Twice daily synoptic charts at surface, 850, 700 and 500 hPa and mean sea surface temperature maps for the winter season as well as each month were used to study the climatological aspects of explosive cyclones over the western North Pacific and East Asia coastal areas in the September-April periods of 1974-1984. Geographical distribution of frequency, interannual and seasonal variations of frequency and frequency distribution of different intensities of explosive cyclones were analyzed. The relationships of cyclones to a 500 hPa trough, lower-tropospheric baroclinity and sea surface temperature gradients were studied at the formation and explosive stages.

It was found that explosive cyclones tended to form and to deepen rapidly along the shoreward edge of the warm Kuroshio current over the area of the maximum SST gradient. They also frequently formed and deepened rapidly about 700-800 km ahead of the 500 hPa trough. Results suggest that the flux of sensible heat and latent heat from the warm ocean surface and latent heating over the cyclone area in addition to the baroclinic process may have had positive effects on the formation and rapid deepening of explosive cyclones over the western North Pacific.