Evaluation of the boreal summer intraseasonal oscillation modulation on western North Pacific tropical cyclone genesis in CMIP6 HighResMIP models

This study evaluates the simulated modulation of western North Pacific (WNP) tropical cyclone (TC) genesis by the boreal summer intraseasonal oscillation (BSISO) in five high-resolution models from the Coupled Model Intercomparison Project phase 6 (CMIP6) High Resolution Model Intercomparison Project (HighResMIP). By comparing reanalysis data with historical simulations from these five HighResMIP models during 1979-2014, we find that these models can realistically capture observed BSISO features including northward propagation, propagation speed and life cycle. These models can also simulate the modulation of WNP TC genesis by the BSISO in observations. Similar to observations, there is a significant difference in simulated TC genesis frequency between active and inactive BSISO phases, which in most models can be largely explained by changes in large-scale environmental factors and synoptic-scale wave trains. Compared with observations, however, there is a poleward shift of intraseasonal variability of TC genesis in all model simulations. This shift is likely due to a northward shift of the simulated WNP monsoon trough and an associated northward shift of simulated BSISO activity, as well as changes in synoptic-scale eddy kinetic energy in these models. This study documents the ability of HighResMIP models to reproduce the BSISO and its modulation on TCs, and also highlights the importance of the large-scale monsoon circulation in TC genesis.