Reduced TC Activity and Enhanced Anticyclone in the WNP in a Warmer World: Projection and Mechanism

GFDL high-resolution (25-km) AGCM HiRAM was used for AMIP-type time-slice simulations for the present (1979-2008) and the end of century (2074-2100). HiRAM well simulates mean climatology, Asian Monsoon seasonal evolution, and frontal activity. Strength of simulated extreme precipitation is compatible with TRMM precipitation. The ensemble-mean SST increase projected by CMIP5 CGCMs under RCP8.5 was superimposed on the present SST to force the end-of-century simulation. Tropical cyclone activity in the western North Pacific is projected to be significantly weakened at the end of the 21^st century. This result was reproduced by using MRI-AGCM of 20-km resolution and in the time-slice experiments forced by different projected SST patterns. This projected change is triggered by the contraction of convection toward the tropics and the corresponding anomalous subsidence poleward of the equatorial convection belt. Strongest response occurs in the western North Pacific and results in significantly weakened convection and westward extension of the subtropical anticyclone in the western North Pacific. Relative contribution of SST changes in various basins to the changes in the WNP is assessed. Hypothesis is proposed to explain why the response to the global warming in the western North Pacific is stronger than those in other regions.