Processes Driving Drift‐Ice Evolution and Its Interaction With the Oceanic and Atmospheric Boundary Layers

Abstract Sea ice is a crucial component of polar climate systems and is undergoing substantial changes in both hemispheres due to evolving climatic conditions. Arctic sea ice is transitioning from perennial to seasonal cover, and the Southern Ocean sea ice is exhibiting recent minima and enhanced seasonality. As global warming continues, the role of sea ice in polar climate systems is expected to transform further. However, many theoretical frameworks and parameterizations in current sea‐ice models are based on observations from an earlier era dominated by thicker multi‐year ice. Here, we synthesize the physical processes governing the dynamics and thermodynamics of drift ice—the mobile pack ice—and its coupling with the atmospheric and oceanic boundary layers. Our goal is to provide a coherent theoretical framework of the sea‐ice evolution equations and to summarize parameterizations of sub‐grid processes used across models of varying complexity. These include representations of momentum and scalar fluxes, ice‐thickness distribution and redistribution, snow and melt‐pond processes, wave–ice interactions, and physical–biogeochemical feedbacks. We also examine how sea ice impacts ocean stratification and mixing, as well as the atmospheric boundary layer and clouds. Finally, we highlight recent observational findings and outline priorities for improving the representation of drift‐ice processes, particularly in light of the changing climate and ice state.