Tele-connected rainfall extremes over West and East Asia in April 2024 tied to Indian Ocean heating

Record-breaking rainfall occurred coherently over subtropical West Asia (WA) and East Asia (EA) in April 2024, causing catastrophic damages around the Persian Gulf and South China. Strong barotropic cyclones are directly responsible for the long-lasting extreme rainfall over WA and EA. Based on observational analyses and numerical simulations by a linear baroclinic model (LBM), here we show evidences that these two rainfall extremes are tele-connected and are tied to the record-breaking latent heat release over tropical Indian Ocean (TIO). The record-breaking latent heat release over TIO triggers a stationary Rossby wave train propagating northward, with a barotropic anticyclone over Northern Indian Ocean and a barotropic cyclone over WA, leading to extreme WA rainfall. The intense latent heat release associated with the extreme rainfall over WA triggers another stationary Rossby wave train along the Asian subtropical jet (ASJ), with a wavelength of about 50~55 degrees in longitude. This wave train anchors a downstream barotropic cyclone anomaly on the eastern periphery of Tibetan Plateau with southerly flow from South China Sea to Eastern China, in favor of excessive rainfall over the EA region.

The above mechanism not only explains why rainfall extremes in WA and EA are located at a same latitude (20°-30°N) along the ASJ, but also clarifies why the intense rainfall over WA and EA occurred in April 2024 rather than other seasons. Spring 2024 was associated with a rapid decay of an El Niño event, and convection over TIO was suppressed by descending branch of Walker circulation before April. Along with the decay of warm SST anomaly over equatorial Pacific, TIO became warmer than Pacific in April, giving rise to intense convection over TIO which triggered the stationary Rossby waves. Although record-strong latent heating anomaly over TIO persisted from April into May in 2024, the substantially northward shifted ASJ in May cannot anchor the stationary Rossby waves in response to TIO heating, since subtropical circulation response to tropical heating is strongly dependent on the basic state flow. This work highlights the importance of both basic state and tropical heating anomaly in shaping tele-connected Asian climate extremes during the decaying phase of El Niño.

 

References: He C, Kucharski F (2025) Tele-connected rainfall extremes over West and East Asia in April 2024 tied to Indian Ocean heating. Accepted by Clim Dynam.