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.