A major issue in radar quantitative precipitation estimation is the contamination of radar echoes by non-meteorological targets such as ground clutter,chaff,clear air echoes etc.In this study,a fuzzy logic algorithm f...A major issue in radar quantitative precipitation estimation is the contamination of radar echoes by non-meteorological targets such as ground clutter,chaff,clear air echoes etc.In this study,a fuzzy logic algorithm for the identification of non-meteorological echoes is developed using optimized membership functions and weights for the dual-polarization radar located at Mount Sobaek.For selected precipitation and non-meteorological events,the characteristics of the precipitation and non-meteorological echo are derived by the probability density functions of five fuzzy parameters as functions of reflectivity values.The membership functions and weights are then determined by these density functions.Finally,the nonmeteorological echoes are identified by combining the membership functions and weights.The performance is qualitatively evaluated by long-term rain accumulation.The detection accuracy of the fuzzy logic algorithm is calculated using the probability of detection（POD）,false alarm rate（FAR）,and clutter–signal ratio（CSR）.In addition,the issues in using filtered dual-polarization data are alleviated.展开更多
Using China New Generation Weather Radar （CINRAD） level-Ⅱ data, the original algorithms for removing isol-ated non-meteorological echoes and ground clutters in radar data, which have been applied to Weather Surveil...Using China New Generation Weather Radar （CINRAD） level-Ⅱ data, the original algorithms for removing isol-ated non-meteorological echoes and ground clutters in radar data, which have been applied to Weather Surveillance Radar-1988 Doppler （WSR-88D） in the USA and Severe Weather Automatic Nowcast （SWAN） system in China, are modified and improved. To remove isolated non-meteorological echoes, the new algorithm introduces a constraint parameter （Po） to distinguish whether a window of 5 x 5 points is isolated as external echoes. A statistical analysis of 150 radar scans （5 cases, with each case comprising 30 scans） under three different echo types （small-scale convec-tion, typhoon, and large-scale synoptic system） shows that the constraint parameter Po ≤ 0.167 is suitable for remov- ing isolated non-meteorological echoes while preserving the edge of meteorological echoes. A new parameter, NDZ, which promotes the ability of the algorithm to identify the ground clutters appearing at two adjacent elevation angles, is constructed based on the vertical continuity of reflectivity. These improved algorithms are tested for four cases （three cases of isolated non-meteorological echoes and one case of ground clutters）. Based on the statistics of 232 volume scans of radar data （on a temporal resolution of 1 h） measured at Nanchang station from 0000 UTC 5 to 1600 UTC 14 March 2015, it is found that the improved algorithms not only eliminate most （over 95% under clear-sky conditions） of the isolated non-meteorological echoes and ground clutters （including those appearing at two adjacent elevation angles）, but also well preserve the structure of meteorological echoes （storms）.展开更多
针对2013年早春期间一次大范围冰雹天气过程,采用NCEP再分析资料、探空资料及雷达资料对此次冰雹过程的成因及特征进行分析。结果表明：此次冰雹天气的影响系统主要是500 h Pa高空槽、西南涡、高空急流、低空急流,地面辐合线及地面冷锋...针对2013年早春期间一次大范围冰雹天气过程,采用NCEP再分析资料、探空资料及雷达资料对此次冰雹过程的成因及特征进行分析。结果表明：此次冰雹天气的影响系统主要是500 h Pa高空槽、西南涡、高空急流、低空急流,地面辐合线及地面冷锋;在降冰雹时,大气呈上干下湿的状态,700 h Pa和500 h Pa温差从06时逐渐增大,18时达到最大,500 h Pa与850 h Pa假相当位温差超过16℃,0～6 km的垂直风切变为26.3 m/s,K指数达到了34℃,SI指数为-2.7;在降大冰雹的回波中出现三体散射、弱回波区或有界弱回波区、强而高大的回波墙和悬垂回波,50 d Bz的反射率因子的顶高超过-20℃层等特征。在降冰雹前,垂直液态积分含水量迅速下降,可用于冰雹的预警,同时,中层存在超过30 m/s的大风速带,并伴随明显的冷平流与强的风切变;雷暴初生源地均在低海拔地区,受黔东南地形的影响雷暴分裂东移,地势抬升及暖湿空气的迎风坡有利于降雹。展开更多
基金supported by a grant(14AWMP-B079364-01) from Water Management Research Program funded by Ministry of Land,Infrastructure and Transport of Korean government
文摘A major issue in radar quantitative precipitation estimation is the contamination of radar echoes by non-meteorological targets such as ground clutter,chaff,clear air echoes etc.In this study,a fuzzy logic algorithm for the identification of non-meteorological echoes is developed using optimized membership functions and weights for the dual-polarization radar located at Mount Sobaek.For selected precipitation and non-meteorological events,the characteristics of the precipitation and non-meteorological echo are derived by the probability density functions of five fuzzy parameters as functions of reflectivity values.The membership functions and weights are then determined by these density functions.Finally,the nonmeteorological echoes are identified by combining the membership functions and weights.The performance is qualitatively evaluated by long-term rain accumulation.The detection accuracy of the fuzzy logic algorithm is calculated using the probability of detection（POD）,false alarm rate（FAR）,and clutter–signal ratio（CSR）.In addition,the issues in using filtered dual-polarization data are alleviated.
