MEDLEY

The ocean surface mixed layer mediates the transfer of heat, freshwater, momentum, and trace gases between atmosphere, sea ice, and ocean. Thus, the mixed layer transfer function must be represented accurately in climate models, especially in the North Atlantic and in the Arctic oceans which are, respectively, hotspots of anthropogenic CO2 storage and warming. Large discrepancies in mixed layer depths are found in low resolution CMIP5 models, in part because these models do not parameterize properly the spatial heterogeneities induced by the presence of sea ice and (sub)mesoscale ocean eddies. The objectives of MEDLEY are 1) to evaluate the spatial heterogeneity of fluxes and processes controlling the ocean mixed layer, and 2) to take into account this heterogeneity to improve the representation of the mixed layer transfer function in climate models. MEDLEY brings together state of the art observations, groundbreaking submesoscale-resolving models, an innovative sea-ice model, and the latest generation of climate models (with an eddying ocean) involved in the HighResMIP intercomparison. By pooling their expertise, MEDLEY members will produce the most complete evaluation of the mixed layer dynamics in climate models, from the North Atlantic to the Arctic ocean. MEDLEY will improve our understanding of the relationship between air-sea fluxes and mixed layer properties, taking into account the mediation of the fluxes induced by the fractured sea ice cover. It will evaluate the effect of heterogeneities on mixed layer properties, including currents and kinetic energy, as well as the relationship between the mixed layer and the interior through the stratified transition layer. MEDLEY will impact European climate models based on the NEMO modelling platform by improving the representation of sea ice and mixed layer processes. We will create new diagnostics for model evaluation to ensure that the mixed layer transfer function is better constrained in future climate models.