Flash Density Research Articles

Performance and emissions of a CI engine using a diesel, jatropha biodiesel and biodiesel adopting Al2O3 nanomaterial as fuel blend.

A nanocomposites of aluminum dioxide was employed as a fuel additive in a compression engine test. Nanoparticle stability in diesel was measured by their impact on the fuel's flash point, density, and viscosity. When compared to other forms of fuel, conventional biodiesel has superior qualities. Al2O3 was also put through its paces in terms performance of engine and pollution testing. The thermal efficiency of the engine's brakes may be improved by adding nanoparticles in to the jatropha biodiesel. Using Al2O3 nanoparticles has been shown to reduce brake-specific fuel consumption by 23%. In addition, this solution can cut hydrocarbon emissions by 19%.

Seasonal–Diurnal Distribution of Lightning over Bulgaria and the Black Sea and Its Relationship with Sea Surface Temperature

A seasonal–diurnal analysis of land-sea contrast in lightning activity over Bulgaria and the Black Sea over 10 years is presented here. The maximum number of flashes over both surface types is registered during the summer (with a peak over Bulgaria in June and over the Black Sea in July) and a minimum number in winter (December/February, respectively). During spring, the maximum flash density is observed over Bulgaria (in May), while in autumn, it is over the Black Sea (in September). The results show that only in autumn lightning activity dominates over the Black Sea compared to over land (Bulgaria), while in winter, spring, and summer is vice versa. For this reason, an additional investigation was conducted to determine whether there is a relationship between lightning activity and the sea surface temperature (SST) of the Black Sea in autumn. The analysis reveals that the influence of SST on the formation of thunderstorms over the Black Sea varies depending on the diurnal time interval, with the effect being more significant at night. At nighttime intervals, there is a clear trend of increasing mean flash frequency per case with rising SST (linear correlation coefficients range from R = 0.92 to 0.98), while during the daytime, this trend is not as evident. This indicates that, during the day, other favorable atmospheric processes have a greater influence on the formation of thunderstorms than sea-surface temperature, while in the autumn night hours, the higher SST values probably play a more significant role in thunderstorms formation, in combination with the corresponding orographic conditions.

Formulation Ratio Effectiveness of Green Metal Working Fluid (GMWF) as a Bio Alternative for Green Manufacturing

Metalworking fluid (MWF) is essential for ensuring quality products and extended tool life during machining operations. While there are various sources of MWF, the need to minimize health hazards associated with mineral-based metal working fluid now calls for more environmentally friendly green metal working fluid (GMWF) from bio-degradable sources. Also, the effectiveness of vegetable-based GMWF significantly depends on the degree of functionalization. Though some studies considered the issue, the comparative analysis of the effect formulations (variation in concentration) of the constituting elements of the GMWF, especially for the base vegetable oil under consideration; has been grossly underreported. In this study, a GMWF emulsion has been developed from soybeans, palm fruits, and coconut with varying formulation ratios. Physicochemical characterization such as flash point, fire point, pour point, pH, density, and viscosity of the developed GMWF were analyzed. Also, a performance evaluation of the said GMWF was carried out and the investigation has shown that the physicochemical properties of the developed GMWF matched, as a potential substitute for conventional mineral-based MWF. Additionally, a performance evaluation conducted during a mechanical machining operation revealed that the GMWF showed an improved surface roughness of about 10.77% compared to conventional mineral MWF. Observations during the machining operation further revealed that the formulated GMWF demonstrated some level of environmental tolerance as it was not associated with misting or the discharge of fumes. The research outcome will impact green machining science and MWF technology for sustainable mechanical machining and cutting fluid development.

A Hail Climatology for Canada using a Lightning Proxy

Abstract Hail is a significant weather hazard in Canada, but its spatial and temporal distribution is poorly understood. We compiled a Canadian hail report database for 2005-2022, containing 7000 unique entries with estimates of the timing and location of the hail reports and estimated hail diameter. We developed a methodology to construct an estimate of the hail climatology across Canada using manual hail observations at airports and a lightning proxy. First, we estimated the probability of hail occurrence at airport locations across the country at any given hour using Bayesian inference. Next, we interpolated in space the probabilities to obtain smooth prior probabilities of hail occurrence at any location in Canada. Then, we refined these probabilities using lightning flash density as a proxy for the likelihood of hail, severe hail (diameter greater than 20 millimeters) or significant severe hail (diameter greater than 50 millimeters). Finally, we aggregated the posterior probabilities of hail, severe hail and significant severe hail over time and space and compared them with the number of reports found in the 2005-2022 Canadian hail database. Our results indicate that the posterior probabilities of hail are not consistent with the observed hail reports, and suggest that there are many gaps in hail reporting in Canada.

