An overview of aerosol properties in clear and cloudy sky based on the
CALIPSO observations
Abstract
A full understanding of the climatological properties of aerosols is an
important step towards characterizing their effects on the regional and
global climate. Utilizing the observations from Cloud-Aerosol Lidar and
Infrared Pathfinder Satellite Observations (CALIPSO), we study
cloud-free and cloudy aerosol properties with attentions on aerosol and
cloud layer vertically relative positions. On a global scale, the
cloud-free aerosols account for 55.9% of all detected aerosols with a
mean optical depth ( ) and uncertainty of 0.135 {plus minus} 0.047.
The cloudy aerosols, accounting for 44.1%, have a larger and
uncertainty of 0.143 {plus minus} 0.074 compared to the cloud-free
aerosols. The above-cloud aerosols (4.2%), primarily composed of
elevated smoke, dust/volcanic ash and polluted dust, have a much smaller
(0.056 0.038). The below-cloud aerosols (21.3%) have ~
0.165 0.087, showing close probability density distributions, aerosol
types, backscatter-depolarization ratio diagram, and lidar ratio-color
ratio diagram with the cloud-free aerosols. In addition, 27.4% of the
detected aerosol profiles are found to have cloud layers vertically
connected to aerosol layers. The lidar backscatter profiles of these
aerosols have larger median values than the cloud-free, above-cloud and
below-cloud aerosols. The seasonal variability of the cloud-free and the
cloudy aerosols significantly varies with regions. This study implies
that quantifying the impact of clouds, particularly cirrus due to the
wide coverage of cirrus-aerosol overlap, on aerosol direct radiative
effect is crucial to assess aerosols’ roles in the Earth-climate system.