Response Characteristics of the East Asian Winter Monsoon to ENSO Events
The ENSO phenomenon, which is known to be the most prominent signal in air- sea interactions, plays an important role in the interannual variability of East Asian winter monsoon. In this paper, the responses of East Asian winter monsoon to ENSO events are analyzed using the composite method based on the Oceanic Ni(n)o Index (ONI) and NCEP/NCAR reanalysis data with classification of the winters from 1950 - 2005 into 5 categories of strong El Ni(n)o, strong La Ni(n)a, weak El Ni(n)o, weak La Ni(n)a and non-ENSO event The results show that response of the East Asian circulation in low latitudes to ENSO events has quasi-linear characteristics, i.e. response of the tropical atmosphere to the warm events is reverse to that of cold events, and that to weak ENSO events is similar to strong ENSO events except for weakened intensity. However, distribution of circulation anomalies in middle and high latitudes does not show obvious phase reversal for warm and cold ENSO events, indicating that response of the atmosphere to SST anomaly is complex. The signals of significant response of the extratropical atmosphere to strong El Ni(n)o events are represented mainly by enhancement of the westerly flow in middle and high latitudes in East A-sia, positive anomalous temperature in northern Asia, eastward extension of anomalous wind shear in the middle and lower reaches of the Yangtze River. The anomalous Philippine Sea anticyclone, working together with intensified trough in south branch of westerlies, is favorable for the southerly flow in the South China Sea and along the southeast coast of China. But, during the strong La Ni(n)a events, the ridge in the middle and lower reaches of the Yangtze River is not evident, and the southern part of China and the South China Sea are covered by northerly anomaly, with shrinked area that passes significance test Under weak El Ni(n)o events, the southwesterly flow in the northwest of the anticyclonic anomaly in the Philippine Sea is shifted eastward, and separated with southwesterly flow ahead of the trough in south branch of westerlies, resulting in the southerly anomaly in South China and the South China Sea less notable than that under strong El Ni(n)o events. It is very interesting to see anomalous systems in weak La Ni(n)a cases to be similar to those with strong El Ni(n)o but with inverse phase. As shown by scattered plots of ONI index and NTI index that represents warmth status in northern Asia, the NTI is positive in 8 out of 9 winters with strong El Ni(n)o and 1 out of 7 winters with weak El Ni(n)o, and negative in 4 out of 8 winters with strong La Ni(n)a and 11 out of 12 winters with weak La Ni(n)a, and there is no clear evidence that occurrences of extreme warm and cold winters in Asia are closely linked with ENSO events.
国家科技期刊平台
NSTL
万方数据
维普
