Fall velocity–diameter relationships for four different snowflake types(dendrite,plate,needle,and graupel) were investigated in northeastern South Korea,and a new algorithm for classifying hydrometeors is proposed fo...Fall velocity–diameter relationships for four different snowflake types(dendrite,plate,needle,and graupel) were investigated in northeastern South Korea,and a new algorithm for classifying hydrometeors is proposed for distrometric measurements based on the new relationships.Falling ice crystals(approximately 40 000 particles) were measured with a two-dimensional video disdrometer(2DVD) during a winter experiment from 15 January to 9 April 2010.The fall velocity–diameter relationships were derived for the four types of snowflakes based on manual classification by experts using snow photos and 2DVD measurements:the coefficients(exponents) for different snowflake types were 0.82(0.24) for dendrite,0.74(0.35) for plate,1.03(0.71) for needle,and 1.30(0.94) for graupel,respectively.These new relationships established in the present study(PS) were compared with those from two previous studies.Hydrometeor types were classified with the derived fall velocity–diameter relationships,and the classification algorithm was evaluated using 3 × 3 contingency tables for one rain–snow transition event and three snowfall events.The algorithm showed good performance for the transition event:the critical success indices(CSIs) were 0.89,0.61 and 0.71 for snow,wet-snow and rain,respectively.For snow events,the algorithm performance for dendrite and plate(CSIs = 1.0 and 1.0,respectively) was better than for needle and graupel(CSIs = 0.67 and 0.50,respectively).展开更多
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
基金funded by the Korea Meteorological Administration Research and Development Program under Grant KMIPA2015-1010
文摘Fall velocity–diameter relationships for four different snowflake types(dendrite,plate,needle,and graupel) were investigated in northeastern South Korea,and a new algorithm for classifying hydrometeors is proposed for distrometric measurements based on the new relationships.Falling ice crystals(approximately 40 000 particles) were measured with a two-dimensional video disdrometer(2DVD) during a winter experiment from 15 January to 9 April 2010.The fall velocity–diameter relationships were derived for the four types of snowflakes based on manual classification by experts using snow photos and 2DVD measurements:the coefficients(exponents) for different snowflake types were 0.82(0.24) for dendrite,0.74(0.35) for plate,1.03(0.71) for needle,and 1.30(0.94) for graupel,respectively.These new relationships established in the present study(PS) were compared with those from two previous studies.Hydrometeor types were classified with the derived fall velocity–diameter relationships,and the classification algorithm was evaluated using 3 × 3 contingency tables for one rain–snow transition event and three snowfall events.The algorithm showed good performance for the transition event:the critical success indices(CSIs) were 0.89,0.61 and 0.71 for snow,wet-snow and rain,respectively.For snow events,the algorithm performance for dendrite and plate(CSIs = 1.0 and 1.0,respectively) was better than for needle and graupel(CSIs = 0.67 and 0.50,respectively).
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.