A Global Quantification of the Physical Processes Leading to Near-Surface Cold Extremes

Kinematic backward trajectories are used to globally quantify the contributions of temperature advection, adiabatic compression and diabatic processes to near-surface temperature anomalies (hereafter T ') during the coldest day of each year (TN1day events) based on ERA5. Diabatic cooling dominates TN1day anomalies in the climatologically coldest regions, while advection forms TN1day anomalies over most ocean regions. Over most extratropical land masses, TN1day anomalies arise from a combination of both processes. The mean age and formation distance of TN1day anomalies vary strongly in space, from one to 8 days, and 500-5,500 km, respectively. Five distinct types of TN1day events are identified from these physical and spatio-temporal characteristics, and their geographical occurrence is investigated. Furthermore, advective, adiabatic and diabatic contributions typically cancel each other partially, but less so for the most intense TN1day events, which occur when the atmosphere's ability to dampen near-surface temperature anomalies is limited.

Automated summary

Kinematic backward trajectories are used to globally quantify the contributions of different processes to near-surface temperature anomalies. Diabatic cooling dominates in the coldest regions, while advection is the main factor in most ocean areas. TN1day anomalies over extratropical land masses arise from a combination of both processes. The mean age and formation distance of TN1day anomalies vary strongly in space. Five distinct types of TN1day events are identified based on physical and spatio-temporal characteristics.