SLS - Elizabeth Yankovsky

Elizabeth Yankovsky
Wednesday, April 28, 2021 - 12:00pm to 1:00pm

Modeling and parameterizing submesoscale turbulence in dense Arctic overflows

Dense gravity currents forced by surface buoyancy loss over shallow shelf regions are important contributors to subsurface and abyssal ventilation throughout the polar regions yet remain challenging to represent accurately in models. In the first part of t he talk, I will present idealized experiments of Arctic shelf overflows employing both the nonhydrostatic MITgcm as well as the hydrostatic GFDL - MOM6. In the highest - resolution simulations (where the submesoscale range is well - resolved), the overflow under goes geostrophic adjustment and develops bottom - intensified and surface - intensified jets. The density front along the topography combined with geostrophic velocity shear initiates submesoscale symmetric instability, which leads to the onset of secondary sh ear instability, dissipation of geostrophic energy, and mixing. We explore the impact of vertical coordinate and model resolution on the representation of these turbulent processes. We find that in isopycnal coordinates limited vertical resolution in abyss al regions leads to inadequate representation of submesoscale turbulence. In the second part of the talk, I will present a parameterization for capturing the effects of submesoscale symmetric instability. The parameterization is based on identifying unstab le regions through a Richardson number criterion and subsequently flattening isopycnals towards a balanced state (similar to the Gent - McWilliams parameterization for baroclinic instability). A fraction of the potential energy released by the isopycnal flat tening is passed to the shear mixing parameterization, so that potential energy extracted from the large - scale flow by the instabilities is converted to kinetic energy and used for vertical mixing. Parameterizing the effect of submesoscale instabilities, p articularly in the dynamically rich polar regions, becomes crucial as ocean models move towards resolving mesoscale eddies and fronts but not the submesoscale phenomena they host.

About this Series:

The Atmosphere, Ocean and Climate Sack Lunch Seminar Series is an informal seminar series within PAOC that focuses on more specialized topics than the PAOC Colloquium. Seminar topics include all research concerning the science of atmosphere, ocean and climate. The seminars usually take place on Wednesdays from 12-1pm. The presentations are either given by an invited speaker or by a member of PAOC and can focus on new research or discussion of a paper of particular interest.