Accelerated Arctic warming causes Eurasian cooling via nonlinear feedback of reduced synoptic eddy activities in winter

Abstract The Arctic has been experiencing an accelerated/amplified wintertime warming almost synchronously with a cooling in Eurasia during recent decades. Whether and how the warming can cause the Eurasian cooling remains under debate. By identifying daily Arctic warming events on different timescales, we investigate such a causality from a nonlinear perspective and propose a novel mechanism explaining the causality in which a cross-timescale dynamical feedback of daily weather disturbances referred to as synoptic eddies onto mean state is found to be critical. We find direct observational evidence that the Eurasian cooling not only in magnitude but in occurrence frequency is a response to those Arctic warming events with a 2-day lag. We further find that the Arctic warming causes a large reduction of synoptic eddy activities along around 60 o N which tend to produce a meridional dipole in geopotential height anomalies characterized by an equivalent barotropic anomalous low (high) and a lower-level cooling (warming) over Eurasia (the Arctic) via nonlinear eddy-to-mean flow feedback in terms of the QGPV dynamics. The eddy feedback-induced near-surface northeasterly anomalies enlarge the Eurasian cooling via increasing cold temperature advection.