EDDY MIXING
The ocean is a critical regulator of the Earth’s climate over timescales of decades to millennia. Through its circulation and biological activity, heat, carbon and other climatically important tracers are distributed around the globe and stored in its interior. Notably, since man started emitting carbon dioxide (CO2) into the atmosphere, the ocean appears to have been the main sink for CO2. In the quest to observe, understand and model the ocean, however, we are confronted by a major challenge: the ubiquity of oceanic turbulence on space scales of hundreds of meters to hundreds of kilometers and time-scales of days. These “mesoscale” motions are vividly illustrated in both models and data – see Fig. 1. The mesoscale is so energetic (it contains 90% of the ocean’s kinetic energy) that it often masks the mean circulation, which only emerges after averaging in space and time. Physically the mesoscale markedly enhances the rate at which the ocean mixes tracers both in the horizontal and the vertical. It acts as the "bridge" between energy input on the large scale and dissipation on microscales, although the detailed pathways remain uncertain.
Our research focuses on understanding the role of ocean turbulence in climate and developing parameterization to represent ocean turbulence in climate models.
Figure 1. (a) Snapshot of surface speed in a 15km resolution global simulation of the MITgcm constrained by observations (as in ECCO). Notice the rich eddy structure in the velocity field.
Selected references
Ferrari, R., S. M. Griffies, G. Nurser, and G. K. Vallis, 2010: A Boundary Value Problem for the Parameterized Mesoscale Eddy Transport, Ocean Modelling, Vol. 32, 143-156.
Ferrari, R. and M. Nikurashin, 2010: Suppression of eddy mixing across jets in the Southern Ocean, J. Phys. Oceanogr., Vol. 40, 1501-1519.
Smith, S., and R. Ferrari, 2009: Production and dissipation of compensated T-S variance by mesoscale stirring in the NATRE region, J. Phys. Oceanogr., Vol. 39, 2477-2501.
Plumb, R., and R. Ferrari, 2005: Transformed Eulerian-mean theory. I: Non-quasigeostrophic theory for eddies on a zonal mean flow,J. Phys. Oceanogr., Vol. 35, 165-174.
