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 reflectivity 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 dual-wavelength cloud radar in Chinese Academy of Meteorological Sciences was used to observe clouds and precipitations in Longmen, Guangdong Province.In this paper, under the assumption of the Gamma’s DSD, the effects of temperature and turbulence on the ratio of Ka-band and Ku-band reflectivity density spectra and their relationships 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.Secondly, 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 coefficient.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.
[1]Adhikari N B, Iguchi T, Takahashi N, al et, 2007.Rain retrieval performance of a dual-frequency precipitation radar technique with differential-attenuation constraint [J].IEEE Transaction on Geoscience and Remote Sensing, 45(8): 2612-2618.DOI: 10.1109/IGARSS.2006.14.
[2]Barber P, Yeh C, 1975.Scattering of electromagnetic wave by arbitrarily shaped dielectric bodies[J].Applied Optics, 14 (12): 2864-2872.DOI: 10.1364/AO.14.002864.
[3]Firda.J M, Sekelsky S M, Mcintosh R E, 1999.Application of dual-frequency millimeter-wave Doppler spectra for the retrieval of drop size distributions and vertical air motion in rain[J].Journal of Atmospheric & Oceanic Technology, 16(2): 216-236.DOI: 10.1175/1520-0426(1999)016<0216: aodfmw>2.0.co; 2.
[4]Gossard E E, 1994.Measurement of cloud droplet size spectra by Doppler Radar[J].Journal of Atmospheric and Oceanic Technology, 11(3): 712-726.DOI: 10.1175/1520-0426(1994)0112.0.CO; 2.
[5]Gossard E E, Snider J B, Clothiaux E E, al et, 1997.The potential of 8-mm radars for remotely sensing cloud drop size distributions.[J].Journal of Atmospheric and Oceanic Technology, 14: 76-87.DOI: 10.1175/1520-0426(1997)0142.0.CO; 2.
[6]Gorgucci E, Baldini L, 2016.A self-consistent numerical method microphysical retrieval in rain using GPM dual-wavelength radar.[J].Journal of Atmospheric and Oceanic Technology, 33(10): 2205-2223.DOI: 10.1175/JTECH-D-16-0020.1.
[7]Kollias P, Albrecht B A, Marks F D, 2002.Why mie? Accurate observations of vertical air velocities and raindrops using a cloud radar[J].Bulletin of the American Meteorological Society, 83(10): 1471-1483.DOI: 10.1175/BAMS-83-10-1471.
[8]Kollias P, Albrecht B A, Marks F D, 2003.Cloud radar observations of vertical drafts and microphysics in convective rain[J].Journal of Geophysical Research, 108(1): 40-53.DOI: 10.1029/2001 jd002033.
[9]Kathleen F J, Gregory T, Keran J C, al et, 2014.Gamma Distribution parameters for cloud drop distributions from multicylinder measurements[J].Journal of Applied Meteorology and Climatology, 53(6), 1606-1617.
[10]Liao L, Meneghini R, 2005.A study of air/space-borne dual-wavelength Radar for estimation of rain profiles[J].Advances in Atmospheric Sciences, 22(6): 841-851.DOI: 10.1007/BF02918684.
[11]Liu L P, Zheng J F, Ruan Z, al et, 2015.Comprehensive radar observations of clouds and precipitation over the Tibetan Plateau and preliminary analysis of cloud properties[J].Journal of Meteorological Research, 29(4): 546-561.DOI: 10.1007/s13351-015-4208-6
[12]Liu L P, Ruan Z, Zheng J F, al et, 2017a.Comparing and merging observation data from Ka-Band Cloud Radar, C-Band Frequency-Modulated continuous wave Radar and Ceilometer systems[J].Remote Sensing, 9(12), 1282. DOI: 10.3390/rs9121282.
[13]Liu L P, Zheng J F, Wu J Y, 2017b.A Ka-band solid-state transmitter cloud radar and data merging algorithm for its measurements[J].Advances in Atmospheric Sciences, 34(4): 545-558.DOI: 10.1007/s00376-016-6044-8.
