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.

Based on CPC (Climate Prediction Center) daily precipitation data, NCEP/NCAR daily reanalysis data and NOAA outgoing longwave radiation data from May to August for the period 1981—2020, the characteristics of main modes of summer intra-seasonal precipitation anomalies in eastern China (named Southern type and Jiang-huai type precipitation anomalies) and the evolution features of associated atmospheric intra-seasonal oscillation (ISO) signals in tropical and mid-to-high latitudes are analyzed using EOF decomposition and lead-lag composite analysis. The causes of intra-seasonal precipitation anomalies are preliminarily discussed as well. The results show that: (1) The Southern type precipitation anomaly events are almost evenly distributed in early, middle and late summer, while the Jiang-huai type precipitation anomaly events mainly occur in middle summer. (2) In early summer, the Southern type precipitation anomalies are mainly presented as precipitation anomalies in the south of the Yangtze River, and in middle and late summer, while the precipitation anomalies in the north of the Yangtze River are also significant. (3) The Southern type precipitation anomaly events are affected by atmospheric ISO signals in the tropical and mid-to-high latitudes. The warm and moist air transport carried by the tropical atmospheric convection and the cold air activity accompanied by the propagation of the Rossby wave train in the mid-to-high latitudes generate water vapor convergence in the southern region, which is conducive to the development and maintenance of precipitation anomalies. In addition, atmospheric ISO signals in the tropical and mid-to-high latitudes are modified by intra-seasonal variations of sea surface temperature, subtropical high and jet stream. From early summer, mid-summer to late summer, the ISO source and propagation path of the tropical atmosphere have changed, and the propagation path and intensity of the Rossby wave train in the upper troposphere at mid-to-high latitudes are also different. (4) Reversed change of the middle and lower reaches of the Yangtze River and South China coast appears during Jiang-huai type precipitation anomaly events, accompanied by the east-west movement of the Western Pacific Subtropical High. The convective anomaly propagating northward and northwestward from the equatorial western Pacific Ocean and the intra-seasonal combined variation of the blocking highs over the Ural Mountains and the Sea of Okhotsk at mid-to-high latitudes are the main reasons for the formation of Jiang-huai type precipitation anomalies.