. Intercomparisons of spectral line profiles
among LASCO, SUMER, and UVCS are also planned. The LASCO research is
supported by NASA Grant NDPR S92835D; the UVCS research is supported by
NASA Contract NAS5-31250 to the Smithsonian Astrophysical Observatory,
by the Italian Space Agency and by Switzerland, and SUMER is financially
supported by BMFT/DARA, CNES, NASA and PRODEX (Swiss Contribution).

---------------------------------------------------------
Title: Transition region studies with the SOHO-SUMER EUV-spectroscope.
Authors: Curdt, W.; Wilhelm, K.
1996joso.proc..148C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: SUMER - Solar Ultraviolet Measurements of Emitted Radiation
Authors: Wilhelm, K.; Curdt, W.; Marsch, E.; Schühle, U.; Lemaire,
P.; Gabriel, A.; Vial, J. -C.; Grewing, M.; Huber, M. C. E.; Jordan,
S. D.; Poland, A. I.; Thomas, R. J.; Kühne, M.; Timothy, J. G.;
Hassler, D. M.; Siegmund, O. H. W.
1995SoPh..162..189W Altcode:
The instrument SUMER - Solar Ultraviolet Measurements of Emitted
Radiation is designed to investigate structures and associated dynamical
processes occurring in the solar atmosphere, from the chromosphere
through the transition region to the inner corona, over a temperature
range from 104 to 2 × 106K and above. These
observations will permit detailed spectroscopic diagnostics of plasma
densities and temperatures in many solar features, and will support
penetrating studies of underlying physical processes, including plasma
flows, turbulence and wave motions, diffusion transport processes,
events associated with solar magnetic activity, atmospheric heating,
and solar wind acceleration in the inner corona. Specifically, SUMER
will measure profiles and intensities of EUV lines; determine Doppler
shifts and line broadenings with high accuracy; provide stigmatic
images of the Sun in the EUV with high spatial, spectral, and temporal
resolution; and obtain monochromatic maps of the full Sun and the inner
corona or selected areas thereof. SUMER will be flown on the Solar
and Heliospheric Observatory (SOHO), scheduled for launch in November,
1995. This paper has been written to familiarize solar physicists with
SUMER and to demonstrate some command procedures for achieving certain
scientific observations.

---------------------------------------------------------
Title: Some design and performance features of SUMER: solar
ultraviolet measurements of emitted radiation
Authors: Wilhelm, Klaus; Curdt, W.; Marsh, E.; Schuehle, Udo H.;
Lemaire, Philippe; Gabriel, Alan H.; Vial, J. -C.; Grewing, Michael;
Huber, Martin C.; Jordan, S. D.; Poland, Arthur I.; Thomas, Roger J.;
Kuehne, Mikhael; Timothy, J. Gethyn; Hassler, Donald M.; Siegmund,
Oswald H.
1995SPIE.2517....2W Altcode:
The instrument SUMER (solar ultraviolet measurements of emitted
radiation) is designed to investigate structures and associated
dynamical processes occurring in the solar atmosphere from the
chromosphere through the transition region to the inner corona, over a
temperature range from 104 to 2 multiplied by 106
K and above. The observations will be performed, on board SOHO (solar
and heliospheric observatory) scheduled for launch in November 1995,
by a scanning, normal-incidence telescope/spectrometer system in
the wavelength range from 500 to 1610 angstrom. Spatial resolution
requirements compatible with the pointing stability of SOHO are less
than 1000 km corresponding to about 1-arcsec angular resolution. Doppler
observations of EUV line shifts and broadenings should permit solar
plasma velocity measurements down to 1 km s-1. We report
here on some specific features of this instrument related to its
pointing as well as its spatial and spectral resolution capabilities.

---------------------------------------------------------
Title: SUMER - Solar Ultraviolet Measurements of Emitted Radiation
Authors: Wilhelm, K.
1995LNP...444..245W Altcode: 1995cmer.conf..245W
The experiment Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) is designed for the investigations of plasma flow
characteristics, turbulence and wave motions, plasma densities
and temperatures, structures and events associated with solar
magnetic activity in the chromosphere, the transition zone and the
corona. Specifically, SUMER will measure profiles and intensities
of extreme ultraviolet (EUV) lines emitted in the solar atmosphere
ranging from the upper chromosphere to the lower corona; determine line
broadenings, spectral positions and Doppler shifts with high accuracy;
provide stigmatic images of selected areas of the Sun in the EUV with
high spatial, temporal and spectral resolution and obtain full images
of the Sun and the inner corona in selectable EUV lines, corresponding
to a temperature range from 104 to 2 × 106
K. SUMER will be flown on the ESA/NASA spacecraft Solar and Heliospheric
Observatory (SOHO) to be launched in September 1995. SOHO will be
positioned near the first Lagrangean point (L1) of the Sun-Earth system.

---------------------------------------------------------
Title: Study of the quiet corona with the SOHO/SUMER spectrometer
Authors: Lemaire, P.; Wilhelm, K.
1994AdSpR..14d.171L Altcode: 1994AdSpR..14..171L
The SOHO/SUMER spectrometer is developed to study the low corona and
chromosphere-corona transition zone. The main scientific objectives are
oriented towards the search of mechanisms producing the coronal heating
and driving the first impulse of the solar wind. The main contribution
will be given by an accurate measurement of line profiles, intensities
and shifts combined with high angular resolution on the solar disk and
above the limb. In this paper, we recall the scientific objectives,
we describe the corresponding instrument capabilities and we show how
the observations can be performed and the kind of data expected. The
complementary role of the SOHO coronal instruments in coordinating
observations to optimize the quality of the data is emphasized.

---------------------------------------------------------
Title: 'SUMER' - Solar Ultraviolet Measurements of Emitted Radiation
Authors: Wilhelm, K.; Curdt, W.; Gabriel, A. H.; Grewing, M.; Huber,
M. C. E.; Jordan, S. D.; Kuhne, M.; Lemaire, P.; Marsch, E.; Poland,
A. I.; Schuhle, U.; Thomas, R. J.; Timothy, J. G.; Vial, J. -C.
1994scs..conf..619W Altcode: 1994IAUCo.144..619W
SUMER is designed for the investigations of plasma flow characteristics,
turbulence and wave motions, plasma densities and temperatures,
structures and events associated with solar magnetic activity in the
chromosphere, the transition zone and the corona. The spatial and
spectral resolution capabilities of the instrument are considered in
some detail, and a new detector concept is introduced.

