Role of the SST anomaly structures in response of cyclogenesis to global warming

Abstract

Projections of future changes in tropical cyclone genesis are still subject to debate since no consensus has been reached, yet, among the General Circulation Models which participated in the last IPCC Assessment Report (AR4). Making the hypothesis that the main reason for such a dispersion in the responses come from the diversity of sea surface temperature anomaly structures obtained in the coupled atmosphere/ocean systems, an ensemble of experiments has been conducted with the CNRM/Météo-France ARPEGE/Climate model, forced with climatological sea surface temperatures (SST) issued from 15 of the 22 coupled models of the AR4. In this chapter, responses in the original AR4 simulations and ARPEGE experiments were compared for two indices representing global cyclogenesis of tropical cyclones: the Convective Yearly Genesis Parameter and the Genesis Potential Index. CYGP responses in the ARPEGE experiment present a dispersion similar to the one from original AR4 scenarios, suggesting that the SST anomaly structures play a significant role in these responses. Additional experiments, using year-to-year varying SST, suggested that the interannual variability of SST cannot explain the dispersion. Additionally, looking at the mean ensemble response for original AR4 and ARPEGE SST forced simulations, tropical Indian Ocean and parts of the West Pacific, North of 20°N, appear to deliver a consistent response, which ARPEGE is able to reproduce and even to enhance. This implies that use of a single model in sensitivity experiments may be an interesting approach in suppressing all dependencies on the models characteristics and configurations.