Open AccessCharacterization of Z e and LDR of nonspherical and inhomogeneous ice particles for 95‐GHz cloud radar: Its implication to microphysical retrievals
Author(s) -
Sato Kaori,
Okamoto Hajime
Publication year - 2006
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2005jd006959
Subject(s) - radius , orientation (vector space) , physics , effective radius , optics , range (aeronautics) , discrete dipole approximation , rayleigh scattering , geometry , computational physics , scattering , materials science , mathematics , astrophysics , galaxy , computer science , composite material , computer security
Effect of density, shape, and orientation on radar reflectivity factor ( Z e ) and linear depolarization ratio ( LDR ) at 95 GHz are investigated by using the discrete dipole approximation (DDA) for ice cloud studies. We consider hexagonal plate, hollow hexagonal column, and hollow bullet rosette in horizontal (2‐D) or three‐dimensional (3‐D) random orientation. We first validate a widely used method to take into account the density and shape effects by the combinational use of Mie theory with the Maxwell‐Garnett mixing rule (the MG‐Mie method). It is found that the MG‐Mie method underestimates Z e and its applicability is limited to sizes smaller than 40 μ m. On the basis of the DDA, it is possible to separately treat density, aspect ratio, orientation, and shape. Effect of density turns out to be minor. Orientation and shape are the major controlling factors for Z e especially at effective radius r eff > 100 μ m and LDR except for very large sizes where the effect of orientation in LDR diminishes. Comparison between the DDA results and the analytical solution for 3‐D Rayleigh spheroids show that LDR in the small size range is characterized by the target boundary and aspect ratio. In the large size range, LDR reveals features of a single target element; for example, LDR of bullet rosette is similar to that of a single branch of the particle. Combinational use of Z e and LDR is effective in microphysics retrieval for LDR < −23 dB. For LDR > −23 dB, additional information such as Doppler velocity is required.