24th Pacific Science Congress (PSC-24)

From mid-June to mid-July, cold air surges southward from high latitudes and prevents the East Asian summer monsoon from advancing northward, generating a quasi-stationary front from central-east China to Japan, known as Meiyu-Baiu rainfall. An extreme event occurred in 2020, bringing record-breaking precipitation and severe floods that forced millions to relocate. Dynamical predictions failed to capture its severity, particularly the exceptionally heavy rainfall in July. Through analyses of observations and AGCM simulations, we find that excessive East Siberian atmospheric blockings during the 2020 Meiyu season increased cold air outbreaks into the Meiyu region, halted the front's northward advance, and enhanced its intensity. The frequent East Siberian blockings are attributed to earlier melting of Arctic sea-ice along the Siberian coast. The combined effect of Arctic sea-ice loss and tropical Indian Ocean warming explains the extremely heavy Meiyu in July 2020. Following this finding, we analyzed their combined effect in large ensemble and built a statistical prediction model for extremely heavy Meiyu, demonstrating Arctic sea-ice's potential contribution to Meiyu seasonal prediction.

Arctic,Meiyu,Summer monsoon