Characteristics of Solar Flare Doppler Shift Oscillations Observed with the Bragg Crystal Spectrometer on Yohkoh

摘要

This paper reports the results of a survey of Doppler shift oscillationsmeasured during solar flares in emission lines of S XV and Ca XIX with theBragg Crystal Spectrometer (BCS) on Yohkoh. Data from 20 flares that showoscillatory behavior in the measured Doppler shifts have been fitted todetermine the properties of the oscillations. Results from both BCS channelsshow average oscillation periods of 5.5 +/- 2.7 minutes, decay times of 5.0+/-2.5 minutes, amplitudes of 17.1 +/- 17.0 km/s, and inferred displacements of1070 +/- 1710 km, where the listed errors are the standard deviations of thesample means. For some of the flares, intensity fluctuations are also observed.These lag the Doppler shift oscillations by 1/4 period, strongly suggestingthat the oscillations are standing slow mode waves. The relationship betweenthe oscillation period and the decay time is consistent with conductive dampingof the oscillations.