Single-scattering properties of droxtals

Yang, Ping; Baum, Bryan A.; Heymsfield, Andrew J.; Hu, Y.; Huang, Hung‐Lung; Tsay, Si‐Chee; Ackerman, S. A.

doi:10.1016/s0022-4073(02)00347-3

Cited by 128 publications

(83 citation statements)

References 13 publications

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“…The Baum05 categorizes ice particles into six habits and uses a size-dependent habit distribution to simulate the variation of ice particle habits with size. For example, ice particles smaller than 60 µm are assumed to be 100% droxtal, which has 20 facets and is designed to represent small quasi-spherical ice particles (Yang et al, 2003;Zhang et al, 2004), and a mixture of 15% bullet rosettes, 50% solid hexagonal columns and 35% hexagonal plates is assumed for particles within 60 to 1000 µm. The justification for this habit distribution lies in the consistency between the theoretically-derived ice water content and median mass diameter based on this habit distribution and the in situ measurements.…”

Section: Modis and Polder Ice Optical Thickness Retrieval Algorithmsmentioning

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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Section: Modis and Polder Ice Optical Thickness Retrieval Algorithmsmentioning

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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“…The geometric details for various ice particle habits can be found in Yang and Liou (1998). Droxtals are described further in Yang et al (2003) and Zhang et al (2004).…”

Section: B Ice Particle Scattering Propertiesmentioning

confidence: 99%

Bulk Scattering Properties for the Remote Sensing of Ice Clouds. Part II: Narrowband Models

Baum

Yang

Heymsfield

et al. 2005

Journal of Applied Meteorology

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258

216

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This study examines the development of bulk single-scattering properties of ice clouds, including single scattering albedo, asymmetry factor, and phase function, for a set of 1117 particle size distributions obtained from analysis of FIRE-I, FIRE-II, ARM-IOP, TRMM-KWAJEX, and CRYSTAL-FACE data. The primary focus is to develop bandaveraged models appropriate for use by the MODIS imager on the EOS Terra and Aqua platforms, specifically for bands located at wavelengths of 0.65, 1.6, 2.1, and 3.75 µm.Our results indicate that there are substantial differences in the bulk scattering properties of ice clouds formed in areas of deep convection and those that exist in areas of much lower updraft velocities.Band-averaged bulk scattering property results obtained from a particle-size dependent mixture of ice crystal habits are compared to those obtained assuming only solid hexagonal columns. The single scattering albedo is lower for hexagonal columns than for a habit mixture for the 1.6, 2.1, and 3.75 µm bands, with the differences increasing with wavelength. In contrast, the asymmetry factors obtained from the habit mixture and only the solid hexagonal column are most different at 0.65 µm, with the differences decreasing as wavelength increases. At 3.75 µm, the asymmetry factor results from the two habit assumptions are almost indistinguishable. The asymmetry factor, single-scatter albedo, and scattering phase functions are also compared to the MODIS V1 models. Differences between the current and V1 models can be traced to the microphysical models, specifically the number of both the smallest and the largest particles assumed in the size distributions.3

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“…The ensemble due to Baum et al (2005) comprises droxtals (these shapes are supposed to represent the smaller ice crystals in the particle size distribution function, see Yang et al (2003) for further details), hexagonal ice columns and plates, hollow columns, bullet-rosettes and ice aggregates (the ice aggregate consists of eight hexagonal elements arbitrarily attached, the aspect ratio of which remains invariant with respect to size, see Yang and Liou (1998)). This ensemble is supposed to represent some typical distribution of shapes that is observed in cirrus using the Cloud Particle Imager (CPI) probe due to Lawson et al (1998).…”

Section: Introductionmentioning

confidence: 99%

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

Baran

C.‐Labonnote²

2007

Quart J Royal Meteoro Soc

129

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ABSTRACT:In this paper a self-consistent scattering model for cirrus is presented. The model consists of an ensemble of ice crystals where the smallest ice crystal is represented by a single hexagonal ice column. As the overall ice crystal size increases, the ice crystals become progressively more complex by arbitrarily attaching other hexagonal elements until a chain-like ice crystal is formed, this representing the largest ice crystal in the ensemble. The ensemble consists of six ice crystal members whose aspect ratios (ratios of the major-to-minor axes of the circumscribed ellipse) are allowed to vary between unity and 1.84 for the smallest and largest ice crystal, respectively. The ensemble model's prediction of parameters fundamental to solar radiative transfer through cirrus such as ice water content and the volume extinction coefficient is tested using in situ based data obtained from the midlatitudes and Tropics. It is found that the ensemble model is able to generally predict the ice water content and extinction measurements within a factor of two. Moreover, the ensemble model's prediction of cirrus spherical albedo and polarized reflection are tested against a space-based instrument using one day of global measurements. The space-based instrument is able to sample the scattering phase function between the scattering angles of approximately 60°and 180°, and a total of 37 581 satellite pixels were used in the present analysis covering latitude bands between 43.75°S and 76.58°N. It is found that the ensemble model phase function is well able to minimize significantly differences between satellite-based measurements of spherical albedo and the ensemble model's prediction of spherical albedo. The satellite-based measurements of polarized reflection are found to be reasonably described by more simple members of the ensemble. The ensemble model presented in this paper should find wide applicability to the remote sensing of cirrus as well as more fundamental solar radiative transfer calculations through cirrus, and improved solar optical properties for climate and Numerical Weather Prediction models.

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Single-scattering properties of droxtals

Cited by 128 publications

References 13 publications

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

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

Bulk Scattering Properties for the Remote Sensing of Ice Clouds. Part II: Narrowband Models

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

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