Lightning-induced Electron Precipitation Events Research Articles

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.

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.

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.

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.

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.

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.

Trimpi perturbations from large ionisation enhancement patches

A number of increasingly sophisticated and realistic models have been developed in order to investigate the interaction between sub-ionospherically propagating VLF waves and regions of ionisation enhancement (LIE 1 1 The “L” in “LIE” stands for “LEP-produced” ) in the D-region caused by lightning-induced electron precipitation enhancements (LEP). This LEP-produced LIE can result in phase and amplitude perturbations on received VLF radio signals that are referred to as Trimpis or more precisely, classic Trimpis, to distinguish them from “early/fast Trimpis” or “VLF sprites” which are not caused by LEP and are not considered here. It is important, for comparison with experimentally observed Trimpi effects, that the spatial extent of the D-region electron density ( N e) perturbation is modeled accurately. Here, it is argued that most previous modeling has used patch (LIE) sizes that are typically up to 100 km in both latitudinal and longitudinal extent, which are generally smaller than those that actually occur for real lightning induced electron precipitation events. It would also appear that maximum Δ N e values assumed have often been too large, and the patches (LIEs) have been incorrectly modelled as circular rather than elliptical in horizontal extent. Consequently, in the present work, Trimpi perturbations are determined for LIEs with smaller maximum Δ N e, larger spatial extent and elliptical shape. Calculations of VLF Trimpis have been made as a function of the horizontal coordinates of the LIE centre, over the whole rectangular corridor linking transmitter and receiver. The Trimpi modelling program is fully 3D, and takes account of modal mixing at the LIE. The underlying theory assumes weak Born scattering, but the code calculates a non-Born skin depth attenuation function for the LIE in question. The LIE is modelled as an electron density enhancement with a Gaussian profile in all coordinates. Results for a large elliptical LIE ∼ 200 × 600 km show that significant Trimpis, ∼−0.4 dB in amplitude and ∼+4° in phase are predicted, using modest maximum Δ N e values ∼ 1.5 el/cc. Such an electron density enhancement is well within the range that would be expected to result from experimentally observed fluxes of electron precipitation following wave particle interactions with whistler-mode waves.

Numerical simulation of LEP Trimpis observed at Poitiers, France, on signals from VLF transmitters

Transient amplitude and phase perturbations on subionospheric VLF signals, known as the Trimpi effect, are caused by the scattering of VLF radiation from localized ionization enhancements in the nighttime D-region. The patches of ionization are due to precipitation from the radiation belts of keV electrons, that is induced by lightning-generated whistlers.This work is concerned with the numerical simulation of such VLF perturbations, termed LEP (lightning-induced electron precipitation) or classic Trimpis. Two different codes are used to compute the VLF propagation in the Earth-ionosphere waveguide in the presence of a D-region inhomogeneity. The first is based on mode theory, and the second on the FDTD (finite-difference time-domain) method. Both codes are two-dimensional and, therefore, relevant only to LEP events lying on the transmitter-receiver great circle path (TRGCP). A method of simulation is proposed to interpret quantitatively VLF amplitude and phase changes in terms of the approximate location and size of the associated ionospheric perturbation along the TRGCP. The method is applied to LEP Trimpis observed at Poitiers ( L = 2) on signals from the NAA and GQD transmitters. Results are discussed in the light of the information that may be deduced from the high-resolution analysis of VLF temporal signatures. A sequence of simultaneous LEP Trimpis observed at Poitiers on three widely separated transmission paths is studied; two alternative interpretations are proposed.

