University of Chicago Press for the American Astronomical Society
Astrophysical Journal vol:719 pages:1335-1342
The solar atmosphere is structured and inhomogeneous, both horizontally and vertically. The omnipresence of coronal magnetic loops implies gradients of the equilibrium plasma quantities such as the density, magnetic field, and temperature. These gradients are responsible for the excitation of drift waves that grow both within the twocomponent fluid description (both in the presence of collisions and without it) and within the two-component
kinetic descriptions (due to purely kinetic effects). In this work, the effects of the density gradient in the direction perpendicular to the magnetic field vector are investigated within the kinetic theory, in both electrostatic (ES) and electromagnetic (EM) regimes. The EM regime implies the coupling of the gradient-driven drift wave with the Alfv´en wave. The growth rates for the two cases are calculated and compared. It is found that, in general, the ES regime is characterized by stronger growth rates, as compared with the EM perturbations. Also discussed is the stochastic heating associated with the drift wave. The released amount of energy density due to this heating should be more dependent on the magnitude of the background magnetic field than on the coupling of the drift and Alfv´en waves. The stochastic heating is expected to be much higher in regions with a stronger magnetic field.
On the whole, the energy release rate caused by the stochastic heating can be several orders of magnitude above
the value presently accepted as necessary for a sustainable coronal heating. The vertical stratification and the very
long wavelengths along the magnetic loops imply that a drift-Alfv´en wave, propagating as a twisted structure along
the loop, in fact occupies regions with different plasma-β and, therefore, may have different (EM–ES) properties,
resulting in different heating rates within just one or two wavelengths.