Contrasting Impacts of Three Types of ENSO Event on Boreal Autumn Rainfall over Southwest China

摘要

The autumn precipitation over southwest China is one of the main causes of meteorological disasters. Using observed monthly station rainfall data and HadISST and NCEP/NCAR analysis data, the impacts of three types of El Ni &#241 o-Southern Oscillation (ENSO) events on the boreal autumn rainfall over southwest China were determined. Over southwest China, autumn rainfall constitutes > 20% of the total annual rainfall and a marked decline in autumn rainfall commenced around 1990. During La Ni &#241 a events, there is surplus (deficit) over the middle (northwest and southeast) of southwest China. In cnetral Pacific (CP) El Ni &#241 o events, the autumn rainfall anomaly shows a deficiency over China. The large-scale atmospheric circulation anomalies in the three ENSO categories also exhibit distinct characteristics. During CP El Ni &#241 o autumns, the pressure anomaly over the North Pacific Ocean displays a “ ” structure, with a high-pressure anomaly over the Asian continent. An anomalous cyclone appears over the western North Pacific (WNP). In EP El Ni &#241 o autumns, the pressure anomaly over the North Pacific Ocean has a “ ” structure, with a low-pressure anomaly over the Asian continent. An anomalous anticyclone appears over the WNP and the 500-hPa anomalies are opposite to those of CP El Ni &#241 o events. During La Ni &#241 a autumns, the characteristics of circulation present the opposite structure to those of CP El Ni &#241 o events. This work is of certain significance for an in-depth understanding of the impacts of ENSO on the autumn precipitation over southwest China.