中国东部城市下垫面变化对南海夏季风爆发影响的数值模拟

A numerical study of the impact of urban land-use change over eastern China on South China Sea monsoon onset

本文利用美国国家大气研究中心(NCAR)开发的公用大气环境模式(CAM5.1)进行了中国东部大规模城市下垫面变化对南海夏季风爆发影响的数值模拟研究.结果表明:CAM5.1模式能够很好地模拟出东亚夏季风系统季节演变过程中大尺度环流场和降水分布的变化.敏感性试验结果表明中国东部大规模城市群的发展会使得南海夏季风提前1侯爆发;控制试验中5月中旬南海地区东南风向西南风的转变,以及降水量激增现象的出现,均较无城市试验中提前.同时,城市化快速发展阶段与南海夏季风爆发的年代际变化存在时间段的吻合,初步推断城市下垫面发展可能是1993年之后南海季风提前爆发的原因之一.对南海季风爆发影响的原因分析可以看出,城市化引起的下垫面物理属性变化,使得从春至夏的季节转变中,东部(110°-120°E)中高纬度陆地对大气的感热加热增强,减小了海陆之间的热力对比,加快陆地低层大气降压,从而引导南海季风提前爆发.

A large-scale coastal city zone over eastern China represented by the three large urban agglomerations of the Yangtze River Delta,the Pearl River Delta,and the Beijing-Tianjin-Hebei region is most active and developed areas in China and has experienced quick urbanization.The influence of urban land-use change over eastern China on South China Sea summer monsoon onset is investigated using Community Atmosphere Model Version 5 .1 （CAM5.1）.Two experiments were designed：（1）urban land cover determined by actual underlying surface land use data from 2000 and（2）no urban areas over eastern China（20＆#176;-50＆#176;N,100＆#176;-125＆#176;E）.Simulated the seasonal transition of large-scale atmospheric circulation and precipitation distribution agree well with the corresponding measurements.Comparison of the two runs shows that urbanization over eastern China may advance the date of South China Sea monsoon onset by one pentad,and the transition of zonal wind as well as dramatical enhancement of precipitation over South China Sea in mid-May are correspondingly advanced.Note that the age of rapid development of urbanization over eastern China is consistent with interdecadal advance of South China Sea monsoon onset after 1993.It is inferred that urbanization may be one of the reasons for the interdecadal variation of monsoon onset. Possible mechanisms were analyzed and it was found that the decreased land surface albedo caused by urbanization will induce strengthened sensible heating from land to air in the middle to high latitudes over eastern China continent between 110°E and 120°E,and the thermal contrast between ocean and land is reduced,which caused advancing the formation of land low pressure,and leading the earlier onset of South China Sea summer monsoon.