Insights into ground strike point properties in Europe through the EUCLID lightning location system

Abstract. Evaluating the risk of lightning strikes to a particular structure typically involves adhering to the guidance outlined in IEC 62305-2. Among the multitude of factors influencing the overall risk, flash density emerges as a crucial parameter. According to its definition, each flash is assigned only one contact point to ground. Nevertheless, it is well known that, on average, flashes exhibit multiple ground termination points as shown by high-speed camera observations. In this research, lightning data collected by the European Cooperation for Lightning Detection (EUCLID) network are utilized in combination with a ground strike point (GSP) algorithm that aggregates individual strokes within a flash into ground strike points. This approach enables the examination of spatio-temporal patterns of GSPs across Europe throughout a decade, spanning from 2013 to 2022. Average GSP densities exhibit variations across the European continent, mirroring the observed patterns in flash densities. The highest densities are concentrated along the Adriatic Sea and the western Balkan region, reaching peak values of up to 8.5 GSPs km−2 yr−1. The spatial distribution of the mean number of ground strike points per flash reveals a noticeable increase in the Mediterranean, Adriatic, and Baltic Sea regions compared to inland areas. Moreover, it has been determined that the average number of GSPs per flash reaches its peak between September and November. Additionally, a daily pattern is discernible, with the lowest number of GSPs per flash occurring between 12:00 and 18:00 UTC (universal time coordinated). It is found that 95 % of the separation distances between distinct GSPs are less than 6.7 km. Lastly, it is worth noting that the presence of the Alps has an impact on GSP behaviour, resulting in lower GSP counts in comparison to the surrounding areas, along with the shortest average distances between different GSPs.

Improving the lightning forecast with the WRF model and lightning data assimilation: Results of a two-seasons numerical experiment over Italy

We show, for the first time over Italy and over part of the central Mediterranean Basin, the impact of lightning data assimilation (LDA) on the strokes forecast for a long period. We use the Weather Research and Forecasting (WRF) model coupled with the Dynamic Lightning Scheme (DLS) at convection allowing horizontal resolution (3 km). We carried out a two-seasons experiment (summer 2020 and fall 2021) providing the forecast of lightning and precipitation for the next 6 h (nowcasting), considering two sub-periods (0-3 h and 3-6 h) for verification. The LDA is done through a nudging scheme that increases the water vapor mass in the mixed-phase region based on observed flash density rates and simulated graupel mixing ratio. No changes are made to the model run if spurious convection is predicted or no flashes are observed. LDA can trigger convection missed by the control forecast, without LDA, and/or can redistribute the strokes predicted to be more consistent with observations. LDA has a positive impact on strokes forecast, improving correct forecasts and reducing false alarms. This improvement is however confined to the first three-hours of forecast with negligible to negative impact for longer time ranges, in line with other studies. The improvement pattern is different in summer and fall, depending on the convection development.The analysis of the Fraction Skill Score shows the usefulness of the forecast for practical purposes, considering the current areas used by the Civil Protection Department to issue meteorological alerts for intense convective events over Italy. Finally, it is shown that the forecast at the short-range (0−3h) using LDA can improve the strokes forecast issued on the previous day, not using LDA, and the methodology of this paper can be applied to issue warnings and alerts as the storm is approaching.A brief examination of rainfall forecast shows positive impact of LDA at the short-range (0-3 h), with neutral impact for longer time ranges. The different impact of LDA on the strokes and precipitation forecasts is also highlighted.

