Background wind effect on propagation of nonmigrating diurnal tides in the middle atmosphere

Abstract

The propagation characteristics of the nonmigrating diurnal tides are investigated numerically using a 2-dimensional (latitude-height) steady state model for a realistic atmosphere characterized by background mean zonal winds, meridional temperature gradients, mechanical and thermal dissipation, and tropospheric forcing obtained from a General Circulation Model. The mechanical and thermal dissipation is parameterized through eddy viscosity and conductivity, respectively, in addition to the molecular viscosity and conductivity.

It is found that the westward (eastward) propagating diurnal nonmigrating tides possess significant amplitudes compared to those of the migrating tide at upper mesospheric and lower thermospheric heights in the hemisphere where the westerlies (easterlies) are dominant. Hence, it is shown that the Doppler effect due to the presence of background mean zonal winds makes it possible for the diurnal nonmigrating tides of higher zonal wave numbers (both westward and eastward) to propagate up into the middle to high latitude regions of both hemispheres.