Abstract This study investigates the synergistic effect of sea surface temperature (SST) and sea ice concentration (SIC) on the extended‐range predictability of the 2008 East Asian extreme cold event. Through integrated analysis of ERA5 reanalysis, ECMWF sub‐seasonal reforecasts, and OpenIFS sensitivity experiments, eastern North Atlantic SST anomalies and Barents‐Kara Seas SIC deficits are identified as critical predictability sources for East Asian cold events at extended‐range timescales, particularly during its maintenance phases following the initial cooling. Diagnoses from experiments show that suppressed SST and SIC anomalies first induce lower‐tropospheric temperature perturbations through diabatic heating and convection processes. The resultant thermal anomalies then propagate via convection and advection processes, enhancing meridional thermal gradients. Moreover, convergence of wave activity flux is a key factor for blocking enhancement. As suppressing SST and SIC anomalies, accelerated westerly winds induced by enhanced meridional temperature gradients and planetary wave activity flux divergence weaken the blocking system and the eventual occurrence of the East Asian cold event. Critically, co‐suppressing SST and SIC anomalies induce antagonistic effects, weakening their impacts on the event compared to single‐perturbation scenarios. The blocking region exhibits weaker geopotential height responses accompanied by branched westerly anomalies. In addition, a nonlinear wave bifurcation mechanism is observed, which splits Rossby wave energy into distinct northern and southern branches, thereby reducing blocking persistence through divergent wave energy propagation along competing pathways. These results highlight the importance of synergistic effects of SST and SIC anomalies in East Asian extreme cold event predictions over an extended range.
Sun et al. (Thu,) studied this question.
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