Scattering Phase Function of Bullet Rosette Ice Crystals

Iaquinta, Jean; Isaka, Harumi; Personne, Pascal

doi:10.1175/1520-0469(1995)052<1401:spfobr>2.0.co;2

Cited by 72 publications

(51 citation statements)

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“…Hypothesis (2) says that a signi®cant amount of smaller particles have an appreciable in¯uence on the radiative characteristics of ice clouds by enlarging the number of backscattered photons and herewith increasing cloud albedo. Model calculations (Macke, 1993;Iaquinta et al, 1995;Strauss, 1996) make hypothesis (1) appear unlikely, whereas recent in situ measurements as presented in the previous section support hypothesis (2). Therefore, the ice cloud parameterization used in the RCM was modi®ed by assuming hexagonally shaped ice particles in the solar spectral range, and cirrus particle size distributions in the small-particle regime as based on our measurements (see Sect.…”

Section: Measurements Of Microphysical Properties In Cirrus Clouds Anmentioning

confidence: 78%

On the regional climatic impact of contrails: microphysical and radiative properties of contrails and natural cirrus clouds

et al. 1997

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Abstract. The impact of contrail-induced cirrus clouds on regional climate is estimated for mean atmospheric conditions of southern Germany in the months of July and October. This is done by use of a regionalized onedimensional radiative convective model (RCM). The in¯uence of an increased ice cloud cover is studied by comparing RCM results representing climatological values with a modi®ed case. In order to study the sensitivity of this eect on the radiative characteristics of the ice cloud, two types of additional ice clouds were modelled: cirrus and contrails, the latter cloud type containing a higher number of smaller and less of the larger cloud particles. Ice cloud parameters are calculated on the basis of a particle size distribution which covers the range from 2 to 2000 lm, taking into consideration recent measurements which show a remarkable amount of particles smaller than 20 lm. It turns out that a 10% increase in ice cloud cover leads to a surface temperature increase in the order of 1 K, ranging from 1.1 to 1X2 K in July and from 0.8 to 0X9 K in October depending on the radiative characteristics of the air-trac-induced ice clouds. Modelling the current contrail cloud cover which is near 0.5% over Europe yields a surface temperature increase in the order of 0X05 K.

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Section: Measurements Of Microphysical Properties In Cirrus Clouds Anmentioning

confidence: 78%

On the regional climatic impact of contrails: microphysical and radiative properties of contrails and natural cirrus clouds

et al. 1997

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“…Ice crystals resembling bullet rosettes are often observed in mid-latitude cirrus and aged anvil cirrus clouds (Iaquinta et al, 1995;Lawson et al, 2006;Um and McFarquhar, 2007;Baran, 2009;Baum et al, 2011). Optical properties of bullet rosettes are calculated using the same GO code described above .…”

Section: Bullet Rosettesmentioning

confidence: 99%

Remote sensing of ice crystal asymmetry parameter using multi-directional polarization measurements – Part 1: Methodology and evaluation with simulated measurements

et al. 2012

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Abstract. We present a new remote sensing technique to infer the average asymmetry parameter of ice crystals near cloud top from multi-directional polarization measurements. The method is based on previous findings that (a) complex aggregates of hexagonal crystals generally have scattering phase matrices resembling those of their components; and (b) scattering phase matrices systematically vary with aspect ratios of crystals and their degree of microscale surface roughness. Ice cloud asymmetry parameters are inferred from multi-directional polarized reflectance measurements by searching for the closest fit in a look-up table of simulated polarized reflectances computed for cloud layers that contain individual, randomly oriented hexagonal columns and plates with varying aspect ratios and roughness values. The asymmetry parameter of the hexagonal particle that leads to the best fit with the measurements is considered the retrieved value. For clouds with optical thickness less than 5, the cloud optical thickness must be retrieved simultaneously with the asymmetry parameter, while for optically thicker clouds the asymmetry parameter retrieval is independent of cloud optical thickness. Evaluation of the technique using simulated measurements based on the optical properties of a number of complex particles and their mixtures shows that the ice crystal asymmetry parameters are generally retrieved to within 5 %, or about 0.04 in absolute terms. The retrieval scheme is largely independent of calibration errors, range and sampling density of scattering angles and random noise in the measurements. The approach can be applied to measurements of past, current and future airborne and satellite instruments that measure multi-directional polarized reflectances of ice-topped clouds.

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“…Such models have been developed based on images of ice crystals obtained by probes installed on aircraft flying through clouds. In addition to the calculation of single-scattering properties of pristine ice crystal shapes such as hexagonal columns and plates (e.g., Takano and Liou, 1989;Macke et al, 1996) and bullet rosettes (e.g., Iaquinta et al, 1995), recent studies have extended the calculations to more complex shapes such as aggregates of columns (Yang and Liou, 1998;Baran and Labonnote, 2007), bullet rosettes and plates (Um and McFarquhar, 2009) and to longer wavelengths (Baran, 2005;Yang et al, 2005). Although some earlier studies used images from optical array probes, which have 15 to 25 µm resolution, to develop the idealized models, more recent studies have used higher resolution (2.3 µm) images from a Cloud Particle Imager (CPI).…”

Section: Introductionmentioning

confidence: 99%

Dependence of the single-scattering properties of small ice crystals on idealized shape models

McFarquhar

2011

Atmos. Chem. Phys.

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Abstract. The projections of small ice crystals (with maximum dimension <50 µm) appear quasi-circular when imaged by probes on aircraft flying through cloud. Therefore, idealized models constructed to calculate their singlescattering properties have included quasi-spherical models such as Chebyshev particles, Gaussian random spheres, and droxtals. Recently, an ice analogue grown from sodium fluorosilicate solution on a glass substrate, with several columns emanating from a common center of mass, was shown to be quasi-circular when imaged by state-of-the-art cloud probes. In this study, a new idealized model, called the budding Bucky ball (3B) that resembles the shape of the small ice analogue is developed. The corresponding single-scattering properties (scattering phase function P 11 and asymmetry parameter g) are computed by a ray-tracing code. Compared with previously used models, 3B scatters less light in the forward and more light in the lateral and backward directions. The Chebyshev particles and Gaussian random spheres show smooth and featureless P 11 , whereas droxtals and 3Bs, which have a faceted structure, show several peaks in P 11 associated with angles of minimum deviation. Overall, the difference in the forward (lateral; backward) scattering between models are up to 22% (994%; 132%), 20% (510%; 101%), and 16% (146%; 156%) for small ice crystals with respective area ratios of 0.85, 0.77, and 0.69. The g for different models varies by up to 25%, 23%, and 19% for particles with area ratios of 0.85, 0.77, and 0.69, respectively. Because the single-scattering properties of small ice crystals depend both on the choice of the idealized model and the area ratios used to characterize the small ice crystals, higher resolution observations of small ice crystals or direct observations of their single-scattering properties are required.

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Scattering Phase Function of Bullet Rosette Ice Crystals

Cited by 72 publications

References 0 publications

On the regional climatic impact of contrails: microphysical and radiative properties of contrails and natural cirrus clouds

On the regional climatic impact of contrails: microphysical and radiative properties of contrails and natural cirrus clouds

Remote sensing of ice crystal asymmetry parameter using multi-directional polarization measurements – Part 1: Methodology and evaluation with simulated measurements

Dependence of the single-scattering properties of small ice crystals on idealized shape models

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