Energetics and 3D Structure of Elementary Events in Solar Coronal Heating.

Parker first proposed (1972) that coronal heating was the necessary outcome of an energy flux caused by the tangling of coronal magnetic field lines by photospheric flows. In this paper we discuss how this model has been modified by subsequent numerical simulations outlining in particular the substantial differences between the "nanoflares" introduced by Parker and "elementary events," defined here as small-scale spatially and temporally isolated heating events resulting from the continuous formation and dissipation of field-aligned current sheets within a coronal loop. We present numerical simulations of the compressible 3D MHD equations using the HYPERION code. We use two clustering algorithms to investigate the properties of the simulated elementary events: an IDL implementation of a density-based spatial clustering of applications with noise technique, and our own physical distance clustering algorithm. We identify and track elementary heating events in time, both in temperature and in Joule heating space. For every event we characterize properties such as density, temperature, volume, aspect ratio, length, thickness, duration, and energy. The energies of the events are in the range of 10¹⁸–10²¹ erg, with durations shorter than 100 s. A few events last up to 200 s and release energies up to 10²³ erg. While high temperatures are typically located at the flux tube apex, the currents extend all the way to the footpoints. Hence, a single elementary event cannot at present be detected. The observed emission is due to the superposition of many elementary events distributed randomly in space and time within the loop. [ABSTRACT FROM AUTHOR]