Tropical Cyclogenesis Bias over the Central North Pacific in CMIP6 Simulations

Current coupled climate models contain large biases in simulating tropical cyclogenesis, reducing the confi-dence in tropical cyclone (TC) projection. In this study, we investigated the influence of sea surface temperature (SST) biases on TC genesis in the Coupled Model Intercomparison Project phase 6 simulations from 1979 to 2014. Positive TC genesis biases were found over the tropical central North Pacific (CNP) in most of climate models, including the high-resolution mod-els. Compared to coupled models, TC genesis density (TCGD) simulations over CNP in uncoupled models forced by observa-tional SST improved obviously. A warm SST bias over the tropical CNP in the coupled models is the main cause of TC genesis biases. The SST bias-induced diabatic heating leads to an anomalous Gill-type atmospheric circulation response, which con-tributes to a series of favorable environmental conditions for TC formation over the CNP. Numerical experiments were also performed with HiRAM to demonstrate the influence of SST biases on the TCGD simulation, further confirming our conclu-sion. The current results highlight the importance of improving TC simulation in state-of-the-art climate models by reducing SST simulation bias.