[14]Meneghini R, Kozu T, Kumagai H, al et, 1992.A study of rain estimation methods from space using dual-wavelength radar measurements at near-nadir incidence over ocean [J].Journal of Atmospheric and Oceanic Technology, 9(4): 364-382.DOI: 10.1175/1520-0426(1992)009<0364: ASOREM>2.0.CO; 2.
[15]Mardiana R, Iguchi T, Takahashi N, 2004.A dual-frequency rain profiling method without the use of the surface reference technique[J].IEEE Transactions on Geoscience and Remote Sensing, 42(10), 2214-2225.DOI: 10.1109/TGRS.2004.834647.
[16]Meneghini R, Kim H, Liao L, al et, 2015.An initial assessment of the surface reference technique applied to data from the dual-frequency precipitation radar (DPR) on the GPM Satellite[J].Journal of Atmospheric and Oceanic Technology, 32(12): 2281-2296.DOI: 10.1175/JTECH-D-15-0044.1.
[17]Natasha L M, Johannes V, Eugene E C, 2000.Cloud droplet size distributions in low-level stratiform clouds [J].Journal of the Atmospheric Sciences, 57(2): 295–310.DOI: 10.1175/1520-0469(2000)057<0295: cdsdil>2.0.co; 2.
[18]Shupe M D, Kollias P, Poellot M, al et, 2008.On deriving vertical air motions from Cloud Radar Doppler Spectra [J].Journal of Atmospheric and Oceanic Technology, 25(4): 547.DOI: 10.1175/2007JTECHA1007.1.
[19]Tridon F, Battaglia A, 2015.Dual-frequency radar Doppler spectral retrieval of rain drop size distributions and entangled dynamics variables[J].Journal of Geophysical Research: Atmospheres, 120: 11, 5585-5601.DOI: 1002/2014jd023023.
[20]Tokay A, Short D A, 1996.Evidence from tropical raindrop of the origin of rain from stratiform versus convective cloud[J].Journal of Applied Meteorology, 35(3): 355-371.DOI: 10.1175/1520-0450(1996)035<0355: EFTRSO>2.0.CO; 2.
[21]Vivekanandan J, Zhang G F, Politovich M K, 2001.An assessment of droplet size and liquid water content derived from dual-wavelength radar measurements to the application of aircraft icing detection [J].Journal of Atmospheric and Oceanic Technology, 18(11): 1787-1798.DOI: 10.1175/1520-0426(2001)018<1787: aaodsa>2.0.co; 2.
[22]Zheng J F, Liu L P, Zhu K, al et, 2017.A method for retrieving vertical air velocities in convective clouds over the Tibetan Plateau from TIPEX-III Cloud Radar Doppler Spectra[J].Remote Sensing, 9(9): 964.DOI: 10.3390/rs9090964.
[23]刘黎平, 谢蕾, 崔哲虎, 2014.毫米波云雷达功率谱密度数据的检验和在弱降水滴谱反演中的应用研究[J].大气科学, 38（2）: 223-236.DOI: 10.3878/j.issn.1006-9895.2013.12207.
[24]彭亮, 陈洪滨, 李柏, 2012.3 mm多普勒云雷达测量反演云内空气垂直速度的研究[J].大气科学, 36(1): 1-1.
[25]马宁堃, 刘黎平, 郑佳峰, 2019.利用Ka波段毫米波云雷达功率谱反演云降水大气垂直速度和雨滴谱分布研究[J].高原气象, 38（2）: 325-339.DOI: 10.7522/j.issn.1000－0534.2018.00127．
[26]阮悦, 阮征, 魏鸣, 等, 2017.基于雷达的高原夏季对流云垂直结构分析研究[J].高原气象, 36（1）: 93-105.DOI: 10.7522/j.issn.1000－0534.2017.00127．
[27]姚志刚, 杨超, 赵增亮, 等, 2018.毫米波雷达反演层状云液态水路径研究[J].高原气象, 37（1）: 223-233.DOI: 10.7522/j.issn. 1000－0534.2016.00025．
