Role of basic flow in influence of ENSO on winter circulation over the Northern Hemisphere
基本气流在ENSO对北半球冬季大气环流影响中的作用

Role of basic flow in the influence of the ENSO event on the winter circulation over the Northern Hemisphere is investigated from the observational facts, the theory and the numerical experiments in this paper. The difference between the basic flow during the onset of the ENSO event in the winter of 1972/1973 and that during the onset of the usual ENSO event is pointed out with analysis of observational data . In the winter of 1972 /1973 , since the westerly at high latitudes was stronger than the normal, the general circulation anomaly pattern over the Northern Hemisphere caused by the ENSO event was different from that due to the usual ENSO events. The circulation anomaly pattern over the Northern Hemisphere caused by usual ENSO events is of PNA pattern, a cooling winter used to be in the northeast of China and cooling surge frequently intrudes into China. However, in the winter of 1972/1973, the circulation anomaly pattern was not PNA pattern , a warming winter was in the northeast of China, the activities of cooling air were weak .