Linking MOSAiC Observations of Air-Ice-Ocean Interactions to Arctic Cyclone Sector and Evolutionary Stage

Arctic cyclones (ACs) produce significant dynamic and thermodynamic impacts on sea ice and even the upper ocean. While examining the extensive MOSAiC observations for evidence of air-ice-ocean interactions and their characteristics, it has become clear that both the portion of the cyclone where the observations are made (the cyclone “sector”) and the time in the evolution of the cyclone both affect the nature of the air-ice-ocean interaction. In their baroclinic evolutionary stage, ACs generally have a warm-frontal sector, a warm sector, and a cold frontal sector, similar to mid-latitude baroclinic systems. During their mature evolutionary stage, ACs lack these sectors; instead, they are equivalent barotropic with a cyclone center positioned below the upper-level disturbance (often a tropopause polar vortex), with a lowered tropopause, and a cold anomaly at the surface and a warm anomaly at the tropopause. Hence, in a mature AC’s have a cold-core sector at low levels within a warmer annulus, often also containing a low-level jet (LLJ). Many AC cases observed at MOSAiC were in the baroclinic stage with a distinct approaching warm front (warm frontal sector) during which the key air-ice interaction was thermodynamic in nature through enhanced downwelling longwave radiation associated with the deep frontal clouds. In some cases for which the transition had not proceeded sufficiently far, the subsequent warm sector and cold-front sectors were observed, and associated baroclinic LLJs impacted the sea-ice dynamics and deformation. Thermodynamic impacts on the sea ice were also noted in the post-cold frontal sector through the cold-air advection, thinning of clouds, and changes in cloud microphysics. For cases transitioning to the mature stage, the cold-core sector was observed with much shallower stratocumulus clouds, and a subtle change in the thermodynamic forcing due to the mixed-phase nature of these clouds. The subsequent transition to the annulus with warmer air and LLJ again changed the nature of both the thermodynamic and dynamic impacts on the sea ice.

The sector and evolutionary modulation of the observed thermodynamic and dynamic impacts will be illustrated using several MOSAiC case studies and summarized.