The Asymmetry Parameter of Cirrus Clouds Composed of Hollow Bullet Rosette–Shaped Ice Crystals from Ray-Tracing Calculations

Schmitt, Carl; Iaquinta, Jean; Heymsfield, Andrew J.

doi:10.1175/jam2384.1

Cited by 22 publications

(33 citation statements)

References 29 publications

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“…There is increasing evidence that ice crystals that exist in cirrus have some form of air inclusions (Heymsfield and Miloshevich, 1995;Macke et al, 1996b;Labonnote et al, 2000;Bailey and Hallett, 2004;Schmitt et al, 2006) and the original ray-tracing code due to Macke et al (1996a) allows for the possibility of spherical air bubble inclusions. In this paper randomization of the ice crystal ensemble is achieved through two processes.…”

Section: The Single-scattering Properties and Ray-tracing Methodsmentioning

confidence: 99%

“…Such chains of ice crystals are observed in cirrus (Heymsfield and Miloshevich, 2003;Lawson et al, 2003;Connolly et al, 2005). Bullet-rosettes are included in the ensemble as these are commonly observed in midlatitude and arctic regions Schmitt et al, 2006). The assumed geometry of the bullet-rosette has been previously described in Macke et al (1996a).…”

Section: The Ensemble Modelmentioning

confidence: 99%

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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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Section: The Single-scattering Properties and Ray-tracing Methodsmentioning

confidence: 99%

Section: The Ensemble Modelmentioning

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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“…Ray-tracing results have shown that the scattering properties of hollow bullet rosettes are substantially different from those of solid bullet rosettes at visible wavelengths (Schmitt et al 2006). For hollow crystals the asymmetry parameter was lower (0.84 versus 0.87) for rosettes with skinny bullets, but the trend reversed for rosettes with squat bullets (0.80 versus 0.73).…”

Section: Introductionmentioning

confidence: 97%

On the Occurrence of Hollow Bullet Rosette– and Column-Shaped Ice Crystals in Midlatitude Cirrus

Schmitt

Heymsfield

2007

Journal of the Atmospheric Sciences

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Cirrus clouds in mid-and high latitudes are frequently composed of bullet rosette-and column-shaped ice crystals, which can have hollow ends. Bullet rosette-shaped ice crystals are composed of a number of bullets radiating from a central point. Research has shown that the light-scattering properties of ice particles with hollow ends are different from the scattering properties of solid ice particles. Knowledge of the frequency of occurrence of hollow particles is important to more accurately calculate the radiative properties of cirrus clouds.This note presents the results of a survey of cirrus cloud ice crystal replicas imaged from balloon-borne Formvar (polyvinyl formal) replicators. Fifty percent to 80% of the replicated bullet rosette-and columnshaped particles had hollow ends. In bullets longer than 150 m in length, the length of the hollows of the bullets averaged 88% of the total length of the bullet. The combined length of both hollow portions of column-shaped ice crystals varied from 50% of the length of the column for 30-m-long columns to 80% of the length of the columns longer than 200 m. Asymmetry parameter values estimated from cirrus cloud aircraft particle size distributions are higher by 0.014 when hollow crystals are considered. This difference leads to a 2.5 W m Ϫ2 increase for hollow crystals at the surface for a 0.5 optical depth cloud, demonstrating the importance of the incorporation of hollow particle scattering characteristics into radiative transfer calculations.

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“…Similar to surface roughness, internal structure is also known to influence the scattering properties of ice crystals. One theoretical study modelled cavities using hexagonal based pyramids which were identified by CPI particle images [52]. Ray Tracing results from these models showed a reduction in asymmetry parameter for hollow particles at certain aspect ratios.…”

Section: Introductionmentioning

confidence: 99%

Cloud chamber laboratory investigations into scattering properties of hollow ice particles

Smith

Connolly

Baran

et al. 2015

Journal of Quantitative Spectroscopy and Radiative Transfer

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Copyright 2015 The Authors. Published by Elsevier Ltd.This is an open access article under the CC-BY license (http://creativecommons.org/licenses/by/4.0/). Date of Acceptance: 16/02/2015Measurements are presented of the phase function, P11, and asymmetry parameter, g, of five ice clouds created in a laboratory cloud chamber. At ???7 ??C, two clouds were created: one comprised entirely of solid columns, and one comprised entirely of hollow columns. Similarly at ???15 ??C, two clouds were created: one consisting of solid plates and one consisting of hollow plates. At ???30 ??C, only hollow particles could be created within the constraints of the experiment. The resulting cloud at ???30 ??C contained short hollow columns and thick hollow plates. During the course of each experiment, the cloud properties were monitored using a Cloud Particle Imager (CPI). In addition to this, ice crystal replicas were created using formvar resin. By examining the replicas under an optical microscope, two different internal structures were identified. The internal and external facets were measured and used to create geometric particle models with realistic internal structures. Theoretical results were calculated using both Ray Tracing (RT) and Ray Tracing with Diffraction on Facets (RTDF). Experimental and theoretical results are compared to assess the impact of internal structure on P11 and g and the applicability of RT and RTDF for hollow columns

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The Asymmetry Parameter of Cirrus Clouds Composed of Hollow Bullet Rosette–Shaped Ice Crystals from Ray-Tracing Calculations

Cited by 22 publications

References 29 publications

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

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

On the Occurrence of Hollow Bullet Rosette– and Column-Shaped Ice Crystals in Midlatitude Cirrus

Cloud chamber laboratory investigations into scattering properties of hollow ice particles

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