Dong Zheng

Performance Evaluation for a Lightning Location System Based on Observations of Artificially Triggered Lightning and Natural Lightning Flashes

AbstractPerformance evaluation for the lightning location system (LLS) of the power grid in Guangdong Province, China, was conducted based on observation data of the triggered lightning flashes obtained in Conghua, Guangzhou, during 2007–11 and natural lightning flashes to tall structures obtained in Guangzhou during 2009–11. The results show that the flash detection efficiency and stroke detection efficiency were about 94% (58/62) and 60% (97/162), respectively. The arithmetic mean and median values for location error were estimated to be about 710 and 489 m, respectively, when more than two reporting sensors were involved in the location retrieval (based on 87 samples). After eliminating one obviously abnormal sample, the absolute percentage errors of peak current estimation were within 0.4%–42%, with arithmetic mean and median values of about 16.3% and 19.1%, respectively (based on 21 samples).

Lightning Distribution and Eyewall Outbreaks in Tropical Cyclones during Landfall

AbstractCloud-to-ground lightning data and storm intensity data (winds and central pressure) for 33 northwest Pacific tropical cyclones were used to analyze lightning distributions during the period of landfall in China. Lightning activities varied enormously from storm to storm with an average flash rate over 500 km of radius from 3 to 3201 flashes per hour, and no obvious relationship between average intensity and average flash rate occurred. The maximum flash density shifted from the eyewall region (0–60 km) to outer rainbands (180–500 km) as the intensity level increased. The average ratio of flash density in the eyewall to outer rainband was highest (1:0.5) for storms with the level of a tropical storm (17.2–24.4 m s−1) and lowest (1:8.6) for severe typhoons (41.5–50.9 m s−1). After storm landfall, flash density in the rainband decreased more rapidly in severe typhoons than in severe tropical storms (24.5–32.6 m s−1) and typhoons, but increased in tropical depressions (10.8–17.1 m s−1) and tropical s...

Attachment processes of two natural downward lightning flashes striking on high structures

A field observation experiment of lightning flashes occurring on high structures was conducted in the summer of 2009, at Guangzhou, Guangdong Province, China. Two downward negative lightning flashes, which stroke on high structures and are numbered as L01 and L02, have been analyzed in this paper. L01 stroke on a 610 m TV Tower and L02 on a 432 m structure. The analysis shows that: (1) Both lightning discharges exhibit long upward connecting leader with their lengths of longer than 450 m for L01 and of about 177 m for L02, respectively; (2) The upward-moving leader of L01 only has a single channel, while that of L02 has two branches; (3) For each event the average 2D progression velocity of upward-moving leader is of the order of 105 m/s; (4) There are no obvious difference between the 2D progression velocities of the upward-moving leader and the downward-moving leader during the last several hundreds of microseconds before the return stroke; (5) There exists a downward propagation optical phenomenon with a velocity of about 3.4 × 107 m/s at the bottom several tens of meters channel of L01 (below the junction point) after the connection of upward and downward moving leaders. This downward propagation appears to support the presence of the bidirectional extension of the return-stroke channel from the junction point.

Relationship between lightning activity and tropical cyclone intensity over the northwest Pacific

Lightning data from the World Wide Lightning Location Network along with tropical cyclone (TC) track and intensity data from the China Meteorological Administration are used to study lightning activity in TCs over the northwest Pacific from 2005 to 2009 and to investigate the relationship between inner core lightning and TC intensity changes. Lightning in TCs over the northwest Pacific is more likely to occur in weak storms at tropical depression (10.8–17.1u2009mu2009s−1) and tropical storm (17.2–24.4u2009mu2009s−1) intensity levels, in agreement with past studies of Atlantic hurricanes. The greatest lightning density (LD) in the inner core appears in storms undergoing an intensity change of 15–25u2009mu2009s−1 during the next 24u2009h. Lightning is observed in all storm intensity change categories: rapid intensification (RI), average intensity change (AIC), and rapid weakening (RW). The differences in LD between RI and RW are largest in the inner core, and the LD for RI cases is larger than for RW cases in the inner core (0–100u2009km). Lightning activity there, rather than in the outer rainbands, may be a better indicator for RI prediction in northwest Pacific storms. There was a marked increase in the lightning density of inner core during the RI stage for Super Typhoon Rammasun (2008). Satellite data for this storm show that the RI stage had the highest cloud top height and coldest cloud top temperatures, with all the minimum black body temperature values being below 200u2009K in the inner core.

