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SOHO/EIT Observations of the 1997 April 7 Coronal Transient: Possible Evidence of Coronal Moreton Waves
Michels, D. J.; Thompson, B. J.; Gurman, J. B. +7 more
We report observations obtained with the Extreme ultraviolet Imaging Telescope (EIT) on board SOHO of a large-scale coronal transient propagating across the disk of the Sun at a speed of 250 km s-1, in apparent association with a flare and coronal mass ejection. The observations consist of a series of images taken in the Fe XII 195 Å ba…
An Empirical Model of a Polar Coronal Hole at Solar Minimum
Romoli, M.; Raymond, J. C.; Naletto, G. +28 more
We present a comprehensive and self-consistent empirical model for several plasma parameters in the extended solar corona above a polar coronal hole. The model is derived from observations with the SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) during the period between 1996 November and 1997 April. We compare observations of H I Lyα and O …
On the Doppler Shifts of Solar Ultraviolet Emission Lines
Peter, H.; Judge, P. G.
We examine emission-line profiles observed with the Solar Ultraviolet Measurement of Emitted Radiation (SUMER) instrument during the roll of the SOHO spacecraft on 1997 March 20. SUMER data were acquired in selected wavelength bands including lines from the low chromosphere to the corona. Our main aim is to determine the center-to-limb behavior of…
Spectroscopic Constraints on Models of Ion Cyclotron Resonance Heating in the Polar Solar Corona and High-Speed Solar Wind
Kohl, John L.; Cranmer, Steven R.; Field, George B.
Using empirical ion velocity distributions derived from Ultraviolet Coronagraph Spectrometer (UVCS) and Solar Ultraviolet Measurements of Emitted Radiation (SUMER) ultraviolet spectroscopy, we construct theoretical models of the nonequilibrium plasma state of the polar solar corona. The primary energy deposition mechanism we investigate is the dis…
Three-dimensional Stereoscopic Analysis of Solar Active Region Loops. I. SOHO/EIT Observations at Temperatures of (1.0-1.5) × 106 K
Klimchuk, J. A.; Aschwanden, Markus J.; Gary, G. Allen +5 more
The three-dimensional structure of solar active region NOAA 7986 observed on 1996 August 30 with the Extreme-Ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO) is analyzed. We develop a new method of dynamic stereoscopy to reconstruct the three-dimensional geometry of dynamically changing loops, which allows…
Slow Magnetosonic Waves in Coronal Plumes
Nakariakov, V. M.; DeForest, C. E.; Ofman, L.
Recent observations of polar plumes in the southern solar coronal hole by the Extreme-Ultraviolet Imaging Telescope (EIT) on board the SOHO spacecraft show signatures of quasi-periodic compressional waves with periods of 10-15 minutes. The relative wave amplitude was found to increase with height in the plumes up to about 1.2 Rsolar. Us…
On the Origin of Impulsive Electron Events Observed at 1 AU
Krucker, Säm; Thompson, Barbara J.; Lin, Robert P. +1 more
A statistical survey of 12 impulsive electron events detected at energies down below 1 keV and 58 events detected above 25 keV observed at 1 AU by the 3-D Plasma and Energetic Particles experiment on the Wind spacecraft is presented. Timing analysis of the velocity dispersion reveals two different kinds of electron events: (1) events released from…
LASCO and EIT Observations of Helical Structure in Coronal Mass Ejections
Michels, D. J.; Howard, R. A.; Dere, K. P. +2 more
Observations of coronal mass ejections (CMEs) by the Large Angle Spectrometric Coronagraph (LASCO) on the Solar and Heliospheric Observatory (SOHO) show a significant fraction with circular intensity patterns. In the past, these would have been called ``disconnection'' events, but we suggest that these are evidence of CMEs containing helical magne…
Helioseismic Constraints on the Structure of the Solar Tachocline
Thompson, M. J.; Christensen-Dalsgaard, J.; Schou, J. +4 more
This paper presents a series of helioseismic inversions aimed at determining with the highest possible confidence and accuracy the structure of the rotational shear layer (the tachocline) located beneath the base of the solar convective envelope. We are particularly interested in identifying features of the inversions that are robust properties of…
Plasma Properties in Coronal Holes Derived from Measurements of Minor Ion Spectral Lines and Polarized White Light Intensity
Fineschi, Silvano; Kohl, John L.; Raymond, John C. +5 more
Recent observations of the Lyα λ1216, Mg X λ625, and O VI λ1038 spectral lines carried out with the Ultraviolet Coronagraph Spectrometer (UVCS) on board SOHO at distances in the range 1.35-2.1 RS in the northern coronal hole are used to place limits on the turbulent wave motions of the background plasma and the thermal motions of the pr…