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The lightning clustering algorithm for spaceborne lightning observations clusters events into flash products and plays a crucial role in lightning-related research. This paper modified the lightning clustering algorithm based on the routine algorithm of Lightning Mapping Imager (LMI) and applied it to lightning events recorded by the LMI in 2019 to study the flash duration and flash area and specially to reveal the extreme lightning. To reveal the temporal and spatial features of lightning, the MCA (modified cluster algorithm) flash products defined flash duration and flash area. The results showed that continental regions have higher lightning frequencies but smaller events per flash, flash durations and flash areas than the ocean. The Tibetan Plateau has a low lightning frequency and smaller flash duration and area than eastern China. The flash count, events per flash, flash duration and flash area are higher during nighttime than during daytime. The relationship between flash duration and flash area showed distinct regional differences. In the MCA flash product, about 0.6% (0.1%) flashes have duration (area) that exceeds 1.0 s (5,000 km2). Finally, we analyzed two extreme lightning cases in eastern China, where the longest flash duration was 4.748 s and the largest flash area was 17,100 km2. This research contributes to advancing our understanding in the features of space-based lightning in the Eastern Hemisphere and applications to convection study. • Clustering algorithm was modified to study lightning with extreme duration and area. • Lightning duration and area both implied regional differences. • Quantitative relationship of duration and area was established in different regions. • The longest flash duration/largest flash area was 4.75 s/17100 km2 in eastern China. [ABSTRACT FROM AUTHOR]

Western Siberia is exposed to extreme wind events caused by severe convective storms. However, our knowledge on such storms in Siberia is still fragmentary compared to other parts of the world primarily due to the lack of weather radar data. These storms cause substantial damage, which signifies the need for comprehensive assessment of their characteristics and predictability even on the basis of existing data. In this paper, we present a case study analysis of a severe weather outbreak that occurred on 25–26 May 2020 in Western Siberia, during a record six-month heatwave that lasted in Siberia from January to June. The outbreak resulted in six fatalities and substantial economic losses. Using various satellite data and damage reports we found that two consecutive mesoscale convective systems (MCSs) developed within the outbreak having an exceptionally long total track about 2000 km and causing large-scale forest damage with a total area of 64.5 km2. Such an exceptionally long path was supported by a strong mid-tropospheric jet, which settled extremely high values of wind shear that fostered the development of the outbreak. To analyze the accuracy of the forecast of the MCS and three associated windstorms on 26 May, we performed a set of simulations with the COSMO and ICON numerical weather prediction models launched with convection-permitting resolution (2.2 km) with different forecast lead times. Both models successfully predicted the most severe windstorm with the <50 km spatial displacement and the <1.5 h time shift, but COSMO generally simulated more strong wind. However, two other windstorms of that day were predicted with lower accuracy. The simulation results revealed a limited sensitivity of the model to variations in initial soil temperature and moisture. Together with the better performance of the forecast with >24 h lead time, this emphasized the predominant role of large-scale dynamics and the minor role of local factors in the outbreak formation and development. In particular, the intrusion of the upper tropospheric high potential vorticity streamer along the blocking periphery induced strong deep convection and determined the severe character of the outbreak. Specifically, the studied outbreak had an exceptional longevity compared to other long-lived windstorms observed in Northern Eurasia at the blocking periphery. • Severe weather outbreak occurred during a record six-months heatwave. • Two consecutive MCSs had an exceptionally long total path about 2000 km. • The outbreak formed under extreme values of wind shear and storm-relative helicity. • COSMO and ICON models successfully predicted the most severe windstorm. • Large-scale dynamics had a predominant role in the outbreak formation. [ABSTRACT FROM AUTHOR]

The time-of-arrival (TOA) method realizes the lightning location based on the time synchronization of all stations. However, this paper proposes the Difference of Pulse Interval (DOPI) method, which completely abandons the necessity of time synchronization of the lightning positioning network. Using the difference of the double-pulse interval of seven stations, two lightning radiation sources can be located at the same time. In this paper, the principle of DOPI method is described, and the positioning feasibility of the method is simulated. And use the electric field data of a lightning flash to verify the positioning performance of the DOPI method. The positioning results of the measured data show that the three-dimensional position of lightning discharges can be accurately located by using the DOPI method on the basis of completing the pulse matching. • Lightning positioning can be achieved only based on the difference of pulse interval (DOPI) between different stations. • The error of the DOPI method is equivalent to the error of the existing positioning system. • The DOPI method can reduce the hardware system complexity of the lightning mapping system. [ABSTRACT FROM AUTHOR]

