The Possible Influence of Upstream Upper-Level Baroclinic Processes on the Development of the QE II Storm

Abstract

An analysis of the QE II storm of 9?11 September 1978 presents evidence for the existence of upper-level baroclinic processes upstream of the rapidly developing cyclone. The analysis shows that a deepening shortwave trough was located 400 to 500 km upstream of the site of the storm 12 h prior to rapid cyclogenesis. The trough was associated with 1) a polar jet marked by 65 m s?1 winds in its core and significant vertical and horizontal wind shear, 2) positive vorticity advection and divergence at the 300 mb level, and 3) an intense frontal zone that extended from 300 mb down to the surface. It also appears that a tropopause fold likely extruded stratospheric air down to the 700?800 mb level, 400?500 km upstream of the surface low and 12 h prior to the explosive development phase of the cyclone. These findings raise questions about Gyakum's assertion that the QE II storm developed in an area in which the baroclinic support was confined to the lower troposphere and the related assertion by Anthes et al. that upper-level forcing upstream of the area of rapid cyclogenesis was weak and apparently not important in this case.