Effect Of Urban Clusters On The Regional Boundary Layer And On The Cloud And Precipitation In The Yangtze River Delta Area

In this thesis, based on the satellite dataset and model simulation, the effect of large-scale urbanization on the regional boundary layer and climate environment of the Yangtze River Delta area were analyzed. The main contents and results are as follows:Based on the high resolution satellite dataset (PATMOS-x,0.5°×0.5°,25years; TRMM3B42,0.25°×0.25°,11years), the spatiotemporal variations of cloud amount and precipitation over the Yangtze River Delta were analyzed. The results indicate that low-level cloud amount and precipitation in summer are mainly impacted by the local environment. The low-level cloud amounts rise more dramatically over and around Shanghai-SXC (Suzhou, Wuxi and Changzhou)-Hangzhou areas. And the increasing center is located nearby downwind of Shanghai city. At the same time, the maximum center of summer precipitation is also located downwind of Shanghai, just with a father distance from Shanghai.In order to enhance the capability of the single layer urban canopy model (SLUCM), the evaluation and parameters sensitivity study of the SLUCM was done based on the surface energy balance observations, in Nanjing. And a set of parameters which are more suitable to the highly urbanized Nanjing city were given.By the improved model, a clear day with southeasterly wind was simulated to study the effects of urban clusters in the Yangtze River Delta (YRD) area on the regional boundary layer, and then to explore the possible mechanisms of the urbanization effects on cloud and precipitation. The main results are as follows:(1) urbanization will warm and dry the low level boundary layer (below about1km) on a large scale, and lead to the upper boundary layer (about1.2～1.8km) cool and wet.(2) The interaction between the sea (and lake) breeze and urban effect results in strong convergence at the low levels over the coastal area. Locations of the strongest convergence belts are on the edge of urban heat island. However, the convergence in over and around the inland urban clusters are very weak. The urban induced enhancement in the convergence at the low levels is likely to be the key factor of the urban effect on the cloud progress.(3) Simulations of cloud and precipitation results also indicate that urbanizations can improve the cloud and precipitation over the coastal area in the afternoon. And the maximum increased center is located downwind of Shanghai.