Trends of lightning flash density over India during different seasons

AbstractLightning flash rate data measured by the Tropical Rainfall Measuring Mission (TRMM) for the period 1996–2013 over India are analysed to study the spatial and temporal variation of lightning over India during different seasons. The convective available potential energy (CAPE) and other thermodynamic parameters data for the same period are taken for analysis. This study confirms a systematic increase in lightning flash rate density in India during the last two decades. The annual lightning flash rate density is high along the windward side of the Himalayan foothills with two peaks, one over northwestern parts of India (>50 flashes·km−2·year−1) and the other over northeastern parts of India (>40 flashes·km−2·year−1). The pre‐monsoon (March–May) (0.176 flasheskm−2·year−1) and monsoon (June–September) (0.159 flashes·km−2·year−1) lightning trends are the largest contributors in explaining the annual trend of 0.099 flashes·km−2·year−1. All seasons have shown more or less positive trends while post‐monsoon (October–December) has shown a negative trend (−0.013 flashes·km−2·year−1). The seasonal variations show that the lightning is increasing more over northwest India during the monsoon and northeast India during the pre‐monsoon. To further understand the connection between lightning and climate change, a few thermodynamic or microphysical properties are also analysed. This analysis suggests that the high CAPE values together with thermodynamics and cloud microphysical processes are necessary for organized convection and lightning over this region. Additionally, correlation analysis is adopted to identify the main influencing factors and regions contributing to lightning variability. The increase in lightning activity is found to be due to an increase in CAPE, low‐level moisture content and temperature. The increase in temperature and moisture is attributed to the land use land cover (LULC) changes in India. The impact of the above proxies on lightning varies from region to region and season to season. As several regions are undergoing rapid transformation due to human activity, this study provides insights into the need to understand land use related changes to local and regional lightning activity.

Recurrent Lightning Spots: Where Lightning Strikes More Than Twice

AbstractThe expression “lightning never strikes twice” is questioned in this paper because, among the randomness of lightning impacts, some spots are hit even more than twice year after year. This article introduces the recurrent lightning spots (RLS) concept, which are locations periodically impacted by cloud‐to‐ground lightning every consecutive year over a certain period. RLS are investigated in two regimes, with markedly different lightning climatology but similar orography, for 10 consecutive years: Catalonia (North East of Spain, Europe) and Barrancabermeja (North Central Colombia, South America). Results revealed 148 and 916 RLS in Catalonia and Barrancabermeja, respectively. RLS in both regions are typically found to be related to tall structures, mountain peaks, and steep terrain. The method allowed us to identify those tall towers and orographic relief frequently affected by lightning that are not detected with the mere computation of the ground flash density. In the case of Catalonia, some RLS are found offshore. Besides the scientific interest in understanding lightning, the new concept of RLS provides additional and valuable information applicable to lightning protection engineering.

Spatiotemporal Distributions of the Thunderstorm and Lightning Structures over the Qinghai–Tibet Plateau

Utilizing data from the Tropical Rainfall Measuring Mission (TRMM) satellite’s precipitation radar (PR) and lightning imaging sensor (LIS), this study explores the spatiotemporal distributions of thunderstorm and lightning structures over the Qinghai–Tibet Plateau (QTP), an aspect that has not been explored previously. The structural aspects are crucial when considering the impact of thunderstorm and lightning activity in the atmospheric processes. Thunderstorms over the QTP show clear spatial variations in both vertical height and horizontal extension. In the southern region, the average heights of 20 dBZ and 30 dBZ echo tops typically exceed 11.2 and 9.3 km, respectively. Meanwhile, in the eastern part, the average coverage areas for reflectivity greater than 20 dBZ and 30 dBZ consistently surpass 1000 and 180 km2, respectively. The spatial distribution of thunderstorm vertical development height relative to the surface aligns more closely with the horizontal extension, indicating stronger convection in the eastern QTP. The thunderstorm flash rate shows an eastward and northward prevalence, while the thunderstorm flash density peaks in the western and northeastern QTP, with a minimum in the southeast. Furthermore, in the eastern QTP, lightning duration, spatial expansion, and radiance are more pronounced, with the average values typically exceeding 0.22 s, 14.5 km, and 0.50 J m−2 sr−1 μm−1, respectively. Monthly variations reveal heightened values during the summer season for thunderstorm vertical extension, areas with reflectivity greater than 30 dBZ, and lightning frequency. Diurnal variations highlight an afternoon increase in thunderstorm vertical and horizontal extension, lightning frequency, duration, and spatial scale. From a statistical perspective, under weak convective conditions, lightning length exhibits a positive correlation with thunderstorm convection intensity, contrasting with the opposite relationship suggested by previous studies. This article further analyzes and discusses the correlations between various thunderstorm and lightning structural parameters, enhancing our understanding of the distinctive features of thunderstorm and lightning activities in the QTP.

