Lightning-induced Electron Precipitation Research Articles

Lightning-induced relativistic electron precipitation from the inner radiation belt.

The Earth's radiation belts are maintained by a number of acceleration, loss and transport mechanisms, and the electron fluxes at any given time are highly variable. Microbursts, which are rapid (sub-second) bursts of energetic electrons entering the atmosphere from the magnetosphere, are one of the key loss mechanisms controlling radiation belt fluxes. Such rapid bursts are typically observed from the outer radiation belt and driven by interactions with whistler mode chorus waves, but they can also occur in the inner belt and slot region, driven by lightning-generated whistlers. This lightning-induced electron precipitation is typically observed at 10s-100s keV, but here we present direct observations of this phenomenon at MeV energies. This unveils a coupling between near-Earth processes, such as lightning, and radiation belt processes, such as relativistic electron microbursts, bridging the gap between Earth weather and space weather.

First observation results of Macao Science Satellite 1 on lightning-induced electron precipitation

AbstractThe mid-energy electron detector (MEED) is a space-borne instrument onboard Macao Science Satellite 1 (MSS-1) dedicated to monitoring the typical charged particle radiation characteristics in the satellite orbit and the process of their occurrence and development, including short bursts of lightning-induced electron precipitation (LEP). This paper presents the first results of the LEP measurements by the MSS-1. 47 LEP events are identified with the routine operation for 3 months since satellite launch, all within the range of 1.5<L<3.0 (where L represents the McIlwain L-parameter), and the causative lightning discharges are definitively geo-located for these LEP events. The LEP events occur within <1 s of the causative lightning and consist of 40–300 keV electrons. A preliminary observation result indicates that, with medium-energy electron detectors, MSS-1 can present in-situ observations of large regions of enhanced background precipitation and reveal their fine spatiotemporal characteristics and spectral signatures. The collaborative VLF ground-based measurements at the Great Wall Station, Antarctica also have a good correspondence with LEP measurements of MSS-1. The observations also imply that lightning activity has a modulation effect on the energetic electron energy-spatial structure.

Response of the Earth’s Lower Ionosphere to Solar Flares and Lightning-Induced Electron Precipitation Events by Analysis of VLF Signals: Similarities and Differences

The lower ionosphere influences the propagation of electromagnetic (EM) waves, satellite and also terrestrial (anthropic) signals at the time of intense perturbations and disturbances. Therefore, data and modelling of the perturbed lower ionosphere are crucial in various technological areas. An analysis of the lower ionospheric response induced by sudden events during daytime-solar flares and during night-time-lightning-induced electron precipitation was carried out. A case study of the solar flare event recorded on 7 September 2017 and lightning-induced electron precipitation event recorded on 16 November 2004 were used in this work. Sudden events induced changes in the ionosphere and, consequently, the electron density height profile. All data are recorded by Belgrade (BEL) radio station system and the model computation is used to obtain the ionospheric parameters induced by these sudden events. According to perturbed conditions, variation of estimated parameters, sharpness and reflection height differ for analysed cases. Data and results are useful for Earth observation, telecommunication and other applications in modern society.

Chemical Response of the Upper Atmosphere Due to Lightning‐Induced Electron Precipitation

AbstractTerrestrial lightning frequently serves as a loss mechanism for energetic electrons in the Van Allen radiation belts, leading to lightning‐induced electron precipitation (LEP). Regardless of the specific causes, energetic electron precipitation from the radiation belts in general has a significant influence on the ozone concentration in the stratosphere and mesosphere. The atmospheric chemical effects induced by LEP have been previously investigated using subionospheric VLF measurements at Faraday station, Antarctica (65.25°S, 64.27°W, L = 2.45). However, there exist large variations in the precipitation flux, ionization production, and occurrence rate of LEP events depending on the peak current of the parent lightning discharge, as well as the season, location, and intensity of the thunderstorm activity. These uncertainties motivate us to revisit the calculation of atmospheric chemical changes produced by LEP. In this study, we combine a well‐validated LEP model and first‐principles atmospheric chemical simulation, and investigate three intense storms in the year of 2013, 2015, and 2017 at the magnetic latitude of 50., 32., and 35., respectively. Modeling results show that the LEP events in these storms can cumulatively drive significant changes in the , , and concentration in the mesosphere. These changes are as high as , , and at 75–85 km altitude, respectively, and comparable to the effects typically induced by other types of radiation belt electron precipitation events. Considering the high occurrence rate of thunderstorms around the globe, the long‐term global chemical effects produced by LEP events need to be properly quantified.

