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Enhanced Positive Cloud-to-Ground Lightning in Thunderstorms Ingesting Smoke from Fires
Abstract
Smoke from forest fires in southern Mexico was advected into the U.S. southern plains from April to June 1998. Cloud-to-ground
lightning (CG) flash data from the National Lightning Detection Network matched against satellite-mapped aerosol plumes imply
that thunderstorms forming in smoke-contaminated air masses generated large amounts of lightning with positive polarity (+CGs).
During 2 months, nearly half a million flashes in the southern plains exhibited +CG percentages that were triple the climatological
norm. The peak currents in these +CGs were double the expected value. These thunderstorms also produced abnormally high numbers
of mesospheric optical sprites.
... This may increase the hazard potential of the +CG lightning relative to the -CG lightning. Also, +CG lightning is commonly known to remain associated with luminous phenomena in the upper atmosphere such as sprites (Lyons et al., 1998a(Lyons et al., , 1998bBoccippio et al., 1995). It is also reported that +CG lightning often involves long horizontal channels, thereby increasing its hazard potential (Peterson and Stano, 2021). ...
... For example, Pawar et al. (2012) have shown that thunderstorms occurring in the presence of high aerosol optical depth may become inverted polarity storms and produce a large number of +CG lightning. Lyons et al. (1998aLyons et al. ( , 1998b observed the dramatic increase of +CG lightning over United stated southern plains due smoke ingested aerosol particles. Along with the monsoon circulation there exhibit a long range dust and sea salt transport over the Indian subcontinent (Lau et al., 2017). ...
... Gole and Midya (2021) reported a reduction in pollution levels during the COVID-19 lockdown year, along with positive correlations between lightning and surface pollutants across major Indian cities. In North America, the observed increase in positive polarity CG flashes has been attributed to the introduction of Mexican fire smoke into the region, subsequently serving as a source of fuel for thunderstorms (Lyons et al. 1998;Murray et al. 2000). This phenomenon establishes a connection between atmospheric convection, aerosols, This preprint research paper has not been peer reviewed. ...
The impacts of the COVID-19 lockdown on thunderstorm properties, influenced by changes in air quality, were investigated in Northeastern (Kohima, 25.66° N, 94.08° E) and Eastern (Rampurhat, 24.17° N, 87.78° E) India using seven years of ground-based observations. During the lockdown period (LP), Cloud-to-Ground (CG) flashes decreased by 67% and 51% over Kohima and Rampurhat respectively. Reductions were noted in the number of thunderstorms and various intensity parameters such as duration, flashes per thunderstorm, Peak Flash Rate (PFR), IC: CG ratio, and lightning peak currents. Significant changes in anthropogenic aerosols were observed, with notable reductions in SO₂, NO₂, and PM₁₀ levels. Regardless of the specific raindrop formation mechanism in the two regions, higher concentrations of moderate to larger raindrops were observed during LP. Also, the mixed-phase region of thunderstorms shows a reduction in water content (both liquid and ice) in the mixed phase and the total column. Daily-scale analysis reveals non-linear associations between pollutant concentrations and CG flashes in both regions, with relative humidity (RH) potentially influencing these relationships. Overall, thunderstorm intensity parameters, mixed-phase processes, and rain DSDs were associated with reduced pollutant concentrations during LP. The similarity of trends in multiple parameters during PLP-LP-ALP aligns with established facts, affirming that reduced pollutants lead to noticeable changes in thunderstorm characteristics. The partial rebound of pollutants and other parameters during ALP remained below pre-lockdown levels, which might suggest the lasting impacts of reduced human activities on atmospheric conditions. Further research is necessary to confirm if these measures could mitigate climatic changes and potentially guide policymakers in addressing such changes. This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4911254
... Research on their influences on lightning activity, however, is much less partly due to the much fewer available observations of lightning counts compared to precipitations. Existing studies have revealed possible linkages between aerosols and lightning frequency over land from observations (Lyons et al 1998, Naccarato et al 2003, Altaratz et al 2010, Alizadeh-Choobari and Gharaylou 2017, Blossey et al 2018. Wang et al (2011) showed that high aerosol loading tended to enhance the frequency of heavy rainfalls and lightning strikes over a megacity in China, and attributed the enhancement to changes in cloud microphysics and the release of latent heat released by aerosols. ...
