Identification Method of Hail Weather Based on Fuzzy-logical Principle

Based on previous researches and hail warning indexes in Hebei Province, five main radar identification indices for hail detection are given: Storm maximum reflectivity, storm maximum vertical integrated liquid water content, echo top, vertical integrated liquid (VIL) density and storm center height. The corresponding membership functions of each identification index in different seasons are also calculated. Identification method of hail on fuzzy-logical principles is established adopting the equal weight coefficient method.Based on radar mosaic data, disaster report of hail and route sounding data, 103 hail cases from 2008 to 2012 in North China are statistically analyzed and tested. The hitting rate of hail, the leading time and position of hail are given.The hitting rate, the false alarm rate and the critical success index of regional hail in North China are 73.9%, 36.4% and 51.9%, respectively, and all the scattered hail in Shijiazhuang can be identified. When the radar identification index is greater, the corresponding probability and the maximum diameter of hail is also bigger. The identification index is above 0.85 when the maximum diameter is more than 30 mm. On the spatial distribution, the area of identified storm and hail station is consistent. The hail station is nearby and around the corresponding storm monomer. The omission of hail occurs mostly in Zhangjiakou and Chengde, which may be caused by radar band range and regional characteristics. In contrast of single factor identification, the accuracy rate of comprehensive recognition is improved, and it also has a high degree of automation. The first time when the recognition criterion continuous is greater than the threshold value is always ahead of the epoch of hail, and the mean leading time is 30 minutes. By the recognition of hail in Shijiazhuang, the hitting rate, the false alarm rate and the critical success index of radar own recognition software are 100%, 78.2% and 21.8%, respectively, while the result of identification method on fuzzy-logical principles reaches 100%, 44.4% and 55.6%. Obviously, all hails are correctly identified, while the false alarm rate is significantly reduced, and the critical success index is increased.In summary, the automatic identification method based on fuzzy-logical principles is efficient and feasible, with more automatic algorithm. It can reduce the forecaster workload and has important practical guiding significance for short-term forecasting, nowcast warning and system development.