THE DAYTIME PBL HEATING PROCESS OVER COMPLEX TERRAIN IN CENTRAL JAPAN UNDER FAIR AND CALM WEATHER CONDITIONS .1. MESOSCALE CIRCULATION AND THE PBL HEATING RATE

Using a new analysis technique, the heat budget of the daytime atmospheric planetary boundary layer (PBL) over a complex terrain was obtained for 55 meteorological stations in central Japan under fair weather and weak synoptic wind conditions. Under such conditions, the daytime wind and temperature fields in the PBL are dominated by thermally induced local circulations. The PBL heating rate Q(s) at each station was estimated from routine observational data. The topographical features of the meteorological stations were divided into five categories: cape, coastal plain (within 20 km of the coastline), inland plain, basin bottom, and mountainous area. The basin bottom and inland plain exhibit large values of Q(s) due to local subsidence heating acting as a compensating current of the upslope flow. The mountainous area, on the other hand, has a small value of Q(s) since the upslope flow removes heated air from this region. In the cape and a large part of the coastal plain, cold air advection due to the sea breeze depresses Q(s). The daytime PBL heating causes a surface pressure depression proportional to Q(s), resulting in a thermal low over the inland area.