The Formation of a Surface Anticyclone over the Yellow and East China Seas in Spring

A surface anticyclone develops in April over the Yellow-East China Seas. The Yellow-East China Sea anticyclone (YESA) is confined in the marine atmospheric boundary layer but highly influential during the onset of sea fog season along the Chinese coast. This paper investigates the mechanism for YESA formation using atmospheric reanalysis, satellite observations and model experiments. Our analysis indicates that YESA is composed of three parts: (1) the westerlies to the north are the surface extension of the westerly wind jet; (2) the southerlies on the Chinese coast are due to the thermal wind between the warm continent and cool Yellow-East China Seas; (3) the northeasterlies to the south are due to the thermal wind between the cool East China Sea and warm Kuroshio Current. The regional atmospheric model successfully simulates the YESA under realistic boundary conditions. In an experiment where the Bohai-Yellow Seas are replaced with flat land, the surface anticyclone is pushed south and forms offshore along the new land-sea boundary, consistent with the thermal high mechanism over the cool sea surface temperature.