SST effect on the pre-monsoon intraseasonal oscillation over the South China Sea based on atmospheric-coupled GCM comparison

The role of sea surface temperature (SST) variability in the pre-monsoonal (April to July) intraseasonal oscillation (ISO) over the South China Sea (SCS) is investigated using the Community Earth System Model Version 2 (CESM2). An Atmospheric Model Intercomparison Project (AMIP) simulation forced by daily sea surface temperatures (SSTs) derived from a parallel coupled general circulation model (CGCM) run was compared with observations and the mother coupled simulation. In the coupled model, the SST warming leads the peak convection about 1/4 period as in observations. The paralell uncoupled model fails to simulate this phase relationship, implying the importance of air-sea coupling in reproducing realistic ISO. Due to the near-quadrature phase relationship between SST and precipitation ISOs during the ISO events, it is difficult to distinguish the active/passive role of SST from observations alone. Significant correlation in intraseasonal precipitation between the daily SST-forced AMIP and mother CGCM runs indicates that SST plays a role in driving the atmospheric ISO.