Comparative Analysis of Kerosene Grade Fuel from Pyrolysis of HDPE and LDPE Waste Plastics

To curb the menace of plastic waste and energy crisis, this study investigated the conversion of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) grades of plastics to kerosene. Plastics sourced from dumpsites within Port Harcourt metropolis in Rivers State, Nigeria were shredded and pyrolyzed (thermally degraded under inert condition at a temperature range of 350-400oC). The obtained hydrocarbon liquid was distilled using distillation column at a temperature range of 150-270oC and characterised to evaluate the physico-chemical parameters such as flash point, density, copper corrosion, and calorific value and compared against the acceptable standard. The result showed that these properties were within the permissible limit. However, the sulphur content and smoke point of HDPE and LDPE were above and below the limits, respectively. The GC-MS and GC-FID results of kerosene samples obtained from both grades of plastics indicates that the product comprised C9 to C17 grades.

Conversion of Low-Density Polyethylene (LDPE) and Mixed Low-Density Polyethylene with Polyethylene Terepthalate (LDPE and PET) into Hybrid Fuel

This research aims to provide the recycling techniques of low-density polyethylene (LDPE) and mixture of polyethylene terephthalate (PET) with low-density polyethylene (LDPE) waste. As a means of converting abundant waste to wealth, pyrolysis of LDPE and mixed LDPE - PET was carried out in a batch reactor made of stainless steel at temperatures between 450 – 460OC. The vapor produced from melting the waste was condensed to form the liquid hydrocarbon (fuel oil) product. The effect of reaction time and product yield were investigated. The physicochemical properties of the pyrolysis oil measured include density, specific gravity, flash point, color, fire point, flammability and viscosity. For the LDPE the flash point, fire point, density, specific gravity, and viscosity was found to be 39.5 oC, 48 oC, 8.1872, 0.793g/cm, 0.775g/cm3, and 1.566 cSt respectively while for the Mixture of LDPE with PET the flash point, fire point, density, specific gravity, viscosity and Sulphur content was found to be 44 oC, 48 oC, 8.1872, 0.7837g/cm, 0.7916 g/cm3, 1.1660 cSt and 8.1872 respectively. These values were found to be within the range of kerosene values. The fuel was tested in both kerosene lamp and petrol generator.

Development of GIS-based Ground Flash Density and its Statistical Analysis for Lightning Performance Evaluation of Transmission Lines in Peninsular Malaysia

Malaysia is one of the world's highest lightning regions, making it an ideal location for studying lightning activities, as they cause many power outages on overhead transmission lines. This study presents ground flash density (GFD) mapping and statistical analysis of lightning flash data in Peninsular Malaysia, which will be used to evaluate the lightning performance of transmission lines. Using Geographical Information System (GIS) software, the GFD map and lightning flash data for statistical analysis were extracted. MATLAB was then used to perform statistical analysis and obtain the probability of peak lightning current using the generalized extreme value (GEV) distribution. This study analyzed six years of lightning flash data from 2012 to 2017 recorded by the Lightning Location System (LLS) and used the Peninsular Malaysia base map from the Department of Survey and Mapping Malaysia (JUPEM). Results show that the GFD mapping approach effectively classifies GFD distribution and identifies areas with high lightning activity. 81% of 4,536,380 lightning flashes were negative polarity, with a higher mean peak current magnitude than positive ones. More lightning activity was observed during the Southwest Monsoon (June-September) and the first Inter-Monsoon season (April-May). Pahang had the most lightning flashes due to its large land area. The GFD map overlaid on the transmission line demonstrated how lightning performance on the transmission line can be assessed. These findings are useful for utility and protection engineers to improve the performance of transmission lines.

Mechanistic and kinetic aspects of florfenicol degradation by [rad]OH: Chloride moiety resistance

