| Summary: | The narrow belt of easterly winds that surrounds Antarctica exerts important controls over ocean currents and the production and movement of sea ice. We use the ERA5 reanalysis to investigate the structure of these winds and their variability on monthly to interannual timescales. Meridional cross-sections through the coastal zone reveal that the climatological easterlies are relatively shallow ( < 2 km deep) and are tightly-bound to the steep coastal slopes in all sectors of the continent, generally extending no more than 400 km offshore. The strongest easterlies are found over the steep coastal slopes, a region characterised by strong and persistent katabatic winds. However, the easterlies are much deeper than the katabatic drainage flow, which is typically no more than a few hundred metres deep. This suggests that, rather than katabatic forcing, the primary driver of the easterlies is the strong baroclinicity associated with the distortion of the broad-scale thermal gradients by the high Antarctic orography. The coastal easterlies are locally enhanced on synoptic timescales when a deepening cyclone moves southward from the circumpolar trough (CPT) towards the coast. On longer timescales, the easterlies are linked to variations in the strength and position of the high-latitude westerlies to the north of the CPT. Around most of East Antarctica, the strength of the coastal easterlies is well-correlated with variations in the Southern Annular Mode while, around West Antarctica, variability in the depth and location Amundsen-Bellingshausen Sea Low is the primary control.
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