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