Coherent tropopause disturbances on the periphery of continental anticyclones as triggers for mesoscale convective systems

Coherent disturbances on the dynamic tropopause (CTDs) occur at all times of the year, and frequently originate from the circumpolar vortex in high latitudes. However, a subset of CTDs originate as fractures from the equatorward end of northeast-to-southwest oriented potential vorticity (PV) "tails" that lie eastward of quasi-stationary midlatitude upper-level anticyclones. These fractured CTDs typically move westward along the equatorward flanks of these anticyclones in the lower midlatitudes and the subtropics.

A subset of these westward-moving CTDs, known as "ridge rollers" (RRs), may circumnavigate the anticyclone as they curve poleward and then eastward around the western and poleward sides of the anticyclone. As these RRs encounter the westerlies on the poleward periphery of the anticyclone, they may interact with other sub-synoptic scale disturbances embedded in the westerlies. The importance of these RRs is that they may be associated with convection along the anticyclone periphery with organized mesoscale convective systems (MCSs) occurring on the poleward periphery where the aforementioned upper-level westerly flow, and associated jet-entrance region, provides enhanced ascent and deep-layer shear in a warm, moist and unstable air mass. This poster presentation will illustrate the behavior of RRs and their role in triggering MCSs with case studies from July 1995 and February 2004 over the US and Australia, respectively.