Major cause of unprecedented Arctic warming inJanuary 2016: Critical role of an Atlantic windstorm

Abstract

Vertical structure of Arctic warming during winter is essentially bottom-heavy. A number of studies have suggested that this is largely due to the enhanced upward turbulent heat fluxes under sea ice loss. Recently, an alternative physical mechanism has been proposed that the synoptically driven moisture intrusion from the lower latitudes is responsible for the bottom-heavy warming profile. In January 2016, the Arctic experienced an unprecedented jump of air temperature. During this event, strong warm and moist air intrusion were observed, as well as the loss of sea ice in the Barents and Kara Seas, providing an invaluable opportunity to examine the relative importance of individual factors for the extreme Arctic warming. Observational analyses reveal that this extreme warming was mainly caused by the entry of a strong Atlantic windstorm into the Arctic, which brought about the enormous intrusion of moist and warm air masses into the Arctic. Numerical experiments show that the warming effect of sea ice loss and associated upward turbulent heat fluxes is relatively minor in this event. This suggests the importance of the synoptically driven warm and moist air intrusion into the Arctic as an essential mechanism for extreme Arctic warming.