Consistency analysis and correction for observations from the radar at Nanjing

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.