The role of boundary-layer convergence zones and horizontal rolls in the initiation of thunderstorms: a case study

Abstract

The study examines the initiation of a line of thunderstorms that developed along a preexisting, quasi-stationary boundary-layer convergence line on 17 July 1987. The storms were triggered at the intersection of the convergence line with horizontal rolls where enhanced updrafts were present. The primary effect of the convergence line was to deepen the moist layer locally and provide a region potentially favorable to deep convection. The critical factor governing the time of storm development was apparently related to the attainment of a balance between horizontal vorticity in the opposing flows on either side of the convergence line. The effect was to cause the updrafts in the convergence line to become more erect and the convergence zone deeper. Modeling results for this case also indicated that storm initiation was very sensitive to the depth of the convergence- line circulation. -from Authors