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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 18 Mar 2020

Submitted as: research article | 18 Mar 2020

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This preprint is currently under review for the journal ACP.

Multi-model evaluation of aerosol optical properties in the AeroCom phase III Control experiment, using ground and space based columnar observations from AERONET, MODIS, AATSR and a merged satellite product as well as surface in-situ observations from GAW sites

Jonas Gliß1, Augustin Mortier1, Michael Schulz1, Elisabeth Andrews2, Yves Balkanski3, Susanne E. Bauer20,19, Anna M. K. Benedictow1, Huisheng Bian4,5, Ramiro Checa-Garcia3, Mian Chin5, Paul Ginoux6, Jan J. Griesfeller1, Andreas Heckel7, Zak Kipling9, Alf Kirkevåg1, Harri Kokkola10, Paolo Laj11, Philippe Le Sager12, Marianne Tronstad Lund15, Cathrine Lund Myhre13, Hitoshi Matsui14, Gunnar Myhre15, David Neubauer16, Twan van Noije12, Peter North7, Dirk J. L. Olivié1, Larisa Sogacheva17, Toshihiko Takemura18, Kostas Tsigaridis19,20, and Svetlana G. Tsyro1 Jonas Gliß et al.
  • 1Norwegian Meteorological Institute, Oslo, Norway
  • 2Cooperative Institute for Research in Environmental Sciences,University of Colorado, Boulder, Colorado, USA
  • 3Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Gif sur Yvette Cedex, France
  • 4Maryland Univ. Baltimore County (UMBC), Baltimore, MD, USA
  • 5NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
  • 6NOAA, Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA
  • 7Dept. of Geography, Swansea University, Swansea, UK
  • 9European Centre for Medium-Range Weather Forecasts, Reading, UK
  • 10Atmospheric Research Centre of Eastern Finland, Finnish Meteorological Institute, Kuopio, Finland
  • 11Univ. Grenoble Alpes, CNRS, IRD, Grenoble INP, Institute for Geosciences and Environmental Research (IGE), Grenoble, France
  • 12Royal Netherlands Meteorological Institute, De Bilt, the Netherlands
  • 13NILU – Norwegian Institute for Air Research, Kjeller, Norway
  • 14Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan
  • 15CICERO Center for International Climate and Environmental Research, Oslo, Norway
  • 16Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
  • 17Finnish Meteorological institute, Climate Research Program, Helsinki, Finland
  • 18Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka, Japan
  • 19Center for Climate Systems Research, Columbia University, New York, USA
  • 20NASA Goddard Institute for Space Studies, New York, USA

Abstract. Within the framework of the AeroCom (Aerosol Comparisons between Observations and Models) initiative, the present day modelling of aerosol optical properties has been assessed using simulated data representative for the year 2010, from 14 global aerosol models participating in the Phase III Control experiment. The model versions are close or equal to those used for CMIP6 and AerChemMIP and inform also on bias in state of the art ESMs. Modelled column optical depths (total, fine and coarse mode AOD) and Angstrom Exponents (AE) were compared both with ground based observations from the Aerosol Robotic Network (AERONET, version 3) as well as space based observations from AATSR-SU instruments. In addition, the modelled AODs were compared with MODIS (Aqua and Terra) data and a satellite AOD data-set (MERGED-FMI) merged from 12 different individual AOD products. Furthermore, for the first time, the modelled near surface scattering (under dry conditions) and absorption coefficients were evaluated against measurements made at low relative humidity at surface in-situ GAW sites.

Statistics are based mainly on normalised mean biases and Pearson correlation coefficients from colocated model and observation data in monthly resolution. Hence, the results are mostly representative for the regions covered by each of the observation networks. Model biases established against satellite data yield insights into remote continental areas and oceans, where ground-based networks lack site coverage. The satellite data themselves are evaluated against AERONET observations, to test our aggregation and re-gridding routines, suggesting relative AOD biases of −5 %, −6 %, +9 % and +18 % for AATSR-SU, MERGED-FMI, MODIS-aqua and MODIS-terra, respectively, with high correlations exceeding 0.8. Biases of fine and coarse AOD and AE in AATSR are found to be +2 %, −16 % and +14.7 % respectively, at AERONET sites, with correlations of the order of 0.8.

The AeroCom MEDIAN and most of the participating models underestimate the optical properties investigated, relative to remote sensing observations. AERONET AOD is underestimated by 21 % ± 17 %. Against satellite data, the model AOD biases range from −38 % (MODIS-terra) to −17 % (MERGED-FMI). Correlation coefficients of model AODs with AERONET, MERGED-FMI and AATSR-SU are high (0.8–0.9) and slightly lower against the two MODIS data-sets (0.6–0.8). Investigation of fine and coarse AODs from the MEDIAN model reveals biases of −10% ± 20 % and −41 % ± 29 % against AERONET and −13 % and −24 % against AATSR-SU, respectively. The differences in bias against AERONET and AATSR-SU are in agreement with the established satellite bias against AERONET. These results indicate that most of the AOD bias is due to missing coarse AOD in the regions covered by these observations.

Underestimates are also found when comparing the models against the surface GAW observations, showing AeroCom MEDIAN mean bias and inter-model variation of −44 % ± 22 % and −32 % ± 34 % for scattering and absorption coefficients, respectively. Dry scattering shows higher underestimation than AOD at ambient relative humidity and is in agreement with recent findings that suggest that models tend to overestimate scattering enhancement due to hygroscopic growth. Broadly consistent negative bias in AOD and scattering suggest a general underestimate in aerosol effects in current global aerosol models.

The large diversity in the surface absorption results suggests differences in the model treatment of light absorption by black carbon (BC), dust (DU) and to a minor degree, organic aerosol (OA). Considerable diversity is found among the models in the simulated near surface absorption coefficients, particularly in regions associated with dust (e.g. Sahara, Tibet), biomass burning (e.g. Amazonia, Central Australia) and biogenic emissions (e.g. Amazonia). Regions associated with high anthropogenic BC emissions such as China and India exhibit comparatively good agreement for all models.

Evaluation of modelled column AEs shows an underestimation of 9 % ± 24 % against AERONET and −21 % against AATSR-SU. This suggests that overall, models tend to overestimate particle size, with implications for lifetime and radiative transfer calculations.

An investigation of modelled emissions, burdens and lifetimes, mass-specific-extinction coefficients (MECs) and optical depths (ODs) for each species and model reveals considerable diversity in most of these parameters. These are discussed in detail for each model individually. Inter-model spread of aerosol species lifetime appears to be similar to that of mass extinction coefficients, suggesting that AOD uncertainties are still associated to a broad spectrum of parameterised aerosol processes.

Jonas Gliß et al.

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Jonas Gliß et al.

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Short summary
Optical properties from 14 global aerosol models participating in the AeroCom initiative are evaluated against ground and space based observations. On average, models underestimate all optical variables investigated by around −20 % (AOD), −10 % (fine AOD, Ang. Exp.) and around −35 % to −40 % (coarse AOD and surface scattering and absorption coefficients). This suggests that current models are still missing considerable aerosol mass on a global scale, with implications for aerosol radiative effects.
Optical properties from 14 global aerosol models participating in the AeroCom initiative are...