Combined analysis of local downslope wind “Hiroto-kaze” induced by Typhoon “TOKAGE” in Japan

Downslope winds are observed when critical combinations of the topographic and the atmospheric conditions are satisfied. "Hiroto-kaze” is one of the strongest local downslope winds in Japan, which blows on the south foot of Mt. Nagi (1250m) located in the north-eastern part of Okayama prefecture. The wind continues to blow when the typhoons are passing within a few hundred kilometers south or southeast of Mt. Nagi . In 2004, "Hiroto-kaze" was observed in two cases. The one accompanied by Typhoon MEARI was, a typical "Hiroto-kaze", while the other associated with Typhoon TOKAGE was super "Hiroto-kaze" in magnitude and damaged area. In the latter case, extensive damage of fallen trees spread over the northern Okayama prefecture.

In this study, numerical simulations with a meso-scale non-hydrostatic model and observed wind data are combined with the fallen tree distribution from satellite data and in-situ investigations. We will investigate the relationships between the distributions of damaged area and the local meteorological conditions focusing on their flow regimes.

We will further discuss the differences in the mechanisms of flow developments between these two events.