Noninductive Charging Research Articles

Impact of ice multiplication on the cloud electrification of a cold-season thunderstorm: a numerical case study

Abstract. Ice microphysics controls cloud electrification in thunderstorms, and the various secondary ice production (SIP) processes are vital in generating high ice concentrations. However, the role of SIP in cold-season thunderstorms is not well understood. In this study, the impacts of SIP on the electrification in a thunderstorm that occurred in late November are investigated using model simulations. The parameterizations of four SIP processes are implemented in the model, including the rime splintering, ice–ice collisional breakup, shattering of freezing drops, and sublimational breakup of ice. In addition, a noninductive charging parameterization and an inductive charging parameterization, as well as a bulk discharging model, are coupled with the spectral bin microphysics scheme. The macroscopic characteristics and the temporal evolution of this thunderstorm are well modeled. The radar reflectivity and flash rate obtained by adding four SIP processes are more consistent with the observations than those without SIP. Among the four SIP processes, the rime splintering has the strongest impact on the storm. The graupel and snow concentrations are enhanced while their sizes are suppressed due to the SIP. The changes in the ice microphysics result in substantial changes in the charge structure. The total charge density changes from an inverted tripole structure to a dipole structure (tripole structure at some locations) after four SIP processes are considered in the model, mainly due to the enhanced collision between graupel and ice. These changes lead to an enhancement of the vertical electric field, especially in the mature stage, which explains the improved modeling of flash rate. The results highlight that cold-season cloud electrification is very sensitive to the SIP processes.

Numerical Simulation of Charge Structure Evolution during the Feeder-Type Cells Merging

Formation of the multipolar charge structure during feeder-type cell merging has important consequences in severe convective weather. This study used the Weather Research and Forecasting model with electrification and discharge parameterization schemes to simulate the feeder-type cell merging process in the tail of a squall line that occurred on 27 June 2020 in Hubei Province (China). The results showed that the two cells involved in the merging process were at different life stages, but that the distribution of the inductive charging zones in the parent and child cells was broadly the same as that of the non-inductive charging zones. The charging zones were restricted to the mixed-phase region (between the 0 and −40 °C layers) with a cloud water content of >0.2 g/kg in the updraft zone, and the magnitude of the inductive charging rate was slightly smaller than that of the non-inductive charging rate. The differences in the vertical wind shear between the parent and child cells caused differences in the content, charge number, and polarity of the hydrometeors, which resulted in obvious differences in the charge structure characteristics between the two cells. Overall, the cloud droplets, ice, snow, and graupel were the main charged hydrometeors in the cells, whereas the rain and hail had little charge.

Giant Planet Lightning in Nonideal Gases

Lightning has been directly observed or inferred on all giant planets, generally accepted to be occurring in their water clouds. However, much as Earth has both cloud–cloud and cloud–ground lightning, this does not mean all flashes occur in a narrow altitude range: on Jupiter, the Galileo spacecraft detected lightning flashes apparently below the cloud base, explicable as lightning due to precipitation, and the Juno SRU detected small flashes far above it, at pressures of only 1–2 bars. We use a computationally light 1D entraining plume model, incorporating particle growth and noninductive charging, which predicts this wide range of Jovian lightning provides freezing point depressions caused by ammonia, and modify it to use a van der Waals equation of state instead of an ideal gas, as well as integrating the evaporation of rain; this allows modeling of planets colder than Jupiter, where clouds and lightning occur at greater pressures. For Saturn, the uppermost lightning is predicted at 3–4 bars; unlike on Jupiter, ammonia is not required to match the Cassini observations. For Uranus and Neptune, depending on their convective structures, very high rates of lightning are possible in the deep water clouds; while deeper than on Jupiter or Saturn, lightning is predicted likely to peak above the water cloud base, at pressures around 100 bars. Voyager 2's radio observations of Uranian and Neptunian sferics may thus be either due to attenuation of deep water lightning of this type, or due to lightning in the shallow ammonia clouds; future observations are required to resolve this dichotomy.

