Does regional air–sea coupling improve the simulation of the summer monsoon over the western North Pacific in the WRF4 model?

ABSTRACTA new regional coupled ocean–atmosphere model, WRF4-LICOM, was used to investigate the impacts of regional air–sea coupling on the simulation of the western North Pacific summer monsoon (WNPSM), with a focus on the normal WNPSM year 2005. Compared to WRF4, WRF4-LICOM improved the simulation of the summer mean monsoon rainfall, circulations, sea surface net heat fluxes, and propagations of the daily rainband over the WNP. The major differences between the models were found over the northern South China Sea and east of the Philippines. The warmer SST reduced the gross moist stability of the atmosphere and increased the upward latent heat flux, and then drove local ascending anomalies, which led to the increase of rainfall in WRF4-LICOM. The resultant enhanced atmospheric heating drove a low-level anomalous cyclone to its northwest, which reduced the simulated circulation biases in the stand-alone WRF4 model. The local observed daily SST over the WNP was a response to the overlying summer monsoon. In the WRF4 model, the modeled atmosphere exhibited passive response to the underlying daily SST anomalies. With the inclusion of regional air–sea coupling, the simulated daily SST–rainfall relationship was significantly improved. WRF4-LICOM is recommended for future dynamical downscaling of simulations and projections over this region.