The Role of Shearwise and Transverse Quasigeostrophic Vertical Motions in the Midlatitude Cyclone Life Cycle

TLDR: In this paper, the authors analyzed the physical role played by each of these components of vertical motion in the midlatitude cyclone life cycle and showed that the origin and subsequent intensification of the lower-tropospheric cyclone responds predominantly to column stretching associated with the updraft portion of the shear-wise QG vertical motion.

Abstract: The total quasigeostrophic (QG) vertical motion field is partitioned into transverse and shearwise couplets oriented parallel to, and along, the geostrophic vertical shear, respectively. The physical role played by each of these components of vertical motion in the midlatitude cyclone life cycle is then illustrated by examination of the life cycles of two recently observed cyclones. The analysis suggests that the origin and subsequent intensification of the lower-tropospheric cyclone responds predominantly to column stretching associated with the updraft portion of the shearwise QG vertical motion, which displays a single, dominant, middle-tropospheric couplet at all stages of the cyclone life cycle. The transverse QG omega, associated with the cyclones’ frontal zones, appears only after those frontal zones have been established. The absence of transverse ascent maxima and associated column stretching in the vicinity of the surface cyclone center suggests that the transverse ω plays little role i...