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The causes for the differences in the lightning frequency between two heavy rainfall events, the 2017 northern Kyushu heavy rainfall event and the 2018 heavy rainfall event in central Japan, were examined using a numerical model coupled with an explicit bulk lightning model. These heavy rainfall events occurred near the Baiu frontal system of Japan in July, but the characteristics of rainfall differed. The former case was categorised as an extreme rainfall and extreme convective event by previous satellite observational studies, and the lightning frequency was high. Conversely, the latter case was categorised as an extreme rainfall without extreme convection event, and the lightning frequency was low. The numerical model used in this study successfully reproduced the differences in the lightning frequency between the two cases. Our analyses indicated that the differences in the lightning frequency between the two cases were attributed to the differences in the vertical structure of the charge separation rate and the charge density, which originated from the difference in the vertical distribution of graupel. Difference in the lightning frequency between two heavy rainfall events (e.g. heavy rainfall on 5 July 2017 and 6 July 2018) was firstly reproduced by a numerical model coupled with a bulk lightning model. The two events both occurred around Baiu frontal system on July in Japan, but the reason of the difference in the lightning frequency was not clear. Our analyses elucidated that the differences in the lightning frequency between the two cases originated from the differences in the vertical distribution of graupel, and consequently, due to the vertical structure of the charge separation rate and the charge density.

To characterize lightning processes that produce terrestrial gamma ray flashes (TGFs), we have analyzed broadband (<1 Hz to 30 kHz) lightning magnetic fields for TGFs detected by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) satellite in 2004–2009. The majority (96%) of 56 TGF‐associated lightning signals contain single or multiple VLF impulses superposed on a slow pulse that reflects a process raising considerable negative charge within 2–6 ms. Some TGF lightning emissions also contain VLF signals that precede any appreciable slow pulse and that we term precursor sferics. The analyses of 9 TGFs related to lightning discharges with location uncertainty <100 km consistently indicate that TGFs are temporally linked to the early portion of the slow process and associated VLF impulses, and not to precursor sferics. The nearly universal presence of a slow pulse suggests that the slow process plays an important role in gamma ray production. In all cases the slow process raises negative charge with a typical mean current moment of +30 kA km. The resulting charge moment change ranges from small values below +10 C km to a maximum of +200 C km, with an average of +64 C km. The current moment waveform extracted from TGF sferics with single or multiple VLF impulses also shows that the slow process initiates shortly before the major TGF‐associated fast discharge. These features are generally consistent with the TGF‐lightning sequence reported by Lu et al. (2010), suggesting that the majority of RHESSI TGFs are produced during the upward negative leader progression prevalent in normal polarity intracloud flashes. Key Points Charactering lightning signals associated with terrestrial gamma‐ray flashes Identifying main waveform features associated with terrestrial gamma‐ray flashes More observations consistent with the TGF‐lightning sequence previously reported

The lightning flash frequency (LFF, also referred to as lightning flash rate) in four models from the Coupled Models Intercomparison Project, phase 6 is examined. For the present day (PD, 1995–2014), the models exhibit very divergent simulation of LFF in terms of multi–annual averages, interannual variability, and temperature sensitivity. The global mean multi–annual average flash frequency differs by a factor of two between the models, and only two of four models are within the reasonable distance from the LIS/OTD (Lightning Imaging Sensor/Optical Transient Detector) satellite retrievals. The model–data and inter–model differences are even more pronounced at a regional scale and during northern summer. CMIP6 simulations show a general increase in lightning flash frequency from the present day to the late 21st century, especially for the simulations with higher anthropogenic CO2 emissions into the atmosphere. LFF sensitivity coefficient β, which is based on differences between PD and the late 21st century are positive over most continental areas with typical values from 10 to 20%K-1 for annual mean LFF and from 20 to 60%K-1 for JJA averages over the northern extra–tropical continents (and even up to 100%K-1 in some regions for individual models). At the global scale and for annual averages, this sensitivity is from 5 to 17%K-1. In addition, this sensitivity is markedly different from its counterpart derived from the regression of LFF on surface air temperature for PD period. The latter counterpart is negative at the global scale and changes sign between different regions (i.e, it is positive over the North America south–east and is negative over the south–western part of North America and over the India Peninsula). These regional peculiarities are reasonably simulated by the models.

The results of simultaneous radar, radiometric, and lightning location measurements are analyzed to reveal interrelations between the characteristics of electric discharges and the parameters of a cumulonimbus cloud developing near Saint Petersburg. The dependences of the cloud electric activity on the radar characteristics as well as on the parameters derived from the Meteosat SEVIRI radiometer measurements are considered. It is found that lightning frequency highly correlates with the volume of supercooled cloud regions with high values of reflectivity. An increase in the lightning frequency occurs about 20 minutes after the moment when supercooled cloud volumes with reflectivity above 35–55 dBZ reach the maximum values. The maximum precipitation flux precedes the maximum lightning frequency.

