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Climatological statistics of stratospheric inertia-gravity waves deduced from historical rocketsonde wind and temperature data

Ten years of rocketsonde observations of wind and temperature in the 28-57 km height range at 12 stations (spanning 8oS to 76oN) were analyzed. The aim was to determine the geographical and seasonal variation of statistics relating to the propagation of inertia-gravity waves. As noted by earlier investigators, there is a clear tendency for the rocketsonde hodographs to display clockwise rotation with height in the extratropical northern hemisphere. This is consistent with the notion that the variations are dominated by inertia-gravity waves with upward energy propagation. By using the wind and temperature data simultaneously it was possible to determine a dominant direction of horizontal wave propagation for each profile. This quantity has an impressive seasonal variation in mid-latitudes, with strong eastward propagation apparent in summer and generally westward propagation in winter. This seasonal cycle is consistent with theoretical notions of how the mean flow ought to affect wave propagation. Two stations within 10 o of the equator are included in this analysis. The results at these near-equatorial stations contrast strongly with those at higher latitudes. There is a clear tendency for the hodographs at these stations to display quite linear polarization (rather than the systematic rotation generally seen at higher latitudes). The wind variations also show a remarkable tendency to align themselves in the zonal direction. When the wind and temperature variations are used together, it can be shown that the variations seen are consistent with a clear dominance of eastward propagation. Indirect observational inferences [e.g., Hartmann, 1976; Hamilton, 1983; Smith and Lyjak, 1985] and results from simple theoretical models [e.g., Lindzen, 1981; Holton, 1982] suggest that inertia-gravity (IG) waves of less than planetary scales play a significant role in the general circulation of the stratosphere. It is quite clear that in at least some comprehensive general circulation models (GCMs) the vertical momentum transports associated with resolved IG waves