Quantification of Ionospheric Perturbations From Lightning Using Overlapping Paths of VLF Signal Propagation

AbstractLightning induced perturbations of the lower ionosphere are investigated with very low frequency (VLF) remote sensing on a unique overlapping propagation path geometry. The signals from two VLF transmitters (at different frequencies) are observed at a single receiver after propagation through a common channel in the Earth‐ionosphere waveguide. This measurement diversity allows for greater certainty in quantification of perturbations to the ionospheric D region. Changes in amplitude and phase are modeled with the Long Wave Propagation Capability (LWPC) software package to quantify changes in reference height and steepness of the two parameter D region electron density model. Since the nighttime D region profile prior to the perturbation is found to strongly affect the resulting quantification, and is highly variable and generally unknown at nighttime, an error minimization method for identifying the most likely ionospheric disturbance independent of the ambient profile is used. Analysis of 12 large lightning perturbations resulting from discharges with peak currents greater than 160 kA shows that the ionospheric reference height can change by 2–8 km. We investigate both early/fast events (direct ionization and heating from lightning) and lightning‐induced electron precipitation (LEP) events, induced by lightning hundreds of kilometer away. LEP events increase D region electron density while early/fast events can lead to a increase or decrease in electron density. Multi‐point observations along a VLF propagation path are needed to further improve ionospheric perturbation quantification with VLF remote sensing.

Chemical Response of the Upper Atmosphere due to Lightning-induced Electron Precipitation

Chemical Response of the Upper Atmosphere due to Lightning-induced Electron Precipitation

Ionospheric D Region Disturbances due to FAC and LEP Associated With Three Severe Geomagnetic Storms as Observed by VLF Signals

AbstractThe effects of one super and two intense storms on three European very low frequency (VLF) transmitter signals received at Algiers (Algeria) station, are presented. Two VLF transmitters (DHO and GQD) are located almost at the same mid‐latitude and third transmitter (NRK) at a high latitude, allowing us to study the latitudinal dependence of the storm effect on the VLF propagation. Two kind of ionospheric disturbances were considered: Direct effect of the field aligned currents (FACs) and the second concerning with the lightning‐induced electron precipitation (LEP) events. The FACs effect was clearly evident on the recorded signal amplitude during the daytime and nighttime. Our analysis of the short‐duration VLF perturbations due to LEP events showed that the ducted and non‐ducted LEPs are the majority of VLF perturbations and a small fraction of LEP events was associated with magnetospherically reflected waves on the high latitude transmitter path (NRK–Algiers). The coincident observation of LEP on the mid‐latitude transmitters (DHO and GQD) signals implies that the disturbance was large as much as the distance between the two transmitters (728 km). The modeling using Long‐Wave Propagation Capability (LWPC) code of LEP associated VLF perturbations considering Gaussian distribution of electron density enhancements, showed a decrease in the D‐region reference height from its usual value 87 km to 83.3 km for ducted LEP and 80.3 km for non‐ducted LEP event and that the non‐ducted event exhibited a wider disturbed region.

