Local Weather

Parker, Douglas J.; Kassimou, Abdou; Orji, Bernard N.; Osika, David; Hamza, Ibrahim; Diop-Kane, Mariane; Fink, Andreas H.; Galvin, Jim; Guichard, Françoise; Lamptey, Benjamin; Hamidou, Hama; Linden, Roderick van der; Redl, Robert; Lebel, Thierry; Tubbs, Chris

doi:10.1002/9781118391297.ch4

Cited by 21 publications

(46 citation statements)

References 69 publications

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“…This is not so clear from the wind intensity (Fig. 4d-f) but Parker et al (2017) explain that the sea breeze does not behave as a gravity current since the monsoon flow is strong but rather as a deepening of the boundary layer from the coast to inland. As shown in Fig.…”

Section: Better Diurnal Cycle In Cp4amentioning

confidence: 89%

Improved climatological precipitation characteristics over West Africa at convection-permitting scales

et al. 2019

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The West African climate is unique and challenging to reproduce using standard resolution climate models as a large proportion of precipitation comes from organised deep convection. For the first time, a regional 4.5 km convection permitting simulation was performed on a pan-African domain for a period of 10 years (1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006). The 4.5 km simulation (CP4A) is compared with a 25 × 40 km convection-parameterised model (R25) over West Africa. CP4A shows increased mean precipitation, which results in improvements in the mature phase of the West African monsoon but deterioration in the early and late phases. The distribution of precipitation rates is improved due to more short lasting intense rainfall events linked with mesoscale convective systems. Consequently, the CP4A model shows a better representation of wet and dry spells both at the daily and sub-daily time-scales. The diurnal cycle of rainfall is improved, which impacts the diurnal cycle of monsoon winds and increases moisture convergence in the Sahel. Although shortcomings were identified, with implications for model development, this convection-permitting model provides a much more reliable precipitation distribution than its convectionparameterised counterpart at both daily and sub-daily time-scales. Convection-permitting scales will therefore be useful to address the crucial question of how the precipitation distribution will change in the future.

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Section: Better Diurnal Cycle In Cp4amentioning

confidence: 89%

Improved climatological precipitation characteristics over West Africa at convection-permitting scales

et al. 2019

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“…Level 2 products are provided as granules with a spatial resolution of 10 km at nadir. The standard deviation on the AOD retrieval (Remer et al, 2005) over land (ocean) is 0.15 ± 0.05 × AOD (0.05 ± 0.03 × AOD). We also use level 3 daily sea surface temperature (SST) data derived from the 11 µm thermal infrared band available at 9.26 km spatial resolution for daytime passes (Werdell et al, 2013).…”

Section: Space-borne Observationsmentioning

confidence: 99%

“…Parker et al, 2005;Lothon et al, 2008;. On hot, cloud-free summer days, land-sea breeze systems can develop at the coast (in conditions of moderate background monsoon flow, Parker et al, 2017), which contribute to the transport of pollutants emitted along the urbanized coastal strip of SWA.…”

Section: Introductionmentioning

confidence: 99%

Aerosol distribution in the northern Gulf of Guinea: local anthropogenic sources, long-range transport, and the role of coastal shallow circulations

et al. 2018

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Abstract. The complex vertical distribution of aerosols over coastal southern West Africa (SWA) is investigated using airborne observations and numerical simulations. Observations were gathered on 2 July 2016 offshore of Ghana and Togo, during the field phase of the Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa project. This was the only flight conducted over the ocean during which a downward-looking lidar was operational. The aerosol loading in the lower troposphere includes emissions from coastal cities (Accra, Lomé, Cotonou, and Lagos) as well as biomass burning aerosol and dust associated with long-range transport from central Africa and the Sahara, respectively. Our results indicate that the aerosol distribution on this day is impacted by subsidence associated with zonal and meridional regional-scale overturning circulations associated with the land–sea surface temperature contrast and orography over Ghana and Togo, as typically observed on hot, cloud-free summer days such as 2 July 2016. Furthermore, we show that the zonal circulation evidenced on 2 July is a persistent feature over the Gulf of Guinea during July 2016. Numerical tracer release experiments highlight the dominance of aged emissions from Accra on the observed pollution plume loadings over the ocean, in the area of aircraft operation. The contribution of aged emission from Lomé and Cotonou is also evident above the marine boundary layer. Given the general direction of the monsoon flow, the tracer experiments indicate no contribution from Lagos emissions to the atmospheric composition of the area west of Cotonou, where our airborne observations were gathered. The tracer plume does not extend very far south over the ocean (i.e. less than 100 km from Accra), mostly because emissions are transported northeastward near the surface over land and westward above the marine atmospheric boundary layer. The latter is possible due to interactions between the monsoon flow, complex terrain, and land–sea breeze systems, which support the vertical mixing of the urban pollution. This work sheds light on the complex – and to date undocumented – mechanisms by which coastal shallow circulations can distribute atmospheric pollutants over the densely populated SWA region.