基金Supported by the Jiangxi Provincial Department of Science and Technology project(20171BBG70004)Open Project of the State Key Laboratory of Severe Weather,Chinese Academy of Meteorological Sciences(2016LASW-N11)National Natural Science Foundation of China(41575098)
文摘Using China New Generation Weather Radar （CINRAD） level-Ⅱ data, the original algorithms for removing isol-ated non-meteorological echoes and ground clutters in radar data, which have been applied to Weather Surveillance Radar-1988 Doppler （WSR-88D） in the USA and Severe Weather Automatic Nowcast （SWAN） system in China, are modified and improved. To remove isolated non-meteorological echoes, the new algorithm introduces a constraint parameter （Po） to distinguish whether a window of 5 x 5 points is isolated as external echoes. A statistical analysis of 150 radar scans （5 cases, with each case comprising 30 scans） under three different echo types （small-scale convec-tion, typhoon, and large-scale synoptic system） shows that the constraint parameter Po ≤ 0.167 is suitable for remov- ing isolated non-meteorological echoes while preserving the edge of meteorological echoes. A new parameter, NDZ, which promotes the ability of the algorithm to identify the ground clutters appearing at two adjacent elevation angles, is constructed based on the vertical continuity of reflectivity. These improved algorithms are tested for four cases （three cases of isolated non-meteorological echoes and one case of ground clutters）. Based on the statistics of 232 volume scans of radar data （on a temporal resolution of 1 h） measured at Nanchang station from 0000 UTC 5 to 1600 UTC 14 March 2015, it is found that the improved algorithms not only eliminate most （over 95% under clear-sky conditions） of the isolated non-meteorological echoes and ground clutters （including those appearing at two adjacent elevation angles）, but also well preserve the structure of meteorological echoes （storms）.
文摘针对2013年早春期间一次大范围冰雹天气过程,采用NCEP再分析资料、探空资料及雷达资料对此次冰雹过程的成因及特征进行分析。结果表明：此次冰雹天气的影响系统主要是500 h Pa高空槽、西南涡、高空急流、低空急流,地面辐合线及地面冷锋;在降冰雹时,大气呈上干下湿的状态,700 h Pa和500 h Pa温差从06时逐渐增大,18时达到最大,500 h Pa与850 h Pa假相当位温差超过16℃,0～6 km的垂直风切变为26.3 m/s,K指数达到了34℃,SI指数为-2.7;在降大冰雹的回波中出现三体散射、弱回波区或有界弱回波区、强而高大的回波墙和悬垂回波,50 d Bz的反射率因子的顶高超过-20℃层等特征。在降冰雹前,垂直液态积分含水量迅速下降,可用于冰雹的预警,同时,中层存在超过30 m/s的大风速带,并伴随明显的冷平流与强的风切变;雷暴初生源地均在低海拔地区,受黔东南地形的影响雷暴分裂东移,地势抬升及暖湿空气的迎风坡有利于降雹。
