In this thesis, we formulate a new 3-dimensional planetary geostrophic (PG) ocean general circulation model in spherical coordinates for use in ocean-climate studies. The model equations consist of full prognostic temperature and salinity equations and diagnostic momentum equations. The model is verified by comparison with results obtained by the well known Bryan-Cox model at coarse resolution. Extensive process studies are carried out to determine the roles played by various processes in determining the thermocline structure and the thermohaline circulation, especially the role of convective overturning. A secondary circulation theory which treats the thermohaline circulation as a geostrophic flow instead of frictional current is proposed, and the implications of the results to 2-dimensional latitude/depth models are discussed. / The model is also used to examine the stability and variability of the thermohaline circulation, especially the role played by air-sea heat flux at the surface. We show that the large reduction in the surface heat flux under mixed boundary conditions (restoring on temperature and flux on salinity) is essential for the occurrence of the "polar halocline catastrophe" (F. Bryan. 1986). Replacing the infinite heat capacity atmosphere implied by mixed boundary conditions with an atmosphere that can adjust thermally to the ocean, the amount of the heat flux reduction is less and thus the polar halocline catastrophe is less likely to occur; when it does occur, it is less severe. This is demonstrated by coupling our model to a simple zero heat capacity atmosphere (Schopf, 1983). Instead of a total collapse of the thermohaline circulation, the results show a decaying oscillation of 20 years period. / The ocean model is next coupled to a thermodynamic sea ice model to examine the effect of sea ice on the stability and variability of the thermohaline circulation. A robust 17-year period oscillation is obtained, and a new mechanism involving a feedback between ice cover and temperature is proposed. Conceptual models are formulated for further interpretation of the results, and to compare the thermal insulation and salinity rejection effects due to an anomalous ice cover, on the density of the surface water. The heat budget required for ice formation leads to a constraint on the convective overturning, and hence the transfer of heat and salt from the deep ocean to the bottom of the ice. As a result, the thermal insulation effect is dominant, at least for the case of annual mean surface forcing examined here.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.41214 |
| Date | January 1993 |
| Creators | Zhang, Sheng, 1956- |
| Contributors | Lin, C. A. (advisor), Greatbatch, R. J. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Atmospheric and Oceanic Sciences.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001357636, proquestno: NN91684, Theses scanned by UMI/ProQuest. |
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