Profiles of heating in turbulent coronal magnetic loops

¹ Space and Atmospheric Physics Department, The Blackett Laboratory, Imperial College, London SW7 2BW, UK e-mail: e.buchlin@imperial.ac.uk
² Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Largo E. Fermi 2, 50125 Firenze, Italy
³ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA

Received: 16 January 2007
Accepted: 21 March 2007

Abstract

Context.The location of coronal heating in magnetic loops has been the subject of a long-lasting controversy: does it occur mostly at the loop footpoints, at the top, is it random, or is the average profile uniform?

Aims.We try to address this question in model loops with MHD turbulence and a profile of density and/or magnetic field along the loop.

Methods. We use the Shell-Atm MHD turbulent heating model described in Buchlin & Velli (2007, ApJ, 662, 701), with a static mass density stratification obtained by the HydRad model (Bradshaw & Mason 2003, A&A, 401, 699). This assumes the absence of any flow or heat conduction subsequent to the dynamic heating.

Results. The average profile of heating is quasi-uniform, unless there is an expansion of the flux tube (non-uniform axial magnetic field) or the variation of the kinetic and magnetic diffusion coefficients with temperature is taken into account: in the first case the heating is enhanced at footpoints, whereas in the second case it is enhanced where the dominant diffusion coefficient is enhanced.

Conclusions. These simulations shed light on the consequences on heating profiles of the complex interactions between physical effects involved in a non-uniform turbulent coronal loop.