---------------------------------------------------------
Title: SUMER: temperatures, densities, and velocities in the outer
solar atmosphere.
Authors: Lemaire, P.; Wilhelm, K.; Axford, W. I.; Curdt, W.; Gabriel,
A. H.; Grewing, M.; Huber, M. C. E.; Jordan, S. D.; Kuehne, M.;
Marsch, E.; Poland, A. I.; Richter, A. K.; Thomas, R. J.; Timothy,
J. G.; Vial, J. C.
1992ESASP.348...13L Altcode: 1992cscl.work...13L
The SUMER instrumentation, that will be mounted on the SOHO spacecraft,
is in development under MPAE leadership. It has some capability
to improve the solar angular resolution and the spectral resolution
already obtained in the far UV to the extreme UV, corresponding to the
temperature range between 104 and a few 106K. The
authors give some insights into the SUMER spectrometer that is developed
to study the dynamics and to infer temperatures and densities of the
low corona and the chromosphere-corona transition zone in using the
50 - 160 nm wavelength range. First, they recall the SUMER scientific
goals and the technics used. Then, after a brief description of the
instrumentation the expected performances are described. The way the
observations can be conducted is emphasized and it is shown how SUMER
is operated in coordination with other SOHO instrumentations and in
cooperation with ground-based observations.

---------------------------------------------------------
Title: "SUMER" - Solar Ultraviolet Measurements of Emitted Radiation.
Authors: Wilhelm, K.; Axford, W. I.; Curdt, W.; Gabriel, A. H.;
Grewing, M.; Huber, M. C. E.; Jordan, S. D.; Kühne, M.; Lemaire, P.;
Marsch, E.; Poland, A. I.; Richter, A. K.; Thomas, R. J.; Timothy,
J. G.; Vial, J. C.
1992eocm.rept..225W Altcode:
The experiment Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) is designed for the investigations of plasma flow
characteristics, turbulence and wave motions, plasma densities
and temperatures, structures and events associated with solar
magnetic activity in the chromosphere, the transition zone and the
corona. Specifically, SUMER will measure profiles and intensities
of extreme ultraviolet (EUV) lines emitted in the solar atmosphere
ranging from the upper chromosphere to the lower corona; determine line
broadenings, spectral positions and Doppler shifts with high accuracy;
provide stigmatic images of selected areas of the Sun in the EUV with
high spatial, temporal and spectral resolution and obtain full images of
the Sun and the inner corona in selectable EUV lines, corresponding to a
temperature range from 104 to more than 1.8×106K.

---------------------------------------------------------
Title: SUMER - Solar ultraviolet measurements of emitted radiation
Authors: Wilhelm, K.; Axford, W. I.; Gurdt, W.; Marsch, E.; Richter,
A. K.; Grewing, M.; Gabriel, A. H.; Lemaire, P.; Vial, J. -C.; Huber,
M. C. E.
1992sws..coll..129W Altcode:
The SUMER (solar ultraviolet measurements of emitted radiation)
experiment is described. It will study flows, turbulent motions, waves,
temperatures and densities of the plasma in the upper atmosphere of
the Sun. Structures and events associated with solar magnetic activity
will be observed on various spatial and temporal scales. This will
contribute to the understanding of coronal heating processes and the
solar wind expansion. The instrument will take images of the Sun in EUV
(extreme ultraviolet) light with high resolution in space, wavelength
and time. The spatial resolution and spectral resolving power of the
instrument are described. Spectral shifts can be determined with
subpixel accuracy. The wavelength range extends from 500 to 1600
angstroms. The integration time can be as short as one second. Line
profiles, shifts and broadenings are studied. Ratios of temperature
and density sensitive EUV emission lines are established.

---------------------------------------------------------
Title: Observations of Antarctic auroral electron precipitation with
high stability in time and longitude
Authors: Barrow, C. H.; Wilhelm, K.; Watermann, J.; Evans, D. S.
1991AnGeo...9..259B Altcode:
Electron flux measurements were made in the energy range 0.1 to 12.5
keV, by the electron spectrometer 1ES019 on board Spacelab 1, during
the period 29 November to 7 December 1983. The spacecraft was in a 57
deg inclination circular orbit at an altitude of about 250 km with
an orbital period of 90 min. Although the experiment was originally
designed for artificial electron beam response observations, several
periods of natural energetic electron precipitation were also recorded
and these have been surveyed and catalogued. The data are interesting
because of the high resolution of the electron spectrometer, the
relatively low spacecraft altitude for the observations and the path of
Spacelab 1 almost along the auroral oval. On 30 November 1983 Spacelab
1 observed electron precipitation during four successive Southern
Hemisphere passes, one of which is of particular interest as the NOAA-7
Satellite, which measured electron flux in the energy range of 0.3 to
20 keV at an altitude of about 850 km, was then quite close in space
and time. As correlative riometer and magnetometer observations suggest
that auroral conditions remained stable during the 25-min period between
the two sets of observations, the observations are used to infer the
gross spatial structure of the auroral precipitation over the midnight
sector. Comparison of the electron energy spectra observed by Spacelab 1
and NOAA-7 at different magnetic local times and at different altitudes
suggests a high degree of longitudinal homogeneity in the precipitation.

---------------------------------------------------------
Title: Auroral beam-plasma interactions: Particle correlator
investigations
Authors: Gough, M. Paul; Christiansen, Peter J.; Wilhelm, Klaus
1990JGR....9512287G Altcode:
Plasma wave instabilities may occur above discrete auroral arcs where
the natural accelerated auroral electron component meets the cold
ionospheric plasma. These wave-particle interactions were studied on
the CAESAR II rocket by measuring the modulations in energetic electron
flux in the frequency ranges 0-10 MHz and 0-10 kHz. Near apogee (700 km)
a strong modulation of 7.5 keV electrons at 1.4 MHz (~fUH)
was observed where df(v)/dv was positive, just below the auroral beam
velocity. The measurement is shown to be consistent with instabilities
driven by both Landau and cyclotron resonant interactions with upper
hybrid waves, and alsod with the earlier observation of modulatins at
2.65 MHz (~fUH) seen on a low altitude rocket E2-B (apogee
230 km).

---------------------------------------------------------
Title: Wake phenomena observed by an ionospheric sounding rocket
Authors: Svenes, K. R.; Troim, J.; Maehlum, B. N.; Wilhelm, K.
1990P&SS...38..395S Altcode:
Measurements from the ionospheric sounding rocket POLEWARD LEAP have
been analyzed in order to study the nature of wake phenomena. Some
outstanding events, which apparently resulted from the interaction
between the incoming particles and the F-layer plasma, are discussed. It
is shown that the suprathermal electron fluxes observed during the
auroral particle precipitation were clearly spin modulated, and that
they usually occurred in the wake region of the rocket. In addition,
background measurements of both the auroral particle precipitation
and the ambient plasma are presented.

