14 August 2017

Measuring the Impact of Mesoscale Eddies in the Ocean’s Climate

Understanding the role of oceanic mesoscale eddies on the climate via an equilibrated force balance

he vertical axis is z-position and the horizontal axis is y-position. The field shown is the vertical flux of eastward momentum by mesoscale eddies with units of m^2/s^2 per unit density. The simulation clearly and unambiguously shows that all of the imposed wind stress is moved from the ocean surface to the ocean bottom by mesoscale eddies.
The vertical axis is is buoyancy (with lighter fluid at the top) and the horizontal axis is y-position. The field shown is the thickness-weighted meridional velocity. When weighted with thickness, we find the the lightest fluid motion to toward the pole at all meridional positions.
Science

With unprecedented fidelity we are able to clearly explain the full force balance in an idealized configuration of the Southern Ocean.

Impact

The role of the mesoscale eddies is to move the imposed surface wind stress to the ocean bottom; eddies accomplish this through the vertical transport of eastward momentum.  The climate of the Southern Ocean as we know is impossible to realize without the action of mesoscale eddies.

Summary

Ocean mesoscale eddies are the weather of the ocean and act as vehicles for the transport and mixing of heat, carbon and momentum. This work makes significant progress toward accurately measuring the force that mesoscale eddies exert on mean, climatological ocean flow by closing the momentum force balance in an eddy-rich re-entrant channel similar to that of the Southern Ocean. We find that mesoscale eddies play a leading role in the force balance. In fact, the very structure of the ACC and the entire Southern Ocean depends on the existence of mesoscale eddies to move the atmosphere-driven wind stress from the ocean surface to the ocean floor. The vertical motion induced by mesoscale eddies brings, in an alternating manner, warm (light) and cold (dense) waters to the ocean's surface, thereby moving heat into and out of the ocean. In summary, this work has taken a significant step toward the construction of a robust conceptual model to interpret and quantify the role of ocean mesoscale eddies in the Earth's climate system.

Contact
Todd D Ringler
Los Alamos National Laboratory
Publications
2017.  "A Thickness-Weighted Average Perspective of Force Balance in an Idealized Circumpolar Current."  Journal of Physical Oceanography 47(2): 285-302, doi:10.1175/JPO-D-16-0096.1.