A regional, size-dependent, and causal effective medium model for Asian and Saharan mineral dust refractive index spectra

Stegmann, Patrick G.; Yang, Ping

doi:10.1016/j.jaerosci.2017.10.003

Cited by 33 publications

(29 citation statements)

References 51 publications

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“…The calculation of the optical properties is based on the wavelength-dependent refractive indices of dust used by Rieger et al (2017), which is in good agreement (difference <5% in the shortwave) with the recent dust refractive index databases for North Africa (Stegmann & Yang, 2017). For spherical particles, the results of the Mie calculations conducted by Gasch et al (2017) are used.…”

Section: Calculation Of Dust Optical Propertiesmentioning

confidence: 92%

Effects of Particle Nonsphericity on Dust Optical Properties in a Forecast System: Implications for Model‐Observation Comparison

et al. 2019

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Mineral dust is a key player in the Earth system that affects the weather and climate through absorbing and scattering the radiation. Such effects strongly depend on the optical properties of the particles that are in turn affected by the particle shape. For simplicity, dust particles are usually assumed to be spherical. But this assumption can lead to large errors in modeling and remote sensing applications. This study investigates the impact of dust particle shape on its direct radiative effect in a next‐generation atmospheric modeling system ICON‐ART (ICOsahedral Nonhydrostatic weather and climate model with Aerosols and Reactive Trace gases) to verify if accounting for nonsphericity enhances the model‐observation agreement. Two sets of numerical experiments are conducted by changing the optical shape of the particles: one assuming spherical particles and the other one assuming a mixture of 35 randomly oriented triaxial ellipsoids. The simulations are compared to MISR (Multiangle Imaging Spectroradiometer), AERONET (Aerosol Robotic Network), and CALIPSO (Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation) observations (with focus on North Africa). The results show that consideration of particle nonsphericity increases the dust AOD (Aerosol Optical Depth) at 550 nm by up to 28% and leads to slight enhancement of the agreement between modeled and measured AOD. However, the model performance varies significantly when focusing on specific regions in North Africa. These differences stem from the uncertainties associated with particle size distribution and emission mechanisms in the model configuration. Regarding the attenuated backscatter, the simulated profile assuming nonsphericity differs by a factor of 2 to 5 from the experiment assuming spherical dust and is in a better agreement with the CALIPSO observations.

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Section: Calculation Of Dust Optical Propertiesmentioning

confidence: 92%

Effects of Particle Nonsphericity on Dust Optical Properties in a Forecast System: Implications for Model‐Observation Comparison

et al. 2019

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“…This database is the first one as far as we know to document the regional differences in dust LW refractive index due to the regional characteristics of dust chemical composition. We also call special attention to a newly developed database of Saharan and Asian dust (Stegmann and Yang, 2017).…”

Section: Introductionmentioning

confidence: 99%

Net radiative effects of dust in the tropical North Atlantic based on integrated satellite observations and in situ measurements

Song

Zhang

et al. 2018

Atmos. Chem. Phys.

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In this study, we integrate recent in situ measurements with satellite retrievals of dust physical and radiative properties to quantify dust direct radiative effects on shortwave (SW) and longwave (LW) radiation (denoted as DRE SW and DRE LW , respectively) in the tropical North Atlantic during the summer months from 2007 to 2010. Through linear regression of the CERES-measured top-ofatmosphere (TOA) flux versus satellite aerosol optical depth (AOD) retrievals, we estimate the instantaneous DRE SW efficiency at the TOA to be −49.7 ± 7.1 W m −2 AOD −1 and −36.5±4.8 W m −2 AOD −1 based on AOD from MODIS and CALIOP, respectively. We then perform various sensitivity studies based on recent measurements of dust particle size distribution (PSD), refractive index, and particle shape distribution to determine how the dust microphysical and optical properties affect DRE estimates and its agreement with the above-mentioned satellite-derived DREs. Our analysis shows that a good agreement with the observation-based estimates of instantaneous DRE SW and DRE LW can be achieved through a combination of recently observed PSD with substantial presence of coarse particles, a less absorptive SW refractive index, and spheroid shapes. Based on this optimal combination of dust physical properties we further estimate the diurnal mean dust DRE SW in the region of −10 W m −2 at TOA and −26 W m −2 at the surface, respectively, of which ∼ 30 % is canceled out by the positive DRE LW . This yields a net DRE of about −6.9 and −18.3 W m −2 at TOA and the surface, respectively. Our study suggests that the LW flux contains useful information on dust particle size, which could be used together with SW observations to achieve a more holistic understanding of the dust radiative effect.Published by Copernicus Publications on behalf of the European Geosciences Union.

