TRANSIENT BRIGHTENINGS OF INTERCONNECTING LOOPS - MORPHOLOGY OF THE SUDDEN BRIGHTENINGS

We study sudden brightenings of coronal loops that interconnect active regions. Such brightenings often occur within one or two days after the birth of a new interconnecting loop, as well as in some old interconnections. The brightenings of young loops are obviously associated with the emergence of new magnetic flux near their footpoints, whereas some enhancements of old loops may be triggered by slowly moving disturbances propagating from other centers of activity. A few loop brightenings are associated with flares, but the loop does not brighten in consequence of energy supply from the flare. Both the flare and the loop brightening are independent consequences of one common agent, presumably newly emerging flux. Temperatures in brightened loops are between 3 and 4 × 106 K and densities are < 2 × 109 cm-3, probably < 5 × 108 cm-3 in some old loops. The top part of a loop is the site of the most intense brightening in the initial phase of a loop enhancement. The most frequent lifetime of these brightenings is 6 to 7 hr. © 1979 D. Reidel Publishing Co.