Coherent Doppler lidar observation and numerical simulation of gap wind Kiyokawa-dashi in Japan

This study presents the coherent Doppler lidar (CDL) observations and numerical simulations of local strong easterly wind Kiyokawa-dashi, which is most famous gap wind in Japan. Main goal of this study is to clarify the three dimensional structure and dynamics of Kiyokawa-dashi under the different synoptic situations. Observations were conducted in August 29 and 30, 2004. A 2μm eye-safe airborne CDL developed by the National Institute of Information and Communications Technology (NICT) established at the exit of the narrow valley of Mogami-River. The vertical scanning of CDL with the velocity-azimuth display technique shows that the easterly wind was confined below 600 m, which is almost same or slightly lower than the crest, and accelerated at the down stream side. The upper layer above the easterly wind was weak westerly and these vertical structures were common to the all of the events. Horizontal scanning sounds the line-of-sight (LOS) wind velocity up to 6 km of downstream and presents detailed temporal wind shift within 5-10 minutes. Numerical simulations have been performed with non hydrostatic atmospheric model (MRI-NPD NHM) with horizontal grid spacing down to 1 km. Many of the observed structures were realistically simulated, but it still has a bias that the detailed temporal evolution wasn't shown in the numerical simulation. The CDL captured the fine structure and temporal variations of Kiyokawa-dashi. It is a powerful and useful system for studying the wind field.