Guangshu Zhang

Magnetic field measuring system and current retrieval in artificially triggering lightning experiment

A magnetic field measuring system with two rectangular loops perpendicular toeach other is developed and used to detect the total horizontal magnetic field producedby lightning discharges. Two sets of antenna with low gain and high gain aredesigned separately in order to obtain both small and large signals. The systemwas tested experimentally in a high-voltage laboratory, and the results showthat the system is reliable, and the waveforms detected by the system are very similarto the source current. The corresponding maximum current that can be measuredby the system with low gain antenna and high gain antenna locating at a distanceof 60 m from a lightning channel, is about 84.4 kA and 37.7 kA, respectively.For artificially triggered lightning flashes the magnetic field waveforms detectedat 60 m from the channel reflect quite well the channel base currents. UsingAmpere’s law of magnetostatics, the inferred currents from the magnetic fieldsfor three artificially triggered lightning return strokes were 39.8 kA, 29.1 kA and43 kA, respectively, which are close to the directly measured results of 41.6 kA,29.6 kA and 38 kA at the base of the discharge channel. The system can be a usefultool in the research of close electromagnetic environment of lightning flashes.

Study of charge structure and radiation characteristic of intracloud discharge in thunderstorms of Qinghai-Tibet Plateau

The comprehensive observations on lightning discharges were conducted in Naqu area of Qinghai-Tibet Plateau in summer of 2002. The electric structures of thunderstorms and the characteristics of lightning discharges at initial stage were analyzed by using the observation data. The results show that most of intracloud (IC) lightning flashes were polarities inverted in thunderstorms with tripole electric charge structure and occurred between negative charge region located in the middle of the thunderstorm and positive charge region located at the bottom of the thunderstorm. The radiation characteristics of discharge processes in cloud with longer lasting time involved in Cloud-to-Ground (CG) lightning flashes were similar to that of IC discharges. A lot of radiation pulses were produced in these discharge processes. Because the IC discharges took place at the bottom of thundercloud and were near the ground, they may produce more serious damage to equipment on the ground therefore should not be neglected in lightning protection.

Experimental study on location accuracy of a 3D VHF lightning-radiation-source locating network

This paper reports the investigation of the location accuracy of a three-dimensional (3D) lightning-radiation-source locating system using sounding balloon measurements. By comparing the information from the balloon-borne VHF transmitter flight path and locations using simple geometric models, the location uncertainties of sources both over and outside the network were estimated. For radiation sources inside the network and below an altitude of 7 km, the horizontal uncertainty was 12–48 m and the total mean value was 21 m (rms), and the vertical uncertainty was 20–78 m and the total mean value was 49 m (rms). Outside the network, the location uncertainties increased with distance. The geometric model showed that range and altitude errors increased as a function of the range squared whereas the range errors increased parabolically with distance, and that was confirmed by the covariance calculation results. The standard deviation was used inside the network and covariance was used outside the network. The results indicated that location errors from a simple geometric model exhibited good agreement with standard experimental data. The geometry of the network, set of measurements, and calculation method were verified as suitable. The chi-square values of the least squares goodness of fit algorithm were verified and the timing error (Δtrms) of the fitting formula was estimated. The distribution of the chi-square values was less than 5, corresponding to a timing error of 50–66 ns (rms).

Analyzing the transmission structures of long continuing current processes from negative ground flashes on the Qinghai‐Tibetan Plateau

This paper presents a new overlap and progressive method using either a one-point charge model or a point dipole model for studying the electric field change data of lightning and tests the suitability of the proposed method by analyzing the slow electric field change of the long continuing current data from two negative ground flashes. The current measurements of the ground flashes are from the Composite Observing Experiment for Lightning project carried out in the Datong region of Qinghai Province, China, in 2009, obtained from field observations synchronized through high-precision GPS clocks at seven observation stations. Analysis shows that the time-averaged current can reach 800 A, and the current intensity relates to the height of the top of the return stroke before the continuing current process. The two current processes studied in this work neutralized a large amount of negative charge, 39.5C and 60.8C, respectively. The neutralized charges from the negative charge layer are typically at 2.5–4.7 km above ground. The intracloud transition of the positive leader is a complex process, and the horizontal propagation of the positive leader plays an important role in current duration as well as horizontally influencing the center of the electrical dipole moment with an obvious change of up to 3.0 km. The proposed analysis method is very useful compared to previous methods in terms of determining infinitesimal changes in long continuing currents. This works new analysis method will help increase understanding of the fine physical processes of long continuing current processes.

Correlation Analysis between Initial Preliminary Breakdown Process, the Characteristic of Radiation Pulse, and the Charge Structure on the Qinghai-Tibetan Plateau

Using synchronous data from a three-dimensional lightning VHF radiation source mapping system, broadband electric field changes, and the radiation intensity of lightning on the Qinghai-Tibetan Plateau, we divided the preliminary breakdown process into two processes by subdividing the original definition: an initial preliminary breakdown process and a subsequent preliminary breakdown process. We comparatively analyzed the initial preliminary breakdown process and the initial pulse cluster for different types of lightning in a thunderstorm and studied the correlation between the propagation direction of the initial streamer and the polarity of the initial pulse cluster, as well as the correlation between the propagation path of the initial streamer and the charge structure of the thunderstorm. The statistical analysis shows that the streamer propagation distance of the initial preliminary breakdown process maintained good consistency with the number of the initial pulse clusters generated in the initial preliminary breakdown process. When the initial preliminary breakdown process included multiple pulse clusters, the initial streamer exhibited a discontinuous discharge channel through a stepped development travelling upward or downward. Each step corresponded to a pulse cluster. The amplitude of the radiation and the broad electric field change pulse first increased and then decreased in each pulse cluster. The polarity of the initial pulse cluster was consistent with the propagation direction of the initial streamer in the initial preliminary breakdown process, and the propagation direction of the initial streamer was consistent with the charge structure of the thunderstorms.