Microphysical and Kinematic Characteristics of Anomalous Charge Structure Thunderstorms in Cordoba, Argentina

Some thunderstorms in Cordoba, Argentina, present a charge structure with an enhanced low-level positive charge layer, and practically nonexistent upper-level positive charge. Storms with these characteristics are uncommon in the United States, even when considering regions with a high frequency of anomalous charge structure storms such as Colorado. In this study, we explored the microphysical and kinematic conditions inferred by radar that led to storms with this unique low-level anomalous charge structure in Argentina, and compared them to conditions conducive for anomalous and normal charge structures. As high liquid water contents in the mixed-phase layer lead to positive charging of graupel and anomalous storms through the non-inductive charging mechanism, we explored radar parameters hypothesized to be associated with large cloud supercooled liquid water contents in the mixed-phase layer and anomalous storms, such as mass and volume of hail and high-density graupel, large reflectivity associated with the growth of rimed precipitation to hail size, and parameters that are proxies for strong updrafts such as echo-top and Zdr column heights. We found that anomalous storms had higher values of mass and volume of hail in multiple sub-layers of the mixed-phase zone and higher frequency of high reflectivity values. Low-level anomalous events had higher hail mass in the lower portion of the mixed-phase zone when compared to normal events. Weaker updraft proxies were found for low-level anomalous events due to the shallow nature of these events while there was no distinction between the updraft proxies of normal and anomalous storms.

Six years of electrified convection over the island of Corsica monitored by SAETTA: General trends and anomalously electrified thunderstorms during African dust south flow events

By means of the SAETTA 3D lightning mapping array, the total lightning activity has been detected in a 240 km × 240 km square domain centred on the island of Corsica located in the West Mediterranean basin, and characterized by a maritime and mountainous environment, with a complex and relatively high relief. The study period covers the months from April to December of the 6 years from 2014 to 2019. Observations are reported with a horizontal resolution of 1 km and a vertical resolution of 0.1 km in terms of density of VHF sources emitted by lightning, and of number of lightning day, in plane- and vertical- projections. Vertical distributions of VHF sources are also provided monthly for the whole period and over the full domain. These 3D long term observations show that the number of lightning days is more important on the main relief of the island. The density of VHF sources exhibits a sharp maximum over the confluence area of the 3 main valleys in the center of the northern part of the island, characterized by a recurrent and vertically well developed lightning activity. The period from 11:00 UTC to 14:00 UTC in July, and in a lesser extent in June and August, is at the origin of this density maximum. This behavior is thus due to a diurnal convection. The whole lightning activity is characterized by 2 maxima in June and September. The first one is linked with the diurnal convection in phase with the maximum elevation of the Sun. The second one must be due to usual large-scale organized thunderstorm events of the fall season. The vertical distribution of VHF sources exhibits an increase in the number of VHF sources from April to August at all altitudes, as well as an increase in the altitude of the main upper peak (from 5.8 km to 10 km) and of the secondary lower peak (from 4.2 km to 6.7 km) of this distribution. From August to December, the opposite evolution appears, except that October is characterized by a strong anomaly with a single intense lower peak at 5.5 km, apparently due to 2 strong events corresponding to anomalously electrified thunderstorms. Several of these anomalously electrified thunderstorms (negative dipoles) are reported. They are all characterized by the movement of cloud cells spatially small and relatively undeveloped vertically propagating from southwest to northeast and associated with a strong transport of desert dust from the African continent. The analysis of the meteorological environment of some of the studied events allows concluding that in each of the studied cases elevated convection was triggered, above the relatively dry atmospheric boundary layer characterized by a strong convective inhibition. The low cloud liquid water content which is a key parameter of the non-inductive charging process is probably a good candidate to explain the anomalous electrification of these events.

