Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 15, 6775-6788, 2015
https://doi.org/10.5194/acp-15-6775-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
18 Jun 2015
Parameterization of convective transport in the boundary layer and its impact on the representation of the diurnal cycle of wind and dust emissions
F. Hourdin1, M. Gueye2, B. Diallo1, J.-L. Dufresne1, J. Escribano1, L. Menut1, B. Marticoréna3, G. Siour3, and F. Guichard4 1Laboratoire de Météorologie Dynamique, CNRS/IPSL/UMPC, Paris, France
2LPAOSF, UCAD, Dakar, Sénégal
3LISA, UMR CNRS 7583, UPEC, UPD, IPSL, Créteil, France
4CNRM-GAME, UMR CNRS 3589, Météo France, Toulouse, France
Abstract. 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.

Citation: Hourdin, F., Gueye, M., Diallo, B., Dufresne, J.-L., Escribano, J., Menut, L., Marticoréna, B., Siour, G., and Guichard, F.: Parameterization of convective transport in the boundary layer and its impact on the representation of the diurnal cycle of wind and dust emissions, Atmos. Chem. Phys., 15, 6775-6788, https://doi.org/10.5194/acp-15-6775-2015, 2015.
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Short summary
New parameterizations of the convective boundary layer are used to better represent the diurnal cycle of near-surface wind over Sahara and Sahel in a climate model and the associated emission of dust.
New parameterizations of the convective boundary layer are used to better represent the diurnal...
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