Winter SST Variation Patterns in the Subtropical Western Pacific Associated with Indian Ocean Dipole and Their Influences on East Asian Winter Climate

Using NOAA (National Oceanic and Atmospheric Administration) observational SST (Sea Surface Temperature), GPCP (Global Precipitation Climatology Project) precipitation, and atmospheric circulation variables from the ERA-20C (ECMWF's first atmospheric reanalysis of the 20th century) reanalysis, winter SST variation patterns in the tropical western Pacific, which are related to the tropical Indian Ocean SST Dipole (IOD), and their impacts on East Asian climate are studied. Two types of SSTA (SST anormaly) pattern are found:A regional unanimous warm/cold pattern and a dipolar mode with SST anomalies in the western side opposite to that in the eastern side of the region. The two types of SSTA pattern both are favorable for winter precipitation suppression in southeastern China, but the domain sizes affected are different. The unanimous SSTA pattern affects a larger region from South China to the middle and lower reaches of Yangtze River. The impact of the SSTA dipole pattern is only confined to South China, leading to less rainfall in South China but more rainfall in the middle and lower reaches of Yangtze River. The corresponding atmospheric circulation anomalies can explain these rainfall anomalies. Although an anomalous cyclone occurs over the Philippine Sea in both of the cases, its strength and location are different. The cyclone forced by the unanimous warm SST pattern is stronger, and thus the anomalous westerly and northeasterly in the rear extend to a wider region, leading to a dry condition in a larger domain. In contrast, the cyclone forced by the dipolar pattern is weaker and the anomalous easterly and northeasterly are confined to a smaller area, leading to a dry condition only in southern China. Sensitive experiments by an AGCM, i.e., ECHAM5, validate the above results.