Structure of a Frontal System over the Northeast Pacific Ocean

Gordon A. Mcbean Atmospheric Science Programme, Department of Geography, University of British Columbia, Vancouver, B.C., Canada

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Ronald E. Stewart Atmospheric Environment Service, Downsview, Ontario, Canada

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Abstract

A frontal system passed over the Storm Transfer and Response Experiment project area on 17 November 1980. As revealed by ship-born rawinsonde, surface, and radar information, this northeast Pacific storm exhibited three components: it linked surface and 500-mb troughs with marked surface windshift and associated confluence and horizontal wind shear, but exhibiting no surface temperature change; a midtropospheric cold katafront; and an upper moisture front that was moving ahead more rapidly than the other components. The upper moisture front was marked by a moisture gradient across the trailing edge of a large cloud region that moved with the winds at 500 mb or higher. Due to the horizontal thermal homogeneity of the marine boundary layer, the confluence associated with the surface trough did not cause low-level cold frontogenesis. High θw values of the upper portion of the frontal system indicate that air was advected from much farther south. Important characteristics of frontal system evolution over the eastern sections of oceans where the atmosphere may not have had time to reach equilibrium with the underlying ocean surface are noted.

Abstract

A frontal system passed over the Storm Transfer and Response Experiment project area on 17 November 1980. As revealed by ship-born rawinsonde, surface, and radar information, this northeast Pacific storm exhibited three components: it linked surface and 500-mb troughs with marked surface windshift and associated confluence and horizontal wind shear, but exhibiting no surface temperature change; a midtropospheric cold katafront; and an upper moisture front that was moving ahead more rapidly than the other components. The upper moisture front was marked by a moisture gradient across the trailing edge of a large cloud region that moved with the winds at 500 mb or higher. Due to the horizontal thermal homogeneity of the marine boundary layer, the confluence associated with the surface trough did not cause low-level cold frontogenesis. High θw values of the upper portion of the frontal system indicate that air was advected from much farther south. Important characteristics of frontal system evolution over the eastern sections of oceans where the atmosphere may not have had time to reach equilibrium with the underlying ocean surface are noted.

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