Lightning Ground Flash Density Research Articles

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.

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.

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.

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.

Spatial distribution and frequency of lightning activity and lightning flash density maps for Australia

The spatial distribution and frequency of lightning activity in Australia have been analyzed using lightning data obtained by ground‐based lightning detection instruments denoted CIGRE‐500 and CGR3 and by NASA satellite‐based instruments denoted OTD and LIS. The geographical distribution of lightning incidence is described by a map of total lightning flash density, Nt (i.e., cloud‐to‐ground and intracloud flashes). A high level of lightning activity, Nt > 10 km−2yr−1, is observed in the northern parts of Australia, and a decrease in total flash density occurs southward to Nt < 5 km−2yr−1 in the central and southern parts of Australia. The peak lightning occurrence is in the northwestern part of the Australian continent with Nt values up to about 35 km−2yr−1 centered around 16°S 126°E. A reduction in Nt by a factor of about 10 for a change in latitude from 10°S to 40°S was found, which is in agreement with the earlier studies. The data from all the sources were used to estimate the cloud flash‐to‐ground flash ratio, Z, which at the studied localities was found to be in a range of values from 0.75 to 7.7. We concluded that for the range of latitude over Australia the most representative value of Z is about 2 ± 30%, and it is relatively independent of latitude. We used this to develop a map of average annual lightning ground flash density, Ng, the first for Australia. Ng varies from over 6 km−2yr−1 in the northern parts of Australia to about 1 km−2yr−1 and below in the southern parts.

Study of the Winter Lightning Ground Flash Density Investigated by the Lightning Location Systems

A network of lightning location systems covering the entire Japanese Archipelago has been operational since the late 1980s. However, the operational records appear to be distorted relative to winter lightning flash densities. The maximum flash density registered was 0.3 flashes/km/sup 2/ per one winter season, a mere one-tenth of the corresponding figure for severe summer lightning anywhere along the archipelago. On the other hand, the fault frequencies of overhead transmission lines constructed in the severe winter lightning districts are comparable with those of severe summer lightning districts. The author submits to resolve the apparent disparity by introducing two analytical parameters, namely 1) the propagation velocity of the return strokes of the winter lightning, and 2) the seasonal difference in the altitude of the lightning charge in the cloud. Consequently, the author proposes a certain seasonal modification of the threshold level applicable to the operation of lightning location systems.

Geographical and seasonal characteristics of the relationship between lightning ground flash density and rainfall within the continent of Australia

Ground-based observations of annual rainfall and lightning incidence collected over periods ranging from 9 to 22 years at 23 stations around the continent of Australia were used to compute values of ‘rain yield’, defined as the mass of rain produced per lightning ground flash (units: kg fl − 1) over a given area of ground. The rain yield was found to vary considerably with geographical location, season and climatic conditions. Of the 23 stations, 5 were mid-continental and these showed a mean rain yield of 2.64 × 10 8 kg fl − 1 in contrast to the coastal and near-coastal stations that showed a corresponding mean value of 9.91 × 10 8 kg fl − 1. The difference was statistically significant at the confidence level of 95%. When the stations were classified according to seasonal climate zones, the winter and winter-dominant rainfall stations showed a rain yield of 1.28 × 10 9 kg fl − 1 while the summer and summer-dominant rainfall stations showed a significantly lower value of 5.44 × 10 8 kg fl − 1. Again the difference was statistically significant at the 95% confidence level. Every one of the 23 stations showed mean winter rain yields that were significantly higher than the summer values. These differences are attributed to surface heating which controls such parameters as cloud base height and convective available potential energy in the atmosphere. In terms of the behaviour of the rain yield with geographical, seasonal and climatic conditions, the Australian observations are in good agreement with studies in other parts of the world.

Lightning Fatalities on the South African Highveld

A review of the Southern Africa medical literature shows a paucity of published data regarding lightning fatalities. The South African Highveld has a lightning ground flash density of 6 to 9 flashes/km/year, with a high incidence of thunderstorm days per year (some 40-70). The Highveld has a largely urban population, many of whom have low socioeconomic status and poor education, housing, and other infrastructures and hence (possibly) are at greater exposure risk. Thirty-eight victims of lightning-related death were identified from the records of the 6 large medicolegal mortuaries on the South African Highveld, serving a population of approximately 7 million, for the period 1997 to 2000. Analysis of the records revealed that 95% of all victims were black, 79% were male, and the average age was 36 years. Lightning strikes occurred from September through to April (normal summer rainfall period), and the most strikes took place in the late afternoon (3:00 pm to 6:00 pm). All except 1 case occurred outdoors. In the autopsy reports, mention was made of singeing of hair in 68% of cases, and mention of damage to clothing was made in 26% of cases. Cutaneous thermal injuries were noted in 34 of the 38 cases, with apparent electrothermal injuries of the feet noted in 4 cases. Fifty-two percent of victims sustained some form of associated blunt-force injury (including abrasions, contusions, etc). Specific keraunopathologic injuries were described in only 2 of the cases. Twenty-one cases had some form of internal organ injury. This study serves to illustrate the relatively high incidence of lightning strikes in the region and calls for a more systematic and detailed investigative protocol in lightning-related deaths.

Lightning Ground Flash Density and Thunderstorm Duration in the Continental United States: 1989–96

Abstract The mean annual flash density, thunderstorm duration, and flash rates were calculated using 121.7 million cloud-to-ground lightning flashes in the continental United States for the period 1989–96. Florida had flash densities over 11 flashes km−2 yr−1, while the Midwest, Oklahoma, Texas, and the Gulf Coast had densities greater than 7 flashes km−2 yr−1. There was a relative minimum in flash density (three flashes km−2 yr−1) in the Appalachian Mountains and Missouri. Thunderstorm duration values exceeded 120 h yr−1 in Florida and 105 h yr−1 in New Mexico, Arizona, and the Gulf Coast. The maximum annual flash rates exceeded 45 flashes h−1 in the Midwest, along the Florida coasts, and along the mid-Atlantic coast with the minimum flash rates, 15 flashes h−1, over the Appalachian and Rocky Mountains. The relationship between thunderstorm duration and flash density is Flash_Density = 0.024(Flash_Hours)1.29 producing expected flash densities that are within 30% of the measured densities for over 70% of ...

Comments on “Lightning Ground Flash Density in the Contiguous United States—1989”

Comments on “Lightning Ground Flash Density in the Contiguous United States—1989”

A unified probabilistic theory of the incidence of direct and indirect lightning strikes

The basic probabilistic properties of direct lightning strikes and field-induced effects are identified, reviewed, and combined into a unified and comprehensive setting. The probabilistic aspects of the incidence of direct and indirect lightning strikes and their effects on general power systems are modeled and analyzed on the basis of a concept of system perception. The bias of the statistical distribution of the perceived lightning current amplitudes, as stemming from impairment of the natural lightning distribution by censoring of distant and weak strikes, is formalized into a general problem setting. Here the perceptive zone, viewed as a function of the natural lightning current amplitude, is the key concept. The effective area of the perceptive zone, defined through the number of perceived flashes per year and the lightning ground flash density, is obtained as a statistical average. The implications of the general theory are further studied under special conditions regarding system geometry, functional perceptive zone strike current amplitude relationship, and natural lightning current amplitude distribution. It is demonstrated that the problem lends itself to a simple analytical study assuming point or line type geometry, power function type amplitude relationship, and log-normal amplitude distribution. >

Lightning Ground Flash Density in the Contiguous United States-1989

Lightning Ground Flash Density in the Contiguous United States-1989