SEASONAL AND HEIGHT VARIATIONS OF OROGRAP HICALLY INDUCED MESOSCALE FLUCTUATIONS IN THE MIDDLE ATMOSPHERE

Direct and indirect observations that reveal mesoscale orographic dist urbances in the middle atmosphere are discussed. Variations in the wav e energy density with season and height for latitudes of about 40 degr ees N are analyzed. The relation between the wave energy density and h eight is extrapolated roughly up to the mesopause heights. The orograp hic contribution to the monthly mean wave energy per unit mass in the upper mesosphere and near the mesopause is shown to be no greater than 50 J/kg even over high mountains. The wave field at these heights is a collection of short packets of gravity waves that penetrate from the lower atmospheric layers under favorable conditions. The wave energy density of wave packets may be several times larger than the monthly m ean wave energy density.