An Intercomparison of Simulated Rainfall and Evapotranspiration Associated with a Mesoscale Convective System over West Africa

Guichard, Françoise; Asencio, N.; Peugeot, Christophe; Bock, Olivier; Redelsperger, Jean‐Luc; Cui, Xuefeng; Garvert, Matthew F.; Lamptey, Benjamin; Orlandi, E.; Sander, Julia; Fierli, F.; Gaertner, Miguel Ángel; Jones, Sarah; Lafore, Jean‐Philippe; Morse, Andrew P.; Nuret, Mathieu; Boone, Aaron; Balsamo, Gianpaolo; Rosnay, Patricia de; Decharme, Bertrand; Harris, Phil; Bergès, Jean

doi:10.1175/2009waf2222250.1

Cited by 25 publications

(32 citation statements)

References 52 publications

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“…These findings are in agreement with Guichard et al (2010), who show that the initial and boundary conditions significantly control the locations of rainfall over West Africa, and that explicit moist convection improves the precipitation distribution, MCS trajectory and propagation speed but cannot correct for weaknesses in the analysis. Klüpfel et al (2011b) also suggest that the boundary-layer convergence zone was the most important triggering mechanism for this case.…”

Section: The Relative Importance Of the Different Triggering Mechanismssupporting

confidence: 90%

“…They concluded that although there were major variations in the precipitation produced in the simulations, the timing of convection initiation was influenced mainly by the atmospheric forcing. A similar result was found by Guichard et al (2010), who found that the conditions used to initialize both mesoscale and global models had a significant control on the location of rainfall at synoptic scales.…”

Section: Convection and Land-surface Interaction Over West Africasupporting

confidence: 82%

“…This JULES simulation was forced with 0.5 • near-surface boundary conditions provided by the AMMA Land Surface Model Intercomparison Project, ALMIP (Boone et al, 2009), along with satellite-derived Bergès et al, 2010). The model was constrained daily by adjusting nonzero EPSAT-SG rainfall amounts for each 3 km pixel to give the root-mean-squared best fit between modelled and observed LST, yielding a fine resolution soil moisture estimate on the domain (10-20 • N, 10 • W-10 • E) at 0.0275 • (∼3 km) resolution.…”

Section: Model Experiments and Set-upmentioning

confidence: 99%

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

Birch

Parker

O’Leary

et al. 2012

Quart J Royal Meteoro Soc

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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.

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Section: The Relative Importance Of the Different Triggering Mechanismssupporting

confidence: 90%

Section: Convection and Land-surface Interaction Over West Africasupporting

confidence: 82%

Section: Model Experiments and Set-upmentioning

confidence: 99%

See 1 more Smart Citation

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

Birch

Parker

O’Leary

et al. 2012

Quart J Royal Meteoro Soc

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“…This period includes a mesoscale convective system which formed on 28 August over Nigeria, crossing the central part of the domain. A more detailed description of this mesoscale convective system can be found in Guichard et al (2010). European Centre for Medium-Range Weather Forecasts (ECMWF) analysis data have been used for assigning initial and lateral boundary conditions.…”

Section: Set-up Of Simulationsmentioning

confidence: 99%

“…The control simulation has been compared with observations in a different study (Guichard et al, 2010), and therefore we only summarise here the main aspects of that comparison. That study is a model intercomparison focused on precipitation and evaporation for the mesoscale convective system of 28-29 August 2005.…”

Section: Control Simulation Analysismentioning

confidence: 99%

A modelling case‐study of soil moisture–atmosphere coupling

Gaertner

Domínguez

Garvert³

2010

Quart J Royal Meteoro Soc

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A sensitivity analysis of a moist convection case-study of the 2005 West African monsoon has been performed with the limited-area model PROMES. In the control simulation, soil moisture was initialized based on European Centre for Medium-Range Weather Forecasts (ECMWF) soil moisture. A relatively wet patch appears over an area that was affected later by the passage of a squall line. The control simulation is able to reproduce a squall line that crosses over this wet surface, which makes it possible to analyse the sensitivity of the modelled convective system to a soil moisture increase up to saturation in the cited patch. The wetter land surface in the sensitivity run generates a cooler and moister area in the near-surface atmospheric fields compared to the control run, and the surface wind differences between both runs show a divergent pattern. The humidity and temperature differences follow the diurnal cycle of the monsoon flow, as the cool and moist atmospheric perturbation remains over the wet patch during the afternoon, and moves towards the northeast during the night. There is a clear interaction between the soil moisture perturbation and an approximating African Easterly Wave. This interaction generates larger differences between the two runs on the second simulation day than on the first. The precipitation is reduced over the wet patch in the sensitivity run, but over a larger area a precipitation increase is obtained, reflecting a complex soil moisture-precipitation feedback.

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A seamless assessment of the role of convection in the water cycle of the West African Monsoon

Birch

Parker

Marsham

et al. 2014

J. Geophys. Res. Atmos.

114

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A suite of 40 day UK Met Office Unified Model simulations over West Africa during summer 2006 are analyzed to investigate the causes of biases in the position of the rainbelt and to understand the role of convection in the regional water budget. The simulations include climate, global operational, and limited area runs (grid spacings from 1.5 to 40 km), including two 12 km runs, one with parameterized and one with explicit convection. The most significant errors in the water cycle terms occur in the simulations with parameterized convection, associated with the diurnal cycle and the location of the convection. Errors in the diurnal cycle increase the northward advection of moisture out of the Sahel toward the Sahara but decrease the advection of moisture into the Sahel from further south, which limits the availability of moisture for Sahelian rainfall. These biases occur within the first 24 h, showing that they originate from the representation of fast physical processes, specifically, the convection scheme. Once these rainfall regimes have been established, the terms of the water budgets act to reinforce the biases, effectively locking the rainbelt's latitude. One of the simulations with parameterized convection does, however, produce a better latitudinal distribution of rainfall because on the first day it is better able to trigger convection in the Sahel. Accurate representation of the diurnal cycle of convection and the ability to trigger convection in a high convective inhibition environment is key to capturing the water cycle of the region and will improve the representation of the West African Monsoon.

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An Intercomparison of Simulated Rainfall and Evapotranspiration Associated with a Mesoscale Convective System over West Africa

Cited by 25 publications

References 52 publications

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

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

A modelling case‐study of soil moisture–atmosphere coupling

A seamless assessment of the role of convection in the water cycle of the West African Monsoon

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