Effects of Air-Sea Interaction on the East-Asian Monsoon Simulation : A Regional Climate Study

It is well known that the sea surface temperature (hereafter, referred to as SST) is a critical component which influences the exchange of energy between the atmosphere and ocean. Since SST influences atmosphere as well as is controlled by atmospheric conditions, accurate SST data from observation or predicted by model plays a crucial role in weather forecast and research. However, the spatial and temporal resolution of SST data is too poor to reflect accurate condition of ocean. Thus, representation of phenomena which occurs in air-sea interface has a limitation to reflect air-sea interaction in weather forecasts and climate simulation. It is expected that simulations from RCMs produce better results than GCMs when the air-sea interaction is considered since RCMs represent more realistic condition. However, although simulations can produce more realistic results when air-sea interactions are considered in RCMs, receiving the initial condition due to long-term simulation is difficult and processes related to data assimilation between observed value and the model are complicated. For example, full RCMs ignore observed SST data and consider the SST constant value because RCMs deal with short range forecast. The purpose of this study is to investigate the effects of air-sea interaction on the simulated EAM by using the RCM. The monsoonal system is a kind of air-sea interaction because there are exchanges of heat and moisture between land and ocean. Since East Asia is affected by the Northern Pacific ocean, the inclusion of air-sea interaction in forecast model will also contribute to improving the forecast skill over East Asia. Wang et al. (2005) indicated that the coupled ocean-atmosphere processes are crucial in the monsoon regions where atmospheric feedback on SST is critical. This study focuses on the impact of air-sea interaction by using three methods which represent what happen at air-sea interface. A model used in this study is the WRF model. The methods which represent the air-sea interaction in this study include 1) the ocean mixed layer model based on Pollard et al. (1973), 2) the prognostic sea surface skin temperature scheme based on Zeng and Beljaars (2005), and 3) the roughness length formula based on Donelan et al. (2004). 2. Methodology used in this study