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

Schmitt, Carl; Heymsfield, Andrew J.

doi:10.1175/2007jas2317.1

Cited by 30 publications

(26 citation statements)

References 20 publications

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“…Compact aggregates and spatial bullet rosettes are also seen and tend to be more common in the midlatitudes (Um and McFarquhar, 2007). Some of the particles observed by the CPI probe appear to have hollow structures, a feature noted by Magono and Lee (1966), Schmitt and Heymsfield (2007), Baran (2012), and Yang et al (2008c, specifically, the photograph by Steven Warren shown in Fig. 1 of this reference).…”

Section: Introductionmentioning

confidence: 73%

Ice particle habit and surface roughness derived from PARASOL polarization measurements

et al. 2014

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Abstract. Ice clouds are an important element in the radiative balance of the earth's climate system, but their microphysical and optical properties still are not well constrained, especially ice particle habit and the degree of particle surface roughness. In situ observations have revealed common ice particle habits and evidence for surface roughness, but these observations are limited. An alternative is to infer the ice particle shape and surface roughness from satellite observations of polarized reflectivity since they are sensitive to both particle shape and degree of surface roughness. In this study an adding-doubling radiative transfer code is used to simulate polarized reflectivity for nine different ice habits and one habit mixture, along with 17 distinct levels of the surface roughness. A lookup table (LUT) is constructed from the simulation results and used to infer shape and surface roughness from PARASOL satellite polarized reflectivity data over the ocean. Globally, the retrievals yield a compact aggregate of columns as the most commonly retrieved ice habit. Analysis of PARASOL data from the tropics results in slightly more aggregates than in midlatitude or polar regions. Some level of surface roughness is inferred in nearly 70 % of PARASOL data, with mean and median roughness near σ = 0.2 and 0.15, respectively. Tropical region analyses have 20 % more pixels retrieved with particle surface roughness than in midlatitude or polar regions. The global asymmetry parameter inferred at a wavelength of 0.865 µm has a mean value of 0.77 and a median value of 0.75.

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Section: Introductionmentioning

confidence: 73%

Ice particle habit and surface roughness derived from PARASOL polarization measurements

et al. 2014

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“…The featureless phase functions are known to be related to crystals with mesoscopic surface roughness, aggregates and particles with inclusions. Consequently, surface roughness and internal structure have gained recognition as important factors in the scattering properties of ice crystals [42][43][44][45][46][47]. These small scale features cannot be accurately determined from cloud probe images and consequently may be overlooked in particle models.…”

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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“…Recent laboratory data reveal that most ice particles at low temperatures (2408 to 2708C) have columnar shapes (with variable aspect ratio length/diameter) and that the very small crystals growing at low ice supersaturation are compact faceted polycrystals (Bailey and Hallett 2009). Often ice particles are hollow (Weickmann 1945;Schmitt and Heymsfield 2007). Ice particles may result from homogeneous freezing of initially liquid (water or solution) droplets, which then grow by deposition of water vapor.…”

Section: Introductionmentioning

confidence: 99%

Effective Radius of Ice Particles in Cirrus and Contrails

Schumann

Mayer

Gierens

et al. 2011

Journal of the Atmospheric Sciences

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This paper discusses the ratio C between the volume mean radius and the effective radius of ice particles in cirrus and contrails. The volume mean radius is proportional to the third root of the ratio between ice water content and number of ice particles, and the effective radius measures the ratio between ice particle volume and projected cross-sectional area. For given ice water content and number concentration of ice particles, the optical depth scales linearly with C. Hence, C is an important input parameter for radiative forcing estimates. The ratio C in general depends strongly on the particle size distribution (PSD) and on the particle habits. For constant habits, C can be factored into a PSD and a habit factor. The PSD factor is generally less than one, while the habit factor is larger than one for convex or concave ice particles with random orientation. The value of C may get very small for power-law PSDs with exponent n between 24 and 0, which is often observed. For such PSDs, most of the particle volume is controlled by a few large particles, while most of the cross-sectional area is controlled by the many small particles. A new particle habit mix for contrail cirrus including small droxtal-shape particles is suggested. For measured cirrus and contrails, the dependence of C on volume mean particle radius, ambient humidity, and contrail age is determined. For cirrus, C varies typically between 0.4 and 1.1. In contrails, C 5 0.7 6 0.3, with uncertainty ranges increasing with the volume radius and contrail age. For the small particles in young contrails, the extinction efficiency in the solar range deviates considerably from the geometric optics limit.

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

Cited by 30 publications

References 20 publications

Ice particle habit and surface roughness derived from PARASOL polarization measurements

Ice particle habit and surface roughness derived from PARASOL polarization measurements

Cloud chamber laboratory investigations into scattering properties of hollow ice particles

Effective Radius of Ice Particles in Cirrus and Contrails

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