Lightning activity constitute the major destructive component of thunderstorms over India. Hence, an understanding of the long-term variability in lightning occurrence and intensity and their interrelation with various causative factors is required. Long-term (1998–2014) Tropical Rainfall Measuring Mission (TRMM) satellite-based lightning observations depict the most frequent lightning occurrences along the Himalayan foothills, the Indo-Gangetic plains and coastal regions, while the intensity of these lightning strikes is found to be strongest along the coastal regions and in the Bay of Bengal. In addition, both of the abovementioned lightning properties show a very strong intensification (∼ 1 %–2.5 % annually) across all Indian regions during the 1998–2014 period with the maximum trends along the coasts. Accordingly, a detailed statistical dominance analysis is performed which reveals total column water vapor (TCWV) to be the dominant factor behind the intensification in lightning events, while instability, measured by the convective available potential energy (CAPE), and aerosol optical depth (AOD) jointly control the lightning frequency trends. An increase in surface temperatures has led to enhanced instability and, hence, stronger moisture transport to the upper-troposphere and lower-stratosphere regions, especially along the coasts. This transported moisture helps deplete the ozone concentration, leading to reduced temperatures and elevated equilibrium levels, which finally results in stronger and more frequent lightning events, as also evidenced by the trend analysis. Consequently, the relationships between lightning and its causative factors have been expressed in the form of multilinear regression equations, which are then employed in multiple global circulation models (GCMs) to understand the long-term impact of urbanization on lightning over the period from 1950 to 2100. The analysis reveals a uniform increase in lightning occurrence and intensity using both urbanization scenarios; however, accelerated growth is observed in the RCP8.5 projections after the year 2050, as also observed from the surface warming trends. As a result, lightning frequency and intensity values across the Indian region are expected to increase ∼ 10 %–25 % and 15 %–50 %, respectively, by the end of the century with the highest risk along the coasts; hence, this requires immediate attention from policymakers.

Using ADTD three‐dimensional lightning monitoring data from Shanghai for the years 2022–2024, a comparative analysis was conducted on the evolution patterns of lightning during severe convective weather events such as short‐duration heavy rainfall, thunderstorm gales, and hail. The main conclusions are as follows: Severe convective intra‐cloud (IC) flashes are primarily distributed below 10 km, with the proportions concentrated within the [0, 10 km] range for hail, thunderstorm gales, and short‐term heavy rainfall IC flashes being 83%, 81.2%, and 80.7%, respectively. At the 850 hPa level, the high‐density areas of IC lightning for thunderstorm gales and short‐duration heavy rainfall corresponded well with the high‐density areas of cloud‐to‐ground (CG) lightning. At the 700 hPa level, the high‐density areas of IC lightning for thunderstorm gales showed a good correspondence with the high‐density areas of CG lightning. The lightning density and coverage area exhibit a characteristic of decreasing layer by layer from the ground to the 500 hPa level. The extreme value ranges of lightning frequency distribution per 10 kA interval for the three types of severe convective weather were similar, all falling within the [10, 20 kA] range. From 2022 to 2024, three‐dimensional lightning activity during severe convective weather in Shanghai primarily occurred from April to September, with the peak lightning frequency observed in August. Diurnal variation showed high oscillations between 13:00 and 17:00, peaking at 15:00. The monthly distributions of lightning associated with short‐duration heavy rainfall, thunderstorm gales, and hail were consistent with the overall characteristics of three‐dimensional lightning in severe convective weather. Lightning during short‐duration heavy rainfall mainly occurred in the afternoon and early evening, thunderstorm gale lightning was concentrated between 14:00 and 16:00, and hail lightning primarily occurred between 11:00 and 17:00. In terms of spatial distribution of lightning activity, the Pudong New Area and Chongming District are the main clustering areas. Short‐duration heavy rainfall lightning was predominantly located in Pudong District, while hail lightning was mainly concentrated in Chongming District. Using 2022–2024 ADTD data, this study analyzes 3D lightning in Shanghai's severe convection. Activity peaks in August and afternoon hours, varies by weather type, and concentrates spatially in Pudong and Chongming. Results provide key references for selecting lightning indicators in forecasting and warning systems.

Extensive degradation of near-surface permafrost is projected during the twenty-first century1, which will have detrimental effects on northern communities, ecosystems and engineering systems. This degradation is predicted to have consequences for many processes, which previous modelling studies have suggested would occur gradually. Here we project that soil moisture will decrease abruptly (within a few months) in response to permafrost degradation over large areas of the present-day permafrost region, based on analysis of transient climate change simulations performed using a state-of-the-art regional climate model. This regime shift is reflected in abrupt increases in summer near-surface temperature and convective precipitation, and decreases in relative humidity and surface runoff. Of particular relevance to northern systems are changes to the bearing capacity of the soil due to increased drainage, increases in the potential for intense rainfall events and increases in lightning frequency. Combined with increases in forest fuel combustibility, these are projected to abruptly and substantially increase the severity of wildfires, which constitute one of the greatest risks to northern ecosystems, communities and infrastructures. The fact that these changes are projected to occur abruptly further increases the challenges associated with climate change adaptation and potential retrofitting measures.

