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UBC Theses and Dissertations

Structure of the northeast Pacific wave cyclone of 19 November 1980 Gratham, Christopher H.


The frontal system that passed over the Storm Transfer and Response Experiment Study area on 19 November 1980 was the third vigorous system in succession to affect this region of the northeast Pacific Ocean. This study marks the first detailed investigation of a frontal wave over the Gulf of Alaska and as such provides structural details not shown in other studies. Precipitation and changes in temperature, wind velocity, and pressure were associated with the passage of both the warm and cold fronts. The thermal structure exhibits a well defined warm sector with regions of large baroclinicity in both the warm and cold frontal zones. Data from radiosonde releases from the northern-most of two observing platforms indicate a mid-level upper moisture front above the kata cold front. Throughout these northern cross-sections, gradients in the warm and cold frontal zones are of similar magnitudes while sections from the southern ship show a warm frontal zone that is more intense than the cold transition region. Along-frontal gradients of equivalent potential temperature are of the same order of magnitude as the cross-frontal gradients. Horizontal wind components relative to the storm indicate strong inflow to the system at lower layers from both south and east. The wind exits the system to the west and south. Upper level winds are westerly throughout. Gradients of wind components are strongest in frontal zones, which results in the cold front coincident with the peak axis in the vertical component of relative vorticity. The field of horizontal divergence also exhibits its largest magnitudes in the frontal zones, with convergence in the warm frontal zone and divergence in the cold transition region. This seldom observed feature of divergence at the cold front leads to a downwelling motion in this region and categorizes the front as a kata-cold trout. Most of the upward vertical velocity occurs in and around the warm frontal zone as a result of horizontal convergence in this region. Relative isentropic analysis indicates that there are three main air streams within the system. The warm conveyor belt flows to the north in the warm sector and rises gradually as it makes it way to the north. Ahead of the warm front and behind the cold front are two cold air streams that flow to the north and south respectively. Analysis of the kinematic, frontogenesis indicates that confluence and infrequently studied shear effects are the most important processes influencing the frontal gradients. Analysis of uncertainty in the terms of the prognostic kinematic frontogenesis equations reveals that the diabatic heat and twisting terms that others have found important are smaller than their estimated errors in this study.

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