Measurements of the horizontal scales and phase velocities of short period mesospheric gravity waves at Adelaide, Australia

Abstract

Sixteen days of MF Doppler radar measurements of the zonal scales of short period (≤ 1 h) internal atmospheric gravity waves propagating in the upper mesosphere and lower thermosphere, made in five 2-5 day periods, in each season, for the years 1981 and 1982 are presented. For one period of observation the zonal and meridional scales are presented. The horizontal scale for these observations increases from values of about 20 km at periods less than 20 min to values of about 40 km at periods of 36 and 60 min. In the 16 days of measurement a total of 414 events consistent with a gravity wave interpretation were determined and for these the zonal scale was found to increase from values of about 30 km at 10 min to about 80 km at 100 min. For an isotropic wavefield this suggests horizontal scales of about 20 and 55 km, respectively. Momentum fluxes of up to 3 m2s-2 were found to be associated with waves with periods of less than 1 h, but more typical values at periods of around 30 min were found to be 1 m2s-2. The flux convergence associated with individual short period gravity wave events appears easily able to provide substantial (~ 50 ms-1day-1) mean flow accelerations. © 1987.