Long-term (2005-2021) observations from the World Wide Lightning Location Network (WWLLN) reveal significantly larger flash counts over heavily trafficked shipping lanes in the northeastern Indian Ocean compared to nearby regions. Here, we use the online coupled meteorology-chemistry model WRF-Chem to examine the impact of aerosols from shipping emissions on lightning activity over one of the world’s busiest shipping lanes (5-7°N, 82-92°E). We conduct three case simulations in January 2013, 2015, and 2018 when frequent lightning activities were recorded. The WRF-Chem model with lightning parameterized based on convective cloud-top height captures the temporal evolution of lightning activities but overestimate the magnitude of lightning counts. We find that all three cases consistently show enhanced lightning flash counts due to shipping-induced aerosols by 6.2-22.3%, accompanied with increased cloud droplet number, cloud water concentration, radar reflectivity, and cloud-top height. Sensitivity simulations show that aerosol-cloud-interactions (ACIs) from shipping aerosols consistently enhance the strength of convection and lightning frequency in all three cases, by increasing cloud condensation nuclei (CCN) and cloud droplet numbers, delaying precipitation of cloud water, allowing the lift and accumulation of water vapor, increasing release of latent heat, and finally invigorating convections. In comparison, aerosol-radiation-interactions (ARIs) show inconsistent contributions to convection and lightning, which enhance lightning frequency in the 2013 and 2015 cases but decrease lightning frequency in the 2018 case. This inconsistency may be attributed to differences in the number and vertical structure of shipping aerosols and cloud droplet in the three cases. Our study thus approves the certain but complicated anthropogenic impacts on lightning activities through shipping-induced aerosols, which has important implications for understanding future trends in lightning and its impact on atmospheric chemistry and climate.
... The aviation industry is a major user of LLSs, with air traffic controllers redirecting flights as soon as weather hazards are detected. LLS alarms are also equipped in fire detectors in forestry areas, outdoor activities, and sports facilities to warn the public [20,21]. Many outdoor activities such as recreation centers and outdoor facilities such as transmission lines can be influenced by lightning [22][23][24][25]. ...
Cloud-to-ground (CG) lightning is a natural phenomenon that poses significant threats to human safety, infrastructure, and equipment. The destructive impacts of lightning strikes on humans and their property have been a longstanding concern for both society and industry. Countries with high thunderstorm frequencies, such as Malaysia, experience significant fatalities and damage due to lightning strikes. To this end, a lightning locating system (LLS) was developed and deployed in a 400 km² study area at the University Technology Malaysia (UTM), Johor, Malaysia for detecting cloud-to-ground lightning discharges. The study utilized a particle swarm optimization (PSO) algorithm as a mediator to identify the best location for a lightning strike. The algorithm was initiated with 30 particles, considering the outcomes of the MDF and TDOA techniques. The effectiveness of the PSO algorithm was found to be dependent on how the search process was arranged. The results of the detected lightning strikes by the PSO-based LLS were compared with an industrial lightning detection system installed in Malaysia. From the experimental data, the mean distance differences between the PSO-based LLS and the industrial LLS inside the study area was up to 573 m. Therefore, the proposed PSO-based LLS would be efficient and accurate to detect and map the lightning discharges occurring within the coverage area. This study is significant for researchers, insurance companies, and the public seeking to be informed about the impacts of lightning discharges.
... In [12,13], the authors related the anthropogenic increase in aerosol concentration in large urban centers to the decrease in positive CG. From a different point of view, smoke aerosol caused by forest fires contributes to the increase in positive lightning [14][15][16]. The final stage of Tropical Cyclones (TCs) is usually accompanied by intense positive CG lightning activity. ...
