Author name code: wilhelm ADS astronomy entries on 2022-09-14 author:"Wilhelm, Klaus" ------------------------------------------------------------------------ Title: Anomalous Sun Flyby of 1I/2017 U1 (`Oumuamua) Authors: Wilhelm, Klaus; Dwivedi, Bhola Bibcode: 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. Title: On the radial acceleration of disc galaxies Authors: Wilhelm, Klaus; Dwivedi, Bhola N. Bibcode: 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. Title: Impact Models of Gravitational and Electrostatic Forces Authors: Wilhelm, Klaus; Dwivedi, Bhola N. Bibcode: 2020ptgy.book....5W Altcode: No abstract at ADS Title: Plasma Flows in the Cool Loop Systems Authors: Rao, Yamini K.; Srivastava, Abhishek K.; Kayshap, Pradeep; Wilhelm, Klaus; Dwivedi, Bhola N. Bibcode: 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. Title: Gravitational redshift and the vacuum index of refraction Authors: Wilhelm, Klaus; Dwivedi, Bhola N. Bibcode: 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. Title: A physical process of the radial acceleration of disc galaxies Authors: Wilhelm, Klaus; Dwivedi, Bhola N. Bibcode: 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. Title: Understanding disk galaxy rotation velocities without dark matter contribution--a physical process for MOND? Authors: Wilhelm, K.; Dwivedi, B. N. Bibcode: 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. 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. Bibcode: 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 http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/581/A26 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. Bibcode: 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). Title: Anomalous Earth flybys of spacecraft Authors: Wilhelm, Klaus; Dwivedi, Bhola N. Bibcode: 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. Title: Solar Coronal Plumes and the Fast Solar Wind Authors: Dwivedi, Bhola N.; Wilhelm, Klaus Bibcode: 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. Title: On the potential energy in a gravitationally bound two-body system Authors: Wilhelm, Klaus; Dwivedi, Bhola N. Bibcode: 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. Title: Photon in a cavity - a Gedankenexperiment Authors: Wilhelm, Klaus; Dwivedi, Bhola N. Bibcode: 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. Title: Secular perihelion advances of the inner planets and asteroid Icarus Authors: Wilhelm, Klaus; Dwivedi, Bhola N. Bibcode: 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. Title: On the gravitational redshift Authors: Wilhelm, Klaus; Dwivedi, Bhola N. Bibcode: 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. 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. Bibcode: 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. Title: Increase of the mean Sun-Earth distance caused by a secular mass accumulation Authors: Wilhelm, Klaus; Dwivedi, Bhola N. Bibcode: 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. 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. Bibcode: 2013opsg.book.....H Altcode: No abstract at ADS 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. Bibcode: 2013ops..book.....H Altcode: No abstract at ADS Title: An impact model of Newton's law of gravitation Authors: Wilhelm, Klaus; Wilhelm, Horst; Dwivedi, Bhola N. Bibcode: 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. Title: Gravity, massive particles, photons and Shapiro delay Authors: Wilhelm, Klaus; Dwivedi, Bhola N. Bibcode: 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. Title: SUMER Observations of Coronal-Hole Temperatures Authors: Wilhelm, Klaus Bibcode: 2013mspc.book...57W Altcode: No abstract at ADS Title: SUMER Observations of Coronal-Hole Temperatures Authors: Wilhelm, Klaus Bibcode: 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<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. Title: An explanation of the Pioneer anomaly involving accelerated atomic clocks Authors: Wilhelm, K.; Dwivedi, B. N. Bibcode: 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. 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. Bibcode: 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. Title: Quantitative solar spectroscopy Authors: Wilhelm, K. Bibcode: 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. Title: Study of the structures of the explosive events in the UV Authors: Niembro-Hernandez, R. T.; Mendoza-Torres, J. E.; Wilhelm, K. Bibcode: 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. Title: Spectroscopic Diagnostics of Polar Coronal Plumes Authors: Wilhelm, K.; Dwivedi, B. N.; Curdt, W. Bibcode: 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. Title: Photons - from source to detector Authors: Wilhelm, Klaus; Frohlich, Claus Bibcode: 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. Title: Postscript Authors: Huber, Martin C. E.; Pauluhn, Anuschka; Culhane, J. Len; Timothy, J. Gethyn; Wilhelm, Klaus; Zehnder, Alex Bibcode: 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. Title: