EXtinction, SCattering and Absorption of Light for AirBorne Aerosol Research (EXSCALABAR)
Atmospheric aerosols consist of microscopic particles of natural and anthropogenic origin which scatter and absorb sunlight and hence influence the climate of the Earth. Aerosols that predominantly scatter sunlight tend to cool the Earth as they reflect sunlight back to space, while aerosols that predominantly absorb sunlight tend to warm the Earth. Human activities including burning of fossil-fuels, bio-fuels and deforestation have not only increased concentrations of atmospheric carbon dioxide, but have vastly increased concentrations of atmospheric aerosols, which have in turn modulated the global warming from increased concentrations of greenhouse gases. While considerable progress has been made in the measurement and global modelling of atmospheric aerosol optical properties and spatial distributions, one key factor in determining the climatic impact remains poorly constrained: the degree of aerosol absorption. This quantity is fundamentally key to determining whether atmospheric aerosols cool or warm the planet. There is therefore a pressing need to better constrain the impact of aerosol absorption on atmospheric radiative transfer to fully understand its role in global and regional scale climate change. Under the EXSCALABAR project, the University of Exeter and the Met Office (CASE industrial partner) will perform high quality aerosol optical and microphysical measurements of extinction, scattering and absorption with which to challenge (and ultimately improve) the representation of aerosols in climate and numerical weather prediction models. Pioneering aerosol optical characterisation techniques, specifically cavity ringdown extinction spectroscopy and photoacoustic absorption spectroscopy have previously been developed by the CASE industrial partner supervisor (Dr Justin Langridge, Met Office) for airborne research in the USA. In particular the photoacoustic technique has been shown to provide vastly improved aerosol absorption measurements compared to contemporary methods. In addition to developments for in-situ measurements, Professor Jim Haywood has pioneered airborne remote sensing techniques for measuring the spectral radiative effects of biomass burning, mineral dust, volcanic ash, and industrial pollution aerosols across the solar and terrestrial wavelengths and has considerable aerosol modelling experience at a range of spatial scales. The EXSCALABAR project will exploit the synergy of these research interests and will encompass both technological and numerical modelling activities. The cavity ringdown extinction and photoacoustic absorption technologies will be developed for use on-board the joint NERC-Met Office FAAM BAe-146 research aircraft, thus providing an aerosol measurement capability that is unique outside of the USA. The instrument will be deployed in conjunction with existing airborne remote sensing instrumentation from the FAAM aircraft over the UK and on major deployments in summer 2016. The combined in-situ and remotely sensed aerosol and radiative measurements will be used to perform a comprehensive radiative closure analysis focussed on spectral aerosol absorption and single scattering albedo. Results of this analysis will be used to update to the spectral aerosol properties represented in the HadGEM climate model and assess their climatic impacts. The studentship will span a broad range of activities including development of state-of-the-art spectroscopic instrumentation, participation in aircraft-based field missions and scientific analysis of results using radiative transfer models. The instrumentation will be available to the UK research community beyond the lifetime of the EXSCALABAR project, providing significant legacy for the FAAM aircraft and the UK atmospheric research community.
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