TY - JOUR

T1 - Optimal numerical methods for determining the orientation averages of single-scattering properties of atmospheric ice crystals

AU - Um, Junshik

AU - McFarquhar, Greg M.

N1 - Funding Information:
This research was supported by the Office of Science ( BER ), United States Department of Energy under Grant nos. DE-FG02-09ER64770 , DE-SC0001279 , and DE-SC0008500 and by the National Science Foundation through the Extreme Science and Engineering Discovery Environment resources provided by National Institute for Computational Sciences under Grant no. TG-ATM100017 . This research is part of the Blue Waters sustained-petascale computing project, which is supported by the National Science Foundation (award number OCI 07-25070) and the state of Illinois. Blue Waters is a joint effort of the University of Illinois at Urbana-Champaign and its National Center for Supercomputing Applications. Data were obtained from the Atmospheric Radiation Measurement program archive, sponsored by the DOE , Office of Science, Office of Biological and Environmental Research Environmental Science Division. We thank M.A. Yurkin and A.G. Hoekstra for the ADDA code, Okada for the Halton sequence code, Penttilä for advice of orientation average, and D. Wojtowicz for allocating computing power. We thank the anonymous reviewers whose comments considerably improved the manuscript.

PY - 2013/9

Y1 - 2013/9

N2 - The optimal orientation averaging scheme (regular lattice grid scheme or quasi Monte Carlo (QMC) method), the minimum number of orientations, and the corresponding computing time required to calculate the average single-scattering properties (i.e., asymmetry parameter (g), single-scattering albedo (ωo), extinction efficiency (Qext), scattering efficiency (Qsca), absorption efficiency (Qabs), and scattering phase function at scattering angles of 90° (P11 (90°)), and 180° (P11 (180°))) within a predefined accuracy level (i.e., 1.0%) were determined for four different nonspherical atmospheric ice crystal models (Gaussian random sphere, droxtal, budding Bucky ball, and column) with maximum dimension D = 10 μm using the Amsterdam discrete dipole approximation at λ = 0.55, 3.78, and 11.0 μm.The QMC required fewer orientations and less computing time than the lattice grid. The calculations of P11 (90°) and P11 (180°) required more orientations than the calculations of integrated scattering properties (i.e., g, ωo, Qext, Qsca, and Qabs) regardless of the orientation average scheme. The fewest orientations were required for calculating g and ωo. The minimum number of orientations and the corresponding computing time for single-scattering calculations decreased with an increase of wavelength, whereas they increased with the surface-area ratio that defines particle nonsphericity.

AB - The optimal orientation averaging scheme (regular lattice grid scheme or quasi Monte Carlo (QMC) method), the minimum number of orientations, and the corresponding computing time required to calculate the average single-scattering properties (i.e., asymmetry parameter (g), single-scattering albedo (ωo), extinction efficiency (Qext), scattering efficiency (Qsca), absorption efficiency (Qabs), and scattering phase function at scattering angles of 90° (P11 (90°)), and 180° (P11 (180°))) within a predefined accuracy level (i.e., 1.0%) were determined for four different nonspherical atmospheric ice crystal models (Gaussian random sphere, droxtal, budding Bucky ball, and column) with maximum dimension D = 10 μm using the Amsterdam discrete dipole approximation at λ = 0.55, 3.78, and 11.0 μm.The QMC required fewer orientations and less computing time than the lattice grid. The calculations of P11 (90°) and P11 (180°) required more orientations than the calculations of integrated scattering properties (i.e., g, ωo, Qext, Qsca, and Qabs) regardless of the orientation average scheme. The fewest orientations were required for calculating g and ωo. The minimum number of orientations and the corresponding computing time for single-scattering calculations decreased with an increase of wavelength, whereas they increased with the surface-area ratio that defines particle nonsphericity.

KW - ADDA

KW - Cirrus

KW - Discrete dipole approximation

KW - Nonspherical particles

KW - Numerical orientation average

KW - Single-scattering properties

KW - Small atmospheric ice crystals

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U2 - 10.1016/j.jqsrt.2013.05.020

DO - 10.1016/j.jqsrt.2013.05.020

M3 - Article

AN - SCOPUS:84881237657

SN - 0022-4073

VL - 127

SP - 207

EP - 223

JO - Journal of Quantitative Spectroscopy and Radiative Transfer

JF - Journal of Quantitative Spectroscopy and Radiative Transfer

ER -