Middle Atmosphere Gravity Wave Drag Climatology in the Southern Hemisphere

PULIDO M; THUBURN J

Foz Iguazu (Brazil)

Conferencia; VIII International Conference on Southern Hemisphere Meteorology and Oceanography (AMS); 2006

American Meteorological Society

An estimate of the gravity wave drag (GWD) in the middle atmosphere of the Southern Hemisphere for 2000-2002 is examined. The technique to estimate gravity wave drag is based on variational assimilation principles. It uses an adjoint model of a middle atmosphere dynamical model to minimize a cost function that measures the differences between  model states and observations. The control variables are the horizontal components of GWD. Met Office analyses are used as observations and initial conditions. GWD seasonal cycle presents a deceleration center during winter time centered at 65S with a peak of -60 m/s/day, this is located at higher latitudes than the polar jet (~55-60S). In summer there is also a deceleration center but much weaker (~15 m/s/day). During 2002 and before the unprecedented sudden stratospheric warming takes place, the estimated GWD deceleration center presents a weaker forcing and is located at higher altitudes than previous years. The explanation of this behavior may be ascribed to wave filtering mechanism since a weaker polar jet together with high planetary wave activity are present at that time.