西宁地区大气边界层风、温场特征研究

Research on the Characteristics of Wind and Thermal Field for Atmospheric Boundary Layer in Xining

利用西宁地区2009—2011年地面气象及高空探测资料,统计及数值模拟研究了大气边界层风、温场特征。结果表明,西宁地面风场状况受地形的影响较大,风场复杂。地面较高频率风向与河谷走向基本一致,谷底平均风速较小,在北川河谷及湟中县西南为风速低值区。高空和地面主导风向在100 m以下发生转换,7:00高空以西风和西西北风为主,19:00则以东东南风和西西北风为主,风速均以西风和西西北风最大。风速垂直切变在冬季大,夏季小,夏季傍晚的风速垂直切变明显高于清晨。温度场特征表现为冬季出现逆温频率高,夏季低,清晨出现逆温层厚度较傍晚厚且逆温增温率强。逆温特征较黄土高原河谷城市及黄土高原较湿润地区更为明显,但较黄土高原干旱区则相对弱。混合层高度特征表现为春、夏季较高,冬季最小,气温相当的干旱季节混合层高度大于湿润季节,日混合层平均高度约在200~3 000 m变化,变化幅度大,扩散条件的日变化相差较大。

Based on ground meteorological and upper altitude data from 2009 to 2011 in Xining district, the characteristics of wind and thermal fields in atmospheric boundary layer was studied and simulated. The results show that, the surface wind field in Xining was complex,which had a great influence on terrain. The wind direction at higher frequencies agreed with valley's changes. The average wind speed in valley floor was lower, about 1 m· s-1, and it had features of low wind speed in Beichuan Valley and Southwest Huangzhong County. The high and surface dominant wind direction was conversed below 100m, and the high dominant wind direction was mainly W and WNW at 7:00, however the dominant wind direction was mainly ESE and WNW, and the maximum wind speed was mainly W and WNW at 19:00. The vertical wind shear index is about 0.6 in winter, and about 0.45 in summer. The change of vertical speed in winter is greater than that in summer, and is greater during the nighttime in summer than during the daytime. The feature of thermal fields showed that the temperature inversion frequency is about 30% higher in winter than in summer. The characteristics of thermal fields were higher frequency and deeper inversion layer in the morning than in the evening. The characteristics of inversion in Xining district were more obvious than that in the valley city and humid region of Loess Plateau, weaker than that in the arid region of Loess Plateau. The characteristics of mixing layer height in winter and spring was higher, and the lowest in winter, while the mixing layer height in arid season is higher in humid season within the same temperature of air. The daily mean of mixing layer height has larger variation, from 200 to 3000 m, and larger daily variation of diffusive condition.