宜昌冬季两次降水过程大气边界层的观测分析

Observational Analysis on Atmospheric Boundary Layer over Yichang During Two Precipitation Processes in Winter

利用宜昌2007年12月10—25日的加密观测资料,分析了两次低值系统经过宜昌时大气边界层的温湿风廓线结构及其日变化特征。结果表明:位温廓线具有明显的日变化特征,对流边界层在白天出现和发展,其高度可达600 m,而稳定边界层在夜间出现和发展,其高度可达300 m,降水会抑制对流边界层和稳定边界层的发展;湿度廓线结构及其日变化与对流边界层的发展有关,总体上湿度随高度减小,贴近地面的薄层湿度随高度减小较快,而混合层内湿度随高度变化较小,出现降水时,近地层的湿度有明显增加,大气边界层内湿度随高度快速平稳减小;风速廓线结构比较复杂,总体上风速随高度增大,在大气边界层低层有时会出现一个风速极大值,风速廓线没有明显的日变化特征,大气边界层内风向变化较大,但以偏东风为主。

With the intensive observation at Yichang during 10-25 December, 2007, analysis on the parameter profiles and its diurnal variation of atmospheric boundary layer （ABL） when two low-pressure systems passing Yichang is carried out. The results show that the equivalent potential temperature profile has a clear pattern of diurnal variation, in which the convective boundary layer （CBL） appears and develops in day while the stable boundary layer （SBL） at night, the heights of CBL and SBL can reach 600 m and 300 m respectively, but the developing of CBL and SBL is restrained when precipitation occurs; the specific humidity （q） profile and its diurnal variation are related to the developing of CBL, q decreases with the altitude on the whole at a faster speed in surface layer and the slower one in mixed layer; when the precipitation occurs, q becomes large in surface layer and decreases fastly with the altitude at a stable speed; the wind profile is complex without obvious diurnal variation features, but wind speed has an increase tendency with the altitude on the whole with a maximum in lower ABL sometimes, and the wind direction is a variable relatively largely in ABL, but most ones are in the partial east.