Aerosol effects on electrification and lightning discharges in a multicell thunderstorm simulated by the WRF-ELEC model

Abstract. To investigate the effects of aerosols on lightning activity, the Weather Research and Forecasting (WRF) Model with a two-moment bulk microphysical scheme and bulk lightning model was employed to simulate a multicell thunderstorm that occurred in the metropolitan Beijing area. The results suggest that under polluted conditions lightning activity is significantly enhanced during the developing and mature stages. Electrification and lightning discharges within the thunderstorm show characteristics distinguished by different aerosol conditions through microphysical processes. Elevated aerosol loading increases the cloud droplets numbers, the latent heat release, updraft and ice-phase particle number concentrations. More charges in the upper level are carried by ice particles and enhance the electrification process. A larger mean-mass radius of graupel particles further increases non-inductive charging due to more effective collisions. In the continental case where aerosol concentrations are low, less latent heat is released in the upper parts and, as a consequence, the updraft speed is weaker, leading to smaller concentrations of ice particles, lower charging rates and fewer lightning discharges.

Sounding observation of vertical electric field in eyewall of Typhoon Wipha (No. 1907) during landing period

In the summer of 2019, one case of electric field sounding in eyewall of No.1907 typhoon named Wipha was obtained in Wenchang, Hainan Island, China. Up to now, it has been the first case of electric field sounding results obtained in a typhoon system. In this paper, based on the observations of satellite, meteorological radar, ground electric field and cloud-to-ground flash location data of Hainan province, China, the basic characteristics of the typhoon are analyzed in detail. Owing to the limitation of cloud-to-ground flash location system, only flash activities of the typhoon before and after landing period are analyzed and the result does not show obvious features as reported by other researches. Referring to the radar reflectivity and sounding path, we confirm that the sounding penetrates through the eyewall region of the typhoon from cloud base to top. The electric field profile and the charge region distribution in the sounding path area are analyzed, and the results show that four positive and three negative charge regions exist between 5.74 and 9.10 km above sea level and the corresponding temperatures range from –2.4 to –16.7 ℃ of the seven charge regions. The mean charge densities of each charge region from bottom to top are 0.63 nC/m<sup>3</sup>, –0.33 nC/m<sup>3</sup>, 0.31 nC/m<sup>3</sup>, –1.03 nC/m<sup>3</sup>, 1.70 nC/m<sup>3</sup>, 1.57 nC/m<sup>3</sup> and –1.20 nC/m<sup>3</sup>, respectively. According to the preliminary analysis, we consider that the two positive charge layers at the top should be in the same charge region. Under the comprehensive consideration of the thickness of charge regions, the intensities of these six charge regions are 0.33 nC/m<sup>2</sup>, –0.07 nC/m<sup>2</sup>, 0.06 nC/m<sup>2</sup>, –0.87 nC/m<sup>2</sup>, 0.73 nC/m<sup>2</sup>, and –0.18 nC/m<sup>2</sup>, respectively. We can find that there are three dominant charge regions with largest intensity and they are the lowest positive charge region, the middle main negative region, and upper main positive charge region. And these vertical distributions of the three dominant charge regions are characterized by a tripole charge structure. These results are basically consistent with some simulation results. In addition, a negative screen charge region with a shallow depth in a range of 15–20 dBZ of the upper cloud boundary can be found. Combining the popular charging mechanisms, the similarity of tripole charge structure between our sounding and normal thunderstorm are discussed, and we preliminary consider that the non-inductive charging mechanism and the inductive charging mechanism, which originate from normal convection, are also suitable for eyewall region of typhoon.

Multiple Environmental Influences on the Lightning of Cold-Based Continental Cumulonimbus Clouds. Part I: Description and Validation of Model

