Fig. 1. Global average aerosol index from TOMS satellite.
Insert shows typical dust plume event from Bodele depression in Northern Chad

Fig. 2. Making observations during dust storm in the Bodele depression

The unique Bodélé Dust Experiment (BoDEx 2005, see Nature 'The dustiest place on Earth' 434: 816-819, 2005). This was the first ever field campaign in the Bodélé Depression in Northern Chad, the world's greatest single dust source (Fig 1,2). The Bodele Depression is an ancient palaeo lake bed containing fine diatomite sediment laid down about 5000 years ago when palaeolake Mega-Chad was last inundated. Key results include:

(i) First identification and observation of the 'Bodélé low level jet', responsible for the high dust emission (Fig. 3)

Fig 3. Mean wind speed (colours) and direction (arrows) at 925hPa height showing Bodele low level jet.
 Northeasterly 'Harmattan' flow is accelerated by topography surrounding Bodele Depression

(ii) The first observations of optical and physical properties of the diatomite material that makes up dust from the Bodele (Fig. 4)

Fig. 4. Bodele dust. SEM picture of diatomite fragments on filter (top). Plot of single scattering albedo (bottom)

(iii) The discovery that the Bodélé depression contributes about 50% of the total mineral dust transported to the Amazon basin (Fig. 5).

Fig 5. Satellite analysis of dust emission and transport from Bodele to Atlantic and South America (from Koren et al. 2006)