X‐ray Signatures of Lightning‐Induced Electron Precipitation

AbstractWe present detailed numerical modeling to predict expected X‐ray signatures from lightning‐induced electron precipitation (LEP) events. Simulations include the transionospheric propagation of the lightning electromagnetic pulse; ray tracing through the magnetosphere, including Landau damping; wave‐particle interactions resulting in loss cone fluxes; and Monte Carlo simulation of the electron precipitation process, including bremsstrahlung photon production and propagation to a balloon observing platform. Modeling is included to show that our simulated events are consistent with subionospheric very low frequency observations of LEP. Simulations show that these events should be observable from balloon‐based platforms. The modeled LEP event signatures, including X‐ray flux, spectrum, and pulse shape, are then compared with observations of energetic X‐ray pulses from the Balloon Array for Radiation‐belt Relativistic Electron Losses 1U balloon taken in January 2013 and are shown to be highly consistent with the observations. The pulses were observed near , while the balloon was off the coast of Antarctica at about 70°S, 5–20°W. Correlations with GOES imagery and global lightning data, together with analysis of the temporal and spectral signatures of these pulses, led to the initial suggestion that these events could be signatures of LEP. However, for only a fraction of these events could a causative lightning discharge be identified in global lightning data sets. This poor correlation may be partially attributed to causative strokes being missed by the global lightning networks; nonetheless, we discuss other possible explanations for these events.

A statistical study over Europe of the relative locations of lightning and associated energetic burst of electrons from the radiation belt

Abstract. The DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) spacecraft detects short bursts of lightning-induced electron precipitation (LEP) simultaneously with newly injected upgoing whistlers. The LEP occurs within < 1 s of the causative lightning discharge. First in situ observations of the size and location of the region affected by the LEP precipitation are presented on the basis of a statistical study made over Europe using the DEMETER energetic particle detector, wave electric field experiment, and networks of lightning detection (Météorage, the UK Met Office Arrival Time Difference network (ATDnet), and the World Wide Lightning Location Network (WWLLN)). The LEP is shown to occur significantly north of the initial lightning and extends over some 1000 km on each side of the longitude of the lightning. In agreement with models of electron interaction with obliquely propagating lightning-generated whistlers, the distance from the LEP to the lightning decreases as lightning proceed to higher latitudes.

Observation of local and conjugate ionospheric perturbations from individual oceanic lightning flashes

Very low frequency (VLF) remote sensing observations of multifaceted local and conjugate ionospheric perturbations from geographically identified and well‐characterized oceanic lightning discharges are presented for the first time. Lightning‐induced electron precipitation (LEP) events are shown to produce disturbances first in the conjugate hemisphere and subsequently in the hemisphere of the causative lightning discharge in agreement with theoretical predictions. A rough threshold peak current of ∼100 kA is identified for lightning discharges to generate LEP events for the geomagnetic conditions present during observations. The occurrence of early VLF events and the subsequent duration of their recovery do not seem to fit any simple metric of lightning discharge peak current or proximity to great circle path. Knowledge of the full spectral density of the lightning electromagnetic pulse, not just its peak current, and the subionospheric mode structure are likely necessary to determine if a specific lightning discharge will generate an early VLF perturbation.

Ionospheric effects of whistler waves from rocket-triggered lightning

[1] Lightning-induced electron precipitation (LEP) is one of the primary mechanisms for energetic electron loss from Earth's radiation belts. While previous works have emphasized lightning location and the return stroke peak current in quantifying lightning's role in radiation belt electron loss, the spectrum of the lightning return stroke has received far less attention. Rocket-triggered lightning experiments performed at the International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida, provide a means to directly measure the spectral content of individual lightning return strokes. Using an integrated set of numerical models and directly observed rocket-triggered lightning channel-base currents we calculate the latitudinal dependence of the precipitation signature. Model results indicate that rocket-triggered lightning may produce detectable LEP events and that return strokes with higher ELF (3 Hz–3 kHz) content cause proportionally more ionospheric ionization and precipitate more electrons at higher latitudes than return strokes with proportionally higher VLF (3 kHz–30 kHz) content. The predicted spatio-temporal signature of the induced electron precipitation is highly dependent upon the return stroke spectral content. As a result, we postulate that rocket-triggered lightning experiments enable us to the estimate the spectral profile of energetic electrons precipitated from the Earth's radiation belts.