---------------------------------------------------------
Title: 8-25 eV high resolution solar spectrometer
Authors: Lemaire, Philippe; Wilhelm, Klaus
1989SPIE.1140..522L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Reply
Authors: Lieu, R.; Wilhelm, K.; Watermann, J.
1989JGR....94.9158L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: SUMER - Solar ultraviolet measurements of emitted radiation.
Authors: Curdt, W.; Wilhelm, K.; Axford, W. I.; Marsch, E.; Richter,
A. K.; Gabriel, A. H.; Lemaire, P.; Vial, J. -C.; Grewing, M.; Huber,
M. C. E.; Jordan, S. D.; Poland, A. I.; Thomas, R. J.; Timothy, J. G.
1989AGAb....2...14C Altcode: 1989amt..conf...14C
No abstract at ADS

---------------------------------------------------------
Title: SUMER: Solar Ultraviolet Measurements of Emitted Radiation
Authors: Wilhelm, K.; Axford, W. I.; Curdt, W.; Gabriel, A. H.;
Grewing, M.; Huber, M. C. E.; Jordan, M. C. E.; Lemaire, P.; Marsch,
E.; Poland, A. I.
1988sohi.rept...31W Altcode:
The SUMER (solar ultraviolet measurements of emitted radiation)
experiment is described. It will study flows, turbulent motions, waves,
temperatures and densities of the plasma in the upper atmosphere of
the Sun. Structures and events associated with solar magnetic activity
will be observed on various spatial and temporal scales. This will
contribute to the understanding of coronal heating processes and the
solar wind expansion. The instrument will take images of the Sun in EUV
(extreme ultra violet) light with high resolution in space, wavelength
and time. The spatial resolution and spectral resolving power of the
instrument are described. Spectral shifts can be determined with
subpixel accuracy. The wavelength range extends from 500 to 1600
angstroms. The integration time can be as short as one second. Line
profiles, shifts and broadenings are studied. Ratios of temperature
and density sensitive EUV emission lines are established.

---------------------------------------------------------
Title: Space shuttle charging or beam-plasma discharge: What can
electron spectrometer observations contribute to solving the question?
Authors: Watermann, J.; Wilhelm, K.; Torkar, K. M.; Riedler, W.
1988JGR....93.4134W Altcode:
Several cooperative plasma experiments were carried out on board
Spacelab-1, the ninth payload of the Space Transportation System
(STS-9). Among them, the electron spectrometer 1ES019A was designed
to observe 0.1-12.5 keV electron fluxes with high temporal and spatial
resolution, while the SEPAC electron beam accelerator emitted electron
beams with currents up to 280 mA and maximum energies of 5 keV. Since
the question of orbiter charging to high voltages has controversially
been discussed in several publications on STS-3 and STS-9 electron beam
experiments, an attempt is made to relate information from the return
electron flux observed during the SEPAC operations to the vehicle
charging interpretation. A close examination reveals that most of
our observations can be understood if the occurrence of a beam-plasma
discharge is assumed at least for electron beam intensities above 100
mA. This would provide a substantial return current capability. High
orbiter charging effects during electron beam accelerator electron
emissions are consequently not supported by our observations.

---------------------------------------------------------
Title: Observations of low-latitude electron precipitation
Authors: Lieu, R.; Watermann, J.; Wilhelm, K.; Quenby, J. J.; Axford,
W. I.
1988JGR....93.4131L Altcode:
Low-latitude electron precipitation outside the well-known region of
the trapped Van Allen radiation belt has been known for some time, as
has the occurrence of equatorial aurora. Observation by the Spacelab
1 electron spectrometer, working between 0.1 and 12.5 keV electron
energy has revealed an unexpectedly high occurrence rate and flux
intensity for these events. Data were analysed for 16 orbital passes,
between +/-30 latitude, outside the South Atlantic anomaly. Many
precipitation events with flux levels above 2×104 el
cm-2 sr-1 were observed,
each consisting of two separate electron populations (1) a low-energy
component (0.1-1 keV) with a power law spectrum, and (2) a high-energy
component (1-12.5 keV) with a distinct flattening of spectral slope,
sometimes with a peak, and exhibiting a “flare-up” behavior on a
maximum time scale of 1.5 hours. Detailed study of the four orbital
passes which of 1.5 hours. Detailed study of the four detected the most
intense fluxes (&gt;3×105 el cm-2
s-1) of 1- to 12.5-keV electrons showed
intensity minima at the magnetic equator, with peaks on either side
(L~1.12) and pitch angle distributions that indicate a significant
nontrapped population. The observations place a lower limit of ~0.1
Vm-1 on the peak electric fields responsible
for acceleration of the electrons.

---------------------------------------------------------
Title: Position of comet P/Halley at the Giotto encounter
Authors: Curdt, W.; Wilhelm, K.; Craubner, A.; Krahn, E.; Keller, H. U.
1988A&A...191L...1C Altcode:
Images of the Halley Multicolor Camera (HMC) were analyzed to evaluate
the fly-by geometry of the Giotto spacecraft past Comet Halley. The
position of the comet at closest approach was determined with respect to
the spacecraft. Based on the orbit information of Giotto the absolute
position of the cometary nucleus could be obtained with very high
precision.

---------------------------------------------------------
Title: Spacelab-1 observations of suprathermal electrons induced by
artificial electron beams
Authors: Watermann, J.; Wilhelm, K.; Torkar, K. M.; Riedler, W.
1988AdSpR...8a.111W Altcode: 1988AdSpR...8..111W
Suprathermal electrons precipitated in response to SEPAC electron
accelerator activity on board Spacelab 1 have been observed by
a channeltron electron spectrometer covering the energy range
from 0.1 to 12.5 keV. Three series of beams of 1 to 5 seconds
duration with current strengths up to 300 mA and energies up
to 5 keV induced electron fluxes up to 1011 electrons
eV-1cm-2s-1sr-1. The FO-2
series showed a very high electron enhancement below and at the beam
energy and a distinct fall off above it, while the FO-7-1 and FO-7-2
series showed a somewhat lower electron enhancement without indication
of the beam energy in the flux density curves. A characteristic feature
of all SEPAC series was an enhanced electron flux above the beam
energy of more than 100 times the background level. The return flux
distribution did not respect the forbidden single particle trajectory
regime resulting from spacecraft obstruction but seemed to depend
mainly on the coelevation angle according to the beam direction and
on the line of sight from the spectrometer to the accelerator.

---------------------------------------------------------
Title: Return flux measurements in response to short-time electron
beams aboard Spacelab-1
Authors: Torkar, K. M.; Riedler, W.; Wilhelm, K.; Watermann, J.;
Beghin, C.
1988AdSpR...8a.115T Altcode: 1988AdSpR...8..115T
Measurements of the returning electron flux distribution in response
to 8 keV, 10 to 100 mA, 20 to 40 ms electron beams of the PICPAB
particle accelerator on board Spacelab-1 were performed by an electron
spectrometer in the energy range from 0.1 to 12.5 keV (experiment
1ES019A). The electron flux followed almost immediately the beam within
the sampling interval of 1 ms. A major flux increase was found at low
energies, but also up to the beam energy. The effects of different
beam currents and of payload charging are discussed.

