The synergistic effect of the North Pacific and the North Tropical Atlantic sea surface temperature on winter–spring cold events in Eastern North America

Cold events occur in North America (NA) frequently, which pose a significant threat to extensive damage to traffic and agriculture. Research on cold events in NA has mainly focused on the individual impacts of the sea surface temperature (SST) variabilities in the North Pacific and the North Atlantic, with less analysis of their synergistic effect. Here we utilize observational data and numerical experiments to show that the positive North Pacific Victoria mode (VM) and the negative North Tropical Atlantic (NTA) SST exert significant synergistic effects on the winter–spring cold events in eastern NA via Rossby waves propagation. Specifically, the VM-related negative western North Pacific (WNP) SST anomalies are linked to upper-tropospheric wind convergence anomalies in situ, which excite a Rossby wave train from the WNP to the North Atlantic and thus strengthen the high-level negative geopotential height anomalies (GHAs) over eastern NA and the positive air-ocean feedback over the North Atlantic. As a result, the negative GHAs strengthened by the positive VM and negative NTA SST cause increased extreme cold events. Further results reveal that the negative GHAs and cold events in eastern NA during the co-occurrence of the positive VM and negative NTA SST events are more than three times stronger than those for the two kinds of single events. This study suggests that the synergistic effect of the positive VM and negative NTA SST anomalies could advance our comprehensive understanding of the combined effect of the inter-basin SST anomalies on the mid-to-high-latitude climate.