The role of synoptic eddies on remote response of Eurasian atmosphere to the tropical forcing associated with 2021/2022 winter

Abstract

AbstractIn this paper, the role of eddy feedback in the formation and excitation of stream function anomaly pattern over Eurasian atmosphere (SFA) during 2021/2022 December–February (DJF) season is examined in terms of a low‐order linear model with a synoptic eddy and low frequency (SELF) feedback empirical closure onto the empirical orthogonal function decomposition bases (EOF‐bases). The results show that the SFA can be produced roughly and the SELF feedback plays important role in shaping the SFA during 2021/2022 DJF over Eurasian atmosphere. The SFA can be produced roughly owing to the internal action of the linear dynamical system. However, the importance of the external forcing on the formation of SFA depends on the role of the eddy feedback to a different degree. For the North Atlantic oscillation (NAO)‐like pattern with the wave train at high latitudes, the external forcing in the tropical Atlantic contributes greater with eddy feedback. While for the wave train at lower latitudes, the forcing will have little influence with the increase of the SELF feedback. A set of experiments with isolated forcing show that the forcing over tropical Atlantic Ocean can induce the wave train patterns alike the SFA, but the forcing to the east over South Asian to western Indian Ocean also contributes for shaping the SFA, especially the anomalous cyclone over Tibetan Plateau (TP). The combined effects of the response to both the tropical Atlantic Ocean and the eastern forcing over South Asian to western Indian Ocean contributes much to the formation of the two wave trains over Eurasia, thereby a negative stream function centre over TP, which might be the main cause for the excessive DJF rainfall over South China during 2021/2022. The diagnosis of the role of synoptic eddy on the atmospheric response to the external forcing for specific events can be helpful for understanding the causes for the formation of extreme climate events deeply.