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“…The energy balance at the surface is more complicated than that at the TOA because the energy flows by conduction and convection of heat and moisture through turbulent fluid motion must be considered in addition to the radiation 92 . The surface energy balance is composed of four main terms: net radiation, sensible heat flux, latent heat flux, and ground heat flux, given here by the surface energy budget (Q) equation 93 , 94 : …”

Section: Methodsmentioning

confidence: 99%

“…GH (Ground Heat flux) is the energy loss through the lower boundary by heat conduction 92,93 . SH (Sensible Heat flux) and LH (Latent Heat flux) are positive upward, and represent the energy loss from the Earth's surface to the atmosphere associated with heat transfer and evaporation, respectively 94 . All these radiation fluxes are in W/m 2 and positive quantities 93 .…”

Section: Model Description and Experiments We Used Version 402 Of mentioning

confidence: 99%

Dust radiative forcing and its impact on surface energy budget over West Africa

Chaibou

Sha

2020

Sci Rep

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Dust is the dominant aerosol type over West Africa (WA), and therefore accurate simulation of dust impact is critical for better prediction of weather and climate change. the dust radiative forcing (DRf) is estimated using two sets of experiments in this study: one without and the other with dust aerosol and its feedbacks with the Weather Research and forecasting with chemistry model (WRf-chem). Results show that DRF presents a net warming effect at the top-of-atmosphere (TOA) and in the atmosphere (ATM), and cooling at the surface (SFC). The net DRF over WA is estimated to be 9 W/m 2 at the TOA, 23 W/m 2 in the ATM, and − 13 W/m 2 at the Sfc. furthermore, dust-induced a reduction of sensible heat up to 24 W/m 2 and SFC temperature up to 2 °C cooling over WA, an increase of latent heat up to 12 W/m 2 over Sahara, a decrease up to 24 W/m 2 over the vegetated surfaces and an increase in the surface energy balance up to 12 W/m 2 over WA. The presence of dust significantly influences the surface energy budget over WA, suggesting that dust effects should be considered in more climate studies to improve the accuracy of climate predictions. Aerosols play a vital role in the climate system and have been among the major uncertainties in predictions of future climate change 1. West Africa (WA) is one of the most vulnerable regions to climate change, with the Sahara desert as the major source of dust aerosols in the world 2-5. The vulnerability is higher in the Sahel region, which has experienced a long period of drought in the late 1960s and 1980s. Numerous studies have pointed out that dust loading over the Sahel has increased significantly between the 1960s and 1980s, and is the consequence of drying of the region 6-13. Since the 1990s, better rainfall conditions appear to occur in the Sahel region 14-16. On this basis, a comprehensive investigation of dust impact on climate variability and drought in WA is essential, where the economy depends mostly on rainfed agriculture and transhumant livestock 11,15,17-19. To improve our understanding, the scientific community has launched several field campaigns, such as SaHAran Dust Experiments (SHADE) 20 , SAharan Mineral dUst experiMent (SAMUM) 21 , African Monsoon Multidisciplinary Analysis (AMMA) 22 , etc. Dust aerosols emitted from the Sahara and Sahel are considerably higher than any other desert in the world. The surface wind speed is the primary controlling factor of the emission and transport of dust particles into the atmosphere to great distances by convective events that develop actively in the desert 2,3,5,23,24. More than half of dust deposited in the oceans comes from elsewhere in North Africa. Saharan dust contains nutrients that fertilize soils and water, block or reflect sunlight, affect the formation of clouds and cyclones 25-27. Interactions of dust particles with radiation in the troposphere (absorption, scattering, etc.) are the basis in changing atmospheric state parameters, which may induce significant changes in climate. Dust aerosols influence many proces...

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Local Weather

Cited by 21 publications

References 69 publications

Improved climatological precipitation characteristics over West Africa at convection-permitting scales

Improved climatological precipitation characteristics over West Africa at convection-permitting scales

Aerosol distribution in the northern Gulf of Guinea: local anthropogenic sources, long-range transport, and the role of coastal shallow circulations

Dust radiative forcing and its impact on surface energy budget over West Africa

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