On the Importance of Aerosol Composition for Estimating Incoming Solar Radiation: Focus on the Western African Stations of Dakar and Niamey during the Dry Season

• Published in: Atmosphere
• Main Authors: Drame, Mamadou, Ceamanos, Xavier, Roujean, Jean, Boone, Aaron, Lafore, Jean, Carrer, Dominique, Geoffroy, Olivier
• Other Authors: Centre national de recherches météorologiques (CNRM), Météo France-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physique de l'Atmosphère et de l'Océan Siméon Fongang (LPAO-SF), École Supérieure Polytechnique de Dakar (ESP), Université Cheikh Anta Diop Dakar, Sénégal (UCAD)-Université Cheikh Anta Diop Dakar, Sénégal (UCAD)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2015
• Subjects: solar radiation; aerosols; West Africa; dust; LSA-SAF; [PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph]; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDE]Environmental Sciences; Aerosol Robotic Network
• Online Access: https://hal.archives-ouvertes.fr/hal-02267714; https://hal.archives-ouvertes.fr/hal-02267714/document; https://hal.archives-ouvertes.fr/hal-02267714/file/drame_atmosphere-06-01608.pdf; https://doi.org/10.3390/atmos6111608

International audience The article investigates the impact of aerosol composition on the estimation of the downwelling surface shortwave flux (DSSF). This initiative forms part of the efforts to improve the DSSF distributed by the Land Surface Analysis Satellite Application Facility (LSA-SAF). This operational product assumes invariant aerosol properties under clear sky conditions, which can be inaccurate for some regions of the world. This is the case of West Africa, where aerosol activity is not only highly variable due to frequent dust storms but also rich because of the coexistence of different aerosol species. This study was carried out over the West African stations of Dakar and Niamey, which represent different aerosol scenarios. Several dates during the dry season of 2006 were selected and classified into four different day types according to aerosol activity: standard, clean, mixture and dusty days. The diurnal evolution of DSSF and its direct and diffuse components were estimated for the selected dates by the current LSA-SAF algorithm and two other approaches using aerosol measurements from the Aerosol Robotic Network (AERONET) as input. The first OPEN ACCESS Atmosphere 2015, 6 1609 alternative approach took the diurnal evolution of the total aerosol optical depth (AOD) into account, assuming a default desert aerosol type. Experiments with this method showed a significant improvement in the estimated DSSF compared to the current LSA-SAF algorithm. For example, root mean square error (RMSE) improved from 170 W/m 2 to 50 W/m 2 for dusty days in Dakar and from 73 W/m 2 to 21 W/m 2 for mixture days in Niamey. This improvement resulted from the consideration of a time-varying AOD, which accounted for the rapidly changing aerosol load for these two day types. The second alternative approach tested included consideration of the diurnal variation of the aerosol load and composition. Again, this was done using AERONET data on the fine and coarse aerosol modes, which may be associated with different sized dust ...