Climatology of Mesoscale Warm and Cold Fronts in the Kanto Plain

Abstract

   A statistical analysis is made of mesoscale warm fronts (MWFs) and mesoscale cold fronts (MCFs) in the Kanto plain by using hourly surface data covering eleven years. A series of objective criteria are used to select 190 MWFs and 177 MCFs, and composite analyses are made of their local structure, seasonal and diurnal variabilities, and the larger-scale environment.
   MWFs are associated with southeast-southwest winds or northwest winds blowing against a shallow cold-air pool having a depth of a few hundred meters. The MWF associated with southeast-southwest winds corresponds to the warm-air intrusion during the passage of a cyclone, while the MWF associated with northwest winds corresponds to a strong northwesterly surge. The frequency of MWFs is highest between 06 and 12 JST.
   The MCF generally occurs during a cold-air surge. From late autumn to winter, the MCF is mainly associated with northwest winds accompanied by shallow cold air in its leading edge, and is more frequent in the nighttime than in the daytime. From spring to summer, MCFs associated with northeast or east winds are more frequent than those associated with northwest winds, and have a strong tendency to occur in the afternoon.