Quantitative Solar Spectroscopy Authors: Wilhelm, Klaus Bibcode: 2010RvMA...22...81W Altcode: No abstract at ADS Title: 2.3 Solar short-wavelength telescopes and spectrometers on space missions Authors: Wilhelm, Klaus Bibcode: 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'. Title: The extra-terrestrial vacuum-ultraviolet wavelength range Authors: Timothy, J. Gethyn; Wilhelm, Klaus; Xia, Lidong Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 2009LanB...4B...14W Altcode: 2009LanB...4B.4113W No abstract at ADS Title: Coronal Active Regions Authors: Wilhelm, Klaus Bibcode: 2009LanB...4B..175W Altcode: 2009LanB...4B.4126W No abstract at ADS Title: Solar Transition Region and Quiet Corona Authors: Wilhelm, Klaus Bibcode: 2009LanB...4B...87W Altcode: 2009LanB...4B.4115W No abstract at ADS Title: Prominences and Ejecta Authors: Wilhelm, Klaus Bibcode: 2009LanB...4B..165W Altcode: 2009LanB...4B.4125W No abstract at ADS Title: Flares Authors: Wilhelm, Klaus Bibcode: 2009LanB...4B..180W Altcode: 2009LanB...4B.4127W No abstract at ADS Title: Active Regions Authors: Wilhelm, Klaus Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 2005A&A...435..733W Altcode: Observations of the solar equatorial corona between heights of 36 Mm and 184 Mm above the limb obtained by the SOHO spectrometers CDS and SUMER in December 2003 are presented and discussed with special emphasis on the widths of the spectral lines Mg x at 62.50 nm, Al xi at 55.00 nm and 56.82 nm, Ca x at 55.78 nm, and Si xi at 58.09 nm. SUMER observed, in addition, the lines Mg x 60.98 nm, Ca x 57.40 nm, Fe xii 124.20 nm, Fe xvii 115.31 nm, and Ca xiii 113.37 nm. The Si xii 52.11 nm line was only observed by CDS. A different behaviour of the line width of Mg x 62.50 nm as a function of height above the limb had been found in studies carried out independently with both instruments at different times. It is the aim of this joint investigation to (a) study instrumental effects on line-width results; and (b) provide a thorough analysis of line profiles with altitude for the new campaign. Title: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Title: Solar VUV Measurements obtained by SOHO Instruments and their radiometric Calibration (Invited) Authors: Wilhelm, K. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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<3 105 b: Te~3 105 c: Te~4 105 d: 6 105<Te <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. Bibcode: 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: The SUMER spectral atlas of solar-disk features Authors: Curdt, W.; Brekke, P.; Feldman, U.; Wilhelm, K.; Dwivedi, B. N.; Schühle, U.; Lemaire, P. Bibcode: 2001A&A...375..591C Altcode: A far-ultraviolet and extreme-ultraviolet (FUV, EUV) spectral atlas of the Sun between 670 Å and 1609 Å in the 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). The atlas contains spectra of the average quiet Sun, a coronal hole and a sunspot on the 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 almost 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. These lines are clearly marked in the atlas. The spectra include emissions from atoms and ions in the temperature range 6*E3 K to 2*E6 K, i.e., continua and emission 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 to study 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. Brief descriptions of the data reduction and calibration procedures are given. The spectral radiances are determined with a relative uncertainty of 0.15 to 0.30 (1sigma ) and the wavelength scale is accurate to typically 10 mÅ. The atlas is also available in a machine readable form. Table A.1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/375/591 Title: Plumes and oscillations in the sunspot transition region Authors: Maltby, P.; Brynildsen, N.; Kjeldseth-Moe, O.; Wilhelm, K. Bibcode: 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 Bibcode: 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 & 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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>=3×106 K) and Their Potential Use in Plasma Diagnostics Authors: Feldman, U.; Curdt, W.; Landi, E.; Wilhelm, K. Bibcode: 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>=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. Bibcode: 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. Bibcode: 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 <=20 mÅ(1σ), and in one case <=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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 1999CSci...77.1521D Altcode: No abstract at ADS Title: Plasma Flows In Coronal Hole Regions Authors: Landi, E.; Mullan, D.; Poletto, G.; Wilhelm, K. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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<=Rsolar<=1.50 along the Solar Equatorial Plane Authors: Feldman, U.; Doschek, G. A.; Schühle, U.; Wilhelm, K. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 1999Sci...283..810H Altcode: No abstract at ADS Title: Beobachtungen der ruhigen Sonne im ultravioletten Licht. Das Spektrometer SUMER auf SOHO. Authors: Wilhelm, K. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1998ApJS..119..105W Altcode: We present high-resolution observations of the higher H Lyman series lines taken with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) experiment flown on the Solar and Heliospheric Observatory (SOHO) spacecraft. We have used systematic observations extending from disk center to the solar limb to compute average profiles for representative solar features of the quiet Sun, limb-brightening curves, and full-disk, quiet-Sun profiles for Lyβ through Lyλ(11) and the Lyman continuum. The effects of radiative transfer are apparent in all of the line profiles we studied. The average quiet-Sun profiles for Lyβ through Lyɛ are self-reversed, and the remaining lines are flat-topped. The characteristics of the line profiles vary markedly with intensity. We observe strong enhancements in the red wings of network profiles, while the faint cell-center profiles are nearly symmetric. We also find that the intensities of the H Lyman lines increase at the limb, although the limb brightening is weak compared to optically thin transition region emission lines and largely obscured by the intensity variations observed in the quiet Sun. Title: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1998A&A...336L..90D Altcode: It has long been established that the high speed solar wind streams observed at 1 A.U. originate from the coronal hole regions of the Sun. Theoretical modelling of the acceleration mechanism depends critically on the value of the maximum of temperature existing close to the Sun. Measurements of the temperature in coronal holes prior to SOHO are unreliable. The very low luminosity leads to extreme observational difficulties, in particular due to light scattering in the instrument telescopes. Using the two SOHO spectrometers CDS and SUMER, electron temperatures have now been measured as a function of height above the limb in a polar coronal hole. Temperatures of around 0.8 MK are found close to the limb, rising to a maximum of less than 1 MK at 1.15 R_sun, then falling to around 0.4 MK at 1.3 R_sun. With these low temperatures, the classical Parker mechanism cannot alone explain the high wind velocities, which must therefore be due to the direct transfer of momentum from MHD waves to the ambient plasma. Title: Ion Temperatures in a Solar Polar Coronal Hole Observed by SUMER on SOHO Authors: Tu, C. -Y.; Marsch, E.; Wilhelm, K.; Curdt, W. Bibcode: 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, <δv2>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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 <=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. Bibcode: 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. Bibcode: 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 < 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1998ASPC..155..171B Altcode: 1998sasp.conf..171B No abstract at ADS Title: Solar EUV and UV Emission Line Observations Above a Polar Coronal Hole Authors: Wilhelm, K.; Bodmer, R. Bibcode: 1998sce..conf..371W Altcode: No abstract at ADS Title: Results from the SUMER Telescope and Spectrometer - Solar Ultraviolet Measurements of Emitted Radiation - on SOHO Authors: Wilhelm, Klaus Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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, & 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. Bibcode: 1997ApJ...490L.187W Altcode: Using observations from the Solar Ultraviolet Measurements of Emitted Radiation experiment flown on the Solar and Heliospheric Observatory spacecraft, we have measured Doppler wavelength shifts in the north polar coronal hole in the 1032 and 1038 Å emission lines of O VI and the 1036 and 1037 Å emission lines of C II relative to chromospheric emission lines. These observations were obtained on 1996 November 2 when the north polar coronal hole boundary extended southward to about 750'' (cosθ=0.65). Our measurements indicate the presence of average net redshifts in coronal holes at temperatures of less than 2.9×105 K. Measurements of systematic wavelength shifts in the Ne VIII resonance lines relative to the quiet Sun suggest a transition to average net outflows near 6.3×105 K in the coronal hole. Title: 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. Bibcode: 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. Bibcode: 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 < 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 > 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, & 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 {<atop >} 5.8, having different FIP effects. Title: Sonnenradiometrie mit SUMER auf SOHO. Authors: Hollandt, J.; Curdt, W.; Schühle, U.; Wilhelm, K. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 > 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1997ApJ...484L..91W Altcode: Using observations from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) experiment flown on the Solar and Heliospheric Observatory (SOHO) spacecraft, we have measured Doppler wavelength shifts and nonthermal broadening in the 1032 and 1038 Å emission lines of O VI and the 1036 and 1037 Å emission lines of C II. Near Sun center the C II lines exhibit an average redshift of 2 +/- 3 km s-1, consistent with earlier observations in this temperature range. The O VI emission lines exhibit average Doppler velocities of 5 +/- 3 km s-1, suggesting the presence of redshifted material at 2.9 × 105 K. For the O VI lines, the average nonthermal component of the observed line width is 34 +/- 3 km s-1. Title: Electron Densities in the Solar Polar Coronal Holes from Density-Sensitive Line Ratios of Si VIII and S X Authors: Doschek, G. A.; Warren, H. P.; Laming, J. M.; Mariska, J. T.; Wilhelm, K.; Lemaire, P.; Schühle, U.; Moran, T. G. Bibcode: 1997ApJ...482L.109D Altcode: We derive electron densities as a function of height in the north and south polar coronal holes from a forbidden spectral line ratio of Si VIII. Si VIII is produced at about 8 × 105 K in ionization equilibrium. We also derive densities from a similar line ratio of S X (1.3 × 106 K). The spectra were obtained with the Solar Ultraviolet Measurements of Emitted Radiation spectrometer flown on the Solar and Heliospheric Observatory spacecraft. In addition to the primary mechanism of electron impact excitation, the derivation of theoretical level populations for Si VIII and S X includes both proton and resonance capture excitation. We compare the coronal hole results to quiet-Sun coronal measurements obtained outside the east and west limbs. We find for distances of a few arcseconds outside the solar limb that the average line-of-sight electron densities in the coronal holes are about a factor of 2 lower than in quiet-Sun regions. The decrease of density with height is exponential in the polar holes. We also confirm the result known from a variety of earlier observations that the temperature of most of the plasma in coronal holes does not exceed about 106 K. Title: Translimb Spectroscopy with SOHO/SUMER Authors: Ayres, T. R.; Lemaire, P.; Schuhle, U.; Wilhelm, K.; Ruedi, I.; Solanki, S. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 1997SPD....28.0118M Altcode: 1997BAAS...29..882M Coronal holes are thought to be the source of high-speed solar wind streams. It is, however, unclear at what height the outflow of material first becomes apparent. Using the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) experiment on the Solar and Heliospheric Observatory (SOHO), we have obtained observations in the north polar coronal hole, its boundary region, and the adjacent quiet Sun at wavelengths that cover emission lines of O VI at 1032 and 1038 Angstroms, Ne VIII at 770 Angstroms, and Mg X at 625 Angstroms. These lines are formed at temperatures of 0.3, 0.8, and 1.25 MK, respectively, and should thus help to determine the temperature at which outflows are first detected. For O VI and Mg X, we will report on Doppler shift measurements made relative to cooler chromospheric lines. Since there are no suitable emission lines from ions formed in the chromosphere for the Ne VIII line, we are only able to measure relative differences between the coronal hole and the adjacent quiet Sun. We will also report on the magnitude of the nonthermal broadening in these lines in the different solar regions. This work was supported by a NASA SOHO Guest Investigator Program grant. Title: Doppler Shifts and Nonthermal Broadening in the Quiet Solar Transition Region: O VI Authors: Warren, H. P.; Mariska, J. T.; Wilhelm, K.; Lemaire, P. Bibcode: 1997SPD....28.0117W Altcode: 1997BAAS...29..882W Using observations from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) experiment flown on the Solar and Heliospheric Observatory (SOHO ) spacecraft, we have measured Doppler wavelength shifts and nonthermal broadening in the 1032 and 1038 Angstroms emission lines of Ovi and the 1036 and 1037 Angstroms emission lines of Cii. Near Sun center the Cii lines exhibit an average redshift of 2+/-3km s(-1) , consistent with earlier observations in this temperature range. The Ovi emission lines exhibit average Doppler velocities of 5+/-3km s(-1) suggesting the presence of redshifted material at 2.9*E(5) K. For the Ovi lines, the average nonthermal component of the observed line width is 34+/-3km s(-1) . These observations indicate a tendency for brighter regions to have larger average redshifts and line widths than faint features although the relationship is very weak. Preliminary analysis of observations at the limb suggests that the Doppler velocities for Ovi do not approach zero as would be expected for predominately radial motions. Title: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1997ApJ...477L.119D Altcode: Using spectra obtained