AbstractIn this two-part paper, influences from environmental factors on lightning in a convective storm are assessed with a model. In Part I, an electrical component is described and applied in the Aerosol–Cloud model (AC). AC treats many types of secondary (e.g., breakup in ice–ice collisions, raindrop-freezing fragmentation, rime splintering) and primary (heterogeneous, homogeneous freezing) ice initiation. AC represents lightning flashes with a statistical treatment of branching from a fractal law constrained by video imagery.The storm simulated is from the Severe Thunderstorm Electrification and Precipitation Study (STEPS; 19/20 June 2000). The simulation was validated microphysically [e.g., ice/droplet concentrations and mean sizes, liquid water content (LWC), reflectivity, surface precipitation] and dynamically (e.g., ascent) in our 2017 paper. Predicted ice concentrations (~10 L−1) agreed—to within a factor of about 2—with aircraft data at flight levels (−10° to −15°C). Here, electrical statistics of the same simulation are compared with observations. Flash rates (to within a factor of 2), triggering altitudes and polarity of flashes, and electric fields, all agree with the coincident STEPS observations.The “normal” tripole of charge structure observed during an electrical balloon sounding is reproduced by AC. It is related to reversal of polarity of noninductive charging in ice–ice collisions seen in laboratory experiments when temperature or LWC are varied. Positively charged graupel and negatively charged snow at most midlevels, charged away from the fastest updrafts, is predicted to cause the normal tripole. Total charge separated in the simulated storm is dominated by collisions involving secondary ice from fragmentation in graupel–snow collisions.

How Does the Melting Impact Charge Separation in Squall Line? A Bin Microphysics Simulation Study

AbstractA new electrification and discharge model was developed based on a two‐moment bin microphysical scheme coupled with the Weather Research and Forecasting (WRF) model. Based on the electrical model, the role of the noninductive charging mechanism associated with the melting processes of both snow and graupel (rimed particles) in the charge structure formation in the stratiform region of an organized convective system was examined. Our results showed that the snow melting charging mechanism forms a substantial positive charge layer near and below 0°C isotherm in the stratiform region of a squall line. It was also found that the graupel melting charging process mostly enhanced the positive charge layer in the convective region with little impact in the stratiform region. The in situ charging of noninductive collisional and melting processes and the charge transportation from the convective core all contribute to the charge structure formation in the stratiform region of a squall line.

Charging processes during the dissipation stage of thunderstorms

Electric field and Maxwell current density measurements made below thunderstorms at Pune (India) have been analyzed to study the charging processes occurring during dissipation stage of thunderstorms. These observations suggest that during the dissipation stage of thunderstorm different charging processes contribute to the cloud electrification depending on the type of thunderstorms. Our observations suggest that updraft may not be sufficient to activate charging mechanism inside cloud during the dissipation stage in small thunderstorms. However, in big thunderstorms, non-inductive charging mechanism may be active during the dissipation stage. The recovery curves of electric field and Maxwell current density measured during dissipation stage of inverted polarity thunderstorms suggests that inductive charging mechanism may also contribute to the thunderstorm electrification.

The relationship between lightning flash rate and ice-related volume derived from dual-polarization radar

To conduct accurate lightning prediction and nowcasting, it is important to clarify the relationship between electrification and microphysical properties in clouds. Using the dual-polarization Doppler radar with the hydrometeor classification algorithm and lightning observation, radar-derived microphysical properties related to lightning flash rate were investigated in terms of 10 isolated thunderstorm cases over the Kanto Plain, Japan, with 351 radar volume scans conducted every 5 min during the summer period. In this study, the ice-related particles within the 35 dBZ volume (V35IC) showed the highest correlation coefficient (r = 0.75) and the lowest normalized root mean square error (NRMSE = 8.3%) in relation to cloud-to-ground lightning (CG), and also best to intra-cloud lightning (IC, r = 0.69, NRMSE = 8.1%). The correlation between V35IC and CG flash rate was better than that of the mixed-phase (between 0 °C and − 40 °C) 35 dBZ volume (r = 0.64), without considering the microphysical particles. The second-best radar-derived microphysical property was the ice mass consisting of the radar grids of all the ice-related particles (r = 0.72). These results suggest that an effective lightning indicator in terms of a radar-derived property is the ice-related particle volume, in addition to the traditionally used graupel and hail. The ice-related particle volume in the colder region of the thunderstorm (air temperature lower than −10 °C) showed a higher correlation with CG and IC than that in the warmer region, especially in terms of IC. These results are consistent with the non-inductive charging theory that has been well accepted in previous studies. Following time-lag correlation analysis from 0 to −30 min every 5 min before thunderstorm initiation, it was found that the ice-related index of V35IC demonstrated the slowest decrease (r = 0.75–0.65 in 30 min) in the correlation coefficient with time lapse and may be suitable as a lightning nowcast indicator.

