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Convergence zones and their impact on the initiation of a mesoscale convective system in West Africa

By Vera Klupfel, Norbert Kalthoff, Leonard Gantner and Christopher M. Taylor

Abstract

During the African Monsoon Multidisciplinary Analysis (AMMA) campaign in 2006, extended surface and boundary-layer measurements were performed to study the influence of soil-moisture patterns on the generation of thermallyforced circulations and triggering of deep convection. However, not all processes involved in the triggering of a mesoscale convective system (MCS) could be identified in previous studies. Therefore, COSMO (Consortium for Smallscale Modeling) simulations were carried out investigating possible trigger mechanisms. On 31 July 2006, an MCS was initiated and on 01 August, soilmoisture inhomogeneities resulted in a thermally-forced circulation with an associated convergence zone, but no deep convection was triggered. It was found that the MCS on 31 July was influenced by a cyclonic vortex and favoured by the superposition of two convergence zones of different origin. Initiation of the MCS occurred in the simulation when moist monsoon air was transported to the north, associated with a cold pool ahead of another MCS, and reached the convergence zone. On 01 August, the simulation reproduced the thermally forced circulation caused by the soil-moisture pattern, which had been produced by the precipitation of theMCS. However, due to low humidity in the boundary layer and low convective available potential energy (CAPE), the lifting along the convergence zone did not trigger deep convection

Topics: Meteorology and Climatology
Year: 2012
DOI identifier: 10.1002/qj.979
OAI identifier: oai:nora.nerc.ac.uk:15630
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