---------------------------------------------------------
Title: Detailed Analysis of a Surface Feature on Comet p/ Halley
Authors: Schwarz, G.; Craubner, H.; Delamere, A.; Gobel, M.; Gonano,
M.; Huebner, W. F.; Keller, H. U.; Kramm, R.; Mikusch, E.; Reitsema,
H.; Whipple, F. L.; Wilhelm, K.
1987A&A...187..847S Altcode:
The surface of the nucleus of comet P/Halley is visible on many images
taken by the Halley Multicolour Camera on board the Giotto spacecraft. A
number of structural features like "mountains" or "surface dips"
are clearly discernible. This paper outlines the methods that can be
applied to analyze a surface feature with the aim of obtaining its
characteristics. A relatively large craterlike surface feature is
selected for detailed analysis and an attempt is made to determine
its size and shape as well as to assess the attainable accuracy. The
surface topography is computed using a photoclinometric approach,
while dimensions are determined based on apparent object sizes and an
estimate of aspect angle.

---------------------------------------------------------
Title: Reconstruction of the orientation and shape of the nucleus
of comet Halley.
Authors: Szego, K.; Kondor, A.; Toth, I.; Sagdeev, R. Z.; Wilhelm,
K.; Keller, H. U.
1987ESASP.278..463S Altcode: 1987dsc..proc..463S
In this paper a constructive modelling technique is developed for the
analysis of the imaging data of VEGA and GIOTTO. As a first result
the position of the small and big ends of the nucleus is obtained
unambiguously for the different encounters.

---------------------------------------------------------
Title: Caesar Investigations
Authors: Rinnert, K.; Wilhelm, K.; Kohl, H.; Schlegel, K.; Dehmel, G.;
Luehr, H.; Kloecker, N.; Oelschlaegel, W.; Gough, M. P.; Holback, B.
1987ESASP.270..299R Altcode: 1987erbp.symp..299R
The Coordinate Auroral Experiment using Scatter And Rocket
investigations was performed by combining high resolution in-situ
measurements using rocket-borne instrumentation and ground-based
observations with EISCAT. Magnetosphere/ionosphere interaction during
discrete auroral arc conditions was studied by observing energetic
charged particle distributions and electrodynamic processes as well
as parameters of the ionospheric plasma associated with the arc. The
electric and magnetic field configurations and the current systems
related to the arc were investigated. Two identical payloads were
built and launched with Skylark 12 motors from Andoya (Norway).

---------------------------------------------------------
Title: Observations of Field-Aligned Current Structures during Caesar
Flight II
Authors: Luehr, H.; Oelschlaegel, W.; Rinnert, K.; Wilhelm, K.
1987ESASP.270..305L Altcode: 1987erbp.symp..305L
Magnetic field measurements from a sounding rocket are described. High
resolution magnetic field vector measurements were obtained. A precision
star sensor was employed. The magnetic effects of the polar electrojet
as well as of field-aligned currents were measured. Close to apogee,
small-scale field-aligned current structures identified by combination
of E and B-field measurements as active acceleration regions, are
observed.

---------------------------------------------------------
Title: On the shape of Comet Halley's nucleus
Authors: Keller, H. U.; Thomas, N.; Wilhelm, K.
1987BAAS...19Q.878K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Halley multicolour camera
Authors: Keller, H. U.; Schmidt, W. K. H.; Wilhelm, K.; Becker, C.;
Curdt, W.; Engelhardt, W.; Hartwig, H.; Kramm, J. R.; Meyer, H. J.;
Schmidt, R.; Gliem, F.; Krahn, E.; Schmidt, H. P.; Schwarz, G.; Turner,
J. J.; Bouyries, P.; Cazes, S.; Angrilli, F.; Bianchini, G.; Fanti,
G.; Brunello, P.; Delamere, A.; Reitsema, H.; Jamar, C.; Cucchiaro, A.
1987JPhE...20..807K Altcode:
The Halley multicolor camera (HMC) is a high-resolution imaging
system on board the ESA Giotto spacecraft to comet Halley. The
fast spin of this spacecraft (15 RPM) required a unique and highly
specialized design and complex fully autonomous operation. Design
criteria and trade-offs and operational aspects are emphasized in this
instrument description. Actual performance numbers are given whenever
available. The imaging quality is demonstrated by sample images taken
from the earth and the comet.

---------------------------------------------------------
Title: Rotation and precession of comet Halley
Authors: Wilhelm, K.
1987Natur.327...27W Altcode:
Measurements obtained during the recent appearance of comet Halley
suggest that its nucleus undergoes free and forced precession
motions. Periodicities of 2.2 and 7.4 days can be explained by a
2.2-day rotation about the minor axis and a free-precessional period
of 14.8 days.

---------------------------------------------------------
Title: Dust-gas interaction deduced from Halley multicolor camera
observations
Authors: Huebner, W. F.; Keller, H. U.; Wilhelm, K.; Whipple, Fred L.;
Delamere, W. A.; Reitsema, H. J.; Schmidt, H. U.
1986ESASP.250b.363H Altcode: 1986ehc2.conf..363H
The dust and gas productions of comet Halley were measured by the
dust counter and the mass spectrometer on the Giotto spacecraft. These
instruments give only little information about the spatial asymmetry of
the activity. The asymmetry in the dust production is clearly evident
from the dust jets seen in the Halley Multicolour Camera images. Since
the dust is entrained by the gas, the gas production must be similarly
asymmetric. The authors relate the intensity profiles along and across
several dust jets to their source regions on the nucleus. Properties
of the dust jets are investigated. A few compact, but highly active
source regions on the nucleus produce most of the visible dust and
can account for most of the gas produced by the comet.

---------------------------------------------------------
Title: Dust activity of Comet Halley's nucleus
Authors: Keller, H. U.; Delamere, W. A.; Huebner, W. F.; Reitsema,
H.; Schmidt, H. U.; Schmidt, W. K. H.; Whipple, Fred L.; Wilhelm, K.
1986ESASP.250b.359K Altcode: 1986ehc2.conf..359K
Images obtained by the Halley multicolor camera using the clear filter
with a pass band from 300 to 1000 nm were used to study dust activity
in the comet nucleus. Comparisons with ground based observations
confirm that dust production towards the Sun increases in activity
relative to the southern background source while the Giotto spacecraft
was approaching. This is in agreement with the assumption that the
sunward activity becomes stronger when the source rotates towards the
Sun. Estimated dust column density is 90 billion/sqm, with optical
thickness less than or = 0.3. Surface reflectivity is less than 1%,
indicating a very rough surface with large fractions of shadowed areas.

---------------------------------------------------------
Title: Observations by the Halley Multicolour Camera
Authors: Keller, H. U.; Arpigny, C.; Barbiert, C.; Bonnet, R. M.;
Cazes, S.; Cordini, M.; Cosmovici, C. B.; Curdt, W.; Delamere, W. A.;
Huebner, W. F.; Hughes, D. W.; Jamar, C.; Kramm, R.; Malaise, D.;
Reitsema, H.; Schmidt, H. U.; Schmidt, K.; Schmidt, W. K. H.; Seige,
P.; Whipple, F. L.; Wilhelm, K.
1986ESASP.250b.347K Altcode: 1986ehc2.conf..347K
The Halley Multicolour Camera (HMC) was the only remote sensing
instrument on board the Giotto spacecraft. HMC operated successfully up
to the moment when a power surge on the spacecraft impaired operations
of several instruments. The very last image frame of HMC was transmitted
from about 12 s before closest approach. The first image of comet
Halley was taken by HMC on 9 March. The observations of the HMC have
consolidated our perception of the nature of comets.

