2014 Appleton medal and prize
Professor David Marshall, University of Oxford. For his fundamental contributions to understanding the fluid dynamics of the global ocean circulation through the development of penetrating conceptual models.
Marshall has made many fundamental contributions to understanding the fluid dynamics of the global ocean circulation. His work typically involves the development of idealised theoretical and computational models that isolate critical processes.
Many of his most penetrating contributions elucidate interactions between turbulent ocean eddies and the large-scale circulation. These eddies, the oceanic analogue of weather systems, occur on scales of 1-10s of kilometres and are poorly resolved, if at all, by the computational ocean models currently used for climate prediction. Marshall and collaborators have developed a novel dynamical framework for diagnosing and parameterising eddy-mean flow interaction that preserves the symmetries and conservation laws of the underlying equations of motion, thereby revealing the true geometric nature of the eddy forcing. Separate work has revealed that western boundaries act as graveyards for westward propagating eddies, with satellite observations suggesting this is a major eddy energy sink.
Marshall has made fundamental contributions to understanding how the global circulation adjusts to surface forcing, including a highly-cited conceptual model for the adjustment of the meridional overturning circulation, which continues to influence theoretical and observational work in this area. Recent work suggests Southern Ocean eddies may control the global equilibration time scale, a disturbing but important result to the extent that eddies are poorly represented in climate models. Further work has elucidated how ocean circulation is steered by variable bottom topography, in particular quantifying the extent to which stratification shields the surface circulation from the topographic variations.
In addition to his research, Marshall has made sustained contributions to training the next generation of environmental physicists, through innovative undergraduate teaching in which he exposes physics students to fluid dynamics and climate physics, through invited lectures at many international summer schools, and through his research group, alumni of which occupy faculty positions across the United Kingdom.