Marine Cold Air Outbreaks along the Gulf Stream and Kuroshio Current in a Warmer Climate

Marine Cold Air Outbreaks (MCAOs) along Western Boundary Currents trigger strong air–sea interactions at the entrance of storm tracks and act as a moisture source for extratropical cyclones. While MCAOs are expected to become less frequent and weaker in a warmer climate, the physical understanding of the driving processes behind these changes remains limited. Using Community Earth System Model version 2 simulations for present-day and future climates, we identify strong MCAO events and compute 7-day backward trajectories directly from climate model output to examine changes in the processes affecting MCAO air parcels. We find that future MCAOs weaken due to the expected increase in air temperature, and to changes in the cooling rates over regions, such as the Hudson Bay, projected to remain ice-free. However, despite the reduction in intensity, the moistening effect associated with MCAOs is expected to increase, with potential implications for the water cycle in the extratropics.