Vertical reflectivity structures near lightning flashes in the stratiform regions of mesoscale convective systems

Using an S-band Doppler radar and a very high frequency (VHF) radiation source location system, 254 lightning flashes occurring in stratiform regions (stratiform lightning flashes) of 14 mesoscale convective systems (MCSs) in Chongqing, China, were observed and used to analyze the structure of vertical reflectivity in the area around the lightning channel. In most stratiform lightning flashes, the vertical reflectivity structures can be grouped into three general categories: single-layer, double-layer, and triple-layer. The single-layer structure flashes are the most numerous (65.0%), followed by the double-layer (26.8%) and triple-layer (1.2%) flashes. The regions with the single-layer structure and the double-layer structure are inferred to have mesoscale updrafts of different intensity in the middle of stratiform region. Around 62.3% of the single-layer structure flashes initiate within 0–4 km above the vertical reflectivity core, and the main initiation range of these flashes widens with increasing value of the vertical reflectivity core. Around 49.2% and 12.7% of the double-layer structure flashes initiate within 3–6 km and 1–2 km above the vertical reflectivity core, respectively. The probability of lightning initiation at a greater distance to the vertical reflectivity core is higher than that at a shorter distance. This may imply that some electrifications occurring during the melting process are not as strong as expected and a non-riming non-inductive charging process occurring in a weak but broad mesoscale updraft in the middle of stratifom region may be more important for initiation of stratiform lightning flashes.

Geostationary Lightning Mapper and Earth Networks Lightning Detection Over the Contiguous United States and Dependence on Flash Characteristics

AbstractThis study compared the detection capabilities of the Geostationary Lightning Mapper (GLM) and ground‐based Earth Networks Total Lightning Network (ENL) over the contiguous United States (CONUS) from 25 April 2017 to 5 May 2018. GLM detection efficiency (DE) relative to ENL varied spatially with greater DE in the southeastern United States and lower DE in the Northern Plains. Regions with greater DE were often regions where most intracloud flashes had normal positive polarity, while lower DE regions frequently had inverted negative intracloud. According to the tripolar noninductive charging model, inverted intracloud flashes are lower altitude than normal intracloud flashes. This lower altitude flash may result in greater cloud scattering of the optical lightning signal, which at cloud top is less than the GLM detection limits. DE was generally also greater for greater absolute peak current flashes, which serves as a proxy for optical energy. Additionally, GLM observed flashes to be generally greater in area and duration in the eastern relative to the western CONUS, which may result in the greater DE. GLM DE was also varied with the solar zenith angle as greatest DE occurred at night. ENL DE relative to GLM was varied spatially over CONUS with greater DE over eastern CONUS. ENL DE was greater for flashes of greater GLM flash radiant energy, area, and duration.

Numerical Simulation of the Formation of a Large Lower Positive Charge Center in a Tibetan Plateau Thunderstorm

AbstractNumerical modeling is applied to elucidate the formation mechanism of the large lower positive charge centers (LPCCs) observed during thunderstorms over the Tibetan Plateau based on the simulation of a storm at the northeastern boundary of the plateau. Four sensitivity tests were carried out to explore the impacts of inductive charging, reversal temperature, and the choice of noninductive charging scheme. The results show that the unique environmental conditions of the Qinghai‐Tibet Plateau, which include weak convection and low freezing level, are fundamental to the formation of large LPCC. A weakened charge density in the upper positive charge center highlights the role of a LPCC in lightning initiation although the charge density of the LPCC has no obvious change compared to that in the LPCC of the typical tripole structure. This accounts for Tibetan Plateau thunderstorms having low frequencies of lightning flashes, which occur mainly in the lower dipole. Inductive electrification, which provided more than 50% of the positive charge on graupel and increased the positive and negative charge on cloud drops by 2 orders of magnitude, is an important complement to the lower dipole of the tripole charge structure originally established by noninductive electrification. The inductive electrification also evidently enhances the LPCC and the middle negative charge center while slightly reducing the upper positive charge center. Subsequently, the lightning activity is strengthened, and lightning flashes are more likely to be initiated at the lower dipole. Varying the reversal temperatures and noninductive charging scheme does not fundamentally affect the formation of the LPCC.

