The possible impact of the winter monsoon intensity and sea surface temperature (SST) gradient on the activity of explosively developing extratropical cyclones around Japan is investigated using the Weather Research Forecasting model. Two independent long-term integrations over 18 winters from 1993/94 to 2010/2011 are conducted using prescribed observed SST data (OS run) and spatially smoothed data (SS run). The OS run is successful in reproducing the spatial distributions of the explosive cyclone activity in the vicinity of Japan under both strong and weak winter monsoon conditions. Under strong monsoon conditions, the Kuroshio, the Kuroshio Extension, and the Japan Sea subpolar fronts give rise to enhanced near-surface baroclinicity through the increase in heat and moisture fluxes from the ocean surface, resulting in frequent occurrence of the explosive cyclone activity along those fronts.
2013 by the Meteorological Society of Japan