UVCS/SOHO PAPERS - Pre '93



1992

1992-04:    UVCS: The ultraviolet coronograph spectrometer for SOHO

KOHL, JOHN L.; NOCI, GIANCARLO

1992, In ESA, Proceedings of the First SOHO Workshop: Coronal Streamers, Coronal Loops, and Coronal and Solar Wind Composition p 23-26 (SEE N93-31343 12-92) Category: Solar Physics Origin: STI NASA/STI


The Ultraviolet Coronagraph Spectrometer (UVCS) will provide spectroscopic observations of the solar corona out to 10 solar radii from Sun center. This capability is expected to expand greatly the number of plasma parameters that can be specified by remote sensing techniques. The UVCS plasma diagnostic techniques are expected to provide a sufficient number of empirically derived parameters to significantly constrain theories of solar wind acceleration, coronal heating, and solar wind composition. The measured line profiles and intensities are sensitive to random velocity distributions, densities of coronal protons, electrons, and ions.


1992-03:   A Two-Dimensional MHD global coronal model: steady-state streamers

Wang, A-H, Wu, S. T., Suess, S. T., Poletto, G.

1992, in Solar Wind VII, E. Marsch and R. Schwenn, Eds., Pergamon Press, Oxford, 311


1992-02:    Ly-alpha radiation from coronal transients

SPADARO, DANIELE; VENTURA, R.; MARTIN, R.; WU, S. T.; WANG, A. H.
1992, in ESA, Proceedings of the First SOHO Workshop: Coronal Streamers, Coronal Loops, and Coronal and Solar Wind Composition p 105-108 (SEE N93-31343 12-92)

The intensity and profile of the Lyman alpha spectral line expected from the extended coronal plasma evolving during a coronal transient, when observed in the plane of the sky in the range of heliocentric distance 1.5 to 4 solar radii, are calculated. The numerical values of temperature, density and outflow speed inside the coronal transient are those determined by Wu and Wang under the assumption of a single fluid, three dimensional, time dependent magnetohydrodynamic model of the outer solar atmosphere. The dependence of the Lyman alpha line on the physical parameters of the examined structure is discussed. These results may help in preparing and interpreting UVCS/SOHO (Ultraviolet Coronagraph/Solar and Heliospheric Observatory) observations of coronal transients.


1992-01:    Predicting Ly-alpha intensities in coronal streamers

NOCI, GIANCARLO; POLETTO, GIANNINA; SUESS, STEVEN T.; WANG, A. -H.; WU, S. T.


1992, in ESA, Proceedings of the First SOHO Workshop: Coronal Streamers, Coronal Loops, and Coronal and Solar Wind Composition p 93-96 (SEE N93-31343 12-92)

SOHO (Solar and Heliospheric Observatory) UVCS (Ultraviolet Coronagraph Spectrometer) will make long term observations of coronal streamers in UV lines, providing a new tool for the analysis of structures which have been known for decades but are still far from being adequately described. Work to evaluate the Lyman alpha brightness of coronal streamers is reported, adopting the streamer models obtained, via a time dependent numerical relaxation technique. This will yield understanding on the role of geometric versus physical factors in determining the streamer lyman alpha intensity and provide guidelines for UVCS observational operations. Future prospects along this line of research are summarized.


1991


1991-03:    UV observational techniques for the extended solar corona

KOHL, J. L.; GARDNER, L. D.; HUBER, M. C. E.; NICOLOSI, P.; NOCI, G.; NALETTO, G,; ROMOLI, M.; SPADERO, D.; TONDELLO, G.; and WEISER, H.

(Solar corona and solar wind; Proceedings of Symposium 9 of the 28th COSPAR Plenary Meeting, The Hague, Netherlands, June 25-July 6, 1990. A91-29501 11-92) Advances in Space Research (ISSN 0273-1177), vol. 11, no. 1, 1991, p. 359-367.

The SOHO Ultraviolet Coronograph Spectrometer is being developed for spectroscopic determinations of temperatures, densities and flow velocities in the extended solar corona. Determinations of plasma parameters for the primary particles (electrons and protons) and for several minor ions are planned. The techniques and instrumentation to be used must overcome the relatively low intensity levels and potentially high stray light levels intrinsic to observations of the extended corona while also providing high radiometric accuracy and relatively high spectral and spatial resolution. This paper concentrates on the instrument characteristics that are required to observe the resonantly scatter H I Lyman-alpha line at heliocentric heights from 1 to 10 solar radii.


