scholarly journals Shattering during Sampling by OAPs and HVPS. Part I: Snow Particles

2005 ◽  
Vol 22 (5) ◽  
pp. 528-542 ◽  
Author(s):  
Alexei Korolev ◽  
George A. Isaac
Keyword(s):  
Remote Sensing ◽  
Wind Shear ◽  
High Volume ◽  
Sample Volume ◽  
Particle Sizes ◽  
Small Particles ◽  
Cloud Particle ◽  
Ice Particles ◽  
Imaging Probes ◽  
Cloud Parameterization

Abstract The data on cloud particle sizes and concentrations collected with the help of aircraft imaging probes [optical array probes OAP-2DC, OAP-2DP, and the High Volume Precipitation Spectrometer (HVPS)] are widely used for cloud parameterization and validation of remote sensing. The goal of the present work is to study the effect of shattering of ice particles during sampling. The shattering of ice particles may occur due to 1) mechanical impact with the probe arms prior to their entering the sample volume, and 2) fragmentation due to interaction with turbulence and wind shear generated by the probe housing. The effect of shattering is characterized by the shattering efficiency that is equal to the ratio of counts of disintegrated particles, to all counts. The shattering efficiency depends on the habit, size, and density of ice particles, probe inlet design, and airspeed. For the case of aggregates, the shattering efficiency may reach 10% or even more. The shattering of ice particles results in an overcounting of small particles and an undercounting of large ones. The number of fragments in the images of shattered particles may reach several hundreds. It was found that particles as small as 600 μm may shatter after impact with the probe arms. The effect of particle shattering should be taken into account during data analysis and carefully considered in future designs of airborne cloud particle size spectrometers.

scholarly journals Characterising optical array particle imaging probes: implications for small-ice-crystal observations

2021 ◽  
Vol 14 (3) ◽  
pp. 1917-1939
Author(s):  
Sebastian O'Shea ◽  
Jonathan Crosier ◽  
James Dorsey ◽  
Louis Gallagher ◽  
Waldemar Schledewitz ◽  
...  
Keyword(s):  
Field Experiments ◽  
Field Measurements ◽  
Sample Volume ◽  
Ice Crystal ◽  
Cloud Particle ◽  
Ice Clouds ◽  
Cloud Properties ◽  
Imaging Probes ◽  
New Methodologies ◽  
Particle Imaging

Abstract. The cloud particle concentration, size, and shape data from optical array probes (OAPs) are routinely used to parameterise cloud properties and constrain remote sensing retrievals. This paper characterises the optical response of OAPs using a combination of modelling, laboratory, and field experiments. Significant uncertainties are found to exist with such probes for ice crystal measurements. We describe and test two independent methods to constrain a probe's sample volume that remove the most severely mis-sized particles: (1) greyscale image analysis and (2) co-location using stereoscopic imaging. These methods are tested using field measurements from three research flights in cirrus. For these cases, the new methodologies significantly improve agreement with a holographic imaging probe compared to conventional data-processing protocols, either removing or significantly reducing the concentration of small ice crystals (< 200 µm) in certain conditions. This work suggests that the observational evidence for a ubiquitous mode of small ice particles in ice clouds is likely due to a systematic instrument bias. Size distribution parameterisations based on OAP measurements need to be revisited using these improved methodologies.

Ground-Based Remote Sensing of Cloud Particle Sizes during the 26 November 1991 FIRE II Cirrus Case: Comparisons with In Situ Data

1995 ◽  
Vol 52 (23) ◽  
pp. 4128-4142 ◽  
Author(s):  
S. Y. Matrosov ◽  
A. J. Heymsfield ◽  
J. M. Intrieri ◽  
B. W. Orr ◽  
J. B. Snider
Keyword(s):  
Remote Sensing ◽  
Particle Sizes ◽  
Cloud Particle ◽  
In Situ Data

scholarly journals Laboratory and Flight Tests of 2D Imaging Probes: Toward a Better Understanding of Instrument Performance and the Impact on Archived Data

2018 ◽  
Vol 35 (7) ◽  
pp. 1533-1553 ◽  
Author(s):  
Colin Gurganus ◽  
Paul Lawson
Keyword(s):  
Laboratory Tests ◽  
Sample Volume ◽  
Cloud Particle ◽  
Flight Tests ◽  
Data Archives ◽  
Imaging Probes ◽  
Research Aircraft ◽  
Water Drops ◽  
2D Imaging ◽  
Archived Data