---------------------------------------------------------
Title: Nucleus morphology of Comet Halley
Authors: Reitsema, H. J.; Delamere, W. A.; Huebner, W. F.; Keller,
H. U.; Schmidt, W. K. H.; Wilhelm, K.; Schmidt, H. U.; Whipple, Fred L.
1986ESASP.250b.351R Altcode: 1986ehc2.conf..351R
The images of Halley which were obtained by the Halley Multicolour
Camera have been used to determine the projected size and shape of
the nucleus. The location of the terminator and numerous surface
features have been determined. There is good correlation between the
brightest surface features and the dust jets; however, many bright
features are seen which are not associated with jets. Most of the
observed features are circular and appear to be related to surface
elevation. The angularity of the terminator gives an indication of
the three-dimensional structure of the face which was observed.

---------------------------------------------------------
Title: A three-dimensional model of the nucleus of Comet Halley
Authors: Wilhelm, K.; Cosmovici, C. B.; Delamere, W. A.; Huebner,
W. F.; Keller, H. U.; Reitsema, H.; Schmidt, H. U.; Whipple, Fred L.
1986ESASP.250b.367W Altcode: 1986ehc2.conf..367W
The nucleus of comet Halley was observed by the Halley Multicolour
Camera (HMC) during the last minutes of the fly-by sequence before
reaching the point of closest approach. The phase angle change during
the observational period was less than 17°. HMC data can thus only
define a two-dimensional contour of the nucleus at a certain time. The
authors will outline the overall geometry during the HMC observations
and relate the findings to information available from other sources
at different times. The nucleus of the comet will be described
as a tri-axial ellipsoid with major axes of 16, 10 and 9 km. The
rotation axis was directed towards δ1950 = -(40±5)°
and α1950 = (50±10°). The rotation with a period of P =
(54±1) h was in a prograde sense with respect to the orbital motion.

---------------------------------------------------------
Title: Radiometric observations of the nucleus of Comet Halley
Authors: Delamere, W. A.; Reitsema, H. J.; Huebner, W. F.; Schmidt,
H. U.; Keller, H. U.; Schmidt, W. K. H.; Wilhelm, K.; Whipple, Fred L.
1986ESASP.250b.355D Altcode: 1986ehc2.conf..355D
The images of Halley which were obtained by the Halley Multicolour
Camera have been used to determine the surface brightness of the
nucleus. Radiometric values of jet-free areas of the surface are
presented and a range of possible surface brightness values are
derived. These direct measures are compared with brightnesses derived
from the size of the nucleus, as determined from HMC images, and
ground-based observations obtained before the onset of coma activity.

---------------------------------------------------------
Title: Electric field configuration and plasma parameters in the
vicinity of a faint auroral arc
Authors: Rinnert, K.; Kohl, H.; Schlegel, K.; Wilhelm, K.
1986JATP...48..867R Altcode:
To study auroral arc physics, coordinated rocket and EISCAT measurements
were made across a faint arc. Observed plasma parameters and dc electric
fields from both methods are discussed. The precipitation event was a
moderate one and obviously a localized and temporary disturbance. The
electric field configuration in the vicinity of the associated arc
measured on board the rocket payload (apogee at 703 km) and deduced
from EISCAT measurements of the plasma drift are discussed. The main
features of the electric field in the arc region can be explained by
polarization fields, but there is also some evidence of field-aligned
electric fields.

---------------------------------------------------------
Title: Dust-gas interaction deduced from Halley multicolour camera
observations
Authors: Huebner, W. F.; Delamere, W. A.; Keller, H. U.; Reitsema,
H. J.; Schmidt, H. U.; Whipple, F. L.; Wilhelm, K.
1986esla.sympQ....H Altcode:
The dust and gas productions of Comet Halley were measured by the dust
counter and the mass spectrometers on the Giotto spacecraft. These
instruments give only little information about the spatial asymmetry
of the activity. The asymmetry in the dust production is clearly
evident from the dust jets seen in the Halley Multicolor Camera
images. Since the dust is entrained by the gas, production must be
similarly asymmetric. The intensity profiles along and across several
dust jets are related to their source regions on the nucleus. Properties
of the dust jets are investigated. A few compact, but highly active
source regions on the nucleus produce most of the visible dust and
can account for most of the gas produced by the comet.

---------------------------------------------------------
Title: Specialized image processing technique applied to Halley
multicolour camera images of the Earth
Authors: Wilhelm, Klaus; Schmidt, Wolfgang K. H.; Hartmann, Gerd K.
1986GeoRL..13..813W Altcode:
A special image processing technique has been applied to earth images
taken by the Halley Multicolour Camera (HMC) on-board ESA's space probe
Giotto on its way to a close encounter with comet Halley on March 14,
1986. The method depends on the knowledge of the point spread function
of the optical system. Deconvolution has been achieved by a direct
inversion of the convolution process subject to boundary conditions that
would correspond to non-linear filter processes. Experimental evidence
is presented that under the prevailing conditions the technique can
provide pixel resolution. Comparison with weather satellite images
allow verification of the results for the earth observations.

---------------------------------------------------------
Title: First Halley Multicolour Camera imaging results from Giotto
Authors: Keller, H. U.; Arpigny, C.; Barbieri, C.; Bonnet, R. M.;
Cazes, S.; Coradini, M.; Cosmovici, C. B.; Delamere, W. A.; Huebner,
W. F.; Hughes, D. W.; Jamar, C.; Malaise, D.; Reitsema, H. J.; Schmidt,
H. U.; Schmidt, W. K. H.; Seige, P.; Whipple, F. L.; Wilhelm, K.
1986Natur.321..320K Altcode:
The first imaging results from the Halley Multicolour Camera (HMC)
during the Giotto fly-by of comet Halley provide images centred on
the brightest part of the inner coma which show the silhouette of
a large, solid and irregularly shaped cometary nucleus and jet-like
dust activity visible in reflected sunlight. A first assessment of the
data yields information on the dimensions and shape of the nucleus and
dust emission activity. The nucleus is at least 15 km long and ~10 km
wide; its geometrical albedo is very low (&lt;4%). Only minor parts
of the surface are active, most of it beirig covered by non-volatile
material. Dust jets dominate the inner coma and are restricted to the
sub-solar hemisphere. Preliminary interpretations of these observations
are presented. The parameters of the fly-by trajectory relative to
the nucleus are given.

