为了获得更加准确的冬季降水数据,针对PARSIVEL^2(Particle Size and Velocity)测量降雪时近地面水平风的影响进行了订正及误差计算。订正结果表明:一定风速下,不考虑风的影响会造成小粒子直径的明显低估,而对于同一粒径段的粒子,风速越...为了获得更加准确的冬季降水数据,针对PARSIVEL^2(Particle Size and Velocity)测量降雪时近地面水平风的影响进行了订正及误差计算。订正结果表明:一定风速下,不考虑风的影响会造成小粒子直径的明显低估,而对于同一粒径段的粒子,风速越大,计算过程中对于粒子直径的低估越明显。风速不超过2 m s^-1时,其降雪粒子下落末速度计算误差在3%左右,直径计算误差在7%以内(水平偏转角度45°)。在对2018年1月4日南京一次降雪过程中获取的真实雪花谱的分析中可以看出,忽略风的影响会导致雪花谱峰值的偏移和谱的缩窄,这会造成小粒子数浓度的高估和大粒子数浓度的低估,进而影响微物理量的计算。具体表现在雷达反射率因子Z和降雪强度I的低估,及Z-I关系拟合系数a值的实际数值会大于计算值,b值则偏小。但当风速较大时,近地面流场比较复杂,垂直向湍流运动不可忽略,此种订正方法很可能不再适用。建议在以后的业务观测中增设防风圈或在后续的数据处理中增加针对风的订正,以排除风对降雪测量的影响。展开更多
Microphysical characteristics of the raindrop size distribution(RSD)in Typhoon Morakot(2009) have been studied through the PARSIVEL disdrometer measurements at one site in Fujian province,China during the passage of t...Microphysical characteristics of the raindrop size distribution(RSD)in Typhoon Morakot(2009) have been studied through the PARSIVEL disdrometer measurements at one site in Fujian province,China during the passage of the storm from 7 to 10 August 2009.The time evolution of the RSD reveals different segments of the storm.Significant difference was observed in the microphysical characteristics between the outer rainband and the eyewall;the eyewall precipitation had a broader size distribution(a smaller slope) than the outer rainband and eye region.The outer rainband and the eye region produced stratiform rains while the eyewall precipitation was convective or mixed stratiform-convective.The RSD was typically characterized by a single peak distribution and well represented by the gamma distribution.The relations between the shape(μ)and slope(Λ)of the gamma distribution and between the reflectivity(Z)and rainfall rate(R)have been investigated.Based on the NW-Dm relationships,we suggest that the stratiform rain for the outer rainband and the eye region was formed by the melting of graupel or rimed ice particles,which likely originated from the eyewall clouds.展开更多
双频雷达通过估计降水的雨滴谱分布(Rain Drop Size Distribution,DSD)参数来估测降水,相比多普勒天气雷达利用Z-I关系估测降水的方法,估测结果更加准确。真实的雨滴谱分布随时空不断变化,难以准确描述。本研究的目的是评估将其描述成Ga...双频雷达通过估计降水的雨滴谱分布(Rain Drop Size Distribution,DSD)参数来估测降水,相比多普勒天气雷达利用Z-I关系估测降水的方法,估测结果更加准确。真实的雨滴谱分布随时空不断变化,难以准确描述。本研究的目的是评估将其描述成Gamma分布模型对双频雷达估测降水造成的误差。研究中利用架设在广东龙门和西藏那曲的雨滴谱仪观测资料,计算Ku/Ka双频雷达的反射率因子,利用双频雷达算法反演降水率R和衰减系数k,并将其与雨滴谱仪直接计算的结果进行比较,探讨双频雷达反演算法中DSD模型对反演结果造成的影响,并对比反演误差的地区差异性。研究结果表明:DSD参数对双频雷达反演降水的影响在那曲和龙门地区有一定的差异。从双频技术反演的质量加权的粒子直径(Dm)、Ka波长衰减系数(kKa)、Ku波长衰减系数(kKu)和降水率(R)来看,当Gamma分布的形状因子μ分别取2、3和4时,龙门地区对四个参数的反演都能得到较为稳定准确的结果,相对误差基本<10%。而就kKa和5~40 mm·h^-1的降水率而言,那曲和龙门有很大的不同,在龙门当μ取3时相对误差最小,都在0值附近波动,而那曲则要需要μ值在4和6附近才能使得相对误差达到最小。展开更多
