Parameterising wakes for oceanographic models

This PhD scholarship is offered by the EPSRC CDT in Offshore Wind Energy Sustainability and Resilience; a partnership between the Universities of Durham, Hull, Loughborough and Sheffield. This project is supported by Centre for Environment, Fisheries and Aquaculture Science (CEFAS) and The National Oceanography Centre (NOC). The successful applicant will undertake six-months of training with the rest of the CDT cohort at the University of Hull before continuing their PhD research at Loughborough University.

The offshore wind sector is rapidly expanding to meet net-zero energy demands. Individual turbines and farms are getting larger and further from shore, with individual turbines spanning 240 m in diameter and farms reaching 600 km2. Forced by spatial constraints and enabled by floating technology, farms are now developing in deeper waters, occupying increasingly vast areas.

Oceanographic flow processes are highly sensitive to sea surface boundary conditions (Christiansen et al., 2022), which are in turn critically dependent on atmospheric forcing. Atmospheric flows past offshore wind turbines produce highly turbulent and extensive wakes. These wakes are a necessary result of energy extraction from the wind.

They are a key motivation for spatial planning of offshore wind farms where turbine placement is optimised for maximum energy extraction while minimising costs associated with infrastructure and spatial footprint (Giebel et al., 2016). The turbulent wakes propagate downstream, leading to wake-wake interactions and farm-scale atmospheric flow processes with a significantly reduced wind speed in the lee of an offshore wind farm (Platis et al., 2018). It has been recently shown that such large-scale atmospheric interactions can have a significant effect on sea-surface conditions, manifested through a locally reduced wind shear stress (Christiansen et al., 2022).

Large-scale deployment of offshore wind farms in shelf seas therefore poses an emerging oceanographic problem; shelf seas are vital for life both on and below water through their control on the vertical transport of nutrients, and their role as a key component of the biogeochemical cycle (van Berkel et al., 2020). These are crucially dependent on general circulation and water column structure, which are both highly sensitive to conditions at the sea surface (Dorrell et al., 2022). Yet the impact of offshore wind expansion on sea surface conditions and subsequent regional scale effects is poorly understood and has only recently gained research interest.

While wake parameterisations for atmospheric models have received significant interest over the last decade, the current state-of-the-art oceanographic models make sweeping assumptions regarding the form of sea-surface forcing, particularly concerning wake-wake interactions, spatial variability, and turbulent modifications (Christiansen et al., 2022). These limitations must be overcome for accurate prediction of oceanographic responses t