1973 September 7 two-ribbon flare. I - Morphology and loop expansion. II - Physical properties of the loops in the arcade

Abstract

XUV data are presented for a two-ribbon flare of H-alpha class 2B and X-ray class X1 which occurred on September 7, 1973. The morphology and loop expansion rates observed in coronal lines of Fe XIV and Ca XVII are compared with data from the chromospheric line H-alpha. The loop arcades at different temperatures and different loops in a given arcade show different expansion rates. Consideration is given to the relationship of the observed arcade loop system to various surface features. The loop aspect ratio and electron density are derived as a function of position along the loop for the coronal plasma. These values are used to derive the energy density and to discuss scaling laws relating loop length, temperature, and pressure. The observed radiative cooling times for individual loops are compared to times calculated from radiative conductive and enthalpy cooling times. Also, the observed energy density is compared with that calculated from a reconnection model. 34 refs.