ModIs Dust AeroSol (MIDAS): A global fine resolution dust optical depth dataset

Monitoring and describing the spatiotemporal variability of dust aerosols is crucial to understand
their multiple effects, related feedbacks and impacts within the Earth system. This study describes
the development of the MIDAS (ModIs Dust AeroSol) dataset (Gkikas et al., 2020). MIDAS provides
columnar daily dust optical depth (DOD at 550 nm) at global scale and fine spatial resolution (0.1° x 0.1°)
over a decade (2007-2016). This new dataset combines quality filtered satellite aerosol optical
depth (AOD) retrievals from MODIS-Aqua at swath level (Collection 6, Level 2), along with DOD-to-AOD
ratios provided by MERRA-2 reanalysis to derive DOD on the MODIS native grid. The uncertainties of
MODIS AOD and MERRA-2 dust fraction with respect to AERONET and CALIOP, respectively, are taken into
account for the estimation of the total DOD uncertainty (including measurement and sampling uncertainties).
MERRA-2 dust fractions are in very good agreement with CALIOP column-integrated dust fractions across
the “dust belt”, in the Tropical Atlantic Ocean and the Arabian Sea; the agreement degrades in
North America and the Southern Hemisphere where dust sources are smaller. MIDAS, MERRA-2 and
CALIOP DODs strongly agree when it comes to annual and seasonal spatial patterns; however, deviations
of dust loads’ intensity are evident and regionally dependent. Overall, MIDAS is well correlated
with ground-truth AERONET-derived DODs (R=0.882), only showing a small negative bias
(-0.009 or -5.307%). Among the major dust areas of the planet, the highest R values (up to 0.977)
are found at sites of N. Africa, Middle East and Asia. MIDAS expands, complements and upgrades
existing observational capabilities of dust aerosols and it is suitable for dust climatological
studies, model evaluation and data assimilation. MIDAS gridded data sets can also be accessed at
https://react.space.noa.gr/midas/ (Gkikas et al., 2020).