ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-13-675-2013 Assessment of the Level-3 MODIS daily aerosol optical depth in the context of surface solar radiation and numerical weather modeling Ruiz-Arias J. A. 1 2 3 Dudhia J. 3 Gueymard C. A. 4 Pozo-Vázquez D. 1 2 Solar Radiation and Atmosphere Modeling Group, Physics Department, University of Jaén, Jaén, Spain Center of Advanced Studies in Energy and Environment, University of Jaén, Jaén, Spain Mesoscale and Microscale Meteorology Division, National Center for Atmospheric Research, Boulder, Colorado, USA Solar Consulting Services, Colebrook, New Hampshire, USA 18 01 2013 13 2 675 692 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/13/675/2013/acp-13-675-2013.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/13/675/2013/acp-13-675-2013.pdf

The daily Level-3 MODIS aerosol optical depth (AOD) product is a global daily spatial aggregation of the Level-2 MODIS AOD (10-km spatial resolution) into a regular grid with a resolution of 1° × 1°. It offers interesting characteristics for surface solar radiation and numerical weather modeling applications. However, most of the validation efforts so far have focused on Level-2 products and only rarely on Level 3. In this contribution, we compare the Level-3 Collection 5.1 MODIS AOD dataset from the Terra satellite available since 2000 against observed daily AOD values at 550 nm from more than 500 AERONET ground stations around the globe. Overall, the mean error of the dataset is 0.03 (17%, relative to the mean ground-observed AOD), with a root mean square error of 0.14 (73%, relative to the same), but these errors are also found highly dependent on geographical region. We propose new functions for the expected error of the Level-3 AOD, as well as for both its mean error and its standard deviation. Additionally, we investigate the role of pixel count vis-à-vis the reliability of the AOD estimates, and also explore to what extent the spatial aggregation from Level 2 to Level 3 influences the total uncertainty in the Level-3 AOD. Finally, we use a radiative transfer model to investigate how the Level-3 AOD uncertainty propagates into the calculated direct normal and global horizontal irradiances.

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