Lightning Ground Flash Research Articles

Correlation analysis of preliminary breakdown and first return stroke process in negative ground flash as a function of Northeast and Southwest monsoon in tropic

The separation duration of Preliminary Breakdown to the First Return Stroke (PB-RS duration) and the ratio between the highest amplitude pulse of Preliminary Breakdown and the first Return Stroke pulse (PB/RS ratio) were successfully used as a tool by many researchers to determine the relationship between lightning ground flashes and physical changes (latitude, regional and thunderstorm). Malaysia is one of the countries with the highest lightning flash density globally, and the occurrences of ground flashes are mainly due to monsoon seasons. Monsoons in Malaysia are Northeast, Southwest, and two transition periods. However, there is no available information to relate the lightning activities in Malaysia under the influence of all monsoon seasons. The above statements motivated our team to present a new statistical analysis of lightning flashes under two seasons' effects (Northeast and Southwest). 83 out of 332 electric radiation field data (fast fields) from six thunderstorms were selected and analyzed. The data was recorded using a 12-bit high-speed transient recorder (HDO 4024) with a resolution of tens of nanoseconds and sampling of 12.5 MS/s. PB/RS ratio between the monsoons is similar to each other. Whereas, the PB-RS separation, has two factors longer during the Southwest monsoon than during the Northeast monsoon. We classified the PB/RS ratio into four categories (>100%, 50-100%, 20-50%, and < 20%) as an indication of the preliminary breakdown strength. It found that the weakest pulse train (PB/RS ratio is less than 20%) has shown a longer duration of PB-RS and produces higher lightning return strokes in a negative ground flash than the strong one. The results in this study could be evident that the lower strength of preliminary breakdown is correlated to a lower Low Positive Charge Region (LPCR), which means the initial breakdown process only requires low energy to break the LPCR. Hence, these features have shown the highest number of stroke counts compared to pronounced ones. However, it would be more remarkable if one could provide bulky data for this specific study.

The Impact of High-Resolution SRTM Topography and Corine Land Cover on Lightning Calculations in WRF

The goal of this study is to investigate the impact of high-resolution SRTM and Corine Land Cover on the number of cloud–ground lightning flashes and their spatial distribution simulated by a numerical weather-prediction model. Two lightning episodes were selected: (1) over a non-complex terrain and (2) over a complex terrain, the Alps. Significant discrepancies were found in the geographical distribution of the land-cover classes and also in the topography between Corine Land Cover and 30-arc seconds USGS. In general, the timing and the spatial distribution of Cloud-to-Ground (CG) lightning by the model were well-represented when compared to the observations. In general, more CG flashes were calculated by the simulation with USGS Land Cover and topography than the simulation with Corine Land Cover and SRTM topography. It appears that the differences in sensible and latent heat fluxes between the simulations were caused by the differences in land-cover classes. Moreover, differences in the vertical wind speeds, specific humidity, temperature and the convective available potential energy were found when compared to observations, resulting in the differences in cloud–ground lightning flashes between the simulation with the SRTM topography and Corine Land Cover and the simulation with the USGS Land Cover and topography. Using the high-resolution land cover and topography data may help to reduce uncertainties in CG lightning calculations by the model.

A Methodology for Protection of Trees Against Lightning Strikes as a Measure to Prevent Fires and Loss of Human Life

Some regions may be characterized by a very low annual lightning ground flash density, and yet lightning strikes seem to have been in those areas the cause of widespread wildfires in forested areas. Due to global climate change, these occurrences seem to be an increasing threat. In this article, the authors discuss the withstand capability of trees against lightning and introduce the criteria for the deployment of tree lightning protection systems to protect forested areas, where deemed necessary by the tree risk assessment. This work analytically identifies the critical trunk radius of the tree below which the tree may explode in the case of a lightning strike and ignite the surrounding vegetation. The critical heights of trees requiring lightning protection systems to prevent loss of human life and cultural heritage are also identified.