Lightning Electromagnetic Pulses, or LEMPs, propagate in the Earth–ionosphere waveguide and can be detected remotely by ground-based lightning electric field sensors. LEMPs produced by different types of lightning processes have different signatures. A single thunderstorm can produce thousands of LEMPs, which makes their classification virtually impossible to carry out manually. The lightning classification is important to distinguish the types of thunderstorms and to know their severity. Lightning type is also related to aerosol concentration and can reveal wildfires. Artificial Intelligence (AI) is a good approach to recognizing patterns and dealing with huge datasets. AI is the general denomination for different Machine Learning Algorithms (MLAs) including deep learning and others. The constant improvements in the AI field show us that most of the Lightning Location Systems (LLS) will soon incorporate those techniques to improve their performance in the lightning-type classification task. In this study, we assess the performance of different MLAs, including a SVM (Support Vector Machine), MLP (Multi-Layer Perceptron), FCN (Fully Convolutional Network), and Residual Neural Network (ResNet) in the task of LEMP classification. We also address different aspects of the dataset that can interfere with the classification problem, including data balance, noise level, and LEMP recorded length.
... While it is unclear how aerosol impacts differ in terrestrial versus maritime environments, we expect findings from other regions and modeling studies to have some applicability to the MC. These include a host of aerosol-induced micro-and macro-physical changes in clouds (e.g., Tao et al., 2012;Dey et al. 2011), such as delays in warm rain formation (Berg et al., 2008) and congestus and overall storm invigoration (e.g., Lyons et al., 1998;Wang et al., 2009;Storer et al., 2014). Modeling studies are largely consistent in warm phase cloud processes, but less so as ice nucleation begins to take hold (Khain et al., 2005;van den Heever et al., 2006;Saleeby et al., 2010;Cotton et al., 2012;Fan et al., 2013;Grant and van den Heever, 2015;Sheffield et al., 2015;Mace and Abernathy, 2016;Gryspeerdt et al., 2017). ...
The NASA Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP ² Ex) employed the NASA P-3, Stratton Park Engineering Company (SPEC) Learjet 35, and a host of satellites and surface sensors to characterize the coupling of aerosol processes, cloud physics, and atmospheric radiation within the Maritime Continent’s complex southwest monsoonal environment. Conducted in the late summer of 2019 from Luzon Philippines in conjunction with the Office of Naval Research Propagation of Intraseasonal Tropical OscillatioNs (PISTON) experiment with its R/V Sally Ride stationed in the North Western Tropical Pacific, CAMP ² Ex documented diverse biomass burning, industrial and natural aerosol populations and their interactions with small to congestus convection. The 2019 season exhibited El Nino and associated drought, high biomass burning emissions, and an early monsoon transition allowing for observation of pristine to massively polluted environments as they advected through intricate diurnal mesoscale and radiative environments into the monsoonal trough. CAMP ² Ex’s preliminary results indicate 1) increasing aerosol loadings tend to invigorate congestus convection in height and increase liquid water paths; 2) lidar, polarimetry, and geostationary Advanced Himawari Imager remote sensing sensors have skill in quantifying diverse aerosol and cloud properties and their interaction; and 3) high resolution remote sensing technologies are able to greatly improve our ability to evaluate the radiation budget in complex cloud systems. Through the development of innovative informatics technologies, CAMP ² Ex provides a benchmark dataset of an environment of extremes for the study of aerosol, cloud and radiation processes as well as a crucible for the design of future observing systems.
The impacts of the COVID-19 lockdown on thunderstorm properties, influenced by changes in air quality, were investigated in Northeastern (Kohima, 25.66° N, 94.08° E) and Eastern (Rampurhat, 24.17° N, 87.78° E) India using seven years of ground-based observations. During the lockdown period (LP), Cloud-to-Ground (CG) flashes decreased by 67 % and 51 % over Kohima and Rampurhat respectively. Reductions were noted in the number of thunderstorms and various intensity parameters such as duration, flashes per thunderstorm, Peak Flash Rate (PFR), IC: CG ratio, and lightning peak currents. Significant changes in anthropogenic aerosols were observed, with notable reductions in SO₂, NO₂, and PM₁₀ levels. Regardless of the specific raindrop formation mechanism in the two regions, higher concentrations of moderate to larger raindrops were observed during LP. Also, the mixed-phase region of thunderstorms shows a reduction in water content (both liquid and ice) in the mixed phase and the total column. Daily-scale analysis reveals non-linear associations between pollutant concentrations and CG flashes in both regions, with relative humidity (RH) potentially influencing these relationships. Overall, thunderstorm intensity parameters, mixed-phase processes, and rain DSDs were associated with reduced pollutant concentrations during LP. The similarity of trends in multiple parameters during PLP-LP-ALP aligns with established facts, affirming that reduced pollutants lead to noticeable changes in thunderstorm characteristics. The partial rebound of pollutants and other parameters during ALP remained below pre-lockdown levels, which might suggest the lasting impacts of reduced human activities on atmospheric conditions. Further research is necessary to confirm if these measures could mitigate climatic changes and potentially guide policymakers in addressing such changes.
