Mesoscale Air Motions Associated with a Tropical Squall Line

Abstract

Composites of radar and wind observations in a coordinate system attached to a moving tropical squall line confirm that such a squall system is composed of two separate circulation features: a convective squall-line region and a stratiform anvil region. The squall-line region is characterized by mesoscale boundary-layer convergence, which feeds deep convective updrafts, and mid-to-upper-level divergence associated with outflow from the cells. The anvil region is characterized by mid-level convergence, which feeds both a mesoscale downdraft below the anvil and a mesoscale updraft within the anvil cloud. Before this study, the mesoscale updraft in the anvil cloud of the tropical squall system had been somewhat speculative, and both the anvil updraft and downdraft had been inferred only qualitatively. The occurrence of the anvil updraft is now proven and quantitative profiles of the mesoscale anvil updraft and downdraft have been obtained.