Temporal and spatial dynamics of a local wind in Japan, “Kiyokawa‐dashi”: Insights from high‐density observations and numerical simulations

Abstract The Kiyokawa‐dashi is a local wind that occurs over the Shonai Plain in Japan. It becomes strongest at the exit of the Mogami Gorge, which is 1.5 km wide and 16 km long, cutting through a small mountain range approximately 0.4 to 0.8 km high, 10 km wide, and 57 km long. The Kiyokawa‐dashi occasionally causes damage to rice crops and is thus recognized as one of Japan's three major notorious local winds. This study aims to investigate the spatiotemporal changes of the Kiyokawa‐dashi through surface meteorological observations and numerical simulations. High‐density near‐surface observations conducted at approximately 1‐km intervals, utilizing 17 anemometers, revealed that the typical Kiyokawa‐dashi exhibits transitional characteristics, shifting from localized to widespread across the plain over time. Numerical simulations utilizing the Weather Research and Forecasting model were employed to understand the three‐dimensional structure and dynamics of the transitional‐type Kiyokawa‐dashi. The simulated results and hydraulic theory indicate that during the initiation stage, the blowing region of the Kiyokawa‐dashi is localized at the exit of the Mogami Gorge, as airflow selectively passes through the gorge to reach the leeward plain. However, during the mature stage, the simulated Kiyokawa‐dashi covers the entire Shonai Plain, as airflow over the mountains or through the gorge reaches the leeward plain. Consequently, the Kiyokawa‐dashi exhibits spatial characteristics of a shallow foehn at its initiation and a deep foehn at its mature stage. Additionally, it was found that the Mogami Gorge accelerates the onset of the Kiyokawa‐dashi. This study provides valuable insights into the law of similarity regarding the influence of topography on airflows over mountains. Despite significant differences in size, the small mountain range and the Mogami Gorge exhibit dynamic effects akin to the Alps and its valleys, underscoring the universality of such phenomena.