Clarify-2017: Aerosol-Direct Radiative Forcing Measurements and Modeling from the Microscale to the Continental Scale

The Cloud-aerosol-radiation interaction and forcing; Year 2017 (CLARIFY-2017) campaign involved the deployment of the UK’s FAAM aircraft to Ascension Island during the period August-September 2017. One of the primary aims of CALRIFY-2017 was to examine and quantify the positive radiative forcing from aerosols that occurs when strongly absorbing biomass burning aerosols overlie highly reflectance stratocumulus clouds. Figure 1 shows that the direct radiative forcing derived from general circulation models is highly variable.

A total of 100 flight hours were performed examining aerosol-radiation and aerosol-cloud interactions, many targeting quantification of the positive radiative forcing of biomass burning aerosol above cloud. The new high-accuracy EXSCALABAR (EXtinction, SCattering and Absorption of Light for AirBorne Aerosol Research) was developed consisting of five Cavity Ring-down (CRD) Spectrometer and five Photo-acoustic Spectrometer (PAS), together with standard aerosol microphysical instruments. The PAS was calibrated using ozone which, unlike suggestions in some previous work, was shown to be a suitable calibration method. Highly accurate measurements of aerosol absorption and extinction and thus the aerosol single scattering albedo at multiple wavelengths and including the effects of relative humidity were made facilitating calculations of Angstrom and Absorption Angstrom exponents. Additional measurements were made with an SP2 and Aerosol Mass Spectrometer. The results from these measurements will be discussed with particular emphasis on discrepancies in inferred absorption enhancement from coatings of organic and inorganic material on a black carbon core. The results from flights targeting the spectrally resolved and broadband radiative closure of partially absorbing aerosol above clouds will also be discussed. The development of new retrievals of absorbing aerosols above clouds using the geostationary SEVIRI sensor will be critically examined for a number of case studies. These data sets provide a robust and comprehensive set of observations with which to challenge models with a range of spatial resolutions; the Met office global numerical weather prediction and climate model will be challenged with these observations and the results presented.