Circulations associated with a mature-to-decaying midlatitude mesoscale convective system. Part I: surface features - heat bursts and mesolow development

Abstract

The mesoscale convective system under investigation developed in an environment with weak vertical shear and had a lifetime of 9-12 h. It consisted in its mature stage of a southward-moving arc-shaped line of deep convective cells with a trailing stratiform precipitation region to the north. Thirty-three percent of the surface rain in the portion of the mesonetwork experiencing storm passage was from the stratiform region. An intense mesoscale downdraft developed beneath the stratiform cloud with a strong mesohigh at the surface. A wake low was positioned just to the rear of the trailing stratiform region. Local "heat bursts' were observed within the wake low. During the final dissipation of the stratiform precipitation (in a matter of 2 h), the surface mesohigh transformed into a mesolow. Observations suggest that at least part of this transformation process can be explained as a collapsing cool pool or spreading density current. -from Authors