scholarly journals Cirrus optical thickness and crystal size retrieval from ATSR-2 data using phase functions of imperfect hexagonal ice crystals

1999 ◽  
Vol 104 (D24) ◽  
pp. 31721-31730 ◽  
Author(s):  
Wouter H. Knap ◽  
Michael Hess ◽  
Piet Stammes ◽  
Robert B. A. Koelemeijer ◽  
Phil D. Watts
Keyword(s):  
Optical Thickness ◽  
Crystal Size ◽  
Ice Crystals ◽  
Hexagonal Ice ◽  
Phase Functions

Interpretation of ATSR-2 measurements of cirrus clouds using phase functions of imperfect hexagonal ice crystals

1998 ◽  
Author(s):  
Wouter H. Knap ◽  
M. Hess ◽  
Piet Stammes ◽  
Robert B. A. Koelemeijer ◽  
Philip D. Watts
Keyword(s):  
Cirrus Clouds ◽  
Ice Crystals ◽  
Hexagonal Ice ◽  
Phase Functions

Scattering phase functions of horizontally oriented hexagonal ice crystals

2006 ◽  
Vol 100 (1-3) ◽  
pp. 91-102 ◽  
Author(s):  
Guang Chen ◽  
Ping Yang ◽  
George W. Kattawar ◽  
Michael I. Mishchenko
Keyword(s):  
Ice Crystals ◽  
Hexagonal Ice ◽  
Scattering Phase ◽  
Phase Functions

Considerations for Modeling Thin Cirrus Effects via Brightness Temperature Differences

1995 ◽  
Vol 34 (2) ◽  
pp. 447-459 ◽  
Author(s):  
E. O. Schmidt ◽  
R. F. Arduini ◽  
B. A. Wielicki ◽  
R. S. Stone ◽  
S-C. Tsay
Keyword(s):  
Brightness Temperature ◽  
Surface Area ◽  
Careful Consideration ◽  
Ice Crystals ◽  
Ice Crystal ◽  
Polynomial Coefficients ◽  
Hexagonal Ice ◽  
Scattering Phase ◽  
Phase Functions ◽  
Very High

Abstract Brightness temperature difference (BTD) values are calculated for selected Geostationary Operational Environmental Satellite (GOES-6) channels (3.9, 12.7 µm) and Advanced Very High Resolution Radiometer channels (3.7, 12.0 µm). Daytime and nighttime discrimination of particle size information is possible given the infrared cloud extinction optical depth and the BTD value. BTD values are presented and compared for cirrus clouds composed of equivalent ice spheres (volume, surface area) versus randomly oriented hexagonal ice crystals. The effect of the hexagonal ice crystals is to increase the magnitude of the BTD values calculated relative to equivalent ice sphere (volume, surface area) BTDs. Equivalent spheres (volume or surface area) do not do a very good job of modeling hexagonal ice crystal effects on BTDs; however, the use of composite spheres improves the simulation and offers interesting prospects. Careful consideration of the number of Legendre polynomial coefficients used to fit the scattering phase functions is crucial to realistic modeling of cirrus BTDs. Surface and view-angle effects are incorporated to provide more realistic simulation.

scholarly journals On the scattering behaviour of bullet-rosette and bullet-shaped ice crystals

1996 ◽  
Vol 14 (5) ◽  
pp. 566-573
Author(s):  
B. Strauss
Keyword(s):  
Ray Tracing ◽  
Ice Crystals ◽  
Asymmetry Factor ◽  
Model Calculations ◽  
Geometrical Features ◽  
The Asymmetry ◽  
Particle Length ◽  
Phase Functions ◽  
Tracing Method ◽  
Factor G

Abstract. The scattering behaviour of bullet-rosette and bullet-shaped ice particles is investigated using model calculations (ray tracing method) with special emphasis on the asymmetry factor g. Because the variability of the geometrical features of these particles is very large, some representative shapes are used in the calculations. The model is based on geometrical optics, and particles are assumed to be oriented randomly; a wavelength of 0.56 μm is considered; absorption is neglected. The scattering behaviour of bullet rosettes is compared to that of single branches out of the bullet rosette. It turns out that there are slight differences in the asymmetry factor values, depending on the lengths of the branches (∆g~0.02) and on the angles between the branches (∆g~0.01). Bullets show some special features in their phase functions due to the pyramid. The length of the particle influences the asymmetry factor (∆g~0.10), as does the shape of the pyramid (∆g~0.07). The influence of the pyramidal shape decreases with increasing particle length. Bullets were compared to hexagonally shaped columns. This was done for two columns, one as long as the columnar part of the bullet (length without pyramid), and one for a column as long as the bullet including the pyramid. Asymmetry factor values of bullets with a pyramidal angle of 28° deviate less than ∆g~0.01 from the range given by the two values of the columns.

