Feedback processes responsible for El Nino-La Nina amplitude asymmetry

To analyze El Nino-La Nina asymmetry, Bjerknes Stability Index analysis applied separately for El Nino and La Nina events. The growth rate of the El Nino is larger than that of the La Nina. Their difference is mainly due to an increased positive dynamical feedback. The enhanced sensitivity of the ocean's dynamic response to wind stress in El Nino is a primary cause for the increase in the positive dynamical feedbacks and is originated from the nonlinear response of atmospheric pattern to sea surface temperature (SST) anomalies, in particular the eastward shift of maximum wind loading and the equator-confined wind patch during El Nino. The sensitivity of the wind intensity to SST anomalies is larger during El Nino; however, its impact is not greater than others. Difference in the negative feedbacks is mainly attributed to the damping by shortwave feedback, with the latent heat flux feedback being a secondary contributor.