Cloud‐to‐ground (CG) lightning occurs frequently in Jiangsu Province, China. High‐speed rail (HSR) spans across the province, covering a large geographic area. Studying the occurrence of lightning and the characteristics of strikes in HSR corridors is of great significance for the lightning protection and safe operation of the HSR. Based on the terrain, lightning detection data, and catenary engineering parameters along 12 HSR corridors in Jiangsu Province, this study provides detailed analyses of the lightning characteristics, the cumulative probability distribution (CPD) of lightning current amplitudes, and the lightning strike characteristics on the catenary in these areas. The results show that CG lightning mainly occurs from 05:00 a.m. to 10:00 a.m. and mostly happens in the summer season. The CG lightning density along the HSR corridors in southern Jiangsu Province is relatively high. According to the CPD of lightning current amplitudes and the fitting curves obtained by the Levenberg–Marquardt method, the “a” values are relatively larger for the Nanjing–Anqing, Nanjing–Hangzhou, and Shanghai–Chengdu HSR lines, which indicates that the lightning current amplitudes along these three HSR corridors are larger than those along other lines. In terms of the CG lightning intensity index, which is the combination of lightning current intensity and CG lightning frequency, its values are relatively larger in the Zhenjiang section of the Shanghai–Nanjing riverside line, the Wuxi section of the Shanghai–Nanjing intercity line, and the Yangzhou section of the Lianyungang–Zhenjiang line. The large‐value areas of the tripping rate of the catenary caused by direct lightning strikes are relatively consistent with those of CG lightning density. The direct‐lightning‐strike tripping rate along the feeder F wire is considerably larger than that along the trolley wire T. In the absence of overhead lightning shield wires along HSR lines, the maximum tripping rate of wire F caused by direct lightning strikes is 24.3 times (100 km)−1 a−1, the minimum tripping rate is 2.6 times (100 km)−1 a−1, and the average tripping rate is 10.6 times (100 km)−1 a−1. In contrast, along wire T, the maximum tripping rate caused by direct lightning strikes is 7.6 times (100 km)−1 a−1, the minimum value is 0.8 times (100 km)−1 a−1, and the average value is 3.3 times (100 km)−1 a−1. When considering overhead lightning shield wires, the probability of direct lightning strikes on wire F drops to 0.12 times (100 km)−1 a−1, and that on wire T is negligible. Accordingly, the average tripping rate caused by backflashovers is 3.5 times (100 km)−1 a−1. Based on the terrain, lightning detection data, and catenary engineering parameters along 12 HSR corridors in Jiangsu Province, this study provides detailed analyses of the lightning characteristics, the cumulative probability distribution (CPD) of lightning current amplitudes, and the lightning strike characteristics on the catenary in these areas.

This study examines the characteristics of tropical cyclone (TC) lightning distribution and its relationship with TC intensity and environmental vertical wind shear (VWS) over the western North Pacific. It uses data from the World Wide Lightning Location Network and operational global analysis data from National Centers for Environmental Prediction Final Analysis for 230 TCs during 2005–17. The spatial distribution of TC lightning frequency and normalized lightning rate demonstrates that the VWS dominates the azimuthal distribution of the lightning. The flashes are active in the downshear-left side of the inner core and the downshear-right side of the outer region. TC lightning distribution for various VWS strengths and TC intensities are further investigated. As VWS increases, the flashes of lightning become more asymmetric and exhibit a higher proportion at the outer region of the downshear side. Moreover, the same features occur as TC intensity decreases. A series of composite analyses indicated that stronger TCs with weaker VWS exhibit a more compact and symmetric lightning distribution, whereas weaker TCs with stronger VWS have a more asymmetric lightning distribution. Furthermore, the TC lightning distribution and its association with TC intensity changes are also examined for three lead times. Results show that among the composite analyses of five TC intensity changes, the lightning distribution for rapid intensification type exhibits more inner-core lightning and is more axisymmetric than the distributions for other categories. These features result from favorable environmental conditions comprising greater upper-level divergence, sea surface temperature, maximum potential intensity, and weaker vertical wind shear.

The cross-correlation between annual lightning frequency and solar activity and the heliospheric magnetic field (HMF) is examined on a global scale using corrected data from the World Wide Lightning Location Network (WWLLN) for the period 2009 to 2022. Relatively large regions with significant cross-correlation coefficients (p<0.05) between the yearly lightning rates and sunspot number (SSN) are found in eastern Africa, part of South America overlapping with the South Atlantic Anomaly, and the Indian Ocean and west coast of Australia. The main region that shows a significant correlation between lightning activity and the By component of the HMF and the magnetopause reconnection Kan–Lee electric field matches the South Atlantic Anomaly quite well. Also shown are areas that show a significant cross-correlation of lightning activity with the El Niño–Southern Oscillation index. Similar areas of significant cross-correlation are obtained if simulated thunder days are used instead of lightning counts. Possible mechanisms leading to the observed correlations and limitations of the current study are discussed. The findings of the present study do not support previous works indicating that cosmic ray intensity is in phase with the global occurrence of lightning, but they do not rule out the role of cosmic rays in lightning ignition in developed thunderclouds and the role of energetic particles precipitating from the magnetosphere in the significant correlation between lightning and the By component of the HMF (SSN) in the South Atlantic Anomaly.