Analyzing the Energetics of Explosive Events Observed by SUMER on SOHO

Abstract

The SUMER spectrometer on SOHO has obtained numerous observations of optically thin chromosphere-corona transition-region line profiles with high spatial, spectral, and temporal resolution. Many of these profiles exhibit asymmetries and broadenings associated with impulsive mass motions (explosive events) in the solar atmosphere. We present here a new method of analyzing non-Gaussian line profiles to calculate the distribution of fluid velocities and hence the associated energy flux. We illustrate this method through a preliminary analysis of explosive event line profiles observed by SUMER. We derive the magnitudes of the energy fluxes directed both toward and away from the observer, and their (``net flux'') differences. We also identify and quantify the various components of each (i.e., kinetic, thermal and nonthermal enthalpy, and the high-energy component associated with the skewed tail of the distribution). The global energy contribution of explosive events to the solar atmosphere is then estimated under two different ``grouping'' assumptions. This preliminary analysis reveals an average net upward energy flux over the entire Sun of 10⁴-10⁵ ergs cm^-2 s^-1, up to an order of magnitude larger than previous estimates based on characteristic velocities of the fluid. Furthermore, the global estimate for the separate upward- and downward-directed energy fluxes is 10⁵-10⁶ ergs cm^-2 s^-1, which is comparable to the energy flux required for heating of the quiet corona and indicates that explosive events may indeed have significant implications for the energy balance of the chromosphere and corona.