Propagation pathways of Indo-Pacific rainfall extremes are modulated by Pacific sea surface temperatures

Intraseasonal variation of rainfall extremes within boreal summer in the Indo-Pacific region is driven by the Boreal Summer Intraseasonal Oscillation (BSISO), a quasi-periodic north-eastward movement of convective precipitation from the Indian Ocean to the Western Pacific. Predicting the spatiotemporal location of the BSISO is essential for subseasonal prediction of rainfall extremes but still remains a major challenge due to insufficient understanding of its propagation pathway. Here, using unsupervised machine learning, we characterize how rainfall extremes travel within the region and reveal three distinct propagation modes: north-eastward, eastward-blocked, and quasi-stationary. We show that Pacific sea surface temperatures modulate BSISO propagation - with El Nino-like (La Nina-like) conditions favoring quasi-stationary (eastward-blocked) modes-by changing the background moist static energy via local overturning circulations. Finally, we demonstrate the potential for early warning of rainfall extremes in the region up to four weeks in advance. The study reveals distinct extreme rainfall propagation modes driven by the Boreal Summer Intraseasonal Oscillation in the Indo-Pacific region. These are influenced by Pacific sea surface temperatures and offer the potential for early warnings.

Automated summary

This study characterizes the propagation modes of rainfall extremes in the Indo-Pacific region driven by the Boreal Summer Intraseasonal Oscillation. Pacific sea surface temperatures are found to modulate the propagation of the oscillation, influencing the occurrence of extreme rainfall. The study also demonstrates the potential for early warning of rainfall extremes in the region up to four weeks in advance.