Page 1 © Crown copyright 2004 Aircraft observations of Biomass burning aerosol Ben Johnson, Simon Osborne & Jim Haywood AMMA SOP0 Meeting, Exeter, 15 th May 2007
Page 2 © Crown copyright 2004 DABEX – Aircraft obs of BB aerosol MODIS Fire counts 13 th Jan – 3 rd Feb, 2006 Aircraft Run locations
Page 3 © Crown copyright 2004 Fresh smoke plumes Smoke plumes: Aerosol concentration > 5000 cm -3 Mixing with mineral dust Smoke plume
Page 4 © Crown copyright 2004 Aerosol size distributions PCASP ( μm)
Page 5 © Crown copyright 2004 Absorption of solar radiation Dust Biomass aerosol Not absorbing Highly absorbing Aircraft Mean BB Aircraft mean dust
Page 6 © Crown copyright 2004 Vertical distribution Dust BB aerosol m m m Nephelometer wavelengths Dust BB aerosol Dust Biomass aerosol Mixture
Page 7 © Crown copyright 2004 Aerosol optical properties 550nm) from Mie theory Aerosol typeSingle-scattering albedo (ω) Extinction coefficient K ext (m 2 g -1 ) Asymmetry parameter (g) Angstrom parameter (Å) Fresh BB Aged BB DUST0.98 +/ n dust = i, ρ dust = 2.65 g cm -3, n BB = i, ρ BB = 1.35 g cm -3
Page 8 © Crown copyright 2004 Aerosol direct radiative forcing (Solar only) Edward & Slingo (1996) 2-stream radiation model with 220 bands. Surface albedo = Solar parameters based on January 15th and latitude of 13.5N (Niamey). TOA forcing close to zero !! “hides” large surface and atmospheric changes.
Page 9 © Crown copyright 2004 Comparison with remote sensing data? AERONET/PHOTONS sunphotometers: AOD, size distribution, absorption, angstrom. MODIS Aerosol optical depth MISR Aerosol optical depth
Page 10 © Crown copyright 2004 Remote sensing vs aircraft: Optical depth MISRMODIS Good mean value but underestimates high AODs Not too bad, but only 4 data points!
Page 11 © Crown copyright 2004 Summary Biomass-burning aerosol had very high SW absorption (x2 SAFARI), whereas dust was virtually non-absorbing. Huge variation in size distributions and optical parameters, due to variable proportions of dust and biomass aerosol.
Page 12 © Crown copyright 2004 Collaborations / comparisons More independent estimates of single- scattering albedo. Obs of size distributions, optical and chemical properties and mixing state. Radiative effect / forcing of aerosols. Lidar vertical profiles – aircraft nephelometer
Page 13 (a)(b) Back trajectories from Niamey Origin of low-level dust at 0.5kmOrigin of BB aerosol at 3km
Page 14 © Crown copyright 2004 Remote sensing vs aircraft: Optical depth Aircraft uses profile of Neph+PSAP AERONET slightly lower than aircraft or Microtops Simon Osborne Aircraft