Impact of the vertical velocity field on charging processes and charge separation in a simulated thunderstorm

A three-dimensional (3D) charging-discharging cloud resolution model was used to investigate the impact of the vertical velocity field on the charging processes and the formation of charge structure in a strong thunderstorm. The distribution and evolution of ice particle content and charges on ice particles were analyzed in different vertical velocity fields. The results show that the ice particles in the vertical velocity range from 1 to 5 m s−1 obtained the most charge through charging processes during the lifetime of the thunderstorm. The magnitude of the charges could reach 1014 nC. Before the beginning of lightning activity, the charges produced in updraft region 2 (updraft speed ⩾ 13 m s−1) and updraft region 1 (updraft speed between 5 and 13 m s−1) were relatively significant. The magnitudes of charge reached 1013 nC, which clearly impacted upon the early lightning activity. The vertical velocity conditions in the quasi-steady region (updraft speed between −1 and 1 m s−1) were the most conducive for charge separation on ice particles on different scales. Accordingly, a net charge structure always appeared in the quasi-steady and adjacent regions. Based on the results, a conceptual model of ice particle charging, charge separation, and charge structure formation in the flow field was constructed. The model helps to explain observations of the “lightning hole” phenomenon.

Optical and Electrical Observations of an Abnormal Triggered Lightning Event with two Upward Propagations

This study investigates an abnormal artificially triggered lightning event that produced two positive upward propagations: one during the initial stage (i.e., the upward leader (UL)) and the other after a negative downward aborted leader (DAL). The triggered lightning was induced in a weak thunderstorm over the experiment site and did not produce a return stroke. All of the intra-cloud lightning around the experiment site produced positive changes in the electric field. The initial stage was a weak discharge process. A downward dart leader propagated along the channel produced by the first UL, ending at a height of approximately 453 m and forming a DAL. Under the influence of the DAL, the electric field at a point located 78 m from the rod experienced a steady reduction of about 6.8 kV m−1 over 5.24 ms prior to the initiation of a new upward channel (i.e., the second upward propagation (UP)). The second UP, which started approximately 4.1 ms after the termination of the DAL and propagated along the original channel, was triggered by the DAL and sustained for approximately 2.95 ms. Two distinct current pulses were superimposed on the current of the second UP. The first pulse, which was related to the sudden initiation of the second UP, was characterized by a more rapid increase and decrease and a larger peak value than the second pulse, which was related to the development of the second UP into the area affected by the DAL. The second UP contained both a similar-to-leader process and a following neutralization process. This study introduces a new type of triggering leader, in which a new upward discharge is triggered in an established channel by an aborted leader propagating along the same channel with opposite polarity and propagation direction.

The role of dynamic transport in the formation of the inverted charge structure in a simulated hailstorm

The inverted charge structure formation of a hailstorm was investigated using the Advanced Weather Research and Forecasting (WRF-ARW) model coupled with electrification and discharge schemes. Different processes may be responsible for inverted charge structure in different storms and regions. A dynamical-derived mechanism of inverted charge structure formation was confirmed by the numerical model: the inverted structure was formed by strong updraft and downdraft under normal-polarity charging conditions such that the graupel charged negatively in the main charging region in the middle-upper level of the cloud. The simulation results showed the storm presented a normal charge structure before and after hail-fall; while during the hail-fall stage, it showed an inverted charge structure—negative charge region in the upper level of the cloud and a positive charge region in the middle level of the cloud—appearing at the front edge near the strong updraft in the hailstorm. The charging processes between the two particles mainly occurred at the top of the cloud, where the graupel charged negatively and ice crystals positively due to the strong updraft. When the updraft air reached the top of the storm, it would spread to the rear and front. The light ice crystals were transported backward and forward more easily. Meanwhile, the positively charged ice crystals were transported downward by the frontal subsidence, and then a positive charge region formed between the -10 and -25°C levels. Subsequently, a negative charge region materialized in the upper level of the cloud, and the inverted charge structure formed.

