Boyle94c Boyle, J. S., 1994c: The northern wintertime divergence extrema at 200 hPa and surface cyclones as simulated in the AMIP Integration by the ECMWF General Circulation Model. PCMDI Report 20, Program for Climate Model Diagnosis and Intercomparison, Lawrence Livermore National Laboratory, 30 pp.

Divergence and convergence centers at 200 hPa and mean sea level pressure (MSLP) cyclones were located every 6 hours for a 10-year general circulation model (GCM) simulation with the ECMWF (Cycle 36) for the boreal winters from 1980 to 1988. The simulation used the observed monthly mean sea surface temperature (SST) for the decade. Analysis of the frequency, location, and strengths of these centers and cyclones give insight into the dynamical response of the model to the varying SST.

The results indicate that 1) the model produced reasonable climatologies of upper-level divergence and MSLP cyclones; 2) the model distribution of anomalies of divergence and convergence centers and MSLP cyclones is consistent with 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 occur chiefly over the ocean in the midlatitudes but are more land-based in the tropics, except in the Indian Ocean; and 6) locations of divergence and convergence centers can be a useful tool for the intercomparison of global atmospheric simulations.