The characteristics of gusty winds in winter season in Shonai Plane, Japan

Wind disasters often concentrate in localized area though the parent convective storms have far larger scales. Our observational study aims to clear the relation between the gusty winds and the convective storms. The instantaneous wind velocities were observed with 12 supersonic anemometers aligned parallel to the Dai-ni Mogami River Bridge in Shonai plane faced on the Sea of Japan. The upper layer was simultaneously observed by an X-band Doppler radar settled on Amarume station located at 4km south from the Dai-ni Mogami River Bridge. Observation period is from March 2007 to March 2009. Gusty winds were conditionally sampled referring to triangle wave patterns in which the instantaneous velocity peak exceeded 20 m/s. We detected more than 9000 gusty events for the observation period. They occurred mainly in winter. The mean wind direction of the gusty winds was northwest corresponding to the direction of winter monsoon. 95% of events were accompanied by convective cell. Though typical echo patterns showing the existence of downburst or gust front were not observed, temperature drop of about 2 degree was observed in two events of which maximum velocity exceeded 25 m/s. The vertical distribution of Doppler velocity of the echo showed the profile of low level jet.