Rain microstructure retrievals using 2-D video disdrometer and C-band polarimetric radar

摘要

Measurements using the 2-D video disdrometer (2DVD) taken during a heavyrainfall event in Huntsville, Alabama, are analysed. The 2DVD images wereprocessed to derive the rain microstructure parameters for each individualdrop, which in turn were used as input to the T-matrix method to compute theforward and back scatter amplitudes of each drop at C-band. The polarimetricradar variables were then calculated from the individual drop contributionover a finite time period, e.g., 1 min. The calculated co-polarreflectivity, differential reflectivity, specific differential propagationphase and the co-polar correlation coefficient were compared withmeasurements from a C-band polarimetric radar located 15 km away. Anattenuation-correction method based on the specific differential propagationphase was applied to the co-polar and differential reflectivity data fromthe C-band radar, after ensuring accurate radar calibration. Time seriescomparisons of the parameters derived from the 2DVD and C-band radar datashow very good agreement for all four quantities, the agreement beingsometimes better than the computations using the 1-min drop sizedistribution and bulk assumptions on rain microstructure (such as meanshapes and model-based assumptions for drop orientation). The agreement isparticularly improved in the case of co-polar correlation coefficient sincethis parameter is very sensitive to variation of shapes as well asorientation angles. The calculations mark the first attempt at utilizingexperimentally derived "drop- by-drop" rain microstructure information tocompute the radar polarimetric parameters and to demonstrate the value ofutilizing the 2-D video disdrometer for studying rain microstructure undervarious precipitation conditions. Histograms of drop orientation angles aswell as the most probable drop shapes and the corresponding variations werealso derived and compared with prior results from the 80 m fall "artificialrain" experiment.