Impact of soil moisture and convectively generated waves on the initiation of a West African mesoscale convective system

Birch, C.E.; Parker, D.J.; O'Leary, A.; Marsham, J.H.; Taylor, C.M. ORCID: https://orcid.org/0000-0002-0120-3198; Harris, P.P.; Lister, G.M.S.. 2013 Impact of soil moisture and convectively generated waves on the initiation of a West African mesoscale convective system. Quarterly Journal of the Royal Meteorological Society, 139 (676). 1712-1730. 10.1002/qj.2062

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Abstract/Summary

A mesoscale convective system (MCS) case study was observed over northeast Mali as part of the African Monsoon Multidisciplinary Analysis (AMMA) on 31 July 2006. Observations of this case suggest that the soil-moisture heterogeneity and atmospheric gravity waves emitted from a ‘parent’ MCS were important trigger mechanisms for this system. This study uses high-resolution Met Office Unified Model (MetUM) simulations to assess the importance of the synoptic circulation, land-surface and gravity waves in the initiation and development of the MCS. During the early afternoon shallow convection developed over a region of dry soil within a synoptic-scale convergence zone, which was caused by the confluence of the southerly monsoon flow with winds associated with the circulation around the Saharan heat low. Two pronounced waves were emitted from a nearby ‘parent’ storm and propagated towards the convergence zone. When the second wave reached the location of the shallow convection, deep convection was immediately initiated. Further convective cells developed later in the afternoon over dry soil, many adjacent to strong soil moisture gradients; these aggregated with the main storm, which later developed into the case study MCS. A comparison of model simulations with/without the soil-moisture heterogeneity and gravity waves shows that the synoptic-scale circulation and convergence zones, specified by the atmospheric analysis, were the most important factors for the successful simulation of the MCS. If the location of the initiation of the system is to be forecast accurately, the land-surface, that is, the soil moisture, must be represented adequately. In order to reproduce the timing of the secondary initiation of convection correctly the model must be able to capture gravity waves that are emitted by existing systems.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1002/qj.2062
Programmes:	CEH Topics & Objectives 2009 - 2012 > Biogeochemistry > BGC Topic 2 - Biogeochemistry and Climate System Processes > BGC - 2.3 - Determine land-climate feedback processes to improve climate model predictions
UKCEH and CEH Sections/Science Areas:	Reynard
ISSN:	0035-9009
Additional Keywords:	mesoscale convective system (MCS), secondary initiation, gravity wave, soil moisture, AMMA
NORA Subject Terms:	Meteorology and Climatology
Date made live:	21 Dec 2012 09:46 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/20887

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