This paper presents a cloud electrification model, which we embedded in the Wisconsin Dynamic and Microphysical Model-2 and labels it CEMW. WISDYMM-2 makes use of two-moment cloud microphysics to produce 5 hydrometeor types (e.g., cloud-droplets, raindrops, cloud-ice, snow, and graupel) that are used by CEMW for storm electrification where storm convection is initiated by a warm air bubble that is placed over an assumed flat terrain with no surface friction. In this paper, CEMW was used to examine cloud electrification in a simulated (idealized) thundercloud and to examine the impact of various formulations of the ion generation rate by cosmic rays (G) on how the storm and individual hydrometeor charges were structured. Results showed that the CEMW generates reasonable electric charge structures, which is qualitatively similar to those published by Brothers et al. (2018) in that it consists of a number of smaller positively and negatively charged regions. This structure differs from a charge structure generally depicted by conceptual models based on conventional balloon measurements of electric field. However, simulated balloon measurements in the idealized thunder clouds further revealed that CEMW produces electrostatic charge distributions and electric field profiles that are in good agreement with those reported by real balloon measurements. How charge is structured by CEMW was tested by formulating G (the ion generation rate) in two different ways. First, we derived G assuming fair weather conditions, which is the usual way applied in cloud electrification modelling. Second, we calculated Gs using the Cosmic Ray Atmospheric Cascade: Cosmic Ray Induced Ionization model for several values of solar modulation potential and cut-off rigidity. The results show that the structure of the electric charge fields does not differ much depending on G, but the fundamental difference between G is in the amount of electric discharges. Total charge distribution after 16 min 40 s of integration. The red dotted line shows the boundary of cloud defined as an area with a mixing ratio higher than 1e-7, solid black contours show positive vertical air velocity oriented upwards (1, 10 and 15 m/s), and dashed black contours indicate negative vertical air velocity (−1, −5 and − 10 m/s). [Display omitted] • A cloud electrification model was created within the Wisconsin Dynamic/Microphysical Model cloud model 2. • The ion generation rate by cosmic rays differs in dependence on the manner of how it is calculated. • Simulated balloon measurements of electric fields corresponds to real measurements. • Amounts of discharges significantly depend on ion generation rate by cosmic rays. [ABSTRACT FROM AUTHOR]

The paper presents a systematic description about the observation scheme analysis and practical observation of artificially triggered lightning with a ground-based microwave radiometer together with other discharging observation instruments at Guangzhou Field Experiment Site for Lightning research and testing in Conghua, Guangdong in the thunderstorm season of the 4 consecutive years from 2016 to 2019. The results from statistical analysis of the brightness temperature data observed from 2017 to 2019 show that: (1) The frequencies such as 28, 30, 51.25 and 51.76 GHz in atmospheric window are more likely to respond with outstanding brightness temperature pulses than other observation frequencies of the radiometer; (2) When the elevation angle is 30°, the observation distance is relatively short (99 m in this study), and the "lightning observation mode" is adopted, the efficiency for a ground-based microwave radiometer to capture the lightning heating effect caused by artificially triggered lightning can be improved; (3) The observation efficiency of the 3 years as a whole is 71.4% but gradually increases year by year; (4) The radiometer observation data can be used to reveal the characteristics of lightning heating effects such as duration and lightning current integral; (5) Combined with the lightning current data measured by a coaxial shunt during the experiment, it was found that the estimated lightning heating effect durations based on 25 artificially triggered lightning observations are well consistent with the lightning current durations, as shown by the correlation coefficient of 0.73. This also implies that the radiometer working on the lightning observation mode presented by this paper can observe the lightning heating effect and estimate its duration. • Triggered lightning is observed with a ground-based microwave radiometer in 2016–2019. • Observation scheme is formed based on the simulation calculations and data analysis. • Lightning heating duration averaged 0.5 s, variations are the same as current duration. • The observation efficiency is 71.4% and keeps increasing every year from 2017 to 2019. [ABSTRACT FROM AUTHOR]

