The Role of Cyclones in Moisture Transport into the Arctic

In this study, ERA5 reanalysis is used to quantify cyclone-induced moisture transport into the Arctic on a seasonal basis (1998-2018). Moist airstreams are spatially identified and temporally linked to individual cyclones (50-90 degrees N). Results show that cyclones account for 74% of the annual poleward flux across 70 degrees N. For these cyclone cases, which primarily emerge over the central Arctic in summer or otherwise originate from the North Atlantic, the amount of moisture transport is found to closely depend on track orientation and poleward propagation. Cyclone tracks oriented in the poleward direction along with coupling to an upper-level vortex which influences the steering flow are the most important characteristics that determine the moisture flux into the Arctic. Back trajectories highlight low-level moisture source regions over the Atlantic Gulf Stream throughout the year and over the high-latitude continental land surface during the warm season. Plain Language Summary In this study, moisture transport into the Arctic is quantified on a seasonal basis for a 20-year period (March 1998 to February 2018) using reanalysis data and a companion cyclone database. Our analysis focuses on individual cyclones (between 50 degrees N and 90 degrees N) and the poleward motion of their attendant moist airstreams, which are detected and quantified at 70 degrees N. Results show that cyclones account for nearly three-quarters of the average annual moisture transport into the Arctic. Cyclone track orientation, specifically a more poleward track, and upper-level steering flow were found to be key characteristics in cases with higher moisture transport amount. Under such scenarios, cyclones primarily develop over the coastal Arctic Seas in summer or otherwise enter the Arctic from the North Atlantic or high-latitude continental zones. Moisture transport source regions were also identified using trajectory calculations. The Atlantic Gulf Stream is highlighted as a potential source throughout the year, while continental evaporation becomes a potentially significant moisture source during the warmer months.