Effect of Particle Shape, Density, and Inhomogeneity on the Microwave Optical Properties of Graupel and Hailstones

Guanglin Tang, Ping Yang, Patrick G. Stegmann, R. Lee Panetta, Leung Tsang, Benjamin Johnson

Research output: Contribution to journalArticle

6 Scopus citations

Abstract

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.

Original languageEnglish (US)
Article number8002644
Pages (from-to)6366-6378
Number of pages13
JournalIEEE Transactions on Geoscience and Remote Sensing
Volume55
Issue number11
DOIs
StatePublished - Nov 2017
Externally publishedYes

Keywords

  • Bicontinuous medium
  • effective medium
  • graupel
  • hailstone
  • inhomogeneity
  • remote sensing

ASJC Scopus subject areas

  • Electrical and Electronic Engineering
  • Earth and Planetary Sciences(all)

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