Abstract:The two main periodic oscillations of ENSO are identified using the method of SSA(singular spectrum analysis).Then by use of NCEP/NCAR reanalysis data and wind stress data,the linear and nonlinear responses of spatial fields to the two main components of Nino3.4 index are investigated in terms of the method of spatially symmetric and asymmetric components.Results show that the linear response of spatial fields determines their phase relations with ENSO,and the nonlinear response the spatially asymmetries of the fields.Their joint effects of linear response A(1) and nonlinear response A(2) fall into 4 collocation cases.The spatial oscillation in areas where A(1)>0,A(2)>0(case 1)and A(1)>0,A(2)<0(case 2)is in phase with ENSO,while the oscillation in areas A(1)<0,A(2)>0(case 4)and A(1)<0,A(2)<0(casse 3)is out of phase with ENSO.In the warm episode of ENSO,the oscillation of composite field is enhanced in areas where A(1)>0,A(2)>0(case 1)and A(1)<0,A(2)<0(case 3),and weakened in areas where A(1)>0,A(2)<0(case 2)and A(1)<0,A(2)>0(case 4).The maximum spatial asymmetry area is always close to the maximum linear response area.The maximum asymmetry for SLP lies in the Southern Pacific where A(1)>0,A(2)>0(case 1)and A(1)<0,A(2)>0(case 4);for SSTA in the equatorial East Pacific where A(1)>0,A(2)>0(case 1);forτx in the equatorial west-central Pacific where A(1)>0,A(2)>0(case 1);forτy in the equatorial north and south sides of the central Pacific where A(1)<0,A(2)<0(case 3)and A(1)>0,A(2)>0(case 1).Those distributive characters enable the oscillation in major anomalous areas to be stronger when ENSO is in a warm episode,thus favorable for the formation of ENSO warm event.This accords with the phenomenon that the ENSO warm events in the recent 38 years are generally stronger than normal.