Relationship between Cold and Hot Post--Solar Flare Loops and the Impact on the Reconnection Flare Model

Abstract

The relationship between cold and hot postflare loops has been studied using the 1973 September 7 and 1974 January 15 flare images recorded by the Skylab S082 spectroheliograph. The images are of intense emission lines in the extreme ultraviolet region that span the 1 × 10<SUP>4</SUP> (He I) to 3.2 × 10<SUP>6</SUP> K (Ni XVIII) temperature range. The analysis of the images does not support the widely held notion that cold loops are always smaller than hot loops, lie below hot loops, and are similar in shape. It is found that the coldest and hottest loops often differ significantly in size and shape. Based on the analysis of a time sequence of Skylab images of cold and hot loops, there is no evidence that the loop system expands in a discontinuous manner, as would be the case if higher loops were sequentially formed and activated by reconnection of the magnetic field. It is found that the individual coronal loops expand in a gradual manner. These conclusions are consistent with images of postflare loop systems in the 10<SUP>7</SUP> K range that were recorded by the soft X-ray telescope on the Yohkoh spacecraft. Previous observations and interpretations of postflare loop systems, which led to the formulation of the reconnection flare model, are reexamined. In light of recent high-quality imagery that spans the temperature range from 10<SUP>4</SUP> to 10<SUP>7</SUP> K, it is concluded that the observations do not support all aspects of the reconnection flare model as presently articulated. Elements of the reconnection flare model that are inconsistent with the modern observations should be reconsidered.