UARS MLS GW Variances in January

This diagram shows MLS zonal mean GW variances in January (1992-1994) in comparison with CIRA zonal wind climatology [Fleming, et al., 1990]. (Only GW variances on ascending orbits are used). Similar to the stratospheric/mesospheric jets, which are tilted southward with height, the GW variances also exhibit such tiltness. When the GW variance is reduced at a higher altitude, it often indicates that some wave components have been removed from the wave package. These removed waves are likely to deposite momumentum fluxes in the background winds causing the deceleration in the mean flow. At latitudes of~60N, mountain waves and jetstream-induced GWs, along with planetary waves, are the major forcings to decelerate the polar stratospheric vortex. At latitudes of ~25S, convection-induced GWs are the primary sources to slowdown the subtropical westward wind near 60km. The lowest GW variances are observed around the zero wind lines. Compared to the GW variance in July, the January variances are weaker by a factor of 2 according to UARS MLS observations.