Quantifying Cloud Adjustments and the Radiative Forcing due to Aerosol-Cloud Interactions in Satellite Observations of Warm Marine Clouds
Alyson Douglas, Tristan L’Ecuyer
Abstract
Abstract. Aerosol-cloud interactions and their resultant forcing remains one of the largest sources of uncertainty of future climate scenarios. The effective radiative forcing due to aerosol-cloud interactions (ERFaci) is a combination of two different effects, how aerosols modify cloud brightness (RFaci) and how cloud extent reacts to aerosol (CA). Using satellite observations of warm clouds from the NASA A-Train constellation from 2007 to 2010 along with MERRA-2 reanalysis and aerosol from the SPRINTARS model, we evaluate the ERFaci and its components, the RFaci and CA, while accounting for the liquid water path and local environment. We estimate the ERFaci to be −0.32 ± 0.16 W m−2. The RFaci dominates the ERFaci contributing 80 % (−0.21 ± 0.15 W m−2), while the CA enhances this cooling by 20 % (−0.05 ± 0.03 W m−2). Both the RFaci and CA vary in magnitude and sign regionally, and can lead to opposite, negating effects under certain environmental conditions. Without considering the two terms separately, and without constraining cloud-environment interactions, weak regional ERFaci signals may be erroneously attributed to buffering or a damped susceptibility to aerosol.