The activity of explosively developing extratropical cyclones in the vicinity of Japan in intimate association with the occurrence of heavy snowfall on the Japan Sea side of central Japan is examined using Japanese long-term reanalysis projected data (JRA-25), with additional data from the Japan Meteorological Agency climate data assimilation system (JCDAS). On a monthly basis, the explosive extratropical cyclone tracks tend to concentrate around the Kuroshio Current off the Pacific coast of Japan and the Japan Sea at the heavy snowfall phase, whereas the tracks disperse over the broader areas in the light snowfall phase. The heavy and light snowfall phases correspond well to the strong and weak phases of the East Asian winter monsoon circulation respectively, and the monsoon variability influences the local monthly snowfall on the Japan Sea side of central Japan through change in the explosive cyclone activity. On a daily basis, stationary Rossby wave packets propagating eastward along the northern Eurasian and South Asian waveguides, i.e., subpolar and subtropical teleconnection types, contribute to the occurrence of extraordinarily heavy snowfall events through the development of explosive cyclones. The subpolar teleconnection type facilitates not only the intensification and southward migration of a cold continental high in East Asia, but also the rapid growth of an explosive cyclone around Japan by inducing the equatorward advection of higher potential vorticity from high latitudes. Both developments lead to the reinforcement of an east-west gradient in sea level pressure (SLP) across Japan, thereby providing a favorable condition for the heavy snowfall events. For the subtropical teleconnection type, the explosive cyclone system is primarily responsible for the occurrence of extremely heavy snowfall events through enhanced zonal SLP gradient. It is also found that the explosive cyclone activity differs in terms of geographical location and track between the subpolar and subtropical teleconnection types.
2012 by Meteorological Society of Japan