The Occlusion Process in a Midlatitude Cyclone over Land

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  • 1 Department of Atmospheric Sciences, University of Washington, Seattle, Washington
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Abstract

A historical review highlights the lack of consensus regarding the structure and evolution of occluded fronts and cyclones. In order to better understand the occlusion process, this paper and its companion examine a model simulation of the 14–16 December 1987 cyclone over the eastern United States. The structure of an occluded front was observed at low levels as the cold front caught up with the warm front, while aloft an upperlevel frontal zone appeared to play a role in the occlusion process. Although the thermal structure of this storm suggested that a cold-type occlusion should have formed, the model simulation produced a warm-type occlusion structure. An extensive review of the literature on occluded fronts suggested that cold-type occlusions are rare, if they exist at al1. Finally, the occluded front simulated in this case is compared critically to the Norwegian, “T-bone,” and other conceptual models of cyclone evolution.

Abstract

A historical review highlights the lack of consensus regarding the structure and evolution of occluded fronts and cyclones. In order to better understand the occlusion process, this paper and its companion examine a model simulation of the 14–16 December 1987 cyclone over the eastern United States. The structure of an occluded front was observed at low levels as the cold front caught up with the warm front, while aloft an upperlevel frontal zone appeared to play a role in the occlusion process. Although the thermal structure of this storm suggested that a cold-type occlusion should have formed, the model simulation produced a warm-type occlusion structure. An extensive review of the literature on occluded fronts suggested that cold-type occlusions are rare, if they exist at al1. Finally, the occluded front simulated in this case is compared critically to the Norwegian, “T-bone,” and other conceptual models of cyclone evolution.

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