The influence of the global warming on tropical cyclones has been examined using a high resolution AGCM. Two ten-year integrations were performed with the JMA global model at T106 horizontal resolution. For the control experiment, the observed SST for the period 1979-1988 is prescribed, while for the doubling CO2 (2 × CO2) experiment, SST anomaly due to the global warming estimated from a coupled model transient CO2 experiment (Tokioka et al. 1995) is added to the SST used in the control experiment. The results of experiments show that a significant reduction in the frequency of tropical cyclones is possible in response to the greenhouse gas-induced global warming. The most significant decrease is indicated over the North Pacific. On the other hand, a considerable increase in tropical cyclone frequency is indicated for the North Atlantic. As for the maximum intensity of tropical cyclones, no significant change has been noted.
It has been found that the regional change in tropical cyclone frequency is closely related to the distribution of the SST anomaly, and the change in convective activity associated with it. The results of the experiment indicate that the change in tropical cyclogenesis is strongly controlled by dynamical factors associated with the change in SST distribution, rather than the thermodynamical factors associated with the change in absolute value of local SST. On the other hand, for the decrease in the global total number of tropical cyclones on doubling CO2, a weakening of tropical circulation associated with the stabilization of the atmosphere (the increase in dry static stability), seems to be responsible. It is found that the rate of increase in the tropical precipitation due to the global warming is much less than the rate of increase in the atmospheric moisture. With this little increase in precipitation (convective heating), a considerable increase in the dry static stability of the atmosphere leads to a weakening of the tropical circulation.
2002 by Meteorological Society of Japan