Aerosol effects on the lightning intensity and polarity of a continental supercell storm were investigated using a three‐dimensional lightning scheme within the Weather Research and Forecasting model. We find that both intra‐cloud (IC) and cloud‐to‐ground (CG) flashes are enhanced by the increasing number of cloud condensation nuclei (CCN), especially the percentage of positive CG (+CG) strokes peaking at 42%. Electrical characteristics of the storm varied in different aerosol scenarios through microphysical processes. Added aerosols increase the number of cloud droplets and ice‐phase hydrometeors. The greater ice‐crystal concentration and larger graupel size ensure sufficient charge separation, leading to higher charge density and more lightning discharges. In addition, an inverted polarity charge structure with a strong positive‐charge region in the mid‐levels was formed mainly due to the positively charged graupel in the presence of higher supercooled cloud water content. Positive lightning channels originating from this positive‐charge region propagated to the ground, producing more +CG strokes. When the aerosol concentration was low, the charge density in the upper positive‐charge region was much lower due to smaller ice‐particle content. Consequently, there were barely any +CG strokes. Most of the negative CG flashes deposited positive charge in the lower negative‐charge region.
The number of fires in the Amazon region increased dramatically at the beginning of 2022 compared to 2021.
Considering that this period is also characterized by a large incidence of cloud-to-ground (CG) lightning in this
region, we investigated if these phenomena may be related to each other. Two regions of Brazil were considered
in the analysis: Mato Grosso state, on the border of the Amazon region where most of the deforestation occurs,
and Amazonas state, in the interior of the Amazon region. In the first four months of 2022, 26,554 fires and
approximately 3 million CG lightning flashes in Mato Grosso and 2468 fires and about 3.4 million CG lightning
flashes in Amazonas were recorded. By comparison, in 2021, 16,844 fires and approximately 2.7 million CG
lightning flashes in Mato Grosso and 1258 fires and about 3.2 million CG lightning flashes in Amazonas were
recorded. In this study, we examined whether these phenomena were linked on a 2 to 9-day timescale, utilizing
wavelet coherence analysis of both fire and lightning data. Our results indicate that these phenomena are linked
(p < 0.05) for several weeks in both regions in both years. Additionally, correlations for 2022 were notably
higher (above 0.90 versus 0.80) when the incidence of fires and lightning was higher, lending support to the
notion of a relationship between these two events. Considering the periodicity characteristics of our results and
that most fires in these regions are human-induced, we conclude that anthropogenic fires may affect lightning
activity through aerosol-cloud particle interactions, with additional and not previously documented implications
for climate change. Assuming the same is happening in other regions of the planet, we may face a new aspect not
considered in the present global climate model projections.
A clear association between large peak current cloud-to-ground lightning flashes of positive polarity and sprites and elves in the stratosphere and mesosphere has been previously demonstrated. This paper reports on the first climatology of large peak current cloud-to-ground (LPCCG) lightning flashes compiled from the U.S. National Lightning Detection Network. Analysis of almost 60 million CG flashes from 14 summer months (1991–95) reveals distinct geographic differences in the distribution of positive and negative polarity LPCCGs, arbitrarily defined as flashes with peak currents 75 kA. Large peak current positive CGs (LPCCGs) are concentrated in the High Plains and upper Midwest, the region in which a large majority of optical sprite and elves observations have been obtained. By contrast, large peak current negative CGs (LPCCGs) preferentially occur over the coastal waters of the Gulf of Mexico and the southeastern United States. A total of 1.46 million LPCCGs were found, of which only 13.7% were CGs. Almost 70% of the LPCCGs, however, occurred in the central United States (30–50N, 88–110W). The percentage of all LPCCGs that were positive approached 30% in the central United States compared to 4.5% for the remainder of the country. A CG is 3.1 times more likely to exceed 75 kA than is a CG flash on a national basis. Yet in terms of absolute numbers for all ranges of peak current 75 kA, negative CGs are clearly dominant. For peak currents 75 and 200 kA, negative CGs outnumbered positive CGs by ratios of 6.4 and 4.1, respectively. In the central United States, however, during evening hours the number of LPCCGs almost reaches parity with LPCCGs. Average stroke multiplicity also exhibited regional differences. Over a half million negative CGs and over 1000 positive CGs were found with multiplicity 10.
