Hydrodynamic Modeling of Active Region Loops

Abstract

Recent observations with the Transition Region and Coronal Explorer (TRACE) have shown that many apparently cool (MK) active region loops are much brighter and have flatter temperature profiles than T ∼ 1-1.5 e static loop models predict. Observations also indicate that these loops can persist much longer than a characteristic cooling time. Using time-dependent hydrodynamic simulations, we explore the possibility that these active region loops are actually a collection of small-scale filaments that have been impulsively heated and are cooling through the TRACE 171 A ˚ (Fe ix/x) and 195 A ˚ (Fe xii) bandpasses. We find that an ensemble of independently heated filaments can be significantly brighter than a static uniformly heated loop and would have a flat filter ratio temperature when observed with TRACE.