EPHEMERAL LAKES AND DESERT DUST: REDUX Seminar

The emission of dust plays an important role in the Earth system through interaction with biogeochemical cycles and direct/indirect radiative forcing of the atmosphere. We currently predict the impacts of dust emission through use of global numerical models. However, the relative sophistication of existing models of dust transport/processing/deposition far outstrips validation against in situ observations. The impact of dust in the Earth’s system depends on key characteristics: particle size, shape, mineralogy. Whilst these can change during dust transport, they are initially determined by the sources from which particles are entrained. However, our understanding of spatial/temporal controls on erodibility/erosisivity parameters for dust emissions are poorly constrained.

Ephemeral lakes within the world’s drylands emit a disproportional amount of dust. We can also see from global satellite-derived records of dust flux that emissions from ephemeral lake basins display significant inter-annual variability in magnitude. Working on large ephemeral lakes in southern Africa, Mahowald et al., (2003) and Bryant et al., (2007) attempted to link variability in records of dust flux derived from the TOMS, with measurements of ephemeral flooding within lake basins derived from AVHRR; both data sets displaying rather coarse spatial/temporal resolution. Although tentative links between regional climate and records of dust emission were proven, the course spatial and temporal resolution of the data used precluded any real understanding of controls on dust emissions at the sub-basin scale. However, recent work - involving a return to the same lake basins but with much better data - using a combination of MSG-SEVIRI data (to capture individual dust emission events), MODIS (to capture surface inundation), and ERA-Interim data (to capture wind magnitude/frequency) have finally been able to highlight significant controls on erodibility/erosisivity parameters at the sub-basin scale. These data form the basis of continued efforts to improve models of dust emission from ephemeral lake sources.

References
Bryant, R.G., Bigg, G.R., Mahowald, N.M., Eckhardt, F.D., and Ross, S.G., (2007). Dust emission response to climate in southern Africa. Journal of Geophysical Research - Atmospheres.
doi:10.1029/2005JD007025
Mahowold, N.M., Bryant, R.G., del Corral, J. and Steinberger, L. (2003). Ephemeral Lakes and desert dust sources. Geophysical Research Letters, 30(2).
doi:10.1029/2002GL016041