Cloud-to-ground lightning flash density and the number of lightning flashes hitting wind turbines in Japan

The current status of the Japanese coastal region shows that winter lightning has seriously damaged wind turbines owing to its larger electrical charge than summer lightning. In Japan, 64% of serious wind turbine damage occurred in winter. Typically, lightning flash density is used to evaluate lightning risk in an area. Herein, we discuss the extent of lightning damage on wind turbines in Japan and cloud-to-ground (CG) lightning flash density based on the Japanese Lightning Detection Network, the largest lightning location system in Japan. Consequently, we found no correlation between the number of lightning flashes hitting wind turbines and summer lightning ground flash densities in the surrounding areas of a wind turbine. Approximately 95% of the lightning flashes that hit the turbine occurred in winter. The probabilities of lightning flashes hitting wind turbines were 0.12% in summer and 5.6% in winter. We developed a map showing the probability of lightning flashes hitting wind turbines in Japan. The probabilities obtained using this map were quite similar to the CG lightning flash density in winter. Therefore, we propose that lightning risk for wind turbines should not be evaluated based on the annual CG lightning flash density in Japan.

Analysis of Lightning and Precipitation Activities in Three Severe Convective Events Based on Doppler Radar and Microwave Radiometer over the Central China Region

Hubei Province Region (HPR), located in Central China, is a concentrated area of severe convective weather. Three severe convective processes occurred in HPR were selected, namely 14–15 May 2015 (Case 1), 6–7 July 2013 (Case 2), and 11–12 September 2014 (Case 3). In order to investigate the differences between the three cases, the temporal and spatial distribution characteristics of cloud–ground lightning (CG) flashes and precipitation, the distribution of radar parameters, and the evolution of cloud environment characteristics (including water vapor (VD), liquid water content (LWC), relative humidity (RH), and temperature) were compared and analyzed by using the data of lightning locator, S-band Doppler radar, ground-based microwave radiometer (MWR), and automatic weather stations (AWS) in this study. The results showed that 80% of the CG flashes had an inverse correlation with the spatial distribution of heavy rainfall, 28.6% of positive CG (+CG) flashes occurred at the center of precipitation (>30 mm), and the percentage was higher than that of negative CG (−CG) flashes (13%). Moreover, the quantity of thunderstorm cells in Case 1 was more than other cases, the peak time of +CG flashes was prior to that of total CG flashes in Case 2 and Case 3, and the time of +CG flashes’ peak in Case 2 was prior to that of precipitation at about 2 h. Based on the analysis of the cloud environment, there are three main reasons for the differences of CG flashes and precipitation. Firstly, the structure of the LWC vertical profile and the height of the LWC peak are different, and high LWC makes it difficult for the collision of ice particles to generate electricity. Secondly, the differences between convective available potential energy (CAPE), precipitation, and CG flashes is caused by the sudden increase of VD from 1.5 km to 3 km, and thirdly, the production of CG flashes is very sensitive to RH at the surface layer and the total CG flashes increase as the RH increasing.

Discriminating cloud to ground lightning flashes based on wavelet analysis of electric field signals

Lightning discharges produce electromagnetic radiation in a wide frequency range, but its propagation in a certain frequency range are usually used by lightning detection networks. Investigation of lightning activities in time-frequency domain can be obtained by using the wavelet transform. This study proposes a new approach using the discrete wavelet transform (DWT) algorithm to classify the detected lightning strikes. The measuring station would capture lightning electric field in 500 ms time scale and then utilizes a wavelet based recognizer algorithm to duly differentiate the cloud to ground flash from other cloud activities. Wavelet transform allows the expansion of transient events into a small number of coefficients. A total of 200 lightning flashes were randomly selected among the captured lightning discharges in South of Malaysia in one year. Initially, the cloud to ground and other cloud activities were manually analysed and discriminated. Then, these lightning flashes were analysed using different mother wavelets such as Haar, symmlet, Coiflet, and Daubechies by means of MATLAB program. Haar mother wavelet gives the best result for CG decomposition analysis. A total of 24 decomposition layers were chosen and the energy level of each layer was calculated to obtain the correlation between energy fluctuation and type of signal. The investigations reveal that the CG discharges have higher energy in 17th to 20th layers compared to the rest. However, the opposite results were obtained for the case of other cloud activities. To increase the accuracy of the wavelet transform approach algorithm, another filter was added to the algorithm flowchart. The proposed CG discrimination algorithm successfully classified 92% of the randomly selected flashes.

