Dust Aerosol Effects on Cirrus and Altocumulus Clouds in Northwest China

Dust aerosol effects on the properties of cirrus and altocumulus cloud in Northwest China were studied for the period March-May 2007 by using the satellite data of Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), Aqua, and CloudSat. Dusty clouds were defined as those mixed with dust aerosols or existing in dust aerosol conditions, while pure clouds were those in a dust-free environment. For dusty altocumulus clouds, the mean values of cloud optical depth (OPD), cloud liquid water path (LWP), cloud ice water path (IWP), cloud effective particle radius (Re), and cloud effective particle diameter (De) were 6.40, 40.23 g m-2, 100.70 g m-2, 8.76 m, and 40.72 m, respectively. For pure altocumulus clouds, the corresponding mean values were 9.28, 76.70 g m-2, 128.75 g m-2, 14.03 m, and 48.92 m, respectively. These results show a significant decrease of OPD, LWP, IWP, Re, and De of approximately 31%, 48%, 22%, 38%, and 17% because of the effects of dust aerosols. Moreover, the effects of dust aerosols on liquid-phase altocumulus clouds were greater than on ice-phase altocumulus clouds. Regarding dusty cirrus clouds, the mean values of OPD, IWP, and De were 5.11, 137.53 g m-2, and 60.44 m, respectively. In contrast, the mean values were 6.69, 156.17 g m-2, and 66.63 m, respectively, for pure cirrus clouds, with a 24% decrease in OPD, a 12% decrease in IWP, and a 9% decrease in De. These results indicate that dust aerosols can significantly change cloud properties, leading to a reduction of OPD, LWP, and effective particle size for both altocumulus and cirrus clouds in Northwest China.