Feedback between dust particles and atmospheric processes over West Africa during dust episodes in March 2006 and June 2007 1Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany
*now at: Institute for Atmospheric and Climate Science, Swiss Federal Institute of Technology (ETH), Zurich, Switzerland
**now at: BASF, Ludwigshafen, Germany
Received: 22 Jan 2010 – Published in Atmos. Chem. Phys. Discuss.: 23 Mar 2010 Abstract. We used the comprehensive model system COSMO-ART to quantify the impact of
mineral dust on the radiative fluxes, the temperature and the feedback
between dust particles and their emissions. We simulated two dust storms
over West Africa in March 2006 and in June 2007. Simulations with and
without coupling of the actual dust concentration with the radiative fluxes
and the thermodynamics were carried out for each case. The model results for
the 2006 case were compared with observations of the AMMA campaign.
Revised: 30 Jun 2010 – Accepted: 26 Sep 2010 – Published: 17 Nov 2010
At the surface the shortwave radiative effect of mineral dust can be
described by a linear relation between the changes in net surface radiation
and the aerosol optical depth (AOD). For an AOD at 450 nm of 1 the average
shortwave radiation reduction amounts −140 W m−2 during noon. The
longwave radiative effect of mineral dust is nonlinear, with an average
increase of +70 W m−2 for an AOD (450 nm) of 1. At the top of the
atmosphere the effect of the dust layer with an AOD of 1 on radiative fluxes
is not as significant as at the surface. It is slightly positive for the
shortwave and approximately 26 W m−2 for the longwave radiation.
The height range and the extension of the dust layer determine the effect of
dust particles on the 2 m temperature. When the dust layer is attached to
the surface and lasts for several days it leads to an increase of the
surface temperature even during daytime. In case of an elevated dust layer
there is a decrease in 2 m temperature of up to 4 K during noon.
It is shown, that the temperature changes caused by mineral dust may result
in horizontal temperature gradients which also modify near surface winds.
Since surface wind thresholds decide the uptake of dust from the surface, a
feedback on total emission fluxes is established. The coupled model provides
an increase in the total emission fluxes of dust particles by about 16%
during the dust storm in March 2006 and 25% during the dust episode in
Citation: Stanelle, T., Vogel, B., Vogel, H., Bäumer, D., and Kottmeier, C.: Feedback between dust particles and atmospheric processes over West Africa during dust episodes in March 2006 and June 2007, Atmos. Chem. Phys., 10, 10771-10788, doi:10.5194/acp-10-10771-2010, 2010.