Investigating the role of new emission parameterizations in a regional model of the Saharan dust cycle
Final Report Abstract
Mineral dust is one of the major tropospheric aerosol components but its concentrations are highly variable in time and space. In fact, mineral dust emissions are sporadic and spatially heterogeneous and have to be described rigorously. Moreover, the dust cycle is sensitive to size dependent processes occurring during atmospheric transport, like dry and wet deposition. Within this project, simulations of Saharan dust emission, transport and deposition were performed using new developments of the regional model LM-MUSCAT for the SAharan Mineral dUst experiMent (SAMUM-1), which took place in May-June 2006. Up to date surface soil datasets developed specially to model dust emissions were used, and a new representation of the dust size distribution is proposed. Compared to previous model studies performed with LM-MUSCAT, the advantage of our approach is that no tuning factor on the erosion threshold is needed for the whole Sahara. The performances and limitations of LM-MUSCAT to model the regional dust cycle are discussed. The spatio-temporal variability of simulated Saharan emissions is evaluated using a back-tracking approach to locate dust sources with Meteosat Second Generation (MSG) infrared difference images, and using dust observations of North African meteorological stations. 78 Tg Saharan dust are emitted during the studied period. The model dust size distributions agree well with SAMUM-1 airborne measurements, previous model simulations and AErosol RObotic NETwork (AERONET) inversion products. Our ability to simulate the vertical cross section of dust plume is also discussed with regard to airborne lidar measurements and former simulations. The horizontal distribution of model-derived aerosol optical thickness (AOT) is compared with Aqua-MODIS Deep Blue AOT and Ozone Monitoring Instrument (OMI) aerosol index. To investigate the Saharan dust budget (emission and deposition), dry and wet deposition rates are simulated. 67% of the dust is deposited in the vicinity of the emitted source areas over North Africa and close marine areas, and 33% are long-range transported towards other continent and remote ocean areas. However, meteorological dynamics still appear sometimes as a limiting factor to correctly reproduce the dust load, as well as the vertical advection and horizontal distributions. In order to improve the simulation of such dust events, more detailed investigations concerning the meteorological fields should be done in future studies. Moreover, specific work on the influence of the vegetation and the human activities on the mineral dust contents should be performed to better constrain the simulations from partly vegetated and semi-arid areas.
Publications
- Regional investigations on Saharan dust events using the LM-MUSCAT-DES model, 3rd International Workshop on Mineral Dust, Leipzig (Germany), September 2008
Laurent, B., I. Tegen, B. Heinold, K. Schepanski, B. Weinzierl, A. Petzold
- Simulation of the Saharan dust cycle with the LM-MUSCAT-DES regional model during SAMUM 2006, IGAC, Annecy (France), September 2008
Laurent, B., I. Tegen, B. Heinold, K. Schepanski, B. Weinzierl, A. Petzold
- A model study of Saharan dust emissions and distributions during SAMUM-1 campaign, J. Geophys. Res., 2009
Laurent, B., I. Tegen, B. Heinold, K. Schepanski, B. Weinzierl, M. Esselborn
