The two responses of the EastAsian atmospheric circulation in early summer to the preceding El NiNo event and their influence on the rainfall over China.

Using the monthly mean geopotential height, wind vector at 850 hPa and 500 hPa of the NCEP/NCAR reanalysis data, the sea surface temperature (SST) of the CPC and the Community Atmosphere Model V3.0, we examined the impact of the preceding El NiNo event on the East Asian circulation. The results are: (1) The climate simulations show that there are two kinds of major impact of El NiNo in the mature phase on the atmospheric circulation over East Asia in next early summer. The two ways of the impacts are embodied in the development of the low level anticyclonic circulation around the Philippines and the active midlevel OkhotskJapan wavetrainlike pattern (OKJ pattern) that accompanies the development of the Okhotsk High. The latter one has been more easily simulated by the climate model. Both the two kinds of anomalous circulation were observed from the reanalysis data. The positive rainfall in the southern part of China with the two anomalous circulation patterns in next June was also simulated after the positive SST anomaly in the Nino3 region was added in autumn, which indicates a delayed impact of El NiNo on the East Asian summer monsoon. The anomalous circulations resulted in the strong southerlies in the area to the south of the Yangtze River. On the other hand, the northward progress of the summer monsoon which is characterized by the movement of the subtropical high was significantly suppressed by the wide scope of scattering wave activity flux over the sea area from Japan to the dateline of North Pacific in the middle latitudes. This suggests that the delayed impact of the ENSO event is one of the major factors that cause the climate pattern of the flooding in the southern China and drought in the northern China. (2) The statistic analysis indicates that the more rainfall occurring in South China is strongly influenced by the development of the Okhotsk high and the anticyclone around the Philippines in early summer. Either of them can result in flooding in the southern China and vice versa. The Okhotsk high plays more and more important role in causing the southern flooding recently. The Okhotsk high, the rainfalls in the northern/southern China, the ENSO events and the anticyclone around Philippines have their respective decadal variabilities, which suggests their different responses to the global climate warming.