It is generally accepted that atmospheric pollutants can be transported over distances described as synoptic in scale. However, the redistribution and removal of the various pollutant species may be significantly influenced, often in a highly episodic way, by phenomena which are inherently mesoscale in nature.
Transient luminous events (sprites, blue jets, elves) above large mesoscale convective systems (MCSs) over the U.S. High Plains have been routinely monitored from the Yucca Ridge Field Station near Fort Collins, Colorado using ground-based low-light video systems. We analyzed 36 sprites above the Nebraska MCS of August 6, 1994. The results lend further support to the hypothesis that sprites are almost uniquely associated with positive cloud-to-ground (+CG) lightning flashes. Sprite-associated +CGs also averaged substantially larger peak currents than the remaining +CG population (81 kA versus 30 kA in this storm system). There is some evidence that sprite-associated +CGs also have higher stroke multiplicity. This study yields no evidence of sprites associated with negative CG events. In the central United States an additional requirement appears to be that the parent MCS has a contiguous radar reflectivity area exceeding 20-25,000 km 2. The majority of the sprites occur above the large stratiform precipitation region and not the high-reflectivity convective core of the MCS. Triangulation of a limited number of paired images (from September 7, 1994) suggests that the sprite is generally centered within 50 km of the parent +CG. Assuming the +CG provides the range, single-image photogrammetric analyses provide estimates of the maximum vertical extent of the sprites. For this storm the sprite tops averaged 77 km with a maximum of 88 km. The bases averaged 50 km but with a few sprite tendrils extending as low as 31 km.
A prescribed fire ignited in western Ontario on August 10, 1989 burned from 1400 to 1700 EDT, generating a plume cloud structure including a portion resembling an anvil. From 1500-1630, 21 ground flashes lowering positive charge from the cloud as well as four negative flashes near the beginning of the time period that were not recognized as ground flashes. These four flashes out of a total of 37 flashes exceeding 90 V/m were the only flashes perceived as lowering negative charge; all the others lowered positive charge. The median current of the positive flashes to ground was 6 kA. Simple charge distribution models indicate that the plume and associated cloud had a monopolar charge distribution with positive charge at altitude and that the fire was most probably the source of this charge. A charge generation rate of 2 nC/sq m/s by the fire could generate enough charge to satisfy the flash discharge rate and amount using the simplest model.
Cloud-to-ground lightning data for the years 1992-95 have been analyzed for geographical distribution of total flashes, positive flashes, and the percentage of flashes that lower positive charge to ground. In the contiguous United States the measured total cloud-to-ground lightning flash counts were 16.3 million (1992), 24.2 million (in both 1993 and 1994), and 22.3 million in 1995. The maximum flash densities occurred in Florida in 1992 (9-11 flashes per square kilometer) and in the Midwest in 1993 (11-13 flashes per square kilometer), coinciding with the storms and floods that dominated the summer of 1993 in the Midwest. In 1994, the area of maximum flash density was again in Florida (11-13 flashes per square kilometer). In 1995, the flash density maxima (9-11 km-2) were in southern Louisiana and near the Kentucky-Illinois border. Positive flash densities had maxima in the Midwest in all four years with values of 0.4 (1992), 1.0 (1993), 0.7 (1994), and 1.8 flashes per square kilometer (1995). The annual mean percentage of flashes that lowered positive charge to ground was between 4% and 5% for the three years, 1992-94, but increased to 9.3% in 1995. The monthly values of the percentage of positive flashes ranged from 3% (August 1992) to 25% (December 1993). The positive flash maxima in the Midwest appear to be near the geographical areas in which cloud-ionosphere discharges (sprites) have been reported.
