南京雷达数据的一致性分析和订正

Consistency analysis and correction for observations from the radar at Nanjing

中文关键词:  TRMM PR  南京雷达  反射率因子  拟合订正

英文关键词:TRMM PR  Nanjing Radar  Reflectivity factor  Fitting correction

中文摘要:

      运用几何匹配法处理了南京雷达和热带测雨卫星(Tropical Rainfall Measuring Mission,TRMM)上搭载的测雨雷达(Precipitation Radar,PR)的反射率因子探测资料,统计分析了2008—2013年共245个时次的匹配数据。 以TRMM PR工作多年持续稳定特征为参照,揭示了南京雷达6 a的探测资料情况。结果表明,南京雷达和TRMM PR探测降水具有较强的一致性,6 a时间里南京雷达存在一定的运行不稳定情况,南京雷达0℃层以下数据存在“3段特征”:时段Ⅰ2008年1月—2010年3月,时段Ⅱ2010年3月—2013年5月,时段Ⅲ2013年5—10月。3个时段之间整体回波强度有差异,时段Ⅱ整体回波强度比时段Ⅰ、Ⅲ偏小2—3 dB;而3个时段内的回波整体保持相对的稳定,南京雷达与TRMM PR的回波强度差值随回波强度的变化呈线性关系;在中低回波值时TRMM PR比南京雷达大,在中高回波值时南京雷达比TRMM PR大。基于两种雷达回波强度值的拟合关系,对南京雷达的反射率因子进行分段线性订正,有效地改善了南京雷达的一致性:3个时段回波强度的整体差异减小到0.75 dB以内;在245个匹配时次和105894个匹配点上南京雷达和TRMM PR的反射率因子的相关系数增大,南京雷达-TRMM PR值的标准差减小。

英文摘要:

      The geometry-matching method is applied to analyze the reflectivity from the radar deployed at Nanjing (GR) and that from the Precipitation Radar (PR) onboard the Tropical Rainfall Measuring Mission (TRMM). In total 245 match-up cases for the period from 2008 to 2013 are obtained and compared using statistical analysis methods. Based on the stability characteristic of TRMM PR, the consistency of radar measurements at Nanjing during the 6-year period is evaluated. The results reveal that the TRMM PR is well corresponding to GR in detecting rainfall. However, GR demonstrated a certain degree of unstable performance from 2008 to 2013. The below-BB-height data from the radar at Nanjing show a "three-stage" feature, i.e., Stage Ⅰ from January 2008 to March 2010, Stage Ⅱ from March 2010 to May 2013,and Stage Ⅲ from May 2013 to October 2013. Distinct differences in overall reflectivity factor can be found among the three stages, and overall reflectivity factor in StageⅡ is smaller than StagesⅠand Ⅲ by 2-3 dB, but overall reflectivity within each stage remains relatively stable. The difference inreflectivity factor between measurements from the radar at Nanjing and that from the TRMM PR varies with increases in echo intensity and shows a linear relationship. The reflectivity factor of TRMM PR surpasses that of radar measurements at Nanjing when intensity echoes are low, while for high intensity echoes the reflectivity factor from the radar at Nanjing surpasses that from TRMM PR. Based on the fitting relationship between reflectivity factors of the two radars, a multiple-segment piecewise linear correction is applied to the reflectivity from the radar at Nanjing. This method can effectively improve the consistency of data from the radar at Nanjing. The difference in overall reflectivity among the three stages is reduced to less than 0.75 dB, while correlation coefficients of mean reflectivity factor for the 245 match-up cases and the 105894 match-up points are both improved. Standard deviations of reflectivity differences (GR-TRMM PR) for the 245 match-up cases and the 105894 match-up points are reduced, too.