里下河地区下垫面变化对降水、气温、风速的影响

近年来,随着苏北地区经济和城市的快速发展,土地覆盖状况发生了显著变化,其中尤以城市化扩展为主。为了分析下垫面变化对天气过程的影响,特别是对降水过程的影响,采用中尺度WRF3.4/Noah/UCM模式,对苏北里下河地区2005年8月6日的一次强降水过程进行了模拟,其中通过改变模式的下垫面特征,设置了三种敏感性分析试验,分别是USGS土地利用类型(CASE1)、修正后的MODIS土地利用类型(CASE2)和城市极端扩张后土地利用类型(CASE3)。研究结果表明,修正后的MODIS土地利用类型数据(CASE2)更能真实地反映里下河地区的下垫面结构,与实测值对比后发现模拟的降水、气温和风速等气象要素更为准确。通过将CASE2、CASE3与CASE1的模拟结果对比发现,城市下垫面增加后会使城市气温明显增加,上空的风速减小;白天地表感热通量增强,潜热通量减小,夜间延长了感热通量由正变负的时间;边界层高度被抬升,在中午前后分别被抬升了近45 m和100 m左右;垂直速度和散度值增大,大气低层的扰动位温增加,云水混合比和雨水混合比均增多。以上这些条件均有助于对流降水天气的发生、发展。

Impact of Underlying Surface Changes in Lixia River Region on Rainfall, Temperature and Wind Velocity

In recent years, with the rapid development of economy and city in northern Jiangsu, land surface cover has modified a lot, especially the expansion of urbanization. To analyze the impact of underlying surface changes on the weather process, especially on the rainfall process, this paper used a mesoscale coupled model WRF3.4/Noah/UCM to simulate a heavy rainfall on the meteorological fields over Lixia river region on 6th August, 2005. Based on changing the underlying surface feature of the model, three kinds of sensitivity analysis tests were set: USGS land cover data (CASE1), modified MODIS land cover data (CASE2) and land cover data after extreme expanding cites(CASE3). The results showed that modified MODIS land cover data (CASE2) had a significant impact on the simulation of the underlying surface feature; the values of rainfall, temperature and wind velocity were simulated better compared with measured data. Urban underlying surface caused the increasing of city temperature, sensible heat flux, the boundary layer height (raised nearly about 45 m and 100 m before and after noon), vertical velocity and divergence, perturbation potential temperature in the lower atmosphere and cloud/rain water mixing ratio, while it decreased wind velocity and latent heat flux. These conditions can contribute to the occurrence and development of convective weather.