南海中北部秋季低空偏东急流分布特征及其形成的机制  

DISTRIBUTION CHARACTERISTICS OF LOW-LEVEL JET IN NORTH-CENTRAL SOUTH CHINA SEA AND ITS FORMATION MECHANISM

作　　者：冯文[1,2] 符式红[2] 吴俞[2] 

机构地区：[1]南京信息工程大学大气科学学院,江苏南京210044 [2]海南省气象台,海南海口570203

出　　处：《热带气象学报》2015年第2期247-254,共8页Journal of Tropical Meteorology

基　　金：国家自然科学基金项目(41365004);2013年度公益性行业科研专项(GYHY201306009);海南省自然科学基金项目(413132)共同资助

摘　　要：借助Biot-Savart定律和二维涡度方程以及美国国家环境预报中心的数据资料,分析了海陆分布的下垫面热力差异与南海中北部低空急流发生和发展的关系。分析结果表明:南海中北部的低空急流由秋季出现在海陆交界处的偏东强风带南移加强而致,最大风速层出现在925 h Pa附近,其形成与海陆热力差异增大有关。进入秋季后,由于太阳辐射的季节变化及北下冷空气的双重作用,东亚大陆近地层的温度下降迅速,而南海洋面温度变化极小,南北温差加剧。两地近地层温度的相对变化,加大了大气上升和下沉运动,使得东亚大陆负相对涡度及南海地区的正相对涡度均得以增强。由Biot-Savart定律可知,东亚大陆和南海地区之间相对涡度通量的加大必将于南海中北部对流层低层诱导出强的辐合风速,形成带状偏东风急流。由于南海南部的涡通量大于东亚大陆地区,因此南海南部高温正涡中心所诱导出的水平速度是构成南海中北部低空急流的最主要分量,而来自东亚大陆低温负涡中心的贡献居次。Based on the Biot-Savart law and using the data from National Center for Environmental Prediction （NCEP）, we study the relationship between thermal contrasts of the underlying surface and the formation and evolution of low-level jets in north-middle South China Sea. The results are shown as follows. The low-level jet in north-central South China Sea results from easterly winds moving southward and strengthening in the junction of land and sea, which has a maximum wind speed layer near 925 hPa and its formation is related to the land-sea thermal contrast. As the radiation from the sun gradually moves from the northern meridian, the temperature on the ground surface of East Asia decreases but the surface temperature of South China Sea keeps constant during the same period. It is shown that this increase in the temperature difference between land and sea is conducive to the formation and development of convection and leads to increasing strength of relative vorticity between positive and negative vertical vortices over the land and sea. According to the Biot-Savart law, the increase in vorticity strength between the East Asia continent and the sea surface of South China will induce correspondingly a large horizontal velocity in the lower troposphere of northern-middle South China Sea. The positive vorticity fields over the sea surface of South China play a predominant role in the formation of low-level jets.

关 键 词：低空急流 Biot-Savart定律 南海中北部 海陆热力差异 相对涡度通量 

分 类 号：P442[天文地球—大气科学及气象学]