On the reflection of linear 3D hydrodynamic waves in a plane atmosphere by an ionization step.
Abstract
We investigate the influence of a variable ionization rate on the propagation behavior of evanescent and acoustic waves in an isothermal atmosphere. For isothermal waves in a pure atomic hydrogen atmosphere the wave equation of the total pressure perturbation can be transformed into the hypergeometric equation, from which by a linear transformation formula of the hypergeometric function simple analytical expressions for the reflection of waves can be obtained. For vertical evanescent waves we compare the reflection caused by a continuous ionization step with that of a corresponding temperature step for which in the 1D case an analytical approach exists. The reflection is significantly different for the two cases, although the sound speed is equal in both atmospheres. We also consider the reflection by a discontinuous ionization step and compare it with the continuous model in order to study the usefulness of such an approximation. We also compare the reflection of waves by a discontinuous ionization step with the reflection by a discontinuous temperature step. We again find basic differences between the two reflection mechanisms which are due to the different behaviour of the first derivatives of the velocity and the pressure perturbation at the discontinuous step.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 February 1995
 Bibcode:
 1995A&A...294..206S
 Keywords:

 HYDRODYNAMICS;
 WAVES;
 SUN: ATMOSPHERE;
 STARS: ATMOSPHERES