On the Thermodynamic Preconditioning of Arctic Air Masses and the Role of Tropopause Polar Vortices for Cold Air Outbreaks From Fram Strait

Abstract

AbstractFram Strait is a hot spot of Arctic cold air outbreaks (CAOs), which typically occur within the northerly flow associated with a strong low tropospheric east‐west pressure gradient between Svalbard and Greenland. This study investigates the processes in the inner Arctic that thermodynamically precondition air masses associated with CAOs south of Fram Strait where they lead to negative potential temperature anomalies often in excess of 15 K. Kinematic backward trajectories from Fram Strait are used to quantify the Arctic residence time and to analyze the thermodynamic evolution of these air masses. Additionally, the study explores the importance of cyclonic tropopause polar vortices (TPVs) for CAO formation south of Fram Strait. Results from a detailed case study and the climatological analysis of the 100 most intense CAOs from Fram Strait in the ERA‐Interim period reveal that (i) air masses that cause CAOs (CAO air masses) reside longer in the inner Arctic compared to those that do not (NO‐CAO air masses), and they originate from climatologically colder regions; (ii) the 10‐day accumulated cooling is very similar for CAO and NO‐CAO air masses indicating that the transport history and northerly origin of the air masses is more decisive for the formation of an intense negative temperature anomaly south of Fram Strait than an enhanced inner Arctic diabatic cooling; (iii) 40% (29%) of the top 40 (100) CAOs are related to a TPV in the vicinity of Fram Strait; (iv) TPVs confine anomalously cold air masses within their associated low tropospheric cold dome leading to enhanced accumulated radiative cooling.