Possibility of Solid Hydrometeor Growth Zone Identification Using Radar Spectrum Width

Abstract

In this study, the correlation between simulated and measured radar velocity spectrum width (σ_v) is investigated. The results show that the dendrites growth zones (DGZs) and needles growth zones (NGZs) mostly contain dendrites (DN) and needles (NE), respectively.

Clear σ_v zones (1.1 < σ_v (m s⁻¹) < 1.3 and 0.3 < σ_v (m s⁻¹) < 0.7 for the DGZ and NGZ, respectively) could be identified in the case studies (27 and 28 February 2016) near altitudes corresponding to temperatures of −15°C and −5°C, according to the Japan Meteorological Agency and mesoscale model reanalysis data. Oblate particles with diverse particle shapes were observed in the DGZ with σ_V > 1.2 m s⁻¹, a differential reflectivity (Z_DR) higher than 0 dB, and a cross-correlation coefficient (ρ_hv) less than 0.96. In contrast, prolate particles with relatively uniform shapes were observed in the NGZ with σ_v < 0.6 m s⁻¹, a Z_DR less than 0 dB, and ρ_hv higher than 0.97.

The simulation results show that the DN exhibited a larger σ_v compared to the NE, and this observed σ_v was strongly dependent on the wind fluctuations (v’) due to turbulence or wind shear. In contrast, the NE exhibited a significantly small σ_v ∼ 0.55 m s⁻¹, which converges irrespective of v’. In addition, a strong correlation between the measured σ_v values at five radar elevation angles (θ = 6.2°, 9.1°, 13.1°, 19°, and 80°) and those simulated in this study confirmed the significance of the analysis results.

摘要

本文研究了模拟和实测雷达速度谱宽之间的相关性。结果表明,枝状固态水凝物增长区（DGZs）和针状固态水凝物增长区（NGZs）主要分别含有枝状冰晶（DN）和针状冰晶（NE）。

根据日本气象厅和中尺度模式再分析数据,在与-15°C和-5°C温度相对应的高度附近案例（2016年2月27日和28日）的研究中,雷达速度谱宽区（DGZ的雷达速度谱宽范围是1.1 m s^–1 至 1.3 m s^–1,NGZ的雷达速度谱宽范围是0.3 m s^–1 至 0.7 m s^–1）可以被清晰地识别出来。在DGZ中观察到具有不同颗粒形状的扁椭球粒子,其雷达速度谱宽大于1.2 m s^–1,差分反射率高于0 dB,互相关系数小于0.96。相比之下,在NGZ中,观察到具有相对均匀形状的长椭球粒子,其雷达速度谱宽小于0.6 m s^–1,差分反射率小于0 dB,互相关系数高于0.97。

模拟结果表明,与NE相比,DN对应着更大的雷达速度谱宽,并且观测到的雷达速度谱宽强烈依赖于湍流或风切变引起的风波动。相比之下,NE表现出明显较小的雷达速度谱宽~ 0.55 m s^–1,其收敛与风波动无关。此外,在五个雷达仰角（θ=6.2°、9.1°、13.1°、19°和80°）下测得的雷达速度谱宽值与本研究中模拟得到的雷达速度谱宽值之间表现出一种强相关性,印证了分析结果的重要性。