H. Y. Alkahby & F. N. Jalbout
Abstract:
In this paper we investigate numerically the effect of
viscosity and Newtonian cooling on upward and downward propagating
magneto-acoustic waves, resulting from a uniform horizontal magnetic
field in an isothermal atmosphere. The results of the numerical
computations are compared with those of asymptotic evaluations. It is
shown that the presence of a small viscosity creates a layer which
acts like an absorbing and reflecting barrier for waves
generated below it and that the presence of the magnetic field
produces a reflecting layer only. The addition of Newtonian cooling
affects mainly the lower region in which it produces waves attenuation
and alters the wavelength. If the Newtonian cooling coefficient is
large compared with the frequency of the waves, the temperature in the
lower region evens out and the wave motion approaches an
isothermal one. This eliminates the attenuation in the wave amplitude
since the isothermal region is dissipationless. This problem is solved
analytically and numerically. The results of the numerical computation
are in a complete agreement with the analytical results.
Published December 9, 1999.
Subject lassfications: 76N10, 76Q35.
Key words: magneto-acoustic waves, Newtonian cooling coefficient,
wave propagation, reflection coefficient.
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Fouad N. Jalbout
Division of the Natural Sciences
Dillard University
New Orleans,LA 70122 USA