A Climatology of Northern Hemisphere Cold Surge

Cold surges, or cold waves, are extreme weather events marked by abrupt drops in surface temperature and strong winds, making them some of the most impactful and concerning phenomena. Unlike cold air outbreaks, which are defined solely by sustained low temperatures, cold surges are characterized by both significant temperature drops and low temperatures. These events can severely disrupt societal activities, posing serious threats to human health, agricultural production, and economic stability. Despite their importance, there is no universally accepted definition of cold surges, and their tracks are often inferred indirectly, using proxies such as the movement of the Siberian High or air particle trajectories. In this study, we propose a unified definition of cold surges and introduce a novel method for their automatic identification and tracking. This algorithm detects cold surges and provides characteristics such as affected areas, duration, temperature drop, and temperature anomalies. Using this method, a Northern Hemisphere cold surge climatology is obtained.Based on the distribution of the frequency of affected areas, the entire Northern Hemisphere is divided into four regions: (1) Africa-Eurasia (AF-EA) ;(2) Pacific Ocean (PO);(3) North America (NA);(4) Atlantic Ocean (AtlO).The characteristics of cold surges in the Northern Hemisphere and these four regions are described. The frequency of cold surges in the Northern Hemisphere shows an increasing trend before 1970 and a decreasing trend after 1970, which is also observed in AF-EA, PO, NA, and AtlO. The duration shows a decreasing trend in the Northern Hemisphere and all four regions. The mean 24-hour temperature drop and the maximum 24-hour temperature show a slight negative (positive) trend in the Northern Hemisphere, AF-EA, and NA (AtlO). The mean and maximum temperature anomalies show a positive trend in the Northern Hemisphere, AF-EA, AtlO, and PO.