Abstract:

The presence of zonal and meridional winds can provide critical layers for upwardly propagating waves whenever the components of the horizontal wind velocity along the direction of wave propagation becomes equal to the horizontal phase velocity. If the background wind is stable (as they are in most cases) the gravity waves would encounter a critical layer and are absorbed into the mean flow with no further significant upward propagation.

OH observations carried out in Colorado in May, June and July of 1988 have revealed gravity waves propagating with preferred directions which are consistent with the forbidden regions (blocking diagrams) computed from background wind profiles of NASA modified by tidal-wave calculations of Forbes and Vial for May, June and July at the Colorado site.

Reference:

Effects of Wind Filtering on OH Airglow Observations of Gravity Wave Propagation. M.J. Taylor, E.H. Ryan, T.F. Tuan, 1991 Fall Meeting, Eos, Transactions, AGU, 72 (44), October 29, 1991, (SA51A-07).