Multiscale simulations of Langmuir cells and submesoscale eddies using XSEDE resources

A proper treatment of upper ocean mixing is an essential part of accurate climate modeling. This problem is difficult because the upper ocean is home to many competing processes. Vertical turbulent mixing acts to unstratify the water column, while lateral submesoscale eddies attempt to stratify the column. Langmuir turbulence, which often dominates the vertical mixing, is driven by an interaction of the wind stress and surface wave (Stokes) drift, while the submesoscale eddies are driven by lateral density and velocity changes. Taken together, these processes span a large range of spatial and temporal scales. They have been studied separately via theory and modeling. It has been demonstrated that the way these scales are represented in climate models has a nontrivial impact on the global climate system. The largest impact is on upper ocean processes, which filter air-sea interactions. This interaction is especially interesting, because it is the interface between nonhydrostatic and hydrostatic, quasigeostrophic and ageostrophic, and small-scale and large-scale ocean dynamics. Previous studies have resulted in parameterizations for Langmuir turbulence and submesoscale fluxes, but these parameterizations assume that there is no interaction between these important processes. In this work we have utilized a large XSEDE allocation (9 million SUs) to perform multi-scale simulations that encompass the Langmuir scale (O(10-100m)) and submesoscale eddies (O(1-10km)). One simulation includes a Stokes drift, and hence Langmuir turbulence, while the other does not.

To adequately represent such disparate spatial scales is a challenge in numerous regards. Numerical prediction algorithms must balance efficiency, scalability, and accuracy. These simulations also present a large challenge for data storage and transfer. However, the results of these simulations will influence climate modeling for decades.