The sensitivity of the Asian summer monsoon simulation to horizontal resolution and air‒sea coupling in the FGOALS-f climate system model

Abstract

The relative importance between horizontal resolution and air‒sea coupling on improving Asian summer monsoon (ASM) simulation skill remains unclear. In this study, we investigated the sensitivity of ASM to horizontal resolution and air‒sea coupling via simulations using a series of versions of the FGOALS-f model. The possible causes of bias are further analyzed. The results show that the Atmospheric Model Intercomparison Project (AMIP) run of high model resolution (25 km) achieves the highest skill on capturing ASM pattern, while the AMIP run of low model resolution (100 km) appears the lowest skill. Further analysis of the hydrological cycle and monsoon dynamics suggested that the simulation of the vertical moisture transport term was the primary contributor to excessive precipitation over the western Pacific. In addition, the excessive release of latent heat and strong ASM circulation are also responsible for the strong precipitation intensity in the AMIP simulation. Importantly, although the air‒sea coupled simulation exhibited the higher skill level, the simulated sea surface temperature (SST) exhibited an overall cold bias. This cold bias partly counteracted excessive moisture transport after air‒sea interaction is considered. Thus, increasing resolution could be helpful for more accurate simulation of advection, and together with the use of prescribed observed daily SST could play more important roles than only considering air‒sea coupling on improving ASM simulations.