1979~2020年东亚季风的时空分布特征
Temporal and Spatial Distribution Characteristic of East Asian Monsoon from 1979 to 2020

为进一步分析东亚季风的时空分布特征，本文利用1979~2020年美国国家环境预报中心(NCEP)和欧洲气象资料中心(ERA5)的再分析资料，对比分析了东亚季风区的风场、水汽输送以及季风指数等特征，结果表明：1) 东亚季风的水平风场垂直结构是以经向风切变为主导的，因此东亚季风为经向型季风。东亚季风的水平风场有着明显的季节性转变，冬季盛行偏北气流，夏季盛行偏南气流。2) 东亚地区水汽输送特征也存在显著的季节性差异。夏季的水汽输送是以经向为主的湿平流；冬季风的水汽输送是以纬向为主的干冷平流。水汽输送的辐合辐散区随季节也有显著变化。3) 东亚夏季风和冬季风强度指数的年际变化都很大并且呈现减弱的趋势，夏季风存在准两年周期，冬季风存在准四年周期。4) NCEP和ERA5两类再分析资料所反映的东亚季风的特征基本一致。
In order to further analyze the temporal and spatial distribution characteristics of the East Asian monsoon, using the reanalysis data of the National Center for environmental prediction (NCEP) and the European Meteorological Data Center (ERA5) from 1979 to 2020, this paper compares and analyzes the characteristics of wind field, water vapor transport and monsoon index in the East Asian monsoon region. The results show that: 1) The vertical structure of the horizontal wind field of the East Asian monsoon is dominated by meridional wind shear, so the East Asian monsoon is a meridional monsoon. The horizontal wind field of the East Asian monsoon has obvious seasonal changes. The northerly air flow prevails in winter and the southerly air flow prevails in summer. 2) There are also significant seasonal differences in water vapor transport characteristics in East Asia. The water vapor transport in summer is mainly meridional wet advection, but dry and cold advection in zonal direction in winter. The convergence and divergence region of water vapor transport also changes significantly with seasons. 3) The interannual variation of East Asian summer monsoon and winter monsoon intensity index is large and shows a weakening trend. There is a quasi biennial cycle for summer monsoon and a quasi quadrennial cycle for winter monsoon. 4) The characteristics of East Asian monsoon reflected by NCEP and ERA5 reanalysis data are basically the same.