Effects of Dust Aerosols on Warm Cloud Properties over East Asia and the Sahara from Satellite Data

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  • SAITO Tetsuhiko
    Japan Weather Association, Tokyo, Japan
  • HAYASAKA Tadahiro
    Center for Atmospheric and Oceanic Studies, Graduate School of Science, Tohoku University, Sendai, Japan

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Abstract

 The effects of dust aerosol particles on the properties of clouds over East Asia and the Sahara are studied using moderate resolution imaging spectroradiometer observations from the Terra and Aqua satellites and simulation results of the chemical weather forecast system (CFORS) model. Dust-contaminated clouds are detected using the brightness temperature difference (BTD) method, in which dust or dust-bearing clouds are detected when the BTD between the 11 µm and 12 µm channels in the window region is negative, and by the CFORS model’s dust vertical profile. Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation data are also used to assess the above procedures. For the Sahara region, no obvious changes to effective particle radius (Re) are attributed to dust aerosols. However, for East Asia, dust aerosols are found to change the cloud microphysical properties, decreasing Re by 12 % and increasing the cloud optical depth by 27 % and the liquid water path by 9 %. Re is found to be negatively correlated with sulfate concentration by CFORS in dust-bearing clouds, but not in dust-free clouds, over East Asia. These findings indicate that mineral dust can act as effective cloud condensation nuclei in environments polluted by water-soluble aerosols such as sulfates. We also estimate the indirect radiative effect of dust aerosols in the East Asia region and determine, by radiative transfer calculation, that the net shortwave radiative flux at the top of the atmosphere decreases and the absorption of shortwave radiation by the atmosphere increases with changes in cloud properties due to dust aerosols.

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