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“…In addition, it becomes clear that for the locations under study, the major dust composition is different. Therefore, the use of different optical properties with respect to the real part of the refractive index for African, Central Asian, and Arctic dust should be considered, as for example shown by Stegmann et al [72]. Similarly, while the variation in the imaginary part is comparatively low for the African transport region, different values should be used for Central Asian and Arctic dust, as well as for near-source situations.…”

Section: Discussionmentioning

confidence: 99%

Differences and Similarities of Central Asian, African, and Arctic Dust Composition from a Single Particle Perspective

et al. 2020

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Mineral dust composition affects a multitude of processes in the atmosphere and adjacent compartments. Dust dry deposition was collected near source in northwest Africa, in Central Asia, and on Svalbard and at three locations of the African outflow regime. Samples were subjected to automated scanning electron microscopy with energy-dispersive X-ray analysis to obtain size and composition of 216,000 individual particles. Results show low temporal variation in estimated optical properties for each location, but considerable differences between the African, Central Asian, and Arctic regimes. No significant difference was found between the K-feldspar relative abundances, indicating comparable related ice-nucleation abilities. The mixing state between calcium and iron compounds was different for near source and transport regimes, potentially in part due to size sorting effects. As a result, in certain situations (high acid availability, limited time) atmospheric processing of the dust is expected to lead to less increased iron solubility for near-source dusts (in particular for Central Asian ones) than for transported ones (in particular of Sahelian origin).Atmosphere 2020, 11, 269 2 of 16 Dust composition also affects the marine and terrestrial biosphere by supplying nutrients, but also supplying substances with adverse health effects [20]. Tropical as well as extra-tropical ecosystems apparently rely in part on atmospheric inputs [21,22]. Ocean surface waters can be depleted in essential nutrients supplied by the dust [23,24], thus composition plays an important role [25,26].Several of these effects are not only affected by the overall composition, but also by the distribution of the compounds between the particles (i.e., internal or external mixing). For example, optical properties are strongly dependent on the mixing state [27,28]. In addition, chemical processes might be considerably affected by the particle mixing state [29].Consequently, a more detailed knowledge of dust composition is expected to yield a better understanding and increased model quality. Information on bulk aerosol is available with respect to different properties (e.g., [6,7,30,31]) and finds its way into models [32]. In contrast, detailed properties like the aerosol mixing state are generally not yet regarded, probably due to scarcity of this information.In the present study, dust from different transport regimes-African near-source and outflow, Central Asian near-source, and a high-latitude source-is analyzed to provide information on its composition and variation. With respect to the importance of the mixing state, a single particle attempt was chosen. A particular focus of this study is the distribution of iron amongst individual particles, and its internal mixture with calcium compounds, as the iron compounds are of high interest for different processes. These processes include radiation absorption, photocatalytic reactions, and ocean fertilization.

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A regional, size-dependent, and causal effective medium model for Asian and Saharan mineral dust refractive index spectra

Cited by 33 publications

References 51 publications

Effects of Particle Nonsphericity on Dust Optical Properties in a Forecast System: Implications for Model‐Observation Comparison

Effects of Particle Nonsphericity on Dust Optical Properties in a Forecast System: Implications for Model‐Observation Comparison

Net radiative effects of dust in the tropical North Atlantic based on integrated satellite observations and in situ measurements

Differences and Similarities of Central Asian, African, and Arctic Dust Composition from a Single Particle Perspective

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