Solar magnetoatmospheric waves. I. An exact solution for a horizontal magnetic field.
Abstract
The linearized theory of magnetoatmospheric waves (involving the combined restoring forces due to buoyancy, compressibility, and magnetic field) is developed for the case of a horizontal magnetic field. A general propagation equation is derived for adiabatic perturbations with arbitrary vertical distributions of the sound speed c, Alfve'n velocity VA, and local density scale height H. An exact analytical solution to the propagation equation is obtained for the case of an isothermal atmosphere permeated by a uniform horizontal magnetic field, without making the usual short wavelength assumption. This solution is applied to an idealized model of the lowcorona chromosphere transition region for comparison with observations of flareinduced coronal waves. The results show that disturbances may propagate horizontally in the low corona in a wave guide formed by the sudden density increase into the chromosphere below and by the rapidly increasing AlfVe'n velocity with height in the corona. The group velocity of the guided wave modes is nearly independent of wavelength, so that a disturbance propagates as a compact wave packet. Subject headings: hydromagnetics Sun: atmospheric motions  Sun: corona  Sun: magnetic fields
 Publication:

The Astrophysical Journal
 Pub Date:
 March 1976
 DOI:
 10.1086/154205
 Bibcode:
 1976ApJ...204..573N
 Keywords:

 Chromosphere;
 Magnetic Field Configurations;
 Magnetohydrodynamic Waves;
 Solar Atmosphere;
 Solar Magnetic Field;
 Adiabatic Conditions;
 Astronomical Models;
 Boundary Value Problems;
 Phase Velocity;
 Solar Corona;
 Vertical Distribution;
 Wave Packets;
 Wave Propagation;
 Solar Physics