| Popis: |
To quantify the relative contributions of Arctic sea ice and unforced atmospheric internal variability to “warm Arctic, cold East Asia” (WACE), this study analyses three sets of large-ensemble simulations carried out by the Norwegian Earth System Model with a coupled atmosphere-land surface model, forced by seasonal sea ice conditions from preindustrial, present-day, and future periods. Each ensemble-member within the same set uses the same forcing but with small perturbations to the atmospheric initial state. Hence, the difference between the present-day (or future) ensemble-mean and the preindustrial ensemble-mean provides the ice-loss-induced response, while the difference of the individual members within the present-day (or future) set is the effect of atmospheric internal variability.Results indicate that both present-day and future sea ice loss can force a negative phase of the Arctic Oscillation with a WACE pattern in winter. The magnitude of ice-induced Arctic warming is over four times larger than the ice-induced East Asian cooling, the latter with a magnitude that is about 30% of the observed cooling. Sea ice loss contributes about 60% (80%) of Arctic winter warming for the present-day (future) climate. Atmospheric internal variability can also induce a WACE pattern with comparable magnitudes between Arctic and East Asia. Ice-loss-induced East Asian cooling can easily be masked by atmospheric internal variability effects because random atmospheric internal variability may induce warming with larger magnitude. Observed WACE pattern occurs as a result of both Arctic sea ice loss and atmospheric internal variability, with the former dominating Arctic warming and the latter dominating East Asian cooling. |
