Tropical ocean temperatures alone did not reproduce the atmospheric pattern behind South China’s exceptional April–May 2024 rainfall. A peer-reviewed observational and modelling study identifies a role for the polar-front jet in steering distant waves toward Northeast Asia. Those circulation changes helped moisture accumulate over southern China, although the proposed mechanism centres on one major event.
A peer-reviewed analysis investigated South China’s exceptional rainfall in April and May 2024. Large parts of Guangxi and Guangdong, two southern Chinese regions, received more than twice their 1991–2020 average. The total was the highest April–May value in a comparison beginning in 1979. Repeated heavy episodes accumulated into the seasonal rainfall total rather than one brief downpour.[1]
An anomalous high-pressure circulation over the tropical western North Pacific strengthened moisture supply from the southwest. Another over Northeast Asia restricted its escape northward. Moisture consequently accumulated between these features over South China. Indian Ocean warmth was associated with the first feature. Tropical Atlantic influences travelled across Eurasia as atmospheric waves.[1]
Numerical experiments needed a polar-front jet anomaly as well as tropical heating to reproduce the required circulation over Northeast Asia. The jet, a fast-flowing current in the upper atmosphere, redirected the wave pathway. Retrospective forecasts underestimated rainfall when their jet structure was biased even though tropical ocean temperatures were captured. This mechanism concerns one event before the South China Sea summer monsoon began; tests across other events are needed to establish its wider applicability.[1]