文摘为了获得更加准确的冬季降水数据,针对PARSIVEL^2(Particle Size and Velocity)测量降雪时近地面水平风的影响进行了订正及误差计算。订正结果表明:一定风速下,不考虑风的影响会造成小粒子直径的明显低估,而对于同一粒径段的粒子,风速越大,计算过程中对于粒子直径的低估越明显。风速不超过2 m s^-1时,其降雪粒子下落末速度计算误差在3%左右,直径计算误差在7%以内(水平偏转角度45°)。在对2018年1月4日南京一次降雪过程中获取的真实雪花谱的分析中可以看出,忽略风的影响会导致雪花谱峰值的偏移和谱的缩窄,这会造成小粒子数浓度的高估和大粒子数浓度的低估,进而影响微物理量的计算。具体表现在雷达反射率因子Z和降雪强度I的低估,及Z-I关系拟合系数a值的实际数值会大于计算值,b值则偏小。但当风速较大时,近地面流场比较复杂,垂直向湍流运动不可忽略,此种订正方法很可能不再适用。建议在以后的业务观测中增设防风圈或在后续的数据处理中增加针对风的订正,以排除风对降雪测量的影响。
基金National Natural Science Foundation of China(40730948,40830958,40921160382)National Grand Fundamental Research 973 Program of China(2009CB421502)
文摘Microphysical characteristics of the raindrop size distribution(RSD)in Typhoon Morakot(2009) have been studied through the PARSIVEL disdrometer measurements at one site in Fujian province,China during the passage of the storm from 7 to 10 August 2009.The time evolution of the RSD reveals different segments of the storm.Significant difference was observed in the microphysical characteristics between the outer rainband and the eyewall;the eyewall precipitation had a broader size distribution(a smaller slope) than the outer rainband and eye region.The outer rainband and the eye region produced stratiform rains while the eyewall precipitation was convective or mixed stratiform-convective.The RSD was typically characterized by a single peak distribution and well represented by the gamma distribution.The relations between the shape(μ)and slope(Λ)of the gamma distribution and between the reflectivity(Z)and rainfall rate(R)have been investigated.Based on the NW-Dm relationships,we suggest that the stratiform rain for the outer rainband and the eye region was formed by the melting of graupel or rimed ice particles,which likely originated from the eyewall clouds.
文摘双频雷达通过估计降水的雨滴谱分布(Rain Drop Size Distribution,DSD)参数来估测降水,相比多普勒天气雷达利用Z-I关系估测降水的方法,估测结果更加准确。真实的雨滴谱分布随时空不断变化,难以准确描述。本研究的目的是评估将其描述成Gamma分布模型对双频雷达估测降水造成的误差。研究中利用架设在广东龙门和西藏那曲的雨滴谱仪观测资料,计算Ku/Ka双频雷达的反射率因子,利用双频雷达算法反演降水率R和衰减系数k,并将其与雨滴谱仪直接计算的结果进行比较,探讨双频雷达反演算法中DSD模型对反演结果造成的影响,并对比反演误差的地区差异性。研究结果表明:DSD参数对双频雷达反演降水的影响在那曲和龙门地区有一定的差异。从双频技术反演的质量加权的粒子直径(Dm)、Ka波长衰减系数(kKa)、Ku波长衰减系数(kKu)和降水率(R)来看,当Gamma分布的形状因子μ分别取2、3和4时,龙门地区对四个参数的反演都能得到较为稳定准确的结果,相对误差基本<10%。而就kKa和5~40 mm·h^-1的降水率而言,那曲和龙门有很大的不同,在龙门当μ取3时相对误差最小,都在0值附近波动,而那曲则要需要μ值在4和6附近才能使得相对误差达到最小。
