兰州城区冬半年冷锋活动及其对空气污染的影响

A SENSITIVITY EXPERIMENT OF PRIMITIVEEQUATION MODEL WITH MIXED p-σCOORDINATES TO THE EXCHANGEBETWEEN LAND AND AIR

对１９８８～１９９１年冬半年（１０月到次年３月）５００ｈＰａ历史天气图资料和兰州市环境监测站自动监测的污染物浓度资料进行了统计分析。结果表明：在两槽一脊天气环流形势控制下，兰州地区的冷锋活动频率最高，占５４．８％；一脊一槽型控制时次之，占３５．５％。冬半年强和较强冷锋最活跃期是３月份，其次是１０月份；弱冷锋天气则在１月份最活跃。冷锋过境后对兰州市区ＳＯ２污染的净化作用最大，其次是ＮＯｘ。其中，前者的平均浓度降低３０％～５０％，最大降低率达７０％～８０％。在冷锋天气过程中，逆温层厚度与污染物浓度的相关性最显著，其次是气温和混合层厚度，并且这三个气象因子在强、较强和弱三种天气条件下，对污染物浓度变化所起的作用有一定的差异。

Abstract A sensitivity experiment of 5 and 9 layers primitive equation models with mixed p-σ coordinates in limited domain to the drag coefficient,which affects the flux exchange between land and air,is performed by use of a cold wave process as an example. The result shows that the model is sensitive to the value of the drag coefficient. The value of the drag coefficient over Qinghai-Xizang Plateau in original model is too small. Increasing the value of the coefficient over the Plateau can improve the predicted results of the model.