Synergistic effects of large-scale three-dimensional circulations in East Asian cold events: A case study of 2021/22

Different from previous studies that mainly focused on the influences of large-scale horizontal circulation on cold events, this paper used the three -type decomposition of the global atmospheric circulation (3P-DGAC), taking the winter of 2021/22 as an example, to investigate the synergistic effects of the local horizontal, meridional and zonal circulations in the cold events of East Asia (EA). We discovered that the large-scale horizontal circulations influencing the two cold events in November and December are typically characterized by a transverse trough turning to a vertical trough, with the northwest path of cold air source in November and the hyperpolar path in December. But for the two consecutive cold events in February, the horizontal circulations are characterized by unstable small trough development, corresponding to small cold air masses splitting southward. Besides, with the development of the trough and ridge system of horizontal circulation, the local clockwise meridional circulation anomalies in the mid -latitude EA are promoted. The strong surface north winds of the meridional circulation anomaly could promote the southward movement of Arctic cold air, leading to the cooling of EA. Due to the presence of updrafts in front of the trough behind the ridge and downdrafts behind the trough in front of the ridge, the local zonal circulation anomalies in northern EA may connect with the East Asian trough (EAT) and the Ural Blocking (UB), which further cause the formation and development of cold events. In addition to the horizontal circulation analyzed in previous studies, this study demonstrated that vertical circulations also played important roles in the outbreak of cold events. Large-scale three-dimensional (3D) circulations work synergistically to affect the accumulation and southward movement of cold air. Our application of 3P-DGAC provides a new idea to analyze the dynamic effects of 3D circulations influencing cold events.