Impact, drivers and pathways of two Arctic atmospheric rivers in April 2020

Abstract. Atmospheric rivers (ARs) play a major role in transporting heat and moisture into the Arctic, yet their thermodynamic structure and regional impacts remain poorly understood. Here, we adopt a combined Eulerian-Lagrangian framework to investigate two intense ARs that penetrated into the central Arctic within one week in April 2020, providing a comprehensive view of their large-scale dynamics, moisture sources, and thermodynamic evolution.

The first AR entered the Arctic via the Siberian sector, driven by a highly anomalous quasi-stationary anticyclone over north-central Siberia. The second followed an Atlantic pathway and was associated with an unusually deep and persistent cyclone over Baffin Bay. Despite their distinct origins and pathways, both events produced extreme surface impacts, including widespread warming across Eurasia exceeding 9 °C over a 7-day period and intense precipitation along the Greenland coast and in the central Arctic. The events coincided with a notable decline in sea ice extent in the Barents-Kara Sea and along eastern Greenland, that is highly correlated with the AR-induced warming and rainfall.

Backward trajectory analysis of air parcels associated with extreme Arctic precipitation reveals distinct pathways and thermodynamic evolution. One group of parcels associated with overall cooling and increases in potential temperature exhibits classic AR characteristics: warm, moist, low-pressure airmasses that ascended upon arrival and released intense precipitation. Moisture sources however differed by pathway: the Atlantic AR drew from the warm Gulf Stream region, while the Siberian AR was fed by continental Eurasia. These findings highlight the diverse origins and mechanisms of ARs and their capacity to drive rapid Arctic climate and cryospheric changes.