Tomas Chor (UCLA) - Mixing in Oceanic Boundary Layers: A Method to Guide Model Development

June 3, 2020 3:00pm
Zoom Seminar


Surface oceanic boundary layers are critical for earth dynamics because they mediate fluxes of important properties (such as momentum, heat and dissolved gases) between the atmosphere and the ocean. These dynamics are dominated by flow structures that range from millimeters to hundreds of meters and are therefore too small to be accurately resolved by global models and need to be parameterized. We focus on a class of eddy diffusivity models known as K-profile parameterization (KPP) in the oceanic community. This model aims to represent turbulent fluxes by separating them into a diffusive and a nondiffusive component. Many different versions of KPP exist and the greatest disparity between them is the way that surface waves modify these profiles. One of the issues is that oceanographers do not know how the diffusive/nondiffusive separation should change with different wave conditions, which is mainly due to the challenge of estimating both components of the flux separately directly from data.

In order to bridge this gap, we introduce a method that estimates this separation of fluxes for KPP based on data alone (i.e. without needing any a priori assumptions of shape or scaling). We use this method to investigate how the fluxes should be partitioned between diffusive and nondiffusive components across a wide range of oceanic regimes, which can be used to modify KPP in an informed manner and thus reduce the huge disparity between its versions in the community. Our results indicate that it is possible to successfully include wave effects in KPP in a very straightforward manner if the shape of the profiles is modified from the one currently used by models. Furthermore we also show that some modifications are needed in the magnitudes of these profiles to more accurately represent observed fluxes.