Abstract
Using observed data and model simulations, an attempt is made to verify that baroclinic instability can be viewed as an interaction and mutual amplification of a pair of upper- and lower-tropospheric potential vorticity (PV) perturbations. This view has recently been advanced by Hoskins et al. and McIntyre. Two episodes from March and May 1989, encompassing two lee-cyclogenetic events east of the Rocky Mountains and one over the central Gulf states, are selected to demonstrate this concept. In order to depict the low-level PV maximum which forms infinitely thin sheets of infinite PV, the display of PV in cartesian space is replaced by a display of absolute vorticity in isentropic space. Perspective computer drawings of iso-surfaces of absolute vorticity in three-dimensional space are found to be a convenient means of conveying the desired information.
