Spatial Structure and Formation Mechanism of Local Winds “Suzuka-oroshi” at the Foothills of Suzuka Mountains, Japan

Abstract

We examined the essential features and formation mechanism of the strong local “Suzuka-oroshi” winds, which are located leeward of the Suzuka Mountains in Japan. This area features favorable topography for downslope windstorms. Climatological analysis revealed that Suzuka-oroshi mainly occurred after an extratropical cyclone with a cold front and passed the Sea of Japan (55 % of all occurrences). Additionally, inversion layers (1–5 km level) were observed in 74 % of cases. Climatological analysis using spatially dense observational data revealed that the strongest winds tended to blow in the northern part of the plain on the leeward side. Numerical simulations for one case by the Weather Research and Forecasting (WRF) model with a 1 km grid increment supported this finding. Simulation results with and without the Suzuka Mountains demonstrated that the strong Suzuka-oroshi in the northern part of the plain comprised downslope windstorms with a transition of flow regime (the internal Froude number was lesser than 1.0 at the windward of mountains and greater than 1.0 above the leeward slope). Additionally, the differences in the height of the mountains between the northern and southern parts resulted in greater wind speed in the northern parts compared to the southern parts.