Decadal trend of synoptic temperature variability over the Northern Hemisphere in winter

Abstract

Abstract Synoptic temperature variability gives rise to cold waves and extreme cold events in winter. Based on four reanalysis datasets, this study investigates the decadal trend of synoptic temperature variability in boreal winter during the period from 1980 to 2019, with particular focus on the sharp drops in synoptic-scale temperature, which are associated with cold waves. The result shows that the synoptic-scale standard deviation of temperature decreases significantly with a trend of − 0.15K/decade (− 0.09 to − 0.21 K/decade among reanalysis datasets) over continental regions in mid to high latitudes. Correspondingly, the rapid cooling events (RCEs), defined based on the day-to-day temperature decrease exceeding 6 K, also shows a general decreasing trend in terms of its frequency and intensity, and the strongest decreasing trend occurs over the eastern North America (ENA) and western Eurasia (WE). The weakening of the RCEs is closely connected to the decreased trend of eddy kinetic energy (EKE), suggesting that the weakened transient eddy activities may have mitigated the synoptic-scale temperature variability and the associated RCEs over mid to high latitudes. This study highlights that the decreased synoptic temperature variability leads to fewer and weaker RCEs at synoptic scale over mid to high latitudes in winter, in addition to the warming trend of mean state.