---------------------------------------------------------
Title: The Giotto Halley multicolor camera
Authors: Schmidt, W. K. H.; Keller, H. U.; Wilhelm, K.; Arpigny,
C.; Barbieri, C.; Biermann, L.; Bonnet, R. M.; Cazes, S.; Cosmovici,
C. B.; Delamere, W. A.
1986gmis.rept..149S Altcode:
The Halley Multicolor Camera (HMC) is a Ritchey-Chretien type
Cassegrain telescope (1000 mm focal length) with CCD imagers in the
focal plane. It is suspended in a revolving mount so that the center
of its field of view can be moved freely in a half plane that contains
the spin axis of the spacecraft. Together with the spinning motion
of the spacecraft, this mobility enables the HMC to image any part of
the whole 4 pi solid angle of the sky. The line-scan imaging technique
uses the spacecraft/s spin for one dimension and the length of the line
for the other dimension of the image. Four line sensors with filters
of different color bands take images almost simultaneously. Onboard
electronics controlled by three microprocessors operate the camera
almost autonomously. The image of the comet will be sought at the
beginning of the encounter operations. Having found it, the camera
will switch to the imaging mode. The contents of the images are to be
telemetered to ground in sections and at the same time used onboard
to update the parameters that describe the spacecraft/s trajectory
relative to the cometary nucleus. With this information, the HMC/s
field of view will be able to track the center of the comet/s image.

---------------------------------------------------------
Title: Observations of artificially induced suprathermal electron
fluxes in board of SPACELAB 1
Authors: Watermann, J.; Wilhelm, K.; Torkar, K. M.; Riedler, W.
1986MitAG..65..166W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Giotto Halley Multicolour Camera.
Authors: Schmidt, W. K. H.; Keller, H. U.; Wilhelm, K.; Arpigny, C.;
Barbieri, C.; Biermann, L.; Bonnet, R. M.; Cazes, S.; Cosmovici,
C. B.; Delamere, W. A.; Huebner, W. F.; Hughes, D. W.; Jamar, C.;
Malaise, D.; Reitsema, H.; Seige, P.; Whipple, F. L.
1986ESASP1070..149S Altcode:
In recent decades, Whipple's "dirty snowball" picture of the cometary
nucleus has become widely, but not universally accepted. Proof
of the nucleus' existence and study of its properties require
pictures in various colour bands, preferably together with other
information. Acquisition of these pictures is the task of Halley
Multicolour Camera (HMC), which is described in detail.

---------------------------------------------------------
Title: Why does the perpendicular electric field increase at the
edge of auroral arcs?
Authors: Bruening, K.; Wilhelm, K.; Goertz, C. K.
1985AdSpR...5d..79B Altcode: 1985AdSpR...5...79B
Radar, rocket and satellite measurements often indicate that there is a
strong increase and subsequent decrease in the perpendicular electric
field when traversing one edge of an auroral arc. The analysis of
rocket measurements, presented here, shows that above an auroral arc
there is a small gradient in the electric field due to polarization
effects in the ionosphere, but that the strong increase at the edge of
the arc can only be explained if the field-aligned currents associated
with the arc are taken into account.

---------------------------------------------------------
Title: Fast magnetospheric echoes of energetic electron beams
Authors: Wilhelm, K.; Bernstein, W.; Kellogg, P. J.; Whalen, B. A.
1985JGR....90..491W Altcode:
Electron beam experiments using rocketborne instrumentation have
confirmed earlier observations of fast magnetospheric echoes of
artificially injected energetic electrons. A total of 234 echoes have
been observed in a pitch angle range from 9° to 110° at energies of
1.87 and 3.90 keV. Out of this number, 95 echoes could unambiguously
be identified with known accelerator operations at 2-, 4-, or 8-keV
energy and highest current levels resulting in the determination of
transit times of typically 300 to 400 ms. In most cases, when echoes
were present in both energy channels, the higher-energy electrons
led the lower-energy ones by 50 to 70 ms. Adiabatic theory applied to
these observations yields a reflection height of 3000 to 4000 km. An
alternative interpretation is briefly examined, and its relative merit
in describing the observations is evaluated. The injection process is
discussed in some detail as the strong beam-plasma interaction that
occurred near the electron accelerator appears to be instrumental in
generating the source of heated electrons required for successful echo
detection for both processes.

---------------------------------------------------------
Title: Examination of Non-Adiabatic Effects during AN Electron Beam
Experiment in the Ionosphere
Authors: Wilhelm, K.
1985ESASP.229..197W Altcode: 1985erbp.symp..197W
Prompt and delayed echo fluxes and superacceleration of electrons
were observed during the sounding rocket flight Several Coordinated
Experiments using an electron accelerator. Magnetospheric electric
fields parallel to the magnetic field were investigated. The degree
of nonadiabatic behavior of the injected electron beam and the return
flux was examined. It is shown that the region of strong beam-plasma
interaction is limited to 300 km in length along the magnetic field
but that backscatter or energetic electrons could occur from much
larger distances. By appraising the difference in transit times of 1.9
and 3.9 keV electrons it is established that a continuous backscatter
model operating out to several thousand kilometres is not consistent
with the observations.

---------------------------------------------------------
Title: Acceleration of electrons in strong beam-plasma interactions
Authors: Wilhelm, K.; Bernstein, W.; Kellogg, P. J.; Whalen, B. A.
1984GeoRL..11.1176W Altcode:
The sounding rocket payload SCEX (Several Compatible Experiments to
utilize an electron accelerator; NASA flight 27.045) launched on January
27, 1982 from the Churchill Research Range provided an opportunity to
observe the effects of strong beam-plasma interactions on the electron
population in a region of space remote from the main payload carrying
the accelerator. We present observations demonstrating that electron
energies of up to four times the injection energy occurred during
accelerator operations in high-current mode. Detailed instrumental
performance characteristics in flight and in the laboratory will be
discussed. The acceleration events occurred at reception pitch angles
between 54° and 126°. Long confinement times seem to be a necessary
condition for generating the energetic electrons. It is proposed that
they result from the length of the interaction region.

---------------------------------------------------------
Title: Electron Flux Intensity Distributions Observed in Response
to Particle Beam Emissions
Authors: Wilhelm, K.; Stuedemann, W.; Riedler, W.
1984Sci...225..186W Altcode:
Modifications of the suprathermal electron population were observed
by an electron spectrometer on Spacelab 1 during electron beam
injections. The instrument covered its energy range (100 to 12,500
electron volts) and field of view (≈ 2π ) with high energy, angle,
and time resolution. The measurements demonstrate the presence of
strong beam-plasma interactions during high-current modes of accelerator
operations. Spacecraft charging could be studied as well as processes
that accelerated electrons to more than four times the injection energy.

---------------------------------------------------------
Title: Magnetospheric sounding-rocket programme at high latitudes
Authors: Wilhelm, K.
1983ESASP.183..455W Altcode: 1983erbp.conf..455W
The ESA 1976 report "Sounding Rocket Programmes in the Spacelab Era"
is reviewed. Operation in conjunction with Spacelab, support of EISCAT
and other ground-based installations, and experimental opportunities
afforded by sounding rockets are discussed.

