Recent asymmetric tropical ocean warming has altered regional propagation of Madden-Julian Oscillation

Abstract

Tropical sea surface temperature warming displays distinct regional patterns, but its influence on Madden-Julian Oscillation propagation remains unclear. Here we investigate how a shift toward La Niña-like conditions around 1999 has affected Madden-Julian Oscillation propagation by comparing two periods: 1979–1998 and 2003–2022. Using satellite observations and reanalysis data, we show that propagation accelerated over the Indian Ocean and the Maritime Continent but slowed over the western Pacific in the later period. These contrasting responses are linked to changes in sea surface temperature patterns and associated atmospheric conditions. Over the Indian Ocean, enhanced low-level horizontal moisture gradients and increased upper-tropospheric stability facilitate propagation, while weakened moisture gradient and suppressed convection hinder it over the western Pacific. Despite complex terrain and atmospheric interactions over the Maritime Continent, background changes still favor enhanced propagation. These findings highlight the sensitivity of Madden-Julian Oscillation behavior to regional ocean–atmospheric conditions, with implications for improving subseasonal prediction.