• The severe convective environment on 29 August 2020 was well captured by GFS forecasts • CAPE, SRH, and EHI lack specificity regarding supercell likelihood, path, or severity • A CM1-based strategy can provide useful details about possible convective structures • The CM1 method offers valuable insights on convective structure location and severity On the morning of 29 August 2020, a supercell developed to the west of Mallorca (Balearic Islands, Spain) and then crossed the island. The storm produced strong winds, at least one EF2 category tornado on the Enhanced Fujita scale, heavy precipitation and large hail. The affected areas suffered power and landline phones outages, massive falling of trees that caused the closure of roads, and material damages on properties and infrastructures. Unfortunately this kind of high impact events are quite common in the western Mediterranean, specially during or near autumn, but generally elude the capabilities of standard forecasting procedures. A better understanding of their development and any improvement in their prediction are crucial to issue better warnings to civil protection and the general public. Assessment of the Convective Available Potential Energy and Storm Relative Helicity present in the prior environment highlights the area where the actual supercell developed. However, neither the severity of the convective system nor other important properties such as its trajectory, can be predicted by the classic analysis of larger scale ingredients. This paper proposes a novel approach to obtain this additional information by applying the CM1 model. This cloud-resolving model was developed precisely to study convective storms and therefore emerges as the ideal tool to provide clues on the likelihood of a supercell and its severity and trajectory. Specifically, we test the systematic run of several CM1 simulations over the favorable area highlighted by the classic analysis and explore the convective structures that can develop and evolve in such environments. The results point out the ability of the CM1-based method to capture for the 29 August 2020 event the supercell formation, its trajectory and severity parameters. Therefore, a CM1-based strategy can provide useful details about eventual convective structures and their characteristics, allowing forecasters to issue better weather warnings at operational level. [ABSTRACT FROM AUTHOR]

Relativistic runaway electron avalanches (RREA) occurring in thunderstorm large-scale electric fields are one of the sources of atmospheric gamma radiation. Relativistic feedback is the generation of RREAs by positrons or backscattered gamma rays of the previously produced RREAs. In strong electric fields, relativistic feedback can make RREAs self-sustainable that hypothetically can cause a terrestrial gamma-ray flash (TGF). This paper introduces a kinetic approach to study the positron relativistic feedback, which is predominant for the directly observed conditions within thunderstorms. The criterion for self-sustaining production of RREAs by the positron feedback in thunderstorms is derived. The discovered criterion allows one to obtain the parameters of the thunderstorm electric field required for self-sustaining RREA development with positron feedback for any altitude. It is shown that the derived conditions of self-sustainable RREA development are not achieved for the parameters of electric field observed in real thunderclouds. • Kinetic formalism to study the relativistic feedback is developed. • Analytical expression for the criterion for self-sustaining production of relativistic runaway electron avalanches by the positron feedback is derived. • Directly observed parameters of the thunderstorm electric field do not correspond to the conditions required for efficient positron feedback. [ABSTRACT FROM AUTHOR]

Understanding the lightning climatological distribution is of great significance but remains challenging which is in part due to the lack of continuous and uniform lightning observations. In this paper, for the first time, an 11-year ground-based cloud-to-cloud lightning dataset of China National Lightning Detection Network from 2010 to 2020 is used to investigate the lightning climatology over China's land area in terms of spatial distribution, seasonal, monthly and diurnal variations. Lightning activity in China's land area generally decreases from south to north and from east to west. The mean cloud-to-ground lightning density of China's land area is 0.9 fl km−2 yr−1, with the average maximums (exceeding 10 fl km−2 yr−1) are found in the south and east coastal provinces, such as Guangdong, Hainan, Fujian and Zhejiang Province. The lightning activity in spring, summer and autumn seems consistent throughout the daytime cycle, with the lightning activity is rather weak in the morning and most active in the afternoon, while winter lightning appears to be more active in the nighttime and in the very early morning produced from nocturnal thunderstorms. The cloud-to-ground lightning activity in the tropical and subtropical areas within 15–25°N is mainly concentrated in the late spring and early summer, with two weak peaks in May and August, while lightning in mid latitudes within 25–55°N mainly occurs in the summer (June–July-August). The percentage of positive cloud-to-ground lightning flashes with peak current higher than 75 kA is more than 3 times than that of negative cloud-to-ground lightning flashes. Meanwhile, the mean peak current of cloud-to-ground lightning flashes shows an inverse diurnal pattern to the cloud-to-ground lightning activity. • Cloud-to-ground lightning climatology over Chinese continent is first investigated. • Lightning activity generally decreases from south to north and from east to west. • More lightning occurs in the summer in mid latitudes within 25–55°N. • Winter lightning is unique, usually produced from nocturnal thunderstorms. [ABSTRACT FROM AUTHOR]

