Static and Impulsive Models of Solar Active Regions

Abstract

The physicalmodeling of active regions (ARs) and of the global corona is receiving increasing interest lately. Recent attempts to modelARs using static equilibrium modelswere quite successful in reproducingAR images of hot soft X-ray (SXR) loops. They however failed to predict the bright extreme-ultraviolet (EUV)warmloops permeatingARs: the synthetic images were dominated by intense footpoint emission.We demonstrate that this failure is due to the very weak dependence of loop temperature on loop length which cannot simultaneously account for both hot and warm loops in the sameAR.We then consider time-dependentARmodels based on nanoflare heating.We demonstrate that such models can simultaneously reproduce EUVand SXR loops in ARs. Moreover, they predict radial intensity variations consistent with the localized core and extended emissions in SXR andEUVARobservations, respectively. We finally showhowtheARmorphologycan be used as a gauge of the properties (duration, energy, spatial dependence, and repetition time) of the impulsive heating.