UARS MLS GW Variances in July

This diagram shows MLS zonal mean GW variances in July (1992-1994) in comparison with CIRA zonal wind climatology [Fleming, et al., 1990]. (only GW variances measured on ascending orbits are used to generate this plot). Below ~60km, the wave activities at ~25N and ~60S appear very strong and seem to make significant impacts on the zonal winds at 60-80km. When these waves reduce their amplitude at higher altitudes, it often indicates that wave saturation/breaking occur. These saturated/breaking waves may interact with the background winds causing the deceleration in the mean flow. The wave sources at latitudes of~60S are likely the combination of mountain waves from South Andes, Drake Passage, and the Antarctic rim. At latitudes of ~25N, the GW sources are primarily from subtropical deep convection. The lowest GW variances are observed around the zero wind lines. Compared to the GW variance in January, the July variances are stronger by a factor of ~2 in the upper stratosphere and lower mesosphere.