AbstractTwo-dimensional (2D) imaging probes, such as the 2D stereo (2D-S) probe and the cloud imaging probe (CIP), are routinely used to provide in situ measurements of cloud particle properties. The basic measurement is shadowgraphs of water drops and ice particles from which particle size distributions, projected particle area, and mass concentrations are determined. These data permeate data archives of domestic and foreign government agencies, universities, and the private sector. This paper provides results from laboratory tests and flight tests on a Learjet research aircraft that give new insights into the performance of the 2D imaging probes, and how their performance may have impacted measurements collected in data archives. The laboratory tests are conducted with the aid of two devices: 1) a droplet generator that provides known concentrations of water drops from 15 to 65 µm ± 1 µm that can be positioned in the probe’s sample volume with 10-µm precision; and 2) a motorized spinning platform that supports transparent disks with small opaque features (i.e., a “spinning disk”), which replicates the effect of particles transecting the probe’s sample volume at translational speeds up to 190 m s−1. The flight tests were conducted with a Learjet research aircraft that collected cloud particle data at true airspeeds from 99 to 170 m s−1. The results provide new insights into how probe optics, time response, and data throughput of the 2D-S and CIP electro-optics impact the measurements of cloud particles. The results, summarized in the conclusions, suggest how archived data are impacted.

scholarly journals Characterising optical array particle imaging probes: implications for small ice crystal observations

2020 ◽  
Author(s):  
Sebastian O'Shea ◽  
Jonathan Crosier ◽  
James Dorsey ◽  
Louis Gallagher ◽  
Waldemar Schledewitz ◽  
...  
Keyword(s):  
Field Experiments ◽  
Field Measurements ◽  
Sample Volume ◽  
Ice Crystal ◽  
Cloud Particle ◽  
Cloud Properties ◽  
Imaging Probes ◽  
New Methodologies ◽  
Particle Imaging ◽  
Shape Data

Abstract. The cloud particle concentration, size and shape data from optical array probes (OAPs) are routinely used to parameterise cloud properties and constrain remote sensing retrievals. This paper characterises the optical response of OAPs using a combination of modelling, laboratory and field experiments. Significant uncertainties are found to exist with such probes for ice crystal measurements. We describe and test two independent methods to constrain a probe's sample volume that removes the most severely mis-sized particles: (1) greyscale image analysis and (2) co-location using stereoscopic imaging. These methods are tested using field measurements from three research flights in cirrus. For these cases, the new methodologies significantly improve agreement with a holographic imaging probe compared to conventional data processing protocols, either removing or significantly reducing the concentration of small ice crystals (

The Ability of the Small Ice Detector (SID-2) to Characterize Cloud Particle and Aerosol Morphologies Obtained during Flights of the FAAM BAe-146 Research Aircraft

2010 ◽  
Vol 27 (2) ◽  
pp. 290-303 ◽  
Author(s):  
Richard Cotton ◽  
S. Osborne ◽  
Z. Ulanowski ◽  
E. Hirst ◽  
P. H. Kaye ◽  
...  
Keyword(s):  
Particle Shape ◽  
Scattering Data ◽  
Atmospheric Conditions ◽  
Cloud Particle ◽  
Laser Scattering ◽  
In Situ Data ◽  
Ice Particles ◽  
Wide Range ◽  
Imaging Probes ◽  
Water Drops

Abstract The Small Ice Detector mark 2 (SID-2), which was built by the University of Hertfordshire, has been operated by the Met Office on the Facility for Atmospheric Airborne Research (FAAM) BAe-146 aircraft during a large number of flights. The flights covered a wide range of atmospheric conditions, including stratocumulus, altocumulus lenticularis, cirrus, and mixed-phase cumulus clouds, as well as clear-sky flights over the sea and over desert surfaces. SID-2 is a laser scattering device that provides in situ data on cloud particle concentration and size. SID-2 also provides the spatial light scattering data from individual particles to give some information on the particle shape. The advantage of SID-2 is that it can characterize the cloud particle shape for particle sizes less than the resolutions of the more usual commercially available ice crystal imaging probes. The particle shape characteristics enable, for example, small just-nucleated ice particles to be discriminated from supercooled water drops. SID-2 also has an open-path inlet that reduces shattering of large cloud particles compared to other probes that use a tube inlet. The aim of this paper is to illustrate the capability of SID-2 to count, size, and determine cloud particle and aerosol shape. This is done by comparing the response of SID-2 to water drops, ice particles, and aerosols with that from other standard aircraft-based probes.

Particle regularity on thylakoid fracture faces is influenced by storage conditions

1995 ◽  
Vol 73 (10) ◽  
pp. 1676-1682 ◽  
Author(s):  
Galina A. Semenova
Keyword(s):  
Particle Density ◽  
Freeze Fracture ◽  
Storage Conditions ◽  
Medium Composition ◽  
Prolonged Storage ◽  
Particle Sizes ◽  
Fracture Face ◽  
Small Particles ◽  
Mean Size ◽  
Regular Arrays

