A self‐consistent scattering model for cirrus. I: The solar region

Baran, Anthony J.; C.‐Labonnote, Laurent

doi:10.1002/qj.164

Cited by 89 publications

(132 citation statements)

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“…The first in situ observations of azimuthal scattering patterns also confirmed that smooth scattering phase functions prevail in cirrus clouds Auriol et al, 2001;Field et al, 2003a;Gayet et al, 2004;Baumgardner et al, 2005). Defaults in crystal geometry, roughness of the ice surface or imperfect internal structure are known to hamper the formation of halos (see among others Baran and Labonnote, 2007). This may explain the rare ground-observed occurrences of these optical phenomena.…”

Section: Introductionmentioning

confidence: 81%

“…This also means that the Polar Nephelometer data contains a signature of pristine ice crystals. Defaults in crystal geometry, roughness of the ice surface or imperfect internal structure do hamper the formation of halo (see among others Baran and Labonnote, 2007). The model from Shcherbakov et al (2006a) has been employed to compute the angular scattering patterns by using measured crystal shape and size and by considering both roughness and internal structure.…”

Section: Discussionmentioning

confidence: 99%

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Optical properties of pristine ice crystals in mid-latitude cirrus clouds: a case study during CIRCLE-2 experiment

et al. 2011

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Abstract. In this paper, we describe in situ observations of mid-latitude cirrus cloud band carried out on 16 May 2007 during the CIRCLE-2 experiment. The Polar Nephelometer and the Cloud Particle Imager (CPI) instruments with PMS FSSP-300 and 2D-C probes were used for the description of the optical and microphysical cloud properties. Two selected cloud regions are compared and discussed in detail. Significant differences in optical properties are evidenced in terms of 22 • halo occurrences even though prevalent planarplate ice crystals are observed in both cloud regions. Featureless scattering phase functions are measured in the first cloud region located near the trailing edge of the cirrus-band at about 11 800 m/−57 • C. In contrast, well pronounced 22 • halo peaks are observed with predominant similar-shaped ice crystals near the cirrus-band leading edge at 7100 m/−27 • C. CPI ice crystal images with Polar Nephelometer observations are carefully analysed and interpreted from a theoretical light scattering model in order to explain occurrence and non-occurrence of the 22 • halo feature. The results highlight that the halo peaks are inherent only in perfect plate ice crystals (or pristine crystals). On the basis of previous datasets in mid-latitude cirrus, it is found that simple pristine crystals are uncommon whereas particles with imperfect or complex shapes are prevalent. As a result, phase functions that are smooth and featureless best represent cirrus scattering properties.

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Section: Introductionmentioning

confidence: 81%

Section: Discussionmentioning

confidence: 99%

Optical properties of pristine ice crystals in mid-latitude cirrus clouds: a case study during CIRCLE-2 experiment

et al. 2011

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“…Idealized models (Yang and Liou, 1998;Baran and Labonnote, 2007;Um and McFarquhar, 2007) of aggregate ice crystals (i.e. aggregates of columns and aggregates of bullet rosettes) have been generated to calculate the single-scattering properties.…”

