Richard J. Greatbatch
The 2020 Fridtjof Nansen Medal is awarded to Richard J. Greatbatch for pioneering contributions to geophysical fluid dynamics and theoretical oceanography, especially mesoscale eddy parameterisations.
During close to four decades, Richard Greatbatch has made important contributions to a broad range of topics in ocean, atmosphere, and geophysical fluid dynamics. His combination of keen physical insight and mathematical rigour has allowed him to deepen our understanding in a remarkable number of different sub-fields.
Greatbatch has made pioneering and seminal contributions to advancing our understanding of eddy-mean flow interaction in the ocean. In 1990, he showed with Kevin Lamb how the vertical momentum transport by geostrophic eddies can be parameterised in non-eddying models through an enhanced vertical viscosity. This idea is mathematically isomorphic to the parameterisation developed by Gent and McWilliams (GM) around the same time and now implemented in virtually all non-eddy-permitting climate models.
While perhaps the GM parameterisation has become better known among non-experts, direct evidence of the impact and standing of Greatbatch’s work was provided by the organisation of an international workshop and special journal issue to celebrate the joint 20th anniversary of the Greatbatch & Lamb and Gent & McWilliams papers. Around the same time, Greatbatch proposed solving a prognostic eddy energy equation to constrain the undetermined eddy diffusivity in the parameterisation, representing that the energy released in baroclinic instability must be converted to eddy energy, thus increasing the eddy diffusivity and feeding back into the rate of mean-to-eddy energy conversion. The results thus obtained are impressive in reproducing the major patterns of eddy energy observed in the ocean as well as broadly realistic eddy diffusivities.
An area both fundamentally and practically relevant concerns the calculation of sea level and sea-level rise with observations and with model output. The fact that ocean models have tended to conserve volume rather than mass, in what is known as the Boussinesq approximation, complicates the calculation of sea level from these models. Greatbatch found a way to think through this conundrum and showed that the issue is not actually as large or as difficult as it first appears. Later he realised that most of the Boussinesq approximation that ocean models routinely make can also be rationalised away by a re-interpretation of the velocity that the model carries, implying that the Boussinesq-approximated ocean models do not actually incur the full error that is traditionally associated with this approximation. This work is typical of Greatbatch’s approach to physical oceanography in that he goes back to fundamental physics and thus is often able to improve the basic tools that we all use in ocean modelling.
No less important than his immediate research accomplishments are Greatbatch’s outstanding contributions towards training the next generation of physical oceanographers and atmospheric scientists. Through his excellent and tireless mentorship, he has nurtured a new generation of ocean and climate scientists, among them no fewer than 25 doctoral students, some of whom are leaders in the field today.
Richard Greatbatch commands the respect of his peers for his creativity, his intellectual acumen and honesty, his passion for the science itself, his deep generosity offered to colleagues and mentees, and his infectious humour expressed in nearly every conversation.