scholarly journals Relationship between temperature and apparent shape of pristine ice crystals derived from polarimetric cloud radar observations during the ACCEPT campaign

2016 ◽  
Vol 9 (8) ◽  
pp. 3739-3754 ◽  
Author(s):  
Alexander Myagkov ◽  
Patric Seifert ◽  
Ulla Wandinger ◽  
Johannes Bühl ◽  
Ronny Engelmann
Keyword(s):  
Free Fall ◽  
Crystal Shape ◽  
Ice Crystal ◽  
Ambient Conditions ◽  
Axis Ratio ◽  
Microwave Scattering ◽  
Cloud Radar ◽  
Ice Particles ◽  
Rapid Changes ◽  
Good Agreement

Abstract. This paper presents first quantitative estimations of apparent ice particle shape at the top of liquid-topped clouds. Analyzed ice particles were formed under mixed-phase conditions in the presence of supercooled water and in the temperature range from −20 to −3 °C. The estimation is based on polarizability ratios of ice particles measured by a Ka-band cloud radar MIRA-35 with hybrid polarimetric configuration. Polarizability ratio is a function of the geometrical axis ratio and the dielectric properties of the observed hydrometeors. For this study, 22 cases observed during the ACCEPT (Analysis of the Composition of Clouds with Extended Polarization Techniques) field campaign were used. Polarizability ratios retrieved for cloud layers with the cloud-top temperatures of  ∼ −5,  ∼ −8,  ∼ −15, and  ∼ −20 °C were 1.6, 0.9, 0.6, and 0.9, respectively. Such values correspond to prolate, quasi-isotropic, oblate, and quasi-isotropic particles, respectively. Data from a free-fall chamber were used for the comparison. A good agreement of detected apparent shapes with well-known shape–temperature dependencies observed in laboratories was found. Polarizability ratios used for the analysis were estimated for areas located close to the cloud top, where aggregation and riming processes do not strongly affect ice particles. We concluded that, in microwave scattering models, ice particles detected in these areas can be assumed to have pristine shapes. It was also found that even slight variations of ambient conditions at the cloud top with temperatures warmer than  ∼ −5 °C can lead to rapid changes of ice crystal shape.

scholarly journals Shape-temperature relationships of pristine ice crystals derived from polarimetric cloud radar observations during the ACCEPT campaign

2016 ◽  
Author(s):  
A. Myagkov ◽  
P. Seifert ◽  
U. Wandinger ◽  
J. Bühl ◽  
R. Engelmann
Keyword(s):  
Free Fall ◽  
Ice Crystals ◽  
Crystal Shape ◽  
Ice Crystal ◽  
Ambient Conditions ◽  
Microwave Scattering ◽  
Cloud Radar ◽  
Ice Particles ◽  
Rapid Changes ◽  
Good Agreement

Abstract. This paper presents first quantitative estimations of ice particle shape at the top of liquid-topped clouds. Analyzed ice particles were formed in the presence of supercooled water and in the temperature range from −20 to −3 °C. The estimation is based on polarizability ratios of ice particles measured by a Ka-band cloud radar MIRA-35 with hybrid polarimetric configuration, manufactured by METEK GmbH. For this study, 22 cases observed during the ACCEPT (Analysis of the Composition of Clouds with Extended Polarization Techniques) field campaign were used. Polarizability ratios retrieved for cloud layers with the cloud top temperatures of ~−5, ~−8, ~−15, and ~−20 °C were 1.6, 0.9, 0.6, and 0.9, respectively. Such values correspond to prolate, quasi-isotropic, oblate, and quasi-isotropic particles, respectively. Data from a free-fall chamber were used for the comparison. A good agreement of detected shapes with well-known shape-temperature dependencies observed in laboratories was found. Polarizability ratios used for the analysis were estimated for areas located close to the cloud top where aggregation and riming processes do not strongly affect ice particles. We concluded, that in microwave scattering models ice particles detected in these areas can be assumed to have pristine shapes. It was also found that even slight variations of ambient conditions at the cloud top with temperatures warmer than ~−5 °C can lead to rapid changes of ice crystal shape.

scholarly journals Particle Habit Imaging Using Incoherent Light: A First Step toward a Novel Instrument for Cloud Microphysics

2011 ◽  
Vol 28 (4) ◽  
pp. 493-512 ◽  
Author(s):  
Roland Schön ◽  
Martin Schnaiter ◽  
Zbigniew Ulanowski ◽  
Carl Schmitt ◽  
Stefan Benz ◽  
...  
Keyword(s):  
Ccd Camera ◽  
Cloud Microphysics ◽  
Resolving Power ◽  
Ice Crystal ◽  
Ambient Conditions ◽  
Incoherent Light ◽  
Cloud Particle ◽  
Ice Particles ◽  
Institute Of Technology ◽  
A Charge

