Numerical Study of the Local Downslope Wind “Hirodo-Kaze” in Japan

Abstract

The ?Hirodo-kaze,? a local strong wind accompanying the downslope winds in Japan, is examined using a mesoscale numerical model. The model successfully reproduces the major features of the observed Hirodo-kaze that occurred in association with Typhoon Pabuk. During the Hirodo-kaze, the severe downslope winds in the transitional flow develop in the lower troposphere below the mean-state critical layer. The Hirodo-kaze is closely linked to the strong wind region accompanying the severe downslope winds. After the cessation of the Hirodo-kaze, distinct mountain waves dominate in the lower troposphere where the Scorer parameter l2 decreases with height. The region of strong wind retreats windward as the Hirodo-kaze ceases. Temporal changes in the characteristics of mountain waves in the lee of Mt. Nagi are primarily attributed to the changes in the large-scale environmental winds due to the movement of the intense cyclone. Environmental conditions favorable for the occurrence of the Hirodo-kaze include strong northerlies in the lower troposphere overlain by southerlies in the middle troposphere. The intense cyclone that moves over the sea southwest of the Kii peninsula creates favorable environmental conditions that support the occurrence of the Hirodo-kaze.