Modelling nanoflares in active regions and implications for coronal heating mechanisms

P J Cargill; H P Warren; S J Bradshaw

doi:10.1098/rsta.2014.0260

Modelling nanoflares in active regions and implications for coronal heating mechanisms

Philos Trans A Math Phys Eng Sci. 2015 May 28;373(2042):20140260. doi: 10.1098/rsta.2014.0260.

Authors

P J Cargill¹, H P Warren², S J Bradshaw³

Affiliations

¹ Space and Atmospheric Physics, The Blackett Laboratory, Imperial College, London SW7 2BW, UK School of Mathematics and Statistics, University of St Andrews, St Andrews KY16 9SS, UK p.cargill@imperial.ac.uk.
² Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA.
³ Department of Physics and Astronomy, Rice University, Houston, TX 77005, USA.

Abstract

Recent observations from the Hinode and Solar Dynamics Observatory spacecraft have provided major advances in understanding the heating of solar active regions (ARs). For ARs comprising many magnetic strands or sub-loops heated by small, impulsive events (nanoflares), it is suggested that (i) the time between individual nanoflares in a magnetic strand is 500-2000 s, (ii) a weak 'hot' component (more than 10(6.6) K) is present, and (iii) nanoflare energies may be as low as a few 10(23) ergs. These imply small heating events in a stressed coronal magnetic field, where the time between individual nanoflares on a strand is of order the cooling time. Modelling suggests that the observed properties are incompatible with nanoflare models that require long energy build-up (over 10 s of thousands of seconds) and with steady heating.

Keywords: emission measure; magnetic reconnection; solar corona.