Nonlinear joint effect of Arctic atmosphere and sea ice on subseasonal prediction of strong and persistent Ural blocking events

Abstract Subseasonal prediction of extreme weather is an important but challenging task. It depends on both initial and boundary conditions. Using a conditional nonlinear optimal perturbation method, we examine the nonlinear joint effect of Arctic atmosphere initial perturbations and sea ice boundary perturbations on subseasonal prediction of Ural blocking. The influences of sea ice and atmosphere are highly nonlinear and non‐additive. The coordinated effects of sea ice and atmosphere can exert stronger influence than the individual perturbations or their linear summation. Our results also reveal the sea ice perturbations in the Barents and Okhotsk Seas, along with atmospheric perturbations over the North Atlantic and Bering Strait, are most critical. Further diagnosis shows that the nonlinear joint effects influence the air–sea heat transfer there, and enhance zonal wind through a temperature gradient, thereby affecting energy transport and weakening the Ural blocking. The above results provide theoretical insights into potential predictability improvement of subseasonal prediction of midlatitude extreme events.