Simulation of the western North Pacific summer monsoon by regional ocean-atmosphere coupled model: impacts of oceanic components

A successful simulation of the western North Pacific summer monsoon needs a regional ocean-atmosphere coupled model (ROAM). How the performance of ROAM relies on the oceanic component model remains unknown. In this study, the authors investigated the effects of different oceanic components on the simulation of western North Pacific (WNP) summer monsoon in a ROAM. Three cases of simulations were performed, viz. the summer of 1998 (El Nio decaying phase), 2004 (El Nio developing phase), and 1993 (the non-ENSO phase). Results show that the coupled simulations for different ENSO phases exhibit improvements in the simulation of location of Meiyu rainband and spatial distribution of monsoon low-level flow over WNP, whereas the systemic cold biases of sea surface air temperature are further increased. The coupled simulations with different oceanic components show similar performance, which is not ENSO phase dependent. For the case of the summer of 1998, a slightly stronger western Pacific subtropical high and colder sea surface air temperature are found in the simulation with colder sea surface temperature (SST) biases. The colder SST biases are partly contributed by the ocean dynamics processes because the sea surface net flux favors a warmer SST. This study suggests that the dependence of performance of ROAM over WNP on oceanic models is much weaker than that on atmospheric models.