The impact of the early summer Tasman Sea–Southern Ocean hybrid teleconnection pattern on middle summer rainfall in East Asia

A meridional dipolar atmospheric teleconnection between the Tasman Sea and the Southern Ocean, which describes a hybrid between the El Niño–Southern Oscillation, Indian Ocean Dipole and Southern Annular Mode, was referred to as the Hybrid Teleconnection (HT) pattern previously. We investigate its connection with East Asian summer rainfall and find the preceding May–June HT can be the precursor of the following July–August East Asian rainfall. The mechanism is examined based on analyses of observational datasets and historical runs of coupled models from phase 6 of the Coupled Model Intercomparison Project (CMIP6). The results suggest that a positive HT with positive 500 hPa geopotential height anomalies over the Tasman Sea but negative over the Southern Ocean in the preceding boreal early summer contributes to generating negative sea surface temperature (SST) anomalies in the western tropical Pacific (WP) by influencing surface heat exchange. The SST anomalies over WP persist into the mid-summer via the thermal memory of seawater, inducing interhemispheric meridional circulation and then exciting a Pacific-Japan-Pattern-like atmospheric circulation anomaly, which manifests as an anticyclone over the subtropical northwestern Pacific along with a cyclone near the Sea of Japan. This pattern induces intensified convergence and vertical ascend motion, and subsequently intensifies rainfall in the Yangtze River Basin.