Occluded Fronts and the Occlusion Process: A Fresh Look at Conventional Wisdom
Traditionally, the formation of an occluded front during the occlusion process in extratropical cyclones has been viewed as the catch-up of a faster-moving cold front to a slower-moving warm front separating the warm-sector air from the low center, as first described in the Norwegian cyclone model over 90 yr ago. In this article, the conventional wisdom, or the commonly held beliefs originating from the Norwegian cyclone model, about occluded fronts and the occlusion process are critically examined. The following four tenets of this conventional wisdom are addressed. First, the occlusion process is better described not by catch-up, but by the wrapping up and lengthening of the warm-air tongue as a result of deformation and rotation around the low center. Second, the merger of the cold front and warm front does not result in the frontal zone with the warmer air ascending over the other frontal zone. Instead, the occluded frontal zone tilts over the more statically stable frontal zone. Because a warmfrontal...