Eddy-mixing entropy and its maximization in forced-dissipative geostrophic turbulence
Journal of Statistical Mechanics: Theory and Experiment
IOP Publishing 2018:2018 (2018) 073206
Abstract:
An equilibrium, or maximum entropy, statistical mechanics theory can be derived for ideal, unforced and inviscid, geophysical flows. However, for all geophysical flows which occur in nature,forcing and dissipation play a major role. Here, a study of eddy-mixing entropy in a forced dissipative barotropic ocean model is presented. We heuristically investigate the temporal evolution of eddy-mixing entropy, as defined for the equilibrium theory, in a strongly forced and dissipative system. It is shown that the eddy-mixing entropy provides a descriptive tool for understanding three stages of the turbulence life cycle: growth of instability; formation of large scale structures; and steady state fluctuations. The fact that the eddy-mixing entropy behaves in a dynamically balanced way is not a priori clear and provides a novel means of quantifying turbulent disorder in geophysical flows. Further, by determining the relationship between the time evolution of entropy and the maximum entropy principle, evidence is found for the action of this principle in a forced dissipative flow. The maximum entropy potential vorticity statistics are calculated for the flow and are compared with numerical simulations. Deficiencies of the maximum entropy statistics are discussed in the context of the mean-field approximation for energy. This study highlights the importance of entropy and statistical mechanics in the study of geostrophic turbulence.Atlantic-Pacific asymmetry in deep-water formation
Annual Review of Earth and Planetary Sciences Annual Reviews 46 (2018) 327-352
Abstract:
While the Atlantic Ocean is ventilated by high-latitude deep water formation and exhibits a pole-to-pole overturning circulation, the Pacific Ocean does not. This asymmetric global overturning pattern has persisted for the past 2–3 million years, with evidence for different ventilation modes in the deeper past. In the current climate, the Atlantic-Pacific asymmetry occurs because the Atlantic is more saline, enabling deep convection. To what extent the salinity contrast between the two basins is dominated by atmospheric processes (larger net evaporation over the Atlantic) or oceanic processes (salinity transport into the Atlantic) remains an outstanding question. Numerical simulations have provided support for both mechanisms; observations of the present climate support a strong role for atmospheric processes as well as some modulation by oceanic processes. A major avenue for future work is the quantification of the various processes at play to identify which mechanisms are primary in different climate states.A Model of the Ocean Overturning Circulation with Two Closed Basins and a Reentrant Channel
JOURNAL OF PHYSICAL OCEANOGRAPHY 47:12 (2017) 2887-2906
Submesoscale Instabilities in Mesoscale Eddies
JOURNAL OF PHYSICAL OCEANOGRAPHY 47:12 (2017) 3061-3085
Characterising the chaotic nature of ocean ventilation
Journal of Geophysical Research: Oceans American Geophysical Union 122:9 (2017) 7577-7594