About the relative importance of compressional heating and current dissipation for the formation of coronal X-ray bright points
Max-Planck-Institut für Sonnensystemforschung, 37191 Katlenburg-Lindau, Germany
2 Geophysical Institute, University of Alaska, Fairbanks, AK 99775, USA
Received: 19 August 2010
Accepted: 5 February 2011
Context. The solar corona is heated to high temperatures of the order of 106 K. The coronal energy budget and specifically possible mechanisms of coronal heating (wave, DC-electric fields, etc.) are poorly understood. This is particularly true for the formation of X-ray bright points (BPs) is concerned.
Aims. We aim to investigate the energy budget, particularly the relative role and contribution of adiabatic compression versus current dissipation to the formation of coronal BPs.
Methods. Our three-dimensional resistive MHD simulation starts with the extrapolation of the observed magnetic field from SOHO/MDI magnetograms, which are associated with a BP observed on 19 December 2006 by Hinode. The initial radially non-uniform plasma density and temperature distribution agrees with an equilibrium model of the chromosphere and corona. The plasma motion is included in the model as a source of energy for coronal heating.
Results. Our investigation of the energy conversion owing to Lorentz force, pressure gradient force, and Ohmic current dissipation for this bright point shows the minor effect of Joule heating compared with the work done by pressure gradient force in increasing the thermal energy by adiabatic compression. Especially at the time when the temperature enhancement above the bright point starts to form, compressional effects are quite dominant over the direct Joule heating.
Conclusions. Choosing non-realistic high resistivity in compressible MHD models for a simulation of solar corona can lead to unphysical consequences for the energy balance analysis, especially when local thermal energy enhancements are being considered.
Key words: Sun: atmosphere / Sun: magnetic topology / magnetohydrodynamics (MHD) / methods: numerical / Sun: corona
© ESO, 2011