[A-CG32] Climate Variability and Predictability on Subseasonal to Centennial Timescales

[ACG32-P01] Anthropogenic forcing changes coastal tropical cyclone frequency

*Shuai Wang^1,2, Hiroyuki Murakami^2,3, William Cooke² (1.Princeton University, 2.NOAA-GFDL, 3.UCAR)

It remains a mystery if and how anthropogenic climate change has altered the global tropical cyclone (TC) activities, mainly due to short reliable TC observations and substantial climate internal variabilities. In this study we show with large-ensemble TC-permitting simulations that the observed changes in global coastal TC frequency since 1980 were caused by anthropogenic greenhouse gases (GHG) and/or aerosols. The observed increases in TC frequency near the US Atlantic coast and Hawaii are likely related to the aerosol and GHG effects, respectively. The observed decrease in the South China Sea could be associated with GHG emissions alone, whereas the observed increase near Japan and Korea would be related to the aerosol and GHG combined effects. These changes are explained by the responses of large-scale environmental conditions to anthropogenic forcing. We find that two kinds of anthropogenic warming are related. First, the anomalous lower-tropospheric warming at midlatitudes under the aerosol and/or GHG effect alters the subtropical jets over the North Atlantic, western North Pacific, and Northeast Asia. Second, the equatorial central Pacific warming under the GHG effect simulates a classical Matsuno-Gill-type circulation pattern in the northern tropical Pacific. These large-scale circulation changes modify the TC genesis and steering conditions, contributing to the observed increases in TC frequency in the global coastal regions as identified above. Our findings suggest the substantial influence of anthropogenic forcing on TC frequency over the heavily populated coastal regions worldwide.