Modelling diffraction by facetted particles

Hesse, E.; Macke, Andreas; Havemann, Stephan; Baran, Anthony J.; Ulanowski, Zbigniew; Kaye, Paul H.

doi:10.1016/j.jqsrt.2011.11.017

Cited by 16 publications

(17 citation statements)

References 17 publications

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“…More work is needed to establish the degree of cubicity and the particle-size distribution of stacking-disordered ice formed in the atmosphere (56). With the knowledge of particle number and surface roughness, the light-scattering behavior in the atmosphere can be estimated (50,(64)(65)(66). This is important, as the backscattering properties of cirrus clouds are one of the major unknowns to quantify the Earth's radiation balance (e.g., ref.…”

Section: Discussionmentioning

confidence: 99%

Extent and relevance of stacking disorder in “ice I_c”

Kuhs

Sippel

Falenty

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

216

280

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A solid water phase commonly known as "cubic ice" or "ice I c " is frequently encountered in various transitions between the solid, liquid, and gaseous phases of the water substance. It may form, e.g., by water freezing or vapor deposition in the Earth's atmosphere or in extraterrestrial environments, and plays a central role in various cryopreservation techniques; its formation is observed over a wide temperature range from about 120 K up to the melting point of ice. There was multiple and compelling evidence in the past that this phase is not truly cubic but composed of disordered cubic and hexagonal stacking sequences. The complexity of the stacking disorder, however, appears to have been largely overlooked in most of the literature. By analyzing neutron diffraction data with our stacking-disorder model, we show that correlations between next-nearest layers are clearly developed, leading to marked deviations from a simple random stacking in almost all investigated cases. We follow the evolution of the stacking disorder as a function of time and temperature at conditions relevant to atmospheric processes; a continuous transformation toward normal hexagonal ice is observed. We establish a quantitative link between the crystallite size established by diffraction and electron microscopic images of the material; the crystallite size evolves from several nanometers into the micrometer range with progressive annealing. The crystallites are isometric with markedly rough surfaces parallel to the stacking direction, which has implications for atmospheric sciences.

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Section: Discussionmentioning

confidence: 99%

Extent and relevance of stacking disorder in “ice I_c”

Kuhs

Sippel

Falenty

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

216

280

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“…Two-dimensional scattering patterns offer high potential for detailed particle characterization. It is possible to recover the shape, size and orientation of small ice particles by comparing such patterns to scattering models such as the Ray Tracing with Diffraction on Facets (RTDF) model (Clarke et al, 2006;Kaye et al, 2008;Hesse et al, 2009Hesse et al, , 2012. Ice particle roughness can also be obtained, as evidenced by experimental patterns from fluorosilicate ice analogue crystals with smooth and rough surfaces, which show distinct differences: while the former have sharp, well-defined bright arcs and spots, the latter have much more random, "speckled" appearance .…”

Section: Introductionmentioning

confidence: 99%

Incidence of rough and irregular atmospheric ice particles from Small Ice Detector 3 measurements

et al. 2014

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Abstract. The knowledge of properties of ice crystals such as size, shape, concavity and roughness is critical in the context of radiative properties of ice and mixed-phase clouds. Limitations of current cloud probes to measure these properties can be circumvented by acquiring two-dimensional lightscattering patterns instead of particle images. Such patterns were obtained in situ for the first time using the Small Ice Detector 3 (SID-3) probe during several flights in a variety of mid-latitude mixed-phase and cirrus clouds. The patterns are analysed using several measures of pattern texture, selected to reveal the magnitude of particle roughness or complexity. The retrieved roughness is compared to values obtained from a range of well-characterized test particles in the laboratory. It is found that typical in situ roughness corresponds to that found in the rougher subset of the test particles, and sometimes even extends beyond the most extreme values found in the laboratory. In this study we do not differentiate between small-scale, fine surface roughness and large-scale crystal complexity. Instead, we argue that both can have similar manifestations in terms of light-scattering properties and also similar causes. Overall, the in situ data are consistent, with ice particles with highly irregular or rough surfaces being dominant. Similar magnitudes of roughness were found in growth and sublimation zones of cirrus. The roughness was found to be negatively correlated with the halo ratio, but not with other thermodynamic or microphysical properties found in situ. Slightly higher roughness was observed in cirrus forming in clean oceanic air masses than in a continental, polluted one. Overall, the roughness and complexity are expected to lead to increased shortwave cloud reflectivity, in comparison with cirrus composed of more regular, smooth ice crystal shapes. These findings put into question suggestions that climate could be modified through aerosol seeding to reduce cirrus cover and optical depth, as the seeding may result in decreased shortwave reflectivity.

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“…Macke et al [12] used the Kirchhoff approximation to model diffraction by polygonal apertures corresponding to the projected particle cross section. The method to calculate diffraction by a circular aperture at oblique incidence by means of the Kirchhoff approximation [15] has been extended to oblique incidence on polygonal apertures and applied to compute scattering patterns and phase function of absorbing facetted particles in fixed orientation [16] (Note that due to the singular directions of rays or beams reflected from faceted particles in geometric optics, 2D scattering patterns for fixed particle orientations do not show the familiar scattering arcs but only scattering points, see e.g. [31]).…”

Section: Introductionmentioning

confidence: 99%

“…[31]). In the first part of this paper we describe how polarisation treatment in [16] was improved by introducing the vector method described by Karczewski and Wolf [17]. Comparisons of phase functions, 2D scattering patterns and azimuthally averaged degree of linear polarisation for hexagonal prisms in fixed orientation are presented.…”

Section: Introductionmentioning

confidence: 99%

Modelling light scattering by absorbing smooth and slightly rough facetted particles

Hesse

Collier

Penttilä

et al. 2015

Journal of Quantitative Spectroscopy and Radiative Transfer

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Date of Acceptance: 03/02/2015A method for approximating light scattering properties of strongly absorbing facetted particles which are large compared to the wavelength is presented. It consists in adding the approximated external diffraction and reflection far fields and is demonstrated for a smooth hexagonal prism. This computationally fast method is extended towards prisms with slightly rough surfaces by introducing a surface scaling factor in order to account for edge effects on subfacets forming the rough surface. These effects become more pronounced with decreasing subfacet dimension to wavelength ratio. Azimuthally resolved light scattering patterns, phase functions and degree of linear polarisation obtained by this method and by the Discrete Dipole Approximation are compared for hexagonal prisms with smooth and slightly rough surfaces, respectively

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Modelling diffraction by facetted particles

Cited by 16 publications

References 17 publications

Extent and relevance of stacking disorder in “ice I_c”

Extent and relevance of stacking disorder in “ice I_c”

Incidence of rough and irregular atmospheric ice particles from Small Ice Detector 3 measurements

Modelling light scattering by absorbing smooth and slightly rough facetted particles

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Modelling diffraction by facetted particles

Cited by 16 publications

References 17 publications

Extent and relevance of stacking disorder in “ice Ic”

Extent and relevance of stacking disorder in “ice Ic”

Incidence of rough and irregular atmospheric ice particles from Small Ice Detector 3 measurements

Modelling light scattering by absorbing smooth and slightly rough facetted particles

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Extent and relevance of stacking disorder in “ice I_c”

Extent and relevance of stacking disorder in “ice I_c”