Tropopause to mesopause gravity waves in August: Measurement and modeling

Global gravity wave (GW) distributions are retrieved from infrared emission limb soundings taken by the CRISTA instrument in August 1997 and by the SABER instrument in August 2003. The investigated altitudes cover the whole middle atmosphere from the tropopause to the mesopause. The data agree semi-quantitatively in their salient features and only small deviations due to the different meteorological conditions in the two years are observed. Of particular interest is the decrease of GW activity at the top of the southern polar vortex and an accompanying shift of GW activity towards the subtropics in the mesosphere. We emulate this feature by two conceptionally different models, the Warner and McIntyre spectral parameterization scheme and the GROGRAT GW ray tracer. Both models indicate that saturation limits and GW breaking are the governing processes in creating this structure. Also, both models can well reproduce the global distributions except for two important points: (1) convectively generated GWs in the northern subtropics are largely underestimated; (2) northern hemisphere high latitude activity is grossly overestimated. These points indicate that GW distribution in general circulation models are not fully realistic. Refined measurements are required to constrain more realistic GW source distributions.