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基于雨滴谱参数反演的C波段双偏振雷达降水类型分类方法

Classification Method of Rain Types Based on Raindrop Size Distribution Retrieval from C-Band Dual-Polarization Radar

  • 摘要: 降水类型分类对分析区域降水微物理特征、多源降水融合误差模型的构建以及雷达定量测量降水估计等都很重要。本文基于2015~2016年南京信息工程大学C波段双偏振雷达数据和南京地区滴谱仪观测资料,提出一种适用于南京地区的雷达降水类型分类方法,并对降水类型分类结果进行对比验证。首先,基于滴谱仪降雨率时序数据、地基雷达反射率因子平面位置显示数据和地基雷达反射率因子时间—高度显示数据,筛选出36次典型层状和对流降水过程。随后,统计3个滴谱仪站点典型层状(对流)降水的雨滴谱(DSD)参数,拟合得到适用于南京地区的降水类型分类线。将基于滴谱数据统计拟合的分类线应用于基于变分法反演的地基雷达DSD参数,进行地基雷达降水类型分类。根据典型层状(对流)过程降水类型分离指数的时间—高度分布,并对比星载双频测雨雷达(DPR)降水分类产品,对分类效果进行验证。最后,将分类结果应用于雷达分类定量降水估计,进一步说明降水分类的应用效果。结果表明,南京地区3个滴谱仪站点的拟合分类线非常一致,3个站点的典型层状(对流)过程均能够很好地分离在分类线两侧;与DPR降水分类产品进行对比分析,发现南京地区分类线的分类效果相对于其他典型降水分类方法,对层状和对流降水的识别率整体最高,分别为84.56%和72.64%;基于降水分类的雷达定量降水估计的测雨精度均优于未分类的测雨公式,且基于差分传播相移率的测雨公式R(KDP)在四种分类测雨公式中整体性能最优,基于水平反射率因子的测雨公式R(ZH)在层状云降水反演中性能最优,基于差分传播相移率的测雨公式R(KDP)在对流云降水反演中性能最优,基于水平反射率因子和差分反射率的测雨公式R(ZH, ZDR)对原有总体测雨公式降水精度的提升最为明显。

     

    Abstract: Understanding the classification of rain types is crucial for analyzing the microphysical characteristics of regional precipitation, constructing multisource precipitation fusion error models, and enhancing radar-based quantitative precipitation estimation. This study proposes a radar-based rain-type classification method tailored for the Nanjing area using data from C-band dual-polarization radar and raindrop disdrometer observations collected by the Nanjing University of Information Science and Technology from 2015 to 2016. The results were compared and verified with other classification methods. First, 36 typical stratiform and convective precipitation processes were filtered out based on the time-series data of rainfall rates from raindrop disdrometers, ground-based radar reflectivity factor plane position indication, and time–height indication. The DSD (raindrop size distribution) parameters of typical stratiform (convective) precipitation at the three disdrometer stations were statistically analyzed, and a precipitation type classification line suitable for the Nanjing area was fitted. Apply the classification line, fitted based on raindrop disdrometer data, to the DSD parameters retrieved from ground-based radar using a variational method for ground-based radar precipitation type classification. By analyzing the time–height distribution of the separation index for precipitation types in typical stratiform (convective) processes and comparing with the precipitation classification products from the DPR (dual-frequency precipitation radar) on satellites, the classification effectiveness was validated. Finally, the classification results were applied to quantitative radar-classification precipitation estimation to further illustrate the application of precipitation classification. The results show that the fitting classification lines of the three raindrop disdrometer stations in Nanjing were consistent. Stratiform and convective precipitation processes could be effectively separated by this line. A comparative analysis with the DPR precipitation classification products revealed that the proposed classification method for Nanjing showed higher accuracy in distinguishing between stratiform and convective precipitation compared to other typical precipitation classification methods, with recognition rates for stratiform and convective precipitation of 84.56% and 72.64%, respectively. Furthermore, radar quantitative precipitation estimation based on this rain-type classification demonstrated better performance than traditional unclassified rain measurement formulas. The rainfall estimation formula R(KDP) based on the specific differential phase demonstrated the best overall performance among the four classification rainfall estimation formulas. The formula R(ZH) based on the horizontal reflectivity factor showed the best performance in stratiform cloud precipitation retrieval, while the formula R(KDP) based on the specific differential phaseperformed best in convective cloud precipitation retrieval. The rainfall estimation formula R(ZH, ZDR) based on both the horizontal reflectivity factor and the differential reflectivity showed the most significant improvement in precipitation accuracy compared to the original overall rainfall estimation formula.

     

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