Anhui Normal University Wuhu 241000 China;
Division of Computational Science E-Institutes of Shanghai Jiaotong Universities Shanghai 200240 China;
Chinese Academy of Meteorological Sciences Beijing 100081 China;
LASG Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 China;
nonlinear; method of variational iteration; perturbation theory; El Ni(n)o-Southern Oscillation model;