A climatological study of the strongest local winds of Japan “Inami‐kaze”

Abstract

AbstractThis study examines the meteorological and climatological features of the Inami‐kaze in the Tonami Plain, the strongest local winds in Japan. The plain faces the Sea of Japan on the north side, while the remaining three sides are surrounded by high mountain ranges. An interview survey to local residents and the distribution of windbreak trees both indicate that the Inami‐kaze is localized to a surprisingly small region near the Inami town (about 6 km parallel to the mountain ridge and 3 km perpendicular to it), at the base of a very small saddle‐like topography in the mountain ridge. Wind statistics with a dense observation network during 2006–2014 (28 Inami‐kaze events) supports the above finding. Indeed, the wind speed is mostly (95%) below 11 m/s at the Tonami town, just 5 km away from the Inami town, while the Inami‐kaze (≥15 m/s) blows at the Inami town. Such a spatial pattern should be formed as a result of downslope windstorm with hydraulic jumps, which is indicated from the internal Froude number change across the mountain (0.9 at the upstream, 1.4 at the mountain top, and 0.3 at downstream). The required synoptic atmospheric condition for the Inami‐kaze is the pressure pattern “extratropical cyclone in the Sea of Japan.” The sufficient condition is the SSW–SSE wind (≥25 m/s) or south wind (around 20 m/s) at the 800‐pressure level over the mountain chain, indicating the allowed directional window is very narrow. On the other hand, the Inami‐kaze has an aspect of foehn. While the Inami‐kaze occur, the potential temperature at the Inami town tends to be higher by 4.7 K on average than in the windward plain on the Pacific Ocean side.