The post journals of certain Hudson's Bay Company forts were examined for evidence that air mass frequencies during the first half of the nineteenth century were markedly different from those of a modern (1955-1959) period. The "partial collective" technique of Bryson was used to determine the modern frequencies and to provide the basis of the conditional probability structure employed to estimate the historic air mass frequencies. There is evidence from each station for which analysis was performed of a greatly increased presence of "Arctic" air, probably as a consequence of a weakened zonal atmospheric circulation and a decrease in the eastward penetration of "Pacific" air. / Arts, Faculty of / Geography, Department of / Graduate

Changes in the physical properties of the atmosphere are caused by geographic influences and dynamic effects. The nature of the surface of the earth over which the air passes is usually the main factor in modifying the air in the lower levels of the troposphere. The ocean area of Hudson Bay in northeastern Canada presents an extensive surface for modification of air. Continental polar air crossing Hudson Bay and continuing into eastern Canada is modified not only by the underlying surface but also by the dynamic effects occurring in the atmosphere during its trajectory over these regions. The amount of modification is of major importance in the climate of the surrounding area, and in the meteorology of North American air masses. It was the purpose of this study: 1. To compute the changes in the physical properties that occur in continental polar air over Hudson Bay, Consequently, a project was undertaken to determine the amount of ice that forms on Hudson Bay in winter. The effect of the formation of ice in changing the modification of air was then studied. [...]

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