Response of Tropical Cyclogenesis to Global Warming in an Ipcc Ar4 Scenario

Jean-Francois Royer and Fabrice Chauvin

Abstract Since currently very few models can reach the high resolutions necessary for a detailed representation of tropical cyclones, most assessments of their response to climate change in coupled scenarios have to be based on indirect estimates of the hurricane activity potential. A modified Convective Yearly Genesis Potential index (CYGP) proposed by Royer et al. (1998) is applied here to the analysis of TC genesis in 15 coupled general circulation models (CGCMs) that have run simulations for the IPCC AR4 for the 20th century and for scenario A2. For the current climate most of the models simulate rather realistic patterns of cyclogene-sis, though the TC genesis in the different ocean basins differs from model to model. The cyclogenesis index shows interdecadal fluctuations and long term trends. In scenario A2 the patterns of response of cyclogenesis at the end of the 21st century differ according to the ocean basins and models. While in some ocean basins like the Indian Ocean, the majority of models compute an increasing trend in TC genesis, the response is less coherent in other basins where some models give a decreasing trend. The lack of coherence of the TC genesis response to future climate change can be associated to the different response patterns of sea surface temperatures (SST) in the coupled models, particularly over the Equatorial Pacific, and to their differences in the simulation of ENSO. Until some better convergence of the model SST response has been achieved, it seems rather premature to draw conclusions about possible future changes in TC genesis.

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