1University of Maryland Baltimore County, Joint Center for Earth System Technology, Baltimore, MD, USA
2NASA Goddard Space Flight Center, Climate and Radiation Laboratory, Greenbelt, MD, USA
3Universities Space Research Association, Columbia, MD, USA
Received: 08 Nov 2012 – Discussion started: 13 Dec 2012
Abstract. Improved characterization of aerosol properties in the vicinity of clouds is important for better understanding two critical aspects of climate: aerosol–cloud interactions and the direct radiative effect of aerosols. Satellite measurements have provided important insights into aerosol properties near clouds, but also suggested that the observations can be affected by 3-D radiative processes and instrument blurring not considered in current data interpretation methods. This study examines systematic cloud-related changes in particle properties and radiation fields that influence satellite measurements of aerosols in the vicinity of low-level maritime clouds. For this, the paper presents a statistical analysis of a yearlong global dataset of co-located MODIS and CALIOP observations and theoretical simulations. The results reveal that CALIOP-observed aerosol particle size and optical thickness, and MODIS-observed solar reflectance increase systematically in a wide transition zone around clouds. It is estimated that near-cloud changes in particle populations – including both aerosols and undetected cloud particles – are responsible for roughly two thirds of the observed increase in 0.55 μm MODIS reflectance. The results also indicate that 3-D radiative processes significantly contribute to near-cloud reflectance enhancements, while instrument blurring contributes significantly only within 1 km from clouds and then quickly diminishes with distance from clouds.
Revised: 26 Feb 2013 – Accepted: 20 Mar 2013 – Published: 16 Apr 2013
Várnai, T., Marshak, A., and Yang, W.: Multi-satellite aerosol observations in the vicinity of clouds, Atmos. Chem. Phys., 13, 3899-3908, doi:10.5194/acp-13-3899-2013, 2013.