Analysis On The Relationship Between Narrow Bipolar Events And Thunderstorms In Jianghuai Region

Narrow Bipolar events(NBEs),a distinct class of intracloud discharge events because of its ability to emit Very Low-Frequency/Low-Frequency(VLF/LF)and High-Frequency/Very High-Frequency(HF/VHF)radiation are observed on the ground and on space.NBEs show a large difference from normal lightning in many aspects such as its isolation,radiation intensity and the relationship with thunderstorm convection.The relationship between narrow bipolar events(NBEs)and thunderstorm parameters and the isolation and radiation intensity of NBEs in different regions of thunderstorms on August 2014 in Jianghuai region was investigated based on the satellite-based NCEP/CPC Global IR data,TRMM PR/TIM data,and the ground-based radar and lightning detection data.The correlation between NBEs and maximum height of 30 dBZ radar echo and lightning frequency was also investigated.The results are as following:1.A great amout of NBEs were positive polarity,about 8%of NBEs were negative.By analyzing the height of NBEs,the results show positive NBEs mainly occurred between 8-16 km.The average height is 12.17 km.Negative NBEs occurred between 16-18 km,and the average height is 16.25 km.NBEs concentrate in the period from 5:00 to 13:00 and more compact than ordinary lightning.2.By analyzing the relationship between NBEs and radar echo,the results show that NBEs mainly clusterred in individual thunderstorms,not all thunderstorms.It is found that NBEs mainly located in the area around 35 dBZ of radar echo,and NBEs mainly occurrd in the area that radar echo larger than 15 dBZ in radar profile.3.NBEs mainly occurred in the area with cloud top temperature of 210-220K,and lightning mainly occurred at the cloud top temperature of 210-230K.Lightning almost never seen in the region where the cloud temperature is larger than 250K.4.By analyzing the relationship between NBEs and maximum height of 30dBZ radar echo and the frequency of lightning,the results also show that NBEs mainly occurred during the high frequency of lightning,and the correlation between NBEs and lightning frequency is stronger than that between NBEs and maximum height of 30 dBZ radar echo.5.The investigate of NBE isolation and the pulse peak intensity of VLF/LF band indicates that most isolated NBEs occurred in the early stage of thunderstorm,and NBEs occurred in the region where radar echo below 15 dBZ was most isolated.The radiation intensity of NBEs which occurred following ordinary lightning are the strongest.6.In combination with three stages of thunderstorms,it was found that NBEs mainly occurred during the development and mature stage of thunderstorms,and were less likely to occur during dissipated stage.