Lectures on Thermodynamics and Ocean Mixing (September 2018).

McDougall, Trevor (2018) Lectures on Thermodynamics and Ocean Mixing (September 2018). Open Access [Teaching resource]

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Abstract

Course Outline
The aim of these lectures is to present the fundamentals of thermodynamics in the context of
fluid flow and mixing in the ocean and the interaction of seawater and ice.
The course will develop thermodynamic concepts that are needed to account for the flow of
heat in the coupled atmosphere-ocean-ice system of planet earth. The thermophysical quantities in the ocean are functions of three variables, namely salinity, temperature and pressure, and this functional dependence complicates what is even meant by seemingly simple concepts such as "specific volume", "specific heat" and "heat content per unit mass". For example, what is a meaningful definition of an “isopycnal surface”? The ocean and atmosphere are in a continuous state of turbulent motion, and the course will derive the appropriate theoretical framework in which these time varying motions should be examined.
This course introduces the conservation laws that govern the fluid dynamics the ocean, in
particular concentrating on what variables should be carried in ocean models given that the
ocean is subject to turbulent fluxes rather than simply molecular fluxes of heat and salt. The
distinctions between variables that are conservative versus those that are non-conservative are emphasized.
Several new results on the interaction of seawater and ice, and particularly of frazil ice, will be introduced. These results add thermodynamic rigor to existing practices. This rigor is now possible because the thermodynamic properties of seawater, ice and humid air have been redefined in 2010, as adopted by the Intergovernmental Oceanographic Commission. Frazil ice is the name used when small crystals of ice form in cold seawater such as occurs at the underside of ice shelves near the poles.
The course will explore some of the implications of this thermodynamic knowledge for how oceanic data should be analyzed. For example, it is possible to developed a closed expression for the mean absolute velocity in the ocean, but it seems to depend on the local value “neutral helicity” of the ocean; a property that is normally understood as being the course of the
mathematically ill-defined nature of neutral density surfaces in the ocean. Results such as this are at the edge of our oceanographic understanding and need further research.
We now know that diapycnal mixing in the deep ocean is stronger near the sea floor. The course will discuss the dynamical implications of this bottom-intensification of diapycnal mixing. We will find that the net diapycnal upwelling of Bottom Water is actually the net GEOMAR Thermodynamics and Ocean Mixing Lectures, Sep. 2018 result of a larger upwelling across density surfaces in the bottom boundary layer partially offset by diapycnal sinking motion in the ocean interior.

Document Type: Teaching resource
Additional Information: Lecturer: Prof. Dr. Trevor McDougall, Scientia Professor of Ocean Physics & ARC Australian Laureate Fellow, University of New South Wales, Australia
Publisher: Trevor McDougall
Date Deposited: 24 Sep 2018 07:01
Last Modified: 25 Sep 2018 13:20
URI: https://oceanrep.geomar.de/id/eprint/44343

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