Douglas Mercer

Thesis Approved August 1996

Atmospheric Water Vapour Transport and the Thermohaline Circulation

Climate change modeling has shown that the ocean circulation is sensitive to the atmospheric hydrological cycle. A zonally averaged ocean climate model (Stocker, Wright, and Mysak, 1992) is used to study two climate phenomena where the hydrological cycle is important, and the model's hydrological cycle is improved. First, model-generated millenial-scale relaxation oscillations are studied as a possible explanation for Dansgaard-Oeshger oscillations. Second, CO_2 increase simulations are used to test an improved atmospheric hydrological cycle.

Relaxation oscillations similar to those of Sakai and Peltier are found using the Wright and Stocker model. The oscillation mechanism responsible for these oscillations is consistent with other work (Winton, 1993; Chen, 1995). A generalized momentum closure scheme is developed, showing that realistic meridional and vertical viscous diffusion terms are negligible in the dynamical balance. The original Wright and Stocker model was not intended for use at high meridional resolution, but adding a meridional viscosity of 10^6 m^2 s^-1 allows this possibility and the resulting model runs are not sensitive to resolution.

In preliminary CO_2 increase simulations, the ocean-only model is forced with a simple scheme to mimic greenhouse warming, resulting in behaviour consistent with previous results based on general circulation models. In particular, model sensitivity to greenhouse warming increases when freshwater fluxes vary in a credible manner. The ocean is then coupled to an atmospheric energy balance model, where the meridional vapour flux is allowed to vary reasonably. The behaviour is similar to before, but with decreased sensitivity to greenhouse warming.

Doug is now at Memorial University of Newfoundland, working on a BES degree. He hopes to teach High School Physics/Math, and to sneak in some water and clouds... You can reach him at

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