Relationship Between Cold And Hot Post-Flare Loops And The Impact On The Reconnection Flare Model
The relationship between cold and hot post-flare loops was studied using the 7 September 1973 and 15 January 1974 flare images recorded by the Skylab S082 spectroheliograph. The images were of intense emission lines in the extreme ultraviolet region that spanned the 1 x 104 K (He I) to 3.2 x 106 K (Ni XVIII) temperature range. The images of the 15 January 1974 flare at 1240 UT are shown in the Figure. The detailed 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 was 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 loop systems expand in a discontinuous manner, as would be the case if higher loops were sequentially formed and activated by reconnection of the magnetic field. It was found that the individual coronal loops expand in a gradual manner. These conclusions are consistent with images of post-flare loop systems in the 107 K range that were recorded by the soft x-ray telescope on the Yohkoh spacecraft. Previous observations and interpretations of post-flare loop systems, which led to the formulation of the reconnection flare model, were re-examined. In light of the recent high-quality imagery that spans the temperature range from 104 to 107 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. A detailed description of this study of Skylab and Yohkoh post-flare loops has been accepted for publication in the Astrophysical Journal.