Recovery signatures and occurrence properties of lightning‐associated subionospheric VLF perturbations

Subionospheric VLF signatures of lightning‐associated ionospheric disturbances observed at multiple sites in the central United States are used to investigate the occurrence properties and recovery signatures of characteristic perturbations exhibiting rapid onset followed by slow recoveries. The two different types of events, so‐called early/fast and lightning‐induced electron precipitation (LEP) [Inan et al., 1996a], are distinguished by the lack of presence of a few hundred millisecond delay between VLF event onsets and causative lightning discharges, respectively. Analysis of recovery signatures of the two types of events indicate subtle but distinct differences in the recovery rates. A majority of early/fast events were found to exhibit a more rapid initial recovery to preevent levels during the first 20 s of recovery, when compared to LEP events. This experimental evidence indicates that the physical nature of the ionospheric disturbance involved in the two classes of events are different, consistent with a recent theoretical suggestion [Inan et al., 1996c]. The occurrence properties of early/fast events observed by the Holographic Array for Ionospheric Lighting (HAIL) receivers indicate that ionospheric disturbances act primarily as forward scatterers.

Satellite observations of lightning‐induced electron precipitation

Lightning‐induced electron precipitation (LEP) from the Earth's radiation belt has been observed on numerous occasions with detectors on the low‐altitude S81‐1/SEEP satellite. A sequence of seven LEP events on September 9, 1982, and eight events on October 20, 1982, are correlated on a one‐to‐one basis with one‐hop whistlers at Palmer, Antarctica. The temporal profile within a LEP burst has a remarkable fine structure. It is shown to be associated with bunches of magnetically guided and focused 100‐to‐200 keV electrons that are repeatedly scattered by the atmosphere and bounce between the northern and southern hemispheres. The delay time between the lightning sferic and the arrival of the first electron bunch increases with increasing L as predicted by the first‐order gyroresonance theory. The global distribution of strong LEP events observed with the SEEP payload correlates with lightning activity and shows a preferred distribution at 2 < L < 3. This L shell range corresponds to the slot region in the electron radiation belt. A single LEP burst (10−3 erg s−1 cm−2) in the slot region is estimated to deplete ∼0.001% of the particles in the region covered by the burst magnetic field lines. The evidence supports the production of structured LEP by ducted rather than nonducted whistlers. It is found that ducted whistlers can be an important pitch angle diffusion mechanism for 100–250 keV electrons in the 2 < L < 3 range although a number of uncertainties in the various parameters remain to be resolved; It is suggested that observations of LEP can be a new tool to measure the presence and transverse dimensions of plasmaspheric whistler mode ducts.

VLF strip holographie imaging of lightning‐associated ionospheric disturbances

A linear array of very low frequency (VLF) receivers, deployed along a line roughly perpendicular to the direction of signal propagation, enables the determination of the size and location of D region disturbances produced by lightning‐induced electron precipitation (LEP) bursts or by lightning‐induced heating in the vicinity of the great circle VLF propagation paths. The configuration essentially constitutes a strip hologram so that the width of both the amplitude and phase perturbation of the signal pattern recorded along the strip are simply related to the size and location of the disturbance for the range of altitude profiles of disturbed ionization expected for LEP events. The validity of the approach is demonstrated both analytically for single waveguide‐mode propagation and also for a realistic propagation path (Annapolis‐Stanford) by using a three‐dimensional numerical model of VLF propagation and scattering in the Earth‐ionosphere waveguide. We also discuss the criteria by which the spacing of discrete elements along the strip can be optimally choosen.

Altitude profiles of localized D region density disturbances produced in lightning‐induced electron precipitation events

A three‐dimensional model of very low frequency (VLF) radio wave propagation in the Earth‐ionosphere waveguide in the presence of lower ionospheric disturbances is used to quantitatively interpret VLF signatures of lightning‐induced electron precipitation (LEP) events observed in two previously reported cases. One case is that of a 28.5‐kHz signal originating in Puerto Rico and propagating to a receiver in Lake Mistissini, Quebec. The other case involves a 24.0‐kHz signal originating in Cutler, Maine, and received at Stanford, California. In both cases, high‐resolution measurements of the VLF signals were made to accurately document characteristic signatures of LEP events (Inan et al., 1988b, 1990). The comparison of the model calculations with the data yields information about the altitude profiles of electron density of both the extra ionization produced by the LEP events and of the ambient ionospheric D region. The comparisons are carried out using generally accepted values of the spatial extent of the disturbed regions and the intensity of the particle flux constituting the LEP burst.