Evolving Active Region Loops Observed with the Transition Region and Coronal explorer. II. Time-dependent Hydrodynamic Simulations

摘要

Observations with the Transition Region and Coronal Explorer (TRACE) have revealed a new class of active region loops. These loops have relatively flat filter ratios, suggesting approximately constant temperatures near 1 MK along much of the loop length. The observed apex intensities are also higher than static, uniformly heated loop models predict. These loops appear to persist for much longer than a characteristic cooling time. Recent analysis has indicated that these loops first appear in the hotter Fe XV 284 ? or Fe XII 195 ? filters before they appear in the Fe IX/Fe X 171 ? filter. The delay between the appearance of the loops in the different filters suggests that the loops are impulsively heated and are cooling when they are imaged with TRACE. In this paper we present time-dependent hydrodynamic modeling of an evolving active region loop observed with TRACE. We find that by modeling the loop as a set of small-scale, impulsively heated filaments we can generally reproduce the spatial and temporal properties of the observed loop. These results suggest that both dynamics and filamentation are crucial to understanding the observed properties of active region loops observed with TRACE.