with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer flown on the Solar and Heliospheric Observatory spacecraft, we deduce the temperature of formation of the Si IV ion in the solar transition region from the Si IV ultraviolet spectral line intensity ratio, 3p 2P3/2-3d 2D3/2,5/2/3s 2S1/2-3p 2P1/2, and compare the result to the temperature predicted under the assumption of ionization equilibrium. The wavelengths are as follows: 2D3/2,5/2, 1128.325, 1128.340 Å 2P1/2, 1402.770 Å. Ratios are derived for typical features of the quiet Sun, such as cell center and network, and are systematically higher than those predicted at the 6.3 × 104 K ionization equilibrium temperature of formation of Si IV. For most solar features the ratios imply a temperature of formation of about 8.5 × 104 K. The ratios for the faintest features imply a temperature of formation of up to 1.6 × 105 K. It is not clear, however, that all the discrepancies between the measured and theoretical ratios are due to a temperature effect. Accurate temperature measurements are important since a large discrepancy from ionization equilibrium has significant implications for the physics of the transition region, such as the possible presence of nonthermal electrons. Title: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1997ESASP.404..679S Altcode: 1997cswn.conf..679S No abstract at ADS Title: A New Sun from SUMER/SOHO Authors: Dwivedi, B. N.; Wilhelm, K. Bibcode: 1997CSci...72..609D Altcode: No abstract at ADS Title: Highlights of the SUMER Observations on SOHO Authors: Wilhelm, K.; Sumer Consortium Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 1996AAS...188.4909D Altcode: 1996BAAS...28R.898D On 7 and 8 March 1996, SOHO instruments engaged in their first joint science operation, a 12-hr observation of polar plumes over the South polar coronal hole. The observing mini-campaign included observations from SOHO, other spacecraft, and ground-based observatories. Contributing SOHO instruments -- in order of altitude, MDI, CDS, SUMER, EIT, UVCS, and LASCO -- made overlapping, simultaneous observations of plume structures from the photosphere out to the LASCO C3 limit of 32 solar radii. MDI provided line-of-sight surface magnetograms with a one-min cadence and 0.6 arcsec resolution; CDS, SUMER, and EIT supplied temperature-sensitive images of the lower corona with varying cadences and resolutions; UVCS measured fluctuations in Ly B intensity across the coronal hole with a one-min cadence at 1.4 R0; and LASCO imaged the entire corona out to 30 R0 in various visible passbands. Plume footpoints in the lower corona are observed by EIT and CDS to vary by a factor of two in EUV brightness with a timescale of tens of minutes, while the structures above are (as as been previously observed) quiescent on at least a ten-hr time scale. We present preliminary results of cross-instrument analysis of the observed plumes, and suggest how this and similar future data sets can be used to constrain quiet-sun wind acceleration and coronal heating models for the coronal hole. This research is supported by the SOI-MDI NASA contract NAG5-3077 at Stanford University. SOHO is project of international cooperation between NASA and ESA. Title: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 - Solar Ultraviolet Measurements of Emitted Radiation Authors: Wilhelm, K.; Curdt, W.; Marsch, E.; Schuehle, U.; Gabriel, A. H.; Lemaire, P.; Vial, J. -C.; Grewing, M.; Huber, M. C. E.; Jordan, S. D.; Poland, A. I.; Thomas, R. J.; Kuehne, M.; Timothy, J. G. Bibcode: 1993BAAS...25.1192W Altcode: No abstract at ADS 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 1989SPIE.1140..522L Altcode: No abstract at ADS Title: Reply Authors: Lieu, R.; Wilhelm, K.; Watermann, J. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 (>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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 (<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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1981giot.proc..105K Altcode: No abstract at ADS Title: Study of magnetospheric substorm events Authors: Wilhelm, K. Bibcode: 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. Bibcode: 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. 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. Bibcode: 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. Bibcode: 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. 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. Bibcode: 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. Bibcode: 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. Bibcode: 1978Ge&Ae..18..893B Altcode: No abstract at ADS Title: Low-Energy Auroral Particle Observations Authors: Wilhelm, K. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1969AIQSY...3..267H Altcode: No abstract at ADS Title: On electrostatic energy analyzers for charged particles. Authors: Wilhelm, K.; Schnell, M. Bibcode: 1969BWisF..69.....W Altcode: No abstract at ADS