---------------------------------------------------------
Title: Fast magnetospheric echoes of artificially injected electrons
observed above a bright auroral arc
Authors: Wilhelm, K.; Bernstein, W.
1983ESASP.183..277W Altcode: 1983erbp.conf..277W
Rocket-borne electron beam experiments confirmed earlier observations
of fast magnetospheric echoes of artificially injected energetic
electrons. A total of 234 echoes were observed at pitch angles from 9
to 10 deg at energies of 1.87 and 3.90 keV. Of these, 102 echoes are
unambiguously related to preceding accelerator operations at 2, 4 or
8 keV energy and highest current levels resulting in the determination
of transit times of typically 300 to 400 msec. When echoes are present
in both energy channels, higher energy electrons lead lower energy
ones by 50 to 70 msec. Adiabatic theory applied to the observations
yields a reflection height of 3000 to 4000 km.

---------------------------------------------------------
Title: Energy dispersion and acceleration of low energy protons and
their relation to electrons during an auroral breakup
Authors: Urban, A.; Torkar, K. M.; Wilhelm, K.
1982JGZG...50..189U Altcode:
Data from simultaneous rocket-borne proton and electron measurement
experiments in the keV range conducted during an auroral breakup are
presented, and a clear correlation is shown in the proton and electron
flux variations. The measured proton spectral variations showing a
sequence of peaks in the energy range 13-5 keV are related to intense
electron precipitation and interpreted in terms of energy dispersion
of the protons over a distance of about nine earth radii. The measured
differential proton spectra for the flight could generally be fitted
by a power law with slope about 0.7. The pitch angle distribution of
the protons was typically isotropic over the upper hemisphere

---------------------------------------------------------
Title: In situ measurements of heating parameters in the auroral
ionosphere
Authors: Thiele, B.; Bostroem, R.; Dumbs, A.; Neske, E.; Schmidtke,
G.; Grossmann, K. U.; Krankowsky, D.; Laemmerzahl, P.; Marklund, G.;
Wilhelm, K.
1981P&SS...29..455T Altcode:
Four sounding rocket payloads were launched in early 1977 to measure
heating parameters in the auroral oval. Geophysical conditions were
different for the four flights: auroral arc substorm main phase
diffuse aurora, and auroral arc with negative bay. The conductivity
tensor and the heating rates of particle and Joule heating are
determined. The heating rates range in the order of a few tens of mWm
-2. These magnitudes accord with those determined with the
aid of backscatter facilities and other sounding rocket observations.

---------------------------------------------------------
Title: A Halley Multicolour Camera
Authors: Keller, H. U.; Arpigny, C.; Barbieri, C.; Benvenuti, P.;
Biermann, L.; Bonnet, R. M.; Cazes, S.; Colombo, G.; Cosmovici,
C. B.; Delamere, W. A.; Heubner, W. F.; Hughes, D. W.; Hunt, G. E.;
Jamar, C.; Mackay, C. D.; Malaise, D.; Schmidt, W. K. H.; Seige, P.;
Whipple, F. L.; Wilhelm, K.
1981giot.proc..105K Altcode:
No abstract at ADS

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Title: Study of magnetospheric substorm events
Authors: Wilhelm, K.
1980ESASP.152..269W Altcode: 1980urbp.symp..269W
High altitude sounding rocket payloads, (four), of the project 'Substorm
phenomena' were launched from the Andoeya Rocket Range during the
period 13 October 1977 to 30 January 1978. The scientific goal was a
detailed investigation of magnetospheric-substorm related particle and
field effects in the auroral zone. Coordination with British and US
rocket programs led to salvoes of up to three payloads launched into
single auroral events providing the opportunity of time history studies
during the course of magnetospheric substorms. A number of ground-based
observations were performed and data summaries are presented.

---------------------------------------------------------
Title: Natural and artificially injected electron fluxes near discrete
auroral arcs
Authors: Wilhelm, K.
1980ESASP.152..407W Altcode: 1980urbp.symp..407W
A sounding rocket payload instrumented in order to inject and
observe energetic electron fluxes in the ionospheric plasma was
flown from Ft. Churchill into a bright auroral display on 9 April
1978. Measurements of one throw-away detector in three energy channels
at 1.9, 4 and 8 keV are discussed in order to relate the observed
electron echoes to the prevailing geophysical conditions.

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Title: Sounding rocket observations of field-aligned current sheets
Authors: Wilhelm, K.; Kloecker, N.; Theile, B.; Ott, W.; Spenner,
K.; Grabowski, R.; Wolf, H.; Stuedemann, W.; Dehmel, G.; Fischer, H. M.
1980ESASP.152..279W Altcode: 1980urbp.symp..279W
A high-altitude sounding rocket payload launched into an auroral
break-up event encountered at least two well developed current sheets
at the northern boundary of the auroral activity region. In the upward
directed current regime, the charge carriers were predominantly
precipitating energetic electrons embedded in a low-density,
high-temperature magnetospheric plasma. The downward directed currents,
on the other hand, were accompanied by a high-density, low-temperature
plasma. Signatures of the current sheets could be identified in the
perpendicular electric field as shock-like intensity and direction
variations as well as in spectral modifications of high-energy electron
and proton fluxes.

---------------------------------------------------------
Title: Field-aligned currents above an auroral arc
Authors: Theile, B.; Wilhelm, K.
1980P&SS...28..351T Altcode:
Simultaneous observations of precipitating electrons and protons in
the energy range from 15 eV to 35 keV and magnetic field variations
were made onboard a sounding rocket payload launched from the Andoya
Rocket Range. The electric current density deduced from the electron
precipitation observed during the passage over an auroral arc was
comparable to that determined from the magnetic field variations. In
addition, a downward current was observed by its magnetic field
signature at the northern edge of the arc which was, however, not
accompanied by significant particle fluxes in the energy range under
consideration. It will be assumed that this current was carried by
thermal electrons of ionospheric origin.

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Title: Study of electric fields parallel to the magnetic lines of
force using artificially injected energetic electrons
Authors: Wilhelm, K.; Bernstein, W.; Whalen, B. A.
1980GeoRL...7..117W Altcode:
Electron beam experiments using rocket-borne instrumentation will be
discussed. The observations indicate that reflections of energetic
electrons may occur at possible electric field configurations parallel
to the direction of the magnetic lines of force in an altitude range
of several thousand kilometers above the ionosphere.

---------------------------------------------------------
Title: Auroral particle fluxes in the ionosphere.
Authors: Wilhelm, K.
1979JGZG...46..151W Altcode:
The observations discussed in this paper were conducted in the framework
of the 'Polar High Atmosphere Sounding Rocket Project' with a view
to determining the contributions of auroral particle fluxes to both
the energy budget and the current system of the upper atmosphere. The
experiment was flown on board four payloads that were launched into
various phases of magnetospheric substorm events to peak altitudes
of approximately 270 km. During undisturbed portions of the flight
times the electron flux below 500 eV was nearly isotropic and could be
described by a power law spectrum. At high energies the spectra were
steeper and exhibited a loss signature in the atmospheric backscatter
cone. In disturbed periods electron fluxes with peaked spectra in the
keV energy range were often superimposed on these distributions. In
addition, strongly field-aligned electron fluxes were frequently
observed at low energies. Results are also presented on the energy
flux carried by electrons and protons and the relationship to optical
auroral emissions.