Antibiotic residues in aquatic environments can be effectively degraded by hydroxyl radical (OH)-based advanced oxidation processes (AOPs). However, the reaction kinetics and mechanisms have not been comprehensive determined due to the limitations of conventional competition kinetic methods and mass spectrometry-based product identification, as these methods fail to exclude interference from secondary radicals and are unable to capture unstable intermediates or transient species. In this study, these limitations were overcome using laser flash photolysis (LFP) and density functional theory (DFT) calculations, allowing accurate determination of the OH-initiated reaction kinetics and degradation mechanisms of florfenicol (FF), a model veterinary antibiotic compound that is frequently detected in the environment. Based on the LFP experiment results, the second order rate constant (k) between OH and FF was determined to be 1.96 × 109 M−1 s−1 by tracking the typical signal of (SCN)2−. Furthermore, DFT calculations revealed two distinct mechanisms for OH addition to the benzene ring and identified hydrogen atom abstraction (HAA) reaction from chiral carbons as being the most favorable initial reaction for OH. In addition, the destruction of chlorine moiety occurred via hydroxylation-chlorine abstraction, rather than direct chlorine abstraction or substitution reactions. The resistance of chlorine moiety to degradation during the initial oxidation process, resulted in the formation of chlorine-containing by-products. This study provided a novel approach to comprehensively investigate the mechanisms of emerging contaminants elimination during OH-based AOPs.

Introducing the Concept of the Volume Lightning Strike Density

This letter introduces the concept of the volume lightning strike density (vLSD) and provides the mathematical framework for transitioning from a 2D to a 3D electrogeometric analysis; this may offer new insights into established methodologies for lightning incidence estimation and risk assessment. The feasibility of the vLSD idea is based on the intensive research conducted on emerging technologies of 3D reconstruction of lightning discharges path. Thus, based on the vLSD concept, a new lightning activity parameter <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">NV</i> (strikes/km3/yr), that is, the average number of lightning strikes with at least one leader branch per cubic kilometer per year in an area, can be quantified in light of the widespread installation of modern lightning discharge recording systems. This work may open new horizons on lightning activity characterization offering an alternative or complementary approach to the traditional concept of the ground flash density, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">NG</i> (flashes/km2/yr); the proposed vLSD concept could also be applied in evaluating the lightning interception efficiency of traditional as well as advanced lightning protection systems especially at critical sites, where enhanced lightning protection is of importance.

The influence of catalyst on the characteristics of biodiesel from waste cooking oil

The aim of this research was to investigate the influence of catalyst on the flash point, viscosity, density, and iodine value of biodiesel. The raw material used in biodiesel production was waste cooking oil. The transesterification process was employed by reacting the catalyst and methanol, followed by mixing them with the waste cooking oil simultaneously. The catalyst concentration variations used in this study were 0.25% and 0.5%. The resulting transesterification mixture was left to settle for approximately 10 minutes. The biodiesel and glycerol were separated after settling, and the biodiesel was washed with distilled water at a temperature of 50°C and then evaporated at 100°C. The flash point test results for catalyst concentrations of 0.25% and 0.5% were 58°C and 48.5°C, respectively. The viscosity test results for catalyst concentrations of 0.25% and 0.5% were 4.567 x 10-6 m2/s and 4.625 x 10-6 m2/s, respectively. The density test results for catalyst concentrations of 0.25% and 0.5% were 889 kg/m3 and 888.3 kg/m3, respectively. The iodine value test results for catalyst concentrations of 0.25% and 0.5% were 112.2 g I2/100g and 114 g I2/100g, respectively. Based on the test data, the flash point, viscosity, density, and iodine value were obtained. The test results indicated that the flash point values from both experiments did not meet the biodiesel quality standards. However, the viscosity and density test results from both experiments met the biodiesel quality standards and were suitable for use. Regarding the iodine value test, the characteristics of the biodiesel from both experiments did not fully meet the biodiesel standard, although the results obtained were not significantly different from the quality standards set by the Ministry of Energy and Mineral Resources

Spatial Structure of Lightning and Precipitation Associated with Lightning-Caused Wildfires in the Central to Eastern United States

The horizontal storm structure surrounding 92,512 lightning-ignited wildfires is examined in the mid to eastern sections of the United States from 2003 to 2015 using Vaisala’s National Lightning Detection Network (NLDN), NCEP’s Stage IV gauge-corrected radar precipitation mosaic, and the US Forest Service’s Fire Occurrence Database. Though lightning flash density peaks strongly around fire ignitions on the instantaneous 1 km scale, on the hourly 10 km scale, both the lightning and precipitation peaks are typically offset from fire ignitions. Lightning density is higher, and precipitation is lower around ignition points compared to non-ignition points. The average spatial distribution of total lightning flashes around fire ignitions is symmetrical, while that of precipitation and positive flashes is not. Though regression is consistent with the claim that positive flashes have a stronger association with ignition than negative flashes, the statistical significance is ambiguous and is contradicted by an unchanging positive flash fraction in the vicinity of wildfires.

