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Abstract

Easterly winds encircling Antarctica influence sea ice concentrations and act as a driver of ocean currents, modifying transport of warm waters towards vulnerable ice shelves. Offshore, these winds are extremely variable on daily timescales, with low-level jets commonly forming parallel to the steep coastal slopes. We use a regional configuration of the UK Met Office Unified Model (MetUM) to investigate the dynamics of coastal easterly jets forming during two strong wind events in east Antarctica. We also test the sensitivity of these easterly jets to uncertain parameters in the MetUM simulations. Model outputs compare favourably with satellite and nearby sonde observations, though the peak wind speeds are underestimated. A momentum budget analysis reveals that although the large-scale forcing acts as a primary control on the offshore winds, a layer of enhanced baroclinicity within the lowest 1000 m is critical to explain the strength of the low-level jet. Advection of near-surface momentum from onshore (e.g. due to katabatic winds) plays a minor role. When sea ice is present, simulated offshore surface winds are quite sensitive to the parameterization of sea ice roughness, which can affect the winds directly and indirectly via its impact on low-level baroclinicity. Stable boundary layer representation also affects both the strength and structure of the jet. Only minor differences between experiments run at 4km and 12km grid lengths are found. Our results point to important and poorly constrained processes underpinning the strength and variability of the offshore coastal easterlies.