NASA - National Aeronautics and Space Administration

This paper presents aircraft measurements of aerosol optical properties and radiative effects from the Dust and Biomass-burning Experiment (DABEX) over West Africa. On 19 January 2006 cloud-free skies and high aerosol loading provided ideal conditions for an intercomparison of aircraft, satellite and ground-based remote sensing instruments. Aerosol size distributions, optical properties, aerosol optical depth (AOD) and downwelling solar radiation were measured by the UK FAAM aircraft in the region of Niamey, Niger. The aircraft in situ measurements showed a mixture of dust and biomass-burning aerosols and indicated an AOD of 0.79 (at 550 nm) that compared well against AODs from the Banizoumbou Aerosol Robotic Network (AERONET) site (0.74) and a Microtops sunphotometer (0.72). AERONET size distributions showed a good degree of similarity with the aircraft in situ measurements. AERONET single-scattering albedos were also in fairly close agreement with the aircraft, having values of 0.85 and 0.87, respectively (at 550 nm). Measurements of downwelling solar radiation from the aircraft compared well with measurements from the Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) at Niamey. Radiative transfer modelling suggested a 130–160 W m−2 instantaneous reduction of downwelling solar radiation by the aerosol column (15–18% of the total flux). Measurements of downwelling solar radiation compared reasonably well against radiative transfer modelling based on the aircraft in situ data. Satellite retrievals of AOD from MISR and MODIS Deep Blue were within 0.05 of the ground-based sunphotometers measurements although there were discrepancies in optical properties retrieved by MISR, as compared to AERONET and the aircraft. Copyright c Royal Meteorological Society, Crown Copyright 2009