Dust wind tracers over the Central Sahara (5 January 2005)

by Jochen Kerkmann (EUMETSAT) and Martin Setvak (CHMI)

As shown in the image of the month Wind-driven land surface features in the Sahara desert, the Borkou region in Northern Chad between the Tibesti Mountains (3415 m) and Ennedi Mountains (1450 m) represents a "bottleneck" for the low-level winds that approach this region from the northeast. As this orographic low-level jet blows further south, exiting the Borkou "bottleneck", by coincidence it passes above the Bodele Depression - a dried salty lake, which serves as a very efficient source of small particles for local dust storms. According to NASA experts, "the dry bowl that forms the Bodele Depression is one of the most active sources of wind-blown dust in the world. The depression is marked by a series of ephemeral lakes, which may be infrequently flooded with mud-laden water from the mountains. When the lakes dry, a layer of loose clay is left behind. The dirt is easily carried on the wind that blows down from the mountains".

The Meteosat-8 images below show a major (continental-scale) dust outbreak that occurred in the beginning of January 2005. As discussed above, huge quantities of dust get picked up in the Bodele Depression and carried towards Niger and Nigeria. Another area where dust easily gets picked up is the area of Agadez (Niger), to the northwest of the Bodele Depression. As the fine dust particles serve as a passive tracer, they nicely show the channelled airflow (streamlines) in the Borkou area and around the major mountain ranges (Tibesti, Massif de l'Air) in the Central Sahara.

Meteosat-8 Images Met-8, 05 January 2005, 12:00 UTC RGB Composite IR12.0-IR10.8, IR10.8-IR8.7, IR10.8 Full Resolution (JPG, 104 KB) Large Area (JPG, 1370 KB) Animation (08:00-16:00 UTC, MPG, 6450 KB) Met-8, 05 January 2005, 12:00 UTC RGB Composite NIR1.6, VIS0.8, VIS0.6 Full Resolution (JPG, 273 KB) Large Area (JPG, 1160 KB) Animation (08:00-16:00 UTC, MPG, 6447 KB) See also: Wind-driven geological features in the Sahara desert (Waw al-Namus, Libya) Sahara dust outbreak across the Western Mediterranean (28 July 2005) Dust storm over West Africa and the Canary Islands (3 March 2004) Met-8 High-Resolution Visible (HRV) image (5 Jan 2005, 08:00 UTC, GIF, 351 KB) Aqua MODIS reduced-resolution image (5 Jan 2005, 12:10 UTC, JPG, 339 KB, source: M. Setvak) Aqua MODIS high-res. (500 m) image (5 Jan 2005, 12:10 UTC, JPG, 4106 KB, source: M. Setvak)

Meteosat-8 images showing continental-scale dust outbreak over the Sahara and the Sahel area Met-8, 05 January 2005, 12:00 UTC RGB Composite IR12.0-IR10.8, IR10.8-IR8.7, IR10.8 Full Resolution (1419 KB) Met-8, 06 January 2005, 12:00 UTC RGB Composite IR12.0-IR10.8, IR10.8-IR8.7, IR10.8 Full Resolution (1407 KB) Met-8, 07 January 2005, 12:00 UTC RGB Composite IR12.0-IR10.8, IR10.8-IR8.7, IR10.8 Full Resolution (1466 KB) Met-8, 08 January 2005, 12:00 UTC RGB Composite IR12.0-IR10.8, IR10.8-IR8.7, IR10.8 Full Resolution (1486 KB)

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