Is the number of days with lightning changing? A study for southeastern Europe of the period 1980–2018

Lightning is one of the leading causes of weather-related fatalities worldwide and also has a strong impact on atmospheric chemistry (i.e., NOx production). Lightning can also lead to power system breakdowns, ignite forest fires, damage wind turbine and lead to perturbation of transportation, in particular to aviation. Thus, knowing when, where lightning strike and which atmospheric environments are more frequently associated with lightning is important. Furthermore, given the increase in the population density in recent decades (i.e., more people are exposed to lightning) and the increased urbanization (i.e., cities are getting larger and thus are more exposed to lightning) is essential to understand the spatial and temporal distribution of storm producing lightning and their environments in the current climate and their changes in the past and coming decades. To address these issues, in this study we analyze the changes in the number of days with atmospheric conditions leading to lightning over southeastern Europe. Here we consider the non-inductive charging mechanism as the main mechanism for cloud electrification. We search for ingredients supporting for this cloud electrification mechanism using a series of parameters (e.g., convective available potential energy, total precipitable water, heights of various isotherms) obtained from vertical profiles collected from radiosonde sites over southeastern Europe (e.g., Romania, Hungary, Bulgaria). This paper will present the changes between 1980 and 2018 in the number of days with condition supporting the occurrence of lightning in urban areas from southeastern Europe.&nbsp

Possible roles of fall speed parameters of different graupel densities on microphysics and electrification in an idealized thunderstorm

AbstractGraupel is often parametrized as “medium‐density” ice particles with a bulk density of 400 kg m−3 and corresponding fixed fall speed parameters in numerical models. In natural clouds, however, graupel has an extensive range of densities, and its fall speed is closely related to its density ρg. In this study, the possible responses of the microphysical and electrical structures of a simulated thunderstorm to varying ρg and its corresponding fall speed parameters were examined using the Advanced Research Weather and Forecasting Model (ARW‐WRF) with an explicit charging and discharge lightning scheme. Six sensitivity tests were performed with different ρg and corresponding fall speed parameters. ρg ranges from 350–850 kg m−3, to represent relatively low‐ (350, 450 kg m−3), medium‐ (550, 650 kg m−3), and high‐ (750, 850 kg m−3) density assumptions. In low‐density cases, the ice water path (IWP) could be comparable with the liquid water path (LWP), while the LWP exceeds the contribution of the IWP to the total water path (TWP) in high‐density cases. The results show that melting rates and precipitation were enhanced when ρg was increased from low to high values, resulting in a smaller size and lighter mean mass due to a shorter residence time and faster fall speed.Different assumptions about graupel density also resulted in different electrical structures in the simulated clouds. The clouds produced in the low‐ and medium‐density cases are mainly charged with conventional tripole or positive dipole structures, while the ones formed in the high‐density cases present “bottom‐heavy” tripole structures. The upper positive regions become weaker, with reduced negative noninductive charging rates, as graupel falls faster and less graupel is negatively charged at higher altitude. It is also found that a faster fall speed of graupel does not necessarily mean stronger flash density, although lightning activities are correlated with higher fall speed.

Geographical Distribution of Thundersnow Events and Their Properties From GPM Ku‐Band Radar