Longitudinal dependence of lightning-induced electron precipitation

[1] Observations of lightning-induced electron precipitation (LEP) events at three geographic regions show characteristics which systematically vary with both longitude and hemisphere. These observations are quantitatively interpreted using a novel atmospheric interaction model designed to predict the characteristics of LEP events at any longitude and midlatitude L-shell by accounting for the effects of precipitating electrons which are backscattered from the atmosphere. The model of atmospheric backscatter (ABS) calculates atmospheric backscatter responses for individual monoenergetic electron beams with a single incident pitch angle using a Monte Carlo model of atmospheric interactions. The ABS model also includes an asymmetric (non-ideal dipole) geomagnetic field model in calculations of the pitch angle of backscattered electrons entering the conjugate hemisphere. Using a realistic distribution of precipitating electrons, the results of this backscatter calculation at three separate longitudes are compared with VLF remote sensing data collected on nearly north-south great circle paths (GCPs). Results predicted by the model and confirmed by data indicate that all four primary LEP characteristics exhibit longitudinal and hemispheric dependence which can be explained in terms of precipitating electrons backscattered from the atmosphere. By combining these effects with previously calculated radiation belt electron loss rates due to lightning at a single location it is possible to estimate the global loss of radiation belt electrons due to lightning.

Optical signatures of lightning-induced electron precipitation

[1] Model calculations are conducted to estimate the optical emission brightness caused by lightning-induced electron precipitation. Pitch angle scattering of energetic radiation belt electrons by lightning-generated whistler mode waves results in precipitation in the upper atmosphere. Assuming a lightning peak current and location, plasmasphere distribution, and radiation belt density and pitch angle distributions, we calculate the secondary ionization production and optical emissions in a number of lines and bands. We find that the brightness in N2 1P and O(1S) may reach a few to 10 R for a 100 kA peak current discharge, with a distinct spatial and temporal signature of 1–2 s. A simple signal-to-noise ratio (SNR) calculation shows that this signature should be detectable with modern photometric instruments with an SNR ∼4. We further investigate the dependence of this brightness on lightning source latitude and peak current.

Sudden amplitude and phase changes in subionospheric VLF transmitter signals observed at Agra, India

The amplitude and phase of VLF transmitter signals NWC (19.8 kHz), NPM (21.4 kHz), and NAA (24 kHz) have been monitored at Agra (geomag. lat. 17.10°N, L=1.15), India using AbsPAL receiver for a period of three years between 01 September, 2002 and 30 August, 2005. Seven cases of abrupt amplitude and phase changes have been identified which varied between 3 and 7 dB and 40° and 80° respectively. The onset duration varied around 5 sec. The observed characteristics have been examined in the light of lightning induced electron precipitation (LEP), solar flares, and lightning, and finally attributed to early/slow perturbation caused by distant sprites and lightning along the propagation paths.

A quantitative comparison of lightning‐induced electron precipitation and VLF signal perturbations

