SOHOObservations of a Coronal Mass Ejection

Abstract

We describe a coronal mass ejection (CME) observed on 1999 April 23 by the Ultraviolet Coronagraph Spectrometer (UVCS), the Extreme-Ultraviolet Imaging Telescope (EIT), and the Large-Angle and Spectrometric Coronagraphs (LASCO) aboard the Solar and Heliospheric Observatory (SOHO). In addition to the O VI and C III lines typical of UVCS spectra of CMEs, this 480 km s~1 CME exhibits the forbidden and intercombination lines of O V at jj1213.8 and 1218.4. The relative intensities of the O V lines represent an accurate electron density diagnostic not generally available at 3.5By combining R _ . the density with the column density derived from LASCO, we obtain the emission measure of the ejected gas. With the help of models of the temperature and time-dependent ionization state of the expanding gas, we determine a range of heating rates required to account for the UV emission lines. The total thermal energy deposited as the gas travels to 3.5 is comparable to the kinetic and gravitational R _ potential energies. We note a core of colder material radiating in C III, surrounded by hotter material radiating in the O V and O VI lines. This concentration of the coolest material into small regions may be a common feature of CMEs. This event thus represents a unique opportunity to describe the morphology of a CME, and to characterize its plasma parameters.

Low-Frequency Observations of Drifting, Non-Thermal Continuum Radio Emission Associated With the Solar Coronal Mass Ejections

“…This explains second harmonic plasma emission for the moving type IV bursts, which requires an electron density of ≈2 × 10 7 cm −3 at 80 MHz. Such values close to the Sun have been reported in the literature from CME observations (Sheridan et al 1978;Stewart & McLean 1982;Gary et al 1985;Gopalswamy & Kundu 1992;Akmal et al 2001;Ciaravella et al 2001;Kathiravan et al 2002;Ramesh et al 2003a expanding arch category mentioned in Section 1) associated with the "legs" of the CME are likely due to plasma emission (Wild 1969;Smerd & Dulk 1971). (3) Calibration of the GLOSS dynamic spectrum of the moving type IV bursts reported in the present work using the galactic background emission as described in Dulk et al (2001) indicates that the spectral indices of the bursts in the frequency range 85-35 MHz are α o ≈ −3.4, −2.5, and −2.7, respectively, for the events observed on 2012 January 16, 23, and 26.…”

UVCS Observations of a Helical CME Structure

“…In the 12 September observations, the Si XII λ1041.26 and Mg X λ1219.7 lines are not present which implies that the temperature of the plasma is significantly less than 10 6 K. The density of this cold plasma (e.g., plasma emitting at C III λ977; Akmal et al 2001) was calculated using a commonly used estimate of the emission measure: where I λ is the intensity of the spectral line, P λ is the radiative loss for a given line, h is distance along the line-of-sight, and n e and n H are the electron and hydrogen densities. The radiative losses for the lines used in determining the emission measure are obtained from an updated version of Raymond & Smith (1977) code.…”

Comparison of SOHO UVCS and MLSO MK4 coronameter densities

“…Methods of determining the coronal electron density with different observations have been investigated by quite a few authors (van de Hulst 1950;Newkirk 1961;Noci et al 1987;Akmal et al 2001). Radio observation and extreme ultraviolet spectroscopy are powerful complementary diagnostic tools with which we can obtain such important information as coronal electron density and temperature of solar coronal plasma (Mancuso et al 2003).…”