Structure and evolution of the April 27, 1981 post-flare loop

Abstract

A time series of H α filtergrams and two-dimensional H α spectral data of the well-known post-flare loop system of April 27, 1981 are obtained at the Yunnan Observatory. The two-dimensional spectral data are analyzed quantitatively by means of the `multi-cloud model' method. The line-of-sight velocity fields of the post-flare loop system are derived for three different times. The post-flare loop system is composed of a loop and an ejection. The loop almost faces the observer and the ejection is along the line-of-sight. A `double-loop' model is proposed in order to explain the structure and evolution of the post-flare loop system. The distributions of the line-of-sight velocity and the evolution time of the post-flare loop system derived from a free-fall model are similar to those obtained from the observations.