An analysis of the initial breakdown pulse for positive cloud-to-ground flashes

In order to further understand the initiating mechanism of positive cloud-to-ground (PCG) flashes, the nature and temporal characteristics of the positive breakdown pulse trains are investigated by electric field data in Conghua of Guangdong province. Considering the difference between the initial polarity of initial breakdown pulses and the first return stoke (RS), three types of bipolar pulse trains, including the same polarity, the opposite polarity and the both polarity, are identified. The percentages are 83.5%, 10% and 5.5%, respectively. The statistic results show that PCG flash with breakdown pulse trains, which occur when the amount of PCG flash is little, is about 11.6% of the total PCG flashes. The average time interval between the peak of adjacent pulses and pulse duration are 270.99 μs and 25.01 μs, respectively. The mean value of pulse train duration and the interval between PBP train and RS is 8.88 ms and 98.48ms, respectively. The average ratio of all samples between the maximum amplitude of pulse train and the amplitude of the first stroke pulse is 0.16. The ratio is smaller in of Guangzhou province than in Hokuriku coast in Japan.

Low-frequency E-field Detection Array (LFEDA)—Construction and preliminary results

In recent years, locating total lightning at the VLF/LF band has become one of the most important directions in lightning detection. The Low-frequency E-field Detection Array (LFEDA) consisting of nine fast antennas was developed by the Chinese Academy of Meteorological Sciences in Guangzhou between 2014 and 2015. This paper documents the composition of the LFEDA and a lightning-locating algorithm that applies to the low-frequency electric field radiated by lightning pulse discharge events (LPDEs). Theoretical simulation and objective assessment of the accuracy and detection efficiency of LFEDA have been done using Monte Carlo simulation and artificial triggered lightning experiment, respectively. The former results show that having a station in the network with a comparatively long baseline improves both the horizontal location accuracy in the direction perpendicular to the baseline and the vertical location accuracy along the baseline. The latter results show that detection efficiencies for triggered lightning flashes and return strokes are 100% and 95%, respectively. The average planar location error for return strokes of triggered lightning flashes is 102 m. By locating LPDEs in thunderstorms, we find that LPDEs are consistent with convective regions as indicated by strong reflectivity columns, and present a reasonable distribution in the vertical direction. In addition, the LFEDA can reveal an image of lightning development through mapping the channels of lightning. Based on three-dimensional locations, the vertical propagation speed of the preliminary breakdown and the changing trend of the leader’s speed in an intra-cloud and a cloud-to-ground flash are investigated. The research results show that the LFEDA has the capability for three-dimensional location of lightning, which provides a new technique for researching lightning development characteristics and thunderstorm electricity.

A Review of Advances in Lightning Observations during the Past Decade in Guangdong, China

This paper reviews recent advances in understanding the physical processes of artificially triggered lightning and natural lightning as well as the progress in testing lightning protection technologies, based on a series of lightning field campaigns jointly conducted by the Chinese Academy of Meteorological Sciences and Guangdong Meteorological Bureau since 2006. During the decade-long series of lightning field experiments, the technology of rocket-wire artificially triggered lightning has been improved, and has successfully triggered 94 lightning flashes. Through direct lightning current waveform measurements, an average return stroke peak current of 16 kA was obtained. The phenomenon that the downward leader connects to the lateral surface of the upward leader in the attachment process was discovered, and the speed of the upward leader during the connection process being significantly greater than that of the downward leader was revealed. The characteristics of several return strokes in cloud-to-ground lighting have also been unveiled, and the mechanism causing damage to lightning protection devices (i.e., ground potential rise within the rated current) was established. The performance of three lightning monitoring systems in Guangdong Province has also been quantitatively assessed.