半干旱地区河谷盆地与低丘缓坡冬季边界层特征差异的对比研究

Comparative Study of Boundary Layer Characteristics between Valley Basin and Gentle Hillside in Semi-Arid Region inWinter

利用WRF模式模拟兰州市西固区河谷盆地和兰州新区低丘缓坡地形两种下垫面的冬季边界层特征,从近地面风场、温度场、位温廓线、地面通量和边界层高度等方面对比分析两种不同下垫面边界层特征的差异,探讨下垫面影响边界层特征的机理。结果表明:下垫面特征对边界层特征影响较大;粗糙下垫面动力特征使得兰州市西固区河谷盆地内的近地面风速低于兰州新区,也是兰州市西固区河谷盆地内日间动量通量明显大于兰州新区的主要原因;相比兰州新区低丘缓坡地形特征形成的均匀近地面流场,兰州西固区河谷盆地内的近地面流场十分复杂;日间,更为干燥的兰州新区接收太阳辐射,地面对大气的热力作用强于河谷盆地的兰州市西固区,使得其最大边界层高度高于兰州市西固区河谷盆地。

In this paper,the characteristics of atmospheric boundary layer over two types of topography,Xigu District,Lanzhou(complex topography)and Lanzhou New District(flat terrain),were simulated by WRF model,the discrepancies between the two types topography on surface wind field,temperature,theta profile,surface flux and atmospheric boundary layer height were analyzed to discuss the effect of topography on the atmospheric boundary layer.The results indicated that:Characteristics of the underlying surface have a considerable influence on the atmospheric boundary layer.Rough underlying surface in Xigu District results in a lower nearsurface wind speed than that in Lanzhou New District,this is also the main reason why the daytime momentum flux in the valley basin of Xigu District was significantly stronger than that of Lanzhou New District.Compared with the homogeneous near-surface flow in Lanzhou New District,the near-surface flow field in the valley basin of Xigu District was highly complicated.Thermal effect of solar radiation in the daytime over dry underlying surface in Lanzhou New District was more efficient than that on river basin in Xigu District,which leads to higher maximum boundary layer height in Lanzhou new area.