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The stratospheric gravity wave field in the Southern Hemisphere is investigated by analyzing observations collected by 27 long-duration balloons that flew between September 2005 and February 2006 over Antarctica and the Southern Ocean. The analysis is based on the methods introduced by Boccara et al. in a companion paper. Special attention is given to deriving information useful to gravity wave drag parameterizations employed in atmospheric general circulation models. The balloon dataset is used to map the geographic variability of gravity wave momentum fluxes in the lower stratosphere. This flux distribution is found to be very heterogeneous with the largest time-averaged value (28 mPa) observed above the Antarctic Peninsula. This value exceeds by a factor of ϳ10 the overall mean momentum flux measured during the balloon campaign. Zonal momentum fluxes were predominantly westward, whereas meridional momentum fluxes were equally northward and southward. A local enhancement of southward flux is nevertheless observed above Adélie Land and is attributed to waves generated by katabatic winds, for which the signature is otherwise rather small in the balloon observations. When zonal averages are performed, oceanic momentum fluxes are found to be of similar magnitude to continental values (2.5-3 mPa), stressing the importance of nonorographic gravity waves over oceans. Last, gravity wave intermittency is investigated. Mountain waves appear to be significantly more sporadic than waves observed above the ocean.

Short-time variability of the atmospheric tides is frequently observed in the meteor region but is not yet fully explained in terms of production mechanisms. This is probably due to the existence of several such mechanisms acting together or separately. In this paper we show that many observations can be explained by nonlinear interactions between tides and planetary waves having periods corresponding to those of the observed tidal amplitude modulations. These nonlinear interactions generate two secondary waves whose frequencies are the sum and difference of frequencies of the primary waves. These two waves beat with the tide, modulating its amplitude with the planetary wave period. A numerical model is used to demonstrate that with primary waves of reasonable amplitudes the nonlinear interactions can be quite large. This is because the importance of nonlinearity depends essentially on the amplitude of the induced fluid velocity in the direction of wave propagation compared to the wave propagation velocity. When two waves propagate simultaneously, the fluid velocity can have a large component in the direction of propagation of one of the waves, and advective (nonlinear) terms can be large. This point is further illustrated in the case of two gravity waves interacting together. Finally, some observational campaigns carried out above Garchy (45øN) are analyzed using a nonparametric method. The results indicate that nonlinear interactions between tides and planetary waves really take place in the upper mesosphere and lower thermosphere.1.