兰州东部地区冬季地面风场特征

根据１９９６年１２月在兰州市东峡口及东部山区多个观测点的地面风观测资料，分析了各个观测点的风向频率、静风频率、平均风速、风向和风速的日变化特征，以及地面流场特征，结果表明，冬季兰州东部地区的最多风向为东风或偏东风，静风频率比较高，平均风速较小，不同地点的风向日变化规律不尽相同。盆地风内速日变化幅度较大，东峡口及其东部山区的风速具有明显的日变化。东峡口外风速在傍晚迅速增大，夜间风速较白天变化为小，上

Characteristics of Surface Wind over the Eastern Part of Lanzhou Basin in Winter

According to the surface wind data observed in the eastern part of L anzhou basin for the Feasibility of Ventilation Project in that part in December1 996,the frequencies of calm and of wind directions,the mean wind speed and the diurnal variations of mean wind di- rection and wind speed at different sites were analyzed together with the surface wind field. The chief characteristics are:the prevailing wind direction is the east,the frequency of calm is high,the mean wind speed is low,the regularities of diurnal variations of wind direction at different sites are different,and the diurnal changes of wind speed in the basin are small while those at the east gorge and its surrounding mountainous area are obvious.At the east gorge,the wind speed increases quickly at nightfall.However its change is small throughout the night as compared with the daytime.In the morning it declines and reaches its minimum in the afternoon.Whereas in the surrounding mountainous area the wind speed increases in early afternoon,and reaches its top at nightfall.By variational technique,surface wind fields of the adjusted parallel type,the convergent type,the divergent type and the shearing type were got while parallel eastwind type is the commonest one,and the eastwind is blocked ob- viously by the hills near the east gorge.