Rotating convection driven by differential bottom heating and its application
Rotating convection driven by differential bottom heating and its application
Date
1996-09
Authors
Park, Young-Gyu
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DOI
10.1575/1912/5721
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Keywords
Heat
Rotating masses of fluid
Ocean circulation
Ocean temperature
Thermoclines
Rotating masses of fluid
Ocean circulation
Ocean temperature
Thermoclines
Abstract
A convection experiment was done with a rotating rectangular tank as a model of oceanic
meridional overturning circulation. Heat flux was fixed at one bottom end of the tank using
an electrical heater. Temperature was fixed at the other end using a cooling plate. All other
boundaries were insulated. The cross sections of temperature field were made at several
locations. In equilibrium, the heat input to the fluid H was the same as the meridional heat
flux (heat flux from the source to the sink), so it was possible to find a scaling law relating
H to the temperature difference across the tank ΔT and rotation rate f. The experimental
result suggests that the meridional heat transport in the experiment was mostly due to
geostrophic flows with a minor correction caused by the bottom friction. If there was
no friction, the scaling law from the experiment resembles the one verified in part in the
numerical model by Bryan and Cox (1967). Flow visualization and temperature sections
showed that there were meridional geostrophic currents that transported heat. When the
typical values of the North Atlantic are introduced, the geostrophic scaling law predicts
meridional heat flux comparable to that estimated in the North Atlantic when the vertical
eddy diffusivity of heat is about 1cm2s-1.
Naturally, this experiment is a only crude model of the oceanic convective circulation.
We do not claim that the geostrophic scaling applies in detail to the oceans, however, it
may have some important use in climate modeling. For example, almost all existing box
models and two-dimensional numerical models of ocean circulation use a frictional scaling
law for buoyancy transport. A box model with the geostrophic scaling law is shown to
be more robust to a change in the boundary forcing so that it is less likely to have a
thermohaline catastrophic transition under the present conditions. It is also shown that a
restoring boundary condition for salinity introduces stability to a thermal mode circulation,
unless the restoring time for salinity is several orders of magnitude larger than that for
temperature.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1996
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Citation
Park, Y. (1996). Rotating convection driven by differential bottom heating and its application [Doctoral thesis, Massachusetts Institute of Technology and Woods Hole Oceanographic Institution]. Woods Hole Open Access Server. https://doi.org/10.1575/1912/5721