Changes in Regional Extreme Cold Events over Northern China and Their Circulation Associations Under Arctic Amplification

In recent decades, rapid Arctic warming has intensified Arctic amplification (AA), and its potential impacts on mid-latitude extreme weather events have received increasing attention. Using meteorological station observations and reanalysis datasets from 1979 to 2024, this study investigates the variations of regional extreme cold events (RECEs) over Northern China and their associated circulation characteristics under different Arctic amplification periods. The Arctic amplification index (AAI850), Siberian High Index (SHI), Ural Ridge Index (URI), and multi-scale atmospheric circulation fields are employed to examine the relationships between Arctic thermal conditions and Eurasian atmospheric circulation anomalies. The results show that: (1) During the study period, AAI850 showed a significant upward trend, while the frequency of RECEs in northern China decreased significantly. At the same time, the cold intensity of the event minimum temperature and the composite intensity of RECEs were significantly enhanced, reflecting a shift from a high-frequency/weak-anomaly mode to a low-frequency/high-intensity mode. (2) In the later Arctic amplification period, the distribution of RECEs shifted toward lower minimum temperatures, the event center moved northward, and the duration structure changed modestly, while the affected area showed no significant change. These findings indicate that the intensification of RECEs is mainly associated with enhanced cold-anomaly intensity, rather than prolonged duration or expanded spatial coverage. (3) AAI850 shows significant correlations with Siberian High and Ural ridge anomalies, suggesting a close association between Arctic amplification and high-latitude circulation anomalies in Eurasia. (4) The circulation analysis reveals widespread increases in 500 hPa geopotential height over the Arctic and Eurasia, regional differences in sea-level pressure changes, and warmer conditions at 850 hPa during the later Arctic amplification period. Nevertheless, northwesterly or northerly wind components persist over parts of northern China, suggesting that southward cold-air transport remains possible despite the warmer thermal background.