Further laboratory studies have been made of the charge transferred when ice crystals collide and then separate from an ice target. Previous results indicated increased charge transfer when cloud droplets were present. The new data show that the size distribution of the droplets is important. When the cloud droplets are too small to collide with the growing target, it charges negatively; for the same liquid water content but with larger droplets that hit the target, it charges positively. The results suggest that the relative growth rate and the surface states of both the interacting bodies may be important in controlling the sign of the charge transfer. It is suggested that these results may explain the observation of negative charge centers in thunderstorms at temperatures warmer than -20°C.
On 20/21 August 1993, deep convective storms occurred across much of Arizona, except for the southwestern quarter of the state. Several storms were quite severe, producing downbursts and extensive wind damage in the greater Phoenix area during the late afternoon and evening. The most severe convective storms occurred from 0000 to 0230 UTC 21 August and were noteworthy in that, except for the first reported severe thunderstorm, there was almost no cloud-to-ground (CG) lightning observed during their life cycles. Other intense storms on this day, particularly early storms to the south of Phoenix and those occurring over mountainous terrain to the north and east of Phoenix, were prolific producers of CG lightning. Radar data for an 8-h period (2000 UTC 20 August-0400 UTC 21 August) indicated that 88 convective cells having maximum reflectivities greater than 55 dBZ and persisting longer than 25 min occurred within a 200-km range of Phoenix. Of these cells, 30 were identified as `low-lightning' storms, that is, cells having three or fewer detected CG strikes during their entire radar-detected life cycle. The region within which the low-lightning storms were occurring spread to the north and east during the analysis period.Examination of the reflectivity structure of the storms using operational Doppler radar data from Phoenix, and of the supportive environment using upper-air sounding data taken at Luke Air Force Base just northwest of Phoenix, revealed no apparent physical reasons for the distinct difference in observed cloud-to-ground lightning character between the storms in and to the west of the immediate Phoenix area versus those to the north, east, and south. However, the radar data do reveal that several extensive clouds of chaff initiated over flight-restricted military ranges to the southwest of Phoenix. The prevailing flow advected the chaff clouds to the north and east. Convective storms that occurred in the area likely affected by the dispersing chaff clouds were characterized by little or no CG lightning.Field studies in the 1970s demonstrated that chaff injected into building thunderstorms markedly decreased CG lightning strikes. There are no data available regarding either the in-cloud lightning character of storms on this day or the technical specifications of the chaff being used in military aircraft anti-electronic warfare systems. However, it is hypothesized that this case of severe, but low-lightning, convective storms resulted from inadvertent lightning suppression over south-central Arizona due to an extended period of numerous chaff releases over the military ranges.
In 4 of the 15 storms, ground flash activity was dominated by positive cloud-to-ground lightning throughout most of the life of the storm. In 11 storms, the dominant polarity of ground flashes switched from positive to negative sometime during the mature stage of the storm. In all cases observed by Doppler radar, storms dominated by positive flashes had at least some rotation, and in most cases they were low-precipitation or classic supercell storms. In all cases for which hail verification efforts were vigorous, large hail was reported during the period when positive ground flashes dominated. In the 11 storms that were tornadic, tornadoes occurred either during or after the period when positive ground flashes dominated. It is inferred that the dominant polarity of lightning is strongly influenced by mesoscale properties of the atmosphere, possibly through systematic effects on other storm properties related to severe weather. -from Authors
No abstract available.
The U.S. National Lightning Detection Network TM (NLDN) has provided light- ning data coveting the continental United States since 1989. Using information gathered from more than 100 sensors, the NLDN provides both real-time and historical lightning data to the electric utility industry, the National Weather Service, and other government and commercial users. It is also the primary source of lightning data for use in research and climatological studies in the United States. In this paper we discuss the design, implementation, and data from the time-of-arrival/magnetic direction finder (TOA/MDF) network following a recent system-wide upgrade. The location accuracy (the maximum dimension of a confidence region around the stroke location) has been improved by a fac- tor of 4 to 8 since 1991, resulting in a median accuracy of 500 m. The expected flash detection efficiency ranges from 80% to 90% for those events with peak currents above 5 kA, varying slightly by region. Subsequent strokes and strokes with peak currents less than 5 kA can now be detected and located; however, the detection efficiency for these events is not quantified in this study because their peak current distribution is not well known.