A General Method for Estimating Bulk 2D Projections of Ice Particle Shape: Theory and Applications

Dunnavan, Edwin L.; Jiang, Zhiyuan

doi:10.1175/JAS-D-18-0177.1

Title: A General Method for Estimating Bulk 2D Projections of Ice Particle Shape: Theory and Applications

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Abstract

The orientation of falling ice particles directly influences estimates of microphysical and radiative bulk quantities as well as in situ retrievals of size, shape, and mass. However, retrieval efforts and bulk calculations often incorporate very basic orientations or ignore these effects altogether. To address this deficiency, this study develops a general method for projecting bulk distributions of particle shape for arbitrary orientations. The Amoroso distribution provides the most general bulk aspect ratio distribution for gamma-distributed particle axis lengths. The parameters that govern the behavior of this aspect ratio distribution depend on the assumed relationship between mass, maximum dimension, and aspect ratio. Individual spheroidal geometry allows for eccentricity quantities to linearly map onto ellipse analogs, whereas aspect ratio quantities map nonlinearly. For particles viewed from their side, this analytic distinction leads to substantially larger errors in projected aspect ratio than for projected eccentricity. Distribution transformations using these mapping equations and numerical integration of projection kernels show that both truncation of size distributions and changes in Gaussian dispersion can alter the modality and shape of projection distributions. As a result, the projection process can more than triple the relative entropy between the spheroidal and projection distributions for commonly assumed model and orientationmore »« less

Authors:

Dunnavan, Edwin L. ^[1]; Jiang, Zhiyuan ^[1]

The Pennsylvania State University, University Park, Pennsylvania

Publication Date:: 2019-01-01

Research Org.:: Pennsylvania State Univ., University Park, PA (United States)

Sponsoring Org.:: USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:: 1489713

Alternate Identifier(s):: OSTI ID: 1611950

Grant/Contract Number:: SC0012827; SC0013953

Resource Type:: Published Article

Journal Name:: Journal of the Atmospheric Sciences

Additional Journal Information:: Journal Name: Journal of the Atmospheric Sciences Journal Volume: 76 Journal Issue: 1; Journal ID: ISSN 0022-4928

Publisher:: American Meteorological Society

Country of Publication:: United States

Language:: English

Subject:: 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; meteorology & atmospheric sciences; cloud microphysics; ice crystals; ice particles; aircraft observations; in situ atmospheric observations; model comparison

Citation Formats


                    Dunnavan, Edwin L., and Jiang, Zhiyuan. A General Method for Estimating Bulk 2D Projections of Ice Particle Shape: Theory and Applications.  United States: N. p., 2019. 
Web.  https://doi.org/10.1175/JAS-D-18-0177.1.

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                    Dunnavan, Edwin L., & Jiang, Zhiyuan. A General Method for Estimating Bulk 2D Projections of Ice Particle Shape: Theory and Applications.  United States.  https://doi.org/10.1175/JAS-D-18-0177.1

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                    Dunnavan, Edwin L., and Jiang, Zhiyuan. Tue .  
"A General Method for Estimating Bulk 2D Projections of Ice Particle Shape: Theory and Applications".  United States.  https://doi.org/10.1175/JAS-D-18-0177.1.

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@article{osti_1489713,

  title        = {A General Method for Estimating Bulk 2D Projections of Ice Particle Shape: Theory and Applications},

  author       = {Dunnavan, Edwin L. and Jiang, Zhiyuan},

  abstractNote = {The orientation of falling ice particles directly influences estimates of microphysical and radiative bulk quantities as well as in situ retrievals of size, shape, and mass. However, retrieval efforts and bulk calculations often incorporate very basic orientations or ignore these effects altogether. To address this deficiency, this study develops a general method for projecting bulk distributions of particle shape for arbitrary orientations. The Amoroso distribution provides the most general bulk aspect ratio distribution for gamma-distributed particle axis lengths. The parameters that govern the behavior of this aspect ratio distribution depend on the assumed relationship between mass, maximum dimension, and aspect ratio. Individual spheroidal geometry allows for eccentricity quantities to linearly map onto ellipse analogs, whereas aspect ratio quantities map nonlinearly. For particles viewed from their side, this analytic distinction leads to substantially larger errors in projected aspect ratio than for projected eccentricity. Distribution transformations using these mapping equations and numerical integration of projection kernels show that both truncation of size distributions and changes in Gaussian dispersion can alter the modality and shape of projection distributions. As a result, the projection process can more than triple the relative entropy between the spheroidal and projection distributions for commonly assumed model and orientation parameters. This shape uncertainty is maximized for distributions of highly eccentric particles and for particles like aggregates that are thought to fall with large canting-angle deviations. Finally as a result, the methods used to report projected aspect ratios and the corresponding values should be questioned.},

  doi          = {10.1175/JAS-D-18-0177.1},

  journal      = {Journal of the Atmospheric Sciences},

  number       = 1,

  volume       = 76,

  place        = {United States},

  year         = {2019},

  month        = {1}

}

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