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

Abstract

Using a high-horizontal-resolution atmospheric general circulationmodel (AGCM), impacts of SST warming and CO2 increase on the tropicalcyclone (TC) climatology are investigated. The SST effect is examinedfrom numerical experiments in which SST is uniformly higher/lowerby 2 K, without changing the atmospheric CO2 concentration. The CO2effect is shown from doubled and quadrupled CO2 experiments witha fixed SST condition. The results demonstrate that the increasesin CO2 have large impacts to reduce TC frequency globally, whilethe 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 shouldhave some influences to activate the atmospheric circulation in termsof vertical mass flux in the tropics. In the high-SST experiment,however, larger warming in the upper troposphere causes higher drystatic stability, which should have some impacts to weaken the atmosphericcirculation. It seems that these two conflicting factors, in termsof TC frequency, may cancel out to a large extent.As the effect of CO2 enhancement, precipitation decreases significantlyin the tropics, which may lead to the reduction in TC frequency.