QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY Q. J. R. Meteorol. Soc. 135: 922–934 (2009) Published online 28 April 2009 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/qj.420 Measurements of aerosol properties from aircraft, satellite and ground-based remote sensing: A case-study from the Dust and Biomass-burning Experiment (DABEX) B. T. Johnson, a *,† S. Christopher, b J. M. Haywood, a ,† S. R. Osborne, a ,† S. McFarlane c C. Hsu, d C. Salustro d,e and R. Kahn d a Met Office, Exeter, UK b University of Alabama, Huntsville, AL, USA c Pacific Northwest National Laboratory, Richland, Washington, USA d Goddard Space Flight Center, Greenbelt, Maryland, USA e Science Systems and Applications, Inc., Lanham, Maryland, USA ABSTRACT: 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 KEY WORDS aircraft measurement; AERONET; MODIS; MISR; optical properties Received 30 October 2008; Revised 25 February 2009; Accepted 11 March 2009 1. Introduction Aerosols scatter and absorb solar radiation and have a direct effect on the Earth’s radiative energy budget. The scattering of solar radiation back to space leads to a cooling of the climate system whereas absorption by aerosols leads to a local heating of the atmosphere. Glob- ally, aerosols are understood to exert a cooling influence since scattering is the more dominant process (IPCC, 2007). However, model estimates of the direct radia- tive forcing by aerosols vary depending on many factors, including the global distribution of aerosol optical depth (AOD), the representation of aerosol optical properties, ∗ Correspondence to: B. T. Johnson, Met Office, FitzRoy Road, Exeter, EX1 3PB, UK. E-mail: ben.johnson@metoffice.gov.uk †The contributions of B. T. Johnson, J. M. Haywood and S. R. Osborne of Met Office, Exeter were prepared as part of their official duties as employees of the UK Government. They are published with the permission of the Controller of Her Majesty’s Stationery Office and the Queen’s Printer for Scotland and the vertical distribution of aerosols in the atmos- phere. The development of satellite remote sensing and ground-based sunphotometer networks such as Aerosol Robotic Network (AERONET) over the past ten years has greatly increased opportunities for the validation of global aerosol transport models and observation-based constraints on the total direct radiative forcing by aerosol. With a growing reliance on remote-sensing methods for quantifying the impact of aerosols on climate, it is impor- tant to assess the performance of such retrieval algorithms against independent field measurements, including in situ measurements from aircraft. Intensive measurements of dust and biomass-burning aerosol were made by the UK Facility for Airborne Atmospheric Measurements (FAAM) aircraft during the Dust and Biomass-burning Experiment (DABEX). This experiment took place from 13 January to 3 February 2006, in the region surrounding Niamey, Niger (West Africa). DABEX was part of the African Monsoon Multi-disciplinary Analysis (AMMA) dry season special Copyright c  Royal Meteorological Society, Crown Copyright 2009