| Summary: | 碩士 === 國立中央大學 === 大氣科學學系 === 105 === Polarimetric radar system provide high temporal and high-spatial resolution data and disdrometers can show the characteristic of Drop Size Distribution (DSD). Base on the information of disdrometer data, dual Polarimetric Radar data can be used to retrieve the parameters of DSD. The DSD varies from case to case or even in the different periods of a case. Therefore, understanding the variety of DSD is helpful to improve the accuracy of DSD parameters retrieved by radar.
The data of Taiwan Experimental Atmospheric Mobile Radar (TEAM-R) and Impact Disdrometer (JWD) observations collected in Taipei Summer Storm Experiment (TASSE) during early September of 2016 was used. From the disdrometer data, the three Gamma distribution parameters including the intercept N_0, the shape (μ) and rate (Λ) parameters can be calculated through moment method. Through the scattering calculation the relations between polarimetric variables and gamma distribution parameters can be derived. The constrain relation between the shape (μ) and rate (Λ) parameters is necessary to retrieve the three Gamma distribution parameters from polarmetric variables Z_DR and K_dp. In this study, two constrain relations were applied: first one is the well known relation proposed by Brandes et al, , the second one is from the statistics during the three days disdrometer observation of thunderstorms in TASSE. The retrieved three dimensional distribution of DSD are compared between these two retrieval applications. A third approach is directly fitting the DSD Gamma parameters with the polarimetric variables to retrieve three Gamma parameters from fitting functions. Because the limitation of very large drop in disdrometer, the third method is not be able to retrieve reasonable DSD at large Z_DR situation.
The retrieved three dimensional DSDs in different stages of thunderstorm reveal very bounty microphysical information. The relatively smaller concentration and drop diameter were found in the initiation stage, while the deep convection was developed one to two order of magnitude of concentration were found through the convective core. More cases studies and much longer statistics and validation should be conducted in the near future.
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