Classification of cloud types using VPR (Vertical Profile of Reflectivity) in Korea

The purpose of this study is to improve the accuracy of quantitative precipitation estimation (QPE) using weather radars. To estimate the quantitative precipitation using Busan radar and Gosan radar, rainfall rate and cumulative rainfall amount by Z = 200R1.6, total Z-R relationships, and classified Z-R relationships were calculated and compared with each one. The Z-R relationships with cloud types were calculated using vertical profile of reflectivity (VPR).

The VPR parameters (BBP and BBT) were identified and applied to classify the cloud types. Bright band was determined when BBP is located between 2 km and 6 km (bright band in mid-latitude generally exists between 2 km and 6 km) and its thickness is within 2 km. The top of bright band was designated as a decreasing 4 dB above maximum reflectivity height and the height of bright band bottom was regarded as a decreasing 2 dB below (Burrows, 2001). Vertical lapse rate of reflectivity was defined as the ratio of the reflectivity at the BBP to the reflectivity at 3 km above the BBP. It turns out that stratiform precipitation can be defined when the lapse rate is greater than 3.5 dB per kilometer (3.5 dB/km). VPR does not fall in the previous threshold conditions when the maximum reflectivity is greater than 40 dBZ and the thickness of bright band (BBT) has wider than 2 km in convective cases. In addition, vertical lapse rates of convective type were smaller than 3.5 dB per kilometer (3.5 dB/km).

As a result of the algorithm, the errors in the rainfall estimation were reduced and the accuracy of quantitative precipitation estimation was improved about 46 % and 10% at both radars.