1991-02:    Coronal observations with SOHO

HUBER, MARTIN C. E.; VON DER LUEHE, OSKAR

(Solar corona and solar wind; Proceedings of Symposium 9 of the 28th COSPAR Plenary Meeting, The Hague, Netherlands, June 25-July 6, 1990. A91-29501 11-92) Advances in Space Research (ISSN 0273-1177), vol. 11, no. 1, 1991, p. 339-348.

The Solar and Heliospheric Observatory (SOHO) is described along with its main purpose - the measurement of the physical properties of coronal structures and the processes occurring in them. The observatory will be launched in 1995 and injected into a halo orbit around the first Lagrange point L1 on the earth-sun line. Attention is focused on experiments performing in the soft X-ray and ultraviolet domains, as well as coronagraphs allowing corona observations on and beyond the solar disk. Experiments related to the energy and composition of the solar wind and more energetic solar particles are outlined. A complementary four-spacecraft Cluster mission targeting plasma structures and processes in the magnetosphere in three dimensions is also described.


1991-01:    Model Dependence of Velocities Derived from Coronal Resonance Lines

Ruth Esser

Intensity measurements of coronal resonance lines can be used to determine the outflow velocities of the scattering particles, provided the distribution of the densities, temperatures and velocities along the line of sight is known. A parameter study is designed and carried out to investigate the effect of surrounding denser regions with different temperatures and velocities, on the velocity deduced from intensity measurements of the H I Lyman alpha line in low density coronal holes. Adv. Space Res., 11, 317, 1991.


1990

1990-01:    Broadening of the Resonantly Scattered H I Lyman Alpha Line Caused by Alfven Waves

Ruth Esser

J. Geophys. Res., 95, 10 261, 1990.

Alfven waves propagating outward from the coronal base set the solar wind into oscillatory motion. The effect of this wave motion on the broadening and shape of the spectral lines of the resonantly scattered Ly-alpha radiation emitted by a low-density coronal hole is investigated at heights above 1.5 R_s from Sun center. Usually it has been assumed that the broadening due to waves can be characterized by a kinetic temperature proportional to the wave velocity amplitude squared, delta v{^2}. It is shown that the accuracy of this approximation depends on the wave velocity amplitude and the assumed wave spectrum.


1989

1989-02:    Line-of-Sight Effects on Spectroscopic Measurements in the Inner Solar Wind Region.

Ruth Esser and George L. Withbroe

J. Geophys. Res., 94, 6886, 1989.

The effect of the integration along the line of sight on the spectral line profiles of the resonantly scattered Lyman alpha radiation emitted by low-density coronal holes at heights above 1.5 R_s from Sun center is investigated. It is shown how the spectral lines from this region are influenced by the Lyman alpha emission from surrounding regions with higher densities. The coronal hole and the surrounding areas are described by a two-fluid solar wind model. It is shown that the line-of-sight effects can be important for the interpretation of the Lyman alpha spectral line measurements in the outer corona and inner solar wind.


1989-01:    UVCS: An Ultraviolet Coronagraph Spectrometer for SOHO

KOHL, J. L.; HARTMANN, L. W.; VANBALLEGOOIJEN, A. A.; WITHBROE, G. L.; RAYMOND, J. C.; WEISER, H.; NOCI, G.; ANTONUCCI, E.; GEISS, J.; GLOECKLER, G.

 ESA, SP-1104, 49-54 (SEE N90-13302 04-92)

 The UltraViolet Coronagraph Spectrometer (UVCS) of SOHO (solar and heliospheric observatory) provides ultraviolet spectroscopic observations of the solar corona out to ten solar radii from sun-center. This capability is expected to greatly expand the number of plasma parameters that can be specified by remote sensing techniques. Plasma diagnostic techniques are expected to provide a sufficient number of empirically derived parameters to significantly constrain theories of solar wind acceleration, coronal heating, and solar wind composition. The spectral line profiles and intensities are sensitive to random velocity distributions and to the effective temperatures of protons, minor ions, and electrons. Ion densities, chemical abundances, and outflow velocities of coronal protons and ions into the solar wind are also taken into consideration.