Sack Lunch Seminar (SLS)

Abstract:
Our goal is to construct a stochastic parameterization of ocean mesoscale eddies in order to account for fluctuations in sub-grid transport, represent upscale turbulent cascades and quantify uncertainties associated with the parameters and the parametrization itself. Numerical simulations are performed in idealised double-gyre configurations to provide a tractable framework for deriving the stochastic closure. The model equation and model output are coarse-grained giving rise to an eddy source term. The eddy source term represents the difference between the high-resolution advection and coarse-resolution advection and reflects the eddy-mean flow interaction. We will use two different techniques to construct a stochastic closure. One approach will entail solving an optimisation problem while the other technique will rely on constructing probability distribution functions (PDFs) of the "eddy forcing" conditional on the resolved scales. A theory for the shape of the PDFs, including their mean, standard deviation, skewness and kurtosis will be presented as function of the coarse resolution model grid size, its forcing and stratification. The implementation of the different stochastic parametrisations in coarser resolution models will be discussed including the numerical challenges involved but also the improved mean state and its variability.