Dynamical downscaling of East Asian winter monsoon changes with a regional ocean-atmosphere coupled model

This study investigated the impacts of regional air-sea coupling on the downscaling of historical and future winter climate changes under the Representative Concentration Pathway (RCP) 8.5 scenario over the Coordinated Regional Climate Downscaling Experiment (CORDEX) East Asia domain. Two sets of dynamical downscaling results were compared using a regional ocean-atmosphere coupled model (FROALS) and the corresponding atmosphere-only regional climate model (RegCM3) at a horizontal resolution of 50 km. Driven by the reanalysis data, the inclusion of the local air-sea coupling process has little impact on the simulation of surface climate over most land regions of East Asia. However, driven by the global climate model, the cold SST anomalies simulated by FROALS were much larger than those driven by the reanalysis data, which favoured a stronger and northward extended low-level anomalous anticyclone. The improved low-level winter monsoon flow partly reduced the dry biases (cold biases) over the Yangtze River valley (north China and Mongolia) in RegCM3. Under the RCP8.5 scenario, a weakened Aleutian Low and relatively weak increase of northeasterly over the southern coast of China were found in the FROALS simulation, which were consistent with those from the driving global climate system model. However, the atmosphere-only RCM exhibited extended regions with decreases in precipitation over east China, and a weaker surface warming over southern China. These projected changes in the atmosphere-only RCM were followed by the evidently enhanced northerly flow in east China, which was mainly caused by the exaggerated decrease in sea-level pressure over the western North Pacific as a result of strong responses to the local SST warming. Our results indicated that a regional air-sea coupled model could be a useful tool for the dynamical downscaling of present and future winter climate changes over East Asia.