Articles | Volume 16, issue 9
Research article
11 May 2016
Research article |  | 11 May 2016

Relationship between low-cloud presence and the amount of overlying aerosols

Chul Eddy Chung, Anna Lewinschal, and Eric Wilcox

Abstract. Aerosols are often advected above cloud decks, and the amount of aerosols over cloud has been assumed to be similar to that at the same heights in nearby clear sky. In this assumption, cloud and aerosol above cloud-top height are considered randomly located with respect to each other. The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) data are analyzed here to investigate this assumption on global scales.

The CALIPSO data reveal that the aerosol optical depth (AOD) above low cloud tends to be smaller than in nearby clear sky during the daytime, and the opposite is true during the nighttime. In particular, over oceanic regions with wide-spread low cloud, such as the tropical southeastern Atlantic Ocean and northeastern Pacific Ocean, the daytime AOD above low cloud is often 40 % smaller than in surrounding clear skies.

Short summary
This is the first study looking at the amount of aerosols above cloud to see whether the amount is greater or less than in nearby clear skies at the same heights. We find that the aerosol amount over cloud differs a lot from that in nearby clear skies over some areas. These results give an indication, for the first time, that clouds might affect the amount of overlying aerosols.
Final-revised paper