Impacts of two types of El Niño events on high-latitude near-surface temperature during winter: Differences and underlying mechanisms

Based on ERA5 reanalysis data and monthly atmospheric circulation indices provided by the Climate Prediction Center (CPC), this study employs composite analysis and dynamical diagnosis methods to comparatively analyze the impacts of Eastern Pacific (EP) and Central Pacific (CP) El Niño events on winter near-surface temperature in high-latitude regions and their underlying physical mechanisms. Results show that the two types of El Niño events influence high-latitude near-surface temperature by triggering different teleconnection wave trains: EP El Niño primarily induces warming over Canada through a positive-phase Pacific-North American (PNA) teleconnection but has weaker effects on the polar region. CP El Niño, in contrast, triggers a negative-phase North Atlantic Oscillation (NAO), leading to warming over Greenland and cooling in the Arctic. In both cases, near-surface temperature anomalies are predominantly driven by temperature advection processes. Further analysis reveals distinct wave propagation mechanisms. During EP El Niño events, robust waves triggered in the central-eastern equatorial Pacific propagate zonally to the North Pacific, forming a classic PNA wave train along the westerly waveguide. CP El Niño events generate weaker waves in the eastern tropical Pacific that cannot penetrate the North Pacific but instead propagate meridionally into the Atlantic, where they amplify under the influence of negative Potential Vorticity (PV) gradients, forming a negative-phase NAO-like response. Notably, CP El Niño is accompanied by pronounced Sea Surface Temperature (SST) anomalies in the subtropical Atlantic. These SST anomalies reinforce the negative NAO phase via transient eddy vorticity feedback, sustaining the anomalous circulation. This study enriches the understanding of how El Niño diversity modulates high-latitude climate variability and provides a theoretical framework for improving seasonal-to-interannual climate predictions in polar regions.