An Observational Study of the Local Easterly Strong Wind “Kiyokawa-dashi” in the Shonai Plains, Yamagata

抄録

　In the Shonai region, Japan, a local easterly strong wind called Kiyokawa-dashi occurs at the exit of the narrow valley connecting the Shinjo Basin and the Shonai Plains. Sometimes, Kiyokawa-dashi brings severe paddy rice damage in spring and summer. This study examines the meteorological properties of Kiyokawa-dashi by using intensive observations which include the double theodolite pilot balloon observation and traveling observation.
　During the experimental period of 2002 and 2003, different types of Kiyokawa-dashi have been observed: blowing locally (Obs-1) and widely (Obs-2). The double theodolite pilot balloon observation showed that the easterly wind was shallow, and a strong low level jet (≥ 10 m/s) appeared at about 200-400 m. These vertical structures were similar in Obs-1 and Obs-2. The strongest surface wind speed (≥ 10 m/s) was observed in the exit region of the valley in Obs-3. In this case, winds along the foot of the lee side of the mountain were weak, i.e. ≤ 3 m/s and the winds in the central region of the plain were relatively strong, i.e. ≥6 m/s.
　The features of the flow fields are complex, and many of the characteristics of the wind fields can be adequately accounted only by consideration of the combined effect of topography and the meteorological conditions.