南海夏季风强弱年东亚地表热力异常特征的合成研究

Composite Study of the Surface Thermal Anomaly over the East Asia in Strong and Weak SCS Summer Monsoon Years

利用NCAR/NCEP1948年1月-2002年12月共55 a 660个月的地表感热通量和地表潜热通量以及其它气象场的月平均再分析资料,计算了期间5-6月平均的南海夏季风湿位涡强度指数。由标准化的湿位涡强度指数距平的年际变化曲线,选择距平值大于0.5的年份为季风爆发的强年,距平值小于-0.5的年份为季风爆发的弱年,对强、弱年东亚及其周边地区的地表潜热通量(LHF)距平、地表感热通量(SHF)距平以及海平面气压(SLP)距平的分布特征进行了合成分析。结果表明,在南海夏季风爆发强年和弱年,其前期冬春季的地表潜热通量、感热通量以及海平面气压场的距平分布有很大不同,前冬的差别更为明显。冬季,LHF和SHF在强、弱年的主要差异在海洋上和近海地区,尤其是西太平洋沿岸,合成距平呈现沿海岸线的东北-西南向的带状分布,强年沿岸为正距平,弱年为负距平。LHF和SHF标准化距平叠加之和有同样的区域分布特征。这种强、弱年的距平分布差异,与低层风场在强、弱年的不同有密切关系,强年东亚冬季风偏强,弱年则反之。强、弱年SLP在前冬的距平差异,验证了上述结论。

The monthly-mean reanalysis data of NCEP/NCAR from January 1948 to December 2002, including the surface sensible heat flux （SHF）, the surface latent heat flux （LHF） and other meteorological fields are used to calculate the average values of intensity index of moist potential vorticity （MPV） of the South China Sea summer monsoon from May to June of these 55 years in this paper. From the standardized time series of the intensity index of MPV, the years with values larger than 0. 5 are defined as strong years of the monsoon, and the years with values less than -0. 5 as weak years. The composite analysis of the anomaly fields of SHF, LHF in these strong and weak years is conducted. The results show that the anomaly fields of SHF and LHF in the previous winters and springs of those strong and weak years are quite different, especially in the previous winters, during which the main differences of LHF and SHF between the strong and the weak years occur over and close to the ocean, particularly along the coastal areas of the Western Pacific. The composite anomalies show the banded distribution going through northeast to southwest along the coastline. The sum of the standardized anomalies of LHF and SHF has the similar distribution. The difference of the anomalies between the strong and the weak years is closely related to the difference in the low level wind fields. The distribution characters of anomaly fields of the sea level pressure in the previous winters support the above-mentioned conclusions.