Chromospheric Evaporation and Warm Rain during a Solar Flare Observed in High Time Resolution with the Coronal Diagnostic Spectrometer aboard the Solar and Heliospheric Observatory

Abstract

We present EUV light curves, Doppler shifts, and line-broadening measurements for a flaring solar active region obtained with the Coronal Diagnostic Spectrometer (CDS) aboard the NASA ESA Solar and Heliospheric Observatory (SOHO) under conditions of (1) comprehensive temporal coverage (including the quiescent preflare, impulsive, and gradual decline phases), (2) high time resolution (9.83 s), and (3) narrow field of view (4^''×20^''). The four strong lines of O III at 599.587 Å, O V at 629.732 Å, Mg X at 624.937 Å, and Fe XIX at 592.225 Å are analyzed and provide diagnostics of plasma dynamics for 4.9<=logT<=6.9. Wavelengths and widths measured during the preflare and late decline phases provide standards against which Doppler shifts and excess line broadening are measured during the impulsive and early decline phases. The entire profile of all four lines is blueshifted early during the impulsive rise of the flare, but only the O III, O V, and Mg X lines subsequently exhibit multiple components and downflows. These downflows provide evidence of ``warm rain'' due to cooling coronal flare plasma following chromospheric evaporation during the impulsive phase. O III and O V exhibit a pronounced precursor brightening during which the Fe XIX emission emerges above the noise; this, combined with the fact that the O III and O V intensities begin their impulsive rise earlier than do those of Mg X and Fe XIX, is consistent with the transport of coronal flare energy to the chromosphere by nonthermal particle beams.