Abstract The imaging unit of the novel cloud particle instrument Particle Habit Imaging and Polar Scattering (PHIPS) probe has been developed to image individual ice particles produced inside a large cloud chamber. The PHIPS produces images of single airborne ice crystals, illuminated with white light of an ultrafast flashlamp, which are captured at a maximum frequency of ∼5 Hz by a charge-coupled device (CCD) camera with microscope optics. The imaging properties of the instrument were characterized by means of crystalline sodium hexafluorosilicate ice analogs, which are stable at room temperature. The optical resolving power of the system is ∼2 μm. By using dedicated algorithms for image processing and analysis, the ice crystal images can be analyzed automatically in terms of size and selected shape parameters. PHIPS has been operated at the cloud simulation chamber facility Aerosol Interaction and Dynamics in the Atmosphere (AIDA) of the Karlsruhe Institute of Technology at different temperatures between −17° and −4°C in order to study the influence of the ambient conditions, that is, temperature and ice saturation ratio, on ice crystal habits. The area-equivalent size distributions deduced from the PHIPS images are compared with the retrieval results from Fourier transform infrared (FTIR) extinction spectroscopy in case of small (<20 μm) and with single particle data from the cloud particle imager in case of larger (>20 μm) ice particles. Good agreement is found for both particle size regimes.

scholarly journals Establishment and preliminary application of forward modeling method for Doppler spectral density of ice particles

2019 ◽  
Author(s):  
Han Ding ◽  
Liping Liu
Keyword(s):  
Particle Size ◽  
Spectral Density ◽  
Cross Section ◽  
Ice Crystals ◽  
Ice Crystal ◽  
Fall Velocity ◽  
Density Data ◽  
Cloud Radar ◽  
Backscattering Cross Section ◽  
Ice Particles

Abstract. Owing to the various shapes of ice particles, the relationships between fall velocity, backscattering cross-section, mass, and particle size are complicated, which affects the application of cloud radar Doppler spectral density data to retrieve the microphysical properties of ice crystals. In this paper, under the assumption of six particle shape types, the relationships between particle mass, fall velocity, backscattering cross-section, and particle size were established based on existing research. Variations of Doppler spectral density with the same particle size distribution (PSD) of different ice particle types are discussed, and the radar-retrieved liquid and ice PSDs, water content, and mean volume-weighted particle diameter are compared with airborne in situ observations in Xingtai, Hebei Province, China, in 2018. The results showed the following: (1) for particles with the same equivalent diameter (De), the fall velocity of aggregates is the largest, followed by hexagonal columns, hexagonal plates, sector plates, and stellar crystals, with ice spheres falling two to three times faster than ice crystals with the same De. Hexagonal columns have the largest backscattering cross-section, followed by stellar crystals and sector plates, and the backscattering cross-sections of hexagonal plates and two kinds of aggregates are very close to those of ice spheres. (2) The width of the simulated radar Doppler spectral density generated by various ice crystal types with the same PSD is mainly affected by particle fall velocity and increased fall velocity rates with increased particle size, as do PSDs retrieved from the same Doppler spectral density data. (3) PSD comparisons showed that each ice crystal type retrieved from the cloud radar corresponded well to aircraft observations within a certain scale range when assuming that only a certain type of ice crystals existed in the cloud, which can fully prove the feasibility of retrieving ice PSDs from reflectivity spectral density.

scholarly journals Establishment and Preliminary Application of the Forward Modeling Method for Doppler Spectral Density of Ice Particles

2020 ◽  
Vol 12 (20) ◽  
pp. 3378
Author(s):  
Han Ding ◽  
Liping Liu
Keyword(s):  
Particle Size ◽  
Spectral Density ◽  
Cross Section ◽  
Ice Crystals ◽  
Doppler Spectrum ◽  
Ice Crystal ◽  
Fall Velocity ◽  
Cloud Radar ◽  
Backscattering Cross Section ◽  
Ice Particles

Owing to the various shapes of ice particles, the relationships between fall velocity, backscattering cross-section, mass, and particle size are complicated. This affects the application of cloud radar Doppler spectral density data in the retrieval of the microphysical properties of ice crystals. In this study, under the assumption of six particle shape types, the relationships between particle mass, fall velocity, backscattering cross-section, and particle size were established based on existing research. Variations of Doppler spectral density with the same particle size distribution (PSD) of different ice particle types are discussed. The radar-retrieved liquid and ice PSDs, water content, and mean volume-weighted particle diameter were compared with airborne in situ observations in the Xingtai, Hebei Province, China, in 2018. The results showed the following. (1) For the particles with the same equivalent diameter (De), the fall velocity of the aggregates was the largest, followed by hexagonal columns, hexagonal plates, sector plates, and stellar crystals, with the ice spheres falling two to three times faster than ice crystals with the same De. Hexagonal columns had the largest backscattering cross-section, followed by stellar crystals and sector plates, and the backscattering cross-sections of hexagonal plates and the two types of aggregates were very close to those of ice spheres. (2) The width of the simulated radar Doppler spectral density generated by various ice crystal types with the same PSD was mainly affected by the particle’s falling velocity, which increased with the particle size. Turbulence had different degrees of influence on the Doppler spectrum of different ice crystals, and it also brought large errors to the PSD retrieval. (3) PSD comparisons showed that each ice crystal type retrieved from the cloud radar corresponded well to aircraft observations within a certain scale range, when assuming that only a certain type of ice crystals existed in the cloud, which could fully prove the feasibility of retrieving ice PSDs from the reflectivity spectral density.

