Spatial distribution of dust's optical properties over the Sahara and Asia inferred from Moderate Resolution Imaging Spectroradiometer
Yoshida, M; Haywood, JM; Yokohata, T; et al.Murakami, H; Nakajimae, T
Date: 7 November 2013
Article
Journal
Atmospheric Chemistry and Physics
Publisher
European Geosciences Union
Publisher DOI
Abstract
There is great uncertainty regarding the role of
mineral dust aerosols in Earth’s climate system. One reason
for this uncertainty is that the optical properties of mineral
dust, such as its single scattering albedo (the ratio of
scattering to total extinction), are poorly constrained because
ground observations are limited to a ...
There is great uncertainty regarding the role of
mineral dust aerosols in Earth’s climate system. One reason
for this uncertainty is that the optical properties of mineral
dust, such as its single scattering albedo (the ratio of
scattering to total extinction), are poorly constrained because
ground observations are limited to a few locations and satellite
standard products are not available due to the excessively
bright surface of the desert in the visible wavelength, which
makes robust retrievals difficult. Here, we develop a method
to estimate the spatial distributions of the aerosol single scattering
albedo (ω0) and optical depth (τa), with daily 1◦ × 1
◦
spatial resolution using data from the Moderate Resolution
Imaging Spectroradiometer (MODIS) as well as model simulations
of radiative transfer. This approach is based on the
“critical surface reflectance” method developed in the literature,
which estimates ω0 from the top of the atmospheric
radiance. We estimate the uncertainties in ω0 over the Sahara
(Asia) to be approximately 0.020 and 0.010 (0.023 and
0.017) for bands 9 and 1, respectively, while the uncertainty
in τa is approximately 0.235 and 0.228 (0.464 and 0.370)
for bands 9 and 1, respectively. The 5–95 % range of the
spatial distribution of ω0 over the Sahara (Asia) is approximately
0.90–0.94 and 0.96–0.99 (0.87–0.94 and 0.89–0.97)
for bands 9 and 1, respectively, and that of τa over the Sahara
(Asia) is approximately 0.8–1.4 and 0.8–1.7 (0.7–2.0
and 0.7–1.9) for bands 9 and 1, respectively. The results for
the Sahara indicate a good correlation between ω0 and the
surface reflectance, and between ω0 and τa. However, the relationships
between ω0, τa, and surface reflectance are less
clear in Asia than in the Sahara, and the ω0 values are smaller
than those in the Sahara. The regions with small ω0 values
are consistent with the regions where coal-burning smoke
and carbonaceous aerosols are reported to be transported in
previous studies. Because the coal-burning and carbonaceous
aerosols are known to be more absorptive and have smaller
ω0 values than dust aerosols, our results indicate that the dust
aerosols in Asia are contaminated by these anthropogenic
aerosols. The spatial distribution of dust optical properties
obtained in our work could be useful in understanding the
role of dust aerosols in Earth’s climate system, most likely
through future collaboration with regional and global modelling
studies.
Mathematics and Statistics
Faculty of Environment, Science and Economy
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