Plasma Heating During a Coronal Mass Ejection Observed by SOHO

TL;DR

This study analyzes plasma heating during a 2000 CME using SOHO UVCS data, revealing that plasma heating can be comparable to or exceed kinetic energy, with implications for understanding CME energy sources.

Contribution

It provides the first detailed time-dependent ionization analysis of plasma heating during a CME, constraining heating mechanisms and energy contributions using UVCS observations.

Findings

Plasma heating during the CME was comparable to or greater than kinetic energy.

Wave heating by photospheric motions could significantly contribute to plasma heating.

Turbulence must be continually replenished and dissipated rapidly during CME evolution.

Abstract

We perform a time-dependent ionization analysis to constrain plasma heating requirements during a fast partial halo coronal mass ejection (CME) observed on 2000 June 28 by the Ultraviolet Coronagraph Spectrometer (UVCS) aboard the Solar and Heliospheric Observatory (SOHO). We use two methods to derive densities from the UVCS measurements, including a density sensitive O V line ratio at 1213.85 and 1218.35 Angstroms, and radiative pumping of the O VI 1032,1038 doublet by chromospheric emission lines. The most strongly constrained feature shows cumulative plasma heating comparable to or greater than the kinetic energy, while features observed earlier during the event show cumulative plasma heating of order or less than the kinetic energy. SOHO Michelson Doppler Imager (MDI) observations are used to estimate the active region magnetic energy. We consider candidate plasma heating mechanisms and provide constraints when possible. Because this CME was associated with a relatively weak flare, the contribution by flare energy (e.g., through thermal conduction or energetic particles) is probably small; however, the flare may have been partially behind the limb. Wave heating by photospheric motions requires heating rates significantly larger than those previously inferred for coronal holes, but the eruption itself could drive waves which heat the plasma. Heating by small-scale reconnection in the flux rope or by the CME current sheet is not significantly constrained. UVCS line widths suggest that turbulence must be replenished continually and dissipated on time scales shorter than the propagation time in order to be an intermediate step in CME heating.