Arindam Chakraborty Centre for Atmospheric and Oceanic Sciences and Divecha Centre for Climate Change Indian Institute of Science Bangalore – 560012, India.
Abstract
It had long been thought that ocean –atmosphere coupling is not necessary for short-to-medium range prediction of atmospheric parameters such as precipitation. Today, most of the numerical prediction centers around the world do use atmosphere-only models for forecast up to about 10 days. Using a global general circulation model (GCM), it had been shown that ocean plays a major role in prediction of summer monsoon precipitation over south Asia even 3 to 5 days in advance. In absence of air-sea coupling and prescribed fixed surface temperature boundary condition over the oceans (SST), initial (1-3 days) error in precipitation forecast over south Asian monsoon region is higher over land as compared to that over ocean (Chakraborty 2010). However, the rate of growth of error over ocean is larger as compared to that over land. In this study, a detailed analysis is performed to access the effect of different types of SST forcing and air-sea coupling in prediction of south Asian summer monsoon 1 to 10 days in advance. It was seen that the rate of growth of error over ocean, when the atmospheric GCM is coupled with a slab-ocean model, is less compared to using prescribed fixed or time-varying SST boundary condition. This study underlines the necessity of two-way ocean-atmosphere interaction for short-to-medium range weather prediction.
Reference: Chakraborty, A., 2010: The Skill of ECMWF Medium Range Forecasts During the Year of Tropical Convection 2008, Monthly Weather Review, 138, 3787-3805.
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