Changes in Potential Intensity of Tropical Cyclones Approaching Japan due to Anthropogenic Warming in Sea Surface and Upper-Air Temperatures

抄録

The intensities of the tropical cyclones (TCs) that approach or make landfall in Japan and the possible changes in these intensities due to global warming have been investigated on the basis of the theoretical model of Holland (1997). This theoretical model calculates the maximum potential intensity (MPI) of a TC as a lower limit of central sea level pressure for a given upper-air temperature profile and underlying sea surface temperature (SST). This study uses the climatology of the JRA-25 long-term reanalysis for the present environment, along with global warming anomalies derived from CMIP3 multi model climate experiments, which are added to the reanalysis climatology to form a warmed environment. A characteristic of the tropical atmosphere is that warming anomalies are amplified toward the upper troposphere, so that TC intensification due to a rise in SST is suppressed to some extent by greater warming aloft. This study evaluates the uncertainty ranges for the MPI changes by considering inter model differences in the warming structure.
The MPI-SST relationship in the present climate is consistent with the historical minimum surface pressure in the western North Pacific when the eyewall relative humidity (RH), one of the model’s key parameters, is set at 88%. The average change in the MPI due to a 1°C rise in the SST is -6.7 hPa [-0.6 to -12.0 hPa], where a negative change indicates intensification and the estimated range in brackets reflects the uncertainty in the warming structure. The error of these MPI changes is estimated to be about 15%, assuming that the likely range of the RH parameter is 88 ± 2%. The fractional change in the surface pressure drop is 3.6%, 8.4%, and 19%, in response to a 0.5, 1.0, and 2.0C rise, respectively, in SST, which is basically comparable to existing studies based on observations and numerical simulations. While TC intensification due to global warming tends to be greater for intense TCs at low latitudes, the tendencies at relatively high latitudes near the main islands of Japan suggest that TC development occurs in a broader region over a more prolonged season in a warmed environment.