Estimate of NO X production in the lightning channel based on three-dimensional lightning locating system

Based on the VHF lightning locating system, a three-dimensional-space cell-gridded approach is used to extract the lighting channel and calculate the length of the channel. Through clustering of the located radiation sources and then extracting the lightning channel, it can accurately obtain the length of the channel. To validate the feasibility of the approach, a simulation experiment is designed, and it shows the length error is no more than 10%. The relationship between the NO production of per unit arc length and atmospheric pressure obtained in laboratory is applied to the NOX production of per unit flash length at different altitudes in this paper. The channel length and the NOX production of 11 negative cloud-to-ground flashes and 59 intracloud flashes in an isolated thunderstorm in the northeastern Qinghai-Tibet Plateau are calculated. The results show that the average channel lengths of per cloud-to-ground and intracloud flash are 28.9 and 22.3 km respectively; the average NOX productions of per cloud-to-ground and intracloud flash are 1.89×1025 and 0.42×1025 molecules, respectively.

Interaction between adjacent lightning discharges in clouds

Using a 3D lightning radiation source locating system (LLS), three pairs of associated lightning discharges (two or more adjacent lightning discharges following an arbitrary rule that their space-gap was less than 10 km and their time-gap was less than 800 ms) were observed, and the interaction between associated lightning discharges was analyzed. All these three pairs of associated lightning discharges were found to involve three or more charge regions (the ground was considered as a special charge region). Moreover, at least one charge region involved two lightning discharges per pair of associated lightning discharges. Identified from electric field changes, the subsequent lightning discharges were suppressed by the prior lightning discharges. However, it is possible that the prior lightning discharge provided a remaining discharge channel to facilitate the subsequent lightning discharge. The third case provided evidence of this possibility. Together, the results suggested that, if the charges in the main negative charge region can be consumed using artificial lightning above the main negative charge regions, lightning accidents on the ground could be greatly reduced, on the condition that the height of the main negative charge region and the charge intensity of the lower positive charge region are suitable.

Fast electric field change pulses location technique

Using both fast and slow electric field change sensors and field mill, multi-station observations on lightning flashes in Chinese Inland Plateau was conducted during the summer of 2004. All of the stations were synchronized by GPS with a time-resolution of ±50 ns. Using the different time of arrival (DTOA), a lightning radiation location technique, based on the fast electric field change sensor, was developed. Radiation pulses in the five intra-cloud (IC) lightning discharges which occurred on 20th August and cloud-to-ground (CG) lightning discharges which occurred on 16th July were analyzed. The results indicated that the technique developed could effectively locate the lightning radiation sources. Furthermore, the lightning discharges were compared with the Doppler radar data. Results showed that the radiation sources were well associated with the storm development.

The regular pulses bursts in electromagnetic radiation from lightning

A special lightning discharge phenomenon named as Regular Pulses Bursts (RPBs) is analysed. The result shows that the RPBs exist in all 69 lightning discharges within 30 minutes recording. The 190 RPBs in 6 typical lightning discharges are analysed in detail, the result indicates that its typical width of pulses is about 1µs, and inter-pulse interval varies from 4 to 8µs. Four types, namely normal RPBs, back RPBs, symmetry RPBs, and reversal RPBs are classified according to inter-pulse interval and pulse polarity. There is no obvious difference between RPBs in negative cloud to ground (CG) lightning and that in intracloud lightning(IC), but polarity change of most RPBs is frequent in positive CG. The results also show that the RPBs tend to occur in the latter portion of lightning discharges, and many cases are found to be associated with intensive VHF radiation. The waveform of the normal-type RPBs is similar to the dart-stepped leader in negative CG, which is considered caused by the recoil streamers. And the back-type RPBs may be caused by the leaders in cloud.

Regular Pulses Bursts Observation using a Time of Arrival Lightning Mapping System with Dual channels

of all the 693 RPBs in this period show that, typical width of pulses in RPBs is about 0.5-1 its, typical interval between pulses of RPBs is about 2-10 its and typical duration of RPBs is from 100 its to 5000 Its. There is always chaotic pulses period prior to or after RPBs. Most RPBs tend to occur in the middle and later stages of lightning discharges. In general, RPBs associates with K-change, M-process or dart-stepped leader. We developed a solution to match pulses caught in seven stations automatically just using intervals between pulses. Then we analyzed some parts of lightning discharge in high temporal resolution (up to dot per 2lts or more). Four RPBs were mapped in three dimensional in a typical intracloud flash, and a dart-stepped leader was also mapped in negative c1oud-to-ground flash, and some special RPBs were researched in this work.