On the influence of the diurnal variations of aerosol content to estimate direct aerosol radiative forcing using MODIS data

• Published in: Atmospheric Environment
• Main Authors: Xu, Hui, Guo, Jianping, Ceamanos, Xavier, Roujean, Jean-Louis, Min, Min, Carrer, Dominique
• Other Authors: State Key Laboratory of Severe Weather (LASW), Chinese Academy of Meteorological Sciences (CAMS), ONERA - The French Aerospace Lab Toulouse, ONERA, Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS), National Satellite Meteorological Center Beijing (NSMC), China Meteorological Administration (CMA)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2016
• Subjects: AEROSOL OPTICAL DEPTH; AEROSOL DIURNAL CYCLE; DIRECT AEROSOL RADIATIVE FORCING; MODIS; AERONET; [PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph]; [SDU.STU.ME]Sciences of the Universe [physics]/Earth Sciences/Meteorology; Aerosol Robotic Network
• Online Access: https://hal.science/hal-01728992; https://hal.science/hal-01728992/document; https://hal.science/hal-01728992/file/xu2016.pdf; https://doi.org/10.1016/j.atmosenv.2016.06.067

International audience Long-term measurements of aerosol optical depth (AOD) from the Aerosol Robotic Network (AERONET) located in Beijing reveal a strong diurnal cycle of aerosol load staged by seasonal patterns. Such pronounced variability is matter of importance in respect to the estimation of daily averaged direct aerosol radiative forcing (DARF). Polar-orbiting satellites could only offer a daily revisit, which turns in fact to be even much less in case of frequent cloudiness. Indeed, this places a severe limit to properly capture the diurnal variations of AOD and thus estimate daily DARF. Bearing this in mind, the objective of the present study is however to evaluate the impact of AOD diurnal variations for conducting quantitative assessment of DARF using Moderate Resolution Imaging Spectroradiometer (MODIS) AOD data over Beijing. We provide assessments of DARF with two different assumptions about diurnal AOD variability: taking the observed hourly-averaged AOD cycle into account and assuming constant MODIS (including Terra and Aqua) AOD value throughout the daytime. Due to the AOD diurnal variability, the absolute differences in annual daily mean DARFs, if the constant MODIS/Terra (MODIS/Aqua) AOD value is used instead of accounting for the observed hourly-averaged daily variability, is 1.2 (1.3) Wm−2 at the top of the atmosphere, 27.5 (30.6) Wm−2 at the surface, and 26.4 (29.3) Wm−2 in the atmosphere, respectively. During the summertime, the impact of the diurnal AOD variability on seasonal daily mean DARF estimates using MODIS Terra (Aqua) data can reach up to 2.2 (3.9) Wm−2 at the top of the atmosphere, 43.7 (72.7) Wm−2 at the surface, and 41.4 (68.8) Wm−2 in the atmosphere, respectively. Overall, the diurnal variation in AOD tends to cause large bias in the estimated DARF on both seasonal and annual scales. In summertime, the higher the surface albedo, the stronger impact on DARF at the top of the atmosphere caused by dust and biomass burning (continental) aerosol. This indicates that the impact on ...