The role of atmosphere climate basic state in the formation of westerly over the equatorial Pacific

The relationship between atmosphere climate basic state and westerly wind anomalies over the equatorial western Pacific is studied by using composite method during 8 El Niño year since 1961.It is found that the western wind anomaly over equatorial western Pacific shows clear seasonal variability similar to that in the atmosphere climate basic state.These characteristics of seasonal variation are successfully simulated with a simple equatorial ocean-atmosphere coupled model.The model results show that the atmosphere basic climate state is very important for generation of western wind anomaly over the equatorial western Pacific.Atmosphere basic climate state effects on the western wind anomaly over the equatorial western Pacific through the heating in the atmosphere model.The effects of SSTA and atmosphere climate basic state on the heating in the atmosphere model vary with the phase of ENSO cycle and geographical location.In the beginning of EN50 cycle,the atmosphere climate basic state plays an important role in forming heating field in the atmosphere model over the equatorial Pacific.During the developing or mature phase of ENSO cycle,the SSTA plays a more important role in forming heating field in the atmosphere model over the mid-eastern equatorial Pacific.Sensitive test of the coupled model to atmosphere climate basic state was made.It shows that the propagating characteristics of westerly wind anomaly along the equatorial Pacific close to the observations.