Dynamical conceptual models of upper-level mobile trough formation: comparison and application

Abstract

While the formation of upper-level mobile troughs has received little observational attention, a variety of theories have been proposed to explain the genesis and intensification of mobile troughs. For purposes of intercomparison and qualitative application to observed cases, these theories are described in terms of the generation of waves along the tropopause potential vorticity discontinuity. These models are then tested on a case of mobile trough formation which occurred on 19–20 April 1991 and which was poorly forecasted by operational models. The ridge-trough system is found to have been produced primarily by Rossby wave propagation along the tropopause from a newly-developed cutoff cyclone located to the west. Both vertical and horizontal propagation contributed to the development. Another mechanism which appeared to have a positive effect was superposition due to vertical shear and horizontal deformation. A vorticity maximum within the newly-formed trough was amplified and advected southeastward by the developing larger-scale ridge/trough system and later participated in a surface cyclogenesis event. DOI: 10.1034/j.1600-0870.1995.00114.x