Observation and Simulation of Lightning Strikes in an Offshore Wind Turbine Cluster

AbstractBased on the detection data of the Guangdong‐Hong Kong‐Macau lightning location system from 2013 to 2022, this paper analyzes the characteristics of lightning strikes in an offshore wind turbine cluster (WTC) in Guangdong. This is the first time to quantify the lightning strikes difference between the inner and outer wind turbines (WTs) and discuss the impact mechanisms of WTCs on the characteristics of lightning strikes by the simulation results of electric potential distribution. The observation results show that the stroke density, cloud‐to‐ground (CG) flash density, and average peak current within the affected area increase by 10.1%, 11%, and 5.1%, respectively, but the lightning multiplicity changes little. The inner and outer WTs show different characteristics of lightning strikes. The stroke density, lightning multiplicity, and average peak current in the area of outer WTs increase by 21%, 4.1%, and 6.8%, respectively, while in the area of inner WTs decrease by 20.2%, 19%, and 3.9%, respectively. The CG flash density in the area of outer WTs increases by 16.1% but changes little in the area of inner WTs. The simulation results show there is a significant difference in the electric potential distribution between the inner and outer WTs: the distortion effect of the outer WTs on spatial electric potential is stronger than that of the inner WTs at a greater height, but the difference is not obvious at a lower height. Such a difference in electric potential distribution leads to different characteristics of lightning strikes between the inner and outer WTs.

OVERVIEW OF FACTORS AFFECTING THE ESTIMATION OF LIGHTNING SHIELDING PERFORMANCE OF OVERHEAD TRANSMISSION LINES

This paper examines the risk of lightning stroke to overhead transmission line. The estimation procedure for the lightning performance of overhead power lines is based on the selected lightning attachment model, available lightning parameter statistics, the transmission tower design and voltage levels, type of overvoltage and other characteristics. In this paper the overview of factors affecting the estimation of lightning shielding performance of overhead transmission lines was performed. Among the factors that can affect the estimation accuracy, one can list insufficiently accurate data on the ground flash density in the area of interest and lack of complete data on statistical distribution of lightning current magnitudes. The paper shows that the influence of wind on the increase in the horizontal exposed distance of the phase conductor is not also taken into account. In this research traditional electro-geometric model was used for estimation of lightning performance of 220 kV overhead power line. Results obtained suggest that swing of suspension insulator strings caused by strong winds may lead to increased risk of lightning shielding failure during thunderstorm. Calculation performed for 3 kA lightning current magnitude shows that at swing angle equal to –1 degree, the horizontal unprotected distance of phase conductor increases by 3.1%, that corresponds to 5.240 m uncovered width. When the swing angle is increased to –5 degree, the uncovered width is increased by 15.8% that corresponds to 5.885 m uncovered width. It is proposed that an increase in the risk of lightning shielding failure as a result of wind load can be accounted by applying an appropriate correction factor in expressions for calculation of shielding failure rate, shielding failure flashover rate, etc. Proposed correction factor should account frequency and strength of wind in the area of transmission line route and depend on transmission line voltage level and tower design. Further efforts should be focused on obtaining and justifying the numerical values ​​of this correction factor.

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 (&gt;100%, 50-100%, 20-50%, and &lt; 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.

Spatiotemporal patterns of long series of cloud-to-ground lightning in Beijing and its cause

Previous studies on the climatic characteristics of lightning activity in Beijing are sparse due to the lack of long-term, continuous and stable lightning location data. In this paper, the long series of lightning location data during 2009–2018 were applied to reveal the spatiotemporal distribution of cloud-to-ground (CG) lightning in Beijing. The spatial characteristics were low west and high east, and the temporal characteristics were frequent in summer. In the complex terrain areas of northeast Beijing, there was a positive relationship between CG density and altitude, with the correlation coefficient higher than 0.8. The northeastern trumpet-shaped terrain had the forced lifting effect on thunderstorms, forming lightning-intensive areas of 500 km2. In addition, urban heat island (UHI) effect provided the necessary thermal conditions for the development of thunderstorms, forming lightning-intensive areas in the built-up areas, with the highest value of CG flash density exceeding 6 fl/km2. Note that the lightning-sparse areas in the urban center exhibited a distinct barrier effect on the spatial patterns of summertime CG lightning in the built-up areas, which was mainly modulated by the type of synoptic background.