Abstract
In this study, observation and simulation data are analyzed to examine the causes of the rapid rise of surface air temperature in the inland area of northwestern Kanto Plain, Central Japan on 20 February 2009. A numerical simulation using the Weather Research and Forecasting (WRF) model shows that the temperature rise was mainly brought about by a downward wind with adiabatic heating over the area. Backward trajectory analysis indicates that the descending air parcel came from the southward warm area, in relation to the passage of a cyclone over the Kanto Plain. At about 1600 JST, the wind at the 850 hPa surface was divided into northward and southward by the central-Japan mountains, and converged over the northwestern Kanto area, which implied the formation of a downward wind. We suggest that the downward wind had the feature of a dry foehn, which was not accompanied by a precipitation process.
