应用气象学报 (May 2021)
Quality Control and Evaluation on Non-cloud Echo of Ka-band Cloud Radar
Abstract
Aiming at non-cloud echoes in Ka-band millimeter wave cloud radar observation, an improved data quality control method is proposed. Using the observation at Pinghe of Fujian from September 2018 to August 2020, the quality of the radar is quantitatively evaluated to study the actual impact of data quality control on cloud-precipitation detection. The non-cloud echoes show the characteristics of weak radar reflectivity factor (Z) and strong depolarization ratio (R) at Pinghe. But statistics show that there is difference from those of Qinghai-Tibet Plateau or Guangdong. Therefore, using the radar reflectivity factor (Z) less than -5 dBZ and linear depolarization ratio (R) greater than -22 dB as the judgment condition, and with the aid of filtering, non-cloud echoes can be effectively filtered. At the same time, a typical example is used to verify the effectiveness of the algorithm. Non-cloud echoes have a significant effect on the detection of cloud below 3 km, especially weak echoes. Non-cloud echoes account for 9.20% of all radar reflectivity factor samples, and 34.05% of all radar linear depolarization ratio samples. For the weak echo below -5 dBZ, the impact of non-cloud echoes is more significant, which accounts for 67.20% of all radar reflectivity factor sample. The detection rate of non-cloud echoes matter is closely related to the radar sensitivity, and the overall decrease with the height increaseing. The detection rate of non-cloud echoes decreases with the height increaseing. Meanwhile, non-cloud echoes have a certain relationship with the boundary layer, with an obvious diurnal change trend. From afternoon to midnight, due to strong turbulent activity, the detection rate of non-cloud echo matter is also higher, and the peak occurs at 1700 BT. From midnight to sunrise, due to the weakening of turbulent motion, the detection rate of non-cloud echo gradually decreases, and the lowest value occurs at 0400 BT. Non-cloud echoes have a significant effect on the vertical distribution of cloud precipitation. After quality control, the number of samples at the height of 0.12-2.5 km for radar reflectivity factor decrease by 17.68%, and the number of samples at the height of 0.12-4 km for radar linear depolarization ratio decrease by 14.29%.
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