Characterization of Ze and LDR of nonspherical and inhomogeneous ice particles for 95‐GHz cloud radar: Its implication to microphysical retrievals
Characterization of Ze and LDR of nonspherical and inhomogeneous ice particles for 95‐GHz cloud radar: Its implication to microphysical retrievals
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DOI：
10.1029/2005jd006959
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发表时间：
2006-11
影响因子：
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通讯作者：
Kaori Sato;H. Okamoto
中科院分区：
文献类型：
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作者：
Kaori Sato;H. Okamoto
[1]采用离散偶极子近似（DDA）研究了冰云的密度、形状和方向对95 GHz雷达反射率因子（Ze）和线性退偏比（LDR）的影响。我们考虑了水平（2-D）或三维（3-D）随机取向的六边形板、空心六边形柱和空心子弹花。我们首先验证了一个广泛使用的方法来考虑密度和形状的影响相结合的使用Mie理论与麦克斯韦-加内特混合规则（MG-Mie方法）。发现MG-Mie方法低估了Ze，其适用范围仅限于小于40 μm的尺寸。在DDA的基础上，可以分别处理密度、纵横比、取向和形状。密度的影响很小。取向和形状是Ze的主要控制因素，特别是在有效半径reff > 100 μm和LDR时，除了非常大的尺寸外，LDR中取向的影响减小。三维瑞利椭球体的DDA结果与解析解的比较表明，在小尺寸范围内，LDR的特征在于目标边界和纵横比。在大尺寸范围内，LDR揭示了单个靶元素的特征;例如，子弹花结的LDR类似于颗粒的单个分支的LDR。Ze和LDR的组合使用在LDR −23 dB的微物理反演中是有效的，需要额外的信息，如多普勒速度。
[1] Effect of density, shape, and orientation on radar reflectivity factor (Ze) 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 Ze and its applicability is limited to sizes smaller than 40 μm. 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 Ze especially at effective radius reff > 100 μm 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 Ze and LDR is effective in microphysics retrieval for LDR −23 dB, additional information such as Doppler velocity is required.