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Recent changes in the leading modes of Madden–Julian oscillation convective activity
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DOI：10.1007/s00382-026-08337-3.png)
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Abstract
En 中文
A common approach to studying the Madden–Julian Oscillation (MJO) relies on indices derived from the first two leading empirical orthogonal function (EOF) modes, under the implicit assumption that these modes do not change over time. However, recent changes in the MJO characteristics imply the possibility of changes in the MJO leading modes, which have not received much attention. Here, we find that the leading EOF modes of MJO convection have, in fact, undergone significant changes since 1979. The changes manifest as a weakening of MJO variability over the tropical south Indian Ocean and a westward shift of the variability center over the southwestern Pacific. The westward shift of MJO variability over the western Pacific is closely associated with changes in the background circulation and moisture, which are attributed to the La Niña-like sea surface temperature changes. Meanwhile, the weakening of MJO variability over the southern Indian Ocean is attributed to the combined reductions in EOF-related moisture variability and vertical velocity variability. Specifically, the decline in moisture variability stems from weakened horizontal advection via eddy–eddy interactions and weakened vertical advection of background moisture driven by the intraseasonal vertical motion anomalies; meanwhile, the reduced vertical velocity variability is attributed to the decreased efficiency of atmospheric moistening via vertical advection. These findings indicate that the information carried by the MJO indices that are based on fixed EOF modes, as well as the associated climate impacts with the leading EOF modes, varies over time, suggesting that caution is warranted when employing EOF-based MJO indices to study the long-term trends of MJO activity and its response to climate change.
Keywords:
Madden–Julian oscillation
Empirical orthogonal function
MJO index
Climate change
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