TY - JOUR
T1 - On the impacts of different definitions of maximum dimension for nonspherical particles recorded by 2D imaging probes
AU - Wu, Wei
AU - McFarquhar, Greg M.
N1 - The work was supported by the office of Biological and Environmental Research (BER) of the U.S. Department of Energy (DE-SC0001279, DESC0008500, and DE-SC0014065) as well as the National Science Foundation (NSF) (Grant AS-1213311). Data have been obtained from the ARM program archive, sponsored by the U.S. DOE Office of Science, BER, Climate and Environmental Sciences Division. The authors want to thank Michael Poellot for discussing the MC3E data quality. The discussions with Alexei Korolev about the depth of field for irregular particles and the extinction calculation directly from OAP probes improved the manuscript considerably.
PY - 2016
Y1 - 2016
N2 - Knowledge of ice crystal particle size distributions (PSDs) is critical for parameterization schemes for atmospheric models and remote sensing retrieval schemes. Two-dimensional in situ images captured by cloud imaging probes are widely used to derive PSDs in term of maximum particle dimension (Dmax). In this study, different definitions of Dmax for nonspherical particles recorded by 2D probes are compared. It is shown that the derived PSDs can differ by up to a factor of 6 for Dmax ≤ 200 mm and Dmax ≥ 2 mm. The large differences for Dmax ≤ 200 mm are caused by the strong dependence of sample volume on particle size, whereas differences forDmax ≥ 2 mm are caused by the small number of particles detected. Derived bulk properties can also vary depending on the definitions of Dmax because of discrepancies in the definition of Dmax used to characterize the PSDs and that used to describe the properties of individual ice crystals. For example, the massweighted mean diameter can vary by 2 times, the ice water content (IWC) by 3 times, and the mass-weighted terminal velocity by 6 times. Therefore, a consistent definition of Dmax should be used for all data and singleparticle properties. As an invariant measure with respect to the orientation of particles in the imaging plane for 2D probes, the diameter of the smallest circle enclosing the particle (DS) is recommended as the optimal definition of Dmax. If the 3D structure of a particle is observed, then the technique can be extended to determine the minimum enclosing sphere.
AB - Knowledge of ice crystal particle size distributions (PSDs) is critical for parameterization schemes for atmospheric models and remote sensing retrieval schemes. Two-dimensional in situ images captured by cloud imaging probes are widely used to derive PSDs in term of maximum particle dimension (Dmax). In this study, different definitions of Dmax for nonspherical particles recorded by 2D probes are compared. It is shown that the derived PSDs can differ by up to a factor of 6 for Dmax ≤ 200 mm and Dmax ≥ 2 mm. The large differences for Dmax ≤ 200 mm are caused by the strong dependence of sample volume on particle size, whereas differences forDmax ≥ 2 mm are caused by the small number of particles detected. Derived bulk properties can also vary depending on the definitions of Dmax because of discrepancies in the definition of Dmax used to characterize the PSDs and that used to describe the properties of individual ice crystals. For example, the massweighted mean diameter can vary by 2 times, the ice water content (IWC) by 3 times, and the mass-weighted terminal velocity by 6 times. Therefore, a consistent definition of Dmax should be used for all data and singleparticle properties. As an invariant measure with respect to the orientation of particles in the imaging plane for 2D probes, the diameter of the smallest circle enclosing the particle (DS) is recommended as the optimal definition of Dmax. If the 3D structure of a particle is observed, then the technique can be extended to determine the minimum enclosing sphere.
KW - Aircraft observations
KW - Algorithms
KW - Cloud microphysics
KW - Data processing
KW - In situ atmospheric observations
KW - Observational techniques and algorithms
KW - Physical Meteorology and Climatology
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U2 - 10.1175/JTECH-D-15-0177.1
DO - 10.1175/JTECH-D-15-0177.1
M3 - Article
AN - SCOPUS:84984670422
SN - 0739-0572
VL - 33
SP - 1057
EP - 1072
JO - Journal of Atmospheric and Oceanic Technology
JF - Journal of Atmospheric and Oceanic Technology
IS - 5
ER -