The implications for dust emission modeling of spatial and vertical variations in horizontal dust flux and particle size in the Bodélé Depression, Northern Chad

The Bodélé Depression has been confirmed as the single largest source of atmospheric mineral dust on Earth. It is a distinctive source because of its large exposure of diatomite and the presence of mega‐barchan dunes. Direct measurements of horizontal dust flux and particle size were made to investi...

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Bibliographic Details
Published in:Journal of Geophysical Research - Atmospheres 2008-02, Vol.113 (D4), p.D04214-n/a
Main Authors: Chappell, Adrian, Warren, Andrew, O'Donoghue, Alice, Robinson, Andrea, Thomas, Andrew, Bristow, Charlie
Format: Article
Language:English
Subjects:
Aerosols and particles
Africa
Atmospheric Composition and Structure
Atmospheric Processes
barchan dune
bodélé depression
Chad
Density
Diatomite
Dust
dust emission modeling
Earth sciences
Earth, ocean, space
Emission
Exact sciences and technology
Flux
Geographic Location
Horizontal
horizontal flux
Land/atmosphere interactions
Mineral dust
Particle size
Radiative processes
Sahara
Sand
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Summary:The Bodélé Depression has been confirmed as the single largest source of atmospheric mineral dust on Earth. It is a distinctive source because of its large exposure of diatomite and the presence of mega‐barchan dunes. Direct measurements of horizontal dust flux and particle size were made to investigate dust emission processes and for comparison with mechanisms of emission assumed in current dust models. More than 50 masts, with traps mounted on each, were located across and downwind of three barchans in 56 km2 study area of the eastern Bodélé. The size‐distribution of surface material is bi‐modal; there are many fine dust modes and a mixed mineralogy with a particle density three times smaller than quartz. Horizontal fluxes (up to 70 m above the playa) of particles, up to 1000 μm in diameter, are produced frequently from the accelerated flow over and around the barchans, even in below‐threshold shear conditions on the diatomite playa. Our data on dust sizes do not conform to retrievals of dust size distributions from radiance measurements made in the same area. Dust emission models for the region may need to be revised to account for: saltators in the Bodélé, which are a mixture of quartz sand and diatomite flakes; the great spatial and vertical variation in the abundance, mass and density of dust and abraders; and the patterns of surface erodibility. All of these have important local effects on the vertical dust flux and its particle sizes.
ISSN:0148-0227
2169-897X
2156-2202
2169-8996
DOI:10.1029/2007JD009032