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| Titel |
Parameterization of convective transport in the boundary layer and its impact on the representation of the diurnal cycle of wind and dust emissions |
| VerfasserIn |
F. Hourdin, M. Gueye, B. Diallo, J.-L. Dufresne, J. Escribano, L. Menut, B. Marticorena, G. Siour, F. Guichard |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 12 ; Nr. 15, no. 12 (2015-06-18), S.6775-6788 |
| Datensatznummer |
250119839
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| Publikation (Nr.) |
 copernicus.org/acp-15-6775-2015.pdf |
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| Zusammenfassung |
| We investigate how the
representation of the boundary layer in a climate model
impacts the representation of the
near-surface wind and dust emission, with a focus on the Sahel/Sahara
region. We show that the combination of vertical turbulent diffusion
with a representation of the thermal cells of the convective
boundary layer by a mass flux scheme leads to realistic
representation of the diurnal cycle of wind in spring, with
a maximum near-surface wind in the morning. This maximum occurs when
the thermal plumes reach the low-level jet that forms during the
night at a few hundred meters above surface. The horizontal
momentum in the jet is transported downward to the surface by
compensating subsidence around thermal plumes in typically less
than 1 h. This leads to a rapid increase of wind speed at
surface and therefore of dust emissions owing to the strong nonlinearity of emission laws. The numerical experiments are performed
with a zoomed and nudged configuration of the LMDZ general
circulation model coupled to the emission module of the CHIMERE
chemistry transport model, in which winds are relaxed toward that of
the ERA-Interim reanalyses. The new set of parameterizations leads to
a strong improvement of the representation of the diurnal cycle of
wind when compared to a previous version of LMDZ as well as to the
reanalyses used for nudging themselves. It also generates dust
emissions in better agreement with current estimates, but the aerosol
optical thickness is still significantly underestimated. |
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