Synoptic climatology of the Ross Ice Shelf and Ross Sea region of Antarctica: k-means clustering and validation

The surface wind regime of the Ross Ice Shelf (RIS) is dominated by northward outflow influenced by drainage from both East and West Antarctica and synoptic disturbances over the Ross Sea. To quantify the effects of the wind regime on the climate of the region, we produce a synoptic climatology of the RIS and Ross Sea via a k-means clustering technique applied to surface (10m) winds from the ERA Interim reanalysis (1979-2011). We describe the generation of the climatology and discuss composites of surface winds, mean sea-level pressure and temperature, which show a high degree of internally consistent structure and are similar to previous synoptic climatologies. While some small-scale features are not fully resolved by the reanalysis, such as the channelling of katabatic flows, we identify a high degree of coherence between clustering results and available in situ data sources, suggesting that the ERA Interim represents the region well. We find that the surface wind field of the ice shelf is highly sensitive to the strength and position of cyclonic disturbances in the Ross Sea, the presence of which can aid outflow from the continental interior. Temperature displays a high level of sensitivity to circulation conditions due to the effects of steep temperature gradients surrounding the shelf and advective heat transport. Cold temperatures on the ice shelf coincide with drainage from East Antarctica, while warmer periods coincide with West Antarctic drainage; this is particularly clear during RIS air stream (RAS) events. The warmest periods occur during southward transport from the Ross Sea. The sensitivity of temperature to the origin of flows suggests circulation changes in the region are likely to significantly impact surface climate. Analysis of the frequency of varying synoptic events and their persistence confirms RAS is a very common and persistent feature of the region.