CLARIFI—Aerosol Direct Radiative Effect in Cloudy Scenes Retrieved from Space–Borne Spectrometers

Abstract

The retrieval of the aerosol direct radiative effect of smoke aerosols in cloudy scenes using space–borne spectrometers is described. The retrieval of aerosol parameters and radiative effects from satellite is often hampered by residual clouds in a scene. However, aerosols that absorb solar radiation in the ultraviolet (UV) reduce the reflectance in the UV measured by space-borne spectrometers, and can be detected even in the presence of clouds. The absorption of radiation by small UV-absorbing aerosol disappears in the shortwave infrared (SWIR) and cloud properties can be retrieved here. This can be used to quantify the aerosol direct radiative effect (DRE) in the cloudy scene, by modelling the aerosol–unpolluted cloud reflectance spectrum and comparing it to the measured aerosol–polluted cloud reflectance spectrum. The algorithm to retrieve the aerosol DRE over clouds is applied here to SCIAMACHY shortwave reflectance measurements of marine cloud scenes. The maximum aerosol direct radiative effect found from these measurements is 124\pm 7 Wm^-2, which means that about 14 % of the incoming solar irradiance was absorbed by the smoke aerosols.