Changes in the impact of MJO-induced oceanic Kelvin waves on ENSO during 1981–2021

The Madden–Julian Oscillation (MJO) influences the El Niño–Southern Oscillation (ENSO) primarily by exciting intraseasonal oceanic Kelvin waves that modulate the central-eastern Pacific thermocline. Analysis over 1981–2021 reveals a regime shift around 1998, when the robust positive correlation between 10‑month‑lead MJO and ENSO weakens from 0.6 to 0.1 and becomes insignificant. Diagnostics reveal that during the post-1998 period, MJO wind and precipitation variations weaken, with eastward propagation stalling near the Dateline—a trend contrasting with projections of MJO intensification under global warming. This is attributable to changes in the mean states, particularly reduction in the mean-state atmospheric moistening efficiency per unit of apparent heating across the tropical Pacific. The mean-state changes are governed primarily by low-frequency climate modes, such as the Atlantic Multidecadal Oscillation and Interdecadal Pacific Oscillation, rather than global warming. Their phase changes around 1998 induce a La Niña‑like background, damping central‑Pacific MJO activities and diminishing the MJO’s influence on ENSO in recent decades. 马登-朱利安振荡 (MJO) 可通过激发海洋开尔文波影响厄尔尼诺-南方涛动 (ENSO) 的发生发展.基于再分析和观测资料以及MJO开尔文波指数, 本研究发现MJO与ENSO仅在1998年前存在显著正相关.这是由于1998年后热带太平洋温呈类La Niña型变化, 导致大气湿润效率降低, 进而造成MJO对流和风场减弱且东传停滞于日界线以东, 最终削弱了MJO对ENSO的影响.该基本态的变化可能是多年代际气候模态如大西洋多年代际振荡,太平洋年代际振荡等引起.