南海夏季风爆发早晚的大气热源特征分析

Analysis of the Characteristics of Atmospheric Heat Sources for Early and Late Outbreaks of South China Sea Summer Monsoon

利用1972—2007年NCEP/NCAR再分析资料计算大气热源,分析了南海夏季风爆发前后大气热源的特征,在此基础上,以南海夏季风爆发偏早年(1983年)和爆发偏晚年(1989年)为例,对比分析大气热源和大气环流特征的差异。结果表明:季风爆发后热源中心有明显的北抬现象,伴随着我国南部至南海区域低层较强的西南风建立;季风爆发偏早年,中层大气在我国以北出现负距平,赤道区域热源中心值较平均水平高,与之对应的是爆发偏晚年热源中心值偏低,偏早年季风爆发前在赤道至南海区域有较大的热源梯度,这种动力和热力形势的配置使季风爆发偏早年Hadley环流强度增强,导致从孟加拉湾向北的水汽输送增多,南海夏季风爆发时间偏早,造成雨带北移的时间提前。

Using the reanalysis data of NCEP/NCAR for 1972 to 2007, we computed the atmospheric heat sources and studied their characteristics before and after the outbreak of the South China Sea summer monsoon （SCSSM）. Then, take as example the early onset year （1983） and late onset year （1989） of the SCSSM to compare and analyze the difference in the characteristics of atmospheric heat sources and atmospheric circulation. The result is shown as follows. After the monsoon onset, the center of the heat source is much more northward shifted as a strong southwesterly wind establishes in the low level from the south of China to the South China Sea. For the early onset year, negative anomalies of middle - level atmosphere ap- pear in areas north of China and the value of an equatorial heat source is higher than usual. For the late onset year, in contrast, this value is relatively low and there are relatively large gradients of the heat source from the equator to the South China Sea region prior to the monsoon onset. Such allocation of dynamics and thermodynamics caused the Hadley circulation to strengthen in the early onset year, consequently increasing the transport of water vapor from the Bay of Bengal and the SCSSM to break out early and advancing the timing of northward shift of the rain belt.