Sea ice is a crucial component of polar climate systems, and is undergoing substantial changes in both the Arctic and the Southern Ocean due to evolving climatic conditions. The Arctic Ocean is undergoing a transition from being perennially ice-covered to be- ing only seasonally ice-covered. The shrinking and thinning of ice cover have been at- tributed to changes in atmospheric and oceanic forcing, as well as to changes in the phys- ical properties of pack ice. The Southern Ocean also shows signs of change, reflected in recent minima and amplified seasonality. As global warming persists in the coming decades, the role of sea ice in polar climate systems is poised for further transformation. How- ever, current theoretical frameworks and parameterization methods used in numerical models to simulate sea ice evolution and its interaction with the oceanic and atmospheric boundary layers are largely rooted in measurements from an earlier era characterized by thicker multiyear ice. In this review we aim to summarize the evolution of physical drivers governing the dynamics and thermodynamics of sea ice, snow, and ocean/atmosphere boundary layers. Furthermore, we describe and assess existing parameterization meth- ods of sub-grid scale processes, discuss recent observational findings, and propose essen- tial improvements.

Arctic cyclones are key drivers of sea ice and ocean variability. During the 2019-2020 Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, joint observations of the coupled air-ice-ocean system were collected at multiple spatial scales. Here, we present observations of a pair of strong mid-winter cyclones that impacted the MOSAiC site as it drifted in the central Arctic pack ice, with analytic emphasis on the second cyclone. The sea ice dynamical response showed spatial structure at the scale of the evolving atmospheric wind field. Internal ice stress and the ocean stress play significant roles, resulting in timing offsets between the atmospheric forcing and the ice response and post-cyclone inertial ringing in the ice and ocean. A structured response of sea ice motion and deformation to cyclone passage is seen, and the consequent ice motion then forces the upper ocean currents through frictional drag. The strongest impacts to the sea ice and ocean from the passing cyclone occur as a result of the surface impacts of a strong atmospheric low-level jet (LLJ) behind the trailing cold front. Impacts of the cyclone are prolonged through the coupled ice-ocean inertial response. The local impacts of the approximately 120 km wide LLJ occur over a 12 hour period or less and at scales of a kilometer to a few tens of kilometers, meaning that these impacts occur at smaller spatial scales and faster time scales than many satellite observations and coupled Earth system models can resolve.