Surface Geostrophic and Observed Winds in the Coastal Zone of Japan

[摘要] Observed winds in coastal zones are dominated mainly by two wind components: the wind component induced by land/sea breeze (LSC: Land/Sea breeze Component) and the wind component associated with the synoptic pressure gradient (SWC: Synoptic Wind Component). This study attempts to investigate the relationships between the Surface Geostrophic Wind (SGW), and the actual surface wind in the coastal zones of Japan, separating the surface wind into two components: the SWC and the LSC.It is possible to separate the SWC from observed wind data through vector accumulation over numerous stations (226 AMeDAS stations) because the Japan Islands are surrounded by seas. Also, extraction of the LSC can be achieved by assuming the main land/sea breeze directions at every station.The calculated mean ratios of the SWC speed to the SGW speed at 1500 JST and 0600 JST are 0.22 and 0.15, respectively. The mean angle of deflection between the SWC and the SGW is 51 degrees measured counterclockwise from the SGW direction to the SWC direction, and the difference between the angles in the daytime and nighttime is very small, while the angle greatly changes with SGW speed. When the SGW speed is small, the deflection angle shows a large value, around 68 degrees. As the SGW speed increases, the deflection angle decreases.The LSC speed shows 1.6ms-1 for sea breeze at 1400 JST, and 0.8ms-1 for land breeze at 0600 JST when the SGW speed is near 0ms-1. However, as expected, these wind components decrease as the SGW speed increases. Eventually, the LSC vanishes when the SGW is over 14ms-1.

[学科分类] 大气科学