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EIT and LASCO Observations of the Initiation of a Coronal Mass Ejection
Llebaria, A.; St. Cyr, O. C.; Michels, D. J. +31 more
We present the first observations of the initiation of a coronal mass ejection (CME) seen on the disk of the Sun. Observations with the EIT experiment on SOHO show that the CME began in a small volume and was initially associated with slow motions of prominence material and a small brightening at one end of the prominence. Shortly afterward, the p…
Polar Plume Anatomy: Results of a Coordinated Observation
Plunkett, S. P.; Thompson, B. J.; Gurman, J. B. +5 more
On 7 and 8 March 1996, the SOHO spacecraft and several other space- and ground-based observatories cooperated in the most comprehensive observation to date of solar polar plumes. Based on simultaneous data from five instruments, we describe the morphology of the plumes observed over the south pole of the Sun during the SOHO observing campaign. Ind…
Time-Distance Helioseismology with the MDI Instrument: Initial Results
Kosovichev, A. G.; Hoeksema, J. T.; Scherrer, P. H. +10 more
In time-distance helioseismology, the travel time of acoustic waves is measured between various points on the solar surface. To some approximation, the waves can be considered to follow ray paths that depend only on a mean solar model, with the curvature of the ray paths being caused by the increasing sound speed with depth below the surface. The …
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…