Open AccessThe implications for dust emission modeling of spatial and vertical variations in horizontal dust flux and particle size in the Bodélé Depression, Northern Chad
Author(s) -
Chappell Adrian,
Warren Andrew,
O'Donoghue Alice,
Robinson Andrea,
Thomas Andrew,
Bristow Charlie
Publication year - 2008
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2007jd009032
Subject(s) - mineral dust , flux (metallurgy) , atmospheric sciences , quartz , radiance , environmental science , particle size , particle size distribution , particle (ecology) , spatial variability , mass flux , mineralogy , geology , aerosol , meteorology , materials science , physics , remote sensing , oceanography , mechanics , paleontology , statistics , mathematics , metallurgy
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 km 2 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 μ m 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.