热岛效应造成的城市边界层热力稳定度变化及其对降水的影响

Change of Urban Boundary Thermal Stability Induced by Heat Island Effect and Its Influence on Precipitation

[目的]研究热岛效应造成的城市边界层热力稳定度变化特征及其对降水的影响。[方法]从热流量方程出发,探讨了因城市加热扰动、热岛效应平均态所引起的城市边界层热力稳定度的变化特征,分析了城市边界层热力稳定度变化对降水的影响,并结合西安地区降水个例进行了验证。[结果]在扰动温度与扰动气流相互作用下,边界层热力扰动稳定度(θ′/z)有利于城区及城市上下游边界层的层结趋于稳定,但中心城区的稳定性弱于郊区,有利于短历时对流降水天气的发生与发展。平均气流(盛行风)、平均水平扰动温度相互作用对热力不稳定分布的影响:当边界层环境气流为上升运动时,边界层平均热力扰动稳定度(θ′/z)表现为上游不稳定、下游稳定的特征,强降水易发生在上游或城市上风方;当边界层环境气流为弱下沉运动时,下游不稳定趋于发展、上游趋于稳定,局地强降水易发生在下游或城市下风方。[结论]该研究在制作城市精细化预报中有一定的参考价值。

[Objective] The aim was to study the characteristics of the changes of the urban boundary thermodynamic stability induced by heat island effect and their influences on precipitation.[Method] Proceeding from the thermodynamic equation,the changes of urban boundary thermodynamic stability caused by the urban heat disturbance and the mean state of heat island effect were discussed.The influence of the changes of urban boundary thermodynamic stability on the precipitation was expounded.Combining with case study of precipitation in Xi＇an,test was verified.[Result] Under interaction between the disturbed temperature and disturbed airflow,the boundary thermal disturbed st ability（θ′/z） was positive in the urban zone,as well as in the upstream and downstream areas of the city.But the stability in the urban zone was weaker than the suburbs,which favored for the short-time convective precipitation.For the boundary mean thermal stability（θ′ z） under the interaction between the mean airflow and mean environmental temperature,if the city zone existed in the front of the warm ridge,the stability in the upstream of the city weakened which increased the instability of the boundary,while it increased in the downstream of the city.It was contrary if the city zone existed in the font of the cold trough.For the mean airflow（prevailing wind） and the mean horizontal disturbed temperature,if it was upward motion in the boundary layer,the boundary mean thermal disturbed stability（θ′/z） was negative in the downstream and positive in the upstream.Strong precipitation occurred in the upstream of the city.It was contrary if it was descending air in the boundary layer.[Conclusion] The above results served some references for the fine city forecast.