Tropical Cyclone Climatology in a High-resolution AGCM -Impacts of SST Warming and CO2 Increase-

Abstract

Using a high-horizontal-resolution atmospheric general circulation model (AGCM), impacts of SST warming and CO2 increase on the tropical cyclone (TC) climatology are investigated. The SST effect is examined from numerical experiments in which SST is uniformly higher/lower by 2 K, without changing the atmospheric CO2 concentration. The CO2 effect is shown from doubled and quadrupled CO2 experiments with a fixed SST condition. The results demonstrate that the increases in CO2 have large impacts to reduce TC frequency globally, while the SST changes have relatively small influences on the TC frequency. The SST warming causes significant increase in climatological precipitation, and this indicates intensification of convective heating and should have some influences to activate the atmospheric circulation in terms of vertical mass flux in the tropics. In the high-SST experiment, however, larger warming in the upper troposphere causes higher dry static stability, which should have some impacts to weaken the atmospheric circulation. It seems that these two conflicting factors, in terms of TC frequency, may cancel out to a large extent. As the effect of CO2 enhancement, precipitation decreases significantly in the tropics, which may lead to the reduction in TC frequency.