The Regional Climate Effect Of SST Front In The Vicinity Of The Kuroshio In East China Sea

Based on the investigation of the local climate effect of sea surface temperature front (SST front, SSTF) in the vicinity of the Kuroshio in the East China Sea, the formation mechanism of Yellow-East China Sea anticyclone (YESA) is studied.Various satellite data, the JRA-25 (Japan reanalysis of 25 years) reanalyzed data and WRF (Weather Research Forecast) model are used to investigate the in situ effect of the ESKF (East China Sea Kuroshio Front) in the MABL (marine atmospheric boundary layer). The intensity of the ESKF is most robust from January to April in its annual circle. The local strong surface northerly/northeasterly winds are observed right over the ESKF in January and in April and the wind speeds decrease upward in the MABL. The thermal wind effect that is derived from the baroclinic MABL forced by the strong SST gradient contributes to the strong surface winds, to a large degree. The convergence zone existing along the warm flank of the ESKF is stronger in April than in January corresponding to the steeper SST gradient. The collocations of the cloud cover maximum and precipitation maximum are basically consistent with the convergence zone. The clouds develop higher (lower) in the warm (cold) flank of the ESKF due to the less (more) stable stratification in the MABL. The lowest clouds are observed in April on the cold flank of the ESKF and over the Yellow Sea due to the existence of the pronounced temperature inversion. The numerical experiments with smoothed SST support the results from the observations.In the scale of montly mean, a surface anticyclone develops in spring over the Yellow-East China Sea. YESA is confined in the atmospheric boundary layer (ABL) but highly influential on the onset of sea fog season on 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:(a) the westerlies to the north are the surface extension of the westerly wind jet; (b) the southerlies on the Chinese coast are due to the thermal wind between the warm continent and cool Yellow-East China Sea; and (c) the northeasterlies to the south are due to the thermal wind between the cool East China Sea and warm Kuroshio Current. A regional atmospheric model successfully simulates the YESA under realistic boundary conditions. In an experiment where the Bohai-Yellow Sea is replaced with flat land, the surface anticyclone is pushed south and forms along the new land-sea boundary, consistent with the thermal high mechanism.