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Discussion papers
https://doi.org/10.5194/acp-2018-1218
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-1218
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 04 Dec 2018

Research article | 04 Dec 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Simulation of the transport, vertical distribution, optical properties and radiative impact of smoke aerosols with the ALADIN regional climate model during the ORACLES-2016 and LASIC experiments

Marc Mallet1, Pierre Nabat1, Paquita Zuidema2, Jens Redemann3, Andrew Mark Sayer4,5, Martin Stengel6, Sebastian Schmidt7, Sabrina Cochrane7, Sharon Burton8, Richard Ferrare8, Kerry Meyer5, Pablo Saide9, Hiren Jethva4,5, Omar Torres5, Robert Wood10, David Saint Martin1, Romain Roehrig1, Christina Hsu5, and Paola Formenti11 Marc Mallet et al.
  • 1Centre National de Recherches Météorologiques, UMR3589, Météo-France-CNRS, Toulouse, France
  • 2Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Miami, FL, USA
  • 3University of Oklahoma, USA
  • 4Universities Space Research Association, Columbia, MD, USA
  • 5NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 6Deutscher Wetterdienst (DWD), Offenbach, Germany
  • 7University of Colorado, Boulder, USA
  • 8NASA Langley Research Center, Hampton, Virginia, USA
  • 9University of California, Los Angeles (UCLA), USA
  • 10University of Washington, Seattle, USA
  • 11Laboratoire Interuniversitaire des Systèmes Atmosphériques, UMR CNRS 7583, Université Paris Est Créteil et Université Paris Diderot, Institut Pierre Simon Laplace, France

Abstract. Estimates of the direct radiative forcing (DRF) from absorbing smoke aerosols over the Southeast Atlantic Ocean (SAO) requires simulation of the microphysical and optical properties of stratocumulus clouds (Sc) as well as of the altitude and shortwave (SW) optical properties of biomass burning aerosols (BBA). In this study, we take advantage of the large number of observations acquired during the ORACLES-2016 and LASIC projects during September 2016 and compare them with datasets from the ALADIN-Climate regional model. The model provides a good representation of the liquid water path (LWP) but the low cloud fraction (LCF) is underestimated compared to satellite data. The modeled total column smoke aerosol optical depth (AOD) and Above Cloud AOD (ACAOD) are consistent (~0.7 over continental sources and ~0.3 over SAO at 550nm) with MERRA2, OMI or MODIS data. The simulations indicate smoke transport over SAO occurs mainly between 2 and 4km, consistent with surface and aircraft lidar observations. The BBA single scattering albedo (SSA) is slightly overestimated compared to AERONET, and more significantly when compared to Ascension Island surface observations. The difference could be due to the absence of internal mixing treatment in the ALADIN-Climate model. The SSA overestimate leads to underestimate the simulated SW radiative heating compared to ORACLES data. For September 2016, ALADIN-Climate simulates a positive (monthly mean) SW DRF of about +6Wm−2 over SAO (20°S–10°N and 10°W–20°E) at the top of the atmosphere (TOA) and in all-sky conditions. Over the continent, the presence of BBA is shown to significantly decrease the net surface SW flux, through direct and semi-direct effects, which is compensated by a decrease (monthly mean) in sensible heat fluxes (−25W/m−2) and surface land temperature (−1.5°C) over Angola, Zambia and Congo notably. The surface cooling and the lower tropospheric heating tends to decrease the continental planetary boundary layer (PBL) height by about ~200m.

Marc Mallet et al.
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The model is able to represent LWP but not the LCF. AOD is consistent over the continent but also over ocean (ACAOD). Differences are observed in SSA due to the absence of internal mixing in ALADIN-Climat. A significant regional gradient of the forcing at TOA is observed. An intense positive forcing is simulated over the Gabon. Results highlight the significant effect of enhanced moisture on BBA extinction. The surface dimming modifies the energy budget.
The model is able to represent LWP but not the LCF. AOD is consistent over the continent but...
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