Ground-based Observation of Dust Optical Properties in the Chinese Dust Source Region and Intercomparison with MISR Aerosol Retrievals

Long-term continuous observation of dust aerosol optical thickness (AOT) near the dust source regions is of great importance for various applications, including the computation of seasonal and diurnal dust radiative forcing and the validation of satellite retrievals. Using 22 months of Sunphotometer (SP) AOT data collected near the Taklamakan and Gobi dust source regions (Dunhuang, 40.09◦N, 94.41◦E) in 1999 and 2000, this paper examines the diurnal and seasonal change of dust AOT and dust Angstrom exponent. The comparison between SP AOT with Multi-angle ¨ Imaging Spectroradiometer (MISR) AOT product is also performed. Results showed that most dust events are during the spring through early summer months with a season-invariant diurnal change of more than 10% for AOT and 30% for Angstrom exponent. Larger AOT and smaller Angstr ¨ om exponent values usually appeared late in the afternoon. ¨ Comparison showed that MISR AOT overestimates SP AOT by 0.05, but such overestimation decreases as SP AOT increases. Overall, MISR AOT has a good agreement with the SP AOT with linear correlation coefficients (R) of 0.94, and fall within the predicted uncertainties (0.05 or 20% of SP AOT, whichever is larger). Due to the diurnal change of AOT, the difference between daily-averaged SP AOT and the instantaneous MISR AOT is about 0.09. This study implies that large diurnal variations of aerosol properties at or near dust source regions may be significant enough for consideration in regional radiative forcing, air quality and numerical modeling studies.