More Frequent Atmospheric Rivers and Associated Precipitation Extremes Induced by the Baroclinic Annular Mode

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Abstract
Atmospheric rivers (ARs) play a crucial role in the global hydrological cycle, yet how the intrinsic midlatitude atmospheric variability modulates their activity on subseasonal timescales remains poorly understood. Here, we show that AR frequency and landfall in both hemispheres vary strongly with the strength and phase of the Baroclinic Annular Mode (BAM). During its positive phase, BAM increases AR occurrence by up to ∼50% and AR‐driven precipitation extremes by up to ∼40% relative to climatology. Stronger and more frequent ARs during the positive phase of the BAM are primarily driven by enhanced potential‐to‐kinetic energy conversion, which favors AR growth and intensification, particularly in the storm‐track regions. This response is consistent with dynamically enhanced poleward moisture transport due to a more baroclinically unstable and stormier environment. The results underscore the importance of BAM‐related intrinsic midlatitude storm‐track variability in modulating global AR activity and its potential to improve extended‐range AR prediction on subseasonal timescales.

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