A New Perspective on the All-Sky Aerosol Direct Radiative Forcing over Southern Africa and Southeast Atlantic

The direct radiative forcing of absorbing aerosols above maritime stratocumulus clouds generally results in a positive shortwave (SW) radiative forcing at top-of-atmosphere (TOA) over the ocean. This forcing sign results from a reduction of scattered radiation at TOA due to absorbing aerosol’s SW absorption. However, the direct radiative forcing for a combination of all-sky (clear sky, cloud-free aerosol, aerosol-free cloud, and aerosols above clouds) alters the magnitude of the forcing. The mean radiative forcing also alters when accounting for all-sky scenarios over land. A combination of satellite measurements (polar-orbiting and geostationary) and radiative transfer calculations are used to perform optical depth retrieval and to assess the all-sky radiative forcing for both southern Africa and the southeast Atlantic based on aerosol properties from both in-situ and ground-based observations.