The spatial distribution of mineral dust and its shortwave radiative forcing over North Africa: modeling sensitivities to dust emissions and aerosol size treatments
Other literature type
Leung, L. R.
McFarlane, S. A.
Gustafson, W. I.
Fast, J. D.
(issn: 1680-7324, eissn: 1680-7324)
A fully coupled meteorology-chemistry-aerosol model
(WRF-Chem) is applied to simulate mineral dust and its shortwave (SW)
radiative forcing over North Africa. Two dust emission schemes (GOCART and
DUSTRAN) and two aerosol models (MADE/SORGAM and MOSAIC) are adopted in
simulations to investigate the modeling sensitivities to dust emissions and
aerosol size treatments. The modeled size distribution and spatial
variability of mineral dust and its radiative properties are evaluated using
measurements (ground-based, aircraft, and satellites) during the AMMA SOP0
campaign from 6 January to 3 February of 2006 (the SOP0 period) over North
Africa. Two dust emission schemes generally simulate similar spatial
distributions and temporal evolutions of dust emissions. Simulations using
the GOCART scheme with different initial (emitted) dust size distributions
require ~40% difference in total emitted dust mass to produce
similar SW radiative forcing of dust over the Sahel region. The modal
approach of MADE/SORGAM retains 25% more fine dust particles (radius<1.25 μm)
but 8% less coarse dust particles (radius>1.25 μm)
than the sectional approach of MOSAIC in simulations using the same
size-resolved dust emissions. Consequently, MADE/SORGAM simulates 11%
higher AOD, up to 13% lower SW dust heating rate, and 15% larger (more
negative) SW dust radiative forcing at the surface than MOSAIC over the
Sahel region. In the daytime of the SOP0 period, the model simulations show
that the mineral dust heats the lower atmosphere with an average rate of
0.8 ± 0.5 K day<sup>−1</sup> over the Niamey vicinity and 0.5 ± 0.2 K day<sup>−1</sup>
over North Africa and reduces the downwelling SW radiation at the
surface by up to 58 W m<sup>−2</sup> with an average of 22 W m<sup>−2</sup> over North
Africa. This highlights the importance of including dust radiative impact in
understanding the regional climate of North Africa. When compared to the
available measurements, the WRF-Chem simulations can generally capture the
measured features of mineral dust and its radiative properties over North
Africa, suggesting that the model is suitable for more extensive simulations
of dust impact on regional climate over North Africa.