Roles of airsea and land-air interactions on East Asian monsoon variability during transition seasons

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We examined thermal and dynamical structures of the lower atmosphere over the extratropical temperature front near Kuroshio extension and Oyashio where the deformation scale is less than a few of 100km. In addition, we also see the relation of sea surface temperature (SST) and surface air temperature to the surface wind velocity not only in the extratropics, but also tropics for the comparison. Over the warm flank of the thermal front near Kuroshio extension, the planetary boundary layer develops to 1000-1500m height because the static stability near the surface is very unstable. This unstable condition enhances the vertical mixing of the momentum, heat and moisture. As a result, a mixed momentum induces the acceleration of the surface wind over the warm water. This notion is not agreement with the conventional view of the extratropical air-sea interaction : the strong surface wind induces the cool ocean. These results indicate that that the ocean does in fact make feed back to the atmosphere. This does not mean that the traditional relationship is wrong, but rather that in these mid-latitude regions, a two-way relationship between the atmosphere and ocean exists. In addition, our analysis shows that the atmospheric response to this oceanic forcing appears to include the anomalous storm track activity. The observed atmospheric anomalies, which may be, in part, forced by the preexisting SST anomalies in those regions.