Origin of Harmattan dust settled in Northern Ghana — Long transported or local dust?

Lyngsie, Gry; Awadzi, Theodore W.; Breuning‐Madsen, Henrik

doi:10.1016/j.geoderma.2011.07.026

Cited by 17 publications

(9 citation statements)

References 35 publications

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“…A recent analysis of this data set by Klose et al [2010] suggests that dust observed in the Sahel is primarily windborne dust transported from the Sahara. On the other hand, Bou Karam et al [2008] studied several cases of dust storms generated within the monsoon flow over the Sahel, and Lyngsie et al [2011] found that dust collected in northern Ghana had a local origin.…”

Section: Modis Dust Sourcesmentioning

confidence: 99%

Global‐scale attribution of anthropogenic and natural dust sources and their emission rates based on MODIS Deep Blue aerosol products

Ginoux

Prospero

Gill

et al. 2012

Reviews of Geophysics

1,267

1,305

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[1] Our understanding of the global dust cycle is limited by a dearth of information about dust sources, especially small-scale features which could account for a large fraction of global emissions. Here we present a global-scale highresolution (0.1 ) mapping of sources based on Moderate Resolution Imaging Spectroradiometer (MODIS) Deep Blue estimates of dust optical depth in conjunction with other data sets including land use. We ascribe dust sources to natural and anthropogenic (primarily agricultural) origins, calculate their respective contributions to emissions, and extensively compare these products against literature. Natural dust sources globally account for 75% of emissions; anthropogenic sources account for 25%. North Africa accounts for 55% of global dust emissions with only 8% being anthropogenic, mostly from the Sahel. Elsewhere, anthropogenic dust emissions can be much higher (75% in Australia). Hydrologic dust sources (e.g., ephemeral water bodies) account for 31% worldwide; 15% of them are natural while 85% are anthropogenic. Globally, 20% of emissions are from vegetated surfaces, primarily desert shrublands and agricultural lands. Since anthropogenic dust sources are associated with land use and ephemeral water bodies, both in turn linked to the hydrological cycle, their emissions are affected by climate variability. Such changes in dust emissions can impact climate, air quality, and human health. Improved dust emission estimates will require a better mapping of threshold wind velocities, vegetation dynamics, and surface conditions (soil moisture and land use) especially in the sensitive regions identified here, as well as improved ability to address small-scale convective processes producing dust via cold pool (haboob) events frequent in monsoon regimes.Citation: Ginoux, P., J. M. Prospero, T. E. Gill, N. C. Hsu, and M. Zhao (2012), Global-scale attribution of anthropogenic and natural dust sources and their emission rates based on MODIS Deep Blue aerosol products, Rev. Geophys., 50, RG3005,

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Section: Modis Dust Sourcesmentioning

confidence: 99%

Global‐scale attribution of anthropogenic and natural dust sources and their emission rates based on MODIS Deep Blue aerosol products

Ginoux

Prospero

Gill

et al. 2012

Reviews of Geophysics

1,267

1,305

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“…Sediment accumulation data from southern Chad, southwestern Niger, northern Nigeria, and northern Ghana suggest a dramatic decline in dust flux downwind from source; values decline further southwestward over the Gulf of Guinea (Figure c). However, a model of declining flux with distance from source may be oversimple: in northern Ghana, for example, a significant proportion of Harmattan dust fall is of local origin [ Lyngsie et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Holocene dust records from the West African Sahel and their implications for changes in climate and land surface conditions

et al. 2014

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We reconstructed aeolian dust accumulation during the Holocene from two radiocarbon-dated lake-sediment sequences from the Manga Grasslands in northeastern Nigeria in order to investigate long-term changes in the Harmattan dust system over West Africa and evaluate their possible causes. Flux values were low in the early Holocene, decreasing further to a minimum at around 6.2 kyr B.P. after which time they increased, steadily until around 2 kyr B.P. and then more sharply after this time. The long-term variations in dust flux agree broadly with changes in the exposed area of the Lake Chad Basin to the northeast of the study sites, which vary inversely with the volume of Paleolake Megachad. More proximal sources of dust, including the fine fraction of local dune sand and floodplains of nearby rivers, have also made a contribution to the total dust load during times of enhanced dune and fluvial activity. Sharp rises in dust flux over the past century may be related to human activity. Broad patterns of change in dust flux during the Holocene agree with other reconstructions over the same period. However, we see no evidence for a stepped rise during the middle Holocene, as seen at some sites from the northeastern tropical Atlantic, suggesting that controls on the Harmattan dust system have differed from those affecting dust deposition elsewhere across northern Africa.

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“…(a) Tamale—the 5 day period of the dust plume (6–10 January 2007), (b) Kade—the 5 day period of the dust plume (6–10 January2007), (c) Tamale—the 3 month sampling period (1 December 2006 to 28 February 2007), data from Lyngsie et al . [] and, (d) Kade—the 3 month sampling period (1 December 2006 to 28 February 2007). Please pay attention to the different scale bars.…”

Section: Resultsmentioning

confidence: 99%

“…All this indicates that deposition of long transported dust at Tamale is possible and can be assumed to happen. Nevertheless, a study by Lyngsie et al [2011] finds that deposited dust sampled at Tamale outside the Harmattan season has similar elemental composition as dust sampled in the Harmattan season and further that dust sampled within the Harmattan period is missing the trace element signature found in Bod el e sediments, making it likely that a majority of deposited dust is of local origin, with long transported dust being a minor constituent.…”

Section: Discussionmentioning

confidence: 99%

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Influence of the inter tropical discontinuity on Harmattan dust deposition in Ghana

Lyngsie

Olsen

Awadzi³

et al. 2013

Geochem Geophys Geosyst

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[1] The Harmattan is a dry dust-laden continental wind, and in the boreal winter Harmattan dust plumes affects many West African countries, including Ghana. When the Harmattan is strongest the southern part of Ghana is affected by the Inter Tropical Discontinuity (ITD). In this study, we investigate if the ITD functions as a barrier, preventing long transported Harmattan dust to settle south of, and below, it. This is done by analyzing a Harmattan dust outbreak, mapped using Earth observation (EO) data from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) onboard the Meteosat Second Generation (MSG) platform, coupled with data from West African AERONET stations, and comparing these observations with wind data from NOAA's Air Resources Laboratory (ARL) program and the mineral suite of samples from seasonal dust deposits in north and south Ghana. In northern Ghana traces of minerals indicate a weak influence of particles from an arid environment, which is found consistent with the mapped dust plumes and NE wind directions. In southern Ghana the mineral composition show no sediments of an arid origin, the mapped dust plumes is less intense, and the surface wind directions and wind mass trajectories are more varying with lower wind speeds. Based on the results of this study it is concluded that dust deposited, or measured near ground, in the Harmattan period under the ITD, and south of it, does not contain material from the Chad Basin due to the local winds conditions.

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Origin of Harmattan dust settled in Northern Ghana — Long transported or local dust?

Cited by 17 publications

References 35 publications

Global‐scale attribution of anthropogenic and natural dust sources and their emission rates based on MODIS Deep Blue aerosol products

Global‐scale attribution of anthropogenic and natural dust sources and their emission rates based on MODIS Deep Blue aerosol products

Holocene dust records from the West African Sahel and their implications for changes in climate and land surface conditions

Influence of the inter tropical discontinuity on Harmattan dust deposition in Ghana

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