scholarly journals Heat Transfer in the Core Compressor Under Ice Crystal Icing Conditions

2017 ◽  
Author(s):  
Alexander Bucknell ◽  
Matthew McGilvray ◽  
David R. H. Gillespie ◽  
Geoff Jones ◽  
Alasdair Reed ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Particle Diameter ◽  
Energy Parameter ◽  
National Research Council ◽  
Heated Plate ◽  
Ice Crystal ◽  
Transfer Enhancement ◽  
The Core ◽  
Ice Particles

It has been recognised in recent years that high altitude atmospheric ice crystals pose a threat to aircraft engines. Instances of damage, surge and shutdown have been recorded at altitudes significantly greater than those associated with supercooled water icing. It is believed that solid ice particles can accrete inside the core compressor, although the exact mechanism by which this occurs remains poorly understood. Development of analytical and empirical models of the ice crystal icing phenomenon is necessary for both future engine design and this-generation engine certification. A comprehensive model will require the integration of a number of aerodynamic, thermodynamic and mechanical components. This paper studies one such component, specifically the thermodynamic and mechanical processes experienced by ice particles impinging on a warm surface. Results are presented from an experimental campaign using a heated and instrumented flat plate. The plate was installed in the Altitude Icing Wind Tunnel (AIWT) at the National Research Council of Canada (NRC). This facility is capable of replicating ice crystal conditions at altitudes up to 9 km and Mach numbers up to 0.55 [1]. The heated plate is designed to measure the heat flux from a surface at temperatures representative of the early core compressor, under varying convective and icing heat loads. Heat transfer enhancement was observed to rise approximately linearly with both total water content and particle diameter over the ranges tested. A Stokes number greater than unity proved to be a useful parameter in determining whether heat transfer enhancement would occur. A particle energy parameter was used to estimate the likelihood of fragmentation. Results showed that when particles were both ballistic and likely to fragment, heat transfer enhancement was independent of both Mach and Reynolds numbers over the ranges tested.

scholarly journals Microphysical properties and fall speed measurements of snow ice crystals using the Dual Ice Crystal Imager (D-ICI)

2020 ◽  
Vol 13 (3) ◽  
pp. 1273-1285 ◽  
Author(s):  
Thomas Kuhn ◽  
Sandra Vázquez-Martín
Keyword(s):  
Remote Sensing ◽  
Vertical Direction ◽  
Ice Crystals ◽  
Ice Crystal ◽  
Double Exposure ◽  
Shape Information ◽  
Microphysical Properties ◽  
Ice Particles ◽  
Crystal Properties ◽  
Fall Speed

Abstract. Accurate predictions of snowfall require good knowledge of the microphysical properties of the snow ice crystals and particles. Shape is an important parameter as it strongly influences the scattering properties of the ice particles, and thus their response to remote sensing techniques such as radar measurements. The fall speed of ice particles is another important parameter for both numerical forecast models as well as representation of ice clouds and snow in climate models, as it is responsible for the rate of removal of ice from these models. We describe a new ground-based in situ instrument, the Dual Ice Crystal Imager (D-ICI), to determine snow ice crystal properties and fall speed simultaneously. The instrument takes two high-resolution pictures of the same falling ice particle from two different viewing directions. Both cameras use a microscope-like setup resulting in an image pixel resolution of approximately 4 µm pixel−1. One viewing direction is horizontal and is used to determine fall speed by means of a double exposure. For this purpose, two bright flashes of a light-emitting diode behind the camera illuminate the falling ice particle and create this double exposure, and the vertical displacement of the particle provides its fall speed. The other viewing direction is close-to-vertical and is used to provide size and shape information from single-exposure images. This viewing geometry is chosen instead of a horizontal one because shape and size of ice particles as viewed in the vertical direction are more relevant than these properties viewed horizontally, as the vertical fall speed is more strongly influenced by the vertically viewed properties. In addition, a comparison with remote sensing instruments that mostly have a vertical or close-to-vertical viewing geometry is favoured when the particle properties are measured in the same direction. The instrument has been tested in Kiruna, northern Sweden (67.8∘ N, 20.4∘ E). Measurements are demonstrated with images from different snow events, and the determined snow ice crystal properties are presented.

Particle motions in sheared suspensions XIII. The spin and rotation of disks

1962 ◽  
Vol 12 (1) ◽  
pp. 88-96 ◽  
Author(s):  
H. L. Goldsmith ◽  
S. G. Mason
Keyword(s):  
Couette Flow ◽  
Angular Rotation ◽  
Axis Ratio ◽  
Dissipation Of Energy ◽  
Sheared Suspensions ◽  
Good Agreement

The motions of single disks suspended in a liquid undergoing Couette flow have been studied in detail. The angular rotation and the axial spin of the disks were found to be in good agreement with the theory of Jeffery, provided the equivalent axis ratio re was used instead of the measured axis ratio r. It was found that non-interacting disks move in constant orbits without a tendency to drift into orbits corresponding to a minimum dissipation of energy. Discontinuous changes in orbit were observed to occur following two-body collisions.

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