Interannual Variability of Wintertime Marine Cold Air Outbreaks over the High-Latitude North Atlantic

Understanding the interannual variability of wintertime marine cold air outbreak (MCAO) frequency is essential, as these events play a key role in shaping air–sea interactions, driving deep ocean convection, and influencing regional climate variability. This study analyzes the two leading modes of the wintertime MCAO variability over the high latitudes of the North Atlantic on interannual timescale and their relation to large-scale teleconnection patterns and oceanic mixed layer depth (MLD). The first mode is a meridional dipole pattern, reflecting the out-of-phase variations of the MCAO frequency between the northwestern and the subtropical North Atlantic. It is strongly tied to the seasonal mean North Atlantic Oscillation/Arctic Oscillation and the associated zonal temperature advection at around 55°N from northeastern Canada towards the North Atlantic. The second mode is a zonal dipole pattern, reflecting the out-of-phase variations of the MCAO frequency between the Nordic Seas and the western North Atlantic. The mode is strongly tied to the Scandinavian pattern and the associated meridional temperature advection from the Arctic via Fram Strait. Though these associations are observed between the seasonal MCAO frequency and the seasonal mean teleconnection patterns, they also feature a good relationship on daily timescale. This establishes a bridge between the annual frequency of synoptic MCAO events and the seasonal mean circulation and teleconnections. Both modes are associated with significant heat loss from the ocean, lowering the SST. The positive phase of the EOF1 mode corresponds to a local deepening of the mixed layer over southern Greenland. In contrast, the positive phase of the EOF2 mode not only causes a deepening of the mixed layer in the Nordic Seas but also affects the depth of the mixed layer over southern Greenland through transport by oceanic currents.