Analyses of Southerly Winds along the Kitakami Basin when the Yamase Prevails

The Yamase is a cold, humid, northeasterly wind blowing toward the coast on the Pacific side of the Tohoku region of Japan during summer. However, the Yamase blows in a southerly direction in the Kitakami Basin. Inthis study, analyses of data and numerical experiments using the Weather Research and Forecasting(WRF) model were conducted to determine the reason for this southerly direction. The results of numerical experiments indicated that the Yamase is southerly in the Kitakami Basin where theactual topography is reduced to 90% of the average terrain height. Meanwhile, it is easterly in areas of the Kitakami Basin when the topography is reduced to 80% of the average terrain height. The results of numerical experiments were consistent with those of mechanical analyses using the Foude number and Rossby number. Analyses of the Yamase in the Kitakami Basin therefore suggest that its characteristics are influenced by topographic obstacles and gravitational flow