Search Publications
An Empirical Study of the Electron Temperature and Heavy Ion Velocities in the South Polar Coronal Hole
Gloeckler, George; Geiss, Johannes; Fisk, Lennard A. +2 more
The solar wind ions flowing outward through the solar corona generally have their ionic fractions `freeze-in' within 5 solar radii. The altitude where the freeze-in occurs depends on the competition between two time scales: the time over which the wind flows through a density scale height, and the time over which the ions achieve ionization equili…
EUV Blinkers: The Significance of Variations in the Extreme Ultraviolet Quiet Sun
Harrison, Richard A.
A search for microflare activity in the extreme ultraviolet (EUV) quiet Sun using the Coronal Diagnostic Spectrometer (CDS) aboard the Solar and Heliospheric Observatory (SOHO) spacecraft has not resulted in the identification of microflare activity, but has resulted in the identification of a hitherto unknown phenomenon: enhancements of a factor …
Doppler Shifts in the Quiet-Sun Transition Region and Corona Observed with SUMER on SOHO
Wilhelm, K.; Brekke, P.; Hassler, D. M.
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 tempera…
In-Flight Performance of the Virgo Solar Irradiance Instruments on SOHO
Dewitte, Steven; Chevalier, André; Fröhlich, Claus +7 more
The in-flight performance of the total and spectral irradiance instruments within VIRGO (Variability of solar IRradiance and Gravity Oscillations) on the ESA/NASA Mission SOHO (SOlar and Heliospheric Observatory) is in most aspects better than expected. The behaviour during the first year of operation of the two types of radiometers and the sunpho…
High-Velocity Flows in an Active Region Loop System Observed with the Coronal Diagnostic Spectrometer (Cds) on SOHO
Harrison, R. A.; Kjeldseth-Moe, O.; Brekke, P.
EUV spectra of coronal loops above an active region show clear evidence of strong dynamical activity. We present an example where the Ov 629 Å line, formed at 240 000 K, is shifted from its reference position corresponding to line-of-sight velocities greater than 50 km s-1 with the shift extending over a large fraction of a loop. The ob…
Performance and Early Results from the GOLF Instrument Flown on the SOHO Mission
Baudin, F.; Christensen-Dalsgaard, J.; García, R. A. +21 more
GOLF in-flight commissioning and calibration was carried out during the first four months, most of which represented the cruise phase of SOHO towards its final L1 orbit. The initial performance of GOLF is shown to be within the design specification, for the entire instrument as well as for the separate sub-systems. Malfunctioning of the polarising…
First View of the Extended Green-Line Emission Corona At Solar Activity Minimum Using the Lasco-C1 Coronagraph on SOHO
Llebaria, A.; St. Cyr, O. C.; Plunkett, S. P. +21 more
The newly developed C1 coronagraph as part of the Large-Angle Spectroscopic Coronagraph (LASCO) on board the SOHO spacecraft has been operating since January 29, 1996. We present observations obtained in the first three months of operation. The green-line emission corona can be made visible throughout the instrument's full field of view, i.e., fro…
Measurements of Frequencies of Solar Oscillations from the MDI Medium-l Program
Kosovichev, A. G.; Scherrer, P. H.; Schou, J. +2 more
Inversions of solar internal structure employ both the frequencies and the associated uncertainties of the solar oscillation modes as input parameters. In this paper we investigate how systematic errors in these input parameters may affect the resulting inferences of the sun's internal structure. Such systematic errors are likely to arise from ina…
High-Resolution Observations of the Extreme Ultraviolet Sun
Harrison, R. A.; Culhane, J. L.; Fludra, A. +9 more
This paper presents first results of the Coronal Diagnostic Spectrometer (CDS) recently launched aboard the Solar and Heliospheric Observatory (SOHO). CDS is a twin spectrometer, operating in the extreme ultraviolet range 151-785 Å. Thus, it can detect emission lines from trace elements in the corona and transition region which will be used to pro…
Application of Spectroscopic Diagnostics to Early Observations with the SOHO Coronal Diagnostic Spectrometer
Young, P. R.; Mason, H. E.; Harrison, R. A. +4 more
The Coronal Diagnostic Spectrometer (CDS) has as a scientific goal the determination of the physical parameters of the solar plasma using spectroscopic diagnostic techniques. Absolute intensities and intensity ratios of the EUV spectral emission lines can be used to obtain information on the electron density and temperature structure, element abun…