Can coupled models perform better in the simulation of sub-seasonal evolution of the western North Pacific subtropical high than atmospheric models in boreal summer?

This study examines the climatological sub-seasonal evolution of the western North Pacific subtropical high (WNPSH) in boreal summer using observation and multiple state-of-the-art climate models, which has not been focused by previous research. The two sub-seasonal shifts in boreal summer are analyzed, one from June to July (J-J) and another from July to August (J-A). In observation, the WNPSH consistently retreats eastward and jumps northward (weakens) from June to August. Driven by observed sea surface temperature (SST), the multi-models ensemble (MME) of atmospheric general circulation models (AGCMs) that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) can reproduce the weakening of WNPSH from June to July, but fail to simulate the weakening from July to August. This may be due to the sub-seasonal variation of local SST increasing from June to July but decreasing from July to August. Compared with AGCMs simulation, CMIP5 coupled models MME largely improve the sub-seasonal variation of the WNPSH and associated precipitation change. Thus, it is argued that coupled models should be adopted in studies of the WNPSH on sub-seasonal timescales.