Acoustic waves in a stratified atmosphere

III. Temperature inhomogeneities

¹ Osservatorio Astronomico di Torino, Strada dell'Osservatorio 20, 10025 Pino Torinese, Italy e-mail: rossi@to.astro.it
² Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA e-mail: wolf@cfa.harvard.edu
³ Dipartimento di Fisica Generale dell'Università, Via Pietro Giuria 1, 10125 Torino, Italy e-mail: massaglia@ph.unito.it

Corresponding author: G. Bodo, bodo@to.astro.it

Received: 3 December 1999
Accepted: 15 February 2001

Abstract

In a gravitationally stratified atmosphere, small temperature variations distort the paths of acoustic waves from the rectilinear paths in an isothermal atmosphere. For temperature increasing upward, low-frequency waves near the acoustic cutoff frequency propagating at a given polar angle are refracted towards the vertical direction (focused) and high-frequency waves, away from the vertical (defocused). Similarly, for temperature increasing towards the axis of a vertical cylinder, low-frequency waves are focused and high-frequency waves are defocused. This effect of temperature inhomogeneities may be important for wave propagation in the chromospheric K_2v bright point phenomenon.