A new understanding of the causes of future change in El Niño teleconnection

Abstract

Understanding and elucidating future changes in El Niño teleconnection is crucial because of the influence of El Niño on the globe via teleconnection. Existing climate models have consistently projected an eastward and poleward shift in El Niño teleconnection in the future, but the causes and dynamical processes of this shift have been poorly explained. Particularly, no study has examined the characteristic changes in the barotropic Rossby waves that form the teleconnection. This study investigates dynamic processes by analyzing the wavelength of the Rossby waves through spectral analysis, measuring the distance between circulation anomalies, and exploring the dispersion relationship of the barotropic Rossby waves. The results revealed that the wavelength of waves forming the teleconnection is expected to increase in warmer climate with an increase in the proportion of zonal-wavenumber-2 wave. Because changes in the mean state, including the strengthening of the westerly in the high-emission scenario, alter the frequencies of waves according to their zonal wavenumbers, this process is more notably manifested in the Southern Hemisphere, where the inter-model spread of the mean state is smaller, than in the Northern Hemisphere. Consequently, this will result in a shift in the position of El Niño's influence on the high latitudes of both Hemispheres. Specifically, in the Southern Hemisphere, it is anticipated that ocean warming in the seas in front of West Antartica and moisture transport towards Antarctica, induced by El Niño, will shift eastward in the high-emission scenario compared to its conventional position.