Aspects of convective activity and extreme events in a transient climate change simulation

Some aspects of the characteristic changes of convective activity in a warmer climate (following IPCC scenario IS92a), as simulated with the ECHAM4/OPYC GCM are analysed. Data of total rain, convective rain, convective height, frequency of convective events and mass fluxes are investigated for, both, the boreal summer (JJA) and the boreal winter (DJF) season. In either case the mean global convective rain rate and the frequency of deep convective events decrease from the 1981-90 decade to the 2071-80 decade (representative Of 1 X CO2 and 2 X CO2 forcing), but the frequency of strong convective rain events, shallow convective events and the total rain rate increase. Thus, although the surface temperature is increased in the 2071-80 decade and more latent heat is available, deep convective events are reduced most pronounced on the southern hemisphere. These changes in convective activity are related to a change in the tropical circulation accounting for the effect of an interhemispheric asymmetry in surface warming in the 2 x CO2 climate similar to that reported by MURPHY and MITCHELL (1995).