Observation And Simulation Of Lightning Electromagnetic Transmission Characteristics By Using JASA

During the occurrence of lightning,a strong current and electromagnetic pulse(LEMP)are formed,which are not only the direct disaster-causing factors of thunderstorm disasters,but also provide necessary information for the inversion of lightning current and other parameters,observation of thunderstorm process,and even the construction of the global lightning positioning system.It is of great significance to the study of lightning physics and the prevention and control of thunderstorm disasters.Therefore,the research work on the transmission characteristics of lightning electromagnetic waves has always received great attention from the academic community.This paper uses the lightning observation and positioning system(hybrid longbaseline Jianghuai Tiandian array)independently developed by the research group based on lightning low-frequency/very low-frequency electromagnetic wave signals to compare and statistically analyze the electromagnetic wave data of cloud lightning and ground lightning,combined with numerical simulation As a result of the study,the variation characteristics of the amplitude and delay of cloud-to-ground lightning electromagnetic waves during the transmission process in the ground-ionosphere waveguide cavity were explored.The main conclusions are as follows:(1)A method for analyzing the relative field strength attenuation of concentric circles at equal distances is proposed.Using lightning pulse waveforms recorded by modern lightning detection networks,this paper presents a method for measuring the propagation decay exponent of lightning pulse waveforms using the concentric circle technique.This method does not require accurate calibration of the site gain of the sensor,and uses the fixed distance of the lightning pulse to one station and the change of the distance to another station to explore the characteristics of the attenuation of the lightning pulse waveform with distance.(2)Study the transmission law of cloud and ground lightning amplitude attenuation and invert the ground conductivity in the observation area.Using this method to statistically analyze nearly 200,000 cases of cloud and ground lightning electromagnetic wave data observed by the hybrid long-baseline Jianghuai Tiandian array,we found that the electromagnetic wave amplitude of lightning in the actual transmission process presents a good exponential decay characteristic with distance y=ax-b,while the attenuation indices are cloud flash b=1.02 and ground flash b=1.13;at the same time,under the same propagation path,the cloud flash pulse suffers less attenuation than the ground flash pulse;the study also found that even if the propagation attenuation Similarly,the ratio of electric field gain also has large fluctuations.This result shows that even if the antenna sensor is calibrated for site gain,the gain coefficient of the actual single measurement may fluctuate greatly relative to the calibrated gain coefficient.Comparing the characteristic parameters of lightning electromagnetic wave radiation attenuation observed by the hybrid long-baseline Jianghuai Tiandian array with the results of numerical simulation,the electromagnetic wave amplitude attenuation is affected by the ground conductivity.According to the field strength attenuation factor,the conductivity of the Jianghuai area is inferred to be 5×10-3 S/m～10×10-3 S/m,this conclusion is in good agreement with the measured earth conductivity in the Huaihe River Basin.(3)The delay characteristics of the lightning transmission process are studied and a reference is provided for the improvement of the JASA positioning algorithm.In the transmission process of lightning electromagnetic waves,affected by the transmission effect,there is a certain delay,which in turn affects the positioning accuracy and efficiency of the lightning positioning network based on time difference of arrival(TOA).Using the large-sample lightning events observed by the mixed long-baseline JAC Tiandian array and the measured lightning electromagnetic wave waveform data,the time delay of lightning electromagnetic waves in the long-distance transmission process was statistically analyzed.Taking the LT station as an example,it was determined that The time delay parameter is 1.7μs per 100 kilometers;using this time delay parameter,the positioning results of the lightning location station network are corrected.By comparing and analyzing the positioning results before and after correction,it can be found that the delay parameter can effectively improve the positioning accuracy of the lightning positioning system,and the better the improvement effect is as the distance increases.At the same time,it is worth pointing out that using the lightning location method with a mixture of long and short baselines can effectively compensate for the rapid decline in the location accuracy of lightning events outside the short-baseline location station network.The long-short baseline mixed positioning method provides an effective solution for high-precision positioning of a lightning positioning station network with large spacing.In addition,this paper establishes an electromagnetic model of lightning electromagnetic transmission in COMSOL,compares and analyzes the mixed longbaseline Jianghuai Tiandian array field observation data and numerical simulation research results,and verifies the field observation lightning transmission attenuation law,and also through the field strength attenuation factor The time delay factor and other characteristic parameters provide a new way of thinking for the inversion of ground conductivity.The research work of this paper proposes a method of measuring the propagation attenuation index of lightning pulse waveform with concentric circles,and uses largescale measured data to reveal the attenuation characteristics of amplitude and delay during the transmission of lightning electromagnetic waves,which provides a new method for the study of lightning electromagnetic wave transmission characteristics.The research idea has enriched the academic community’s understanding of the characteristics and influencing factors of lightning electromagnetic wave transmission.