This article analyses two long-lived supercell thunderstorms formed on 11th May 2017 afternoon in a complex topographic area in northern Catalonia (NE Iberian Peninsula). The objectives of this paper are (i) to document a case study that affected a mountainous region in the southern side of the Pyrenees, (ii) to describe thermodynamic and dynamic environmental conditions, (iii) to study how the topography affects the life cycle of both storm cells and (iv) to demonstrate the high correlation between Lightning Jump and radar parameters in complex terrain. ERA5 reanalysis was used to assess the synoptic framework and environmental storm conditions, whereas remote-sensing data (Doppler radar, satellite and lightning observations) and terrain characteristics were considered to study the evolution of both cells. Reanalysis data revealed some differences between preconvective environments for both thunderstorms, showing more favourable conditions for supporting supercells (i.e. stronger deep-layer shear) for the first thunderstorm than for the second one. The analysis suggests substantial interaction between topography and storm cells, influencing their internal dynamics and the development of mesocyclones. The results of this study contribute to enhance our understanding of supercell storms evolution on mountain areas and may be useful to increase the situational awareness of weather forecasters in future similar convective storm events over complex terrain regions. • Supercells rarely occur in the Pyrenees and its surrounding area, and few cases have been reported. • The event shows an extraordinary case with two probable supercells in few hours. • Remote sensing and NWP fields show many supercell signatures, although the ground registers lack makes difficult to confirm. • There were many differences between both supercells, although the track and the environment were similar. • The topography played a significant role in the life cycle of the supercells in the thunderstorm scale. [ABSTRACT FROM AUTHOR]

We investigate the initiation of four lightning flashes detected from ground by means of the Colombia Lightning Mapping Array (Colombia-LMA) and simultaneously observed from space by the optical sensors of the Atmosphere-Space Interactions Monitor (ASIM) on board the International Space Station (ISS), the Geostationary Lightning Mapper (GLM), and the Lightning Imaging Sensor on the ISS. The initiations of the flashes are characterized by isolated and predominant optical blue pulses (337.0 nm). In three of the flashes, red emissions (777.4 nm), a dominant line of hot lightning, were not detected during their initiation. In these cases, the initiations were also accompanied by bipolar VLF/LF waveform with a narrow short duration (<40 μs) and VHF emissions with high radio frequency power (<269 kW). The detection of the blue emissions without any red luminosity supports that the fast breakdown processes at the flash initiation can be exclusively of streamer nature. The onset of the fourth flash was associated with both blue and red radiation, and with weak narrow bipolar waveform in VLF/LF and low VHF power. The flashes initiated between the midlevel negative and upper positive charge regions. This paper presents and discusses the first fast breakdown processes observed simultaneously from ground by means a Lightning Mapping Array (LMA) and from space during the onset of lightning flashes. • Isolated ASIM 337 nm pulses at flash initiation support the streamer nature of fast breakdown detected by radio measurements. • Lightning mapping array located the events between the main negative and upper positive charge regions at 9-14 km altitude. • Peaks in 337 nm radiance at the flash initiation did not correlate with the amplitudes of the VHF power and VLF sferics. [ABSTRACT FROM AUTHOR]

In this paper, a three-dimensional convolutional neural network model (3DCNN) is proposed to nowcast a short-lived, local convective storm event by using unique 3-D observations of Multi-Parameter Phased Array Weather Radar (MP-PAWR) over Tokyo, Japan on 1 August 2019. Using statistics and forecast skill scores, nowcast skills of 3DCNN were examined with those of a three-dimensional advection nowcast model (3DNOW) which generates extrapolation-based forecasts with lead time up to 10 min. In analyzing the skill scores, two groups of a total rain area and convective rain area were made by different radar reflectivity (Z) thresholds of 10 dB Z and 37.5 dB Z , respectively. For the total rain area, it is found that 3DCNN outperformed both the 3DNOW and persistence forecast, showing the higher threat scores for all lead times. For the convective rain area, the 3DCNN and 3DNOW's performances were similar at early lead times, showing almost the same threat scores. However, the threat score of 3DCNN dropped lower than that of 3DNOW at a lead time of 10 min, indicating that 3DNOW has the better skill at relatively long lead times. Nowcasts of 3DNOW showed a limitation to yield a larger saturated Z area related to increased errors in advection vectors at longer lead times although this led to increasing the threat score. • A 3-D convolutional neural network (3DCNN) model is proposed to nowcast a local storm event using unique 3-D radar data. • 3DCNN's forecast skill was better than the 3-D advection nowcast model (3DNOW) for the total rain area. • For the convective rain area, 3DNOW showed the higher threat scores at longer lead times than 3DCNN. [ABSTRACT FROM AUTHOR]