The effect of wind on the propagation rate of acoustic-gravity waves

Abstract

A method is described for deriving acoustic-gravity wave velocity in the presence of wind shear. It is used to calculate numerical weighting factors for a few special cases of two and three layer model atmospheres. These show that the wind velocity in a cold layer between two warm layers has a predominant positive influence on group velocity, and the wind at higher levels a negative influence, while phase velocity is quite differently affected.

The theory is illustrated by world-wide data relating to the Russian megaton explosion of 30 October 1961, and a study of global winds at the time. It was found possible to account for world-wide variations in wave propagation rate largely by a simple regression on the sine of the explosion longitude, which made possible estimates of effective wind over various ray path lengths. This was found, on the global scale, to be the mean of the wind in the 9–16 km layer, that is, approximately the mean wind in the “sound channel”. Negative weightings at higher levels predicted by the model appear to be incorrect, and due to its inadequacy. The data strongly suggest that the “level of effective mean wind” is approximately that of the tropopause in middle latitudes.