TY - JOUR
T1 - Effect of Particle Shape, Density, and Inhomogeneity on the Microwave Optical Properties of Graupel and Hailstones
AU - Tang, Guanglin
AU - Yang, Ping
AU - Stegmann, Patrick G.
AU - Lee Panetta, R.
AU - Tsang, Leung
AU - Johnson, Benjamin
N1 - Funding Information:
Manuscript received March 20, 2017; revised May 30, 2017; accepted June 16, 2017. Date of publication August 4, 2017; date of current version October 25, 2017. This work was supported in part by the National Science Foundation under Grant AGS-1338440 and in part by National Oceanic and Atmospheric Administration under Grant NA15NES4400003. (Corresponding author: Guanglin Tang.) G. Tang, P. Yang, P. G. Stegmann, and R. L. Panetta are with the Department of Atmospheric Sciences, Texas A&M University, College Station, TX 77843 USA (e-mail: tangguanglin@gmail.com).
Publisher Copyright:
© 1980-2012 IEEE.
PY - 2017/11
Y1 - 2017/11
N2 - Atmospheric ice particles can be rimed and contaminated (e.g., by soot attachments). Previous optical property calculations usually assume rimed particles such as graupel and hailstones to be homogeneous spheres with fixed densities. The relevant dielectric constants are estimated with the effective medium approximation (EMA), although such particles are predominately nonspherical, porous, and contain small interior grains. This paper assesses the effects of nonsphericity, density, and inhomogeneity of graupel and hailstones on their optical properties. The bicontinuous medium approximation (BMA) is employed to simulate the particle internal structure. Conical shapes are compared with spherical and spheroidal shapes to assess the effect of nonsphericity. At frequencies lower than 89 GHz, the optical properties are more sensitive to particle's mass density than to overall particle shape, and the internal structure plays an insignificant role when the particle effective diameter (a quantity involving the particle size distribution) is smaller than approximately 10 mm, and the internal grain size is smaller than 0.2 mm. With a small grain size, the BMA phase function converges to the EMA phase function with an effective refractive index calculated with the Bruggeman formulation. Simulated top of atmosphere radiances at three microwave frequencies, 18.7, 36.5, and 89 GHz, are quite sensitive to ice particle effective diameter between 1 and 5 mm, ice fraction between 0.1 and 0.9, and ice water path between 1 and 5 kg/ m2. Thus, these frequencies are suitable for retrieving the microphysical properties.
AB - Atmospheric ice particles can be rimed and contaminated (e.g., by soot attachments). Previous optical property calculations usually assume rimed particles such as graupel and hailstones to be homogeneous spheres with fixed densities. The relevant dielectric constants are estimated with the effective medium approximation (EMA), although such particles are predominately nonspherical, porous, and contain small interior grains. This paper assesses the effects of nonsphericity, density, and inhomogeneity of graupel and hailstones on their optical properties. The bicontinuous medium approximation (BMA) is employed to simulate the particle internal structure. Conical shapes are compared with spherical and spheroidal shapes to assess the effect of nonsphericity. At frequencies lower than 89 GHz, the optical properties are more sensitive to particle's mass density than to overall particle shape, and the internal structure plays an insignificant role when the particle effective diameter (a quantity involving the particle size distribution) is smaller than approximately 10 mm, and the internal grain size is smaller than 0.2 mm. With a small grain size, the BMA phase function converges to the EMA phase function with an effective refractive index calculated with the Bruggeman formulation. Simulated top of atmosphere radiances at three microwave frequencies, 18.7, 36.5, and 89 GHz, are quite sensitive to ice particle effective diameter between 1 and 5 mm, ice fraction between 0.1 and 0.9, and ice water path between 1 and 5 kg/ m2. Thus, these frequencies are suitable for retrieving the microphysical properties.
KW - Bicontinuous medium
KW - effective medium
KW - graupel
KW - hailstone
KW - inhomogeneity
KW - remote sensing
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U2 - 10.1109/TGRS.2017.2726994
DO - 10.1109/TGRS.2017.2726994
M3 - Article
AN - SCOPUS:85028969277
SN - 0196-2892
VL - 55
SP - 6366
EP - 6378
JO - IEEE Transactions on Geoscience and Remote Sensing
JF - IEEE Transactions on Geoscience and Remote Sensing
IS - 11
M1 - 8002644
ER -