Intercomparison of airborne and surface-based measurements during the CLARIFY, ORACLES and LASIC field experiments
Authors: Barrett Paul Alan , Abel Steven J. , Coe Hugh , Crawford Ian , Dobracki Amie , Haywood James M. , Howell Steve , Jones Anthony , Langridge Justin , McFarquhar Greg , Nott Graeme , Price Hannah , Redemann Jens , Shinozuka Yohei , Szpek Kate , Taylor Jonathan , Wood Robert , Wu Huihui , Zuidema Paquita , Bauguitte Stephane , Bennett Ryan , Bower Keith , Chen Hong , Cochrane Sabrina P. , Cotterell Michael , Davies Nicholas , Delene David , Flynn Connor , Freedman Andrew , Freitag Steffen , Gupta Siddhant , Noone David , Onasch Timothy B. , Podolske James , Poellot Michael R. , Schmidt Sebastian K. , Springston Stephen , Sedlacek III Arthur J. , Trembath Jamie , Vance Alan , Zawadowicz Maria , Zhang Jianhao 
Published: March 2022

Abstract. Data are presented from intercomparisons between two research aircraft, the FAAM BAe-146 and the NASA Lockheed P3, and between the BAe-146 and the surface-based DOE (Department of Energy) ARM (Atmospheric Radiation Monitoring) Mobile Facility at Ascension Island (8 S, 14.5W, a remote island in the mid-Atlantic). These took place from 17 August to 5 September 2017, during the African biomass burning season. The primary motivation was to give confidence in the use of data from multiple platforms with which to evaluate numerical climate models. The three platforms were involved in the CLouds-Aerosol-Radiation Interaction and Forcing for Year 2017 (CLARIFY-2017), ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES), and Layered Atlantic Smoke and Interactions with Clouds (LASIC) field experiments. Comparisons from flight segments on six days where the BAe-146 flew alongside the ARM facility on Ascension Island are presented, along with comparisons from wing-tip to wing-tip flight of the P3 and BAe-146 on 18th August 2017. The intercomparison flight sampled a relatively clean atmosphere overlying a moderately polluted boundary layer, while the 6 fly-bys of the ARM site sampled both clean and polluted conditions 2–4 km upwind. We compare and validate characterisations of aerosol physical, chemical, and optical properties, atmospheric radiation, and cloud microphysics between platforms. We assess the performance of measurement instrumentation in the field, under conditions where sampling conditions are not tightly controlled as in laboratory measurements where calibrations are performed. Solar radiation measurements compared well between airborne platforms. Optical absorption coefficient measurements compared well across all three platforms, even though absolute magnitudes were often low (< 10 Mm−1) and close to the sensitivity limits of measurement instrumentation thereby confounding assessments of the comparability of absorption Ångström exponent characterisations. Aerosol absorption measurements from airborne platforms were more comparable than aircraft-to-ground observations. Scattering coefficient observations compared well between airborne platforms, but agreement with ground-based measurements was worse, potentially caused by small differences in sampling conditions or actual aerosol population differences. Chemical composition measurements followed a similar pattern, with better comparisons between the airborne platforms. Thermodynamics, aerosol, and cloud microphysical properties generally compared well.