Climatological study on valuable local winds, “Obonai-dashi,” in Japan

Obonai-dashi are local winds that blow into the Obonai District located on the western base of the Ou Mountains in Japan. Residents believe the Obonai-dashi provide agricultural benefits. This study statistically clarified the climatological features of the Obonai-dashi and discussed possible reasons for their perceived benefits. Our statistical analysis of 377 Obonai-dashi events between 2010 and 2022 revealed that they occurred frequently from April to September. Four synoptic weather patterns causing the Obonai-dashi were identified: cyclones on the Sea of Japan (23.7%); migratory anticyclones (19.4%); the Okhotsk high (15.8%); and cyclones along the Pacific coast of Japan (12.9%). The Obonai District tended to be moderately warmer than normal condition in spring and moderately cooler in summer during Obonai-dashi events. The Obonai District generally tended to be warmer than its surrounding areas, including both the Pacific side and the Sea of Japan side, except when compared with the Sea of Japan side under the influence of the Okhotsk high. These findings statistically support a local hypothesis regarding the agricultural benefits: in spring, the moderately warm condition due to the Obonai-dashi helps plants and trees grow, while in summer, their moderate coolness makes it easier for farmers to work. Since statistic period of this study was limited to normal or warm summers, the conclusions of this study may not be applicable to severe cold summers.