Sub Microsecond Analysis of Negative Cloud-To-Ground Lightning Flashes

This paper expounds a development software for the identification of lightning discharge in cloud-to-ground flashes. The study was to reduce a misleading detection of the electric field radiation of a lightning discharge profile by considering the important parameters of sub microseconds structure of lightning return stroke. The software was built-in MATLAB. The development of the software considered the important parameter of return strokes such as peak value, zero crossing, rising time and fast transition time. We used a modelling technique for training and patterning the 19 return stroke from electric radiation field generated by the negative cloud-ground lightning flashes recorded in Universiti Teknikal Malaysia Melaka. The 19 return strokes data were recorded by using Lecroy HDO4024 with 5 MS/s. The results showed that the software had the ability to recognize the lightning parameters such as peak value, zero crossing, rising time and fast transition time. In conclusion, the software was able solved the uncertainty of the unknown cloud-to-ground lightning flashes parameter. This paper expounds a programmed development software for the used to do identification of the characteristi cs o o f the lightning d is charge either in cloud -to - and ground flashes cloud and ground flashes of the lightning strikes . Th e study was to reduc e e a m is leadi ng detection of the electric field radiation of a lightning d is charge profile by considering the important pa ra meters o f sub microseconds structure of lightning return stroke . programmed should resolved the problem of unidentified signal o f lightning strikes. The softw are was built-in MATLAB . The development of the softw are considered the important parameter of return stroke s such as peak value, software to recognize t he pattern of the lightning strikes of cloud-to-gr ound flashes or cloud-to-cloud flashes by determining the multiple parameters suc h as zero crossing, rising time and fast transition time. MAKLUMKAN KAEDAH YG “MUNGKIN” MELIBATKAN TRAIN BEBERAPA DATA CTH — We used a modelling technique A for training and patterning the 19 return stroke from electric radiation field generated by the negative cloud - ground lightning flashes recorded in Universiti Teknikal Malaysia Melaka . The 19 return strokes data were recorded by using Lec r oy HDO4024 with 5 MS/s. First, the lightning pattern is described, then the programmed was tested to recognize all the parameters to identify the types of the lightning strikes. The results show ed s th at the e software had the ability to recognize the lightning parameters such as peak value, zero crossing, rising time and fast transition time. In conclusion, t he softw are was able solve d the uncertainty of the unknown cloud - to - ground unknown lightning flas hes parameter. At last, some suggestions are given to improve the system for future research. Masukan Brief of conclusion…. Normal 0 false false false MS X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:Table Normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:Times New Roman,serif; mso-ansi-language:MS; mso-fareast-language:MS;}

Some Characteristics of Multiple Stroke Negative Cloud to Ground Lightning Flashes in Padang

Some Characteristics of Multiple Stroke Negative Cloud to Ground Lightning Flashes in Padang