VLF signal perturbations recorded on the Holographic Array for Ionospheric/Lightning Research (HAIL) are quantitatively related to a comprehensive model of lightning‐induced electron precipitation (LEP) events. The model consists of three major components: a test‐particle model of gyroresonant whistler‐induced electron precipitation, a Monte Carlo simulation of energy deposition into the ionosphere, and a model of VLF subionospheric signal propagation. For the two representative LEP events studied, the model calculates peak VLF amplitude perturbations within a factor of three of those observed, well within the expected variability of radiation belt flux levels. The phase response of the observed VLF signal to precipitation varied dramatically over the course of the two nights and this variability in phase response is not properly reproduced by the model. The model calculates a peak in the precipitation that is poleward displaced ∼6° from the causative lightning flash, consistent with observations. The modeled precipitated energy flux (E > 45 keV) peaks at ∼1 × 10−2 (ergs s−1 cm−2), resulting in a peak loss of ∼0.001% from a single flux tube at L ∼ 2.2, consistent with previous satellite measurements of LEP events. The precipitation calculated by the model is highly dependent on the near‐loss‐cone trapped radiation belt flux levels assumed, and hence our main objective is not to compare the model calculations and the VLF signal observations on an absolute basis but is rather to develop metrics with which we can characterize the VLF signal perturbations recorded on HAIL in terms of the associated precipitation flux. Metrics quantifying the ionospheric density enhancement (NILDE) and the electron precipitation (Γ) along a VLF signal path are strongly correlated with the VLF signal perturbations calculated by the model. A conversion ratio Ψ, relating VLF signal amplitude perturbations (ΔA) to the time‐integrated precipitation (100–300 keV) along the VLF path (Ψ = Γ/ΔA), of 1.2 ± 0.3 × 1010 (el m−1/dB) is suggested for precipitation events of similar location and characteristics to those examined. The total precipitation (100–300 keV) induced by one of the representative LEP events is estimated at ∼1.8 ± 0.4 × 1016 electrons, calculated directly from the conversion ratio Ψ and observations of VLF signal perturbations.

VLF observation of long ionospheric recovery events

We introduce a new class of Early/fast VLF events with recoveries of up to 20 min, much longer than typical Early/fast and Lightning‐induced Electron Precipitation (LEP) events which recover to pre‐event levels in ≲200 s. Three distinct types of long recovery events are observed, each exhibiting different characteristics, with the observed features of at least some of the event types consistent with the possibility of persistent ionization at altitudes below 60 km as put forth by Lehtinen and Inan (2007).

DEMETER satellite observations of lightning‐induced electron precipitation

DEMETER spacecraft detects short bursts of lightning‐induced electron precipitation (LEP) simultaneously with newly‐injected upgoing whistlers, and sometimes also with once‐reflected (from conjugate hemisphere) whistlers. For the first time causative lightning discharges are definitively geo‐located for some LEP bursts aboard a satellite. The LEP bursts occur within <1 s of the causative lightning and consist of 100–300 keV electrons. First in‐situ observations of large regions of enhanced background precipitation are presented. The regions are apparently produced and maintained by high rate of lightning within a localized thunderstorm.

Electron precipitation events driven by lightning in hurricanes

In mid‐September of 2003, Hurricane Isabel passed through the Great Circle Path (GCP) of a subionospherically propagating LF signal between the NAU transmitter in Puerto Rico and a receiver located outside Boston. Cloud‐to‐ground lightning flashes detected by the Long‐Range Lightning Detection Network (LRLDN) and located in the outer rainbands of the hurricane were associated with perturbations in the received LF signal consistent with lightning‐induced electron precipitation (LEP) events. The number of perturbations, detected on the LF signal, exhibiting the known characteristics (rapid onset followed by slow recovery) of LEP events tended to increase with the occurrence of hurricane‐associated lightning near the GCP. The majority (>65%) of causative lightning flashes (those flashes recorded in the LRLDN data that were time‐correlated with spherics associated with LEP events in the VLF/LF data) occurred within 500 km of the GCP; and those flashes associated with Isabel typically occurred in the outer rainbands of the hurricane. While lightning generally occurs more frequently in the outer rainbands of hurricanes than in other tropical oceanic storms, there is no indication that the hurricane‐associated lightning is more likely to induce electron precipitation events than lightning associated with other storm systems. Hurricane Floyd (in September of 1999) and Hurricane Fabian (in August/September of 2003) also passed near the GCP of subionospherically propagating VLF/LF signals, and the received signals exhibited similar perturbation patterns.

