Reevaluation of Mineral aerosol radiative forcings suggests a better agreement with satellite and AERONET data

By Y. Balkanski, Michael Schulz, T. Claquin, S. Guibert. 2006

451 citations recorded by the source corpus.

Modelling studies and satellite retrievals do not agree on the amplitude and/or sign of the direct radiative per- turbation from dust. Modelling studies have systematically overpredicted mineral dust absorption compared to estimates based upon satellite retrievals. In this paper we first point out the source of this discrepancy, which originates from the shortwave refractive index of dust used in models. The imag- inary part of the refractive index retrieved from AERONET over the range 300 to 700 nm is 3 to 6 times smaller than that used previously to model dust. We attempt to constrain these refractive indices using a mineralogical database and varying the abundances of iron oxides (the main absorber in the visible). We first consider the optically active min- eral constituents of dust and compute the refractive indices from internal and external mixtures of minerals with rela- tive amounts encountered in parent soils. We then compute the radiative perturbation due to mineral aerosols for inter- nally and externally mixed minerals for 3 different hematite contents, 0.9%, 1.5% and 2.7% by volume. These constant amounts of hematite allow bracketing the influence of dust aerosol when it is respectively an inefficient, standard and a very efficient absorber. These values represent low, central and high content of iron oxides in dust determined from the mineralogical database. Linke et al. (2006) determined inde- pendently that iron-oxides represent 1.0 to 2.5% by volume using x-Ray fluorescence on 4 different samples collected over Morocco and Egypt. Based upon values of the refrac- tive index retrieved from AERONET, we show that the best agreement between 440 and 1020 nm occurs for mineral dust internally mixed with 1.5% volume weighted hematite. This representation of mineral dust allows us to compute, using a general circulation model, a new global estimate of min- eral dust perturbation between -0.47 and -0.24 Wm 2 at the top of the atmosphere, and between -0.81 and -1.13 Wm 2 at the surface for both shortwave and longwave wavelengths. The anthropogenic dust fraction is thought to account for be- tween 10 and 50% of the total dust load present in the at- mosphere. We estimate a top of the atmosphere forcing be- tween -0.03 and -0.25 Wm 2 , which is markedly different that the IPCC range of -0.6 to +0.4 Wm 2 (IPCC, 2001). The 24-h average atmospheric heating by mineral dust dur- ing summer over the tropical Atlantic region (15 N-25 N; 45 W-15 W) is in the range +22 to +32 Wm 2 1 which compares well with the 30±4 Wm 2 1 measured by Li et al. (2004) over that same region. The refractive indices from Patterson et al. (1977) and from Volz (1973) overestimate by a factor of 2 the energy absorbed in the column during sum- mer over the same region. This discrepancy is due to too large absorption in the visible but we could not determine if this is linked to the sample studied by Patterson et al. (1997) or to the method used in determining the refractive index.

View Paper: https://www.semanticscholar.org/paper/cc43cd8c02b74214941402d43500b0af4c91f19b

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

Citations in the corpus

The dynamical core, physical parameterizations, and basic simulation characteristics of the atmospheric component AM3 of the GFDL global coupled model CM3 (2011, background): “The refractive indices of sulfate and black carbon are from Haywood and Ramaswamy (1998), organics from Hess et al. (1998), sea salt from Tang et al. (1997), and dust from Balkanski et al. (2007), assuming a 2.7% content of hematite.”
The MERRA-2 Aerosol Reanalysis, 1980 Onward. Part II: Evaluation and Case Studies. (2017, background): “2006), and dust has a large impact on Earth’s radiative budget because it absorbs and scatters both solar and thermal radiation (Balkanski et al. 2007; Colarco et al. 2014).”
Atmospheric iron deposition: global distribution, variability, and human perturbations. (2009, methodology): “These data have been very useful in improving models and our understanding of dust (e.g., Ginoux et al. 2001, Luo et al. 2003, Balkanski et al. 2007).”
Saharan dust absorption and refractive index from aircraft-based observations during SAMUM 2006 (2009, unknown): “Recent studies (Dubovik et al., 2002; Balkanski et al., 2007; Todd et al., 2007) have demonstrated that the values commonly used for the imaginary part of the refractive index (Patterson et al., 1977; Shettle and Fenn, 1979; d’Almeida et al., 1991) are overestimating aerosol light absorption.”
The global influence of dust mineralogical composition on heterogeneous ice nucleation in mixed-phase clouds (2008, background): “As discussed by Balkanski et al (2006), both external and internal mixtures of different minerals can possibly be generated during dust emission.”
Impact of radiatively interactive dust aerosols in the NASA GEOS‐5 climate model: Sensitivity to dust particle shape and refractive index (2014, background): “Scattering and absorption of shortwave (i.e., solar) and longwave (i.e., thermal) radiation by dust particles directly influence Earth’s radiation balance [Sokolik and Toon, 1996; Balkanski et al., 2007].”
The physics of wind-blown sand and dust (2012, methodology): “Numerical simulations and water tank experiments of dune formation under various flow conditions provided insights into the formative wind regimes of diverse martian dune shapes: (a) Barchan dunes of different sizes at Arkhangelsky crater (left) together with the corresponding shapes obtained in num”
Aerosol light absorption and its measurement: A review (2009, background): “8mm effective diameter) particles such as mineral dust (MD) [11,12] and will not be discussed in detail here.”