秋冬季节京津渤地区局地环流特征及气溶胶分布规律

在平稳天气条件下,京津渤地区受燕山山脉地形影响,形成地形局地环流。地形环流的高度一般在1700m左右,平均水平范围约100—200km。平原中,北京、天津等大城市的作用,又使局地环流流场产生扰动,城市环流的高度约450m,水平范围约30—40km。城市环流的水平辐合可达5×10~(-4)sec~(-1)。在平原增热明显的日子里,渤海湾沿岸出现向岸风,海风深入内陆的距离约30—40km,厚度约300多米,海风与陆上西南风造成辐合,其辐合量达×10~(-4)sec~(-1)。 当京津渤地区在典型的局地环流控制时,如有城市环流和海风环流相迭加,可以出现严重的污染状况,大气气溶胶浓度可比平常情况下高一个量级。

CHARACTERISTICS OF LOCAL CIRCULATIONAND AEROSOL DISTRIBUTION OVER BEIJING-TIANJIN AREA DURING AUTUMN AND WINTER

Under stable synoptic conditions, there is a local terrain circulation induced by the Yan Mountains, over Beijing-Tianjin area during autumn and winter, the vertical and horizontal scales of which are 1700m and 100-200km respectively. Over the plain of this same area, flow fields of local circulationare perturbed by the presence of the two cities-Beijing and Tianjin. Theheight and horizontal region of the city-induced circulation are about 450m and 30-40km respectively. The magnitude of the horizontal convergence of a city-induced circulation can be 5×10^-4sec-1.Sea breeze occurs in coastal regions of the Bohai Sea at a time when the plain has been strongly heated up. The height and inland coverage of the sea breeze are about 300m and 40km respectively. There is a line of convergence between the sea breeze and the southwestern flow over land, the magnitude of which is 3×10^-4sec-1. Anytime when a typical local terrain circulation, a city-induced circulation and a sea breeze circulation exist over the Beijing-Tianjin area at the same time, air pollution may become severe and the aerosol concentration is higher than usual by one order of magnitude.