Detection of Aerosol Radiative Forcing Associated with Aerosol-Cloud Interactions

Abstract:

Despite frequent documentation of aerosol effects on cloud microphysical and radiative forcing, the robustness and prevalence of these effects is still highly uncertain.
Here we explore the detectability of aerosol effects on shallow cloud radiative forcing at the cloud scale using large numbers of numerical simulations (~ 220), as well as analysis of 14 years of data at the Department of Energy’s Southern Great Plains Ground site in Oklahoma.
The modeling shows that in spite of a demonstrated inherent sensitivity of shallow cloud forcing to both meteorological and aerosol drivers, the detectability of aerosol effects on albedo and cloud forcing is highly sensitive to the covariability of aerosol and meteorology: One set of 100 simulations with a typically used sampling of initial meteorological and aerosol conditions exhibits a clear aerosol effect on cloud albedo while a second set of 120 simulations with an equidistant-in-phase-space sampling of the same initial conditions as the first set displays almost no aerosol effect on albedo.
The surface remote sensing data also show no clear aerosol effect on cloud radiative forcing for the 14 year period. We conclude that routine simulation, and accompanying measurements of aerosol-cloud-radiation interactions that sample naturally covarying meteorological and aerosol conditions are essential for constraining the magnitude of aerosol-cloud radiative forcing.