The Northern Wintertime Divergence Extrema at 200 hPa and MSLP Cyclones as Simulated in the AMIP Integration by the ECMWF General Circulation Model

Abstract

Divergence and convergence centers at 200 hPa and mean sea level pressure (MSLP) cyclones are located every 6 hours for a 10-year GCM simulation for the boreal winters from 1980 to 1988. The simulation used the observed monthly mean SST for the decade. Analysis of the frequency, locations, and strengths of these centers and cyclones give insight into the dynamical response of the model to the varying SST. It is found that 1) the model produces reasonable climatologies of upper-level divergence and MSLP cyclones. 2) The model distribution of anomalies of divergence/convergence centers and MSLP cyclones is consistent with available observations for the 1982?83 and 1986?87 El Niño events. 3) The tropical Indian Ocean is the region of greatest divergence activity and interannual variability in the model. 4) The variability of the divergence centers is greater than that of the convergence centers. 5) Strong divergence centers are chiefly oceanic events in the midlatitudes but are more land based in the tropics, except in the Indian Ocean. 6) Locations of divergence/convergence centers can he a useful tool for the intercomparison of global atmospheric simulations.