On the characteristics of positive lightning ground flashes in Sweden

In this study the stroke characteristics of positive cloud-to-ground flashes in Sweden were obtained from the electric field records measured from 14 thunderstorms. The electric fields were measured with nanosecond resolution. Together with the fast and the slow electric field records, the narrowband radiation field at 3 and 30MHz signals were also measured simultaneously. Out of a total of 107 flashes, 30 flashes had two strokes, 7 had three strokes and 3 flashes had four strokes. The arithmetic and geometric means of the interstroke intervals were found to be 116 and 70 ms, respectively. The arithmetic and geometric mean ratio between the peak electric field of the Subsequent Return Stroke (SRS) and the first Return Stroke (RS) were 0.48 and 0.36, respectively. Of the 40 positive multiple-stroke ground flashes, 5% have at least one SRS with field peak higher than the first RS. The percentage of SRS with field peaks greater than the first RS was 6%. In our best of our knowledge, this is the first time a large sample of positive return strokes in Sweden was analysed. It was found to be statistically more significant than the previous studies.

Unique Stroke-Multiplicity of Positive Lightning in Malaysia

This paper presents the unique characteristics of positive lightning generated vertical electric field waveforms recorded in Malaysia. The focus of the study was the waveforms due to positive lightning and their number of return strokes in a flash. A total of 172 lightning ground flash records were analysed, out of which 57 flashes contained positive lightning with a number of them having high numbers of subsequent return strokes which is somewhat unusual with observations elsewhere. The field measurements were done by using a parallel plate antenna coupled with a recording system. In contrary to the majority of positive lightning return strokes that has been recorded previously, where the average multiplicity is one, this study showed an average multiplicity of 3.86 which is almost four times higher than that is usually observed.

Spatial and temporal variations of thunderstorm activities over Sri Lanka

Spatial and temporal variation of frequencies of thunderstorms over Sri Lanka using thunder day data is presented. A thunder day is simply a calendar day in which thunder is heard at least once at a given location. Two sets of data were collected and analyzed: annual totals for 10 climatological stations for a period of 50 years and monthly totals for 20 climatological stations for a period of 20 years. The average annual thunder days over Sri Lanka was found to be 76. Among the climatological stations considered, a high number of annual thunder days was recorded in Ratnapura (150 days/year), followed by Colombo (108 days/year) and Bandarawela (106 days/year). It appears that there are no widespread long-term increasing or decreasing trends in thunderstorm frequencies. However, Colombo, the capital of Sri Lanka which has over two million people shows an increasing trend of 0.8 thunder days per year. Although there is a high variability between stations reporting the number of thunder days, the overall pattern within a year is clear. Thunderstorm frequencies are high during two periods: March–May and September–November, which coincide with the first inter-monsoon and second inter-monsoon periods. Compared to the dry zone, the wet zone, especially the southwestern region, has high thunderstorm activity. There is a clear spatial difference in thunderstorm activities during the southwest and northeast monsoon seasons. During both these seasons, enhanced thunderstorm activities are reported on the leeward side of the mountain range. A slight reduction in the thunderstorm activities was found in the high elevation areas of the hill country compared to the surrounding areas. A lightning ground flash density map derived using annual thunder days is also presented.

A Method for Retrieving the Ground Flash Fraction and Flash Type from Satellite Lightning Mapper Observations

AbstractAn analytic perturbation method is introduced for retrieving the lightning ground flash fraction in a set of N lightning flashes observed by a satellite lightning mapper. The value of N must be large, typically in the thousands, and the satellite lightning optical observations consist of the maximum group area (MGA) produced by each flash. Moreover, the method subsequently determines the flash type (ground or cloud) of each of the N flashes. Performance tests of the method were conducted using simulated observations that were based on Optical Transient Detector (OTD) and Lightning Imaging Sensor (LIS) data. It is found that the mean ground flash fraction retrieval errors are below 0.04 across the full range 0–1 under the nominal conditions defined. In general, it is demonstrated that the retrieval errors depend on many factors (i.e., the number N of satellite observations, the magnitude of random and systematic instrument measurement errors, the ground flash fraction itself, and the number of samples used to form certain climate distributions employed in the method). The fraction of flashes accurately flash typed by the method averaged better than 78%. Overall, the accuracy of ground flash fraction and flash-typing retrievals degrade as the simulated population ground and cloud flash MGA distributions become more identical. Finally, because the analytic perturbation method was found to be quite robust (i.e., it performed well for several arbitrary underlying MGA distributions), it is not restricted to the lightning problem studied here but can be applied to any inverse problem having a similar problem statement.