Section: Introductionmentioning

confidence: 99%

Single‐scattering properties of aggregates of plates

McFarquhar

2009

Quart J Royal Meteoro Soc

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During the 2006 Tropical Warm Pool International Cloud Experiment (TWP-ICE) sponsored by the Atmospheric Radiation Measurement programme, the Scaled Composites Proteus aircraft executed spiral profiles and flew horizontal legs through aging anvils, fresh anvils, and cirrus of unknown origin in the vicinity of Darwin, Australia. Pristine ice crystals including both plates and bullet rosettes, their aggregates, and unclassifiable ice crystals were observed by a Cloud Particle Imager. The widths of observed plates ranged between 80 µm and 200 µm. When a fresh dissipating anvil was observed on 2 February, aggregates of plates contributed 46.2% of the total area of measured ice crystals with maximum dimensions greater than 200 µm, while it was only 7.2% and 1.0% for 27 and 29 January, respectively, when aged cirrus was sampled. Because aggregates of plates have been observed to make large contributions to projected ice crystal area near convection during TWP-ICE and other projects, their single-scattering properties that have not been previously examined are investigated here.The dependence of the scattering phase function P 11 , asymmetry parameter g, and single-scattering albedo ω 0 on three parameters (the area ratio AR, normalized projected area A n , and a newly defined aggregation index AI which varies between 0 and 1 with ice crystals with more compact shape having lower AI ) defining the three-dimensional shapes of aggregates of plates were calculated using a geometric ray-tracing code at wavelengths λ of 0.55, 1.38 and 2.13 µm. The scattering properties depended on the crystal morphology with, for example, the g of an aggregate of plates with a high AI of 0.818 differing by +6.89% (+6.44%; +4.55%) from that with a lower AI of 0.378 at λ of 0.55 µm (1.38 µm; 2.13 µm), but by only +0.29% (+0.25%; −0.03%) from those of the component plates. The ω 0 at absorbing λ increased with AI, 1 − AR, and A n . Adding ray distortion to the aggregates caused a decrease in forward scattering and an increase in lateral and backward scattering, decreasing g, an effect that weakened with λ due to absorption. The aggregates of plates with low AI were more influenced by ray distortion compared to those with high AI. The dependence of scattering properties on crystal morphology noted here should be considered when computing bulk scattering properties of ice clouds to determine its importance for climate and remote-sensing studies.

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“…Over the last two decades, several major ice cloud measurement campaigns have been carried out (Cox et al, 1987;Jensen et al, 2004;Gallagher et al, 2005). Based on the in-situ and remotely-sensed data obtained from these campaigns, a number of ice particle models have been developed and used for ice cloud retrievals (e.g., McFarquhar and Heymsfield, 1996;Baran et al, 2001;McFarquhar, 2001;McFarquhar et al, 2002;Baum et al, 2005;Baran and Labonnote, 2007). Unfortunately, as will be shown hereafter, these models generally differ substantially from one another.…”

Section: Introductionmentioning

confidence: 99%

Influence of ice particle model on satellite ice cloud retrieval: lessons learned from MODIS and POLDER cloud product comparison

et al. 2009

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Abstract. The influence is investigated of the assumed ice particle microphysical and optical model on inferring ice cloud optical thickness (τ ) from satellite measurements of the Earth's reflected shortwave radiance. Ice cloud τ are inferred, and subsequently compared, using products from MODIS (MODerate resolution Imaging Spectroradiometer) and POLDER (POLarization and Directionality of the Earth's Reflectances). POLDER τ values are found to be substantially smaller than those from collocated MODIS data. It is shown that this difference is caused primarily by the use of different ice particle bulk scattering models in the two retrievals, and more specifically, the scattering phase function. Furthermore, the influence of the ice particle model on the derivation of ice cloud radiative forcing (CRF) from satellite retrievals is studied. Three sets of shortwave CRF are calculated using different combinations of the retrieval and associated ice particle models. It is shown that the uncertainty associated with an ice particle model may lead to two types of errors in estimating CRF from satellite retrievals. One stems from the retrieval itself and the other is due to the optical properties, such as the asymmetry factor, used for CRF calculations. Although a comparison of the CRFs reveals that these two types of errors tend to cancel each other, significant differences are still found between the three CRFs, which indicates that the ice particle model affects notCorrespondence to: Z. Zhang (zzbatmos@umbc.edu) only optical thickness retrievals but also CRF calculations. In addition to CRF, the effect of the ice particle model on the derivation of seasonal variation of τ from satellite measurements is discussed. It is shown that optical thickness retrievals based on the same MODIS observations, but derived using different assumptions of the ice particle model, can be substantially different. These differences can be divided into two parts. The first-order difference is mainly caused by the differences in the asymmetry factor. The second-order difference is related to seasonal changes in the sampled scattering angles and therefore dependent on the sun-satellite viewing geometry. Because of this second-order difference, the use of different ice particle models may lead to a different understanding of the seasonal variation of τ .

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A self‐consistent scattering model for cirrus. I: The solar region

Cited by 89 publications

References 70 publications

Optical properties of pristine ice crystals in mid-latitude cirrus clouds: a case study during CIRCLE-2 experiment

Optical properties of pristine ice crystals in mid-latitude cirrus clouds: a case study during CIRCLE-2 experiment

Single‐scattering properties of aggregates of plates

Influence of ice particle model on satellite ice cloud retrieval: lessons learned from MODIS and POLDER cloud product comparison

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