Climatological study of airflow channelling in relation to surface geostrophic wind

Abstract

Abstract The aim of this study was to climatologically investigate forced and pressure‐driven channelling flow in the Kitakami Basin, Japan, through the use of observational surface wind and sea‐level pressure data collected over 23 years, which corresponded to 15,584 channelling flow events. Our results indicated that forced channelling tends to occur when the direction of the surface geostrophic wind is parallel to the valley axis. Contrastingly, pressure‐driven channelling tends to occur when the component perpendicular to the valley axis of the surface geostrophic wind is larger than that parallel to the valley axis of the surface geostrophic wind. The channelling flow type was determined by the wind direction of the surface geostrophic wind, which was more pronounced when the mountain Froude number of the flow across the valley was less than 1. This indicates that the type of channelling flow depends on the surface geostrophic wind speed. Moreover, neither channelling flow type was dominant when the component parallel to the valley axis of the surface geostrophic wind was slightly larger than the orthogonal component. This suggests that the flow type cannot be explained using the surface geostrophic wind alone, irrespective of whether forced channelling or pressure‐driven channelling is dominant.

Keywords

• channelling flow
• climatology
• forced channelling
• local winds
• mountain meteorology
• pressure‐driven channelling