---------------------------------------------------------
Title: Results of an analysis of synchronous recordings of Pi2-type
geomagnetic pulsations at five stations located at the same latitude
Authors: Baranskii, L. N.; Troitskaia, V. A.; Sterlikova, I. V.;
Gokhberg, M. B.; Muench, J.; Wilhelm, K.; Kharchenko, I. P.; Ivanov,
N. A.
1978Ge&Ae..18..893B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Low-Energy Auroral Particle Observations
Authors: Wilhelm, K.
1978ESASP.135...63W Altcode: 1978esrb.rept...63W
Low-energy auroral electron observations were conducted on several
recent sounding rocket flights during various substorm phases. During
undisturbed portions of the flight time the electron flux below
500 eV was nearly isotropic and could be described by a power law
spectrum. At high energies the spectra were steeper and exhibited
a loss cone signature. In disturbed periods nearly mono-energetic
electron fluxes in the keV range were often superimposed on these
distributions. In addition, strongly field-aligned electrons were
frequently observed at low energies. A mechanism for field-aligned
electric field acceleration is suggested.

---------------------------------------------------------
Title: Fluctuations of the auroral zone current system and geomagnetic
pulsations
Authors: Wilhelm, K.; Muench, J. W.; Kremser, G.
1977JGR....82.2705W Altcode:
Recordings of Pi 1 and Pi 2 pulsations obtained on a short-distance
network of magnetometer stations were used to investigate the
relationship between fluctuations of the auroral zone currents
and geomagnetic pulsations. During the early part of the substorm
expansion phase the pulsations of the D and H components are decoupled
from each other at all stations. Similarly, the pulsations of the
D components are not significantly correlated at stations with
separation distances of approximately 100 km. For this interval the
pulsations of the H component are interpreted as being predominantly
the magnetic effect of fluctuations of the auroral electrojet, and the
pulsations of the D component as being a consequence of fluctuations
of Birkeland sheet currents. The conclusion can be drawn from these
observations that the Birkeland currents are not directly connected in
the north-south direction. Thus a considerable east-west component of
the currents is required in order to maintain current continuity in
the ionosphere. These effects disappear in the late expansion phase
and early recovery phase.

---------------------------------------------------------
Title: Preliminary results of a Soviet-German experiment on
synchronous detection of geomagnetic pulsations along meridional
and latitudinal chains of stations
Authors: Troitskaia, V. A.; Baranskii, L. N.; Gokhberg, M. B.;
Sterlikova, I. V.; Belenkaia, B. N.; Muench, J.; Wilhelm, K.; Volkner,
H.; Ziebert, M.; Hillebrand, O.
1976Ge&Ae..16.1090T Altcode:
No abstract at ADS

---------------------------------------------------------
Title: SOUNDING-ROCKET PROGRAMMES IN THE SPACELAB ERA - Report of
an ESA ad hoc Study Group
Authors: Wilhelm, K.; et al.
1976ESASP.115...93W Altcode: 1976epsr.conf...93W
No abstract at ADS

---------------------------------------------------------
Title: LES PROGRAMMES DE FUSEES-SONDES A L'ERE du SPACELAB - Rapport
établi par le Groupe d'étude ad hoc de l'ASE
Authors: Wilhelm, K.; et al.
1976ESASP.115..111W Altcode: 1976epsr.conf..111W
No abstract at ADS

---------------------------------------------------------
Title: Sounding-Rocket Experiments for Detailed Studies of
Magnetospheric Substorm Phenomena
Authors: Stüdemann, W.; Wilhelm, K.
1974esrs.conf..201S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On the morphology of auroral-zone X-ray events - II. Events
during the early morning hours.
Authors: Kremser, G.; Wilhelm, K.; Riedler, W.; Brønstad, K.; Trefall,
H.; Ullaland, S. L.; Legrand, J. -P.; Kangas, J.; Tanskanen, P.
1973JATP...35..713K Altcode:
Auroral-zone electron precipitation during early morning hours
(0200-0600 hr magnetic local time) has been analysed with the
aid of X-ray measurements from northern Scandinavia together with
recordings of geomagnetic variations and cosmic noise absorption
(CNA). The electron precipitation can be divided in two parts:
one occurring close to the location of the electrojet, the other,
when the electrojet is far away or absent. The main features of
these two types of precipitation distinctly resemble those found
earlier in the midnight hours and in the late-morning (SVA-events),
respectively. Both types of precipitation may occur simultaneously
in the early morning hours. The SVA-type precipitation may extend to
very early local times, and the midnight-type precipitation towards
dawn. Fast pulsations of the X-ray intensity were found in both
types. The midnight-type precipitation apparently stems directly from
the acceleration process. The SVA-precipitation was observed to be
delayed with respect to the break-up phase in the midnight sector and
showed characteristic variations of the energy spectrum in a sense as to
support the assumption that drifting electrons were the cause of this
phenomenon. It is proposed to call the part characteristic for local
times around midnight 'direct precipitation' and the SVA-like part
'drift precipitation'.

---------------------------------------------------------
Title: Book reviews
Authors: Schuiling, R. D.; Vesseur, H. J. A.; Wilhelm, Klaus; Hassan,
H.; van Sabben, D.; de Jager, C.; van Kampen, N. G.
1972SSRv...13..190S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Electron precipitation associated with a sudden commencement
of a geomagnetic storm
Authors: Ullaland, S. L.; Wilhelm, K.; Kangas, J.; Riedler, W.
1970JATP...32.1545U Altcode:
Balloon observations of X-rays produced by precipitated electrons
were made in the morning sector of the auroral zone at the time of
the geomagnetic storm sudden commencement ( SSC) of July 27, 1966. The
impulsive precipitation event lasted 4 min, both the rise and fall times
being nearly 1 min. On a shorter time scale a pronounced variation
with a period of 1.8-1.9 sec existed, which occurred together with
hm-emissions of the same period range. Besides the rapid fluctuations
in the precipitation a 50-sec period was also present. The energy
spectrum of the observed X-ray flux was rather steep, characterized by
an e-folding energy of E0 = 18-22 keV. The SSC apparently
triggered a polar magnetic substorm in the midnight sector of the
auroral zone.

---------------------------------------------------------
Title: Balloon measurements of solar protons in northern Scandinavia
on 7 July 1966.
Authors: Heristchi, Dj.; Kangas, J.; Kremser, G.; Legrand, J. -P.;
Masse, P.; Palous, M.; Pfotzer, G.; Riedler, W.; Wilhelm, K.
1969AIQSY...3..267H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On electrostatic energy analyzers for charged particles.
Authors: Wilhelm, K.; Schnell, M.
1969BWisF..69.....W Altcode:
No abstract at ADS