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| Titel |
The role of roughness in predicting transport thresholds on desert surfaces: temporal and spatial variability |
| VerfasserIn |
James King, Karsten Haustein, Giles F. S. Wiggs, Frank Eckardt, David S. G. Thomas, Richard Washington |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250084532
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| Zusammenfassung |
| Dust emission schemes in climate models are relatively simple and tuned to represent
observed background aerosol concentrations. A key component of the dust emission scheme
is the sediment transport threshold, which is a function of soil size distribution, soil moisture,
air and soil particle density, and surface roughness. For a particular region or landform that is
not vegetated the variable that controls the transport threshold is soil moisture.
This is because it is assumed that the other components vary little (air and soil
particle densities) or are kept constant (soil size distribution and surface roughness).
This in turn puts the emphasis very heavily on soil moisture and wind stress as the
key drivers of dust emission for specific landforms and dust emission schemes.
This highlights the necessity for current models to tune their model parameters to
observations.
Observations of dust emission were undertaken in 2011 and 2012 on Sua Pan in
Botswana, a large, flat, unvegetated salt pan, as part of the Dust Observation for Models
(DO4 Models) campaign. The observations consisted of eleven meteorological stations
placed within a 144 km2 region recording wind velocity, soil moisture, soil and air
temperature, horizontal transport, vertical transport, and radiative properties. Out of the
measured and calculated erodibility parameters responsible for predicting transport threshold
within current schemes, surface soil moisture and aerodynamic roughness length varied the
most over the duration of the project and spatially across the pan. In some cases, the
aerodynamic roughness length of the bare soil increased by three orders of magnitude within
a three month period. This increase in roughness would almost double the modelled threshold
shear velocity required for this surface to be emissive. The temporal and spatial
variability of the calculated transport threshold is explored with observed data and
compared with the modelled transport threshold for this region for the campaign
duration. These results suggest that for dry saline lakes and other evaporite and
unvegetated emissive surfaces a more detailed aerodynamic roughness dataset is
required to accurately resolve dust production within this landform classification. |
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