Apparent and real roughness

Gale, Maria Fernanda Ruiz; Hogert, Elsa N.; Gaggioli, N.G.

doi:10.1016/j.optlaseng.2007.03.003

Cited by 6 publications

(1 citation statement)

References 16 publications

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“…Concerning the mineral dust grains as surrogates for ice particles, while the refractive index of mineral dust is higher, the difference in roughness that would be caused by such change is small: if dust is substituted for ice, the same speckle pattern should be obtained if dust roughness is 1.31/n m of that of ice (Ruiz Gale et al, 2007), where n m , the refractive index of mineral dust, is typically ≈ 1.52. So the dust particles may represent both the scattering properties and possibly also the shape of atmospheric ice crystal quite well, at least as far as solid (as opposed to hollow), simple (as opposed to branched or aggregated) crystals are concerned.…”

Section: Discussionmentioning

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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Section: Discussionmentioning

confidence: 99%