Feedback processes responsible for El Niño-La Niña amplitude asymmetry

To analyze El Niño-La Niña asymmetry, Bjerknes Stability Index analysis applied separately for El Niño and La Niña events. The growth rate of the El Niño is larger than that of the La Niña. 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 Niño 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 Niño. The sensitivity of the wind intensity to SST anomalies is larger during El Niño; 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. Key Points Larger El Niño is due to the larger ocean dynamic sensitivity to SST forcing Ocean response to SST is related to the nonlinearity of wind's pattern to SST Larger damping of El Niño is mainly due to shortwave feedback.