scholarly journals Characterization of Arctic mixed-phase cloud properties at small scale and coupling with satellite remote sensing

2017 ◽  
Author(s):  
Guillaume Mioche ◽  
Olivier Jourdan ◽  
Julien Delanoë ◽  
Christophe Gourbeyre ◽  
Guy Febvre ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Crystal Size ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Small Scale ◽  
Vertical Profiles ◽  
Liquid Droplets ◽  
Ice Crystal ◽  
High Concentration ◽  
Ice Crystal Size

Abstract. This study aims to characterize the microphysical and optical properties of ice crystals and supercooled liquid droplets within low-level Arctic mixed-phase clouds (MPC). We compiled and analyzed cloud in situ measurements from 4 airborne campaigns (18 flights, 71 vertical profiles in MPC) over the Greenland Sea and the Svalbard region. Cloud phase discrimination and representative vertical profiles of number, size, mass and shapes of ice crystals and liquid droplets are assessed. The results show that the liquid phase dominates the upper part of the MPC with high concentration of small droplets (120 cm−3, 15&tinsp;μm), and averaged LWC around 0.2 g m−3. The ice phase is found everywhere within the MPC layers, but dominates the properties in the lower part of the cloud and below where ice crystals precipitate down to the surface. The analysis of the ice crystal morphology highlights that irregulars and rimed are the main particle habit followed by stellars and plates. We hypothesize that riming and condensational growth processes (including the Wegener-Bergeron-Findeisein mechanism) are the main growth mechanisms involved in MPC. The differences observed in the vertical profiles of MPC properties from one campaign to another highlight that large values of LWC and high concentration of smaller droplets are possibly linked to polluted situations which lead to very low values of ice crystal size and IWC. On the contrary, clean situations with low temperatures exhibit larger values of ice crystal size and IWC. Several parameterizations relevant for remote sensing or modeling are also determined, such as IWC (and LWC) – extinction relationship, ice and liquid integrated water paths, ice concentration and liquid water fraction according to temperature. Finally, 4 flights collocated with active remote sensing observations from CALIPSO and CloudSat satellites are specifically analyzed to evaluate the cloud detection and cloud thermodynamical phase DARDAR retrievals. This comparison is valuable to assess the sub-pixel variability of the satellite measurements as well as their shortcomings/performance near the ground.

Backscattering by hexagonal ice crystals

1999 ◽  
Author(s):  
Edward I. Naats ◽  
Anatoli G. Borovoi ◽  
Ulrich G. Oppel
Keyword(s):  
Ice Crystals ◽  
Hexagonal Ice

scholarly journals Crystal growth rates in polar firn

1993 ◽  
Vol 18 ◽  
pp. 208-210
Author(s):  
Hitoshi Shoji ◽  
Atau Mitani ◽  
Kohji Horita ◽  
Chester C. Langway
Keyword(s):  
Growth Rate ◽  
Plastic Deformation ◽  
Crystal Growth ◽  
Growth Rates ◽  
Strain Field ◽  
Crystal Size ◽  
Ice Core ◽  
Transformation Process ◽  
Ice Crystals ◽  
Air Bubbles

Continuous crystal-size measurements made on the G6 Antarctic ice core (100m deep) show enhanced growth rates above a depth of 30 m (Zone 1) and in the interval between 70 and 80 m (Zone 2). Crystal growth in Zone 1 most probably takes place by a process of sublimation and condensation. The higher growth rate in Zone 2 is most probably related to the pore close-off transformation process in which a non-uniform strain field is created to form air bubbles by plastic deformation and “cannibalization” of individual ice crystals.

Morphological Instability of Polyhedral Ice Crystals Growing in Air at Low Temperature

1985 ◽  
Vol 6 ◽  
pp. 222-224 ◽  
Author(s):  
T. Gonda ◽  
H. Gomi
Keyword(s):  
Low Temperature ◽  
Growth Rates ◽  
Crystal Size ◽  
Air Pressure ◽  
Experimental Results ◽  
Ice Crystals ◽  
Polar Regions ◽  
Morphological Instability ◽  
Skeletal Structures ◽  
Snow Crystals

The morphology of snow crystals growing at a low temperature has been experimentally studied. The habit and the morphological instability of the crystals vary remarkably with air pressure. In addition, the morphological instability of the crystals depends not only on air pressure but also on supersaturation, crystal size, the ratio of growth rates and the ratio of axial lengths. It is supposed from the experimental results that long prisms with small skeletal structures forming at low supersaturation are precipitating in polar regions.

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