Improved projections of winds at the crossroads between Antarctica and the Southern Ocean

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The coastal region of Antarctica links the Southern Ocean to the Antarctic continent and is where many of the key interactions that govern Antarctica's impact on the global climate system take place. Scientists have studied winds at mid-latitudes over the Southern Ocean and over the Antarctic continent, but much less attention has been paid to the marine winds just offshore from Antarctica. Numerical models of the ocean and atmosphere are now run on small enough grids that these coastal winds can be resolved and represented reliably. However, this needs to be tested in the current generation of climate models. It is important that climate models have a good representation of these coastal winds for the following reasons: - Coastal winds influence the flow rate of major Antarctic glaciers and their associated impacts on global sea level. - Winds over coastal polynyas (areas of unfrozen sea within the ice pack) drive cooling and sinking of the densest water in the world ocean, known as Antarctic Bottom Water (AABW), which contributes to storing the extra heat and carbon released into the atmosphere by humans. - Realistic surface wind fields in climate models are needed to produce realistic distributions of sea ice. This is important in controlling the amount heat and moisture convergence into the Antarctic continent by capping off evaporation and heat loss from the ocean surface. Additionally, since sea ice formation enriches surface waters with salt, it is integral to the formation and sinking of dense AABW. Reliable projections of future change in AMCWs, and related regional and global impacts, will require their realistic representation in climate models. We will make use of a new collection of state-of-the-art climate model output, the Coupled Model Inter-comparison Project Phase 6 (CMIP6). In collaboration with the Met Office, sensitivity studies using their IPCC-class Unified Model (MetUM) will enable us to understand how sensitive AMCWs are to changes in model configuration. This will tell us which physical processes climate models need to get right to accurately represent the structure and variability of AMCWs. We will improve the evaluation of observed winds from Antarctic stations, research and supply vessels, drifting buoys, and marine winds from satellites to assess the quality of a range of different gridded wind data products, which are based on both observations and observationally-constrained numerical modelling. The best performing products will be used to evaluate climate model performance. An established framework for model evaluation is the concept of climate model 'metrics', which can quantify a key process or feature of the climate system, usually with a single value, that can be calculated from both model output and observational reference data (in our case observationally-based wind products). We will develop and use metrics to evaluate the performance of CMIP6 models in representing AMCWs, including configurations participating in its high-resolution sub-project HighResMIP. This, along with improved process understanding, will help to reduce uncertainty in projections of future change.The research outcomes will be: - Improved 21st century projections of AMCWs from the latest state-of-the-art climate and earth system models.- Observational metrics of AMCWs that can be applied to gridded climate model output. - A dataset of historical in-situ meteorological observations of marine coastal Antarctica building on the NERC ORCHESTRA project.- Identify the best of the current generation of wind products for the Antarctic coastal region. - Evaluation of the representation of AMCWs in the MetUM which, in combination with planned sensitivity studies, should ultimately facilitate accelerated model development.- Career development for two early career researchers giving experience in climate modelling, analysing large datasets, networking and communication skills.