Heating the solar corona by plasma loops

Mathematical Institute, University of Oxford, 24–29 St Giles', Oxford OX1 3LB, UK e-mail: ashbourn@maths.ox.ac.uk;leslie.woods@balliol.oxford.ac.uk

Received: 23 October 2005
Accepted: 23 May 2006

Abstract

We investigate the heating of the corona via plasma loops. It is shown that it may be possible to maintain the high corona temperatures using plasma loops as conduits. Under certain conditions heat can flow across magnetic fields up temperature gradients, a mechanism that has been previously applied to the heating of plasma loops. A typical conduit loop is hotter than the ambient plasma in the upper chromosphere and transition layer, and is cooler than the ambient plasma in the background corona. Hence, heat enters the loop at the bottom, is transported by a combination of conduction (if there is a negative temperature gradient), convection and shock waves up the loop into the corona. Typical values show that this type of heating is sufficient to maintain both the quiet and active corona and that it also has the non-homogeneous temperature distribution observed in the lower corona. The behaviour of some brightening events seen in TRACE data support the proposed convective and shock wave mechanisms. The model offers a possible explanation of a long-standing problem, namely why the corona is so hot.