Influence of ENSO Event on Rainfall Anomaly over Yunnan Province and Its Neighboring Regions during Late Spring－Early Summer

Using the monthly gridded precipitation data in China, the NOAA extended reconstruction sea surface temperature (SST) data, and the NCEP/NCAR reanalysis data, the authors investigate the impact of the ENSO on the interannual variability of late spring－early summer rainfall in Yunnan Province and the relevant physical mechanism. The analysis of composite and correlation study reveal a strong negative correlation between the rainfall anomaly in Yunnan Province and the Niño index. An El Niño (La Niña) event is concurrent with less (more) precipitation during late spring－early summer (April－May) in Yunnan Province. Further analysis of atmospheric circulation demonstrates that an El Niño (La Niña) event is coincident with an anomalous easterly (westerly) over the Arabian Sea and the Bay of Bengal in the lower troposphere, a stronger anomalous anticyclone (cyclone) over the Bay of Bengal, as well as a stronger (weaker) subtropical anticyclone in the northwestern Pacific Ocean. The correlation between height at 200 hPa and rainfall anomaly during late spring-early summer (AprilñMay) in Yunnan Province reveals a relevant Indian Ocean－Asia teleconnection (IA) pattern. The water vapor transport indicates that during an El Niño (La Niña) event there is a stronger water vapor divergence (convergence) over the region. All above evidences demonstrate that, in comparison with the physical processes in controlling the interannual variation of the summer rainfall in southeastern China and the Yangtze River－Huaihe River valley, the conversion of Indian Ocean－Asia teleconnection pattern from winter to spring is dominant in determination of the rainfall anomaly in Yunnan Province during late spring－early summer, and particularly the increased water vapor transport associated with the intensification of the anomalous cyclone over the Bay of Bengal plays an important role.