The Gent–McWilliams parameterization: 20/20 hindsight

It has now been 20 years since the Gent and McWilliams paper on “Isopycnal Mixing in Ocean Circulation Models” was published in January 1990 issue of the Journal of Physical Oceanography. That paper was highlighted at the CLIVAR Working Group on Ocean Model Development “Workshop on Ocean Mesoscale Eddies” which was held at the UK Meteorological Office in April 2009, and this review paper is based on the talk given at that Workshop. It contains some hindsights on how the parameterization of the effect of mesoscale eddies on the mean flow came about; which is a question that I am asked quite often. A few important results from including the parameterization in a non-eddy-resolving ocean model are recalled. Including this parameterization, along with other improvements to all the components, in the first version of the Community Climate System Model resulted in the first non-drifting control simulation in a climate model that did not require flux corrections. Also included are brief comments on how the Gent and McWilliams eddy parameterization has been modified and improved since the original proposal in 1990.