On the occurrence and spatial extent of electron precipitation induced by oblique nonducted whistler waves

Two different 4‐hour sequences of subionospheric Very Low Frequency (VLF) signal perturbations are examined to characterize electron precipitation induced by nonducted obliquely propagating whistlers. These lightning‐induced electron precipitation (LEP) events are typically associated with cloud‐to‐ground lightning discharges. The temporal and spatial signatures of LEP events associated with two disparate storms occurring over two 4‐hour periods are examined. A distributed set of VLF observing sites, known as the Holographic Array for Ionospheric and Lightning Research (HAIL), captures the full latitudinal extent of the events, providing evidence that 90% of the precipitation occurs over a region 8° ± 1° and 9° ± 1° in latitudinal extent for the two time periods. The measured peak of the precipitation is poleward displaced (6°45′ ± 30′ and 7°45′ ± 30′ for the two case studies) from the causative discharge. Analysis indicates that the onset delay and the duration of precipitation steadily increase with increasing L‐value, while the signal recovery time is independent of L‐value for the LEP events associated with both storms. The causative lightning discharges associated with the two storms were located at different latitudes. For lightning occurring in the storm at higher latitudes, the associated LEP events are of longer duration and exhibit precipitation in a smaller area displaced less from the causative discharge. The onset delays and event durations increase more rapidly with increasing L‐value for events associated with lightning occurring in the storm at higher latitudes. The general spatial and temporal signatures are consistent with those expected for LEP events induced by nonducted whistlers.

Lightning‐induced energetic electron flux enhancements in the drift loss cone

With its relatively low altitude (520 × 670 km) orbit, SAMPEX is mostly below the stable trapping region where charged particles repeatedly drift around the Earth, especially at midlatitudes. Recent analyses of SAMPEX data have revealed a surprisingly common set of observations of enhanced energetic (>150 keV) electron fluxes at L < 3, during times when SAMPEX was located such that any electrons that it observed were in the drift loss cone (and were thus destined to be precipitated upon reaching the longitude of the South Atlantic Magnetic Anomaly in the course of their eastward drift). The data were acquired with the Heavy Ion Large Telescope on board SAMPEX, which provides high time resolution measurements (30 ms sample rate) of electrons above energy thresholds of 150 keV and 1 MeV. Preliminary examination of 1995 SAMPEX data (when the >150 keV detector was available) revealed hundreds of cases of newly enhanced drift loss cone fluxes in localized L shell regions often associated with individual thunderstorms. In one case, SAMPEX data from three consecutive days (95/196, 95/197, and 95/198) were analyzed as the satellite proceeded northbound over the same ground track from west of New Zealand and Hawaii toward Alaska, with the underlying lightning activity documented by the Optical Transient Detector on board the OrbView‐1 satellite (750 km, 70° inclination circular orbit). Enhanced fluxes observed on SAMPEX during day 95/197 were directly associated with an oceanic storm just to the west of the SAMPEX ground track, which was well placed to generate the observed drift loss cone flux enhancements. The drift loss cone electron flux enhancements were also observed 20 min later as SAMPEX crossed the same L shells in the north and in subsequent orbits, indicating that lightning‐induced precipitation of electrons into the drift loss cone persisted at least for a few hours. Data from UARS satellite, passing through the same region within the same hour, also confirmed the presence of L‐dependent structure and further allowed the determination of the electron energy spectra, which exhibited a general shape and range strikingly similar to previously documented spectral characteristics of lightning‐induced electron precipitation (LEP) events in the bounce loss cone [Voss et al., 1998]. This similarity lends support to the argument that the observed drift loss cone features are produced by the LEP process. In summary, SAMPEX data indicate that globally distributed thunderstorms may continually precipitate energetic electrons from the radiation belts, producing transient enhancements in the drift loss cone that are detected within the few hour periods as they drift around the Earth and precipitate in the South Atlantic Magnetic Anomaly.