Specific temperature, storage times, and medium composition enable initiation of regular arrays of intramembranous particles on the exoplasmic fracture face during prolonged storage of isolated chloroplasts at 4 °C, producing about 2 – 10 regular arrays with 2 – 30 particles in each array, with a period of about 36 nm, oriented in 1 – 4 directions. The particle sizes do not change throughout the time of storage (1 – 4 weeks). The second type of particle regularity arises during prolonged storage of chloroplasts in greater than 1 M sucrose at −18 °C. Rounded areas of small particles tightly packed into paracrystalline arrays are found among less densely packed particles. The density of small particles is 4700 particles/μm2, and the mean size is 11 nm, whereas the particle density of the background is 1600 particles/μm2 with a mean particle size of 13 nm compared with 1200 particles/μm2 and mean size 16 nm in fresh chloroplasts. Based on the reduction of particle sizes and manner of packing on the fracture face, it is proposed that the small particles are a light-harvesting complex, separate from photosystem II and aggregated into paracrystalline arrays. The thylakoid lipids may participate in formation of particle regularity. Key words: thylakoid membrane, freeze fracture, particle regularity, low temperatures.

scholarly journals Modeling the dynamical sinking of biogenic particles in oceanic flow

2017 ◽  
Vol 24 (2) ◽  
pp. 293-305 ◽  
Author(s):  
Pedro Monroy ◽  
Emilio Hernández-García ◽  
Vincent Rossi ◽  
Cristóbal López
Keyword(s):  
Three Dimensional ◽  
Finite Size ◽  
Equation Of Motion ◽  
Particle Dynamics ◽  
Particle Sizes ◽  
Small Particles ◽  
Physical Processes ◽  
Mesoscale Simulation ◽  
Sinking Particles ◽  
Theoretical Results

Abstract. We study the problem of sinking particles in a realistic oceanic flow, with major energetic structures in the mesoscale, focussing on the range of particle sizes and densities appropriate for marine biogenic particles. Our aim is to evaluate the relevance of theoretical results of finite size particle dynamics in their applications in the oceanographic context. By using a simplified equation of motion of small particles in a mesoscale simulation of the oceanic velocity field, we estimate the influence of physical processes such as the Coriolis force and the inertia of the particles, and we conclude that they represent negligible corrections to the most important terms, which are passive motion with the velocity of the flow, and a constant added vertical velocity due to gravity. Even if within this approximation three-dimensional clustering of particles can not occur, two-dimensional cuts or projections of the evolving three-dimensional density can display inhomogeneities similar to the ones observed in sinking ocean particles.

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.

scholarly journals Intercomparison study and optical asphericity measurements of small ice particles in the CERN CLOUD experiment

2017 ◽  
Vol 10 (9) ◽  
pp. 3231-3248 ◽  
Author(s):  
Leonid Nichman ◽  
Emma Järvinen ◽  
James Dorsey ◽  
Paul Connolly ◽  
Jonathan Duplissy ◽  
...  
Keyword(s):  
Light Scattering ◽  
Single Particle ◽  
Optical Measurements ◽  
Optical Observations ◽  
Atmospheric Measurements ◽  
Optical Probes ◽  
Cloud Particle ◽  
Ice Particles ◽  
Cloud Particles ◽  
Ice Fraction

Abstract. Optical probes are frequently used for the detection of microphysical cloud particle properties such as liquid and ice phase, size and morphology. These properties can eventually influence the angular light scattering properties of cirrus clouds as well as the growth and accretion mechanisms of single cloud particles. In this study we compare four commonly used optical probes to examine their response to small cloud particles of different phase and asphericity. Cloud simulation experiments were conducted at the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at European Organisation for Nuclear Research (CERN). The chamber was operated in a series of multi-step adiabatic expansions to produce growth and sublimation of ice particles at super- and subsaturated ice conditions and for initial temperatures of −30, −40 and −50 °C. The experiments were performed for ice cloud formation via homogeneous ice nucleation. We report the optical observations of small ice particles in deep convection and in situ cirrus simulations. Ice crystal asphericity deduced from measurements of spatially resolved single particle light scattering patterns by the Particle Phase Discriminator mark 2 (PPD-2K, Karlsruhe edition) were compared with Cloud and Aerosol Spectrometer with Polarisation (CASPOL) measurements and image roundness captured by the 3View Cloud Particle Imager (3V-CPI). Averaged path light scattering properties of the simulated ice clouds were measured using the Scattering Intensity Measurements for the Optical detectioN of icE (SIMONE) and single particle scattering properties were measured by the CASPOL. We show the ambiguity of several optical measurements in ice fraction determination of homogeneously frozen ice in the case where sublimating quasi-spherical ice particles are present. Moreover, most of the instruments have difficulties of producing reliable ice fraction if small aspherical ice particles are present, and all of the instruments cannot separate perfectly spherical ice particles from supercooled droplets. Correlation analysis of bulk averaged path depolarisation measurements and single particle measurements of these clouds showed higher R2 values at high concentrations and small diameters, but these results require further confirmation. We find that none of these instruments were able to determine unambiguously the phase of the small particles. These results have implications for the interpretation of atmospheric measurements and parametrisations for modelling, particularly for low particle number concentration clouds.

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