IMPACT OF ENSO ON THE PRECIPITATION OVER CHINA IN WINTER HALF-YEARS

Abstract:

In this paper, the impact of ENSO on the precipitation over China in the winter half-year is investigated diagnostically. The results show that positive precipitation anomalies with statistical significance appear over southern China in El Niño episodes, which are caused by the enhanced warm and humid southwesterlies along the East Asian coast in the lower troposphere. The enhanced southwesterlies transport more water vapor to southern China, and the convergence of water vapor over southern China increases the precipitable water and specific humidity. In La Niña episodes, although atmospheric elements change reversely, they are not statistically significant as those in El Niño periods. The possible physical mechanism of the different impact of ENSO cycle on the precipitation over southern China is investigated by analyzing the intraseasonal oscillations (ISOs) in El Niño and La Niña winter half-years, respectively. By comparing the characteristics of ISOs in El Niño and La Niña, a physical mechanism is proposed to explain the different responses of the precipitation over China to ENSO in the winter half-year. In El Niño episodes, over western North Pacific (WNP) and South China Sea (SCS) the ISOs are inactive and exert little effect on water vapor transport and convergence, inducing positive precipitation anomalies with statistical significance over southern China in El Niño episodes. In La Niña episodes, however, the ISOs are active, which weaken the interannual variation signals of ENSO over WNP and southern China and lead to the insignificance of the interannual signals related to ENSO. Therefore, the different responses of precipitation over China to ENSO in the winter half-year are possibly caused by the difference of intraseasonal oscillations over WNP and SCS between El Niño and La Niña.