Analysis on Lightning Striking Selectivity and Lightning Protection

According to the national standard (GB-50057-1994) of lightning protection design, we can calculate the number of lightning ground flash density around them. However, this technique would have some defects. In order to improve the predicting accuracy of the lightning striking of tall buildings, there are three methods, i.e. a broken line method, the method of Faraday cage, and ball method. The electrical geometry model of rolling ball method as the theoretical basis for calculating is easy. In order to analyze lightning striking selectivity of buildings, the shielding between buildings were discussed based on the electric geometric model (ball method). It is different lightning probability for different monomer buildings, building groups, different distance, different geographical environment, and climate environment. And some protection measurements were proposed to improve the lightning shielding performances.

Performance of lightning locating systems in extracting lightning flash characteristics

A study was carried out to compare the negative cloud to ground lightning discharges recorded using Swedish lightning locating system against time correlated direct field measurements. Only the first 200ms time window was investigated. A total of 167 flashes were recorded and time matched against the lightning locating system records. The comparison shows that for negative cloud-to-ground lightning flashes, the stroke detection efficiency of lightning locating system is at 93% for detecting the first stroke accurately. The efficiency drops to about 77% in detecting all strokes accurately. Thus, the system tends to give a low value for average multiplicity and a significantly higher value for parameters such as percentage of single stroke flashes. In agreement with the direct field measurements, when the individual strokes are identified correctly, both systems show the expected 2:1 ratio between the first and subsequent stroke peak field. Data also shows that the LLS system has a tendency of identifying isolated cloud pulses as positive return strokes. Hence one must take into account the systematic deficiency in lightning locating systems when reporting characteristics of cloud to ground lightning flashes.

Lightning ground flash patterns over Paris area between 1992 and 2003: Influence of pollution?

12 summers of cloud-to-ground (CG) lightning flashes data over a 200km×200km domain centered on Paris (France) have been analyzed to infer the possible influence of pollution on lightning activity. Lightning flashes densities are calculated on a 5km×5km grid, filtered for discarding extremely high events, and differentiated from weekdays to week-end days, with a specific insight upwind, over, and downwind Paris. Lightning flashes are more numerous in the North-East part of the domain and increasingly large events progressively concentrate over Paris and over some hills around. The former result indicates a possible influence of pollution on lightning activity downwind of Paris; the latter probably illustrates the influence of the urban heat island and of the relief on the convection strengthening. Furthermore, the number of positive CG flashes is rather uniformly distributed on the whole domain, except in the North-East where it appears somewhat relatively lower meanwhile negative CG are relatively more numerous in that region. This corresponds to a reduction in the percentage of positive CG downwind of Paris. Additionally, lightning activity appears weaker downwind of Paris during weekend days. A specific daily analysis of the lightning density in circles distributed along the direction of prevailing wind through Paris shows that the lightning activity appears higher downwind during the days most worked as Tuesday, Wednesday and Thursday. This higher electric activity persists up to about 40km on Wednesday, and up to about 80km on Tuesday and Thursday (most days worked). The electrification seems therefore more important downwind of Paris during the more polluted days.

