TY - JOUR

T1 - What can we conclude about the real aspect ratios of ice particle aggregates from two-dimensional images?

AU - Jiang, Zhiyuan

AU - Oue, Mariko

AU - Verlinde, Johannes

AU - Clothiaux, Eugene E.

AU - Aydin, Kultegin

AU - Botta, Giovanni

AU - Lu, Yinghui

N1 - Funding Information:
The National Science Foundation, underGrant AGS-122818, supported the work of Z. Jiang, J. Verlinde, K. Aydin, and Y. Lu. Authors M. Oue, G. Botta, and E. E. Clothiaux were supported under Grant DE-FG02_05ER64058 from the U.S. Department of Energy Atmospheric System Research Program, anOffice of Science, Office of Biological and Environmental Research program. We acknowledge the contributions of the three anonymous reviewers whose very thoughtful comments strengthened the paper substantially.
Publisher Copyright:
© 2017 American Meteorological Society.

PY - 2017

Y1 - 2017

N2 - A simple numerical experiment was performed to investigate the result published in many papers that measurements indicate that aggregates may be well represented as oblate spheroids with mean aspect ratio (semiminor axis to semimajor axis length) of 0.6. The aspect ratio measurements are derived from two-dimensional projections of complex three-dimensional aggregates. Here, aggregates were modeled as ellipsoids with semiprincipal axes of length a, b, and c, which include oblate spheroids (a = b) as a class, and the projected aspect ratios of large numbers of two-dimensional projections of them were sampled. When sampling oblate spheroids with aspect ratio 0.6 over random orientations, the mean projected aspect ratio is 0.746. A mean projected aspect ratio of 0.6 is obtained for an oblate spheroid with aspect ratio of 0.33. When sampling randomly oriented ellipsoids with semiminor axes (b, c) varying from 0.10 to 1.00 in steps of 0.01, representing many complex shapes, the mean projected aspect ratio is 0.595, close to the measured mean projected aspect ratio of aggregates of 0.6. These experiments demonstrate that the conclusion one may safely draw from the projected aspect ratio measurements is that the mean aspect ratio of aggregates is lower than 0.6. Moreover, the projected aspect ratio distributions from measurements suggest a mixture of aggregate shapes, rather than only oblate spheroids as is often assumed.

AB - A simple numerical experiment was performed to investigate the result published in many papers that measurements indicate that aggregates may be well represented as oblate spheroids with mean aspect ratio (semiminor axis to semimajor axis length) of 0.6. The aspect ratio measurements are derived from two-dimensional projections of complex three-dimensional aggregates. Here, aggregates were modeled as ellipsoids with semiprincipal axes of length a, b, and c, which include oblate spheroids (a = b) as a class, and the projected aspect ratios of large numbers of two-dimensional projections of them were sampled. When sampling oblate spheroids with aspect ratio 0.6 over random orientations, the mean projected aspect ratio is 0.746. A mean projected aspect ratio of 0.6 is obtained for an oblate spheroid with aspect ratio of 0.33. When sampling randomly oriented ellipsoids with semiminor axes (b, c) varying from 0.10 to 1.00 in steps of 0.01, representing many complex shapes, the mean projected aspect ratio is 0.595, close to the measured mean projected aspect ratio of aggregates of 0.6. These experiments demonstrate that the conclusion one may safely draw from the projected aspect ratio measurements is that the mean aspect ratio of aggregates is lower than 0.6. Moreover, the projected aspect ratio distributions from measurements suggest a mixture of aggregate shapes, rather than only oblate spheroids as is often assumed.

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U2 - 10.1175/JAMC-D-16-0248.1

DO - 10.1175/JAMC-D-16-0248.1

M3 - Article

AN - SCOPUS:85015256788

VL - 56

SP - 725

EP - 734

JO - Journal of Applied Meteorology and Climatology

JF - Journal of Applied Meteorology and Climatology

SN - 1558-8424

IS - 3

ER -