Effect of ENSO on the Autumn Rainfall Anomaly in Northwest China
ENSO对中国西北地区秋季异常降水的影响

Based on the SVD method, the effect of ENSO on the autumn rainfall anomaly in northwest China were analyzed by using the data from the preiod 1960-1994. Crossed-correlation between the time coefficient of sea surface temperature in SVD and the geopotential height at 500 hPa and the sea level pressure were used to study the circulation features that cause the rainfall anomaly in an El Nio/La Nia year. The results show that good correlation really exists between the SSTA in east equatorial Pacific and the autumn rainfall anomaly in northwest China. In the year of El Ni o, northwest China is dry in autumn, where the rainfed area, the middle east Gansu, the southern Ningxia and the northern Shaanxi is the significant dry region. The circulation features of geopotential height at 500 hPa are that the PNA pattern appears, the strong anomaly centers are located in low latitudes, the west Pacific subtropical high is intensified and extends westward and its ridge line moves southward; the winter prevailing 1-wave flow pattern is abnormaly developed in autumn, Xinjiang ridge is intensified, East Asia trough is also intensified and moves westward. At the sea-surface pressure level, the stronger anomaly centers are located in high latitudes, the Ural high is strengthened, the Aleutian low is enhanced. The case of the La Nia year is opposite.