Mass and Heat Balances of the Local Front over the Kanto Plain in Early Winter

The local front observed over the Kanto plain on December 5, 1996 has been analyzed as an example of one of those that often appear when a synoptic-scale low advances in the Japan Sea in early winter. Winds in the lower layer, blowing from the northern and western mountains since the previous night, supplied cold air to the middle of the plain. Before dawn, synoptic-scale southerly winds intensified from the south of the plain, and the local front formed along the southern margin of the cold air mass. The southerly winds over the lifted frontal surface entrained the cold air from the lower layer and transported it northward in a “transition layer, ” characterized by relatively cold southerly winds. The depths of the transition and lower layers tended to be maintained above the inland areas north of the front. The front advanced northward, corresponding to the surplus of the northward flow in the transition layer over the cold air supply in the lower layer. As a result of the persistent cold air flow, even during the daytime, the front became stationary over the middle of the plain in the afternoon. Additionally, a very shallow (-50m) structure of the frontal head existed prior to the frontal passage through the central area of Tokyo.