Propagation pathways of Indo-Pacific rainfall extremes and their connection to the large-scale circulation

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.

Here, by using unsupervised machine learning tools, we illustrate how these extremes travel within the region on three distinct propagation pathways: north-eastward, eastward-blocked, and quasi-stationary. The Pacific sea surface temperatures modulate the propagation - with El Ni\~no-like (La Ni\~na-like) conditions favoring quasi-stationary (eastward-blocked) modes [1].

We additionally show that these rainfall extremes are also influencing the variability of heavy rainfalls on large spatial scales between North India and the Sahel zone, modulated by the tropical easterly jet (TEJ). Our analysis suggests that the BSISO fuels this connection, further reinforced by La Ni\~na-like conditions in the tropical Pacific.

[1] Strnad, F.M., Schlör, J., Geen, R., Boers, N. and Goswami, B.; Propagation pathways of Indo-Pacific rainfall extremes are modulated by Pacific sea surface temperatures. Nat Commun 14, 5708 (2023). https://doi.org/10.1038/s41467-023-41400-9