Impacts Of Two Types Of El Nino On The East Asian Circulation Interannual Variability

In this study, two types of El Nino events are classified based on spatial patterns of the sea surface temperature anomaly(SSTA). One is the east Pacific (EP) El Nino, which can be regarded as conventional El Nino, and is characterized by relatively large SSTA in Nino-3 region (5°S-5°N,150°-90°W). The other one is central Pacific El Nino, which can be also called warm pool El Nino, El Nino Modoki, its SSTA mostly is confined near date line(5°S-5°N,160°E-150°W). The main conclusions of this paper are derived as follows:(1) Two types of El Nino are separately classified based on their peaks of SST index are in winter or not(CP El Nino is diveded into three parts:autumn, winter and spring). Spatial patterns and evolution processes of SSTA, outgoing longwave radiation and circulation are distinctively different according to the season which their peak belong to. For EP El Nino, when the peak is in winter, its SSTA in tropical Pacific is stronger, at the same time, the tropical Indian Ocean SSTA thansformation from IOD to basin-wide pattern is more obvious. Spatial pattern and evolution process of anomalous OLR is basicly agreed with SSTA viration in tropical ocean. Furthemore, anomalous westerly wind and PSAC over the equatorial region is more clear. However, it is more complicated for CP El Nino, especially when the peak is in the developing fall.Not only the tropical central Pacific SSTA is strongest, the SSTA in the central of tropical Indian Ocean is also clear.(2) According to the wave active flux, the Rossby wave energy propagation of EP El Nino in winter mid-high lattitude is more apparent than CP El Nino, especially over the Pacific region. In summer, no matter EP or CP El Nino, they are both weaker than in winter. The strong areas of Rossby wave dispersion are mainly distributed near the westerlies, and they are also more apparent in EP El Nino than in CP El Nino.(3) Composite analysis of NAO index in two kinds of El Nino years seperately from November to September indicates that EP(CP)-NAO index is positive(negtive) in December(more obvious) and February; EP(CP)-NAO index is negtive(positive) in May, July(most obvious) and September.(4) We use AM2.I atmospheric model developed by GFDL to simulate the atmospheric circulations of EP and CP El Nino. The model results are basically in accordance with the reanalysis data. These results suggest that the atmospheric response to the diabatic heating associated with two kinds of El Nino can explain well observed differences in circulation.