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| Titel |
Saharan Airborne Dust Flux Measurements from the Fennec Campaign |
| VerfasserIn |
Phil Rosenberg, Doug Parker, Claire Ryder, Luis Garcia-Carreras, John Marsham, James Dorsey, Ian Brooks, Angela Dean, Jonathan Crosier, Jim McQuaid, 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 |
250081242
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| Zusammenfassung |
| The Fennec campaign of 2011involved deployment of the Facility for Airborne Atmospheric
Measurements BAe 146 (FAAM Bae 146) scientific research aircraft to Fuerteventura with
research flights over the remote Saharan desert in Mali and Mauritania. The aims of the
Fennec campaign were to characterise the dynamics, radiation and dust environment in this
inaccessible region.
The FAAM BAe 146 operated a suite of instruments which measured size distributions of
dust including a Passive Cavity Aerosol Spectrometer Probe, a Cloud Droplet Probe and a
Cloud Imaging Probe (part of a Cloud, Aerosol and Precipitation Spectrometer). These
instruments were able to reliably generate particle size distributions over the approximate
range 0.1 to 200 μm and for the first time were simultaneously operated at high temporal
resolution of at least 10 Hz. Combining these dust measurements with the measured 3D wind
vectors has allowed size resolved dust flux estimates to be derived using the eddy covariance
method. To the authors’ knowledge this is the first time such estimates have been successfully
derived from aircraft data.
Although the FAAM BAe 146 is capable of low level flying with straight and level runs at
minimum altitudes of ~100 m (higher in poor visibility), this is still significantly higher than
mast based flux measurements making comparison of the total flux with surface based
observations difficult. However, these observations give useful measures of the size
dependence of the particle flux and the spectral signature of the dynamics of vertical dust
transport.
The size resolved measurements show that dust mass flux includes significant
contributions up to particle diameters ~100 μm. This is much larger than the limit seen by
other studies and is even more surprising given that the measurements were made at heights
so far above the saltation layer. Spectral analysis shows three distinct dynamical regimes. The
first appears to be linked to chaotic turbulence with horizontal scales of ~100 m. The second
seems to be linked to features on scales ~1 km, similar to the order of the boundary layer
depth. Finally, in the third regime, the concentration and wind measurements have a very
asymmetric cross correlation series in the along flight direction which may indicate a
preferred orientation for turbulent eddies caused buy e.g. shear. These characteristics
are linked to the weather conditions and dust uplift mechanisms for each case. |
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