两类El Ni?o事件对我国西南地区冬季降水的影响

采用1960~2014年西南地区93个站的逐月降水资料以及NCEP/NCAR再分析月平均资料，分析了东部型El Ni?o（EP El Ni?o）和中部型El Ni?o（CP El Ni?o）对我国西南地区冬季降水的不同影响。结果表明，EP ElNi?o年冬季和CP El Ni?o事件中1994/1995年、2002/2003年冬季，我国西南地区受异常偏东风影响，获得来自孟加拉湾和南海的水汽供应。同时，西南地区存在明显的幅合上升运动，上升运动异常增强，对流加强，导致西南地区冬季降水偏多；而CP El Ni?o事件中1968/1969年、1977/1978年，2004/2005年、2009/2010年冬季，我国西南地区受异常西北风影响，来自孟加拉湾和南海的水汽减少。同时，西南地区存在明显的幅散下沉运动，上升运动异常减弱，对流减弱，导致西南地区冬季降水偏少。

Impacts of Two Types of El Niño Events on Winter Precipitation in Southwest China

The present study analyzes different effects of EP El Niño and CP El Niño on winter precipitation in Southwest China using monthly precipitation data collected at 93 stations in southwestern region of China and the NCEP/NCAR monthly reanalysis data. The results show that in the winters of EP El Niño years and the two winters (i.e., 1994/1995 and 2002/2003) of CP El Niño years, the southwestern region of China was affected by abnormal easterly winds with water vapor supply coming from the Bay of Bengal and the South China Sea. At the same time, obvious convergence and ascending motion occurred in Southwest China and the updraft was abnormally strong, leading to severe convection and higher than normal winter precipitation in Southwest China. However, in the winters of CP El Niño years (i.e., 1968/1969, 1977/1978, 2004/2005, and 2009/2010), Southwest China was affected by abnormal northwesterly winds, and the water vapor supply from the Bay of Bengal and the South China Sea decreased. Meanwhile, significant divergence and descending motion developed in Southwest China, which suppressed the rising of airmass and weakened convection, leading to the decrease in precipitation in the winter in Southwest China.