Coronal heating by MHD waves

¹ Department of Mathematics, K.G.K.(P.G.) College, Moradabad 244001 (UP), India e-mail: nagendrakgk@rediffmail.com
² Department of Physics, Hindu College, Moradabad 244001 (UP), India

Received: 2 September 2005
Accepted: 26 January 2006

Abstract

Aims.We study the possible role of magnetohydrodynamic (MHD) waves in the heating of solar corona and magnetic coronal loops.

Methods.Taking into account viscosity and thermal conductivity, we obtained a general fifth order dispersion relation for MHD waves propagating in a homogeneous, magnetically structured, compressible low-β plasma. The general fifth order dispersion relation has been solved numerically, and we discuss its application to magnetic coronal loops with the help of data provided by the NIXT mission.

Results.The dispersion relation results in three modes, namely slow, fast, and thermal. The damping of both slow- and fast-mode waves depends upon the plasma density, the temperature, the magnetic field strength, and the angle of propagation relative to the background magnetic field. Slow-mode waves contribute to the heating of the solar corona, if one considers that they are generated in the corona by turbulent motions at magnetic reconnection sites. Calculations of wave damping rates determined from the dispersion relation indicate that slow-mode waves with periods of less than 60 s damp sufficiently rapidly and dissipate enough energy to balance the radiative losses, whereas the fast-mode waves with periods of less than 3 s may damp at rates great enough to balance the radiative losses in active regions. In the case of magnetic coronal loops, it is observed that slow-mode waves with frequencies greater than 0.003 Hz and fast mode waves with frequencies greater than 0.28 Hz (high frequency) are needed for coronal heating and to balance the radiative losses in active regions.