AbstractSix‐years (2010–2015) of snow lightning characteristics and climatology, including seasonal, diurnal, and surface temperature distribution, are generated. The World Wide Lightning Location Network (WWLLN) and the National Lightning Detection Network lightning observations are collocated with Modern‐Era Retrospective Analysis for Research and Application (MERRA‐2) temperatures. Cold season lightning events are identified as lightning with the MERRA‐2 two‐meter surface temperature colder than 0 °C and then further classified as snow lightning or thundersnow, when the entire vertical temperature profile is below 2 °C, and as freezing rain lightning when there is a temperature warmer than 2 °C somewhere in the column above the freezing surface. The statistics of snow lightning events from WWLLN and National Lightning Detection Network are well matched and are consistent with the climatology of thundersnow days reported at ground‐based stations over the United States. Using 4 years of observations from the Global Precipitation Measuring Mission Ku band radar, 443 Thunder Snow Features (TSFs) are defined, having a contiguous area of nonzero near surface snow precipitation derived from the Ku band radar and MERRA‐2 data, along with collocated WWLLN lightning flashes. The majority (about 394) are found over high mountainous regions such the Himalayas, Tibet, the Andes, and the Zagros mountain regions. Low‐elevation TSFs (45) are observed over the continental and coastal regions. Though only a small number of TSFs are identified with 4 years of Global Precipitation Mission data, most TSFs have maximum radar reflectivity above 30 dBZ at temperature colder than −10 °C, which indicates the importance of the noninductive charging process in these events.

Three‐dimensional radio images of winter lightning in japan and characteristics of associated charge structure

We conducted lightning observational campaigns using a three‐dimensional (3D) lightning mapper called the Broadband Observation network for Lightning and Thunderstorms (BOLT) and C‐band radar to further understand the distinct characteristics of winter lightning in the coastal area of the Sea of Japan. We succeeded in locating 3D intracloud (IC) flashes, cloud‐to‐ground (CG) flashes, and upward lightning during winter. The basic characteristics of winter lightning, such as leader speeds and charge structure associated with an IC discharge, are similar to summer lightning. A noticeable difference between the winter lightning and the summer lightning is that the altitudes of the source locations associated with winter lightning are substantially lower than those associated with summer lightning. We performed a statistical comparison of winter and summer lightning. This comparison shows that the BOLT source altitude distributions during winter and summer peak at 2.1 and 7.5 km, respectively. Conversely, the distributions of the BOLT temperatures, which are the temperatures corresponding to the BOLT source altitudes, during both winter and summer show similar trends and have large values near −10 °C. These results indicate that a similar charge separation process, likely a noninductive charging mechanism, primarily contributes to thunderstorm electrification during both winter and summer. We show that the horizontal extent of the winter flashes is substantially larger than that of the summer flashes. This result implies that the charge regions in winter thunderstorms cover a wide area and, therefore, produce CG flashes with large charge transfers. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Investigating the Relative Contributions of Charge Deposition and Turbulence in Organizing Charge within a Thunderstorm

Abstract Large-eddy-resolving simulations using the Collaborative Model for Multiscale Atmospheric Simulation (COMMAS), which contains microphysical charging and branched-lightning parameterizations, produce much more complex net charge structures than conventionally visualized from previous observations, simulations, and conceptual diagrams. Many processes contribute to the hydrometeor charge budget within a thunderstorm, including advection, hydrometeor differential sedimentation, subgrid turbulent mixing and diffusion, ion drift, microphysical separation, and the attachment of ion charge deposited by the lightning channel. The lightning deposition, sedimentation, and noninductive charging tendencies contribute the most overall charge at relatively large scales, while the advection tendency, from resolved turbulence, provides the most “texture” at small scales to the net charge density near the updraft region of the storm. The scale separation increases for stronger storm simulations. In aggregate, lightning deposition and sedimentation resemble the smoother distribution of the electric potential, while evidence suggests individual flashes could be responding to the fine texture in the net charge. The clear scale separation between the advection and other net charge tendencies suggest the charge advection is most capable of providing net charge texture; however, a clear-cut causality is not obtained from this study.

On the Contribution of Turbulence to the Electrification of Thunderclouds

The contribution of turbulence to the electrification of thunderstorm clouds is considered for the first time using a model of the large-scale electric field generation in a weakly conducting media containing two fractions of colliding hydrometeors. The calculation results are compared with experimental data. It has been found that scenarios of electric-field generation and growth are significantly different for inductive and noninductive charging mechanisms. The range of thundercloud parameters (of conductivity and particle radii) for which the electric field grows exponentially in the case of inductive charging has been found. In the case of noninductive charging, it has been shown that the electric field strength grows linearly in time due to intensive fluctuations of the electric charge. The linear growth of the electric field can be a significant factor when approaching the threshold of the discharge initiation.