An Overview of Aerosol Properties in Clear and Cloudy Sky Based on CALIPSO Observations

Abstract

A full understanding of the climatological properties of aerosols is an important step towards characterizing their effects on climate. Utilizing the observations from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations, we study cloud-free and cloudy aerosol properties with attention on aerosol and cloud layer relative vertical positions. On a global scale, the cloud-free aerosols account for about 56% of all detected aerosols with a mean optical depth ((Formula presented.)) and mean uncertainty of 0.135 ± 0.047. The cloudy aerosols, accounting for 44%, have a larger (Formula presented.) and larger mean uncertainty of 0.143 ± 0.074 compared to the cloud-free aerosols. The above-cloud aerosols (∼4%), primarily composed of elevated smoke, dust/volcanic ash and polluted dust, have a much smaller (Formula presented.) of (0.056 ± 0.038). The below-cloud aerosols (∼21%) have (Formula presented.) ∼ 0.165 (Formula presented.) 0.087. The below-cloud and cloud-free aerosols show close (Formula presented.) probability density distributions and similar aerosol types, indicating that cloud-free aerosol climatologies from passive sensors are likely representative of all-sky conditions. In addition, about 27% of the detected aerosol profiles are found to have cloud layers vertically connected to the detected 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 variations of the cloud-free and the cloudy aerosols significantly vary with regions. Our results imply 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.