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| Titel |
The Role of Deep Convection and Low-Level Jets Forcing Dust Emissions in West Africa: A High-Resolution Regional Dust Modelling Study |
| VerfasserIn |
B. Heinold, P. Knippertz, S. Fiedler, J. H. Marsham, I. Tegen |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250068001
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| Zusammenfassung |
| West Africa is the world’s most important source of atmospheric mineral dust, which impacts
weather and climate through its contribution to the direct and indirect aerosol effects. Mineral
dust also has an impact on the biogeochemical and hydrological cycle, and affects
human health and air quality. Quantitative estimates of the various effects require an
adequate representation of modelled peak-wind generating mechanisms that cause dust
emissions.
Daytime downward mixing of momentum from nocturnal low-level jets (LLJs) and
convective cold pools (haboobs) have been identified as important meteorological drivers of
dust emissions in the Sahel and Sahara. Previous work using 10-day continental-scale
convection-permitting simulations of summertime West Africa, performed using the UK Met
Office Unified model as part of the Cascade project, has shown that these processes dominate
the modelled dust-generating winds, with haboobs being very poorly represented in models
with parameterised deep convection. This previous work did not, however, model dust
emission explicitly. As part of the “Desert Storms” project (funded by the European
Research Council), we expand on this work here using newly available 40-day
Cascade runs with dust emissions calculated in an offline model driven with the
modelled surface winds at 40, 12, 4 and 1.5-km horizontal grid-spacings (6 days
only at 1.5 km). These calculations include different versions of dust emission
parameterisations and soil surface properties, allowing separation of meteorological and
land-surface effects. A major focus is on the statistical analysis of the diurnal cycle of
wind speed and dust emission, for which the long simulation period provides a
robust basis. The diurnal cycle gives insight into the role of different meteorological
processes and is expected to affect the subsequent dust transport in the boundary
layer.
The high-resolution results show dust emission patterns in fascinating detail. For the first
time it could be shown how dust mobilisation is characterised by both long-lived large
propagating haboobs and numerous smaller-scale short-lived microburst-like events. The
results suggest that the role of moist convective processes is sensitive to land surface
characteristics in the southern Sahara and Sahel region, where convective outflows are most
frequent. The findings will ultimately lead to a better representation of these dust-generating
processes in global and regional scale dust models. |
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