Dr Xiaoming Zhai, University of East Anglia, School of Environmental Sciences
Dr Andrew Meijers, British Antarctic Survey
Mesoscale eddies are small-scale ocean features, around 10-100 km in size, which are analogous to the atmosphere’s weather systems. They play many roles in the ocean circulation, such as transporting heat, salt and carbon over large distances, and influence climate as a result. Eddies result from instability processes, where small perturbations, such as temperature wiggles, grow rapidly from an otherwise stable circulation. However, it has been known for some time that eddies are not passively spawned from the ocean’s density distribution (its stratification); instead, they play an active role in setting the stratification of the ocean (Marshall et al., 2003). Consequently, processes that affect the eddy field can indirectly affect the stratification too. One such process is the relative wind stress effect, in which the wind stress at the surface of the ocean is calculated using the difference between the atmospheric wind and the ocean velocity. This introduces a drag on small-scale features, such as mesoscale eddies, that can directly dissipate them and have widespread effects on the ocean (Wilder et al., 2022; Munday et al., 2021; Renault et al., 2016).
The student will use numerical models with simplified forcing and geometry to investigate how the relative wind effect impacts the role of eddies in setting ocean stratification. They will apply fundamental theories of ocean circulation to develop their understanding and quantitatively predict the stratification (see Marshall et al., 2002). By introducing the curvature of the Earth (the beta effect/plane), the student will extend their results to include this important extra effect and ultimately consider the stratification of wind-driven subtropical gyres (Radko & Marshall, 2003). Wind-driven gyres play key roles in the heat transport of the ocean and can influence climate in important ways.
This project would suit a mathematically inclined student with a degree in physics, mathematics or physical oceanography. Experience with Python, Matlab or Fortran would be an advantage, although all necessary training will be provided. An interest in the theory of ocean circulation and numerical modelling is essential. The student will be encouraged to participate in field work where the opportunity presents itself.