Lightning Activities and Ground Flash Density in Niger Delta Coast

Lightning Activities and Ground Flash Density in Niger Delta Coast

The lightning climatology of South Africa

In 2005, the South African Weather Service installed a state-of-the-art cloud-to-ground lightning detection network across the country. The data recorded by this network in 2006 was utilised in the development of an initial lightning climatology of South Africa. Until 2010, this climatology was based on data from a single year. This paper updates this climatology with the lightning data for the 2006–2010 period, which is the first actual lightning climatology by the South African Weather Service based on data covering 5 years. A number of different maps were created from these lightning data. These were lightning ground flash density, median peak kiloampere, percentage positive and average flash multiplicity maps. These four maps were in turn used to develop lightning intensity risk, positive lightning risk and total lightning risk maps. Analysis of the maps showed that the highest concentrations of lightning are found over the central to northern interior of the country, with areas along the northern parts of the eastern escarpment experiencing the highest flash densities and falling within the extreme risk category. Both the positive and total lightning risks are severe for almost the entire country. Only towards the west of the country does the lightning risk decrease. This lightning climatology can now be used throughout South Africa for various disciplines. It will be especially useful for setting lightning safety standards and identifying priority areas for installing lightning conductors and conducting public awareness campaigns.

Statistical characteristics of ground lightning flashes over the Korean peninsula using Cloud-to-Ground lightning data from 2004–2008

Lightning is one of most serious threats to successful launch operations. The objective of this study was to investigate the characteristics of Cloud-to-Ground (CG) lightning flashes in the South Korean peninsula from statistical information, to support space launch operations. The CG flash density, number of flashes, flash polarity, flash hours, median peak current and the interrelationship between flash hours and flash density were calculated using lightning observation data for 2004–2008 from the Korea Meteorology Administration (KMA). During this period 2,314,034 CG strokes and 1,152,475 CG flashes over the South Korean peninsula were detected by the Korean Meteorological Administration Lightning Detection Network (KLDN). Lightning occurred intensively during June, July and August. The mean percentage of positive flashes was 8.72%. The median peak current of positive flashes showed seasonal variations, while the median peak current of negative flashes did not. The maximum and minimum of median peak current for positive flashes was 76.2 kA in January and 17.6 kA in August respectively. Linear regression analysis was conducted to assess the relationship between flash hours and density. The correlation coefficient was derived by 0.5680.

Polarity asymmetry of sprite‐producing lightning: A paradox?

Sprites and halos in the mesosphere are produced electrostatically by lightning ground flashes whose polarity is positive, by a margin of at least 1000 to 1 in collected observations. The initiation of these events is controlled by the vertical charge moment change of the flash. Schumann resonance ELF methods have been used to measure the charge moments of millions of flashes worldwide. The bipolar distributions of these events show stronger positive than negative tails, consistent with the predominance of “positive” sprites, but the negative tail of supercritical events is still of the order of 10% of the total supercritical population, more than 1 order of magnitude larger than the observed fraction of “negative” sprites. This juxtaposition constitutes a paradox. The suggested resolution of the paradox is that the more impulsive population of supercritical negative flashes is producing dim halos that are not readily detected in conventional video imagery. Additional sensitive, high‐resolution, and high‐speed imager (<1 ms) studies of halos and their lightning parents are needed to verify this hypothesis.

Characteristics of cloud-to-ground lightning flashes over Sweden

A detailed study of the characteristics of cloud-to-ground (CG) lightning flashes over Sweden was carried out for the period 1987–2000 using data obtained from the Swedish lightning-locating network. Results are presented by analysing over half a million lightning ground flashes. The average variation of the annual mean of the total number of flashes was found to be 37%. About 12% of the CG flashes were positive flashes and their average variation about the annual mean was 26%. The average peak currents were fairly constant over the years with variations as little as 4% for negative flashes and 5% for positive flashes. The average peak current values for negative and positive flashes were −29.90 and +63.97 kA respectively. A correlation between the mean monthly flash count and percentage of positive flashes was seen. A similar relationship is seen with the mean monthly flash count and the peak currents for both polarities. In general, high flash density and high peak currents were observed in the southern part of Sweden where most of the major cities are located. Flash densities exceeding 0.4 flashes km−2 were observed for several large cities. The maximum flash rate of 32 flashes h−1 within a 10 km radius was seen in Jönköping (14.18°E, 57.78°N) in the province of Småland.