Atmospheric Chemistry and Physics
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2009
10.5194/acp-9-8017-2009
http://www.atmos-chem-phys.net/9/8017/2009/
http://www.atmos-chem-phys.net/9/8017/2009/acp-9-8017-2009.html
http://www.atmos-chem-phys.net/9/8017/2009/acp-9-8017-2009.pdf
8017
8038
2009-10-23
Vertical structure of aerosols and water vapor over West Africa during the African monsoon dry season
S.-W. Kim
kimsw@air.snu.ac.kr
P. Chazette
F. Dulac
J. Sanak
B. Johnson
S.-C. Yoon
Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ, Gif-Sur-Yvette, France
Met Office, Exeter, UK
School of Earth and Environmental Sciences, Seoul National University, Seoul, Korea
now at: School of Earth and Environmental Sciences, Seoul National University, Seoul, Korea
We present observations of tropospheric aerosol and water vapor transport
over West Africa and the associated meteorological conditions during the
AMMA SOP-0 dry season experiment, which was conducted in West Africa in
January–February 2006. This study combines data from ultra-light aircraft
(ULA)-based lidar, airborne in-situ aerosol and gas measurements, standard
meteorological measurements, satellite-based aerosol measurements, airmass
trajectories, and radiosonde measurements. At Niamey (13.5° N,
2.2° E) the prevailing surface wind (i.e. Harmattan) was from the
northeast bringing dry dusty air from the Sahara desert. High concentrations
of mineral dust aerosol were typically observed from the surface to 1.5 or 2 km
associated with the Saharan airmasses. At higher altitudes the prevailing
wind veered to the south or southeast bringing relatively warm and humid
airmasses from the biomass burning regions to the Sahel (<10° N).
These elevated layers had high concentrations of biomass burning aerosol and
were typically observed between altitudes of 2–5 km. Meteorological analyses
show these airmasses were advected upwards over the biomass burning regions
through ascent in Inter-Tropical Discontinuity (ITD) zone. Aerosol vertical
profiles obtained from the space-based lidar CALIOP onboard CALIPSO during
January 2007 also showed the presence of dust particles (particle
depolarization (δ)~30%, lidar Ångström exponent (<i>LAE</i>)<0,
aerosol backscatter to extinction ratio (<i>BER</i>): 0.026~0.028 sr<sup>−1</sup>) at
low levels (<1.5 km) and biomass burning smoke aerosol (δ<10%, <i>LAE</i>:
0.6~1.1, <i>BER</i>: 0.015~0.018 sr<sup>−1</sup>) between 2 and 5 km. CALIOP data
indicated that these distinct continental dust and biomass burning aerosol
layers likely mixed as they advected further south over the tropical
Atlantic Ocean, as indicated an intermediate values of δ (10~17%),
<i>LAE</i> (0.16~0.18) and <i>BER</i> (0.0021~0.0022 sr<sup>−1</sup>).
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