Where Do Cold Air Outbreaks Occur, and How Have They Changed Over Time?

Cold air outbreaks (CAOs) occur in many regions of the globe and can be detrimental to the agricultural industry and human health, especially in less prepared regions. A systematic CAO classification was developed using two different climate reanalysis data sets from 1979–2018. Trends in CAOs were calculated for different regions across the globe and the results from each reanalysis data set compared with one another to identify discrepancies. CAOs occur more frequently in the Northern Hemisphere than the Southern Hemisphere with the highest number of CAOs in Europe, Central Eurasia, and North America. CAOs were found to have decreased in spatial extent, frequency, duration, and magnitude across much of the globe, particularly across Alaska, Canada, and the North Atlantic, while an increase in CAOs was observed in Eastern Europe, Central Eurasia, and the Southern Ocean. Early and late winter CAOs have also become much less frequent in most regions.