Record-breaking warm spell in December 2023 and the synergistic influences from the Siberian high and the polar front jet.

In December 2023, a super warm spell occurred in the North China Plain, setting a new daily maximum temperature record for all Decembers since 1961. By using station observed temperatures in China and NCEP/NCAR reanalysis datasets, this paper examines the extremity of the event. The peak temperature anomaly during the event exceeded 13 °C for the entire region mean and exceeded 22 °C for a single station, both of which have never been observed before. Further analyses indicated that the super warm spell event was not limited in a local area, but rather had a significant large-scale background, characterized by a remarkable dipole temperature anomaly spatial pattern in the Eurasian continent. Composite analyses revealed that one of the dominant circulation factors was the Siberian high. Prior to the occurrence of the historic warm spell days, the Siberian high was generally weaker than normal by 2–3 standard deviations. During this super warm spell event, the Siberian high was the fifth weakest in the research period. The composite results indicate that the weaker Siberian high weakened the local meridional pressure gradient and blocked the cold air from high latitudes. In addition to the Siberian high, the sea level pressure anomaly pattern in Asia, both in the composite and in 2023, also shows a typical dipole structure. The dipole structure weakens the large-scale meridional pressure gradient and maintains the zonal circulation in the Eurasian continent. This may be related to the anomalous polar front jet. In December 2023, the polar front jet was the strongest during the research period. A stronger polar front jet typically weakens the winter monsoon by promoting zonal circulations, resulting in higher temperatures across most of Asia. Thus, it can be inferred that the super warm spell in early December 2023 in the North China Plain was the result of a combination of the polar front jet and the Siberian high. • A record-breaking warm spell in Dec 2023 occurred under a large-scale dipole of temperature anomalies in Eurasia continent. • The common and individual general circulation characteristics are compared and diagnosed. • The strongest polar front jet and the fifth weakest Siberian high in December jointly contributed to the event. [ABSTRACT FROM AUTHOR]