Combined physical and biogeochemical assessment of mesoscale eddy parameterisations in ocean models: eddy induced advection at non-eddying resolutions
AbstractOcean components of Earth System Models employed for climate projections as yet do not routinely resolve mesoscale eddies for computational cost reasons, and the associated subgrid processes are still parameterised in these numerical models. While the performance of physics parameterisations in a numerical ocean model is normally assessed via examining the associated physical responses, biogeochemical responses are also important, but are often treated separately. Given recent advances in mesoscale eddy parameterisations, specifically for the eddy induced advection, this work systematically examines the improvements brought about by the inclusion of a time and space varying eddy induced velocity coefficient, and examine the joint consequences for physical and biogeochemical responses in the context of an idealised but ocean relevant model. Relative to a high resolution mesoscale eddy resolving model, the more updated mesoscale eddy parameterisation is able to capture aspects of the model truth in the physical responses. However the biogeochemistry response is rather more subtle, where a 'better' response with the conventional eddy parameterisation with a constant coefficient could arise from a physically inconsistent response. The present work provides some baseline model sensitivities from which future assessments employing other parameterisations or in more complex settings could compare against.