High spatial and temporal resolution observations of the solar CA II H line

Abstract

A 24 minute time series of photographic Ca II H line spectra made with high spatial and spectral resolution has been analyzed to provide data on the range of line profile variations in the quiet sun. Distribution functions of the line-core intensity and the ratio of emission peak intensities are exhibited and are used to classify the associated line profiles. It is shown that the range of profile variation is significantly larger than that covered by the models A-F of Vernazza, Avrett, and Loeser, especially in relation to the darkest profiles in which no core emission can be detected. Time-resolved spectra are used to show that the 3-minute chromospheric oscillation involves upward-propagating excitation which leads to intense heating in the cell points. It is conjectured that these observations provide a direct picture of the processes responsible for a significant part of the nonradiative heating of the quiet chromosphere.