The Asian monsoon strongly affects the thermal structure of the JES (Chu et al., 1998a). During the winter monsoon season, a very cold northwest wind blows over the JES as a result of the Siberian High Pressure System. By late April, numerous frontally-generated events occur making late April and May highly variable in terms of wind speeds and number of clouds. During this period storms originating in Mongolia may cause strong, warm westerlies. By late May and early June, the summer surface atmospheric low pressure system begins to form over Asia. Initially this low pressure system is centered north of the Yellow Sea producing westerly winds. In late June, this low begins to migrate to the west setting up the southwest monsoon that dominates the summer months. The winds remain variable through June until Manchurian low pressure system strengthens. Despite the very active weather systems, the mean surface wind speed over the JES in summer is between 3 and 4 m/s, which is weaker than in winter. By July, however, high pressure (the Bonin High) to the south and the low pressure over Manchuria produce southerly winds carrying warm, moist air over the East China Sea/Yellow Sea. In the summer, warm air and strong downward net radiation stabilize the upper layer of the water and causes the surface mixed layer to shoal. October is the beginning of the transition back to winter conditions. The southerly winds weaken and let the sea surface slope reestablish the winter pattern.
The datasets used were the objectively analyzed fields of surface marine
climatology and anomalies of fluxes of heat, momentum, and fresh water. The
fields are derived from individual observations in the Comprehensive
Ocean-Atmosphere Data Set (COADS) from 1945 to December 1989 and are analyzed
on a 1
by 1 grid (da Silva et al., 1994).