Intercomparison of Numerical Models of Flaring Coronal Loops

Abstract

The past decade of solar observations from space, which has seen the extension of high spatial resolution and temporal cadence into the XUV spectral regime, has demonstrated convincingly that the corona is pervaded at all times by loop-shaped features that appear to be closely aligned with ambient magnetic field lines. This structuring is most strikingly evident in solar active regions. Together with photospheric magnetograms, the orientations of these loop structures allow the magnetic topology of much of the corona to be mapped out in detail. Whereas some fraction of the coronal volume may be permeated by open field lines or may even be virtually field-free, the plasma contained therein is of a lower density than that contained in the loops and is thereby more difficult to diagnose. Consequently, most interpretative studies have concentrated on the development and application of loop models to active region phenomena. Especially important to devise, but nonetheless difficult, are quantitative models for describing temporal changes of the plasma resulting from, for example, fluctuations of loop energy input. The extreme case is that which occurs during a solar flare, when the energy supply of a given magnetic loop may vary by many orders of magnitude on a time scale of a few seconds or less.