Dust and the low-level circulation over the Bodele Depression, Chad: Observations from BoDEx 2005

[1] Dust plays an important role in climate, recognition of which has led to a concentrated research effort in field campaigns, development and analysis of remotely sensed data, and modeling to better understand dust. There have, however, been very few direct surface-based field measurements from key dust source regions. The Bodele,Chad, has been shown to be one of the premier sources of dust in the world. This paper reports on the Bodele Field Experiment (BoDEx 2005) which took place during February and March 2005 and presents the first surface-based measurements of the circulation over the Bodele. On the basis of Pilot Balloon and AWS data, we confirm the existence of the Bodele Low Level Jet (LLJ) and show that winds undergo a strong diurnal cycle such that strongest surface winds typically occur in the midmorning when momentum is mixed downward in turbulence induced by radiative heating. In contrast, the core of the LLJ, near 500 m, peaks during the evening and is weakest during the day. The LLJ was present on all days during BoDEx 2005, but winds at the surface reached speeds necessary for large-scale dust entrainment on only a few days. The winds strength during the main dust plume event of BoDEx ( 10 - 12 March 2005) was in the bottom third of March plume events of the last 4 years. Pathways of dust transport from the Bodele using a trajectory model show potential advection of dust over the west African coastline within 5 days.