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Publications - Occasional Papers

Physical Mechanisms Responsible for the Major Synoptic Systems in the Eastern Canadian Arctic in the Winter and Summer of 1973

INSTAAR Occasional Paper 22

1976, 205 pp. (cost: $5)

In this study the physical processes producing the major centers of synoptic activity in the eastern Canadian Arctic are examined. We choose the total vertical velocity at 85 centibars as an indicator of the intensity of the synoptic activity. A diagnostic three-dimensional atmospheric model from which the total vertical velocity from six physical processes may be computed is designed and validated. These processes are: the differential advection of vorticity, the thickness advection, the release of latent heat, the effects of the surface enthalpy flux, and the influence of friction and orography at the surface. By partitionment of this diagnostic model (the omega equation) into the component vertical velocities the magnitude and relative importance of each process may be determined.

The significance of each physical mechanism is examined at 48 hour intervals throughout the history of a mid-latitude depression system which enters the region as a developing cyclone on July 13, 1973 and leaves on July 22 as a stagnant vortex. The relationships between the large scale flow (the advected properties) and the local influences at various stages of development and decay are of interest. Also discussed is the effect of this synoptic system on the local thermal regime. An important ice melt event occurred during this interval along the eastern Baffin Island coast.

For the winter and summer seasons of 1973 the major synoptic systems in the area are identified by pattern (eigenvector) classification of the 85 centibar total vertical velocity field. For each synoptic feature the average physical processes responsible for the vertical circulation are determined by empirical comparison of patterns in each component field with the pattern of the synoptic feature, and by comparison of magnitudes of the total and component vertical velocities at the center of the feature throughout time. The physical linkages proposed by considerations of these two independent tests are verified by subjective analysis of individual cases. Seasonal trends of these mechanistic linkages are also discussed.

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