Ka/Ku双波段云雷达探测云降水滴谱和空气垂直运动速度的能力模拟分析

Simulation Analysis on Retrieving Capabilities for Rain Drop Size Distribution and Air Vertical Motion with Single and Dual Wave Length Cloud Radars

由于湍流、雷达探测灵敏度等对单波长云雷达探测回波强度谱密度的影响,造成了云雷达探测空气垂直运动速度和雨滴谱的误差,而双波长云雷达利用Mie散射造成的不同粒子后向散射大小差异来提高空气上升速度探测精度,从而提高反演雨滴谱的能力,并且可提高订正雨区衰减的能力。为此中国气象科学研究院研发了Ka/Ku双波段云雷达,并于2019年4月开始在广东龙门进行了云降水观测。本文针对该双波段云雷达观测模式和灵敏度等参数,在Gamma滴谱假设条件下,模拟分析了Ka、Ku波段功率谱及其比值与云降水参数、温度和湍流的关系,研究了雷达灵敏度、湍流对空气垂直速度、雨滴谱反演和衰减订正的影响,并利用个例数据进行了风场反演试验,讨论了双波段探测微降水动力和微物理参数的优势。结果表明:(1)温度只能影响两个波段功率谱比值(Ratio)的大小,对其峰值位置基本没有影响,而湍流对其峰值位置的影响不超过0.5 m·s^-1;(2)湍流、雷达灵敏度对单波段云雷达探测空气垂直速度的影响比较明显,湍流使空气上升速度被高估,雷达最小可测回波强度随高度的增加而增加使该参数被低估,其影响远远大于温度和湍流对双波段云雷达反演空气垂直速度的影响;(3)对于单波段雷达来说,雷达灵敏度和湍流明显影响雨滴谱、含水量和衰减系数的探测,湍流使得雨滴谱拓宽,低估含水量和衰减系数;而雷达灵敏度却使反演的雨滴谱变窄,增加小粒子数浓度,并高估了含水量和衰减系数;(4)选取2019年4月15^-16日的个例进行空气上升速度的反演,并与模拟分析的结果进行对比。结果显示实际观测数据反演的空气上升速度与模拟分析结果中的趋势较为一致。这项工作为单波段和双波段云雷达的多普勒功率谱数据分析和云降水微物理和动力参数的反演可提供参考。

The factors such as the turbulence and the sensitivity of radar detection affect,the Doppler spectral and,introduce error of the air vertical motion velocity and Rain Drop Size Distributions(DSD)retrievals with single wavelength cloud radar.However,the dual-wavelength cloud radar,which uses the differences of reflec‐tivity spectra density for two wavelengths due to Mie scattering,not only improves the detection accuracy of the air vertical motion velocity and DSD,but also reduces the errors of the attenuation correction.A Ka/Ku dualwavelength cloud radar in Chinese Academy of Meteorological Sciences was used to observe clouds and precipi‐tations in Longmen,Guangdong Province.In this paper,under the assumption of the Gamma’s DSD,the ef‐fects of temperature and turbulence on the ratio of Ka-band and Ku-band reflectivity density spectra and their re‐lationships with DSD parameters were analyzed,the effects of the sensitivity of the cloud radar on retrieved air vertical velocity,DSD and attenuation correction were simulated,The advantages of the Ka/Ku dual-wavelength radar on detecting micro-precipitation dynamics and microphysical parameters were discussed.The results show that,the variations of temperature affect the value of maximum ratio of the power spectrum for the two bands,but don’t affects the peak position.The effects of turbulence on the peak position are less than 0.5 m·s^-1.Second‐ly,the effects of turbulence,and reflectivity sensitivity on air vertical velocities retrieved by single-band cloud radar are far greater than that by dual-wavelength cloud radar.Turbulence underestimated the air vertical velocity and the low,radar sensitivity overestimated it.Thirdly,for single wavelength cloud radar,turbulence expanded the DSD,underestimated the number contend for small drops,liquid water content(LWC)and attenuation coef‐ficient.Low radar sensitivity narrowed the DSD,overestimated the number contend for small drops,LWC and attenuation coefficient.Finally,the precipitation cases during April 15 and 16,2019 were chosen to examine the retrieval of air vertical motion and compared with the simulation result.The work provides base for retrieval of the microphysical and dynamic parameters of cloud and precipitation with both single-band and dual-band cloud radars.