Aerosols changing with distance to shallow clouds: reality or artifact?

Analyzing the interactions between aerosols and shallow clouds requires knowledge of aerosol properties in the vicinity of these shallow clouds. During the past decade, a number of remote sensing studies reported that aerosol optical thickness and particle size increase with cloud cover and/or proximity to low clouds. Part of the observed changes likely comes from aerosols swelling in the humid air around clouds and from cloud processing of aerosols. At the same time, remote sensing artifacts such as 3D radiative effects and uncertainties in distinguishing aerosols from thin or small clouds can also play a role. Moreover, overall aerosol statistics calculated as a function of distance to cloud can also be affected by the correlation between aerosol properties and cloud cover, as far-from-cloud aerosol statistics is dominated by data from scenes with lower cloud fractions, while near-cloud aerosol statistics is dominated by data from scenes with higher cloud fractions.

In this presentation we discuss some recent satellite observations of aerosols in the vicinity of shallow clouds. The presentation will also review our current understanding of remote sensing artifacts and will discuss how these artifacts can be mitigated by combining observations from several A-train instruments, thus helping to accurately measure aerosol properties in the vicinity of low-level clouds.