Growing electric field parallel to magnetic field due to transverse kinetic drift waves in inhomogeneous corona

Abstract

The transverse drift wave, which is unstable due to purely kinetic effects, and driven by the density and magnetic field gradients, is discussed in context of its application to the solar corona. The gradients of the two quantities are opposite to each other, as required by the equilibrium pressure balance, and they are in the plane perpendicular to the magnetic field vector. The transverse drift wave has such properties that it propagates strictly perpendicularly to both the magnetic field vector and the mentioned gradients. It is electromagnetic, with the perturbed electric field in the direction of the equilibrium magnetic field, while the perturbed magnetic field vector is in the direction of the equilibrium gradients. Such an orientation of the electric field implies a possibility of acceleration of coronal plasma particles along the background magnetic field, in both directions, outward and inward. In the case of locally open magnetic structures, the outwardly moving particles should contribute to the solar wind. Those moving inwards eventually arrive in the lower solar atmosphere where the mean free path is short and, due to collisions, they should disperse their energy to the surrounding plasma and contribute to heating. It is also shown that accelerated particles can additionally be stochastically heated by the wave. This completely new stochastic heating mechanism is found here for the first time. It takes place provided that the particles are simultaneously accelerated by the wave to large enough velocities in the parallel direction. The model is applicable to any inhomogeneous coronal environment, like magnetic loops, coronal holes and the so-called EIT waves, named after the Extreme-ultraviolet Imaging Telescope (EIT) used for their first detection.