Seasonal Change of the Mixed Layer Structure at Tsukuba

[摘要] The integrated surface sensible heat flux and the maximum mixing depth are obtained by routine aerological data and daily maximum and minimum temperature data measured at the Tateno Aerological Observatory located 60km east of Tokyo. Annual variations of the components of the surface heat balance are also estimated from the integrated surface heat flux, net radiation and the downward flux of short-wave radiation. Annual variations of the convective velocity scale, the standard deviation of the vertical velocity fluctuations, and the eddy diffusivity are estimated by the surface heat flux and mixed layer height. The potential temperature gradient of the stable layer capping the mixed layer is 0.003°C/m during the winter season, 0.005°C/m in midsummer, and 0.003°C/m under the travelling anticyclones. The integrated surface sensible heat flux from sunrise to a time when the daily maximum temperature occurs is largest in early spring (170ly), smallest in winter (50ly). The maximum mixing depth is highest in March (1, 500m) and lowest in December (700m). The surface sensible heat flux is largest in spring because of low temperatures, aridity, and a small amount of evapotranspiration. The Bowen ratio is unity in May and November. The lowest value of the Bowen ratio is 0.4 in July. Agreement of the abovementioned values with more accurate observations, is reasonably high. So this simple method for estimating parameters of the mixed layer structure is ascertained to be useful.

[学科分类] 大气科学